Dušan Vučelić

Potential of proton-enhanced 13C n.m.r. for the classification of kerogens

Abstract High resolution n.m.r. spectroscopy, involving the technique of cross-polarization, along with magicangle spinning, was used in the structural characterization of eight kerogens of different origins, selected to represent the three types of kerogens (types I–III evolution paths). The influence of cross-polarization dynamics on the sensitivity of the method and the ratio of individual fractions in the spectrum was studied in more detail. It is suggested that an analysis of the influence of the mixing time is necessary prior to definitive characterization of any sample. Good separation of signals in aliphatic, aromatic, and carboxylic regions was achieved. The general correlation between the 13C n.m.r. structural characteristics and the classification based on ultimate analysis of the kerogens (types I–III, van Krevelen atomic H/C vs. O/C diagrams) was found to be satisfactory. The structural features of kerogens derived from 13C n.m.r. analysis agreed quite well with characteristics constituting the above mentioned classification. The 13C n.m.r. method used in this paper may be considered promising in the classification of kerogens.

Analysis of the organic matter of oil shales by nuclear magnetic resonance

Abstract 13C NMR spectroscopy was applied in the investigation of the structure of the organic matter in oil shales. By using Proton Enhanced Nuclear Induction Spectroscopy, a fair resolution of aliphatic and aromatic carbon signals was achieved. This method provided information on the relative ratio of aliphatic and aromatic carbons within a given set of samples (Aleksinac, Kimmeridge, Colorado, Australian torbanite and Estonian kukersite).

Thermogravimetry and differential scanning calorimetry of natural and synthetic melanins

The thermal stability of natural melanins from bovine eyes, black human hair and the hard core of banana peel, synthetic melanins obtained enzymatically or by autoxidation of various precursors, and chemically modified synthetic melanins was studied by DSC and TG analysis. It was shown that the resistance of melanins to thermal degradation depends on their origin. Synthetic melanins were found to be more stable to thermal decomposition than natural melanins. Methylation of melanins caused a significant increase in thermal stability. The DSC curves of melanins reveal typical relaxation phenomena in the temperature range 293–413 K.ZusammenfassungMittels DSC und TG wurde die thermische Stabilität von natürlichen Melaninen aus Rindsaugen, aus schwarzem menschlichen Haar und aus Hartteilen von Bananenschalen, weiterhin von enzymatisch oder durch Autoxidation aus verschiedenen Präkursoren synthetisierten Melaninen sowie von chemisch modifizierten synthetischen Melaninen untersucht. Es zeigte sich, daß die Beständigkeit von Melaninen gegenüber thermischem Abbau von ihrem Ursprung abhängt. Synthetische Melanine erwiesen sich in der thermischen Zersetzung als stabiler als Melanine natürlichen Ursprunges. Durch Methylierung wird eine eindeutige Steigerung der thermischen Stabilität verursacht. Im Temperaturbereich 293–413 K zeigen weisen die DSC-Kurven der Melanine typische Relaxationserscheinungen auf.

Structural analysis of Aleksinac oil shale kerogen by high-resolution solid-state 13C n.m.r. spectroscopy

Abstract A sample of kerogen from Aleksinac oil shale was examined by high-resolution solid-state 13C n.m.r. spectroscopy. The presence and relative proportions of kerogen structural units were estimated using a combination of NQS and T1ϱC methods with a peak-synthesis technique applied to the 13C CP—MAS spectrum. Relaxation parameters from these experiments were used to estimate differences in relative ‘mobility’ of various structural units. The kerogen was found to be highly aliphatic and to contain ∼ 79% long-chain aliphatic plus alicyclic structures, as well as ∼ 9% aromatic structures. These findings are in good agreement with the characterization of the same kerogen from its oxidation products.

