Mechanically robust 3D graphene macroassembly with high surface area

We report the synthesis of a three-dimensional (3D) macroassembly of graphene sheets with electrical conductivity (～10(2) S m(-1)) and Young's modulus (～50 MPa) orders of magnitude higher than those previously reported, super-compressive deformation behavior (～60% failure strain), and surface areas (>1300 m(2) g(-1)) approaching theoretically maximum values.     

Widely tunable midinfrared difference frequency generation in orientation-patterned GaAs pumped with a femtosecond Tm-fiber system

We demonstrate a midinfrared source tunable from 6.7 to 12.7 μm via difference frequency generation (DFG) in orientation-patterned GaAs, with 1.3 mW average output power. The input pulses are generated via Raman self-frequency shift of a femtosecond Tm-doped-fiber laser system in a fluoride fiber. We numerically model the DFG process and show good agreement between simulations and experiments. We use this numerical model to show an improved design using longer pump pulses.     

On the spontaneous induction of chirality in the preparation of Werner's complex cis-[CoBr(NH3)(en)2]Br2

The product obtained directly from the standard reaction to produce Werner's complex cis-[CoBr(NH3)(en)2]Br2 is shown, via structure determination from powder X-ray diffraction data, to be a racemic crystalline phase; implications of this observation in relation to previous reports that this reaction leads to significant enantiomeric excesses are discussed.     

Highly efficient one-step conversion of cyclohexane to adipic acid using single-site heterogeneous catalysts

A solid source of 'active' oxygen (acetylperoxyborate, APB), when dissolved in aqueous solution in the presence of a single-site microporous catalyst containing redox centres (Fe(III)AlPO-31, Mn(III)AlPO-5, Fe(III)AlPO-5), converts cyclohexane with high efficiency (ca. 88%) and exceptionally high selectivity (ca. 81%) to adipic acid at 383 K; this procedure is also effective in converting styrene to styrene oxide and -pinene and (+)-limonene to their corresponding epoxides.     

Ligand rearrangement reactions of Cr(CO)6 in alcohol solutions: experiment and theory

The ligand rearrangement reaction of Cr(CO)6 is studied in a series of alcohol solutions using ultrafast infrared spectroscopy and Brownian dynamics simulations. Excitation with 266 nm light gives Cr(CO)5 which is quickly solvated by a ligand from the bath. In alcohol solutions, solvation by an alkyl or hydroxyl site can occur; all alkyl bound complexes eventually rearrange to hydroxyl bound complexes. This rearrangement has been described using both an intermolecular (stochastic) and intramolecular (chainwalk) mechanism. Experiments alone do not allow for characterization of the mechanism, and therefore, theoretical calculations were carried out for the first time by modeling the ligand rearrangement as a diffusive walk along a potential defined by the different interaction possibilities. Experiments and simulations were carried out for Cr(CO)6 in 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 2-methylbutanol, and 3-methylbutanol. The trends in the theoretical and experimental rearrangement times are similar for all simulations carried out indicating that the two mechanisms have very similar ensemble behavior when bath effects are taken into account. The nature of the mechanism responsible for motion along the alcohol chain is not of primary importance in isolating the kinetic behavior because of the highly diffusive nature of the reaction. Future experimental and theoretical work will be directed at identifying a definitive assignment of the reaction mechanism.     

Determination of band curvatures by angle-resolved two-photon photoemission in thin films of C60 on Ag(111)

The thickness-dependent interfacial band structure was determined for thin films of C(60) on Ag(111) by angle-resolved two-photon photoemission spectroscopy. Dispersions of molecular-orbital derived bands (HOMO, LUMO+1, and LUMO+2) were acquired, and limits were placed on their possible effective masses. A group theoretic approach is also incorporated to further understand the properties of these states. The HOMO, LUMO+1, and LUMO+2 bands possess (best-fit) effective masses of -7 m(e), -7 m(e), and -12 m(e), respectively. These values are consistent with theoretical calculations, averaged over the closely spaced subbands for each state, and provide practical limits on the effective fundamental charge-transport properties of C(60) films.     

Atomic and molecular parity nonconservation and sum frequency generation solutions to the ozma problem

Two Ozma problems are defined. Parity nonconservation is necessary for their solutions. Both problems may be solved by beta decay or atomic optical activity. Atomic and molecular sum frequency generation is chosen, as it supplies rich methods of effecting "gedanken" solutions to the Ozma problems. A new method of measuring a parameter manifesting molecular parity violations is advanced.     

19-electron intermediates in the ligand substitution of CpW(CO)3* with a Lewis base

The photochemical reactions of [CpW(CO)3]2 with the Lewis base P(OMe)3 are examined on the nanosecond and microsecond time scales using step-scan FTIR spectroscopy. Photolysis at 532 nm produces the 17-electron (17e) radicals CpW(CO)3*, which are in equilibrium with the 19-electron (19e) radicals CpW(CO)3P(OMe)3* on the nanosecond time scale. The reactions of the 19e radical are directly observed for the first time; the major reaction pathway is spontaneous loss of a carbonyl to form the 17e species CpW(CO)2P(OMe)3*, with a barrier of 7.6 +/- 0.3 kcal/mol for this process. The minor reaction pathway (<20%) at this concentration of P(OMe)3 (85 mM) is disproportionation to form the products CpW(CO)3P(OMe)3+ and CpW(CO)3-. On the microsecond time scale, the 17e radicals CpW(CO)2P(OMe)3* dimerize to form the ligand substitution product [CpW(CO)2P(OMe)3]2. These results indicate that the 19e species is a stable intermediate rather than transition state in the ligand substitution reaction, and this type of reactivity is likely to be typical of 17e organometallic radicals which undergo associative substitution mechanisms.     

NMR studies of organic polymorphs and solvates

This review article describes the applications of NMR to the study of polymorphs and related forms (solvates) of organic (especially pharmaceutical) compounds, for which it is of increasing academic and practical importance. The nature of the systems covered is briefly introduced, as are the techniques constituting solid-state NMR. The methodologies involved are then reviewed under a number of different headings, ranging from spectral editing through relaxation times to shielding tensors and NMR crystallography. In each case the relevant applications are described. Whilst most studies concentrate on structural matters, motional effects are not neglected. A special section discusses studies of solvates (especially hydrates), and another reviews quantitative analysis.