A Facile,One‐Step Conversion of 6‐O‐Trityl and 6‐O‐TBDMS Monosaccharides into the Corresponding Formate Esters

A convenient method has been developed for a facile and high‐yield conversion of 6‐O‐tert‐butyldimethylsilyl and 6‐O‐trityl protected monosaccharides to their formate esters, which may serve as useful intermediates for the replacement of the primary hydroxyl group of sugars by other functional groups.     

Leaching dynamics of uranium in a contaminated soil site

Samples from a potentially contaminated industrial area were analyzed for uranium using neutron activation analysis (NAA). Uranium concentration values had a typical uncertainty of 2 % and a detection limit of 1 Bq/kg. To investigate the potential leaching dynamics into ground water two techniques were employed. The US EPA Toxicity Characterization Leaching Procedure (TCLP) and the Sequential Extraction Procedure (SEP) were used to determine the concentration of uranium in the leachates. TCLP and SEP showed that very little of the uranium leached into solution under different chemical conditions. Values of uranium leachates ranged from 0.05 to 3.5 Bq/L; a concentration much lower than the results found in the soil concentrations which ranged from 29 to 155 Bq/kg. NAA showed an 8 % uncertainty for leachates with a detection limit of 0.13 Bq/L. To mimic environmental conditions and acid rain, pH 4.3 water was used as the extraction solvent instead of the acetic acid routinely used in TCLP. Results confirmed that very low amounts of uranium leached with values ranging from 0.0002 to 0.0122 Bq/L. These values represent 0.01–1 % of the uranium in the soil samples. The distribution of uranium in soil according to particle size was also investigated to evaluate its potential movement and possible contamination of the water table. Particles below 250 μm in diameter showed a linear increase in uranium concentration whereas those with a larger diameter had constant uranium content.     

Thermotropic liquid crystals based on ferrocenylbiphenyl and ferrocenylterphenyl

4′‐Ferrocenyl‐1,1′‐biphenyl‐4‐yl 4‐alkoxybenzoates Fc–(C₆H₄)₂–OC(O)–C₆H₄–O–C _n H_2n+1 (n = 8, 10, 12) (3a–c), representing a new class of ferrocene‐containing thermotropic mesogens with nematogenic properties, were prepared. Two approaches were used for the construction of these mesogens: (i) reaction of 4′‐ferrocenyl‐1,1′‐biphenyl‐4‐ol with 4‐alkoxybenzoylchlorides, and (ii) crosscoupling of tris(4‐ferrocenylphenyl)boroxine with the corresponding halobenzenes. Crosscoupling was also applied for the synthesis of terphenyl‐containing mesogens Fc–(C₆H₄)₃–OC(O)–C₆H₄–O–C _n H_2n+1 (n = 10, 12) (6a,b) and (RC₅H₄)Fe‐[C₅H₄–(C₆H₄)₃–OC(O)–C₆H₄–O–C₁₀H₂₁] (11a, R = Et; 11b, R = n?Bu). The latter compounds also form nematic phases. Mesogens 6a,b form mesophases with wider temperature ranges than their biphenyl‐containing counterparts 3b,c. The most pronounced mesomorphism was displayed by compounds 11a and 11b, which have mesophases in the ranges 141–253°C and 120–238°C, respectively. The purity of compounds was established by ¹H NMR spectra and elemental analysis. Mesophases were identified by polarizing optical microscopy and differential scanning calorimetry.     

Evaluating glutamate and aspartate binding mechanisms to rutile (α-TiO2) via ATR-FTIR spectroscopy and quantum chemical calculations

Attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy and quantum chemical calculations were used to elucidate the influence of solution chemistry (pH, amino acid concentration) on the binding mechanisms of glutamic and aspartic acid to rutile (α-TiO(2)). The amino acids, glutamate and aspartate, contain carboxyl and amine groups whose dissociation over a pH range results in changes of molecular charge and reactivity, including reactions with mineral surfaces. At pH 3, a decrease of IR bands corresponding to protonated carboxyl groups is observed upon reaction with TiO(2) and indicates involvement of distal carboxyl groups during sorption. In addition, decreased IR bands arising from carboxyl bonds at 1400 cm(-1), concomitant to shifts to higher wavenumbers for ν(as)(γ-COO(-)) and ν(as)(α-COO(-)) (particularly at low glutamate concentrations), are indicative of inner-sphere coordination of both carboxyl groups and therefore suggest a "lying down" surface species. IR spectra of aspartate reacted with rutile are similar to those of solution-phase samples, without peak shifts indicative of covalent bonding, and outer-sphere coordination is predicted. Quantum chemical calculations were carried out to assist in elucidating molecular mechanisms for glutamate binding to rutile and are in reasonable agreement with experimental data. The combined use of ATR-FTIR data and quantum calculations suggests three potential surface configurations, which include (1) bridging-bidentate where glutamate is "lying down" and binding occurs through inner-sphere coordination of both α- and γ-carboxyl groups; (2) chelating-monodentate in which glutamate binds through inner-sphere coordination with the γ-carboxyl group in a "standing up" configuration (with or without protonation of the α-carboxyl); and (3) another bridging-bidentate configuration where glutamate is binding to rutile via inner-sphere coordination of the α-carboxyl group and outer-sphere coordination with the γ-carboxyl ("lying down").     

