Biomedical subjects
Publications and source records attributed to Chong Zheng.
The hydrogen bond rigidified backbones of aromatic oligoamides are temporarily interrupted by replacing the amide hydrogens with the acid-labile 2,4-dimethoxybenzyl (DMB) group, which allows the efficient preparation of long folding oligomers that, upon removal of the DMB groups, fold into multiturn helices. [structure: see text]
The mRPE65 protein is one form of the RPE65 protein and plays a very important role in the visual cycle. However, its 3D structure and detailed mechanism of function are still unclear because of difficulties with isolation and crystallization. This computational study reports a model for the mRPE65 protein structure derived from a model for sRPE65. The natural substrate for RPE65 has been shown to be a retinyl ester and, by utilizing the Autodock and the Ligplot programs, the interactions between the ester and the protein as well as the effects of several mutations on these interactions are studied. Finally, the position of the binding site is proposed based on an iterative process and the effects of the mutations on the binding site are also discussed.
Alkoxy side-chain-flanked diarylsulfonamide serves as a reliable structural motif for constructing macrocyclic aromatic tetrasulfonamides. This 90 degrees structural motif is persistent both in solution and in the solid state, which allows the one-step formation of tetrasulfonamide macrocycles. These macrocycles adopt a cone-shaped conformation in solution and in the solid state. For each molecule, an interior cavity surrounded by the aromatic residues is formed. The cavity sizes of the macrocycles can be tuned by incorporating aromatic residues of proper sizes. Guest (solvent) molecules are found in the cavities and bound by side chains. In solution, 1H NMR shows that the cone conformations undergo rapid interconversion at room temperature. The alkoxy side chains are found to be indispensable for maintaining the cone conformation. In addition, these porous molecules self-assemble into hollow tubular structures in the solid state. A variety of host molecules and building blocks for constructing nanoporous solid-state structures can be expected from these molecules.
The RPE65 protein is located in the retinal pigment epithelial cells and plays an important role in the visual cycle. Although numerous experimental results demonstrate that it participates in the visual cycle, its detailed structure and function are not clear yet because of difficulties in isolation and crystallization. This paper describes a computational modeling study to propose a three-dimensional (3D) structure and suggest a possible mechanism for the function of the protein. The 3D-PSSM server is used to obtain the preliminary 3D structural model of the RPE65 protein. The coordinates of the side chains are obtained from the SCWRL program. Finally, two software packages, Jackal and Tinker with the CHARMM force field are used to fix and refine the preliminary structural model. Based on the obtained 3D structural model, a possible mechanism for the protein function is discussed.
Aromatic tetrasulfonamide macrocycles carrying alkoxy side chains adopt a stable cone conformation in both the solid state and solution.
The title compounds were synthesized from Ln, LnX(3) (Ln = La, Ce; X = Cl, Br), and Sb under an Ar atmosphere at 950 degrees C. They crystallize in the space group P6(3)/m (No. 176) with lattice constants a = 21.232(5) and 20.862(2) Angstroms and c = 4.323(2) and 4.2728(7) Angstroms for La(9)Sb(16)Br(3) and Ce(9)Sb(16)Cl(3), respectively. The solids are the most metal-rich members in the reduced rare earth metal halide family and contain partial structures which are characteristic of reduced halides and intermetallic phases. These are the [Ln(6)X(6)](infinity) hexagon stars, Sb-centered [Ln(3)Sb](infinity) trigonal prismatic columns, and stripes of Sb square meshes. Computational analysis indicates that their electronic structure is valence-precise in the reduced halide part, but electron-deficient in the intermetallic part. Susceptibility and resistivity measurements reveal the metallic nature of the compounds.
Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation.
