Formamide clusters

Figure 5.27 Formamide clusters (with net binding energies in parentheses).

By dynamic light scattering it was found that, in surfactant stabilized dispersions of nonaqueous polar solvents (glycerol, ethylene glycol, formamide) in iso-octane, the interactions between reversed micelles are more attractive than the ones observed in w/o microemulsions, Evidence of intermicellar clusters was obtained in all of these systems [262], Attractive intermicellar interactions become larger by increasing the urea concentration in water/AOT/ -hexane microemulsions at/ = 10 [263],... 

Recently, we demonstrated that the Zintl clusters [Geg]" react with chalcogen atoms (S, Se, and Te) in the presence of surfactant templates to form ordered mesoporous Ge-rich chalcogenides [74]. The mesostructured frameworks grow through a coupling reaction of (Ge9)-clusters with chalcogens in formamide/ethy-lenediamine mixture solution in an unusual reaction that seems to be a redox process (5). 

The electrochemistry of the extracted FeMo cofactor has also been studied in depth [20]. Extracted At-methyl formamide (NMF) solutions of FeMo-co contain the intact cluster, probably with retention of the exogenous homocitrate ligand. Protein ligation are replaced with NMF ligands at... 

Nitrogenase, which catalyzes the reduction of N2 to two molecules of NH3, has a different molybdenum -iron cofactor (FeMo-co). It can be obtained by acid denaturation of the very oxygen-labile iron-molybdenum protein of nitrogenase followed by extraction with d i methyl formamide.655,656 The coenzyme is a complex Fe-S-Mo cluster also containing homocitrate with a composition MoFe7S9-homocitrate (see Fig. 24-3). Nitrogenase and this coenzyme are considered further in Chapter 24. 

Figure 4.11 Formamide-water clusters considered in this work.

Figure 4.12 n —s> 7t vertical excitation energy in formamide-water clusters with various stand-alone methods. L, M, and S stand for the large (6-311+C(d,p)), medium (6-31C(d))r and small (3-21C) basis sets, respectively. 

Non-aqueous synthetic methods have recently been used to assemble mesoporous transition metal oxides and sulfides. This approach may afford greater control over the condensation-polymerization chemistry of precursor species and lead to enhanced surface area materials and well ordered structures [38, 39], For the first time, a rational synthesis of mesostructured metal germanium sulfides from the co-assembly of adamantanoid [Ge4S ()]4 cluster precursors was reported [38], Formamide was used as a solvent to co-assemble surfactant and adamantanoid clusters, while M2+/1+ transition metal ions were used to link the clusters (see Fig. 2.2). This produced exceptionally well-ordered mesostructured metal germanium sulfide materials, which could find application in detoxification of heavy metals, sensing of sulfurous vapors and the formation of semiconductor quantum anti-dot devices. 

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)...

Glass beads can be used as an illustration of hydrophobia interactions. Thus, glass beads covered with dichloro-dimethylsilane can be regarded as solid hydrocarbon particles. Only hydrophobic interactions are possible. In a structured solvent such as water or formamide, the beads cluster together. When the polarity of the solvent is decreased by addition of alcohols the clusters disintegrate [79]. 

In addition to divalent metal cations, trivalent and tetravalent cations (i.e. ln +, Ga +, Sb +, and Sn +) were also effective as linking agents to organize [Ge4Sio]" clusters to form hexagonally ordered mesostractures. In this case, cetylpyridinium bromide was nsed as the surfactant, and formamide served as the solvent. The mesophases made with Ga + and Sb + showed intense visible photoluminescence at77K. 

Ge4Sio]" and [Fe4S4CLi] clusters was synthesized from a formamide solution containing the surfactant cetylpyridinium bromide. ... 

All protic solvents undergo multiple relaxation processes due to the presence of hydrogen bonding. In the case of water and formamide (F), the data can be described in terms of two Debye relaxations. For the alcohols and A-methyl-formamide (NMF), three Debye relaxations are required for the description. In all of these solvents, the low-frequency process involves the cooperative motion of hydrogen-bonded clusters. In the case of water and the alcohols the high-frequency process involves the formation and breaking of hydrogen bonds. The intermediate process in the alcohols is ascribed to rotational diffusion of monomers. Studies of dielectric relaxation in these systems have been carried out for the -alkyl alcohols up to dodecanol [8]. Values of the relaxation parameters for water and the lower alcohols are summarized in table 4.5. 

The cofactor and the P-cluster are distinct entities as shown by the fact that in the presence of thiophenol and 80% N-methyl formamide solutions, A vinekmdii gives rise to cofactor and (0S)4F4S4 signals61). 

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