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In situ transmission electron microscopy based nanopillar compression is utilized to investigate the mechanical properties of zinc dialkyldithiophosphate (ZDDP) tribological films. Small scale testing provides localized insights into the properties of ZDDP films that spatially vary in composition at the nanoscale. Large variations in yield strength, between 0.82 and 4.8 GPa, are measured and correlated with local chemistry changes. Lower density regions of the film that tend to be carbon-rich have lower yield stresses, than higher density regions that tend to be zinc-, iron-, and sulfur-rich. It is hypothesized that the strong compositional dependence in mechanical properties at the nanoscale is an important factor contributing to the efficacy of ZDDP as an antiwear tribological film.

Knowledge of their bulk physical properties often guides selection of appropriate tribological coating materials. However, these properties as well as the microstructure evolve dramatically under the extreme conditions imposed during mechanical wear. The dynamic response ultimately governs the material’s wear performance; thus, understanding the dynamic evolution of the system is critical. This work characterizes the change in mechanical properties and microstructure as a function of wear cycles in model MoS2 films using a combination of nanowear testing, transmission electron microscopy, and site-specific nanopillar compression. Notably, mechanical wear enhances the mechanical properties of the MoS2 while simultaneously evolving a microstructure that reduces the coefficient of friction and wear rate. We hypothesize that this self-optimizing behavior underpins the exceptional lubricity and antiwear performance of MoS2.

An aerosol-assisted chemical vapor method leading to iron sulfide scales of varying phases and morphologies by reaction of pipeline steels with sulfur compounds has been developed. This chemical vapor reaction methodology is useful for generating model iron sulfide scales pertinent to the interaction of sour crude oil with piplelines used in the oil and gas industry.

A series of methylating reagents: methanol, dimethylether and dimethylcarbonate, have been evaluated for their ability to methylate 2,3-dimethylbut-2-ene to yield triptyls (a mixture of triptane and triptene). The results presented highlight that dimethylcarbonate is a far superior methylating agent compared to methanol or dimethylether, providing a higher yield of triptyls. .

Knowledge of their bulk physical properties often guides selection of appropriate tribological coating materials. However, these properties as well as the microstructure evolve dramatically under the extreme conditions imposed during mechanical wear. The dynamic response ultimately governs the material's wear performance; thus, understanding the dynamic evolution of the system is critical. This work characterizes the change in mechanical properties and microstructure as a function of wear cycles in model MoS

Novel single-site platinum catalysts have been synthesized by reacting platinum(II) organometallics with partially dehydroxylated silica. The resulting materials have been characterized by various methods such as IR, MAS NMR, and EXAFS. Further, the single-site platinum catalysts were calcined in air to remove the ligand and produce nanosized platinum particles, that were characterized by TEM and H2 chemisorption. All catalysts were tested for the hydrogenation of toluene. The single-site platinum catalysts were less active than a commercial Pt/SiO2 catalyst with comparable platinum loading, and this has been ascribed to ligand effects. Conversely, the nanosized platinum catalysts were more active than the commercial Pt/SiO2 catalyst due to their high dispersion and small particle sizes.

Robust, bifunctional catalysts comprising Rh(CO)(Xantphos) exchanged phosphotungstic acids of general formulas [Rh(CO)(Xantphos)]+n[H3–nPW12O40]n− have been synthesized over silica supports which exhibit tunable activity and selectivity toward direct vapor phase methanol carbonylation. The optimal Rh:acid ratio = 0.5, with higher rhodium concentrations increasing the selectivity to methyl acetate over dimethyl ether at the expense of lower acidity and poor activity. On-stream deactivation above 200 °C reflects Rh decomplexation and reduction to Rh metal, in conjunction with catalyst dehydration and loss of solid acidity because of undesired methyl acetate hydrolysis, but can be alleviated by water addition and lower temperature operation.

Rhodium/iodide catalysts modified with the xantphos ligand are active for the homogeneous carbonylation of methanol to acetic acid using either pure CO or CO/H2. Residues from catalytic reactions contain a Rh(III) acetyl complex, [Rh(xantphos)(COMe)I2] (1), which was isolated and crystallographically characterized. The xantphos ligand in 1 adopts a “pincer” κ3-P,O,P coordination mode with the xanthene oxygen donor trans to the acetyl ligand. The same product was also synthesized under mild conditions from [Rh(CO)2I]2. Iodide abstraction from 1 in the presence of donor ligands (L = MeCN, CO) gives the cationic acetyl species [Rh(xantphos)(COMe)I(L)]+, whereas in CH2Cl2 migratory CO deinsertion gives [Rh(xantphos)(Me)I(CO)]+ (4), which reacts with H2 to liberate methane, as observed in catalytic reactions using syngas. A number of Rh(I) xantphos complexes have been synthesized and characterized. Oxidative addition of methyl iodide to the cation [Rh(xantphos)(CO)]+ is very slow but can be catalyzed by additi...

