Authors:Hernane T. Barcelos, Luclecia D. Nunes, Guilherme W. Tavares, Edesio F. C. Alcantara, and Alexandre G. S. Prado
every case, all samples were analyzed in triplicate.
The adsorption of divalentcations by SiHa was followed calorimetrically by titration using an adiabatic calorimeter PARR 6755. In a typical experiment
Authors:A. Hernández-Medina, A. Negrón-Mendoza, S. Ramos-Bernal, and G. Sánchez-Mejorada
Thermally stimulated luminescence and optical absorption measurements were performed on NaCl single crystals, both single
and double doped. The NaCl single crystals were exposed to gamma rays from a 60Co source at both low and room temperatures. The radiation-induced defects were mainly F and H centers, and the absorption
bands for the F centers were centered at 464 nm. Bleaching with F-light showed the participation of the F center generated
by gamma radiation on the TL phenomenon. The results suggest that NaCl single crystals, both single and double doped can be
used as dosimeters, within certain doses.
Double nitrates of Na and K having the composition 2MINO3·LnIII(NO3)3·2H2O(LnIII=Pr, Nd, Sm, Eu, Gd, Tb and Dy) and of Ni and Cu with the composition 3MII(NO3)2·2LnIII(NO3)3·24H2O (LnIII=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) have been prepared and their -radiolytic decomposition studied up to 500 kGy. G(NO
) values of K double nitrates at 230 kGy follow the order Dy3+>Pr3+=Nd3+=Sm3+>Tb3+>Eu3+> Gd3+·G(NO
) for NI double nitrates are higher than those of Cu double nitrates. Variation of G(NO
) with cationic radii and the number of f electrons in lanthanide ion show a minimum at Eu. Thermal decomposition studies of double nitrates were also carried out.
The kinetics of the exchange between MnO or Mn3O4 and Co2+, Cu2+, Ni2+, or Zn2+ ions in solution, was determined by measuring the γ-activity of56Mn acquired by the solution after shaking with the neutron irradiated solid. The results indicated a fast exchange followed
by a slower apparently diffusion-controlled exchange. The exchange capacity increased in the series: Co2+<Ni2+<Cu2+=Zn2+ for MnO and Ni2+<Co2+<Zn2+<Cu2+ for Mn3O4. The trends could not be satisfactorily explained by the ionic radii or crystal field stabilisation-energies. In the case
of MnO, the results were discussed in terms of the estimated standard enthalpy change of the exchange reaction.
, Mn2+, Co2+, Ni2+; L = hexaethyl p-tert-butylcalixarene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants
of the ML2+ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the following order: Cd2+ < Ca2+ < Mn2+ < Cu2+, Zn2+ <
Authors:Vera da S. Augusto Filha, Oberto da Silva, J. da Costa, Albaneide Wanderley, Maria da Fonseca, and Luiza Arakaki
Calorimetric titration was applied to study
the interaction of zinc, cadmium and mercury on surface of silica gel modified
with 2-aminoethanethiol, using 3-chloropropyltrimetoxysilane as precursor
silylating agent. The anchored Sil–SNH2 surface
gave 0.70 mmol g–1 of molecules covalently
bonded per gram of silica. This surface displayed a chelating moiety containing
sulfur and nitrogen basic centers, which are potentially capable of extracting
cations from aqueous solutions, such as MCl2 (M=Zn, Cd, Hg). This process of extraction was carried
out by the batch method when similar chemisorption isotherms were observed
for all cations.
The data were adjusted to modified Langmuir equation.
The sequence of the maximum retention capacity was Hg>Cd>Zn. The processes
of cation interactions showed exothermic enthalpies. The calculated ΔG values are in agreement with the spontaneity of
the proposed reactions and conformed to the values found by using Langmuir
model applied to these systems. The endothermic entropic values, as expected,
indicated that the reactions are favorable.
Authors:J. Orbán, Sz. Halasi, G. Papp, Szilvia Barkó, and Beáta Bugyi
The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases
of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties
of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free
energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated
form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated
form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between
the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between
the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of
these proteins as well.
Authors:G. Papp, Beáta Bugyi, Z. Ujfalusi, Sz. Halasi, and J. Orbán
The effect of pH was characterised on the thermal stability of magnesium saturated skeletal and cardiac α-actin isoforms with
differential scanning calorimetry (DSC) at pH 7.0 and 8.0. The calorimetric curves were further analysed to calculate the
enthalpy and transition entropy changes. The activation energy was also determined to describe the energy consumption of the
initiation of the thermal denaturation process. Although the difference in Tmvalues is too small to interpret the difference between the a-actin isoforms, the values of the activation energy indicated
that the α-skeletal actin is probably more stable compared to the α-cardiac actin. The difference in the activation energies
indicated that lowering the pH can produce a more stable protein matrix in both cases of the isoforms. The larger range of
the difference in the values of the activation energies suggested that the α-cardiac actin is probably more sensitive to the
change of the pH compared to the α -skeletal actin.
Mono- and divalent cations of trace elements were not retained at all on a cation-exchange column in the presence of a colloid. When the colloid was dissolved, cations sorbed and eluted from the column in a normal way.