Novel chiral dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal complexes

The synthesis and characterization of cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens are reported in detail. To understand structure-property relationships in these materials the terminal alkoxy chains and the central metal atom have been varied. Our studies reveal that chiral dimesogenic bidentate ligands with n -butyloxy chains exhibit smectic A (SmA), twist grain boundary and chiral nematic (N * ) mesophases while substitution with either n -decyloxy or 3,7-dimethyloctyloxy chains also show a ferroelectrically switchable chiral smectic C (SmC * ) mesophase. The metal complexes with n -butyloxy chains show only the SmA phase whereas higher chain length derivatives exhibit N * phase irrespective of the metal atom present. The ligands are thermally stable whereas their metal complexes, especially Pd(II) systems, seem to be heat sensitive. Spontaneous polarization, response time and tilt angle measurements have been carried out in the smectic C * phase of the two ligands.     

A gadolinium(III) complex: synthesis,structure, photophysical profile and its role in the degradation of nitroaromatics

The synthesis and structural characterization of a gadolinium(III) complex with phenanthroline and thiocyanate ligands have been accomplished. The X-ray crystal structure reveals that Gd(III) in a slightly distorted square anti-prism coordinated with four thiocyanate ions and two phenanthroline molecules; one phenanthroline is protonated which compensates the charge of Gd(III) center. The crystal structure shows chemically significant non-covalent interactions like hydrogen bonding involving the thiocyanate ligand and π–π interactions between uncoordinated phenanthrolinium and coordinated phen. Investigation on the intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that close contacts are mainly associated with weak interactions. The fingerprint plots demonstrate that these weak interactions are important for crystal packing. The Gd(III) complex shows photophysical activity. The compound is capable of degrading toxic pollutants like nitroaromatics and may have far reaching consequences for cleaning these toxic pollutants from industrial effluents.     

Antimicrobial flavonoids isolated from Indian medicinal plant Scutellaria oblonga inhibit biofilms formed by common food pathogens

Scutellaria oblonga Benth., a hitherto phytochemically unexplored Indian medicinal folklore plant was extracted with acetone and subjected to chromatography to yield nine flavonoids, for the first time from this plant. Antimicrobial assays were performed against 11 foodborne pathogens, and three molecules (Techtochrysin, Negletein and Quercitin-3-glucoside) depicted significant activity. These molecules were assessed for their rate of antibacterial action using time–kill curves which depicted complete inhibition of most of the bacteria within 12–16 h. The significant biofilm-reducing capability exhibited by these three molecules formed a significant finding of the current study. In most of the experiments, a 90–95% reduction in biofilms was observed. Thus, flavonoids as natural molecules from S. oblonga could be further researched to be used as potent antimicrobial and antibiofilm agents.     

Structure of nonpremixed reaction zones in numerical isotropic turbulence

Results from direct numerical simulation of low heat release, turbulent nonpremixed reacting flows modeled using single-step reactions with constant and temperature-dependent rate laws are discussed, and compared with laminar predictions. The mixture fraction and its dissipation rate are statistically independent in regions of intense reaction, partially supporting a commonly made assumption in flamelet-based models. In the presence of a finite rate reverse reaction, the reaction zone spans the entire range of mixture fraction. The joint pdf of the reactive scalars evolves to an equilibrium that is dictated by a balance between the reactive and mixing fluxes in composition space. When the temperature-dependent rate law is implemented, strain-induced extinction is observed for a Zel'dovich (modified) number of 10. As the ratio of local flow to chemical time scale is decreased below unity, a larger fraction of the flow field experiences this mode of extinction. The critical turbulent scalar dissipation rate is compared with laminar values and asymptotic predictions.The first two authors express their acknowledgment to the donors of The Petroleum Research Fund, administered by the American Chemical Society for partial support of this work through a type G grant. We also acknowledge the Council for Research and Creative Writing at the University of Colorado for providing partial financial support.     

Dual Binding of an Antibody and a Small Molecule Increases the Stability of TERRA G‐Quadruplex

In investigating the binding interactions between the human telomeric RNA (TERRA) G‐quadruplex (GQ) and its ligands, it was found that the small molecule carboxypyridostatin (cPDS) and the GQ‐selective antibody BG4 simultaneously bind the TERRA GQ. We previously showed that the overall binding affinity of BG4 for RNA GQs is not significantly affected in the presence of cPDS. However, single‐molecule mechanical unfolding experiments revealed a population (48 %) with substantially increased mechanical and thermodynamic stability. Force‐jump kinetic investigations suggested competitive binding of cPDS and BG4 to the TERRA GQ. Following this, the two bound ligands slowly rearrange, thereby leading to the minor population with increased stability. Given the relevance of G‐quadruplexes in the regulation of biological processes, we anticipate that the unprecedented conformational rearrangement observed in the TERRA‐GQ–ligand complex may inspire new strategies for the selective stabilization of G‐quadruplexes in cells.     

