Reaction of hydroxide ion with 1,3,5-trinitrobenzene in cationic micelles: evidence of variable counterion binding to micellar head groups

1985 ◽  
Vol 63 (3) ◽  
pp. 598-601 ◽  
Author(s):  
Leong-Huat Gan
Keyword(s):  
Rate Constant ◽  
Hexadecyltrimethylammonium Bromide ◽  
Ion Distribution ◽  
Counterion Binding ◽  
Hydroxide Ion ◽  
Micellar Systems ◽  
Cationic Micelles ◽  
Head Groups ◽  
Distribution Constants ◽  
The Stability

Cationic micelles of hexadecyltrimethylammonium bromide, chloride, and hydroxide (CTABr, CTACl, and CTAOH) greatly enhance the stability of anionic σ-complex formed by hydroxide ion and 1,3,5-trinitrobenzene (TNB). The counterion binding to the micellar head groups is assumed to vary but is governed by a distribution constant. Different distribution constants are used for different types of counterion. Using this treatment, the rate constant – surfactant concentration profiles for the reactions of TNB with hydroxide ion in CTAOH, CTABr, and CTACl can all be satisfactorily accounted for, yielding consistent results in various conditions. The ion distribution constants, KOH = 55 mol−1 dm3, KBr = 1800 mol−1 dm3, and KCl = 420 mol−1 dm3 and the rate constant KM = 3600 s−1 are obtained. In view of the success of this treatment, the assumption of a constant β value associated with the pseudophase model at best could only be viewed as an approximation, valid only for micellar systems with tightly bound counterions such as those in the micelles of CTABr.

scholarly journals Complexes of Copper and Iron with Pyridoxamine, Ascorbic Acid, and a Model Amadori Compound: Exploring Pyridoxamine’s Secondary Antioxidant Activity

Antioxidants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 208
Author(s):  
Guillermo García-Díez ◽  
Roger Monreal-Corona ◽  
Nelaine Mora-Diez
Keyword(s):  
Antioxidant Activity ◽  
Ascorbic Acid ◽  
Rate Constant ◽  
Stable Complex ◽  
Aqueous Environment ◽  
Oh Radicals ◽  
Bidentate Ligands ◽  
Superoxide Radical Anion ◽  
Amadori Compound ◽  
The Stability

The thermodynamic stability of 11 complexes of Cu(II) and 26 complexes of Fe(III) is studied, comprising the ligands pyridoxamine (PM), ascorbic acid (ASC), and a model Amadori compound (AMD). In addition, the secondary antioxidant activity of PM is analyzed when chelating both Cu(II) and Fe(III), relative to the rate constant of the first step of the Haber-Weiss cycle, in the presence of the superoxide radical anion (O2•−) or ascorbate (ASC−). Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. The aqueous environment is modeled by making use of the SMD solvation method in all calculations. This level of theory accurately reproduces the experimental data available. When put in perspective with the stability of various complexes of aminoguanidine (AG) (which we have previously studied), the following stability trends can be found for the Cu(II) and Fe(III) complexes, respectively: ASC < AG < AMD < PM and AG < ASC < AMD < PM. The most stable complex of Cu(II) with PM (with two bidentate ligands) presents a ΔGf0 value of −35.8 kcal/mol, whereas the Fe(III) complex with the highest stability (with three bidentate ligands) possesses a ΔGf0 of −58.9 kcal/mol. These complexes can significantly reduce the rate constant of the first step of the Haber-Weiss cycle with both O2•− and ASC−. In the case of the copper-containing reaction, the rates are reduced up to 9.70 × 103 and 4.09 × 1013 times, respectively. With iron, the rates become 1.78 × 103 and 4.45 × 1015 times smaller, respectively. Thus, PM presents significant secondary antioxidant activity since it is able to inhibit the production of ·OH radicals. This work concludes a series of studies on secondary antioxidant activity and allows potentially new glycation inhibitors to be investigated and compared relative to both PM and AG.

Counterion binding on mixed anionic/cationic micelles

1988 ◽  
Vol 266 (10) ◽  
pp. 954-957 ◽  
Author(s):  
N. Filipović-Vinceković ◽  
D. Škrtić
Keyword(s):  
Counterion Binding ◽  
Cationic Micelles

scholarly journals Superactivity and conformational changes on alpha-chymotrypsin upon interfacial binding to cationic micelles

2004 ◽  
Vol 378 (3) ◽  
pp. 1059-1066 ◽  
Author(s):  
M. Soledad CELEJ ◽  
Mariana G. D'ANDREA ◽  
Patricia T. CAMPANA ◽  
Gerardo D. FIDELIO ◽  
M. Lucia BIANCONI
Keyword(s):  
Conformational Changes ◽  
Tertiary Structure ◽  
Enzyme Stability ◽  
Catalytic Efficiency ◽  
Tryptophan Fluorescence ◽  
Enzyme Activation ◽  
Hexadecyltrimethylammonium Bromide ◽  
Negative Band ◽  
Cationic Micelles ◽  
Α Helix

