Magnetic behaviour of nickel-cyclam complexes in mesoporous silica: EPR investigations

Electron paramagnetic resonance (EPR) investigations are carried out on mesoporous silica (SBA15) functionalized by Ni-cyclam complexes (1,4,8,11-tetraazacyclotetradecane groups chelating nickel ions). The magnetic behaviour of nickel-cyclam groups, their mutual interactions and dispersions in the mesoporous silica are compared with respect to the doping rates and the synthesis procedures. The spin-spin interactions and the relaxation processes were clarified from the thermal evolution in the temperature range (4 K, 300 K) of the paramagnetic spin susceptibilities and EPR line widths. Thus, the relaxation mechanisms seem marked by the Jahn-Teller effect on the nickel ions mediated by exchange interactions between nearest spins. Isolated Ni-cyclam molecules are involved in some samples while others show the formation of clusters where phonon-assisted one-dimensional (1D) ferromagnetic ordering occurs below 45 K. The performed experiments point out the efficiency of the EPR technique to probe the degree of functionalization of mesoporous silica by Ni-cyclam molecules and to give valuable feedback to improve the synthesis routes.

Numerical analysis of simultaneous TL/TSC measurements

Thermoluminescence (TL) and thermally stimulated conductivity (TSC) are closely related phenomena. Simultaneous detection of luminescence and conductivity allows one to acquire more information concerning the basic trapping processes occurring during heating of a sample. In this paper a new formula for simultaneous TL/TSC measurement is derived under quasiequilibrium (QE) conditions. Numerical analysis of the obtained experimental data requires fitting of only two unknown parameters. The new method of analysis was verified for computer generated TL/TSC curves. The practical usefulness of this method is demonstrated in application to the measurements performed for the a-alumina single crystal. The analysis, in general, confirms earlier results for the peak B'. The results obtained for the peak D' are not so clear. Most likely they reveal some complex factors that are not taken into account.

TL emission spectra from differently doped LiF:Mg detectors

There are two widely applied types of thermoluminescent detectors based on LiF:Mg luminophor: Lif:Mg,Ti and highly sensitive LiF:Mg,Cu,P. The role of luminescence centres in these materials is usually attributed to defects connected with, respectively, titanium and phosphorus dopants. In order to check how composition of dopants introduced into the LiF lattice influences emission spectra, measurements on a series of variously doped LiF:Mg samples were performed. Apart from LiF:Mg,Cu,P and LiF:Mg,Ti detectors with different concentration of activators, an experimental sample being a kind of a 'hybrid' between both standard materials was also prepared. It was synthesised with concentrations of magnesium and copper identical to those used for LiF:Mg,Cu,P preparation. but instead of phosphorus it was doped with titanium (LiF:Mg,Cu,Ti). The measurements of the emission spectra were performed by using a liquid nitrogen cooled CCD 1024E detector with an SP150 spectrograph. During the measurements the samples were placed inside a cryostat in a vacuum. Resulting data were numerically deconvoluted for individual peaks with respect to the wavelength and the temperature. The glow curve shape of this material resembles that of LiF:Mg,Cu,P, while sensitivity is at the level of LiF:Mg,Ti. Preliminary results indicate that emission of the LiF:Mg,Cu,Ti sample is similar to that of LiF:Mg,Cu,P rather than to LiF:Mg,Ti, showing a maximum for wavelengths well below 400 nm.

Combination treatment in stable effort angina using trimetazidine and metoprolol: results of a randomized, double-blind, multicentre study (TRIMPOL II). TRIMetazidine in POLand

AIMS

To assess the antiischaemic efficacy and tolerability of the metabolic agent trimetazidine in combination with metoprolol in patients with stable effort angina.

METHODS

This was a randomized, multicentre, double-blind, placebo-controlled parallel group study. A total of 426 male and female patients with stable, effort-induced angina and documented coronary artery disease received either placebo or trimetazidine 20 mg three times daily in addition to metoprolol 50 mg twice daily. Treadmill exercise tests were performed at weeks (-1), 0, 4 and 12.

RESULTS

After 12 weeks, there were significantly greater improvements in the metoprolol + trimetazidine group than in the metoprolol + placebo group in: time to 1 mm ST segment depression, total workload, time to onset of angina, maximum ST segment depression, mean weekly number of angina attacks, mean weekly nitrate consumption, and grade of anginal pain. There was no evidence of any development of tolerance to trimetazidine. The tolerability of trimetazidine was excellent.

