ALBERT

Description: Hydroperoxides and the corresponding peroxy radicals are important intermediates during the partial oxidation of methyl ethyl sulfide (CH 3 SCH 2 CH 3 ) in both atmospheric chemistry and in combustion. Structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔH f o , S o and C p (T)) of 3 corresponding hydroperoxides CH 2 (OOH)SCH 2 CH 3 , CH 3 SCH(OOH)CH 3 , CH 3 SCH 2 CH 2 OOH of methyl ethyl sulfides, and the radicals formed via loss of a hydrogen atom are important to understanding the oxidation reactions of MES. The lowest energy molecular structures were identified using the density functional B3LYP/6-311G(2d,d,p) level of theory. Standard enthalpies of formation (ΔH f o 298 ) for the radicals and their parent molecules were calculated using the density functional B3LYP/6-31G(d,p), B3LYP/6-31 + G(2d,p), and the composite CBS-QB3 ab initio methods. Isodesmic reactions were used to determine ∆H f o values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6-31G(d,p) level theory. Contributions for S o 298 and C p (T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions. The recommended values for enthalpies of formation of the most stable conformers of CH 3 SCH 2 CH 2, CH 2 (OOH)SCH 2 CH 3 , CH 3 SCH(OOH)CH 3 , and CH 3 SCH 2 CH 2 OOH are −14.0, −33.0, −37.2, and −32.7 kcal/mol, respectively. Group additivity values were developed for estimating properties of structurally similar and larger sulfur-containing peroxides. Groups for use in group additivity estimation of sulfur peroxide thermochemical properties were developed. HOOCH 2 SCH 2 CH 3 bond dissociation energies (kcal/mol). Structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔH f o , S o , and Cp(T)) of CH 3 SCH 2 CH 3 , CH 2 (OOH)SCH 2 CH 3 , CH 3 SCH(OOH)CH 3 , CH 3 SCH 2 CH 2 OOH, and their radicals formed via loss of a hydrogen atom are investigated using B3LYP density functional theory and composite CBS-QB3 methods. Isodesmic reactions were used to determine Δ f H o values, and contributions for S o 298 and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation. Group additivity values were developed for estimating properties of structurally similar and larger sulfur-containing peroxides.

Description: The free radical activity of lespedezacoumestan was investigated toward hydroxyl (˙OH) radical in polar and nonpolar media using density functional theory. Four reaction mechanisms including radical adduct formation, hydrogen atom transfer, sequential single electron-proton transfer (SET-PT), and sequential proton loss electron transfer were considered. The rate constants and branching ratio for all possible sites of reaction were calculated and reported for the first time. According to the obtained results, lespedezacoumestan reacts faster with ˙OH radical in aqueous solution than in nonpolar media. Also, lespedezacoumestan is an excellent ˙OH radical scavenger regardless of the environment polarity. The free radical activity of lespedezacoumestan was investigated toward hydroxyl (˙OH) radical in polar and nonpolar media using density functional theory. Four reaction mechanisms including radical adduct formation, hydrogen atom transfer, sequential single electron-proton transfer, and sequential proton loss electron transfer were considered. The rate constants and branching ratio for all possible sites of reaction were calculated and reported for the first time. According to the obtained results, lespedezacoumestan reacts faster with ˙OH radical in aqueous solution than in nonpolar media. Also, lespedezacoumestan is an excellent ˙OH radical scavenger regardless of the environment polarity.

Description: Because of their numerous biological as well as industrial importance, the study of Schiff bases is an emerging field for the researchers, in recent time. In this study, we have designed some Schiff bases derived from biologically important precursors. The antioxidant activities of the designed compounds are thoroughly studied theoretically using density functional theory taking various parameters like bond dissociation enthalpy, ionization enthalpy, proton dissociation enthalpy, and electron transfer enthalpy followed by the study of effects of solvent, spin density, and molecular orbital on antioxidant activity of the compounds. The comparison of antioxidant activity of the compounds with that of phenol and their parent aldehydes reveals the superior antioxidant activity of the designed compounds. This study contributes towards the information of an important bridge between bioorganic and computational chemistry. A detailed theoretical calculation on BDE, IP, PDE, PA, and ETE suggests that the antioxidant ability of Schiff bases derived from biologically important phenolic aldehydes and diaminobenzenes exhibit better antioxidant ability than that of their parent aldehydes and thus, can play an important role as dietary antioxidants. Solvent polarity plays a major role in deciding the mechanistic possibility of their antioxidant abilities.

Description: We report a comparative computational study of 2 series of molecules with C–N bonding squaraines (NSQ) and C–C bonding squaraines (CSQ), having absorption from visible to near infrared region (350-800 nm). The NSQ are considered as molecules with break-in conjugation, and CSQ are considered as molecules with complete conjugation in molecular backbone. The lowest electronic excitations in CSQ molecules are always having around 200 nm red shifted absorption than its corresponding NSQ molecules. The reason for this drastic red shift in CSQ series than NSQ has been systematically studied by density functional theory, time-dependent density functional theory, and symmetry adopted cluster configuration interaction methods. The CSQ series are showing less charge transfer than NSQ, but having small diradical character. This study may be helpful in design and synthesis of new squaraine dyes, which are useful in materials applications. Linear optical properties of 2 series of squaraine molecules (NSQ & CSQ) have been studied by DFT, TDDFT, and SAC-CI methods. Both the series (NSQ & CSQ) are considered as donor-acceptor-donor–type of molecules, but NSQ series are showing larger charge transfer than CSQ series. The larger red shift of the CSQ when compared with its corresponding NSQ is due to the extended pi backbone along with presence of some diradicaloid character. These molecules are transparent in visible to NIR region, which is suitable for application in the region of interest.

Description: The complex formation of bis(18-crown-6)stilbene ( 1 ) and its supramolecular donor-acceptor complex with N , N ′-bis(ammonioethyl) 1,2-di(4-pyridyl)ethylene derivative ( 2 ) with alkali and alkaline-earth metal perchlorates has been studied using absorption, steady-state fluorescence, and femtosecond transient absorption spectroscopy. The formation of 1 ∙M n + and 1 ∙(M n + ) 2 complexes in acetonitrile was demonstrated. The weak long-wavelength charge-transfer absorption band of 1 · 2 completely vanishes upon complexation with metal cations because of disruption of the pseudocyclic structure. The spectroscopic and luminescence parameters, stability constants, and 2-stage dissociation constants were calculated. The initial stage of a recoordination process was found in the excited complexes 1 ∙M + and 1 ∙(M + ) 2 (M = Li, Na). The pronounced fluorescence quenching of 1 · 2 is explained by very fast back electron transfer ( τ et  = 0.397 ps). The structure of complex 1 · 2 was studied by X-ray diffraction; stacked ( 1 · 2 ) m polymer in which the components were connected by hydrogen bonding and stacking was found in the crystal. These compounds can be considered as novel optical molecular sensors for alkali and alkaline-earth metal cations. A decrease in the 3 characteristic relaxation times of complex 1 · 2 with decreasing length of the ammonioalkyl N -substituents of the acceptor was demonstrated by femtosecond differential absorption spectroscopy.

Description: In the present investigation, we study catalytic activity of copper nanoparticles stabilized onto a nitro functionalized polystyrene resin (Cu NPs@ Nitro-Resin). The size of stabilized copper nanoparticles was found between 3 and 9 nm. This work reports a cost-effective and sustainable protocol for the synthesis of propargylamines. Herein, we have developed microwave-assisted synthesis of propargylamine from 3 components coupling of aldehyde, alkynes, and amines (A 3 coupling) in truly heterogeneous catalytic system. Reaction parameters, such as solvent, catalyst concentration reaction time, and recyclability, were investigated, and reaction conditions were optimized. The present method has advantages such as environmentally benign, ease to handle, short reaction time (≈25 min), excellent yields (98%), low E-factor (0.15), and high atom economy (94%). Catalytic activity of copper nanoparticles (size 3-9 nm) stabilized onto a nitro functionalized polystyrene resin (Cu NPs@ Nitro-Resin) is investigated for synthesis of propargylamines by A 3 coupling. A rapid microwave-enhanced, sustainable, and cost-effective protocol for the synthesis of propargylamine library (26 compounds) is reported.

Description: In this work, we mainly focus on the excited-state intramolecular proton transfer mechanism of a new molecule 9,10-dihydroxybenzo[h]quinoline (9-10-HBQ). Within the framework of density functional theory and time-dependent density functional theory methods, we have theoretically investigated its excited-state dynamical process and our theoretical results successfully reappeared previous experimental electronic spectra. The ultrafast excited-state intramolecular proton transfer process occurs in the first excited state (S 1 state) forming 9-10-HBQ-PT1 structure without potential energy barrier along with hydrogen bond (O 3 –H 4 ···N 5 ). Then the second proton may transfer via another intramolecular hydrogen bonded wire (O 1 –H 2 ···N 3 ) with a moderate potential energy barrier (about 7.69 kcal/mol) in the S 1 state forming 9-10-HBQ-PT2 configuration. After completing excited-state dynamical process, the molecule on the first excited electronic state would come back to the ground state. We not only clarify the excited-state dynamical process for 9-10-HBQ but also put forward new predictions and successfully explain previous experimental results. 1. The reinforced intramolecular hydrogen bond O 3 –H 4 •••N 5 of 9-10-HBQ in the S 1 state facilitates the first ESIPT reaction. 2. The first ESIPT is a nonbarrier process, which provides the impetus for the second ESIPT reaction. 3. The stepwise excited-state double proton transfer mechanism could be confirmed, based on which the previous experimental results can be successfully explained.

Description: We have studied the mechanism of solvolysis of arenesulfonyl chlorides by propan-1-ol and propan-2-ol at 303-323 K. Kinetic profiles were appropriately fit by first-order kinetics. Reactivity increases with electron-donating substituents. Ortho -alkyl substituted derivatives of arenesulfonyl chlorides show increased reactivity, but the origin of this “positive” ortho -effect remains unclear. Likely, ortho -methyl groups restrict rotation around the C-S bond, facilitating the attack of the nucleophile. No relevant reactivity changes have been found with propan-1-ol and propan-2-ol in terms of nucleophile steric effect. The existence of isokinetic relationships for all substrates suggests a single mechanism for the series. Solvolysis reactions of all substrates in both alcohols show isokinetic temperatures (T iso ) close to the working temperature range, which is an evidence of the process being influenced by secondary reactivity factors, likely of steric nature in the TS. Solvation plays a relevant role in this reaction, modulating the reactivity. In some cases, the presence of t -Bu instead of Me in para- position leads to changes in the first solvation shell, increasing the energy of the reaction ( ca. 1 kJ·mol −1 ). The obtained results suggest the same kinetic mechanism of solvolysis of arenesulfonyl chlorides for propan-1-ol and propan-2-ol, as in MeOH and EtOH, where bimolecular nucleophilic substitution (S N 2) takes place with nucleophilic solvent assistance of one alcohol molecule and the participation of the solvent network involving solvent molecules of the first solvation shell. Ortho -alkyl–substituted derivatives of arenesulfonyl chlorides show increased reactivity in the framework of a single mechanism of alcoholysis in propan-1-ol and propan-2-ol as nucleophiles/solvents. Solvolysis of all substrates in both alcohols shows isokinetic temperatures (T iso ) close to the working temperature range, which indicates that the process is influenced by secondary reactivity factors, likely of steric nature, in the TS. Obtained results suggest the same kinetic mechanism of solvolysis of arenesulfonyl chlorides for propan-1-ol and propan-2-ol, as in MeOH and EtOH, where bimolecular nucleophilic substitution (S N 2) takes places with nucleophilic solvent assistance of an alcohol molecule, and some solvent molecules of the first solvation shell forming a solvent network.

Description: The tautomerism of the aliphatic MeC(NH 2 )═NOH and the aromatic PhC(NH 2 )═NOH amidoximes in protic (H 2 O, MeOH) and aprotic (Me 2 CO, Me 2 SO, and CHCl 3 ) solvents was studied by density functional theory calculations at the M06-2X/6-311+G(d,p) level of theory. In both types of solutions, these species exist in 3 tautomeric forms, viz, ( Z )- or ( E )-amidoximes, and ( Z )-aminonitrone. The ( Z )-form is the dominant, and energy gap between the ( Z )- and ( E )-tautomers of the amidoximes slightly depends on the nature of a solvent and significantly higher than that for other oxime species. For the amidoximes, the zwitterionic ( Z )-aminonitrone form is stabilized by protic solvents. The oxime-nitrone energy gap is reduced by electron-donor substituents at the oxime moiety at different types of oxime species. The tautomerism of various amidoximes in protic and aprotic solvents was studied by DFT calculations at the M06-2X/6-311+G(d,p) level of theory. In both types of solutions, these species exist in 3 tautomeric forms, ie, ( Z )- or ( E )-amidoximes and ( Z )-aminonitrone, and the former form is the dominant. The oxime-nitrone energy gap is reduced by electron-donor substituents at the oxime moiety, and it is the lowest in the case of amidoximes due to strong + M effect of the NH 2 group.

Description: The present paper reports a study on the energetics of protonation of a hydrogenase biomimetic complex, [Fe 2 (μ-adt)(CO) 4 (PMe 3 ) 2 ] (adt = N-benzylazadithiolate), and of its homologue featuring triphenylphosphine ligands in place of trimethylphosphines. Formation of a terminal hydride on one of the Fe centres was considered first, given the key relevance of terminal hydride species in the enzymatic mechanism. Theoretical calculations highlight that, in a vacuum, terminal protonation of the selected Fe ion in the PPh 3 -bearing organometallic complex is highly favoured when compared to the analogous reaction involving the PMe 3 -containing species, but the trend is inverted in the case of models optimized in a continuum polarizable. An unexpected parallel is thus established between relative basicities of PPh 3 and PMe 3 in vacuum or in solution phase [C. A. Tolman, J. Am. Chem. Soc. 1970 , 92 , 2953; G. M. Bancroft, Inorg. Chem. 1986 , 25 , 3675], and the energetics of terminal hydride formation upon protonation of [FeFe]-hydrogenase biomimetic complexes bearing such organophosphorous ligands. Bridging hydride formation was also considered in the present study: calculations showed that protonation of the PMe 3 -bearing organometallic complex is again strongly favoured in vacuo, as compared to the case of the PPh 3 -containing model. However, protonation energies become significantly smaller when solvent effects are taken into account. Such differences between protonation reactions modelled in vacuo and in the polarizable continuum are rationalized in light of the different electrostatic properties of the diiron complexes here considered. Implications for the design and modelling of biomimetic catalysts are briefly discussed in light of recent literature. Theoretical calculations highlight a parallel between relative basicities of PPh 3 and PMe 3 in vacuum or in solution phase, and the energetics of metal protonation in [FeFe]-hydrogenase biomimetic complexes bearing such ligands. Implications for the design and modeling of biomimetic catalysts is briefly discussed in light of the recent literature.

