Isolation, purification and kinetic characterization of prolyl endopeptidase from Titicum aestivum
- Authors: Abrahams, Adriam Mark
- Date: 2013
- Subjects: Endopeptidases , Wheat , Chemical kinetics , Pharmacokinetics
- Language: English
- Type: Thesis , Masters , MSc (Biochemistry)
- Identifier: vital:11269 , http://hdl.handle.net/10353/d1004356 , Endopeptidases , Wheat , Chemical kinetics , Pharmacokinetics
- Description: PEP activity has been described in several locations and has mostly been linked to a variety of neurological disorders such as schizophrenia, amnaesia, depression as well as other disease states such as anorexia nervosa, bulimia nervosa and blood pressure regulation. The enzyme has also been previously isolated from a variety of archae, microorganisms and several eukaryotic species but no prolyl endopeptidases have been isolated from plants. Plants have high levels of proline and glutamine rich peptides in seeds. We therefore hypothesize plants must express PEPs during germination. Bioinformatics tools were used to identify known PEPs and putative plant PEPs. A global sequence alignment of putative plant PEPs and other known PEPs indicated that the active site amino acids Ser, His and Asp are conserved in putative plant PEP sequences. Furthermore, putative plant PEPs showed similar secondary structures to known PEPs and when a rice PEP was modelled onto porcine brain PEP structure, a high degree of similarity was found. Germination studies of wheat seed showed an increase of PEP activity over time with maximum PEP activity reached after 4 days of germination, which remained at this level until 9 days of germination, implying a function for PEP in plant seed germination. Wheat PEP was purified using ion exchange and gel filtration chromatography with a final yield of less than 1 percent and a relative purity (only 2 bands detected by SDS-PAGE). The purified wheat PEP had a molecular weight of approximately 55kDa, substrate specificity for chymotrypsin-like substrates (N-Suc-Ala-Ala-Pro-Phe-pNa, Km value of 0.58 mM, Kcat of 29.37 s–1; Kcat /Km 50813.14s–1 M–1); a pH optimum of 7.9; temperature optima of 37oC and a high sensitivity to temperature as indicated by loss of activity at temperatures above 40oC. Inhibition studies using E64, Leupeptin and PMSF confirmed that the wheat PEP is from the Serine protease family and is most likely a trypsin-like protease.
- Full Text:
- Date Issued: 2013
- Authors: Abrahams, Adriam Mark
- Date: 2013
- Subjects: Endopeptidases , Wheat , Chemical kinetics , Pharmacokinetics
- Language: English
- Type: Thesis , Masters , MSc (Biochemistry)
- Identifier: vital:11269 , http://hdl.handle.net/10353/d1004356 , Endopeptidases , Wheat , Chemical kinetics , Pharmacokinetics
- Description: PEP activity has been described in several locations and has mostly been linked to a variety of neurological disorders such as schizophrenia, amnaesia, depression as well as other disease states such as anorexia nervosa, bulimia nervosa and blood pressure regulation. The enzyme has also been previously isolated from a variety of archae, microorganisms and several eukaryotic species but no prolyl endopeptidases have been isolated from plants. Plants have high levels of proline and glutamine rich peptides in seeds. We therefore hypothesize plants must express PEPs during germination. Bioinformatics tools were used to identify known PEPs and putative plant PEPs. A global sequence alignment of putative plant PEPs and other known PEPs indicated that the active site amino acids Ser, His and Asp are conserved in putative plant PEP sequences. Furthermore, putative plant PEPs showed similar secondary structures to known PEPs and when a rice PEP was modelled onto porcine brain PEP structure, a high degree of similarity was found. Germination studies of wheat seed showed an increase of PEP activity over time with maximum PEP activity reached after 4 days of germination, which remained at this level until 9 days of germination, implying a function for PEP in plant seed germination. Wheat PEP was purified using ion exchange and gel filtration chromatography with a final yield of less than 1 percent and a relative purity (only 2 bands detected by SDS-PAGE). The purified wheat PEP had a molecular weight of approximately 55kDa, substrate specificity for chymotrypsin-like substrates (N-Suc-Ala-Ala-Pro-Phe-pNa, Km value of 0.58 mM, Kcat of 29.37 s–1; Kcat /Km 50813.14s–1 M–1); a pH optimum of 7.9; temperature optima of 37oC and a high sensitivity to temperature as indicated by loss of activity at temperatures above 40oC. Inhibition studies using E64, Leupeptin and PMSF confirmed that the wheat PEP is from the Serine protease family and is most likely a trypsin-like protease.
