Water gelation of an amino acid-based amphiphile

The water immobilization by a simple amino acid-containing cationic surfactant was investigated. A variety of techniques, such as (1)H NMR spectroscopy, circular dichroism (CD), steady-state fluorescence spectroscopy, and field-emission scanning electron microscopy (FESEM) were applied to determine the formation and architecture of the hydrogel. The new gelator with a minimum gelation concentration (MGC) of 0.3 % w/v shows prolonged stability and a low melting temperature (39 degrees C). (1)H NMR experiments revealed that intermolecular hydrogen bonding between the amide groups and pi-pi stacking of the indole rings are the two regulating parameters for gelation. Furthermore, fluorescence studies with 8-anilino-1-naphthalenesulfonic acid (ANS) as the probe indicate the participation of hydrophobicity during gelation. The luminescence study using both ANS and pyrene, along with FESEM results, indicate a critical concentration, well below the MGC, at which fibres begin to form. These cross-link further to give thicker fibers, leading to the formation of a hydrogel (0.3 % w/v). This new hydrogelator expresses high supramolecular chirality, as evidenced by the CD spectra. In addition, the gelator molecule was found to be nontoxic up to a concentration of 4 mM (0.2 % w/v). The high supramolecular chirality, prolonged stability, low melting point, and biocompatibility of the molecule make it a focus of chemical and biological interest.     

Surface characterisation of ethylene-propylene-diene rubber upon exposure to aqueous acidic solution

Two types of pure ethylene propylene diene rubbers were exposed to two different acids for varying period of time. Surface characterisation was carried out using X-ray photoelectron spectroscopy (XPS). Two EPDM rubbers selected for this study were comparable in co-monomer compositions but significantly different with respect to molar mass and the presence of long chain branching. Both rubbers contained 5-ethylidene-2-norbornene (ENB) as diene. Solution cast films of pure EPDM samples were exposed in two different acidic solutions, viz. chromosulphuric (Cr (VI)/H₂SO₄) and sulphuric acid (H₂SO₄) (20%, v/v) at ambient temperature from 1 to 12 weeks. XPS analysis indicated that several oxygenated species were formed on the surface of both rubbers after exposure. It was postulated from the XPS analyses that both aqueous acidic solutions attacked the olefinic double bonds (CC) of ENB. Furthermore, 20% Cr (VI)/H₂SO₄ also attacked the allylic carbon-hydrogen (CH) bonds of ENB resulting in more oxygenated species on the surface compared to 20% H₂SO₄ under identical conditions. Cr (VI) in the 20% Cr (VI)/H₂SO₄ was found to play an important role in alteration of surface chemistry. Studies using a model system consisting of EPDM mixed with Cr (VI) and Cr (III) salts revealed that the change of oxidation state from Cr (VI) to Cr (III) as a consequence of direct involvement of Cr (VI) in the chemical alteration of EPDM surfaces. Interestingly, the presence of long chain branching and molar mass did not significantly influence the chemical processes owing to the acid treatment.     

Vinylene‐Linked Covalent Organic Frameworks by Base‐Catalyzed Aldol Condensation

Two 2D covalent organic frameworks (COFs) linked by vinylene (?CH=CH?) groups (V‐COF‐1 and V‐COF‐2) are synthesized by exploiting the electron deficient nature of the aromatic s‐triazine unit of C₃‐symmetric 2,4,6‐trimethyl‐s‐triazine (TMT). The acidic terminal methyl hydrogens of TMT can easily be abstracted by a base, resulting in a stabilized carbanion, which further undergoes aldol condensation with multitopic aryl aldehydes to be reticulated into extended crystalline frameworks (V‐COFs). Both V‐COF‐1 (with terepthalaldehyde (TA)) and V‐COF‐2 (with 1,3,5‐tris(p‐formylphenyl)benzene (TFPB)) are polycrystalline and exhibit permanent porosity and BET surface areas of 1341 m² g^?1 and 627 m² g^?1, respectively. Owing to the close proximity (3.52 Å) of the pre‐organized vinylene linkages within adjacent 2D layers stacked in eclipsed fashion, [2+2] photo‐cycloadditon in V‐COF‐1 formed covalent crosslinks between the COF layers.     

Phosphite‐Catalyzed C−H Allylation of Azaarenes via an Enantioselective [2,3]‐Aza‐Wittig Rearrangement

A phosphite‐mediated [2,3]‐aza‐Wittig rearrangement has been developed for the regio‐ and enantioselective allylic alkylation of six‐membered heteroaromatic compounds (azaarenes). The nucleophilic phosphite adducts of N‐allyl salts undergo a stereoselective base‐mediated aza‐Wittig rearrangement and dissociation of the chiral phosphite for overall C?H functionalization of azaarenes. This method provides efficient access to tertiary and quaternary chiral centers in isoquinoline, quinoline, and pyridine systems, tolerating a broad variety of substituents on both the allyl part and azaarenes. Catalysis with chiral phosphites is also demonstrated with synthetically useful yields and enantioselectivities.     

