Charge Complex Formation

When proteins and polysaccharides carry an opposite charge, complex formation is driven by the attractive electrostatic interactions between the two biopolymers. Soluble and insoluble complexes may be formed depending on the strength of the interactions, the balance of negative... 

The first quantitative model, which appeared in 1971, also accounted for possible charge-transfer complex formation (45). Deviation from the terminal model for bulk polymerization was shown to be due to antepenultimate effects (46). Mote recent work with numerical computation and C-nmr spectroscopy data on SAN sequence distributions indicates that the penultimate model is the most appropriate for bulk SAN copolymerization (47,48). A kinetic model for azeotropic SAN copolymerization in toluene has been developed that successfully predicts conversion, rate, and average molecular weight for conversions up to 50% (49). 

Complex Ion Formation. Phosphates form water-soluble complex ions with metallic cations, a phenomenon commonly called sequestration. In contrast to many complexing agents, polyphosphates are nonspecific and form soluble, charged complexes with virtually all metallic cations. Alkali metals are weakly complexed, but alkaline-earth and transition metals form more strongly associated complexes (eg, eq. 16). Quaternary ammonium ions are complexed Htde if at all because of their low charge density. The amount of metal ion that can be sequestered by polyphosphates generally increases... 

For any adsubble method, if the material to be removed (termed the colligend) is not itself surface-active, a suitable surfactant (termed the collector) may be added to unite with it and attach or adsorb it to the bubble surface so that it may be removed (Sebba, Ion Flotation, Elsevier, New York, 1962). The union between colligend and collector may be by chelation or other complex formation. Alternatively, a charged colhgend may be removed through its attraction toward a collector of opposite charge. 

The possible mechanism of ionization, fragmentation of studied compound as well as their desoi ption by laser radiation is discussed. It is shown that the formation of analyte ions is a result of a multi stage complex process included surface activation by laser irradiation, the adsoi ption of neutral analyte and proton donor molecules, the chemical reaction on the surface with proton or electron transfer, production of charged complexes bonded with the surface and finally laser desoi ption of such preformed molecules. 

Method of Rh(III) - Ru(III) separation and isolation them from rai e and nonferrous metals based on formation of different charged complexes with varied stability has been proposed. Possibility of sepai ation of Ru(III), Rh(III), Pd(II), Pt(II) by water-soluble extractants from concentrated thiocyanate solutions has been displayed. Accelerated procedures of extraction-photometric determination of Rh(III), Ru(III) in solutions and waste products, which ai e chai acterized by high selectivity, availability, usage of non-toxic extractants have been worked out. 

The charge-tranter concept of Mulliken was introduced to account for a type of molecular complex formation in which a new electronic absorption band, attributable to neither of the isolated interactants, is observed. The iodine (solute)— benzene (solvent) system studied by Benesi and Hildebrand shows such behavior. Let D represent an interactant capable of functioning as an electron donor and A an interactant that can serve as an electron acceptor. The ground state of the 1 1 complex of D and A is described by the wave function i [Pg.394]

The ethylenediamine derivative [31] possesses higher promoting activities than other diamines. This phenomenon may be ascribed to the copromoting effect of the two amino groups on the decomposition of persulfate through a CCT (contact charge transfer complex) formation. So we proposed the initiation mechanism via CCT as the intimate ion pair and deprotonation via CTS (cyclic transition state) as follows ... 

Equilibrium constants for complex formation (A") have been measured for many donor-acceptor pairs. Donor-acceptor interaction can lead to formation of highly colored charge-transfer complexes and the appearance of new absorption bands in the UV-visible spectrum may be observed. More often spectroscopic evidence for complex formation takes the font) of small chemical shift differences in NMR spectra or shifts in the positions of the UV absorption maxima. In analyzing these systems it is important to take into account that some solvents might also interact with donor or acceptor monomers. 

In the last two decades a number of phenomena found many years ago in azo coupling and other substitution reactions have been elucidated with regard to their structural and mechanistic basis. These include charge-transfer complex formation, radical pairs as transient intermediates, and changes in product ratios due to mixing effects — a phenomenon which was not understandable at all only a few years ago (see Secs. 12.8 and 12.9). 

The proton is not the only entity that can dissociate from a substrate or bond to it. We can enumerate other interactions, such as metal-ligand complexation, ion-pair formation, charge-transfer complex formation, etc. For the sake of brevity, we treat all of these as... 

Hence, reactions which proceed via complex formation or stripping reactions involving transfer of a relatively massive moiety either are not observed or are registered at grossly distorted intensities. An additional complication is that elastic or nonreactive scattering collisions may allow a primary ion to be detected as a secondary ion. Simple charge transfer... 

During the cationic homopolymerization, orbital effects as well as charge effects are essential in contrast to the EDA complex formation where apparently orbital effects dominate. The polymerizations are also aided by appearence of negative partial charges at the p-C-atom. 

Analytical ultracentrifugation (AUC) Molecular weight M, molecular weight distribution, g(M) vs. M, polydispersity, sedimentation coefficient, s, and distribution, g(s) vs. s solution conformation and flexibility. Interaction complex formation phenomena. Molecular charge No columns or membranes required [2]... 

On the basis of the point-charge model formalism, applied on the experimental nuclear quadrupole splitting rationalization, I Agxp I, the results obtained were interpreted in terms of strong complex formation by either Me2Sn(OH)2 or Me3Sn(0H)(H20) with (n = 1 or 2, obtained in phosphate buffer) and... 

The ability of compounds with double bonds to act both as electron donors and as electron acceptors in charge transfer complex formation is well known (81,82). Hammond (83) has studied the correlations of association constants and of the energy of the charge transfer absorption of 2-substituted-l,4-benzoquinones complexed with hexamethylbenzene with the Hammett equation. Charton (84) has studied the correlation with eq. (2) of association constants of 1-substituted propenes with Ag. ... 

We have studied stoichiometry of complex formation between DNA and PLL and found that the complexes formed in low-salt-buffer solutions are of a 1 1 charge ratio [92]. The same 1 1 stoichiometry was found experimentally for DNA complexed with other synthetic polycations of different nature in low-salt aqueous solutions [such as poly (diallyldimethylammonium chloride), poly(dimethyhmino)ethylene(dimethylimino)ethy-lene-l,4-dimethylphenylmethyl ene dichloride, andpoly(4-vinyl-A-methylpyridinium bromide)] [93]. 

More recently, Kim et al. synthesized dendritic [n] pseudorotaxane based on the stable charge-transfer complex formation inside cucurbit[8]uril (CB[8j) (Fig. 17) [59]. Reaction of triply branched molecule 47 containing an electron deficient bipyridinium unit on each branch, and three equiv of CB[8] forms branched [4] pseudorotaxane 48 which has been characterized by NMR and ESI mass spectrometry. Addition of three equivalents of electron-rich dihydrox-ynaphthalene 49 produces branched [4]rotaxane 50, which is stabilized by charge-transfer interactions between the bipyridinium unit and dihydroxy-naphthalene inside CB[8]. No dethreading of CB[8] is observed in solution. Reaction of [4] pseudorotaxane 48 with three equiv of triply branched molecule 51 having an electron donor unit on one arm and CB[6] threaded on a diaminobutane unit on each of two remaining arms produced dendritic [ 10] pseudorotaxane 52 which may be considered to be a second generation dendritic pseudorotaxane. 

Fig. 17. Dendritic [4]pseudorotaxanes and [10]pseudorotaxanes based on the stable charge-transfer complex formation in CB[8] cavity...

---