- Full Text:
- Date Issued: 2013
Studies directed towards the synthesis of chromone carbaldehyde-derived HIV-1 protease inhibitors
- Authors: Molefe, Duduzile Mabel
- Date: 2008
- Subjects: Protease Inhibitors , HIV infections , HIV (Viruses) , AIDS (Disease) , Proteolytic enzymes , Heterocyclic compounds -- Derivatives , Chemical kinetics , Nuclear magnetic resonance spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4526 , http://hdl.handle.net/10962/d1015542
- Description: A series of chromone-3-carbaldehydes have been prepared using Vilsmeier-Haack methodology while a corresponding series of chromone-2-carbaldeydes have been synthesized via the Kostanecki-Robinson reaction. Baylis-Hillman reactions have been conducted on both series of chromone carbaldehydes using three different catalysts, viz., 1,4-diazabicyclo(2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec- 7-ene (DBU) and 3-hydroxyquinuclidine (3HQ), and acrylonitrile, methyl acrylate and methyl vinyl ketone as the activated alkenes. These reactions have typically (but not always!) afforded both normal Baylis-Hillman and dimeric products. Attention has also been given to the use of 1-methyl-2-pyrrolidine (1-NMP), an ionic liquid, to replace normal organic solvents, and it has been found that, in the presence of DABCO, chromone-3-carbaldehydes afford the dimeric products alone. Reactions of chromone-3-carbaldehydes with methyl vinyl ketone have yielded unexpected, novel adducts, which appear to arise from preferential attack at C(2) in the chromone nucleus. Research on chromone-2-carbaldeydes under Baylis-Hillman conditions has also resulted in the formation of some interesting products instead of the expected Baylis-Hillman adducts. The Baylis-Hillman products have been explored as substrates for aza-Michael reactions using various amino derivatives including protected amino acids in the presence of the tetrabutylammonium bromide (TBAB) and the ionic liquid, 3-butyl-1- methylimidazoleboranetetrafluoride (BmimBF₄), as catalysts. The aza-Michael products have been targeted as truncated ritonavir analogues for investigation as potential HIV -1 protease inhibitors, and representative compounds have been subjected to enzyme inhibition assays to explore the extent and type of inhibition. Lineweaver-Burk and Dixon plots have indicated competitive inhibition in one case as well as non-competitive inhibition in another, and the inhibition constants (Ki) have been compared with that of the ritonavir. Computer modelling studies have also been conducted on selected chromonecontaining derivatives, using the ACCELRYS Cerius² platform. Interactive docking of the chromone-containing ligands into the HIV -1 protease receptor site, using the Ligandfit module, has indicated the importance of hydrogen-bonding interactions mediated by bridging water molecules situated in the receptor cavity. NMR spectroscopy has been used to elucidate complex and competing mechanistic pathways involved in the Baylis-Hillman reactions of selected 2-nitrobenzaldehydes with MVK in the presence of DABCO - reactions which afford the normal BaylisHillman product, the MVK dimer and syn- and anti-Baylis-Hillman type diadducts. The kinetic data confirm the concomitant operation of two pathways and reveal that, in the initial stage of the reaction, the product distribution is kinetically controlled, whereas in the latter stage, thermodynamic control results in the consumption of the normal Baylis-Hillman product and predominance of the anti-diadduct.
