Buffer temperature dependence

These same dependencies will, in general, apply to the heat of ionization of the buffer acid, AH. Thermodynamic quantities, namely, AH°, have been reported for some buffer substances, and it is found that A//° is temperature dependent. Bates and Hetzer studied the temperature dependence of for the important buffer tris(hydroxymethyl)aminomethane (TRIS), finding... 

Polyelectrolyte complexes composed of various weight ratios of chitosan and hyaluronic acid were found to swell rapidly, reaching equilibrium within 30 min, and exhibited relatively high swelling ratios of 250-325% at room temperature. The swelling ratio increased when the pH of the buffer was below pH 6, as a result of the dissociation of the ionic bonds, and with increments of temperature. Therefore, the swelling ratios of the films were pH-and temperature-dependent. The amount of free water in the complex films increased with increasing chitosan content up to 64% free water, with an additional bound-water content of over 12% [29]. 

The wavelength of maximum absorption and the molar absorptivity are very dependent on pH, buffer, temperature, solvent, and the presence of other materials that may interact with anthocyanins. In addition, anthocyanin absorption follows a linear relationship with concentration only when present at low levels therefore considerable dilution is usually necessary. Absorbance normally should vary from 0.2 to 1.0 unit in order to obey Lambert-Beer s law. However, absorbance values as high as 1.5 to 2.0 absorbance units may be valid for sophisticated new instruments. 

Fig. 2.13. (A) Temperature dependence of pH in Japanese thermal waters. Lines indicate the temperature dependence of pH when pH is buffered by the K-feldspar-K-mica-quartz (or chalcedony at less than 200°C) assemblage at a Na + K concentration of 0.1 and 0.01 mol/kg H2O. Symbols are as in Fig. 2.11. (B) Temperature dependence of pH of Icelandic thermal waters. Large circles indicate well discharges. Small dots represent hot spring waters (Chiba, 1991).

FIG. 5. Maintenance of the superficial buffer barrier depends on NCX-assisted Ca2+ transport from the SR lumen to the extracellular space. (A) Rate of loss of SR Ca2+ content, measured as a caffeine transient, into Ca2+ free perfusate at room temperature. (B) Rate of decline in [Ca2+ I from an elevated level, measured as fura 2 fluorescence ratio, into Ca2+ free superfusate, which is either Na+ free or contains 10 /rM CPA or is Na+ free and contains CPA. (C) This cartoon represents a model for maintained buffering by the superficial SR of Ca2+ entry. Ca2+ taken up by SERCA is subsequently released into the SR-PM junctional space from where it is extruded by the NCX. 

Amino-2-deoxy aldoses. The behaviour of O-unprotected sugars is exemplified in D-gluco series after basic hydrolysis of the starting 2-benzamidoglycoside followed by buffering the medium with carbon dioxide and treatment with thiophosgene, an intermediate isothiocyanate was obtained.320 However, NMR revealed a temperature-dependent equilibrium of this isothiocyanate with a trans-fused OZT (Scheme 5). 

This work was carried out to confirm minimal temperature dependence of Ps02 H20 over sodium citrate solutions and to determine the dependence of Pgo P O on solution composition. Measurements of pH as a function of temperature and solution composition have been performed in order to separate the effects of the specific buffer on Psc / O Design calculations are presented to estimate the steam requirements on typical applications. 

The primary characteristic of an acid/base buffer affecting steam requirements is the temperature dependence of Pgc /P O-Since PSC /P O of the citrate system is independent of temperature, the ideal minimum steam requirement (moles H20/moles SO2) of a simple stripper is equal to the ratio, °f the... 

Temperature dependence of pH and PsO / HoO over sodium citrate buffer solutions is insignificant. 

In the case of carboxypeptidase B, Shaklai et al.(2lT> compared the relative contributions to the protein phosphorescence from tyrosine and tryptophan for the apoenzyme, the zinc-containing metalloenzyme in the absence of substrate, the metalloenzyme in the presence of the substrate iV-acetyl-L-arginine, and the metalloenzyme in the presence of the specific inhibitor L-arginine. The tyrosine tryptophan emission ratio of the metalloenzyme was about a factor of four smaller than that of the apoenzyme. Binding of either the substrate or the inhibitor led to an increase in the emission ratio to a value similar to that of the apoenzyme. The change in the tyrosine tryptophan phosphorescence ratio was attributed to an interaction between a tyrosine and the catalytically essential zinc. The emission ratio was also studied as a function of pH. The titration data are difficult to interpret, however, because a Tris buffer was used and the ionization of Tris is strongly temperature dependent. In general, the use of Tris buffers for phosphorescence studies should be avoided. 

Strambini and Galley have used tryptophan anisotropy to measure the rotation of proteins in glassy solvents as a function of temperature. They found that the anisotropy of tryptophan phosphorescence reflected the size of globular proteins in glycerol buffer in the temperature range -90 to -70°C.(84 85) Tryptophan phosphorescence of erythrocyte ghosts depolarized discontinuously as a function of temperature. These authors interpreted the complex temperature dependence to indicate protein-protein interactions in the membrane. 