CONCLUSIONS

Therapy with trimetazidine plus metoprolol produced significant improvements in exercise stress tests and the symptoms of angina relative to metoprolol alone. With its metabolic effect, devoid of any haemodynamic action, trimetazidine is useful for combination therapy in patients with stable angina insufficiently controlled by monotherapy with a beta-blocker.

Experimental heart failure in rats: effects on cardiovascular circadian rhythms and on myocardial beta-adrenergic signaling

OBJECTIVES

Patients with chronic heart failure frequently show blunted circadian blood pressure profiles. The mechanisms involved in the loss of physiological day-night variation are still unclear, but a continuously active sympathetic nervous system could play a role. The present study evaluated long-term consequences of rat heart failure on cardiovascular circadian patterns in vivo, and on density and function of cardiac beta-adrenoceptor subtypes in vitro, as a marker of cardiac adrenergic drive.

METHODS

Heart failure in rats was induced by coronary artery ligation leading to infarct sizes of >30% of left ventricular circumference. Blood pressure and heart rate were monitored for 10 weeks after infarction using radiotelemetry. Density and function of cardiac beta(1) and beta(2)-adrenoceptors were measured by radioligand binding and adenylyl cyclase stimulation.

RESULTS

During the activity period at night blood pressure and heart rate were lower in rats with heart failure than in sham controls, leading to reduced night-day variation in the heart failure group. Depression of circadian rhythmicity in blood pressure was found over the whole study period, while that in heart rate occurred with a lag-time of several weeks. In failing left ventricles beta-adrenoceptors showed reduced high affinity agonist binding, a shift in the beta(1):beta(2) ratio towards the beta(2)-subtype, and decreased beta(1)-adrenergic stimulation of adenylyl cyclase. In right ventricles no differences were found between failing and control rats. The blunted nocturnal increase in blood pressure and heart rate as well as beta(1)-adrenergic desensitization were correlated with the severity of left ventricular dysfunction.

CONCLUSIONS

Heart failure in rats leads to disturbed circadian patterns in blood pressure and heart rate, and to desensitization of cardiac beta(1)-adrenoceptors, indicating chronic sympathetic overactivity.

Impact of chromium ions on nucleoside triphosphates and nucleic acids

Chromatography on hydroxyapatite, polarography, and spectroscopy have been used to evaluate the interactions of Cr(III) and Cr(VI) with DNA and nucleoside triphosphates. Cr(III) catalyzes the removal of pyrophosphate from nucleoside triphosphate (NTP) molecules. It also causes extensive aggregations of DNA through DNA-DNA cross-linking. Cr(VI) does not affect the DNA structure unless reduced to lower oxidation states.

Famotidine, the new antiulcero-genic agent, a potent ligand for metal ions

Potentiometric, polarographic, and spectroscopic results obtained for Cu2+ and Ni(2+)-famotidine systems clearly indicated that this anti-ulcerogenic drug is a very potent chelating agent able to coordinate cupric ion that was at pH below 2. This drug exhibits excellent histamine H2 receptor blocking effects and its effective coordination to metal ions may have significant biological implications. Famotidine is found to be a very effective ligand for Ni2+ ions also.

Metal binding ability of hypermodified nucleosides of t-RNA. Potentiometric and spectroscopic studies on the metal complexes of N-[(9-beta-D-ribofuranosylpurin-6-yl)-carbamoyl] threonine

Copper(II), nickel(II), zinc(II), manganese(II), and magnesium(II) complexes of t6A (N-[9-beta-D-ribofuranosylpurin-6-yl)carbamoyl] threonine and t6Ade (N6(threoninocarbonyl)adenine) were studied by potentiometric and spectroscopic methods. It was found that t6Ade has three dissociable protons in the accessible pH range (N1 and N9 of purine and carboxylate), while only two pK values are characteristic of t6A. Magnesium(II) and manganese(II) do not interact effectively with these ligands, but copper(II) and nickel(II) ions form very stable complexes with the coordination of purine N1, deprotonated amide nitrogen, and carboxylate oxygen donors.