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  • 1
    ISSN: 0947-6539
    Keywords: hydrogen bonds ; molecular recognition ; polyelectrolyte multilayers ; surface chemistry ; thin films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Functional polyanions were prepared by copolymerization of sulfopropyl acrylate and sulfopropyl methacrylate with monomers bearing triaminopyrimidine or barbituric acid functionalities, respectively. Functionalized polyelectrolyte multilayers were assembled from these copolymers by stepwise alternating adsorption with poly(choline methacrylate). These multilayers are suited for molecular recognition of substrates that are complementary to the functional groups incorporated. Thus, multilayers containing triaminopyrimidine moieties selectively bind barbituric acid, and vice versa, when exposed to solutions of the 1:1 complex of barbituric acid and triaminopyrimidine. The molecular recognition process was monitored by UV/Vis spectroscopy, time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and photoelectron spectroscopy (XPS). Remarkably, after successful recognition and binding of the complementary substrates to the multilayers, the stepwise layering could be continued.
    Additional Material: 6 Ill.
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  • 2
    ISSN: 0947-6539
    Keywords: hydrogen bonds ; LFER ; molecular recognition ; NMR spectroscopy ; nucleobases ; thermodynamics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Association energies ΔGt in chloroform, in part also in carbon tetrachloride, were determined by NMR titrations of suitably substituted nucleosides and several synthetic analogues. Based on these and on many literature data, two simple free energy increments were derived describing the ΔGt values of 58 complexes within 1.8 kJ mol-1. With chloroform as solvent the increment for the primary interaction between donor and acceptor is 7.9 kJ mol-1, for the secondary one 2.9 kJ mol-1, irrespective of whether the latter is attractive or repulsive. Addition of only 1% methanol to CCl4 led to a decrease in association constants by a factor of 25. Calorimetric titrations of G-C nucleoside derivatives in CCl4 showed substantial contributions from G dimers, in line with NMR titrations, and surprisingly small decreases in entropy. Preliminary NOE measurements allowed us to single out some of the possible association modes; they are also in line with expected self- and triple-association modes of the nucleobases. These modes are generally in accord with nucleobase associations predicted by MM calculations in the literature, which in turn agree with predictions based solely on the increments derived in the present work.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0947-6539
    Keywords: boronic acids ; heme proteins ; molecular recognition ; myoglobin ; saccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylboronic acid groups as sugar recognition sites were successfully introduced into native myoglobin by a cofactor-reconstitution method. Spectrophotometric pH titration demonstrated the sugar-induced pKa shift of the H2O coordinated to the heme center of the semisynthetic myoglobin bearing phenyl-boronic acids (met-Mb(PhBOH)2). By means of circular dichroism (CD) and paramagnetic 1H NMR spectroscopies, it was proven that sugars that were bound to phenylboronic acid sites induced the rearrangement of the heme crevice to reinforce the heme cofactor-apoprotein interactions. The structural changes that were induced by the binding of sugars subsequently enhanced the dioxygen storage activity of Mb(PhBOH)2. Such sugar-induced structural and functional changes did not occur for other modified Mbs that had no sugar-recognition units. Interestingly, a randomly modified Mb with phenylboronic acid units did not show any sugar response. In Mb(PhBOH)2, the information from the sugar-binding event was efficiently transmitted to the active center, so that the activity was efficiently altered upon sugar binding. In conclusion, the active site specific incorporation of molecular recognition units as nonnatural functional molecules can provide a novel strategy for the design of stimuli-responsive semisynthetic proteins.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0947-6539
    Keywords: adenine ; catalysis ; molecular recognition ; template effects ; transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of receptors were prepared all containing two adenine binding sites linked by various spacers. Their ability to act as templates in the coupling of two adenine derivatives, an active ester and an amine, in CHCl3 was evaluated. The accelerations varied from none to 700-fold. Binding studies of the coupling product with these templates confirmed involvement of both binding sites. When the spacer was a 1,10-phenanthroline unit, an efficient hydrolysis reaction of the active ester was observed. Another series of receptors were prepared containing one adenine receptor and various polar functional groups. The molecules were evaluated as catalysts in the coupling of an adenine-derived active ester and n-butyl-amine. The orientation as well as the nature of the functional group greatly influenced the coupling rate. A carboxylate group was most effective, accelerating the intracomplex reaction 250-fold.
