Stabilisation of [Fe2(CO)9] and [Ru2(CO)9] bu substitution with bridging diphosphorus ligands

Reaction of [Fe₂(CO)₉] with a half molar amount of R₂PYPR₂ (Y = CH₂, R = Ph, Me, OMe or OPrⁱ; Y = N(Et), R = OPh, OMe or OCH₂; Y = N(Me), R = OPrⁱ or OEt) leads to the ready formation of a product which on irradiation with ultraviolet light rapidly decarbonylates to the heptacarbonyl derivative [Fe₂(μ-CO)(CO)₆{μ-R₂PYPR₂}]. Treatment of the latter with a slight excess of the appropriate ligand results, under photochemical conditions, in the formation of the dinuclear pentacarbonyl complex [Fe₂(μ-CO)(C))₄{μ-R₂PYPR₂}₂] but under thermal conditions in the formation of the mononuclear species [Fe(CO)₃{R₂PYPR₂}]. Reaction of [Ru₃(CO)₁₂] with an equimolar amount of (RO)₂PN(R′)P(OR)₂ (R′ = Me, R = Prⁱ or Et; R′ = Et, R = Ph or Me) under either thermal or photochemical conditions produces [Ru₃(CO)₁₀{μ-(RO)₂PN(OR)₂}] which reacts further with excess (RO)₂PN(R′)P(OR)₂ on irradiation with ultraviolet light to afford the dinuclear compound [Ru₂(μ-CO)(CO₄{μ-(RO)₂PN(R′)P(OR)₂}₂]. The molecular structure of [Ru₂(μ-CO)(CO)₄{μ-(MeO)₂PN(Et)P(OMe)₂}₂], which has been determined by X-ray crystallography, is described.     

BROMOC-D: Brownian Dynamics/Monte-Carlo Program Suite to Study Ion and DNA Permeation in Nanopores

A theoretical framework is presented to model ion and DNA translocation across a nanopore confinement under an applied electric field. A combined Grand Canonical Monte Carlo Brownian Dynamics (GCMC/BD) algorithm offers a general approach to study ion permeation through wide molecular pores with a direct account of ion-ion and ion-DNA correlations. This work extends previously developed theory by incorporating the recently developed coarse-grain polymer model of DNA by de Pablo and colleagues [Knotts, T. A.; Rathore, N.; Schwartz, D. C.; de Pablo, J. J. J. Chem. Phys. 2007, 126] with explicit ions for simulations of polymer dynamics. Atomistic MD simulations were used to guide model developments. The power of the developed scheme is illustrated with studies of single-stranded DNA (ss-DNA) oligomer translocation in two model cases: a cylindrical pore with a varying radius and a well-studied experimental system, the staphylococcal α-hemolysin channel. The developed model shows good agreement with experimental data for model studies of two homopolymers: ss-poly(dA)(n) and ss-poly(dC)(n). The developed protocol allows for direct evaluation of different factors (charge distribution and pore shape and size) controlling DNA translocation in a variety of nanopores.     

Fluorescence study of arene probe microenvironment in the intraparticle void volume of zeolites interfaced with bathing polar solvents

