scholarly journals Thermodynamic and kinetic analysis of the Escherichia coli thioredoxin-C′ fragment complementation system

1999 ◽  
Vol 339 (3) ◽  
pp. 721-727 ◽  
Author(s):  
Alokesh K. GHOSHAL ◽  
Chittoor P. SWAMINATHAN ◽  
Celestine J. THOMAS ◽  
Avadhesha SUROLIA ◽  
Raghavan VARADARAJAN
Keyword(s):  
Escherichia Coli ◽  
Fluorescence Spectroscopy ◽  
Room Temperature ◽  
Intact Protein ◽  
Titration Calorimetry ◽  
Peptide Fragments ◽  
State Process ◽  
Α Helix ◽  
Kinetics Of ◽  
Covalent Complex

Escherichia coli thioredoxin was cleaved with CNBr at its single Met residue at position 37, which lies in the middle of a long α-helix. The two fragments, 1-37 and 38-108, were purified and characterized by using CD and fluorescence spectroscopy. Both fragments lack structure at neutral pH and room temperature. The secondary and tertiary structural contents of the non-covalent complex formed on the mixing of the two peptide fragments are 47% and 35% of the intact protein respectively. The thermodynamics and kinetics of fragment association were characterized by titration calorimetry and stopped-flow fluorescence spectroscopy. Single phases were observed for both association and dissociation, with rate constants at 298 K of kon = 4971±160 M-1·s -1 and koff = 0.063±0.009 s-1 respectively. The ratio kon/koff was very similar to the binding constant determined by titration calorimetry, suggesting that binding is a two-state process. The values for ∆Cp, ∆H0 and ∆G0 at 298 K for dissociation of the complex were 5.7 kJ·mol-1·K-1, 45.3 kJ·mol-1 and 29.8 kJ·mol-1 respectively. The value for ∆H0 was linearly dependent on temperature from 8-40 °C, suggesting that ∆Cp is independent of temperature. The values for ∆Cp and ∆G0 are very similar to the corresponding values for the unfolding of intact thioredoxin at 25 °C. However, both ∆H0 and ∆S are significantly more positive for dissociation of the complex, suggesting a decreased hydrophobic stabilization of the complex relative to the situation for intact thioredoxin.

Survival of Microorganisms in Stored Pasta

1979 ◽  
Vol 42 (4) ◽  
pp. 330-334 ◽  
Author(s):  
M. K. RAYMAN ◽  
J.-Y. D'AOUST ◽  
B. ARIS ◽  
C. MAISHMENT ◽  
R. WASIK
Keyword(s):  
Escherichia Coli ◽  
Saccharomyces Cerevisiae ◽  
Room Temperature ◽  
Penicillium Expansum ◽  
Prolonged Storage ◽  
E Coli ◽  
Death Kinetics ◽  
D Values ◽  
Aspergillus Repens ◽  
Kinetics Of

Numbers of Staphylococcus aureus, Saccharomyces cerevisiae and Penicillium expansum in artificially contaminated pasta declined exponentially during storage at room temperature; corresponding D values ranged from 18–21 days, 40–45 days and 130–160 days. In contrast to the rapid death kinetics of Aspergillus repens and Escherichia coli, Streptococcus faecium survived after 180 days of storage. These results suggest that streptococci are more reliable than E. coli as indicators of fecal contamination in pasta. Detection of Salmonella infantis and Salmonella typhimurium after 360 days indicates that prolonged storage of pasta is not effective for decontamination of infected products.

