scholarly journals Recognition of hydrogen isotopomers by an open-cage fullerene

2013 ◽  
Vol 371 (1998) ◽  
pp. 20110629 ◽  
Author(s):  
Yasujiro Murata ◽  
Shih-Ching Chuang ◽  
Fumiyuki Tanabe ◽  
Michihisa Murata ◽  
Koichi Komatsu
Keyword(s):  
Equilibrium Constants ◽  
Equilibrium Mixture ◽  
Size Difference ◽  
Binding Affinities ◽  
Kinetic Isotope ◽  
Molecular Sizes ◽  
Lower Temperature ◽  
Kinetics Of ◽  
Pressure Hydrogen

We present our study on the recognition of hydrogen isotopes by an open-cage fullerene through determination of binding affinity of isotopes H 2 /HD/D 2 with the open-cage fullerene and comparison of their relative molecular sizes through kinetic-isotope-release experiments. We took advantage of isotope H 2 /D 2 exchange that generated an equilibrium mixture of H 2 /HD/D 2 in a stainless steel autoclave to conduct high-pressure hydrogen insertion into an open-cage fullerene. The equilibrium constants of three isotopes with the open-cage fullerene were determined at various pressures and temperatures. Our results show a higher equilibrium constant for HD into open-cage fullerene than the other two isotopomers, which is consistent with its dipolar nature. D 2 molecule generally binds stronger than H 2 because of its heavier mass; however, the affinity for H 2 becomes larger than D 2 at lower temperature, when size effect becomes dominant. We further investigated the kinetics of H 2 /HD/D 2 release from open-cage fullerene, proving their relative escaping rates. D 2 was found to be the smallest and H 2 the largest molecule. This notion has not only supported the observed inversion of relative binding affinities between H 2 and D 2 , but also demonstrated that comparison of size difference of single molecules through non-convalent kinetic-isotope effect was applicable.

The retroaldol reaction of 3-methyl-2-butenal

1983 ◽  
Vol 61 (1) ◽  
pp. 171-178 ◽  
Author(s):  
J. Peter Guthrie ◽  
Brian A. Dawson
Keyword(s):  
Sodium Hydroxide ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Aqueous Sodium Hydroxide ◽  
Initial Increase ◽  
Aqueous Sodium ◽  
Rate Determining Step ◽  
Kinetics Of

In aqueous sodium hydroxide solutions at 25 °C, 3-methyl-2-butenal, 1c, undergoes retroaldol cleavage to acetone and acetaldehyde. The kinetics of the retroaldol reaction were followed spectrophotometrically at 242 nm and showed simple first order behavior. When 3-methyl-3-hydroxybutanal, 2c, was added to aqueous sodium hydroxide solutions at 25 °C, there was an initial increase in absorbance at 242 nm, attributed to formation of 1c, followed by a 20-fold slower decrease; the rate of the slow decrease matches the rate of disappearance of 1c under the same conditions. Analysis of the kinetics allows determination of the three rate constants needed to describe the system: khyd = 0.00342; kdehyd = 0.00832; kretro = 0.0564; all M−1 s−1. The equilibrium constant for enone hydration is 0.41. Rate constants for the analogous reactions for acrolein and crotonaldehyde could be obtained from the literature. There is a reasonable rate–equilibrium correlation for the retroaldol step. For the enone hydration step, rate and equilibrium constants respond differently to replacement of hydrogen by methyl. It is proposed that this results from release of strain after the rate-determining step by rotation about a single bond; this decrease in strain is reflected in the equilibrium constant but not in the rate constant.

Kinetics, isotope effects of the reaction of 1-(4-nitrophenyl)-1-nitroalkanes with DBU in tetrahydrofuran and chlorobenzene solvents

1990 ◽  
Vol 68 (12) ◽  
pp. 2242-2248 ◽  
Author(s):  
Wlodzimierz Galezowski ◽  
Arnold Jarczewski
Keyword(s):  
Proton Transfer ◽  
Isotope Effects ◽  
Equilibrium Constants ◽  
Ion Pairs ◽  
Proton Transfer Reaction ◽  
Kinetic Isotope ◽  
Enthalpy Of Activation ◽  
Deuteron Transfer ◽  
Proton Transfer Reactions ◽  
Kinetics Of

