New Molybdenyl Iodates: Hydrothermal Preparation and Structures of Molecular K2MoO2(IO3)4 and Two-Dimensional β-KMoO3(IO3)

Two new molybdenyl iodates, K₂MoO₂(IO₃)₄ (1) and β-KMoO₃(IO₃) (2), have been prepared from the reactions of MoO₃ with KIO₄ and NH₄Cl at 180°C in aqueous media. The structure of 1 consists of molecular [MoO₂(IO₃)₄]²⁻ anions separated by K⁺ cations. The Mo(VI) centers are ligated by two cis-oxo ligands and four monodentate iodate anions. Both terminal and bridging oxygen atoms of the iodate anions form long ionic contacts with the K⁺ cations. β-KMoO₃(IO₃) (2) displays a two-dimensional layered structure constructed from ²_∞[(MoO₃(IO₃)]¹⁻ anionic sheets separated by K⁺ cations. These sheets are built from one-dimensional chains formed from corner-sharing MoO₆ octahedra that run along the b-axis that are linked together through bridging iodate groups. K⁺ cations separate the layers from one another and form long contacts with oxygen atoms from both the iodate anions and molybdenyl moieties. Crystallographic data: 1, monoclinic, space group C2/c, a=12.8973(9) Å, b=6.0587(4) Å, c=17.694(1) Å, β=102.451(1)°, Z=4, MoKα, λ=0.71073, R(F)=2.64% for 97 parameters with 1584 reflections with I>2σ(I); 2, monoclinic, space group P2₁/n, a=7.4999(6) Å, b=7.4737(6) Å, c=10.5269(8) Å, β=109.023(1)°, Z=4, MoKα, λ=0.71073, R(F)=2.73% for 83 parameters with 1334 reflections with I>2σ(I).     

Measurement of cell migration on surface-bound fibronectin gradients

A novel technique for the quantitative observation of cell migration along linear gradient substrates functionalized with adhesive proteins is presented. Gradients of the cell adhesion molecule fibronectin are generated by the cross diffusion of functionalizable alkanethiols on gold and characterized by X-ray photoelectron spectroscopy and surface plasmon resonance. Two distinct migration assays are described that characterize the movement of either sparsely populated noncontacting cells or a confluent monolayer of cells into free space. The drift speed of bovine aortic endothelial cells is measured and shown to increase along a fibronectin gradient when compared to a uniform control substrate using both assays. The results of these experiments establish reproducible conditions for studies of cell migration on gradients of surface-bound ligands.     

On the choice of active space orbitals in MCSCF calculations

We describe a procedure which may be used to aid selection of the active space in multiconfigurational self-consistent field (MCSCF) calculations for general chemical systems. Starting from a restricted Hartree-Fock calculation, we define a hierarchy of interacting virtual orbitals for every occupied orbital. The most strongly interacting orbitals are then taken to constitute the active space in a configuration interaction (CI) calculation. The natural orbital occupation numbers obtained from the CI calculation are then used to choose the active space to be used in a subsequent MCSCF calculation. We illustrate our method on a number of systems (Li₂, B₂, C₂, carbonyl oxide and the transition state for oxidation of H₂S by dioxirane). In all these cases, ‘intuitive’ active spaces are inadequate, as are active spaces derived from the natural orbitals of unrestricted Hartree-Fock calculations.     

Response Characteristics of Arsenic-Sensitive Bioreporters Expressing the gfp Reporter Gene

This paper describes the development of an analytical technique for arsenic analyses that is based on genetically-modified bioreporter bacteria bearing a gene encoding for the production of a green fluorescent protein (gfp). Upon exposure to arsenic (in the aqueous form of arsenite), the bioreporter production of the fluorescent reporter molecule is monitored spectroscopically. We compared the response measured as a function of time and concentration by steady-state fluorimetry (SSF) to that measured by epi-fluorescent microscopy (EFM). SSF is a bulk technique; as such it inherently yields less information, whereas EFM monitors the response of many individual cells simultaneously and data can be processed in terms of population averages or subpopulations. For the bioreporter strain used here, as well as for the literature we cite, the two techniques exhibit similar performance characteristics. The results presented here show that the EFM technique can compete with SSF and shows substantially more promise for future improvement; it is a matter of research interest to develop optimized methods of EFM image analysis and statistical data treatment. EFM is a conduit for understanding the dynamics of individual cell response vs. population response, which is not only a matter of research interest, but is also promising in the practical terms of developing micro-scale analysis.     

Thermoplastic polyurethanes containing 12-hydroxymethylabietanol

Thermoplastic polyurethane elastomers incorporating the resin acid-derived 12-hydroxymethylabietanol (12-HMA) were prepared, and some physical properties are reported. A polyester macroglycol was prepared from 12-HMA, adipic acid, and ethylene glycol. This macroglycol then was combined with either poly(tetramethylene adipate) glycol (PTAd) or poly(ethylene adipate) glycol (PEAd) and 1,4-butanediol to give a glycol blend of 300 average hydroxyl equivalent weight (OHE). The glycol mixture then was combined with diphenylmethane 4,4′-diisocyanate (MDI) (NCO/OH = 1.0) to give urethane polymers soluble in tetrahydrofuran. Polymers were prepared with 0, 5, 10, 15, 20, and 25%, by weight, 12-HMA with PTAd as the other macroglycol and with 0, 10, 15, and 20% 12-HMA with PEAd as the other macroglycol. At 15% 12-HMA, polymers were made from glycol mixtures having 275 and 350 average OHE to demonstrate the effect of changing the hard-segment concentration. The presence of 12-HMA is shown to have its maximum effect on tensile properties at 15–20% in the PTAd series and at 10% in the PEAd series. In general, this effect is an increase in tensile strength and modulus and a decrease in elongation when compared with a similar polymer without the 12-HMA.