Electrochemical detection of peptides

A general method of wide applicability for the determination of peptides is described. Peptides longer than dipeptides react in the classical biuret reaction with Cu(II) to yield electroactive Cu(II)-peptide complexes that can be oxidized to the corresponding Cu(III) complexes. This allows the sensitive electrochemical detection of peptides following their separation by reversed-phase liquid chromatography. The reaction chemistry, which is reversible, allows for the determination of peptides that lack an electroactive group or a primary amine. Selectivity for a model peptide is 10(3)-10(4) over nonelectroactive amino acids.     

Oxyethylated secondary amides as soil wetting agents

Polydisperse adducts, RCONR’ (CH₂CH₂O)_xH, with attractive wetting properties were prepared by oxyethylating aliphatic and aromatic secondary amides to calculated x values of 5 to 20. Moderate wetting profiles were observed with adducts where R and R’ contained 15 to 18 carbon atoms and had short ethylene oxide chains. These products, however, contained unreacted amide and/or ester contaminants. Consequently, the products showed high water solubility, fairly flat surface tension curves and average wetting ability. In the transition of adducts derived from aliphatic amides to those from aromatic amides, unreacted amide concentration decreased and ester contaminant increased.     

Optimizing substrate surface and catalyst conditions for high yield chemical vapor deposition grown epitaxially aligned single-walled carbon nanotubes

Single-crystal stable-temperature (ST)-cut quartz substrates, which have a (0 1 1 1) crystallographic plane with their surface normal lying close to 38° from the y axis ([0 1 0]), were annealed in air prior to use as a support for aligned carbon nanotube growth by chemical vapor deposition. Very smooth substrate surfaces were obtained with annealing times in the vicinity of 15 h at a temperature of 750 °C. These smooth surfaces are ideal for the growth of horizontally aligned SWCNTs with high spatial density, while less dense SWCNTs were obtained with less smooth surfaces. Under optimized growth conditions, only SWCNT are observed and they can grow to lengths in excess of 100 μm. Our findings suggest structural defects interfere with the growth process. A binary Fe/Co catalyst was employed to grow the nanotubes. No obvious dependence on the Fe:Co ratio is observed.     

Mutagenesis of the conserved residue Glu259 of Gsalpha demonstrates the importance of interactions between switches 2 and 3 for activation

We previously reported that substitution of Arg258 within the switch 3 region of Gsalpha impaired activation and increased basal GDP release due to loss of an interaction between the helical and GTPase domains (Warner, D. R., Weng, G., Yu, S., Matalon, R., and Weinstein, L. S. (1998) J Biol. Chem. 273, 23976-23983). The adjacent residue (Glu259) is strictly conserved in G protein alpha-subunits and is predicted to be important in activation. To determine the importance of Glu259, this residue was mutated to Ala (Gsalpha-E259A), Gln (Gsalpha-E259Q), Asp (Gsalpha-E259D), or Val (Gsalpha-E259V), and the properties of in vitro translation products were examined. The Gsalpha-E259V was studied because this mutation was identified in a patient with Albright hereditary osteodystrophy. S49 cyc reconstitution assays demonstrated that Gsalpha-E259D stimulated adenylyl cyclase normally in the presence of GTPgammaS but was less efficient with isoproterenol or AlF4-. The other mutants had more severely impaired effector activation, particularly in response to AlF4-. In trypsin protection assays, GTPgammaS was a more effective activator than AlF4- for all mutants, with Gsalpha-E259D being the least severely impaired. For Gsalpha-E259D, the AlF4--induced activation defect was more pronounced at low Mg2+ concentrations. Gsalpha-E259D and Gsalpha-E259A purified from Escherichia coli had normal rates of GDP release (as assessed by the rate GTPgammaS binding). However, for both mutants, the ability of AlF4- to decrease the rate of GTPgammaS binding was impaired, suggesting that they bound AlF4- more poorly. GTPgammaS bound to purified Gsalpha-E259D irreversibly in the presence of 1 mM free Mg2+, but dissociated readily at micromolar concentrations. Sucrose density gradient analysis of in vitro translates demonstrated that all mutants except Gsalpha-E259V bind to beta gamma at 0 degreesC and were stable at higher temperatures. In the active conformation Glu259 interacts with conserved residues in the switch 2 region that are important in maintaining both the active state and AlF4- in the guanine nucleotide binding pocket. Although both Gsalpha Arg258 and Glu259 are critical for activation, the mechanisms by which these residues affect Gsalpha protein activation are distinct.     

