Department of Chemistry

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IIT Jodhpur

K-Ras is one of the most frequently mutated signal transducing human oncogenes. Ras signaling activity requires correct cellular localization of the GTPase. The spatial organization of K-Ras is controlled by the prenyl binding protein PDEδ, which enhances Ras diffusion in the cytosol. Inhibition of the Ras-PDEδ interaction by small molecules impairs Ras localization and signaling. Here we describe in detail the identification and structure guided development of Ras-PDEδ inhibitors targeting the farnesyl binding pocket of PDEδ with nanomolar affinity. We report kinetic data that characterize the binding of the most potent small molecule ligands to PDEδ and prove their binding to endogenous PDEδ in cell lysates. The PDEδ inhibitors provide promising starting points for the establishment of new drug discovery programs aimed at cancers harboring oncogenic K-Ras. © 2014 American Chemical Society.

World University root node

Journal of Medicinal Chemistry

Structure guided design and kinetic analysis of highly potent benzimidazole inhibitors targeting the PDEδ prenyl binding site

The reaction of bis(tri-n-butyltin)oxide, [nBu3Sn]2O, with HO2C-C6H4-4-CF3 (R fTol-CO2H) affords a coordination polymer [nBu 3SnO2C-RfTol]n (1). 1 undergoes hydrolysis in the presence of atmospheric moisture, at room temperature, resulting in the formation of the diorgano stannoxane [{nBu2SnO 2C-RfTol}2O]2 (2). The transformation of 1 to 2 is accompanied by a Sn-C bond cleavage reaction. Formation of 2 also occurs in a direct reaction, involving [nBu 3Sn]2O and RfTol-CO2H in the presence of water. 2 can also be prepared in a 1:1 reaction of di-n-butyltin oxide, [nBu2SnO]n with RfTol-CO2H. The conversion of 2 from 1 was monitored by 119Sn NMR spectroscopy over a period of eight days. The molecular structure of 2 reveals a tetranuclear assembly consisting of two pairs of structurally distinct six-coordinate tin atoms. Extensive hydrogen-bonding interactions (C-H···O, C-H···F) and weak F···F interactions involving organo-fluorine atoms in the crystal structure result in the formation of a three-dimensional supramolecular architecture for 2. Copyright © 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Zeitschrift fur Anorganische und Allgemeine Chemie

Ambient temperature Sn-C bond cleavage reaction involving the Sn-n-butyl group. weak f···f interactions in the solid state structure of [{nBu2SnO2C-C6H4-4-CF 3}2O]2

Activity of palladium catalysts on different crystalline and amorphous supports was studied using hydrogenation of 1-phenylethenylphosphonic acid with molecular hydrogen as an example. Nanoscale Pd0 deposited on the surface of multi-wall carbon nanotubes (MWCNT) supported on microparticles of titanium oxide has proved the highest efficiency. The starting acid was quantitatively reduced for 1 h in the presence of this catalyst, 11 cycles of hydrogenation were carried out without loss of catalytic activity. © 2014 Springer Science+Business Media New York.

Russian Chemical Bulletin

Catalytic activity of Pd catalysts on different supports in hydrogenation of 1-phenylethenylphosphonic acid

A highly diastereodivergent synthesis of tetrasubstituted cyclohexanes has been achieved using modularly designed organocatalysts (MDOs) which are self-assembled in situ from amino acids and cinchona alkaloid derivatives. Diastereodivergence is realized through controlling the stereoselectivity of the individual steps of a tandem Michael/Michael reaction. Up to 8 of the 16 possible stereoisomers have been successfully obtained in high stereoselectivities using MDOs for the tandem reaction and an ensuing epimerization. The method was used in the enantioselective synthesis of the natural products (-)-α- and β-lycoranes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Angewandte Chemie - International Edition

Highly diastereodivergent synthesis of tetrasubstituted cyclohexanes catalyzed by modularly designed organocatalysts

We report a highly transparent, low resistance Ag metal network templated by a cracked polymer thin film and its incorporation in an organic solar cell. The performance of this scalable metallic network is comparable to that of conventional ITO electrodes. This is a general approach to replace ITO in diverse thin film devices. This journal is © the Partner Organisations 2014.

Fulltext

Physical Chemistry Chemical Physics

A cracked polymer templated metal network as a transparent conducting electrode for ITO-free organic solar cells

We present an outdoor interlaboratory stability study of fully printed and coated indium-tin-oxide (ITO)-free polymer solar cell modules in JNCASR Bangalore (India), ECN (Holland), and DTU (Denmark) carried over more than 1 year. The modules comprising a fully printed and coated stack (Ag grid/PEDOT:PSS/ZnO/P3HT:PCBM/PEDOT:PSS/Ag grid) were prepared in two successive generations and evaluated for outdoor operational stability according to the test protocols laid out by the International Summit on OPV stability (ISOS-3). The modules (70-100 cm2 active area) were encapsulated between two sheets of low-cost plastic barrier material with the use of a UV curing adhesive. The impact of differences in the climatic conditions on the performance of the modules is highlighted and the performance of the modules under storage conditions in parallel with the outdoor study is investigated. While all Gen-I modules failed, the best devices of Gen-II module in which simple improvement in the encapsulation scheme (Gen-II modules) was carried out maintained 95% of the initial performance after 1 year of outdoor testing. We provide detailed insight into the failure mode and offer a discussion on the need for improvement in flexible encapsulation. Finally, recommendations on future encapsulation schemes are also presented. The long-term (over 1 year) stability of indium-tin-oxide (ITO)-free polymer solar cell modules (up-to 100 cm2) in outdoor and under storage are investigated in three different countries. Degradation is observed to be highly localized owing to encapsulation shortcomings. Simple improvement in the encapsulation method is carried out with dramatic improvement in the stability (shown in figure). © 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Advanced Engineering Materials

