Selectfluor-mediated mild oxidative halogenation and thiocyanation of 1-aryl-allenes with TMSX (X = Cl,Br, I,NCS) and NH4SCN

Presence of TMSX (X = Cl, Br, I) unleashes the oxidative character of Selectfluor and provides a mild dihalogenation method for 1-arylallenes. Preference for 2,3-addition was observed with TMSCl in MeCN irrespective of the nature of the substituent on the aryl moiety, whereas 1,2-addition was preferred in [BMIM][BF₄]. With TMSBr and TMSI only products corresponding to 2,3-addition were observed. Reactions carried out with TMSBr in IL solvents gave the corresponding monobromoalkenes as a major product along with the isomeric dibromo-alkenes. Reaction with NH₄SCN provided convenient access to dithiocyanate derivatives. The same products were formed via TMS-NCS/Selectfluor. Formation of common products via TMSNCS and NH₄SCN points to the formation and interplay of SCN⁺/NCS⁺ as incipient electrophiles.     

Ionic and dipolar solvation dynamics in liquid water

The solvation time correlation function for solvation in liquid water was measured recently. The solvation was found to be very fast, with a time constant equal to 55 fs. In this article we present theoretical studies on solvation dynamics of ionic and dipolar solutes in liquid water, based on the molecular hydrodynamic approach developed earlier. The molecular hydrodynamic theory can successfully predict the ultrafast dynamics of solvation in liquid water as observed from recent experiments. The present study also reveals some interesting aspects of dipolar solvation dynamics, which differs significantly from that of ionic solvation. Dedicated to Prof. C N R Rao on his 60th birthday     

Estimates of the number of quantal bound states in one and three dimensions

Using the relation between the number of bound states and the number of zeros of the radial eigen-functionψ(r), or equivalently, that ofφ(r)=rψ(r) in the range 0⩽r⩽∞, the upper bounds on the number of bound states generated by potentialV(r) in different angular momentum channels are obtained in three dimension. Using a similar procedure, the upper bound on the number of bound states in one dimension is also deduced. The analysis is restricted to a class of potentials for whichE=0 is the threshold. By taking a number of specific examples, it is demonstrated that both in one and three dimensions, the estimate of the upper bound obtained by this procedure is very close to or equal to the exact number of bound states. The correlation of the present method with the Levison’s theorem and WKB approximation is discussed.     

New modifications in 15 UD pelletron at nuclear science centre

The 15 UD pelletron at NSC has been operational and performed well during the last 11 years. There have been major modifications performed for upgradation of pelletron system over this period. Major upgradations which have been implemented are new resistor network system for voltage gradient, doublet to singlet unit conversion for accelerator units, turbopump based gas stripper system etc. In addition accelerator mass spectroscopy program has also been started. A new multi-cathode source, Wien filter etc. have been procured and will be added soon in the system. An overview of the most significant upgradations undertaken and other activities for the system are being reported in the present paper.     

Microwave spectral studies of rotational isomerism in substituted ethanethiols: 2-Aminoethanethiol and 2-chloroethanethiol

Microwave spectra were observed and analyzed for 2-aminoethanethiol and 2-chloroethanethiol. The amino compound exists in two gauche rotameric conformations, one exhibiting an intramolecular SH?N hydrogen bond. The hydrogen-bonded conformer lies higher in energy by 274 ± 90 cal mole^?1 and has the following rotational constants (in MHz): A = 12 040.1 ± 11.3, B = 3352.24 ± 0.03, and C = 2881.99 ± 0.03. For the non-hydrogen-bonded conformer the rotational constants (in MHz) are A = 11 929.9 ± 10.2, B = 3395.01 ± 0.03, and C = 2877.82 ± 0.03. Dipole moment measurements for the H-bond conformer led to μ_a = 2.68 D, μ_b = 0.88 D, and μ_c = 0.37 D, while for the non-H-bond form the values are μ_a = 1.51 D, μ_b = 0.0 D, and μ_c = 0.62 D. In the case of chloroethanethiol, the only assigned spectral lines were the unresolved J → J + 1 a-type bands of a trans conformation. For this molecule the combination rotational constant B + C has the value 2955.17 ± 0.02 MHz for the ³⁵Cl species and 2879.73 ± 0.02 MHz for the ³⁷Cl species.     

Heterocycle-based isomeric chromophores with substantially varying NLO properties: a new structure-property correlation study

A number of heterocycle-based aromatic and quinonoid molecular systems have been considered for the theoretical study of their electric response properties. The nonlinear optical (NLO) parameters have been calculated by using the ab initio MO and DFT methods. An approximate scheme for calculating the first hyperpolarizability (beta) and second hyperpolarizability (gamma) in the framework of the sum-over-state (SOS) method have been proposed by exploiting the generalized Thomas-Kuhn sum rule (TK-SR). The NLO properties in the present scheme can be evaluated solely from the ground-state dipole moment (mu) and linear polarizability (alpha) and have been found to correlate fairly with the ab initio calculated values. The approximate scheme can be reasonably used to explain the wider range of variation of higher-order polarizabilities in terms of the above quantities. The position of the N atom in the thiazole ring at the ortho position (versus meta position) to the acceptor increases beta and decreases gamma for aromatic compounds, while the reverse trend is found with quinonoid compounds. In the case of the pyridine ring, the shifting of the N atom toward the acceptor enhances gamma, with insignificant variation of beta predicted for both the aromatic and quinonoid molecules. The negative contribution of the cubic polarizability of the quinonoid species increases linearly with alpha(2)/mean transition energy (Delta E).     

