Kinetic study of the reaction between cystine and sulfide in alkaline solutions

1987 ◽  
Vol 65 (4) ◽  
pp. 770-774 ◽  
Author(s):  
David K. Liu ◽  
S. G. Chang
Keyword(s):  
Hydrogen Sulfide ◽  
Amino Acid ◽  
Ionic Strength ◽  
Rate Constants ◽  
Amino Acid Analysis ◽  
Ph Dependence ◽  
Alkaline Solutions ◽  
Visible Spectroscopy ◽  
Uv Visible ◽  
Ph Dependent

The reaction between cystine (CySSCy) and hydrogen sulfide ion (HS−) in alkaline solutions has been studied by amino acid analysis and uv–visible spectroscopy. The reaction occurs in two reversible steps to form cysteine (CySH), S-thiocysteine (CySS−), and disulfide (S22−), as represented by the reactions [Formula: see text] and [Formula: see text]. The equilibrium and rate constants were pH dependent due to the presence of various charge types of reactants and products. The rate constants at 25 °C, pH 10.0, and μ = 0.17 M were determined to be: k1 = 3.7 ± 0.4 M−1 min−1, k−1 = 5.5 ± 0.6 M−1 min−1, k2 = 6.1 ± 0.5 M−1 min−1, and k−2 = 122 ± 20 M−1 min−1. When the rate constant k1 is expressed as k1 = A exp (−Ea/RT), values of A = (4.7 ± 0.3) × 1011 M−1 min−1 and Ea = 15.8 ± 0.9 kcal mol−1 were obtained. The ionic strength and pH dependence of k1 were also studied.

scholarly journals Degradasi Tirosina Menggunakan Mangkinfoto Berasaskan TiO2

2012 ◽  
Author(s):  
Rusmidah Ali ◽  
Siti Salamah Maisoan @ Selamat
Keyword(s):  
Amino Acid ◽  
Metal Ions ◽  
Uv Light ◽  
Degradation Process ◽  
Aqueous System ◽  
Visible Spectroscopy ◽  
Photo Degradation ◽  
Efficient System ◽  
Catalyst Powder ◽  
Uv Visible

Asid amino merupakan bahan asas dalam tisu tumbuhan dan haiwan. Tirosina (Tr) salah satu jenis asid amino yang mengandungi gelang aromatik, telah dipilih sebagai sampel untuk proses degradasi dalam medium akueus. Ini bertujuan melihat kesan penggunaan mangkinfoto dalam sinaran ultralembayung (λ < 400 nm) atau cahaya matahari ke atas molekul tirosina. Kajian telah dijalankan menggunakan sistem cahaya, mangkin serbuk TiO2, hidrogen peroksida, H2O2 dan ion logam. Penambahan ion logam seperti Ni2+, Cu2+, Ag+, Mn2+, Co2+, Fe2+ dan Cd2+ dan agen pengoksidaan, iaitu hidrogen peroksida adalah untuk mendapatkan kaedah yang paling cekap. Keputusan menunjukkan penambahan H2O2 dan ion Fe2+ dan Ni2+ berjaya meningkatkan kecekapan proses degradasifoto tirosina. Ion Ni2+ memberikan keputusan terbaik berbanding ion-ion lain. Ion Cu2+, Ag+, Mn2+ dan Cd2+ merencat proses degradasi. Keputusan juga menunjukkan cahaya matahari adalah setanding dengan cahaya ultralembayung. Kepekatan H2O2 terbaik adalah 5.0 x 10-2M dan semakin banyak TiO2 digunakan semakin baik peratus degradasi tirosina. Oleh itu kaedah optimum untuk proses degradasifoto ialah Tr 2.5 x 10-4 M + TiO2 + H2O25.0 x 10-3 M + Mn+ 1.0 x 10-2 M. Proses degradasifoto dikaji menggunakan spektroskopi ultralembayung-nampak pada julat panjang gelombang 400-200 nm. Kata kunci: Tirosina; degradasifoto; serbuk TiO; akueus Amino acid is a basic component in plant or animal tissue. Tyrosine (Tr), an amino acid which contains aromatic ring, was chosen as a sample for a photodegradation process in an aqueous system. The purpose of the experiment is to study the effect of photocatalysis under UV (λ < 400 nm) or sunlight on tyrosine. The experiment was carried out by using UV light, catalyst powder (TiO2), hidrogen peroxide H2O2 and metal ions system. The addition of oxidising agent H2O2 and metal ions such as Ni2+, Cu2+, Ag+, Mn2+, Co2+, Fe2+ and Cd2+ were used in order to achieve the most efficient system. Results showed that the system with added H2O2 and metal ions such as Ni2+ and Fe2+ had successfully enhanced the process of the tyrosine photodegradation. Other metal ions system such as Cu2+, Ag+, Mn2+ and Cd2+ were found to inhibit the degradation process. The results also showed that sunlight was comparable to ultraviolet light. The best H2O2 concentration was 5.0 x 10-2 M and the percentage of tyrosine degradation increased with the addition of more TiO2) by mass. Therefore, the optimum condition for tyrosine photodegradation process was in Tr 2.5 x 10-4 M + TiO2 + H2O2 5.0 x 10-3 M + H2O2 1.0 x 10-2 M. The dissappearance of tyrosine in the photo degradation process was monitored by UV-visible spectroscopy between 400-200 nm. Key words: Tyrosine; photodegradation; TiO2 powder; akueus

