A 3-D bonding perspective of the factors influencing the relative stability of the S1/S0 conical intersections of the penta-2,4-dieniminium cation (PSB3)

A balanced treatment of the covalent and ionic contributions to the ground and excited states originating from torsion about double bonds is known to be strongly dependent on the presence of dynamic electron correlation. We undertake an analysis of the minimum energy pathways corresponding to deactivation of the first excited singlet state of PSB3. In doing so we consider torsion about the three double bonds including other intramolecular degrees of freedom, such as the bond length alternation. The 3-D bond-path analysis provides a new ‘bond-localized orbital-like’ directional interpretation of bonding. Therefore, we present a more sophisticated method of determination of the degree of covalent and ionic contributions known to be responsible for altering the relative stability of the S₁/S₀ conical intersections. The results presented suggest that the commonly used simplified multi-reference methodologies that often result in incorrect predictions for the excited state deactivation reaction mechanism.     

Molecular engineering of the electronic,structural, and electrochemical properties of nanostructured 1-methyl-4-phenyl 1,2,4 triazolium-based [PhMTZ][X<Subscript>1–10</Subscript>] ionic liquids through anionic changing

In the present work, molecular engineering of the physicochemical characteristics of ion pairing in 1-methyl-4-phenyl 1,2,4 triazolium-based ionic liquids [PhMTZ][X] (X_1–10 = CH₃CO₂ ^?, Cl^?, NO₃ ^?, CF₃CO₂ ^?, BF₄ ^?, ClO₄ ^?, N(CN)₂ ^?, PF₆ ^?, NTf₂ ^?, and C(CN)₃ ^?) are explored using at M06-2X/6–311++G(d,p) level. The binding Gibbs free energy of ion pairs are reevaluated using ab initio MP2 method and dispersion corrected M06-2X-D3, B2PLYP, B2PLYP-D, and mPW2PLYP-D functionals. Comparison of Gibbs free bottom electrodes (BEs) calculated by B2PLYP and B2PLYP-D functionals reveals that the contribution of dispersion energy to the total BEs vary from 9% for X1 to 17% for X = 10. Besides, the range of the dispersion contribution estimated by M06-2X-D3 functional is found to be 0.6% for X₂ to 5% for X₃. The Gibbs free BEs in solvent media, Gibbs free energy and enthalpy of formation, electrochemical windows, anodic and cathodic stability, volumetric and electron density properties, charge transfer values, and electrostatic maps are evaluated.     

Processing and Properties of Nanocomposite Filament Yarns with Various Filler Concentrations from Two Different Modification Methods

In this research, the possibility of producing and processing nanocomposite polypropylene filament yarns with permanent antimicrobial efficiency has been assessed by comparing two different methods. Therefore two approaches were used to mix various blending contents of antimicrobial agents based on silver/TiO₂ nano particles with PP: 1) mixing of PP powder and inorganic nanocomposite powder as an antibacterial agent with the appropriate concentration in a twin screw extruder, preparing modified granules and feeding them to the melt spinning machine, 2) producing masterbatch by a twin screw extruder and blending it with PP in the melt spinning process. In both methods, pure PP and all other combined samples had an acceptable spinnability at the spinning temperature of 240 °C and take-up speed of 2000 m/min. After producing as-spun filament yarns by a pilot plant melt spinning machine, samples were drawn, textured and finally weft knitted. Physical and structural properties of as-spun and drawn yarns with constant and variable draw ratios were investigated and compared. Moreover, the DSC, SEM and FTIR techniques have been used for samples characterization. Finally antibacterial efficiency of knitted samples was evaluated. The experimental results indicated that the maximum crystallinity reduction of modified as-spun yarns reached 5%. But by applying method 2 (masterbatch), crystallinity of modified as-spun yarns remained unchanged compared to pure yarn. However, drawing procedure has compensated this difference. By applying the second method, the drawing generally improved the increase of tenacity and modulus of modified fibers, whereas in method 1 the opposite effect was noticed in the case of constant draw ratio. Although the biostatic efficiency of nanocomposite fibers was excellent in both methods, modified fabrics obtained from method 1 showed higher bioactivity.     

