Covalent hydration model

Solvolyses of the [Fe(phen)3] + ion in DMSO-H2SO4 and [Fe(5-N02-phen)3] + ion in aqueous-organic solvent mixtures containing Me2CO, Bu OH, or H2O2 have not been interpreted in terms of a covalent hydrate model. The reaction in DMSO-H2SO4 is strongly catalysed by Cl ion and an ion-pair mechanism is favoured as discussed previously. The reactions of [Fr(5-N02-phen)3] + ion in non-aqueous solvents are discussed further in Chapter 5. 

The reduced form of the respiratory coenzyme diphosphopyridine nucleotide (DPNH), which is vitally important for all cellular metabolism, is changed by dilute acid to a substance that, in the light of the following model experiments, may be a covalent hydrate. The 1,4-and 1,6-dihydro derivatives of l-benzylpyridine-3-carboxamide furnish a single substance when dissolved in dilute acid at 20° and the solution is basified. The stable yellow product, which has a prominent peak at 292 nm, was assigned the constitution 1-benzyl-6-hydroxy-1,4,5,6-tetra-hydropyridine-3-carboxamide61 (see Scheme 2). 3-Acetyl-1 -benzyl- 1,4-... 

Little is also known about photoelectron spectra of pteridines. The unsubstituted nucleus and its 4-methyl- and 2,4,6,7-tetramethyl derivative have been recorded and analyzed in terms of both a simple Huckel-model and semiempirical calculations <86CB1275>. The assignment of the n- and n-type PE bands of pteridine indicates that the low energy band is associated with an ionization process involving the nitrogen n electrons and followed by rc-bands. Furthermore, the pKa of free pteridine, which is masked in aqueous solution by partial covalent hydration, is suggested from the PE data to be in the order of —2. 

An electrostatic hydration model, previously developed for ions of the noble gas structure, has been applied to the tervalent lanthanide and actinide ions. For lanthanides the application of a single primary hydration number resulted in a satisfactory fit of the model to the experimentally determined free energy and enthalpy data. The atomization enthalpies of lanthanide trihalide molecules have been calculated in terms of a covalent model of a polarized ion. Comparison with values obtained from a hard sphere modeP showed that a satisfactory description of the bonding in these molecules must ultimately be formulated from the covalent perspective. 

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

A more complete and much more rigorous description of bonding in complexes would be provided by a quantum mechanical treatment. Such a treatment is especially needed in the case of departures from the ionic model and increasing contribution of covalent bonding (ion pairs, soft donors and acceptors). However only a few studies have been reported. They are mainly concerned with cation hydration and use either semi-empirical 19—21) or non-empirical methods 22—24). A non-empirical treatment of cation NH3 systems has also been performed recently (25). However the present state of the computations is still far from providing a complete description of the system including the medium. The latter may be taken into account by a Bom-type "solvaton (27,26). Heats of hydration may then be calculated (27). A discussion of this aspect of the problem is deferred to a later date, awaiting especially a more complete analysis of non-empirical calculations. In the course of the discussion of... 

Protein function at solid-liquid interfaces holds a structural and a dynamic perspective [31]. The structural perspective addresses macroscopic adsorption, molecular interactions between the protein and the surface, collective interactions between the individual adsorbed protein molecules, and changes in the conformational and hydration states of the protein molecules induced by these physical interactions. Interactions caused by protein adsorption are mostly non-covalent but strong enough to cause drastic functional transformations. All these features are, moreover, affected by the double layer and the electrode potential at electrochemical interfaces. Factors that determine protein adsorption patterns have been discussed in detail recently, both in the broad context of solute proteins at solid surfaces [31], and in specific contexts of interfacial metalloprotein electrochemistry [34]. Some important elements that can also be modelled in suitable detail would be ... 

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