Positive muon as a probe of magnetization density in ferromagnetic metal vacancies

The hyperfine field at a positive muon site trapped in a ferromagnetic metal vacancy is calculated and found to be more positive than that in the interstitial position. It is suggested that the muons can be used to enrich our knowledge of the electron spin distributions in metal vacancies that so far has not been possible.     

Reaction of hypochlorous acid with imidazole: formation of 2-chloro- and 2-oxoimidazoles

Reaction of hypochlorous acid (HOCl) with imidazole (Im) taken as a model for the 5-membered ring of guanine, leading to the products 2-chloro- and 2-oxo-imidazoles was investigated at the B3LYP/6-31+G* and B3LYP/AUG-cc-pVDZ levels of density functional theory. For all cases, single point energy calculations were performed at the MP2/AUG-cc-pVDZ level of theory using the geometries optimised at the B3LYP/AUG-cc-pVDZ level. Intrinsic reaction coordinate calculations were performed to ensure genuineness of all the calculated transition states. Effect of aqueous media was investigated by solvating all the species involved in the reactions using the polarizable continuum model. It is found that 2-chloroimidazole (2-ClIm) can be formed following three different reaction schemes while 2-oxoimidazole (2-oxoIm) can be formed following two different reaction schemes. The calculated barrier energies show that formation of 2-oxoIm would be less favored than that of 2-ClIm, which explains the experimental observations on relative yields of 8-chlorodeoxyguanosine and 8-oxodeoxyguanosine.     

Circular dichroism (CD) spectroscopy of the assembly and disassembly of SNAREs: The proteins involved in membrane fusion in cells

In this study, we report for the first time that both t-SNAREs and v-SNARE and their complexes in buffered suspension, exhibit defined peaks at CD signals of 208 and 222 nm wavelengths, consistent with a higher degree of helical secondary structure. Surprisingly, when incorporated in lipid membrane, both SNAREs and their complexes exhibit reduced folding. In presence of NSF–ATP, the SNARE complex disassembles, as reflected from the CD signals demonstrating elimination of α-helices within the structure.     

Separation, characterization, and quantitation of process-related substances of the anti-hypertensive drug doxazosin mesylate by reversed-phase LC with PDA and ESI-MS as detectors

A simple and rapid reversed-phase liquid chromatography (LC) method with photodiode array (PDA) and electrospray ionization (ESI)-mass spectrometry (MS) as detectors was developed and validated to separate, identify, and quantitate the related substances of Doxazosin mesylate (DXZN) for monitoring the reactions involved during process development. The high-performance liquid chromatography profiles of related-substances of DXZN are used as fingerprints to follow the procedures used in the manufacturing units. The separation is accomplished on an Inertsil ODS-3 column with acetonitrile-ammonium acetate (10 mM, pH 4.0) as the mobile phase, using a gradient elution mode and monitoring the eluents by a photodiode array detector at 265 nm at ambient temperature. LC-ESI-MS-MS is used to identify the additional impurities formed during the synthesis. The identified impurities were synthesized and characterized by UV, Fourier transform-IR, 1H NMR, and MS data. The detection limits for the impurities are 0.74 - 4.14 x 10(-9) g, and the method is found to be suitable not only for the monitoring of synthetic reactions, but also for quality assurance of DXZN in bulk drugs and formulations.     

Green Synthetic Approach: An Efficient Eco-Friendly Tool for Synthesis of Biologically Active Oxadiazole Derivatives

Green synthetic protocol refers to the development of processes for the sustainable production of chemicals and materials. For the synthesis of various biologically active compounds, energy-efficient and environmentally benign processes are applied, such as microwave irradiation technology, ultrasound-mediated synthesis, photo-catalysis (ultraviolet, visible and infrared irradiation), molecular sieving, grinding and milling techniques, etc. Thesemethods are considered sustainable technology and become valuable green protocol to synthesize new drug molecules as theyprovidenumerous benefits over conventional synthetic methods.Based on this concept, oxadiazole derivatives are synthesized under microwave irradiation technique to reduce the formation of byproduct so that the product yield can be increased quantitatively in less reaction time. Hence, the synthesis of drug molecules under microwave irradiation follows a green chemistry approach that employs a set of principles to minimize or remove the utilization and production of hazardous toxic materials during the design, manufacture and application of chemical substances.This approach plays a major role in controlling environmental pollution by utilizing safer solvents, catalysts, suitable reaction conditions and thereby increases the atom economy and energy efficiency. Oxadiazole is a five-membered heterocyclic compound that possesses one oxygen and two nitrogen atoms in the ring system.Oxadiazole moiety is drawing considerable interest for the development of new drug candidates with potential therapeutic activities including antibacterial, antifungal, antiviral, anticonvulsant, anticancer, antimalarial, antitubercular, anti-asthmatic, antidepressant, antidiabetic, antioxidant, antiparkinsonian, analgesic and antiinflammatory, etc. This review focuses on different synthetic approaches of oxadiazole derivatives under microwave heating method and study of their various biological activities.     