scholarly journals Mannitol-1-phosphate dehydrogenase of Escherichia coli Chemical properties and binding of substrates

1986 ◽  
Vol 239 (2) ◽  
pp. 435-443 ◽  
Author(s):  
T Chase
Keyword(s):  
Amino Acid ◽  
Amino Acid Analysis ◽  
Dissociation Constants ◽  
Ph Dependence ◽  
Covalent Binding ◽  
Polyacrylamide Gel Electrophoresis ◽  
Thiol Group ◽  
Covalent Modification ◽  
Protective Effects ◽  
Phosphate Complex

Mannitol-1-phosphate dehydrogenase was purified to homogeneity, and some chemical and physical properties were examined. The isoelectric point is 4.19. Amino acid analysis and polyacrylamide-gel electrophoresis in presence of SDS indicate a subunit Mr of about 22,000, whereas gel filtration and electrophoresis of the native enzyme indicate an Mr of 45,000. Thus the enzyme is a dimer. Amino acid analysis showed cysteine, tyrosine, histidine and tryptophan to be present in low quantities, one, three, four and four residues per subunit respectively. The zinc content is not significant to activity. The enzyme is inactivated (greater than 99%) by reaction of 5,5′-dithiobis-(2-nitrobenzoate) with the single thiol group; the inactivation rate depends hyperbolically on reagent concentration, indicating non-covalent binding of the reagent before covalent modification. The pH-dependence indicated a pKa greater than 10.5 for the thiol group. Coenzymes (NAD+ and NADH) at saturating concentrations protect completely against reaction with 5,5′-dithiobis-(2-nitrobenzoate), and substrates (mannitol 1-phosphate, fructose 6-phosphate) protect strongly but not completely. These results suggest that the thiol group is near the catalytic site, and indicate that substrates as well as coenzymes bind to free enzyme. Dissociation constants were determined from these protective effects: 0.6 +/- 0.1 microM for NADH, 0.2 +/- 0.03 mM for NAD+, 9 +/- 3 microM for mannitol 1-phosphate, 0.06 +/- 0.03 mM for fructose 6-phosphate. The binding order for reaction thus may be random for mannitol 1-phosphate oxidation, though ordered for fructose 6-phosphate reduction. Coenzyme and substrate binding in the E X NADH-mannitol 1-phosphate complex is weaker than in the binary complexes, though in the E X NADH+-fructose 6-phosphate complex binding is stronger.

scholarly journals The composition of cartilage proteoglycans. An investigation using high-and low-ionic-strength extraction procedures

1973 ◽  
Vol 131 (3) ◽  
pp. 541-553 ◽  
Author(s):  
Robert W. Mayes ◽  
Roger M. Mason ◽  
David C. Griffin
Keyword(s):  
Amino Acid ◽  
Ionic Strength ◽  
Density Gradient ◽  
Amino Acid Analysis ◽  
Chondroitin Sulphate ◽  
High Ionic Strength ◽  
Guanidinium Chloride ◽  
Equilibrium Conditions ◽  
Chondroitin Sulphate Proteoglycans ◽  
Low Ionic Strength

