Cheng-Han Yang

Self-assembly of two mixed-ligands metal-organic coordination polymers, [MII2(DPA)2(C4O4)(C2O4)] (M = Cu, Zn)

Abstract Two coordination polymers with the formula of [M 2 (DPA) 2 (C 4 O 4 )(C 2 O 4 )] ∞ (M=Cu 1 , Zn 2 ; DPA=dipyridylamine) were synthesized under hydrothermal conditions. Both complexes are crystallized in triclinic system, space group P 1 with the cell parameters: a=8.3078(3) A , b=9.1192(3) A , c=9.2316(3) A , α=115.164(1)°, β=94.283(1)°, γ=103.559(1)°, V=603.17(4) A 3 , Z=2 for complex 1 and a=8.5348(2) A , b=9.0451(2) A , c=9.0862(3) A , α=114.305(1)°, β=100.493(1)°, γ=97.318(1)°, V=612.34(2) A 3 , Z=2 for complex 2 , respectively. X-ray single-crystal structural determinations reveal that these two complexes are both composed of one-dimensional zigzag chains built up via the [M(DPA)] 2+ fragments and alternately bridged bidentate μ 1,3 -C 4 O 4 2− , tetradentate C 2 O 4 2− ligands. The coordination environments of the M(II) centers adopt a slightly distorted trigonal bipyramid bonded with two N atoms of DPA, one O atom of squatate and two O atoms of oxalates. The intrachains N–H⋯O and C–H⋯O hydrogen bonds play an important role on the additional stabilization in constructing the open frameworks.

Color tuning associated with heteroleptic cyclometalated Ir(III) complexes: influence of the ancillary ligand.

We report the preparation of a series of new heteroleptic Ir(III) metal complexes chelated by two cyclometalated 1-(2,4-difluorophenyl)pyrazole ligands (dfpz)H and a third ancillary bidentate ligand (L=X). Such an intricate design lies in a core concept that the cyclometalated dfpz ligands always warrant a greater pi pi* gap in these series of iridium complexes. Accordingly, the lowest one-electron excitation would accommodate the pi* orbital of the ancillary L=X ligands, the functionalization of which is then exploited to fine-tune the phosphorescent emission wavelengths. Amongst the L=X ligands designed, three classes (series 1-3) can be categorized, and remarkable bathochromic shifts of phosphorescence were observed by (i) replacing the 2-benzoxazol-2-yl substituent (1a) with the 2-benzothiazol-2-yl group (1b) in the phenolate complexes, (ii) converting the pyridyl group (2a) to the pyrazolyl group (2b) and even to the isoquinolyl group (2c) in the pyrazolate complexes and (iii) extending the pi-conjugation of the benzimidazolate ligand from 3a to 3b. Single-crystal X-ray diffraction study on complex [(dfpz)Ir(bzpz)] (2b) was conducted to confirm their general molecular architectures. Complex 2b was also used as a representative example for fabrication of multilayered, green-emitting phosphorescent OLEDs using the direct thermal evaporation technique.

Synthesis and structure of a novel two-dimensional bilayer framework of a [M(C5O5)(dpe)] coordination polymer

The novel coordination polymers [M(μ3-C5O5)0.5(μ4-C5O5)0.5 (anti-dpe)0.5(gauche-dpe)0.5] [M = Mn 1a, Fe 1b, Cd 1c; dpe = 1,2-bis(4-pyridyl)ethane] consist of a two-dimensional bilayered framework, each being constructed from the cross-linkage of two infinite 2D [M(μ3-C5O5)0.5(μ4-C5O5)0.5(anti-dpe)0.5] brick-wall layers by gauche-dpe ligands.

Probing water environment of Trp59 in ribonuclease T1: insight of the structure-water network relationship.

In this study, we used the tryptophan analogue, (2,7-aza)Trp, which exhibits water catalyzed proton transfer isomerization among N(1)-H, N(7)-H, and N(2)-H isomers, to probe the water environment of tryptophan-59 (Trp59) near the connecting loop region of ribonuclease Tl (RNase T1) by replacing the tryptophan with (2,7-aza)Trp. The resulting (2,7-aza)Trp59 triple emission bands and their associated relaxation dynamics, together with relevant data of 7-azatryptophan and molecular dynamics (MD) simulation, lead us to propose two Trp59 containing conformers in RNase T1, namely, the loop-close and loop-open forms. Water is rich in the loop-open form around the proximity of (2,7-aza)Trp59, which catalyzes (2,7-aza)Trp59 proton transfer in the excited state, giving both N(1)-H and N(7)-H isomer emissions. The existence of N(2)-H isomer in the loop-open form, supported by the MD simulation, is mainly due to the specific hydrogen bonding between N(2)-H proton and water molecule that bridges N(2)-H and the amide oxygen of Pro60, forming a strong network. The loop-close form is relatively tight in space, which squeezes water molecules out of the interface of α-helix and β2 strand, joined by the connecting loop region; accordingly, the water-scant environment leads to the sole existence of the N(1)-H isomer emission. MD simulation also points out that the Trp-water pairs appear to preferentially participate in a hydrogen bond network incorporating polar amino acid moieties on the protein surface and bulk waters, providing the structural dynamic features of the connecting loop region in RNase T1.

Homology Modeling and Molecular Dynamics Simulation Combined with X-ray Solution Scattering Defining Protein Structures of Thromboxane and Prostacyclin Synthases

A combination of molecular dynamics (MD) simulations and X-ray scattering (SAXS) has emerged as the approach of choice for studying protein structures and dynamics in solution. This approach has potential applications for membrane proteins that neither are soluble nor form crystals easily. We explore the water-coupled dynamic structures of thromboxane synthase (TXAS) and prostacyclin synthase (PGIS) from scanning HPLC-SAXS measurements combined with MD ensemble analyses. Both proteins are heme-containing enzymes in the cytochrome P450 family, known as prostaglandin H2 (PGH2) isomerase, with counter-functions in regulation of platelet aggregation. Currently, the X-ray crystallographic structures of PGIS are available, but those for TXAS are not. The use of homology modeling of the TXAS structure with ns-μs explicit water solvation MD simulations allows much more accurate estimation of the configuration space with loop motion and origin of the protein behaviors in solution. In contrast to the stability of the conserved PGIS structure in solution, the pronounced TXAS flexibility has been revealed to have unstructured loop regions in connection with the characteristic P450 structural elements. The MD-derived and experimental-solution SAXS results are in excellent agreement. The significant protein internal motions, whole-molecule structures, and potential problems with protein folding, crystallization, and functionality are examined.

P-212: Architecture Design for Efficient True-Blue Phosphorescent OLEDs

In this paper, we report an effective architecture for true-blue phosphorescent OLEDs using a series of novel blue-emitting Ir complexes. It incorporates double-emitting layers (one hole-transport, one electron-transport) and double buffer layers, for achieving balanced carrier injection/transport and carrier/exciton confinement. The efficiencies of true-blue phosphorescent OLEDs can be up to 13.7% photon/electron, 20.4 cd/A, 14 lm/W, with the true-blue CIE coordinates of (0.157, 0.189).