Acid-alkaline transition

The sixth coordination position of the heme iron in cytochrome c peroxidase, which is normally occupied by H2O, is available for reactions with extraneous ligands such as fluoride, cyanide, and azide, as well as substrates and substrate analogs. The acidic-alkaline transition of a hemo-protein, which is caused by the ionization of the bound water ligand, is usually accompanied by significant spectral changes. However, the visible absorption spectrum of cytochrome c peroxidase is not appreciably... 

Haem electronic structure in deoxy myoglobin Acid-alkaline transition in ferric myoglobin Oxy and carbonmonoxy myoglobins F relaxation mechanism... 

Fig. 27. Schematic representation of the acid-alkaline transition in metMb.

Cation-selective ionophores are the most successful in polymeric ISEs and selectivi-ties exceeding ten orders of magnitude became quite common. The cation-ionophore binding occurs dominantly due to Lewis interactions and could be understood in terms of hard and soft acid and bases theory (HSAB). While hard base oxygen atoms originate from ester, ether or carbonyl functionalities, and interact with hard acid alkaline cations, the softer sulfur or nitrogen atoms better bind with transition metal ions. Cation... 

Thymol Blue (Thymolsulfonphthalein) A dark, brown-green, crystalline powder. Slightly soluble in water soluble in alcohol and in dilute alkali solutions. Acid transition interval from pH 1.2 (red) to 2.8 (yellow). Alkaline transition interval from pH 8.0 (yellow) to 9.2 (blue). 

The effect of solution pH on the magnitude of a.c. voltammetry peaks for cytochrome c at the 4,4 -bipyridine/gold electrode was studied in 0.02 M phosphate, 1.0 M NaC104 electrolyte. The a.c. peak current exhibited a maximum at pH 7 and decreased on either side of this value over the range pH 5 to pH 10. On the basic side the decrease is due to the cytochrome c State III to State IV conformational transition and the decrease on the acidic side was attributed to protonation of the adsorbed 4,4 -bipyridine molecules. A pK for the alkaline transition was given as 9.1 and it was noted to be close to the previously reported value of 9.3. However, this value is different from the values of 7.8 to 8.0 previously reported for perchlorate-containing solutions and the reason for this difference is not clear. 

O-donor macrocycles can bind alkali, alkaline, and rare earth metals predominantly by electrostatic forces. By contrast, N-donor macrocycles can bind softer Lewis acids like transition metals, and in this particular case, the interactions are predominantly coordinate in nature. Thia-substituted ligands are much softer than O- and N-donor macrocycles and can selectively bind softer Lewis acids like Ag+ and Hg ". ... 

The remarkable stability of acyl enzymes also indicates that protein conformation is stabilized in several steps in the catalytic process (Bender and Kezdy, 1964 Zerner and Bender 1964 Bernhard and Lau, 1972 Bernhard and Rossi, 1968). Acyl proteases are locked in a conformation which prevents acid and alkaline transitions, (Hess et al., 1970, GhHis, 1971). Stabilization of the acyl enzyme (DIP or tosyl elastase) is indicated by a shift of the transition curve, transition being induced by GuHCl, toward higher concentrations of denaturant (c , varies from 1.6 for elastase to 2.3 for DIP elastase at pH 5.4 and from 2.6 to 3.25 for these two forms respectively at pH 8.0) (Gh61is and Zilber, 1982). 

Grown Ethers. Ethylene oxide forms cycHc oligomers (crown ethers) in the presence of fluorinated Lewis acids such as boron tritiuoride, phosphoms pentafluoride, or antimony pentafluoride. Hydrogen fluoride is the preferred catalyst (47). The presence of BF , PF , or SbF salts of alkah, alkaline earth, or transition metals directs the oligomerization to the cycHc tetramer, 1,4,7,10-tetraoxacyclododecane [294-93-9] (12-crown-4), pentamer, 1,4,7,10,13-pentaoxacyclopentadecane [33100-27-6] (15-crown-6), andhexamer, 1,4,7,10,13,16-hexaoxacyclooctadecane [17455-13-9]... 

Quinoxaline-2,3-dithione (2,3-dimercaptoquinoxaline) (90) forms chelates with several transition elements and is used as a colorimetric agent for the detection and quantitative estimation of nickeT and also for the quantitative estimation of palladium. " Nickel gives a pink coloration with (90) in ammoniacal solution, and palladium an orange-red color in AA-dimethylformamide solution containing a little hydrochloric acid. Spectrophotometric studies of the chelate compounds of (90) with Ni(II), Co(II), and Pd(II) in alkaline solu-... 

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