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Betainy jako akceptory protonu

Dega-Szafran Z., Szafran M.

Wiadomości Chemiczne

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2017

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[Z] 71, 7-8

609--628

EN

Ammonium alkanoates (ammonioalkanocarboxylates) are zwitterions (or inner salts, or betaines), because they possess formally charged ammonium and carboxylate groups separated by one or more sp3 carbon atoms. The chemistry of betaines has become a subject of particular interest due to their applications in biological research, especially with regard to their important role in aminoacid synthesis as methyl transfer agents. The crystals of many betaine complexes display interesting physical properties, exhibiting phase transitions with ferroelectric, antiferroelctric and ferroelastic behavior. Betaines containing a hydrophobic chain in the range of 8–20 carbon atoms show the unique properties characteristic for amphoteric surfactants and their current industrial application is in toiletries and personal care products. The conformational structure of zwitterionic molecules depends on several factors. The electrostatic attraction between two charged groups depends strongly on arm flexibility (energy differences between rotational trans and gauche isomers), bulkiness and hydration of charged groups preventing their close approach, solvent and arm electrical properties which control electrostatic attraction between two opposite charged groups, and polarization of solvent around the molecule caused by the dielectric discontinuity between solvent and solute interior (image charge effect). Electrostatic interaction is the common determinant and probably the most important element in structure-reactivity correlation in organic and biological systems. On the other hand, organic compounds are thought to be pure even though they may be a mixture of conformational isomers. This is because the isomers covert rapidly with each other at room temperature and their individual reactivates are little known. Occasionally the conformers may be stabilized in the crystallographic matrixes of polymorphic structures. This article describes structures of seven groups of aliphatic, aromatic and alicyclic betaines and numbers of their new hydrogen-bonded complexes with mineral and organic acids.

2

Theoretical Studies on the Preferential Binding of Anions to a Benzimidazole Based Anion Receptor

Zhao J. Y., Zhang Y., Li R.Q., He W. J.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 4

651-659

EN

The structures and the trend to wards binding of anthracen-9-ylmethyl- (1Hbenzoimidazol- 2-yl)-amine (I) with some anions were studied with B3LYP/LanL2DZ level of theory. The influence of hydrogen bonding on the structures was investigated. The corrected values of the dissociation energy for the hydrogen-bonded complexes were used to predict the trend to wards binding of receptor unit with anions, which has the order: F– greater than CH3COO– greater than NO2 - greater than Cl– greater than CN– greater than H2PO4 - greater than NO3 - greater than Br– greater than NCS– greater than I– greater than ClO4 - . This order is in good agreement with experimentally observed results. Upon hydrogen bonding, the vibrational frequencies of N–H stretching vibrations are shifted to lower wave- number, the delatan(N–H) for the com plexes are in the range from 159 cm–1 to 1130 cm–1. The IR intensities of the N–H stretching vibrations in crease dramatically in the hydrogen-bonded complexes.

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Hydrogen bonded complexes of coumarin 153

Królicki R., Jarzęba W., Soroushian B., Lampre I., Mostafavi M.

Bulletin of the Polish Academy of Sciences. Chemistry

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2002

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Vol. 50, No. 4

435-449

EN

Detailed studies of the hydrogen-bonded complexes of coumarin 153 (C153) have been carried out. It has been shown that nonlinear shifts of the steady-state absorption and fluorescence spectra taken in toluene-methanol solvent mixtures are caused by the formation of hydrogen bonded complexes between C153 and methanol, while preferential solvation plays a minor role only. IR measurements confirmed the ability of C153 to form hydrogen-bonded complexes with methanol and phenol. The stoichiometry of the formed complexes and relevant equilibrium constants have been estimated. Femtosecond solvation dynamics measurements of C153 in the toluene-methanol mixture (xMeOH = 0.2) showed that the average solvation time is higher than that in the pure solvents indicating slower relaxation of methanol in the mixture. The slow component of solvation dynamics (ok 20ps) can be attributed to translational diffusion of methanol to the first solvation shell of C153 and to the relatively slow reorientational motion of methanol involved in formation of hydrogen bond with the excited C153.