- Full Text:
- Date Issued: 2008
- Authors: Molefe, Duduzile Mabel
- Date: 2008
- Subjects: Protease Inhibitors , HIV infections , HIV (Viruses) , AIDS (Disease) , Proteolytic enzymes , Heterocyclic compounds -- Derivatives , Chemical kinetics , Nuclear magnetic resonance spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4526 , http://hdl.handle.net/10962/d1015542
- Description: A series of chromone-3-carbaldehydes have been prepared using Vilsmeier-Haack methodology while a corresponding series of chromone-2-carbaldeydes have been synthesized via the Kostanecki-Robinson reaction. Baylis-Hillman reactions have been conducted on both series of chromone carbaldehydes using three different catalysts, viz., 1,4-diazabicyclo(2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec- 7-ene (DBU) and 3-hydroxyquinuclidine (3HQ), and acrylonitrile, methyl acrylate and methyl vinyl ketone as the activated alkenes. These reactions have typically (but not always!) afforded both normal Baylis-Hillman and dimeric products. Attention has also been given to the use of 1-methyl-2-pyrrolidine (1-NMP), an ionic liquid, to replace normal organic solvents, and it has been found that, in the presence of DABCO, chromone-3-carbaldehydes afford the dimeric products alone. Reactions of chromone-3-carbaldehydes with methyl vinyl ketone have yielded unexpected, novel adducts, which appear to arise from preferential attack at C(2) in the chromone nucleus. Research on chromone-2-carbaldeydes under Baylis-Hillman conditions has also resulted in the formation of some interesting products instead of the expected Baylis-Hillman adducts. The Baylis-Hillman products have been explored as substrates for aza-Michael reactions using various amino derivatives including protected amino acids in the presence of the tetrabutylammonium bromide (TBAB) and the ionic liquid, 3-butyl-1- methylimidazoleboranetetrafluoride (BmimBF₄), as catalysts. The aza-Michael products have been targeted as truncated ritonavir analogues for investigation as potential HIV -1 protease inhibitors, and representative compounds have been subjected to enzyme inhibition assays to explore the extent and type of inhibition. Lineweaver-Burk and Dixon plots have indicated competitive inhibition in one case as well as non-competitive inhibition in another, and the inhibition constants (Ki) have been compared with that of the ritonavir. Computer modelling studies have also been conducted on selected chromonecontaining derivatives, using the ACCELRYS Cerius² platform. Interactive docking of the chromone-containing ligands into the HIV -1 protease receptor site, using the Ligandfit module, has indicated the importance of hydrogen-bonding interactions mediated by bridging water molecules situated in the receptor cavity. NMR spectroscopy has been used to elucidate complex and competing mechanistic pathways involved in the Baylis-Hillman reactions of selected 2-nitrobenzaldehydes with MVK in the presence of DABCO - reactions which afford the normal BaylisHillman product, the MVK dimer and syn- and anti-Baylis-Hillman type diadducts. The kinetic data confirm the concomitant operation of two pathways and reveal that, in the initial stage of the reaction, the product distribution is kinetically controlled, whereas in the latter stage, thermodynamic control results in the consumption of the normal Baylis-Hillman product and predominance of the anti-diadduct.
- Full Text:
- Date Issued: 2008
The kinetics and associated equilibria of high oxidation state osmium complexes
- Authors: McFadzean, Belinda Julie
- Date: 2007
- Subjects: Chemical equilibrium , Osmium , Chemical kinetics , Chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10371 , http://hdl.handle.net/10948/732 , Chemical equilibrium , Osmium , Chemical kinetics , Chemistry
- Description: The reduction of osmium tetroxide by a series of alcohols was studied spectrophotometrically. The reaction was observed to occur in two steps, unlike previously reported studies on this reaction. The identities of both reactants and products were established via a range of techniques. Equilibrium and kinetic data were gathered and reaction models were evaluated using equilibrium and kinetic modelling software. The following complexation reaction model emerged that simulates both the equilibrium and kinetic data. Os(VIII) + RCH2OHOs(VI) + RCHO2 Os(VIII) + Os(VI)k+2k1Complexk-2 Conditional rate constants and equilibrium constants were generated. Rate constants for the alcohol reactions were correlated with the Taft σ* constant. The ρ* value obtained (-1.4) is consistent with a hydride transfer mechanism coupled with synchronous removal of the hydroxyl proton. The identity of the osmium(VIII)-osmium(VI) complex has been suggested. Thermodynamic parameters were also reported. The rate constants for benzyl alcohol and 2-chloroethanol deviated from those predicted by the Taft plot. An explanation of enhanced resonance effects is offered for benzyl alcohol and an alternative reaction mechanism, involving proton abstraction, is offered for 2-chloroethanol. The reaction of the oxidation products of alcohols, namely ketones, with osmium tetroxide produced rate constants that were, perhaps surprisingly, far larger than those of the alcohols. A reaction mechanism for the oxidation of the ketones is suggested, which involves the enolate ion as the reactive starting reagent.
