In situ analysis of CO during chemisorption and oxidation on graphite: Supported Pt by FTIR-microspectrometry

For chemisorption and oxidation on Pt/HOPG (highly-orientated pyrolytic) graphite, reflectance Fourier Transform Infrared (FTIR)-microspectrometry reveals a variable state and reactivity for CO. Even for model surface science systems, where surface heterogeneity is minimal, surface diffusion may be too slow relative to the reaction rate to avoid segregation of reactants into surface islands under steady-state conditions. Thus in CO oxidation on Pt (where the relevant surface diffusion coefficients are such that D sub O less than D sub CO) then reactant CO islands exists at the perimeters of which the surface reaction is thought to occur. Furthermore CO can chemisorb on metals in linear and bridge forms to extents which vary with precise faces predominantly exposed coverage, etc. Infrared has long been used to probe the nature of adsorbed CO on model film and heterogeneous surfaces, but it may now be that FTIR-microspectrometry will allow the state of this adsorbate and reactant to be investigated with a spatial resolution of 4.4 microns on model (and real) catalytic surfaces

Fourier transform infrared cell for surface studies at controlled temperatures and in controlled atmospheres with time resolution and spatial resolution

A new micro-Fourier transform infrared cell has been constructed and evaluated using (i) the transformation of aurichalcite crystals at 298-475 K, (ii) the adsorption/desorption of pyridine on a Cu2O/ZnO junction, and (iii) the adsorption of CO on Pt/alumina pellets; it enables spatial and time resolution of processes in such diverse samples held at known thermal and baric conditions. The potential of this cell in catalytic and analytical science is considered

The interaction of p21Ras with neurofibromin

rasgenes encode guanine nucleotide binding proteins that act as molecular switches for signal transduction pathways controlling cell growth and differentiation. In the GTP- bound form the Ras protein is active and interacts with effector proteins to propagate a signal from the outside of the cell to the nucleus or cytoskeleton. Ras has a low intrinsic GTPase activity which is accelerated by the GTPase-activating proteins (GAPs), p120-GAP and neurofibromin. Two aspects of the interaction between Ras and the catalytic domain of neurofibromin (NF1334) have been studied. (1) The GTPase-activating activity of both p120-GAP and neurofibromin are inhibited by mitogenic lipids such as phosphatidic acid and arachidonic acid. Previous data on the differential inhibition of the two GAPs led to the hypothesis that both were effectors in a Ras-controlled mitogenic pathway. The mechanism of inhibition of NF1334 by arachidonic acid was studied by measuring the catalytic activity under multiple turnover conditions, using p-((6-phenyl)-1,3,5-hexatrienyl)benzoic acid as a fluorescent probe for ligands binding to GAPs and using a scintillation proximity assay to measure direct binding of Ras to NF1334. The inhibition by arachidonic acid included a major component that is competitive with Ras.GTP and an additional non-competitive type effect consistent with protein denaturing activity. This suggested that insomuch as the mitogenic effects of lipids are mediated via inhibition of GAPs, GAPs are not Ras effector proteins. (2) Basic residues within the catalytic domains of p120-GAP and neurofibromin have been suggested to play an important role in GAP-stimulated catalysis and Ras binding. Two invariant arginine residues within NF1334, R1276 and R1391, were mutated to alanine and their effects on maximal catalysis (kcat) affinity (Kd) for Ras measured under single turnover conditions. Both R1276 and R1391 are required for efficient catalysis by NF1334 as removal of either results in a 1000-fold loss of activity. R1276 is not thought to be directly involved in Ras binding as the affinity of R1276A for H-Ras or [Leu61]H-Ras is only moderately reduced (ca. 3-fold). The reduction in affinity of R1391A for H-Ras is more marked (ca. 10-20 fold) but most notable for [Leu61]H-Ras (ca. 100-fold) suggesting a role for this residue in Ras binding. The high affinity of [Leu61]H-Ras for NF1334 over H-Ras is completely lost with the R1391 NF1334, suggesting that the high affinity is related to an interaction with R1391 of NF133

Analysis of Pt/SnO(sub x) during catalysis of CO oxidation

Temperature-programmed reduction using 6kPaH2 suggests that a sample consisting of 3 percent Pt supported directly on SnO2 is, under conditions of catalysis of CO oxidation used here, best represented as 3 percent Pt/SnO sub x, since the support is likely to partially reduced, probably in the vicinity of the metal/oxide interface. Catalytic measurements at 421 to 424 K show that this 3 percent Pt/SnO sub x is significantly more active per unit area of Pt than 6 percent Pt/SiO2 in catalyzing the oxidation of CO. In situ micro-FTIR reveals that while the latter has predominantly linearly bound CO on the surface under reaction conditions, the Pt/SnO sub x also has a species absorbing at 2168 cm(exp -1) which may be CO upon Pt in a positive oxidation state or weakly chemisorbed CO on zero-valent Pt. This may be directly involved in the low temperature oxidation of CO on the Pt/SnO sub x, since being weakly held the activation energy for its surface diffusion to the metal/oxide interface will be low; such mobile species could allow the high rates of surface transport and an increase in the fraction of the surface over which the CO oxidation occurs. FTIR also reveals carbonate-type species on the P/SnO sub c surface

