Modification of photochemical reactivity on formation of inclusion complexes: photorearrangement of benzyl phenyl ethers and methyl phenoxyacetates

The photorearrangement of benzyl phenyl ethers and methyl phenoxyacetates was investigated in methanol and in complexes with cyclodextrin in both the solid state and aqueous solutions. Irradiation in cyclodextrin media leads to a large change in product distribution with a very significant ortho selectivity different from that found in methanol where the reaction is non-selective. For meta-substituted ethers and phenoxyacetates, an impressive regioselectivity between the two ortho-rearranged isomers is observed and this is significantly enhanced by increasing the substituent chain length which acts as a spacer to induce a tight fit between the host and the guest. The observed results are rationalized on the basis of specific orientations of the unsubstituted and meta-substituted ethers and phenoxyacetates in the cyclodextrin cavity.

Photodimerization of coumarins in solid cyclodextrin inclusion complexes

The photodimerizations of coumarin and eight of its derivatives are found to proceed selectively in solid inclusion complexes with beta- and gamma-cyclodextrins (beta- and gamma-CD). The distribution of photodimers from these complexes is compared with those from the neat coumarin solids and their solutions in a variety of solvents. By assuming that the stereochemistry of the dimers reflects the packing arrangements of their precursors in the CD complexes, several hypotheses concering the locations and arrangements of the coumarins in the host toruses have been made. The stoichiometries of the complexes have been assigned on the basis of the presence or absence of photodimers and from NMR integration ratios of characteristic coumarin and saccharide protons. The relative orientations of substituted coumarins within a complex are inferred from the stereochemistry of the photodimers. Depending upon the substitution pattern of the coumarin molecules and the type of CD employed, complexes whose guest-host stoichiometries are 1:1, 2:1, and 2:2 have been identified. In several instances, dimers not available from irradiation of neat solid coumarins or their solutions have been obtained from the CD complexes.

The two-step positive temperature coefficient in resistance characteristics of n-(Ba,Pb)TiO3 ceramics created through inclusion of grain boundary modifier additives

Donor-doped n-(Ba,Pb)TiO3 polycrystalline ceramics exhibit distinctly two-step positive temperature coefficient of resistance (PTCR) characteristics when formulated with suitable combinations of B2O3 and Al2O3 as grain boundary modifiers by heterogeneous addition. B2O3 or Al2O3 when added singularly resulted in either steep or broad PTCR jumps respectively across the phase transition. The two-step PTCR is attributed to the activation of the acceptor states, created through B2O3 and Al2O3, for various temperature regimes above the Curie point (T-c). The changing pattern of trap states is evident from the presence of Ti4+-O--Al3+ type hole centres in the grain boundary layer regions, identified in the electron paramagnetic resonance (EPR) spectra. That charge redistribution occurs among the inter-band gap defect states on crossing the Curie temperature is substantiated by the temperature coefficient in the EPR results. Capacitance-voltage results clearly show that there is an increase in the density of trap states with the addition of B2O3 and Al2O3. The spread in energy values of these trap states is evident from the large change in barrier height (phi similar or equal to 0.25-0.6 eV) between 500 and 650 K.

Electrical resistivity studies of benzidine-TCNQ and its inclusion compound under high pressure

Electrical resistivity studies of the charge transfer complex benzidine—TCNQ and its inclusion compound, have been carried out up to pressures 8 GPa. Two types of behaviour were observed in these complexes under high pressure and this difference is interpreted and discussed.

Functional regulation of PVBV Nuclear Inclusion protein-a protease activity upon interaction with Viral Protein genome-linked and phosphorylation

Regulation of NIa-Pro is crucial for polyprotein processing and hence, for successful infection of potyviruses. We have examined two novel mechanisms that could regulate NIa-Pro activity. Firstly, the influence of VPg domain on the proteolytic activity of NIa-Pro was investigated. It was shown that the turnover number of the protease increases when these two domains interact (as: two-fold; trans: seven-fold) with each other. Secondly, the protease activity of NIa-Pro could also be modulated by phosphorylation at Ser129. A mutation of this residue either to aspartate (phosphorylation-mimic) or alanine (phosphorylation-deficient) drastically reduces the protease activity. Based on these observations and molecular modeling studies, we propose that interaction with VPg as well as phosphorylation of Ser129 could relay a signal through Trp143 present at the protein surface to the active site pocket by subtle conformational changes, thus modulating protease activity of NIa-Pro. (C) 2011 Elsevier Inc. All rights reserved.

