THE REACTION OF POLYISOPRENE WITH TITANIUM TETRACHLORIDE

1963 ◽  
Vol 41 (4) ◽  
pp. 937-953 ◽  
Author(s):  
Morton A. Golub ◽  
Jorge Heller
Keyword(s):  
Double Bond ◽  
Titanium Tetrachloride ◽  
First Order ◽  
First Order Kinetics ◽  
Carbonium Ion ◽  
Fused Ring ◽  
Ring Structures ◽  
Methylene Groups ◽  
Pseudo First Order ◽  
Total Disappearance

The reaction of titanium tetrachloride with hevea, balata, and synthetic cis-polyisoprene in benzene at 80 °C has been studied. The most prominent change in the infrared spectra of these polymers is the nearly total disappearance of the 12 μ band after prolonged reaction with TiCl4. The diminution of this band, associated with the loss of the original —C(CH3)=CH— units, whether cis or trans, followed pseudo-first-order kinetics, the rate varying with [TiCl4]n, where n is 1.0 in the case of the cis polymers and 1.5 in the case of the trans polymer. Contrary to previous reports, practically no cis–trans isomerization of polyisoprene occurs in the course of this reaction, the data being explained entirely by cyclization. With the help of cis-1,4 polymers of isoprene-3-d and 2-methyl-d3-1,3-butadiene-1,1-d2, it was concluded that cyclization, involving a TiCl4-induced carbonium ion mechanism, leads to the formation of six-membered rings fused into predominantly bicyclic structures, connected by methylene groups and/or uncyclized monomer units. Each of the fused ring structures contains a single tetra-, tri-, or di-substituted double bond, the relative amounts of which are in the order tetra- > tri- > di-substituted.

Tetracyclosqualene and Its Bearing on the Structure of Cyclized Rubber

1964 ◽  
Vol 37 (2) ◽  
pp. 486-490 ◽  
Author(s):  
Morton A. Golub ◽  
Jorge Heller
Keyword(s):  
Double Bond ◽  
Ir Spectra ◽  
Nmr Spectra ◽  
Bicyclic Structure ◽  
Fused Ring ◽  
Ring Structures ◽  
Methylene Groups ◽  
Cis And Trans ◽  
Rule Out

Abstract Recently we reported that cyclized rubber consists of six-membered rings fused into predominantly bicyclic structures which are connected by methylene groups and/or uncyclized isoprene units. Each of the fused ring structures is presumed to contain a single tetra-, tri- or di-substituted double bond, the relative amounts of which are in the order, tetra- > tri- > di-substituted. The predominantly bicyclic structure was not rigorously established, but it was considered reasonable on the basis of a comparison of the nmr spectra of cyclized cis-polyisoprene and cyclized cis-poly (2-methyl-d3-1,3-butadiene-1,1-d2). However, although a predominantly monocyclic structure was clearly excluded, it was not possible to rule out a structure in which the average number of rings per fused segment (“cyclicity”) exceeds two and may even be as high as three. In an effort to determine this cyclicity more accurately, we now compare the nmr and ir spectra of cyclized cis- and trans-polyisoprenes with the corresponding spectra of tetracyclosqualene (TCS). The latter is known to have a structure consisting of two bicyclic segments connected by two methylene groups.

In-vitro Kinetic Hydrolysis Study of Metronidazole Derivatives with Carvacrol and Eugenol Using Validated RP-HPLC Method

2020 ◽  
Vol 16 ◽  
Author(s):  
M. Alarjah
Keyword(s):  
Half Life ◽  
Hplc Method ◽  
Hydrolysis Rate ◽  
First Order ◽  
First Order Kinetics ◽  
Rp Hplc ◽  
Pharmacokinetic Properties ◽  
Pseudo First Order ◽  
Kinetic Hydrolysis

