Unique bonding pattern and resulting bond stretch isomerism in

The bond‐stretch isomers are characterized by a principal change in the bond‐length with the rest of the molecule being unaltered. The electronic structure regulates the bond stretch isomerism phenomenon in which has been investigated with density functional theory, ab initio CASSCF, highly efficient n‐electron valence state perturbation theory and multireference configuration interaction calculations. Two isomers are distinguished on different potential energy surfaces and the corresponding avoided crossing is also studied in details. The bonding pattern in two isomers are analysed through adaptive natural density partitioning analysis and quantum theory of atoms in molecules analysis. The bonds in both the isomers primarily involve the 2p orbitals, which overlap face‐to‐face in long‐bond isomer. Whereas, in‐plane π‐bonding occurs at the short‐bond isomer leading to unusual bent bond. © 2015 Wiley Periodicals, Inc.     

Dielectric and electro-optic properties of two biphenylyl benzoate-based ferroelectric mesogens with tilted hexagonal phases

ABSTRACT

Two partially fluorinated ferroelectric liquid crystals (2F3R, 3F3R) with biphenylyl benzoate core have been investigated by frequency domain dielectric spectroscopy and electro-optic method. Both the compounds exhibit SmC* phase over a wide range of temperature along with tilted hexatic phase SmF* and soft crystal phases SmJ* (in 2F3R) and SmG* (in 3F3R) and one coexistence phase of (SmF*+SmC*). Both BOO phason and tilt phason relaxations are observed in SmF* phase and cooperative relaxation behaviour is also observed in crystal-like smectic phases. Goldstone mode relaxation is observed in SmC* phase and Maxwell Wagner mode is observed in all the phases. In 2F3R soft mode is detected in both SmC* and SmA* phases but not in 3F3R which melts directly to isotropic phase from SmC* phase. Compounds possess moderate values of spontaneous polarisation and exhibit quite sharp electrical response especially in 2F3R. Rotational viscosities, pitch and elastic constant are also measured. Effect of chain length and fluorination on various physical parameters has been discussed.     

Dynamics of Hydrogen Bonding in Three-Component Nanorotors

The dynamics of hydrogen bonding do not only play an important role in many biochemical processes but also in Nature's multicomponent machines. Here, a three-component nanorotor is presented where both the self-assembly and rotational dynamics are guided by hydrogen bonding. In the rate-limiting step of the rotational exchange, two phenolic O-H–N,N_{(phenanthroline)} hydrogen bonds are cleaved, a process that was followed by variable-temperature ¹H NMR spectroscopy. Activation data (ΔG^≠₂₉₈=46.7 kJ mol⁻¹ at 298 K, ΔH^≠=55.3 kJ mol⁻¹, and ΔS^≠=28.8 J mol⁻¹ K⁻¹) were determined, furnishing a rotational exchange frequency of k₂₉₈=40.0 kHz. Fully reversible disassembly/assembly of the nanorotor was achieved by addition of 5.0 equivalents of trifluoroacetic acid (TFA)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) over three cycles.     

A mild and efficient one-pot synthesis of \upbeta -amino carbonyl compounds via Mannich reaction under ambient temperature condition

We have developed an efficient protocol for the synthesis of $\upbeta $ -amino carbonyl compounds using phenylboronic acid as effective and eco-friendly catalyst via one-pot three-component Mannich reaction. Excellent yields, mild reaction condition, and simple experimental work-up procedure are some of the advantages of this method, which makes it a useful protocol for the synthesis of $\upbeta $ -amino carbonyl compounds.     

Tuning of the o-C(arom)-N bond-formation reactivity of aniline using ruthenium(II) templates

Chemical reactions of aniline with two face-capped ruthenium(II) templates viz. CpRu(II)Cl(PPh(3))(2) and (Bnz)(2)Ru(II)(2)Cl(4) have been studied to develop an insight into the role of the metal template for the rare type of o-C(arom)-N bond-forming reaction in aniline.     

Colored non-gaussian noise driven open systems: generalization of Kramers' theory with a unified approach

In this paper we have calculated escape rate from a meta stable state in the presence of both colored internal thermal and external nonthermal noises. For the internal noise we have considered usual gaussian distribution but the external noise may be gaussian or non-gaussian in characteristic. The calculated rate is valid for low noise strength of non-gaussian noise such that an effective gaussian approximation of non-gaussian noise wherein the higher order even cumulants of order "4" and higher are neglected. The rate expression we derived here reduces to the known results of the literature, as well as for purely external noise driven activated rate process. The latter exhibits how the rate changes if one switches from non-gaussian to gaussian character of the external noise.     

