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  • entropy  (2)
  • UmuC  (1)
  • 5'-O-demethyl-8-O-methyl-dioncophylline A
  • 1995-1999  (2)
  • 1985-1989  (1)
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  • 1995-1999  (2)
  • 1985-1989  (1)
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  • 1
    ISSN: 1572-8927
    Keywords: Deuterium chloride ; deuterium oxide ; electrochemical cell ; emf ; enthalpy ; entropy ; free energy ; heat capacity ; isotope effect ; standard potential ; thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The themodynamic properties of solutions of deuterium chloride (DCl) in deuterium oxide (D2O) have been determined from emf measurements of the electrochemical cell without transference from 5 to 50°C, and from 0.002 to 1.0 mol-kg−1. The standard potential of the silver/silver chloride electrode relative to the platinum/deuterium electrode has been determined. An equation for the Gibbs energy as a function of temperature has been derived from which the enthalpy, entropy, and heat capacity have been computed. Equations for the activity coefficient and the osmotic coefficient of DCl in D2O have been developed. The excess Gibbs energy of the solution and the excess partial molar free energy as a function of temperature have been calculated, from which the other excess thermodynamic properties have been computed. The values for the heat capacity and the apparent molar heat capacity have been compared with calorimetric data in the literature. The relative partial molar enthalpy has been calculated. The solvent isotope effect on the excess thermodynamic functions is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Escherichia coli ; Salmonella typhimurium ; SOS mutagenesis ; Chimeric proteins ; UmuC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract UnlikeEscherichia coli, the closely related bacteriumSalmonella typhimurium is relatively unresponsive to the mutagenic effects of DNA-damaging agents. Previous experiments have suggested that these phenotypic differences might result from reduced activity of theS. typhimurium UmuC protein. To investigate this possibility, we have taken advantage of the high degree of homology between the UmuC proteins ofE. coli andS. typhimurium and have constructed a series of plasmid-encoded chimeric proteins. The possibility that the phenotypic differences might be due to differential expression of the respective UmuC proteins was eliminated by constructing chimeric proteins that retained the first 25 N-terminal amino acids of either of the UmuC proteins (and presumably the same translational signals), but substituting the remaining 397 C-terminal amino acids with the corresponding segments from the reciprocal operon. Constructs expressing mostlyE. coli UmuC were moderately proficient for mutagenesis whereas those expressing mostlyS. typhimurium UmuC exhibited much lower frequencies of mutation, indicating that the activity of the UmuC protein ofS. typhimurium is indeed curtailed. The regions responsible for this phenotype were more precisely localized by introducing smaller segments of theS. typhimurium UmuC protein into the UmuC protein ofE. coli. While some regions could be interchanged with few or no phenotypic effects, substitution of residues 212–395 and 396–422 ofE. coli UmuC with those fromS. typhimurium resulted in reduced mutability, while substitution of residues 26–59 caused a dramatic loss of activity. We suggest, therefore, that the primary cause for the poor mutability ofS. typhimurium can be attributed to mutations located within residues 26–59 of theS. typhimurium UmuC protein.
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  • 3
    ISSN: 1572-8927
    Keywords: Dissociation constant ; buffers ; NaMOPS ; temperature dependence ; emf ; Gibbs energy ; enthalpy ; entropy ; heat capacity ; zwitterion ; liquid junction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The second dissociation constant pK2 of 3-(N-morpholino)propanesulfonic acid (MOPS) has been determined at eight temperatures from 5 to 55°C by measurements of the emf of cells without liquid junction, utilizing hydrogen electrodes and silver–silver chloride electrodes. The pK2 has a value of 7.18 ± 0.001 at 25°C and 7.044 ± 0.002 at 37°C. The thermodynamic quantities ΔG°, ΔH°, ΔS°, and ΔC p o have been derived from the temperature coefficients of the pK 2. This buffer at ionic strength I = 0.16 mol-kg−1 close to that of blood serum, has been recommended as a useful secondary pH standard for measurements of physiological fluids. Five buffer solutions with the following compositions were prepared: (a) equimolal mixture of MOPS (0.05 mol-kg−1) + NaMOPS, (0.05 mol-kg−1); (b( MOPS (0.05 mol-kg−1) + NaMOPS (0.05 mol-kg−1) + NaCl (0.05 mol-kg−1); (c) MOPS (0.05 mol-kg−1) + NaMOPS (0.05 mol-kg−1); + NaCl (0.11mol-kg−1); (d) MOPS (0.08 mol-kg−1) + NaMOPS (0.08 mol-kg−1); and (e)MOPS (0.08 mol-kg−1) + NaMOPS (0.08 mol-kg−1) + NaCl (0.08 mol-kg−1).The pH values obtained by using the pH meter + glass electrode assembly are compared with those measured from a flow–junction calomel cell saturated with KCl (cell B), as well as those obtained from cell (A) without liquid junction at 25 and 37°C. The conventional values of the liquid junction potentials E j have been obtained at 25 and 37°C for the physiological phosphate reference solution as well as for the MOPS buffers (d) and (e) mentioned above.
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