Fluorescence methodologies have been utilized to examine micropolarity, intramolecular motion, and singlet quenching in the intraparticle void volume of zeolites X, Y, and ultrastable Y (USY) interfaced with bathing polar solvents. Micropolarity was assessed from the 3-to-1 band ratio (III/I) of the fluorescence spectrum of pyrene (PY) and from lambda(max) of the fluorescence spectrum of 1-pyrenecarboxaldehyde (1-PCA). In zeolites bathed in anhydrous solvents, both PY and 1-PCA reported increased micropolarity according to the trend USY < bulk solvent < NaX approximately NaY. For example, in NaY (USY), III/I ranged from 0.44 (0.98) in acetonitrile to 0.52 (1.34) in n-hexanol, compared to 0.60, 1.06, and 1.62 in bulk acetonitrile (ACN), n-hexanol, and n-hexane, respectively. The polarity studies reveal that the ionic nature of NaX and NaY and the hydrophobic nature of USY strongly influence the microenvironment of the arene despite the presence of desorbing polar solvents. Constraints on intramolecular motion were examined in polar-solvated NaX through measurements of the fluorescence lifetime of trans-stilbene. Lifetimes ranged from 113 ps in NaX-ACN to 671 ps in NaX-tert-butyl alcohol. The latter value is close to that observed in bulk glycerol. Diffusion-controlled quenching of PY fluorescence by O2 and a series of nitrocompounds dissolved in solvents bathing the zeolite was examined by a time-resolved approach. For all of the quenchers and solvents studied, quenching was more efficient in USY compared to NaX and NaY. Interestingly, the rate of O2 quenching in USY-MeOH was only 12 times lower than that in bulk MeOH. In contrast, in NaY-MeOH and NaX-MeOH the rate of O2 quenching was too low to be measured. The rate constants in these systems were therefore taken as the rate constant for diffusion-controlled quenching of trapped electrons measured previously. These values were 600 times and 10(5) times lower than the rate of fluorescence quenching in USY-MeOH, respectively. The O2 quenching studies show that dispersive interactions of polar solvents with the cavity walls dominate in USY because of the hydrophobic nature of the USY surface. In NaX and NaY, stronger ion-dipole and hydrogen bonding interactions dominate and lead to more restricted access and lowered quenching efficiency. Perrin (or static) quenching of pyrene fluorescence was also examined to infer the concentration of nitromethane (NM) in the void volume of NaX and NaY bathed in MeOH, ACN, or H2O. The results indicate that access of NM to the interior of NaY is more inhibited in ACN compared to MeOH, presumably because of the higher dipole moment of ACN and its resulting stronger association with the zeolite surface. At similar levels of static quenching equated to a similar NM concentration in the zeolite, dynamic quenching by NM varied by no more than a factor of 2 in all systems compared. This implies that the rate of NM diffusion in solvated zeolite interiors is similar regardless of zeolite or solvent properties. In contrast to O2 diffusion in zeolites, NM exhibits a high dipole moment and can therefore migrate through polar-solvated zeolite apertures by adsorbing to the zeolite. Overall, the results of this study show a close relationship between the behavior of probes and quenchers in the confines of polar-solvated zeolite interiors and the chemical properties of the zeolite. Differences between weakly and strongly interacting surfaces are revealed clearly in the results.     

Probability distribution analysis of single-molecule fluorescence anisotropy and resonance energy transfer

Analysis of anisotropy in single-molecule fluorescence experiments using the probability distribution analysis (PDA) method is presented. The theory of anisotropy-PDA is an extension of the PDA theory recently developed for the analysis of F?rster resonance energy transfer (FRET) signals [Antonik, M.; et al. J. Phys. Chem. B 2006, 110, 6970]. The PDA method predicts the shape of anisotropy histograms for any given expected ensemble anisotropy, signal intensity distribution, and background. Further improvements of the PDA theory allow one to work with very low photon numbers, i.e., starting from the level of background signal. Analysis of experimental and simulated data shows that PDA has the major advantage to unambiguously distinguish between shot noise broadening and broadening caused by heterogeneities in the sample. Fitting of experimental histograms yields anisotropy values of individual species, which can be directly compared with those measured in ensemble experiments. Excellent agreement between the ensemble data and the results of PDA demonstrates a good absolute accuracy of the PDA method. The precision in determination of mean values depends mainly on the total number of photons, whereas the ability of PDA to detect the presence of heterogeneities strongly depends on the time window length. In its present form PDA can be also applied to computed fluorescence parameters such as FRET efficiency and scatter-corrected fluorescence anisotropy. Extension of the PDA theory to low photon numbers makes it possible to apply PDA to dynamic systems, for which high time resolution is required. In this way PDA is developed as a sensitive tool to detect biomolecular heterogeneities in space and time.     

Disjunctivity and Alternativity in Projection Logics

We study the notions of disjunctivity and alternativity of orthomodular posets inthe context of orthoprojections or skew projections in C ^*-algebras.     

基于风洞试验的不同坡度多跨锯齿屋面风压特性研究

多跨锯齿屋面因其具有跨度大、结构轻盈的特点成为典型的风灾易损结构.目前国内规范对锯齿屋盖的风荷载规定较为粗略,简单给定了统一的风压系数参考值,在实际工程应用中具有一定的局限性.本文以某4跨锯齿房屋为研究对象,通过风洞试验测试了15°、21°、26°、30°和40°等5种不同屋面坡度对锯齿屋盖风压特性的影响.试验结果表明...