Quantum phases in a doped Mott insulator on the Shastry-Sutherland lattice

We propose the projected BCS wave function as the ground state for the doped Mott insulator SrCu2(BO3)2 on the Shastry-Sutherland lattice. At half filling this wave function yields the exact ground state. Adding mobile charge carriers, we find a strong asymmetry between electron and hole doping. Upon electron doping an unusual metal with strong valence bond correlations forms. Hole doped systems are d-wave resonating valence bond superconductors in which superconductivity is strongly enhanced by the emergence of spatially varying plaquette bond order.     

Towards Maintenance‐Free Biosensors for Hundreds of Bind/Release Cycles

A single aptamer bioreceptor layer was formed using a common streptavidin–biotin immobilization strategy and employed for 100–365 bind/release cycles. Chemically induced aptamer unfolding and release of its bound target was accomplished using alkaline solutions with high salt concentrations or deionized (DI) water. The use of DI water scavenged from the ambient atmosphere represents a first step towards maintenance‐free biosensors that do not require the storage of liquid reagents. The aptamer binding affinity was determined by surface plasmon resonance and found to be almost constant over 100–365 bind/release cycles with a variation of less than 5 % relative standard deviation. This reversible operation of biosensors based on immobilized aptamers without storage of liquid reagents introduces a conceptually new perspective in biosensing. Such new biosensing capability will be important for distributed sensor networks, sensors in resource‐limited settings, and wearable sensor applications.     

Assessment of recharge source to springs in upper Beas basin of Kullu region,Himachal Pradesh,India using isotopic signatures

Journal of Radioanalytical and Nuclear Chemistry - Environmental stable and radioisotope data of springs located in Kullu region of Himachal Pradesh are interpreted to identify the recharge source...     

ExcelAutomat 1.3: Fragment analysis based on the distortion/interaction-activation strain model

The distortion/interaction-activation strain model (D/I-ASM), a fragment analysis method, is applied to study the structure–reactivity relationship in reactions. The application of D/I-ASM involves the generation of input files for points along a reaction profile, submission of input files to a quantum software package, processing of parameters from the resulting output files and generation of graphical plots. The ExcelAutomat tool (Laloo et al., J. Comput. Aided Mol. Des. 2017, 31, 667) provides a framework and library in Visual Basic for Application programming language to process such files. New routines were written in ExcelAutomat 1.3 to facilitate processing of files for D/I-ASM. The worksheet “ASM” was included where initial parameters needed can be defined. The routines for D/I-ASM were tested successfully on bimolecular nucleophilic substitution, cycloaddition, and barrierless reactions. The automation of fragment analysis by ExcelAutomat 1.3 is compatible with Microsoft Excel and LibreOffice Calc. The extensible tool processes files from Gaussian and GAMESS-US packages. © 2018 Wiley Periodicals, Inc.     

Simultaneous densitometric determination of shikonin,acetylshikonin, and β‐acetoxyisovaleryl‐shikonin in ultrasonic‐assisted extracts of four Arnebia species using reversed‐phase thin layer chromatography

A simple, precise, and rapid high‐performance thin‐layer chromatographic (HPTLC) method for the simultaneous quantification of pharmacologically important naphthoquinone shikonin ( 1 ) together with its derivatives acetylshikonin ( 2 ), and β‐acetoxyisovalerylshikonin ( 3 ) in four species of genus Arnebia (A. euchroma, A. guttata, A. benthamii, and A. hispidissima) from the Indian subcontinent has been developed. In addition, the effect of solvents with varying polarity (hexane, chloroform, ethyl acetate, and methanol) for the extraction of these compounds was studied. HPTLC was performed on precoated RP‐18 F_254S TLC plates. For achieving good separation, mobile phase consisting of ACN/methanol/5% formic acid in water (40:02:08 v/v/v) was used. The densitometric determination of shikonin derivatives was carried out at 520 nm in reflection/absorption mode. The method was validated in terms of linearity, accuracy, precision, robustness, and specificity. The calibration curves were linear in the range of 100–600 ng for shikonin and acetylshikonin, and 100–1800 ng for β‐acetoxyisovalerylshikonin. Lower LOD obtained for compounds 1 – 3 were 18, 15, and 12 ng, respectively, while the LOQ obtained were 60, 45, and 40 ng, respectively.     

