Difference spectrophotometric studies

Difference Spectrophotometric Studies. In Reference 9, Hg2+ was found very strongly to inhibit the cellulase from P. notatum. To investigate the influence of Hg2+ upon the spectral properties of the cellulase, difference spectrophotometric studies were carried out. The spectra were recorded at room temperature in a Beckman DB spectrophotometer half an hour after mixing the enzyme solution with the mercuric acetate solution. The difference spectrum of cellulase in the presence of Hg2+ was compared with that of tryptophan under similar conditions. The similarity between the two difference spectra for cellulase and tryptophan in... 

Quantitative information about the equilibrium between olefin and Br2 on the one hand and CTC s and bromonium ion species on the other (Scheme 4) has been obtained by the already mentioned UV-Vis spectrophotometric study of the adamantylideneadamantane Br2 system (ref. 10). The spectrophotometric UV-Vis data of a large set of solutions of different reagents concentrations have been used to dissect, using a program based on NLLSQ fitting procedures, the complex spectra in those of the single species present at the equilibrium, as shown in Figure 5. 

In an earlier spectrophotometric study of this enzyme, a red shift of the reduced nicotinamide absorbance had been noted in the difference spectrum of the binding of reduced coenzyme to the purified protein. Fisher et al.92> had pointed out that this is characteristic of most B-stereo-specific dehydrogenases, so Biellman et al. have made a successful prediction for Fisher. Fisher s suggestion that the supernatant and mitochondrial forms of malate dehydrogenase have different stereospecificities for NAD+ has not been substantiated, however 89>. 

The adduct formation from the reaction of the 3,5-dinitropyridine with MeONa was first reported by Fyfe.13 In DMSO solution the reaction is accompanied by the disappearance of the NMR spectrum of the substrate and the appearance of three new signals of equal intensity. Furthermore, one of the three ring proton signals is much more shielded than in the substrate, due to the hybridization change from sp2 to sp3. The observed pattern is in agreement with structure 1. Subsequent NMR and spectrophotometric studies have shown that the isomeric adduct 2 competitively forms together with 1 and eventually turns into the latter, due to a substantial difference in stability.35,36,45 The conversion 2 — 1 is accelerated by methanol. The more... 

From a quantitative study of model substances it was established that, for ethynodiol diacetate and norethynodrel contaminated with 0.05-5% norethisterone acetate and norethisterone respectively, the ellipticity varies linearly with the concentration and values that were found were in accordance with the results from the preceding difference spectrophotometric determination. 

Of course, the problems of hydrolysis can be obviated by using non-aqueous solvents, and pseudo-metal ions have the necessary solubilities. For example, spectrophotometric studies (18) of complex formation equilibria between 2,2 -bipyridine (bipy) and dialkyltin dichloride have been reported. The log K values for complexes R2SnCl2-bipy are 3.19 (R, n-C4H9), 3.36 (R, CH3), and 6.7 (R, Cl) in acetonitrile. There is surprisingly little difference between the constants for dimethyl- and the dibutyltin dichloride complexes. The equilibrium constant for the dibutyl-tin dichloride complex increases with increasing dielectric constant of an alcohol solvent. 

Warner and his collaborators 80, 106) first proposed involvement of tyrosyl residues as ligands for the ferric ion on the basis of potentiometric and spectrophotometric titration data. This has been further substantiated by chemical modification 107, 108) and other difference spectrophotometric 67) studies. Apparently two or three tyrosyl 81, 108), two histidyl 83, 108—110) and an equivocal number of tryptophanyl 111 a, b) residues are present at each binding site 112). EPR evidence indicates that oxygen and as many as 4 nitrogen nuclei interact with the metal 113, 114). Furthermore, bicarbonate is bound to the protein, resulting in the usual salmon-pink colored form of the ferric complex which is otherwise colorless (115 a,b). The minimal possible distance be-... 

The previous sections have concerned several organic compounds and their UV-visible spectrophotometric responses. Some inorganic constituents can also be studied directly with this technique, such as several oxyanions, for example. Figure 1 presents the different species studied. 

Spectroscopy is the study of the interaction between matter and electromagnetic radiation— radiant energy that displays the properties of both particles and waves. Several different spectrophotometric techniques are used to identify compounds. Each employs a different type of electromagnetic radiation. We will start here by looking at ultraviolet and visible (UVWis) spectroscopy. We will look at infrared (IR) spectroscopy in Chapter 13 and nuclear magnetic resonance (NMR) spectroscopy in Chapter 14. 

The equilibrium constants for reactions 17, 18, and 19 are Kl7, Kl8, and K19, respectively, and these equilibrium constants differ greatly. For tetraphen-ylethene [(C6H5)2C = C(C6H5)2], which will be denoted by T, all three constants are known. They were determined from the results of spectrophotometric studies (7) of the system T,T ,Na+ and T2 ,2Na+ in THF, in conjunction with the conductometric studies that led to the values of Kdisu and Kdiss,2 for reactions 20 and 21, respectively ... 