The catalytic behaviour of α-CT (α-chymotrypsin) is affected by cationic micelles of CTABr (hexadecyltrimethylammonium bromide). The enzyme–micelle interaction leads to an increase in both the Vmax and the affinity for the substrate p-nitrophenyl acetate, indicating higher catalytic efficiency for bound α-CT. The bell-shaped profile of α-CT activity with increasing CTABr concentrations suggests that the micelle-bound enzyme reacts with the free substrate. Although more active with CTABr micelles, the enzyme stability is essentially the same as observed in buffer only. Enzyme activation is accompanied by changes in α-CT conformation. Changes in tertiary structure were observed by the increase in intensity and the red shift in the α-CT tryptophan fluorescence spectrum, suggesting the annulment of internal quenching and a more polar location of tryptophan residues. Near-UV CD also indicated the transfer of aromatic residues to a more flexible environment. CTABr micelles also induces an increase in α-helix, as seen by far-UV CD and FTIR (Fourier-transform infrared) spectroscopies. The far-UV CD spectrum of α-CT shows an increase in the intensity of the positive band at 198 nm and in the negative band at 222 nm, indicating an increased α-helical content. This is in agreement with FTIR studies, where an increase in the band at 1655 cm−1, corresponding to the α-helix, was shown by fitting analysis and difference spectroscopy. Spectral deconvolution indicated a reduction in the β-sheet content in micelle-bound α-CT. Our data suggest that the higher catalytic efficiency of micelle-bound α-CT results from significant conformational changes.

Counterion micellar effects upon the reaction of low-spin diimine iron(II) complexes

1989 ◽  
Vol 67 (2) ◽  
pp. 305-309 ◽  
Author(s):  
Francisco Ortega ◽  
Elvira Rodenas
Keyword(s):  
Ion Exchange ◽  
Exchange Model ◽  
Micellar Solutions ◽  
Micellar Effects ◽  
Hydroxide Ion ◽  
Cationic Micelles ◽  
Rate Effects ◽  
Rate Of Reaction

The rate of reaction of tris(1,10-phenanthroline)iron(II) ion (1a), tris(3,4,7,8-tetramethyl-1,10-phenanthroline)iron(II) ion (1b), and tris(4,7-diphenhyl-1, 10-phenanthroline)iron(II) ion (1c) with hydroxide ion, in cationic micelles, is strongly affected by the concentration of micellar counterion in solution. The reaction of la in CTACl is modestly speeded up by the addition of added KCl, while the reactions of 1b and 1c are strongly inhibited by the addition of large amounts of KCl and KBr to micellar solutions of CTACl and CTABr, respectively. These rate effects fit the pseudophase-ion exchange model, assuming the binding of the substrates to the micelles depends upon the counterion concentration. Keywords: counterion micellar effects, low-spin diimine iron(II) complexes.

scholarly journals pH effect on stability and kinetics degradation of nitazoxanide in solution

2020 ◽  
Vol 4 (1) ◽  
pp. 12-17
Author(s):  
Fábio Barbosa ◽  
Leonardo Pezzi ◽  
Julia Sorrentino ◽  
Martin Steppe ◽  
Nadia Volpato ◽  
...  
Keyword(s):  
Rate Constant ◽  
Degradation Product ◽  
Degradation Rate ◽  
Degradation Kinetics ◽  
Ph Effect ◽  
Degradation Rate Constant ◽  
Main Degradation Product ◽  
Wide Ph Range ◽  
The Stability ◽  
Ph Range

Stability studies correspond to a set of tests designed to assess changes in the quality of a given drug over time and under the influence of a number of factors. Among these factors, pH plays an important role, due to the catalytic effect that hydronium and hydroxide ions can play in several reactions. In the present study, the degradation kinetics of nitazoxanide was evaluated over a wide pH range, and the main degradation product generated was identified by LC-MS/MS. Nitazoxanide showed first-order degradation kinetics in the pH range of 0.01 to 10.0 showing greater stability between pH 1.0 and 4.0. The degradation rate constant calculated for these pH was 0.0885 x 10-2 min-1 and 0.0689 x 10-2 min-1, respectively. The highest degradation rate constant value was observed at pH 10.0 (0.7418 x 10-2 min-1) followed by pH 0.01 (0.5882 x 10-2 min-1). A major degradation product (DP-1) was observed in all conditions tested. Through LC-MS/MS analysis, DP-1 was identified as a product of nitazoxanide deacetylation. The effect of pH on the stability of nitazoxanide and the kinetic data obtained contribute to a better understanding of the intrinsic stability characteristics of nitazoxanide.

