Biomedical subjects

Yuegang Zhang

Publications and source records attributed to Yuegang Zhang.

5 recordsLinked to original sources

PubMed2006

Characterizing challenging microcrystalline solids with solid-state NMR shift tensor and synchrotron X-ray powder diffraction data: structural analysis of ambuic acid.

Synchrotron X-ray powder diffraction and solid-state (13)C NMR shift tensor data are combined to provide a unique path to structure in microcrystalline organic solids. Analysis is demonstrated on ambuic acid powder, a widely occurring natural product, to provide the complete crystal structure. The NMR data verify phase purity, specify one molecule per asymmetric unit, and provide an initial structural model including relative stereochemistry and molecular conformation. A refinement of X-ray data from the initial model establishes that ambuic acid crystallizes in the P2(1) space group with unit cell parameters a = 15.5047(7), b = 4.3904(2), and c = 14.1933(4) A and beta = 110.3134(3) degrees . This combined analysis yields structural improvements at two dihedral angles over prior NMR predictions with differences of 103 degrees and 37 degrees found. Only minor differences of +/-5.5 degrees , on average, are observed at all remaining dihedral angles. Predicted hydroxyl hydrogen-bonding orientations also fit NMR predictions within +/-6.9 degrees . This refinement corrects chemical shift assignments at two carbons and reduces the NMR error by approximately 16%. This work demonstrates that the combination of long-range order information from synchrotron powder diffraction data together with the accurate shorter range structure given by solid-state NMR measurements is a powerful tool for studying challenging organic solids.

Cyclohexanones↗

PubMed2006

Controlled precipitation of solubilized carbon nanotubes by delamination of DNA.

Polyaromatic molecules, such as rhodamine 6G and methylene blue, were found capable of precipitating DNA-solubilized single-walled carbon nanotubes from solution through a competitive binding mechanism whereby DNA is displaced from the nanotube surface, allowing the nanotubes to rebundle. This delamination of DNA also occurred when complementary oligonucleotides were used to hybridize specifically to the DNA coating on the nanotubes. These findings were expanded to include techniques for controlled desolubilization and to provide additional elucidation into the interaction of SWNTs and noncovalent solubilizing agents.

Binding, Competitive↗

PubMed2005

Similarity in structures of racemic and enantiomeric ibuprofen sodium dihydrates.

The crystal structures of two ibuprofen sodium dihydrates, racemic sodium (RS)-2-(4-isobutylphenyl)propanoate dihydrate or (RS)-NaIBDH, Na+.C13H17O2-.2H2O, and enantiomeric sodium (S)-2-(4-isobutylphenyl)propanoate dihydrate or (S)-NaIBDH, Na+.C13H17O2-.2H2O, have been determined in the space groups P-1 and P1, respectively. The unit cells of the two triclinic structures have similar lattice parameters and cell volumes. The constituent ions have similar coordination environments, but differ slightly in their hydrogen-bonding interactions. The dominance of the interactions between the O atoms and the Na+ cations explains the structural similarity of these two structures, despite the fact that one is heterochiral while the other is homochiral.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2003

Multiple conformations of benzil in resorcinarene-based supramolecular host matrixes.

Six supramolecular complexes incorporating benzil as a guest, CMCR*bipy*benzil (alpha) 1 (CMCR = C-methylcalix[4]resorcinarene), CMCR*bipy*benzil (beta) 2, CMCR*2bpe*benzil*ethanol 3 (bpe = trans-1,4-bis(pyridyl)ethylene), CMCR*2bpe*benzil*2H2O 4, CMCR.2bpeh*benzil*ethanol 5 (bpeh = bis-(1-pyridin-4-yl-ethylidene)-hydrazine), and CECR*2bpe.benzil 6 (CECR = C-ethylcalix[4]resorcinarene), have been synthesized by hydrothermal and conventional methods and characterized by X-ray diffraction. Resorcinarene adopts a boat conformation in 1-4 and a bowl conformation in 5 and 6. Compounds 1-4 show a brick-wall-like framework, in which two benzil molecules are incorporated. For 5, bpeh spacers link CMCR molecules to give a one-dimensional wavelike polymer in which one benzil guest is embedded within the polymer cavity. Complex 6 forms a carcerand-like capsule in which two benzil guests are encapsulated. The O=C-C=O torsion angles vary from 91.8 to 139.3 degrees and correlate with the length of the central C-C bond. The benzil concentration, which is approximately 6.2 mol/L in the neat crystals, varies between 1.01 and 1.51 mol/L in the structures studied, corresponding to a 6-fold dilution. The benzil molecules are disordered in the larger cavities of 4 and 5. The two benzoyl fragments are almost perpendicular in 3, which has the next largest cavity size when solvent volume is excluded, whereas a nearly trans-coplanar conformation occurs for the cavity with the smallest volume in 6.

Journal Article↗

PubMed1998

Multitemperature Resonance-Diffraction and Structural Study of the Mixed-Valence Complex [Fe(3)O(OOCC(CH(3))(3))(6)(C(5)H(5)N)(3)].

The Fe-O and Fe-N bond lengths at two iron sites of the mixed-valence complex [Fe(3)O(OOCC(CH(3))(3))(6)(C(5)H(5)N)(3)] show a pronounced temperature dependence; the bonds from two of the Fe atoms to the central oxygen atoms vary by more than 0.10 Å on cooling to 10 K whereas the bond from the third iron atom is essentially invariant. The variation is such that the longest Fe-O bonds at ambient temperature are the shorter ones at 10 K, with the crossover occurring at about 90 K. The bonds to the axial pyridine ligand show the opposite dependence. The variation is attributed to an equilibrium between different configurations, which interconvert through vibronic coupling, a process that involves electron transfer between the metal atoms. The position of the absorption edge for each of the iron atoms has been determined by resonance-diffraction experiments at the Fe K edge, performed at four different temperatures. At each temperature, the order of the absorption edges corresponds to that of the experimentally determined bond lengths. The crossover near 90 K is confirmed by the resonance experiments. The absorption-edge positions are related to the formal oxidation state by calibration with reference complexes of known oxidation state. The experiments demonstrate the close relation between the changes in coordination geometry and the oxidation states of the iron atoms.

Journal Article↗