Buffering curves

While it is conceivable that an excess of bases in the cell solution might be protective against mild sulfur burn, this possibility has not yet been tested. On the other hand, a small increase in buffer capacity might reduce sulfur burn. An example of this effect may be seen in the buffer curves of the leaf sap in two of the United States Department of Agriculture s muskmelon varieties. No. 5, which is susceptible to sulfur burn, has a buffer curve which lies 0.2 to 0.3 pH unit closer to the acid side than the buffer curve of the sulfur burn-resistant variety, No. 11353 (Figure 1). 

Scheme 3.2-5. Buffer curve diagram range of existence for the many intermediates classified into subsystems. Solid lines buffer curves for the system COD2Ni/diphenoxi-phenylphosphine/ butadiene. Broken lines remaining curves for this system (only supposed, but demonstrable for other Lewis bases). Areas with higher steady state concentration shaded, (m = 2 to 4, n = 0 or 1,...

Three approaches have been used in attempting to account for the buffer behavior of milk in terms of the properties of its components. These are calculation, fractionation, and titration of artificial mixtures. Whittier (1933A.B) derived equations for dB/dpH in calcium phosphate and calcium citrate solutions, taking into account available data on dissociation constants and solubility products. Presumably this approach could be extended to calculate the entire buffer curve. It demands precise knowledge of the dissociation constants of the several buffers, the dissociation of the calcium and magnesium complexes, and the solubility products of the calcium and magnesium phosphates under the conditions of a titration of milk. 

Lucey, J. A., Gorry, C., and Fox, P. F. (1993). Changes in the acid-base buffering curves during the ripening of Emmental cheese. Milchwissenschaft 22, 224-231. 

Fig. 20.3. Calibration plots for methyl mercury obtained in phosphate buffer (curve a) and biphasic system (phosphate buffer/toluene mixture curve b) using the glucose oxidase biosensor and invertase in solution 0.15 pg/mL, I app = + 0.60 V vs. Ag/AgCl reaction time = 5 min and incubation time-10 min.

Coleman, N. T and G. W. Thomas. 1964. Buffer curves of acid clays as affected by the presence of ferric iron and aluminum. Soil Sci. Soc. Am. Proc. 18 187-190. 

The internal and external buffering systems were included in the computations as follows. The important intracellular buffer is hemoglobin, and its buffer capacity under the conditions of these experiments was assumed to be 2.54 mM acid/mM Hb/pH 28, 29). Extracellularly, hemoglobin concentrations were very low, and other buffers (water, lactate, phosphate, etc.) became important. Therefore, an empirical buffering curve for the extracellular fluid was determined by plotting concentration of acid added vs. the plateau pH values. Then, the buffering power of the extracellular fluid at any given extracellular pH was assumed to equal the slope of the curve at that pH. 

The R/Rq—E curves of NAD components such as NMN, nicotinamide, adenine, and adenosine are shown in Fig. 26, in which the curves are drawn separately as in Fig. 12. Compared with measurements using only the phosphate buffer (curve a), the presence of these components also causes a decrease in reflectivity as shown by the R/Ro E curves (curves b—e). These observations suggest that NAD and its components are adsorbed on the electrode surface. Other electrochemical data (e.g., differential capacitance) are consistent with this suggestion. 

Fig. 3. Log fo2 vs temperature. Fe20j-Fej04 and Fej04-Fej.x0 buffer curves (solid lines). CO/CO2 8as mixtures (dotted lines) (21). Numbers are percentages of CO2, that is, CO2K.CO + CO2) (22).

X-ray scattering curves (see Fig. 9) are extracted by simple subtraction of the sample and buffer curves, and in the cases of linear or area detectors are normalized for detector responses by ... 

Individual membrane proteins can be solubilized by the use of detergents, and the protein-detergent complex can be studied. This method requires monodisperse complexes (i.e the bound micelles should be of similar size and mass) and these are not difficult to prepare. Since the protein-detergent complex exists in equilibrium with free detergent micelles, the buffer background samples should contain detergent also at the equilibrium concentration so that the buffer curve subtraction will lead to the protein-detergent curve only. 

Recently, much effort has been made on the facilitation of direct electron transfer of the SODs by self-assembled monolayers (SAMs) confined onto Au electrodes. For instance, Ohsaka et al. have formed various kinds of SAMs of alkanethiols onto an Au electrode and studied the electron transfer properties of the SODs [98]. Here, we will use the SAM of cysteine as an example to demonstrate the electron transfer of the SODs promoted by the SAMs of alkanethiols. Figure 6.1 depicts cyclic voltanunograms (CVs) obtained at a cysteine-modified Au electrode (curves a and b) in 25 mM phosphate buffer containing 0.56 mM Cu, Zn-SOD (the concentration used represents that of the Cu or Zn site of Cu, Zn-SOD). For comparison, the CV obtained at a bare Au electrode (curve c) under the same conditions was also given. As shown, the cysteine-modified electrode exhibits one pair of well-defined voltammetric peaks in the SOD-containing phosphate buffer (curve a). These redox peaks were not obtained at the bare Au electrode (curve c). This observation suggests that the direct electron transfer between Cu, Zn-SOD and Au electrode does not occur actually at the bare electrode, but it can be significantly promoted at Au electrode modified with the SAM of cysteine. 

Figure 4.7 CVs for the oxidation of AA (1.0 mM] at bare [curve a] and l-butyl-3-methyl imidazolium chloride [[BMIM][Cl]]-modified [curve b] GC electrodes in 0.10 M phosphate buffer. Curves a and b represent CVs obtained at the above electrodes in the same solution containing no AA. Scan rate, 100 mV s" Reprinted with permission from Ref. [48]. Copyright 2005 American Chemical Society.

Fig. I. Cyclic voltammograms (I-a, Il-a, Ill-a) at a scan rate of 100 mV s" and RDE voltammograms (I-b, Il-b, Ill-b, c, d) at an electrode rotation rate of 1000 rpm, and a scan rate of 10 mV s on a glassy carbon disk electrode with 0.2 M Na2S04 at 25°C. I for 1 mM -complex 3 at pH 10.0. II for 1 mM Ni -complex at pH 7.3 (Tris buffer) curve a and b for Fe -complex 3, curve c for Fe -complex 7 (aeration product of Fe -complex 3), curve d for free ligand 1 no further oxidation wave was seen up to -f 0.5 V vs. SCE.

Chronic pulmonary failure may be further complicated by metabolic disturbances tending to metabolic alkalosis or metabolic acidosis. The mechanism leading to alkalosis is not always clear, but among the factors that may influence it are the loss of hydrogen and Cl ions, because of vomiting or because of selective Cl and potassium depletion as a result of undernourishment, and prolonged treatment with diuretics. It is usually assumed that severe respiratory acidosis is always accompanied by metabolic acidosis. This reasoning is based on the fact that when the same CO2 tensions are achieved in the blood in vivo and in vitro,the plasma concentration of bicarbonate for identical pH s is lower in vivo than in vitro. In reality, this bicarbonate deficit seems to result because (I) the buffer curve of the blood CO2 has a lower slope in vivo than in vitro and (2) hyperventilation in vivo leads to lactic acid accumulation in he blood. 

B) Concanavalin A in phosphate buffer (curve 1) and concanavcdtn A in phosphate buffer + 0.018 M sodiumdodecylsulphate(curve2). Description in text (Adaptedfiom, Mattice, W.L et at. Biochemistry, 15 4264. 1976)... 

---