Spectrophotometric determination of boron in human hair with azomethine H

Summary Investigation of methods of hair sample mineralization was made. The most profitable method of hair mineralization was by combustion in oxygen. Boron was determined spectrophotometrically with azomethine H as a spectrophotometric reagent. Boron in hair was determined in the range of 0–5 g/g.     

Macrocyclic receptors containing sucrose skeleton

Crown ether analogues with incorporated sucrose unit were prepared by reaction of 1′,2,3,3′,4,4′-hexa-O-benzylsucrose with polyethylene ditosylates in up to 52% yield. Stability constants of their complexes with Li⁺, Na⁺, K⁺, NH₄⁺ were determined by the NMR titration method. The macrocycles were also tested as catalysts in the enantioselective Michael reaction, but with little success (ee up to only 22%). The macrocycle containing nitrogen in the ring was also prepared in good yield. All prepared macrocycles were easily converted into the free sucrose crowns (H₂/Pd/C) without destroying the (very labile) glycosidic bond. The crystal structure of the selected receptor was determined.     

Particle analysis for a strengthened safeguards system: Use of a scanning electron microscope equipped with EDXRF and WDXRF spectrometers

The purpose of this study was twofold: the identification of some uranium compounds and a measurement of mixed U/Pu particles with different ratios of these elements. We used a Philips XL-30 scanning electron microscope equipped with an EDAX energy dispersive spectrometer with a Si(Li) detector and a super ultra-thin polymer window and with a Microspec wavelength dispersive spectrometer. A number of WDXRF and EDXRF spectra of U and Pu containing particles were accumulated and evaluated. The software package provided by the manufacturer was used for EDXRF spectra evaluation and calculation of the weight and atomic composition. Eight different U compounds were identified with a different degree of confidence. Several different types of U and Pu particles were measured using the WDXRF spectrometer and the results of the measurements are discussed. The measurement of mixed U-Pu particles showing large differences in the concentration of both elements can best be carried out with the use of WDXRF because the deconvolution of the M lines of U and Pu in the energy dispersive spectra is only possible over a relatively small concentration range. The results of particle analysis are very useful for verifying the absence of undeclared nuclear activities.     

Effect of the peptide secondary structure on the peptide amphiphile supramolecular structure and interactions

Bottom-up fabrication of self-assembled nanomaterials requires control over forces and interactions between building blocks. We report here on the formation and architecture of supramolecular structures constructed from two different peptide amphiphiles. Inclusion of four alanines between a 16-mer peptide and a 16 carbon long aliphatic tail resulted in a secondary structure shift of the peptide headgroups from α helices to β sheets. A concomitant shift in self-assembled morphology from nanoribbons to core-shell worm-like micelles was observed by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). In the presence of divalent magnesium ions, these a priori formed supramolecular structures interacted in distinct manners, highlighting the importance of peptide amphiphile design in self-assembly.     

X-ray fluorescence analysis of polymetallic ores

An analytical procedure for determination of Fe, Ti, V, Ni, Co and Cu, the most important constituents of the polymetallic ore has been developed. Twenty four powdered samples were prepared from the material taken in various places of the ore deposit. The samples were analyzed by wavelength dispersive (WD) and energy dispersive (ED) XRF method. The EDXRF method was applied using radioisotope source as well as a low power X-ray tube (Rh-anode) for excitation of the characteristic K-line radiation of the elements. A Si(Li) detector was used for the detection of radiation. The detection limits and precision of the analytical procedures, using reference materials, were estimated. The accuracy of the different XRF techniques is discussed. The developed analytical procedures based on the XRF method are rapid and quite simple. They can be useful for exploration data accumulation.     

Rapid method of uranium determination in solutions based on X-ray fluorescence and absorption

A method of uranium determination in organic and aqueous solutions has been developed, based on fluorescence L X-ray excitation with a¹⁰⁹Cd source of several mCi activity and counting the excited L_α lines with a proportional counter. To eliminate uranium X-ray absorption by the accompanying elements the intensity of the source radiation (Ag K) transmitted through the analysed solution is measured. The ratio of these two intensities is independent of other elements present in the solution over a very broad range of concentration. The analysis time does not exceed 5 minutes. The precision and accuracy of this method in the range 0.5 to 100 g U/1 are comparable to those of the classical titrimetric method.     

