scholarly journals Inhibition of staphylococcal α-toxin. A kinetic evaluation of aromatic polysulphonic acids as inhibitors of haemolysis

1968 ◽  
Vol 108 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Margaret Robson Wright ◽  
J. P. Arbuthnott ◽  
I. R. W. Lominski
Keyword(s):  
Inhibitory Activity ◽  
Maximum Rate ◽  
Lag Time ◽  
Test Compound ◽  
Rabbit Erythrocyte ◽  
Compound I ◽  
Kinetic Evaluation ◽  
Ph Values ◽  
Inhibitory Compounds ◽  
Kinetics Of

1. The effect of a number of aromatic polysulphonic acids on the kinetics of haemolysis of rabbit erythrocyte suspensions by crude staphylococcal α-toxin was studied at pH8·6 and 6·8. 2. All of the inhibitory compounds caused an increase in the prelytic lag time (τ) of the sigmoid haemolysis curves, an increase in the time to reach 50% haemolysis (t½) and a decrease in the maximum rate of haemolysis (Rmax.). The most inhibitory compounds caused a 50% decrease in Rmax. at concentrations between 0·1 and 0·2mm. 3. The effect of pH varied considerably: compounds (I) and (II) were almost equally inhibitory at both pH values, compounds (IV) and (IX) were more inhibitory at pH6·8 than at pH8·6, and compounds (VII), (VIII), (X), (XI) and (XII) were more inhibitory at pH8·6. 4. Increased time of premixing α-toxin with compound (I) caused increased inhibition. 5. An attempt was made, where possible, to relate the inhibitory activity to the structure of the test compound.

Prothrombin Evaluation as Obtained by Kinetics Studies of Antigen-Antibody Reaction in a Laser Nephelometer

1984 ◽  
Vol 52 (01) ◽  
pp. 015-018 ◽  
Author(s):  
A Girolami ◽  
A Sticchi ◽  
R Melizzi ◽  
L Saggin ◽  
G Ruzza
Keyword(s):  
Liver Cirrhosis ◽  
Cirrhotic Patient ◽  
Maximum Rate ◽  
Serum Proteins ◽  
Clotting Factors ◽  
Kinetics Studies ◽  
Maximum Value ◽  
Time Required ◽  
Antigen Antibody ◽  
Kinetics Of

SummaryLaser nephelometry is a technique which allows the evaluation of the concentration of several serum proteins and clotting factors. By means of this technique it is also possible to study the kinetics of the reaction between antigen and antibody. We studied the kinetics of the reaction between prothrombin and an antiprothrombin antiserum using several prothrombins namely: Prothrombin Padua, prothrombin Molise, which are two congenital dysprothrombinemias, cirrhotic, coumarin or normal prothrombins. Different behaviors in the kinetics of the reactions were shown even when the concentration of prothrombins was about the same in all plasma tested. These differences were analyzed by means of a computer (Apple II 48 RAM) programmed to solve four unknown equations (Rodbard’s equation). From the data so obtained one can see that when voltages at the beginning and at the end of the reaction are in all cases about the same, a clear difference in the time required to reach half the maximum value of the voltage can still be demonstrated. This parameter, which is expressed in minutes, is longer in coumarin and prothrombin Molise than in controls. On the contrary it is shorter in prothrombin Padua and has about the same value of controls in the cirrhotic patient. Moreover the time at which the maximum rate is obtained is longer in coumarin and prothrombin Molise than in controls and shorter in liver cirrhosis and prothrombin Padua. In conclusion data obtained show that coumarin prothrombin behaves in a different way from cirrhotic prothrombin and also that there is a different behaviour between the two congenital dysprothrombinemias.