Investigation of irradiation-induced nucleation processes in silicon and germanium

1995 ◽  
Vol 53 ◽  
pp. 224-225
Author(s):  
Harry A. Atwater ◽  
C.M. Yang ◽  
K.V. Shcheglov
Keyword(s):  
Room Temperature ◽  
Crystal Size ◽  
Initial Distribution ◽  
Engineering Control ◽  
Size Evolution ◽  
Silicon And Germanium ◽  
Ge Quantum Dot ◽  
And Control ◽  
Germanium Quantum Dots ◽  
Kinetics Of

Studies of the initial stages of nucleation of silicon and germanium have yielded insights that point the way to achievement of engineering control over crystal size evolution at the nanometer scale. In addition to their importance in understanding fundamental issues in nucleation, these studies are relevant to efforts to (i) control the size distributions of silicon and germanium “quantum dots𠇍, which will in turn enable control of the optical properties of these materials, (ii) and control the kinetics of crystallization of amorphous silicon and germanium films on amorphous insulating substrates so as to, e.g., produce crystalline grains of essentially arbitrary size.Ge quantum dot nanocrystals with average sizes between 2 nm and 9 nm were formed by room temperature ion implantation into SiO2, followed by precipitation during thermal anneals at temperatures between 30°C and 1200°C[1]. Surprisingly, it was found that Ge nanocrystal nucleation occurs at room temperature as shown in Fig. 1, and that subsequent microstructural evolution occurred via coarsening of the initial distribution.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

Kinetics of the Thermal Disappearance of Radicals Formed During the Radiolysis of Aspartic Acid

2009 ◽  
Vol 59 (12) ◽  
Author(s):  
Mihai Contineanu ◽  
iulia Contineanu ◽  
Ana Neacsu ◽  
Stefan Perisanu
Keyword(s):  
Thermal Resistance ◽  
Aspartic Acid ◽  
Room Temperature ◽  
Esr Spectra ◽  
Complex Mechanism ◽  
Radical Species ◽  
Mechanisms Of Formation ◽  
Kinetics Of

The radiolysis of the isomers L-, D- and DL- of the aspartic acid, in solid polycrystalline state, was investigated at room temperature. The analysis of their ESR spectra indicated the formation of at least two radicalic entities. The radical, identified as R3, resulting from the deamination of the acid, exhibits the highest concentration and thermal resistance. Possible mechanisms of formation of three radical species are suggested, based also on literature data. The kinetics of the disappearance of radical R3 indicated a complex mechanism. Three possible variants were suggested for this mechanism.

The Reactivity of Different Active Forms of Sodium Carbonate with Respect to Sulfur Dioxide

1992 ◽  
Vol 57 (11) ◽  
pp. 2302-2308
Author(s):  
Karel Mocek ◽  
Erich Lippert ◽  
Emerich Erdös
Keyword(s):  
Thermal Decomposition ◽  
Liquid Phase ◽  
Sulfur Dioxide ◽  
Specific Surface ◽  
Surface Area ◽  
Sodium Carbonate ◽  
Room Temperature ◽  
Active Form ◽  
The Other ◽  
Kinetics Of

The kinetics of the reaction of solid sodium carbonate with sulfur dioxide depends on the microstructure of the solid, which in turn is affected by the way and conditions of its preparation. The active form, analogous to that obtained by thermal decomposition of NaHCO3, emerges from the dehydration of Na2CO3 . 10 H2O in a vacuum or its weathering in air at room temperature. The two active forms are porous and have approximately the same specific surface area. Partial hydration of the active Na2CO3 in air at room temperature followed by thermal dehydration does not bring about a significant decrease in reactivity. On the other hand, if the preparation of anhydrous Na2CO3 involves, partly or completely, the liquid phase, the reactivity of the product is substantially lower.

On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

2021 ◽  
pp. 009524432110203
Author(s):  
Sudhir Bafna
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Weight Loss ◽  
Oxygen Consumption ◽  
Dwell Time ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Kinetics Of ◽  
Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

Electrochemical Kinetics of Ag|Ag+and TMPD|TMPD+•in the Room-Temperature Ionic Liquid [C4mpyrr][NTf2]; toward Optimizing Reference Electrodes for Voltammetry in RTILs

2007 ◽  
Vol 111 (37) ◽  
pp. 13957-13966 ◽  
Author(s):  
Emma I. Rogers ◽  
Debbie S. Silvester ◽  
Sarah E. Ward Jones ◽  
Leigh Aldous ◽  
Christopher Hardacre ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Room Temperature ◽  
Room Temperature Ionic Liquid ◽  
Electrochemical Kinetics ◽  
Reference Electrodes ◽  
Kinetics Of
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