Algorithms for planning and control of robot motions [TC Spotlight]

Robot motion planning and control is an essential component in creating autonomous systems that are able to execute high-level tasks for navigating and manipulating objects in challenging environments. Motion planning has led to active research over the past decades. Most of the research focused on the computational issue of generating feasible paths that lead the robot to a desired goal, while generally ignoring control concerns such as feedback, optimum, and uncertainty. The breakthrough achieved with sampling-based algorithms leads to effective techniques for hard, high-dimensional problems, and the recent improvements brought motion-planning algorithms closer to applicability in real problems. Nowadays, the practical interest of the state-of-the-art techniques is no longer restricted to robotics but extends to challenging problems arising in such diverse fields as graphics animation, virtual prototyping, and computational biology.     

Comments, with reply, on A reduced-field design concept forhigh-performance bipolar transistors by D.D. Tang and P.-F. Lu

The comments point out to the authors of the original work (see ibid., vol.10, p.67-69, 1989) a body of work carried out at Bell Laboratories in the 1950s that underlies their development insofar as collector-base junctions are concerned. Particular attention is given to the work of J.M. Early (1952, 1954). A reply is included     

The activated sludge process—IV: Application of the general kinetic model to anoxic-aerobic digestion of waste activated sludge

This paper discusses the application of the general activated sludge model as set out by Dold et al. (Prog. Wat. Technol.12, 47–77, 1980) and extended by Van Haandel et al. (Wat. Res.15, 1135–1152, 1981), to anoxic-aerobic digestion of waste activated sludge. The laboratory scale experimental investigation comprised a 6 day sludge age activated sludge process, the waste sludge from which was fed to a number of digesters operated as follows: single reactor flow-through digesters at 4 or 10 days sludge age (retention times) under aerobic or anoxic-aerobic conditions (with 1.5 and 4 h cycle times) and 3-in-series flow-through aerobic digesters each with 4 days sludge age; all digesters were fed draw-and-fill wise once per day. The general kinetic model simulated accurately all the experimental data without the need to change the values of the kinetic constants. Both theoretical simulations and experimental data indicate that (i) the rate of volatile solids destruction is not affected by the incorporation of anoxic cycles and (ii) the specific denitrification rate constant in a digester is about two-thirds of that in the secondary anoxic reactor of the single sludge activated sludge system; this allows definition of a fourth denitrification rate constant K₄ for the anoxic-aerobic digester with K₄T = 0.046(1.029)^(T-20) mg(NO₃-N) (mgAVSS d)⁻¹, a constant independent of sludge age. An important consequence of (i) and (ii) above is that the denitrification can be integrated readily into the steady state digester model of Marais and Ekama (Wat. SA2, 163–200, 1976) and used for design purposes.     

Stability and change in adult intelligence: I. Analysis of longitudinal covariance structures.

Examines 2 questions of central interest in adult intellectual development—the equivalence of psychometric tests' measurement properties at different ages and the stability of individual differences in intelligence over time. A series of longitudinal factor analyses was performed using the LISREL program to model longitudinal data from K. W. Schaie's (1979, 1983) Seattle Longitudinal Study with individuals aged 20–74 yrs. Ss studied included 162 in Sample 1 and 2,250 in Sample 2. Results indicate complete invariance in the loadings of 5 subtests of the Primary Mental Abilities battery on a general intelligence factor. Individual differences in general intelligence were highly stable over 14-yr epochs, with standardized factor correlations averaging about .9 between adjacent 7-yr testing intervals. Results indicate that most individuals in this relatively select longitudinal sample maintained their relative ordering in intelligence. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gamma ray production cross-sections associated with multiple inelastic scattering of 14 MeV neutrons in lead

The gamma ray angular distributions and differential production cross-sections have been measured for the inelastic scattering of 14 MeV neutrons in lead, using a gamma ray spectrometer based on an associated particle time-of-flight gating technique. The variation of cross-section with sample thickness was measured and the results compared with the predictions of the Monte Carlo computer code MORSE.