Direct observations on nanopillars composed of molybdenum disulfide (MoS2) and chromium-doped MoS2 and their response to compressive stress have been made. Time-resolved transmission electron microscopy (TEM) during compression of the submicrometer diameter pillars of MoS2- and Cr-doped MoS2 (Cr: 0, 10, and 50 at %) allow the deformation process of the material to be observed and can be directly correlated with mechanical response to applied load. The addition of chromium to the MoS2 changed the failure mode from plastic deformation to catastrophic brittle fracture, an effect that was more pronounced as chromium content increased.

Rhodium is used for a number of large processes that rely on homogeneous rhodium-catalyzed reactions, for instance rhodium-catalyzed hydroformylation of alkenes, carbonylation of methanol to acetic acid and hydrodesulfurization of thiophene derivatives (in crude oil). Many laboratory applications in organometallic chemistry and catalysis involve organorhodium chemistry and a wealth of rhodium coordination compounds is known. For these and other areas, 103Rh NMR spectroscopy appears to be a very useful analytical tool. In this review, most of the literature concerning 103Rh NMR spectroscopy published from 1989 up to and including 2003 has been covered. After an introduction to several experimental methods for the detection of the insensitive 103Rh nucleus, a discussion of factors affecting the transition metal chemical shift is given. Computational aspects and calculations of chemical shifts are also briefly addressed. Next, the application of 103Rh NMR in coordination and organometallic chemistry is elaborated in more detail by highlighting recent developments in measurement and interpretation of 103Rh NMR data, in relation to rhodium-assisted reactions and homogeneous catalysis. The dependence of the 103Rh chemical shift on the ligands at rhodium in the first coordination sphere, on the complex geometry, oxidation state, temperature, solvent and concentration is treated. Several classes of compounds and special cases such as chiral rhodium compounds are reviewed. Finally, a section on scalar coupling to rhodium is provided. Copyright © 2004 John Wiley & Sons, Ltd.

A combined single-source precursor approach has been developed for the deposition of thin films of Cr-doped molybdenum disulfide (MoS2) by aerosol-assisted chemical vapor deposition (AACVD). Tris(diethyldithiocarbamato)chromium(III) can also be used for the deposition of chromium sulfide (CrS). Films have been analyzed by a range of techniques including scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, and powder X-ray diffraction (pXRD) to elucidate film morphology, composition, and crystallinity. The presence of Cr in the MoS2 films produces a number of striking morphological, crystallographic, and nanomechanical changes to the deposited films. The chromium dopant appears to be uniform throughout the MoS2 from the scanning transmission electron microscopy (STEM) EDX spectrum imaging of nanosheets produced by liquid-phase exfoliation of the thin films in N-methyl-2-pyrollidone.

Compressed and stretched polyacrylamide hydrogels previously have been shown to offer a robust method for aligning proteins. A simple, funnel-like apparatus is described for generating uniformly stretched hydrogels. For prolate-shaped proteins, gels stretched in the direction of the magnetic field yield two-fold larger alignment than gels compressed to the same aspect ratio in this direction. Empirically, protein alignment is found to be proportional to (c−2.3) 2 [(do/dN) 3 -1], where do and dN are the diameters of the cylindrical gels before and after stretching, respectively, and c is the polyacrylamide weight fraction in percent. Low gel densities, in the 4–7% range, are found to have minimal effects on macromolecular rotational correlation times, τc, and no effect of the compression ratio on τc could be discerned over the range studied (do/dN ≤ 1.4). Application is demonstrated for a sample containing the first Ig-binding domain of protein G, and for a detergent-solubilized peptide.

Gradient-corrected and hybrid variants of density-functional theory are used to compute the geometries and 99Ru chemical shifts of RuO4, [RuCp2], [K4Ru(CN)6], [Ru3(CO)12], [Ru(CO)3X3]- (X=Cl, I), [Ru(CO)2Cl4]2-, [Ru(bipy)3]2+, and [Ru(CO)2(iPr-DAB)(X)(Y)] [XY= Cl2, I2, MeCl, MeI, or (SnMe3)2]. For this set of compounds, substituent effects on delta(99Ru) are somewhat underestimated with the BPW91 pure density functional but are described well by the B3LYP hybrid functional, which can also be used to reproduce empirical trends in electric field gradients (EFGs) at the Ru nucleus qualitatively. In the [Ru(CO)2(iPr-DAB)XY] series, trends in the computed EFGs parallel those in the observed 99Ru NMR linewidths, in accordance with the quadrupolar relaxation mechanism expected for this nucleus. For this series of compounds, the use of X-ray-derived geometries affords a worse correlation between calculated EFGs and experimental linewidths than does the use of optimized geometries.

We demonstrate that hetero- and homonuclear NMR spectra of cyclosporin A and pancreatic trypsin inhibitor (BPTI) can be recorded at room temperature in liquid CO2, a medium of very low viscosity, which has been reported to have no adverse effect on molecular structure or activity of several proteins. Rotational diffusion of cyclosporin A in a CO2/methanol mixture is approximately three-fold faster than in chloroform. Translational diffusion for BPTI, dissolved in liquid CO2 by co-adding detergent and trifluoroethanol, is measured to be faster than in water, but rotational diffusion is not. Development of improved detergents is anticipated to make feasible the encapsulation of most biological macromolecules in water-containing reverse micelles, which can be suspended in a wide array of apolar, supercritical or near-critical solvents.

