Planar triazinium cations from vanadyl-mediated ring cyclizations: the thiazole species for efficient nuclear staining and photocytotoxicity

Planar triazinium cationic species from vanadyl-assisted cyclization of 1-(2-thiazolylazo)-2-naphthol (H-TAN, 1), 1-(2-pyridylazo)-2-naphthol (H-PAN, 2), 2-(2'-thiazolylazo)-p-cresol (H-TAC, 3) and 6-(2'-thiazolylazo)- resorcinol (H-TAR, 5) were prepared and characterized. A dioxovanadium(V) species VO2(TAR)] (4) was also isolated. Compounds 1, 2 and 4 were structurally characterized. Both 1 and 2 have planar structures. Complex 4 has (VO3N2)-O-V coordination geometry. The cyclised triazinium compound forms a radical species within -0.06 to -0.29 V vs. SCE in DMF-0.1 M tetrabutylammonium perchlorate with a second response due to formation of an anionic species. A confocal microscopic study showed higher nuclear uptake for 1 having a fused thiazole moiety than 2 with a fused pyridine ring. The compounds showed a partial intercalative mode of binding to calf thymus DNA. Compound 1 showed plasmid DNA photo-cleavage activity under argon and photocytotoxicity in HeLa and MCF-7 cells with IC50 values of 15.1 and 3.4 mu M respectively in visible light of 400-700 nm, while being essentially non-toxic in the dark with IC50 values of 90.4 and 21.9 mu M. ATDDFT study was done to rationalize the experimental data.

Structural characterization and molecular order of rodlike mesogens with three- and four-ring core by XRD and C-13 NMR spectroscopy

Structural characterizations using XRD and C-13 NMR spectroscopy of two rodlike mesogens consisting of (i) three phenyl ring core with a polar cyano terminal and (ii) four phenyl ring core with flexible dodecyl terminal chain are presented. The three-ring-core mesogen with cyano terminal exhibits enantiotropic smectic A phase while the four-ring mesogen reveals polymesomorphism and shows enantiotropic nematic, smectic C, and tilted hexatic phases. The molecular organization in the three-ring mesogen is found to be partial bilayer smectic Ad type, and the interdigitation of the molecules in the neighboring layers is attributed to the presence of the polar terminal group. For the four-ring mesogen, the XRD results confirm the existence of the smectic C and the tilted hexatic mesophases. A thermal variation of the layer spacing across the smectic C phase followed by a discrete jump at the transition to the tilted hexatic phase is also observed. The tilt angles have been estimated to be about 45 degrees in the smectic C phase and about 40 degrees in tilted hexatic phase. C-13 NMR results indicate that in the mesophase the molecules are aligned parallel to the magnetic field. From the C-13-H-1 dipolar couplings determined from the 2D experiments, the overall order parameter for the three-ring mesogen in its smectic A phase has been estimated to be 0.72 while values ranging from 0.88 to 0.44 have been obtained for the four-ring mesogen as it passes from the tilted hexatic to the nematic phase. The orientations of the different rings of the core unit with respect to each other and also with respect to the long axis of the molecule have also been obtained.

Multi-port network modeling of stub loaded Microstrip ring antenna for dual-band operations

A square ring microstrip antenna can be modified for dual-band operations by appropriately attaching an open ended stub. The input impedance of this antenna is analyzed here using multi-port network modeling (MNM) approach. The coupled feed is included by defining additional terms in the model. A prototype antenna is fabricated and tested to validate these computations.

Conformational Diversity in Contryphans from Conus Venom: cis-trans Isomerisation and Aromatic/Proline Interactions in the 23-Membered Ring of a 7-Residue Peptide Disulfide Loop

Conformational diversity or shapeshifting in cyclic peptide natural products can, in principle, confer a single molecular entity with the property of binding to multiple receptors. Conformational equilibria have been probed in the contryphans, which are peptides derived from Conus venom possessing a 23-membered cyclic disulfide moiety. The natural sequences derived from Conus inscriptus, GCV(D)LYPWC* (In936) and Conus loroisii, GCP(D)WDPWC* (Lo959) differ in the number of proline residues within the macrocyclic ring. Structural characterisation of distinct conformational states arising from cis-trans equilibria about Xxx-Pro bonds is reported. Isomerisation about the C2-P3 bond is observed in the case of Lo959 and about the Y5-P6 bond in In936. Evidence is presented for as many as four distinct species in the case of the synthetic analogue V3P In936. The Tyr-Pro-Trp segment in In936 is characterised by distinct sidechain orientations as a consequence of aromatic/proline interactions as evidenced by specific sidechain-sidechain nuclear Overhauser effects and ring current shifted proton chemical shifts. Molecular dynamics simulations suggest that Tyr5 and Trp7 sidechain conformations are correlated and depend on the geometry of the Xxx-Pro bond. Thermodynamic parameters are derived for the cis trans equilibrium for In936. Studies on synthetic analogues provide insights into the role of sequence effects in modulating isomerisation about Xxx-Pro bonds.