Flying onto global minima on potential energy surfaces: A swarm intelligence guided route to molecular electronic structure

A novel quantum‐classical recipe for locating the global minimum on the potential energy surface of a large molecule and simultaneously predicting the associated electronic charge distribution is developed by interfacing the classical particle swarm optimization with a near optimal unitary evolution scheme for the trial one electron density matrix. The unitary transformation is generated by an antihermitian matrix linked to the molecular electronic Hamiltonian at the instantaneous nuclear configurations discovered by the swarm as it flies. The algorithm is used to predict the extensive reorganization of electronic charge distribution and bond lengths in polythiophene oligomers on doping at various levels.     

Synthesis,characterization and DNA nuclease activity of oxo-peroxomolybdenum(VI) complexes

The synthesis and structural characterization of two oxo-peroxo molybdenum(VI) complexes, [Mo(O)(O)₂(PAA)]^? (1) and [Mo(O)(O)₂(PAH)]^? (2), with phenylacetic acid (PAA) and 2-phenylacetylhydroxamic acid (PAHH) ligands have been accomplished. The coordination geometry of the oxo-peroxo molybdenum(VI) complexes is found to be pentagonal bipyramidal where, in both cases, the ligands are coordinated in bidentate fashion through oxygen atoms. The binding affinities of 1 and 2 with calf-thymus DNA (CT DNA) are determined using absorption spectroscopic measurements. The spectroscopic as well as cyclic voltammetric (CV) studies and viscosity measurements indicate that both complexes interact with CT DNA in the groove. The intrinsic binding constants are 5.2 × 10⁴ M^?1 and 7.3 × 10⁴ M^?1 for 1 and 2, respectively, from UV–vis studies. Complexes 1 and 2 show nuclease activity with plasmid DNA in the presence of H₂O₂. Concentration-dependent nuclease study suggests that 2 possesses higher ability to cleave plasmid DNA compared to 1. The experimental results of the binding of 1 and 2 with DNA are further supported by molecular docking studies.     

Optically Biaxial,Re‐entrant and Frustrated Mesophases in Chiral,Non‐symmetric Liquid Crystal Dimers and Binary Mixtures

Sixteen optically active, non‐symmetric dimers, in which cyanobiphenyl and salicylaldimine mesogens are interlinked by a flexible spacer, were synthesized and characterized. While the terminal chiral tail, in the form of either (R)‐2‐octyloxy or (S)‐2‐octyloxy chain attached to salicylaldimine core, was held constant, the number of methylene units in the spacer was varied from 3 to 10 affording eight pairs of (R & S) enantiomers. They were probed for their thermal properties with the aid of orthoscopy, conoscopy, differential scanning calorimetry and X‐ray powder diffraction. In addition, the binary mixture study was carried out using chiral and achiral dimers with the intensions of stabilizing optically biaxial phase/s, re‐entrant phases and important phase sequences. Notably, one of the chiral dimers as well as some mixtures exhibited a biaxial smectic A (SmA_b) phase appearing between a uniaxial SmA and a re‐entrant uniaxial SmA phases. The mesophases such as chiral nematic (N*) and frustrated phases viz., blue phases (BPs) and twist grain boundary (TGB) phases, were also found to occur in most of the dimers and mixtures. X‐ray diffraction studies revealed that the dimers possessing oxybutoxy and oxypentoxy spacers show interdigitated (SmA_d) phase where smectic periodicity is over 1.4 times the molecular length; whereas in the intercalated SmA (SmA_c) phase formed by a dimer having oxydecoxy spacer the periodicity was found to be approximately half the molecular length. The handedness of the helical structure of the N* phases formed by two enantiomers was examined with the aid of CD measurements; as expected, these enantiomers showed optical activities of equal magnitudes but with opposite signs. Overall, it appears that the chiral dimers and mixtures presented herein may serve as model systems in design and developing novel materials exhibiting the apolar SmA_b phase possessing D_2h symmetry and nematic‐type biaxiality.     

The full automorphism group of T‾

Let $\stackrel{￣}{G}$ be the wonderful compactification of a simple affine algebraic group G of adjoint type defined over $\mathbb{C}$. Let $\stackrel{￣}{T}?\stackrel{￣}{G}$ be the closure of a maximal torus $T?G$. We prove that the group of all automorphisms of the variety $\stackrel{￣}{T}$ is the semi-direct product $N_G(T)?D$, where $N_G(T)$ is the normalizer of T in G and D is the group of all automorphisms of the Dynkin diagram, if $G\ne \mathrm{PSL}(2,\mathbb{C})$. Note that if $G=\mathrm{PSL}(2,\mathbb{C})$, then $\stackrel{￣}{T}=\mathbb{C}{\mathbb{P}}^1$ and so in this case $\text{Aut}(\stackrel{￣}{T})=\mathrm{PSL}(2,\mathbb{C})$.