Temperature and pH dependence

AMMONIUM compounds). Diammonium dimolybdate [27546-07-2] (NH 2 2 7 " ble commercially as the tetrahydrate and prepared from MoO and excess NH in aqueous solution at 100°C, has an infinite chain stmcture based on MoO octahedra. In aqueous solution the behavior of Mo(VI) is extremely pH-dependent (4). Above pH 7 molybdenum(VI) occurs as the tetrahedral oxyanion MoO , but below pH 7 a complex series of concentration-, temperature-, and pH-dependent equiUbria exist. The best known of these equiUbria lead to the formation of the heptamolybdate,... 

Liu, S.C., Fairbanks, G., and Palek, J. (1977) Spontaneous reversible protein cross-linking in the human erythrocyte membrane. Temperature and pH dependence. Biochemistry 16, 4066. 

Background currents of all NO electrodes are sensitive to changes of temperature and pH. Depending on type of electrodes, the effect may be more or less. Clark type NO electrodes are very sensitive to temperature change. The temperature induced response... 

Fig. 17. Temperature and pH dependence of oxygen exchange on the Re(V) center fx = 1.2-1.5 m (KN03). The insert shows a line drawn through the three points at high pH at 34.2°C which indicates a negligible k0 (7). (Adapted with permission from Roodt, A. Leipoldt, J. G. Helm, L. Abou-Hamdan, A. Merbach, A. E. Inorg. Chem. 1995, 34, 560-568. Copyright 1995 American Chemical Society.)...

The Ki for HSA binding to racemic warfarin has been reported for 3-6 pM by various techniques, including frontal analysis and equilibrium dialysis, and is temperature- and pH-dependent. See Loun, B., Hage, D.S. Chiral separation mechanisms in protein-based HPLC columns. 1. Thermodynamic studies of (R)- and (S)-warfarin binding to immobilized human serum albumin. Anal. Chem. 1994, 66, 3814-3822. 

The change in conformation seen here (both in the crystal and in solution) may not be due to the zinc so much as to the anion. The X-ray study showed that the change in zinc coordination took place with uptake of an anion in a very hydrophobic pocket. This is consistent with the binding strength order observed SCbT > I" > CD > SO4". In the solution studies two thiocyanate anions are required for the overall change. Apart from the dependence on cation and anion concentration, the equilibrium position between the conformations in solution is temperature and pH dependent. 

Although hydrolysis of the triazine herbicides is temperature and pH dependent, these herbicides are considered to be hydrolytically stable under the pH and temperature conditions encountered in natural waters. However, the relatively slow hydrolysis rates in natural waters may be enhanced somewhat by the presence of dissolved organic carbon (DOC) (in the form of fulvic acids and a variety of low-molecular-weight carboxylic acids and phenols) that has been shown to catalyze the hydrolysis of several triazine herbicides. Although microbial degradation is probably the most important mechanism of dissipation of the triazine herbicides in soils, abiotic hydrolysis of these herbicides also occurs. Hydrolysis in soils is affected by the pH, organic matter (humic acid) content, and the type and content of clay in the soil. 

Although hydrolytically stable under environmental conditions, the hydrolysis of the triazine herbicides (including metribuzin) in aqueous solution is temperature and pH dependent (Pesticide Manual, 1997). Hydrolysis of atrazine to hydroxyatrazine increased with increasing temperature (Plust et al, 1981 Chan et al, 1992 Hequet et al, 1997) and decreased as pH values near 1 or 13 were changed toward values of 7 or neutrality (Armstrong et al, 1967 Gamble... 

The rate of bacterial growth and hence the rate of nitrification is both temperature and pH dependent. Maximum bacterial activity occurs at about 28°C and a pH of about 8, Below a temperature of about 2°C, the reaction is very slow (Fig. 8.7). Below pH 5.5, the nitrifying bacteria decrease their activity, and below pH 4.5 the nitrification process is severely restricted lack of oxygen also inhibits nitrification. As noted above, oxidation of NH to NO is an enzyme-driven reaction and commonly the Km (see Chapter 7) under optimum conditions is observed to be somewhere around 2.5 mM. Some Km values below 2.5 mM are observed under high pH values when a large fraction of the ammonium is in the NH3 form. 

Similar polymers have been used by S. A. Barker and his colleagues.84 Radical-induced copolymerization of iminodiethyl (4-vinylphenyl)boronate, divinylbenzene, and ethylvinylbenzene gave a polymer on which free sugars can be differentially eluted with distilled water. It is noteworthy that ribose was specifically bound by the polymer (compare, Table I). Separations—particularly those of D-glucose and D-fructose—were shown to be temperature- and pH-dependent. 

Protein Binding. In plasma, about 40% (temperature and pH-dependent) decreased in neonates and in subjects with hepatic cirrhosis. 

