Sultan Qaboos University

About: Sultan Qaboos University is a education organization based out in Muscat, Oman. It is known for research contribution in the topics: Population & Medicine. The organization has 7767 authors who have published 14605 publications receiving 241390 citations. The organization is also known as: SQU.

Characterization of subdomain IIA binding site of human serum albumin in its native, unfolded, and refolded states using small molecular probes.

Abstract: Subdomain IIA binding site of human serum albumin (HSA) was characterized by examining the change in HSA fluorescence in the native, unfolded, and refolded states. The study was carried out in the absence and presence of small molecular probes using steady-state and time-resolved fluorescence measurements. 2-Pyridone, 3-pyridone, and 4-pyridone bear similar molecular structures to those found in many drugs and are used here as probes. They are found to specifically bind in subdomain IIA and cause a reduction in the fluorescence intensity and lifetime of the Trp-214 residue in native HSA which is located in the same subdomain. The efficiency of energy transfer from Trp-214 fluorescence to the probes was found to depend on the degree of the spectral overlap between the donor's fluorescence and the acceptor's absorption. After probe binding in subdomain IIA, the distance between the donor and acceptor was calculated using Forster theory. The calculated quenching rate constants and binding constants were also shown to depend on the degree of spectral overlap. The results point to a static quenching mechanism operating in the complexes. Denaturation of HSA in the presence of guanidine hydrochloride (GdnHCl) starts at [GdnHCl] > 1.0 M and is complete at [GdnHCl] > or = 6.0 M. Upon unfolding, two fluorescence peaks were observed. One peak was assigned to the fluorescence of Trp-214 in a polar environment, and the other peak was assigned to tyrosine fluorescence. A reduction of the fluorescence intensity of the two peaks upon binding of the probes to the denatured HSA indicates that Tyr-263 in subdomain IIA is one of the tyrosine residues responsible for the second fluorescence peak. The results were confirmed by measuring the fluorescence spectra and lifetimes of denatured HSA at different excitation wavelengths, and of L-tryptophan and L-tyrosine free in buffer. The measured lifetimes of denatured HSA are typical of tryptophan in a polar environment and are slightly reduced upon probe binding. Dilution of the denatured HSA by buffer results in a partial refolding of subdomain IIA. This partial refolding is attributed to some swelling of the binding site caused by water. The swelling prevents a full recovery from the denatured state.

Spin-dependent exciton formation in π-conjugated compounds

Abstract: The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent1. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent2,3,4,5, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 ± 1 per cent for the monomer, but 57 ± 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.

Ancient human genomes suggest three ancestral populations for present-day Europeans

Abstract: We sequenced the genomes of a ∼7,000-year-old farmer from Germany and eight ∼8,000-year-old hunter-gatherers from Luxembourg and Sweden. We analysed these and other ancient genomes with 2,345 contemporary humans to show that most present-day Europeans derive from at least three highly differentiated populations: west European hunter-gatherers, who contributed ancestry to all Europeans but not to Near Easterners; ancient north Eurasians related to Upper Palaeolithic Siberians, who contributed to both Europeans and Near Easterners; and early European farmers, who were mainly of Near Eastern origin but also harboured west European hunter-gatherer related ancestry. We model these populations' deep relationships and show that early European farmers had ∼44% ancestry from a 'basal Eurasian' population that split before the diversification of other non-African lineages.

Principal component and multiple regression analysis in modelling of ground-level ozone and factors affecting its concentrations

Abstract: Data on the concentrations of seven environmental pollutants (CH"4, NMHC, CO, CO"2, NO, NO"2 and SO"2) and meteorological variables (wind speed and direction, air temperature, relative humidity and solar radiation) were employed to predict the concentration of ozone in the atmosphere using both multiple linear and principal component regression methods Separate analyses were carried out for day light and night time periods For both periods the pollutants were highly correlated, but were all negatively correlated with ozone Multiple regression analysis was used to fit the ozone data using the pollutant and meteorological variables as predictors A variable selection method based on high loadings of varimax rotated principal components was used to obtain subsets of the predictor variables to be included in the regression model of the logarithm of the ozone data It was found that while high temperature and high solar energy tended to increase the day time ozone concentrations, the pollutants NO and SO"2 being emitted to the atmosphere were being depleted Night time ozone concentrations were influenced predominantly by the nitrogen oxides (NO+NO"2), with the meteorological variables playing no significant role However, the model did not predict the night time ozone concentrations as accurately as it did for the day time This could be due to other factors that were not explicitly considered in this study