Biomedical subjects
Publications and source records attributed to Dohyun Moon.
We have demonstrated a triangular assembly driven by 12 charged hydrogen bonds and pi-pi interactions. This assembly is stable even in polar solvents because of its charged hydrogen-bond nature. Helical arrangement of the complex is confirmed by its crystal structure. A solution structure is assigned to the D(3) isomer corresponding to the solid-state structure by temperature-dependent (1)H NMR experiments.
A novel S4-symmetric icosanuclear manganese metalladiazamacrocycle was synthesized using a pentadentate ligand, N-3-phenyl-trans-2-propenoylsalicylhydrazide (H3L), that has a rigid and bulky terminal N-acyl group. A 20 cyclic repeat of an--(Mn-N-N)--linkage resulted in a highly puckered diaza-bridged 60-membered icosanuclear metallamacrocycle. The steric interaction between the ligands in the cyclic system leads to five consecutive Mn(III) centers in a chemically different--(Mn(A)Mn(B)Mn(C)Mn(D)Mn(E))--environment, with the chiralities of the metal centers being in a rather complicated--(LambdaLambdaDeltaLambdaLambda)(DeltaDeltaLambdaDeltaDelta)--sequence.
An extended 36-membered dodecanuclear manganese metallamacrocycle with S12 symmetry has been synthesized using the ligand N-cyclohexanoylsalicylhydrazide (H3chxshz) by a self-assembly that accommodates a cyclooctane of conformationally strained S4 symmetry in its hydrophobic cavity.
The face-driven corner-linked truncated octahedral nanocages, [Pd6L8]12+ (1, L1 = N,N',N' '-tris(3-pyridinyl)-1,3,5-benzenetricarboxamide; 2, L2 = N,N',N' '-tris(4-pyridinylmethyl)-1,3,5-benzenetricarboxamide), were prepared with eight C3-symmetric tridentate ligands and six square planar tetratopic palladium(II) ions. The combination of the nitrogen donor atom at a approximately 120 degrees kink position of the carboxamido pyridinyl group and the tilted pyridyl versus the facial plane of the ligands can provide the needed curvature for the formation of octahedral cages. The nitrogen atoms can coordinate to the square planar palladium(II) ions to form kinks with approximately 120 degrees angles at the C4-symmetric square planar corners of the truncated octahedron. Depending on the conformation of the ligand, L1, two different truncated octahedral cages of around 2.4 nm in diameters were formed. The major form of 1 with syn-conformational ligands has a cavity volume of approximately 1600 A3. The cage has 12 ports (3.4 x 3.5 A2) at all edges of the octahedron. The minor form of cage 1 with anti-conformational ligands has a slightly increased cavity volume ( approximately 1900 A3) and port size (3.3 x 8.0 A2). The insertion of a methylene group in L2 has not only increased the cavity volume of 2 to approximately 2200 A3 but also enlarged the port size to 4.1 x 8.0 A2. However, an atomic force microscopy (AFM) study of cage 2 showed that the cages had a height of 1.8 +/- 0.1 nm. This value is about 30% smaller than the calculated size of 2.6 nm from the crystal structure. This tip-induced decrease in height in cage 2 suggests the nonrigidity of cage 2.
Explore the source record for details and available documents.
By modulating the secondary building units derived from the primary building units, N-acylsalicylhydrazides (H3 xshz), we have been able to construct isostructural but tunable host networks, [Mn6(xshz)6(dmf)2(bpea)2], with different cavity sizes and shapes where the secondary building units, [Mn6(xshz)6], were linked through exo-bidentate bridging ligand, 1,2-bis(pyridyl)ethane (bpea) to form 3-D networks. With a short length linear N-acyl side chain at the primary building unit, the host networks have a 3-D network with three-dimensional cavities. With an appropriate length linear N-acyl side chain at the primary building unit, the host network keeps the isostructural 3-D network but with two types of one-dimensional channels of reduced cavity volume. The tuned host networks showed not only size selectivity for the guest molecules but also shape selectivity. While the three-dimensional channeled host showed selectivity depending on the length of the podal guests, the one-dimensional channeled host showed selectivity depending on both the length and/or the podality of the guest molecules.