Background: Prodrugs principle is widely used to improve the pharmacological and pharmacokinetic properties of some active drugs. Much effort was made to develop metronidazole prodrugs to enhance antibacterial activity and or to improve pharmacokinetic properties of the molecule or to lower the adverse effects of metronidazole. Objective: In this work, the pharmacokinetic properties of some of monoterpenes and eugenol pro metronidazole molecules that were developed earlier were evaluated in-vitro. The kinetic hydrolysis rate constants and half-life time estimation of the new metronidazole derivatives were calculated using the validated RP-HPLC method. Method: Chromatographic analysis was done using Zorbbax Eclipse eXtra Dense Bonding (XDB)-C18 column of dimensions (250 mm, 4.6 mm, 5 μm), at ambient column temperature. The mobile phase was a mixture of sodium dihydrogen phosphate buffer of pH 4.5 and methanol in gradient elution, at 1ml/min flow rate. The method was fully validated according to the International Council for Harmonization (ICH) guidelines. The hydrolysis process carried out in an acidic buffer pH 1.2 and in an alkaline buffer pH 7.4 in a thermostatic bath at 37ºC. Results: The results followed pseudo-first-order kinetics. All metronidazole prodrugs were stable in the acidic pH, while they were hydrolysed in the alkaline buffer within a few hours (6-8 hr). The rate constant and half-life values were calculated, and their values were found to be 0.082- 0.117 hr-1 and 5.9- 8.5 hr., respectively. Conclusion: The developed method was accurate, sensitive, and selective for the prodrugs. For most of the prodrugs, the hydrolysis followed pseudo-first-order kinetics; the method might be utilised to conduct an in-vivo study for the metronidazole derivatives with monoterpenes and eugenol.

New insights on the UV/TiO2 photocatalytic treatment of thiomersal and its 2-sulfobenzoic acid product

2021 ◽  
Vol 02 ◽  
Author(s):  
Emmanuel M. de la Fournière ◽  
Jorge M. Meichtry ◽  
Graciela S. Custo ◽  
Eduardo A. Gautier ◽  
Marta I. Litter
Keyword(s):  
Degradation Products ◽  
Acidic Ph ◽  
Cosmetic Products ◽  
Acid Product ◽  
First Order ◽  
First Order Kinetics ◽  
Photocatalytic Destruction ◽  
Pseudo First Order ◽  
Mineralization Degree ◽  
Suitable Technique

Background: Thiomersal (TM), a complex between 2-mercaptobenzoic acid (2-MBA) and ethylmercury (C2H5Hg+), is an antimicrobial preservative used in immunological, ophthalmic, cosmetic products, and vaccines. Objective: TM has been treated by UV/TiO2 photocatalysis in the presence or absence of oxygen at acidic pH. C2H5Hg+, 2-MBA, and 2-sulfobenzoic acid (2-SBA) were found as products. A 2-SBA photocatalytic treatment was undertaken to study sulfur evolution. Methods: Photocatalytic runs were performed using a UVA lamp (λmax = 352 nm), open to the air or under N2. A suspension of the corresponding TM or 2-SBA salt and TiO2 was prepared, and pH was adjusted. Suspensions were stirred in the dark for 30 min and then irradiated. TM, 2-MBA, 2-SBA, and C2H5Hg+ were quantified by HPLC, sulfur by TXRF, and the deposits on the photocatalyst were analyzed by chemical reactions. The mineralization degree was followed by TOC. Sulfate was determined using BaCl2 at 580 nm. Results: Photocatalytic destruction of TM and total C2H5Hg+ was complete under N2 and air, but TM degradation was much faster in air. The evolution of TM and the products followed a pseudo-first-order kinetics. Conclusion: TiO2-photocatalytic degradation is a suitable technique for the treatment of TM and its degradation products. In contrast to other organomercurial compounds, TM degradation is faster in the presence of O2, indicating that the oxidative mechanism is the preferred pathway. A significant TM mineralization (> 60%, NPOC and total S) was obtained. TM was more easily degraded than 2-SBA. Sulfate was the final product.

