Structural Modulation of Nitrogen-Rich Covalent Organic Frameworks for Iodine Capture.

Developing efficient adsorbent materials for iodine scavenging is essential to mitigate the threat of radioactive iodine causing adverse effects on human health and the environment. In this context, we explored N-rich two-dimensional covalent organic frameworks (COFs) with diverse functionalities for iodine capture. The pyridyl-hydroxyl-functionalized triazine-based novel 5,5',5″-(1,3,5-triazine-2,4,6-triyl)tris(pyridine-2-amine) (TTPA)-COF possesses high crystallinity (crystalline domain size: 24.4 ± 0.6 nm) and high porosity (specific BET surface area: 1000 ± 90 m2 g-1). TTPA-COF exhibits superior vapor-phase iodine adsorption (4.43 ± 0.01 g g-1) compared to analogous COF devoid of pyridinic moieties, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)-COF. The high iodine capture by TTPA-COF is due to the enhanced binding affinity conferred by the extra pyridinic active sites. Furthermore, the crucial role of long-range order in porous adsorbents has been experimentally evidenced by comparing the performance of iodine vapor capture of TTPA-COF with an amorphous network polymer having identical functionalities. We have also demonstrated the high iodine scavenging ability of TTPA-COF from the organic and aqueous phases. The mechanism of iodine adsorption by the heteroatom-rich framework is elucidated through FTIR, XPS, and Raman spectral analyses. The present study highlights the need for structural tweaking of the building blocks toward the rational construction of advanced functional porous materials for a task-specific application.

Metal complexes of 4,6-O-ethylidene-ß-d-glucopyranosylamine derivatives and their application in organic synthesis.

Glycosylamine derivatives of 4,6-O-ethylidene-d-glucose have been used for complexing the alkali, alkaline earth and transition metal ions. Three different series of ligands have been reported where N-(o-carboxyphenyl)-4,6-O-ethylidene-ß-d-glucopyranosylamine has been used for complexing the diamagnetic (Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Zn2+, Cd2+, Hg2+) metal ions. N-(2-Hydroxybenzoyl)-L-alanyl-4,6-O-ethylidene-ß-d-glucopyranosylamine selectively interacts with molecular cupric acetate and the adduct acts as a catalyst in selective oxidation of primary and secondary alcohols into their corresponding carbonyl compounds. Salicylidene derivatives of 4,6-O-ethylidene-ß-d-glucopyranosylamine have been used in complexing Ni2+, Cu2+, Zn2+, VO2+, MoO22+ and UO22+ metal ions, where Cu(II) and Mo(VI) complexes have been further used in the organic synthesis. Dinuclear copper complex exhibited catecholase like activity and also catalyzed the oxidation of primary and secondary alcohols selectively into their corresponding carbonyl compounds. Trinuclear copper complex has been reported to activate the C-Cl bond of solvent chloroform in the presence of mild organic bases below room temperature. Mo(VI) complex has been used as a catalyst for epoxidation, organic sulfide oxidation and synthesis of bis(indolyl)methanes.

Metal-free synthesis of aminomethylated imidazoheterocycles: dual role of tert-butyl hydroperoxide as both an oxidant and a methylene source.

A novel and efficient aminomethylation approach has been developed for the regioselective functionalization of imidazoheterocycles under metal-free conditions. A wide range of imidazoheterocycles and 2/4-aminoazaheterocycles successfully provided corresponding aminomethylated imidazoheterocycles in moderate to excellent (33-80%) yields. The isotopic labelling study suggested that TBHP played a dual role as both an oxidant and a methylene source in this transformation. The developed protocol follows a radical pathway which is supported by radical trapping experiments.

C-HCl- hydrogen bonds in solution and in the solid-state: HgCl2 complexes with cyclen-based cryptands.

Structural evidence is reported for C-HCl- hydrogen bonds in solution and in the solid state of HgCl2 complexes with cyclen-based cryptands. These cyclen-based cryptands (1) and (2) are bridged by di- and triethylene glycol units, respectively, between two aromatic rings. The X-ray structure indicates that the 2/HgCl2 complex contains an acetonitrile molecule in the cavity.

Synthesis, evaluation and molecular docking studies of amino acid derived N-glycoconjugates as antibacterial agents.

