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
A comparative study of the catechin components in the barks of wattle species related to Acacia Mernsii
- Authors: Maihs, Edwin Alfred
- Date: 1962
- Subjects: Wattles (Plants) Acacia mearnsii Acacia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4482 , http://hdl.handle.net/10962/d1012793
- Description: The distribution of flavonoid constituents in the barks of Acacia mearnsii De Wild.(black wattle) , A· decurens Willd. (green wattle), A. dealbata Link.(silver wattle) and A. pycnantha Benth.(golden wattle) has been studied. Bark extracts of the four wattle species have been fractionated into low molecular weight fractions containing mainly catechins and other low molecular weight constituents, and high molecular weight fractions containing the bulk of the polymerized tannins. The low molecular weight fractions have been further fractionated by "preparative paper chromatography". (-)-Robinetinidol, (-)-7:3': 4': 5'-tetrahydroxy flavan- 3-ol, a new naturally occurring catechin, (+)-catechin and (+)-gallocatechin have been isolated from the barks of A. mearnsii, A. dealbata and A. pycnantha. (-)-Epicatechin and (-)-epigallocatechin have been identified in the bark extracts of A. dealbata and A. pycnantha, but appeared to be absent in the barks of A. mearnsii and A. decurrens. (-)-Epicatechin has been isolated fron A. dealbata, and both (-}-epicatechin and (-)-epigallocatechin were isolated from A. pycnantha. (-)-Epicatechin gallate, (-)-epigallocatechin gallate and gallic acid were isolated from A. pycnantha only. These three constituents appeared to be absent in the barks of the three other wattle species. (-)-Epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate which were not available for direct comparison, were subsequently isolated from green tea where they are present as major phenolic constituents. A method for the quantitative estimation of polyphenolic substances on two dimensional paper chromatograms has been developed, and a photoelectric densitometer constructed. Two spray reagents, ammoniacal silver nitrate and bisdiazotised benzidine, were found to give straight line relationships of instrument deflection against log concentration for flavonoid substances. This estimation method for the first time supplied means for a detailed study of the concentration of catechin constituents in the bark extracts of A. mearnsii, A. decurrens, A. dealbata, A. pycnantha and of A. mearnsii x A. decurrens hybrids. The concentration of catechin constituents has been shown to vary considerably between species whereas variation within species was small. In the latter respect silver wattle is an exception. Taxonomic significance may possibly be attached to the distribution of catechin constituents in the bark of the four Acacia species. The concentration of (-)-robinetinidol, which appears to be the characteristic compound of these Acacias, progressively decreases in the sequence black-, black x green hybrid, green-, silver- and golden wattle, while the number of catechin constituents of the "phloroglucinol series" increases in the same sequence. It thus appears, that by the examination of their bark components, a differentiation between species of a subgenera may be possible. Two tannins, constituents D and B, which are related to the leuco-anthocyanidins (flavan-3:4-diols) have been found in the barks of the four wattle species. One of the two, constituent D, was isolated in a pure form from the barks of A. mearnsii and A. pycnantha. Constituent D was found to generate robinetinidin and an orange pigment, the structure of which has not yet been fully identified. Compound D and its acetyl- and methoxyl derivatives did not crystallize. From the results of alkaline-, acidic- and enzymatic degradations, colour reactions and light-absorption studies, combustion analysis of the compound and its derivatives and molecular weight estimations, constituent D is surmised to be a dimer of 7:3': 4': 5'-tetrahydroxyflavan-3:4-diol (leuco-robinetinidin), The isolation of this complex leuco-anthocyanidin tannin represents the first isolation of a flavonoid tannin from commercial vegetable tannin sources. The second tannin obtained from the bark of A.mearnsii, "constituent B" appears to consist of two overlapping substances, which have not yet been separated. The tannin (B) was found to have an average molecular weight of 676 and it is considered likely that both substances may be dimolecular. On heating with mineral acid robinetinidin, fisetinidin and an orange pigment are generated, the pigment being identical with the pigment generated from constituent D. It may therefore be assumed that "Constituent B" consists of a mixture of complex leuco-robinetinidins and leucofisetinidins. The distribution of complex leuco-anthocyanidins in the bark extracts of Acacia mearnsii, A. decurrens, A. dealbata and A. pycnantha has been examined. A correlation between the distribution of leuco-anthocyanidins in the bark of the four wattle species, and accepted systematics, does not, apparently, exist.
