Letter: Nucleoside complexing. A charge reversed chelate compound between guanosine and chloride ion

Tb(III)-doped silica nanoparticles for sensing: effect of interfacial interactions on substrate-induced luminescent response

The present work introduces the easy modification of the water-in-oil microemulsion procedure aimed at the doping of the Tb(III) complexes within core or shell zones of the silica nanoparticles (SNs), which are designated as "core-shell", "shell", and "core". The dye molecules, chelating ligands, and copper ions were applied as the quenchers of Tb(III)-centered luminescence through dynamic or/and static mechanisms. The binding of the quenchers at the silica/water interface results in the quenching of the Tb(III) complexes within SNs, which, in turn, is greatly dependent on the synthetic procedure. The luminescence of "core" SNs remains unchanged under the binding of the quenchers at the silica/water interface. The quenching through dynamic mechanism is more significant for "core-shell" and "shell" than for "core" SNs. Thus, both "core-shell" and "shell" SNs have enough percentage of the Tb(III) complexes located close to the interface for efficient quenching through the energy transfer. The quenching through the ion or ligand exchange is most efficient for "core-shell" SNs due to the greatest percentage of the Tb(III) complexes at the silica/water interface, which correlates with the used synthetic procedure. The highlighted regularities introduce the applicability of "core-shell" SNs used as silica beads for phosphatidylcholine bilayers in sensing their permeability toward the quenching ions.

Structures and Chemical Equilibria of Some N-Heterocycles Containing Amide Linkages

Structures and chemical equilibria of 5-carboxy-2-thiouracil (1), 5,6-diphenyl-3-hydroxy-1,2,4-triazine (2),  1-phenyl-3-methyl-5-pyrazolone (3) and 2-mercapto-4,6-dimethylpyrimidine hydrochloride (4) are reported. Their electronic transitions are assigned and pK values are evaluated and discussed.

Precise ultraviolet absorbance study of the interactions of amino acids and mononucleosides in aqueous solution

The association constants of various amino acids or their derivatives (methyl esters, amides, etc.) with mononucleosides in aqueous solutions have been measured by using precise ultraviolet difference absorbance photometry. Some of the results are in agreement with those of the previous solubility experiments. The superiority of this ultraviolet absorbance method over the solubility experiments is that it can discriminate between stacking and hydrogen-bonding interactions. New types of specific interactions of some amino acids with nucleic acid bases by using a peptidyl carboxylate ion and another donor or acceptor in their side chains have been found using this technique.

On coordination modes of adenine in cadmium(II) complexes

Complexes of cadmium(II) derivatives with adenine from water or by simulation of physiological conditions are obtained. The complexes have been studied by spectroscopic, conductometric, 1H-NMR, and by TG and DSC measurements. Possible coordination modes of the ligand are proposed.

13C magnetic resonance investigation of mercury (II) binding to nucleosides and thiolated nucleosides in dimethyl sulfoxide

Natural abundance, proton-decoupled 13C magnetic resonance spectroscopy is shown to be a useful technique for identifying the mercury (II) binding sites on nucleosides and especially thiolated nucleosides. Measurements made on dimethyl sulfoxide-d6 solutions, 0.5 M in nucleoside and 0.15 M in mercury, reveal that both CH3 HgCl and HgCl2 bind principally to the sulfur atoms of s6 Guo and s8 Guo. The 13C NMR spectra of the unthiolated nucleosides in the presence of excess (4:1) mercury reveal that HgCl2 binds to N-3 of cytidine, to more than one site on adenosine and guanosine, but not strongly to uridine. Excess HgCl2 shifts the thiocarbonyl carbon atoms in s6 Guo and s8 Guo approx. 16 ppm upfield compared to the free nucleosides, and there is evidence for additional coordination to N-7 of s6 Guo. Binding to the ribose hydroxyl groups is clearly ruled out. At least in these instances, 13C NMR proves to be useful for assigning the mercury (II) binding sites, complementing the results of proton magnetic resonance studies. Proton NMR data for the binding of CH3 HgCl and HgCl2 to s6 Guo and s8 Guo are also presented.