Hydrogen-bonded clusters

Gerber R B, McCoy A B and Garcia-Vela A 1995 Dynamics of photoinduced reactions in the van der Waals and in the hydrogen-bonded clusters Femtosecond Chemistry Proc. Berlin Conf. Femtosecond Chemistry (Berlin, March 1993) ed J Manz and L Woeste (Weinheim Verlag Chemie) pp 499-531... 

Hydrogen-bonded clusters are an important class of molecular clusters, among which small water clusters have received a considerable amount of attention [148, 149]. Solvated cluster ions have also been produced and studied [150, 151]. These solvated clusters provide ideal model systems to obtain microscopic infonnation about solvation effect and its influence on chemical reactions. 

Figure 2-2. Left Association of two dipolar water molecules by a hydrogen bond (dotted line). Right Hydrogen-bonded cluster of four water molecules. Note that water can serve simultaneously both as a hydrogen donor and as a hydrogen acceptor.

Water forms hydrogen-bonded clusters with itself and with other proton donors or acceptors. Hydrogen bonds account for the surface tension, viscosity, liquid state at room temperature, and solvent power of water. 

The elasticity of thermoplastic polyurethane rubbers (which are also known as thermoplastic urethanes or TPUs) is a function of their morphology which comprises hard and soft phases. The hard phases consist of hydrogen bonded clusters of chain segments, which are linked by flexible chain segments that make up the soft phase. The hard blocks, which are the minor phase, exist as separate domains within a continuous matrix of the majority soft phase, as shown schematically in Fig. 25.9. 

One method to study energy-selected ions is threshold ionization, in which ions with precisely defined energy contents are produced. These ions can then be used to study unimolecular fragmentation, ion-molecule reactions, van der Waals clusters, and hydrogen-bonded clusters [62]. 

T. Yamaguchi, New horizons in hydrogen bonded clusters in solution. Pure Appl. Chem. 71, 1741 1751 (1999). 

M. Quack and M. A. Suhm, Potential energy hypersurfaces for hydrogen bonded clusters (HF) , in Conceptual Perspectives in Quantum Chemistry, Conceptual Trends in Quantum Chemistry, Vol. Ill, J. L. Calais and E. S. Kryachko, ed., Kluwer, Dordrecht, 1997, pp. 415 463. 

N. Nishi, S. Takahashi, M. Matsumoto, A. Tanaka, K. Muraya, T. Takamuku, and T. Yamaguchi, Hydrogen bonding cluster formation and hydrophobic solute association in aqueous solution of ethanol. J. Phys. Chem. 99, 462 468 (1995). 

Fig. 6-31. Coordination structure of adsorbed water molecules on an interface of metal electrodes (a) hydrogen-bonded clusters, (b) bilayer clusters of adsorbed water molecules, (c) a superficial ( 3 x V ) KdO lattice of adsorbed water molecules on a (111) surface plane of face-centered cubic metals. (HsOli = first la] r of adsorbed water molecules. [From Thiel-Madey, 1987.]...

TABLE 2.5. Total and Relative Energies of Hydrogen-Bonded Clusters (HF) ... 

N. Mikami, Spectroscopic study of intracluster proton transfer in small size hydrogen-bonding clusters of phenol, Bull. Chem. Soc. Jpn, 68 (1995) 683-695. 

K. Kleinermanns, M. Gerhards and M. Schmitt, Electronic spectroscopy of aromatic molecules in jet-cooled hydrogen bonded clusters - structure and fluxionality, Her. Bunsen-Ges. Phys. Chem., 101 (1997) 1785-1798. 

One interesting challenge that reactions in van der Waals and hydrogen-bonded clusters offer is the possibility of studying specifically how weak interactions or microsolvation bonds affect a chemical reaction or dissociation process. In that sense, theoretical studies of weakly bound clusters have proved to be useful in learning about the crossover in behavior from that of an isolated nonsolvated molecule in the gas phase to that for a molecule in a liquid or solid solvent. 

In the mass spectrometric investigations of most hydrogen-bonded clusters, the protonated clusters form the dominant cluster ions as a result of a rapid proton transfer reaction (Mark and Castleman 1985). Castleman and coworkers have extensively investigated the neat expansions of methanol (Morgan and Castleman 1987, 1989 Morgan et al. 1989 Zhang et al. 1991) and observed the protonated cluster ions to form the most intense cluster series. In the case of methanol, the exoergic proton transfer reaction may be written as ... 

Figure 21-15. Attachment of an excess tt electron to a cyclic hydrogen-bonded cluster facilitates inter-molecular proton transfer (a) formic acid dimer, (b) formamide dimer, and (c) formic acid-formamide (Figure 1 of ref. [51]. Reused with permission. Copyright 2005, American Institute of Physics)...

Fig. 13.10. Hydrogen-bonding pattern in the crystal structure of methyl 1,5-dithio-a-D-ribopyra-noside quarterhydrate. Four molecules form a hydrogen-bonded cluster around the water molecule. The perimeter of the cluster is hydrophobic and the packing of the 4(C6H1203S2)-H20 clusters is van der Waals. Note the eight-membered homodromic cycle and the homodromic spiral involving the water molecule. The swivel indicates hydrogen bonding to the next asymmetric unit [MDTRPY20]...

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