Chirality surface parameters

Apart from the above-discussed parameters for HPLC optimization of chiral resolution on antibiotic CSPs, some other HPLC conditions may be controlled to improve chiral resolution on these CSPs. The effect of the concentrations of antibiotics (on stationary phase) on enantioresolution varied depending on the type of racemates. The effect of the concentrations of teicoplanin has been studied on the retention (k), enantioselectivity (a), resolution (Rs), and theoretical plate number (N) for five racemates [21]. An increase in the concentration of teicoplanin resulted in an increase of a and Rs values. The most surprising fact is that the theoretical plate number (N) increases with the increase in the concentration of teicoplanin. It may be the result of the resistance of mass transfer resulting from analyte interaction with free silanol and/or the linkage chains (antibiotics linked with silica gel). This would tend to trap an analyte between the silica surface and the bulky chiral selector adhered to it. This is somewhat... 

The physico-chemical parameters of the chemical stimuli which have been shown to have relevance and to be interrelated to the sensory response it elicits as specific odor or taste, are the factors controlling concentration at the receptor areas (solubility, hydrophilicity, lipophilicity, volatility, and partition coefficients), molecular features (size, shape, stereochemical and chirality factors and functional groups), and electronic features (polarity and dipoles) controlling positioning and contact at receptor surfaces (53). Many of these physico-chemical data are not available for many of the chemical stimulants, and till they are gathered, structure-response studies will be much restricted. The effects of interactions of the above parameters appear to a larger degree in the perception of odor, the dimensions of which are many and complex viz. nuances, composite... 

The understanding of how chirality is introduced at surfaces via the adsorption of organic molecules has wimessed a real step-change in the past decade and a number of important parameters and phenomena have been revealed from the dramatic images obtained by STM and from the detailed insights attained by a range of surface spectroscopic techniques and theoretical calculations. A number of excellent... 

Early studies on monolayers of chiral molecules like 2-hydroxyalkanes, amphiphilic amino acids, 2-methylhexacosanoic acid esters, and hydroxy-hexadecanoic acid and its esters have been reviewed. The interesting question about monolayers of chiral molecules is whether the parameters which can be determined and the phase transitions are different for pure enantiomers and racemates. For components of biomembranes like phosphatidylcholines 10 this appears not to be the case," but for synthetic compounds like iV-(a-methylbenzyl-stearamide) 11 specific interactions between the molecules of the enantiomers are observed (Chart 2). ° In recent years, advanced techniques have been developed to probe the order in monolayers at the air-water interface, including surface X-ray diffraction, and microscopic techniques, viz. fluorescence microscopy, and Brewster angle microscopy (BAM). The X-ray diffraction technique has been used to identify homochiral and heterochiral two-dimensional domains in mono-layers of racemic amphiphilic amino acids on subphases containing glycine. Fluorescence microscopy requires the introduction in the monolayer of a small... 

Let us fix the parameter 2A = 0.34 nm which is equal to the graphite inter-layer separation. The chirality and the radius of single-wall carbon nanotube are uniquely specified by the chiral vector C/, = iai +112 2 - ( i. 2)> where ni,ri2 are integers and ai, a2 are the unit cell basis vectors of graphite [1]. The chiral vector C is a circumferential lattice vector defined on nanotube surface, and C is perpendicular to the tube axis. For armchair nanotubes n =ri2 = n, and the tube radius r is defined by r = C/, /2ti = a f3n/2n, where a = 0.249 nm is the lattice constant for graphite. These values of r are used in our calculations. 

The steiic attributes of a molecule include its size and shape. Molecular size or bulk is easily assessed from properties such as molecular weight, volume, or surface area. A summary of parameters for molecular bulk is provided by Livingstone (2000). Molecular shape is much more difficult to parameterize, and there is no single descriptor capable of doing so (Patel and Cronin, 2001b). Different aspects of molecular shape, such as chirality, linearity, and branching, are often addressed individually (Livingstone, 2003). 

Furthermore, neither PGA nor PLA possess intrinsic bioactivity. Cellular responses to implants of these polymers are mediated mostly by surface adsorbed proteins, surface topography, and local acidity. Crystallinity seems to be another parameter affecting cell adhesion on PLA/PGA polymers. The effects are believed to be a result of differences in protein conformation stemming from variations in binding to amorphous versus crystalline polymer surfaces. The chirality of crystalline regions may also play a role in controlling cellular response, but the detailed mechanisms of these effects are not fully understood. 

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