Outdoor operational stability of indium-free flexible polymer solar modules over 1 year studied in India, Holland, and Denmark

A single micro/nanowire network of a metal deposited over a large area on a transparent substrate serves as a transparent conducting electrode with optoelectronic properties that are enhanced in many ways relative to the conventional indium tin oxide films. The wire surface is extremely smooth and the junctions are seamless, thanks to the crackle lithography process. The method is applicable to various metals and hybrid materials as well as to flexible and curved substrates. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Advanced Materials Interfaces

Fabrication of Large Area, High-Performance, Transparent Conducting Electrodes Using a Spontaneously Formed Crackle Network as Template

In this study, we demonstrate that a disposable chip periodically patterned with suitable ligands, an ordinary cellphone camera, and a simple pattern recognition software, can potentially be used for quantitative diagnostics. A key factor in this demonstration is the design of a calibration grid around the chip that, through a contrast transfer process, enables reliable analysis of the images collected under variable ambient lighting conditions. After exposure to a dispersion of amine terminated silica beads used as analyte mimicking pathogens, an epoxy-terminated glass substrate microcontact printed with octadecyltrichlorosilane (250 μm periodicity) developed a characteristic pattern of beads which could be easily imaged with a cellphone camera of 3.2 MP pixels. A simple pattern recognition algorithm using fast Fourier transform produced a quantitative estimate of the analyte concentration present in the test solution. In this method importantly, neither the chip fabrication process nor the fill-factor of the periodic pattern need be perfect to arrive at a conclusive diagnosis. The method suggests a viable platform that may potentially find use in fault-tolerant and robust point-of-care diagnostic applications. © 2014 American Chemical Society.

ACS Applied Materials and Interfaces

Cellphone camera imaging of a periodically patterned chip as a potential method for point-of-care diagnostics

Common mode failures create the major impact on the system reliability in many real time systems. In this paper, we incorporate the concept of common mode faults (CMF) for the reliability prediction of fault tolerant software system consisting of N-version with different failure characteristics. The common mode faults may occur simultaneously in two or more versions due to faults in the common communication buses or shared environmental factors, failure of common source of power, design mistake, etc. The recursive algorithm based on universal generating function approach is presented to obtain the system probabilities. Various performance measures of the fault tolerant software system are established. Furthermore, by setting appropriate parameters, some special cases are illustrated numerically. © Operational Research Society of India 2013.

OPSEARCH

Reliability assessment of N-version software fault tolerant system with common mode failures

The reactions of RSnCl3 [R = 2-(phenylazo)phenyl] with phosphonic acids, RPO3H2 (R = t-Bu, C6H 11) or (ArO)2PO2H (Ar = 4-NO2-C 6H5O) in refluxing THF afforded hexatin cages, [(RSn) 6(μ-OH)6(μ3-O)2(t-BuPO 3)4]·5THF (1), [(RSn)6(μ-OH) 6(μ3-O)2(C6H11PO 3)4]·THF (2) and [(RSn)6(μ-OH) 4(μ3-O)2{(NO2C6H 4O)PO3}4]·THF (3), respectively. On the other hand, the reactions of RSnCl3 with 1,1,2,3,3-pentamethylene phosphinic acid [cycPO2H] or Ph2P(O)OH under similar reaction conditions afforded trinuclear O-capped clusters [(RSn) 3(μ3-O) (μ2-OH)3 (μ-cycPO2)3] [cycPO2]·CH 3CN·H2O (4) and [(RSn) 3(μ3-O) (μ2-OH)3 (μ-Ph 2PO2)3] [Ph2PO2] ·CH3CN·CH2Cl2 (5) respectively. Molecular structures of 1-3 reveal that the intramolecular N→Sn coordination found in RSnCl3 is hemilabile; 1-3 do not contain such a feature and the tin atoms in these compounds are six coordinate, possessing a 1C, 5O coordination environment in a distorted octahedral geometry. The cage structures in 1-3, containing two trinuclear sub-units, are formed as a result of the coordination action of several ligands: 4 μ3- (η1η1η1)[RPO3] 2-, 2 μ3-O2- and 6 μ-OH. The molecular structures of 4-5 reveal them to be cationic trinuclear complexes where 3 tin and 4 oxygen atoms occupy the vertices of a distorted cube while one of the vertices is unoccupied. The molecular structures of 4-5 also reveal that the intramolecular N→Sn coordination present in RSnCl3 is absent in these compounds attesting to the hemilabile nature of this interaction. © 2014 The Royal Society of Chemistry.