Description: The new Schiff base 1-[(2-{1-[(dicyclohexylamino)-methyl]-1H-indol-3-yl}-ethylimino)-methyl]naphthalen-2-ol (HL) was prepared from 1-{[2-(1H-Indol-3-yl)-ethylimino] methyl}-naphthalen-2-ol and dicyclohexyl amine. From this Schiff base, monomeric complexes [M (L) n (H 2 O) 2 Cl 2 ] with M = Cr, Fe, Mn, Cd, and Hg were synthesized and characterized based on elemental analysis (EA), FT-IR, mass(MS), UV-visible, thermal analysis, magnetic moment, and molar conductance. The results showed that the geometrical structural were octahedral geometries for the Cr(III) and Fe(III) complexes, square planer for Pd(II) complex, and tetrahedral for Mn(II), Cd(II), and Hg(II) complexes. Kinetic parameters such as ΔE*,ΔH*, ΔG*, and K of the thermal decomposition stages were calculated from the TGA curves using Coats-Redfern method. Additionally, density functional theory (DFT) was applied for calculations of both electronic structure and spectroscopic properties of synthesized Schiff base and its complexes. The analysis of electrostatic potential (EPS) maps correlates well with the computed energies providing on the dominant electrostatic nature of N-H---O interactions. The biological activities had been tested in vitro against Staphylococcus aureus , Pseudomonas aeruginosa , as well fungi like Penicillium expansum , Fusarium graminearum , Macrophomina phasealina , and Candida albicans bacteria in order to assess their antimicrobial potential. A new Schiff base was prepared from 1-{[2-(1 H -indol-3-yl)-ethylimino]methyl}-naphthalen-2-ol and dicyclohexyl amine. Monomeric complexes [M(L) n (H 2 O) 2 Cl 2 ] with M = Cr, Fe, Mn, Cd, and Hg were synthesized and characterized based on elemental analysis, Fourier transform infrared, mass spectrometry,ultraviolet-visible, thermal analysis, magnetic moment, and molar conductance. These findings showed that the geometrical structures were octahedral geometries for the Cr(III) and Fe(III) complexes, square planar for the Pd(II) complex, and tetrahedral for the Mn(II), Cd(II), and Hg(II) complexes.

Description: No abstract is available for this article.

Description: No abstract is available for this article.

Description: The nucleophile-electrophile interactions in the reaction system “N,N-dimethylaniline – acetic acid – epichlorohydrin” have been investigated using kinetic methods and computer modeling. The observed orders of reactions have been determined for the overall reaction as well as for individual stages. The kinetic equations have been proposed; the activation parameters of the reactions have been evaluated. The behavior of the initial (amine) and intermediate (carboxylate) nucleophiles has been detailed in reaction pathway. Amine reacts with oxirane activated by acidic reagent while carboxylate-anion—with both activated and nonactivated epichlorohydrin. The mechanism of oxirane ring opening by acid reagent in the presence of tertiary amine has been proposed, which comprise parallel-consecutive compensation stages of reaction product formation. It has been demonstrated that the observed reaction order with respect to acid reactant depends upon the nature of electrophilic reagent (activated/nonactivated oxirane) and the ratio of the rates of compensation stages. The nucleophile-electrophile interactions in the reaction system “N,N-dimethylaniline – acetic acid – epichlorohydrin” have been investigated using kinetic methods. The behavior of the initial (amine) and intermediate (carboxylate) nucleophiles has been detailed in reaction pathway. Amine reacts with oxirane activated by acidic reagent while carboxylate-anion—with both activated and non-activated epichlorohydrin.

Description: 3-Chloro-1,2,3,4-tetrahydro-1,4-epoxynaphthalen-2-yl)-3-hydroxy-5,5-dimethylcyclohex-2-en-1-one, synthesized by the reaction of oxabenzonorbornadiene with Mn(OAc) 3 and dimedone in the presence of HCl in acetic acid, was submitted to ring-opening reactions with BBr 3 and H 2 SO 4 . Reaction with BBr 3 yielded 2 products, a 5-membered ring and an 8-membered ring, with the former being the major product. However, the H 2 SO 4 -supported reaction exclusively formed an 8-membered ring. The mechanism of formation of these products was supported by theoretical calculations. The reaction of oxabenzonorborna-diene with dimedone and Mn(OAc) 3 in the presence of HCl gave an adduct that was submitted to the ring-opening reactions. The BBr 3 -supported ring-opening reaction of the adduct gave a five-membered ring, however, reaction with formed a bicyclic system.

Description: The changes of the free energy of activation δ∆ G ≠ exp and the activation entropy δ∆ S ≠ in the framework of the isokinetic relationship δ∆ G ≠ exp versus ( T iso  −  T exp ) δ∆ S ≠ were explored quantitatively to predict the isokinetic temperature T iso for the aromatic nucleophilic substitution reactions in solution. The simple isokinetic relationship was found for S N Ar reactions: δ∆ G ≠ exp  = (0.12 ± 0.41) + (0.97 ± 0.02) ( T iso  −  T exp ) δ∆ S ≠ r = 0.998, s = 1.43, n = 13 where T iso and T exp are the isokinetic and experimental temperatures, respectively. The δ∆ G ≠ exp and δ∆ S ≠ values are the changes of the free energy of activation and activation entropy, respectively.

Description: In this study, a new series of cadmium halide/pseudohalide complexes with a novel Schiff base ligand containing imidazolidine ring has been successfully synthesized. The structure of the ligand and its complexes was characterized by analysis tools such as Fourier transform infrared, UV-visible, proton and carbon nuclear magnetic resonance spectra, molar conductance, and thermal analysis. Also cadmium bromide and iodide nanostructure complexes have been prepared via sonochemical method. X-ray powder diffraction and scanning electron microscopy techniques confirmed nanostructure sheets for these 2 cadmium complexes. All the newly prepared compounds were screened for their antimicrobial activities, against 4 bacterial and 2 fungal strains using disk diffusion and serial dilution methods. The CdL(N 3 ) 2 and CdLCl 2 complexes showed the best antimicrobial activity as compared with other compounds. Moreover, DNA cleavage potential of all compounds was investigated by agarose gel electrophoresis method. The results showed remarkable ability of some cadmium complexes for DNA cleavage. Furthermore, thermal behaviors of all cadmium complexes were studied in the range of room temperature to 800°C under nitrogen atmosphere. The complexes were thermally decomposed via 2 to 4 steps. Cadmium metal was suggested as final residue at the end of thermal decomposition process.

Description: In contrast to typical borepins, which appear about 40.0 kcalmol −1 more stable than their corresponding tautomeric boranorcaradienes, we have found 2 species, which have reversed this trend and pushed the equilibrium in favor of their corresponding boranorcaradienes. They are namely 1a,9b-dihydro-1 H -borireno[2,3- h ]pyridazino[4,3- f ]cinnoline and 1a,9b-dihydro-1 H -borireno[2,3- h ]pyrimido[5,4- f ]quinazoline which stand up among 14 isomeric systems probed, at B3LYP/AUG-cc-pVTZ, M06-2X/AUG-cc-pVTZ, MP2/AUG-cc-pVTZ, and HF/AUG-cc-pVTZ. Energy barriers are calculated in gas-phase, where the possibility of a rapid interconversion of the isomers is ruled out. Generally, dibenzoboranorcaradienes assume C s symmetry with planar geometry and dihedral angle of zero degree. In contrast, their corresponding borepins show a high tendency for puckering with dihedral angle of ~66°. The preference of the latter for puckered non-planar geometries is evidenced by natural bonding orbitals calculations and visually through their frontier molecular orbitals. Main interactions appear to be hyperconjugations of σ and π bonds across the rings. Position and number of nitrogen atoms on the fused rings seem to affect the energy gap, dipole moment, symmetry, dihedral angle, the chemical shift, NICS, bond lengths, and charge distribution. Typical borepins ( a ) appear nearly 40.0 kcalmol −1 more stable than their corresponding tautomeric boranorcaradienes ( b ). Here, we discuss substituent effects on thermodynamic and kinetic parameters involved in tautomerization of 14 bimolecular systems [( 1a to 14a ) ⇌ ( 1b to 14b )] involving mono-, di-, tri-, and tetra-aza substituted 6 H -dibenzo[ c,e ]borepins as well as 1a,2,7b-tetrahydro-1 H -indeceno[4,5- b ]borirenes, at B3LYP/AUG-cc-pVTZ, MP2/AUG-cc-pVTZ and HF/AUG-cc-pVTZ levels. Among them, 2 new boranorcaradienes are found, which appear more stable than their respective borepins. They are namely, 1a,9b-dihydro-1 H -borireno[2,3- h ]pyridazino[4,3- f ]cinnoline ( 6b ) and 1a,9b-dihydro-1 H -borireno[2,3- h ]pyrimido[5,4- f ]quinazoline) ( 7b ).

Description: Three unsymmetrical diarylethenes with a 6-membered quinoline moiety were synthesized to investigate the effects of the substituents on their photochromism, and fluorescence, and the structure of one diarylethene was determined by single crystal X-ray diffraction analysis. Quinoline was connected directly to the central perfluorocyclopentene ring as an aryl moiety and available to participate in photoisomerization reaction in solution, amorphous films, and crystalline phase. These diarylethenes exhibited good photochromism with excellent thermal stability and obvious fatigue resistance. The electron-donating methoxy group could enhance the absorption maxima of closed-ring isomers and the quantum yields of cyclization and cycloreversion, but the electron-withdrawing trifluoromethyl had an opposite effect. In addition, they functioned as notable fluorescence switches in both solution and polymethylmethacrylate films, and the trifluoromethyl group and the methoxy group both increased the emission intensity. The results revealed that the quinoline moiety and substituents played a vital role in the process of photoisomerization reactions for these diarylethenes. Three unsymmetrical diarylethenes with a 6-membered quinoline moiety were synthesized, and the substituent effects on their photochromic properties were studied systematically.

Description: Coupled-cluster calculations were performed for 1,3-disilacyclobutane-1,3-diylidene disilylenes at the CCSD(T)//CCSD/cc-pVDZ level of theory to investigate the ground-state spin multiplicity and structures of these unique molecules in detail. The cis -bent disilene with an R 2 Si═SiR 2 double-bonding structure was found to be the most energetically stable structure for the 2,2,4,4-tetrafluoro-substituted compound. In contrast, the singlet disilylene structures (R 2 Si:) with a 4-membered ring geometry were calculated to be more energetically stable than the disilene structures for 1,3-disilacyclobutane-1,3-diylidene disilylenes with electron-donating substituents such as H and SiH 3 . Thus, the perfluoro-substituted disilylene was found to be a candidate for the synthesis of cis -bent disilenes. The cis -bent disilene with an R 2 Si═SiR 2 double-bonding structure was found to be the most energetically stable structure for the 2,2,4,4-tetrafluoro-substituted compound. In contrast, the singlet disilylene structures (R 2 Si:) with a 4-membered ring geometry were calculated to be more energetically stable than the disilene structures for 1,3-disilacyclobutane-1,3-diylidene disilylenes with electron-donating substituents such as H and SiH 3 .

Description: No abstract is available for this article.

Description: The physicochemical aspects of functioning the luminescent converters for a rational modification of the emission spectra of light-emitting diodes are considered. These converters use laser dyes' coumarins 314, 334, and 343 to transfigure the primary light-emitting diode spectrum. The fine control of the emission spectra of the mentioned coumarins in polymeric matrices was achieved by introducing nonionic detergents. The relevant characteristics of the photochemical persistence of coumarins in the polymer layers are acquired. The use of the coumarins-based luminescent spectral converters allows to transform the emission spectrum of the primary light-emitting diode source into a spectrum, which mimics that of the natural daylight. The fine control of the emission spectra of the coumarins in polymeric matrices of the spectral converters is achieved by introducing therein the nonionic detergents.

Description: An octafluorinated 2,11-diaza[3 2 ]paracyclophane derivative 12 was prepared, and its photochemical reaction was investigated. Upon irradiation at 300 nm, the fluorinated azacyclophane 12 underwent efficient photodimerization of the benzene cores to afford the corresponding photoisomer 13 , which possessed cage diene benzene dimer structure (pentacyclo[6.4.0.0. 2,7 0. 3,12 0 6,9 ]dodeca-4,10-diene skeleton). The cage diene structure was established by single-crystal X-ray diffraction analysis. The cage diene 13 thermally isomerized to a syn - o , o ′-dibenzene isomer 22 . The activation parameters for the thermal isomerization were determined to be E a  = 121 kJ mol −1 , ΔH ≠  = 118 kJ mol −1 , ΔS ≠ (293 K)  = 22 J mol −1  K −1 , and ΔG ≠ (293 K)  = 111 kJ mol −1 . It was revealed that, by photoirradiation at 300 nm, the syn - o , o ′-dibenzene isomer 22 underwent facile intramolecular [π4s + π4s] cycloaddition to reproduce the cage diene isomer 13 . Fluorinated azacyclophane was synthesized, and its photoreaction was investigated. Upon photolysis, the 2 benzene cores of the azacyclophane dimerized to produce a cage diene benzene dimer. The structure and photo- and thermal behavior of the cage diene isomer were also revealed.

Description: This review is devoted to the critical analysis of the existing contradictory ideas about kinetic description and the mechanisms of electrophilic aromatic substitution (EAS), ie, reversible arene sulfonation and hydrolysis (protodesulfonation) of arenesulfonic acids. Contemporary scientific and educational literature contains prevailing, widespread points of view on the multistage nature processes of the EAS that proceed via π- and σ-complexes and are accompanied by arenium ion formation. This interpretation does not account for determining influence of the medium, and the process accompanies the loss of aromaticity. The review presents an alternative point of view: These processes proceed via single-stage and the same transition state. To substantiate this position, we reviewed in detail the contemporary ideas on the solvated proton structure, the limits of applicability of acidity function Н о and excess acidity Х scales, and the experimental solubility data of arenesulfonic acid hydrates in sulfuric acid. This solubility depends on the medium acidity (h o ), which provides the formation of 3 conjugated types of hydrates: anionic (АrSO 3 − ·H 2 O), hydroxonium-arene sulfonated (АrSO 3 − ·H 3 O + ), and the hydroxonium complex with the H-form of АrSO 3 Н·H 3 O + acid. In sulfuric acid solutions with an excess of water, irreversible hydrolysis proceeds with the participation of ArSO 3 − ·H 3 O + . However, protodesulfonation becomes reversible and proceeds with the participation of ArSO 3 Н·H 3 O + in solutions with an excess of sulfuric acid. A conclusion has been made about determining the role of the hydrated proton environment by means the formation of a cyclic transition state. An alternative 2-stage mechanism of EAS is logically and energetically unsubstantiated and, therefore, should be rejected. The hydrated proton environment plays the determining role in the formation of a cyclic transition state of electrophilic aromatic substitution (EAS), ie, reversible arene sulfonation and hydrolysis (protodesulfonation) of arenesulfonic acids. The mechanism of these processes is realized as single stage and occurring in an acidic water medium via the same transition state, but an alternative 2-stage mechanism of EAS, that proceed via π- and σ-complexes, is logically and energetically should be considered less reasonable.

