On the systematic position of some Asian enigmatic genera of Asclepiadoideae (Apocynaceae)

The phylogenetic structure of Asclepiadoideae (Apocynaceae) has been elucidated at the tribal and subtribal levels in the last two decades. However, to date, the systematic positions of seven Asian genera, Cosmostigma, Graphistemma, Holostemma, Pentasachme, Raphistemma, Seshagiria and Treutlera, have not been investigated. In this study, we examine the evolutionary relationships among these seven small enigmatic Asian genera and clarify their positions in Asclepiadoideae, using a combination of plastid sequences of rbcL, rps16, trnL and trnL- F regions. Cosmostigma and Treutlera are resolved as members of the non-Hoya clade of Marsdenieae with strong support (maximum parsimony bootstrap support value BSMP = 96, maximum likelihood bootstrap support value BSML = 98, Bayesian-inferred posterior probability PP = 1.0). Pentasachme is resolved as sister of Stapeliinae to Ceropegieae with moderate support (BSMP = 64, BSML = 66, PP = 0.94). Graphistemma, Holostemma, Raphistemma and Seshagiria are all nested in the Asclepiadeae-Cynanchinae clade (BSMP = 97, BSML = 100, PP = 1.0). The study confirms the generally accepted tribal and subtribal structure of the subfamily. One exception is Eustegia minuta, which is placed here as sister to all Asclepiadeae (BSMP = 58, BSML = 76, PP = 0.99) and not as sister to the Marsdenieae + Ceropegieae clade. The weak support and conflicting position indicate the need for a placement of Eustegia as an independent tribe. In Asclepiadeae, a sister group position of Cynanchinae to the Asclepiadinae + Tylophorinae clade is favoured (BSMP = 84, BSML = 88, PP = 1.0), whereas Schizostephanus is retrieved as unresolved. Oxystelma appears as an early-branching member of Asclepiadinae with weak support (BSMP = 52, BSML = 74, PP = 0.69). Calciphila and Solenostemma are also associated with Asclepiadinae with weak support (BSMP = 37, BSML = 45, PP = 0.79), but all alternative positions are essentially without support. The position of Indian Asclepiadoideae in the family phylogeny is discussed. (c) 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 601-619.

Dynamic recovery and recrystallization during high-temperature tensile deformation of a free-standing Pt-aluminide bond coat

Free-standing Pt-aluminide (PtAl) bond coat, when subjected to tensile testing at high temperatures (T >= 900 degrees C), exhibits significant decrease in strength and increase in ductility during deformation at strains exceeding that corresponding to the ultimate tensile strength (UTS), i.e., in the post-UTS regime. The stress-strain curve is also marked by serrations in this regime. Electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM) studies suggest dynamic recovery and recrystallization (DRR) as the mechanisms for the observed tensile behavior in the coating. Activation energy values suggest vacancy diffusion assists DRR. The fine recrystallized grains formed after deformation had a strong < 110 > texture. (c) 2014 Elsevier B.V. All rights reserved.

Effect of quantum nuclear motion on hydrogen bonding

This work considers how the properties of hydrogen bonded complexes, X-H center dot center dot center dot Y, are modified by the quantum motion of the shared proton. Using a simple two-diabatic state model Hamiltonian, the analysis of the symmetric case, where the donor (X) and acceptor (Y) have the same proton affinity, is carried out. For quantitative comparisons, a parametrization specific to the O-H center dot center dot center dot O complexes is used. The vibrational energy levels of the one-dimensional ground state adiabatic potential of the model are used to make quantitative comparisons with a vast body of condensed phase data, spanning a donor-acceptor separation (R) range of about 2.4-3.0 angstrom, i.e., from strong to weak hydrogen bonds. The position of the proton (which determines the X-H bond length) and its longitudinal vibrational frequency, along with the isotope effects in both are described quantitatively. An analysis of the secondary geometric isotope effect, using a simple extension of the two-state model, yields an improved agreement of the predicted variation with R of frequency isotope effects. The role of bending modes is also considered: their quantum effects compete with those of the stretching mode for weak to moderate H-bond strengths. In spite of the economy in the parametrization of the model used, it offers key insights into the defining features of H-bonds, and semi-quantitatively captures several trends. (C) 2014 AIP Publishing LLC.

