Theoretical models of nonlinear effects in two-component cooperative supramolecular copolymerizations

The understanding of multi-component mixtures of self-assembling molecules under thermodynamic equilibrium can only be advanced by a combined experimental and theoretical approach. In such systems, small differences in association energy between the various components can be significantly amplified at the supramolecular level via intricate nonlinear effects. Here we report a theoretical investigation of two-component, self-assembling systems in order to rationalize chiral amplification in cooperative supramolecular copolymerizations. Unlike previous models based on theories developed for covalent polymers, the models presented here take into account the equilibrium between the monomer pool and supramolecular polymers, and the cooperative growth of the latter. Using two distinct methodologies, that is, solving mass-balance equations and stochastic simulation, we show that monomer exchange accounts for numerous unexplained observations in chiral amplification in supramolecular copolymerization. In analogy with asymmetric catalysis, amplification of chirality in supramolecular polymers results in an asymmetric depletion of the enantiomerically related monomer pool

Tuning the coordination chemistry of cyclotriveratrylene ligand pairs through alkyl chain aggregation

Propylated cyclotriveratrylene (CTV) ligands display different coordination chemistry over their methylated congeners as a result of increased solubility, an affinity for alkyl chain aggregation and steric factors. The propylated ligand tris(isonicotinoyl)-tris(propoxy)-cyclotricatechylene (L1p) forms a 1D coordination polymer within complex {[Ag(L1p)[Co(C2B 9H11)2]](DMF)}∞ (complex 1p), and a 2D sheet of 4·82 topology in {[Cd(L1p)(ONO 2)2(H2O)]·(DMF)·0.5(Et 2O)}∞ (complex 2p), neither of which are formed with the analogous methylated ligand tris(isonicotinoyl)-cyclotriguaiacylene (L1m). Both complexes 1p and 2p display multiple sites of aggregation of hydrophobic groups. The new propylated ligand tris(2-quinolylmethyl)-tris(propoxy)- cyclotricatechylene (L2p) forms a 1D coordination polymer with Ag(i) in complex{[Ag2(L2p)2][Co(C2B9H 11)2]2·1.5(MeNO2)} ∞ (complex 3p) and a novel, compressed octahedral structure with palladium(ii) cations, [Pd6(L2p)4(CF 3CO2)12] (complex 4p). Neither complex was accessible with the methylated congener tris(2-quinolylmethyl)- cyclotriguaiacylene (L2m)

Determination of platinum (II,IV) and palladium(II) as thiocyanate complexes by capillary zone electrophoresis analysis of carboplatin and similar drugs.

International audienceThe thiocyanate complexes of Pd(II), Pt(II) and Pt(IV) were studied by capillary zone electrophoresis. Pd(II) can be detected in the form of the thiocyanate complex at 305 nm with higher sensitivity than in the form of its chloro complex (absorption maximum 214 nm). A detection limit equal to 5 ppb for Pd has been finally achieved. The possibility of simultaneous determination of Pd(II) and Pt(IV) in the form of thiocyanate complexes has also been demonstrated. When the method optimized for the determination of Pt(II) was applied to the drugs Cykloplatin and Ribocarbo (containing carboplatin) and Platidiam (containing cisplatin), good agreement of the platinum content with the declared value was obtained. Samples of vehicle exhaust particulates (National Institute for Environmental Studies, Japan, No. 8 reference material) were also analyzed

Design and Synthesis of New PolytopicLinkers for Bio-chemical Assemblies

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Determination of rimantadine in pharmaceutical preparations by capillary zone electrophoresis with indirect detection or after derivatization

International audienceRimantadine is synthetic analog of amantadine; both are antiviral agents used for prophylaxis and treatment of influenza A. A capillary zone electrophoretic (CZE) procedure for the determination of rimantadine has been developed. As the direct determination of rimantadine is poorly sensitive because the compound is almost transparent in the UV/Vis range, several indirect methods were studied. Two were found to be the particularly useful: (a) indirect detection using 5 mM 4-methylbenzylamine in 1:4 methanol-water as absorbing background electrolyte, with detection at 210 nm, and (b) derivatization of rimantadine with 1,2-naphthoquinone-4-sulfonic acid in alkaline medium and subsequent determination of the derivative by CZE (40 mM tetraborate, pH 9.2, detection at 280 nm). Uncoated capillary tubing, 44 cm length ×75 μM i.d., was used for both determinations. The detection limits were 0.1 and 2 ppm for methods a and b, respectively. The methods were used to determine rimantadine in pharmaceutical products and for dissolution testing of Flumadin® tablets

Experimental Investigation of the Effect of Macromolecular Crowding on Protein Conformation

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Symmetry numbers and statistical factors in self-assembly and multivalency

Evaluation of statistical factors in self-assembly processes is not a firmly settled question. As a contribution to solve this problem, a critical re-examination of the symmetry number method and generalization of the direct count method are presented. The two approaches, producing the same results, mutually reinforce their role with respect to other discordant methods whose results cannot be independently checked. The direct count method moreover serves as a rationale for the apparently odd results the symmetry number method sometimes provides. The two methods thus turn out to be complementary to each other. Discussion of some exemplary cases points to the importance and subtlety of the role played by the geometrical features of assemblies involving intramolecular bonds

Tuneable intramolecular intermetallic interactions as a new tool for programming linear heterometallic 4f-4f complexes

Statistical mechanics predicts that the design of pure organized heteropolymetallic chains of metal ions bound to linear receptors depends on controlled deviations from the mixing rule DeltaE(MiMj) = 1/2 (DeltaE(MiMi) + DeltaE(MjMj)), whereby DeltaE(MiMj) is the intramolecular intermetallic interaction between neighboring metal i and metal j along the receptor. A thorough investigation of linear polymetallic trivalent lanthanide triple-stranded helicates shows that such deviations are amplified by an increase in the nuclearity of the final complexes and are thus easily evidenced in the tetranuclear heterobimetallic helicates [La(4-y)Lu(y)(L6)3](12+) (y = 0-4). The chemical and physical origins of this unprecedented behavior are discussed together with its practical consequences for programming pure heteropolymetallic 4f-4f complexes

Apparent non-statistical binding in a ditopic receptor for guanosine

Analysis of stepwise association constants for guests binding to more than one site in a receptor is expected to give a ratio of the first association constant to the second of about 4 : 1 on statistical grounds (since a second guest should have an equal chance of binding to a different site on the same, or a new molecule). Taking account of self-association in our analysis of a system in which the binding sites are close together, we observe a ratio closer to 1 : 1, indicative of non-statistical, or cooperative binding. The longer homologue built around two alkynes displays a very different ratio of stepwise association constants of about 7 : 1. We discuss the origins of this unusual behaviour in terms of steric interactions within the receptors and their corresponding complexes with guanosine derivatives

Enzymatic activity in crowded media as investigated by capillary electrophoresis based assay. Application to hyaluronidase

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