Description: The interactions between the trinuclear cyanine all- trans -2,2'-[3-[(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)ethylidene]-1,4-pentadiene-1,5-diyl]-bis[1,3,3-trimethyl]-3H-indolium with representative G4-DNA sequences, namely, 22AG [d(AG 3 T 2 AG 3 T 2 AG 3 T 2 AG 3 )], c-myc [d(TGAG 3 TG 3 TAG 3 TG 3 TA 2 )], c-kit [d(AG 3 AG 3 CGCTG 3 AG 2 AG 3 )], and a2 [d(ACAG 4 TGTG 4 ACAG 4 TGTG 4 )] and with double-stranded DNA, ct DNA and ds26 [d(CA 2 TCG 2 ATCGA 2 T 2 CGATC 2 GAT 2 G)], are studied by photometric and fluorimetric titrations, CD-spectroscopic analysis, and 1 H-NMR spectroscopy. It is demonstrated that the heptamethine cyanine binds to quadruplex DNA by terminal π-stacking and to duplex DNA by aggregation along the DNA backbone. The ligand does not bind selectively to quadruplex DNA as compared with duplex DNA, but the two DNA forms can be differentiated with this ligand based on the different development of its absorption and emission properties upon ligand-DNA association. The trinuclear [2.2.2.]heptamethine cyanine enables the discrimination between quadruplex and duplex DNA based on the different developments of absorption and emission properties upon ligand-DNA association.

Description: This report examines the effect of substrate design upon the Truce-Smiles rearrangement, an intramolecular nucleophilic aromatic substitution reaction. The length of the molecular spacer that tethers the carbanion nucleophile to the substituted benzene ring was found to have a strong influence on the ability of the substrate to undergo the reaction successfully. Our experimental results show highest yield of desired aryl migration product for substrates designed with a 3-atom tether, which proceed through a 5-membered spirocyclic intermediate. The results are interpreted in comparison with a survey of Truce-Smiles rearrangements described in the literature and found to be consistent. Computational studies support the observed reactivity trend and suggest an explanation of a favorable combination of ring strain and electrostatic repulsion leading to optimal reactivity of the substrate designed with a 3-atom tether. Comparison of our results with trends for related ring-closing reactions illustrate the unique electrostatic features of the system studied herein. A study of the effect of tether length in the Truce-Smiles rearrangement, an intramolecular nucleophilic aromatic substitution reaction, is presented. Experimental results are supported by computational modelling of reaction pathway potential energy surfaces.

Description: Different reactive oxygen species were detected by the molecular probes 1-3 that were composed of the phthalimide fluorophore as reporter and a methionine-derived thioether side-chain as receptor part. The sulfoxides that were formed as the primary oxidation products show strong fluorescence in the blue-green (430-540 nm) spectral region. Self-sensitized oxidation by singlet oxygen is in general inefficient indicating rapid electron-transfer quenching of the excited probe molecules. With hydrogen peroxide as thermal oxidant conversion to the sulfoxides is slow but can be accelerated by addition of titanium(IV) catalysts, whereas hypochlorite as oxidant behaves much more reactive even under uncatalyzed conditions. Singlet oxygen that is generated by energy transfer from the photosensitizer Rose Bengal was detected by sensor 1a with rate constants of 〉10 7 M –1  s –1 , a typical rate constant for the oxidation of thioethers to sulfoxides. New fluorescent molecular probes for reactive oxygen species were composed of prefluorescent phthalimide reporters and fluorescence-quenching methionine-derived receptors. The sulfoxides that are the sole primary oxidation products show strong fluorescence in the blue-green (430-540 nm) spectral region, whereas the probes are nearly nonfluorescent due to rapid intramolecular electron-transfer quenching of the excited molecules. All probes can be switched on with singlet oxygen, hydrogen peroxide, and hypochlorite as oxidants with different efficiencies.

Description: Multiple proton transfer (PT) is an essential process in long-range proton transport such as proton relay in enzymes. 7-Hydroxyquinoline (7HQ) undergoes alcohol-mediated PT in both the excited and ground states, and this system has been investigated as a biomimetic model. In the present study, the reaction pathway of triple PT in a 7HQ-methanol cluster, 7HQ·(MeOH) 2 , in the ground state has been investigated using density functional theory calculations to clarify the reaction mechanism and the origin of the experimentally observed kinetic isotope effect (KIE). The PT takes place in an asynchronous concerted fashion, in which the oxygen atom in 7HQ first accepts a proton from the directly hydrogen-bonded MeOH. The rate constants and primary H/D KIEs have been estimated with canonical variational transition state theory in combination with the small curvature tunneling approximation. The tunneling effect on the PT rate is significant, and the KIE is much greater than 1 at room temperature. The rule of the geometric mean for the KIEs breaks down because of the asynchronicity in the motions of 3 protons and tunneling effect. In addition, the rate constant is smaller, the KIE is larger, and the activation energy is higher compared with the experimental values in heptane solution, suggesting that the PT dynamics in solution is governed by not only the intrinsic PT process but also thermal fluctuation of the solute and solvent molecules, which plays an important role in the configurational change of the 7HQ·(MeOH) 2 complex. The reaction pathway of triple PT in a 7HQ-methanol cluster, 7HQ∙(MeOH) 2 , has been investigated using DFT calculations. The PT takes place in an asynchronous concerted fashion, in which the oxygen atom in 7HQ first accepts a proton from MeOH. The tunneling effect is significant, and the KIE is much greater than one. The rule of the geometric mean for the KIE breaks down because of the asynchronicity in the motions of 3 protons and tunneling effect.

Description: Low-temperature NMR studies revealed aggregate formation in cyclopropyllithium compounds. For C 3 H 5 Li (1), a static tetramer [ 1 J ( 6 Li, 13 C) = 6.5 Hz] was found in diethylether (DEE), while in tetrahydrofuran (THF) a dimer and a fluxional tetramer [ 1 J ( 6 Li, 13 C) = 9.3 and 4.7 Hz, respectively] were detected. Trans- 2,3-dimethyl-1 (2) yielded in DEE/THF (1:1) diastereomeric dimers [ 1 J ( 6 Li, 13 C) = 9.3 Hz] and 2,2,3,3-tetramethyl-1 (3) formed dimers in DEE and DEE/THF [ 1 J ( 6 Li, 13 C) = 10.0 and 9.6 Hz, respectively]. For bis-( trans -2,3-dimethylcyclopropyl)-mercury (7), ligand exchange could be detected by the isotopic fingerprint method with 199 Hg NMR at room temperature. 199 Hg NMR in connection with specific deuteration may thus be used for ligand exchange studies in the field of organomercury compounds. NMR-spectroscopy was used to study the aggregation behavior of cyclopropyllithium compounds. For the parent system 1 a static tetramer was found in diethyl-ether (DEE) and a dimer and a fluxional tetramer in tetrahydrofuran (THF). trans -2,3-Dimethyl- 1 ( 2 ) and 2,2,3,3-tetramethyl- 1 form only dimers in DEE/THF (1:1), those of 2 as two diastereomers, while ligand exchange in ( 2 ) 2 -mercury was detected with 199 Hg NMR.

Description: N-oxyphthalimides are stable and easily accessible compounds that can produce oxygen radicals upon 1-electron reduction. We present a systematic study of electrochemical properties of N-oxyphthalimide derivatives (PI-ORs) in DMF by cyclic voltammetry. In all cases, electron transfer to the substrate leads to decomposition of the intermediate radical anion via the N―O bond cleavage. In the case of benzyloxyphthalimide or its derivatives containing electron-donating substituents, reductive electron transfer induces the chain decomposition of the substrate to phthalimide (PI) radical-anion and the corresponding carbonyl compound. The PI radical-anion product is a powerful reductant that can transfer an electron to the reactant PI-OR, thus establishing a catalytic cycle for reductive N―O scission. This self-catalytic process is reflected in a considerable decrease in the reduction current for the substrate (〈1e - /molecule). By contrast, reductive fragmentations of benzyl derivatives containing electron-withdrawing substituents in the aromatic ring or at the benzylic position, as well as tosyl and alkyl derivatives, occur via a 1-electron mechanism. A sequence of N―O and C―C scissions was engineered to support the intermediacy of O-centered radicals in these processes. Systematic study of electrochemical properties of N -oxyphthalimide derivatives (PI-ORs) is presented. In all cases, electron transfer to the substrate leads to the N-O bond cleavage. In the case of benzyloxyphthalimide or its derivatives containing electron-donating substituents, reductive electron transfer induces the chain decomposition of the substrate to phthalimide (PI) radical-anion and the corresponding carbonyl compound. In contrast, reductive fragmentations of benzyl derivatives containing electron-withdrawing substituents, as well as tosyl and alkyl derivatives occurs via a one-electron mechanism.

Description: New poly-phenylenevinylenes PPVs containing 1,3,4-thiadiazole as candidates for organic semiconductors have been theoretically studied at density functional theory (DFT) and time-dependent DFT levels. This study has been conducted in order to investigate the geometrical and electronic properties as well as the conductivity of a series of PPV–thiophene–1,3,4–thiadiazole–thiophene (H–PhTAT–H) containing –CHO, –CH 2 –P(=O)(OCH 3 ) 2 , and phenyl–CHO (PhCHO) terminal groups. The impact of terminal groups on the optical bandgaps, electron affinity, LUMO energy, and intramolecular reorganization energy was studied for different oligomers and for a limit polymer. The incorporation of terminal groups did not affect the chain length evolution and the vertical transition energy E vert value for a polymer limit compared with the unsubstituted oligomer (H–PhTAT–H). All studied properties showed that CHO–PhTAT–PhCHO and H–PhTAT–H oligomers can be considered as n-type semiconductors. Poly-phenylenevinylenes PPVs containing 1,3,4-thiadiazole are considered to be relevant candidates for n-type organic semiconductors. This study has been theoretically conducted to reveal the impact of terminal groups on the optical bandgaps, electron affinity, LUMO energy, and intramolecular reorganization energy for different oligomers and for a limit polymer.

Description: Density functional theory (DFT) calculations introduced triplet ground states for [6] n SiC-cyclacenes and -acenes with alternate silabenzene rings including silicon atoms in 2 opposite edges ( n  = 6, 8, 10, 12). The singlet-triplet energy gap (ΔE (S-T) ), binding energy per atom (BE/n), and NBO calculation with very small band gap (ΔE LUMO-HOMO ) confirmed the triplet ground states. In contrast to polyacenes, the singlet [6] n SiC-cyclacenes displayed more stability improvement than triplets, through n increasing. This may open the way for synthesis of larger stable [6] n SiC-cyclacenes. The ΔE (S-T) , BE/n, and the strain energy through homodesmic equations indicated more stability for larger [6] n SiC-cyclacenes, which was more noticeable in singlet states. Cyclacenes and acenes with high conductivity and full point charge were introduced as suitable candidates for hydrogen storage. Samples of our scrutinized [6] n SiC-cyclacenes and [6] n SiC-polyacenes, [6] 8 SiC-Cyclacenes and [6] 8 SiC-acenene, ( n  = 6, 8, 10, and 12).

Description: A series of metal-free compounds, ie, planar triprotonated triazine, triazineH 3 Cl(PF 6 ) 2 ( 1 ), planar triprotonated triazineH 3 Br(PF 6 ) 2 ( 2 ), and nonplanar monoprotonated triazineHPF 6 ( 3 ), were prepared. Abbreviations used are triazine = tri-2-pyridyltriazine. Ruthenium complexes [RuCl(bpy)(L)](PF 6 ), [RuCl(bpy)(L)](PF 6 ) 2 , and [Ru(L) 2 ](PF 6 ) 2 were also prepared, where bpy is 2,2′-bipyridine and L's are triazine ( 4 ) and monoprotonated triazine ( 5 ), respectively. Ruthenium complexes [Ru(triazine) 2 ](PF 6 ) 2 ( 6 ) were also prepared and crystallized. The X-ray crystal structures of the 3 compounds 1 , 2 , and 3 and the complex 6 were determined. They were also characterized by electrospray ionization mass spectrometry, UV-vis spectroscopy, and density functional theory calculations. In 4 and 5 , spin densities were analyzed to characterize the triplet states in those complexes. Both the complexes have 3 MLCT triplet states. In particular, that of 4 is very stable, which leads to the high quantum yield ( Φ  〉 0.20) of the emission.

Description: Environment-sensitive hydrogel is a sensitive hydrogel that responses to outside stimuli. A new temperature- and pH-sensitive hydrogel is able to been prepared by radiation polymerization or emulsion polymerization method combining with the excellent thermosensitive poly(N-isopropyl acrylamide) (PNIPAM), and the pH-sensitive chitosan (CS). However, it is different to understand the reaction mechanisms thoroughly unless we can obtain more details at the molecular level. In this work, the reaction mechanism of chitosan and acrylamides (AMs, that is AM or NIPAM) dimer was shed light on by using the density functional theory (DFT), to investigate all possible reaction channels and reveal the underlying nature of polymerization at the micro level. The geometric structures of all stationary points in the reaction pathways were optimized. The reaction takes place via 3 possible reaction channels, which are RCSN + AMs   RCSN/AMs, RCSO3 + AMs   RCSO3/AMs, and RCSO5 + AMs   RCSO5/AMs. Comparing the energy barriers of these reaction pathways at a higher level, RCSO5 + AMs   RCSO5/AMs is the main pathway for forming RCS/AMs. According to the variations of bond-lengths and the corresponding vibration peaks, it is confirmed that there are intramolecular hydrogen bond interactions in RCSO3/AMs dimer and RCSO5/AMs dimer. The reaction of chitosan (CS) and acrylamides (AMs, that is AM or NIPAM) dimer takes place via 3 possible reaction channels, which are RCSN+AMs RCSN/AMs, RCSO3+AMs RCSO3/AMs, and RCSO5+AMs RCSO5/AMs. Comparing the energy barriers of these reaction pathways at a higher level, RCSO5+AMs RCSO5/AMs is the main pathway for forming RCS/AMs. According to the variations of bond lengths and the corresponding vibration peaks, it is confirmed that there are intramolecular hydrogen bond interactions in RCSO3/AMs dimer and RCSO5/AMs dimer.

Description: The kinetics and activation parameters for the reaction between 2-amino-benzamide and some benzaldehyde derivatives in the presence of formic acid have been reported and discussed. A linear plot of lnk vs l/T showed that the reactions obey the Arrhenius equation. Both the Arrhenius and the Eyring equations were used to calculate the activation energy. The effect of nitro groups was studied on different positions of benzaldehyde. For all substituents, the reactions followed second-order kinetics, and the partial orders of reactions were recognized with respect to each reactant. Comparisons between the magnitudes of ΔH ‡ and T ΔS ‡ showed that the reactions were enthalpy controlled. The validity of the isokinetic relationship and the compensation effect was tested, and the isokinetic temperature (β) was obtained. A linear enthalpy-entropy plot (ΔH ‡ versus ΔS ‡ )  showed that the compensation effect is established, and this process occurs via a same mechanism across a series of reactions. From the Van't Hoff and Exner's plots, the isokinetic temperature was obtained. Herein, we investigate the validity of the isokinetic relationship and compensation effect in addition to the kinetic studies.

