• Volume 122, Issue 3

May 2010,   pages  295-451

• Supramolecular chemistry and crystal engineering

Advances in supramolecular chemistry and crystal engineering reported from India within the last decade are highlighted in the categories of new intermolecular interactions, designed supramolecular architectures, network structures, multi-component host-guest systems, cocrystals, and polymorphs. Understanding self-assembly and crystallization through X-ray crystal structures is illustrated by two important prototypes - the large unit cell of elusive saccharin hydrate, Na16(sac)$_{16} . 30$H2O, which contains regular and irregular domains in the same structure, and by the Aufbau build up of zinc phosphate framework structures, e.g. ladder motif in [C3N2H12][Zn(HPO4)2] to layer structure in [C3N2H12][Zn2(HPO4)3] upon prolonged hydrothermal conditions. The pivotal role of accurate X-ray diffraction in supramolecular and structural studies is evident in many examples. Application of the bottomup approach to make powerful NLO and magnetic materials, design of efficient organogelators, and crystallization of novel pharmaceutical polymorphs and cocrystals show possible future directions for interdisciplinary research in chemistry with materials and pharmaceutical scientists. This article traces the evolution of supramolecular chemistry and crystal engineering starting from the early nineties and projects a center stage for chemistry in the natural sciences.

• Lewis acidic metal catalysed organic transformations by designed multi-component structures and assemblies

This paper presents the recent developments in designing multi-component structures including metal-organic frameworks containing Lewis acidic metal ions. The emphasis has been given to understand the design elements adopted to synthesize such structures bearing Lewis acidic metal ion. Further, few important Lewis acidic metal catalysed organic transformation reactions have been discussed demonstrating the importance of such materials for practical purposes.

• Anaerobic DNA cleavage in red light by dicopper(II) complexes on disulphide bond activation

Binuclear complexes [Cu(𝜇-RSSR)]2 (1) and [M2(𝜇-PDS)(H2O)]2 (M = Cu(II), 2; Fe(II), 3), where H2RSSR is a reduced Schiff base derived from 2-(thioethyl)salicylaldimine having a disulphide moiety and H2PDS is derived from dimerization of D-penicillamine, have been prepared, structurally characterized, and their photo-induced DNA cleavage activity studied. The crystal structure of 1 shows the complex as a discrete binuclear species with each metal in a CuN2O2 square-planar geometry (Cu…Cu, 6.420 Å). The tetradentate RSSR2- acts as a bridging ligand. The sulphur atoms in the disulphide unit do not interact with the metal ions. Complexes 1-3 do not show any DNA cleavage activity in darkness. The copper(II) complexes exhibit chemical nuclease activity in the presence of 3-mercaptopropionic acid. Cleavage of supercoiled DNA has been observed in UV-A light of 365 nm for 1 and red light of 647.1 nm for both 1 and 2 in air. Mechanistic data reveal the involvement of the disulphide unit as photosensitizer generating hydroxyl radicals ($^{\bullet}$OH) as the reactive species. Photo-induced DNA cleavage in red light seems to involve sulphide radicals in a type-I process and hydroxyl radicals. The dicopper(II) complexes show significant anaerobic photo-induced DNA cleavage activity in red light under argon following type-I pathway without involving any reactive oxygen species.

• Studies on electron transfer reactions: Reduction of heteropoly 10-tungstodivanadophosphate by thioglycolic acid in aqueous medium

Rates of electron transfer reaction of thioglycolic acid with vanadium(V) substituted Keggintype heteropolyanion, [PVVVVW10O40]5-, in acetate-acetic acid buffers have been measured spectrophotometrically at 25°C. The order of the reaction with respect to substrate and oxidant is unity. The reaction shows simple second order kinetics at constant pH. The rate of the reaction increases with increase of pH of the medium. The mono-anion HSCH2COO- and di-anion -SCH2COO- are found to be the reactive species. Rate constants for mono-anion and di-anion are evaluated from rate law derived from the mechanism. By applying Rehm-Weller relationship, self exchange rate constant for the -SCH2COO-/S$^{\bullet}$ CH2COO- couple was evaluated as $3.3 \times 10^3$ dm3 mol-1 s-1 at 25°C.