Effect of Floating-Body and Stress Bias on NBTI and HCI on 65-nm SOI pMOSFETs

Grounded-body (GB) core-logic/high-speed (HS) and input/output (I/O) silicon-on-insulator pMOSFETs from 65-nm technology are shown to degrade more than floating-body (FB) devices under negative bias temperature instability (NBTI) stress. However, in both cases, worst case degradation occurs when stressed under equal gate and drain voltages (V_g = V_d), whereby degradation is simultaneously induced by both NBTI and hot carrier injection (HCI) simultaneously ("concurrent HCI-NBTI"), the relative importance of each mechanism depending on the type of device and the bias level. The degradation of I/O pMOSFETs stressed under V_g = V_d at room temperature shows predominantly NBTI-like behavior at higher stress voltages, whereas it shows concurrent HCI-NBTI behavior at lower stress voltages. By contrast, the degradation of HS pMOSFETs stressed under V_g = V_d shows concurrent HCI-NBTI behavior over the entire stress bias range. In both cases, FB devices degrade more than GB devices for higher stress voltage values, but the FB effects weaken and the degradations become comparable for lower stress bias.     

Growth of Y-junction bamboo-shaped CNx nanotubes on GaAs substrate using single feedstock

Nitrogen-doped Y-junction bamboo-shaped carbon nanotubes were synthesized by chemical vapor deposition of monoethanolamine/ferrocene mixture on GaAs substrate at 950 °C. The use of monoethanolamine as the C/N feedstock simplifies the experimental arrangement by producing ammonia during the growth process. The structure, morphology and graphitization of as-grown nitrogen-doped carbon nanotubes (CN_x) were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy analysis. TEM analysis indicates that nanotubes have a bamboo-like structure. The nitrogen concentration on as-grown CN_x nanotube was found to be 7.8 at.% by X-ray photoelectron spectroscopy (XPS) analysis. XPS analysis also indicated that there are two different types of nitrogen atoms (pyridinic and graphitic) in these materials. The possible growth mechanism of formation of Y-junction CN_x nanotubes was briefly discussed. Field emission measurement suggested that as-grown CN_x nanotubes are excellent emitters with turn-on and threshold fields of 1.6 and 2.63 V/μm, respectively. The result indicated that monoethanolamine proves to be an advantageous precursor to synthesize Y-junction nitrogen-doped carbon nanotubes and such nanotubes might be an effective material to fabricate various field emission devices.     

Working group report: Quark gluon plasma

The 10th Workshop on High Energy Physics Phenomenology (WHEPP-10) was held at the Institute of Mathematical Sciences, Chennai during January 2–13, 2008. One of our working grops (WG) is QCD and QGP. The discussions of QGP WG include matter at high density, lattice QCD, charmonium states in QGP, viscous hydrodynamics and jet quenching, colour factor in heavy ion collisions and RHIC results on photons, dileptons and heavy quark. There were two plenary talks and several working group talks with intense discussions regarding the future activities that are going to be persued.      

Topics in Noncommutative Geometry Inspired Physics

In this review article we discuss some of the applications of noncommutative geometry in physics that are of recent interest, such as noncommutative many-body systems, noncommutative extension of Special Theory of Relativity kinematics, twisted gauge theories and noncommutative gravity.     

Phase transitions in liquid crystal 6O.4 (p-<Emphasis Type="Italic">n</Emphasis>-hexyloxybenzylidine-p′-<Emphasis Type="Italic">n</Emphasis>-butylaniline)

DSC measurements on p-n-hexyloxybenzylidine-p′-n-butylaniline (6O.4) showed that the crystalline to liquid crystalline (K-S _H) transition at 33.7°C observed in the heating cycle does not revert even when the sample is cooled down to −100°C. Hence it is inferred that a physically stable supercooled liquid crystalline phase is formed on cooling 6O.4. To investigate the K-S _H transition further the techniques of polarized microscopy and X-ray diffraction were used which concurred with the DSC results. Quasielastic neutron scattering measurements carried out to study the re-orientational motions in the ordered phases of 6O.4 (K and S _H) show that while in the crystalline phase (at RT) the re-orientational motion is found to involve only the core of the molecule, in the S _H phase (at 45°C) the dynamics involves the whole molecule and this motion is found to persist even when the sample cools back to room temperature corroborating the results of the DSC, microscopy and X-ray diffraction.