Showing papers by "Dillip Kumar Chand published in 2003"
TL;DR: Proton binding by the two tren-based tris-macrocycles L1 and L2, composed, respectively, by three 1,4,7,10-tetrazacyclodecane ([12]aneN4) and three 1-oxa-4, 7, 10-triazacyCLodecANE ([12]-aneN3O) macrocyclic moieties appended to a tris unit (tren = tris(2-aminoethyl)amine), has been analyzed by means of potentiometric and 1
Abstract: Proton binding by the two tren-based tris-macrocycles L1 and L2, composed, respectively, by three 1,4,7,10-tetrazacyclododecane ([12]aneN4) and three 1-oxa-4,7,10-triazacyclododecane ([12]aneN3O) macrocyclic moieties appended to a “tren” unit (tren = tris(2-aminoethyl)amine), has been analyzed by means of potentiometric and 1H and 13C NMR measurements in aqueous solutions This study reveals that the ligands form highly charged polyammonium cations at neutral pH, containing six acidic protons equally distributed among the three macrocyclic units A potentiometric and UV-vis spectrophotometric study shows that both ligands can form stable trinuclear Cu(II) complexes in a wide pH range In the polynuclear complexes each metal is coordinated to a single macrocyclic unit While the Cu(II) complexes with L1 do not show any tendency to form hydroxylated complexes, the mono-, di- and trinuclear L2 complexes give stable hydroxo-complexes, present in aqueous solutions from slightly acidic to alkaline pH values Melting point studies indicate that the new tris-macrocyles and their Cu(II) complexes lead to stronger stabilization of double-stranded nucleic acids than those observed earlier with analogous ditopic macrocyclic ligands, again with preference for RNA-type polymers compared to DNA The copper complexes promote cleavage of plasmid DNA and of bis-p-nitrophenyl phosphate (BNPP) Particular rate enhancements for BNPP with some complexes are attributed to the simultaneous action of three metal ions and partially to the formation of hydroxo complexes at neutral pH
61 citations
TL;DR: In this article, discrete self-assemblies prepared by designed pyridine appended ligands with cis-protected Pd(II) ion were described, where the assembly so obtained from the combination of a ligand and (5) may be considered as a module or reminiscent of the assembly that is expected from the complexation of same ligand with naked Pd (II) resulted in discrete structures.
Abstract: Discrete self-assemblies prepared by designed pyridine appended ligands with cis-protected Pd(II) ion (5) are described. If ligands 2, 3 and 4 are separately treated with (5), the formation of (i) dynamic equilibrium of macrocyclic M2L2
(6) and M4L4 assemblies (7); (ii) macrocyclic M2L2 product (9); and (iii) macrobicyclic M3L2
(11) occurred, respectively. The assembly so obtained from the combination of a ligand and (5) may be considered as a module or reminiscent of the assembly that is expected from the complexation of same ligand with naked Pd(II). In fact, complexation of the above mentioned ligands with naked Pd(II) resulted in discrete structures. This is in contrast to the possible polymeric structure usually obtained from such types of ligands in combination with naked Cd(II), Ni(II) etc. The result that the ligands 2, 3, and 4 with naked Pd(II) give macrotricyclic M2L4
(8); macropentacyclic M4L8
(10); and M6L8 spherical assembly (12), respectively, establishes interesting strategies. Thus we have shown rational comparison of a particular ligand for either cis-protected or naked Pd(II) ion for first time.
53 citations