These data have led to the development of a catalytic mechanism, shown in Scheme 6, that has been further refined by kinetic isotope effect (KIE) experiments. Substrate binds to Cu(II), replacing bound solvent. The metal coordination facilitates the deprotonation of the substrate hydroxyl group. The proton is transferred to Tyr495, which dissociates from copper. The temperature and pH dependence of the visible absorption and circular dichroism spectra indicate that galactose oxidase exists as an equilibrium of the Tyr495-Cu(II) form (TyroN) and the protonated Tyr495 state. 

Separations on AGP-type phases show unusual temperature and pH dependences. An example of the separation on chiral AGP column is shown in Figure 3-20, together with the pH dependence of the enantiomers retention. 

The modified Mth RIRl, Mxe GyrA, and Ssp DnaB mini-inteins have been recently applied to the isolation of proteins with an N-terminal cysteine residues (29,30). These inteins undergo temperature- and pH-dependent C-termi-nal cleavage when the N-terminal cysteine residue of the intein is substituted with alanine (Table 2). The target protein is recombinantly expressed as a fusion protein with the C-terminal intein tag (31) (Fig. 3B). After intein splicing the protein that possesses N-terminal cysteine is generated. Moreover, such a protein can be obtained by total chemical synthesis and different chemical labels or non-canonical amino acids can be site-specifically incorporated into the sequence. 

Chen Y. and Brantley S. L. (1997) Temperature- and pH-dependence of albite dissolution rate at acid pH. Chem. Geol. 135, 275-292. 

Because all the rules that apply to absorbance detection apply equally well to CD, it is convenient to think of CD as a modified form of absorption spectrophotometry. Spectra are temperature- and pH-dependent non-linear correlations of signal versus concentration are commonplace and are produced for the same reasons, such as chemical equilibria, polychromatic radiation, stray light, etc. Fluorescence emission CD (FDCD) spectroscopy is observed whenever an analyte meets all... 

Weiss, G. Knoch, A. Laicher, A Stanislaus, F. Daniels, R. Simple coacervation of hydroxypropyl methyl cellulose phthalate (HPM(7P). I. Temperature and pH dependency of coacervate formation. Int. J. Pharm. 1995,124 (1), 87-96. 

When garlic is mechanically disrupted, alliinase or alliin lyase (EC 4.4.1.4.) catalyzes the conversion of the cysteine sulfoxides to the biologically active diallyl thiosulfinates via sulfenic acid intermediates (Block, 1992). Alliinase is localized to a few vascular bundle sheath cells around the veins or phloem, whereas alliin and other cysteine sulfoxides are found in the clove mesophyll storage cells. This enzyme is approximately 10 times more abundant in the cloves than in the leaves and accounts for at least 10% of the total protein in the cloves (Ellmore and Feldberg, 1994). Alliinase is temperature and pH dependent optimal activity is between pH 5.0-10.0, but allinase can be irreversibly deactivated at pH 1.5-3.0 (Krest and Keusgen, 1999). 

Kenley RA, Lee MO, Sakumar L, Powell MF. Temperature and pH dependence of fluocino-lone acetonide degradation in a topical cream formulation. Pharm Res 1987 4 342-347. 

The poly(vinylpyridine) chloride was then copolymerized with NIPAM in the presence of N,N -mclhylcncbisacrylamide to obtain graft copolymer gels. These gels were found to be temperature- and pH-dependent. But above 33 °C, the authors showed aggregation of the poly(NIPAM) phase and a pH > 5.5 leads to aggregation of the poly(vinylpyridine). However, the pH effect remains minor compared with that of temperature. 

Kuckling D, Adler H-J P, Arndt K-F, Ling L, Habicher WD (2000) Temperature and pH-dependent solubility of novel poly(A-isopropyacrylamide)-copolymers. Macromol Chem Phys 201 273-280... 

Kuckling D, Richter A, Amdt K-F (2003a) Temperature and pH dependent swelling behavior of poly(A-isopropyl-acrylamide)-copolymer hydrogels and their use in flow control. Macromol Mater Eng 288 144-151... 

Figure 4. Temperature and pH dependence of the B1 and the B2 components. The photosignals generated in Trissl-Montal films are shown in A and in C for their pH and temperature dependence, respectively. The corresponding photosignals obtained from a multilayered thin film are shown in B and in D. The plot in B shows superposition of photosignals obtained from the same film at pH 7, <5, 9, and 10. Continued on next page.

KUC Kuckling, D., Adler, H.-J.P., Arndt, K.F., Ling, L., and Habicher, W.D., Temperature and pH dependent solubihty of novel poly(A-isopropylacrylamide) copolymers,Macrowzo/. Chem. Phys., 201, 273, 2000. 

Moradian-Oldak. J. Leung, W. Fincham, A.C. Temperature and pH-dependent supramolecular self-assembly of amelogenin molecule A dynamic light scattering analysis. J. Struct. Biol. 1998. 122. 320-327. 

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