Chemical effects induced by gas–liquid jet flow

2022 ◽  
Author(s):  
Zhiliang Zhang ◽  
Jiaqi Lu ◽  
Bingqian Lv ◽  
Wei Liu ◽  
Shuyuan Shen ◽  
...  
Keyword(s):  
Methylene Blue ◽  
Jet Flow ◽  
Reaction Process ◽  
Liquid Jet ◽  
First Order ◽  
First Order Kinetics ◽  
Chemical Effects ◽  
Pseudo First Order

The gas-liquid jet flow was proved to be capable of inducing chemical consequences which can lead to the decomposition of methylene blue (MB). The reaction process follows a pseudo-first-order kinetics....

scholarly journals Probing the active site residues in aromatic donor oxidation in horseradish peroxidase: involvement of an arginine and a tyrosine residue in aromatic donor binding

1996 ◽  
Vol 314 (3) ◽  
pp. 985-991 ◽  
Author(s):  
Subrata ADAK ◽  
Abhijit MAZUMDER ◽  
Ranajit K. BANERJEE
Keyword(s):  
Active Site ◽  
Native Enzyme ◽  
Tyrosine Residue ◽  
Tyrosine Residues ◽  
First Order ◽  
First Order Kinetics ◽  
Aromatic Donor ◽  
Pseudo First Order ◽  
Modified Enzyme ◽  
Compound Ii

The plausible role of arginine and tyrosine residues at the active site of horseradish peroxidase (HRP) in aromatic donor (guaiacol) oxidation was probed by chemical modification followed by characterization of the modified enzyme. The arginine-specific reagents phenylglyoxal (PGO), 2,3-butanedione and 1,2-cyclohexanedione all inactivated the enzyme, following pseudo-first-order kinetics with second-order rate constants of 24 M-1·min-1, 0.8 M-1·min-1 and 0.54 M-1·min-1 respectively. Modification with tetranitromethane, a tyrosine-specific reagent, also resulted in 50% loss of activity following pseudo-first-order kinetics with a second-order rate constant of 2.0 M-1·min-1. The substrate, H2O2, and electron donors such as I- and SCN- offered no protection against inactivation by both types of modifier, whereas the enzyme was completely protected by guaiacol or o-dianisidine, an aromatic electron donor (second substrate) oxidized by the enzyme. These studies indicate the involvement of arginine and tyrosine residues at the aromatic donor site of HRP. The guaiacol-protected phenylglyoxal-modified enzyme showed almost the same binding parameter (Kd) as the native enzyme, and a similar free energy change (∆G´) for the binding of the donor. Stoicheiometric studies with [7-14C]phenylglyoxal showed incorporation of 2 mol of phenylglyoxal per mol of enzyme, indicating modification of one arginine residue for complete inactivation. The difference absorption spectrum of the tetranitromethane-modified against the native enzyme showed a peak at 428 nm, characteristic of the nitrotyrosyl residue, that was abolished by treatment with sodium dithionite, indicating specific modification of a tyrosine residue. Inactivation stoicheiometry showed that modification of one tyrosine residue per enzyme caused 50% inactivation. Binding studies by optical difference spectroscopy indicated that the arginine-modified enzyme could not bind guaiacol at all, whereas the tyrosine-modified enzyme bound it with reduced affinity (Kd 35 mM compared with 10 mM for the native enzyme). Both the modified enzymes, however, retained the property of the formation of compound II (one-electron oxidation state higher than native ferriperoxidase) with H2O2, but reduction of compound II to native enzyme by guaiacol did not occur in the PGO-modified enzyme, owing to lack of binding. No non-specific change in protein structure due to modification was evident from circular dichroism studies. We therefore suggest that the active site of HRP for aromatic donor oxidation is composed of an arginine and an adjacent tyrosine residue, of which the former plays an obligatory role in aromatic donor binding whereas the latter residue plays a facilitatory role, presumably by hydrophobic interaction or hydrogen bonding.

