Some naturally occurring buffers

A major part of the buffering capacity of blood is also due to the haemoglobin/oxyhaemoglobin equilibrium and its effect on carbon dioxide transport, but the quantitative treatment of acid-base equilibrium in blood is complicated by the rates of reversible hydration of carbon dioxide (catalysed by carbonic anhydrase) and by the chloride shift from erythrocytes. 

Living plant tissue is also buffered, but less closely, the normal pH range in vegetative tissue being 4.0 to 6.2. The main buffers are phosphates, carbonates and organic acids, commonly malic, citric, oxalic, tartaric and some amino acids, with smaller amounts of other organic acids which are intermediates in biochemical cycles. 

Open ocean pH values usually lie within the range pH 7.9—8.3. Sillen (1967) showed, on the basis of a multicompartment model, that this constancy was due mainly to equilibria with aluminosilicates, and that the contribution by dissolved carbon dioxide was slight. 

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Buffers are often added to maintain a constant pH in biochemical research6 and naturally occurring buffer systems within body fluids and cells are very important (Box 6-A). Among the most important natural buffers are the proteins themselves, with the imidazole groups of histidine side chains providing much of the buffering capacity of cells around pH 7 (Figs. 3-1 and 3-2). Table 3-1 lists some useful biochemical buffers and their pKa values. Here are a few... 

Using stoichiometric model systems, it can be shown that some naturally occurring redox processes have a pronounced pH-controlling action, even in the presence of substances that act as buffers. High pH values can be reached particularly in systems where higher metal oxides act as oxidizers whereas an acid condition often develops when free oxygen is the oxidizer. However, in most natural systems carbonates and silicates have a more pronounced pH controlling effect than redox processes. 

Some naturally occurring polymers have been reported to exhibit efflux pump modulating properties. For example, a drug delivery system based on chitosan has been shown to nearly double the oral bioavailability of the P-glycoprotein substrate rhodamine 123 in vivo in rats in comparison with buffer control (Foger et al. 2006c). 

The borate liberated on dissolution of the perborate contributes to the alkalinity, cm act as a buffer, and may help solubilize some molecules via reactions such as borate/cis diol complexation. For example, during the alkaline hydrolysis of fats and natural oils, complexation of borate with, for example, glycerol may help shift the equilibrium favorably. The cis diol functionality is very common on naturally occurring molecules. Borate is a weak builder, but this effect may be boosted by adding other species (e.g., saccharate) [12]. 

Tribasic calcium phosphate occurs in nature as minerals, oxydapatite, whitlockite, voelicherite, apatite, phosphorite. It has many industrial applications. Some are similar to the monobasic and dibasic salts. It is used in fertilizers, dental products, ceramics and pohshing powder. Some other important applications are in plastics as a stabdizer as an anticaking agent as a nutrient supplement in cattle food for clarifying sugar syrup as a mordant in dyeing textiles and as a buffer to control pH. 

As with any assay, conditions for a QES assay must be optimized in terms of buffer composition, particularly pH and potential salt and metal ion effects. Eurther-more, the specificity of cleavage should be verified by an independent method, such as reverse-phase HPLC. Given the aromatic nature of both fluorophore and quencher, even low levels of QFS and cleavage products can be easily detected by UV absorbance. This method will also determine whether any absence of fluorescence is due to lack of cleavage or to a low fluorescent yield, as occurred with some of the ECE substrates discussed in Note 1. 

Normally, the chiral pollutants in the environment occur at low concentrations and therefore a sensitive detection method is essential and is required in chiral CE. The most commonly used detectors in the chiral CE are UV, electrochemical, fluorescence, and mass spectrometry. Mostly, the detection of the chiral resolution of drugs and pharmaceutical in CE has been achieved by a UV mode and therefore the detection of the chiral pollutants may be achieved by the same method. The selection of the UV wavelength depends on the type of buffer, chiral selector, and the nature of the environmental pollutants. The concentration and sensitivity of UV detection are restricted insofar as the capillary diameter limits the optical path length. It has been observed that some pollutants, especially organochloro pesticides, are... 

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