An outline of the use of supercritical solvents in NMR spectroscopy is given, with emphasis on instrumentation and applications. Especially the advantages of the low viscosity of supercritical solvents, resulting in appreciable reductions of the line widths of NMR resonances of quadrupole nuclei (I > 1/2), are discussed. The main focus of the review is on the development of transition metal and 14N NMR spectroscopy, to aid the analysis of transition metal complexes. The choices of the supercritical solvent and ligand modifications are discussed in the context of solubility and reduction of the line width.

An outline of the use of supercritical solvents in NMR spectroscopy is given, with emphasis on instrumentation and applications. Especially the advantages of the low viscosity of supercritical solvents, resulting in appreciable reductions of the line widths of NMR resonances of quadrupole nuclei (I > 1/2), are discussed. The main focus of the review is on the development of transition metal and 14N NMR spectroscopy, to aid the analysis of transition metal complexes. The choices of the supercritical solvent and ligand modifications are discussed in the context of solubility and reduction of the line width.

The morphologies of three dilute liquid crystalline phases, which are widely used for biological NMR spectroscopy, are investigated by the study of tracer self-diffusion. The aqueous liquid crystalline media investigated include the common phospholipid bicelle medium, a phase consisting of a mixture of pentaethyleneglycol mono dodecyl ether and hexanol, and a medium containing cetylpyridinium bromide and hexanol. Threonine and water were used as tracer molecules for probing the aqueous environment, and tetramethylsilane (TMS) was for probing the lipophilic environment. Pulsed field gradient NMR was used to measure tracer self-diffusion rates in three orthogonal directions. Although results for the water-soluble tracers in bicelle media do not contradict the widely accepted disk-shaped bicelle model, the high TMS diffusion rate observed in the bilayer plane requires extensive transient edge-to-edge contacts of such disks. This morphology is essentially that of a heavily perforated lamellar bilayer phase and explains why this medium remains liquid crystalline well below the Onsager limit for disk-shaped nematogens. Below 25 degrees C, a bicelle mixture consisting of dimyristoyl phosphatidyl choline and dihexanoyl phosphatidyl choline remains isotropic, but tracer diffusion obstruction indicates that the particles are significantly oblate. The diffusion anisotropy in the penta(ethyleneglycol) mono dodecyl ether liquid crystals confirms the previously proposed alpha-lamellar phase. However, weak inhibition of aqueous-phase self-diffusion in the z direction points to the presence of bridge- or caplike obstructions, and the bilayers appear slightly permeable to water. If the previously proposed concentric cylinder superstructure of bilayers applies, the diffusion data indicate that the most outer cylinder must have a diameter greater than 50 microm. The tracer self-diffusion data for the cetylpyridinium bromide/hexanol medium is only compatible with a planar alpha-lamellar phase, with its local director orthogonal to the magnetic field, and a very large domain size over which the director remains parallel.

Appreciable decreases of the line widths of NMR resonances of the quadrupolar nuclei 14N, 53Cr, 59Co, 91Zr, and 95Mo have been obtained in supercritical solvents and in low-viscosity liquefied gases. Several α-diimines R1N=C(R2)−C(R2)=NR1 and their coordination compounds have been studied. Regarding the solubility of two α-diimines and some Cr, Zr, and Mo complexes it appears that the addition of small amounts of a modifier (acetone, CH2Cl2, THF) results in enhanced solubility of compounds without detrimental effects on the line widths. The use of HP NMR tubes (with and without pressure sensor) is very appropriate for measurements of NMR spectra under high pressure in supercritical fluids and liquefied gases of low viscosity. In several cases it appeared that the use of liquefied gases is more straightforward than the use of supercritical fluids, and gives similar or better results in terms of reduction of line widths.

The ruthenium(II) organometallic and coordination complexes of type Ru(X)(Y)(CO)2(i-Pr-DAB) (i-Pr-DAB = 1,4-diisopropyl-1,4-diaza-1,3-butadiene; X, Y = Cl, Br, I, Me, Et, i-Pr, neo-Pe, Ph3Sn, Me3Sn, Ph3Pb, Ph3Ge, Mn(CO)5, RuCp(CO)2) have been analyzed by means of 99Ru NMR spectroscopy. The 99Ru NMR resonances for these compounds are generally sharp, allowing scalar couplings to group 14 nuclei to be observed. Correlation times τc have been determined from NOE factors and 13C T1 values for selected compounds and were found to parallel the molecular weight of the compounds studied. The M−Ru−M‘ and M−Ru−X complexes have 99Ru NMR resonances in distinct chemical shift regions. In the series M−Ru−M‘ a correlation between the inverse of the crystal field splitting energy ΔE and δ(99Ru) exists. These complexes have a HOMO which is delocalized over the M−Ru−M‘ σ system and a LUMO which has predominantly π*-DAB character; therefore, (ΔE)-1 is dominant in the paramagnetic shielding of the ruthenium nucleus. The diff...