Determination of plutonium in the presence of uranium by alpha-spectrometry

The plutonium determination by alpha-particle spectrometry with semiconductor detectors in the presence of uranium has been described. It has been found that plutonium as well as uranium can be electrodeposited quantitatively on nickel or stainless steel discs from solutions in isopropanol. The time of deposition does not exceed 35–40 min. The determination of plutonium is possible within the uranium to plutonium weight ratio of 4000 with the accuracy better than 2%.     

Calculations of the exciton coupling elements between the DNA bases using the transition density cube method

Excited states of the double-stranded DNA model (A)12.(T)12 were calculated in the framework of the Frenkel exciton theory. The off-diagonal elements of the exciton matrix were calculated using the transition densities and ideal dipole approximation associated with the lowest energy pipi* excitations of the individual nucleobases as obtained from time-dependent density functional theory calculations. The values of the coupling calculated with the transition density cubes (TDC) and ideal dipole approximation (IDA) methods were found to be significantly different for the small interchromophore distances. It was shown that the IDA overestimates the coupling significantly. The effects of structural fluctuations of the DNA chain on the magnitude of dipolar coupling were also found to be very significant. The difference between the maximum and minimum values was as large as 1000 and 300 cm(-1) for the IDA and TDC methods, respectively. To account for these effects, the properties of the excited states were averaged over a large number of conformations obtained from the molecular dynamics simulations. Our calculations using the TDC method indicate that the absorption of the UV light creates exciton states carrying the majority of the oscillator strength that are delocalized over at least six DNA bases. Upon relaxation, the excitation states localize over at least four contiguous bases.     

A Functional Role for Aβ in Metal Homeostasis? N‐Truncation and High‐Affinity Copper Binding

Accumulation of the β‐amyloid (Aβ) peptide in extracellular senile plaques rich in copper and zinc is a defining pathological feature of Alzheimer′s disease (AD). The Aβ1–x (x=16/28/40/42) peptides have been the primary focus of Cu^II binding studies for more than 15 years; however, the N‐truncated Aβ4–42 peptide is a major Aβ isoform detected in both healthy and diseased brains, and it contains a novel N‐terminal FRH sequence. Proteins with His at the third position are known to bind Cu^II avidly, with conditional log K values at pH 7.4 in the range of 11.0–14.6, which is much higher than that determined for Aβ1–x peptides. By using Aβ4–16 as a model, it was demonstrated that its FRH sequence stoichiometrically binds Cu^II with a conditional K_d value of 3×10⁻¹⁴ M at pH 7.4, and that both Aβ4–16 and Aβ4–42 possess negligible redox activity. Combined with the predominance of Aβ4–42 in the brain, our results suggest a physiological role for this isoform in metal homeostasis within the central nervous system.     

Example of a Model for AdS/QFT Duality

Models of hadrons that are rooted in light-front (LF) formulation of QCD have been linked to the classical field equations in a 5-dimensional anti-de Sitter (AdS) gravitational background in terms of the Brodsky-de Téramond LF holography. We discuss the classical equations of motion for the expectation values of operators in quantum field theory whose nature resembles the Ehrenfest equations of quantum mechanics and which thus appear to provide a general justification for the holographic picture. The required expectation values are obtained by distinguishing one effective constituent of a hadron, the one that is struck by an external electro-weak or gravitational probe, and integrating over relative motion variables of all other constituents in all Fock components. The scale-dependent Fock decomposition of hadronic states is defined using the renormalization group procedure for effective particles. The AdS modes dual to the incoming and outgoing hadrons in the corresponding transition matrix elements are thus found equivalent to the Gaussian form distribution functions for the effective partons struck by external probes.