scholarly journals Aggregation of p-Nitrophenyl Alkanoates in Aqueous Solution. Limitations on Their Use as Substrates in Enzyme Model Studies

1973 ◽  
Vol 51 (21) ◽  
pp. 3494-3498 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Critical Concentration ◽  
Solubility Limit ◽  
Modest Increase ◽  
Model Studies ◽  
Critical Concentrations ◽  
Low Concentrations ◽  
Enzyme Model ◽  
Hydrolysis Of

p-Nitrophenyl alkanoates are aggregated at extremely low concentrations in aqueous solution. Second-order rate constants for imidazole or hydroxide catalyzed hydrolysis are independent of ester concentration up to a critical concentration of ester, and then decrease with increasing ester concentration. The critical concentrations at 25 °C are: p-nitrophenyl hexanoate, 1 × 10−4 M; octanoate, 9.6 × 10−6 M; decanoate, 1.2 × 10−6 M. For the dodecanoate ester, the critical concentration was estimated as ca. 10−7 M. Addition of 10% methanol causes only a modest increase in the critical concentration. The critical concentration probably represents the solubility limit of the ester. The rate constants for the hydrolysis of the longer chain esters evaluated here are significantly larger than those in the literature, suggesting that the earlier work was done using conditions where the esters were aggregated.

The kinetics and mechanisms of the acid-catalysed hydrolysis of t-butyl formate in aqueous solution.

1969 ◽  
Vol 22 (1) ◽  
pp. 19 ◽  
Author(s):  
RA Fredlein ◽  
I Lauder
Keyword(s):  
Aqueous Solution ◽  
Acid Solution ◽  
Rate Constants ◽  
Aqueous Acid ◽  
Hydronium Ion ◽  
Low Concentrations ◽  
Order Of Magnitude ◽  
Catalytic Rate ◽  
Hydrolysis Of ◽  
Tracer Experiments

The hydrolysis of t-butyl formate in aqueous acid solution has been studied over the range 35-83�. At low concentrations of catalysing acid, specific hydronium-ion catalysis is enhanced by the formic acid produced during the reaction. A series of oxygen-18 tracer experiments was performed, taking into account the formation of isobutylene, which is a by-product of hydrolysis by alkyl-oxygen fission. ��� The percentage alkyl-oxygen fission varies from 3 at 35� to 40 at 76�. Catalytic rate constants for reactions by the AAL1 and the AAC2 mechanisms are expressed respectively by the equations ���������������� k?1 = 1016.6exp(-28000/RT)�� 1. mole-1 sec-1���������������� k?2 = 107.8exp(-13600/RT)�� 1. mole-1 sec-1����������������� The rate constants found for the BAL1 mechanism are of order-of- magnitude significance only.

scholarly journals Proteolytic removal of three C-terminal residues of actin alters the monomer-monomer interactions

1993 ◽  
Vol 289 (3) ◽  
pp. 897-902 ◽  
Author(s):  
M Mossakowska ◽  
J Moraczewska ◽  
S Khaitlina ◽  
H Strzelecka-Golaszewska
Keyword(s):  
Electron Microscopy ◽  
Steady State ◽  
Ionic Strength ◽  
Rate Constants ◽  
Initial Rate ◽  
Critical Concentration ◽  
Rate Of Polymerization ◽  
Low Ionic Strength ◽  
Hydrolysis Of

Homogeneous preparations of actin devoid of the three C-terminal residues were obtained by digestion of G-actin with trypsin after blocking proteolysis at other sites by substitution of Mg2+ for the tightly bound Ca2+. Removal of the C-terminal residues resulted in the following: an enhancement of the Mg(2+)-induced hydrolysis of ATP in low-ionic-strength solutions of actin; an increase in the critical concentration for polymerization; a decrease in the initial rate of polymerization; and an enhancement of the steady-state exchange of subunits in the polymer. Electron microscopy indicated an increased fragility of the filaments assembled from truncated actin. The results suggest that removal of the C-terminal residues increases the rate constants for monomer dissociation from the polymer ends and from the oligomeric species.