• Adsorption of DOPC vesicles on hydrophobic substrates in the presence of electrolytes: A QCM and reflectometry study

The adsorption of lipid Dioleoylphosphatidylcholine (DOPC) vesicles on a hydrophobic substrate has been investigated in aqueous buffer solution by means of the quartz crystal microbalance (QCM) and reflectometry. DOPC vesicles were prepared by the injection method on a hydrophobic substrate using 1-octadecanethiol (ODT) self-assembled on a gold-coated AT-cut quartz. The reflection spectrometry measurements of the adsorbed vesicles showed nearly monolayer formation in few cases, while in most other experiments, the frequency changes measured suggested multilayer formation assuming the usual Sauerbrey equation to hold in the present system as well. Presence of NaCl, KCl, Na2SO4 and ethanol in the aqueous phase during the formation of vesicles suggest that the multilayer formation can be hastened in some cases. Atomic force microscopic study corroborate the thicknesses that range between 8 and 20 nm for high concentration of electrolytes or ethanol suggesting coalescence of vesicles leading to several bilayers possibly stacked over each other.

• Physicochemistry of hexadecylammonium bromide and its methyl and ethanolic head group analogues in buffered aqueous and gelatin solution

In this work, the interfacial and bulk behaviour of the amphiphiles hexadecylammonium bromide and its methyl and ethanolic head group analogues in buffered aqueous and gelatin solution has been examined. The analogues are of two categories: the methyl and the combined methyl and ethanolic head group representatives are considered as Group A compounds, and all non-methyl but ethanolic head group species are taken as Group B compounds. Different physical techniques have been employed to ascertain the amphiphilic behaviour in solution. The self-aggregation of these surfactants at different pH has been studied along with pH dependent interfacial activity of gelatin. The interaction of the two categories of the surfactants with gelatin at different pH has been investigated. A scheme for this interaction at various stages of the process has been proposed. The influence of the surfactant head groups on the interaction process has been assessed.

• A theoretical study of the carbenoids LiCH2X (X = Cl, Br, I) cyclopropanation reaction with ketene

A computational study for the [2 + 1] addition of the lithium carbenoids LiCH2X (X = Cl, Br, I) with ketene have been investigated by means of the B3LYP hybrid density functional method. All the reactions examined displayed similar concerted mechanisms for the cyclopropanation of these reagents. The lithium carbenoids react with ketene via an asynchronous attack on one CH2 or C group of ketene with relatively low barrier to reaction in the range of 25.34-33.74 kJ/mol in THF solvent. The trend of the lithium carbenoids reaction barrier with ketene is LiCH2Cl &lt; LiCH2Br &lt; LiCH2I. The results show that the reactions could be highly chemical reactivity with low barriers and could be favoured in experiment. The reactions could proceed easily at lower temperature. The computational results are briefly compared to other carbenoid reactions and related species.

• Thermal and hydrothermal stability of ZrMCM-41 mesoporous molecular sieves obtained by microwave irradiation

ZrMCM-41 mesoporous molecular sieves were synthesized by using the zirconium sulfate as zirconium source and using cetyltrimethyl ammonium bromide as a template under microwave irradiation condition. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma (ICP) technique, Fourier transform infrared spectroscopy (FT-IR) and N2 physical adsorption, respectively. The effect of the different initial ZrO2 : SiO2 molar ratio, the different thermal treatment temperature and hydrothermal treatment time on textural property was investigated. The results show that the obtained products possess a typical mesoporous structure of MCM-41 and have specific surface areas in the range of 598.1 ∼ 971.4 m2/g and average pore sizes in the range of ca. 2.46 ∼ 3.43 nm. On the other hand, the BET specific surface area and pore volume of the synthesized ZrMCM-41 mesoporous molecular sieve decrease with the increased amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering deteriorates. The mesoporous structure of the ZrMCM-41 mesoporous molecular sieve still retains after calcination at 750°C for 3 h or hydrothermal treatment at 100°C for 6 days, however, the mesoporous ordering is poor.

