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methan by wael Khalil

Analytical biochemistry, 2008

BIOEQS is a global analysis and simulations program for complex biomolecular interaction data dev... more BIOEQS is a global analysis and simulations program for complex biomolecular interaction data developed in the 1990's [1,2]. Its continued usefulness derives from the fact that it is based on a numerical solver for complex coupled biological equilibria, rather than on closed-form analytical equations for the binding isotherms. It is therefore quite versatile, allowing easy testing of multiple binding models and analysis of systems too complex for closed form solutions. However, a major drawback to a generalized use of this program has been the lack of a graphical user interface (GUI) for setting up the binding models and experimental conditions, as well as visualizing the results. We present here a new GUI for BIOEQS that should be useful in both research and teaching applications.

Canadian journal of chemistry, 1987

Analytical potentiometry is a powerful technique to investigate multiple species in solution and ... more Analytical potentiometry is a powerful technique to investigate multiple species in solution and their formation constants. However, there have been some difficulties in this method resulting primarily from the theoretical approach. In this paper we critically examined them ...

Inorganica Chimica Acta, 1972

Evidence is given for an acid-base dissociation reaction of tris (ethylenediamine) cobalt (III) i... more Evidence is given for an acid-base dissociation reaction of tris (ethylenediamine) cobalt (III) ion in basic aqueous solutions. The evidence is based on the nmr chemical shifts of the methylene protons and on the u.v. absorption spectra of Co(en)33+ ion in basic solution. The equilibrium constant of the deprotonation reaction is estimated by each of the two methods.

Biotechnology and bioengineering, 2004

High-level yeast inocula was investigated as a means of overcoming the toxicity problem in ethano... more High-level yeast inocula was investigated as a means of overcoming the toxicity problem in ethanol fermentation of acid hydrolyzate of wood cellulose. When the inoculum level exceeded 108 initial cells/mL, 50% of the yeast cells survived the initial cell death period during which furfural and HMF were depleted. The fermentation thus proceeded to completion by virtue of cell regrowth. The specific ethanol productivity in batch fermentation on the basis of viable cells was comparable to that of pure glucose fermentation. Continuous fermentation with cell recycle was superior to batch fermentation in that there was no overall cell decline and the ethanol yield was substantially higher. The maximum ethanol productivity in continuous fermentation was 4.9 g/L h and it occurred at a dilution rate of 0.24 hr−1.

Enzyme and Microbial Technology, 1996

The inhibitory effects of six lignocellulose degradation products on glucose fermentation by Sacc... more The inhibitory effects of six lignocellulose degradation products on glucose fermentation by Saccharomyces cerevisiae and Zymomonas mobilis on xylose fermentation by Pichia stipitis and Candida shehatae were studied in batch cultures. Toxic compounds were added in varying concentrations and subsequent inhibitions on growth and ethanol production were quantified. Vanillin was shown to be a strong inhibitor of both growth and ethanol production by xylose fermenting yeasts and S. cerevisiae when it was added to the culture media at a concentration of 1 g l−1. Fermentative activities of Z. mobilis were greatly sensitive to the presence of hydroxybenzaldehyde (0.5 g l−1). Analysis of culture media extracts showed that some of the inhibitors, particularly vanillin and furaldehyde, could be assimilated by the tested microbial strains which resulted in the partial recovery in both growth and ethanol production processes on prolonged incubation.

Enzyme and microbial technology, 1986

Xylose, the dominant sugar in red oak acid prehydrolysate, was fermented to ethanol. In batch cul... more Xylose, the dominant sugar in red oak acid prehydrolysate, was fermented to ethanol. In batch cultures of xylose concentrations ranging from 10 to 100 g l−1, Pichia stipitis CBS 5776 yielded 0.50–0.40 g ethanol per g xylose consumed. Model compounds of inhibitors generated in the acid prehydrolysis of red oak hemicelluloses, lignin and extractives, hindered the fermentation. Recycled yeasts and treatments with molecular sieve or mixed bed ionresins facilitated the ethanol fermentation of red oak acid prehydrolysate. A maximal ethanol concentration of 9.9 g l−1 was obtained from an acid prehydrolysate containing 21.7 g l−1 of xylose. Fermentation inhibitors derived from red oak lignin and extractives were identified.