- Full Text:
- Date Issued: 1962
- Authors: Maihs, Edwin Alfred
- Date: 1962
- Subjects: Wattles (Plants) Acacia mearnsii Acacia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4482 , http://hdl.handle.net/10962/d1012793
- Description: The distribution of flavonoid constituents in the barks of Acacia mearnsii De Wild.(black wattle) , A· decurens Willd. (green wattle), A. dealbata Link.(silver wattle) and A. pycnantha Benth.(golden wattle) has been studied. Bark extracts of the four wattle species have been fractionated into low molecular weight fractions containing mainly catechins and other low molecular weight constituents, and high molecular weight fractions containing the bulk of the polymerized tannins. The low molecular weight fractions have been further fractionated by "preparative paper chromatography". (-)-Robinetinidol, (-)-7:3': 4': 5'-tetrahydroxy flavan- 3-ol, a new naturally occurring catechin, (+)-catechin and (+)-gallocatechin have been isolated from the barks of A. mearnsii, A. dealbata and A. pycnantha. (-)-Epicatechin and (-)-epigallocatechin have been identified in the bark extracts of A. dealbata and A. pycnantha, but appeared to be absent in the barks of A. mearnsii and A. decurrens. (-)-Epicatechin has been isolated fron A. dealbata, and both (-}-epicatechin and (-)-epigallocatechin were isolated from A. pycnantha. (-)-Epicatechin gallate, (-)-epigallocatechin gallate and gallic acid were isolated from A. pycnantha only. These three constituents appeared to be absent in the barks of the three other wattle species. (-)-Epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate which were not available for direct comparison, were subsequently isolated from green tea where they are present as major phenolic constituents. A method for the quantitative estimation of polyphenolic substances on two dimensional paper chromatograms has been developed, and a photoelectric densitometer constructed. Two spray reagents, ammoniacal silver nitrate and bisdiazotised benzidine, were found to give straight line relationships of instrument deflection against log concentration for flavonoid substances. This estimation method for the first time supplied means for a detailed study of the concentration of catechin constituents in the bark extracts of A. mearnsii, A. decurrens, A. dealbata, A. pycnantha and of A. mearnsii x A. decurrens hybrids. The concentration of catechin constituents has been shown to vary considerably between species whereas variation within species was small. In the latter respect silver wattle is an exception. Taxonomic significance may possibly be attached to the distribution of catechin constituents in the bark of the four Acacia species. The concentration of (-)-robinetinidol, which appears to be the characteristic compound of these Acacias, progressively decreases in the sequence black-, black x green hybrid, green-, silver- and golden wattle, while the number of catechin constituents of the "phloroglucinol series" increases in the same sequence. It thus appears, that by the examination of their bark components, a differentiation between species of a subgenera may be possible. Two tannins, constituents D and B, which are related to the leuco-anthocyanidins (flavan-3:4-diols) have been found in the barks of the four wattle species. One of the two, constituent D, was isolated in a pure form from the barks of A. mearnsii and A. pycnantha. Constituent D was found to generate robinetinidin and an orange pigment, the structure of which has not yet been fully identified. Compound D and its acetyl- and methoxyl derivatives did not crystallize. From the results of alkaline-, acidic- and enzymatic degradations, colour reactions and light-absorption studies, combustion analysis of the compound and its derivatives and molecular weight estimations, constituent D is surmised to be a dimer of 7:3': 4': 5'-tetrahydroxyflavan-3:4-diol (leuco-robinetinidin), The isolation of this complex leuco-anthocyanidin tannin represents the first isolation of a flavonoid tannin from commercial vegetable tannin sources. The second tannin obtained from the bark of A.mearnsii, "constituent B" appears to consist of two overlapping substances, which have not yet been separated. The tannin (B) was found to have an average molecular weight of 676 and it is considered likely that both substances may be dimolecular. On heating with mineral acid robinetinidin, fisetinidin and an orange pigment are generated, the pigment being identical with the pigment generated from constituent D. It may therefore be assumed that "Constituent B" consists of a mixture of complex leuco-robinetinidins and leucofisetinidins. The distribution of complex leuco-anthocyanidins in the bark extracts of Acacia mearnsii, A. decurrens, A. dealbata and A. pycnantha has been examined. A correlation between the distribution of leuco-anthocyanidins in the bark of the four wattle species, and accepted systematics, does not, apparently, exist.
