Magnetic nanoparticles can promote many attractive functions in biomedicine, which may contribute to the prevention of human disease but also may be potentially harmful. In the present study, the interaction of Fe 2 O 3 nanoparticles with human hemoglobin (Hb) was studied by fluorescence, circular dichroism and UV/vis spectroscopies. Fluorescence data revealed that the fluorescence quenching of Hb by Fe 2 O 3 nanoparticles was the result of the formed complex of Fe 2 O 3 nanoparticles-Hb. Binding constants and other thermodynamic parameters were determined at three different temperatures. The hydrophobic interactions are the predominant intermolecular forces to stabilize the complex. Circular dichroism studies did not show any changes in the content of secondary structure of hemoglobin after Fe 2 O 3 nanoparticles treatment. This study provides important insight into the interaction of Fe 2 O 3 nanoparticles with hemoglobin, which may be a useful guideline for further using of these nanoparticles in biomedical applications.
A novel monofunctional benzyldithiocarbamate, C(6)H(5)CH(2)NHCSSNa (I), and a bifunctional p-xylidine-bis(dithiocarbamate), NaSSCNHCH(2)C(6)H(4)CH(2)NHCSSNa (II), as sodium salts, were synthesized by reaction between p-xylylenediamine or benzylamine with CS(2) in the presence of NaOH. They were characterized by spectroscopic techniques such as (1)H NMR, IR, and elemental analysis. These water-soluble compounds were examined for their inhibition of both activities of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. l-3,4- Dihydroxyphenylalanine (L-DOPA) and l-tyrosine were used as natural substrates for the catecholase and cresolase enzyme reactions, respectively. Kinetic studies showed noncompetitive inhibition of I and mixed type inhibition of II on both activities of MT. The inhibition constant (K(I)) of II was smaller than that of I. Raising the temperature from 27 to 37 degrees C caused a decrease in K(I) values of I and an increase in values of II. The binding process for inhibition of I was only entropy driven, which means that the predominant interaction in the active site of the enzyme is hydrophobic; meanwhile, the electrostatic interaction can be important for the inhibition of II due to the enthalpy driven binding process. Fluorescence studies showed a decrease of emission intensity without a shift of emission maximum in the presence of different concentrations of compounds. An extrinsic fluorescence study did not show any considerable change of the tertiary structure of MT. Probably, the conformation of inhibitor-bound MT is stable and inflexible compared with uninhibited MT.
Two structurally related compounds, phenyl dithiocarbamate sodium salt (I) and p-phenylene-bis (dithiocarbamate) sodium salt (II) were prepared by reaction of the parent aniline and p-phenylenediamine with CS₂ in the presence of sodium hydroxide. These water soluble compounds were characterized by spectroscopic techniques, IR, ¹H NMR and elemental analysis. The inhibitory effects of both compounds on both activities of mushroom tyrosinase (MT) from Agricus bisporus were studied at two temperatures, 27°C and 37°C. L-3, 4-dihydroxyphenylalanine (L-DOPA), and l-tyrosine were used as natural substrates for the catecholase and cresolase enzyme reactions, respectively. Kinetic analysis confirmed noncompetitive inhibition mode of I and mixed type of II on both activities of MT; I and II inhibit MT with inhibition constants (K(I)) of 300 µM and 4 µM, respectively. Analysis of thermodynamic parameters indicated predominant involvement of hydrophobic interactions in binding of I and electrostatic ones in binding of II to MT. It seems that II is a more potent MT inhibitor due to its two charged head groups able to chelate copper ions in the enzyme active site. Intrinsic fluorescence studies as a function of concentrations of both compounds showed unexpectedly quenching of emission intensity without any shift of emission maximum. Extrinsic ANS-fluorescence indicated that only binding of I induces limited changes in the tertiary structure of MT, in agreement with the postulated hydrophobic nature of the binding mechanism.
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