Comparison of Templating Abilities of Urea and Thioruea During Photodimerization of Bipyridylethyelene and Stilbazole Crystals

Photodimerization of cocrystals of four bispyridylethylenes and two stilbazoles with urea as a template in the solid state has been investigated following our success with thiourea. Four investigated olefins photodimerized quantitatively to a single dimer in the crystalline state only. The reactivity of urea–olefin crystals is understood on the basis of their packing arrangements in the crystalline state. In reactive crystals the adjacent reactive molecules are within 4.2 Å and parallel, whereas the unreactive ones have their adjacent molecules are farther than 4.6Å and nonparallel. Thus, with the knowledge of crystal packing the reactivity of urea–olefin crystals is predictable on the basis of Schmidt's topochemical postulates. The templating property of urea, similar to thiourea, derives from its ability to form hydrogen bonds with itself and the guest olefins. Despite the similarities in molecular structures of urea and thiourea their subtle electronic properties, yet to be fully understood, affect the crystal packing and consequently their reactivity in the crystalline state. Further work is needed to fully exploit the templating properties of urea.     

Synthesis, complexation studies and biological activity of some novel mono and tricyclic cyclophane amides and cyclophane sulfonamides

A series of mono, tricyclic cyclophane tetraamides and cyclophane sulfonamides have been synthesized and characterized from spectral and XRD studies. All the cyclophane amides form charge transfer (CT) complex with TCNQ. The cyclophane amides show moderate to good anti-inflammatory activity. Some of them were active against Gram positive (Klebsiella pneumonia) and Gram negative (Escherichia coli and Staphylococcus aureus) human pathogens.     

l-Proline-catalysed three-component domino reactions for the diastereoselective synthesis of 5,6-disubstituted 3-thiomorpholinones

l-Proline-catalysed three-component domino reactions of ethyl 2-[(2-oxo-2-arylethyl)sulfanyl]acetate, aromatic aldehydes and ammonia provide a rapid and facile access to novel trans-6-aroyl-5-aryl-3-thiomorpholinones. This diastereoselective reaction presumably proceeds via a domino sequence comprising enamine formation, Mannich reaction and intramolecular amidation individual steps and resulting in the generation of one C-C and two C-N bonds in a one-pot operation. The reaction also creates two contiguous stereocenters with complete diastereoselectivity.     

New four-component reactions in water: a convergent approach to the metal-free synthesis of spiro[indoline/acenaphthylene-3,4′-pyrazolo[3,4-b]pyridine derivatives

New four-component domino reactions are described that allow the one-pot synthesis of spiro[indoline/acenaphthylene-3,4′-pyrazolo[3,4-b]pyridine derivatives from the reaction of phenylhydrazine, 3-aminocrotononitrile, isatin/acenaphthylene-1,2-dione, and cyclic 1,3-dicarbonyl compounds, including cyclohexane-1,3-diones, barbituric acid, and 2-thioxodihydropyrimidine-4,6(1H,5H)-dione, in the presence of (±)-camphor-10-sulfonic acid (CSA). These processes take place in water and involve the generation of two rings and five new bonds (two C-C, two C-N and one CN) in a single synthetic operation, with expedient work-up and diminished waste generation due to the absence of extraction and purification steps.     

Assessment of indoor radiation dose received by the residents of natural high background radiation areas of coastal villages of Kanyakumari district,Tamil Nadu,India

Radiation exposure and effective dose received through two routes of exposure, viz. external and internal, via inhalation, by residents of 10 villages belonging to Natural High Background Radiation Areas (NHBRA) of coastal regions of Kanyakumari District and Tamil Nadu in India were studied. While the indoor gamma radiation levels were monitored using Thermo Luminescent Dosimeters (TLDs), the indoor radon and thoron gas concentrations were measured using twin chamber dosimeters employing Solid State Nuclear Track Detectors (SSNTDs, LR-115-II). The average total annual effective dose was estimated and found to be varying from 2.59 to 8.76 mSv.     