Ring opening of activated cyclopropanes with NIS/NaN3: synthesis of C-1 linked pseudodisaccharides

NIS/NaN3 mediated ring opening of various donor-acceptor cyclopropanes has been investigated. The study shows the necessity of the donor oxygen lone pair in such ring opening reactions. This methodology has been utilized in the synthesis of C-1 linked pseudodisaccharides through the use of click chemistry. (C) 2013 Elsevier Ltd. All rights reserved.

Beyond the ``Coffee Ring'': Re-entrant Ordering in an Evaporation-Driven Self-Assembly in a Colloidal Suspension on a Substrate

We study the phenomenon of evaporation-driven self-assembly of a colloid suspension of silica microspheres in the interior region and away from the rim of the droplet on a glass plate. In view of the importance of achieving a large-area, monolayer assembly, we first realize a suitable choice of experimental conditions, minimizing the influence of many other competing phenomena that usually complicate the understanding of fundamental concepts of such self-assembly processes in the interior region of a drying droplet. Under these simplifying conditions to bring out essential aspects, our experiments unveil an interesting competition between ordering and compaction in such drying systems in analogy to an impending glass transition. We establish a re-entrant behavior in the order disorder phase diagram as a function of the particle density, such that there is an optimal range of the particle density to realize the long-range ordering. The results are explained with the help of simulations and phenomenological theory.

Exclusive ring opening of gem-dihalo-1,2-cyclopropanated oxyglycal to oxepines in AgOAc

Treatment of gem-dihalo-1,2-cyclopropanated D-oxyglycal with primary, secondary, and unsaturated alcohols, in the presence of AgOAc, leads to the formation of chloro-oxepines exclusively. Reaction of the resulting 2-chloro-oxepines with excess alcohol in the presence of AgOAc, do not promote further reactions. This result is in contrast to the reactions of D-glucal derived halo-oxepine with alcohols known previously that lead to the formation of furanoses as the major product under similar reaction conditions. Observation of this study consolidates the reactivity differences of gem-dihalo-1,2-cyclopropanated oxyglycals, as compared to gem-dihalo- 1,2-cyclopropanated glycals. (C) 2014 Elsevier Ltd. All rights reserved.

Novel synthesis of carbohydrate fused alpha-amino gamma-lactams and glycopeptides by NIS mediated ring opening of donor-acceptor substituted cyclopropanes

alpha-Amino gamma-lactams have been synthesized from carbohydrate derived cyclopropanecarboxylates using N-iodosuccinimide (NIS) and NaN3. Cyclopropane ring opening with NIS and NaN3 in different solvents has been studied. Reductive cyclization of the intermediate di-azides leads to the carbohydrate fused alpha-amino gamma-lactam and gamma-lactams. Additionally, the methodology has been successfully extended to the synthesis of a glycopeptide. (C) 2014 Elsevier Ltd. All rights reserved.

A Contraction Mapping Approach for Robust Estimation of Lagged Autocorrelation

We consider the zero-crossing rate (ZCR) of a Gaussian process and establish a property relating the lagged ZCR (LZCR) to the corresponding normalized autocorrelation function. This is a generalization of Kedem's result for the lag-one case. For the specific case of a sinusoid in white Gaussian noise, we use the higher-order property between lagged ZCR and higher-lag autocorrelation to develop an iterative higher-order autoregressive filtering scheme, which stabilizes the ZCR and consequently provide robust estimates of the lagged autocorrelation. Simulation results show that the autocorrelation estimates converge in about 20 to 40 iterations even for low signal-to-noise ratio.