Description: No abstract is available for this article.

Description: The Nicholas reaction is a proven and versatile tool in glycoside chemistry. Its application is less clear-cut, if the intermediate Nicholas cation has two reactive sides that enable different reactions. Density functional theory (DFT) calculations are used to rationalize the observed difference in product yields for the Nicholas epimerization and substitution obtained from experiments with very similar glycosides. Substituents, which can increase the rigidity of the backbone, should be avoided in epimerization reactions as they can slow down reorientation of the intramolecular ion pair so that the substitution reaction dominates. Comparative DFT calculation show that substituents increasing the rigidity of the backbone can prevent the Nicholas epimerization while having no significant influence on the Nicholas substitution reaction.

Description: Every day, more evidence accumulates, leading to the conclusion that the stereoelectronic model through the n O    σ* C─O interaction is of minor relevance or even inoperative to explain conformational preference in the specific O─C─O segment. In the present study, dimethoxymethane (DMM) and some model spiroketals were chosen to develop a reliable and easy to apply methodology that is simple to interpret by experimental chemists. The general conformation observed in these molecules, present in many biologically active natural products, is the gauche - gauche ( g , g ) in DMM and bis-diaxial in spiroketals. To study this conformational preference, this paper presents a new approach, where general trends for the atomic and molecular energetic components, as well as localization and delocalization indices, and their bonded (Δ b ) and nonbonded (Δ nb ) electronic contributions are analyzed. In addition, group contributions to the electron localization and polarization are also defined, agreeing with the conformational preference. It is clear that electronic localization/delocalization is capable of reproducing experimental observations, showing an adequate correlation of this property to the cos θ term in the context of Pople's analysis. It is proposed that electron delocalization between electronegative atoms or total delocalization between nonbonded atoms is not the major contributors to the axial conformational preference observed in spiroketals. Conformational preference shows defined trends in terms of group delocalization in DMM and ring localization and charge transfer between groups in spiroketals. This way, electronic delocalization can be used to evaluate the anomeric effect, using just a few parameters, which makes the method broadly functional. A new approach to study conformational preference with a reliable methodology that is simple to apply and interpret is presented. Trends for atomic and molecular energetic components, and localization and delocalization indices, and their electronic contributions are analyzed. Group contributions to electron localization and polarization agree with conformational preference. Electronic localization/delocalization reproduces experimental observations, showing adequate correlation to Pople's cos θ term. Electronic delocalization can be used to evaluate the anomeric effect, using few parameters, making the method broadly functional.

Description: No abstract is available for this article.

Description: Even though all the p - N , N -dimethylaminobenzonitrile ( p -DMABN), cis - o -DMABDI, and cis - p -DMABDI (the N , N -dimethylamino analogues of green fluorescence protein chromophore) have the same electron-donating N , N -dimethylamino group, unlike the dual fluorescence of p -DMABN, both cis - o -DMABDI and cis - p -DMABDI display single fluorescence. To figure out the interesting phenomena, the CAM-TD-B3LYP method and the cc-pVDZ basis set were used to explore geometries, molecular orbitals, electronic transition, dipole moment, and potential energy surfaces of the S 1 excited states of cis - o -DMABDI and cis - p -DMABDI. We found that the S 1 excited states of cis - o -DMABDI and cis - p -DMABDI are 1 (π, π*) charge transfer excited states with twisted structures, where the N , N -dimethylaminobenzene moiety functions as an electron donor, the methyleneimidazolone moiety serves as an electron acceptor, and the electron donor is linked with the electron acceptor by the C─C single bond (P-bond). The fluorescent emissions of cis - o -DMABDI and cis - p -DMABDI predicted by the CAM-TD-B3LYP/cc-pVDZ level are quite consistent with the experimental results. For the cis - o -DMABDI and cis - p -DMABDI, the S 1 locally excited state is less stable than the S 1 twisted intramolecular charge transfer state, and the S 1 LE state is not a stationary point (global minimum). That is why both cis - o -DMABDI and cis - p -DMABDI display single fluorescence. The locally excited S 1 is less stable than twisted intramolecular charge transfer S 1 , and the locally excited S 1 is not a stationary point. That is why both cis - o -DMABDI and cis - p -DMABDI display single fluorescence.

Description: Host-guest interactions are essential in chemistry, biology, medicine and environmental science. In this combined experimental and theoretical contribution, the encapsulation of 7-methoxycoumarin (herniarin, 7MC) with p- sulfonatocalix[4]arene ( p- SC4) is studied using absorption and fluorescence spectroscopy, cyclic voltammetry and computational approaches. The 1:1 stoichiometry is confirmed using Job's plot. Our results show that the keto group of 7MC is the main source for electrochemical conversion of this complex. The excited state 7MC radiative decay is studied using time-correlated single photon counting technique. The computed UV-Vis absorption spectra for this complex at gas phase and solvent are online with the experimental spectra. Moreover, we determined the binding energy and the binding constant of the 7MC- p- SC4 complex. Density functional theory computations revealed that stabilization of the complex formed by p- SC4 and 7MC is due to weak noncovalent and dispersive types of interactions. A comparison with encapsulation of amino acids by p- SC4 is also conducted. Finally, we show that the flexibility of p- SC4 and the weak nature of its interaction with 7MC are on the origin of the reversibility of encapsulation, which is mandatory for applications such as drug delivery. The encapsulation of herniarin (7-methoxycoumarin) with p- sulfonatocalix[4]arene is studied by both experimental and computational techniques. The 1:1 stoichiometry of the complex is identified. The spectral and electrochemical studies confirmed the efficient binding of herniarin with the host molecule. The parallel mode of binding and mode of interactions are identified by the computations.

Description: Spectroscopic evidence recorded in solutions of diphenyloctatetraene in n -octane, cyclooctane, and 2,2,4-trimethylpentane by sudden immersion of the sample at 77 K or by changing the solution temperature slowly between 293 and 77 K allow us to conclude that the distinct spectroscopic behavior of the polyene compounds, on extending its polyene chain, does not lie in the existence of a ghost state 2 1 Ag, as first excited electronic state of the system, but resides in a structural problem that influences whether its first electronic transition for absorption can be monitored or not at its lowest vibrational levels. The excitation spectra shown disregard the necessary existence of an underlying 2 1 Ag state to explain the photophysics of polyenes whose chain involves 3 double bonds or more. Normalized fluorescence excitation spectra for diphenylocta-1,3,5,7-tetraene 5 × 10 −5 M in n -octane (in red) and cyclooctane (in green) are obtained by monitoring light at 513 nm. The spectra are recorded by immersing the diphenylocta-1,3,5,7-tetraene sample directly in liquid nitrogen.

Description: In the present work, the pyrolysis reaction mechanism of both furfuryl benzoate and furfuryl acetate was evaluated at the M06/6-311++g(d,p) level. The uncommon methylenecyclobutenone compound and either the benzoic or the acetic acid were determined as the products of a multistep process consisting in two [3 + 3] rearrangements and a subsequent hydrogen α-elimination step, through a cyclic 5-membered transition state (TS), being the latter the rate-limiting step for both reactants. Furthermore, a deeper analysis on the basis of the reaction force formalism showed that the TS is formed in two stages: The first one is characterized by the weakening of the C─O bond, and the second one is where the H atom is transferred from the C atom to its nearest O atom. The H─O bond formation was determined to contribute the most to the electronic activity occurring during the TS formation as suggested by a reaction electronic flux analysis. Accordingly, natural bond orbital calculations showed that the most significant changes occur in the charge distribution of the O and H atoms. Finally, a negligible effect of the substituting group on the reaction was determined since similar activation energies were obtained for the pyrolysis of furfuryl benzoate and furfuryl acetate; however, a minor difference was evidenced in the reaction force results. In this sense, the structural contribution to the activation energy is larger than the electronic one for the furfuryl benzoate reaction, , whereas the opposite is observed for the furfuryl acetate reaction, . This pyrolysis reaction proceeds by a multistep process consisting in two [3 + 3] rearrangements and a subsequent hydrogen α-elimination step, through a cyclic 5-membered transition state (TS), being the latter the rate-limiting step.

Description: Aromatic nucleophilic substitution reaction of 1-fluoro-2,4-dinitrobenzene with piperidine was kinetically investigated in ethylene glycol-choline chloride and glycerol-choline chloride as 2 deep eutectic solvents (DESs) mixed with dimethyl sulfoxide, in whole mole fractions, at room temperature. The investigation of the reaction in different concentrations of the piperidine shows that the reaction follows the base-catalyzed mechanism. The measured rate coefficients of the reaction demonstrated a sharp decreasing in all mixtures with the increasing mole fraction of DESs. Linear free energy relationship investigations confirm that hydrogen bond donor ability in addition to polarity-polarizability of the media has a major effect on the reaction rate. The decrease in the rate coefficient is attributed to not only hydrogen-bonding donor interactions of the media with piperidine as both reactant and catalyst but also the preferential solvation of reactants by DES compared with the intermediate of the reaction. The kinetical studies of reaction between 1-fluoro-2,4-dinitrobenzene and piperidine in 2 deep eutectic solvents mixed with dimethyl sulfoxide showed that the reaction follows the base-catalyzed mechanism. Linear free energy relationship investigations confirmed that hydrogen bond donor ability in addition to polarity-polarizability of the media has a major effect on the reaction rate.

Description: In this article, we describe the static gas-phase pyrolysis, microwave-induced pyrolysis, and photolysis reactions of trifluoromethyl sulfonyl dihydropyridines. The goal of this work was to find a methodology that allows obtaining of substituted pyridines—which are known to be difficult to synthesize—to be reused in a new substitution reaction. We demonstrated that it is possible to achieve the rearomatization process by the elimination of the trifluoromethyl sulfonyl moiety through the 3 processes, with the static pyrolysis being the best method to obtain the substituted pyridines. In addition, we propose the 1,4-elimination (CF 3 SO 2  + H) as the first step, since it is the less energetic process, as has also been corroborated by calculations. A competitive reaction (CO 2 extrusion) also occurs, yielding undesired products. Static gas-phase pyrolysis, microwave-induced pyrolysis, and photolysis reactions of trifluoromethyl sulfonyl dihydropyridines.

Description: Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au 3 cluster on RO • vs its impacts on RO–H bond dissociation enthalpy, at B3LYP/ LACVP+* level (R═H, methyl, ethyl, n -propyl, i -propyl, n -butyl, t -butyl, and phenyl). In the presence of Au 3 cluster, bond dissociation enthalpy of O–H bond and the spin density at the RO • oxygen are reduced dramatically. These are clear evidences for both the Au 3 facilitation of the RO–H bond breakage and its scavenging of RO • radical. Since O–Au anchoring bond is responsible for the interaction of Au 3 cluster and ROH (or RO • ), its nature was interpreted by means of the quantum theory of atoms in molecules and the natural bond orbital. The results indicate that O–Au bond is stronger and has more covalent character in RO • –Au 3 than in ROH–Au 3 . The interaction of Au 3 cluster with RO • is 1.5 to 3 times more than that with ROH. As a result, gold cluster scavenging property appears more prominent than its free radical initiation activity. Anticancer character of gold cluster has been indicated through its free radical scavenging properties, which is in contrast to its free radical promoting abilities. Hence, the stabilizing effect of Au 3 cluster on RO• vs its impacts on RO–H bond dissociation enthalpy (BDE) is demonstrated at DFT.

Description: The harmonic oscillator model of aromaticity (HOMA) index is an excellent structural indicator of aromaticity. We found that HOMA values for internal benzene rings in large pericondensed polycyclic aromatic hydrocarbons are often overestimated because of the local aromaticity of adjacent benzene rings. The occurrence of this phenomenon was confirmed by comparing the HOMA with the corresponding SSE(LA) values; SSE(LA) is a graph-theoretical index of local aromaticity not disturbed by the aromaticity of the adjacent benzene rings. Mean bond length values were likewise assessed by comparing them with the corresponding HOMA and SSE(LA) values. Local aromaticity indices for internal benzene rings in large pericondensed PAHs have often been overestimated because of the local aromaticity of adjacent benzene rings.

Description: One of the most fundamental properties in chemistry is the bond dissociation energy, the energy required to break a specific bond of a molecule. In this paper, the Fe–N homolytic bond dissociation energies [Δ H homo (Fe–N)'s] of 2 series of (meta-substituted anilinyl)dicarbonyl(η 5 -cyclopentadienyl) iron [ m -G-C 6 H 4 NHFp ( 1 )] and (meta-substituted α-acetylanilinyl)dicarbonyl(η 5 -cyclopentadienyl) iron [ m -G-C 6 H 4 N(COMe)Fp ( 2 )] were studied using density functional theory methods with large basis sets. In this study, Fp is (η 5 -C 5 H 5 )Fe(CO) 2 , and G is NO 2 , CN, COMe, CO 2 Me, CF 3 , Br, Cl, F, H, Me, MeO, and NMe 2 . The results show that Tao-Perdew-Staroverov-Scuseria, Minnesota 2006, and Becke's power-series ansatz from 1997 with dispersion corrections functionals can provide the best price/performance ratio and accurate predictions of Δ H homo (Fe–N)'s. The ΔΔ H homo (Fe–N)'s ( 1 and 2 ) conform to the captodative principle. The polar effects of the meta-substituents show the dominant role to the magnitudes of ΔΔ H homo (Fe–N)'s. σ α · and σ c · values for meta-substituents are all related to polar effects. Spin-delocalization effects of the meta-substituents in ΔΔ H homo (Fe–N)'s are small but not necessarily zero. RE plays an important role in determining the net substituent effects on Δ H homo (Fe–N)'s. Insight from this work may help the design of more effective catalytic processes. The Fe–N homolytic bond dissociation energies [Δ H homo (Fe–N)'s] of 2 series of (meta-substituted anilinyl)dicarbonyl(η 5 -cyclopentadienyl) iron [ m -G-C 6 H 4 NHFp ( 1 )] and (meta-substituted α-acetylanilinyl)dicarbonyl(η 5 -cyclopentadienyl) iron [ m -G-C 6 H 4 N(COMe)Fp ( 2 )] were studied using density functional theory methods with large basis sets. The results show that Tao-Perdew-Staroverov-Scuseria, Minnesota 2006, and Becke's power-series ansatz from 1997 with dispersion corrections functionals can provide the best price/performance ratio and accurate predictions of Δ H homo (Fe–N)'s. The polar effects of the meta-substituents show the dominant role to the magnitudes of ΔΔ H homo (Fe–N)'s.