1. A proteoglycan fraction (the proteoglycan subunit fraction) was prepared from extracts, with 0.15m-KCl (low-ionic-strength) and 0.5m-LaCl3, 2.0m-CaCl2 and 4.0m-guanidinium chloride (high-ionic-strength), of bovine nasal cartilage by equilibrium-density-gradient centrifugation, essentially as described by Hascall & Sajdera (1969). 2. The use of different centrifugation times showed that near-equilibrium conditions were reached by 48h for the fractions prepared from the high-ionic-strength extracts. The fraction isolated from the low-ionic-strength extract required a longer centrifugation time to reach equilibrium conditions. 3. The composition of the proteoglycan fractions from the various extracts was compared by analyses of their carbohydrate and amino acid contents. Difference indices were calculated from the amino acid analysis to compare the degree of compositional relationship between the protein components of the proteoglycans. 4. Small compositional differences were found between the proteoglycans isolated from the various high-ionic-strength extracts. The protein content of the fractions from the CaCl2 extract and the guanidinium chloride extract showed the greatest difference in this respect, although their amino acid analysis was similar. 5. The proteoglycan fraction isolated from the low-ionic-strength extract shows marked differences in composition from the fractions isolated from the high-ionic-strength extracts. Its protein and glucosamine contents were lower whereas its hexuronic acid and galactosamine contents were higher than those of the latter. It also exhibits major differences in its amino acid composition. The glucosamine:galactosamine ratio of the fraction from the low-ionic-strength extract indicates that it may be an almost exclusively chondroitin sulphate–proteoglycan. Its analysis correlates closely with that of a low-molecular-weight proteoglycan isolated from pig laryngeal cartilage by Tsiganos & Muir (1969). 6. The proteoglycan fractions from both the low- and high-ionic-strength extracts migrate as a single band in zone electrophoresis carried out in a sucrose-density gradient at both pH3.0 and pH7.0, although each showed evidence of band widening during the electrophoresis. All the proteoglycan fractions migrated with the same electrophoretic mobility at pH3.0, irrespective of the differences in composition between them. 7. The differences between the proteoglycans from the low- and high-ionic-strength extracts are discussed and the view is advanced that they may be due to association between predominantly chondroitin sulphate–proteoglycans and a keratan sulphate-enriched proteoglycan species.

scholarly journals A study of the subunit structure and the thiol reactivity of bovine liver uridine diphosphate glucose dehydrogenase

1972 ◽  
Vol 129 (4) ◽  
pp. 821-830 ◽  
Author(s):  
P. A. Gainey ◽  
T. C. Pestell ◽  
C. F. Phelps
Keyword(s):  
Amino Acid ◽  
Amino Acid Analysis ◽  
Peptide Mapping ◽  
Ph Dependence ◽  
Glucose Dehydrogenase ◽  
Group Analysis ◽  
Subunit Structure ◽  
Uridine Diphosphate ◽  
Thiol Groups ◽  
Thiol Reactivity

1. The amino acid analysis of UDP-glucose dehydrogenase is reported. 2. N-Terminal-group analysis indicates only one type of N-terminal amino acid, methionine, to be present. 3. Peptide ‘mapping’ in conjunction with the amino acid analysis indicates that the subunits of the enzyme are similar if not identical. 4. The various kinetic classes of thiol group were investigated by reaction with 5,5′-dithiobis-(2-nitrobenzoate). 5. NAD+, UDP-glucose and UDP-xylose protect the two rapidly reacting thiol groups of the hexameric enzyme. 6. Inactivation of the enzyme with 5,5′-dithiobis-(2-nitrobenzoate) indicates the involvement of six thiol groups in the maintenance of enzymic activity. 7. The pH-dependence of UDP-xylose inhibition of the enzyme was investigated. 8. The group involved in the binding of UDP-xylose to the protein has a heat of ionization of about 33kJ/mol and a pK of 8.4–8.6. 9. It is suggested that UDP-xylose has a cooperative homotropic effect on the enzyme.