Biotechnology and …, 2000

Economic optimization of the production of ethanol by simultaneous saccharification and fermentat... more Economic optimization of the production of ethanol by simultaneous saccharification and fermentation (SSF) requires knowledge about the influence of substrate and enzyme concentration on yield and productivity. Although SSF has been investigated extensively, the optimal conditions for SSF of softwoods have yet not been determined. In this study, SO2-impregnated and steam-pretreated spruce was used as substrate for the production of ethanol by SSF. Commercial enzymes were used in combination with the yeast Saccharomyces cerevisiae. The effects of the concentration of substrate (2% to 10% w/w) and of cellulases (5 to 32 FPU/g cellulose) were investigated. SSF was found to be sensitive to contamination because lactic acid was produced. The ethanol yield increased with increasing cellulase loading. The highest ethanol yield, 68% of the theoretical based on the glucose and mannose present in the original wood, was obtained at 5% substrate concentration. This yield corresponds to 82% of the theoretical based on the cellulose and soluble glucose and mannose present at the start of SSF. A higher substrate concentration caused inefficient fermentation, whereas a lower substrate concentration, 2%, resulted in increased formation of lactic acid, which lowered the yield. Compared with separate hydrolysis and fermentation, SSF gave a higher yield and doubled the productivity.

Biotechnology and Bioengineering, 1979

High concentrations of both ethanol and sugar in the fermentation broth inhibit the growth of yea... more High concentrations of both ethanol and sugar in the fermentation broth inhibit the growth of yeast cells and the rate of product formation. Inhibitory effects of ethanol on the yeast strain Saccharomyces cerevisiae NRRL-Y-132 were studied in batch and continuous chemostat cultures. Growth was limited by either glucose or ethanol. Feed medium was supplemented with different ethanol concentrations. Ethanol was found to inhibit growth and the activity of yeast to produce ethanol in a noncompetitive manner. A linear kinetic pattern for growth and product formation was observed according to μ = μm (1 – P/Pm) and v = vm (1 – P/Pm′), where μm is the maximum specific growth rate at P = 0 (hr−1); Pm is the maximum specific product formation rate at P = 0 (hr−1); Pm is the maximum ethanol concentration above which cells do not grow (g/liter); Pm′ is the maximum ethanol concentration above which cells do not produce ethanol (g/liter). Substrate inhibition studies were carried out using short-time experimental techniques under aerobic and anaerobic condition. The degree of substrate inhibition was found to be higher than that has been reported for ethanol fermentation of pure sugar. The kinetic relationships thus obtained were used to compute growth, substrate utilization, and alcohol production patterns and have been discussed with reference to batch and continuous fermentation of enzymatically produced bagasse hydrolysate.

Biotechnology and Bioengineering, 2004

Rapid fermentation of bagasse hydrolysate to ethanol under anaerobic conditions by a strain of Sa... more Rapid fermentation of bagasse hydrolysate to ethanol under anaerobic conditions by a strain of Saccharomyces cerevisiae has been studied in batch and continuous cultures at pH 4.0 and 30°C temperature with cell recycle. By using a 23.6 g/liter cell concentration, a concentation of 9.7% (w/v)ethanol was developed in a period of 6 hr. The rate of fermentation was found to increase with supplementation of yeast vitamins in the hydrolysate. In continuous culture employing cell recycle and a 0.127 v/v/m air flow rate, a cell mass concentration of 48.5 g/liter has been achieved. The maximum fermentor productivity of ethanol obtained under these conditions was 32.0 g/liter/hr, which is nearly 7.5 times higher than the normal continuous process without cell recycle and air sparging. The ethanol productivity was found to decrease linearly with ethanol concentration. Conversion of glucose in the hydrolysate to ethanol was achieved with a yield of 95 to 97% of theoretical.