A crossed molecular beams and ab initio study on the formation of C6H3 radicals. an interface between resonantly stabilized and aromatic radicals

The crossed molecular beams reaction of dicarbon molecules, C(2)(X(1)Σ(g)(+)/a(3)Π(u)) with vinylacetylene was studied under single collision conditions at a collision energy of 31.0 kJ mol(-1) and combined with electronic structure calculations on the singlet and triplet C(6)H(4) potential energy surfaces. The investigations indicate that both reactions on the triplet and singlet surfaces are dictated by a barrierless addition of the dicarbon unit to the vinylacetylene molecule and hence indirect scattering dynamics via long-lived C(6)H(4) complexes. On the singlet surface, ethynylbutatriene and vinyldiacetylene were found to decompose via atomic hydrogen loss involving loose exit transition states to form exclusively the resonantly stabilized 1-hexene-3,4-diynyl-2 radical (C(6)H(3); H(2)CCCCCCH; C(2v)). On the triplet surface, ethynylbutatriene emitted a hydrogen atom through a tight exit transition state located about 20 kJ mol(-1) above the separated stabilized 1-hexene-3,4-diynyl-2 radical plus atomic hydrogen product; to a minor amount (<5%) theory predicts that the aromatic 1,2,3-tridehydrobenzene molecule is formed. Compared to previous crossed beams and theoretical investigations on the formation of aromatic C(6)H(x) (x = 6, 5, 4) molecules benzene, phenyl, and o-benzyne, the decreasing energy difference from benzene via phenyl and o-benzyne between the aromatic and acyclic reaction products, i.e., 253, 218, and 58 kJ mol(-1), is narrowed down to only ～7 kJ mol(-1) for the C(6)H(3) system (aromatic 1,2,3-tridehydrobenzene versus the resonantly stabilized free radical 1-hexene-3,4-diynyl-2). Therefore, the C(6)H(3) system can be seen as a "transition" stage among the C(6)H(x) (x = 6-1) systems, in which the energy gap between the aromatic isomer (x = 6, 5, 4) is reduced compared to the acyclic isomer as the carbon-to-hydrogen ratio increases and the acyclic isomer becomes more stable (x = 1, 2).     

A new rhodamine based colorimetric 'off-on' fluorescence sensor selective for Pd2+ along with the first bound X-ray crystal structure

A new fluorescence rhodamine derivative bearing an 8-aminoquinoline moiety has been designed and synthesized for selective sensing of Pd(2+) in the presence of other competing metal ions in aqueous media. Pd(2+) induced spirolactam ring opening of rhodamine is confirmed for the first time by the X-ray crystal structure of the bound Pd(2+)-complex.     

Structure and dynamics of poly(oxyethylene) cholesteryl ether wormlike micelles: rheometry, SAXS, and cryo-TEM studies

In this article, we provide direct evidence for 1-D micellar growth and the formation of a network structure in an aqueous system of poly(oxyethylene) cholesteryl ether (ChEO(20)) and lauryl diethanolamide (L-02) by rheometry, small-angle X-ray scattering (SAXS), and cryo-transmission electron microscopy (cryo-TEM). The ChEO(20) self-assembles into spheroid micelles above the critical micelle concentration and undergoes a 1-D microstructural transition upon the incorporation of L-02, which because of its lipophilic nature tends to be solubilized into the micellar palisade layer and reduces the micellar curvature. The elongated micelles entangle with each other, forming network structures of wormlike micelles, and the system shows viscoelastic properties, which could be described by the Maxwell model. A peak observed in the zero-shear viscosity (η(0)) versus L-02 concentration curve shifted toward higher L-02 concentrations and the value of maximum viscosity (η(0?max)) increased with the increasing ChEO(20) mixing fraction with water. We observed that η(0?max) increased by 2 to 4 orders of magnitude as a function of the ChEO(20) concentration. The Maxwell relaxation time (τ(R)) shows a maximum value at a concentration corresponding to η(0?max) (i.e., τ(R) increases with L-02 concentration and then decreases after attaining a maximum value, whereas the plateau modulus (G(0)) shows monotonous growth). These observations demonstrate microstructural transitions in two different modes: L-02 first induces 1-D micellar growth and as a result the viscosity increases, and finally after the system attains its maximum viscosity, L-02 causes branching in the network structures. The microstructure transitions are confirmed by SAXS and cryo-TEM techniques.     

HDX Workbench: Software for the Analysis of H/D Exchange MS Data

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is an established method for the interrogation of protein conformation and dynamics. While the data analysis challenge of HDX-MS has been addressed by a number of software packages, new computational tools are needed to keep pace with the improved methods and throughput of this technique. To address these needs, we report an integrated desktop program titled HDX Workbench, which facilitates automation, management, visualization, and statistical cross-comparison of large HDX data sets. Using the software, validated data analysis can be achieved at the rate of generation. The application is available at the project home page http://hdx.florida.scripps.edu .