Hydrogen bonds, adsorption

A common theme is the existence of modified (enantioselective) sites and unmodified (racemic) sites. For the case of the tartaric acid modified Ni, it is postulated that the tartaric acid is adsorbed on the surface and stereodirects (through hydrogen bonding) adsorption of the incoming 3-ketoesters.18 19 Support for this comes from an isotope effect from deuterium labeling.23 Increased enantioselectivities resulting from co-modification with NaBr is believed to result from poisoning the racemic sites.24 A similar technique in... 

Abstract—A discussion is given of the conditions for operation of hydrogen bond adsorption in a variety of processes where vapourized or dissolved organic substances are adsorbed, by inorganic or organic solids. 

From non-aqueous solvents hydrogen bond adsorption of most proton donors occurs on inorganic oxides but on nylon and wool fibres only hydroxylic compounds are strongly adsorbed, either from non-aqueous solvents or in the vapouy phase. 

The role of hydrogen bonds in liquid or vapour-phase adsorption processes has not hitherto been very clearly defined. The present paper is a brief review of some recent investigations in this laboratory, many of them unpublished, which it is believed may help to define the conditions favouring hydrogen bond adsorption especially from dilute solutions, by inorganic and organic substrates. 

Methods used here to identify hydrogen bond adsorption from solution include ... 

Data such as those in Table 1 are a useful gqide in studying the possibility of hydrogen bond adsorption in different systems, but they must be used with eaution. Even if two groups are shown to interact when present in substances in solution it does not always follow that they will do so under adsorption conditions. This will be discussed below. ... 

Hydrogen Bond Adsorption- of Mono-functional, Solutes... 

Little information is available upon hydrogen bond reactions in vapour phase adsorption, except in the important reactions of proteins and textile fibres with moisture, which have received widespread study. In these reactions substrate-water hydrogen bonds are undoubtedly responsible for the initial monolayer adsorption of water with increase in vapour pressure the adsorbed water condenses into multilayers by formation of water-water hydrogen bonds. Adsorption of organiq molecules of low molecular weight, in the vapour phase, on nylon or wool is considerably greater when they contain a hydroxylic group than when they do not [8] (Table 5), so that the hydroxy-compounds... 

Variable temperature MAS NMR was used to characterize the structure and dynamics of hydrogen bonded adsorption complexes between various adsorbates and the Brpnsted acid site in H ZSM-5 the Brpnsted proton chemical shift of the active site was found to be extremely sensitive to the amount of type of adsorbate (acetylene, ethylene, CO and benzene) introduced (105). Zscherpel and coworkers performed maS NMR spectroscopic measurements in order to investigate the interaction between Lewis acid sites in H ZSM-5 and adsorbed CO. A new measure for the "overall" Lewis acidity of zeolites was derived from the C MAS NMR spectroscopic data. In addition, the chemical shift of CO adsorbed... 

Even in molecules with no functional groups which are expected to interact with silanol sites on silica gel through hydrogen bonding, adsorption on solid surfaces modifies their electronic states and their photophysical processes but the mechanism of adsorption interaction is not elucidated in detail. 

Support for a neutral hydrogen-bonded adsorption complex comes also from a measurement of the distance between the methanol and the zeolite protons in H-MOR by wide line NMR at 4 K [28],... 

A porous polyamide resin is shown to possess hydrogen bond acceptor properties suitable for the separation of polyphenolic solutes such as phenolic acids, flavonols, and flavonoids. The separation is achieved in the presence of solvent mixtures of acetic acid and ethanol. The extent of hydrogen bond adsorption is reviewed based on data obtained from the elution behavior of a variety of simple polyphenolic solutes. Polyamide adsorption chromatography was applied for the purification of resveratrol and polydatin from Polygonum cuspidatum Sieb. Zucc [38]. 

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