Derivatives of isatin in aqueous solution. I. Kinetics of ring opening of Isatin-5-sulfonate

1981 ◽  
Vol 34 (2) ◽  
pp. 365 ◽  
Author(s):  
H Stunzi
Keyword(s):  
Ring Opening ◽  
Rate Of Change ◽  
Spectroscopic Methods ◽  
Ph Values ◽  
Buffer Region ◽  
Pka Value ◽  
Back Titration ◽  
Kinetics Of ◽  
Derivatives Of ◽  
Sulfonate Anion

The reactions of isatin-5-sulfonate anion (si-) which cause a hysteresis in pH titrations were studied by pH-metric and n.m.r, spectroscopic methods. Rapid alkalimetric titrations [I 0.15 M (KNO3),37�] gave the pKa value corresponding to the addition of OH- to si- [pKa(ring) 9.55]. The slow ring opening to the sulfonatoisatate dianion (sia2-) led to a drift of the pH values towards an equilibrium buffer region. Its pKa, value [pKa(eq) 3.44] corresponds to the reaction si-+H2O ↔ sia 2-+H+ Rapid back-titration gave the pKa value of the ring-opened species Hsia- [pKa(open) c. 1.3]. The rate law for the ring opening d[sia]/dt=k2 [siOH](OH)+k1*[si] was obtained from the rate of change of pH. N-Methylisatin-5-sulfonate behaves analogously.

Vulcanization of Rubber in the Presence of N,N-Diethyl-2-Benzothiazolylsulfenamide as Accelerator

1960 ◽  
Vol 33 (2) ◽  
pp. 361-372 ◽  
Author(s):  
B. A. Dogadkin ◽  
O. N. Beliatskaya ◽  
A. B. Dobromyslova ◽  
M. S. Feldshtein
Keyword(s):  
Induction Period ◽  
Maximum Rate ◽  
Initial Period ◽  
Pure Oxygen ◽  
Butadiene Rubber ◽  
Sulfur Vulcanization ◽  
Analogous Manner ◽  
Chemical Crosslinks ◽  
Main Period ◽  
Kinetics Of

Abstract 1. The vulcanization of rubber in the presence of N,N-diethyl-2-benzothiazolylsulfenamide is characterized by an S-shaped curve for the addition of sulfur with an initial induction period in the reaction. The modulus and number of crosslinks are changed in an analogous manner to the structure of the vulcanizate. 2. The energy of activation of the addition of sulfur in the initial period is equal to 30 kcal per mole as against 14 kcal per mole in the main period. 3. The induction period is increased if the sodium-butadiene rubber is purified from alkali. 4. Molecular oxygen present in the compound being vulcanized decreases the induction period and increases the rate of the addition of the sulfur in the main period. An induction period is not observed when vulcanization is carried out in an atmosphere of pure oxygen. 5. The interaction of N,N-diethyl-2-benzothiazolylsulfenamide with rubber (in the absence of sulfur) at vulcanization temperatures is accompanied by the formation of MBT, diethylamine, and the addition of the elements of the accelerator to the rubber. The kinetics of this process were studied. 6. The interaction of N,N-diethyl-2-benzothiazolyl sulfenamide with rubber leads to the formation of chemical crosslinks between the molecules of rubber (the effect of vulcanization). 7. The change of N,N-diethyl-2-benzothiazolyl sulfenamide under the conditions of normal sulfur vulcanization has the same character as in the interaction of it with rubber. The kinetics of the formation of MBT have a maximum which coincides with the maximum rate of the addition of sulfur to the rubber. 8. A mechanism is presented for the vulcanization and acceleration actions of N,N-diethyl-2-benzothiazolyl sulfenamide which provides for the extraction of hydrogen by the accelerator radicals from the molecular chains of the rubber with the formation of MBT, diethylamine and polymer radicals which are able to interact with the sulfur.

scholarly journals Kinetics of thiamin cleavage by sulphite

1969 ◽  
Vol 113 (4) ◽  
pp. 611-615 ◽  
Author(s):  
J. Leichter ◽  
M. A. Joslyn
Keyword(s):  
Aqueous Solutions ◽  
Rate Constant ◽  
Sulphur Dioxide ◽  
First Order ◽  
Ph Values ◽  
Rate Of Reaction ◽  
Kinetics Of