The compounds Ce(10)Cl(4)Ga(5) and Ln(3)ClGa(4) (Ln = La, Ce) were synthesized from stoichiometric mixtures of Ln, LnCl(3), and Ga under Ar atmosphere in sealed Ta ampules at 910-1020 degrees C for 25-26 days. Ce(10)Cl(4)Ga(5) is isostructural to La(10)Cl(4)Ga(5) (space group I4/mcm, No. 140) with lattice constants a = 7.9546(11) A, c = 31.793(6) A. Ln(3)ClGa(4) represents a new structural type, also in the space group I4/mcm, with a = 8.1955(8) and 8.1123(11) A, c = 11.363(2) and 11.229(2) A, respectively, for Ln = La and Ce. Ce(10)Cl(4)Ga(5) features building blocks of Ga-centered Ce(6) trigonal prisms and distinctive two-dimensional intermetallic CuAl(2) and U(3)Si(2) type nets. Its electronic structure falls within the realm of reduced rare-earth halides. Ln(3)ClGa(4) also contains the intermetallic CuAl(2) type nets, but the interstitials are inverted: The building blocks are Cl-centered Ln(6) octahedra. Its electronic structure is characterized by strong peripheral Ln-Ga bonding stabilizing the Ln(6)Cl octahedron which normally would have its Ln-Ln antibonding orbitals filled with electrons from interstitials beyond chalcogen. Magnetic susceptibility and conductivity measurements confirm the metallic nature of all three compounds.
The reactions of Ln(NO(3))(3) (Ln = La, Er) with 1,4-phenylendiacetic acid (H(2)PDA) under hydrothermal conditions produce isostructural lanthanide coordination polymers with the empirical formula [Ln(2)(PDA)(3)(H(2)O)] x 2H(2)O. The extended structure of [Ln(2)(PDA)(3)(H(2)O)] x 2H(2)O consists of Ln-COO triple helices cross-linked through the [bond]CH(2)C(6)H(4)CH(2)[bond] spacers of the PDA anions, showing 1D open channels along the crystallographic c axis that accommodate the guest and coordinated water molecules. Evacuation of [Er(2)(PDA)(3)(H(2)O)] x 2H(2)O at room temperature and at 200 degrees C, respectively, generates [Er(2)(PDA)(3)(H(2)O)] and [Er(2)(PDA)(3)], both of which give powder X-ray diffraction patterns consistent with that of [Er(2)(PDA)(3)(H(2)O)] x 2H(2)O. The porosity of [Er(2)(PDA)(3)(H(2)O)] and [Er(2)(PDA)(3)] is further demonstrated by their ability to adsorb water vapor to form [Er(2)(PDA)(3)(H(2)O)] x 2H(2)O quantitatively. Thermogravimetric analyses show that [Er(2)(PDA)(3)] remains stable up to 450 degrees C. The effective pore window size in [Er(2)(PDA)(3)] is estimated at 3.4 A. Gas adsorption measurements indicate that [Er(2)(PDA)(3)] adsorbs CO(2) into its pores and shows nonporous behavior toward Ar or N(2). There is a general correlation between the pore size and the kinetic diameters of the adsorbates (CO(2) = 3.3 A, Ar = 3.40 A, and N(2) = 3.64 A). That the adsorption favors CO(2) over Ar is unprecedented and may arise from the combined differentiations on size and on host-guest interactions.
Backbone-rigidified oligo(m-phenylene ethynylenes) fold into crescent or helical conformations in non-polar organic solvents.
A general strategy for creating nanocavities with tunable sizes based on the folding of unnatural oligomers is presented. The backbones of these oligomers are rigidified by localized, three-center intramolecular hydrogen bonds, which lead to well-defined hollow helical conformations. Changing the curvature of the oligomer backbone leads to the adjustment of the interior cavity size. Helices with interior cavities of 10 A to >30 A across, the largest thus far formed by the folding of unnatural foldamers, are generated. Cavities of these sizes are usually seen at the tertiary and quaternary structural levels of proteins. The ability to tune molecular dimensions without altering the underlying topology is seen in few natural and unnatural foldamer systems.
A new ternary chromium sulfide, BaCrS(2), was synthesized. This solid state compound crystallizes in the orthorhombic, centrosymmetric space group Pmmn (No. 59) with a = 4.2606(6) Å, b = 4.7944(7) Å, c = 9.443(1) Å, V = 192.89(5) Å(3), and Z = 2. The solid is similar to a previously known structure BaNiS(2) in which the Ni atom is coordinated to five sulfur atoms in a square pyramidal fashion. In BaCrS(2), the square pyramid distorts such that the two S(basal)-Cr-S(basal) angles are no longer equal. Thus the BaCrS(2) solid is orthorhombic whereas BaNiS(2) is tetragonal. The distortion from the square pyramidal coordination in the title compound is traced to the broken degeneracy of the d(xy)() and d(xz)() set by a computational analysis.