Six amino acid derived N-glycoconjugates of d-glucose were synthesized, characterized and tested for antibacterial activity against G(+)ve (Bacillus cereus) as well as G(-)ve (Escherichia coli and Klebsiella pneumoniae) bacterial strains. All the tested compounds exhibited moderate to good antibacterial activity against these bacterial strains. The results were compared with the antibacterial activity of standard drug Chloramphenicol, where results of A5 (Tryptophan derived glycoconjugates) against E. coli and A4 (Isoleucine derived glycoconjugates) against K. pneumoniae bacterial strains are comparable with the standard drug molecule. In silico docking studies were also performed in order to understand the mode of action and binding interactions of these molecules. The docking studies revealed that, occupation of compound A5 at the ATP binding site of subunit GyrB (DNA gyrase, PDB ID: 3TTZ) via hydrophobic and hydrogen bonding interactions may be the reason for its significant in vitro antibacterial activity.

Selective retention of methanol over ethanol by a cyclen-based cryptand/copper(II) complex.

A cyclen-based cryptand (2) was prepared in a two-step synthesis from dioxocyclen. When a Cu(CF3SO3)2 complex with 2 was prepared in methanol, the 2/Cu(CF3SO3)2 complex incorporated one methanol in the cavity formed by the diethyleneoxy unit and the NH group of the cyclen. When prepared in ethanol, the 2/Cu(CF3SO3)2 complex similarly incorporated one ethanol. Cold electrospray ionization mass spectrometry (CSI-MS) of the 2/Cu(CF3SO3)2/alcohol complexes selectively retains methanol over ethanol under CSI-MS conditions.

CMPO-functionalized C3-symmetric tripodal ligands in liquid/liquid extractions: efficient, selective recognition of Pu(IV) with low affinity for 3+ metal ions.

Structural modifications of carbamoylmethylphosphine oxide (CPMO)-functionalized triphenoxymethane platforms are described, and the influence of these changes on the ability of the ligand to extract actinides from simulated acidic nuclear waste streams has been evaluated. The ligand system has been shown to have excellent binding efficiency and a selectivity for An(IV) in comparison to the a simple monomeric CMPO ligand under analogous conditions. Both the extraction efficiency and selectivity are strongly dependent on the flexibility and electronic properties of the ligating units in the triphenoxymethane construct. The Tb(III) and Bi(III) nitrate complexes of tris-CMPO derivatives have been isolated, and their structures were elucidated by NMR, ESI FT-ICR MS, and X-ray analysis, providing information on the interactions between metal ions and the tris-CMPO molecules.

Tetranuclear copper(II) complexes bridged by alpha-D-glucose-1-phosphate and incorporation of sugar acids through the Cu4 core structural changes.