The kinetics of the reaction of[Formula: see text](R = Me, Et, i-Pr; NPNE, NPNP, MNPNP respectively; L is H or D) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) base in tetrahydrofuran (THF) and chlorobenzene (CB) solvents are reported. The products of these proton transfer reactions are ion pairs absorbing at λmax = 460–480 nm. The equilibrium constants in THF were [Formula: see text]and in CB [Formula: see text]for NPNE, NPNP, MNPNP respectively. The thermodynamic parameters of the reactions are also quoted. The substrate reacts with DBU in both THF and CB solvents in a normal second-order proton transfer reaction. In the case of deuteron transfer, isotopic D/H exchange is much faster than internal return. The reactions show low values of enthalpy of activation ΔH* = 14.3, 18.1, 24.2 and 13.0, 15.1, 18.6 kJmol−1 for NPNE, NPNP, and MNPNP in THF and CB respectively, and large negative entropies of activation −ΔS* = 141, 139, 146; 140, 146, 160 J mol−1 deg−1 for the same sequence of substrates and solvents. The kinetic isotope effects are large, (kH/kD)20°c = 12.2, 13.0, 10.1; 12.9, 12.0, 10.2 for the above sequence of substrates and solvents, and show no difference with changes in either steric hindrance of the C-acids or polarity of the solvents. Keywords: proton transfer, kinetic isotope effect.

Kinetics of the Metallation of Coproporphyrin-I in Water with Cadmium(II) and Manganese(II)

1998 ◽  
Vol 02 (02) ◽  
pp. 139-144 ◽  
Author(s):  
VITO BARTOCCI ◽  
RITA GIOVANNETTI ◽  
ENRICO CARSETTI
Keyword(s):  
Reaction Rate ◽  
Equilibrium Constants ◽  
Kinetic Method ◽  
Molar Absorptivity ◽  
Solution Properties ◽  
Alkaline Ph ◽  
Influence Of Temperature On ◽  
Kinetics Of ◽  
Coproporphyrin I

The reaction of 3,8,13,18-tetramethyl-21H,23H-porphine-2,7,12,17-tetrapropionic acid or coproporphyrin-I ( CPI ) with cadmium(II) was studied spectrophotometrically and its kinetic and equilibrium constants were determined. The influence of temperature on the reaction rate was also studied. At different ratios of [ CPI ]/[ Cd(II) ] two types of complex were formed: CdII ( CPI ) and ( CdII )2( CPI ); an investigation of the solution properties and the mechanism of aggregation of ( CdII )2( CPI ) at different pH were performed. It is verified that cadmium(II) accelerates the reaction of the incorporation of manganese(II) into CPI by the substitution of cadmium(II) with manganese(II) in the CdII ( CPI ) complex; the kinetics and mechanism of this substitution reaction at alkaline pH were studied. A sensitive kinetic method for the determination of cadmium(II) at ppb levels has been established; the molar absorptivity and the Sandell's sensitivity (for A = 0.001) of the recommended procedure at 458 nm and 300 s after the start of the reaction are (6.175 ± 0.026) × 105 1 mol−1 cm−1 and (1.820 ± 0.008) × 10−4 μg cm−2 respectively.

The mechanisms of oxidation of formaldehyde and formic acid by ions of chromium (VI), vanadium (V) and cobalt (III)

1963 ◽  
Vol 274 (1359) ◽  
pp. 480-499 ◽  
Keyword(s):  
Formic Acid ◽  
Chromic Acid ◽  
Isotope Effects ◽  
Secondary Alcohol ◽  
Kinetics Of Oxidation ◽  
Chromium Vi ◽  
Kinetic Isotope ◽  
Kinetics Of ◽  
Cyclic Intermediate

The kinetics of oxidation of formaldehyde, formic acid and their deuterated isomers have been studied with chromic acid (part A) and also with vanadium (v), and cobalt (III) as oxidants (part B). In each case the reaction mechanism resembles that for the oxidation of a secondary alcohol by the same oxidant. Thus formaldehyde is oxidized in its hydrated form, H 2 C(OH) 2 . The quantitative study of kinetic and solvent effects leads to clarification of further details concerning secondary stages in the oxidations effected by chromic acid, whilst the determination of thermodynamic parameters for the oxidations by one electron abstracting reagents (part B) shows that any direct correlation between activation energies and kinetic isotope effects involves unwarrantable assumptions. It is probable that these reactions proceed through cyclic intermediate complexes.

Oxidation of geosmin and MIB in water using O3/H2O2: kinetic evaluation

2006 ◽  
Vol 6 (2) ◽  
pp. 63-69 ◽  
Author(s):  
G. Park ◽  
M. Yu ◽  
J.-Y. Koo ◽  
W.H. Joe ◽  
H. Kim
Keyword(s):  
Drinking Water ◽  
Water Utilities ◽  
Kinetic Evaluation ◽  
Blue Green Algae ◽  
Treatment Processes ◽  
Odor Thresholds ◽  
Lower Temperature ◽  
Kinetics Of ◽  
Ozonation Process

