Coulometric determination of NAD+ and NADH in normal and cancer cells using LDH, RVC and a polymer mediator

An electrochemical method for the measurement of NAD(+) and NADH in normal and cancer tissues using flow injection analysis (FIA) is reported. Reticulated vitreous carbon (RVC) electrodes with entrapped l-lactate dehydrogenase (LDH) and a new redox polymer containing covalently bound toluidine blue O (TBO) were employed for this purpose. Both NAD(+) and NADH were estimated coulometrically based on their reaction with LDH. The latter was immobilized on controlled pore glass (CPG) by cross-linking with glutaraldehyde and packed within the RVC. The concentrations of NAD(+) and NADH in the tissues, estimated using different electron mediators such as ferricyanide (FCN), meldola blue (MB) and TBO have also been compared. The effects of flow rate, pH, applied potential (versus Ag/AgCl reference) and adsorption of the mediators have also been investigated. Based on the measurements of NAD(+) and NADH in normal and cancer tissues it has been concluded that the NADH concentration is lower, while the NAD(+) concentration is higher in cancer tissues. Amongst the electron mediators TBO was found to be a more stable mediator for such measurements.     

Gas phase photoisomerization of urocanic acid – a theoretical study

The photochemistry of urocanic acid is investigated theoretically by means of time-dependent density functional theory. The topology of the potential energy surface along the isomerization pathway and close to the Franck–Condon region is investigated and consequences for the photoisomerization reactions are outlined. A recently published supersonic jet spectroscopy study is reinterpreted in the light of these and earlier theoretical results to give a clear picture of the gas phase photochemistry. It is found that the photochemistry of the two isomers is fundamentally different, in contrast to the situation in solution.     

Evaluation of partition measurements in liquid-liquid segmented flow

The different configurations possible for an FIA extraction system for partition measurements have been tested and the corresponding evaluation formulae based on determinations at different phase flow ratios, verified. Increased flexibility results from the possibility of using samples dissolved in either aqueous or organic phase. Choosing the best configuration in every case makes it possible to extend the range of measurable conditional partition constants without excessive losses in precision.     

Double photoionisation spectra of small molecules and a new empirical rule for double ionisation energies

Complete double photoelectron spectra are presented for 18 small molecules where the location of charges in the cations and dications is relatively clearly defined. The data demonstrate the importance of a coulombic repulsion contribution to the double ionisation energies. Examination of data for a wide range of molecules leads to a new empirical rule to calculate double ionisation energies from the molecules’ single ionisation energies and maximum dimensions. Where single and double ionisation energies are known the rule allows the deduction of plausible intercharge distances.     

Evaluation of a dialysis probe for continuous sampling in fermentors and in complex media

A dialysis probe is described for continuous sampling from complex solutions, such as fermentation broth, milk or waste water, to yield samples suitable for liquid chromatography, flow injection analysis, enzyme calorimetry, etc. The analyte is transferred to a flow stream separated from the sample by a dialysis membrane that is protected from fouling by a strong tangential flow of the sample solution. This flow is accomplished by placing a magnetic stirring bar close to the membrane surface. The device is constructed of materials permitting the probe to be steam-sterilized when mounted inside a fermentor.     

Conformations of silicon-containing rings. 5. Conformational properties of 1-methyl-1-silacyclohexane: gas electron diffraction,low-temperature NMR,and quantum chemical calculations

The molecular structure of 1-methyl-1-silacyclohexane 3 has been determined by gas electron diffraction (GED). The conformational preference of the methyl group was studied experimentally in the gas phase (GED) and in solution (low-temperature (13)C NMR) and by quantum chemical calculations (HF, MP2, and B3LYP with 6-31G basis sets and mPW1PW91/6-311G(2df,p)). Both experimental methods result in a preference of the equatorial position of the methyl group, 68(7)% in the gas phase at 298 K and 74(1)% in solution at 110 K. The calculations predict 68-73% equatorial conformer at room temperature. From coalescence temperatures, Gibbs free energies of activation for ring inversion DeltaG++ (eq --> ax) = 5.81(18) and DeltaG++ (ax --> eq) = 5.56(18) kcal mol(-1) were derived. The calculated values for DeltaG++ (eq --> ax) are 5.92 (B3LYP) and 5.84 kcal mol(-1) (mPW1PW91).     

Studies of two-phase equilibria by liquid-liquid segmented flow extraction of dithiocarbamic acids into various solvents

A method for the study of two-phase equilibria by extraction in liquid-liquid segmented flow is presented. The main advantage of the method is the very rapid equilibration achieved. In many cases a contact time of 5 sec is sufficient. By performing the measurements needed on-line with the extraction the total residence time of a substance studied in the system can be kept below 10 sec. This makes it possible to study two-phase equilibria of moderately unstable compounds. Other advantages are the semi-enclosed design, which minimizes contact with solvent fumes and increases the speed of operation after the system has been set up. The system has been used for a study of the two-phase equilibria of dithiocarbamic acids. The dithiocarbamates are often used for the separation and preconcentration of metals, and co-extraction of the reagent can cause severe interference in the final determination. By means of the extraction constants presented, the extraction of diethyldithiocarbamic acid and pyrrolidine-dithiocarbamic acid into Freon 113, carbon tetrachloride, methyl isobutyl ketone and chloroform can be estimated.     

Hume’s Ontology

The paper claims that Hume??s philosophy contains an ontology, i.e. an abstract exhaustive classification of what there is. It is argued that Hume believes in the existence of a mind-independent world, and that he has a classification of mind-related entities that contains four top genera: perception, faculty, principle and relation. His ontology is meant to be in conformity with his philosophy of language and epistemology, and vice versa. Therefore, crucial to Hume??s ontology of mind-independent entities is his notion of ??supposing relative ideas??. Entities that are referred to by means of ordinary ideas can be truly classified, whereas entities that are referred to by means of relative ideas can only be hinted at. When Hume??s ontology is highlighted and systematised, his notion ??the faculty of imagination?? becomes highly problematic. However, the exposition also makes it clear that Hume deserves the honorary title: the first cognitive scientist.