Transient nutations of photoelectrons from alkali metal anions

Transient nutations of the magnetization of photoelectrons ejected from rubidium and cesium anions are described. The nature of the nutations requires that the time between photoexcitation and appearance of the photoelectron is less than ≈10^?7 s.     

6-Aryl-1-azabicyclo [5.4.0] undecanes

Some 6-aryl-6-hydroxy-l-azabicyclo[5.4.0]undecanes and their esters were synthesized as potential cardiovascular agents and analgetics of the proheptazine type, respectively. Also, 6-aryl-1-azabicyclo[5.4.0]undecanes were prepared as rigid structures related to the phenethylamine CNS stimulants.     

Structures of anti,Z-4,4-dimethyl-3-thiosemicarbazide, syn,E,Z-2,4-dimethyl-3-thiosemicarbazide and syn,E-1-cyclopentano-3-thiosemicarbazone

The structures of three alkyl derivatives of thiosemicarbazide are described: anti,Z-4,4-dimethyl-3-thiosemicarbazide (1), syn,E,Z-2,4-dimethyl-3-thiosemicarbazide (2), and syn,E-1-cyclopentano-3-thiosemicarbazone (3). Crystal data: for 1: triclinic, P-1 (#2), a = 5.802(1)Å, b = 6.935(1)Å, c = 8.104(2)Å, = 78.35(1)°, = 82.13(1)°, = 70.71(1)°, and Z = 2; for 2: orthorhombic, Pbca (#61), a = 9.417(3)Å, b = 8.624(2)Å, c = 15.169(3)Å, and Z = 8; for 3: triclinic, P-1 (#2), a = 6.068(3)Å, b = 8.145(4)Å, c = 8.666(5)Å, = 83.75(4)°, = 86.16(5)°, = 74.07(4)°, and Z = 2. In general, molecules are linked by N–H···S hydrogen bonds with sulfurs accepting two or three hydrogen bonds. Structures 2 and 3, which adopt the syn conformation, form N–H···N intramolecular hydrogen bonds. The solid-state structures are consistent with their infrared and proton nuclear magnetic resonance spectra.     

Protein–small molecule docking with receptor flexibility in iMOLSDOCK

We have earlier reported the iMOLSDOCK technique to perform ‘induced-fit’ peptide–protein docking. iMOLSDOCK uses the mutually orthogonal Latin squares (MOLSs) technique to sample the conformation and the docking pose of the small molecule ligand and also the flexible residues of the receptor protein, and arrive at the optimum pose and conformation. In this paper we report the extension carried out in iMOLSDOCK to dock nonpeptide small molecule ligands to receptor proteins. We have benchmarked and validated iMOLSDOCK with a dataset of 34 protein–ligand complexes as well as with Astex Diverse dataset, with nonpeptide small molecules as ligands. We have also compared iMOLSDOCK with other flexible receptor docking tools GOLD v5.2.1 and AutoDock Vina. The results obtained show that the method works better than these two algorithms, though it consumes more computer time. The source code and binary of MOLS 2.0 (under a GNU Lesser General Public License) are freely available for download at https://sourceforge.net/projects/mols2-0/files/.     

Combined experimental and theoretical study on aromatic hydroxylation by mononuclear nonheme iron(IV)-oxo complexes

The hydroxylation of aromatic compounds by mononuclear nonheme iron(IV)-oxo complexes, [FeIV(Bn-tpen)(O)]2+ (Bn-tpen=N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine) and [FeIV(N4Py)(O)]2+ (N4Py=N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), has been investigated by a combined experimental and theoretical approach. In the experimental work, we have performed kinetic studies of the oxidation of anthracene with nonheme iron(IV)-oxo complexes generated in situ, thereby determining kinetic and thermodynamic parameters, a Hammett rho value, and a kinetic isotope effect (KIE) value. A large negative Hammett rho value of -3.9 and an inverse KIE value of 0.9 indicate that the iron-oxo group attacks the aromatic ring via an electrophilic pathway. By carrying out isotope labeling experiments, the oxygen in oxygenated products was found to derive from the nonheme iron(IV)-oxo species. In the theoretical work, we have conducted density functional theory (DFT) calculations on the hydroxylation of benzene by [FeIV(N4Py)(O)]2+. The calculations show that the reaction proceeds via two-state reactivity patterns on competing triplet and quintet spin states via an initial rate determining electrophilic substitution step. In analogy to heme iron(IV)-oxo catalysts, the ligand is noninnocent and actively participates in the reaction mechanism by reshuttling a proton from the ipso position to the oxo group. Calculated kinetic isotope effects of C6H6 versus C6D6 confirm an inverse isotope effect for the electrophilic substitution pathway. Based on the experimental and theoretical results, we have concluded that the aromatic ring oxidation by mononuclear nonheme iron(IV)-oxo complexes does not occur via a hydrogen atom abstraction mechanism but involves an initial electrophilic attack on the pi-system of the aromatic ring to produce a tetrahedral radical or cationic sigma-complex.     