Photoinduced electron transfer (PET) based Zn2+ fluorescent probe: transformation of turn-on sensors into ratiometric ones with dual emission in acetonitrile

Ratiometric sensors for the detection of metal ions have gained increasing attention due to its self-calibration tendency for the environmental effects. In this context, we have synthesized and characterized a dual emitting ratiometric Zn(2+) probe (1) having acridinedione as a fluorophore and N,N-bis(2-pyridylmethyl)amine (BPA) as a receptor unit. Existence of two different conformation of the molecule with photoinduced electron transfer (PET) from amine moiety to the acridinedione fluorophore leads to dual emission, namely locally excited (425 nm) and anomalous charge transfer emission (560 nm) in aprotic solvents. In the presence of one equivalent of Zn(2+), a 15-fold fluorescence enhancement in the locally excited state together with the quenching of charge transfer emission is observed. The intensity changes at the two emission peaks allow a ratiometric detection of Zn(2+) under PET signaling mechanism. The utilization of PET process for the ratiometric fluorescence change will further signify the importance of PET mechanism in sensing action. Addition of Zn(2+) to 1 in acetonitrile/water mixtures shows a single emission peak with fluorescence enhancement.     

Droplet synthesis of well-defined block copolymers using solvent-resistant microfluidic device

Well-defined diblock copolymers were synthesized via an exothermic RAFT route by a droplet microfluidic process using a solvent-resistant and thermally stable fluoropolymer microreactor fabricated by a non-lithographic embedded template method. The resulting polymers were compared to products obtained from continuous flow capillary reactor and conventional bulk synthesis. The droplet based microreactor demonstrated superior molecular weight distribution control by synthesizing a higher molecular weight product with higher conversion and narrow polydispersity in a much shorter reaction time. The high quality of the as-synthesized block copolymer PMMA-b-PS led to a generation of micelles with a narrow size distribution that could be used as a template for well-ordered mesoporous silica with regular frameworks and high surface areas.     

Interfacial regions governing internal cavities of dendrimers. Studies of poly(alkyl aryl ether) dendrimers constituted with linkers of varying alkyl chain length

This report deals with a study of the properties of internal cavities of dendritic macromolecules that are capable of encapsulating and mediating photoreactions of guest molecules. The internal cavity structures of dendrimers are determined by the interfacial regions between the aqueous exterior and hydrocarbon like interior constituted by the linkers that connect symmetrically sited branch points constituting the dendrimer and head groups that cap the dendrimers. Phloroglucinol-based poly(alkyl aryl ether) dendrimers constituted with a homologous series of alkyl linkers were undertaken for the current study. Twelve dendrimers within first, second, and third generations, having ethyl, n-propyl, n-butyl, and n-pentyl groups as the linkers and hydroxyl groups at peripheries in each generation, were synthesized. Encapsulation of pyrene and coumarins by aqueous basic solutions of dendrimers were monitored by UV-vis and fluorescence spectroscopies, which showed that a lower generation dendrimer with an optimal alkyl linker presented better encapsulation abilities than a higher generation dendrimer. Norrish type I photoreaction of dibenzyl ketone was carried out within the above series of dendrimers to probe their abilities to hold guests and reactive intermediate radical pairs within themselves. The extent of cage effect from the series of third generation dendrimers was observed to be higher with dendrimers having an n-pentyl group as the linker.     

Highly selective, sensitive and quantitative detection of Hg2+ in aqueous medium under broad pH range

Amidothiourea linked acridinedione derivatives selectively detect Hg(2+) in unbuffered aqueous solution under broad pH range with both single- and two-photon excitation. The observed linear fluorescence intensity change allows the quantitative detection of Hg(2+) in the concentration range of 22 nM-0.33 μM with the lower detection limit of 2 nM.     

Physicochemical studies of green phosphorescent light-emitting materials from cyclometalated heteroleptic iridium(III) complexes

A series of novel imidazole ligands were synthesized and characterized. Phosphorescence studies of series of heteroleptic cyclometalated iridium(III) complexes reveal that these complexes possess dominantly (3)MLCT and (3)π-π* excited states and the solvent shifts of these complexes are interpreted by Richardt-Dimroth and Marcus solvent functions. The results consistent with prior assignments on the absorption band to a metal-to-ligand charge transfer excited state associated with chelating ligand. Emission kinetic studies exploited that the radiative transition (k(r)), increases with increasing λ(em) and linear correlation exists between ln(k(nr)) and energy gap. Electronic transition theory is applied to study the effect of E(g) and ΔQ(e) on non-radiative transition (k(nr)). With a larger ΔQ(e), favouring vibrational overlap and leading to a larger value for k(nr).