Synthesis,Magnetic Properties,and STM Spectroscopy of Cobalt(II) Cubanes [CoII4(Cl)4(HL)4]

Reaction of cobalt(II) chloride hexahydrate with N‐substituted diethanolamines H₂L^2–4 ( 3 ) in the presence of LiH in anhydrous THF leads under anaerobic conditions to the formation of three isostructural tetranuclear cobalt(II) complexes [Co^II₄(Cl)₄(HL^2–4)₄] ( 4 ) with a [Co₄(μ₃‐O)₄]⁴⁺ cubane core. According to X‐ray structural analyses, the complexes 4 a , c crystallize in the tetragonal space group I4₁/a, whereas for complex 4 b the tetragonal space group P$\bar 4$ was found. In the solid state the orientation of the cubane cores and the formation of a 3D framework were controlled by the ligand substituents of the cobalt(II) cubanes 4 . This also allowed detailed magnetic investigations on single crystals. The analysis of the SQUID magnetic susceptibility data for 4 a gave intramolecular ferromagnetic couplings of the cobalt(II) ions (J₁≈20.4 K, J₂≈7.6 K), resulting in an S=6 ground‐state multiplet. The anisotropy was found to be of the easy‐axis type (D=?1.55 K) with a resulting anisotropy barrier of Δ≈55.8 K. Two‐dimensional electron‐gas (2DEG) Hall magnetization measurements revealed that complex 4 a is a single‐molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep‐rate dependencies below a blocking temperature of about 4.4 K. The hysteresis loops collapse at zero field owing to fast quantum tunneling of the magnetization (QTM). The structural and electronic properties of cobalt(II) cubane 4 a , deposited on a highly oriented pyrolytic graphite (HOPG) surface, were investigated by means of STM and current imaging tunneling spectroscopy (CITS) at RT and standard atmospheric pressure. In CITS measurements the rather large contrast found at the expected locations of the metal centers of the molecules indicated the presence of a strongly localized LUMO.     

The Langevin Hull: Constant pressure and temperature dynamics for non-periodic systems

We have developed a new isobaric-isothermal (NPT) algorithm which applies an external pressure to the facets comprising the convex hull surrounding the system. A Langevin thermostat is also applied to the facets to mimic contact with an external heat bath. This new method, the "Langevin Hull", can handle heterogeneous mixtures of materials with different compressibilities. These systems are problematic for traditional affine transform methods. The Langevin Hull does not suffer from the edge effects of boundary potential methods, and allows realistic treatment of both external pressure and thermal conductivity due to the presence of an implicit solvent. We apply this method to several different systems including bare metal nanoparticles, nanoparticles in an explicit solvent, as well as clusters of liquid water. The predicted mechanical properties of these systems are in good agreement with experimental data and previous simulation work.     

Rapid synthesis of 1-deoxygalactonojirimycin using a carbamate annulation

A remarkably efficient synthesis of the biologically important iminosugar 1-deoxygalactonojirimycin (DGJ) is presented. Key to this strategy is the development of a novel carbamate annulation reaction that favours formation of a six-membered carbamate-containing piperidine skeleton over its five-membered counterpart.     

Electron paramagnetic resonance detection of irradiated foodstuffs

This item deals with identification of irradiated foodstuffs by means of Electron Paramagnetic Resonance (EPR). EPR is the most accurate method for such routine applications since radicals are stabilized for a long time in all (part of) foods which are in solid and dry state; consequently, EPR can be applied to meat and fish bones, fruit and relative products (from vegetal origin), seafoods, etc.     

A helium diffraction study of the p(2 × 2) phase of oxygen on Pd(100)

The p (2 × 2) ordered structure of oxygen on Pd(100) was investigated with He diffraction, Best-fit intensity calculations of the very rich diffraction spectra yield a corrugation amplitude of 0.68 Å for the oxygen adatom hills, and require the oxygens to be located in the fourfold coordinated hollows. Surface charge-density calculations were performed in analogy to the well-studied O/Ni(100) system by superposition of atomic charge densities, taking into account the oxygen adatoms in a singly negative state. The corrugation amplitude measured was reproduced with the oxygens ～ 0.9 Å above the topmost palladium layer.     

Kinetics of the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one under simulated atmospheric conditions

Relative rate coefficients for the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one have been determined at 298 K and atmospheric pressure by the relative rate technique. OH radicals were generated by the photolysis of methyl nitrite in synthetic air mixtures containing ppm levels of nitric oxide together with the test and reference substrates. The concentrations of the test and reference substrates were followed by gas chromatography. Based on the value k(OH + cyclohexene) = (6.77 ± 1.35) × 10^?11 cm³ molecule^?1 s^?1, rate coefficients for k(OH + 3‐methyl‐2‐cyclohexen‐1‐one) = (3.1 ± 1.0) × 10^?11 and k(OH + 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one) = (2.4 ± 0.7) × 10^?11 cm³ molecule^?1 s^?1 were determined. To test the system we also measured k(OH + isoprene) = (1.11 ± 0.23) × 10^?10 cm³ molecule^?1 s^?1, relative to the value k(OH + (E)‐2‐butene) = (6.4 ± 1.28) × 10^?11 cm³ molecule^?1 s^?1. The results are discussed in terms of structure–activity relationships, and the reactivities of cyclic ketones formed in the photo‐oxidation of monoterpene are estimated. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 7–11, 2002     

The synthesis of the molecular chaperone 2,5-dideoxy-2,5-imino-d-altritol via diastereoselective reductive amination and carbamate annulation

The iminosugar 2,5-dideoxy-2,5-imino-d-altritol (DIA, 2) is a powerful competitive inhibitor of α-galactosidase A and has shown much promise as a pharmacological chaperone for the treatment for Fabry disease. Notwithstanding, syntheses of DIA are in want of optimisation. Accordingly, we report on the total synthesis of DIA in 7 steps and in 22% overall yield from readily available d-tagatose. This is the shortest and most efficient synthesis of DIA to date, with key steps in our synthetic strategy including a diastereoselective reductive amination and an I₂-mediated carbamate annulation.     

A TIME SERIES APPROACH TO STOCK-RECRUITMENT ANALYSIS: TRANSFER FUNCTION NOISE MODELLING

Perceived relationships between stock size and recruitment have long been a corner-stone of fisheries management. These relationships are often used to design harvest strategies for ensuring that sufficient spawning stock exists to generate desired levels of recruitment in subsequent years. However, existing models fail to recognize and exploit the autocorrelation structure of both the recruitment and stock time series. The time series approach to modelling stock and recruitment presented in this paper takes this autocorrelation structure into account. The performance of the time series model is compared to existing stock-recruitment models using North Sea herring and Pacific halibut data.     

A simple relation between bulk and surface properties of nuclear matter

Starting from a previously derived relation between the derivatives of the bulk nucleon energy e(n_c) and the surface tension σ(n_c) with respect to the central density n_c we obtain a simple model-independent relation between the values of n_c, σ(n_c), the surface parameter t and the bulk modulus K_∞ at saturation. This relation is checked for values obtained in ETF calculations. K_∞=230 MeV is calculated from the well-known experimental values of n₀, σ₀ and t₀.