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0947-6539
    Keywords: barbiturates ; macrocycles ; molecular recognition ; receptors ; zinc complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new bis-zinc(II) receptor (Zn2L), which has two macrocyclic 12-membered tetraamine (cyclen) ZnII complexes connected through a p-xylene bridge, has been synthesized as a novel host molecule to recognize barbiturates (such as barbital (bar)) in aqueous solution. Each of the zinc(II) ions in the biszinc(II) receptor was originally intended to match the dianionic barbital anion (bar2-) with supplementary hydrogen bonds between the cyclen NH's and the three carbonyl oxygens in complementary positions to yield a 1:1 complex, Zn2L-bar2-. From an aqueous solution of equimolar Zn2L and barbital at pH 8, however, a cyclic 2:2 complex, (Zn2L-bar2-)2, was isolated and characterized by X-ray crystal analysis. The NMR study in 10% (v/v) D2O/H2O has revealed dissociation of (Zn2L-bar2-)2 solely into the original target 1:1 complex Zn2L-bar2- and established the dimerization constant for 2Zn2L-bar2- → (Zn2L-bar2-)2, Kd ( = [(Zn2L-bar2-)2]/[Zn2L-bar2-]2) to be 103.4 M-1. The thermodynamic parameters were evaluated from the NMR measurements at 25, 35, 45, and 55°C: ΔG = -1.9 × 104 J mol-1, ΔH = - 3.3 × 104 J mol-1, ΔS = - 49 J mol-1 K-1 at 25°C. Potentiometric pH titration of Zn2L (1 mM) and barbital (1 mM) disclosed extremely facile deprotonation of the two imido groups of barbital at pH less than 7 to form the dianionic barbital-bound ZnII complexes Zn2L-bar2- and (Zn2L-bar2-)2, where-by the barbital binding affinity for Zn2L was estimated to be Kbar ( = [Zn2L-bar2-]/[uncomplexed Zn2L][uncomplexed barbital]) = 105.8 M-1 at pH 8 and 25°C with I = 0.10 (NaNO3). The significance of the bis-zinc(II) receptor in stabilizing the dianionic barbital is evident by comparison with the interaction of ZnII-cyclen complex (ZnL) with barbital, which yields only a 1:1 monoanionic barbital complex, ZnL-bar- (Kbar = [ZnL-bar-]/[uncomplexed ZnL][uncomplexed barbital] = 104.2M-1 at pH 8 and 25°C with I = 0.10 (NaNO3)).
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  • 6
    ISSN: 0947-6539
    Keywords: interlocking moleucles ; molecular recognition ; pseudorotaxanes ; rotaxanes ; template syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of three new rotaxanes - two [2]rotaxanes and a [3]rotaxane - formed by a “threading followed by stoppering” approach is described. These template-directed syntheses rely on the formation of pseudorotaxane intermediates, which self-assemble in solution from functionalized secondary dialkylammonium hexafluorophosphate threads and macrocyclic polyether rings (either dibenzo-[24]crown-8 or its asymmetric constitutional isomer). The stoppers - substituted 1,2,3-triazoles-were created by thermally allowed 1,3-dipolar cycloadditions between azido groups, which terminate the threads, and di-tert-butyl acetylenedicarboxylate.
    Additional Material: 3 Ill.