- Full Text:
- Date Issued: 1962
A critical investigation into the methods of determining sulphur in plant material
- Authors: Smith, Anthony John Hibbert
- Date: 1962
- Subjects: Plants -- Effect of sulfur on , Plants -- Nutrition , Sulfur
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4520 , http://hdl.handle.net/10962/d1014526
- Description: Although sulphur is one of the more abundant elements present in plants, its importance as a plant nutrient has been underestimated until comparatively recently. Scientific literature over the past few years, however, shows that interest in the determination of sulphur in natural waters, soil and plant materials has been renewed. Perhaps the main reason for the non-recognition of the importance of sulphur as a plant nutrient is the fact that sulphur-deficiency seldom occurs since sufficient sulphur is usually added to the soil in rainfall (particularly near industrial towns) to supply all the sulphur requirements of plants. In addition, sulphur is frequently present in fertilizers added to soils to counteract deficiency in other elements, especially phosphorus. Superphosphates, for example contain up to 60%, gypsum. Sulphur is also added to the soil in some instances in order to reduce the soil pH, the elemental sulphur being fairly readily oxidised in the soil to sulphuric acid. The organic fraction in the soil also contains sulphur. , [From Introduction]. Although sulphur is one of the more abundant elements present in plants, its importance as a plant nutrient has been underestimated until comparatively recently. Scientific literature over the past few years, however, shows that interest in the determination of sulphur in natural waters, soil and plant materials has been renewed. Perhaps the main reason for the non-recognition of the importance of sulphur as a plant nutrient is the fact that sulphur-deficiency seldom occurs since sufficient sulphur is usually added to the soil in rainfall (particularly near industrial towns) to supply all the sulphur requirements of plants. In addition, sulphur is frequently present in fertilizers added to soils to counteract deficiency in other elements, especially phosphorus. Superphosphates, for example contain up to 60%, gypsum. Sulphur is also added to the soil in some instances in order to reduce the soil pH, the elemental sulphur being fairly readily oxidised in the soil to sulphuric acid. The organic fraction in the soil also contains sulphur.
- Full Text: false
- Date Issued: 1962
- Authors: Smith, Anthony John Hibbert
- Date: 1962
- Subjects: Plants -- Effect of sulfur on , Plants -- Nutrition , Sulfur
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4520 , http://hdl.handle.net/10962/d1014526
- Description: Although sulphur is one of the more abundant elements present in plants, its importance as a plant nutrient has been underestimated until comparatively recently. Scientific literature over the past few years, however, shows that interest in the determination of sulphur in natural waters, soil and plant materials has been renewed. Perhaps the main reason for the non-recognition of the importance of sulphur as a plant nutrient is the fact that sulphur-deficiency seldom occurs since sufficient sulphur is usually added to the soil in rainfall (particularly near industrial towns) to supply all the sulphur requirements of plants. In addition, sulphur is frequently present in fertilizers added to soils to counteract deficiency in other elements, especially phosphorus. Superphosphates, for example contain up to 60%, gypsum. Sulphur is also added to the soil in some instances in order to reduce the soil pH, the elemental sulphur being fairly readily oxidised in the soil to sulphuric acid. The organic fraction in the soil also contains sulphur. , [From Introduction]. Although sulphur is one of the more abundant elements present in plants, its importance as a plant nutrient has been underestimated until comparatively recently. Scientific literature over the past few years, however, shows that interest in the determination of sulphur in natural waters, soil and plant materials has been renewed. Perhaps the main reason for the non-recognition of the importance of sulphur as a plant nutrient is the fact that sulphur-deficiency seldom occurs since sufficient sulphur is usually added to the soil in rainfall (particularly near industrial towns) to supply all the sulphur requirements of plants. In addition, sulphur is frequently present in fertilizers added to soils to counteract deficiency in other elements, especially phosphorus. Superphosphates, for example contain up to 60%, gypsum. Sulphur is also added to the soil in some instances in order to reduce the soil pH, the elemental sulphur being fairly readily oxidised in the soil to sulphuric acid. The organic fraction in the soil also contains sulphur.