Smart polymer mediated purification and recovery of active proteins from inclusion bodies

Obtaining correctly folded proteins from inclusion bodies of recombinant proteins expressed in bacterial hosts requires solubilization with denaturants and a refolding step. Aggregation competes with the second step. Refolding of eight different proteins was carried out by precipitation with smart polymers. These proteins have different molecular weights, different number of disulfide bridges and some of these are known to be highly prone to aggregation. A high throughput refolding screen based upon fluorescence emission maximum around 340 nm (for correctly folded proteins) was developed to identify the suitable smart polymer. The proteins could be dissociated and recovered after the refolding step. The refolding could be scaled up and high refolding yields in the range of 8 mg L-1 (for CD4D12, the first two domains of human CD4) to 58 mg L-1 (for malETrx, thioredoxin fused with signal peptide of maltose binding protein) were obtained. Dynamic light scattering (DLS) showed that polymer if chosen correctly acted as a pseuclochaperonin and bound to the proteins. It also showed that the time for maximum binding was about 50 min which coincided with the time required for incubation (with the polymer) before precipitation for maximum recovery of folded proteins. The refolded proteins were characterized by fluorescence emission spectra, circular dichroism (CD) spectroscopy, melting temperature (T-m), and surface hydrophobicity measurement by ANS (8-anilinol-naphthalene sulfonic acid) fluorescence. Biological activity assay for thioredoxin and fluorescence based assay in case of maltose binding protein (MBP) were also carried out to confirm correct refolding. (C) 2012 Elsevier B.V. All rights reserved.

Inclusion of body doping in compact models for fully-depleted common double gate MOSFET adapted to gate-oxide thickness asymmetry

Since it is difficult to find the analytical solution of the governing Poisson equation for double gate MOSFETs with the body doping term included, the majority of the compact models are developed for undoped-body devices for which the analytical solution is available. Proposed is a simple technique to included a body doping term in such surface potential based common double gate MOSFET models also by taking into account any differences between the gate oxide thickness. The proposed technique is validated against TCAD simulation and found to be accurate as long as the channel is fully depleted.

Accommodating Unwelcome Guests in Inorganic Layered Hosts: Inclusion of Chloranil in a Layered Double Hydroxide

The host-guest chemistry of most inorganic layered solids is limited to ion-exchange reactions. The guest species are either cations or anions to compensate for the charge deficit, either positive or negative, of the inorganic layers. Here, we outline a strategy to include neutral molecules like ortho- and para-chloranil, that are known to be good acceptors in donor-acceptor or charge-transfer complexes, within the galleries of a layered solid. We have succeeded in including neutral ortho- and para-chloranil molecules within the galleries of an Mg-Al layered double hydroxide (LDH) by using charge-transfer interactions with preintercalated p-aminobenzoate ions as the driving force. The p-aminobenzoate ions are introduced in the Mg-Al LDH via ion exchange. The intercalated LDH can adsorb ortho- and para-chloranil from chloroform solutions by forming charge-transfer complexes with the p-aminobenzoate anions present in the galleries. We use X-ray diffraction, spectroscopy, and molecular dynamics simulations to establish the nature of interactions and arrangement of the charge-transfer complex within the galleries of the layered double hydroxide.