Description: When N -benzyl- N′ -methylacetamidinium hydrochloride (pKa=11.8) is dissolved in D 2 O/DCl(1 M), an equilibrium of 2 54:46 stereoisomers in an ~2:1 =(R)N δ + H(D) D/H ratio is formed. Therefore, 2 R =N-benzyl ( E and Z ) and 2 R = N -methyl (E and Z) groups attached to the corresponding H(D) ( Z and E ) for a total of 8 1 H-NMR signals are observed. Consequently, their rates of H and D transfer to D 2 O can be measured by means of the 1 H-NMR broadness (line shape) of the =( R )N δ + H doublets and =( R )N δ + D broad singlets. Acidity selectivity is observed for both processes. In fact, the relative proton and deuterium transfer rates follow the acidity order: =(PhCH 2 )N δ + -H( E ) 〉 =(PhCH 2 )N δ + -H( Z ) 〉 =(Me)N δ + -H( E ) 〉 =(Me)N δ + -H( Z ). Proton transfer rates are in the range of 8 to 0.5 s -1 with α  = .92. This tendency is independently supported by the observed experimental chemical shift deuterium isotopic perturbation. The rate-limiting step for proton exchange is the breaking of the hydrogen bond due to the fast amidine reprotonation (~10 11  s). =(R)N δ + D/=(R)N δ + H equilibration is reached at ~80 s, and it can be measured by the relative =( R) N δ + H versus =( R) N δ + D signal integrations. The equilibrium of the 4 =(R)N δ + H(D) centers is shifted toward deuterium, but they are further shifted in the more basic centers. Equilibrium is completely shifted toward D in the 4 centers when OD − contributes with the exchange process at pD 〉 3. Proton and deuterium transfer rates (k 12 and k 43 ) in N -benzyl- N '-methylacetamidinium ions in D 2 O at [DCl] = 1 M follows the acidity order of the 4 =(R)N δ+ -H groups. D/H equilibration ( K 14  ~ 4) is reached at approximately 84 s. It is shifted toward deuterium in the 4 =(R)N δ+ -H(D) center. Therefore, the D/H equilibrium ( K 14 ) follows the opposite order than the =(R)N δ+ -H groups acidity and the rates of H and D transfer.

Description: Theoretical design on a new molecular switch and fluorescent chemosensor double functional device of aza-crown ether (2,2′-dipyridine-embedded N -(9-anthraceneyl(pyrenyl)methyl)aza-15-crown-5) was explored. The interactions between ligands and a series of alkaline earth metal cations (Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ ) were investigated. The fully optimized geometry structures of the free ligands ( L 1, L 2 ) and their metal cation complexes ( L 1 /M 2+ , L 2 /M 2+ ) were calculated with the B3LYP/6-31G(d) method. The natural bond orbital analysis, which is based on optimized geometric structures, was used to explore the interaction of L 1 /M 2+ , L 2 /M 2+ molecules. The absorption spectra of L 1, L 2 , L 1 /M 2+ , and L 2 /M 2+ , and their excited states were studied by time-dependent density functional theory. A new type molecular device L 2 (2,2′-dipyridine-embedded N -(9-pyrenyl methyl)aza-15-crown-5) is designed, which not only has the selectivity for Sr 2+ , and construct allosteric switch, but also has fluorescent sensor performance. Theoretical design on a new molecular switch and fluorescent chemosensor double functional device of aza-crown ether (2,2′-dipyridine-embedded N -(9-anthraceneyl(pyrenyl)methyl)aza-15-crown-5) was explored. The change of molecular configuration of free ligands under certain light conditions, which is the combination with alkaline earth metal, can produce fluorescence effect. Therefore, explore the combination of free ligands to produce the most fluorescent alkaline earth metal ions.

Description: The gas-phase elimination kinetics of tetrahydropyranyl phenoxy ethers: 2-phenoxytetrahydro-2 H -pyran, 2-(4-methoxyphenoxy)tetrahydro-2 H -pyran, and 2-(4- tert -butylphenoxy)tetrahydro-2 H -pyran were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor toluene. The working temperature and pressure were 330 to 390°C and 25 to 89 Torr, respectively. The reactions yielded DHP and the corresponding 4-substituted phenol. The eliminations are homogeneous, unimolecular, and satisfy a first-order rate law. The Arrhenius equations for decompositions were found as follows: 2-phenoxytetrahydro-2 H -pyran log k 1 (s −1 ) = (14.18 ± 0.21)  −  (211.6 ± 0.4) kJ mol −1 (2.303 RT) −1 2-(4-methoxyphenoxy)tetrahydro-2 H -pyran log k 1 (s −1 ) = (14.11 ± 0.18)  −  (203.6 ± 0.3) kJ mol −1 (2.303 RT) −1 2-(4- tert -butylphenoxy)tetrahydro-2 H -pyran log k 1 (s −1 ) = (14.08 ± 0.08)  −  (205.9 ± 1.0) kJ mol −1 (2.303 RT) −1 The analysis of kinetic and thermodynamic parameters for thermal elimination of 2-(4-substituted-phenoxy)tetrahydro-2 H -pyranes suggests that the reaction proceeds via 4-member cyclic transition state. The results obtained confirm a slight increase of rate constant with increasing electron donating ability groups in the phenoxy ring. The pyran hydrogen abstraction by the oxygen of the phenoxy group appears to be the determinant factor in the reaction rate. In this work, the gas-phase thermal elimination kinetics of 3 tetrahydropyranyl phenoxy ethers were determined. The analysis of kinetic and thermodynamic parameters for thermal elimination of 2-(4-substituted-phenoxy)tetrahydro-2 H -pyranes suggests that the reaction proceeds via 4-membered cyclic transition state. The results obtained confirm a slight increase of rate constant with increasing electron donating ability groups in the phenoxy ring.

Description: No abstract is available for this article.

Description: The photocatalytic degradation of methylene blue solution by 8 photocatalytic diphenylanthrazoline compounds was investigated. All diphenylanthrazoline compounds exhibited a good photocatalytic activity towards the methylene blue solution. The removal rate for chemical oxygen demand (COD Cr ) in the methylene blue solution at 12 hours was ~54.1% to 96.3%. 2,8-Bis(4-triphenylamino)-4,6-diphenyl-1,9-anthrazoline ( TM-2-d ) was selected for further investigation because of its better photocatalytic activity. To study the optimal reaction conditions for the photocatalytic degradation of dye wastewater, photocatalyst was applied to degrade methylene blue solution. The decolorization rate for simulated dye solutions can exceed 99% in 10 hours, and the COD Cr removal rate exceeded 91%. These organic semiconductor materials, diphenylanthrazoline compounds, displayed comparative photocatalytic properties to the inorganic semiconductor materials, which can be used in the photocatalytic degradation of organic pollutants. The photocatalytic degradation of methylene blue solution by 8 diphenylanthrazoline compounds was investigated. The removal rate for COD Cr in methylene blue solution at 12 hours was ~54.1% to 96.3%. These pure organic semiconductor materials displayed comparative photocatalytic properties to the inorganic semiconductor materials.

Description: The paper represents an attempt to provide a sound theoretical subsidy for the so-called “curved arrow formalism,” which proved unprecedented usefulness in shaping our ideas about the mechanisms of organic reactions. The basic idea is to characterize the extent to which the electron pairs are conserved or broken for a given nuclear configuration by the probability of finding the pair of electrons of opposite spin in a given point of space. This probability is quantitatively given by the αβ component of the pair density, with coinciding positions of both electrons. As a function of 3 variables, the quantity Π αβ (r, r) can be displayed in 3D and the monitoring of the snapshots of this quantity for different points along the reaction path thus can bring new interesting insights into the details of bond reorganization in the course of reactions. The paper reports the application of the above approach for the detailed scrutiny of the differences in the electron reorganization of allowed and forbidden pericyclic reactions at the level of simple topological description in terms of overlap determinant method. Despite its simplicity, the approach provided new interesting insights into the factors underlying the different role of electron pairs in allowed and forbidden pericyclic reactions, and we believe that this simple approach could inspire further straightforward extensions that would allow to apply its formalism at the level of contemporary sophisticated computations to real systems of chemical interest. The proposed approach relies on the idea to characterize the extent to which the electron pairs are conserved or broken by the probability of finding the pair of electrons of opposite spin at a given point of space. This probability is given by the αβ component of the pair density Π αβ ( r ,  r ) , and monitoring of this quantity in the form of snapshots for different points along the reaction path brings new insights into the destiny of electron pairs in chemical reactions.

Description: The reactions of glycine, a simple amino acid, with glyoxylate, a simple α-oxocarboxylate, were investigated in water as a function of time, pH, and temperature and followed using a combination of quantitative 13 C nuclear magnetic resonance and high-resolution mass spectrometry. Three sets of experiments are reported: (1) reaction of 13 C-labeled glycine with unlabeled glyoxylate, (2) reaction of unlabeled glycine with 13 C-labeled glyoxylate, and (3) the reaction of 13 C-labeled glycine with 13 C-labeled glyoxylate. Competing transaminations, aldol reactions, and decarboxylations were observed; the mechanistic description for each of these processes is presented. 3-Hydroxy-2-aminosuccinate, a product of reaction between glycine and glyoxylate, was shown to promote both the decarboxylation of glyoxylate and transamination of glyoxylate to glycine. These observations may have implications for the mechanism of attenuation of ethylene glycol toxicity. The aqueous reaction of 13 C-labeled glycine with unlabeled glyoxylate undergoes a transamination process to produce 13 C-labeled glyoxylate and unlabeled glycine. A competing aldol process produces 2-amino-3-hydroxysuccinate, which promotes the decarboxylation of glyoxylate.

Description: A Molecular Electron Density Theory study of the zw-type 32CA reactions of acetonitrile oxide (NO) with two 7-oxanorborn-5-en-2-ones (ONBs) has been performed at the DFT B3LYP/6-31G(d) computational level. These cycloadditions proceed through one-step mechanisms with high activation energies and present low para regio and complete syn diastereofacial selectivities. While the non-polar character of these zw-type 32CA reactions, which is the consequence of the insufficient electrophilic activation of ONBs, according to the analysis of the conceptual DFT reactivity indices, accounts for the high activation energies, and low para regioselectivity, NCI topological analyses at the anti/syn pairs of para TSs reveal that the steric hindrance encountered between the NO framework and the ONB side containing the carbonyl group along the anti approach mode is responsible for the complete syn diastereofacial selectivity. The zw-type [3 + 2] cycloaddition reactions between acetonitrile oxide and 7-oxanorborn-5-en-2-ones present low para regio and complete syn diastereofacial selectivities. The nonpolar character of these zw-type [3 + 2] cycloaddition reactions accounts for the high activation energies and low para regioselectivity, while the steric hindrance found along the anti approach mode is responsible for the complete syn diastereofacial selectivity.

Description: New ligand 4-((2-Hydroxy1-naphthyl) methylene amino)-1.5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (HL) was synthesized from the reaction of 2-hydroxy-1-naphthaldehyde and 4-aminophenaz one. A complexes of this ligand [VO(II)(HL)(SO 4 )], [Pt(IV)(L)Cl 3 ], [Re(V)(L)Cl 3 ]Cl, and [M(II)(L)Cl] (M═Pd(II), Ni(II), Cu(II)) were synthesized. The resulted compounds were characterized by IR, NMR ( 1 H and 13 C), mass spectrometry, element analysis, and UV-Vis spectroscopy. Additionally, the spectroscopic studies revealed octahedral geometries for the Re(V), Pt(IV) complexes, and square pyramidal for VO(II), square planar for Pd(II) complex, and tetrahedral for the Ni(II) and Cu(II) complexes. Thermodynamic parameters (ΔE * , ΔH * , ΔS * , ΔG * , and K) were calculated using from the TGA curve Coats-Red fern method. Therefore, hyper Chem-8 program has been used to predict structural geometries of compounds in the gas phase. Finally, the synthesized Schiff base and its metal complexes were screened for their biological activity against bacterial species, 2 Gram-positive bacteria ( Bacillus subtilis and Staphylococcus aureus ) and 2 Gram-negative bacteria ( Escherichia coli and Pseudomonas aeruginosa ). Complexes of this ligand [VO(II)(HL)(SO 4 )], [Pt(IV)(L)Cl 3 ], [Re(V)(L)Cl 3 ]Cl, and [M(II)(L)Cl] (M═Pd(II), Ni(II), Cu(II)) were synthesized. The resulted compounds were characterized by IR, NMR ( 1 H and 13 C), mass spectrometry, element analysis, and UV-Vis spectroscopy.

Description: New 2-(4′-9 H -carbazole-9-yl)-styryl-1 H -phenathro[9,10-d]imidazole-1-yl)benzonitrile (SPICN-Cz) and 4-(2-(4-(diphenylamino)phenyl-styryl-1H-phenathro[9,10-d]imidazole-1-yl)benzonitrile (SPICN-TPA) have been synthesised, and their photophysical, electrochemical, and electroluminescent properties were analysed in comparison with their cyano-free parent compounds, SPI-Cz, and SPI-TPA. Solvatochromic effects show the transformation of an excited state character from locally excited (LE) state to charge transfer (CT) state. Using time-dependent density functional theory calculation, the excited state properties of these donor-acceptor blue emissive materials have been analysed. Their excited state properties have been tuned by replacing the strong donor triphenylamine to weak donor carbazole to achieve the combination of high photoluminance efficiency locally excited (LE) component and high exciton-utilizing CT component in one excited state. Hybridization processes between LE and CT components of SPICN-Cz and SPICN-TPA in the emissive state have been discussed. The nondoped organic light emitting diode device based on SPICN-Cz exhibit better electroluminescent performances than those of SPICN-TPA–based device: high external quantum efficiency of 2.58 %, current efficiency of 2.90 cd A -1 , and power efficiency of 2.26 lm W -1 with Commission Internationale de l'Éclairage (CIE) coordinates of (0.15, 0.12). The excited state modulation and the composition of LE and CT states in the donor-acceptor system could be useful to design low-cost, high-efficiency fluorescent organic light emitting diode materials. Experimental details, computational details, molecular design, solvatochromic experiments, charge transfer indexes, photophysical properties, solvatochromic effects, thermal properties and lifetime decay, EL performances, figures of natural transition orbitals, computed hole and particle distribution, transition density matrix and tables of photophysical constants, and computational parameters are provided as the supporting materials.

Description: No abstract is available for this article.

