Rupam Sarma

Solid-state hydrogen bonded assembly of N,N′-bis(glycinyl)-pyromellitic diimide with aromatic guests

The compound N,N′-bis(glycinyl)pyromellitic diimide (L) forms inclusion compounds with aromatic hydrocarbons such as anthracene (D1), phenanthrene (D2) and perylene (D3) as well as tetrathiafulvalene (D4). The aromatic guest molecules are held in the spaces between the aromatic units of extended self-assembly of L derived from the hydrogen bonding between the carboxylic acid end groups of L. The crystal structures of each of these inclusion compounds are determined along with the parent compound L. A R44(12) hydrogen bond pattern involving the carboxylic groups and two bridging methanol molecules is observed in the anthracene inclusion compound of L, whereas in the case of other inclusion compounds conventional R22(8) type hydrogen bonding is observed. While forming inclusion compounds of L with tetrathiafulvalene, the carboxylic acid of L has R22(8) and C11(3) types of hydrogen bonding patterns in the lattice. Preferential inclusion compound formation of L with anthracene over isomeric phenanthrene is observed.

Competitive oxygen-18 kinetic isotope effects expose O–O bond formation in water oxidation catalysis by monomeric and dimeric ruthenium complexes

Competitive oxygen kinetic isotope effects (18O KIEs) on water oxidation initiated by ruthenium oxo (RuO) complexes are examined here as a means to formulate mechanisms of O–O bond formation, which is a critical step in the production of “solar hydrogen”. The kinetics of three structurally related catalysts are investigated to complement the measurement and computation of 18O KIEs, derived from the analysis of O2 relative to natural abundance H2O under single and multi-turnover conditions. The findings reported here support and extend mechanistic proposals from 18O tracer studies conducted exclusively under non-catalytic conditions. It is shown how density functional theory calculations, when performed in tandem with experiments, can constrain mechanisms of catalytic water oxidation and help discriminate between them.

Aromatic N-oxide bridged copper(II) coordination polymers: Synthesis, characterization and magnetic properties

Abstract The complexes [Cu2(o-NO2–C6H4COO)4(PNO)2] (1), [Cu2(C6H5COO)4(2,2′-BPNO)] n (2), [Cu2(C6H5COO)4(4,4′-BPNO)] n (3), [Cu(p-OH–C6H4COO)2(4,4′-BPNO)2·H2O] n (4), (where PNO=pyridine N-oxide, 2,2′-BPNO=2,2′-bipyridyl-N,N′-dioxide, 4,4′-BPNO=4,4′-bipyridyl-N,N′-dioxide) are prepared and characterized and their magnetic properties are studied as a function of temperature. Complex 1 is a discrete dinuclear complex while complexes 2–4 are polymeric of which 2 and 3 have paddle wheel repeating units. Magnetic susceptibility measurements from polycrystalline samples of 1–4 revealed strong antiferromagnetic interactions within the {Cu2}4+ paddle wheel units and no discernible interactions between the units. The complex 5, [Cu(NicoNO)2·2H2O] n ·4nH2O, in which the bridging ligand to the adjacent copper(II) ions is nicotinate N-oxide (NicoNO) the transmitted interaction is very weakly antiferromagnetic.

Fluorescence Quenching and Enhancement by H-bonding Interactions in Some Nitrogen Containing Fluorophores

The benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (1) shows solvent dependent fluorescence emission. The compound shows quenching of fluorescence emission on interaction with polyhydroxy compounds such as 1,3-dihydroxybenzene, 1,4-dihydroxybenzene. The result on fluorescence quenching is attributed to the hydrogen bonding interactions. Similar observation of fluorescence quenching by protic solvent is observed with isoindolo[2,1-a] perimidin-12-one (2). In the case of 2-(2-amino-phenyl)-isoindole-1,3-dione (3) enhancement of fluorescence emission in methanol solution is observed over benzene solution. This is explained on the basis of intermolecular hydrogen bonding. The crystal structure of adduct of 1 with 1,3-dihydroxybenzene, 1,4-dihydroxybenzene respectively and 3 are reported.

Structural aspects and properties of salt and inclusion compounds of 8-hydroxyquinoline based amides

The structural aspects of two amide containing isoquinoline derivatives namely N-cyclohexyl-2-(quinolin-8-yloxy) acetamide (1) and N-(2,6-dimethylphenyl)-2-(quinolin-8-yloxy) acetamide (2) are studied. On treatment with mineral acids such as sulfuric acid, hydrochloric or phosphoric acid N-cyclohexyl-2-(quinolin-8-yloxy) acetamide forms gels whereas on treatment with nitric acid it forms crystalline solid. Acids having non-planar anions facilitate the gel formation and the acids having planar anion such as nitrate and carboxylate were not suitable for gelation of 2. N-(2,6-Dimethylphenyl)-2-(quinolin-8-yloxy) acetamide forms crystalline salts on treatment with mineral acids. The crystal structure of compounds 1, 2 and two salts are reported. Compound 2 forms 2 : 1 host–guest complexes with 1,4-dihydroxybenzene as well as with 1,5-dihydroxynaphthalene. The crystal structures of both compounds are reported. These host–guest complexes have much stronger fluorescence emission at lower wavelength than the parent compound, however, the protonated state of compound 2 is not fluorescence active. The compound 1 on protonation shows fluorescence at much higher wavelength than the parent compound, whereas compound 1 on interaction with 1,4-dihydroxybenzene fluorescence occurs at a lower wavelength. The crystal structure of N-[3-(4-methoxy-phenyl)propyl]-2-(quinolin-8-yloxy)acetamide is determined and found to have parallel sheet structure.