A Gibbs-ensemble based technique for Monte Carlo simulation of electric double layer capacitors (EDLC) at constant voltage

Current methods for molecular simulations of Electric Double Layer Capacitors (EDLC) have both the electrodes and the electrolyte region in a single simulation box. This necessitates simulation of the electrode-electrolyte region interface. Typical capacitors have macroscopic dimensions where the fraction of the molecules at the electrode-electrolyte region interface is very low. Hence, large systems sizes are needed to minimize the electrode-electrolyte region interfacial effects. To overcome these problems, a new technique based on the Gibbs Ensemble is proposed for simulation of an EDLC. In the proposed technique, each electrode is simulated in a separate simulation box. Application of periodic boundary conditions eliminates the interfacial effects. This in addition to the use of constant voltage ensemble allows for a more convenient comparison of simulation results with experimental measurements on typical EDLCs. (C) 2014 AIP Publishing LLC.

Estimation of the 2.0(5) helix type i -> i hydrogen bond energy at Aib*-Oxa motif: an isodesmic approach

Bending at the valence angle N-C-alpha-C' (tau) is a known control feature for attenuating the stability of the rare intramolecular hydrogen bonded pseudo five-membered ring C-5 structures, the so called 2.0(5) helices, at Aib. The competitive 3(10)-helical structures still predominate over the C5 structures at Aib for most values of tau. However at Aib*, a mimic of Aib where the carbonyl 0 of Aib is replaced with an imidate N (in 5,6-dihydro-4H-1,3-oxazine = Oxa), in the peptidomimic Piv-Pro-Aib*-Oxa (1), the C(5)i structure is persistent in both crystals and in solution. Here we show that the i -> i hydrogen bond energy is a more determinant control for the relative stability of the C5 structure and estimate its value to be 18.5 +/- 0.7 kJ/mol at Aib* in 1, through the computational isodesmic reaction approach, using two independent sets of theoretical isodesmic reactions. (C) 2014 Elsevier Ltd. All rights reserved.

Continuity equation based nonquasi-static charge model for independent double gate MOSFET

Using the numerical device simulation we show that the relationship between the surface potentials along the channel in any double gate (DG) MOSFET remains invariant in QS (quasistatic) and NQS (nonquasi-static) condition for the same terminal voltages. This concept along with the recently proposed `piecewise charge linearization' technique is then used to develop the intrinsic NQS charge model for a Independent DG (IDG) MOSFET by solving the governing continuity equation. It is also demonstrated that unlike the usual MOSFET transcapacitances, the inter-gate transcapacitance of a IDG-MOSFET initially increases with the frequency and then saturates, which might find novel analog circuit application. The proposed NQS model shows good agreement with numerical device simulations and appears to be useful for efficient circuit simulation.

Pressure-Induced Bond Rearrangement and Reversible Phase Transformation in a Metal-Organic Framework

Pressure-induced phase transformations (PIPTs) occur in a wide range of materials. In general, the bonding characteristics, before and after the PIPT, remain invariant in most materials, and the bond rearrangement is usually irreversible due to the strain induced under pressure. A reversible PIPT associated with a substantial bond rearrangement has been found in a metal-organic framework material, namely tmenH(2)]Er(HCOO)(4)](2) (tmenH(2)(2+) = N,N,N',N'-tetramethylethylenediammonium). The transition is first-order and is accompanied by a unit cell volume change of about 10%. High-pressure single-crystal X-ray diffraction studies reveal the complex bond rearrangement through the transition. The reversible nature of the transition is confirmed by means of independent nanoindentation measurements on single crystals.

