Oxyacetylene torch testing and microstructural characterization of tantalum carbide.

Tantalum carbide samples have been subjected to high-temperature testing at ∼2300°C using an oxyacetylene torch to evaluate their potential for ultra-high temperature applications. While large samples cracked during the rapid heating, indicating their inability to withstand thermal shock, small samples survived the severe test conditions. The oxidation products formed were characterized and found to comprise different phases of Ta2 O5 . The ultra-high temperature experienced by the samples resulted in the formation of many interesting microstructures, including the formation of submicron sized grains, which has not been reported previously in the literature, as well as the expected evidence of melting.

Thermodynamics and mechanisms for decomposition of protonated glycine and its protonated dimer.

We present a full molecular description of fragmentation reactions of protonated glycine (G) and its protonated dimer, H(+)G(2), by studying their collision-induced dissociation (CID) with Xe using a guided ion beam tandem mass spectrometer (GIBMS). In contrast to previous results, it is clear that H(+)G decomposes by loss of CO followed by H(2)O. Analysis of the energy-dependent CID cross sections provides the 0 K barriers for these processes as well as for the binding energy of the dimer after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. Relaxed potential energy surface scans performed at the B3LYP/6-31G(d) level are used to map the reaction surfaces and identify the transition states (TSs) and intermediate reaction species for the reactions, structures that are further optimized at the B3LYP/6-311+G(d,p) level. Single-point energies of the key optimized structures are calculated at B3LYP and MP2(full) levels using a 6-311+G(2d,2p) basis set. These theoretical results are compared to extensive calculations in the literature and to the experimental energies. The combination of both experimental work and quantum chemical calculations allows for a complete characterization of the elementary steps of H(+)G and H(+)G(2) decomposition. These results make it clear that H(+)G is the simplest model for the ''mobile proton'', a key concept in understanding the fragmentation of protonated proteins.

Infrared multiple photon dissociation spectroscopy of cationized asparagine: effects of metal cation size on gas-phase conformation.

Gas-phase structures of cationized asparagine (Asn) including complexes with Li(+), Na(+), K(+), Rb(+), Cs(+), and Ba(2+), as well as protonated Asn, are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by a free electron laser. Experimental spectra for the alkali metal cation complexes exhibit systematic trends, whereas spectra for Ba(2+)(Asn) and H(+)(Asn) are more distinct. To identify the structures formed experimentally, measured IRMPD spectra are compared to spectra calculated at a B3LYP/6-311+G(d,p) level with several effective core potentials and basis sets evaluated for the heavy metal systems. The dominant conformation ascertained for complexes with the smaller metal cations, Li(+)(Asn) and Na(+)(Asn), is a charge-solvated, tridentate [N,CO,CO] structure that binds the metal cation with the amine group of the amino acid backbone and to the carbonyl oxygen atoms of the backbone and amino acid side chain. For the larger alkali metal cation complexes, K(+)(Asn), Rb(+)(Asn), and Cs(+)(Asn), an additional charge-solvated, tridentate [COOH,CO] structure that binds the metal cation with the two oxygen atoms of the backbone carboxylic acid group and the carbonyl oxygen atom of the Asn side chain may also be present. The Ba(2+)(Asn) spectrum is characteristic of a single charge-solvated [N,CO,CO] conformation, in contrast to Gly, Trp, Arg, Gln, Pro, Ser, Val, and Glu, which all take on a zwitterionic structure when complexed to Ba(2+). In no case do the cationized Asn complexes show definitive evidence of forming a zwitterionic structure in the complexes studied here. For H(+)(Asn), a mixture of two [N,CO] structures, which differ only in the orientation the side chain and are calculated to be nearly identical in energy, explains the experimental spectrum well.

Thermodynamics and mechanism of the deamidation of sodium-bound asparagine.

