Investigations of pressure induced structural phase transformations in pentaerythritol

We have investigated the pressure induced structural changes in pentaerythritol {2,2-bis-(hydroxymethyl)-1,3-propanediol} with the help of X-ray diffraction studies. Our results show that this compound undergoes transformations to a lower symmetry phase between 5.2-5.9 GPa. It further undergoes phase transformations at ∼8.5 and ∼11 GPa; eventually evolving to a disordered phase beyond 14-15 GPa in agreement with our earlier Raman studies. On release of pressure from 18.5 GPa, the compound transforms back to the initial tetragonal phase.     

RP-HPTLC densitometric determination and validation of vanillin and related phenolic compounds in accelerated solvent extract of Vanilla planifolia*

A simple, fast and sensitive RP-HPTLC method is developed for simultaneous quantitative determination of vanillin and related phenolic compounds in ethanolic extracts of Vanilla planifolia pods. In addition to this, the applicability of accelerated solvent extraction (ASE) as an alternative to microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE) and Soxhlet extraction was also explored for the rapid extraction of phenolic compounds in vanilla pods. Good separation was achieved on aluminium plates precoated with silica gel RP-18 F(254S) in the mobile phase of methanol/water/isopropanol/acetic acid (30:65:2:3, by volume). The method showed good linearity, high precision and good recovery of compounds of interest. ASE showed good extraction efficiency in less time as compared to other techniques for all the phenolic compounds. The present method would be useful for analytical research and for routine analysis of vanilla extracts for their quality control.     

Motion of aromatic hydrocarbons in the microporous aluminum methylphosphonates AlMePO-alpha and AlMePO-beta

(2)H wide-line NMR has been used, in conjunction with molecular dynamics simulations where appropriate, to follow the reorientation of the monoaromatic compounds benzene, toluene, and p-xylene within the one-dimensional channels of the alpha- and beta-polymorphs of aluminum methylphosphonate, Al(2)(CH(3)PO(3))(3). Variable-temperature, static, (2)H NMR spectra of adsorbed d(6)-benzene, d(3)-, d(5)-, and d(8)-toluenes, and d(3),d(3)-p-xylene were matched by line shape simulation. The motion of p-xylene in both polymorphs is approximated by the long axis of the molecule describing a cone within the channels, the half-angle of which is greater for the slightly wider channels in AlMePO-beta (27-30 degrees cf. 18-19 degrees). The (2)H NMR of d(3)-toluene is simulated using a similar model, whereas the signal from aromatic deuterons in d(5)- and d(8)-toluenes is simulated by a ring undergoing 2pi/3 flips around the para axis. The reorientation of benzene shows the largest differences between the two pore structures. In AlMePO-beta it tumbles with little restriction, although at low temperatures the spectral details are better matched by allowing the molecule to spend a greater proportion of its time closer to the wall. In AlMePO-alpha the much broader line shape arises from constrained motion within the strongly triangular channels. Molecular dynamics simulations of benzene in the two structures confirm the differences. They support a model for benzene in AlMePO-alpha where its motion is restricted to rotations about its 6-fold axis and 2pi/3 jumps between symmetry-related sites in the pores, so that the plane of the aromatic ring remains approximately parallel to the c-axis.     

Laponite–Gelatin Nanofibrous Microsphere Promoting Human Dental Follicle Stem Cells Attachment and Osteogenic Differentiation for Noninvasive Stem Cell Transplantation

Nanofibrous microspheres (NFM) are emerging as prominent next-generation biomimetic injectable scaffold system for stem cell delivery and different tissue regeneration where nanofibrous topography facilitates ECM-like stem cells niches. Addition of osteogenic bioactive nanosilicate platelets within NFM can provide osteoconductive cues to facilitate matrix mediated osteogenic differentiation of stem cells and enhance the efficiency of bone tissue regeneration. In this study, gelatin nanofibrous microspheres are prepared containing fluoride-doped laponite XL21 (LP) using the emulsion mediated thermal induce phase separation (TIPS) technique. Systematic studies are performed to understand the effect of physicochemical properties of biomimicking NFM alone and with different concentrations of LP on human dental follicle stem cells (hDFSCs), their cellular attachment, proliferation, and osteogenic differentiation. The study highlights the effect of LP nanosilicate with biomimicking nanofibrous injectable scaffold system aiding in enhancing stem cell differentiation under normal physiological conditions compared to NFM without LP. The laponite–NFM shows suitability as excellent injectable biomaterials system for stem cell attachment, proliferation and osteogenic differentiation for stem cell transplantation and bone tissue regeneration.     

