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Anion Binding (anion + binding)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Macrocyclic Hexaureas: Synthesis, Conformation, and Anion Binding

CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2009
Denys Meshcheryakov Dr.
Abstract Varied flexibility: Cyclic oligoureas are formed by using anions as templates. Linking of six xanthene and/or diphenyl ether fragments by urea groups leads to the formation of five macrocyclic compounds with a 48-membered ring with variable flexibility (see picture). Their interaction with anions shows a strong influence of acetate and chloride ions on the cyclization from four precursor molecules. Five macrocylic compounds XXXXXX, XXDXXD, XDXDXD, XDDXDD, and DDDDDD with 48-membered rings, in which six xanthene and/or diphenyl ether fragments are linked through six urea (-NH-C(O)-NH-) groups, have been synthesized. In the cyclization step, a linear diamine was allowed to react with the appropriate diisocyanate by using a [5+1] (i.e., "XDXDX+D" for XDXDXD), [4+2] (DDDDDD), or [3+3] (XDDXDD) procedure. Compounds XXXXXX and XXDXXD were prepared from two molecules of the dimeric amine XX and two molecules of the respective monomeric diisocyanate (X or D) in a [2+1+2+1] (or 2×[2+1]) reaction. The (nonoptimized) yields in the cyclization step ranged from 45 to 80,%. The linear precursor diamines or diisocyanates were obtained by analogous condensation reactions by using partial protection with a tert -butoxycarbonyl group. All the macrocyclic compounds and synthetic intermediates were characterized by 1H,NMR and mass spectra. Three different crystal structures were obtained for XDDXDD, which show the molecule in a more or less strongly folded conformation determined by intramolecular hydrogen bonding. The interaction of the hexaureas with selected anions was studied by 1H,NMR spectroscopy and UV absorption spectrophotometry. [source]

Addressing Association Entropy by Reconstructing Guanidinium Anchor Groups for Anion Binding: Design, Synthesis, and Host,Guest Binding Studies in Polar and Protic Solutions

CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2008
Vinod
Abstract The bicyclic hexahydropyrimidino[1,2a]pyrimidine cationic scaffold has a well-known capacity to bind a variety of oxoanions (phosphates, carboxylates, squarates, phosphinates). Based on this feature, the parent host was supplemented with sec -carboxamido substituents to generate compounds 1,3 in an effort to improve the anion-binding affinity and selectivity and to learn about the role and magnitude of entropic factors. Bicyclic guanidinium compounds were prepared by a convergent strategy via the corresponding tetraester 22 followed by catalytic amidation. Host,guest binding studies with isothermal titration calorimetry in acetonitrile probed the behavior of artificial hosts 1,3 in comparison with the tetraallylguanidinium compound 4 on binding p -nitrobenzoate, dihydrogenphosphate, and 2,2,-bisphenolcyclophosphate guests that showed enhanced affinities in the 105,106,M,1 range. Contrary to expectation, better binding emerges from more positive association entropies rather than from stronger enthalpic interactions (hydrogen bonding). In an NMR spectroscopy titration in DMSO, o -phthalate was sufficiently basic to abstract a proton from the guanidinium function, as confirmed by an X-ray crystal structure of the product. The novel carboxamide-appended anchor groups also bind carboxylates and phosphates, but not hydrogen sulfate in methanol with affinities in excess of 104,M,1. The energetic signature of the complexation in methanol is inverted with respect to acetonitrile solvent and shows a pattern of general ion pairing with strong positive entropies overcompensating endothermic binding enthalpies. This study provides an example of the fact that bona fide decoration of a parent guanidinium anchor function with an additional binding functionality may provide the desired enhancement of the host,guest affinity, yet for a different reason than that implemented by design as guided by standard molecular modeling. [source]

Stability of Anion Binding with Monomers of a Cationic Surfactant

CHEMPHYSCHEM, Issue 6 2008
Anna Jakubowska Dr.
Competitive binding: Electrospray ionisation mass spectrometry is used to probe the binding ability of different anions with a cationic surfactant. Bond strengths are estimated from plots of the intensity of the peak assigned to a given complex ion in the mass spectrum versus the cone voltage applied to induce the abstraction of the counterions from the monomers (see graph). [source]

Assessment of adenyl residue reactivity within model nucleic acids by surface enhanced Raman spectroscopy

BIOPOLYMERS, Issue 1 2006
Lydie Grajcar
Abstract We rank the reactivity of the adenyl residues (A) of model DNA and RNA molecules with electropositive subnano size [Ag] sites as a function of nucleic acid primary sequences and secondary structures and in the presence of biological amounts of Cl, and Na+ or Mg2+ ions. In these conditions A is markedly more reactive than any other nucleic acid bases. A reactivity is higher in ribo (r) than in deoxyribo (d) species [pA > pdA and (pA)n , (pdA)n]. Base pairing decreases A reactivity in corresponding duplexes but much less in r than in d. In linear single and paired dCAG or dGAC loci, base stacking inhibits A reactivity even if A is bulged or mispaired (A.A). dA tracts are highly reactive only when dilution prevents self-association and duplex structures. In d hairpins the solvent-exposed A residues are reactive in CAG and GAC triloops and even more in ATC loops. Among the eight rG1N2R3A4 loops, those bearing a single A (A4) are the least reactive. The solvent-exposed A2 is reactive, but synergistic structural transitions make the initially stacked A residues of any rGNAA loop much more reactive. Mg2+ cross-bridging single strands via phosphates may screen A reactivity. In contrast d duplexes cross-bridging enables "A flipping" much more in rA.U pairs than in dA.T. Mg2+ promotes A reactivity in unpaired strands. For hairpins Mg2+ binding stabilizes the stems, but according to A position in the loops, A reactivity may be abolished, reduced, or enhanced. It is emphasized that not only accessibility but also local flexibility, concerted docking, and cation and anion binding control A reactivity. © 2006 Wiley Periodicals, Inc. Biopolymers 82: 6,28, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]