There is also the important issue of data consistency. Many drugs and excipients have had their pK values measured by different methods with very good agreement, provided that all experimental conditions were maintained constant. Examples included atenolol [9.60 0.04 potentiometric, partitioning, and capillary electrophoresis (CE) studies in different laboratories], barbital (5,5-diethylbar-bituric acid) (7.98 0.01 electrometric, potentiometric, and spectrophotometric studies in different laboratories), benzoic acid (4.205 0.015 electrometric, potentiometric, spectrophotometric, and conductance measurements in many separate studies), ephedrine (9.63 0.05 five potentiometric or spectrophotometric studies in different laboratories), isonicotinic acid (pKi = 1.77 0.07, pK2 = 4.90 0.06 five potentiometric or spectrophotometric studies in different laboratories), nicotinic acid (pfCi = 2.07 0.07, pK2 = 4.79 0.04 six potentiometric, spectrophotometric, or capillary zone electrophoresis studies in different laboratories), phenobarbital (5-ethyl-5-phenylbarbituric acid) (7.48 0.02 potentiometric and spectrophotometric studies from several workers in multiple laboratories), nime-sulide (6.51 0.05 potentiometric and spectrophotometric studies in multiple laboratories), and chlorthalidone (9.35, potentiometric 9.36, spectrophotometric/ solubility-pH). The recent comparative studies of Takacs-Novak, Avdeef, and... 

Practically, the aim is to calculate the elements of matrix C[M,1]. In most of the real situations, the molar absorptivities of the chemical components xmder analysis are not known (especially not for a set of different wavelengths). For this reason, the spectrophotometric analysis is conditioned by the spectrophotometric study of a number of standard solutions, where the concentrations of the chemical components of interest are known. The matrix formalism presented allows for the standard solutions used to contain several chemical components (basically, each of the N standard solutions may contain all the M chemical components at known concentrations). In particular cases, it may happen (but it is not mandatory) that each standard solution contains only one chemical component (different from the other chemical components present in the other standard solutions) in this case the matrix Cj, of the concentrations in standard solutions is square (has the same... 

They found that the activity coefficient quotient dependence on the perchlorate molality differed for the CoCI " complex from the dependence shown by the CuCl, MnCI and ZnCl complexes. As a careful spectrophotometric study they did indicated that the CuCl complex existed primarily as the inner-sphere complex [ CuCKOHj) 51. they speculated that the difference was that the CoCr " complex was an outer-sphere complex [ CoCOHj ] cr. ... 

A spectrophotometric study of the oxidation of aldoses by Ce(IV) in dilute sulphuric acid showed that the reactions are first order in both Ce(IV) and sugar. Similar kinetics for D-glucose, D-ribose and D-erythrose indicate a common oxidation mechanism involving cyclic (furanoid or pyranoid) forms in the rate determining radical formation step. Dissimilar kinetic and thermodynamic data for glyceraldehyde, on the other hand, point to a different oxidation pathway for the triose. Formation of an intermediate free radical species in the rate determining step has also been proposed for the Ce(IV) oxidation of L-rhanmose. ... 

In the catalytic reaction, however, the dependence on reductant concentration differs from that previously, with retardation of the rate after an optimum value. The evidence for an initial osmium(vra)-tin(n)-chloro-complex has been substantiated by spectrophotometric studies. 

Palmer et al. [165] have determined the temperature dependence of the equilibrium constant of reaction (5.5.2). Using their data to calculate the potentials for different temperatures would lead to a shift of the line in Fig. 5.5.2 to lower potentials, but having the same slope. The reason for the shift may be the much smaller ionic strength of the solutions used in the spectrophotometrical studies by Palmer. 

For the reasons mentioned above, differential titration and redox potential determinations cannot be used to determine the nature of the heme-linked groups. Under such conditions it seems impossible to solve the whole question of the heme-linked groups of catalases by the aid of the methods we have at our immediate disposal. Some amino acid analyses have been carried out, but these cannot yet contribute to our knowledge of the heme-linked groups. However, some information has been obtained from magnetometric observations, from spectrophotometric studies of different catalase compounds with inhibitors, and from activity determinations in solutions of different pH values and varying concentrations of inhibiting anions. 

Sta.bilizers. Cyanuric acid is used to stabilize available chlorine derived from chlorine gas, hypochlorites or chloroisocyanurates against decomposition by sunlight. Cyanuric acid and its chlorinated derivatives form a complex ionic and hydrolytic equilibrium system consisting of ten isocyanurate species. The 12 isocyanurate equilibrium constants have been determined by potentiometric and spectrophotometric techniques (30). Other measurements of two of the equilibrium constants important in swimming-pool water report significantly different and/or less precise results than the above study (41—43). A critical review of these measurements is given in Reference 44. 

By a spectrophotometric method Rabinowilch and Stockmaycr1 studied the dissociation of the molecular ions (FeCI)4" and (FcBr)4 between 25 and 45°C, and likewise the dissociation of the molecular ion (FeOII)++ into Fc+++ and (Oil)-. Let us consider what different kinds of behavior are to be expected. Ill studying proton transfers, we found that, with rise of temperature, the value of K would either increase or decrease, according to the relative magnitude of ami So here,... 

In general, stabilizers function by reaction with proplnt decompn products. A number of methods have been described and a preliminary evaluation of these methods was conducted by several labs under a cooperative program. Based on results from these screening tests, the PicArsn spec tropho tome trie methods for available stabilizer and primary degradation products were selected for further study. The initial phase of this program was an attempt to standardize the necessary spectrophotometric factors. Significant differences with regard to the factors obtained... 

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