Resonant terahertz generation from InN thin films

Highly efficient conversion from ultrafast optical pulses to their terahertz (THz) counterparts has been achieved with InN thin films. An average THz output power as high as 0.931 microW has been obtained for an average pump power of 1 W, corresponding to a normalized conversion efficiency of 190% mm(-2). Based on our measured dependences of the THz output power on pump polarization, incident angle, pump power, and InN film thickness, resonance-enhanced optical rectification is one of the most plausible mechanisms for the THz generation in the InN films.     

Effects of charging and doping on orbital hybridizations and distributions in TiO2 clusters

Charging and doping are two important strategies used in TiO₂ quantum dots for photocatalysis and photovoltaics. Using small clusters as the prototypes for quantum dots, we have carried out density functional calculations to study the size-specific effects of charging and doping on geometry, electronic structure, frontier orbital distribution, and orbital hybridization. We find that in neutral (TiO₂)_n clusters the charge transfer from Ti to O is almost size independent, while for the anionic (TiO₂)_n clusters the corresponding charge transfer is reduced but it increases with size. When one O atom is substituted with N, the charge transfer is also reduced due to the smaller electron affinity of N. As the cluster size increases, the populations of 3d and 4s orbitals of Ti decrease with size, while the populations of the 4p orbital increase, suggesting size dependence of spd hybridizations. The present study clearly shows that charging and doping are effective ways for tailoring the energy gap, orbital distributions, and hybridizations.     

Borane Derivatives: A New Class of Super‐ and Hyperhalogens

Super‐ and hyperhalogens are a class of highly electronegative species whose electron affinities far exceed those of halogen atoms and are important to the chemical industry as oxidizing agents, biocatalysts, and building blocks of salts. Using the well‐known Wade–Mingos rule for describing the stability of closo‐boranes B_nH_n^2? and state‐of‐the‐art theoretical methods, we show that a new class of super‐ and hyperhalogens, guided by this rule, can be formed by tailoring the size and composition of borane derivatives. Unlike conventional superhalogens, in which a central metal atom is surrounded by halogen atoms, the superhalogens formed according to the Wade–Mingos rule do not have to have either halogen or metal atoms. We demonstrate this by using B₁₂H₁₃ and its isoelectronic cluster CB₁₁H₁₂ as examples. We also show that while conventional superhalogens containing alkali atoms require at least two halogen atoms, a single borane‐like moiety is sufficient to give M(B₁₂H₁₂) clusters (M=Li, Na, K, Rb, Cs) superhalogen properties. In addition, hyperhalogens can be formed by using the above superhalogens as building blocks. Examples include M(B₁₂H₁₃)₂ and M(CB₁₁H₁₂)₂ (M=Li–Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.     

Structure and properties of the aluminum borates Al(BO2)n and Al(BO2)n(-), (n = 1-4)

The geometrical and electronic structures of Al(BO(2))(n) and Al(BO(2))(n)(-) (n = 1-4) clusters are computed at different levels of theory including density functional theory (DFT), hybrid DFT, double-hybrid DFT, and second-order perturbation theory. All aluminum borates are found to be quite stable toward the BO(2) and BO(2)(-) loss in the neutral and anion series, respectively. Al(BO(2))(4) belongs to the class of hyperhalogens composed of smaller superhalogens, and should possess a large adiabatic electron affinity (EA(ad)) larger than that of its superhalogen building block BO(2). Indeed, the aluminum tetraborate possesses the EA(ad) of 5.6 eV, which, however, is smaller than the EA(ad) of 7.8 eV of the AlF(4) supehalogen despite BO(2) is more electronegative than F. The EA(ad) decrease in Al(BO(2))(4) is due to the higher thermodynamic stability of Al(BO(2))(4) compared to that of AlF(4). Because of its high EA and thermodynamic stability, Al(BO(2))(4) should be capable of forming salts with electropositive counter ions. We optimized KAl(BO(2))(4) as corresponding to a unit cell of a hypothetical KAl(BO(2))(4) salt and found that specific energy and energy density of such a salt are competitive with those of trinitrotoluol (TNT).     

Harvest planning in the Brazilian sugar cane industry via mixed integer programming

This work addresses harvest planning problems that arise in the production of sugar and alcohol from sugar cane in Brazil. The planning is performed for two planning horizons, tactical and operational planning, such that the total sugar content in the harvested cane is maximized. The tactical planning comprises the entire harvest season that averages seven months. The operational planning considers a horizon from seven to thirty days. Both problems are solved by mixed integer programming. The tactical planning is well handled. The model for the operational planning extends the one for the tactical planning and is presented in detail. Valid inequalities are introduced and three techniques are proposed to speed up finding quality solutions. These include pre-processing by grouping and filtering the distance matrix between fields, hot starting with construction heuristic solutions, and dividing and sequentially solving the resulting MIP program. Experiments are run over a set of real world and artificial instances. A case study illustrates the benefits of the proposed planning.