Monaural speech segregation using synthetic speech signals

When listening to natural speech, listeners are fairly adept at using cues such as pitch, vocal tract length, prosody, and level differences to extract a target speech signal from an interfering speech masker. However, little is known about the cues that listeners might use to segregate synthetic speech signals that retain the intelligibility characteristics of speech but lack many of the features that listeners normally use to segregate competing talkers. In this experiment, intelligibility was measured in a diotic listening task that required the segregation of two simultaneously presented synthetic sentences. Three types of synthetic signals were created: (1) sine-wave speech (SWS); (2) modulated noise-band speech (MNB); and (3) modulated sine-band speech (MSB). The listeners performed worse for all three types of synthetic signals than they did with natural speech signals, particularly at low signal-to-noise ratio (SNR) values. Of the three synthetic signals, the results indicate that SWS signals preserve more of the voice characteristics used for speech segregation than MNB and MSB signals. These findings have implications for cochlear implant users, who rely on signals very similar to MNB speech and thus are likely to have difficulty understanding speech in cocktail-party listening environments.     

An XRD characterization of the thermal degradation of polyacrylonitrile

Thermal degradation of polyacrylonitrile (PAN) has been studied by combined differential thermal analysis, thermogravimetry, and XRD analysis. On the basis of the experimental observations, it has been suggested that the intramolecular polymerization of nitrile groups to a conjugated polyimine structure is initially limited to only the amorphous zone of PAN, which involves little evolution of off-gases. Polymerization of nitrile group in the crystalline zone starts with the melting of crystallites with the evolution of off-gases from the amorphous-crystalline zone interface. ©1995 John Wiley & Sons, Inc.     

Oxomolybdenum(V) complexes of bis-(2-benzimidazolyl) alkanes

Summary Oxomolybdenum(V) complexes of the type (LH₄) [MoOCl₅] (where LH₂ = dimethylene bis-2-benzimidazole or tetramethylene bis-2-benzimidazole), [MoOCl₃(LH₂)] (where LH₂ = tetramethylene bis-2-benzimidazole), [(Mo₂O₄Cl₂-(H₂O)₃)₂(LH₂)] (where LH₂ = dimethylene bis-2-benzimidazole, tetramethylene bis-2-benzimidazole or hexamethylene bis-2-benzimidazole) and [Mo₂O₃Cl₄(LH₂)₂] (where LH₂ = tetramethylene bis-5-nitro-2-benzimidazole) were prepared and characterised. The mononuclear complexes show u.v.-vis. absorptions characteristic of octahedral molybdenum(V). The dinuclear complexes do not absorb in the visible region, possibly due to the presence of an Mo₂O ₄ ^{2 +}} core, which is also indicated by their diamagnetic behaviour. The biological activities of the free ligands and their complexes have been studied.     

Kinetics and mechanism of the oxidation of neutralized α-hydroxy acids by tris(pyridine-2-carboxylato)manganese(III)

The kinetics of oxidation of the neutralized -hydroxy acids: lactic, -hydroxyisobutyric, mandelic, benzilic and atrolactic acids by tris(pyridine-2-carboxylato)manganese(III) have been studied. The reactions were carried out in a Na(pic)-picH [Na(pic) = sodium salt of pyridine-2-carboxylic acid and picH = pyridine-2-carboxylic acid] buffer medium in the 4.89–6.10pH range. The oxidation rate was found to be independent of pH, and rate follows the order: benzilate > mandelate >atrolactate>lactate > -hydroxy isobutyrate. The oxidation products are MeCHO, Me2CO, PhCHO, Ph2CO and PhCOMe for the respective reactions. A mechanism is proposed involving intermediate formation of hepta-coordinated MnIII complexes in a fast step. The complexes then decompose to give free radicals and MnII in the rate determining step. The free radicals subsequently react with another molecule of the MnIII species to give the respective carbonyl compounds in a fast step.     

Activation Strain Analyses of Counterion and Solvent Effects on the Ion-Pair SN2 Reaction of and CH3Cl

We have computationally studied the bimolecular nucleophilic substitution (S_N2) reactions of M_nNH₂⁽ⁿ⁻¹⁾ + CH₃Cl (M⁺ = Li⁺, Na⁺, K⁺, and MgCl⁺; n = 0, 1) in the gas phase and in tetrahydrofuran solution at OLYP/6-31++G(d,p) using polarizable continuum model implicit solvation. We wish to explore and understand the effect of the metal counterion M⁺ and of solvation on the reaction profile and the stereochemical preference, that is, backside (S_N2-b) versus frontside attack (S_N2-f). The results were compared to the corresponding ion-pair S_N2 reactions involving F⁻ and OH⁻ nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in S_N2 reactivity along the nucleophiles F⁻, OH⁻, and , including solvent and counterion effects. © 2019 Wiley Periodicals, Inc.