Equilibrium reactions of n-butanethiol with some conjugated heteroenoid compounds

1968 ◽  
Vol 46 (5) ◽  
pp. 775-781 ◽  
Author(s):  
R. B. Pritchard ◽  
C. E. Lough ◽  
D. J. Currie ◽  
H. L. Holmes
Keyword(s):  
Functional Group ◽  
Equilibrium Constants ◽  
Phenyl Group ◽  
Reverse Reaction ◽  
Experimental Conditions ◽  
Standard Methods ◽  
Conjugated Systems ◽  
Equilibrium Reactions ◽  
Measurable Rate

The reactions of 2-benzal-1,3-indanediones and the cyano-containing benzalmalononitriles, ethyl benzalcyanoacetates, benzalcyanoacetamides, and benzalcyanoacetanilides with n-butanethiol at 25 °C in 20% ethanol – 80% pH 7 buffer attain equlibrium at a rate too fast to measure by standard methods. The equilibrium constants have been calculated and these in turn related to Hammett σ and Taft σ* constants. The differences in the reactions of these and other gem difunctional systems which react virtually completely with n-butanethiol under the same experimental conditions and at a measurable rate, are attributed to participation of the functional group cis to the phenyl group in the reverse reaction. It is shown that n-butanethiol adds to cinnamalacetophenone by a 1,4-mechanism and the reactions of this nucleophile with similar compounds having extended conjugated systems are discussed.

Free-base corroles: determination of deprotonation constants in non-aqueous media

2007 ◽  
Vol 11 (04) ◽  
pp. 269-276 ◽  
Author(s):  
Jing Shen ◽  
Zhongping Ou ◽  
Jianguo Shao ◽  
Michał Gałęzowski ◽  
Daniel T. Gryko ◽  
...  
Keyword(s):  
Equilibrium Constants ◽  
Aqueous Media ◽  
Free Base ◽  
Organic Base ◽  
Experimental Conditions ◽  
Spectral Changes ◽  
Base Analysis ◽  
Uv Visible ◽  
The Given

A series of free-base corroles with different electron-donating or electron-withdrawing substituents were reacted with piperidine, 4-aminopyridine, 2-methylimidazole, 2-aminopyridine or pyridine in PhCN and the UV-visible spectral changes monitored during conversion of ( Cor ) H 3 to [( Cor ) H 2]- as a function of the concentration and strength of the added organic base. Analysis of the UV-visible spectral changes as a function of the added base concentration enabled calculation of equilibrium constants ( logK ) for deprotonation of each corrole under the given experimental conditions. Relationships are examined between the experimentally measured logK values and previously published spectroscopic and structural properties of the compounds.

Honeybee flight muscle phosphoglucose isomerase: matching enzyme capacities to flux requirements at a near-equilibrium reaction

1997 ◽  
Vol 200 (8) ◽  
pp. 1247-1254 ◽  
Author(s):  
J Staples ◽  
R Suarez
Keyword(s):  
Ionic Strength ◽  
Flight Muscle ◽  
Equilibrium Constants ◽  
Muscle Metabolism ◽  
Phosphoglucose Isomerase ◽  
Glycolytic Flux ◽  
Cell Water ◽  
Economical Design ◽  
Equilibrium Reactions ◽  
Low Ionic Strength

In honeybee flight muscle, there are close matches between physiological flux rates and the maximal activities (Vmax; determined using crude homogenates) of key enzymes catalyzing non-equilibrium reactions in carbohydrate oxidation. In contrast, phosphoglucose isomerase (PGI), which catalyzes a reaction believed to be close to equilibrium, occurs at Vmax values greatly in excess of glycolytic flux rates. In this study, we measure the Vmax of flight muscle PGI, the kinetic parameters of the purified enzyme, the apparent equilibrium constants for the reaction and the tissue concentrations of substrate and product. Using the Haldane equation, we estimate that the forward flux capacity (Vf) for PGI required to achieve physiological glycolytic flux rates is between 800 and 1070 units ml-1 cell water, approximately 45­60 % of the empirically measured Vmax of 1770 units ml-1 cell water at optimal pH (8.0) and low ionic strength (no added KCl). When measured at physiological pH (7.0) and ionic strength (120 mmol l-1 KCl) with saturating levels of substrate, PGI activity is 1130 units ml-1 cell water, a value close to the calculated Vf. These results reveal a very close match between predicted and measured PGI flux capacities, and support the concept of an economical design of muscle metabolism in systems working at very high metabolic rates.