scholarly journals CATION EXCHANGE BETWEEN CELLS AND PLASMA OF MAMMALIAN BLOOD

1950 ◽  
Vol 33 (6) ◽  
pp. 703-722 ◽  
Author(s):  
C. W. Sheppard ◽  
W. R. Martin
Keyword(s):  
Exchange Rate ◽  
Radioactive Isotope ◽  
Specific Activity ◽  
Compartment System ◽  
First Order ◽  
First Order Kinetics ◽  
Mammalian Blood ◽  
The Mean ◽  
Pseudo First Order

The exchange of potassium between cells and plasma of heparinized human blood has been studied in vitro using the radioactive isotope K42. The changes in cell and plasma specific activity are characteristic of a simple two-compartment system. The mean of seven determinations of the exchange rate at 38°C. is 1.8 per cent of the cellular potassium per hour. The results indicate that at 38°C. the rate is relatively insensitive to oxygenation or reduction of the hemoglobin, and to 1200 r of gamma radiation. With varying temperature the rate follows pseudo first order kinetics with a Q10 of 2.35. Below 15°C. the rate of loss of potassium exceeds the rate of uptake.

scholarly journals The role of histidine-118 of inorganic pyrophosphatase from thermophilic bacterium PS-3

1991 ◽  
Vol 278 (2) ◽  
pp. 595-599 ◽  
Author(s):  
N Hirano ◽  
T Ichiba ◽  
A Hachimori
Keyword(s):  
Thermophilic Bacterium ◽  
Complete Loss ◽  
Inorganic Pyrophosphatase ◽  
Histidine Residue ◽  
First Order ◽  
Diethyl Pyrocarbonate ◽  
Lysyl Endopeptidase ◽  
First Order Kinetics ◽  
Pseudo First Order

Treatment of the inorganic pyrophosphatase from thermophilic bacterium PS-3 with diethyl pyrocarbonate resulted in the almost complete loss of its activity, which followed pseudo-first-order kinetics. The presence of Mg2+ prevented the inactivation. Enzyme inactivated with diethyl pyrocarbonate was re-activated by hydroxylamine. The inactivation parallelled the amount of modified histidine residue, and a plot of the activity remaining against the amount of modified histidine residue suggested that the modification of one of two histidine residues totally inactivated the enzyme. The site involved was found to be located in a single lysyl endopeptidase-digest peptide derived from the ethoxy[14C]carbonylated enzyme. Amino acid analysis and sequence analysis of the peptide revealed that it comprised residues 96-119 of the inorganic pyrophosphatase from thermophilic bacterium PS-3. These results, when compared with those reported for the Escherichia coli and yeast enzymes, imply that His-118 of the inorganic pyrophosphatase from thermophilic bacterium PS-3 is located near the Mg(2+)-binding site and thus affects the binding of Mg2+.

Effects of oxidant concentration and temperature on decolorization of azo dye: comparisons of UV/Fenton and UV/Fenton-like systems

2012 ◽  
Vol 65 (11) ◽  
pp. 1970-1974 ◽  
Author(s):  
C. Y. Kuo ◽  
C. Y. Pai ◽  
C. H. Wu ◽  
M. Y. Jian
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Azo Dye ◽  
Activation Energies ◽  
First Order ◽  
First Order Kinetics ◽  
Oxidant Concentration ◽  
Decolorization Efficiency ◽  
Pseudo First Order ◽  
Reactive Red 2

This study applies photo-Fenton and photo-Fenton-like systems to decolorize C.I. Reactive Red 2 (RR2). The oxidants were H2O2 and Na2S2O8; Fe2+, Fe3+, and Co2+ were used to activate these two oxidants. The effects of oxidant concentration (0.3–2 mmol/L) and temperature (25–55 °C) on decolorization efficiency of the photo-Fenton and photo-Fenton-like systems were determined. The decolorization rate constants (k) of RR2 in the tested systems are consistent with pseudo-first-order kinetics. The rate constant increased as oxidant concentration and temperature increased. Activation energies of RR2 decolorization in the UV/H2O2/Fe2+, UV/H2O2/Fe3+, UV/Na2S2O8/Fe2+ and UV/Na2S2O8/Fe3+ systems were 32.20, 39.54, 35.54, and 51.75 kJ/mol, respectively.