The deamidation of asparagine (Asn) residues is the most common type of spontaneous post-translational protein modification and plays a vital role in inflammation, protein transformation, apoptosis, aging, and a number of degenerative diseases. Here we present a full molecular description of asparagine deamidation in the Na(+)(Asn) complex by studying its collision-induced dissociation (CID) with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Advanced methods for analysis of the energy-dependent CID cross section, considering both competing and sequential processes, provide the 0 K barrier for deamidation after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. Relaxed potential energy surface scans performed at the B3LYP/6-31G(d) level identify the transition state (TS) and intermediate reaction species for Na(+)(Asn) deamidation, structures that are further optimized at the B3LYP/6-311+G(d,p) level. Single-point energies of the key optimized structures are calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. This coordinated application of both experimental work and quantum chemical calculations allows for a complete characterization of the elementary steps of this reaction and identification of the rate-limiting elementary step of Asn deamidation. The latter is measured to require 1.61 +/- 0.08 eV and involves formation of a cyclic succinic ring structure.

Experimental and theoretical studies of potassium cation interactions with the acidic amino acids and their amide derivatives.

The binding of K(+) to aspartic acid (Asp), glutamic acid (Glu), asparagine (Asn), and glutamine (Gln) is examined in detail by studying the collision-induced dissociation (CID) of the four potassium cation-bound amino acid complexes with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Formed by electrospray ionization, these complexes have energy-dependent CID cross sections that are analyzed to provide 0 K bond energies after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. Quantum chemical calculations for a number of geometric conformations of each K(+)(L) complex are determined at the B3LYP/6-311+G(d,p) level with single-point energies calculated at B3LYP, B3P86, and MP2(full) levels using a 6-311+G(2d,2p) basis set. Theoretical bond dissociation energies are in good agreement with the experimental values. This coordinated examination of both experimental work and quantum chemical calculations allows for a comprehensive understanding of the molecular interactions of K(+) with the Asx and Glx amino acids. K(+) binding affinities for the amide complexes are systematically stronger than those for the acid complexes by 9+/-1 kJ/mol, which is attributed to an inductive effect of the OH group in the carboxylic acid side chain. Additionally, the K(+) binding affinity for the longer-chain amino acids (Glx) is enhanced by 5+/-1 kJ/mol compared to the shorter-chain Asx because steric effects are reduced. Further, a detailed comparison between experimental and theoretical results reveals interesting differences in the binding of K(+) and Na(+) to these amino acids.

Experimental and theoretical studies of sodium cation interactions with D-arabinose, xylose, glucose, and galactose.

The binding of Na (+) to arabinose (Ara), xylose (Xyl), glucose (Glc), and galactose (Gal) is examined in detail by studying the collision-induced dissociation (CID) of the four sodiated monosaccharide complexes with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Analysis of the energy-dependent CID cross-sections provides 0 K sodium cation affinities for experimental complexes after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations for a number of geometric conformations of each Na (+)(L) complex with a comprehensive analysis of the alpha and beta anomeric forms are determined at the B3LYP/6-311+G(d,p) level with single-point energies calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. This coordinated examination of both experimental work and quantum chemical calculations allows for determination of the bond energy for both the alpha and beta forms of each monosaccharide studied here. An understanding of the energetic contributions of individual structural characteristics as well as the energetic trends in binding among the monosaccharides is developed. Structural characteristics that affect the energetics of binding involve multidentate sodium cation coordination, ring sterics, and hydrogen bonding schemes. The overall trend in sodium binding affinities for the eight ligands follows beta-Ara < alpha-Ara < beta-Xyl < beta-Glc < alpha-Glc < alpha;-Xyl < alpha-Gal < beta-Gal.

Experimental and theoretical studies of sodium cation interactions with the acidic amino acids and their amide derivatives.