Detailed investigation of a gamma-cyclodextrin inclusion complex with L-thyroxine for improved pharmaceutical formulations

Thyroxine is a naturally occurring human hormone produced by the thyroid gland. Clinical applications of thyroxine to treat several chronic disorders are limited by poor water solubility and instability under physiological conditions. An inclusion complex of levo-thyroxine (l-thyroxine), the active form of the hormone with gamma cyclodextrin (gamma-CD) has been obtained and studied with the aim of improving oral delivery rather than the injection formulation of the sodium salt. In addition to greater patient acceptability, inclusion complexes often improve aqueous solubility and bioavailability, stability, and reduce toxicity of drugs, thus providing enhanced pharmaceutical formulations. Physicochemical characterization of the inclusion complex was carried out using Fourier transform infrared spectroscopy, X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy and proton nuclear magnetic resonance spectroscopy. Intermolecular dipolar interactions for the inclusion complex were also studied using 2 dimensional ROESY experiments. Formation of the inclusion complex between the protons H3 and H5 of cyclodextrin with aromatic protons of thyroxine was confirmed by their dipolar interaction. Molecular modelling was used to understand the basis for the complex formation and predict the formation of other complexes. Interestingly, we found that l-thyroxine forms an inclusion complex only with the larger gamma-CD and not with other available alpha and beta forms.

Novel ATPase activity of the polyprotein intermediate, Viral Protein genome-linked-Nuclear Inclusion-a protease, of Pepper vein banding potyvirus

Potyviruses temporally regulate their protein function by polyprotein processing. Previous studies have shown that VPg (Viral Protein genome-linked) of Pepper vein banding virus interacts with the NIa-Pro (Nuclear Inclusion-a protease) domain, and modulates the kinetics of the protease. In the present study, we report for the first time that VPg harbors the Walker motifs A and B, and the presence of NIa-Pro, especially in cis (cleavage site (E191A) VPg-Pro mutant), is essential for manifestation of the ATPase activity. Mutation of Lys47 (Walker motif A) and Asp88:Glu89 (Walker motif B) to alanine in E191A VPg-Pro lead to reduced ATPase activity, confirming that this activity was inherent to VPg. We propose that potyviral VPg, established as an intrinsically disordered domain, undergoes plausible structural alterations upon interaction with globular NIa-Pro which induces the ATPase activity. (C) 2012 Elsevier Inc. All rights reserved.

Charge-transfer-driven inclusion of neutral TCNQ molecules in the galleries of a layered double hydroxide: an experimental and computational study

The layered double hydroxides (LDH) or anionic clays are an important class of ion-exchange materials. They consist of positively charged brucite-like inorganic sheets with charge-compensating exchangeable anions in the interlamellar space. Here we show how neutral TCNQ (7,7,8,8-tetracyanoquinodimethane) molecules can be included within the galleries of an LDH. To do so, we exploit the fact that TCNQ is a good electron acceptor that forms donor acceptor complexes with a variety of donors. The electron donor aniline was intercalated into a Mg-Al LDH as p-aminobenzoate (AB) ions by a conventional ion-exchange reaction. We show here that neutral TCNQ molecules may be driven into the galleries of the layered solid by charge-transfer complex formation with the intercalated p-aminobenzoate anions. We use diffraction and spectroscopic measurements in combination with molecular dynamics simulations and quantum chemical calculations to establish the nature of interactions and arrangement of the charge-transfer complex within the galleries of the layered double hydroxide. Electrostatic interactions between the TCNQ molecules and the anchored AB ions, subsequent to charge transfer, are the driving force for the inclusion of TCNQ molecules in the galleries of the LDH.

Anisotropic thermopiezoelectric solids with an elliptic inclusion or a hole under uniform heat flow

The two-dimensional problem of a thermopiezoelectric material containing an elliptic inclusion or a hole subjected to a remote uniform heat flow is studied. Based on the extended Lekhnitskii formulation for thermopiezoelectricity, conformal mapping and Laurent series expansion, the explicit and closed-form solutions are obtained both inside and outside the inclusion (or hole). For a hole problem, the exact electric boundary conditions on the hole surface are used. The results show that the electroelastic fields inside the inclusion or the electric field inside the hole are linear functions of the coordinates. When the elliptic hole degenerates into a slit crack, the electroelastic fields and the intensity factors are obtained. The effect of the heat how direction and the dielectric constant of air inside the crack on the thermal electroelastic fields are discussed. Comparison is made with two special cases of which the closed solutions exist and it is shown that our results are valid.