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As important naturally occurring chromophores, photophysical/chemical properties of quinoid flavins have been extensively studied both experimentally and theoretically. However, little is known about the transition dipole moment (TDM) orientation of excited-state absorption transitions of these important compounds. This aspect is of high interest in the fields of photocatalysis and quantum control studies. In this work, we employ polarization-associated spectra (PAS) to study the excited-state absorption transitions and the underlying TDM directions of a standard quinoid flavin compound. As compared to transient absorption anisotropy (TAA), an analysis based on PAS not only avoids diverging signals but also retrieves the relative angle for ESA transitions with respect to known TDM directions. Quantum chemical calculations of excited-state properties lead to good agreement with TA signals measured in magic angle configuration. Only when comparing experiment and theory for TAA spectra and PAS, do we find deviations when and only when the S 0 → S 1 of flavin is used as a reference. We attribute this to the vibronic coupling of this transition to a dark state. This effect is only observed in the employed polarization-controlled spectroscopy and would have gone unnoticed in conventional TA.

Electrochemical investigations of the blood oxygen carrier protein include both mediated and direct electron transfer. The reaction of haemoglobin (Hb) with typical mediators, e.g., ferricyanide, can be quantified by measuring the produced ferrocyanide which is equivalent to the Hb concentration. Immobilization of the mediator within the electrode body allows reagentless electrochemical measuring of Hb. On the other hand, entrapment of the protein within layers of polyelectrolytes, lipids, nanoparticles of clay or gold leads to a fast heterogeneous electron exchange of the partially denatured Hb.

Marine organisms have attracted much attention as a source of pharmacological tools or potential drugs. We have produced and screened a library of sponge extracts in search of biologically active compounds that may contain useful pharmaceutical lead structures. Sponges were collected from various locations and their aqueous extracts were freeze dried. Murine right and left atria were used to screen 75 extracts for putative cardiac effects. Among seven extracts with a positive inotropic and chronotropic effect the extract C47 from Ectyoplasia ferox proved to be the most active and was chosen for further analysis. C47 also produced a beta-adrenoceptor-independent, propranolol-resistant positive inotropic effect in human atrial trabeculae. To elucidate one possible mode of action the effects of C47 on L-type Ca(2+) current (I(Ca,L)) were measured with a standard patch-clamp technique. In isolated human atrial myocytes exposure to C47 increased peak amplitude of I(Ca,L) in a concentration-dependent manner. The threshold concentration was 15 microg/ml. In addition, voltage dependency of activation and steady-state inactivation were shifted to more negative potentials. C47 slowed the initial phase of time-dependent current inactivation and the recovery from inactivation. In cell-attached patches of HEK 293 cells expressing human Ca(v)1.2 addition of C47 to the bath solution did not affect gating properties, whereas inclusion of the extract into the pipette solution strongly increased single-channel activity, suggesting a direct effect on the pore-forming channel subunit. Despite its robust effect on I(Ca,L) C47 enhanced cardiac force of contraction by only a fraction of the maximum increase caused by high extracellular concentrations of Ca(2+) and failed to increase vascular tone. These findings suggest that the effect of C47 is restricted to the Ca(2+) channel.

The construction and operation of a measuring device containing an enzyme electrode is described. Glucose oxidase is enclosed in an acrylamide film by means of photopolymerization. The maximal increase of the anodic current of the H2O2 being formed in the enzyme reaction serves as measuring signal. The device gives for diluted serum and blood correlation coefficients above 0,99 according to the methods given in the German Pharmacopeia 7. The measuring time for each specimen is roughly 90 s, the serial variation coefficient 2%.

The paper describes the development of electrochemical methods for analytical determination of uric acid basing on amperometric sensors: with an uricase enzyme electrode, termed "electrochemical-enzymatic" method; with an enzyme-free electrode by indication of the anodic oxidation of uric acid, termed "electrochemical" method. The comparison of analytical quality of both methods shows a sufficient specificity, precision, and accuracy. They show a good correlation with regard to the specific uricase-catalase reference method (UCM): yelectr./enz. = (0.943 xUCM + 19.8) mu mol/l; r = 0.9948 yelectr. = (0.964 xUCM + 6.31) mu mol/l; r = 0.9917 The analysis by the "electrochemical" method can be done with a higher frequency of samples per hour completely without need of enzyme. Both methods are principally suitable for an application in analytic biochemical laboratories.

The electrochemical behaviour of ferricytochrome c, metmyoglobin and methemoglobin was studied using d.c., a.c. and differential pulse polarography, and controlled potential electrolysis. 1. The three hemoproteins yield d.c. polarographic steps, and peaks in differential pulse polarograms, the height of which is proportional to concentration. The charge transfer is influenced by strong adsorption. 2. The concentration dependence of the a.c. polarograms indicates structural changes in the adsorbed molecules. 3. The reduction products of controlled potential electrolysis of metmyoglobin and methemoglobin have absorption spectra identical with the native control samples. The affinity for oxygen and the cooperativity in hemoglobin are not affected by the reaction at the electrode. 4. The charge transfer proceeds via adsorbed, already reduced, molecules to freely diffusible proteins.

The peroxidase activity of deuterohemin and deuterohemin complexes relative to the substrates pyrogallol and ascorbic acid was studied using d.c. polarography in aqueous solution. Imidazole and pyridine served as complex ligands. In the absence of the ligands, a continual rise in the substrate conversion rate with increasing H2O2 initial concentration is observed. Imidazole or pyridine were found to considerably increase the peroxidase activity of deuterohemin at low H2O2 concentrations. At high H2O2 concentrations, the dependence of the reaction rate on H2O2 concentration shows a bend, the reaction rate being in each case higher than that of free hemin under the same conditions. The reason of this fact is discussed to be a retarded formation of activated H2O2 hemin-ligand complexes at high H2O2 concentrations.