Variable charge

Radical polymerization of diallylamine derivatives produce water-soluble polymers of low molecular weight [22,55-57]. In order to increase the molecular weight, acrylamide has been copolymerized with these diallylamine derivatives to produce cationic polymers with variable charge density depending on the content of the structural units of pyrrolidinium rings and acrylamide in polymeric chains [22,55,58-61]. 

C NAMES OF SOME COMMON CATIONS WITH VARIABLE CHARGE NUMBERS ... 

Fig. 8-3 Diagram illustrating the development of positively and negatively charged sites on surfaces of soil constituents, at low and high pH. (Reproduced with permission from R. L. Parfitt (1980). Chemical properties of variable charge soils. In "Soils with Variable Charge" (B. K. G. Theng, ed.), p. 168. New Zealand Society of Soil Science Offset Publications.)...

Hoagland, DA Smisek, DL Chen, DY, Gel and Free Solution Electrophoresis of Variably Charged Polymers, Electrophoresis 17, 1151, 1996. 

Campbell T, Kalia RK, Nakano A, Vashishta P, Ogata S, Rodgers S (1999) Dynamics of oxidation of aluminum nanoclusters using variable charge molecular-dynamics simulations on parallel computers. Phys Rev Lett 82(24) 4866 t869... 

Keffer DJ, Mintmire JW (2000) Efficient parallel algorithms for molecular dynamics simulations using variable charge transfer electrostatic potentials. Int J Quant Chem 80(4-5) 733-742... 

Nakano A (1997) Parallel multilevel preconditioned conjugate-gradient approach to variable-charge molecular dynamics. Comput Phys Commun 104(l-3) 59-69... 

Monatomic cations with constant charges Monatomic cations with variable charges Polyatomic cations Monatomic anions Oxyanions... 

Oades JM, Gillman GP, Uehara G (1989) Interactions of soil organic matter and variable-charge clays. In Coleman DC, Oades JM, Uehara, G (eds) Dynamics of soil organic matter in tropical ecosystems. Nif TAL Project. University of Hawaii, Honolulu, USA, pp 69-95... 

Violante A, Gianfreda L (2000) Role of biomolecules in the formation and reactivity towards nutrients and organics of variable charge minerals and organo-mineral complexes in soil environment. In Bollag J-M, Stotzky G (eds) Soil biochemistry, vol 10. Marcel Dekker, New York, USA, pp 207-270... 

The effect of other inorganic anions (sulfate, molybdate, silicate), low molecular mass organic ligands (LMMOLs, such as oxalate, malate, citrate, tartrate and succinate), and fulvic or humic acid on the sorption of arsenate and arsenite onto variable charge minerals and soils has been studied (Roy et al. 1986 Grafe et al. 2001 Liu et al. 2001 Violante et al. 2005a,b). 

Variable charge-transfer structures of nitrosonium-EDA complexes leading to thermal and photo-induced electron transfer 224... 

Many processes involving carbonates - ubiquitous minerals in natural systems -are controlled by their surface properties. In particular, flotation studies on calcite have revealed the presence of a pH-variable charge and of a point of zero charge (Somasundaran and Agar, 1967). Furthermore, electrokinetic measurements have shown that Ca2+ is a charge (potential) determining cation of calcite. (Thompson and Pownall, 1989). 

Also, the changes in pH will cause changes in the charges of variable-charge clays and organic matter, thus the cation exchange capacity of acid soils will tend to increase and that of alkaline soils decrease. 

The initial increase occurs because 864 sorbed on variable charge clays and oxides is desorbed as the pH increases. The rate of subsequent reduction will be... 

Oxides and hydroxides of Al, Fe, Mn, and Si may exist in the subsurface mainly as a mixture (known also as a solid solution) rather than as pure mineral phases. They are considered amphoteric materials, characterized by no permanent surface charge. Their cation and anion exchange capacities reflect adsorption of potentialdetermining ions such as H+ and OH". Different surfaces have a diverse affinity for H+ and OH" ions and thus exhibit various points of zero charge (PZC). Details of various models for variable charge minerals may be found in the extensive review of McBride (1989). 

It is generally accepted that Fe oxides contribute to the pH dependent or variable charge of soils by ad-/desorption of protons (see chap. 10). The extent of this contribution is a function of the concentration and surface area rather than the type of oxide present. The assumption here is that all oxide surfaces are hydroxylated in an aqueous system. Besides the variable charge, soils also contain minerals, the clay sili-... 

Barrow, N.J. Bowden, J.W. Posner, A.M. Quirk, J.P. (1981) Describing the adsorption of copper, zinc and lead on a variable charge mineral surface. Aust. J. Soil Res. 19 309-321... 

Bolt, G.H. van Riemsdjik, W.H. (1982) Ion adsorption in inorganic variable charge constituents. In Bolt, G.H. (ed.) Soil chemistry. Elsevier Amsterdam,Vol. B, 459-504 Bond, G.C. (1974) Heterogeneous catalysis principles and applications. Clarendon Press, Oxford, 176 p. 

Parfitt, R.L. Smart, R.S.C. (1977) Infrared spectra from binuclear bridging complexes of sulphate adsorbed on goethite (a-FeOOH). J. Chem. Soc. Faraday Trans. I. 73 796-802 Parfitt, R.L. Smart, R.S.C. (1978) The mechanism of sulfate adsorption on iron oxides. Soil Sci. Soc. Am. J. 42 48-50 Parfitt, R.L. (1980) Chemical properties of variable charge soils. In Theng, B.K. (ed.) Soils with variable charge. N. Z. Soc. Soil Sci., Lower Hutt. N. Z., 167-194 Parfitt, R.L. (1982) Competitive adsorption of phosphate and sulphate on goethite (a-FeOOH) A note. New Zealand J. Sci. 25 147-148... 

Rietra, R.P.J.J. Hiemstra,T. Van Riemsdijk, W.H. (1999 a) The relationship between molecular structure and ion adsorption on variable charge minerals. Geochim. Cosmochim. Acta 63 3009-3015... 

Zhang, H. Zhang, X.-N. (1992) Contribution of iron and aluminum oxides to electrokinetic characteristics of variable charge soils in relation to surface charge. Pedosphere 2 31-42 Zhang, J. Buffle, J. (1995) Kinetics of hematite aggregation by polyacrylic acid Importance of charge neutralization. J. Colloid Interface Sci. 174 500-509... 

Bowden, J. W., Nagarajah, S., Barrow, N. J., Posner, A. M. Quirk, J. P. 1980. Describing the adsorption of phosphate, citrate and selenite on a variable charge mineral surface. Australian Journal of Soil Research, 18, 49-60. 

The trickiness of metals with variable charges also applies when you translate a chemical formula into the corresponding chemical name. Here are the two secrets to keep in mind ... 

Name the following compounds that contain elements with variable charge. Don t forget to use Roman numerals ... 

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