Photo-absorption studies on carbonyl sulphide in 30,000–91,000 cm−1 region using synchrotron radiation

Photo-absorption spectrum of carbonyl sulphide (OCS) is recorded in 30,000–91,000 cm^?1 (3300–1050 Å) region at an average resolution of 1.2 Å using Photo-physics beamline on the 450 MeV Indus-1 synchrotron radiation source at RRCAT Indore, India. Owing to significant absorption cross section dependence, spectra of OCS are recorded at various pressures (0.001–5 mbar) to optimize the S/N ratio for band systems appearing at different energy regions. The spectral region below 70,000 cm^?1 has contributions from dissociation mechanism of the ground state of OCS and three valence band systems arising from promotion of a 3π electron to 4π and 10σ orbital. Improved S/N ratio helped in unambiguous assignment of the valence band progressions at 42,000–48,000 cm^?1, 53,000–62,000 cm^?1 and 63,500–70,000 cm^?1 regions to the ¹Δ←X¹Σ⁺ transition, the relatively intense and sharp bands of ¹Π←X¹Σ⁺ transition and intense but broad bands of ¹Σ⁺←X¹Σ⁺ transition, respectively, and obtain the vibrational frequencies. Above 70,000 cm^?1 Rydberg series arising from s, p, d and f orbitals converging to the ionic ground state X²Π of OCS⁺ (90,121 cm^?1) are identified. Long progression in the first few members of the Rydberg series is suggestive of mixed valence character. Quantum defects are evaluated and used to discuss the nature of the molecular orbital. The present study provides a unifying picture of the VUV photo-absorption spectrum of OCS up to its first ionization limit.     

Microwave assisted sample preparation for determining water-soluble fraction of trace elements in urban airborne particulate matter: evaluation of bioavailability

The feasibility of using two different microwave-based sample preparation methods was investigated to determine the total and water-soluble trace metal fraction in airborne particulate matter. The extraction techniques were then applied to urban particulate matter of different sizes in order to evaluate their bioavailability of associated trace metals. While a combination of HNO₃-HF-H₂O₂ was used for the total trace metal fraction of particulate matter, water was employed for the microwave-assisted extraction of water-soluble trace metal fractions. Inductively coupled plasma-mass spectrometry (ICP-MS) was used for the analysis of trace elements. The experimental protocol for the microwave assisted digestion was established using two different SRMs (1648, urban particulate matter and 1649a, urban dust). In the case of water-soluble trace metal fraction, the quantities extracted from the SRMs were compared between ultrasonic and microwave-assisted extractions, and there was a good agreement between the two extraction methods. Blanks values and limits of detection (LODs) for total and water-soluble trace metal concentrations were determined for three different filter substrates (Teflon, Zeflour, and Quartz). Subsequently, the proposed digestion method was evaluated for its extraction efficiency with these filter substrates. Finally, the real-world application of the proposed microwave-based sample preparation methods was demonstrated by analyzing trace elements in airborne particulate samples collected from different outdoor environments in Singapore. The solubility of 11 trace elements detected in the particulate samples is quantified.     

Rapid extraction of water soluble organic compounds from airborne particulate matter.

Water soluble organic compounds (WSOC) in airborne particulate matter (PM) have received considerable attention in recent years due to their abundance and their importance in atmospheric processes. The analysis of WSOC is necessary for quantifying the relative contribution of individual organic compounds to the total WSOC mass. In the present work, we evaluated the performance of a microwave-assisted extraction (MAE) method for the determination of WSOC in PM and compared the data with those of a conventional ultrasonic extraction (USE). The experimental results showed that the MAE method requires a shorter extraction time (5 min) compared to USE. The isolated water-soluble organic fraction of PM was subsequently analyzed using ion chromatography (IC) for low molecular weight organic acids. The rapid MAE method was used in conjunction with IC for the analysis of organic acids in PM samples, collected from different sources.     

Group Structure in Circle Theorem

A general method to discuss the potential flow past two intersecting circles is presented. This is done by introducing two operators L and M , which generate a group G . A procedure called closure is introduced, which determines the order of the group and the angles of intersection of the two circles.     