The binding of Na+ to aspartic acid (Asp), glutamic acid (Glu), asparagine (Asn), and glutamine (Gln) is examined in detail by studying the collision-induced dissociation (CID) of the four sodiated amino acid complexes with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Analysis of the energy-dependent CID cross sections provides 0 K sodium cation affinities for the complexes after accounting for unimolecular decay rates, internal energy of the reactant ions, and multiple ion-molecule collisions. Quantum chemical calculations for a number of geometric conformations of each Na+(L) complex are determined at the B3LYP/6-311+G(d,p) level with single-point energies calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. This coordinated examination of both experimental work and quantum chemical calculations allows the energetic contributions of individual functionalities as well as steric influences of relative chain lengths to be thoroughly explored. Na+ binding affinities for the amide complexes are systematically stronger than those for the acid complexes by 14 +/- 1 kJ/mol, which is attributed to an inductive effect of the OH group in the carboxylic acid side chain. Additionally, the Na+ binding affinity for the longer-chain amino acids (Glx) is enhanced by 4 +/- 1 kJ/mol compared to the shorter-chain Asx because steric effects are reduced.

Experimental and theoretical studies of sodium cation complexes of the deamidation and dehydration products of asparagine, glutamine, aspartic acid, and glutamic acid.

The deamidation and dehydration products of Na+(L), where L = asparagine (Asn), glutamine (Gln), aspartic acid (Asp), and glutamic acid (Glu), are examined in detail utilizing collision-induced dissociation (CID) with Xe in a guided ion beam tandem mass spectrometer (GIBMS). Results establish that the Na+(L) complexes decompose upon formation in our dc discharge/flow tube ion source to form a bis-ligand complex, Na+(L-HX)(HX), composed of a sodium cation, the (L-HX) decomposition product, and HX, where HX = NH3 for the amides and H2O for the acids. Analysis of the energy-dependent CID cross sections for the Na+(L-HX)(HX) complexes provides unambiguous identification of the (L-HX) fragmentation products as 3-amino succinic anhydride (a-SA) for Asx and oxo-proline (O-Pro) for Glx. Furthermore, these experiments establish the 0 K sodium cation affinities for these five-membered ring decomposition products and the H2O and NH3 binding affinities of the Na+(a-SA) and Na+(O-Pro) complexes after accounting for unimolecular decay rates, the internal energy of reactant ions, and multiple ion-molecule collisions. Quantum chemical calculations are determined for a number of geometric conformations of all reaction species as well as a number of candidate species for (L-HX) at the B3LYP/6-311+G(d,p) level with single-point energies calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. This coordinated examination of both the experimental work and quantum chemical calculations allows for a complete characterization of the products of deamidation and dehydration of Asx and Glx, as well as the details of Na+, H2O, and NH3 binding to the decomposition species.

Cost effectiveness of risk reduction: the managed care perspective.

Coronary artery disease (CAD) is responsible for nearly $140 billion in healthcare expenditures each year. A major opportunity for cost savings lies in reducing the overutilization of hospitalization for CAD patients. This goal may be accomplished through several strategies: more precise diagnosis of CAD, primary and secondary prevention, and early intervention. Underutilization of health services and treatment also contributes to higher overall medical costs. Even though drug therapy incurs costs, effective medications can produce substantial savings by reducing the need for additional medical care. For example, lipid-lowering agents are particularly cost effective when used as secondary prevention in patients with CAD; however, only 25% of patients receive such therapy. Likewise, not all patients who suffer acute myocardial infarction are treated with any of the agents proven to reduce the risk of subsequent adverse cardiovascular events. The elimination of variability in prescribing practices should help optimize the cost effectiveness of therapies aimed at reducing CAD risk.

Pyrimidine metabolism in hereditary erythrocyte pyrimidine 5' nucleotidase deficiency.