Hydrogen-Bond-Driven Controlled Molecular Marriage in Covalent Cages

A supramolecular approach that uses hydrogen-bonding interaction as a driving force to accomplish exceptional self-sorting in the formation of imine-based covalent organic cages is discussed. Utilizing the dynamic covalent chemistry approach from three geometrically similar dialdehydes (A, B, and D) and the flexible triamine tris(2-aminoethyl)amine (X), three new 3+2] self-assembled nanoscopic organic cages have been synthesized and fully characterized by various techniques. When a complex mixture of the dialdehydes and triamine X was subjected to reaction, it was found that only dialdehyde B (which has OH groups for H-bonding) reacted to form the corresponding cage B3X2 selectively. Surprisingly, the same reaction in the absence of aldehyde B yielded a mixture of products. Theoretical and experimental investigations are in complete agreement that the presence of the hydroxyl moiety adjacent to the aldehyde functionality in B is responsible for the selective formation of cage B3X2 from a complex reaction mixture. This spectacular selection was further analyzed by transforming a nonpreferred (non-hydroxy) cage into a preferred (hydroxy) cage B3X2 by treating the former with aldehyde B. The role of the H-bond in partner selection in a mixture of two dialdehydes and two amines has also been established. Moreover, an example of unconventional imine bond metathesis in organic cage-to-cage transformation is reported.

Coconut kernel-derived activated carbon as electrode material for electrical double-layer capacitors

Carbonization of milk-free coconut kernel pulp is carried out at low temperatures. The carbon samples are activated using KOH, and electrical double-layer capacitor (EDLC) properties are studied. Among the several samples prepared, activated carbon prepared at 600 A degrees C has a large surface area (1,200 m(2) g(-1)). There is a decrease in surface area with increasing temperature of preparation. Cyclic voltammetry and galvanostatic charge-discharge studies suggest that activated carbons derived from coconut kernel pulp are appropriate materials for EDLC studies in acidic, alkaline, and non-aqueous electrolytes. Specific capacitance of 173 F g(-1) is obtained in 1 M H2SO4 electrolyte for the activated carbon prepared at 600 A degrees C. The supercapacitor properties of activated carbon sample prepared at 600 A degrees C are superior to the samples prepared at higher temperatures.

Tautomeric Preference and Conformation Locking in Fenobam, Thiofenobam, and Their Analogues: The Decisive Role of Hydrogen Bond Hierarchy

The crystal and molecular structures of the potential antidepressant drug fenobam and its derivatives are examined in terms of the preferred form among the two possible tautomeric structures. In this study, chemical derivatization has been utilized as a means to ``experimentally simulate'' the tautomeric preference and conformational variability in fenobam. Eight new derivatives of fenobam have been synthesized, and structural features have been characterized by single-crystal X-ray diffraction and NMR spectroscopy. The specific tautomeric preference found in all of these compounds and their known crystal forms have been construed in terms of the stabilizing intramolecular N-H center dot center dot center dot O and N-H center dot center dot center dot S hydrogen bonding. The hierarchy of intramolecular hydrogen bonds evidenced as the preference of the C-H center dot center dot center dot O hydrogen bond over C-H center dot center dot center dot N and that of the C-H center dot center dot center dot N hydrogen bond over C-H center dot center dot center dot S explains the two distinct conformations adopted by fenobam and thiofenobam derivatives. The relative energy values of different molecular conformations have been calculated and compared.

Heteronuclear proton double quantum-carbon single quantum scalar correlation in solids

A new NMR experiment that exploits the advantages of proton double quantum (DQ) NMR through a proton DQ-carbon single quantum (SQ) correlation experiment in the solid state is proposed. Analogous to the previously proposed 2D H-1 (DQ)-C-13 refocused INEPT experiment (Webber et al., 2010), the correlation between H-1 and C-13 is achieved through scalar coupling evolution, while the double quantum coherence among protons is generated through dipolar couplings. However, the new experiment relies on C-13 transverse coherence for scalar transfer. The new experiment dubbed MAS-J-H-1 (DQ)-C-13-HMQC, is particularly suited for unlabeled molecules and can provide higher sensitivity than its INEPT counterpart. The experiment is applied to four different samples. (C) 2014 Elsevier Inc. All rights reserved.