scholarly journals Probing the Kinetic and Thermodynamic Fingerprints of Anti-EGF Nanobodies by Surface Plasmon Resonance

2020 ◽  
Vol 13 (6) ◽  
pp. 134
Author(s):  
Salvador Guardiola ◽  
Monica Varese ◽  
Marta Taulés ◽  
Mireia Díaz-Lobo ◽  
Jesús García ◽  
...  
Keyword(s):  
Surface Plasmon Resonance ◽  
Surface Plasmon ◽  
Plasmon Resonance ◽  
Molecular Mechanisms ◽  
Tumour Progression ◽  
Equilibrium Constants ◽  
Target Antigen ◽  
Biological Drugs ◽  
Experimental Conditions ◽  
Technical Features

Despite the widespread use of antibodies in clinical applications, the precise molecular mechanisms underlying antibody–antigen (Ab–Ag) interactions are often poorly understood. In this study, we exploit the technical features of a typical surface plasmon resonance (SPR) biosensor to dissect the kinetic and thermodynamic components that govern the binding of single-domain Ab or nanobodies to their target antigen, epidermal growth factor (EGF), a key oncogenic protein that is involved in tumour progression. By carefully tuning the experimental conditions and transforming the kinetic data into equilibrium constants, we reveal the complete picture of binding thermodynamics, including the energetics of the complex-formation transition state. This approach, performed using an experimentally simple and high-throughput setup, is expected to facilitate mechanistic studies of Ab-based therapies and, importantly, promote the rational development of new biological drugs with suitable properties.

Reaction of Glutathione with Conjugated Carbonyls

1975 ◽  
Vol 30 (7-8) ◽  
pp. 466-473 ◽  
Author(s):  
Hermann Esterbauer ◽  
Helmward Zöllner ◽  
Norbert Scholz
Keyword(s):  
Catalytic Effect ◽  
Biological Activities ◽  
Equilibrium Constants ◽  
Reverse Reaction ◽  
Mesityl Oxide ◽  
Forward Reaction ◽  
First Order ◽  
First Order Kinetics ◽  
Proton Donors ◽  
The Stability

Abstract 1. GSH reacts with conjugated carbonyls according to the equation: G SH+R-CH=CH-COR⇆R-CH(SG)-CH2-COR. The forward reaction follows second order, the reverse reaction first order kinetics. It is assumed that this reaction reflects best the ability of conjugated carbonyls to inactivate SH groups in biological systems. 2. The rate of forward reaction increases with pH approx. parallel with αSH. Besides OH- ions also proton donors (e. g. buffers) increase the rate. The catalytic effect of pH and buffer is inter­ preted in view of the reaction mechanism. 3. The equilibrium constants as well as the rate constants for forward (k1) and reverse reaction show an extreme variation depending on the carbonyl structure. Acrolein and methyl vinyl ketone (kt = 120 and 32 mol-1 sec-1 , resp.) react more rapidly than any other carbonyl to give very stable adducts (half-lives for reverse reaction 4.6 and 60.7 days, resp.). Somewhat less reactive are 4-hydroxy-2-alkenals and 4-ketopentenoic acid (k1 between 1 and 3 mol-1 sec-1), but they also form very stable adducts showing half-lives between 3.4 and 19 days. All other carbonyl studied react either very slowly (e. g. citral, ethly crotonate, mesityl oxide, acrylic acid) or form very labile adducts (crotonal, pentenal, hexenal, 3-methyl-butenone). Comparing biological activities of con­ jugated carbonyls their reactivity towards HS (k1) and the stability of the adducts must be considered.