- Full Text: false
- Date Issued: 1962
An investigation of the orientation of certain long-chain fatty acids at the air-water interface
- Authors: Saayman, Henry Martin
- Date: 1962
- Subjects: Fatty acids , Surface chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4496 , http://hdl.handle.net/10962/d1013117
- Description: The results obtained for the cross-sectional areas of the series of long-chain fatty acids may best be summarized with the aid of Graph 9. This graphical representation of the molecular areas, in Ų , against the chain length (n), of the fatty acid molecules, illustrates variation of the areas with chain length for the series in recrystallized form, and also for selected samples in the zone purified and vacuum distilled forms. On the graph, the limits of variation of the molecular areas have been represented as lines of a length corresponding to twice the standard deviation (2S). This is to give representation that the standard deviation may be positive or negative in relation to the mean. For molecules with n odd and lying between 15 and 19, the molecular area decreases. This may be due to the effect of 3 factorsg (1) A general decrease in lateral translation because of the increasing molecular mass (translational kinetic energy per molecule = ½ mc ⁻²), resulting in closer spacing of molecules. (2) A general, but steady decrease in the angle of tilt of the molecules which thus tend to be held more erect in the condensed film. (3) A general decrease in the precessional motion of the hydrophobic chain groups. For molecules with n odd and between 19 and 23, the molecular areas increase probably due to the steady increase in molecular mass causing the long chains to commence to buckle, tilt or topple in their upper regions. This tilting becomes greater because of the increasing gravitational effect on the heavier molecules which tends to make them assume a flatter posture in relation to the surface. The lower values observed for margaric and nonadecanoic acids, may be due to increasing symmetry in the chain, with corresponding economy in packing in condensed monolayers. This effect may be connected with increasing cylindrical symmetry of the hydrocarbon chain for even values of n. The results of this investigution, incomplete as it is, - serve to indicate what might reasonably be expected to happen in the orientation of these fatty acids in monolayers. Further work, especially on a greater range of acids with even n, is clearly necessary in order to establish the tentative ideas which have been suggested. However, in the present research, work was limited to those acids in the series which were obtainable without undue difficulty or delay, those which would spread readily under the conditions of experiments carried out at 20°C, and those which could be purified relatively easily. The acids below n = 15 in the series were found to be too soluble in aqueous substrates, at operating temperatures of 20°C, to yield reliable evidence with the Langmuir trough technique. The acids above n = 23 were unobtainable commercially and the synthesis of those acids from the lower members in the series presented problems of isolating the required specimens and difficulty in purifying these, which were considered b be beyond the scope of the present research. Summary and conclusion, p. 122.