Applied microbiology and biotechnology, 2006

In recent years, growing attention has been devoted to the conversion of biomass into fuel ethano... more In recent years, growing attention has been devoted to the conversion of biomass into fuel ethanol, considered the cleanest liquid fuel alternative to fossil fuels. Significant advances have been made towards the technology of ethanol fermentation. This review provides practical examples and gives a broad overview of the current status of ethanol fermentation including biomass resources, microorganisms, and technology. Also, the promising prospects of ethanol fermentation are especially introduced. The prospects included are fermentation technology converting xylose to ethanol, cellulase enzyme utilized in the hydrolysis of lignocellulosic materials, immobilization of the microorganism in large systems, simultaneous saccharification and fermentation, and sugar conversion into ethanol.

Biotechnology and bioengineering, 1985

The inhibitory effect of ethanol on yeast growth and fermentation has been studied for the strain... more The inhibitory effect of ethanol on yeast growth and fermentation has been studied for the strain Saccharomyces cerevisiae ATCC No. 4126 under anaerobic batch conditions. The results obtained reveal that there is no striking difference between the response of growth and ethanol fermentation. Two kinetic models are also proposed to describe the kinetic pattern of ethanol inhibition on the specific rates of growth and ethanol fermentation: microi/micro0 = 1 - (P/Pm)alpha (for growth) nui/nu0 = 1 - (P/P'm)beta (for ethanol production). The maximum allowable ethanol concentration above which cells do not grow was predicted to be 112 g/L. The ethanol-producing capability of the cells was completely inhibited at 115 g/L ethanol. The proposed models appear to accurately represent the experimental data obtained in this study and the literature data.

Biotechnology and Bioengineering, 1983

Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose ... more Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose to ethanol fermentation processes. New processes are under development whereby ethanol is selectively removed from the fermenting broth to eliminate ethanol inhibition effects. These processes can concentrate minor secondary products to the point where they become toxic to the yeast. Vacuum fermentation selectively concentrates nonvolatile products in the fermentation broth. Membrane fermentation systems may concentrate large molecules which are sterically blocked from membrane transport. Extractive fermentation systems, employing nonpolar solvents, may concentrate small organic acids. By-product production rates and inhibition levels in continuous fermentation with Saccharomyces cerevisiae have been determined for acetaldehyde, glycerol, formic, lactic, and acetic acids, 1-propanol, 2-methyl-1-butanol, and 2,3-butanediol to assess the potential effects of these by-products on new fermentation processes. Mechanisms are proposed for the various inhibition effects observed.

Biotechnology and Bioengineering, 1983

Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose ... more Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose to ethanol fermentation processes. New processes are under development whereby ethanol is selectively removed from the fermenting broth to eliminate ethanol inhibition effects. These processes can concentrate minor secondary products to the point where they become toxic to the yeast. Vacuum fermentation selectively concentrates nonvolatile products in the fermentation broth. Membrane fermentation systems may concentrate large molecules which are sterically blocked from membrane transport. Extractive fermentation systems, employing nonpolar solvents, may concentrate small organic acids. By-product production rates and inhibition levels in continuous fermentation with Saccharomyces cerevisiae have been determined for acetaldehyde, glycerol, formic, lactic, and acetic acids, 1-propanol, 2-methyl-1-butanol, and 2,3-butanediol to assess the potential effects of these by-products on new fermentation processes. Mechanisms are proposed for the various inhibition effects observed.

