Solid-State Buffers

Stewart and Tucker assert that hydrolysis is affected by pH, buffer salts, ionic strength, solvent, and other additives such as complexing agents, surfactants, and excipients, and each of these factors is discussed in some detail. Waterman et al. (31) provide a comprehensive treatment of hydrolysis as it relates to pharmaceuticals, with thorough discussions of mechanisms, formulation considerations, pH, ionic strength, buffers, solid-state considerations, hydrolysis of lyophiles, liquid dosage forms, packaging, etc. 

Switch on and allow the instrument to warm up the time for this will be quite short if the circuit is of the solid-state type. While this is taking place, make certain that the requisite buffer solutions for calibration of the meter are available, and if necessary prepare any required solutions this is most conveniently done by dissolving an appropriate buffer tablet (these are obtainable from many suppliers of pH meters and from laboratory supply houses) in the specified volume of distilled water. 

Enzyme Assay The crude enzyme was extracted from the solid state culture with 100 ml of 0.33% toluene at 4°C. The enzyme activity was assayed by the determination of substrate viscosity diminishing using Ostwald viscometer (5). The enzyme reaction was done at 37°C in 0.05 N acetate buffer pH 5.25. One unit of enzyme was defined as the amount of enzyme that could reduce the viscosity of 2% pectin by 50% in 10 min. 

Avdeef, A., pH-metric solubility. 1. Solubility-pH profiles from Bjerrum plots. Gibbs buffer and pfCa in the solid state. Pharm. Pharmacol. Commun. 1998, 4,165-178. 

Zinc complex formation with 1,3-diketones in aqueous solution has been investigated with pentane-2,4-dione, l,l,l-trifluoropentane-2,4-dione, and 4,4,4-trifluoro-l-(2-thienyl)butane-l, 3-dione. The buffer dimethylarsinic acid was shown to have a catalytic effect on complex formation with pentane-2,4-dione and the proton transfer reactions were affected.471,472 High-resolution solid state 13C NMR studies of bis(2,4-pentanedionato) zinc complexes have been carried out.473... 

The SSI (solid-state imaging) camera on board the Galileo spacecraft transmitted impressive high-resolution pictures of Io s volcanic activity. Active lava lakes, lava curtains , calderas, mountains and plateaus can be seen (McEwen et al., 2000). The Hubble telescope detected both S2 gas and SO2 in a SO2 to S2 ratio of 1 4 in the smoke trail of the volcano Pele. This value suggests an equilibrium between silicate magmas in the neighbourhood of the quartz-fayalite-magnetite buffer (see Sect. 7.2.2). 

Figure 3.92 SERS spectra of (a) SSBipy-Au and (b) PySH-Au electrodes at 0 V vs. SCE in pH 7.0 phosphate buffer/0.1 M NaC104, together with Raman spectra of(c) the buffer employed in (a) and (b) saturated with PySH (c. 50mM). (d) SSBipy in the solid state as a powder. A He/Ne laser (632.8 nm, 30 mW) was used. The signal la belied with an asterisk is due to aqueous CI04. From Taniguchi et at. (1982).

Zacharis, E., Moore, B.D. and Hailing, P.J., Control of enzyme activity in organic media by solid-state acid-base buffers. J. Am. Chem. Soc., 1997, 119, 12396-12397. 

Aromatic sulfides can be selectively converted into sulfoxides or sulfones by using Oxone under solid state conditions or with buffered Oxone in acetonitrile or acetone . 

Potentiometric Sensors Inthe field of ion-selective electrodes, considerable progress has been achieved in the last few years. By buffering the primary ions concentration on a low level in the internal solution, ionic fluxes in the membrane are affected [424-426]. Thus, primary ion leakage into sample solution is hindered, resulting in a tremendous shift of detection limits to lower values for Pb +-selective electrodes, the detection limit up to 10 M level has been achieved for internal solution electrodes [424, 427] and below 10 M for all-solid-state electrodes with conducting polymer solid... 

Marubayashi et al. <1997J(P2)1309> have also shown that solid-state dimerization is possible and propose that there is a buffer zone in the crystal structure of 1,4-dihydropyridines that governs the solid-state photodimerization process. This is exemplified by the fact that dimethyl l,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicar-boxylate 83 cannot undergo solid-state photodimerization (Equation 21), whereas the structurally related (4/ 3, l / 3 )-methyl-l-phenyl-2-piperidinoethyl-l,4-dihydro-2,6-dimethyl-4-(2-thienyl)pyridine-3,5-dicarboxylate 84 affords a single product 5 (Scheme 2). Interestingly, when the photodimerization conditions are applied to the corresponding solution-phase reaction, the sole product is that of aromatization giving product 85. 

Examples of the application of solid state electrochemistry to identifying dyes in textile samples can be provided. Thus, Fig. 2.17 compares the square wave voltam-mograms of (a) saffron blank, and (b) sample from a Tibet temple, attached to fluorine-doped tin oxide (FTO) electrodes immersed into acetate buffer. After initiating the potential scan at -0.85 V in the positive direction, two separated oxidation... 

A drawback of using organo soluble buffers for pH control is that in order to obtain the reaction product in a pure form after the enzymatic reaction, the buffer substances must be removed, which complicates the procedure. The use of solid-state buffers for organic media has thus been proposed, lysine and its hydrochloride being a typical example [73]. In addition, a wide range of biological buffers such as PIPES, MOPS, TES, HEPES, HEPPSO, TAPS, and AMPSO have been used in combination with their sodium or potassium salts [74]. Transfer of ions between the solid-state buffer and the enzyme can be slow in hydrophobic solvents, resulting in lag phases of up to 30 min [69]. 

Lyophilized enzymes have a pH memory, meaning that the activity of the enzyme in organic solvent parallels its pH-activity profile of the aqueous solution from which it was lyophilized [36, 79-81]. However, very often acidic or basic mixtures within a nonaqueous reaction mixture such as reactant, products, or impurities, can disrupt this delicate protonation state, leading to changes in catalytic activity. To counteract this potential problem, solid-state buffers have been developed to protect the enzyme s protonation state in the nonaqueous environment [53, 82]. These solid-state buffers contain pairs of crystalline solids that can be intercon-... 

Table 3.3 Variation of catalytic rate in the presence of different solid state buffers [53].

Solid-state buffer Rate nmol mg min os-chymotrypsin in CH3CN Subtilisin in THF... 

This method was employed for transesterification reactions with both a-chymotrypsin and subtilisin Carlsberg with a variety of H+/Na+ buffers [53]. With both enzymes (which differ widely in secondary and tertiary structures) and two polar solvents, acetonitrile and THF, the activating effect of the solid-state buffer was clearly evident (Table 3.3). The observation that a variety of buffer pairs show success in activating two dissimilar enzymes in synthetically useful solvents makes this method for activation promising and novel. 

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