Description: Combination of natural biodegradable polymer with a synthetic polymer offers excellent properties for the support in drug delivery system. For this purpose, biodegradable conductive nanoparticle polypyrrole based on chitosan (PPC) has been prepared via oxidative polymerization of pyrrole in presence of chitosan using FeCl 3 as oxidant in acidic medium and used as a carrier for 1,2,4-triazoles. The resultant nanoparticles were characterized by X-ray diffraction, Fourier transform infrared analysis, transmission electron microscopy, scanning electron microscopy, and thermal gravimetric analysis. The results indicate that spherical nanoparticle of average diameter 52 ± 8 nm was successfully prepared. The spherical particles were composed of dark sphere surrounded by grey shell. A circumferential dark ring is observed in the shell after loading 1,2,4-triazoles into PPC nanoparticles. The loaded triazoles were released almost linearly against time in a sustained fashion into different pH media. The mechanism of triazoles release was determined using different kinetics equations. The antibacterial activities against the gram-negative and gram-positive bacteria were examined. Furthermore, the antitumor activity of PPC nanoparticles loaded 1,2,4-triazoles was also examined against Ehrlich ascites carcinoma cells and breast cancer cell line (MCF7). Polypyrrole chitosan loaded nanoparticles exhibited higher antitumor activity than 1,2,4-triazoles. The polypyrrole chitosan (PPC) nanoparticles have been prepared by in situ oxidative polymerization of pyrrole in chitosan solution using FeCl 3 as an oxidant. 1,2,4-Triazole derivatives (I-IV) were loaded into PPC nanoparticles (PPCI, PPCII, PPCIII, and PPCIV). The antitumor activity of PPC nanoparticles loaded 1,2,4-triazoles was examined against Ehrlich ascites carcinoma cells and breast cancer cell line (MCF7). PPCIV nanoparticles showed high efficacy against Ehrlich ascites carcinoma tumor cells in vitro.

Description: Oxime chemistry has been proven to be a reliable bioconjugation method for biomedical applications. Because of its stable and bio-orthogonal nature, a number of materials have been devised for in vitro and in vivo applications such as drug delivery, imaging, and biochemical assays. Polymers, synthetic molecules, nanoparticles, and biomolecules carrying alkoxyamine and aldehyde/ketone functional groups could be linked to each other through oxime bond, and a variety of modular platforms could be produced. Formation of oximes is catalyzed in acidic medium, and the proposed reaction mechanism follows classical imine formation pathways. Aniline has been found to accelerate the rate of oxime formation several orders of magnitude. In this computational study, we analyzed the proposed mechanism on model systems using DFT calculations including a solvation model. The energetics of the reaction steps in neutral and acidic conditions as well as in the presence of aniline was performed. Explicit water molecules were included in the calculations to study the energetics of solvent assisted proton transfer steps. In this computational study, we analyzed the proposed oxime formation mechanism on model systems using DFT calculations including a solvation model. The energetics of the reaction steps in neutral and acidic conditions as well as in the presence of aniline were performed. Explicit water molecules were included in the calculations to study the energetics of solvent-assisted proton transfer steps.

Description: A series of difluoramino group–based energetic molecules was designed and the relative properties were investigated by density functional theory. The results show that all the designed molecules have high positive heat of formation which ranges from 479.48 to 724.02 kJ/mol, detonation velocity ranges from 8.01 to 11.26 km/s, detonation pressure ranges from 28.03 to 63.46 GPa, and impact sensitivity ranges from 18.2 to 54.5 cm. Then, compounds D2, D3, D5, E4, E5, E6, and F2 were selected as the potential high energy density materials based on detonation properties and sensitivities. Natural bond orbital charges, electronic density, frontier molecular orbital, electrostatic potential on the surface, and thermal dynamic parameters of the screened molecules (compounds D2, D3, D5, E4, E5, E6, and F2) were also predicted at B3LYP/6-31G( d , p ) level to give a better understanding on the chemical and physical properties of them. A series of difluoramino group-based energetic molecules was designed and the relative properties such as detonation properties, impact sensitivities, electronic density, frontier molecular orbital, electrostatic potential on the surface and thermal dynamic parameters were predicted theoretically.

Description: The compounds stilbenes XArCH=CHArY(XSBY) and 1,2-diphenylpropylenes XArC(Me)=CHArY(XSMBY) have bridging groups CH=CH and C(CH 3 )=CH, respectively, in which the C(CH 3 )=CH has a side-group CH 3 at the carbon-carbon double bond. A series of XSMBY were synthesized, and their longest wavelength maximum λ max (nm) in ultraviolet absorption spectra were measured in this work. We investigated the change regularity of the ν max (cm -1 , ν max  = 1/λ max ) of XSMBY and compared it with that of XSBY. The results indicate that (1) there is no good linear relationship between the ν max of XSMBY and that of XSBY. (2) Because of the influence of the side-group CH 3 , in case of the same couple of groups X and Y, the λ max of XSMBY is shorter than that of XSBY, that is, it has a blue shift. (3) The cross-interaction between the side-group CH 3 and Y has an important effect on the ν max of XSMBY, while the cross-interaction between the side-group CH 3 and X has a little effect on the ν max and can be ignored. (4) The specific cross-interaction between X and Y has important effect on the ν max of XSMBY, whereas it has no important effect on the ν max of XSBY. Compared with the λ max of UV spectra of compounds XSBY, the λ max of compounds XSMBY have blue shift in case of the same couple of groups X and Y. This blue shift is results from the side-group CH 3 at the bridging group C(CH3)=CH in XSMBY molecule. The specific cross-interaction between X and Y has important effect on the λ max of XSMBY, whereas it has little effect on the λ max of XSBY.

Description: Single material organic solar cells become an interesting area of research to overcome the challenges with efficient charge separation efficiencies in conventional organic solar cells. In this article, we have synthesized nonmetallated and metallated porphyrin-fullerene dyad materials (H2P-C60 and ZnP-C60, respectively) with simple structure, comprehensively studied their charge transfer mechanism, and established a proof of concept that nonmetallated porphyrin-fullerene dyads are better candidates to be used in organic solar cells compared with metallated dyads. Absorption and electrochemical analysis revealed the ground state electronic interactions between donor-acceptor moieties in both types of dyads. Driving force (−ΔG o ET ) for intramolecular electron transfer process was calculated by first oxidation and reduction potentials of dyads. The excited state electronic interactions were characterized by time-resolved fluorescence and pump-probe transient absorption experiments. Strong fluorescence quenching of porphyrin along with reduced lifetimes in dyads due to deactivation of singlet excited states by photoinduced charge transfer process between porphyrin/Zn-porphyrin core and fullerene in different polarity solvents was observed. Transient absorption spectroscopy was also applied to identify the transient spectral features, ie, cationic (H2P + /ZnP + ) and anionic (C 60 − ) radicals formed because of the charge separation in both types of dyads. Finally, organic solar cell device was also fabricated using the dyads. We obtained higher V oc , J sc , and fill factor in single material organic solar cell using H2P-C60 compared to previous reports. Important study of charge carrier generation and separation dynamics in metallated and nonmetallated porphyrin-fullerene dyad is discussed in this work. The time-resolved data shows ultrafast charge separation and slow charge recombination in our dyads as desired for optimal solar cells performance. The metal-free porphyrin-fullerene dyad (H2P-C60) shows even better performance in ultrafast charge separation and formation of long-lived charge-separated state than metallated porphyrin-fullerene dayd (ZnP-C60).

Description: The geometries, energies, and nuclear magnetic resonance (NMR) chemical shifts of 3 bases (trimethylphosphine, trimethylamine, and trimethylphosphine oxide), their 3 protonated cations, and 15 hydrogen-bonded complexes (corresponding to the HF, HNC, HCN, HCCH, H 2 O, and CH 3 OH Brønsted acids) have been calculated at the B3LYP/6-311++G(d,p) level. The determination of hydrogen bond acidities by NMR is classically performed using the 31 P chemical shifts Me 3 PO. This method is more reliable than the use of the 15 N NMR chemical shifts of Me 3 N. This work shows that the 31 P NMR chemical shifts of Me 3 P cannot be used. The raison of the difference between Me 3 P on one hand and Me 3 PO and Me 3 N on the other will be discussed. The nuclear magnetic resonance chemical shifts of 15 hydrogen-bonded complexes of trimethylphosphine, trimethylamine, and trimethylphosphine oxide have been calculated at B3LYP/6-311++G(d,p) level. The results show that the determination of hydrogen bond acidities is more reliable with Me 3 PO than Me 3 N and Me 3 P. A model that explains the chemical shift variations on the basis of the deformation and electronic effect of the hydrogen bond is proposed.

Description: In this study, inclusion of 10 guest molecules, adamantyl and naphthyl carboxylic acids with different structural and electronic properties, within a synthetic cavitand octa acid was probed by isothermal calorimetry, 1D and 2D 1 H nuclear magnetic resonance spectroscopy, and molecular dynamic simulations. Under the condition of the experiments (pH ~ 8.7), the guests were included as carboxylate anions with the polar anionic head group facing water and hydrophobic carbon skeleton buried within the cavitand, forming 1:1 host to guest complexes. Importance of weak interactions between the guest and the cavitand interior is reflected in the measured negative ΔH values. Although ΔH was negative for all guests, ΔS was positive for adamantyl guests and negative for naphthyl guests. Quite likely the difference in hydrophobicity between the 2 sets of molecules and the strength of interaction between the guest and the host are responsible for the sign difference in ΔS between the 2 series. The importance of steric factor during inclusion of naphthyl carboxylic acids within octa acid cavity is brought out by the difference in thermodynamic parameters between the 1- and 2-substituted naphthyl carboxylic acids; 2-naphthyl carboxylic acids that can penetrate deeply have larger −ΔH and 1-naphthyl carboxylic acids that can only enter the cavity in an angle have smaller −ΔH. As expected, based on the well-known concept of “enthalpy-entropy compensation,” the molecules that have large −ΔH are accompanied by large −ΔS. Steric and hydrophobic features of guest molecules are reflected in the thermodynamic parameters of the host-guest complexation.

Description: The evaluation of the dielectric properties of s-triazine and its mono-, di-, tri-(trityloxy)triazine derivates as a function of temperature from room temperature to 200°C, and frequency varying from 50 Hz to 5 MHz was performed. The dielectric constant increases with the increase of both temperature and frequency. Moreover, from the measured dielectric loss ε″ we found that there are different types of electric energy losses in the presence of an alternating electric field from which we calculate the entropy ΔS and the enthalpy change ΔH of the dielectric relaxation for each sample. The dielectric relaxation was attributed to the phase transition of the s-triazine derivatives. Additionally, ac-electrical conductivity as a function of frequency at different temperatures were studied. Analysis of ac conductivity data indicates that the correlated barrier hopping model is the most suitable mechanism for the ac-conductance behavior. X-ray diffraction and scanning electron microscopy were performed on the compounds under consideration to determine the grain size of each sample, which was found in the range of 3 to 100 nm. We succeed in preparation of s-triazine derivatives in nano range provided by XRD and SEM. This work includes the study of dielectric properties and ac-electrical conductivity of the prepared compounds. The dielectric constant increases with the increase of both temperature and frequency. Moreover, from the measured dielectric loss ε″, we found that there are different types of electric energy losses in the presence of an ac field from which we calculate the entropy ΔS and the enthalpy change ΔH of the dielectric relaxation for each sample. The dielectric relaxation was attributed to the phase transition of the s-triazine derivatives. Analysis of ac conductivity data indicates that the correlated barrier hopping (CBH) model is the most suitable mechanism for the ac-conductance behavior.

Description: No abstract is available for this article.

Description: The trans -epoxysuccinyl amide group as a biologically active moiety in cysteine protease inhibitors such as loxistatin acid E64c has been used as a benchmark system for theoretical studies of environmental effects on the electron density of small active ingredients in relation to their biological activity. Here, the synthesis and the electronic properties of the smallest possible active site model compound are reported to close the gap between the unknown experimental electron density of trans -epoxysuccinyl amides and the well-known function of related drugs. Intramolecular substituent effects are separated from intermolecular crystal packing effects on the electron density, which allows us to predict the conditions under which an experimental electron density investigation on trans -epoxysuccinyl amides will be possible. In this context, the special importance of the carboxylic acid function in the model compound for both crystal packing and biological activity is revealed through the novel tool of model energy analysis. New syntheses, electron-density determinations and model-energy analyses of model compounds bearing the biologically relevant trans -epoxysuccinyl amide group in comparison with the drugs loxistatin acid (E64c) and loxistatin (E64d) give insight about the varying importance of different functional groups for binding in the enzyme and the crystal.

Description: Mechanistic insights into Heck and Suzuki-Miyaura cross coupling reactions with C 59 M (M = Pd/Ni) catalysts were developed. Density functional theory was used for the analysis of all the intermediates and transition states possible during C-C cross coupling reactions over the catalysts under study. Oxidative addition, a step common to both Heck and Suzuki-Miyaura cross coupling reactions, was observed to proceed with smaller activation barriers over C 59 Pd. Heck coupling of iodobenzene with styrene was observed to proceed via oxidative addition, migratory insertion, and reductive elimination steps. The free energy barriers for oxidative addition, migratory insertion, and reductive elimination steps were 14.8, 11.6, and 4.8 kcal/mol, respectively, over C 59 Pd, and 17.4, 79.3, and 17.4 kcal/mol, respectively, over C 59 Ni, indicating oxidative addition and migratory insertion to be the rate-determining steps over C 59 Pd and C 59 Ni, respectively. Similarly for Suzuki-Miyaura coupling reaction, activation barriers for oxidative addition, transmetalation, and reductive elimination steps were 14.8, 52.4, and 7.9 kcal/mol, respectively, over C 59 Pd, and 17.4, 64.7, and 60.2 kcal/mol, respectively, over C 59 Ni, indicating transmetalation step to be the rate-determining step over both the heterofullerenes. Density functional theory calculations were implemented to test the C-C couplings activities of Pd- and Ni-doped heterofullerenes. The compounds were found to be active for catalyzing Suzuki-Miyaura and Heck coupling reactions.

Description: Herein, we present a mechanistic study on tert -butyl hydroperoxide-promoted guanylation of thioureas by monitoring short lifetime intermediates using electrospray ionisation/time-of-flight high resolution mass spectrometry (ESI-Q-TOF HRMS). Moreover, 1 H nuclear magnetic resonance data allowed us to access kinetic parameters for the main species involved which, allied to the HRMS results, furnished valuable insights over previously reported observations. The results suggested an addition/elimination mechanism involving the aminoiminomethanesulphinic acid, RNC(SO 2 H)NHR′, and the nucleophilic amine as the main pathway to yield the guanidine. Noteworthy, benzoylthiourea consumption rate presented a nonlinear kinetic behaviour, while t BuOOH and the nucleophilic amine consumptions were found to follow second-order kinetics. A mechanistic study of tert -butyl hydroperoxide-promoted guanylation of thioureas by monitoring short lifetime intermediaries using ESI-Q-TOF HRMS is presented. 1 H nuclear magnetic resonance data furnished access to kinetic parameters, which allied to the HRMS results, suggested that an addition/elimination mechanism involving the aminoiminomethanesulphinic acid and the nucleophilic amine is the main pathway to yield the guanidine. Noteworthy, benzoylthiourea consumption rate presented a nonlinear kinetic behaviour, while t BuOOH and BnNH 2 consumptions were found to follow second-order kinetics.