Biotechnology and Bioengineering, 1977

Cell recycle and vacuum fermentation systems were developed for continuous ethanol production. Ce... more Cell recycle and vacuum fermentation systems were developed for continuous ethanol production. Cell recycle was employed in both atmospheric pressure and vacuum fermentations to achieve high cell densities and rapid ethanol fermentation rates. Studies were conducted with Saccharomyces cerevisiae (ATCC No. 4126) at a fermentation temperature of 35°C. Employing a 10% glucose feed, a cell density of 50 g dry wt/liter was obtained in atmospheric-cell recycle fermentations which produced a fermentor ethanol productivity of 29.0 g/liter-hr. The vacuum fermentor eliminated ethanol inhibition by boiling away ethanol from the fermenting beer as it was formed. This permitted the rapid and complete fermentation of concentrated sugar solutions. At a total pressure of 50 mmHg and using a 33.4% glucose feed, ethanol productivities of 82 and 40 g/liter-hr were achieved with the vacuum system with and without cell recycle, respectively. Fermentor ethanol productivities were thus increased as much as twelvefold over conventional continuous fermentations. In order to maintain a viable yeast culture in the vacuum fermentor, a bleed of fermented broth had to be continuously withdrawn to remove nonvolatile compounds. It was also necessary to sparge the vacuum fermentor with pure oxygen to satisfy the trace oxygen requirement of the fermenting yeast.

Journal of Inorganic and Nuclear Chemistry, 1976

Transition Metal Chemistry, 1998

The proton±ligand stability constants of a-pyridoin thiosemicarbazone, a-pyridoin 2-methylthiosem... more The proton±ligand stability constants of a-pyridoin thiosemicarbazone, a-pyridoin 2-methylthiosemicarbazone, a-pyridoin 4-methylthiosemicarbazone and apyridoin (4-phenylthiosemicarbazone) as well as the formation constants of their chelates with Cu II , Ni II , Co II , Zn II and Mn II have been determined. The Calvin± Bjerrum pH titration techniques, as modi®ed by Irving and Rossotti, were employed in aqueous media at different ionic strengths and temperatures. The stability constants of the complexes follow the order: Cu II > Ni II > Co II > Zn II >Mn II which is in accord with the Ir-ving±Williams series. The chelates derived from a-pyridoin 4-phenylthiosemicarbazone have relatively higher stability constants, which may be attributed to the presence of the benzene ring in the chain.

Polymer, 2002

The complexation of copper ions by chitosan and its oligomers is investigated using potentiometri... more The complexation of copper ions by chitosan and its oligomers is investigated using potentiometric and spectrophotometric methods to study the nature of the complexes involved and the role of the degree of polymerisation. Two complexes are demonstrated. Their structure is proposed, the pH range in which they are respectively stable is determined and their stability constants calculated. Finally a degree of polymerisation of 6 appeared as the threshold value for an ef®cient complexation of copper ions by chitosan oligomers. q

Journal of Inorganic and Nuclear Chemistry, 1970

Journal of Inorganic and Nuclear …, 1963

Interactions of the alkaline earth metals with some polyaminopolycarboxylic acids have been inves... more Interactions of the alkaline earth metals with some polyaminopolycarboxylic acids have been investigated by the potentiometric titration method for aqueous solutions of ionic strength approximately 0-1 at 30 °. Metal chelate formation constants have been calculated, and the effects of ligand structure on chelate stability are discussed.

Journal of Inorganic and Nuclear …, 1972

Equilibrium studies at 25 -0.1 °C and /~ = 0-1 M (NaCIO4) are reported for simple and mixed syste... more Equilibrium studies at 25 -0.1 °C and /~ = 0-1 M (NaCIO4) are reported for simple and mixed systems of Cu(II), with citric, rneso-and dl-tartaric acids, aspartic acid and glycine as primary ligands, and orthophosphate, pyrophosphate and sulphate as secondary ligands. Measurements were made with glass and Cu2+-ion-selective electrodes. The formation of mixed complex was favoured (negative values of log KMy~-Iog K2xr, where Y = phosphate or sulphate) over simple complexes in all systems above pH 4.