- Full Text:
- Date Issued: 2007
- Authors: McFadzean, Belinda Julie
- Date: 2007
- Subjects: Chemical equilibrium , Osmium , Chemical kinetics , Chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10371 , http://hdl.handle.net/10948/732 , Chemical equilibrium , Osmium , Chemical kinetics , Chemistry
- Description: The reduction of osmium tetroxide by a series of alcohols was studied spectrophotometrically. The reaction was observed to occur in two steps, unlike previously reported studies on this reaction. The identities of both reactants and products were established via a range of techniques. Equilibrium and kinetic data were gathered and reaction models were evaluated using equilibrium and kinetic modelling software. The following complexation reaction model emerged that simulates both the equilibrium and kinetic data. Os(VIII) + RCH2OHOs(VI) + RCHO2 Os(VIII) + Os(VI)k+2k1Complexk-2 Conditional rate constants and equilibrium constants were generated. Rate constants for the alcohol reactions were correlated with the Taft σ* constant. The ρ* value obtained (-1.4) is consistent with a hydride transfer mechanism coupled with synchronous removal of the hydroxyl proton. The identity of the osmium(VIII)-osmium(VI) complex has been suggested. Thermodynamic parameters were also reported. The rate constants for benzyl alcohol and 2-chloroethanol deviated from those predicted by the Taft plot. An explanation of enhanced resonance effects is offered for benzyl alcohol and an alternative reaction mechanism, involving proton abstraction, is offered for 2-chloroethanol. The reaction of the oxidation products of alcohols, namely ketones, with osmium tetroxide produced rate constants that were, perhaps surprisingly, far larger than those of the alcohols. A reaction mechanism for the oxidation of the ketones is suggested, which involves the enolate ion as the reactive starting reagent.
- Full Text:
- Date Issued: 2007
A comparative kinetic study of the reaction between chromium nitrate solutions and the carboxyl groups of acetate and collage
- Authors: Russell, Allan Edward
- Date: 1962
- Subjects: Chemical kinetics , Chromium , Spectrophotometry , Electrophoresis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4493 , http://hdl.handle.net/10962/d1013101
- Description: The kinetics of the coordination reaction between the carboxyl group of the acetate radical and the trivalent chromium ion has been examined by independent methods at a temperature selected to yield reasonably accurate rate data. The study has been extended to an examination of the rate of chromium "fixation" by the carboxyl groups of hide collagen in a series of miniature tannages carried out under similar conditions for comparative purposes. The effect of olation of the chromium ions in solution on the kinetics of t he coordination reaction has also been examined. The rate of coordination of the acetate radical was followed by solvent extraction and spectrophotometric techniques over a range of concentration and pH levels. The rate data revealed a reaction having typical mass-action characteristics, the rate of reaction depending on the concentration levels of the chromium ion and the ionised acetate radical. An attempt made to distinguish a differential reaction rate in the case of a parallel reaction series using boiled and aged chromium nitrate reactant solutions, failed to reveal any significant differences between the series. The reactant solutions gave absorption spectra characteristic of the trivalent chromium ion with maxima in the 420 mµ and 570 mµ wavelength regions. The changes in optical density occurring in the vicinity of the maxima were followed spectrophotometrically, the height of the 570 mµ being found to increase during the course of reaction, while the height of the 420 mµ peak decreased. The variation in optical density at the 570 mµ peak was found to be directly related to the increase in concentration of the product complex in solution in accordance with the Baer-Bougher law, while the decrease in the height of the 420 mµ peak was related to the properties of unolated OH groups associated with the chromium complex as governed by pH and olation changes during the course of reaction. Boiled and aged chromium nitrate solutions gave reactant solutions having initial optical densities greater than those of the correspending fresh reactant solutions at the 570 mµ peak, and less than those of the fresh solutions at the 420 mµ peak. During the course of reaction, however, the two series converged to the same values. The equilibrium reaction solutions were subjected to paper electrophoretic study which indicated that all tho chromium was present in the form of cationic species. This finding was in accordance with stoicheiometric indications in the solvent extraction studies where coordination in a l : 1 ratio was reflected, giving rise to positively charged complex ions only. Making due allowance for band spreading the numbers of species predicted from the kinetic studies correspond with the electrophoretic patterns found. Application of the classical second order kinetic expression to the solvent extraction rate data, yielded plots having two distinctly linear sections, apparently indicating consecutive second order processes occurring in solution, contrary to the findings of previous workers who assign a first order mechanism to the reaction. This finding was consistent with the view that in the case of both the fresh and aged series, reaction consisted of successive coordination of an acetate radical to each chromium atom of a diol complex. Second order rate "constants" were calculated for each step and their dependency