scholarly journals Effect of the Acidic and Alkaline Solutions on K2CrO4 and K2Cr2O7 by Ultraviolet and Visible Measurement

2019 ◽  
Vol 30 (1) ◽  
pp. 221
Author(s):  
Mohammad Radi Mohammad ◽  
Hasanain Saad Azeez
Keyword(s):  
Ph Value ◽  
Red Shift ◽  
Alkaline Solutions ◽  
Visible Spectroscopy ◽  
Solution Ph ◽  
Effect Of Ph ◽  
Ph Values ◽  
Uv Visible

In this work different amount of acidic (HCl) and alkaline (NaOH) solutions were added to stoke solutions of K2CrO4 and K2Cr2O7 to show the effect of pH values on their spectra. The results of UV-Visible spectroscopy shows that, the Changing of solution pH value when drops of HCl were added led to shift wavelength of K2CrO4 spectrum while no change has been occurred in K2Cr2O7 spectrum. However, Changing PH values solution by adding drops of NaOH led to change in wavelength red shift for K2Cr2O7 while no changes has been occurred in spectrum of K2CrO4.

Determination of Rate Constants in Second-Order Kinetics Using UV-Visible Spectroscopy

2001 ◽  
Vol 55 (1) ◽  
pp. 77-83 ◽  
Author(s):  
Sabina Bijlsma ◽  
Hans F. M. Boelens ◽  
Age K. Smilde
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Visible Spectroscopy ◽  
Uv Visible

Substituent effects upon cation–pseudobase equilibration for isoquinolinium and phthalazinium cations

1981 ◽  
Vol 59 (22) ◽  
pp. 3195-3199 ◽  
Author(s):  
John W. Bunting ◽  
Vivian S.-F. Chew ◽  
Shinta Sindhuatmadja
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Reasonable Agreement ◽  
Ph Dependence ◽  
Substituent Effects ◽  
Correlation Equation ◽  
First Order ◽  
Substituent Constants ◽  
Pseudo First Order ◽  
Correlation Line

pKR+ values have been measured for cation–pseudobase equilibration by 4-X-2-methylisoquinolinium cations (1) (X = Br, CONH2, COC6H5, CN, NO2) at 25 °C, ionic strength 0.1. These pKR+ values are well correlated by Hammett equations using either σ or σ−para substituent constants. The best correlation gives: pKR+ = −8.8 (± 0.3) σp− + 16.5 (± 0.2) (r = 0.998). The value pKR+ = 16.29 measured by Cook et al. (Tetrahedron, 32, 1773 (1976)) for the 2-methylisoquinolinium cation in dimethyl sulfoxide – water solutions is in reasonable agreement with this correlation equation. For the 2-methyl-5-nitrophthalazinium cation, pKR+ = 7.87, and pKRO− = 12.10 for alkoxide ion formation by the pseudobase of this cation.The pH dependence of the pseudo first-order rate constants (kobs) for cation–pseudobase equilibration has been measured for 1:X = CONH2, COC6H5, CN and for the 2-methylphthalazinium cation (3) and its 5-NO2 derivative (4). For each of these cations, [Formula: see text] and kd = k1[H+] + k2 and the parameters [Formula: see text] have been evaluated. For 1:X = CONH2 and CN and 3, kOH is consistent with a correlation line between log kOH and pKR+ established for other isoquinolinium cations (J. Am. Chem. Soc. 99, 1189 (1977)). For 1:X = COC6H5, kOH is seven-fold smaller, and for 4, kOH is five-fold greater than predicted by this correlation line.

Rate constants for the addition of the enolate ion of acetone to quinolinium and acridinium cations

1990 ◽  
Vol 68 (10) ◽  
pp. 1762-1768 ◽  
Author(s):  
John W. Bunting ◽  
Cynthia Fu ◽  
James W. Tam
Keyword(s):  
Ionic Strength ◽  
Aqueous Solutions ◽  
Rate Constants ◽  
Nucleophilic Addition ◽  
Ph Dependence ◽  
Adduct Formation ◽  
Kinetic Control ◽  
Thermodynamic Control ◽  
Hydroxide Ion ◽  
Kinetically Controlled

