I-Jy Chang

Electron tunneling in ruthenium-modified cytochromec

Abstract Distant Fe2+-Ru3+ electronic couplings have been extracted from intramolecular electron-transfer rates in Ru(2,2′-bipyridine)2(imidazole)(histidine-X)2+ (X = 33,39,62,72,79) derivatives of cytochromec. The rates are > 1 · 108 (79); 3.2(4) · 106 (39); 2.6(3) · 106 (33); 9.0(3) · 105 (72); 1.0(2) · 104 s−1 (62); the couplings increase according to 62 (0.006) 0.6 cm−1). The rates (and the couplings) correlate with the lengths of σ-tunneling pathways comprised of covalent bonds, hydrogen bonds, and through-space jumps from the histidines to the heme group.

The Cytochrome c Folding Landscape Revealed by Electron-transfer Kinetics

We have investigated the folding energy landscape of cytochrome c by exploiting the widely different electron-transfer (ET) reactivities of buried and exposed Zn(II)-substituted hemes. An electronically excited Zn-porphyrin in guanidine hydrochloride denatured Zn-substituted cytochrome c (Zn-cyt c) reduces ruthenium(III) hexaammine about ten times faster than when embedded in the fully folded protein. Measurements of ET kinetics during Zn-cyt c folding reveal a burst intermediate in which one-third of the ensemble has a protected Zn-porphyrin and slow ET kinetics; the remaining fraction exhibits fast ET characteristic of a solvent-exposed redox cofactor. The ET data show that, under solvent conditions favoring the folded protein, collapsed non-native structures are not substantially more stable than extended conformations, and that the two populations interchange rapidly. Most of the folding free energy, then, is released when compact structures evolve into the native fold.

Photophysical properties of tricarbonyl(histidine)(diimine)rhenium(I) complexes in aqueous solution

Abstract Four tricarbonyl(histidine)(diimine)rhenium(l) complexes have been prepared, where diimine is 2,2′-bipyridine (bpy), 4,4′dicarboxyl-2,2′-bipyridine (bpy(COO)2)2−, 1,10-phenanthroline (phen), and disulfonate 4,7-diphenyl-1,10-phenanthroline (phen(phS03)2)2−. All complexes exhibit metal-to-ligand charge-transfer (MLCT) absorption in the 350–380 nm range. Excitation into the MLCT absorption bands results in orange luminescence. The emission maxima for these complexes range from 580 to 625 nm in aqueous solution at room temperature. The excited-state energy, broad emission profiles, and long excited-state lifetimes indicate emission from a 3MLCT state. The complexes with phen-type diimine ligands have much longer lifetimes than those with bpy-type diimine ligands: Re(phen(phS03)2)(CO)3(His)-,τ = 170 ns; Re(phen)(CO)3(His)+, τ = 100 ns.

Structure, Photophysical Properties, and DFT Calculations of Selenide-Centered Pentacapped Trigonal Prismatic Silver(I) Clusters

Undecanuclear silver clusters [Ag(11)(mu(9)-Se)(mu(3)-Br)(3){Se(2)P(OR)(2)}(6)] (R = Et, (i)Pr, (2)Bu) were isolated from the reaction of [Ag(CH(3)CN)(4)](PF(6)), NH(4)[Se(2)P(OR)(2)], and Bu(4)NBr in a molar ratio of 4:3:1 in CH(2)Cl(2) at -20 degrees C. Clusters were characterized by elemental analysis, NMR spectroscopy ((1)H, (31)P, and (77)Se), positive FAB mass spectrometry, and X-ray crystallography of the isopropyl derivative. Structural elucidations revealed that the Ag(11)Se core geometry of clusters is a selenide-centered, slightly distorted 3,3,4,4,4-pentacapped trigonal prism surrounded by six diselenophosphato ligands, each in a tetrametallic tetraconnective (mu(2), mu(2)) coordination mode, and three mu(3)-bromide anions. All compounds exhibited orange luminescence both as a solid and in solution. The electronic structure of these clusters was studied by DFT calculations, and their optical properties were rationalized through a TDDFT investigation. The computed metrical parameters of the clusters were consistent with the corresponding X-ray data of [Ag(11)(mu(9)-Se)(mu(3)-Br)(3){Se(2)P(O(i)Pr)(2)}(6)] . The theoretical investigations affirmed that the low-energy absorptions as well as emissions were due to transitions from an orbital mostly of a selenophosphate ligand/central Se atom character to an orbital of metal character.

Multielectron photochemistry of quadruply bonded metal-metal complexes

Abstract The structural, electronic, and oxidation-reduction properties of multiply bonded metal-metal ( ) dimers presage a rich excited state chemistry for these complexes. Our work has emphasized photochemical pathways that utilize ( ) dimers to promote overall multielectron transformations. Multielectron photochemistry can only be achieved by correctly manipulating the molecular and electronic structures of these dimers such that one-electron pathways are circumvented. We now present a summary of the strategy used for the rational design of ( ) multielectron photochemical schemes.

Essential oils from Taiwan: Chemical composition and antibacterial activity against Escherichia coli

The chemical compositions of seven essential oils from Taiwan were analyzed by gas chromatography-mass spectrometry. The eluates were identified by matching the mass fragment patents to the National Institute of Standards and Technology (NIST) 08 database. The quantitative analysis showed that the major components of lemon verbena are geranial (26.9%) and neral (23.1%); those of sweet marjoram are γ-terpinene (18.5%), thymol methyl ether (15.5%), and terpinen-4-ol (12.0%); those of clove basil are eugenol (73.6%), and β-(Z)-ocimene (15.4%); those of patchouli are carvacrol (47.5%) and p-cymene (15.2%); those of rosemary are α-pinene (54.8%) and 1,8-cineole (22.2%); those of tea tree are terpinen-4-ol (33.0%) and 1,8-cineole (27.7%); and those of rose geranium are citronellol (28.9%) and 6,9-guaiadiene (20.1%). These components are somewhat different from the same essential oils that were obtained from other origins. Lemon verbena has the same major components everywhere. Tea tree, rose geranium, and clove basil have at least one major component throughout different origins. The major components and their amounts in sweet marjoram, patchouli, and rosemary vary widely from one place to another. These results demonstrate that essential oils have a large diversity in their composition in line with their different origins. The antibacterial activity of essential oils against Escherichia coli was evaluated using the optical density method (turbidimetry). Patchouli is a very effective inhibitor, in that it completely inhibits the growth of E. coli at 0.05%. Clove basil and sweet marjoram are good inhibitors, and the upper limit of their minimum inhibitory concentration is 0.1%.