Description: A novel stable energetic compound ( E )-1,2-diamino-1,2-dinitrodiboron (DANB) was theoretically designed based on the structure of 1,1-diamino-2,2-dinitroethene (FOX-7). Atomization method in combination with Hess' law was used to predict the heat of formation. The detonation velocity ( D ) and detonation pressure ( P ) of DANB were approximatively estimated by using Kamlet–Jacobs equations. As a result, DANB has huge heat of formation (2013.5 kJ/mol) and specific enthalpy of combustion (−26.4 kJ/g). Furthermore, DANB possesses high crystal density (1.85 g/cm 3 ) and heat of detonation (5476.0 cal/g), which lead to surprising detonation performance ( D  = 10.72 km/s, P  = 51.9 GPa) that is greater than those of FOX-7 ( D  = 8.63 km/s, P  = 34.0 GPa) and CL-20 ( D  = 9.62 km/s, P  = 44.1 GPa). More importantly, DANB is very stable because its bond dissociation energy of the weakest bond ( BDE  = 357.8 kJ/mol) is larger than those of the most common explosives, such as FOX-7 ( BDE  = 200.4 kJ/mol), CL-20( BDE  = 209.2 kJ/mol), HMX( BDE  = 165.7 kJ/mol), and RDX ( BDE  = 161.4 kJ/mol). Therefore, our results show that DANB is a promising candidate for stable and powerful energetic material. Boron-containing energetic compound DANB was investigated by theoretical calculation. It possesses more superior detonation performance and thermodynamic stability than those of CL-20, HMX, RDX, and FOX-7. Our results show that DANB is a promising candidate for stable and powerful energetic material.

Description: Recent studies have shown that general-base assisted catalysis is a viable mechanistic pathway for hydrolysis of smaller anhydrides. Therefore, it is the central purpose of the present work to compare and contrast the number of hydrogen atoms in-flight and stationary in the transition state structure of the base-catalyzed mechanisms of 2 hydrolytic reactions as well as determine if any solvent effects occur on the mechanisms. The present research focuses on the hydrolytic mechanisms of N,N-dimethylformamide (DMF) and acetic anhydride in alkali media of varying deuterium oxide mole fractions. Acetic anhydride has been included in this study to enable comparisons with DMF hydrolysis. Comparative studies may give synergistic insight into the detailed structural features of the activated complexes for both systems. Hydrolysis reactions in varying deuterium oxide mole fractions were conducted in concentrations of 2.0M , 2.5M , and 3.0M for DMF and 0.10M for acetic anhydride at 25°C. Studies in varying deuterium mole fractions allow for proton inventory analysis, which sheds light on the number and types of hydrogen atoms involved in the activated complex. For these systems, this type of study can distinguish between direct nucleophilic attack of the hydroxide ion on the carbonyl center and general-base catalysis by the hydroxide ion to facilitate a water molecule attacking the carbonyl center. The numerical data are used to discuss 3 possible mechanisms in the hydrolysis of DMF. Proton inventory techniques play a crucial role in elucidating mechanisms by identifying the number and types of hydrogens involved in the transition state structures. The transition state structure in simple acetic anhydride hydrolysis has 4 protons; whereas, acetate catalyzed hydrolysis has 2. This study also shows an inverse kinetic isotope effect (k OH- /k OD-  = 0.51 ± 0.03 at 25°C and an hydroxide concentration of 2.0M) for the hydroxide reaction with DMF. In the case of acetic anhydride, sodium chloride had a negative effect on the rate of hydrolysis and the charge of ions involved in the formation of activated complex is 0.378 e .

Description: We are focusing our calculations on the structural stabilities and electronic properties of 26 novel B n N m C 20–( n + m ) heterofullerenes, with n , m  = 1 − 5, at B3LYP/6-311++G** and B3LYP/AUG-cc-pVTZ levels of theory. Vibrational frequency calculations on C 20 and its analogues show that except B 2 N 2 C 16 (1) and B 2 N 2 C 16 (2), all other heterofullerenes are true minima. The heats of atomization energies, binding energy, band gaps (Δ E HOMO-LUMO ), aromaticity, nucleus-independent chemical shifts, thermodynamic stability, kinetic stability against electronic excitation, binding energy as a stability criterion of different configurations, geometrical parameters, conformational structures, conductivity, charge transfer, and possibility for hydrogen storage of these heterofullerenes strongly depend on their number of heteroatoms, topology, filling patterns, and locations as well as “B-site and N-site attachments.” B 5 N 5 C 10 contains 5 alternating boron and nitrogen atoms in the equatorial position. It is predicted to be thermodynamically and kinetically the most stable against electron excites. Thus, it is energetically favorable and its electronic properties as well as stabilities make it perhaps a good candidate for an experimental investigation and testing verification. A flow chart for examination of the stability of fullerene C 20 and some of its scrutinized novel B n N m C 20─(n+m) heterofullerene analogues, at DFT levels.

Description: No abstract is available for this article.

Description: Density functional theoretical calculations have been performed to investigate the changes in electronic structure at ground and excited states of ureidopeptides on substitution with higher chalcogens like sulphur and selenium for oxygen. This replacement results in a reduced preference towards the intramolecular hydrogen bonding interaction, thus linear conformers are found to be stable at both states. Nevertheless, conformational switching observed during this process is mainly due to n to π* transition that leads to the dihedral angle ω change from trans to cis with a rotational barrier of 10 to 17 kcal mol -1 . The computed barrier is lesser than that reported for oxopeptides (20 kcal mol -1 ). And, the hole migration dynamics after immediate ionization illustrates that the hole originated at ureido end evolves in time (2−4 fs) while the hole generated at the carboxylate end will not evolve as reported for ureidopeptides. The usage of these candidates as photoswitches has also been explored. The photoswitching ability of various thio/seleno ureidopeptide models pertaining to an n to π* transition and the charge migration dynamics from ureido end to carboxylate end of the peptidomimetics have been explored.

Description: In this work, the antioxidant ability of fisetin was explored toward hydroxyl (•OH) radical in aqueous and lipid solution using density functional level of theory. Different reaction mechanisms have been studied: hydrogen atom transfer, single electron transfer followed by proton transfer, and radical adduct formation, and sequential proton loss electron transfer. Rate constants for all possible reaction sites have been calculated using conventional transition state theory in conjunction with the Collins-Kimball theory. Branching ratios for the different channels of reaction are reported for the first time. Results show that the reactivity of fisetin toward hydroxyl ( • OH) radical takes place almost exclusively by radical adduct formation regardless of the polarity of the environment. Also, the single-electron transfer process seems to be thermodynamically unfavorable in both media. In this work, the antioxidant ability of fisetin was explored toward hydroxyl (•OH) radical in aqueous and lipid solution using density functional level of theory. Results show that the reactivity of fisetin toward hydroxyl ( • OH) radical takes place almost exclusively by radical adduct formation regardless of the polarity of the environment. Also, the single-electron transfer process seems to be thermodynamically unfavorable in both media.

Description: Hydroxyl radical (•OH) damages DNA/RNA by attacking pyrimidine nucleobases through the addition reaction and H-atom abstraction. It may attack on the new cytosine derivative (5-formylCytosine [5-fCyt]) causing DNA oxidative damage, whereas the study of the related mechanism is still in its infancy. In the present work, 2 distinct mechanisms of •OH-mediated 5-fCyt at the complete basis set methods (CBS-QB3) and CBS-QB3/polarized continuum model approaches have firstly been explored, the addition reaction (paths R1 ~ R3) and the abstraction reaction (paths R4 ~ R6), respectively, and it shows that the addition of •OH to the C5═C6 double bond of 5-fCyt is more favourable than other reactions, indicating that the •OH addition to the C5 and C6 atoms have relatively high probability to happen. The proportion of the C5 and C6 adducts is large and may be detectable experimentally, which is in agreement with the conclusions of •OH-mediated cytosine reaction reported experimentally and theoretically. These hint that the new DNA base (5-fCyt) is easily damaged when exposed the surrounding of •OH environment. Therefore, the reducing free radical production or the addition of some antioxidants should be taken in embryonic stem cells to resistance DNA damage. Our results provide some evidences between 5-fCyt and tumor development for the experimental scientists. The addition of •OH to C5═C6 double bond of 5-fCyt is more favourable than other paths. The ∆ G s≠ of C6 channel is a little higher than C5 route, indicating some amount of regioselectivity, which is in agreement with the conclusions of •OH-mediated cytosine reaction reported experimentally and theoretically.

Description: A series of trans -2-aminocyclohexanol derivatives have been explored as powerful conformational pH triggers. On protonation of the amino group, a conformer with equatorial position of ammonio and hydroxy groups becomes predominant because of an intramolecular hydrogen bond and electrostatic interactions. The energy of these interactions was estimated to be above 10 kJ/mol and in some models exceeded 20 kJ/mol (strong enough to twist a ring in tert -butyl derivatives). As a result of this conformational flip, all other substituents are forced to change their orientation. If the substituents are designed to perform certain geometry-dependent functions, for example, as cation chelators or as lipid tails, such acid-induced transition may be used to control the corresponding molecular properties. The pH sensitivity of conformational equilibria was explored by 1 H nuclear magnetic resonance spectroscopy (NMR), and the titration curves were used for estimation of the pK a values of protonated compounds that varied from 2.6 to 8.5 (in d 4 -methanol) depending on the structure of amino group. Thus, trans -2-aminocyclohexanols can be also used as conformational pH indicators in organic solvents. Trans -2-aminocyclohexanols have been explored as powerful conformational pH triggers by 1 H nuclear magnetic resonance spectroscopy titration. The change of relative conformational stability on protonation in some models exceeded 20 kJ/mol resulting in conformational flip and forcing all substituents to change their orientation. The pK a values of protonated compounds varied from 2.6 to 8.5 (in d 4 -methanol) depending on the structure of amino group.

Description: Rate constants are reported for the reactions of 1-phenoxy-dinitrobenzenes, 3 , 1-phenoxy-dinitrotrifluoromethylbenzenes, 4 , with n -propylamine, and 1-methylheptylamine in acetonitrile as solvent. The results are compared with results reported previously for n -butylamine, pyrrolidine, and piperidine. Decreasing ring activation leads to lower values of k 1 for nucleophilic attack although this may be mediated by reduced steric congestion around the reaction centre. Specific steric effects, leading to rate retardation, are noted for the ortho -CF 3 group. In general, reactant-bearing ortho -CF 3 group were subject to base catalysis irrespective of the amine nucleophile and values of k Am /k −1 are reduced as the size of the amine get bulkier. This is likely to reflect increases in values of k −1 coupled with decreases in values of k Am as the proton transfer from zwitterionic intermediates to catalysing amine becomes less thermodynamically favourable. Specific steric effects of ortho-CF 3 group leads to rate retardation and base catalysis due to increase in k −1 coupled with a decrease in k Am as the proton transfer from zwitterionic intermediates, 6 , to catalysing amine becomes less thermodynamically favourable.

Description: CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 are intermediates during the partial oxidation of CH 3 SCH 2 CH 3 in the atmosphere and in combustion processes. Thermochemical properties (ΔH f o , S o and C p (T)), structures, internal rotor potentials, and C─H bond dissociation energies of the parent molecules and their radicals formed after loss of a hydrogen atom are of value in understanding the oxidation processes of methyl ethyl sulfide. The lowest energy molecular structures were initially determined using the density functional B3LYP/6-311G/(2d,d,p) level of theory. Standard enthalpies of formation (ΔH f o 298 ) for the radicals and their parent molecules were calculated using the density functional B3LYP/6-31G(d,p), B3LYP/6-31 + G(2d,p), and the composite CBS-QB3 ab initio methods using isodesmic reactions. Internal rotation potential energy diagrams and internal rotation barriers were investigated using B3LYP/6-31 + G(d,p) level calculations. The contributions for S o 298 and C p (T) were calculated using the rigid rotor harmonic oscillator approximation on the basis of the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions from the method of Pitzer-Gwinn. The recommended values for enthalpies of formation of the most stable conformers of CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 are −34.6 ± 0.8, −42.4 ± 1.2, and -49.7 ± 0.8 kcal/mol, respectively. The structural and thermochemical data presented for CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 and their radicals are of value in understanding the mechanism and kinetics of methyl ethyl sulfide oxidation under varied temperatures and pressures. Group additivity values are developed for estimating properties of structurally similar, larger sulfur-containing compounds. Thermochemical properties (ΔH f °, S°, and C p (T)), lowest energy structures, internal rotor potentials, and C─H bond dissociation energies of CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 , and their radicals formed after loss of a hydrogen atom were determined using density functional theory computations. Group additivity values are developed for estimating properties of structurally similar, larger sulfur-containing compounds. Such data are of value in understanding the mechanism and kinetics of methyl ethyl sulfide oxidation under varied temperatures and pressures.

Description: Quantum chemical modeling was used to confront substituent effects in olefinic systems with an analogous situation in benzene. The B3LYP/6-311++G(d,p) method was applied to examine electron-donating properties of the amino group in a series of 3- (meta-like) and 4- (para-like) X-substituted cyclohexa-1,3-dienamines (X = NMe 2 , NH 2 , OH, OMe, Me, H, F, Cl, CF 3 , CN, CHO, COMe, CONH 2 , COOH, NO 2 , NO). As in the case of substituted anilines (PCCP, 2016, 18, 11711), the substituent properties were described by σ, charge of the substituent active region(X), and substituent effect stabilization energy descriptors; the amino group was characterized by structural and electronic parameters, whereas a transmitting moiety—by aromaticity index harmonic oscillator model of aromaticity. All applied substituent properties parameters were found to be mutually interrelated, with much better correlations for the para-derivatives than the meta-derivatives. Electron-donating ability of the amino group is stronger affected (circa 1.4 times) by substituent acting from position 4 in cyclohexa-1,3-dienamines than in aniline derivatives. It was also numerically confirmed that the reverse substituent effect acting to para-position is stronger (circa 1.14 times) in olefinic systems than in aromatic ones. Moreover, for 1-4 interactions, an increase of the electron-attracting power of the substituent increases π-electron delocalization in the olefinic series, whereas decreases it in the aromatic ones. Both classical and reverse substituent effects acting from para-position are always stronger in olefinic systems than in aromatic ones. Moreover, for 1-4 interactions the substituent effect on π-electron delocalization in diene systems is opposite to that observed in aromatic ones—an increase of the electron-attracting power of the substituent increases π-electron delocalization in the olefinic series, whereas decreases it in the aromatic ones.

Description: No abstract is available for this article.

Description: The electroluminescence intensity of the phenanthrene-functionalized gold nanoparticles, PMPT-Au nanoparticles/CPB: Ir(PIA) 2 (acac) film, was increased by 4.9 times compared with control device, CPB: Ir(PIA) 2 (acac) due to coupling between the excitons of emissive layer and localized surface plasmonic resonance of PMPT-Au NPs. The maximum luminous efficiencies of devices II to IV with PMPT-Au NPs were 39.2 cd A −1 (11.8 V), 40.1 cd A −1 (10.5 V), and 43.1 cd A −1 (9.0 V), respectively. The increment of current efficiency with PMPT-Au NP coated devices was strongly related to the energy transfer between the radiated light generated from CBP: Ir(PIA) 2 (acac) emissive layer and localized surface plasmonic resonance excited by PMPT-Au NP layer. The PMPT-Au NPs with 2.15% density at the junction of anode: HTL in OLEDs using CBP: Ir(PIA) 2 (acac) as emissive layer lead to enhanced the emission intensity attributed to increasing the radiative rate of OLEDs.