Calorimetry, activity, and micro-FTIR analysis of CO chemisorption, titration, and oxidation on supported Pt

The value of in situ analysis on CO chemisorption, titration and oxidation over supported Pt catalysts using calorimetry, catalytic and micro-FTIR methods is illustrated using silica- and titania-supported samples. Isothermal CO-O and O2-CO titrations have not been widely used on metal surfaces and may be complicated if some oxide supports are reduced by CO titrant. However, they can illuminate the kinetics of CO oxidation on metal/oxide catalysts since during such titrations all O and CO coverages are scanned as a function of time. There are clear advantages in following the rates of the catalyzed CO oxidation via calorimetry and gc-ms simultaneously. At lower temperatures the evidence they provide is complementary. CO oxidation and its catalysis of CO oxidation have been extensively studied with hysteresis and oscillations apparent, and the present results suggest the benefits of a combined approach. Silica support porosity may be important in defining activity-temperature hysteresis. FTIR microspectroscopy reveals the chemical heterogeneity of the catalytic surfaces used; it is interesting that the evidence with regard to the dominant CO surface species and their reactivities with regard to surface oxygen for present oxide-supported Pt are different from those seen on graphite-supported Pt

Gain of 20q11.21 in human pluripotent stem cells impairs TGF-β-dependent neuroectodermal commitment

Gain of 20q11.21 is one of the most common recurrent genomic aberrations in human pluripotent stem cells. Although it is known that overexpression of the antiapoptotic gene Bcl-xL confers a survival advantage to the abnormal cells, their differentiation capacity has not been fully investigated. RNA sequencing of mutant and control hESC lines, and a line transgenically overexpressing Bcl-xL, shows that overexpression of Bcl-xL is sufficient to cause most transcriptional changes induced by the gain of 20q11.21. Moreover, the differentially expressed genes in mutant and Bcl-xL overexpressing lines are enriched for genes involved in TGF-beta- and SMAD-mediated signaling, and neuron differentiation. Finally, we show that this altered signaling has a dramatic negative effect on neuroectodermal differentiation, while the cells maintain their ability to differentiate to mesendoderm derivatives. These findings stress the importance of thorough genetic testing of the lines before their use in research or the clinic

Factors affecting lower academic performance of grade 11 STEM students of ECT Excellencia Global Academy Foundation Inc.

This study aimed to determine the factors affecting the academic performance of grade 11 STEM students of ECT Excellencia Global Academy Foundation Inc. The factors affecting a student’s academic performance arise from several reasons. Accordingly, this study was done to identify the factors affecting the academic performance of grade 11 stem students, which may ultimately help in the improvement of both students and teachers. The students may gain from this research by being able to understand better the elements that may affect their academic performance. They might be able to improve their academic standing by using the findings that this investigation establishes. A quantitative research method was employed. The researchers primarily gathered the data for statistical analysis through which the specified survey questionnaires were distributed to the respondents in this research study. Average weighted mean was used to determine the level of impact of the different factors affecting the respondents’ academic performance

Sub-harmonic entrainment of cortical gamma oscillations to deep brain stimulation in Parkinson's disease: model based predictions and validation in three human subjects

Objectives The exact mechanisms of deep brain stimulation (DBS) are still an active area of investigation, in spite of its clinical successes. This is due in part to the lack of understanding of the effects of stimulation on neuronal rhythms. Entrainment of brain oscillations has been hypothesised as a potential mechanism of neuromodulation. A better understanding of entrainment might further inform existing methods of continuous DBS, and help refine algorithms for adaptive methods. The purpose of this study is to develop and test a theoretical framework to predict entrainment of cortical rhythms to DBS across a wide range of stimulation parameters. Materials and Methods We fit a model of interacting neural populations to selected features characterising PD patients' off-stimulation finely-tuned gamma rhythm recorded through electrocorticography. Using the fitted models, we predict basal ganglia DBS parameters that would result in 1:2 entrainment, a special case of sub-harmonic entrainment observed in patients and predicted by theory. Results We show that the neural circuit models fitted to patient data exhibit 1:2 entrainment when stimulation is provided across a range of stimulation parameters. Furthermore, we verify key features of the region of 1:2 entrainment in the stimulation frequency/amplitude space with follow-up recordings from the same patients, such as the loss of 1:2 entrainment above certain stimulation amplitudes. Conclusion Our results reveal that continuous, constant frequency DBS in patients may lead to nonlinear patterns of neuronal entrainment across stimulation parameters, and that these responses can be predicted by modelling. Should entrainment prove to be an important mechanism of therapeutic stimulation, our modelling framework may reduce the parameter space that clinicians must consider when programming devices for optimal benefit