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Nickel complexes have been widely employed as catalysts in C–C and C–heteroatom bond formation reactions. In addition to Ni(0) and Ni(II) intermediates, several Ni-catalyzed reactions are proposed to also involve odd-electron Ni(I) and Ni(III) oxidation states. We report herein the isolation, structural and spectroscopic characterization, and organometallic reactivity of Ni(III) complexes containing aryl and alkyl ligands. These Ni(III) species undergo transmetalation and/or reductive elimination reactions to form new C–C or C–heteroatom bonds and are also competent catalysts for Kumada and Negishi cross-coupling reactions. Overall, these results provide strong evidence for the direct involvement of organometallic Ni(III) species in cross-coupling reactions and oxidatively induced C–heteroatom bond formation reactions.

Molecular dynamics simulations of the oxidation of benzyl alcohol by horse liver alcohol dehydrogenase (HLADH) have been carried out. The following three states have been studied: HLADH.PhCH(2)OH.NAD(+) (MD1), HLADH.PhCH(2)O(-).NAD(+) (MD2), and HLADH.PhCHO.NADH (MD3). MD1, MD2, and MD3 simulations were carried out on one of the subunits of the dimeric enzyme covered in a 32-A-radius sphere of TIP3P water centered on the active site. The proton produced on ionization of the alcohol when HLADH.PhCH(2)OH.NAD(+) --> HLADH.PhCH(2)O(-).NAD(+) is transferred from the active site to solvent water via a hydrogen bonding network consisting of serine48 hydroxyl, ribose 2'- and 3'-hydroxyl groups, and Hist51. Hydrogen bonding of the 3'OH of ribose to Ile269 carbonyl maintains this proton in position to be transferred to water. Molecular dynamic simulations have been employed to track water1287 from the TIP3 water pool to the active site, thus exhibiting the mode of entrance of water to the active site. With time the water1287 accumulates in two different positions in order to accept the proton from the ribose 3'-OH and from His51. There can be identified two structural substates for proton passage. In the first substate the imidazole Ne2 of His51 is adjacent to the nicotinamide ribose C2'-OH and hydrogen bonding distances for proton transfer through the hydrogen bonded relay series PhCH(2)OH...Ser48-OH...Ribose2'-OH...His51...OH(2) (path 1) average 2.0, 2.0, and 2.1 A and (for His51...OH(2)) minimal distances less or equal to 2.5 A. The structure for path 1 is present 20% of the time span. And in the second substate, there are two possible proton passages: path 1 as before and path 2. Path 2 involves the hydrogen-bonded relay series PhCH(2)OH...Ser48-OH...Ribose2'-OH...Ribose3'-OH...His51.OH(2) with the average bonding distances being 2.0, 2.0, 2.1, and 2.0 A and (for His51...OH(2)) minimal distances less or equal to 2.5 A (20% probability of the time span), respectively. During the molecular dynamics simulation the NAD(+) ribose conformations have stabilized at the C2'-endo-C3'-exo or the C2'-endo conformations. With the C2'-endo conformation the first and second substates are able to persist for different time spans, while with the C2'-endo-C3'-exo conformation the only possible pathway involves the first substate. For both first and second substates the fluctuation of the distances between the ribose-OH protons and N epsilon 2 of His51 imidazole ring is partially contributed by the "windshield wiper" motion of the His51 imidazole ring. Since the imidazole of His-51 contributes only about 10-fold to activity, as estimated from the decrease in activity upon substitution with a Gln, there must be an alternate route for the proton to pass to solvent without going through this histidine. A third pathway involves ribose C3'-OH and Ile-269. In MD2, near attack conformers (NACs) for hydride transfer from PhCH(2)O(-) to NAD(+) represent approximately 60% of E.S conformers. The molecular dynamic study of MD3 at mildly basic pH reveals that reactive ground state conformers (NACs) for hydride transfer from NADH to PhCHO amount to 12 mol % of conformers. In MD3, anisotropic bending of the dihydronicotinamide ring of NADH (average value of alpha(c) = 4.0 degrees and alpha(n) = 0.5 degrees, respectively) is observed.