on pH level demonstrated. The findings of Hamm et al that these were first order reactions independent of acetate co'ncentration are believed to be due to their use of a large excess of acetate in their experiments. The kinetic study was further extended to an examination of the rate of "fixation"of trivalent chromium by the carboxyl groups of hide collagen under comparable conditions in a series of miniaturv tanning experiments in which the tannage substrate was provided in each of two physical forms:- (a) As hide powder where surface development was large, and (b) as prepared pelt pieces in which the fibrous weave pattern was retained. In view of the heterogeneity of the tannage systems, remarkable similarity was observed in the reaction course when compared with that of the acetate coordination studies, particularly in the case of the hide powder tannages. The dependency of the tannage rate data upon concentration and pH conditions was also found to be the same as in the case of the pure chemical system. The exact correlation between the rate data for the tannage and pure chemical systems was demonstrated by means of correlation plots. Close correlation was revealed in the case of hide powder tannage while the smaller degree of correlation observed in the case of the pelt tannage systems was attributed to the modifying effects of diffusion, particularly on the initial reaction velocity. The effect of using boiled and aged chromium solutions in the tannages was to increase the initial rate of chroniill!l "fixation" apparently due to tho coordination of a dial species at each coordination site. After the initial reaction period, the two series showed a tendency to converge as in the case of the spectrophotometric studies on the acetate reaction. The convergence trend was regarded as indicative of the tendency for the chromium in fresh solutions to under go rapid olation to the ame level as in the boiled and aged solutions. The experimental observations made on the various systems lead to the following conclusions:- (a) The mechanism of coordination of the acetate radical ttrivalent chromium appears to involve the successive coordination of ligand to each of the chromium atoms of a diol complex, both coordination steps proceeding by second order reaction mechanisms. (b) At the pH levels at which the reaction is carried out, the formation of elated bodios is rapid so that reaction in the case of both fresh and aged solutions essentially occurs between an elated species and the ionised acetate radical. (c) Modificati0ns in the absorption spectrum of the reactant solution at the 570 mµ peak are directly related to coordination, while changes at the 420 mµ peak are related to the formation of loosely-bound hydroxo chromium compounds, the concentrations of which depend on the pH level. (d) The mechanism of chromium fixation in hide is essentially similar to that operating in the case of coordination of the acetate radical to chromium, involving attachment of chromium to the side chain acid r sidues of collagen. (e ) The effect of olation is to enhance the rate of chromium fixation by hide protein during the initial reaction stages and to render possible bridge formation between adjacent side chains by secondary coordination during the latter reaction stages. (f) Where pelt pieces are used instead of hide powder, the initial rate of chromium fixation is dominated by the rate of diffusion of chromium into the fibrous structure. It should be stressed that the observations made on the various reaction systems cannot be regarded as exhaustive and the conclusions are subject to further confirmation. Consequently, the present study is essentially of a preliminary nature, but it is felt that the need for further investigation along similar lines has been demonstrated.
- Full Text:
- Date Issued: 1962
- Authors: Russell, Allan Edward
- Date: 1962
- Subjects: Chemical kinetics , Chromium , Spectrophotometry , Electrophoresis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4493 , http://hdl.handle.net/10962/d1013101
- Description: The kinetics of the coordination reaction between the carboxyl group of the acetate radical and the trivalent chromium ion has been examined by independent methods at a temperature selected to yield reasonably accurate rate data. The study has been extended to an examination of the rate of chromium "fixation" by the carboxyl groups of hide collagen in a series of miniature tannages carried out under similar conditions for comparative purposes. The effect of olation of the chromium ions in solution on the kinetics of t he coordination reaction has also been examined. The rate of coordination of the acetate radical was followed by solvent extraction and spectrophotometric techniques over a range of concentration and pH levels. The rate data revealed a reaction having typical mass-action characteristics, the rate of reaction depending on the concentration levels of the chromium ion and the ionised acetate radical. An attempt made to distinguish a differential reaction rate in the case of a parallel reaction series using boiled and aged chromium nitrate reactant solutions, failed to reveal any significant differences between the series. The reactant solutions gave absorption spectra characteristic of the trivalent chromium ion with maxima in the 420 mµ and 570 mµ wavelength regions. The changes in optical density occurring in the vicinity of the maxima were followed spectrophotometrically, the height of the 570 mµ being found to increase during the course of reaction, while the height of the 420 mµ peak decreased. The variation in optical density at the 570 mµ peak was found to be directly