- Full Text:
- Date Issued: 1962
- Authors: Saayman, Henry Martin
- Date: 1962
- Subjects: Fatty acids , Surface chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4496 , http://hdl.handle.net/10962/d1013117
- Description: The results obtained for the cross-sectional areas of the series of long-chain fatty acids may best be summarized with the aid of Graph 9. This graphical representation of the molecular areas, in Ų , against the chain length (n), of the fatty acid molecules, illustrates variation of the areas with chain length for the series in recrystallized form, and also for selected samples in the zone purified and vacuum distilled forms. On the graph, the limits of variation of the molecular areas have been represented as lines of a length corresponding to twice the standard deviation (2S). This is to give representation that the standard deviation may be positive or negative in relation to the mean. For molecules with n odd and lying between 15 and 19, the molecular area decreases. This may be due to the effect of 3 factorsg (1) A general decrease in lateral translation because of the increasing molecular mass (translational kinetic energy per molecule = ½ mc ⁻²), resulting in closer spacing of molecules. (2) A general, but steady decrease in the angle of tilt of the molecules which thus tend to be held more erect in the condensed film. (3) A general decrease in the precessional motion of the hydrophobic chain groups. For molecules with n odd and between 19 and 23, the molecular areas increase probably due to the steady increase in molecular mass causing the long chains to commence to buckle, tilt or topple in their upper regions. This tilting becomes greater because of the increasing gravitational effect on the heavier molecules which tends to make them assume a flatter posture in relation to the surface. The lower values observed for margaric and nonadecanoic acids, may be due to increasing symmetry in the chain, with corresponding economy in packing in condensed monolayers. This effect may be connected with increasing cylindrical symmetry of the hydrocarbon chain for even values of n. The results of this investigution, incomplete as it is, - serve to indicate what might reasonably be expected to happen in the orientation of these fatty acids in monolayers. Further work, especially on a greater range of acids with even n, is clearly necessary in order to establish the tentative ideas which have been suggested. However, in the present research, work was limited to those acids in the series which were obtainable without undue difficulty or delay, those which would spread readily under the conditions of experiments carried out at 20°C, and those which could be purified relatively easily. The acids below n = 15 in the series were found to be too soluble in aqueous substrates, at operating temperatures of 20°C, to yield reliable evidence with the Langmuir trough technique. The acids above n = 23 were unobtainable commercially and the synthesis of those acids from the lower members in the series presented problems of isolating the required specimens and difficulty in purifying these, which were considered b be beyond the scope of the present research. Summary and conclusion, p. 122.
- Full Text:
- Date Issued: 1962
Guibourtacacidin: a new Leuco-anthocyanidin from Rhodesian copalwood; (Guibourtia coleosperma)
- Authors: De Bruyn, Guustaaf Cornelis
- Date: 1962
- Subjects: Phanerogams , Angiosperms , Flavonoids , Anthocyanidins
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4459 , http://hdl.handle.net/10962/d1011043
- Description: A new leuco-anthocyanidin, (+)-7,4'dihydroxyflavan- 3:4-diol has been isolated from the heartwood of Guibourtia coleosperma. The heartwood extractives were fractionated by enrichment procedures involving fractional precipitation and Craig partitioning, to give a high RF (subscript) low molecular weight fraction containing the above leuco -anthocyanidin. This was further fractionated by "preparative" paper chromatography . The leuco-anthocyanidin was amorphous and present in low proportion (0.004%) in the wood. On boiling with alcoholic hydrochloric acid the compound gave an anthocyanidin which was identified as 3,7,4'-trihydroxyflavylium chloride. The degradation products formed by alkali fusion, on a micro-scale, were resorcinol and ♭-resorcylic acid, and also p (underscore)-hydroxybenzoic acid. This indicated resorcinol and phenol A and B nuclei respectively. The formation of amorphous dimethyl ether and tetra-acetoxy derivatives indicated two phenolic and two alcoholic hydroxyl groups. The above indicates that the compound was 7,4'-dihydroxyflavan- 3:4- diol and a molecular weight estimation showed it to be monomeric. Comparison of the infrared absorption spectra of the natural dimethyl ether with synthetic (±) dimethoxyflavan- 3:4-diol, to which a tentative 2:3- trans- 3:4-cis conformation had been assigned (Phatak and Kulkarni 94), showed close identity. Crystalline (±)-7, 4 '-dihydroxyflavan- 3:4 - diol was synthesised by catalytic hydrogenation over platinum oxide of the corresponoing (±) -7,4'-dihydroxyflavanonol. The flavanonol was synthesised by sodium hyposulphite reduction of the 7,4 ' -dihydroxyflavonol. The infrared absorption spectra of the natural and synthetic diols were similar but not identical. Chromatographic evidence showed the apparent identity of the synthetic and natural flavan- 3:4- diols, and two possible configurations were assigned for the natural flavan-3:4-diol. The new leuco-anthocyanidin was observed to form an O(underscore)-ethyl ether derivative on manipulation in ethanol. A monomeric leuco- fisetinidin from the heartwood was identified, by two dimensional paper chromatography, as (+) - mollisacacidin. The condensed tannins found also in the heartwood of G.(underscore)- coleosperma appear to be polymeric forms of leuco - fisetinidin and leuco - guibourtinidin. These polymeric tannins form a large proportion of the heartwood extractives and furnish high yields of fisetinidin and guibourtinidin chlorides on boiling with alcoholic hydrochloric acid. Examination of some other members of the Guibourtia spp . by paper chromatography showed that only G (underscore). coleosperma contained the new leuco - anthocyanidin as well as a leuco - fisetinidin. G. (underscore) tessmannii and G. (underscore) demeusii heartwoods contained only leuco-fisetinidin and the related polymers and a close chemical relationship to G.(underscore) coleosperma is thus apparent. G.(underscore) arnoldiana on the other hand is not chemically interrelated with the above members since it appeared to contain only leuco - cyanidin. (±) - 7,4 ' -Dihydroxyflavan- 4-ol was synthesised by hydrogenation of the corresponding flavanone over platinum oxide. Observations were made regarding its reddenig and ease of condensation.