Study on Phenol Oxidation Catalyzed by Persulfate

2013 ◽  
Vol 864-867 ◽  
pp. 96-100
Author(s):  
Shen Xin Li ◽  
Wei Hu ◽  
Ying Wang ◽  
Jian Zhang Li ◽  
Cheng Duan Wang
Keyword(s):  
Schiff Base ◽  
Key Words ◽  
Industrial Wastewater ◽  
Phenol Oxidation ◽  
Molar Ratio ◽  
Optimum Temperature ◽  
First Order ◽  
First Order Kinetics ◽  
Pseudo First Order ◽  
Oxidation System

The phenol oxidation with persulfate catalyzed were studied. Effects of several parameters, such as dose of oxidant, pH, temperature and UV irradiation, were investigated in detail. The results showed that the phenol oxidation by persulfate could be fitted to a pseudo-first order kinetics model. The optimum acidity of the phenol oxidation system in the paper is ca. pH 8.76, the optimum temperature which is ca.70 °C and the optimum molar ratio of persulfate to the phenol is ca.40 in the solution.The results are useful for the treatment of industrial wastewater. Key words: Phenol oxidation Schiff base manganese (III) complexes Persulfate

scholarly journals Mechanism-based inactivation of gastric peroxidase by mercaptomethylimidazole

1993 ◽  
Vol 296 (1) ◽  
pp. 79-84 ◽  
Author(s):  
U Bandyopadhyay ◽  
D K Bhattacharyya ◽  
R K Banerjee
Keyword(s):  
Ph Dependence ◽  
Order Rate Constant ◽  
Order Kinetic ◽  
First Order ◽  
First Order Kinetics ◽  
Mechanism Of Inhibition ◽  
Catalytically Active ◽  
Pseudo First Order ◽  
Inactivation Process ◽  
Gastric Peroxidase

The mechanism of inhibition of gastric peroxidase (GPO) activity by mercaptomethylimidazole (MMI), an inducer of gastric acid secretion, has been investigated. Incubation of purified GPO with MMI in the presence of H2O2 results in irreversible inactivation of the enzyme. No significant inactivation occurs in the absence of H2O2 or MMI, suggesting the involvement of peroxidase-catalysed oxidized MMI (MMIOX.) in the inactivation process. The inactivation follows pseudo-first-order kinetics consistent with a mechanism-based (suicide) mode. The pseudo-first-order kinetic constants at pH 8 are ki = 111 microM, k(inact.) = 0.55 min-1 and t1/2 = 1.25 min, and the second-order rate constant is 0.53 x 10(4) M-1 x min-1. Propylthiouracil also inactivates GPO activity in the same manner but its efficiency (k(inact./ki = 0.46 mM-1 x min-1) is about 10 times lower than that of MMI (k(inact./ki = 5 mM-1 x min-1). The rate of inactivation with MMI shows pH-dependence with an inflection point at 7.3, indicating the involvement in the inactivation process of an ionizable group on the enzyme with a pKa of 7.3. The enzyme is remarkably protected against inactivation by micromolar concentrations of electron donors such as iodide and bromide but not by chloride. Although GPO oxidizes MMI slowly, iodide stimulates it through enzymic generation of I+ which is reduced back to I- by MMI. Although MMIOX. is formed at a much higher rate in the presence of I-, a constant concentration of I- maintained via the reduction of I+ by MMI, protects the active site of the enzyme against inactivation. We suggest that MMI inactivates catalytically active GPO by acting as a suicidal substrate.

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