scholarly journals Proficient Photocatalytic and Sonocatalytic Degradation of Organic Pollutants Using CuO Nanoparticles

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Moondeep Chauhan ◽  
Navneet Kaur ◽  
Pratibha Bansal ◽  
Rajeev Kumar ◽  
Sesha Srinivasan ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Rate Constant ◽  
Degradation Mechanism ◽  
Research Work ◽  
Dye Decolorization ◽  
Copper Oxide Nanoparticles ◽  
Cuo Nps ◽  
First Order Kinetics ◽  
Degradation Of Dyes ◽  
The Stability

In recent years, due to the advancement in nanotechnology, advanced oxidation processes (AOPs), especially sonocatalysis and photocatalysis, have become a topic of interest for the elimination of pollutants from contaminated water. In the research work reported here, an attempt has been made to study and establish a physicochemical mechanism for the catalytic activity of copper oxide nanoparticles (CuO NPs) in AOPs using the degradation of dyes as model contaminants. CuO NPs exhibited brilliant sonocatalytic and photocatalytic activities for the degradation of a cationic dye (Victoria Blue) as well as an anionic dye (Direct Red 81). The degradation efficiency of CuO NPs was calculated by analysing the variation in the absorbance of dye under a UV-Vis spectrophotometer. The influence of different operating parameters on the catalytic activity of CuO NPs, such as the amount of catalysts dose, pH of the solution, and the initial dye concentration, was thoroughly investigated. In addition, the kinetic process for the degradation was also examined. It was observed that both dyes exhibited and followed the pseudo-first-order kinetics relation. The rate constant for sonocatalysis was high as compared to photocatalysis. The rate constant for both sonocatalysis and photocatalysis was successfully established, and reusability tests were done to ensure the stability of the used catalysts. To get an insight into the degradation mechanism, experiments were performed by using ⋅OH radical scavengers. The efficacy of CuO NPs for dye decolorization was found to be superior for the sonocatalyst than the photocatalyst.

The reactivity of p-nitrophenyl esters with surfactants in apolar solvents. VI. Structural effects on the reaction of p-nitrophenyl acetate with alkanediamine bis(dodecanoate) salts

1983 ◽  
Vol 36 (5) ◽  
pp. 907 ◽  
Author(s):  
CJ O'Conner ◽  
TD Lomax
Keyword(s):  
Chain Length ◽  
Rate Constant ◽  
Structural Effects ◽  
Detergent Concentration ◽  
Bimolecular Rate Constant ◽  
Head Groups

The rate of decomposition of p-nitrophenyl acetate has been measured in benzene solutions of a series of alkane-α,ω-diamine bis(dodecanoate) salts. Me(CH2)10CO2-+NH3(CH2)NH3N+ -O2C(CH2)10ME(n=2-7,9,10,12) The micellar rate constant is affected by the diamine chain length, and the bimolecular rate constant is affected both by the chain length (and whether the number of carbon atoms is even or odd) and by the acidity of the diammonium head groups. The Br�nsted plot is linear but the slope in creases with increasing detergent concentration.

scholarly journals Stability of unimolecular films of 32P-labelled lecithin

1967 ◽  
Vol 105 (1) ◽  
pp. 401-407 ◽  
Author(s):  
H. Hauser ◽  
R. M. C. Dawson
Keyword(s):  
Pressure Change ◽  
Ion Concentration ◽  
Hydrolysis Rate ◽  
Ion Distribution ◽  
Rapid Perfusion ◽  
Poisson Boltzmann ◽  
Rate Of Hydrolysis ◽  
Poisson Boltzmann Equation ◽  
The Stability ◽  
Hydrolysis Of

1. The stability of monolayers of a highly unsaturated yeast lecithin labelled with 32P has been investigated by a surface radioactivity technique. 2. Lecithin films on distilled water at all surface pressures between 6 and 48dynes/cm. were completely stable on rapid perfusion of the subphase and on addition of ionic amphipathic substances to the film. 3. Ultrasonically treated lecithin added to the subphase caused a slow loss of surface radioactivity but little pressure change. 4. The addition of proteins to the subphase caused negligible changes in the film even when conditions were favourable for electrostatic heterocoagulation and penetration. 5. Lecithin films were not hydrolysed by a strongly acid subphase at room temperature. The very low rate of hydrolysis produced by alkali was proportional to the subphase OH−ion concentration: the apparent activation energy and temperature coefficient (Q10) of the reaction were 14250 cal. and 2·37 respectively. 6. Alkaline hydrolysis of lecithin monolayers was markedly stimulated by adding methanol (10–20%, v/v) to the subphase. The addition of ionic amphipaths to the monolayer had the expected type of effect on the hydrolysis rate, but its magnitude was far less than that suggested by an application of the Poisson–Boltzmann equation for ion distribution at a charged interface (Davies & Rideal, 1963).

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