Results are presented on the rate of thiamin cleavage by sulphite in aqueous solutions as affected by temperature (20–70°), pH(2·5–7·0), and variation of the concentration of either thiamin (1–20μm) or sulphite (10–5000μm as sulphur dioxide). Plots of the logarithm of percentage of residual thiamin against time were found to be linear and cleavage thus was first-order with respect to thiamin. At pH5 the rate was also found to be proportional to the sulphite concentration. In the pH region 2·5–7·0 at 25° the rate constant was 50m−1hr.−1 at pH5·5–6·0, and decreased at higher or lower pH values. The rate of reaction increased between 20° and 70°, indicating a heat of activation of 13·6kcal./mole.

Growth of Salmonella Enteritidis in the presence of quorum sensing signaling compounds produced by Pseudomonas aeruginosa

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Weijia He ◽  
Huamei Yang ◽  
Xiang Wang ◽  
Hongmei Li ◽  
Qingli Dong
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Quorum Sensing ◽  
Salmonella Enteritidis ◽  
Culture Supernatant ◽  
Lag Time ◽  
Bacterial Communication ◽  
Homoserine Lactones ◽  
Positive Effects ◽  
Kinetics Of

Abstract Quorum sensing (QS) can exist in food-related bacteria and potentially affect bacterial growth through acyl-homoserine lactones (AHLs). To verify the role of QS compounds in the cell-free supernatant, this study examined the effect of supernatant extracted from Pseudomonas aeruginosa culture on the growth kinetics of Salmonella Enteritidis. The results showed that the lag time (λ) of S. Enteritidis was apparently reduced (p < 0.05) under the influence of P. aeruginosa culture supernatant compared with the S. Enteritidis culture supernatant. HPLC-MS/MS test demonstrated that AHLs secreted by P. aeruginosa were mainly C14-HSL with a content of 85.71 μg/mL and a small amount of 3-oxo-C12-HSL. In addition, the commercially synthetic C14-HSL had positive effects on the growth of S. Enteritidis, confirming once again that the growth of S. Enteritidis was affected by AHL metabolized by other bacteria and the complexity of bacterial communication.

Kinetics of the oxidation of reduced nicotinamide adenine dinucleotide by horseradish peroxidase compounds I and II

1986 ◽  
Vol 64 (4) ◽  
pp. 323-327 ◽  
Author(s):  
Mohammed A. Kashem ◽  
H. Brian Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Active Site ◽  
Nicotinamide Adenine Dinucleotide ◽  
Ph Dependence ◽  
Transient State ◽  
Nicotinamide Adenine ◽  
Compound I ◽  
Single Ionization ◽  
Reduced Nicotinamide Adenine Dinucleotide ◽  
Kinetics Of

The transient state kinetics of the oxidation of reduced nicotinamide adenine dinucleotide (NADH) by horseradish peroxidase compound I and II (HRP-I and HRP-II) was investigated as a function of pH at 25.0 °C in aqueous solutions of ionic strength 0.11 using both a stopped-flow apparatus and a conventional spectrophotometer. In agreement with studies using many other substrates, the pH dependence of the HRP-I–NADH reaction can be explained in terms of a single ionization of pKa = 4.7 ± 0.5 at the active site of HRP-I. Contrary to studies with other substrates, the pH dependence of the HRP-H–NADH reaction can be interpreted in terms of a single ionization with pKa of 4.2 ± 1.4 at the active site of HRP-II. An apparent reversibility of the HRP-II–NADH reaction was observed. Over the pH range of 4–10 the rate constant for the reaction of HRP-I with NADH varied from 2.6 × 105 to5.6 × 102 M−1 s−1 and of HRP-II with NADH varied from 4.4 × 104 to 4.1 M−1 s−1. These rate constants must be taken into consideration to explain quantitatively the oxidase reaction of horseradish peroxidase with NADH.