Analytical biochemistry, 2008

BIOEQS is a global analysis and simulations program for complex biomolecular interaction data dev... more BIOEQS is a global analysis and simulations program for complex biomolecular interaction data developed in the 1990's [1,2]. Its continued usefulness derives from the fact that it is based on a numerical solver for complex coupled biological equilibria, rather than on closed-form analytical equations for the binding isotherms. It is therefore quite versatile, allowing easy testing of multiple binding models and analysis of systems too complex for closed form solutions. However, a major drawback to a generalized use of this program has been the lack of a graphical user interface (GUI) for setting up the binding models and experimental conditions, as well as visualizing the results. We present here a new GUI for BIOEQS that should be useful in both research and teaching applications.

Canadian journal of chemistry, 1987

Analytical potentiometry is a powerful technique to investigate multiple species in solution and ... more Analytical potentiometry is a powerful technique to investigate multiple species in solution and their formation constants. However, there have been some difficulties in this method resulting primarily from the theoretical approach. In this paper we critically examined them ...

Inorganica Chimica Acta, 1972

Evidence is given for an acid-base dissociation reaction of tris (ethylenediamine) cobalt (III) i... more Evidence is given for an acid-base dissociation reaction of tris (ethylenediamine) cobalt (III) ion in basic aqueous solutions. The evidence is based on the nmr chemical shifts of the methylene protons and on the u.v. absorption spectra of Co(en)33+ ion in basic solution. The equilibrium constant of the deprotonation reaction is estimated by each of the two methods.

Biotechnology and bioengineering, 2004

High-level yeast inocula was investigated as a means of overcoming the toxicity problem in ethano... more High-level yeast inocula was investigated as a means of overcoming the toxicity problem in ethanol fermentation of acid hydrolyzate of wood cellulose. When the inoculum level exceeded 108 initial cells/mL, 50% of the yeast cells survived the initial cell death period during which furfural and HMF were depleted. The fermentation thus proceeded to completion by virtue of cell regrowth. The specific ethanol productivity in batch fermentation on the basis of viable cells was comparable to that of pure glucose fermentation. Continuous fermentation with cell recycle was superior to batch fermentation in that there was no overall cell decline and the ethanol yield was substantially higher. The maximum ethanol productivity in continuous fermentation was 4.9 g/L h and it occurred at a dilution rate of 0.24 hr−1.

Enzyme and Microbial Technology, 1996

The inhibitory effects of six lignocellulose degradation products on glucose fermentation by Sacc... more The inhibitory effects of six lignocellulose degradation products on glucose fermentation by Saccharomyces cerevisiae and Zymomonas mobilis on xylose fermentation by Pichia stipitis and Candida shehatae were studied in batch cultures. Toxic compounds were added in varying concentrations and subsequent inhibitions on growth and ethanol production were quantified. Vanillin was shown to be a strong inhibitor of both growth and ethanol production by xylose fermenting yeasts and S. cerevisiae when it was added to the culture media at a concentration of 1 g l−1. Fermentative activities of Z. mobilis were greatly sensitive to the presence of hydroxybenzaldehyde (0.5 g l−1). Analysis of culture media extracts showed that some of the inhibitors, particularly vanillin and furaldehyde, could be assimilated by the tested microbial strains which resulted in the partial recovery in both growth and ethanol production processes on prolonged incubation.

Enzyme and microbial technology, 1986

Xylose, the dominant sugar in red oak acid prehydrolysate, was fermented to ethanol. In batch cul... more Xylose, the dominant sugar in red oak acid prehydrolysate, was fermented to ethanol. In batch cultures of xylose concentrations ranging from 10 to 100 g l−1, Pichia stipitis CBS 5776 yielded 0.50–0.40 g ethanol per g xylose consumed. Model compounds of inhibitors generated in the acid prehydrolysis of red oak hemicelluloses, lignin and extractives, hindered the fermentation. Recycled yeasts and treatments with molecular sieve or mixed bed ionresins facilitated the ethanol fermentation of red oak acid prehydrolysate. A maximal ethanol concentration of 9.9 g l−1 was obtained from an acid prehydrolysate containing 21.7 g l−1 of xylose. Fermentation inhibitors derived from red oak lignin and extractives were identified.