Replacement of the phosphodiester linkages of the polyanion DNA with guanidinium linkers provides the polycation deoxyribonucleic guanidine (DNG). Molecular dynamics studies to 1120 ps of the hybrid triplex and 1420 ps of the hybrid duplex formed from octameric DNG strands d(Tg)8 with a complementary DNA oligomer strand d(Ap)8 have been carried out with water explicitly as solvent and Na+Cl- as counterions under periodic boundary conditions using the CHARMM force field and Ewald summation method. The Watson−Crick and Hoogstein hydrogen-bonding patterns of the A/T tracts remained intact without any structural restraints for both hybrid duplex and triplex structures throughout the simulation. And for the hybrid duplex and triplex structures, both 5‘ and 3‘ ends were only partially frayed. In agreement with our previous thermodynamic study the hybrid triplex is more favorable than the hybrid duplex in the simulations. This conclusion is reached by the comparison of the extent of 5‘ end fraying and the bifurc...

Replacement of the phosphodiester linkages of the polyanion RNA with guanidinium linkers provides the polycation ribonucleic guanidine (RNG). Molecular dynamics studies to 1080 ps of the hybrid dup...

A photoelectronic switch of a multilevel memory device has been achieved using a meta-conjugated donor-bridge-acceptor (DBA) molecule. Such a DBA optoelectronic molecule responds to both the optical and electrical stimuli. The device exhibits good electrical bistable switching behaviors under dark, with a large ON/OFF ratio more than 10(6). In cooperation with the UV light, photoelectronic ternary states are addressable in a bistable switching system. On the basis of the CV measurement, charge carriers transport modeling, quantum chemical calculation, and absorption spectra analysis, the mechanism of the DBA memory is suggested to be attributed to the substep charge transfer transition process. The capability of tailoring photoelectrical properties is a very promising strategy to explore the multilevel storage, and it will give a new opportunity for designing multifunctional devices.

We have developed the first high-diffraction-efficiency two-dimensional (2-D) photonic crystals for molecular recognition and chemical sensing applications. We prepared close-packed 2-D polystyrene particle arrays by self-assembly of spreading particle monolayers on mercury surfaces. The 2-D particle arrays amazingly diffract 80% of the incident light. When a 2-D array was transferred onto a hydrogel thin film showing a hydrogel volume change in response to a specific analyte, the array spacing was altered, shifting the 2-D array diffraction wavelength. These 2-D array photonic crystals exhibit ultrahigh diffraction efficiencies that enable them to be used for visual determination of analyte concentrations.

The possibility of both Watson-Crick and Hoogsteen A{center dot}T pairs can result in a triple helical structure for d(T){sub 6}{center dot}d(A){sub 6}{center dot}d(T){sub 6} in solution. In the triple helix the Watson-Crick paired T strand can run antiparallel, while the Hoogsteen paired T strand can run parallel to the A strand. On the basis of 1D/2D NMR studies, we have characterized the structural properties of the triple helix in terms of (a) nature of H-bonding, (b) chain conformations and relative chain orientations, (c) location of triplets T{center dot}A{center dot}T with respect to the helix axis, and (d) effects of NaCl and MgCl{sub 2}. In addition, we experimentally demonstrate that a minor groove specific drug Dst2 (a distamycin analogue) can bind to the triple helix. We show that the nature of thermal transition is altered by Dst2 binding; i.e., the host triple helix shows triple {yields} coil (monophasic) transition in the absence of Dst2, while in its presence the helix shows a triplex {yields} duplex {yields} coil (biphasic) transition.

Four three-dimensionally architectured molecules 1a−d with spiro-annulated structural features were facilely developed. 1a and 1b form uniform and amorphous films via spin-coating due to their rigid three-dimensional architecture. The PL spectra of 1a−d exhibit excellent thermal stability upon air annealing. Their blue color integrity remained after continuous annealing for 12 h at 200 °C in the air. OLED fabrication reveals that all 1a−d exhibit pure blue EL performance and good color integrity at different operating voltages.