Selective growth of Si nanowire arrays via galvanic displacement processes in water-in-oil microemulsions

Galvanic displacement processes are employed in water-in-oil microemulsions to deposit gold nanoclusters selectively on Si surfaces and sidewalls. The gold clusters then serve as catalysts to achieve selective growth of vertically and laterally aligned Si nanowire arrays by chemical vapor deposition via the vapor-liquid-solid growth mechanism. The size of the gold clusters is shown to have a good correlation with the microemulsion parameters, which in turn controls the size of the synthesized nanowires.     

Adsorption kinetics of 1-alkanethiols on hydrogenated Ge(111)

We have investigated the liquid-phase self-assembly of 1-alkanethiols (HS(CH2)n-1CH3, n = 8, 16, and 18) on hydrogenated Ge(111), using attenuated total reflection Fourier transform infrared spectroscopy as well as water contact angle measurements. The infrared absorbance of C-H stretching modes of alkanethiolates on Ge, in conjunction with water contact angle measurements, demonstrates that the final packing density is a function of alkanethiol concentration in 2-propanol and its chain length. High concentration and long alkyl chain increase the steady-state surface coverage of alkanethiolates. A critical chain length exists between n = 8 and 16, above which the adsorption kinetics is comparable for all long alkyl chain 1-alkanethiols. The steady-state coverage of hexadecanethiolates, representing long-chain alkanethiolates, reaches a maximum at approximately 5.9 x 10(14) hexadecanethiolates/cm2 in 1 M solution. The characteristic time constant to reach a steady state also decreases with increasing chain length. This chain length dependence is attributed to the attractive chain-to-chain interaction in long-alkyl-chain self-assembled monolayers, which reduces the desorption-to-adsorption rate ratio (kd/ka). We also report the adsorption and desorption rate constants (ka and kd) of 1-hexadecanethiol on hydrogenated Ge(111) at room temperature. The alkanethiol adsorption is a two-step process following a first-order Langmuir isotherm: (1) fast adsorption with ka = 2.4 +/- 0.2 cm3/(mol s) and kd = (8.2 +/- 0.5) x 10(-6)(s-1); (2) slow adsorption with ka = 0.8 +/- 0.5 cm3/(mol s) and kd = (3 +/- 2) x 10(-6) s(-1).     

Brief syntheses of (±)-methyl shikimate, (±)-methyl epishikimate and structural variants

Two brief syntheses of (±)-methyl shikimate are described in a strategy which offers potentially flexible access to a range of analogues. New intramolecular rearrangement reactions of epoxides derived from methyl 7-oxabicyclo[2.2.1]hept-3-ene 6-carboxylate and methyl bicyclo[2.2.1]hept-3-ene 6-carboxylate are described.     

An improved synthesis of (±)-methyl shikimate through stereoselective cis dihydroxylation of (±)-methyl 5β-hydroxycyclohexa-1,3-dienoate under prévost''s reaction conditions

A Prévost-type reaction under “wet” conditions upon the O-^tbutyl- dimethylsilyl derivative of (±)-methyl 5β-hydroxycyclohexa-1,3-dienoate gives (±)-methyl 3α-acetoxy-4β-hydroxy-5β-^tbutyldimethylsilyloxycyclohexene which may be readily deprotected to afford (±)-methyl Shikimate in very high yield. Less selectivity is observed in a similar reaction upon the parent alcohol and when this compound is reacted under dry conditions the major product is (±)-methyl 4β,5β-epoxy-3β-acetoxycyclohexenoate. An analysis of Prevost reactions with $\text{exo}$ and $\text{endo}$ methyl 7-oxabicyclo [2,2,1]hept-5-en-2-oate is also described.     

Temperature-induced self-pinning and nanolayering of AuSi eutectic droplets

A process for self-pinning of AuSi eutectic alloy droplets to a Si substrate, induced by a controlled temperature annealing in ultrahigh vacuum, is presented. Surface pinning of AuSi 3D droplets to the Si substrate is found to be a consequence of the readjustment in the chemical composition of the droplets upon annealing, as required to maintain thermodynamic equilibrium at the solid-liquid interface. Structural and morphological changes leading to the pinning of the droplets to the substrate are analyzed. Phase separation is observed upon cooling of the droplets, leading to the formation of amorphous Si-rich channels within the core and the formation of crystalline Si nanoshells on the outside. The mechanism leading to the pinning and surface layering provides new insight into the role of alloying during growth of silicon nanowires and may be relevant to the engineering of nanoscale Si cavities.