Intramolecular CH Activation and Metallacycle Aromaticity in the Photochemistry of [FeFe]‐Hydrogenase Model Compounds in Low‐Temperature Frozen Matrices

The [FeFe]‐hydrogenase model complexes [(μ‐pdt){Fe(CO)₃}₂], [(μ‐edt){Fe(CO)₃}₂], and [(μ‐mdt){Fe(CO)₃}₂], where pdt=1,3‐propanedithiolate, edt=1,2‐ethanedithiolate, and mdt=methanedithiolate, undergo wavelength dependent photodecarbonylation in hydrocarbon matrices at 85 K resulting in multiple decarbonylation isomers. As previously reported in time‐resolved solution photolysis experiments, the major photoproduct is attributed to a basal carbonyl‐loss species. Apical carbonyl‐loss isomers are also generated and may undergo secondary photolysis, resulting in β‐hydride activation of the alkyldithiolate bridge, as well as formation of bridging carbonyl isomers. For [(μ‐bdt){Fe(CO)₃}₂], (bdt=1,2‐benzenedithiolate), apical photodecarbonylation results in generation of a 10 π‐electron aromatic FeS₂C₆H₄ metallacycle that coordinates the remaining iron through an η⁵ mode.     

Structure and fragmentation of dimethyl methylphosphonate and trimethyl phosphite

The structures and fragmentation pathways of two isomeric organophosphorus esters, dimethyl methylphosphonate (DMMP) and trimethyl phosphite (TMP) have been determined. The long-lived, low-energy molecular ions of DMMP were found to undergo a keto-to-enol isomerization prior to collision-induced dissociation. This isomerization was established through the comparison of the collision spectra from DMMP, TMP, isotopically labeled DMMP and a model precursor ion. Electron ionization and charge exchange reactions were used to study the isomerization as a function of the internal energy of the molecular ion. The structure of the TMP molecular ion retained the structure of the neutral molecule. The daughter ion spectra of the isomeric fragment ions from DMMP and TMP were used to infer the fragment ion structures. Negative ions of DMMP and TMP were also studied, and their collision spectra were found to be indistinguishable.     

Nonwetting of He and dilute He–He mixtures on Cs

For pure ⁴He on Cs a nonwet phase exists below ≈2 K but for dilute ³He–⁴He mixtures the wetting is reentrant. Measurements of the contact angle with dilute mixtures of liquid helium on Cs can be explained in detail in terms of ³He states together with ripplons at the Cs–He mixture interface, but it is impossible to account for the lower wetting temperatures or contact angles with only ³He states or ripplons. We discuss the influence of surface roughness of the Cs on the contribution of interface excitations to the free energy and suggest that the variety of contact angles found with different samples of Cs is due mainly to their degree of roughness.     

Photochemically Induced Intramolecular Six‐Electron Reductive Elimination and Oxidative Addition of Nitric Oxide by the Nitridoosmate(VIII) Anion

UV photolysis of the nitridoosmate(VIII) anion, OsO₃N^?, in low‐temperature frozen matrices results in nitrogen–oxygen bond formation to give the Os^II nitrosyl complex OsO₂(NO)^?. Photolysis of the Os^II nitrosyl product with visible wavelengths results in reversion to the parent Os^VIII complex. Formally a six‐electron reductive elimination and oxidative addition, respectively, this represents the first reported example of such an intramolecular transformation. DFT modelling of this reaction proceeds through a step‐wise mechanism taking place through a side‐on nitroxyl Os^VI intermediate, OsO₂(η²‐NO)^?.     

The phase diagram of the system La2(SO4)3Ag2SO4

The phase diagram of the system La₂(SO₄)₃Ag₂SO₄ was studied by DTA, XRD, SEM, and optical methods. One double salt is formed at 67 mole% La₂(SO₄)₃ and this melts incongruently at 876±6°C. A eutectic is formed at 8 mole% La₂(SO₄)₃ and at a temperature of 618±3°C. Suppression of decomposition was effected by the sealed tube method, but some reference is made to experiments conducted with a flowing atmosphere of SO₃, SO₂ and O₂.     

Versatile single-shot background-free pulse duration measurement technique,for pulses of subnanosecond to picosecond duration

An extension of the noncollinear second-harmonic generation technique for pulse autocorrelation measurements is described. A diffraction grating is used to produce a tailored, expanded beam, with a differential time delay along its expanded axis. When this beam is combined with an inverted replica of itself at the frequency-doubling crystal, the monitored spatial profile of the generated second-harmonic beam gives directly the duration of the incident laser pulse. A time resolution of better than 1 ps is obtained at 500 nm, and a total measurement range of∼80 ps. The optical system here described enables the extension of the measurement range in a simple manner.     

Zeta potential and electroosmotic mobility in microfluidic devices fabricated from hydrophobic polymers: 1. The origins of charge

This paper combines new experimental data for electrokinetic characterization of hydrophobic polymers with a detailed discussion of the putative origins of charge at water-hydrophobe interfaces. Complexities in determining the origin of charge are discussed in the context of design and modeling challenges for electrokinetic actuation in hydrophobic microfluidic devices with aqueous working fluids. Measurements of interfacial charge are complicated by slip and interfacial water structuring phenomena (see Part 2, this issue). Despite these complexities, it is shown that (i) several hydrophobic materials, such as Teflon and Zeonor, have predictable electrokinetic properties and (ii) electrokinetic data for hydrophobic microfluidic systems is most consistent with the postulate that hydroxyl ion adsorption is the origin of charge.     

Identification of an anti-MRSA dihydrofolate reductase inhibitor from a diversity-oriented synthesis

The screening of a diversity-oriented synthesis library followed by structure-activity relationship investigations have led to the discovery of an anti-MRSA agent which operates as an inhibitor of Staphylococcus aureus dihydrofolate reductase.     

Quantum trajectories in complex space: one-dimensional stationary scattering problems

One-dimensional time-independent scattering problems are investigated in the framework of the quantum Hamilton-Jacobi formalism. The equation for the local approximate quantum trajectories near the stagnation point of the quantum momentum function is derived, and the first derivative of the quantum momentum function is related to the local structure of quantum trajectories. Exact complex quantum trajectories are determined for two examples by numerically integrating the equations of motion. For the soft potential step, some particles penetrate into the nonclassical region, and then turn back to the reflection region. For the barrier scattering problem, quantum trajectories may spiral into the attractors or from the repellers in the barrier region. Although the classical potentials extended to complex space show different pole structures for each problem, the quantum potentials present the same second-order pole structure in the reflection region. This paper not only analyzes complex quantum trajectories and the total potentials for these examples but also demonstrates general properties and similar structures of the complex quantum trajectories and the quantum potentials for one-dimensional time-independent scattering problems.