A patient with hereditary erythrocyte pyrimidine 5' nucleotidase deficiency was studied to determine the mechanism of accumulation of erythrocyte pyrimidine nucleotides. Estimates of the rate of degradation of uridine nucleotides to diffusable products imply that the high levels found in these patients could not be sustained from the degradative pathways alone. Active synthesis of uridine nucleotides was found to occur in erythrocytes from both patient and control blood samples when either uridine or orotate was used as a substrate. The circulating levels of uridine in the blood are such that sufficient nucleotides to account for the high levels seen in these patients could accumulate in the erythrocytes from biosynthetic pathways alone, quite apart from the contribution from degradation of residual ribosomal RNA. This provides scope for new therapeutic approaches; treatment with allopurinol, however, was found to result in an increase, rather than a decrease, in erythrocyte pyrimidine nucleotides.

Adipocyte insulin binding and insulin action in chronic renal failure before and during continuous ambulatory peritoneal dialysis.

In order to investigate the cellular mechanisms of the insulin resistance displayed by subjects with chronic renal failure, adipocyte insulin receptor status and in vitro insulin sensitivity were studied. Adipocytes from uremic subjects displayed normal maximum specific insulin binding (2.55 +/- 0.23 v 2.57 +/- 0.09% per 10 cm2 cell membrane, although half-maximum binding was observed at 91 +/- 8 (uremic) and 139 +/- 11 (control) pmol/L (P less than 0.005). In six subjects restudied after three months of continuous ambulatory peritoneal dialysis, maximum specific insulin binding fell as a consequence of changes in both receptor affinity and number (2.87 +/- 0.20 v 2.05 +/- 0.17% per 10 cm2 cell membrane, P less than 0.01). Basal and maximal rates of lipogenesis were similar in the uremic and control groups, and half-maximal stimulation occurred at 13.5 +/- 4.4 and 21.4 +/- 3.0 pmol/L, respectively (NS). During continuous ambulatory peritoneal dialysis, adipocyte insulin sensitivity did not change significantly as assessed by stimulation of lipogenesis or glucose uptake (half-maximal stimulation at 12.0 +/- 4.0 v 26.4 +/- 11.0 and 23.1 +/- 7.1 v 29.0 +/- 7.5 pmol/L, before and during dialysis, respectively). These data suggest either that adipose tissue and muscle display differential insulin sensitivities in chronic renal failure or that other factors such as circulating inhibitors of insulin action are not detected by in vitro assays.

Methodology for identifying patients at high risk for osteoporotic fracture.

BACKGROUND: Osteoporotic fractures are associated with significant morbidity, mortality, and health care costs. OBJECTIVE: The purpose of this paper is to present and validate a mathematical model that managed care organizations can apply to administrative claims data to help locate members at risk for osteoporotic fracture and estimate future fracture rates. METHODS: Using known risk factors from previous clinical studies, 92,000 members of a large Midwest health plan were placed in 1 of 4 risk categories based on historical claims markers: demographic/lifestyle (age, sex, smoking, alcoholism); steroid use; medical history (previous osteoporotic fracture, ordinary bone fracture, osteoporosis diagnosis, bone mineral density test); or steroid use with medical history. Logistic regression was used to assign a probability of fracture for the 4 groups over the next 2 years. These predictions were compared with actual fracture rates, and refined models were produced. The models were then validated by applying them to current data and comparing the predicted fracture rate for each group to known results. RESULTS: The model predicted that 1.26% of the study members would experience osteoporotic fracture over the next 2 years; the actual result was 1.27%. Within the 4 risk groups, the predicted fracture rates were lower than the actual rates for the demographic risk group (0.87% predicted vs 0.97% actual) and higher than the actual rates for the steroid use (1.78% predicted vs 1.58% actual), medical history (5.90% predicted vs 4.94% actual), and the steroid use with medical history groups (7.80% predicted vs 6.42% actual). CONCLUSION: The application of this risk model to an administrative claims database successfully identified plan members at risk for osteoporotic fracture.

The managed care pharmacy perspective.