Tetranuclear copper(II) complexes containing alpha-D-glucose-1-phosphate (alpha-D-Glc-1P), [Cu4(mu-OH){mu-(alpha-D-Glc-1P)}2(bpy)4(H2O)2]X3 [X = NO3 (1a), Cl (1b), Br (1c)], and [Cu4(mu-OH){mu-(alpha-D-Glc-1P)}2(phen)4(H2O)2](NO3)3 (2) were prepared by reacting the copper(II) salt with Na2[alpha-D-Glc-1P] in the presence of diimine ancillary ligands, and the structure of 2 was characterized by X-ray crystallography to comprise four {Cu(phen)}2+ fragments connected by the two sugar phosphate dianions in 1,3-O,O' and 1,1-O mu4-bridging fashion as well as a mu-hydroxo anion. The crystal structure of 2 involves two chemically independent complex cations in which the C2 enantiomeric structure for the trapezoidal tetracopper(II) framework is switched according to the orientation of the alpha-D-glucopyranosyl moieties. Temperature-dependent magnetic susceptibility data of 1a indicated that antiferromagnetic spin coupling is operative between the two metal ions joined by the hydroxo bridge (J = -52 cm(-1)) while antiferromagnetic interaction through the Cu-O-Cu sugar phosphate bridges is weak (J = -13 cm(-1)). Complex 1a readily reacted with carboxylic acids to afford the tetranuclear copper(II) complexes, [Cu4{mu-(alpha-D-Glc-1P)}2(mu-CA)2(bpy)4](NO3)2 [CA = CH3COO (3), o-C6H4(COO)(COOH) (4)]. Reactions with m-phenylenediacetic acid [m-C6H4(CH2COOH)2] also gave the discrete tetracopper(II) cationic complex [Cu4{mu-(alpha-D-Glc-1P)}2(mu-m-C6H4(CH2COO)(CH2COOH))2(bpy)4](NO3)2 (5a) as well as the cluster polymer formulated as {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-m-C6H4(CH2COO)2)(bpy)4](NO3)2}n (5b). The tetracopper structure of 1a is converted into a symmetrical rectangular core in complexes 3, 4, and 5b, where the hydroxo bridge is dissociated and, instead, two carboxylate anions bridge another pair of Cu(II) ions in a 1,1-O monodentate fashion. The similar reactions were applied to incorporate sugar acids onto the tetranuclear copper(II) centers. Reactions of 1a with delta-D-gluconolactone, D-glucuronic acid, or D-glucaric acid in dimethylformamide resulted in the formation of discrete tetracopper complexes with sugar acids, [Cu4{mu-(alpha-D-Glc-1P)}2(mu-SA)2(bpy)4](NO3)2 [SA = D-gluconate (6), D-glucuronate (7), D-glucarateH (8a)]. The structures of 6 and 7 were determined by X-ray crystallography to be almost identical with that of 3 with additional chelating coordination of the C-2 hydroxyl group of D-gluconate moieties (6) or the C-5 cyclic O atom of D-glucuronate units (7). Those with D-glucaric acid and D-lactobionic acid afforded chiral one-dimensional polymers, {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-D-glucarate)(bpy)4](NO3)2}n (8b) and {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-D-lactobionate)(bpy)4(H2O)2](NO3)3}n (9), respectively, in which the D-Glc-1P-bridged tetracopper(II) units are connected by sugar acid moieties through the C-1 and C-6 carboxylate O atoms in 8b and the C-1 carboxylate and C-6 alkoxy O atoms of the gluconate chain in 9. When complex 7 containing d-glucuronate moieties was heated in water, the mononuclear copper(II) complex with 2-dihydroxy malonate, [Cu(mu-O2CC(OH)2CO2)(bpy)] (10), and the dicopper(II) complex with oxalate, [Cu2(mu-C2O4)(bpy)2(H2O)2](NO3)2 (11), were obtained as a result of oxidative degradation of the carbohydrates through C-C bond cleavage reactions.

Amine mediated proton transfer reaction and C-Cl bond activation of solvent chloroform by a trinuclear copper(II) complex of a glucopyranosylamine derived ligand.

An amine mediated C-Cl bond activation process of the solvent chloroform has been explored by a coordinatively labile trinuclear Cu(II) complex, [Cu3(L1)2(MeOH)(H2O)] (1), derived from N-(3-tert-butyl-2-hydroxybenzylidene)-4,6-O-ethylidene--D-glucopyranosylamine (H3L1). The effect of activation is extremely high with methylamine, resulting in the formation of [Cu(MeNH2)5]Cl2 (2) and [Cu(L2)2] (3; HL2 = 2-tert-butyl-6-[(methylimino)methyl]phenol), however, under identical conditions it is moderate with ethylamine resulting in the isolation of crystals of the intermediate amine bound trinuclear copper(II) complex, [Cu3(L1)2(EtNH2)2(MeOH)2] (5), which was further converted into the mononuclear complex, [Cu(HL1)(EtNH2)] (6), in a novel crystal-to-crystal transformation. The successive isolation of the ethylamine-bound tri- and mononuclear complexes, 5 and 6, supported the occurrence of proton transfer reactions, which might be a key step in C-Cl bond activation. The primary and secondary amines, 2-aminomethylpyridine, N,N-dimethylethylenediamine, and 1,4,7-triazacyclononane, also having chelating features further enhance the rate of activation. No activation has been noted in the case of triethylamine and N,N,N,N-tetramethylethylenediamine. Formation of a carbene-trapped compound, 2,6-xylyl isocyanide, was confirmed in the reaction of complex 1 with 1,4,7-triazacyclononane and 2,6-xylidine in CHCl3, suggesting that the C-Cl bond cleavage led to the generation of dichlorocarbene. In addition, the mononuclear complex 6 has been transformed into a homotrinuclear complex [Cu3(L1)2(MeOH)2] by treatment with Cu(II) ions in MeOH/CHCl3, suggesting the possibility that the former could be regarded as a suitable metalloligand for heterotrimetallic complex synthesis.

