A lysine to arginine substitution at position 146 of rabbit aldolase A changes the rate-determining step to Schiff base formation

Lys146 of rabbit aldolase A [D-fructose-1,6-bis(phosphate):D-glyceraldehyde-3-phosphate lyase, EC 4.1.2.13 [EC] ] was changedto arginine by site-directed mutagenesis. The k_cat of the resultingmutant protein, K146R, was 500 times slower than wild-type insteady-state kinetic assays for both cleavage and condensationof fructose-1,6-bis(phosphate), while the Km for this substratewas unchanged. Analysis of the rate of formation of catalyticintermediates showed K146R was significantly different fromthe wild-type enzyme and other enzymes mutated at this site.Single-turnover experiments using acid precipitation to trapthe Schiff base intermediate on the wild-type enzyme failedto show a build-up of this intermediate on K146R. However, K146Rretained the ability to form the Schiff base intermediate asshown by the significant amounts of Schiff base intermediatetrapped with NaBH₄. In the single-turnover experiments it appearedthat the Schiff base intermediate was converted to productsmore rapidly than it was produced. This suggested a maximalrate of Schiff base formation of 0.022 s^–1, which wasclose to the value of k_cat for this enzyme. This observationis strikingly different from the wild-type enzyme in which Schiffbase formation is >100 times faster than k_cat. For K146Rit appears that steps up to and including Schiff base formationare rate limiting for the catalytic reaction. The carbanionintermediate derived from either substrate or product, and theequilibrium concentrations of covalent enzyme-substrate intermediates,were much lower on K146R than on the wild-type enzyme. The greaterbulk of the guanidino moiety may destabilize the covalent enzyme-substrateintermediates, thereby slowing the rate of Schiff base formationsuch that it becomes rate limiting. The K146R mutant enzymeis significantly more active than other enzymes mutated at thissite, perhaps because it maintains a positively charged groupat an essential position in the active site or perhaps the Argfunctionally substitutes as a general acid/base catalyst inboth Schiff base formation and in subsequent abstraction ofthe C4-hydroxyl proton.     

A comparative study of UV active silane-grafted and ion-exchanged organo-clay for application in photocurable urethane acrylate nano- and micro-composites

A number of urethane acrylate nano- and micro-composites have been developed using both ion exchange and silane grafting chemistry. The organically modified clays which were used contained either methacrylate or acrylate functionalities which were capable of reacting with the acrylate groups in the urethane acrylate matrix. [2-(Acryloyloxy)ethyl]trimethyl-ammonium ion (AOETMA) or [2-(methacryloyloxy)ethyl]trimethylammonium ion (MAOTMA) were exchanged onto montmorillonite (MMT) as shown by an increase in the inter-gallery spacing of the MMT. Silane grafting was undertaken using [3-(acryloxy)propyl]dimethylmethoxysilane (APDMMS) or [3-(methacryloxy)propyl]dimethylmethoxysilane (MAPDMMS) and also showed an increase in inter-gallery spacing. The structures of the resulting urethane acrylate composites were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and showed predominantly intercalated structures with some exfoliation (more evident in the silane-grafted systems). Dynamical mechanical thermal analysis (DMTA) showed a more significant increase in effective crosslink density (as measured from the plateau of the rubbery modulus) in the composites containing the reactive clays as compared to the unmodified clay, supporting the concept that the acrylate and methacrylate functionalities of the modified clays had reacted with the matrix. Other thermal and mechanical properties were also evaluated.     

Electrochemical characterization of 8-hydroxyquinoline-5-sulphonate/aluminium(III) aqueous solutions

8-Hydroxyquinoline-5-sulphonate/Al(III) aqueous solutions were studied both by potentiometric titrations and voltammetric measurements, in order to obtain the number, the stoichiometry and the stability constants of the complexes formed at equilibrium, and to evaluate the redox and (electro)kinetic properties of the free ligand and of the metal/ligand complexes. The complexes formed in 0.2 m (Na)Cl aqueous solution (stability log beta values ± standard deviation) are AlL⁺ (8.95 ± 0.05), AlL₂⁻ (17.43 ± 0.03) and AlL₃³⁻ (24.58 ± 0.05), where “L” denotes the free ligand in the completely deprotonated form (L²⁻, pK_a1 = 3.910 ± 0.008, pK_a2 = 8.319 ± 0.004). AlL₃³⁻ is the predominant Al(III) species in a very wide range of pH, metal and ligand concentrations and metal-to-ligand ratios. The free ligand shows an oxidation wave at 0.62 V versus SCE. The proposed oxidation mechanism includes a first reversible one-electron oxidation of the ligand, followed by a coupling reaction and by a second reversible one-electron oxidation, and finally by a decomposition reaction. The addition of Al(III) lowers the intensity of the oxidation wave due to the formation of the redox-inactive complex AlL₃³⁻. A residual low signal was attributed to the free ligand produced by the complex dissociation, AlL₃³⁻ = AlL₂⁻ + L²⁻. All the kinetic parameters involved in the ligand oxidation and in the complex disruption were calculated on the basis of the agreement between experimental and simulated linear sweep and cyclic voltammetries. Correctness of the mechanisms proposed was further confirmed “a posteriori” by the agreement between potentiometric and linear sweep voltammetric results. The low residual signal observed in the presence of fully formed complex was attributed to the free ligand produced by the complex dissociation, having a kinetic constant estimated 0.2 s⁻¹.     