- Full Text:
- Date Issued: 1962
- Authors: De Bruyn, Guustaaf Cornelis
- Date: 1962
- Subjects: Phanerogams , Angiosperms , Flavonoids , Anthocyanidins
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4459 , http://hdl.handle.net/10962/d1011043
- Description: A new leuco-anthocyanidin, (+)-7,4'dihydroxyflavan- 3:4-diol has been isolated from the heartwood of Guibourtia coleosperma. The heartwood extractives were fractionated by enrichment procedures involving fractional precipitation and Craig partitioning, to give a high RF (subscript) low molecular weight fraction containing the above leuco -anthocyanidin. This was further fractionated by "preparative" paper chromatography . The leuco-anthocyanidin was amorphous and present in low proportion (0.004%) in the wood. On boiling with alcoholic hydrochloric acid the compound gave an anthocyanidin which was identified as 3,7,4'-trihydroxyflavylium chloride. The degradation products formed by alkali fusion, on a micro-scale, were resorcinol and ♭-resorcylic acid, and also p (underscore)-hydroxybenzoic acid. This indicated resorcinol and phenol A and B nuclei respectively. The formation of amorphous dimethyl ether and tetra-acetoxy derivatives indicated two phenolic and two alcoholic hydroxyl groups. The above indicates that the compound was 7,4'-dihydroxyflavan- 3:4- diol and a molecular weight estimation showed it to be monomeric. Comparison of the infrared absorption spectra of the natural dimethyl ether with synthetic (±) dimethoxyflavan- 3:4-diol, to which a tentative 2:3- trans- 3:4-cis conformation had been assigned (Phatak and Kulkarni 94), showed close identity. Crystalline (±)-7, 4 '-dihydroxyflavan- 3:4 - diol was synthesised by catalytic hydrogenation over platinum oxide of the corresponoing (±) -7,4'-dihydroxyflavanonol. The flavanonol was synthesised by sodium hyposulphite reduction of the 7,4 ' -dihydroxyflavonol. The infrared absorption spectra of the natural and synthetic diols were similar but not identical. Chromatographic evidence showed the apparent identity of the synthetic and natural flavan- 3:4- diols, and two possible configurations were assigned for the natural flavan-3:4-diol. The new leuco-anthocyanidin was observed to form an O(underscore)-ethyl ether derivative on manipulation in ethanol. A monomeric leuco- fisetinidin from the heartwood was identified, by two dimensional paper chromatography, as (+) - mollisacacidin. The condensed tannins found also in the heartwood of G.(underscore)- coleosperma appear to be polymeric forms of leuco - fisetinidin and leuco - guibourtinidin. These polymeric tannins form a large proportion of the heartwood extractives and furnish high yields of fisetinidin and guibourtinidin chlorides on boiling with alcoholic hydrochloric acid. Examination of some other members of the Guibourtia spp . by paper chromatography showed that only G (underscore). coleosperma contained the new leuco - anthocyanidin as well as a leuco - fisetinidin. G. (underscore) tessmannii and G. (underscore) demeusii heartwoods contained only leuco-fisetinidin and the related polymers and a close chemical relationship to G.(underscore) coleosperma is thus apparent. G.(underscore) arnoldiana on the other hand is not chemically interrelated with the above members since it appeared to contain only leuco - cyanidin. (±) - 7,4 ' -Dihydroxyflavan- 4-ol was synthesised by hydrogenation of the corresponding flavanone over platinum oxide. Observations were made regarding its reddenig and ease of condensation.