Tri- and tetranuclear copper(II) complexes consisting of mononuclear Cu(II) chiral building blocks with a sugar-derived Schiff's base ligand.

A new sugar-derived Schiff's base ligand N-(3-tert-butyl-2-hydroxybenzylidene)-4,6-O-ethylidene-beta-D-glucopyranosylamine (H3L1) has been developed which afforded the coordinatively labile, alcoholophilic trinuclear Cu(II) complex [Cu3(L1)2(CH3OH)(H2O)] (1). Complex 1 has been further used in the synthesis of a series of alcohol-bound complexes with a common formula of [Cu3(L1)2(ROH)2] (R = Me (2), Et (3), nPr (4), nBu (5), nOct (6)). X-ray structural analyses of complexes 2-6 revealed the collinearity of trinuclear copper(II) centers with Cu-Cu-Cu angles in the range of 166-172 degrees . The terminal and central coppers are bound with NO3 and O4 atoms, respectively, and exhibit square-planar geometry. The trinuclear structures of 2-6 can be viewed as the two {Cu(L1)}- fragments capture a copper(II) ion in the central position, which is further stabilized by a hydrogen-bonding interaction between the alcohol ligands and the sugar C-3 alkoxo group. Complex 2 exhibits a strong antiferromagnetic interaction between the Cu(II) ions (J = -238 cm(-1)). Diffusion of methanol into a solution of complex 1 in a chloroform/THF mixed solvent afforded the linear trinuclear complex [Cu(3)(L1)2(CH3OH)2(THF)2] (7). The basic structure of 7 is identical to complex 2; however, THF binding about the terminal coppers (Cu-O(THF) = 2.394(7) and 2.466(7) A) has introduced the square-pyramidal geometry, indicating that the planar trinuclear complexes 2-6 are coordinatively unsaturated and the terminal metal sites are responsible for further ligations. In the venture of proton-transfer reactions, a successful proton transfer onto the saccharide C-3 alkoxo group has been achieved using 4,6-O-ethylidene-d-glucopyranose, resulting in the self-assembled tetranuclear complex, [Cu4(HL1)4] (8), consisting of the mononuclear Cu(II) chiral building blocks, {Cu(HL1)}.

Crystal-to-crystal transformation from tri- to mononuclear Cu(II) complex with a sugar-derived ligand via proton transfer reaction and rearrangement of hydrogen bonding networks.

Treatment of a glycosylamine derived Cu(II) complex with ethylamine resulted in crystal-to-crystal transformation from trinuclear complex [Cu3(L1)2(EtNH2)2(MeOH)2]x2MeOHxCHCl3 (2x2MeOHxCHCl3) to a dimeric structure of mononuclear complex [Cu(HL1)(EtNH2)] (3) through proton transfer reaction and rearrangement of hydrogen bonding networks.

Trinuclear coordinatively labile Cu(II) complex of 4,6-O-ethylidene-beta-D-glucopyranosylamine derived Schiff base ligand and its reactivity towards primary alcohols and amines.

A novel neutral trinuclear Cu(II) complex of a Schiff base ligand derived from D-glucose has been synthesised and structurally characterised, which exhibits excellent alcohol binding affinity and activates the C-Cl bond of chloroform in the presence of primary amine.

Crystal structure of 4,6-O-ethylidene-N-(2-hydroxybenzylidene)-beta-D-glucopyranosylamine.

4,6-O-Ethylidene-N-(2-hydroxybenzylidene)-beta-D-glucopyranosylamine was synthesized and characterized using analytical, spectral and single-crystal X-ray diffraction methods. The anomeric nature of the saccharide moiety was proposed based on 1H NMR studies and was confirmed by the crystal structure. The lattice structure of this compound was compared with that of its analogues.