White-light-induced fragmentation of methane

We experimentally probe molecular ionization and dissociation of methane molecules in the gas phase upon their irradiation by intense pulses of white light that spans the wavelength range 500-850 nm. White light pulses are generated upon irradiation of BK7 glass by 36-fs-long pulses of intense 820 nm laser light. Comparison is made of the molecular fragmentation patterns obtained using white light that is depolarized with those obtained using single-color (820 nm) light that is highly chirped. On the basis of such comparison, we make hitherto-unavailable estimates of the in situ intensity of white light pulses. Results obtained using white light also indicate that resonances apparently do not play any role in the ionization dynamics that ensue upon irradiation by intense, broadband light; neither are the dynamics affected by the polarization properties of the 820 nm light that is used to generate the white light.     

Application of Doehlert design in optimizing the determination of degraded products of nerve agents by ion-pair liquid chromatography electrospray ionization tandem mass spectrometry

A qualitative method was developed for the determination of degraded products of nerve agents by using ion-pair liquid chromatography electrospray ionization tandem mass spectrometry (IP-LC-ESI-MS(n)). Generally, alkylphosphonic acids (APAs) and O-alkyl alkylphosphonic acids (AAPAs) give deprotonated molecular ion [M-H](-) in negative mode. Interestingly, first time we obtained the molecular radical anion [M](.-) of phosphonic acids in negative mode by using tri-n-butyl amine as an ion-pairing agent. We interpreted this observation as an indication of electrochemical reduction of phosphonic acids in electrospray needle. Three variables such as sheath gas flow, electrospray needle voltage and pH of the mobile phase were investigated to enhance the molecular radical anion [M](.-) signal of each analyte. The Doehlert design was used to obtain the region in which the optimum value of such variables is simultaneously achieved. Limit of detection achieved was 0.5 microg mL(-1) for AAPAs and 10 microg mL(-1) for APAs. Excellent precision was observed with less than 8.61% RSD. Finally, the method was applied for the detection of ethyl methylphosphonic in aqueous extract of soil sample.     

In situ derivatization hollow fiber mediated liquid phase microextraction of alkylphosphonic acids from water

Alkylphosphonic acids (APAs), particularly the methyl-, ethyl-, isopropyl- and n-propyl-phosphonic acids are important markers of extremely toxic nerve agents. Hence, their detection and identification is of vital importance to verification of chemical weapons convention (CWC). Verification analysis of CWC requires development of fast, reliable, simple and reproducible sample preparation methods of water and soil samples. Present investigation is focused on the optimization of alkylation of APAs in water with subsequent extraction of alkylated acids by hollow fiber liquid phase microextraction (HF-LPME). This simple and sensitive sample preparation of APAs from water offered better recoveries in comparison to conventionally used extraction technique. Under optimized conditions, the APAs were detected at the concentration of 0.5-0.75 microg/mL with S/N ratio > or = 5, whereas the LODs for alkyl APAs (monobasic APAs) were achieved up to 0.1 microg/mL. The developed method was finally tested with water samples supplied in 19th official proficiency test conducted by the OPCW.     

A remarkable accelerating effect of Ag-salt on intramolecular cyclization of o-(1-alkynyl)benzenesulfonamides

Herein, we report transition metal-catalyzed intramolecular cyclization of o-(1-alkynyl)benzenesulfonamides to afford 3-substituted benzothiazines regioselectively via a C-N bond forming reaction and Cu-catalyzed sequential C-N and C-C bond formation leading to the corresponding 3,4-disubstituted derivatives.     

UHV STM I(V) and XPS studies of aryl diazonium molecules assembled on Si(111)

Molecular layers formed from 4-trifluoromethylbenzenediazonium tetrafluoroborate and 4-Methylbenzenediazonium tetrafluoroborate have been assembled on H-passivated Si(111) and studied by UHV STM and XPS. STM imaging shows well-developed Si(111) step edges and terraces both on Si(111):H and Si(111) substrates covered with a molecular layer. STM I(V) data acquired at different tip-substrate separations reveals a factor of approximately 10 enhancement in current for positive bias voltage when current flows through the 4-trifluoromethyl molecule when compared to the 4-methyl variant. The observed current enhancement in I(V) can be understood by comparing the projected density of states of the two molecule-Si systems calculated using a density functional theory local density approximation after geometry optimization was performed via the conjugate gradient method. XPS data independently confirm that H-passivated Si(111) remains oxygen free for short exposures to ambient conditions and provide evidence that the molecules chemically react with the silicon surface.     

