Proton-acceptor group

In contrast to those noted above, theoretical investigations of branched complexes in which two or more hydrogen bonds are formed by one proton-acceptor group, as in Structure 2.4, predict an inverse effect. In this case, mutual polarization weakens the hydrogen bonds, leading to anticooperative effects. The various factors governing the influence of the first hydrogen bond on the formation of... 

According to the concept discussed in Refs [24, 25], the F0 factor is responsible for H+ translocation between the environment (in relation to mitochondrion), aqueous phase and the membrane, where fixed proton-acceptor groups X are located. If H+/ATP stoichiometry equals 2, they may be absorbed in the ATP-synthase reaction ... 

For the bonding of the water of crystallization primarily the first coordination sphere of the H2O molecules must be considered, that is number and coordination of the proton acceptor groups and metal ions in the neighborhood of the water molecules. Various classifications are reported in the literature in order to describe the environment of H2O molecules in solid hydrates. The system mostly used is that of Chidambaram et al. which classifies H-bonded water molecules with respect to their lone-pair coordination (see Table 1 and Fig. 1). 

Gp is the only known host giving 25 types of the different isostructurai supramolecular complexes (clathrates). This natural compound demonstrates dozens of kinds of biological activity. Such behavior is explained by its special molecular structure—diversity of the polar functional (six proton-donor and two proton-acceptor) groups, conformational mobility, and racemicity. This finding may be used in the future in order to design or look for the new versatile host compounds. 

It concluded that the main aspect which should be considered is the equilibrium between the formation and rupture of every hydrogen bonds and not the ensemble equilibrium between various associates [89]. Veytsman [114] considered systems of molecules with a one type of proton-donor group and a one type of proton-acceptor group and proposed an approximate combinatorial expression for the number or routes to form hydrogen bonds that does not invoke the existence of associates [89]. 

HCAII is one of the best-characterized enzymes and has therefore served as one of the first test cases to explore the capabilities of AIMD simulations for a first-principles modeling of enzymes. Several full-quantum and mixed QM/MM hybrid simulations have been performed for this system. In these studies the influence of the size of the quantum region and the representation of the electrostatic enviromnent of the protein have been tested. In addition, it was also possible to directly observe part of the enzymatic reaction cycle, namely the initial proton transfer steps from the zinc-boxmd water towards the proton acceptor group His64 located in the upper channel of the active site. In these proton transfer reactions a... 

Functionality. This useful concept is taken from polymer chemistry. In terms of hydrogen-bonded systems, it relates to the number of proton-donor groups (x) and the number of proton-acceptor groups (y), expressed as (x y). Thus, for example, acetone is (0 2), methanol is (1 2) and water is (2 2) functional. 

Surface mobility of adsorbed hydrogen in the catalytic layer favors proton migration between membrane and electrodes and improves Pt utilization. Mobility is usually associated with proton acceptor groups in the vicinity of catalyst nanoparticles. The chemical modification of the surface of carbon supports with proton acceptors has been proposed as a promising strategy to improve the catalytic layer performance [1-4]. 

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