Biotechnology and …, 2000

Economic optimization of the production of ethanol by simultaneous saccharification and fermentat... more Economic optimization of the production of ethanol by simultaneous saccharification and fermentation (SSF) requires knowledge about the influence of substrate and enzyme concentration on yield and productivity. Although SSF has been investigated extensively, the optimal conditions for SSF of softwoods have yet not been determined. In this study, SO2-impregnated and steam-pretreated spruce was used as substrate for the production of ethanol by SSF. Commercial enzymes were used in combination with the yeast Saccharomyces cerevisiae. The effects of the concentration of substrate (2% to 10% w/w) and of cellulases (5 to 32 FPU/g cellulose) were investigated. SSF was found to be sensitive to contamination because lactic acid was produced. The ethanol yield increased with increasing cellulase loading. The highest ethanol yield, 68% of the theoretical based on the glucose and mannose present in the original wood, was obtained at 5% substrate concentration. This yield corresponds to 82% of the theoretical based on the cellulose and soluble glucose and mannose present at the start of SSF. A higher substrate concentration caused inefficient fermentation, whereas a lower substrate concentration, 2%, resulted in increased formation of lactic acid, which lowered the yield. Compared with separate hydrolysis and fermentation, SSF gave a higher yield and doubled the productivity.

Biotechnology and Bioengineering, 1979

High concentrations of both ethanol and sugar in the fermentation broth inhibit the growth of yea... more High concentrations of both ethanol and sugar in the fermentation broth inhibit the growth of yeast cells and the rate of product formation. Inhibitory effects of ethanol on the yeast strain Saccharomyces cerevisiae NRRL-Y-132 were studied in batch and continuous chemostat cultures. Growth was limited by either glucose or ethanol. Feed medium was supplemented with different ethanol concentrations. Ethanol was found to inhibit growth and the activity of yeast to produce ethanol in a noncompetitive manner. A linear kinetic pattern for growth and product formation was observed according to μ = μm (1 – P/Pm) and v = vm (1 – P/Pm′), where μm is the maximum specific growth rate at P = 0 (hr−1); Pm is the maximum specific product formation rate at P = 0 (hr−1); Pm is the maximum ethanol concentration above which cells do not grow (g/liter); Pm′ is the maximum ethanol concentration above which cells do not produce ethanol (g/liter). Substrate inhibition studies were carried out using short-time experimental techniques under aerobic and anaerobic condition. The degree of substrate inhibition was found to be higher than that has been reported for ethanol fermentation of pure sugar. The kinetic relationships thus obtained were used to compute growth, substrate utilization, and alcohol production patterns and have been discussed with reference to batch and continuous fermentation of enzymatically produced bagasse hydrolysate.

Biotechnology and Bioengineering, 2004

Rapid fermentation of bagasse hydrolysate to ethanol under anaerobic conditions by a strain of Sa... more Rapid fermentation of bagasse hydrolysate to ethanol under anaerobic conditions by a strain of Saccharomyces cerevisiae has been studied in batch and continuous cultures at pH 4.0 and 30°C temperature with cell recycle. By using a 23.6 g/liter cell concentration, a concentation of 9.7% (w/v)ethanol was developed in a period of 6 hr. The rate of fermentation was found to increase with supplementation of yeast vitamins in the hydrolysate. In continuous culture employing cell recycle and a 0.127 v/v/m air flow rate, a cell mass concentration of 48.5 g/liter has been achieved. The maximum fermentor productivity of ethanol obtained under these conditions was 32.0 g/liter/hr, which is nearly 7.5 times higher than the normal continuous process without cell recycle and air sparging. The ethanol productivity was found to decrease linearly with ethanol concentration. Conversion of glucose in the hydrolysate to ethanol was achieved with a yield of 95 to 97% of theoretical.