Aluminium(III) and Iron(III) 1,2-Diphenolato Complexes: a Potentiometric Study

1985 ◽  
Vol 38 (5) ◽  
pp. 659 ◽  
Author(s):  
JA Kennedy ◽  
HKJ Powell
Keyword(s):  
Aqueous Solution ◽  
Potentiometric Titration ◽  
Protocatechuic Acid ◽  
Acid System ◽  
Experimental Conditions ◽  
Potentiometric Study ◽  
Hydroxo Complexes ◽  
Equilibrium Reactions ◽  
Ternary Metal ◽  
Metal Ligand

The equilibrium reactions between aluminium(III) and the phenols catechol (LH2), protocatechuic acid (LH3) and catechin (LH4), and between iron(III) and protocatechuic acid have been studied by potentiometric titration in aqueous solution, I 0.10M ( KCl ), 25°C. Stability constants are reported for the mononuclear diphenolato complexes AlLHn-2, Al(LHn-2)2and Al(LHn-2)3, and the hydroxo complexes Al(OH)LHn-2 and Al(OH)(LHn-2)2, n = 2 ( catechol ) or 4 ( catechin ). For protocatechuic acid, the carboxylate -coordinated species lLH22+ and the species AlLH + (carboxyl- protonated ) are also postulated. Analogous species were characterized for the iron(III)- protocatechuic acid system. Stoichiometric end-points were obtained only if an excess of ligand was used (L/M > 4). Monomeric and polymeric aluminium- hydroxo species and ternary metal- ligand - hydroxo species were found to be unimportant under the experimental conditions employed.

Solvent and acidity effects on the UV-visible spectra and protonation-deprotonation of free-base octaethylcorrole

2008 ◽  
Vol 12 (01) ◽  
pp. 1-10 ◽  
Author(s):  
Zhongping Ou ◽  
Hongxia Sun ◽  
Weihua Zhu ◽  
Zulin Da ◽  
Karl M. Kadish
Keyword(s):  
Equilibrium Constants ◽  
Visible Spectrum ◽  
Soret Band ◽  
Free Base ◽  
Tetrabutylammonium Hydroxide ◽  
Experimental Conditions ◽  
Visible Spectra ◽  
Meso Position ◽  
Uv Visible ◽  
Strong Acids

The UV-visible spectrum of free-base octaethylcorrole, (OECor) H 3, was recorded in thirteen different nonaqueous solvents as well as in a mixed acetonitrile/acid solvent containing one of seven different acids. Spectra were also measured in seven different solutions of neat concentrated acid and in CH 3 CN containing piperidine or tetrabutylammonium hydroxide as an added base. The overall data was analyzed as a function of solvent acidity or basicity parameters and the number of protons on the central nitrogens of the macrocycle, the predominant form of the corrole in these solutions being respresented as (OECor)H 3, [ (OECor)H 4]+, [ (OECor)H 2]− or [ (OECor)H ]2− where OECor = trianion of octaethylcorrole. The mono-protonated corrole, [ (OECor)H 4]+, is formed in concentrated acetic acid or in CH 3 CN containing 0.10 M trifluoroacetic acid, H 2 SO 4, HCl , H 3 PO 4 or HClO 4. The mono-deprotonated corrole, [ (OECor)H 2]−, is generated in piperidine while doubly deprotonated [ (OECor)H ]2− exists in solutions of tetrabutylammonium hydroxide. An addition of protons to the macrocycle of [ (OECor)H 4]+ also occurs in the presence of concentrated strong acids and this results in a loss of the characteristic Soret band of the corrole leading presumably to [ (OECor)H 5]2+ where the second proton has been added to a meso-position of the macrocycle. The UV-visible spectral changes upon formation of [ (OECor)H 4]+, [ (OECor)H 2]− or [ (OECor)H ]2− in CH 3 CN were monitored during a titration with the relevent acid or base and equilibrium constants for protonation or deprotonation of (OECor)H 3 were determined using standard equations. The measured logK values are compared to protonation and deprotonation constants obtained for two related corroles and two related porphyrins under the same experimental conditions.

scholarly journals Thermodynamics of metal-ligand bond formation. VIII. Pyridine adducts of zinc(II) β-diketonates

1973 ◽  
Vol 26 (11) ◽  
pp. 2537 ◽  
Author(s):  
DR Dakternieks ◽  
DP Graddon
Keyword(s):  
Benzene Solution ◽  
Equilibrium Constants ◽  
Bond Formation ◽  
Formation Constants ◽  
Adduct Formation ◽  
Enthalpies Of Formation ◽  
Calorimetric Titration ◽  
Experimental Conditions ◽  
Metal Ligand ◽  
Ligand Bond

