Neutral acid clusters

The scope of this paper is to provide an overview of methods used to study properties of electrically neutral molecular clusters initiating particle formation in the troposphere, with focus on quantum chemistry. The review of results is intended to be complete with regard to water-sulfuric acid-ammonia clusters. Concerning studies on clusters including other molecular species, we review representative examples and newest publications. Ionic clusters and clusters involving iodine, related to coastal nucleation, are mentioned in passing. 

The X-ray crystal structures of bovine andP. denitrificans CcO reveal a cluster of acidic residues on subunit 11 near the binuclear Cua center. xhe highly conserved aromatic residue, Trpl43, at the center of this acidic cluster is in van der Waals contact with the Cua center and could be involved in electron transfer with Cc. In order to investigate the location of the binding domain for Cc, a series of R. sphaeroides CcO mutants was prepared in which acidic residues were replaced with neutral Asn or Gin residues (Figure 17, Table 2). When the 1 1 complex between Ru-55-Cc and wUd-type CcO is photoexcited at low-ionic strength, electron transfer Irom heme c to Cua occms with an intracomplex rate constant of... 

Ethylene—Dicarboxylic Acid Copolymers. Partial neutralization of copolymers containing carboxyls in pairs on adjacent carbons, eg, ethylene—maleic acid, has been described (11). Surprisingly, there is no increase in stiffness related to neutralization. Salts with divalent metal cations are not melt processible. The close spacing of the paired carboxyl groups has resulted in ionic cluster morphology which is distinct from that of the commercial ionomer family. 

Ethylene ionomers consist of copolymers of ethylene and an organic add, such as methacrylic acid, the acid moieties of which have been neutralized to form a metal salt. The metal salts from neighboring chains tend to form clusters, such as the one shown schematically in Fig. 18.3. The net result is the overall structure shown in Fig. 18.2 g), in which the ionic clusters form weak crosslinks between adjacent chains. Ionomers also contain short and long chain branches, which are similar to those found in low density polyethylene. 

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