Applied microbiology and biotechnology, 2006

In recent years, growing attention has been devoted to the conversion of biomass into fuel ethano... more In recent years, growing attention has been devoted to the conversion of biomass into fuel ethanol, considered the cleanest liquid fuel alternative to fossil fuels. Significant advances have been made towards the technology of ethanol fermentation. This review provides practical examples and gives a broad overview of the current status of ethanol fermentation including biomass resources, microorganisms, and technology. Also, the promising prospects of ethanol fermentation are especially introduced. The prospects included are fermentation technology converting xylose to ethanol, cellulase enzyme utilized in the hydrolysis of lignocellulosic materials, immobilization of the microorganism in large systems, simultaneous saccharification and fermentation, and sugar conversion into ethanol.

Biotechnology and bioengineering, 1985

The inhibitory effect of ethanol on yeast growth and fermentation has been studied for the strain... more The inhibitory effect of ethanol on yeast growth and fermentation has been studied for the strain Saccharomyces cerevisiae ATCC No. 4126 under anaerobic batch conditions. The results obtained reveal that there is no striking difference between the response of growth and ethanol fermentation. Two kinetic models are also proposed to describe the kinetic pattern of ethanol inhibition on the specific rates of growth and ethanol fermentation: microi/micro0 = 1 - (P/Pm)alpha (for growth) nui/nu0 = 1 - (P/P'm)beta (for ethanol production). The maximum allowable ethanol concentration above which cells do not grow was predicted to be 112 g/L. The ethanol-producing capability of the cells was completely inhibited at 115 g/L ethanol. The proposed models appear to accurately represent the experimental data obtained in this study and the literature data.

Biotechnology and Bioengineering, 1983

Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose ... more Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose to ethanol fermentation processes. New processes are under development whereby ethanol is selectively removed from the fermenting broth to eliminate ethanol inhibition effects. These processes can concentrate minor secondary products to the point where they become toxic to the yeast. Vacuum fermentation selectively concentrates nonvolatile products in the fermentation broth. Membrane fermentation systems may concentrate large molecules which are sterically blocked from membrane transport. Extractive fermentation systems, employing nonpolar solvents, may concentrate small organic acids. By-product production rates and inhibition levels in continuous fermentation with Saccharomyces cerevisiae have been determined for acetaldehyde, glycerol, formic, lactic, and acetic acids, 1-propanol, 2-methyl-1-butanol, and 2,3-butanediol to assess the potential effects of these by-products on new fermentation processes. Mechanisms are proposed for the various inhibition effects observed.

Biotechnology and Bioengineering, 1983

Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose ... more Inhibition by secondary fermentation products may limit the ultimate productivity of new glucose to ethanol fermentation processes. New processes are under development whereby ethanol is selectively removed from the fermenting broth to eliminate ethanol inhibition effects. These processes can concentrate minor secondary products to the point where they become toxic to the yeast. Vacuum fermentation selectively concentrates nonvolatile products in the fermentation broth. Membrane fermentation systems may concentrate large molecules which are sterically blocked from membrane transport. Extractive fermentation systems, employing nonpolar solvents, may concentrate small organic acids. By-product production rates and inhibition levels in continuous fermentation with Saccharomyces cerevisiae have been determined for acetaldehyde, glycerol, formic, lactic, and acetic acids, 1-propanol, 2-methyl-1-butanol, and 2,3-butanediol to assess the potential effects of these by-products on new fermentation processes. Mechanisms are proposed for the various inhibition effects observed.

