Trapping Aluminum Hydroxide Clusters with Trisilanols during Speciation in Aluminum(III)–Water Systems: Reproducible,Large Scale Access to Molecular Aluminate Models

To gain molecular level insights into the properties of certain functions and units of extended oxides/hydroxides, suitable molecular model compounds are needed. As an attractive route to access such compounds the trapping of early intermediates during the hydrolysis of suitable precursor compounds with the aid of stabilizing ligands is conceivable, which was tested for the aluminum(III)/water system. Indeed, trisilanols proved suitable trapping reagents: their presence during the hydrolysis of AlⁱBu₂H in dependence on the amount of water used allowed for the isolation of tri‐ and octanuclear aluminum hydroxide cluster complexes [Al₃(μ₂‐OH)₃(THF)₃(PhSi(OSiPh₂O)₃)₂] ( 1 ) and [Al₈(μ₃‐OH)₂(μ₂‐OH)₁₀(THF)₃(p‐anisylSi(OSiPh₂O)₃)₄] ( 2 ). 1 can be regarded as the Al(OH)₃ cyclic trimer, where six protons have been replaced by silyl residues. While 2 features a unique [Al₈(μ₃‐OH)₂(μ₂‐OH)₁₀]¹²⁺ core. In contrast to most other known aggregates of this type, 1 and 2 can be readily prepared at reasonable scales, dissolve in common solvents, and retain an intact framework even in the presence of excessive amounts of water. This finding paves the way to future research addressing the reactivity of the individual functional groups.     

An experimental investigation on pool boiling heat transfer enhancement using Cu-Al2O3 nano-composite coating

Pool boiling heat transfer performances of Cu-Al₂O₃-coated copper surfaces have been studied experimentally for its potential use in heat transfer applications. In the present study, a two-step electrochemical deposition method is examined. This method provides an easy control on surface properties such as porosity and coating thickness. The deposition method is studied carefully and responsible surface morphology parameters are reported. After performing the pool boiling experiments on coated surfaces with DI water, the maximum critical heat flux of 1800 kW/m² and heat transfer coefficient of 193 kW/m² K, which are 68% and 260% higher than that of bare surface, respectively.     

Evaluation of pigments from methanolic extract of Tagetes erecta and Beta vulgaris as antioxidant and antibacterial agent

The Total Phenolic Content (TPC), antioxidant and antibacterial activities of methanolic extract of Marigold flower (MF) (Tagetes erecta) and Beet root (BR) (Beta vulgaris) were examined. The present work reveals that MF contained greater amount of TPC (42.5 mg/g GAE) as compared to BR (39.4 mg/g GAE). Methanolic extract of MF exhibited excellent DPPH free radical scavenging power (IC₅₀ 0.0716 mg/mL) and reducing power at 1 mg/mL concentration. Similar results have been obtained in FTC and TBA method. The results of antibacterial test indicated that the methanolic extract of MF and BR is significantly effective against both type of Gram-negative (Escherichia coli, Shigella dysenteriae) and Gram-positive (Bacillus subtilis, Staphylococcus aureus) bacterial strains. Therefore, the present study suggests that the Marigold and BR are promising source of herbal medicinal products with noteworthy antioxidant and antibacterial activity.     

Experimental measurements of acoustical properties of snow and inverse characterization of its geometrical parameters

Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with air (+water vapour) saturated pores. Investigation of snow acoustic properties is useful to understand the interaction between snow structure and sound waves, which can be further used to devise non-destructive way for exploring physical (non-acoustic) properties of snow. The present paper discusses the experimental measurements of various acoustical properties of snow such as acoustic absorption coefficient, surface impedance and transmission losses across different snow samples, followed by inverse characterization of different geometrical parameters of snow. The snow samples were extracted from a natural snowpack and transported to a nearby controlled environmental facility at Patsio, located in the Great Himalayan range of India. An impedance tube system (ITS), working in the frequency range 63–6300 Hz, was used for acoustic measurements of these snow samples. The acoustic behaviour of snow was observed strongly dependent upon the incident acoustic frequency; for frequencies smaller than 1 kHz, the average acoustic absorption coefficient was found below than 0.4, however, for the frequencies more than 1 kHz it was found to be 0.85. The average acoustic transmission loss was observed from 1.45 dB cm⁻¹ to 3.77 dB cm⁻¹ for the entire frequency range. The real and imaginary components of normalized surface impedance of snow samples varied from 0.02 to 7.77 and −6.05 to 5.69, respectively. Further, the measured acoustic properties of snow were used for inverse characterization of non-acoustic geometrical parameters such as porosity, flow resistivity, tortuosity, viscous and thermal characteristic lengths using the equivalent fluid model proposed by Johnson, Champoux and Allard (JCA). Acoustically derived porosity and flow resistivity were also compared with experimentally measured values and good agreement was observed between them.     