N -oxide bridged manganese(II) coordination polymers

A simple method for synthesis of manganese(II) coordination polymers with different benzoate ligands and pyridine N-oxide having general composition [Mn(RC6H4CO2)2(PyO)] n is presented (where PyO = pyridine N-oxide and R = H, 1a; R = 4-NO2, 1b; R = 4-Cl, 1c; R = 4-OH, 1d; R = 2-NO2, 1e). All these polymers are characterized by X-ray crystallography and other spectroscopic techniques. The coordination polymers have similar structures, but the positions of the manganese atoms differ. For example, 1c is highly symmetric and a mirror plane exists between each manganese site (2/m). In 1d, the manganese centers are related by an inversion center (−1) whereas in 1e the manganese centers are related by C1 rotation (1). Reaction of manganese(II) acetate tetrahydrate with 4-chlorobenzoic acid and PyO upon crystallization from methanol/pyridine gave crystals of coordination polymer 1c along with aqua-bis-pyridine bis-4-chlorobenzoato manganese(II) (2). The structure of 2 also determined by single-crystal X-ray diffraction has a 1-D hydrogen bonded chain structure. Temperature-dependent zero-field cooled and field-cooled magnetization data of 1a–1c measured at 20 Oe and 1000 Oe show field-dependent magnetization spread over a wide temperature range from 5 to 300 K. These coordination polymers show anti-ferromagnetic behavior below 20 K.

N-oxides in metal-containing multicomponent molecular complexes.

Syntheses and structures of three-component rare cocrystals of 4-nitrobenzoic acid, aromatic N-oxides, and aqua complexes of manganese and zinc and their transformation to metal complexes as well as coordination polymers are presented.

A mixed carboxylate polymer as an intermediate during synthesis of mononuclear bis -3, 5-dimethylpyrazole copper(II) benzoates

The crystal structures of bis-3,5-dimethylpyrazole copper(II) 4-methylbenzoate, bis-3,5-dimethylpyrazole copper(II) 3-methylbenzoate, bis-3,5-dimethylpyrazole copper(II) 4-nitrobenzoate show that 3,5-dimethylpyrazole in the cis or trans positions is related to axial distortion of Cu-O bond in carboxylate groups. A metastable mixed carboxylate co-ordination polymer presumably intermediate to the one described above which has alternate paddlewheel and mononuclear units is structurally characterized.

Layer-by-Layer-Assembled Laccase Enzyme on Stimuli-Responsive Membranes for Chloro-Organics Degradation

Functionalized membranes provide versatile platforms for the incorporation of biocatalysts and nanostructured materials for efficient and benign environmental remediation. The existing techniques for remediating chloro-organics in water consist of both physical and chemical means mostly using metal oxide-based catalysts, despite associated environmental concerns. To offer bioinspired remediation as an alternative, we herein demonstrate a layer-by-layer approach to immobilize laccase enzyme onto pH-responsive functionalized membranes for the degradation of chloro-organics in water. The efficacy of these bioinspired membranes toward dechlorination of 2,4,6-trichlorophenol (TCP) is demonstrated under a pressure-driven continuous flow mode (convective flow) for the first time to the best of our knowledge. Over 80% of the initial TCP was degraded at an optimum flow rate under an applied air pressure of about 0.7 bar or lower. This corresponds to degradation of a substantial amount of the initial substrate in only 36 s residence time, whereas it takes hours for degradation in a batch reaction. This, in fact, demonstrates an energy efficient flow-through system with potentially large-scale applications. Comparison of the stability of the enzyme in the solution phase versus immobilized on the membrane phase showed a loss of some 65% of enzyme activity in the solution phase after 22 d, whereas the membrane-bound enzyme lost only a negligible percentage of the activity in a comparable time span. Finally, the membrane was exposed to rigorous cycles of TCP degradation trials to study its reusability. The primary results reveal a loss of only 14% of the initial activity after 4 cycles of use in a period of 25 d, demonstrating its potential to be reused. Regeneration of the functionalized membrane was also validated by dislodging the immobilized enzyme, followed by immobilization of fresh enzyme onto the membrane.

Formation of symmetry non-equivalent molecules in urea and carbamate derivatives: the role of anion

The perchlorate salts of the compounds 1-phenyl-3-(quinolin-5-yl) urea, 1-phenyl-3-(quinolin-8-yl) urea, and quinoline-8-yl phenylcarbamate, possess symmetry non-equivalent molecules in their unit cell. The role of anion in generating high Z′ is discussed by comparing the structures of the salts and the original compounds.