Description: Two new cavitands substituted with acid and alcohol groups (tetra-acid tetra-alcohol [TATA] and inverted TATA [iTATA]) bearing the same molecular skeleton as octa acid (OA) have been synthesized and their use as photochemical reaction containers explored. Isothermal calorimetric titration experiments suggest that the inclusion of organic molecules within these cavitands is driven both by favorable ΔH and ΔS and the substituents at the portals have little role to play. Comparison of the 2 new cavitands with the previous results on OA reveals that the presence of benzoate anion at the top periphery is essential for the cavitand to be a triplet sensitizer. Polarity within the water-soluble capsules, resulting from TATA and iTATA, was found to be close to that of ethylacetate and hydrocarbons, similar to that of OA. Photophysical studies with anthracene and camphorthione as guests disclose that the capsules made of 2 molecules of cavitands do not disassemble in the time scale of the excited states of the above guests (S 1 in the case of anthracene and T 1 in the case of camphorthione). Capsules ability to confine guests and the resulting photochemical intermediates has been tested by examining the photochemistry of 1-phenyl-3- para -tolyl-2-propanone. The radicals resulting from the Norrish type 1 cleavage of 1-phenyl-3- para -tolyl-2-propanone did not escape the cage and gave products, resulting from 100% cage effect. Availability of TATA and iTATA along with already reported similar cavitands expands the list of water-soluble capsule forming cavitands that could be used as molecular containers. Two new cavitands reported here possess internal cavity similar to that of octa acid. They encapsulate molecules such anthracene, dibenzyl ketone, and coumarin in water by forming a capsular assembly. These hosts provide a hydrophobic “molecular laboratory” in an aqueous environment. Inclusion of organic molecules within these hosts in water is favored by enthalpy and entropy. Of the 2 hosts, only the one with benzoate group at the periphery acts as the triplet sensitizer.

Description: Kinetic parameters of the unusual [2π + 2σ + 2σ]-cycloaddition reactions of quadricyclane ( 1 ) with tetracyanoethylene ( 2 ), 4-phenyl-1,2,4-triazoline-3,5-dione ( 3 ), N -phenylmaleimide ( 4 ), and diethyl azodicarboxylate ( 5 ) are determined experimentally. Additionally, the enthalpies of 1  +  2 reaction in 1,4-dioxane solution (−236.6 ± 1.0 kJ mol −1 ) and 1  +  3 reaction in toluene (−255.0 ± 2.8 kJ mol −1 ) are determined calorimetrically and shown to be the largest in absolute magnitude among all known cycloaddition reactions involving these dienophiles. Solvent effect on the rate of 1 + 3 reaction in 11 solvents is studied and found to be moderate and similar to that of the conventional Diels-Alder and ene reactions. The difference in the reaction rate constants of 1 with different dienophiles can be up to 9 orders of magnitude and is mainly caused by the difference in activation enthalpies. This difference is not correlated with the standard enthalpies of reactions and is likely the result of high sensitivity of the [2π + 2σ + 2σ] reaction rates to the energy of donor-acceptor interactions between the reactants. Rate constants and reaction enthalpies at 25°C of the [2π + 2σ + 2σ]-cycloaddition reactions of quadricyclane with tetracyanoethylene (120 L mol −1  s −1 ; −236.5 kJ mol −1 ), 4-phenyl-1,2,4-triazoline-3,5-dione (0.282; −255.1), N -phenylmaleimide (3.7·10 −7 ; -), and diethyl azodicarboxylate (2.8·10 −6 ; -) are determined experimentally.

Description: Herein, we have studied the interaction between cationic surfactant (conventional [myristyltrimethylammonium bromide, MTAB] as well as gemini surfactant 1, 4-butanediyl-α, ω-bis(dimethyltetradecylammonium bromide) (14-4-14)) and anti-inflammatory sodium salt of ibuprofen (IBU) drug in aqueous solutions by using tensiometry method at 298.15 K. The means of the interaction of drugs by added foreign materials is of paramount importance in the drug delivery. Ibuprofen is used for the relief of pain, fever, and swelling. From this study we have evaluated different parameters, for example, critical micelle concentration ( cmc ), micellar mole fraction of mixed micelles/mixed interface ( X 1 m / X 1 σ ), micellar/surface interaction parameter ( β m / β σ ), activity coefficients ( f 1 m / f 1 σ and f 2 m / f 2 σ ) of the mixed micelles/mixed interface, excess Gibbs free energy of mixed monolayer/mixed micelle formation ( / ), surface excess concentration ( Γ max ) etc. and discussed in detail. The micellar interaction parameter ( β m ) was determined from the critical micelle concentration values of the pure surfactant (MTAB/14-4-14) and IBU ( cmc 1 and cmc 2 ) and the mixed system ( cmc ) using the Rubingh's model. In addition to this, various other parameters such as packing parameters of amphiphiles in the micelles ( P ), volume contribution of the hydrophobic chain ( V 0 ), and its effective length ( l c ), have also been calculated. The value of micellar mole fraction ( ) is found to be more for IBU + 14-4-14 mixtures as compared to IBU + MTAB mixtures at lower mole fraction and vice versa at a higher mole fraction of surfactant. The Δ G o m and Δ G o ads values for all studied systems were found out to be negative, ie, micellization, as well as adsorption processes, are found to be energetically favorable. The interaction between cationic surfactant (conventional as well as Gemini surfactant) and sodium salt of ibuprofen drug have evaluated. The means of the interaction of drugs by added foreign materials is of paramount importance in the drug delivery. The packing parameters of amphiphiles in the micelles ( P ), volume contribution of the hydrophobic chain ( V 0 ), and its effective length ( l c ) have also been calculated. The Δ G o m and Δ G o ads values for all systems were found out to be negative. Protocol for the synthesis of 14-4-14 Gemini surfactant.

Description: The mechanism of the reaction at room temperature between an unactivated 2-alkyl aziridine and carbon dioxide to generate the corresponding oxazolidinone in glass has been studied. Theoretical calculations suggest that this reaction should not proceed at room temperature in the absence of a catalyst. In cases where a reaction was observed, kinetic studies show that the reaction displays a zero-order dependence with respect to aziridine, indicating that free aziridine is not involved in the rate-determining step. An ammonium salt generated in situ acts as a catalyst. The amount of this catalyst is diminutive, which prevented spectroscopic identification, and it is not readily removed from the starting material using chromatography. The mechanism of the reaction between a 2-alkyl aziridine and CO 2 to generate an oxazolidinone has been studied. Calculations suggest that this reaction should not proceed at room temperature in the absence of a catalyst. Kinetic studies show that the reaction displays a zero-order dependence with respect to aziridine, indicating that free aziridine is not involved in the rate-determining step. A small amount of an ammonium salt generated in situ acts as a catalyst.

Description: Various alternative methods for the synthesis of 4 H -dithieno[3,2- b :2′,3′- d ]pyrrole (DTP) starting from commercially available bromothiophene precursors are presented. Crucial steps involve the Cadogan reaction, Ullmann-type C─N couplings, or Buchwald-Hartwig–type aminations to build up the central pyrrole ring of DTP, respectively. The use of ammonia surrogates afforded the fused target heteroacene in overall yields of 33% to 63%, and the corresponding methods are applicable on large scale. Six alternative methods for the synthesis of 4 H -dithieno[3,2- b :2′,3′- d ]pyrrole (DTP) are presented involving Cadogan, Ullmann-type, or Buchwald-Hartwig–type reactions. The use of ammonia surrogates afforded the fused target heteroacene in overall yields of 33% to 63%, and the corresponding methods are applicable on large scale.

Description: The C 2 ─C 6 /Diels-Alder cyclization of enyne-ketoene 1 was studied by experiments, theoretical calculations, and dynamic trajectory computations. The failure to trap possible intermediate(s), indicates a concerted reaction mechanism. A detailed search for stationary points revealed a concerted mechanism and surprisingly a diradical intermediate with no direct connection to the enyne-ketoene 1 . To probe the accessibility of this intermediate quasiclassical trajectories were initiated from the concerted transition state structure. Notably, 36% of the trajectories reach the product zone directly and 5% arrive at the product via the intermediate diradical. Additionally, 31% of the trajectories go to the intermediate zone and stay there within the simulation time limit. The mechanism of the didehydro-Diels-Alder reaction of ( E )-3-phenyl-1-(2-(phenylethynyl)phenyl)prop-2-en-1-one is investigated experimentally as well as computationally. As all experiments to trap an intermediate failed, a detailed computational study was instigated. Molecular dynamics simulation revealed that the concerted transition state acts as a common bottleneck for both the concerted and stepwise paths.

Description: A QM/MM approach using ωB97X-D combined with AMOEBA calculations was used to analyze the energetic disorder in the vicinity of interfaces in amorphous organic heterostructures. Distributions of ground-, excited-, and cationic-state energies as well as of ionization potentials and excitation energies, all being relevant quantities for the transport properties of thin films, were calculated. As already found for bulk amorphous organic semiconductors, local densities of states at molecular interfaces possess Gaussian-shaped profiles with a significant amount of disorder. Assuming a disorder-limited activation of exciton and charge transport, a decrease in the amount of disorder could improve the transport properties. Relating calculated disorders to molecular parameters revealed that in line with the Bässler model, especially the molecular polarity, its change upon electronic excitation, and the molecular polarizability are relevant quantities leading to energetically largely disordered films. Moreover, because of the different mechanisms of exciton and polaron delocalization, a given morphology with disordered charge-transport levels gives not necessarily rise to disordered exciton-transport levels and vice versa. A QM/MM approach using ωB97X-D combined with AMOEBA calculations was used to analyze the energetic disorder in the vicinity of interfaces in amorphous organic heterostructures. Distributions of ground-, excited-, and cationic-state energies as well as of ionization potentials and excitation energies, all being relevant quantities for the charge and exciton transport properties of thin films, were calculated. Similar to amorphous bulk phases, local densities of states at molecular interfaces possess Gaussian-shaped profiles with a significant amount of disorder.

Description: This article presents the development and characterisation of an electrochromic device and its application to detect steel corrosion in reinforced concrete. Steel corrosion inflicts an enormous annual economic damage, which could be reduced by the installation of appropriate monitoring devices. These should be simple, reliable, long lasting, and should not require service or maintenance. The present electrochromic device is constructed in such a way that it uses the macrocell current in an active, chloride-induced corrosion element as power supply to trigger the colour change. This way, the system stays inactive until corrosion occurs. The device consists of diheptyl viologen in a liquid polymer electrolyte made from LiClO 4 and poly(ethylene glycol) with  = 400 g mol −1 . The addition of viologen lowers the resistance but causes no further changes in the electrochemical properties of the polymer electrolyte. Impedance spectra indicate ion transport rather than capacitance effects to dominate the electrochemical properties. Experiments using direct current in the microampere range show electrochromic switching times of several minutes, which is sufficient for the intended monitoring application. An electrochromic device is presented in which the colour change is successfully triggered by the weak electrical currents occurring during steel corrosion in reinforced concrete. The device consists of diheptyl viologen in a LiClO 4 -poly(ethylene glycol) electrolyte sandwiched between an ITO-coated PET sheet and a copper plate. It is simple, easy to construct, and requires little to no service or maintenance throughout the service life. As part of corrosion monitoring systems, it is therefore an ideal component of a sustainable infrastructural development.

Description: Bromination of the widely used triplet sensitizer thioxanthone extends the absorption spectrum into the visible range with only minor loss of lowest triplet state energy (3 kcal/mol for di-bromination). Because of bromine substitution, a slight increase in triplet quantum yield was observed. The di-brominated derivative was effective as organo-photocatalyst in performing [2 + 2] cross-photocycloaddition of acrylimide-based compounds under visible light irradiation. Bromination of the widely used triplet sensitizer thioxanthone extends the absorption spectrum into the visible range with only minor loss of lowest triplet state energy (3 kcal/mol for di-bromination). The di-brominated derivative was effective as organo-photocatalyst in performing [2+2] cross photocycloaddition of acrylimide-based compounds under visible light irradiation.

Description: No abstract is available for this article.

Description: The reaction of oxygen-substituted naphthalenes with singlet oxygen ( 1 O 2 ) has been investigated, and labile endoperoxides have been isolated and characterized at –78°C for the first time. Low-temperature kinetics by UV spectroscopy revealed that alkoxy and silyloxy substituents remarkably increase the rate of photooxygenations compared to 1,4-dimethylnaphthalene, whereas acyloxy-substituted acenes are inert towards 1 O 2 . The reactivities nicely correlate with HOMO energies and free activation energies, which we determined by density functional theory calculations. The lability of the isolated endoperoxides is due to their very fast back reaction to the corresponding naphthalenes even at –20°C under release of 1 O 2 , making them to superior sources of this reactive species under very mild conditions. Finally, a carbohydrate-substituted naphthalene has been synthesized, which reacts reversibly with 1 O 2 and might be applied for enantioselective oxidations in future work. Various naphthalenes 1 are smoothly photooxygenated to afford endoperoxides 2 quantitatively. Important is the low temperature of –78°C and the proper solvent to handle and isolate such labile species. Reactivities nicely correlate with the HOMO energies of naphthalenes 1 . The endoperoxides 2 reconvert quantitatively to the parent naphthalenes 1 under release of singlet oxygen even at –20°C, making them to superior organic sources of this reactive species under very mild conditions.

Description: The solid charge transfer (CT) complexes that have been formed from the reactions of donor benzidine (BZ) and the π-acceptors such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and chloronil (CHL) have been studied and characterized experimentally and theoretically. The experimental work which includes the use of UV-visible spectroscopy to identify the CT band of the CT-complex. The composition of the complexes has been investigated successfully by using spectrophotometric titration and Job method of continuous variation to be 1:1. Furthermore, to calculate the formation constant and molar extinction coefficient, we have used the Benesi-Hildebrand equation. Infrared and proton nuclear magnetic resonance spectral studies were used to characterize and confirm the formation of CT-complex. The experimental studies were well supported by quantum chemical simulations by using density functional theory. The computational analysis of molecular geometry, Mulliken charges, and molecular electrostatic potential surfaces of reactants and complexes is very much helpful in assigning the CT route. The C═O bond length of DDQ and CHL increased upon complexation with BZ. We have also observed that the substantial amount of charge has been transferred from BZ to DDQ and CHL in the process of complexation. An excellent consistency has been achieved between experimental and theoretical results. In this work, the charge-transfer complexes were prepared and characterized by different techniques such as UV-Vis, FTIR, and 1 HNMR. The experimental studies were well supported by quantum chemical simulations by using density functional theory; molecular geometry, Mulliken charges, and molecular electrostatic potential surfaces of reactants and complexes. These are helpful in assigning the CT route. The results reveal that the charge transfer takes place from donor to acceptor.