Trapping Aluminum Hydroxide Clusters with Trisilanols during Speciation in Aluminum(III)–Water Systems: Reproducible,Large Scale Access to Molecular Aluminate Models

To gain molecular level insights into the properties of certain functions and units of extended oxides/hydroxides, suitable molecular model compounds are needed. As an attractive route to access such compounds the trapping of early intermediates during the hydrolysis of suitable precursor compounds with the aid of stabilizing ligands is conceivable, which was tested for the aluminum(III)/water system. Indeed, trisilanols proved suitable trapping reagents: their presence during the hydrolysis of AlⁱBu₂H in dependence on the amount of water used allowed for the isolation of tri‐ and octanuclear aluminum hydroxide cluster complexes [Al₃(μ₂‐OH)₃(THF)₃(PhSi(OSiPh₂O)₃)₂] ( 1 ) and [Al₈(μ₃‐OH)₂(μ₂‐OH)₁₀(THF)₃(p‐anisylSi(OSiPh₂O)₃)₄] ( 2 ). 1 can be regarded as the Al(OH)₃ cyclic trimer, where six protons have been replaced by silyl residues. While 2 features a unique [Al₈(μ₃‐OH)₂(μ₂‐OH)₁₀]¹²⁺ core. In contrast to most other known aggregates of this type, 1 and 2 can be readily prepared at reasonable scales, dissolve in common solvents, and retain an intact framework even in the presence of excessive amounts of water. This finding paves the way to future research addressing the reactivity of the individual functional groups.     

Finite element Galerkin approximations to a class of nonlinear and nonlocal parabolic problems

In this article, a finite element Galerkin method is applied to a general class of nonlinear and nonlocal parabolic problems. Based on an exponential weight function, new a priori bounds which are valid for uniform in time are derived. As a result, existence of an attractor is proved for the problem with nonhomogeneous right hand side which is independent of time. In particular, when the forcing function is zero or decays exponentially, it is shown that solution has exponential decay property which improves even earlier results in one dimensional problems. For the semidiscrete method, global existence of a unique discrete solution is derived and it is shown that the discrete problem has an attractor. Moreover, optimal error estimates are derived in both and ‐norms with later estimate is a new result in this context. For completely discrete scheme, backward Euler method with its linearized version is discussed and existence of a unique discrete solution is established. Further, optimal estimates in ‐norm are proved for fully discrete schemes. Finally, several numerical experiments are conducted to confirm our theoretical findings. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 1232–1264, 2016     

Cycloaddition of cyclohexa-2,4-dienones, ring-closing metathesis, and photochemical reactions: a common stereoselective approach to duprezianane, polyquinane and sterpurane frameworks

A novel approach to three different types of carbocyclic frameworks belonging to dupreziananes, sterpuranes, and polyquinanes from simple aromatic precursors has been presented. Cycloaddition of appropriately appended cyclohexa-2,4-dienones with acyclic dienes gave bridged bicyclic octanes suitably disposed with olefinic chains, which upon ring-closing metathesis led to functionalized tricyclo[5.2.2.0(1,5)]undecanes related to dupreziananes. Photochemical sigmatropic 1,2- and 1,3-acyl shifts in tricyclo[5.2.2.0(1,5)] undecanes upon triplet and singlet excitation provided stereoselective routes to sterpurane and polyquinane frameworks.     

Structural modifications of diamond like carbon films induced by MeV nitrogen ion irradiation

Diamond-like carbon (DLC) films were deposited on Si(1 0 0) substrates using plasma deposition technique. The deposited films were irradiated using 2 MeV N⁺ ions at fluences of 1×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm². Samples have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Analysis of Raman spectra shows a gradual shift of both D and G band peaks towards higher frequencies along with an increase of the intensity ratio, I(D)/I(G), with increasing ion fluence in irradiation. These results are consistent with an increase of sp² bonding. XPS results also show a monotonic increase of sp²/sp³ hybridization ratio with increasing ion fluence. Plan view TEM images show the formation of clusters in the irradiated DLC films. HRTEM micrographs from the samples irradiated at a fluence of 5×10¹⁵ ions/cm² show the lattice image with an average interplanar spacing of 0.34 nm, revealing that the clusters are graphite clusters. The crystallographic planes in these clusters are somewhat distorted compared to the perfect graphite structure.     

Fluoride anion sensing using colorimetric reagents containing binaphthyl moiety and urea binding site

Four 1,1′-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F⁻ over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by ¹H NMR data. The presence of an electron-withdrawing nitro group in N′-aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10⁻⁵ mol dm⁻³ of the receptor and host.     

Synthesis, spectral and biological studies of nitrogen–sulphur donor macrocyclic ligands and their transition metals complexes

Mn(II), Co(II), Ni(II) and Cu(II) complexes have been synthesized with 22 and 24 membered tetramide macrocyclic ligands viz; 1,9,12,20-tetraaza-2,8,13,19-tetraone-5,16-dithiacyclodocosane [L¹] and 1,9,13,21-tetraaza-2,8,14,20-tetraone-5,17-dithiacyclotetracosane [L²] and characterized by elemental analysis, molar conductance, magnetic susceptibility measurements, mass, IR, electronic EPR spectral studies and electrochemical properties. The molar conductance of all the complexes in DMSO solution is corresponding to 1:2 electrolyte. Thus these complexes may be formulated as [M(L′)]Cl₂ [where M = Mn(II), Co(II), Ni(II) and Cu(II) L′ = L¹ and L²]. On the basis of spectral studies a distorted octahedral geometry has been assigned for all the complexes. The ligands and their complexes were also screened in vitro against two pathogenic fungi (F. moniliformae and R. solani) to assess their growth inhibiting potential.