Interaction of calcium channel antagonists with calcium: spectroscopic and modeling studies on diltiazem and its Ca2+ complex

Using spectral techniques, the solution conformation of diltiazem was studied in acetonitrile with special reference to the effect of Ca2+ on the drug structure. Complete assignment of the proton resonances in the 1H-NMR spectrum of the drug was made using one-and two-dimensional spectral analyses. A two-dimensional 1H-NOESY spectrum (in the phase-sensitive mode) was obtained to identify the interproton connectivities in the drug molecule. A molecular modeling program involving Monte Carlo simulation and energy minimization was employed to arrive at the structure of the drug. The program was run with and without the input of the interproton distances derived from the NOESY cross peaks. Both the protocols led to a structure of the drug which was generally similar to that reported from X-ray diffraction data on crystalline diltiazem hydrochloride (Kojic-Prodic, et al. Helv. Chim. Acta 1984, 67, 916-926). However, significant differences between the two structures were seen in the orientations of the substituent groups attached to the benzothiazepine ring. Substantial changes in the circular dichroic (CD) and 1H-NMR spectra of diltiazem were observed on addition of Ca2+ up to a mole ratio of 0.5 Ca2+ per drug. Relatively large changes were seen in 1H resonances of the N-methyl protons and the methylene protons attached to the heterocyclic nitrogen. Analysis of the binding isotherms from CD data at 22 +/- 1 degrees C indicated a 2:1 drug:Ca2+ "sandwich" complex with an estimated dissociation constant of 140 microM. One-dimensional difference NOE and two-dimensional NOESY spectra revealed interproton connectivities between two drug molecules that were compatible with the sandwich complex formation. The interproton distances derived from the volume integrals of the NOESY cross peaks were used as geometrical constraints in modeling the Ca(2+)-bound conformation of diltiazem. The minimum-energy conformation corresponded to the sandwich complex where Ca2+ was coordinated to three oxygens in each of the two drug molecules. Combined with our earlier data on the ability of diltiazem to translocate Ca2+ across the lipid bilayer in synthetic liposomes (Ananthanarayanan, V.S.; Taylor, L.; Pirritano, S.Biochem. Cell Biol. 1992, 70, 608-612), the structural data presented here point to a role for Ca2+ in the interaction of diltiazem with its membrane-bound receptor.     

Effect of NOx on AgI formation in Ag-mordenite

Ag loaded mordenite can be used as a trap for radio-iodine arising from nuclear reprocessing operations. Typically, iodine is trapped in the Ag loaded mordenite by the formation of AgI in the pores of the mordenite, through a solid-vapour reaction. In the presence of NO_x and water vapour, AgI is most likely formed by liquid-vapour reaction between AgNO₃ and I₂. This reaction results in the formation of large aggregates of AgI crystals on the surface of the mordenite, also leading to a yellow colouration of the mordenite, which is not observed when NO_x and water vapour is absent.     

The effect of P2O5 on the structure,sintering and sealing properties of barium calcium aluminum boro-silicate (BCABS) glasses

The effect of P₂O₅ incorporation on the sintering, flow and crystallization characteristics of BCABS glasses of composition (mol%) 35BaO–15CaO–5Al₂O₃–(37 − x)SiO₂–8B₂O₃–xP₂O₅ (0 ≤ x ≤5) is investigated. It is observed that addition of P₂O₅, removes cations (Ba²⁺ and Ca²⁺) from the silicate network, resulting in an increase in polymerization. This is reflected by a reduction in TEC and an increase in sealing temperature. In addition, the removal of cations for charge compensation causes a change in major crystalline phases formed, from BaSiO₃ to Ba(Al₂Si₂O₈). In addition, beyond 3 mol% P₂O₅, crystallization of phosphate phases is evident. Based upon the flow temperature, glasses with 0, 1 and 2 mol% P₂O₅ are selected for sealing. In these glasses, conversion of Cr to Cr₂O₃ is observed_, yielding improved adhesion. However, the 2 mol% P₂O₅ glass showed an increased crystallization tendency, resulting in incomplete sintering. Therefore, 1 mol% P₂O₅ seems a good compromise for sealing with improved adhesion.     

