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  • 1
    Electronic Resource
    Electronic Resource
    Ferrocene-containing chelating ligands. 1. Solution study, synthesis, crystal structure, and electronic properties of bis{N,N'-ethylenebis((ferrocenylmethyl)amine)}copper(II) nitrate (1993)
    s.l. : American Chemical Society
    Inorganic chemistry 32 (1993), S. 1197-1203 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00059a028
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  • 2
    Electronic Resource
    Electronic Resource
    Potential-energy surfaces related to the thermal decomposition of ethyl azide: The role of intersystem crossings (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 2282-2289 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential-energy surfaces of ethyl azide relevant to its thermal decomposition have been studied theoretically. The geometries of minima and transition states on the S0 surfaces, as well as the lowest energy points in the seam of crossing of the triplet and singlet surfaces, have been optimized with the complete active space self-consistent field (CAS-SCF) method, and their energies, re-calculated with second-order multireference perturbation (CAS/MP2) theory and corrected by the zero-point energy (ZPE). The reaction mechanism is described by the following steps: (1) CH3CH2N3→CH3CH2N+N2, (2a) CH3CH2N→H2+CH3CN; (2b) CH3CH2N→CH3CHNH. The CN–N2 fission of ethyl azide is the rate limiting step (1), leading to ethylnitrene either along a spin-allowed path (1a) or along an alternative spin-forbidden one (1b). Both 1a and 1b channels show barriers of similar heights for CN–N2 bond fission, ΔE=42 kcal/mol, ΔE being the energy difference between the minimum of the ground singlet state potential-energy surface of ethyl azide and either the singlet transition state (TS1) or the lowest energy point of the intersystem crossing (ISC1), respectively. The decomposition of ethanimine formed in step (2b) has been studied as well and high energetic transition states have been identified for its decomposition. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.482043
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  • 3
    Electronic Resource
    Electronic Resource
    A method to improve the agreement between calculated and observed vibrational frequencies after scaling of a quantum mechanical force field (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8472-8477 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A systematic method to fit calculated to observed vibrational frequencies has been developed and implemented in a computer program. The procedure consists of the refinement of a scaled quantum mechanical force field (SQMFF) previously obtained according to Pulay's method. The key step in the process is the generation of an intermediate matrix, CΛCT, which is then refined. The above step produces only small corrections to the scaled force constants, yielding a considerable improvement of the fitted frequencies. This scheme of refinement can be carried out using any kind of coordinates. To show the reliability and performance of the proposed method, the force fields of two very different systems, as benzene and tetranitromethane, have been chosen as example tests. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290616
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  • 4
    Electronic Resource
    Electronic Resource
    The role of charge-transfer states of the metal-adsorbate complex in surface-enhanced Raman scattering (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7207-7216 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Surfaced-enhanced Ramon scattering (SERS) spectra of pyrazine are analyzed on the basis of the properties of the electronic states of the metal-adsorbate surface complex. Ab initio CIS calculations have been carried out for the Ag2-pyrazine complex, which have enabled us to find two excited singlets, namely CT0;1B1 and CT1;1A2, with properties quite similar to those of the pyrazine radical anion in its electronic 2B3u and 2Au states, respectively, and with energies falling in the range of the exciting photons usually employed in Raman spectroscopy. SERS spectra of pyrazine are compatible with a resonance Raman enhancement mechanism involving electronic transitions between the ground state S0;1A1 and both CT levels of the surface complex. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1450542
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  • 5
    Electronic Resource
    Electronic Resource
    A multiconfigurational self-consistent field study of the thermal decomposition of methyl azide (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 551-561 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Thermal decomposition of methyl azide has been studied computationally by using the complete active space self-consistent field (CASSCF) method and Møller–Plesset theory using the CASSCF wave function as the zeroth-order wave function (CAS/MP2). The calculations have been performed in conjunction with the 6-31G* basis set. The reaction is predicted to occur in two steps via nitrene intermediate: (1) CH3N3→CH3N+N2; (2a) CH3N→H2+HCN, (2b) CH3N→H2CNH. The rate-limiting step is the N2 extrusion (1), being a competitive mechanism between a spin-forbidden path and a spin-allowed one. The calculated energy barrier height for both processes is found to be isoenergetic, ΔE=41 kcal/mol, where ΔE represents the difference between the energy at the minimum on the singlet state surface of methyl azide and the energy at the minimum energy crossing structure (ISC1) or the singlet transition state (TS1) for the spin-forbidden path and the spin-allowed one, respectively. The nitrene intermediate formed in step (1) can undergo two parallel reactions: (2a) decomposition in H2 and HCN, and (2b) isomerization to methyleneimine. H2 extrusion from the imine generated in step (2b) has been studied as well. Two high energy transition states have been found for 1,1-H2 and 1,2-H2 elimination from methyleneimine, respectively. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479335
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  • 6
    Electronic Resource
    Electronic Resource
    Distribution of cichlid fishes in the littoral of Lake Bacalar, Yucatan Peninsula (1999)
    Springer
    Environmental biology of fishes 54 (1999), S. 35-43 
    Details
    ISSN: 1573-5133
    Keywords: spatial assemblage ; abundance ; substrate ; submerged vegetation ; use of habitat ; Mexico