• A solid-polymer-electrolyte direct methanol fuel cell (DMFC) with Pt-Ru nanoparticles supported onto poly(3,4-ethylenedioxythiophene) and polystyrene sulphonic acid polymer composite as anode

Nano-sized Pt-Ru supported onto a mixed-conducting polymer composite comprising poly(3,4-ethylenedioxythiophene)-polystyrene sulphonic acid (PEDOT-PSSA) is employed as anode in a solid-polymer-electrolyte direct methanol fuel cell (SPE-DMFC) and its performance compared with the SPE-DMFC employing conventional Vulcan XC-72R carbon supported Pt-Ru anode. Physical characterization of the catalyst is conducted by Fourier-transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray analysis (EDAX) in conjunction with cyclic voltammetry and chronoamperometry. The study suggests that PEDOT-PSSA to be a promising alternative catalyst-support-material for SPE-DMFCs.

• Studies on interaction between CdTe quantum dots and 𝛼-chymotrypsin by molecular spectroscopy

In this article, the interaction between 𝛼-Chymotrypsin and CdTe QDs was investigated by fluorescence, synchronous fluorescence, and circular dichroism (CD) spectroscopic methods at pH 7.20 and pH 9.05. The intrinsic fluorescence of 𝛼-Chy is quenched by CdTe QDs. Under different pH conditions, the level of binding constants is determined to be 103 from fluorescence data. The hydrogen bond or van der Waals force is involved in the binding process when pH is 9.05, while the hydrophobic and electrostatic interactions play main role in the binding process when pH is 7.20. The red-shift of synchronous fluorescence spectral peak of protein after the addition of CdTe QDs reveals that the microenvironments around tryptophan residues are disturbed by CdTe QDs. The secondary structure of 𝛼-Chy undergoes slight changes as similar by far-UV CD data. The activity and stability of 𝛼-Chy in the presence of CdTe QDs were also studied. 𝛼-Chy can maintain its high activity and stability under different pH conditions for 24 h in the presence of CdTe QDs.

• Electrochemical investigation of NO at single-wall carbon nanotubes modified electrodes

The NO electro-oxidation was investigated at various single-wall carbon nanotubes (SWCNTs) modified electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared with the glassy carbon electrode, the SWCNTs modified electrodes possess higher electro-catalytic activity to NO electro-oxidation. CV results indicate that the peak current density of NO electro-oxidation at the SWCNT-COOH (SWCNTs with carboxyl groups) modified electrode is the highest and the peak potential is the most negative among the four kinds of electrodes. EIS indicates that the charge transfer resistance of NO electro-oxidation at the SWCNT-COOH modified electrode is the least. The determined factors (charge transfer and mass transfer of diffusion) of NO electro-oxidation are different in varied potential region. The mechanism of NO electro-oxidation reaction at the SWCNTs modified electrodes is also discussed.

• Synthesis and characterization of 𝑁-phosphorylated thioureas RNHC(S)NHP(O)(O𝑖Pr)2 (R = 2-MeC6H4, 2,6-Me2C6H3, 2,4,6-Me3C6H2)