Energy transfer photophysics from serum albumins to sequestered 3-hydroxy-2-naphthoic acid, an excited state intramolecular proton-transfer probe

The steady-state and time-resolved studies of the sensitized emission of the excited-state proton transfer (ESIPT) probe 3-hydroxy-2-naphthoic acid (3HNA) when bound to bovine serum albumin (BSA) and human serum albumin (HSA) indicate that the nonradiative dipole-dipole F?rster type energy transfer from Trp singlet state of proteins to the ESIPT singlet state of 3HNA is greater in the case of HSA. This is supported by the distance and the orientation of the donor-acceptor pair obtained from the protein-ligand docking studies. The docking studies of the complex of BSA-3HNA also indicate that Trp 134 rather than Trp 213 is involved in the energy transfer process. The local environment of Trp 134 in BSA rather than that of Trp 213 is perturbed because of interaction with 3HNA as revealed by the optical resolution of Trp 134 phosphorescence in the complex at 77 K. Docking studies support the larger rotational correlation time, thetac (approximately 50 ns), observed for Trp residue/residues in the complexes of HSA and BSA compared with that in the free proteins.     

Functional group dependent dissociative electron attachment to simple organic molecules

Dissociative electron attachment (DEA) cross sections for simple organic molecules, namely, acetic acid, propanoic acid, methanol, ethanol, and n-propyl amine are measured in a crossed beam experiment. We find that the H(-) ion formation is the dominant channel of DEA for these molecules and takes place at relatively higher energies (>4 eV) through the core excited resonances. Comparison of the cross sections of the H(-) channel from these molecules with those from NH(3), H(2)O, and CH(4) shows the presence of functional group dependence in the DEA process. We analyze this new phenomenon in the context of the results reported on other organic molecules. This discovery of functional group dependence has important implications such as control in electron induced chemistry and understanding radiation induced damage in biological systems.     

A mechanistic approach on the self-organization of the two-component thermoreversible hydrogel of riboflavin and melamine

The riboflavin (R) and melamine (M) supramolecular complex in the mole ratio of 3:1 (RM31) produces a thermoreversible gel in aqueous medium. The gelation mechanism has been elucidated from morphological investigations using optical, electron, and atomic force microscopy together with time-dependent circular dichroism (CD) and photoluminescence (PL) spectroscopy. Optical microscopy indicates spherulitic morphology at lower gelation temperature (相似文献   

Enhanced photoluminescence properties of Gd (x-1) Sr x O: CdO nanocores and their study of optical,structural, and morphological characteristics

Synthesis of Gd doped Sr_x O: CdO (x = 1.4, 1.6, 1.8) nanostructures (NS) was achieved through the coprecipitation method by using CTAB (cetyl trimethyl ammonium bromide) with the purpose to investigate the effect of Gd doping on the optical, structural, morphological, and photoluminescence properties at room temperature. Mixed phase of tetragonal crystal structure verified via X-ray diffraction technique, no structural variation was observed except lattice distortion. Size of the crystallites (D), morphology studied by SEM (scanning electron microscopy) analysis, nanoparticles (NPs) crystalized roughly flake-like morphology with homogeneous particle distribution centered at ~ 78 nm, ~56 nm, ~65 nm, ~88 nm for pure and Gd _(x-1) doped Sr _xO: CdO nanostructure, respectively. Fourier transform infrared spectroscopic investigation (FTIR) revealed the presence of Gd–O–Gd, Cd–O, Sr–O, and OH peaks appeared at ~1321 cm ^?1, ~1550 cm ^?1, ~1400 cm ^?1–3300 cm ^?1 with small variation in vibration modes due to Gd doping. Optical absorptivity observed in the range of 325 nm–359 nm (redshifted) with absorption edges at 346 nm, 364 nm, and 380 nm for Gd _(x-1) doped Sr _xO: CdO nanostructure, respectively. This redshift on the bandgap was discussed in terms of new band levels below conduction band. The energy gap was calculated using Kubelka-Munk theory and was found to be in the range of 3.22 eV–2.61 eV. X-ray photoelectron spectroscopy (XPS) performed to determine chemical composition and binding energies of Gd 3d _3/2, Sr 3d _3/2, and Cd 3d _3/2, O1s, and C1s observed at 150.8 eV, 141.6 eV, 411.0 eV, 530.4 eV, and 285.6 eV indicating Gd⁺³ ion replaces Sr⁺² in all concentrations. Our results showed that Gd-doped Sr _xO: CdO nanoparticles exhibited enhanced photoluminescence (PL) properties in contrast to the pure Gd₂O₃ with Gd⁺³ randomly incorporated into crystal structure, probably in tetrahedral sites. The composition of Gd _0.6 doped Sr _x O: CdO NS exhibited photoluminescent emission spectra, peaks centered at 433 ± 3 nm, 449 ± 3 nm, and 469 ± 2 nm (λ _excitation = 318 nm) and for Gd _0.8 doped Sr _x O: CdO nanostructure showed broad emission peak at 412 ± 2 nm to 433 ± 2 nm (λ _excitation = 380 nm), which indicates a reduction in defects with an increase in Gd doping. The transitions can be ascertained with shielding of 4f shells of Gd ⁺³ ions by 6s, 5d shells by the interaction of other Gd ⁺³ ions.