Carboxylic and phosphates

Sometimes poor centrifugation behaviour of cells can be improved by adding flocculation agents. These agents neutralise the anionic charges (carboxyl and phosphate groups) on the surface of the microbial cells. Examples of flocculation agents are alum, caldum and ferric salts, tannic add etc. 

Biosorption is a rather complex process affected by several factors that include different binding mechanisms (Figure 10.4). Most of the functional groups responsible for metal binding are found in cell walls and include carboxyl, hydroxyl, sulfate, sulfhydryl, phosphate, amino, amide, imine, and imidazol moieties.4 90 The cell wall of plant biomass has proteins, lipids, carbohydrate polymers (cellulose, xylane, mannan, etc.), and inorganic ions of Ca(II), Mg(II), and so on. The carboxylic and phosphate groups in the cell wall are the main acidic functional groups that affect directly the adsorption capacity of the biomass.101... 

Another example of rapid turnover in a micellar system is the cleavage of carboxylic and phosphate esters by o-iodosobenzoate in cationic micelles. This reaction was not studied with a functional micelle, but it is useful to note it in this context (Moss et al., 1983, 1986). 

While the above indicates that Ln3 + and transition metal ions in the presence of at least 1 equi. of OR promote the alcoholysis of carboxylate and phosphate esters, sometimes by spectacular amounts, we have not presented evidence about the mechanism for the catalytic reactions. So far, the underlying theme is that the most active forms of the lanthanide ions are the Ln3 + ( OR) forms, either as a monomer (as in the case of Eu3 + ( OCH3)) or as a dimer (as in the case of La2+( OCH3)2). For the transition metal ions the most active forms are those where one face of the... 

C9H19-C6H4-0-(CH2-CH2-0)2-CH2-S03(NP(E0)2- S03). In contrast to sulfate, carboxylate and phosphate homologues no bond cleavage could be observed in APCI(+) mode. The sulfonate could also be ionised in the positive mode resulting in a [M + NH4]+ ion at m/z 420 [15]. 

An intriguing contrast can be made between carboxylates and phosphates as each interacts with metal ions. In carboxylate-metal ion interactions, zinc and other metal ions typically prefer to be in the plane of the carboxylate group (Carrell et al., 1988). However, the metal ion engaged by phosphate prefers a location that is nearly 1 A out of the plane of the phosphinyl group. Additionally, even though there are several examples of bidentate carboxylate-metal ion interactions, a symmetrically biden-tate phosphinyl-metal ion interaction is not preferred. These differ-... 

Larger anionic species such as sulfate, carboxylate and phosphate necessitate the preparation of larger macropolycycles as receptors. 

As a class, the alkylating agents exert their cytotoxic effects via transfer of their alkyl groups to various cellular constituents. Alkylations of DNA within the nucleus probably represent the major interactions that lead to cell death. However, these drugs react chemically with sulfhydryl, amino, hydroxyl, carboxyl, and phosphate groups of other cellular nucleophiles as well. The general mechanism of action of these drugs... 

The metal ion catalysis is complicated by the fact that the metal ion can combine with the substrate in more than one way. If the metal ion combines simultaneously with the carboxylate and phosphate groups, as indicated by XX, it is apparent that the resulting structure would not be a pathway for the reaction. Thus one would expect the metal substrate system to consist of a mixture of active and inactive forms, with the ratio between them variable and dependent on both the nature of the metal ion and the pH of the solution. 

Organophosphate inhibitors include aminotrimethylenephosphonate (AMP), hydroxyethylidene disphosphonate (HEDP), carboxylates and phosphate esters. They are often used in conjunction with other inhibitors such as zinc. Phosphorates generate protective films are susceptible to rupture, however, and pretreatment of the surfaces is often necessary. Organophosphate inhibitors work best in elevated pH environments, which reduces the corrosivity of the cooling wastes. 

Of special interest, because of its biological significance, is the transport of carboxylates and phosphates. In particular, the transport of nucleotides has been achieved [6.28-6.32] and may be made selective by introduction of additional base pairing interactions [6.31,6.32]. The transport of ATP has significance with respect to bioenergetic processes. Antiviral chemotherapy may take advantage of enhancing the cellular uptake of modified nucleotides by carrier species. 

The emphasis on the study of hemoproteins and the iron-sulfur proteins often distracts attention from other iron proteins where the iron is bound directly by the protein. A number of these proteins involve dimeric iron centres in which there is a bridging oxo group. These are found in hemerythrin (Section 62.1.12.3.7), the ribonucleotide reductases, uteroferrin and purple acid phosphatase. Another feature is the existence of a number of proteins in which the iron is bound by tyrosine ligands, such as the catechol dioxygenases (Section 62.1.12.10.1), uteroferrin and purple acid phosphatase, while a tyrosine radical is involved in ribonucleotide reductase. The catecholate siderophores also involve phenolic ligands (Section 62.1.11). Other relevant examples are transferrin and ferritin (Section 62.1.11). These iron proteins also often involve carboxylate and phosphate ligands. These proteins will be discussed in this section except for those relevant to other sections, as noted above. 

Another metal present in biological media in relatively high concentrations is iron. Most iron ions are strongly coordinated within proteins, although a small fraction of iron ions is loosely bound with carboxylates and phosphates, phospholipids, glycans, and sulphonates. This fraction is usually called labile iron and constitutes a pool of iron ions accessible for incorporation into functional metalloproteins. In contrast to closed shell cations, rather than increasing the fluorescence quantum... 

Activated ester method The reactivity of carboxylates and phosphates can be increased by electron drawn and polarizing compounds, l-chloro-4-nitrobenzene or chloroacetonitril are added to form a reactive ester that polarizes the 5 -phosphate group to a partially positive charge. As noted above, the positivated phosphor atom is susceptible to a nucleophilic attack forming a covalent bond. 

---