Reaction of O,O'-diisopropylphosphoric acid isothiocyanate (𝑖PrO)2P(O)NCS with 2-methylaniline 2-MeC6H4NH2, 2,6-dimethylaniline 2,6-Me2C6H3NH2 or 2,4,6-trimethylaniline 2,4,6-Me3C6H2NH2 leads to the 𝑁-phosphorylated thioureas RNHC(S)NHP(O)(O𝑖Pr)2 (R = 2-MeC6H4-, HLI; 2,6-Me2C6H3-, HLII; 2,4,6-Me3C6H2-, HLIII). The new compounds were investigated by 1H and 31P{1H} NMR spectroscopy, and microanalysis. The molecular structure of the thiourea HLIII was elucidated by single crystal X-ray diffraction analysis. Single crystal X-ray diffraction studies showed HLIII forms both intra- and intermolecular hydrogen bonds, which in turn leads to the formation of polymeric chains. One of the intermolecular hydrogen bonds is of the type N-H$\cdots$S. Moreover, the formation of intermolecular C-H$\cdots \eta^6$-phenyl interactions was established.

• An efficient one-pot synthesis of novel pyrazolophthalazinyl spirooxindoles

A simple and efficient method for the synthesis of novel pyrazolophthalazinyl spirooxindoles by L-proline catalysed one-pot three-component reaction is described.

• Titanium(III) chloride mediated synthesis of furan derivatives: Synthesis of (±)-evodone

Titanocene(III) chloride (Cp2TiCl) mediated one-pot synthesis of furan derivatives has been accomplished. This radical method has been applied for the synthesis of a furanomonoterpene, evodone. Ti(III) species was prepared in situ from commercially available titanocene dichloride (Cp2TiCl2) and zinc dust in THF.

• Multicomponent, solvent-free synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[𝑎]-xanthen-11-one derivatives catalysed by cyanuric chloride

An efficient and direct protocol for the preparation of 12-aryl-8,9,10,12-tetrahydro-benzo[𝑎] xanthen-11-one derivatives employing a three-component one-pot reaction of aryl aldehydes, 2-naphthol and cyclic 1,3-dicarbonyl compounds in the presence of a catalytic amount of cyanuric chloride (2,4,6-trichloro-1,3,5-triazine, TCT) under solvent-free conditions is described. The desired products are obtained in high yields with short reaction times.

• Total synthesis of (±)-divanillyltetrahydrofuran ferulate

A convenient method for the synthesis of sesquilignan threo- and erythro-(±)-divanillyltetrahydrofuran ferulate is described. The synthesis was based on a unified synthetic strategy involving two Stobbe condensations to give the skeleton of lignan, and then reduction reaction to form meso- and threo-(±)-secoisolanciresinol. meso- and threo-(±)-secoisolanciresinol were separated by flash column chromatography, followed by intramolecular reaction with TsCl to afford the key intermediate meso- or threo-(±)-shonanin, then condensation with ferulaic acid to obtain sesquilignan threo- or its analogue erythro-(±)-divanillyltetrahydrofuran ferulate.

• A novel and an efficient catalyst for one-pot synthesis of 2,4,5-trisubstituted imidazoles by using microwave irradiation under solvent-free conditions

(NH4)6Mo7O24.4H2O has been used as an efficient catalyst for an improved and rapid synthesis of 2,4,5-trisubstituted imidazoles by a three-component, one-pot condensation of benzil, aryl aldehydes and ammonium acetate in good yields under solvent-free conditions using microwave irradiation. The reactions in conventional heating conditions were compared with the microwave-assisted reactions.

• Synthesis and antiulcer activity of 2-[5-substituted-1-𝐻-benzo(d) imidazol-2-yl sulfinyl]methyl-3-substituted quinazoline-4-(3𝐻) ones

2-[5-substituted-1-𝐻-benzo(d)imidazol-2-yl sulfinyl]methyl-3-substituted quinazoline-4-(3𝐻)-one derivatives were synthesized and tested for antiulcer activity against pylorus ligation-induced, aspirin induced and ethanol induced ulcer in rat model. All the synthesized compounds were characterized by using IR, MS and 1H NMR spectral and elemental analysis. The compounds were scramed for their antiulcer activity: compounds 5k and 5n showed higher activity than omeprazole used as standard.

• Editor’s Note

• # Journal of Chemical Sciences

Volume 132, 2019
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019