Stability of the Nerve Gas Antidote BIS (4-Hydroxyiminomethyl-1-Pyridinomethyl) Ether Dichloride (Toxogonin®)

1968 ◽  
Vol 2 (9) ◽  
pp. 234-243 ◽  
Author(s):  
Inga Christenson
Keyword(s):  
Aqueous Solution ◽  
Hydrochloric Acid ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Kinetics Of Hydrolysis ◽  
Dilute Aqueous Solution ◽  
Nerve Gas ◽  
Ph Range ◽  
Kinetics Of ◽  
Hydrolysis Of

The products and kinetics of hydrolysis of the nerve gas antidote bis(4-hydroxyiminomethyl - 1 - pyridinemethyl) ether dichloride (Toxogonin ®) have been investigated. A survey of these studies is given: The hydrolytic reactions were studied in the pH range 1 M hydrochloric acid to 1 M sodium hydroxide at 25, 45, 75 and 85° C. Rate constants were determined in dilute aqueous solution, generally with an initial Toxogonin concentration of 0.01 mg per ml. In addition, a report is given concerning two-year storage of 25 percent (w/v) Toxogonin solutions at pH 2.5, 3.0 and 3.5. The solutions were stored in glass or polypropylene ampuls at 5, 15, 25 and 45°C. At 5 and 15C° decomposition was negligible, at 25 and 45 °C average decomposition was 1.5 percent and 3.3 percent, respectively.

Acid-catalyzed hydrolysis of 2-methylene-1,3-dithiolane. 2. Remarkable effects of β substitution on reversibility of the carbon protonation

1986 ◽  
Vol 64 (6) ◽  
pp. 1116-1123 ◽  
Author(s):  
Tadashi Okuyama ◽  
Masayoshi Toyoda ◽  
Takayuki Fueno
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Isotope Exchange ◽  
Relative Stabilities ◽  
The Third ◽  
Initial Carbon ◽  
Acid Catalyzed ◽  
The Individual ◽  
Individual Rate ◽  
Hydrolysis Of

Hydrolyses of 2-ethylidene-(1b), 2-isopropylidene-(1c), and 2-benzylidene-1,3-dithiolane (1d) were kinetically investigated in aqueous solution. All the individual rate constants involved in this three-step reaction were evaluated. Initial carbon protonation is only partially reversible (k2/k−1 = 1.33, 0.68, and 1.02 for 1b, 1c, and 1d, respectively) at higher pH, while the protonation becomes completely reversible below pH 2 where the third step is rate determining. Complete H–D isotope exchange at the β-carbon of 1b and 1d was observed in deuterium media before appreciable hydrolysis took place. It was demonstrated that reversion from the tetrahedral intermediate 3 to 1 occurs extensively during the reaction in the latter acidity range. Relative stabilities and reactivities of the olefinic substrates 1 are discussed.

scholarly journals Drug Exchange between Albumin Nanoparticles and Erythrocyte Membranes

Nanomaterials ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 47 ◽  
Author(s):  
Bilyana Tacheva ◽  
Boyana Paarvanova ◽  
Ivan Ivanov ◽  
Boris Tenchov ◽  
Radostina Georgieva ◽  
...  
Keyword(s):  
Critical Concentration ◽  
Erythrocyte Membranes ◽  
Erythrocyte Suspension ◽  
Physiological Conditions ◽  
Critical Concentrations ◽  
Albumin Nanoparticles ◽  
Drug Substances ◽  
Drug Concentrations ◽  
Low Concentrations ◽  
Biphasic Effect

The effects of thioridazine (TDZ) and chlorpromazine (CPZ) and bovine serum albumin nanoparticles (BSA-NPs) on erythrocyte membranes have been investigated. Two kinds of hemolytic assays were used; hemolysis under hypotonic conditions and hemolysis in physiological conditions. Under hypotonic conditions for 50% hemolysis, both TDZ and CPZ have a biphasic effect on membranes; namely, stabilization at low concentrations and destabilization after reaching a critical concentration. In physiological conditions, there are other critical concentrations above which both drugs hemolyse the erythrocites. In each case, the critical concentrations of TDZ are lower than those of CPZ, which is consistent with the ratio of their partition coefficients. When BSA-NPs are added to the erythrocyte suspension simultaneously with the drugs, the critical concentrations increase for both drugs. The effect is due to the incorporation of a portion of drug substances into the BSA-nanoparticles, which consequently leads to the decrease of the active drug concentrations in the erythrocyte suspension medium. Similar values of the critical concentrations are found when the BSA-NPs are loaded with the drugs before their addition to the erythrocyte suspension in which case the events of the partition are: desorption of the drug from BSA-NPs, diffusion through the medium, and adsorption on erythrocyte membranes. This result suggests that the drugs are not influenced by the processes of adsorption and desorption onto and out of the BSA-NPs, and that the use of BSA-NPs as drug transporters would allow intravenous administration of higher doses of the drug without the risk of erythrocyte hemolysis.

