Synthesis, characterization and thermal behaviour of solid-state compounds of folates with some bivalent transition metals ions

Solid-state M-L compounds, where M stands for bivalent Mn, Co, Ni, Cu and Zn and L is folate (C19H17N7O6), have been synthesized. Simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC), X-ray powder diffractometry, infrared spectroscopy (FTIR), TG-DSC coupled to FTIR, elemental analysis and high-resolution continuum source flame atomic absorption spectrometry technique (HR-CS FAAS) were used to characterize and to study the thermal behaviour of these compounds. The results provided information concerning the composition, dehydration, thermal stability and thermal decomposition. �� 2013 Akad��miai Kiad��, Budapest, Hungary.

Effect of divalent metal ions on the activity and stability of ��-galactosidase isolated from Kluyveromyces lactis

In this study, it was demonstrated that ��-galactosidase can be deactivated and reactivated with EDTA and divalent metal ions. The enzyme was deactivated after 20 minutes in EDTA solution. Maximal deactivation at the lowest EDTA concentration (10-3 mol.L-1) occurred in the presence of Tris-HCl buffer (pH 7.0). The enzyme recovered 50% of its initial activity after 10 minutes at Mg2+concentrations higher than 0.1 mmol.L-1. Experimental concentrations of 0.1 mmol.L-1 Mn2+ and 1.0 mmol.L-1 Co2+ were sufficient to reactivate the enzyme to around 300% of the control activity for the Mn2+ ion and nearly 100% for the Co2+ ion. The enzyme gradually lost its activity when the Co2+ concentration was 10-2 mol.L-1. Ni2+ and Zn2+ were unable to restore the catalytic activity. Km app and Vmax app were 1.95 �� 0.05 mmol.L-1 and 5.40 �� 0.86x10-2 mmol.min-1.mg-1, with o-NPG as substrate. Optimal temperature and pH were 34oC and 7.5. The half-life (t1/2) at 30��C was 17.5 min for the holoenzyme and 11.0 min for the apoenzyme. With respect to pH variation, the apoenzyme proved to be more sensitive than the holoenzyme. Keywords: ��-galactosidase. Divalent metallic ions. Enzyme activity. Stability. RESUMO Efeito de ��ons met��licos divalentes na atividade e estabilidade da ��-galactosidase isolada de Kluyveromyces lactis Este estudo demonstra como a ��-galactosidase pode ser desativada e reativada usando EDTA e ��ons met��licos divalentes. A enzima foi desativada ap��s 20 minutos na presen��a de EDTA. Desativa����o m��xima para a menor concentra����o de EDTA (10-3 mol.L-1) ocorreu na presen��a do tamp��o Tris-HCl. A enzima recuperou 50% de sua atividade inicial ap��s 10 minutos na presen��a de Mg2+ em concentra����es superiores a 0,1mmol.L-1. Concentra����es de 10-4 e 10-3mol.L-1 de Mn2+ e Co2+ foram suficientes para reativar a enzima em 300% comparado ao controle de ��ons Mn2+ e aproximadamente 100% para ��ons Co2+. A enzima perdeu gradualmente a sua atividade quando a concentra����o foi de 10-2 mol.L-1. Ni2+ e Zn2+ foram incapazes de restabelecer a atividade catal��tica. Km app e Vmax app foram 1,95 �� 0,05 mmol.L-1 e 5,40 �� 0,86 x 10-2 mmol.min-1.mg-1. A temperatura e pH ��timos foram 34��C e 7,5. A meia vida da holoenzima foi de 17,5 min a 30��C e para a apoenzima foi de 11,0 min a 30��C. Quanto �� varia����o de pH, a apoenzima provou ser mais sens��vel que a holoenzima. Palavras-chave: ��-galactosidase. ��ons met��licos divalentes. Atividade enzim��tica. Estabilidade.