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The distribution of cichlids in Lake Bacalar was assessed from January to September 1996, in eight shallow-water (〈 2 m) stations, using a 20 m long seine net. Temperature, salinity/conductivity and dissolved oxygen were sensor-obtained; depth, submerged vegetation and bottom type were determined by visual inspection. Affinities between stations, based on fish abundance and environmental parameters, were analyzed by multivariate methods. Littoral of Bacalar town was the site with highest richness, diversity and abundance, probably promoted by the additional urban waste of organic matter. PCA defined two station-groups, one associated with muddy substrates, the other one with rocky/sandy bottoms. Cichlids are more abundant over muddy bottoms with abundant submerged vegetation, probably because of the abundance of prey and shelter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007443408776
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis, spectroscopic characterization and electrochemical behaviour of nickel(II) complexes with C-meso-5,5,7,12,12,14-hexamethylcyclotetradecane (Me6[14]aneN4). Crystal structure of {Ni(Me6[14]aneN4)|I2 (1993)
    Springer
    Transition metal chemistry 18 (1993), S. 523-527 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A series of complexes of formula {Ni(Me6[14]aneN4)X2| (Me6[14]aneN4) = C-meso-5,5,7,12,12,14-hexamethyl-1,4,-8,11-tetraazacyclotetradecane and X = N3 (1), NCO (2), NCS (3), AcO (4) or I (5) has been synthesized. The crystal structure of (5) has been determined by X-ray diffraction methods. The nickel atom is surrounded by a square-planar array of nitrogen atoms, giving a low-spin complex. The macrocyclic ligand shows the most stable conformation, the six-membered rings exhibiting the chair form while the gauche conformation is adopted by the five-membered rings. Spectroscopic and magnetic data for (1)–(4) are consistent with octahedral coordination around the nickel atom, which is achieved by four N atoms of the macrocyclic ligand in a single plane and by two azido-N (1), cyanato-N (2), thiocyanato-N (3) and carboxylato-O (4) groups occupying the axial positions. An electrochemical study of the oxidation of (1)–(5) has been carried out in nonaqueous solvents and the prospects of synthesis of the corresponding nickel(III) species are discussed in the light of the electrochemical data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00136619
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  • 8
    Electronic Resource
    Electronic Resource
    Oxamidato complexes. Part 4. Electrochemical study of the copper(III)/copper(II) couple in monomeric N,N′-bis(substituent)oxamidatocopper(II) complexes (1993)
    Springer
    Transition metal chemistry 18 (1993), S. 69-72 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The electrochemical behaviour of a series of monomeric N,N′-bis(substituent)oxamidato copper(II) complexes of formula Na2[Cu(3,5,3′,5′-X4obbz)]·4H2O [X = Cl (1), Br (2), I (3) and obbz = oxamidobis(benzoato)], Na2-[Cu(obbz)]·4H2O (4), Na2[Cu(5,5′-Me2obbz)]·4H2O (5), Na2[Cu(4,5,4,5′-(MeO)4obbz)]·4H2O(6),Na2[Cu(obp)]· 3.5H2O (7) (obp = oxamidobis(propionato)) and Na2[Cu(pba)]·6H2O (8), [pba = propylenebis(oxamate)] has been investigated by cyclic voltammetry, rotating disk electrode and coulometry in water and dimethylsulphoxide (dmso) solutions. NaNO3 (0.1 M) and n-Bu4NPF6 (0.1 M) were used as supporting electrolytes in H2O and dmso respectively, all solutions being thermostatted at 25 °C. In aqueous solution, the complexes show an oxidation peak ranging from 1.19 to 0.86 V (values referred to the s.c.e.), the corresponding reduction being unobserved, even at high scan rates. In dmso, all the complexes exhibit only one oxidation peak ranging from 0.86 to 0.51 V, the corresponding reduction being observed for all of them except for (3). The oxidation potentials are strongly dependent upon the nature of the N,N′-substituent of the oxamide. The copper(III)-assisted hydrolysis of the oxamidate ligand is analysed in terms of the lack of planarity of the oxamidate ligand induced by the steric effect of the halogen substituent in the 3-position on the phenyl rings. The influence of the nature of the solvent was also studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00136054
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis, characterization and a voltammetric study of (Bu4N)2[Mo2Br6]. Oxidation-reduction mechanism of related compounds (1984)
    Springer
    Transition metal chemistry 9 (1984), S. 447-449 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The synthesis and characterization of (Bu4N)2[Mo2Br6], obtained from Mo(CO)6, (Bu4N)Br and 1,2-dibromoethane, is described. The electrochemical behaviour of [Mo2Br6]−2 and related species is studied, and an oxidation-reduction mechanism is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00620674
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  • 10
    Electronic Resource
    Electronic Resource
    An immunocytochemistry study comparing the occurrence of neuroactive substances in the nervous system of cercariae and metacercariae of the eye flukeDiplostomum spathaceum (1995)
    Springer
    Parasitology research 81 (1995), S. 553-559 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The nervous system of two larval stages (cercariae, metacercariae) of eye flukeDiplostomum spathaceum was investigated immunocytochemically by the application of antisera to the amino acid glutamate and to neuropeptides isolated from invertebrates (Mollusca) and from vertebrates to whole-mount preparations. In cercariae, positive immunoreactivity (IR) was observed with antisera raised against Catch-relaxing peptide (CARP), FMRFamide, α-caudodorsal cell peptide (α-CDCP), substance P, vasotocin, and vasopressin. In metacercariae, in addition to positive staining with these antisera, the ones raised against glutamate, APGWamide, caudodorsal cell hormone I (CDCH-I), and small cardiac peptide B (SCPB) also gave positive IR in the nervous system. In the two larval stages the most extensive pattern of IR was observed with anti-FMRFamide and anti-CARP. In the nervous system of metacercariae the same immunoreactive neurosubstances appeared to be present as in that of cercariae. The increase in the variety of immunoreactive neurosubstances in the more complex nervous system of metacercariae is discussed in relation to parasite development and to host adaptation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00932021
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