Incident investigation on thermal instability of an intermediate using adiabatic calorimeter

Thermal instability is a loss of thermal control which liberates high amount of energy and pressure. An incident took place during drying of an intermediate having amino alcohol functional group in agitated nutsche filter dryer at plant scale. During our investigation using advanced reactive system screening tool (ARSST), thermal decomposition was observed. Onset temperature of decomposition (T _o) is at 85 °C, adiabatic temperature rise due to decomposition (ΔT _ad) is 215 °C, maximum temperature attained due to decomposition (T _max) is 300 °C, maximum self-heat rate (dT/dt)_max is 6,215 °C min^?1, and maximum rate of pressure rise (dP/dt)_max is 1,442 psi min^?1 obtained from ARSST experiments. T _D24 value is 75 °C which was estimated experimentally. The correlations of these results were utilized to identify the root cause of this incident and necessary control measures were taken accordingly.     

Superacid‐Promoted Cyclodehydration Leading to the Imidazo[2,1‐a]isoquinoline Ring System

A series of heterocycle‐substituted acetophenones were prepared and reacted with the Brønsted superacid CF₃SO₃H (triflic acid=trifluoromethanesulfonic acid). Cyclodehydration provided aryl‐substituted imidazo[2,1‐a]isoquinolines and related products (28–85%, seven examples). A mechanism is proposed involving dicationic intermediates.     

L‐Proline‐Catalyzed Asymmetric Direct Aldol Reaction of Heteroaromatic Aldehydes and Acetone: Improvement of Catalytic Efficiency in Ionic Liquid bmim [BF4]

l‐proline in bmim [BF₄] ionic liquid has been successfully used as an efficient and reusable catalyst for the direct asymmetric aldol reaction of acetone with different heteroaromatic aldehydes to afford higher selectivity of the aldol products with good enantioselectivity.     

Organocatalyzed enantioselective synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylates

The organocatalyzed enantioselective synthesis of biologically active 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylate derivatives was achieved using bifunctional cinchona alkaloids as the catalysts. Using quinine thiourea as the catalyst, the tandem Michael addition-cyclization reaction between 1,3-cyclohexanediones and alkylidenecyanoacetate derivatives gives the desired products in high yields (up to 92%) and good ee values (up to 82%).     

Photo-Absorption Studies on Formaldehyde Using Synchrotron Radiation at Indus I

Photo-absorption spectra of formaldehyde (HCHO) is recorded in the range of 6–11.5 eV at various pressures (<0.001–2 mbar) at an average resolution of 1.2 Å using Photophysics beam line at the 450 MeV Indus-1 synchrotron radiation facilities at RRCAT Indore, India. The spectrum is found to consist exclusively of n → Rydberg transitions converging to the ground state of HCHO⁺. The highest identified Rydberg states, observed up to the first ionization limit of HCHO, correspond to 7s, 11p, 9d, and 12f orbitals. Analyzed electronic spectrum along with the intensities and quantum defects are presented. To interpret the observed weak valence transitions instead of strong valence transitions, a theoretical study of Rydberg and valence electronic states of HCHO is performed in the framework of single configuration interaction (CIS) and time-dependent density functional theory (TDDFT) using different basis sets. Electronic transition energies of high-lying singlet and triplet valence states as calculated using TDDFT (B3LYP) level of theory are found to give fairly-good agreement with the experimental data.     

Fe3O4 Nanorods-RGO-ionic Liquid Nanocomposite Based Electrochemical Sensor for Aflatoxin B1 in Ground Paprika

A novel and sensitive method for the determination of aflatoxin B1 (AFA−B1) in ground paprika using a methyltrioctylammonium chloride ionic liquid (IL), iron oxide nanorods (Fe₃O₄ nanorods) and reduced graphene oxide (RGO) fabricated glassy carbon electrode (GCE) was developed. The synthesized nanoparticles, nanocomposites and modified electrode surfaces were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA/DSC) and x-ray diffraction (XRD) analyses. Moreover, the electrochemical performance of the developed sensor was determined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results demonstrate that the sensitivity of AFA−B1 is significantly enhanced on RGO-Fe₃O₄ nanorods-IL-GCE in comparison with bare GCE, RGO-GCE and RGO-Fe₃O₄ nanorods-GCE. The redox peak currents of AFA−B1 exhibited good linear relationship with its concentration in the range from 0.02 to 0.33 ng mL⁻¹ with detection limit of (LOD) 0.03 ng mL⁻¹ and limit of quantification (LOQ) 0.36 ng mL⁻¹ respectively (S/N=3). In addition, the fabricated electrode showed good stability and reproducibility. The proposed technique was effectively applied to identify the AFA−B1 in real ground paprika samples with acceptable results.