Despite the important reproductive and noncontraceptive benefits of hormonal therapy, both oral contraceptives (OCs) and hormone replacement therapy (HRT) are underutilized, with only a small portion of eligible women receiving therapy. Increased use of hormonal therapy will result in greater pharmacy costs, a concern in the present era of cost containment that is reflected in the wide variability in coverage of hormonal therapy provided by managed care organizations. However, pharmacoeconomic research demonstrates that relatively small expenditures in pharmacy costs for hormonal therapy result in significantly lower healthcare costs per patient, through the prevention of unintended pregnancy with OCs and the noncontraceptive health benefits of both OCs and HRT.

Hip joint prosthesis design: effect of stem introducers.

The stress levels in the femoral component of a total hip prosthesis (Corin Taper Fit, Corin Medical Ltd, Cirencester, Gloucestershire, UK) were calculated by finite element (FE) analysis. This prosthesis has two holes drilled in the shoulder to engage a stem introducer. There were no unacceptable stress levels around these holes. Instead the maximum stresses were around the periphery of the shaft of the stem, as has been observed for FE analyses of conventional designs. Three prostheses were also subjected to cyclic mechanical testing (peak load 2.3 kN) according to the appropriate British Standard. The holes were examined for cracks, before and after testing, by stereomicroscopy. All three specimens were able to withstand 5 million loading cycles with no evidence of damage. Thus it is possible to design a femoral component with holes in the shoulder, to accommodate a stem introducer, without creating unacceptable stress concentrations.

Cell morphology and collagen types in equine tendon scar.

The histological appearance of cells and tissues in the reparative scar tissue which forms in the equine superficial flexor tendon following partial rupture was compared to that of normal tendon. The repair fibroblasts were found to be larger and more basophilic than the tenocytes of normal tendon, to have large vesicular nuclei and to resemble the 'myofibroblasts' described in scar tissue elsewhere. The cell to matrix ratio in scarred zones of tendon was found to be increased and the concentration of collagen in these areas was less than in normal tendon. However, the scar tissue collagen was more readily extractable and contained a different pattern of collagen types. Normal equine tendon was found to be composed almost exclusively of type I collagen whereas the scarred tendon had substantial quantities (20 to 30 per cent) of type III collagen in addition to type I. The presence of type III collagen in the scarred tendon was confirmed by indirect immunofluorescence using antibodies to purified type III collagen. These observations suggest that tendon scar tissue is not derived from proliferating tenocytes but from mesenchymal cells resting in peritendinous connective tissue or blood vessels. As a result of the presence of type III collagen, the scarred tendon is also likely to have less tensile strength than normal tendon.

Connective tissue composition of the equine sarcoid.

The connective tissue composition and organisation of the "equine sarcoid" was compared with that of normal adult equine skin to determine whether the cells which produce their respective connective tissue matrices show similar biosynthetic characteristics. No major qualitative difference could be found between the collagen compositions of skin and sarcoid material, although the organisation into fibres of Type III collagen in the sarcoid was markedly greater than that of skin.

Design of spinous process hooks for flexible fixation of the lumbar spine.

A prototype flexible fixation system for the lumbar spine was subjected to tensile testing to failure and cyclic tensile testing in order to determine any regions of weakness. The system consisted of a spinous process hook and two laminar hooks made of stainless steel (316L). Each laminar hook was attached to the spinous process hook by a loop of polyester braid secured by a crimped metal sleeve. In five tensile tests, the system failed by irreversible deformation of the spinous process hook at 2.5 +/- 0.3 kN (mean +/- standard deviation). In three cyclic tests, in which the applied tension varied sinusoidally between 0.04 and 0.4 kN at a frequency of 5 Hz, failure occurred after less than 400,000 loading cycles. This occurred as a result of fatigue crack initiation and propagation in the spinous process hook. A finite element model showed a stress concentration in the region where the crack occurred, which raised the applied stress above the tensile fatigue strength of this stainless steel. The spinous process hook was redesigned for manufacture in a titanium alloy (Ti-6AI-4V ELI) to minimize artefacts in magnetic resonance imaging. Further finite element models showed no unacceptable stress concentrations.