Use of in-tube sorptive extraction techniques for determination of benzene, toluene, ethylbenzene and xylenes in soft drinks

A comparison is made between static headspace analysis and headspace solid-phase dynamic extraction (HS-SPDE) for the quantitative determination of trace level BTEX solvents (benzene, toluene, ethylbenzene and o-, m-, and p-xylene) in soft drinks. Two non-polar extraction phases were investigated for SPDE using an automated sampler with a gas-tight syringe equipped with a special needle coated on the inside with the extraction phase. Following adsorption onto the phase, the analytes were thermally desorbed directly into a GC-MS. The techniques were optimised and evaluated by analysis of spiked soft drink samples. The use of the SPDE device gave comparable results to the static headspace method, with lower detection limits for some compounds, and also offers advantages for applications where lower temperatures are preferred.     

Large-volume sample stacking with polarity switching for the analysis of bacteria by capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis has been utilized for the rapid analysis of bacteria under specific experimental conditions. In this work, a method of large-volume sample stacking with polarity switching was evaluated for the analysis of bacteria by capillary electrophoresis with laser-induced fluorescence detection in order to enhance the detection sensitivity. The results indicated that the proposed method is not only effective for the focusing of bacterial cells, but also for the separation of mixtures of bacteria. With the optimized conditions, an enhancement factor of around 60-fold was obtained when long sample plug (up to 39.6% of capillary volume) was injected. Moreover, with the help of such stacking method, single, sharp, intense peak with high efficiency was observed without multiple peaks attributable to irregular clusters and aggregates of bacterial cells. This simple stacking approach appears to be promising as a rapid sterility test in various fields of applications.     

Single-molecule elasticity measurements of the onset of excluded volume in poly(ethylene glycol)

A polymer must reach a certain size to exhibit significant excluded-volume interactions and adopt a swollen random-walk configuration. We show that single-molecule measurements can sense the onset of swelling by modulating the effective chain size with force: as the force is reduced from a large value, the polymer is first highly aligned, then a Gaussian coil, then finally a swollen chain, with each regime exhibiting a distinct elasticity. We use this approach to quantify the structural parameters of poly(ethylene glycol) and show that they vary in the expected manner with changes in solvent.     

Optical fiber-coupled InGaAs-based terahertz time-domain spectroscopy system

The successful demonstration of an optical fiber-coupled terahertz time-domain spectroscopy (THz-TDS) system is described in this study. The terahertz output power of the emitter with two optical band rejection filters was 132 nW, which is an improvement of 70% over the output power without any filters. This improvement is due to the suppression of an optical modulated signal that is reverse-generated when an alternating current bias exceeding a certain threshold is applied to the emitter. Under the optimal alignment conditions, the terahertz detector in a fiber-coupled THz-TDS system clearly measured water vapor dips in the free space.     

Quenching of surface traps in Mn doped ZnO thin films for enhanced optical transparency

The structural and photoluminescence analyses were performed on un-doped and Mn doped ZnO thin films grown on Si (1 0 0) substrate by pulsed laser deposition (PLD) and annealed at different post-deposition temperatures (500-800 °C). X-ray diffraction (XRD), employed to study the structural properties, showed an improved crystallinity at elevated temperatures with a consistent decrease in the lattice parameter ‘c’. The peak broadening in XRD spectra and the presence of Mn 2p3/2 peak at ∼640 eV in X-ray Photoelectron Spectroscopic (XPS) spectra of the doped thin films confirmed the successful incorporation of Mn in ZnO host matrix. Extended near band edge emission (NBE) spectra indicated the reduction in the concentration of the intrinsic surface traps in comparison to the doped ones resulting in improved optical transparency. Reduced deep level emission (DLE) spectra in doped thin films with declined PL ratio validated the quenching of the intrinsic surface traps thereby improving the optical transparency and the band gap, essential for optoelectronic and spintronic applications. Furthermore, the formation and uniform distribution of nano-sized grains with improved surface features of Mn-doped ZnO thin films were observed in Field Emission Scanning Electron Microscopy (FESEM) images.