Modeling of fixed bed heat storage units utilizing phase change materials

A computer model has been developed for the calculation of the heat exchanged and temperature profiles in a packed bed containing a phase change material. The packed bed is intended as a heat storage unit in which an inert fluid flowing through the bed exchanges heat with an encapsulated spherical shot of the phase change (melting and freezing) material. Examples of predicted bed temperature profiles during heat storage and utilization cycles are given. For A1-12 wt pct Si and Al-30 wt pct Si shot, a sequence of storage and utilization cycles with cyclic cocurrent fluid flow was found to utilize the high latent heat of fusion of the shot efficiently and permit the utilization of the bed as a near isothermal (577°C) heat recuperator.     

Characterization and control of plastic deformation in mesoscale premolded components to realize in‐mold assembled mesoscale revolute joints

This article reports a mold design strategy and a detailed mechanics‐based modeling approach to characterize and control the plastic deformation of premolded components during in‐mold assembly of mesoscale revolute joints. The following new results are reported in this article. First, a mesoscale mold design with varying cavity shape is described to perform in‐mold assembly of the mesoscale revolute joint. Second, a transient computational fluid dynamics (CFD) modeling approach to determine the forces experienced by the mesoscale parts due to injection molding is described. Finally, a mechanics‐based model approach developed using a combination of experimental materials property data and the CFD results as input to a finite element simulation of the deformation response of the mesoscale part is presented for the determination of critical mold design parameters that are necessary for repeatable fabrication of articulating mesoscale revolute joints. Using the advances reported in this article a mesoscale revolute joint has been successfully molded. To the best of our knowledge, this is the first demonstration of in‐mold assembly process using a varying cavity shape mold tocreate an articulating mesoscale revolute joint. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

A new composite of crystalline silicotitanate for sequestration of 137Cs and 90Sr from low-level aqueous waste solution

ABSTRACT

A new composite of crystalline silicotitanate (CST) has been synthesized for the sequestration of Cs and Sr from low-level liquid waste generated in the nuclear industry. The product characterization using X-RAY DEFRACTION (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of CST crystals in the composite. Sorption studies carried out under various test conditions showed that the composite has high affinity for both Cs and Sr. Results of structural characterization of Cs and Sr-loaded CST indicated that the overall structural integrity remained intact after substitution of Na⁺ by Cs⁺ or Sr²⁺. The exceedingly good Cs and Sr sorption performance displayed by the CST composite will find applications in the treatment of nuclear waste.     

P3HT based solution-processed pseudo bi-layer organic solar cell with enhanced performance

We present a solution-processed pseudo bi-layer organic solar cell with poly(3-hexyl thiophene) (P3HT) as donor and indene-C₆₀ bisadduct (ICBA) as acceptor. The devices were fabricated by sequential processing of the active components followed by a thermal annealing treatment. An efficiency of 5.9% was achieved under AM 1.5G irradiation (1000 W/m²). The obtained efficiency is attributed to an enhanced nanomorphology that arises from the inter-diffusion of the ICBA molecules into a layer of pre-organised polymer (P3HT) and also due to the subsequent crystallisation of the ICBA molecules. These processes facilitate efficient charge generation and extraction. Time of flight-secondary ion mass spectroscopy (TOF-SIMS) depth profiling was carried out for different thermal annealing treatments of these pseudo bi-layer devices, which reveals full inter-diffusion of ICBA into the polymer P3HT. Photo-CELIV (charge extraction by linearly increasing voltage) studies elucidates that the thermal annealing imparts crystallinity to the fullerene phase which results in the improvement of charge carrier mobility.     

Development of De-NOx selective catalytic reduction catalyst using V2O5 –TiO2 supported on a ceramic filter candle

This study reports the development of a V₂O₅-TiO₂-based selective catalytic reduction (SCR) catalyst supported on alumina-silicate water filter candles for NO_x abatement. The synthesised catalysts have been characterised by thermogravimetry/differential scanning calorimetry, X-ray diffraction, scanning electron microscope and measurement of NO_x removal performance. The catalyst synthesised under optimal conditions shows NO_x reduction efficiency of >97%. SCR performance has been augmented using O₂ as a carrier gas. This simple, reproducible procedure can have wide applications in NOx abatement.