Fig. 10. (A) Far-ultraviolet CD spectra of fragment 206-316 of thermolysin at different temperatures in 20 raM Tris-HCl buffer, pH 7.2. Numbers near the curves indicate temperature in degrees Celsius. The peptide concentration was 0.2 mg/ml. (B) Temperature dependence of [0]/[0]o at 220 nm of fragment 206-316, where [0]o is the mean residue ellipiticity at 22°C. Reprinted with permission from Peptides Proceedings of the Fifth American Peptide Symposium, John Wiley Sons, Inc., 1977. Copyright by John Wiley Sons, Inc.

The phase transition was traced by monitoring the transmittance of a 500 nm light beam on a Spectronic 20 spectrophotometer (Baush Lomb). The concentration of the aqueous polymer solution was 5 wt%, and the temperature was raised from 15 to 70°C in 2° increments every 10 min. To observe their pH/temperature dependence, the phase transitions of polymers in citric-phosphate buffer solution versus temperature at two pH values (4.0 and 7.4) were measured. 

The time constants measured near 665 and 795 nm at 295 K in PVA film are in good agreement with those measured at 285 K in flowed buffer (Table 1). Even though the kinetics are different at different wavelengths, the temperature dependence in each region appears to be similar the time constant decreases by about a factor of two between 295-285 and 76 K, and is the same at 76 and 5 K. 

For ancient seafloor sulfide deposits an alternative model has been discussed by Ohmoto et al. (1983), in which H2S and sulfides are buffered by precipitated anhydrite and where 5 " S-values reflect temperature dependent equilibrium fractionations between SO4 and H2S. 

An investigator should also be concerned about the buffer since the pKa of a buffer can also vary with temperature . The pH of a buffer solution will vary with temperature depending on the variance of the activity coefficient terms and the pK of the buffer. 

In CE, temperature control is quite important (see Chapter 1), because the viscosity of the buffer employed depends on the temperature. In addition, in the case of pKa measurement, the pKa of the solute as well as the pH of the buffer is changed when the temperature is changed. In our method described earlier, the value of the applied voltage was set according to the deviation from Ohm s law, which results from the temperature rise of the solution inside the capillary (20). Gluck et al. measured the buffer temperature using Co(II), which has temperature-dependent absorbance at 495 nm... 

The pH values derived by the standard buffers are temperature dependent. The pH values between 0 and 60 °C are given in Table 7.5, which also indicates the change of pH at 1 1 dilution (ApHi i). 

Figure 9.19 Temperature dependent circular dichroism spectra of 1.2 x 10 " M melittin in a 43% (w/w) l-palmitoyl-2-linoleoyl-L-3-phosphatidylcholine(PLPC), cubic phase (10 irtM tris-HCl buffer, pH 7.4). Spectra taken during a heating cycle (1, 5 °C 2, 15 °C 3, 25 °C 4, 35 °C 5,45 °C) [0] is the mean residue ellipticity. (Adapted from Landau and Luisi, 1993.)...

In an attempt to say something intelligent about these resistivities, there appears to be some correlation between the pH and resistivity, with low resistivity obtained when the pH is relatively low (only a few experiments have been carried out at relatively low values of pH also note Ref. 22, which describes an anomalously low resistivity even at normal values of pH). The bath described by Ito and Shiraishi [37] is very different from the previous ones, for three reasons the relatively low pH (= 8), the use of thioacetamide instead of thiourea, and the flow system used in this deposition. Very low values of dark resistivity were obtained with this bath and with an unusual temperature dependence (a minimum of 10 fi-cm was found at 63°C, which increased on either side of this temperature value). It was suggested that Cl, from the NH4CI buffer, acted as a dopant however, other chloride baths gave much higher resistivities. 

E° [equation (15.4)] is also referred to as the offset, the zero potential point, or the isopotential point, since theoretically it is defined as the pH that has no temperature dependence. Most pH electrode manufacturers design their isopotential point to be 0 mV at pH 7 to correspond with the temperature software in most pH meters. The offset potential is often displayed after calibration as an indication of electrode performance. Typical readings should be about 0 30 mV in a pH 7 buffer. In reality, E° is composed of several single potentials, each of which has a slight temperature coefficient. These potentials are sources of error in temperature compensation algorithms. 

The pH of cow s milk is commonly stated as falling between 6.5 and 6.7, with 6.6 being the most usual value. It should be emphasized, however, that this value applies only at temperatures of measurement near 25°C. The pH of milk exhibits a greater dependence upon temperature than that of buffers such as phosphate, which is the principal buffer component of milk at pH 6.6. Miller and Sommer (1940) reported a specimen with a pH of 6.64 at 20°C, decreasing to 6.23 at 60°C. Over the same temperature range, a phosphate buffer decreases only from pH 6.88 to 6.84 (Bates 1964). Likewise, Dixon (1963) observed that the pH of milk decreases by about 0.01 unit per degree Celsius between 30 and 10 °C, and emphasized the importance of careful temperature control in making pH measurements. The marked temperature dependence of the pH of milk probably is attributable to insolubilization of calcium phosphate as the temperature is raised and its solution as the temperature is lowered. 

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