Tastes and odors (T&Os) of drinking water have been a major issue for water utilities in Korea, due to the ever-increasing consumers' demand on drinking water quality and complaints on T&Os. Among the T&Os causing chemicals in water, the most common and problematic ones are geosmin and 2-MIB, which are produced by blue–green algae and actinomycetes. The odors of the chemicals are characterized earthy and musty/camphorous. Since the reported odor thresholds of geosmin and 2-MIB are as low as 4.0 and 8.5 ng/L, respectively, they are not readily removed by conventional water treatment processes or by simple ozonation. Therefore, oxidation of the chemicals using hydrogen peroxide (H2O2) along with ozone (O3) has been tried as an alternative. In this study, kinetics of geosmin and 2-MIB ozonation at different initial O3 doses, H2O2/O3 ratios, and temperatures were evaluated. In short, a significant promotion of geosmin and 2-MIB ozonation rate was observed at higher H2O2/O3 ratios at lower temperature; therefore, geosmin and 2-MIB could be successfully removed from water. However, when an ozonation process is designed ozone residual should be considered for satisfactory disinfection; H2O2 addition may promote O3 decomposition and may have an adverse effect on disinfection. Therefore, determination of H2O2 and O3 doses should be carefully made for achieving both disinfection and T&Os removal.

scholarly journals Conformational kinetics reveals affinities of protein conformational states

2015 ◽  
Vol 112 (30) ◽  
pp. 9352-9357 ◽  
Author(s):  
Kyle G. Daniels ◽  
Yang Suo ◽  
Terrence G. Oas
Keyword(s):  
Ligand Binding ◽  
Conformational Change ◽  
Conformational Changes ◽  
Rate Constants ◽  
Conformational Dynamics ◽  
Forward Rate ◽  
Binding Affinities ◽  
Conformational States ◽  
Kinetics Of

Most biological reactions rely on interplay between binding and changes in both macromolecular structure and dynamics. Practical understanding of this interplay requires detection of critical intermediates and determination of their binding and conformational characteristics. However, many of these species are only transiently present and they have often been overlooked in mechanistic studies of reactions that couple binding to conformational change. We monitored the kinetics of ligand-induced conformational changes in a small protein using six different ligands. We analyzed the kinetic data to simultaneously determine both binding affinities for the conformational states and the rate constants of conformational change. The approach we used is sufficiently robust to determine the affinities of three conformational states and detect even modest differences in the protein’s affinities for relatively similar ligands. Ligand binding favors higher-affinity conformational states by increasing forward conformational rate constants and/or decreasing reverse conformational rate constants. The amounts by which forward rate constants increase and reverse rate constants decrease are proportional to the ratio of affinities of the conformational states. We also show that both the affinity ratio and another parameter, which quantifies the changes in conformational rate constants upon ligand binding, are strong determinants of the mechanism (conformational selection and/or induced fit) of molecular recognition. Our results highlight the utility of analyzing the kinetics of conformational changes to determine affinities that cannot be determined from equilibrium experiments. Most importantly, they demonstrate an inextricable link between conformational dynamics and the binding affinities of conformational states.

Determination of microbiological activity during the processing of frost damaged sugar beets

2014 ◽  
pp. 228-231 ◽  
Author(s):  
Maciej Wojtczak ◽  
Aneta Antczak-Chrobot ◽  
Edyta Chmal-Fudali ◽  
Agnieszka Papiewska
Keyword(s):  
Sugar Beet ◽  
Microbiological Activity ◽  
Microbiological Contamination ◽  
Sugar Beets ◽  
Bacterial Metabolites ◽  
Kinetics Of

The aim of the study is to evaluate the kinetics of the synthesis of dextran and other bacterial metabolites as markers of microbiological contamination of sugar beet.

Studies on the Behavior Some Paints in Electro-insulating Fluid Based on Vegetable Esters

2018 ◽  
Vol 69 (5) ◽  
pp. 1139-1144
Author(s):  
Iosif Lingvay ◽  
Adriana Mariana Bors ◽  
Livia Carmen Ungureanu ◽  
Valerica Stanoi ◽  
Traian Rus
Keyword(s):  
Structural Changes ◽  
Oxidation Processes ◽  
High Oleic ◽  
Painting Materials ◽  
Insulating Paper ◽  
Different Types ◽  
Mechanism And Kinetics ◽  
Kinetics Of ◽  
Natural Ester

For the purpose of using three different types of painting materials for the inner protection of the transformer vats, their behavior was studied under actual conditions of operation in the transformer (thermal stress in electro-insulating fluid based on the natural ester in contact with copper for electro-technical use and electro-insulating paper). By comparing determination of the content in furans products (HPLC technique) and gases formed (by gas-chromatography) in the electro-insulating fluid (natural ester with high oleic content) thermally aged at 130 �C to 1000 hours in closed glass vessels, it have been found that the presence the investigated painting materials lead to a change in the mechanism and kinetics of the thermo-oxidation processes. These changes are supported by oxygen dissolved in oil, what leads to decrease both to gases formation CO2, CO, H2, CH4, C2H4 and C2H6) and furans products (5-HMF, 2-FOL, 2 -FAL and 2-ACF). The painting materials investigated during the heat treatment applied did not suffer any remarkable structural changes affecting their functionality in the electro-insulating fluid based on vegetable esters.

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