We report on helical coordination networks that were prepared using a hexanuclear manganese metallamacrocycle as a helical tecton. We were able to prepare the three-dimensional helical coordination networks using a hexanuclear manganese metallamacrocycle, [Mn(6)(lshz)(6)], as a helical tecton, where N-lauroyl salicylhydrazide (H(3)lshz) was used as the primary building unit to generate the helical tecton as a secondary building unit. While the 4(1)/4(3) screw symmetry-linked helical coordination network was obtained when the primary building units had an N-acetyl group, both the 3(1)/3(2) screw symmetry-linked and the 4(1)/4(3) screw symmetry-linked helical coordination networks were obtained simultaneously in the same batch when the primary building unit had a long alkyl N-lauroyl group at the N-acetyl site.
Coupling reactions of CO(2) and epoxide to produce cyclic carbonates were performed in the presence of a catalyst [L(2)ZnX(2)] (L=pyridine or substituted pyridine; X=Cl, Br, I), and the effects of pyridine and halide ligands on the catalytic activity were investigated. The catalysts with electron-donating substituents on pyridine ligands exhibit higher activity than those with unsubstituted pyridine ligands. On the other hand, the catalysts with electron-withdrawing substituents at the 2-position of the pyridine ligands show no activity; this demonstrates the importance of the basicity of the pyridine ligands. The catalytic activity of [L(2)ZnX(2)] was found to decrease with increasing electronegativity of the halide ligands. A series of highly active zinc complexes bridged by pyridinium alkoxy ions of the general formula [((mu-OCHRCH(2)L)ZnBr(2))(n)] (n=2 for R=CH(3); n=3 for R=H; L=pyridine or substituted pyridine) were synthesized and characterized by X-ray crystallography. The dinuclear zinc complexes obtained from propylene oxide adopt a square-planar geometry for the Zn(2)O(2) core with two bridging pyridinium propoxy ion ligands. Trinuclear zinc complexes prepared from ethylene oxide adopt a boat geometry for the Zn(3)O(3) core, in which three zinc and three oxygen atoms are arranged in an alternate fashion. These zinc complexes bridged by pyridinium alkoxy ions were also isolated from the coupling reactions of CO(2) and epoxides performed in the presence of [L(2)ZnBr(2)]. Rapid CO(2) insertion into the zincbond;oxygen bond of the zinc complexes bridged by pyridinium alkoxy ions leads to the formation of zinc carbonate species; these which yield cyclic carbonates and zinc complexes bridged by pyridinium alkoxy ions upon interaction with epoxides. The mechanistic pathways for the formation of active species and cyclic carbonates are discussed on the basis of results from structural and spectroscopic analyses.
By using the tripodal tetradentate ligand tris(2-benzimidazolylmethyl)amine (H(3)ntb), which can have several charge states depending on the number of secondary amine protons, mononuclear octahedral and dinuclear trigonal bipyramidal Fe(III) complexes were prepared. The reaction of mononuclear octahedral [Fe(III)(H(3)ntb)Cl(2)]ClO(4), 1, with 3 equiv of sec-butylamine in methanol led to the formation of mononuclear cis-dimethoxo octahedral Fe(III)(H(2)ntb)(OMe)(2), 2. One equivalent of the sec-butylamine was used to generate the monoanionic H(2)ntb(-) ligand where one of the three amines in the benzimidazolyl groups was deprotonated. The remaining 2 equiv were used to generate two methoxides that were coordinated to the octahedral Fe(III) ion in a cis fashion as demonstrated by the chlorides in 1. Reaction of 1 with excess (7 equiv) sec-butylamine generated the doubly deprotonated dianionic Hntb(2-) that stabilized the dinuclear mu-oxo Fe(III)(2)O(Hntb)(2), 3, adopting a five-coordinate trigonal bipyramidal geometry. The magnetic data for 3 are consistent with the antiferromagnetically coupled Fe(III) (S = 5/2) sites with the coupling constant J = -127 cm(-1).
Explore the source record for details and available documents.