Charge density, solvent polarity and counterion nature effects on the solution properties of some polycations

We report the experimental charge density of HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid], which is a common buffering agent. The structure was refined using the Hansen–Coppens formalism. The ability of the HEPES molecule to form stable intermolecular interactions and intermolecular hydrogen bonds in the crystal structure is discussed in terms of its buffering properties. The protonation mode observed in the crystal structure is different from that expected in solution, suggesting that additional factors must be taken into consideration in order to explain the solution properties of the compound. As ordered HEPES molecules are found in the active sites of proteins in several protein crystal structures, our results will allow for quantitative analysis of the electrostatic potential of the interacting surfaces of those proteins.

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Solute-solvent interactions and the sweet taste of small carbohydrates. Part 1: Effect of solvent polarity on solution properties

Food Chemistry ◽

10.1016/0308-8146(92)90007-o ◽

1992 ◽

Vol 45 (1) ◽

pp. 25-32 ◽

Cited By ~ 11

Author(s):

S SERGHAT ◽

M MATHLOUTHI ◽

T HOOPMAN ◽

G BIRCH

Keyword(s):

Solvent Polarity ◽

Sweet Taste ◽

Solution Properties ◽

Solvent Interactions ◽

Effect Of Solvent

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Incommensurate modulated phases of the NbxTa1-xTe4 charge density wave system

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100120692 ◽

1992 ◽

Vol 50 (1) ◽

pp. 58-59

Author(s):

S. Ritchie ◽

J. C. Bennett ◽

A. Prodan ◽

F.W. Boswell ◽

J.M. Corbett

Keyword(s):

Charge Density ◽

Charge Density Wave ◽

Direct Evidence ◽

Density Wave ◽

Wave System ◽

Modulated Phases ◽

Metal Atoms ◽

Incommensurate Modulation ◽

End Members ◽

Modulation Wave Vector

A continuous sequence of compounds having composition NbxTa1-xTe4; 0 ≤ x ≤ 1 have been studied by electron diffraction and microscopy. Previous studies have shown that the end members of the series, TaTε4 and NbTε4 possess a quasi-one-dimensional character and exhibit charge density wave (CDW) distortions. In these compounds, the subcell structure is tetragonal with axes (a × a × c) and consists of the metal atoms (Nb or Ta) centered within an extended antiprismatic cage of Te atoms. At room temperature, TaTε4 has a commensurate modulation structure with a 2a × 2a × 3c unit cell. In NbTε4, an incommensurate modulation with × ∼ 16c axes is observed. Preliminary studies of the mixed compounds NbxTα1-xTε4 showed a discontinuous jump of the modulation wave vector commensurate to incommensurate when the Nb dopant concentration x, exceeded x ≃ 0.3, In this paper, the nature of the compositional dependence of is studied in greater detail and evidence is presented for a stepwise variation of . This constitutes the first direct evidence for a Devil's staircase in CDW materials.

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