- Full Text:
- Date Issued: 1962
The oxalate complexes of thorium
- Phillpotts, Charles Adrian Richard
- Authors: Phillpotts, Charles Adrian Richard
- Date: 1962
- Subjects: Oxalates , Thorium , Complex compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4488 , http://hdl.handle.net/10962/d1013029
- Description: (1) The ammonium, potassium and sodium salts of three complex thorium oxalates were prepared and studied. (2) Their solubilities and conditions of stability were studied. (3) The reaction between thorium and excess oxalate, and vice versa, was studied by means of conductivity and high frequency conductivity measurements. (4) The formation constant of Th(C₂O₄)₄⁴⁻ and Th(C₂O₄)₃²⁻, and the solubility product of (NH₄)₂Th₂(C₂O₄)₅, were determined by a solubility method.
- Full Text:
- Date Issued: 1962
- Authors: Phillpotts, Charles Adrian Richard
- Date: 1962
- Subjects: Oxalates , Thorium , Complex compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4488 , http://hdl.handle.net/10962/d1013029
- Description: (1) The ammonium, potassium and sodium salts of three complex thorium oxalates were prepared and studied. (2) Their solubilities and conditions of stability were studied. (3) The reaction between thorium and excess oxalate, and vice versa, was studied by means of conductivity and high frequency conductivity measurements. (4) The formation constant of Th(C₂O₄)₄⁴⁻ and Th(C₂O₄)₃²⁻, and the solubility product of (NH₄)₂Th₂(C₂O₄)₅, were determined by a solubility method.
- Full Text:
- Date Issued: 1962
The spectrographic determination of trace elements in citrus leaves
- Authors: Brandt, Peter Jürgen
- Date: 1962
- Subjects: Citrus , Trace elements in plant nutrition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4516 , http://hdl.handle.net/10962/d1013552
- Description: From Introduction: With the rapidly growing knowledge on trace elements and their influence on plant nutrition the need for accurate and rapid methods for their determination arose. The essential plant nutrients are usually divided into two groups. The major or macronutrient elements, necessary in comparatively large amounts, and the trace or micro-nutrient elements. In the case of plants, the first group includes Sulphur, Phosphorus, Potassium, Magnesium, Calcium and Nitrogen. The essential trace elements are Iron, manganese, Boron, Copper, Zinc, Molybdenum and Chlorine. Cobalt is essential for animal nutrition as a constituent of Vitamin B₁₂, but its essentiality for plants has not yet been proved. The latter group consists of metals which are catalysts in enzyme reactions and whose presence in the plant in minute amount determines whether the plant will be able to complete the vegetative or reproductive stage of its life cycle. Molybdenum may be quoted as an example of an essential trace element. It is generally recognised to be the catalyst responsible for the fixation of Nitrogen.
- Full Text:
- Date Issued: 1962
- Authors: Brandt, Peter Jürgen
- Date: 1962
- Subjects: Citrus , Trace elements in plant nutrition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4516 , http://hdl.handle.net/10962/d1013552
- Description: From Introduction: With the rapidly growing knowledge on trace elements and their influence on plant nutrition the need for accurate and rapid methods for their determination arose. The essential plant nutrients are usually divided into two groups. The major or macronutrient elements, necessary in comparatively large amounts, and the trace or micro-nutrient elements. In the case of plants, the first group includes Sulphur, Phosphorus, Potassium, Magnesium, Calcium and Nitrogen. The essential trace elements are Iron, manganese, Boron, Copper, Zinc, Molybdenum and Chlorine. Cobalt is essential for animal nutrition as a constituent of Vitamin B₁₂, but its essentiality for plants has not yet been proved. The latter group consists of metals which are catalysts in enzyme reactions and whose presence in the plant in minute amount determines whether the plant will be able to complete the vegetative or reproductive stage of its life cycle. Molybdenum may be quoted as an example of an essential trace element. It is generally recognised to be the catalyst responsible for the fixation of Nitrogen.
- Full Text:
- Date Issued: 1962
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