Biotechnology and Bioengineering, 1977

Cell recycle and vacuum fermentation systems were developed for continuous ethanol production. Ce... more Cell recycle and vacuum fermentation systems were developed for continuous ethanol production. Cell recycle was employed in both atmospheric pressure and vacuum fermentations to achieve high cell densities and rapid ethanol fermentation rates. Studies were conducted with Saccharomyces cerevisiae (ATCC No. 4126) at a fermentation temperature of 35°C. Employing a 10% glucose feed, a cell density of 50 g dry wt/liter was obtained in atmospheric-cell recycle fermentations which produced a fermentor ethanol productivity of 29.0 g/liter-hr. The vacuum fermentor eliminated ethanol inhibition by boiling away ethanol from the fermenting beer as it was formed. This permitted the rapid and complete fermentation of concentrated sugar solutions. At a total pressure of 50 mmHg and using a 33.4% glucose feed, ethanol productivities of 82 and 40 g/liter-hr were achieved with the vacuum system with and without cell recycle, respectively. Fermentor ethanol productivities were thus increased as much as twelvefold over conventional continuous fermentations. In order to maintain a viable yeast culture in the vacuum fermentor, a bleed of fermented broth had to be continuously withdrawn to remove nonvolatile compounds. It was also necessary to sparge the vacuum fermentor with pure oxygen to satisfy the trace oxygen requirement of the fermenting yeast.

Journal of Inorganic and Nuclear Chemistry, 1976

Transition Metal Chemistry, 1998

The proton±ligand stability constants of a-pyridoin thiosemicarbazone, a-pyridoin 2-methylthiosem... more The proton±ligand stability constants of a-pyridoin thiosemicarbazone, a-pyridoin 2-methylthiosemicarbazone, a-pyridoin 4-methylthiosemicarbazone and apyridoin (4-phenylthiosemicarbazone) as well as the formation constants of their chelates with Cu II , Ni II , Co II , Zn II and Mn II have been determined. The Calvin± Bjerrum pH titration techniques, as modi®ed by Irving and Rossotti, were employed in aqueous media at different ionic strengths and temperatures. The stability constants of the complexes follow the order: Cu II > Ni II > Co II > Zn II >Mn II which is in accord with the Ir-ving±Williams series. The chelates derived from a-pyridoin 4-phenylthiosemicarbazone have relatively higher stability constants, which may be attributed to the presence of the benzene ring in the chain.

Polymer, 2002

The complexation of copper ions by chitosan and its oligomers is investigated using potentiometri... more The complexation of copper ions by chitosan and its oligomers is investigated using potentiometric and spectrophotometric methods to study the nature of the complexes involved and the role of the degree of polymerisation. Two complexes are demonstrated. Their structure is proposed, the pH range in which they are respectively stable is determined and their stability constants calculated. Finally a degree of polymerisation of 6 appeared as the threshold value for an ef®cient complexation of copper ions by chitosan oligomers. q

Journal of Inorganic and Nuclear Chemistry, 1970

Journal of Inorganic and Nuclear …, 1963

Interactions of the alkaline earth metals with some polyaminopolycarboxylic acids have been inves... more Interactions of the alkaline earth metals with some polyaminopolycarboxylic acids have been investigated by the potentiometric titration method for aqueous solutions of ionic strength approximately 0-1 at 30 °. Metal chelate formation constants have been calculated, and the effects of ligand structure on chelate stability are discussed.

Journal of Inorganic and Nuclear …, 1972

Equilibrium studies at 25 -0.1 °C and /~ = 0-1 M (NaCIO4) are reported for simple and mixed syste... more Equilibrium studies at 25 -0.1 °C and /~ = 0-1 M (NaCIO4) are reported for simple and mixed systems of Cu(II), with citric, rneso-and dl-tartaric acids, aspartic acid and glycine as primary ligands, and orthophosphate, pyrophosphate and sulphate as secondary ligands. Measurements were made with glass and Cu2+-ion-selective electrodes. The formation of mixed complex was favoured (negative values of log KMy~-Iog K2xr, where Y = phosphate or sulphate) over simple complexes in all systems above pH 4.