Solvent-free oxidation of benzyl alcohol using titania-supported gold–palladium catalysts: Effect of Au–Pd ratio on catalytic performance

The oxidation of benzyl alcohol with molecular oxygen under solvent-free conditions has been investigated using a range of titania-supported Au–Pd alloy catalysts to examine the effect of the Au–Pd ratio on the conversion and selectivity. The catalysts have been compared at high reaction temperature (160 °C) as well as at 100 °C, to determine the effect on selectivity since at lower reaction temperature the range of by-products that are formed are limited. Under these conditions the 2.5 wt.% Au–2.5 wt.% Pd/TiO₂ was found to be the most active catalyst, whereas the Au/TiO₂ catalyst demonstrated the highest selectivity to benzaldehyde. Toluene, formed via either a hydrogen transfer process or an oxygen transfer process, was observed as a major by-product under these forcing conditions.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Straight‐Line Tracking Control of an Agricultural Vehicle with Finite‐Time Control Technique

For the agricultural vehicle straight‐line tracking system, three control algorithms based upon the finite‐time control technique have been proposed to force the vehicle to track a straight line. Without considering the lumped disturbance, a backstepping‐like finite‐time state‐feedback controller is first developed. On this basis, an adaptive state‐feedback controller in conjunction with integral sliding mode is further developed in the presence of the lumped disturbance. Finally, a sliding mode disturbance observer is given to estimate the lumped disturbance, and the composite control scheme is presented. Under the composite controller, the lumped disturbance can be compensated and thus the disturbance rejection property has been significantly improved. Simulation results verify the proposed control algorithms.     

Mass spectrometric immunoassay and MRM as targeted MS-based quantitative approaches in biomarker development: Potential applications to cardiovascular disease and diabetes

Type 2 diabetes mellitus (T2DM) is an important risk factor for cardiovascular disease (CVD)—the leading cause of death in the United States. Yet not all subjects with T2DM are at equal risk for CVD complications; the challenge lies in identifying those at greatest risk. Therapies directed toward treating conventional risk factors have failed to significantly reduce this residual risk in T2DM patients. Thus newer targets and markers are needed for the development and testing of novel therapies. Herein we review two complementary MS-based approaches—mass spectrometric immunoassay (MSIA) and MS/MS as MRM—for the analysis of plasma proteins and PTMs of relevance to T2DM and CVD. Together, these complementary approaches allow for high-throughput monitoring of many PTMs and the absolute quantification of proteins near the low picomolar range. In this review article, we discuss the clinical relevance of the high density lipoprotein (HDL) proteome and Apolipoprotein A-I PTMs to T2DM and CVD as well as provide illustrative MSIA and MRM data on HDL proteins from T2DM patients to provide examples of how these MS approaches can be applied to gain new insight regarding cardiovascular risk factors. Also discussed are the reproducibility, interpretation, and limitations of each technique with an emphasis on their capacities to facilitate the translation of new biomarkers into clinical practice.     

Effect of polyaluminium chloride on phosphorus removal in constructed wetlands treated with swine wastewater

Total phosphorus (TP) removal in aged constructed wetlands poses a challenge, especially when treated with swine wastewater with high concentrations of phosphorus (P). Our earlier studies with anaerobic lagoon swine wastewater treatment in constructed wetlands showed a decline in P removal (45-22%) with increased years of operation. These particular wetlands have been treated with swine wastewater every year since the first application in 1997. Preliminary lab-scale studies were conducted to evaluate the efficiency of polyaluminium chloride (PAC) in the removal of phosphate-P (PO4-P) from swine wastewater. The experimental objective was to increase the phosphorus treatment efficiency in constructed wetland by adding PAC as a precipitating agent. PAC was added by continuous injection to each wetland system at a rate of 3 L day(-1) (1:5 dilution of concentrated PAC). Swine wastewater was added from an anaerobic lagoon to four constructed wetland cells (11m wide x 40m long) at TP loads of 5.4-6.1 kg ha(-1) day(-1) in two experimental periods, September to November of 2008 and 2009. Treatment efficiency of two wetland systems: marsh-pond-marsh (M-P-M) and continuous marsh (CM) was compared. The wetlands were planted with cattails (Typha latifolia L.) and bulrushes (Scirpus americanus). In 2008, PAC treatment showed an increase of 27.5 and 40.8% of TP removal over control in M-P-M and CM respectively. Similar trend was also observed in the following year. PAC as a flocculant and precipitating agent showed potential to enhance TP removal in constructed wetlands treated with swine wastewater.     

Development of a genetic algorithm for component placement sequence optimization in printed circuit board assembly

This paper describes the development and evaluation of a custom application exploring the use of genetic algorithms (GA) to solve a component placement sequencing problem for printed circuit board (PCB) assembly. In the assembly of PCB’s, the component placement process is often the bottleneck, and the equipment to complete component placement is often the largest capital investment. The number of components placed on a PCB can range from few to hundreds. As a result, developing an application to determine an optimal or near-optimal placement sequence can translate into reduced cycle times for the overall assembly process and reduced assembly costs. A custom application was developed to evaluate the effectiveness of using GA’s to solve the component placement sequencing problem. A designed experiment was used to determine the best representation and crossover type, crossover rate, and mutation rate to use in solving a component sequencing problem for a PCB consisting of 10 components being placed on a single-headed placement machine. Three different representations (path, ordinal, and adjacency) and six appropriate crossover types (partially mapped, ordered, cycle, classical, alternating edges, and heuristic) were evaluated at three different mutation rates and at 11 crossover rates. Two algorithm response variables, the total distance traveled by the placement head and the algorithm solution efficiency (measured as number of generations and algorithm solution time) were used to evaluate the different GA applications. The combination of representation and crossover type along with mutation rate were found to be the most significant parameters in the algorithm design. In particular, path representation with order crossover was found to produce the best solution as measured by the total distance traveled as well as the solution generation efficiency. Increasing the mutation rate led to slightly improved solutions in terms of head travel, but also resulted in increased solution time.