related to the increase in concentration of the product complex in solution in accordance with the Baer-Bougher law, while the decrease in the height of the 420 mµ peak was related to the properties of unolated OH groups associated with the chromium complex as governed by pH and olation changes during the course of reaction. Boiled and aged chromium nitrate solutions gave reactant solutions having initial optical densities greater than those of the correspending fresh reactant solutions at the 570 mµ peak, and less than those of the fresh solutions at the 420 mµ peak. During the course of reaction, however, the two series converged to the same values. The equilibrium reaction solutions were subjected to paper electrophoretic study which indicated that all tho chromium was present in the form of cationic species. This finding was in accordance with stoicheiometric indications in the solvent extraction studies where coordination in a l : 1 ratio was reflected, giving rise to positively charged complex ions only. Making due allowance for band spreading the numbers of species predicted from the kinetic studies correspond with the electrophoretic patterns found. Application of the classical second order kinetic expression to the solvent extraction rate data, yielded plots having two distinctly linear sections, apparently indicating consecutive second order processes occurring in solution, contrary to the findings of previous workers who assign a first order mechanism to the reaction. This finding was consistent with the view that in the case of both the fresh and aged series, reaction consisted of successive coordination of an acetate radical to each chromium atom of a diol complex. Second order rate "constants" were calculated for each step and their dependency on pH level demonstrated. The findings of Hamm et al that these were first order reactions independent of acetate co'ncentration are believed to be due to their use of a large excess of acetate in their experiments. The kinetic study was further extended to an examination of the rate of "fixation"of trivalent chromium by the carboxyl groups of hide collagen under comparable conditions in a series of miniaturv tanning experiments in which the tannage substrate was provided in each of two physical forms:- (a) As hide powder where surface development was large, and (b) as prepared pelt pieces in which the fibrous weave pattern was retained. In view of the heterogeneity of the tannage systems, remarkable similarity was observed in the reaction course when compared with that of the acetate coordination studies, particularly in the case of the hide powder tannages. The dependency of the tannage rate data upon concentration and pH conditions was also found to be the same as in the case of the pure chemical system. The exact correlation between the rate data for the tannage and pure chemical systems was demonstrated by means of correlation plots. Close correlation was revealed in the case of hide powder tannage while the smaller degree of correlation observed in the case of the pelt tannage systems was attributed to the modifying effects of diffusion, particularly on the initial reaction velocity. The effect of using boiled and aged chromium solutions in the tannages was to increase the initial rate of chroniill!l "fixation" apparently due to tho coordination of a dial species at each coordination site. After the initial reaction period, the two series showed a tendency to converge as in the case of the spectrophotometric studies on the acetate reaction. The convergence trend was regarded as indicative of the tendency for the chromium in fresh solutions to under go rapid olation to the ame level as in the boiled and aged solutions. The experimental observations made on the various systems lead to the following conclusions:- (a) The mechanism of coordination of the acetate radical ttrivalent chromium appears to involve the successive coordination of ligand to each of the chromium atoms of a diol complex, both coordination steps proceeding by second order reaction mechanisms. (b) At the pH levels at which the reaction is carried out, the formation of elated bodios is rapid so that reaction in the case of both fresh and aged solutions essentially occurs between an elated species and the ionised acetate radical. (c) Modificati0ns in the absorption spectrum of the reactant solution at the 570 mµ peak are directly related to coordination, while changes at the 420 mµ peak are related to the formation of loosely-bound hydroxo chromium compounds, the concentrations of which depend on the pH level. (d) The mechanism of chromium fixation in hide is essentially similar to that operating in the case of coordination of the acetate radical to chromium, involving attachment of chromium to the side chain acid r sidues of collagen. (e ) The effect of olation is to enhance the rate of chromium fixation by hide protein during the initial reaction stages and to render possible bridge formation between adjacent side chains by secondary coordination during the latter reaction stages. (f) Where pelt pieces are used instead of hide powder, the initial rate of chromium fixation is dominated by the rate of diffusion of chromium into the fibrous structure. It should be stressed that the observations made on the various reaction systems cannot be regarded as exhaustive and the conclusions are subject to further confirmation. Consequently, the present study is essentially of a preliminary nature, but it is felt that the need for further investigation along similar lines has been demonstrated.
- Full Text:
- Date Issued: 1962
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