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Md Alamgir Hossain

Publications and source records attributed to Md Alamgir Hossain.

8 recordsLinked to original sources
PubMed2005

Tritopic (cascade) and ditopic complexes of halides with an azacryptand.

Structural aspects of the binding of halides in the octaaza cryptand (1,4,11,14,17,24,29,36-octa-azapentacyclo[12.12.12.2(6,9).2(19,22).2(31,34)]-tetratetraconta-6(43),7,9(44),19(41),20,22(42),31(39),32,34(40)-nonaene, N(CH2CH2NHCH2-p-xylyl-CH2NHCH2CH2)3N), L1, were examined for fluoride, chloride, and bromide. Crystallographic results for two different fluoride complexes indicated cascade-like coordination, with two fluoride ions inside the tren-based cavity, bridged by a water molecule. In the two different chloride structures, a single chloride and a water molecule occupied the cavity. The bromide structure contained two crystallographically independent cationic cryptands. Unit A consisted of a bromide on one side of the cavity and three disordered water molecules situated between the cryptand arms on the other side. Unit B also had a bromide inside the cavity at one side, but a single molecule of water was centered at the other side of the cavity. Association constants for the three ions, determined by NMR titrations in aqueous solution at pH 5, revealed log Ka=3.15(5), 3.37(3), and 3.34(4) for fluoride, chloride, and bromide, respectively.

Journal Article↗
PubMed2004

Encapsulated sulfates: insight to binding propensities.

Two crystal structures of sulfate inclusion complexes in an aza- and amido-cryptand represent the first examples of encapsulated sulfate in synthetic cryptand receptors and indicate penta- and octa-coordination, respectively.

Amides↗
PubMed2004

Ditopic double pincer palladacycle catalyst for C-C coupling.

A ditopic palladacycle with SCS pincer coordination, L(PdCl)(2) (1), was isolated and structurally characterized and represents the first example of a transition metal complex with a polythioamide-based macrocycle. Preliminary studies of 1 in the catalytic coupling of 4-iodotoluene and styrene indicated it to be robust in the presence of oxygen and high temperatures, with high turnover numbers in relatively short times.

Journal Article↗
PubMed2004

Anion binding with a tripodal amine.

Binding studies of the tren-based amine, L (N,N',N' '-tris(2-benzylaminoethyl)amine), with inorganic anions and two crystal structures, [H(3)L][H(2)PO(4)](3).H(3)PO(4) and [H(3)L][Br](3), are reported. NMR titration results indicate that the ligand binds H(2)PO(4)(-) and HSO(4)(-) more strongly than NO(3)(-) and halides. In the crystal structure of the phosphate complex, the ligand is triprotonated with the three arms pointing outward in a trigonal-planar-like arrangement. Four phosphate species are associated with the receptor, and have been assigned as three H(2)PO(4)(-) counterions located between each of the tren arms, and an additional H(3)PO(4) molecule above the quasi-planar tren. The structure of the bromide complex is slightly different, although again the tren receptor is triprotonated and quasi-planar, but in this case C(2v)-like symmetry is seen with two of the arms pointed in the same direction with a bromide ion in between. The other two bromides lie outside of the tren arms.

Journal Article↗
PubMed2003

A ditopic azacryptate proton cage.

A tosylated azacryptand readily protonates at the bridgehead amines, becoming a potential ditopic anion receptor. The in-in conformation of the amines facilitates encapsulation of two bromide guests and represents the first structural evidence that a proton cage cryptate can bind two anions internally.

Journal Article↗
PubMed2003

Elite new anion ligands: polythioamide macrocycles.

Prototypes for a new class of polythioamide-based macrocycles have been synthesized and anion-binding capabilities assessed. Results indicate higher anion binding for H(2)PO(4)(-), HSO(4)(-), and F(-) for monocycles, but somewhat lessened binding capabilities for bicycles compared with amide corollaries.

Journal Article↗
PubMed2003

Anion receptors: a new class of amide/quaternized amine macrocycles and the chelate effect.

A new class of tetraamide macrocyclic receptors for anions with two quaternized amine functionalities exhibited higher affinities for anions compared with the corresponding neutral amides. In two crystal structures of halide complexes of the prototypes with phenyl and pyridine spacers, the anions are held by hydrogen bonding with the amide hydrogens. The pyridine analogues display higher affinities in general than the phenyl systems, a phenomenon which is attributed to the anion version of the chelate effect.

Journal Article↗