Investigation of the catalytic effects of indigenous minerals in the pyrolysis of Aleksinac oil shale substrates: Steranes, triterpanes and triaromatic steroids in the pyrolysates

Abstract Evidence for catalytic effects of indigenous minerals in the pyrolysis of Aleksinac oil shale kerogen was found by investigating the liquid products obtained in the Micro Activity Test (MAT) pyrolysis of raw shale and its demineralized substrates. By comparing the corresponding fragmentograms of a demineralized sample with those of a substrate containing only silicate minerals, differences in the side-chain isomerisation of the steranes and triterpanes, and in the side-chain cleavage of the triaromatic steroids were observed. These findings corroborated the previous conclusion, based on MAT parameters and TG weight losses, that the catalytic effect of the indigenous mineral components during the pyrolysis of Aleksinac oil shale kerogen is very low.

Indirect method for quantitative determination of bovine serum albumin and transferin by anodic stripping voltammetry with a rotating glassy carbon electrode

Abstract The present study was carried out in order to investigate whether the interaction of multifunctional transport proteins, bovine serum albumin (BSA) and transferin (TF), with some metal (Me) ions, such as Hg(II) and Cu(II), in buffered solution (pH 8.0), may serve as a base for indirect quantitative determination of both proteins. For this purpose anodic stripping voltammetry with a rotating glassy carbon electrode was applied. A sufficient sensitivity on the presence of protein in solution containing Me-ions was obtained only by using a mercury dissolution signal (peak) observed at 0.1 V vs. SCE. Quantities of BSA less than 5×10−7 M were determined with a S.D.±5% (n=10) for a concentration of 3×10−7 M, and for TF the concentration less than 1.5×10−7 M could be determined with S.D.±4% (n=10) for a concentration of 1×10−7 M.

Investigation of catalytic effects of indigenous minerals in the pyrolysis of Aleksinac oil shale organic matter

Abstract The catalytic effect of indigenous minerals in the pyrolysis of Aleksinac (Yugoslavia) oil shale was studied in this paper. The substrates were prepared by gradual removal of the mineral constituents (carbonates, silicates, pyrite) and the free and bound bitumens. The substrates were analyzed by chemical methods, X-ray diffraction, porosimetry, thermal analysis, 13 C NMR, and standard ASTM Micro Activity Test (MAT) designed for the investigation of cracking catalysts. The liquid pyrolysis products were analyzed by organic geochemical techniques as well. Based on the yields of gaseous and liquid products and the coke, conversion degrees, GC analyses (MAT parameters) and weight losses (TG parameter), the catalytic effect of indigenous mineral components in the pyrolysis of Aleksinac oil shale organic matter was found to be very low. The results suggested that principal organic matter changes should be attributed to thermal rather than to catalytic cracking.

The Temperature Peaks of Cell Membrane Permeability

Any change in the structural organization of the cell membrane as the main permeation barrier, should be reflected in its transport behaviour. Studies of the temperature dependence of cellular water transport should therefore provide valuable information on the structural dynamics of the membrane.

Non additivity of ligand effects on 59Co NMR chemical shifts in Co(III) complex compounds

Abstract 59Co chemical shift in a number of Co(III) complexes of the type CoA6-xBx(x = 0–6, A and B denote corresponding ligators) containing mono- and/or bidentate ligands, was measured. In almost all cases studied it was found that chemical shift appear at lower field than expected on the basis of the Rule on Additivity of Ligand Effects on 59Co chemical shift. The non additivity of the ligand effects on 59Co chemical shift has been discussed in terms of ligand field theory. It was shown that negative deviations from additivity has to be expected.

Application of Thermal Analysis for Explaining the Sorption of Benzene and N-Hexane on Silicalite

The origin of kinks (steps) on sorption isotherms was examined for the sorption of benzene and n-hexane on silicalite-1. In both cases sorption revealed the existence of two different binding sites. There was no equilibrium (or a very slow one), between molecules bound at different sites. Sorption energies within particular centres display more or less wide overlapping distributions leading to a single resultant isotherm. Depending on differences in binding energies and degree of overlapping, the resulting isotherms exhibit steps (benzene) or no steps (n-hexane).In fact, the sorption isotherm of benzene being a sum of two elemental isotherms (Ω1 and Ω2) of different shapes is characterized by a ‘kink’, in contrast to n-hexane the elemental isotherms of which are of the same shape.