Spatiotemporal control over the co-conformational switching in pH-responsive flavylium-based multistate pseudorotaxanes

2015 ◽  
Vol 185 ◽  
pp. 361-379 ◽  
Author(s):  
Ana Marta Diniz ◽  
Nuno Basílio ◽  
Hugo Cruz ◽  
Fernando Pina ◽  
A. Jorge Parola
Keyword(s):  
Molecular Organization ◽  
Present System ◽  
Spectroscopic Techniques ◽  
Ph Responsive ◽  
Conformational Switching ◽  
Ph Values ◽  
Stable Species ◽  
Ph Dependent ◽  
Spatiotemporal Control ◽  
Kinetics Of

A multistate molecular dyad containing flavylium and viologen units was synthesized and the pH dependent thermodynamics of the network completely characterized by a variety of spectroscopic techniques such as NMR, UV-vis and stopped-flow. The flavylium cation is only stable at acidic pH values. Above pH ≈ 5 the hydration of the flavylium leads to the formation of the hemiketal followed by ring-opening tautomerization to give the cis-chalcone. Finally, this last species isomerizes to give the trans-chalcone. For the present system only the flavylium cation and the trans-chalcone species could be detected as being thermodynamically stable. The hemiketal and the cis-chalcone are kinetic intermediates with negligible concentrations at the equilibrium. All stable species of the network were found to form 1 : 1 and 2 : 1 host : guest complexes with cucurbit[7]uril (CB7) with association constants in the ranges 105–108 M−1 and 103–104 M−1, respectively. The 1 : 1 complexes were particularly interesting to devise pH responsive bistable pseudorotaxanes: at basic pH values (≈12) the flavylium cation interconverts into the deprotonated trans-chalcone in a few minutes and under these conditions the CB7 wheel was found to be located around the viologen unit. A decrease in pH to values around 1 regenerates the flavylium cation in seconds and the macrocycle is translocated to the middle of the axle. On the other hand, if the pH is decreased to 6, the deprotonated trans-chalcone is neutralized to give a metastable species that evolves to the thermodynamically stable flavylium cation in ca. 20 hours. By taking advantage of the pH-dependent kinetics of the trans-chalcone/flavylium interconversion, spatiotemporal control of the molecular organization in pseudorotaxane systems can be achieved.

scholarly journals Monoamine Oxidase Inhibitory Activity of Biflavonoids from Branches of Garcinia gardneriana (Clusiaceae)

2017 ◽  
Vol 12 (4) ◽  
pp. 1934578X1701200 ◽  
Author(s):  
Maria Angélica Recalde-Gil ◽  
Luiz Carlos Klein-Júnior ◽  
Carolina dos Santos Passos ◽  
Juliana Salton ◽  
Sérgio Augusto de Loreto Bordignon ◽  
...  
Keyword(s):  
Monoamine Oxidase ◽  
Inhibitory Activity ◽  
Ethanol Extract ◽  
Ethyl Acetate Fraction ◽  
Spectrometric Data ◽  
Mao B ◽  
Inhibitory Compounds ◽  
Mao A ◽  
Mao Activity

Garcinia gardneriana is chemically characterized by the presence of biflavonoids. Taking into account that flavonoids are able to inhibit monoamine oxidase (MAO) activity, in the present study, the chemical composition of the branches’ extract of the plant is described for the first time and the MAO inhibitory activity of the isolated biflavonoids was evaluated. Based on spectroscopic and spectrometric data, it was possible to identify volkesiflavone, morelloflavone (1), Gb-2a (2) and Gb-2a-7- O-glucoside (3) in the ethyl acetate fraction from ethanol extract of the branches. Compounds 1-3 were evaluated in vitro and demonstrated the capacity to inhibit MAO-A activity with an IC50 ranging from 5.05 to 10.7 μM, and from 20.7 to 66.2 μM for MAO-B. These inhibitions corroborate with previous IC50 obtained for monomeric flavonoids, with a higher selectivity for MAO-A isoform. The obtained results indicate that biflavonoids might be promising structures for the identification of new MAO inhibitory compounds.

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