Kinetics and mechanism of gold(III) incorporation into tetrakis(1-methylpyridium-4-yl)porphyrin in aqueous solution

2004 ◽  
Vol 08 (11) ◽  
pp. 1269-1275 ◽  
Author(s):  
Ahsan Habib ◽  
Masaaki Tabata ◽  
Ying Guang Wu
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Kinetic Data ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
Hydroxyl Group ◽  
Net Charge ◽  
First Order ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of the reaction of the tetrakis(1-methylpyridium-4-yl)porphyrin tetracation, [ H 2( TMPyP )]4+, with gold(III) ions were studied along with equilibria of gold(III) species in aqueous medium at 25°C, I = 0.10 M ( NaNO 3). The equilibrium constants for the formation of [ AuCl 4-n( OH ) n ]- ( n = 0,…,4), defined as β n = [ AuCl 4- n ( OH ) n ]- [ Cl -] n / [ AuCl 4-][ OH -] n were found to be that log β1 = 7.94 ± 0.03, log β2 = 15.14 ± 0.03, log β3 = 21.30 ± 0.05 and log β4 = 26.88 ± 0.05. The overall reaction was first order with respect to each of the total [ Au (III)] and [ H 2 TMPyP 4+]. On the basis of pH dependence on rate constants and the hydrolysis of gold(III), the rate expression can be written as d [ Au ( TMPyP )5+]/ dt = ( k 1[ AuCl 4-] + k2[ AuCl 3( OH )-] + k3[ AuCl 2( OH )2-] + k4[ AuCl ( OH )3-])[ H 2 TMPyP 4+], where k1, k2, k3 and k4 were found to be (2.16 ± 0.31) × 10-1, (6.56 ± 0.19) × 10-1, (1.07 ± 0.24) × 10-1, and (0.29 ± 0.21) × 10-1 M -1. s -1, respectively. The kinetic data revealed that the trichloromonohydroxogold(III) species, [ AuCl 3( OH )]-, is the most reactive. The higher reactivity of [ AuCl 3( OH )]- is explained by hydrogen bonding formation between the hydroxyl group of [ AuCl 3( OH )]- and the pyrrole hydrogen atom of [ H 2( TMPyP )]4+. Furthermore, applying the Fuoss equation to the observed rate constants at different ionic strengths, the apparent net charge of [ H 2( TMPyP )]4+ was calculated to be +3.5.

Polyfluoroorganoboron-Oxygen Compounds. 7. Studies of Conversion of [(C6HnF5-n)B(OMe)3]- Into [(C6HnF5-n)2B(OMe)2]- (n = 0, 1)

2008 ◽  
Vol 73 (12) ◽  
pp. 1681-1692 ◽  
Author(s):  
Nicolai Yu. Adonin ◽  
Vadim V. Bardin ◽  
Hermann-Josef Frohn
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
High Yields ◽  
Hydrolysis Of ◽  
Conversion Of Salts

Conversion of salts Li[(C6HnF5-n)B(OMe)3] (n = 0, 1) into (Li·DME)[(C6HnF5-n)2B(OMe)2] was studied in dichloromethane-DME solution. The observed rate constants k decrease from (21.4 ± 0.9) × 10-3 l mol-1 s-1 (Li[C6F5B(OMe)3]) over (6.99 ± 0.11) × 10-3 l mol-1 s-1 (Li[(2,3,5,6-C6HF4)B(OMe)3]) to (2.94 ± 0.05) × 10-3 l mol-1 s-1 (Li[(2,3,4,6-C6HF4)B(OMe)3]), while Li[(2,3,4,5-C6HF4)B(OMe)3] does not undergo any transformation. Hydrolysis of (Li·DME)[(C6HnF5-n)2B(OMe)2] leads to corresponding borinic acids, whereas treatment of them with aqueous solution of M[HF2] (M = Bu4N, K) acidified with HF results in M[(C6HnF5-n)2BF2] in high yields.

Facile Enrichment and Photocatalytical Degradation of Low Concentration MB in Aqueous Solution

2011 ◽  
Vol 110-116 ◽  
pp. 2308-2315
Author(s):  
Liu Xue Zhang ◽  
Xiu Lian Wang
Keyword(s):  
Electron Microscopy ◽  
Aqueous Solution ◽  
Fine Particles ◽  
X Ray Diffraction ◽  
High Concentration ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Low Concentrations ◽  
Hydrolysis Of

Fine particles of photoactive anatase-type TiO2, prepared by hydrolysis of tetrabutyl orthotitanate and crystallized under microwave (MV) irradiation, were loaded on adsorbent support attapulgite (ATP). The prepared hybrids TiO2-ATP were characterized with transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and X-ray diffraction (XRD) and photoactivity properties were evaluated separately. The substrates of target were adsorbed on the adsorbent support, and then a high concentration environments of the substrate was formed around the loaded TiO2, resulting in an increase in the photodestruction rate. One of the most interesting features of the resulting catalysts with low titania contain (<30%) is their fast decantability in comparison with that of TiO2. This way one of the most important drawbacks of photocatalysis, the catalysts separation from the solution, was overcome by simple sedimentation and decantation. The low concentrations MB may be removed through enrichment and photodegradation using the prepared TiO2-ATP photocatalyst.

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