A self-consistent Hirshfeld method for the atom in the molecule based on minimization of information loss

Based on the so-called Hirshfeld atom in the molecule scheme, a new AIM method is presented. The method is similar to the Hirshfeld-I scheme, with the AIM weight function being constructed by minimizing the information loss upon formation of the molecule, but now requiring explicitly that the promolecular densities integrate to the same number of electrons as the AIM densities. This new weight function leads to a new iterative AIM scheme, and the resulting operative scheme is examined and discussed. The final results indicate that the newly proposed method does not perform as well as the Hirshfeld-I method.     

Cardinal series to restore NMR-signals dominated by strong inhomogeneous broadening

We have devised two numerical methods of restoring incomplete band-limited NMR-signals to integrity by either interpolating or extrapolating them. Both methods are based on use of the finite cardinal series, whose filtering properties were discussed previously, to model signals. They require no prior knowledge about the system under study, but only that the available parts of the signal were oversampled enough. The methods were tested on two types of computer-simulated signal. It proved superior to the linear prediction methods and Lagrange interpolation when applied to signals measured in highly inhomogeneous magnetic fields. The extrapolation method was then applied to restore experimentally-measured refocused FID-signals of a porous medium. The missing parts of the signal of up to several times the size of its Nyquist period could be recovered by either method.     

Structure of the two-dimensional relaxation spectra seen within the eigenmode perturbation theory and the two-site exchange model

The form of the two-dimensional (2D) NMR-relaxation spectra--which allow to study interstitial fluid dynamics in diffusive systems by correlating spin-lattice (T(1)) and spin-spin (T(2)) relaxation times--has given rise to numerous conjectures. Herein we find analytically a number of fundamental structural properties of the spectra: within the eigen-modes formalism, we establish relationships between the signs and intensities of the diagonal and cross-peaks in spectra obtained by various 1 and 2D NMR-relaxation techniques, reveal symmetries of the spectra and uncover interdependence between them. We investigate more specifically a practically important case of porous system that has sets of T(1)- and T(2)-eigenmodes and eigentimes similar to each other by applying the perturbation theory. Furthermore we provide a comparative analysis of the application of the, mathematically more rigorous, eigen-modes formalism and the, rather more phenomenological, first-order two-site exchange model to diffusive systems. Finally we put the results that we could formulate analytically to the test by comparing them with computer-simulations for 2D porous model systems. The structural properties, in general, are to provide useful clues for assignment and analysis of relaxation spectra. The most striking of them--the presence of negative peaks--underlines an urgent need for improvement of the current 2D Inverse Laplace Transform (ILT) algorithm used for calculation of relaxation spectra from NMR raw data.     

Contact passivation in silicon solar cells using atomic‐layer‐deposited aluminum oxide layers

Atomic‐layer‐deposited aluminum oxide (AlO_x) layers are implemented between the phosphorous‐diffused n⁺‐emitter and the Al contact of passivated emitter and rear silicon solar cells. The increase in open‐circuit voltage V_oc of 12 mV for solar cells with the Al/AlO_x/n⁺‐Si tunnel contact compared to contacts without AlO_x layer indicates contact passivation by the implemented AlO_x. For the optimal AlO_x layer thickness of 0.24 nm we achieve an independently confirmed energy conversion efficiency of 21.7% and a V_oc of 673 mV. For AlO_x thicknesses larger than 0.24 nm the tunnel probability decreases, resulting in a larger series resistance. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Forty years of theory-inspired experiments on charge-transfer via solutions and electrodes: the Georgian accents

Journal of Solid State Electrochemistry - This scholarly review, which also contains some specific historical details, is written by a few of researchers representing two generations succeeding the...     

Unprecedented Route to Ordered Polyaniline: Direct Synthesis of Highly Crystalline Fibrillar Films with Strong π‐π Stacking Alignment

Films of polyaniline (PANI) featuring about 80% crystallinity and characterised with strong π‐π stacking alignment parallel to the film surface have been obtained directly after the original synthesis upon simple drying of the aqueous PANI suspension. A strong anisotropy in the growth of the nano‐sized crystals produced during the synthesis results in the formation of micrometer‐length fibrils perpendicular to the film surface in the course of water evaporation. The regular intercalation of water molecules between the PANI chains seems to be crucial for their ordering throughout the synthesis and film formation.