Equilibrium constants and enthalpies in benzene solution are reported for the formation of 1 : 1-adducts of pyridine with four zinc(II) complexes of β-diketones, determined by calorimetric titration. Adduct formation constants at 30�C fall in the range 300-2000 and enthalpies of formation lie between -15 and - 34 kJ mol-1. Though the enthalpies of formation differ little from those of corresponding copper(II) complexes, the adducts are about a hundred times more stable. The pyridine adduct of bis(2,2,6,6-tetramethylheptane-3,5-dionato)zinc(II) is entropy-stabilized relative to those of other complexes. No evidence was obtained for the addition of a second molecule of pyridine under the experimental conditions used.

scholarly journals A Versatile New Reagent for Nitrosation under Mild Conditions

2021 ◽  
Author(s):  
Jordan D. Galloway ◽  
Cristian Sarabia ◽  
James C. Fettinger ◽  
Hrant Hratchian ◽  
Ryan Baxter
Keyword(s):  
Room Temperature ◽  
Computational Analysis ◽  
Functional Group ◽  
Nitroso Compounds ◽  
Chemical Reagent ◽  
Experimental Conditions ◽  
X Ray ◽  
Mild Conditions ◽  
Rotational Isomers ◽  
First Time

We report a new chemical reagent for transnitrosation under mild experimental conditions. This new reagent is stable to air and moisture across a broad range of temperatures, and is effective for transnitrosation in multiple solvents. Compared to traditional nitrosation methods, our reagent shows high functional group tolerance for substrates that are susceptible to oxidation or reversible transnitrosation. Several challenging nitroso-compounds are accessed here for the first time, including 15N isotopologues. X-ray data confirms two rotational isomers of the reagent are configurationally stable at room temperature, although only one isomer is effective for transnitrosation. Computational analysis describes the energetics of rotamer interconversion, including interesting geometry-dependent hybridization ef-fects.

Uranyl acetate staining under different conditions of preparation, storage and use

1990 ◽  
Vol 48 (3) ◽  
pp. 726-727
Author(s):  
R.H.M. Cross ◽  
A.N. Hodgson ◽  
R.T.F. Bernard
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Biological Tissue ◽  
Storage Time ◽  
Uranyl Acetate ◽  
Experimental Conditions ◽  
Thin Sections ◽  
Standard Methods ◽  
Gut Epithelium ◽  
Transmission Electron

Uranyl acetate is routinely used in the staining of thin sections of biological tissue for transmission electron microscopy. Although many methods for its preparation and use have been described, there is seldom reference to the reasons for variations in concentration, solvent, storage time and staining time. Likewise, possible variations in the effects of staining under different conditions are largely ignored. In order to gain clarity on this issue an attempt has been made to test three variables (solvent, storage time and use in light or dark) under controlled experimental conditions.The tissues used for the experiment were the testis of a marine limpet, the gut epithelium of a fresh-water catfish, and the kidney of a rat; all of which were fixed and embedded by standard methods. The uranyl acetate solutions were prepared at the outset of the experiment and dispensed into small volumes and stored in the dark at 4°C until required.

1.14 Palladium(I)-Mediated Reactions

2021 ◽  
Author(s):  
G. Maestri ◽  
A. Serafino
Keyword(s):  
Visible Light ◽  
Functional Group ◽  
Halogen Bond ◽  
Cross Coupling ◽  
Palladium Complexes ◽  
Synthetic Methods ◽  
Experimental Conditions ◽  
Alkyl Radicals ◽  
Molecular Architectures

AbstractSeveral elegant reactivities can be observed in reactions involving palladium(I) species, allowing access to molecular architectures that are often beyond the capabilities of popular diamagnetic palladium complexes. This review presents three main axes of research in this context, which have mostly emerged in the last decade. Reactions promoted by visible light enable synthetic methods that are unusual in their mild experimental conditions coupled with remarkably broad functional group tolerance. The use of discrete palladium(I) dimers as precatalysts allows one to perform a wide set of cross-coupling protocols, such as Kumada and Negishi reactions, and chalcogenation reactions, with a surgical precision on the carbon—halogen bond that is initially activated. The generation of alkyl radicals and palladium(I) species through a thermal strategy proves useful for the elaboration of substrates with several polyfluorinated fragments, which are otherwise elusive coupling partners for more common two-electron processes.

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