Thermal behaviour of nicotinic acid, sodium nicotinate and its compounds with some bivalent transition metal ions

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

On the Electrochemical Deposition and Dissolution of Divalent Metal Ions

The deposition of Cu2+ and Zn2+ from aqueous solution has been investigated by a combination of classical molecular dynamics, density functional theory, and a theory developed by the authors. For both cases, the reaction proceeds through two one-electron steps. The monovalent ions can get close to the electrode surface without losing hydration energy, while the divalent ions, which have a stronger solvation sheath, cannot. The 4s orbital of Cu interacts strongly with the sp band and more weakly with the d band of the copper surface, while the Zn4s orbital couples only to the sp band of Zn. At the equilibrium potential for the overall reaction, the energy of the intermediate Cu+ ion is only a little higher than that of the divalent ion, so that the first electron transfer can occur in an outer-sphere mode. In contrast, the energy of the Zn+ ion lies too high for a simple outer-sphere reaction to be favorable; in accord with experimental data this suggests that this step is affected by anions.

Simple and direct potentiometric determination of potassium ions in biodiesel microemulsions at a glassy carbon electrode modified with nickel(II) hexacyanoferrate nanoparticles

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Electrochemical Properties of the Oxo-Manganese-Phenanthroline Complex Immobilized on Ion-Exchange Polymeric Film and Its Application as Biomimetic Sensor for Sulfite Ions

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Effect of Zn2+ ions on the structure, morphology and optical properties of CaWO4 microcrystals

Conselho Nacional de Desenvolvimento Cient��fico e Tecnol��gico (CNPq)

Effect of Fe-doping on the structural, microstructural, optical, and ferroeletric properties of Pb1/2Sr1/2Ti1-xFexO3 oxide prepared by spin coating technique

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Effect of Ag nanoparticles on the radiative properties of tellurite glasses doped with Er3+, Yb3+ and Tm3+ ions

Conselho Nacional de Desenvolvimento Cient��fico e Tecnol��gico (CNPq)

Effects of the addition of ions barium on the structural and electrical properties of PZT ceramic

Lead zirconate titanate, with Zr/Ti ratio of 53/47 was prepared by the polymeric precursor method. It was investigated the barium (II) modification at 0.0, 0.2, 0.4 and 0.6 mol% in substitution to the lead (II) cation in A site of perovskite structure. The powder samples were characterized by XRD and the diffraction patterns were used to Rietveld refinement. The percentages of tetragonal and rhombohedral phases and a systematic study of the effect of barium (II) on the morphology and the dielectric properties of PZT were carried out. The results showed that the tetragonal phase is favored and the ceramic density is improved with the barium (II) insertion. The Curie temperature (Tc) is increased besides the slight reduction of dielectric constant (Kc).

Streptococcus mutans adhesion and releasing of metallic ions in dental alloys

AIM: To evaluate the adherence of Streptococcus mutans to the surface of the amalgam and copper/aluminum alloy samples and also evaluate the release of metallic ions. METHODS: The prepared medium was changed every 72 h and analyzed by atomic absorption spectrophotometer. Samples were removed from the prepared medium at 15, 30, 48 and 60 days. RESULTS: The result shows that ions released were statistically different among all groups, and so were both biofilm and pits formation and the corrosion induced by the S. mutans in both types of samples. SEM observation of the samples immersed in the prepared medium with S. mutans showed adherence of microorganisms on the whole surface, in all groups. CONCLUSIONS: The S. mutans adhere to both amalgam and copper/aluminum alloy causing corrosion of those restorations. S. mutans produced a greater ions release in Cu/Al alloy; in amalgam, the ions release was not influenced by exposure to S. mutans.

Local structure and hybridization states in Ba0.9Ca0.1Ti1-xZrxO3 ceramic compounds: Correlation with a normal or relaxor ferroelectric character

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Synergy between polyaniline and OMt clay mineral in Langmuir-Blodgett films for the simultaneous detection of traces of metal ions

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Study on determination and removal of metallic ions from aqueous and alcoholic solutions using a new POSS adsorbent

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Electrochemical behavior and corrosion resistance of Ti-15Mo alloy in naturally-aerated solutions, containing chloride and fluoride ions

Conselho Nacional de Desenvolvimento Cient��fico e Tecnol��gico (CNPq)