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  • 7
    ISSN: 0947-6539
    Keywords: crown ethers ; dialkylammonium salts ; hydrogen bonding ; molecular recognition ; pseudorotaxanes ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A very simple self-assembling system, which produces inclusion complexes with pseudorotaxane geometries, is described. The self-assembly of eight pseudorotaxanes with a range of stoichiometries-1:1, 1:2, 2:1, and 2:2 (host:guest)-has been achieved. These pseudorotaxanes self-assemble from readily available components-well-known crown ethers, such as dibenzo[24]crown-8 and bis-p-phenylene[34]crown-10, and secondary dialkylammonium hexafluorophosphate salts, such as (PhCH2)2NH+2PF-6 and (nBu)2NH+2PF-6-and have been characterized not only in the solid state, but also in solution and in the “gas phase”. The pseudorotaxanes are stabilized largely by hydrogen-bonding interactions and, in some instances, by aryl-aryl interactions.
    Additional Material: 40 Ill.
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  • 8
    ISSN: 0947-6539
    Keywords: hydrogen bonds ; metalloreceptor ; molecular recognition ; nucleobases ; pi interactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thiacyclophane ligands 1 and 2, containing a meta-xylyldithiaether unit, an aromatic spacing unit and a polyether chain, were prepared in good yield in a three-step synthesis. The macrocyclic organopalladium complexes [Pd(L)-(MeCN)][BF4] (3: L = 1; 4: L = 2) were prepared through palladation of the respective thiacyclophane ligand by reaction with [Pd(MeCN)4][BF4]2. These complexes act as metalloreceptors to aromatic amines such as p-aminopyridine (pap), m-aminopyridine (map) and the DNA nucleobases adenine and guanine. Binding occurs through simultaneous first- and second-sphere coordination. This involves three separate interactions: first-sphere σ donation from an aromatic N atom to the Pd centre, second-sphere hydrogen bonds between the NH2 group and polyether O atoms, and π stacking between the electron-poor aromatic rings of the substrate and the electron-rich aromatic spacing units of the receptor. 1H NMR spectra exhibit chemical shift changes indicative of the H-bonding and π-stacking interactions in solution. X-ray structures for thiacyclophane 1, metalloreceptor [Pd(1)(MeCN)][BF4] (3), metalloreceptor/model substrate complexes [Pd(1)(pap)][BF4 (5) and [Pd(2)-(pap)][BF4] (7), and metalloreceptor/nucleobase complexes [Pd(1)(adenine)][BF4] (13), [Pd(2)(adenine)][BF4] (14) and [Pd(1)(guanine-BF3)][BF4] (15b) show details of these interactions in the solid state.
    Additional Material: 10 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 505-508 
    ISSN: 0947-6539
    Keywords: DNA recognition ; triplexes ; molecular recognition ; peptide nucleic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Double-stranded DNA can be viewed as a multifunctional, modular receptor that can be read sequence-selectively in a digital way (base pair per base pair) by a complementary, similarly modular ligand. This principle has been exploited in several approaches to design sequence-specific DNA-binding ligands, such as triplex-forming oligonucleotides, peptide nucleic acids and minor groove binding polyamides.
    Additional Material: 5 Ill.
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  • 10
    ISSN: 0947-6539
    Keywords: amphiphiles ; barbituric acid ; hydrogen bonds ; melamines ; molecular recognition ; monolayers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four alkyl melamine amphiphiles each containing identical triads of hydrogen-bonding sites (hydrogen donor, acceptor, and donor) but different numbers of alkyl chains were examined in order to determine their monolayer properties and binding behavior towards barbituric acid (BA). Their structural organization in supramolecular assemblies at the air-water interface was affected by the bulkiness of the hydrophobic part of the amphiphile. Aqueous BA and amphiphiles with two or three alkyl chains formed a 1:1 alternate network structure. In contrast, a melamine amphiphile with four alkyl chains formed a 2:1 (BA:amphiphile) complex rather than a 1:1 alternate network structure. The 2:1 complex appears to behave like an independent molecular entity without further networking. The results point to the importance of size matching between the hydrophobic part of the monolayer and the underlying hydrogen-bonded network in order to maintain the overall supramolecular structure.
    Additional Material: 8 Ill.
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