Effect of Rayleigh numbers on the evolution of double-diffusive salt fingers

This is a transient two-dimensional numerical study of double-diffusive salt fingers in a two-layer heat-salt system for a wide range of initial density stability ratio (R-rho 0) and thermal Rayleigh numbers (Ra-T similar to 10(3) - 10(11)). Salt fingers have been studied for several decades now, but several perplexing features of this rich and complex system remain unexplained. The work in question studies this problem and shows the morphological variation in fingers from low to high thermal Rayleigh numbers, which have been missed by the previous investigators. Considerable variations in convective structures and evolution pattern were observed in the range of Ra-T used in the simulation. Evolution of salt fingers was studied by monitoring the finger structures, kinetic energy, vertical profiles, velocity fields, and transient variation of R-rho(t). The results show that large scale convection that limits the finger length was observed only at high Rayleigh numbers. The transition from nonlinear to linear convection occurs at about Ra-T similar to 10(8). Contrary to the popular notion, R-rho(t) first decrease during diffusion before the onset time and then increase when convection begins at the interface. Decrease in R-rho(t) is substantial at low Ra-T and it decreases even below unity resulting in overturning of the system. Interestingly, all the finger system passes through the same state before the onset of convection irrespective of Rayleigh number and density stability ratio of the system. (C) 2014 AIP Publishing LLC.

A Short-Channel Common Double-Gate MOSFET Model Adapted to Gate Oxide Thickness Asymmetry

Existing compact models for common double-gate (CDG) MOSFETs are based on the fundamental assumption of having symmetric gate oxide thickness. In this paper, we demonstrate that using the unique quasi-linear relationship between the surface potentials, it is possible to develop compact model for CDG-MOSFETs without such approximation while preserving the mathematical complexity at the same level of the existing models. In the proposed model, the surface potential relationship is used to include the drain-induced barrier lowering, channel length modulation, velocity saturation, and quantum mechanical effect in the long-channel model and good agreement is observed with the technology computer aided design simulation results.

Regioselective Thiolation of Arenes and Heteroarenes: C-H Functionalization Strategy for C-S Bond Formation

A facile transition-metal-free oxidative cross-dehydrogenative coupling reaction involving selective formation of a C-S bond leading to the synthesis of arylthiobenzoxazoles, heteroarylthiobenzoxazoles, and arylthiobenzothiazoles has been described. This highly regioselective C-H functionalization reaction with electron-rich aromatic systems including heteroaromatics is achieved by reversing the reactivity of sulfur in the presence of a suitable oxidant and strong acid.

Hydrogen bonding, halogen bonding and lithium bonding: an atoms in molecules and natural bond orbital perspective towards conservation of total bond order, inter- and intra-molecular bonding

One hundred complexes have been investigated exhibiting D-X center dot center dot center dot A interactions, where X = H, Cl or Li and DX is the `X bond' donor and A is the acceptor. The optimized structures of all these complexes have been used to propose a generalized `Legon-Millen rule' for the angular geometry in all these interactions. A detailed Atoms in Molecules (AIM) theoretical analysis confirms an important conclusion, known in the literature: there is a strong correlation between the electron density at the X center dot center dot center dot A bond critical point (BCP) and the interaction energy for all these interactions. In addition, we show that extrapolation of the fitted line leads to the ionic bond for Li-bonding (electrostatic) while for hydrogen and chlorine bonding, it leads to the covalent bond. Further, we observe a strong correlation between the change in electron density at the D-X BCP and that at the X center dot center dot center dot A BCP, suggesting conservation of the bond order. The correlation found between penetration and electron density at BCP can be very useful for crystal structure analysis, which relies on arbitrary van der Waals radii for estimating penetration. Various criteria proposed for shared-and closed-shell interactions based on electron density topology have been tested for H/Cl/Li bonded complexes. Finally, using the natural bond orbital (NBO) analysis it is shown that the D-X bond weakens upon X bond formation, whether it is ionic (DLi) or covalent (DH/DCl) and the respective indices such as ionicity or covalent bond order decrease. Clearly, one can think of conservation of bond order that includes ionic and covalent contributions to both D-X and X center dot center dot center dot A bonds, for not only X = H/Cl/Li investigated here but also any atom involved in intermolecular bonding.