Metal-free activation of H<Subscript>2</Subscript>O<Subscript>2</Subscript> by synergic effect of ionic liquid and microwave: chemoselective oxidation of benzylic alcohols to carbonyls and unexpected formation of anthraquinone in aqueous condition

H₂O₂ mediated oxidation of alcohols in ionic liquid is revisited, wherein, ionic liquids under the influence of microwave irradiation have been found to facilitate activation of H₂O₂ without any metal catalyst in aqueous condition. The method utilizes a neutral ionic liquid [hmim]Br both as catalyst and solvent for efficient and chemoselective oxidation of benzyl alcohol derivatives on aromatic (β, γ) alcohols, cyclic and aliphatic analogues, which can be a useful synthetic approach in total synthesis of complex organic compounds/natural products. Moreover, an unexpected oxidation of 9-anthracenyl propanol, a polyaromatic benzyl alcohol, resulting in the formation of 9,10-anthraquinone by the loss of propyl side chain was observed. Plausible mechanism and further exploration of this method on various other related substrates are discussed in detail.     

Two-dimensional weak pseudomanifolds on eight vertices

We explicitly determine all the two-dimensional weak pseudomanifolds on 8 vertices. We prove that there are (up to isomorphism) exactly 95 such weak pseudomanifolds, 44 of which are combinatorial 2-manifolds. These 95 weak pseudomanifolds triangulate 16 topological spaces. As a consequence, we prove that there are exactly three 8-vertex two-dimensional orientable pseudomanifolds which allow degree three maps to the 4-vertex 2-sphere.     

A reexamination of the degradation of polyvinylchloride by thermal analysis

Degradation of polyvinylchloride has been reexamined in the light of its DT-DSC-TG analytical behavior up to a temperature of 1000°C in an inert atmosphere. Four distinct stages of degradation have been identified. The first stage is almost eventless with no change in weight for untreated PVC samples. The second stage is almost exclusively dehydrochlorination. The third stage appears to be a structural reorganization involving such processes as cis-trans isomerization, aromatization, and crosslinking. The fourth stage appears to be a structural degradation and is associated with the evolution of hydrocarbons. The role of liberated hydrogen chloride has been better appreciated in catalyzing the above secondary reactions on the polyene residue obtained on partial or total dehydrochlorination. The effect of the particle dimension and chemical and physical pretreatments of the samples, such as low temperature dehydrochlorination by an alkali and vacuum heat treatment, respectively, on the degradation pattern has been studied. © 1994 John Wiley & Sons, Inc.     

Ceria co-doped with calcium (Ca) and strontium (Sr): a potential candidate as a solid electrolyte for intermediate temperature solid oxide fuel cells

Co-doped samples of Ce_0.95?x Ca_0.05Sr _x O_1.95?x , where (x?=?0.00, 0.01, 0.02, and 0.03), have been prepared by auto-combustion method and characterized to explore their use as a solid electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). Crystal structure, microstructure, and ionic conductivity have been characterized by X-ray diffraction, scanning electron microscopy, and impedance spectroscopy, respectively. All the compositions have been found to be single phase. Results show that the samples co-doped with Ca and Sr exhibit higher ionic conductivity than the samples singly doped with Ca in the intermediate temperature range. Ce_0.93Ca_0.05Sr_0.02O_2?δ exhibits maximum conductivity among all the compositions. This may be a potential candidate as a solid electrolyte for IT-SOFCs.     

Electrical conductivity of thermally degraded poly(vinyl chloride)–polyacrylonitrile blends

Finely powdered blends of poly(vinyl chloride) (PVC) and polyacrylonitrile (PAN) have been thermally degraded at 275°C for 24 h in an inert atmosphere to effect complete de-hydrochlorination of PVC to a conjugated polyene structure and simultaneous internal polymerization of nitrile groups in PAN to a conjugated polyimine sequence. The room temperature d.c. conductivity of the degraded blends showed clear synergistic behavior. A maximum conductivity has been observed with a blend of 60 PAN/40 PVC which is about 4 orders of magnitude over the linearly weighted average conductivity of the individual degraded homopolymers. The results have been interpreted in terms of a possible donor-acceptor interaction between the degraded homopolymers leading to mutual doping and, hence, an enhanced electrical conductivity. © 1995 John Wiley & Sons, Inc.