An inhomogeneous multispecies TASEP on a ring

We reinterpret and generalize conjectures of Lam and Williams as statements about the stationary distribution of a multispecies exclusion process on the ring. The central objects in our study are the multiline queues of Ferrari and Martin. We make some progress on some of the conjectures in different directions. First, we prove Lam and Williams' conjectures in two special cases by generalizing the rates of the Ferrari-Martin transitions. Secondly, we define a new process on multiline queues, which have a certain minimality property. This gives another proof for one of the special cases; namely arbitrary jump rates for three species. (C) 2014 Elsevier Inc. All rights reserved.

Molecular topology of three ring nematogens from C-13-H-1 dipolar couplings

Molecules in their liquid crystalline phase undergo rotational motion about the long axis of the molecule and the shape adopted by the rotating molecule plays an important role in influencing the mesophase morphology. In this context, obtaining the topology and the relative orientation of the different sub-units are important steps. For studying the liquid crystalline phase, C-13 NMR spectroscopy is a convenient method and for certain specifically designed nematogens, 2-dimensional separated local field (2D-SLF) NMR spectroscopy provides a particularly simple and straightforward means of arriving at the molecular topology. We demonstrate this approach on two three ring based nematogens designed with a phenyl or a thiophene ring at one of the termini. From the C-13-H-1 dipolar couplings of the terminal carbon obtained using the 2D-SLF NMR technique, the order parameter of the local symmetry axis of the terminal phenyl ring as well as of the long molecular axis could be easily estimated. For the thiophene nematogen, the lack of symmetry of the thiophene moiety necessitates some additional computational steps. The results indicate that the thiophene unit has its local ordering axis oriented away from the long molecular axis by a small angle, consistent with a bent structure expected in view of the thiophene geometry. The experiment also demonstrates the ability of 2D-SLF NMR to provide high resolution spectra by separation of several overlapped resonances in terms of their C-13-H-1 dipolar couplings. The results are consistent with a rod-like topology of the core of the investigated mesogens. The investigation demonstrates the potential of 2D-SLF NMR C-13 spectroscopy for obtaining atomistic level information and its utility for topological studies of different mesogens.

Formation of annular austenitic ring between outer ferrite layer and solid globule in a semi-solid processed SS 304L

The microstructure of an austenitic SS 304L rapidly quenched from its semi-solid state shows a unique annular austenitic ring in between the core of each globule and its ferritic outer layer. On the basis of experimental results and microstructural analysis, it is proposed that the ring is formed as a result of preferential austenitic phase nucleation in a small quantity of liquid entrapped between adjacent solid globules during rapid quenching, in spite of the fact that ferrite is the thermodynamically stable phase for the alloy. (C) 2014 Elsevier B.V. All rights reserved.

Tetrathiomolybdate-Mediated Ring Opening of Isatoic Anhydrides: An Entry to S-Alkyl or S-Aryl 2-Aminobenzenecarbothioate Derivatives

Decarboxylative thioesterification of isatoic anhydrides mediated by benzyl(triethyl)ammonium tetrathiomolybdate gave the corresponding S-alkyl or S-aryl 2-aminobenzenecarbothioate derivatives at 60 degrees C. At ambient temperature, organic disulfides were reductive cleaved in the presence of tetrathiomolybdate to generate thiolate anions in situ; this was followed by attack on isatoic anhydrides to give the corresponding S-alkyl or S-aryl 2-aminobenzenecarbothioate derivatives. Additionally, it was shown that multistep reactions could be performed with tetrathiomolybdate, starting with an alkyl halide as a precursor of an alkyl disulfide, which, in turn, was used for ring opening of isatoic anhydrides.

One-pot synthesis of functionalized beta-amino sulfides/beta-amino selenides via ring opening of cyclic sulfamidates

A number of functionalized beta-amino and gamma-amino sulfides and selenides have been synthesized involving a one-pot process of ring opening of cyclic sulfamidates with `in situ' generated thiolate and selenoate species from diaryl disulfides and diphenyl diselenide using rongalite. A mild and efficient method has been developed for the synthesis of cysteines from serine.

MEMS Tunable Optical Filter Based on Multi-Ring Resonator

We propose a novel MEMS tunable optical filter with a flat-top pass band based on multi-ring resonator in an electrostatically actuated microcantilever for communication application. The filter is basically structured on a microcantilever beam and built in optical integrated ring resonator which is placed in one end of the beam to gain maximum stress on the resonator. Thus, when a DC voltage is applied, the beam will bend, that induces a stress and strain in the ring, which brings a change in refractive index and perimeter of the rings leading to change in the output spectrum shift, providing the tenability as high as 0.68nm/mu N. and it is capable of tuning up to 1.7nm.