Flavonoids and phenol glycosides from Boerhavia diffusa

Four new compounds were isolated from Boerhavia diffusa namely eupalitin 3-O-beta-D-galactopyranosyl-(1' --> 2')-O-beta-D-galactopyranoside (1), 3,3',5-trihydroxy-7-methoxyflavone (4), 4',7-dihydroxy-3'-methylflavone (5) and 3,4-dimethoxyphenyl-1-O-beta-D-apiofuranosyl-(1' --> 3')-O-beta-D-glucopyranoside (7) along with eight known compounds. The structures were elucidated by analysis of their spectroscopic data.     

Structural transformation of MoO<Subscript>3</Subscript> nanobelts into MoS<Subscript>2</Subscript> nanotubes

The structural transformation of MoO₃ nanobelts into MoS₂ nanotubes using a simple sulfur source has been reported. This transformation has been extensively investigated using electron microscopic and spectroscopic techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and energy-dispersive X-ray analysis (SEM-EDAX and TEM-EDX). The method described in this report will serve as a generic route for the transformation of other oxide nanostructures into the chalcogenide nanostructures.     

2‐[(E)‐(4‐Chloro­phenyl)­methyl­ene­amino]‐N‐(X‐methyl­phenyl)‐4,5,6,7‐tetra­hydro‐1‐benzo­thio­phene‐3‐carbox­amide,where X = 2 and 3

The title compounds, both C₂₃H₂₁ClN₂OS, are isomeric, with (I) and (II) being the N‐3‐methyl­phenyl and N‐2‐methyl­phenyl derivatives, respectively. The dihedral angle between the 4‐chloro­phenyl group and the thio­phene ring in (II) [38.1 (1)°] is larger than that in (I) [7.1 (1)°], indicating steric repulsion between the chloro­phenyl and o‐toluidine groups in (II). In both compounds, an intramolecular N—H⋯N hydrogen bond forms a pseudo‐six‐membered ring, thus locking the molecular conformation. In the crystal structures, mol­ecules are connected via N—H⋯O hydrogen bonds, forming chains along the b axis in (I) and along the c axis in (II). Intermolecular C—H⋯O/S and π–π interactions are also observed in (II), but not in (I).     

Pd-catalyzed synthesis of α-aryl ketones through couplings of α-arylacetyl chlorides with triarylbismuths as multi-coupling nucleophiles

The cross-coupling reaction of α-arylacetyl chlorides with triarylbismuths was studied under Pd-catalyzed conditions. The reaction was found to be facile under the established protocol and furnished high yields of α-aryl ketones in short reaction times. This work also demonstrated a facile synthesis of various regio-isomeric mono-, di- and tri-substituted α-aryl ketones in high yields. Triarylbismuths were employed as sub-stoichiometric multi-coupling organometallic nucleophiles in this coupling protocol.     

Crystal Structure Studies of Two Regioisomers of Bromo-4-Aryloxymethylcoumarins

Abstract  

The 4-(2-bromo-4-methyl-phenoxymethyl)-6-methylcoumarin (1) have been synthesized from bromination of corresponding 4-aryloxymethyl coumarin, which is a regioisomer of 4-(2-bromo-4-methyl-phenoxymethyl)-7-methylcoumarin (2) (CCDC-695895). The compound 1 crystallizes with triclinic space group P-1, a = 8.0943(3) ?, b = 9.3502(3) ?, c = 10.1476(4) ?, α = 90.234(2)°, β = 94.065(2)°, γ = 95.106(2)°, Z = 2 and compound 2 crystallizes with monoclinic space group P2₁/n, a = 8.465(5) ?, b = 13.649(5) ?, c = 13.304(5) ?, α = 90.000(5)°, β = 90.740(5)°, γ = 90.000(5)°, Z = 4. Both the compounds are planar with variation in their intermolecular hydrogen bonds between C–H···O and C–H···π.