Chiral recognition in molecular clusters

Molecular complexes represent the simplest model systems for studying the physical and chemical properties of molecules in the transition from the gas phase to the 

This section will focus on the stmcture and energetics of chiral molecular complexes studied with Fourier-transform IR (FT-IR), microwave, LIF, hole burning (HB), IR fluorescence dip spectroscopy, resonance-enhanced multiphoton ionization (REMPl Fig. 5), and RET spectroscopy. 

The LIF spectral shifts Av and the fluorescence lifetimes t concerning the complexes between F/j = (R)- or F = (5)-2-naphthyl-l-ethanol and a variety of primary and secondary aliphatic alcohols and terpenes (M) are hsted in Table 1.102.329,330 

In general, the excitation spectra of the selected [F M] complexes show intense features, accompanied by smaller signals placed at the low energy side. These signals are mainly due to several conformational isomers of the 1 1 complexes, as 

For instance, LIF experiments, carried out on the heterochiral complex between F and M = (7 )-2-butanol, indicate the presence of three new bands at —136, — 114, and — 73 cm from the band origin of the bare F. Similar experiments on the homochiral complex between F and M = (5)-2-butanol exhibit two new bands at — 125 and — 69 cm from the band origin of the bare F. HB experiments show that four different isomers coexist in the jet, two of them corresponding to the 

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One may use the stronger term chirality discrimination when a substantial suppression of one intermolecular diastereomer with respect to the other occurs. This requires multiple strong interactions between the two molecular units and therefore more than simple monofunctional alcohols. Some examples where one of the molecules involved is a chiral alkanol are reported in Refs. 112 and 119 121. Pronounced cases of higher-order chirality discrimination have been observed in clusters of hydroxy esters such as methyl lactate tetramers [122] and in protonated serine octamers [15,123,124]. The presence of an alcohol functionality appears to be favorable for accentuated chirality discrimination phenomena even in these complex systems [113,123,125,126]. Because the border between chirality recognition and discrimination is quite undefined, it is suggested that the two may be used synonymously whenever both molecular partners are permanently chiral [127]. 

Chiral clusters in the gas phase, 39, 147 Chirality and molecular recognition in monolayers at the air-water interface, 28, 45... 

Carbohydrates, similarly to peptides, are natural sources of chirality and also offer a wide range of ncm-covalent interactions. Molecular recognition of carbohydrates by biological receptors mediates a variety of physiologically relevant processes, including recruitment of leucocytes to inflammatory sites, clearance of glycoproteins from the circulatory system, cell interactions in the immune system, as well as adhesion of bacteria or viruses to host cells. It has been shown that multivalency is especially important for carbohydrate-receptor interactions. The glycoside cluster... 

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