The reaction of acetone with four heteroaromatic cations (10-methylacridinium (1), 3-aminocarbonyl-1-methylquinolinium (2a), 3-cyano-1-methylquinolinium (2b), and 3-bromo-1-methylquinolinium (2c)) has been investigated in basic aqueous solutions (pH 9–12, ionic strength 0.1, 25 °C). For each of 2a and 2b, the kinetically controlled product is a 35:65 mixture of the C-2 and C-4 enolate ion adducts; the C-2 adduct subsequently isomerizes to give the C-4 adduct as the only observable species under thermodynamic control. For 2c, the C-2 enolate adduct appears to be favoured both kinetically and thermodynamically. Under kinetic control, the pH-dependence of adduct formation from each cation is consistent with rate-determining attack of the enolate ion upon the heterocyclic cation. Comparisons of regiochemical control of acetone enolate ion attack with hydroxide ion attack upon these same cations indicate that acetone enolate ion shows a more pronounced preference for C-4 attack over C-2 attack than does hydroxide ion. The thermodynamically controlled regiochemistry is similar for each of these two nucleophiles. Keywords: nucleophilic addition, regioselectivity, kinetic control, thermodynamic control, quinolinium cations.

Kinetics and mechanism of the oxidation of proline by periodate

1989 ◽  
Vol 67 (4) ◽  
pp. 634-638 ◽  
Author(s):  
Rosa Pascual ◽  
Miguel A. Herraez ◽  
Emilio Calle.
Keyword(s):  
Amino Acid ◽  
Rate Constants ◽  
Reaction Rate ◽  
Ph Dependence ◽  
Kinetics And Mechanism ◽  
Appreciable Amount ◽  
Kinetics Of Oxidation ◽  
Rate Law ◽  
First Order ◽  
Kinetics Of

The kinetics of oxidation of proline by periodate has been studied at pH 1.40–8.83 and 30.0 °C. The reaction rate is first order in both periodate and amino acid, and the overall reaction follows second-order kinetics. There was no evidence for the formation of an appreciable amount of intermediate. The reaction rate is highest at pH 4–7 and the oxidation is catalysed by [Formula: see text] ions. The pH dependence of the reaction rate can be explained in terms of reaction of periodate monoanion and the protonated and dipolar forms of the amino acid. The mechanism proposed and the derived rate law are consistent with the observed kinetics. The rate constants obtained from the derived rate law are in agreement with the observed rate constants, thus justifying the rate law and the proposed mechanistic scheme. Keywords: oxidation of proline, oxidation by periodate.

scholarly journals Metal Ions and Hydrogen Peroxide. XXV

1972 ◽  
Vol 27 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Peter Waldmeier ◽  
Bernhard Prijs ◽  
Helmut Sigel
Keyword(s):  
Hydrogen Peroxide ◽  
Ionic Strength ◽  
Metal Ions ◽  
Experimental Evidence ◽  
Initial Rate ◽  
Reaction Order ◽  
Ph Dependence ◽  
Initial Concentration ◽  
Ph Dependent ◽  
Ph Range

The decomposition of H2O2, catalyzed by the Co2® complex of 4,4′,4″,4″′-tetrasulfophthalocyanine (CoIIPTS), was investigated in the pH range 3.8 through 10 by measuring the initial rate, v0=d(O2)/dt, of the increasing formation of O2 (25°; I=0.1). In this pH range v0 is proportional to the initial concentration of H2O2 (determined at pH 5.0 and 9.2). Due to the dimerization (log KD=5.47 ±0.09 at natural ionic strength and about 7.63 ±0.16 in 0.1 M NaClO4; 25°) and polymerization of CoIIPTS the catalyst and its reaction order are difficult to establish: Based on the experimental evidence it is suggested that v0 is proportional to the concentration of monomer CoIIPTS. Additionally, there is evidence that the experimentally determined v0 contains the contributions of a pH-independent and a pH-dependent reaction course. These results are analog to those obtained earlier with FeIIIPTS as catalyst. A mechanism for the catalyzed disproportionation of H2O2 by CoIIPTS is proposed. The catalase-like activity of CoIIIPTS (OH) is smaller than that of CoIIPTS and the pH-dependence is different.

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