Cesium salt of a heteropolyacid in nanotubular channels and on the external surface of SBA-15 crystals: preparation and performance as acidic catalysts

The Cs-salt of heteropolyacid with stoichiometry Cs_2.5H_0.5PW₁₂O₄₀ (CsHPW) was deposited selectively at the external surface of the SBA-15 silica microcrystals, inside its mesoporous channels and simultaneously at both location modes. The structure, texture and performance of these CsHPW/SBA-15 composites were compared with that of a reference bulk salt of the same composition. Location of CsHPW salt on the external surface of SBA-15 microcrystals leads to disintegration of its agglomerates increasing acidity of the catalytic phase. A novel preparation strategy consisting of grafting the basic Cs-species at the internal pores surface of SBA-15 stabilized the CsHPW phase inside the channels in form of 5–8 nm nanocrystals at 30–70 wt.% loadings. The catalytic tests demonstrated that insertion of the CsHPW catalytic phase inside the nanotubular channels of SBA-15 in combination with location of an additional amount of this phase at the external surface of SBA-15 microcrystals allows to increase the specific activity of this phase in MTBE synthesis, propionylation of anisole and alkylation of catechol with t-butanol by a factor of 1.5–3. This level of specific activity in combination with high total loading of catalytic phase >60 wt.% permit to get composite catalytic materials with catalytic activity higher by a factor of 1.2–1.5 with respect to the bulk CsHPW catalyst and stabilizing the catalytic phase against colloidization in polar media.     

Involvement of surface cysteines in activity and multimer formation of thimet oligopeptidase

Thimet oligopeptidase is a metalloenzyme involved in regulatingneuropeptide processing. Three cysteine residues (246, 248,253) are known to be involved in thiol activation of the enzyme.In contrast to the wild-type enzyme, the triple mutant (C246S/C248S/C253S)displays increased activity in the absence of dithiothreitol.Dimers, purportedly formed through cysteines 246, 248 and 253,have been thought to be inactive. However, analysis of the triplemutant by native gel electrophoresis reveals the existence ofdimers and multimers, implying that oligomer formation is mediatedby other cysteines, probably on the surface, and that some ofthese forms are enzymatically active. Isolation and characterizationof iodoacetate-modified monomers and dimers of the triple mutantrevealed that, indeed, certain dimeric forms of the enzyme arestill fully active, whereas others show reduced activity. Cysteineresidues potentially involved in dimerization were identifiedby modeling of thimet oliogopeptidase to its homolog, neurolysin.Five mutants were constructed; all contained the triple mutationC246S/C248S/C253S and additional substitutions. Substitutionsat C46 or C682 and C687 prevented multimer formation and inhibiteddimer formation. The C46S mutant had enzymatic activity comparableto the parent triple mutant, whereas that of C682S/C687S wasreduced. Thus, the location of intermolecular disulfide bonds,rather than their existence per se, is relevant to activity.Dimerization close to the N-terminus is detrimental to activity,whereas dimerization near the C-terminus has little effect.Altering disulfide bond formation is a potential regulatoryfactor in the cell owing to the varying oxidation states insubcellular compartments and the different compartmental locationsand functions of the enzyme. Received March 1, 2003; revised June 17, 2003; accepted June 23, 2003.     

Dependence of the growth rate of an AlN layer on nitrogen pressure in a reactor for sublimation growth of AlN crystals

The dependence of the layer growth rate on nitrogen pressure in a reactor has been examined in order to analyze the conditions of growth of AlN thick layers and bulk crystals by the sublimation sandwich method. It is shown that the layer growth rate steadily increases as the pressure in the reactor is lowered within the range 1–0.02 bar. This suggests that a key role in the layer growth kinetics is played by the source-to-substrate transfer of the components (Al, N), rather than by their adsorption (desorption) on the substrate surface.     

Solution structure and dynamics of a serpin reactive site loop using interleukin 1 as a presentation scaffold

Human interleukin-1ß (IL1ß) was used as a presentationscaffold for the characterization of the reactive site loop(RSL) of the serpin 1-antitrypsin (A1AT), the physiologicalinhibitor of leukocyte elastase. A chimeric protein was generatedby replacement of residues 50–53 of IL1ß, correspondingto an exposed reverse turn in IL1ß, with the 10-residueP5-P5' sequence EAIPMSIPPE from A1AT. The chimera (antitrypsin-interleukin,AT-IL) inhibits elastase specifically and also binds the IL1ßreceptor. Multinuclear NMR characterization of AT-IL establishedthat, with the exception of the inserted sequence, the structureof the IL1ß scaffold is preserved in the chimera. Thestructure of the inserted RSL was analyzed relative to thatof the isolated 10-residue RSL peptide, which was shown to beessentially disordered in solution. The chimeric RSL was alsofound to be solvent exposed and conformationally mobile in comparisonwith the IL1ß scaffold, and there was no evidence of persistinginteractions with the scaffold outside of the N- and C-terminallinkages. However, AT-IL exhibits sigificant differences inchemical shift and NOE patterns relative to the isolated RSLthat are consistent with local features of non-random structure.The proximity of these features to the P1-P1' residues suggeststhat they may be responsible for the inhibitory activity ofthe chimera.     

Temperature dependant flash memory erase transient simulation (Part I)

We present a detailed and accurate physics based transient simulation for modeling flash memory erasing at ambient and non-ambient temperatures. Typical cells are erased by moving electrons from the floating gate to the drain, source or substrate. Part I of this paper addresses substrate erase modeling using a simulation based on the solution to Poisson’s equation with temperature as an independent variable. The goal of this paper is to demonstrate the derivation of an accurate erase simulation and show the effects of temperature on the threshold voltage shift during the erase process. Several papers have been published on this topic but fail to present detailed derivations and none using this exact set of equations to model the temperature dependent erasing process.     

High resolution sonographic determination of the normal dimensions of the intracranial extraaxial compartment in the newborn infant

Prominence of the extraaxial space occasionally is encountered in infants referred for ultrasonography to exclude hydrocephalus. The interpretation of this finding can be problematic. We examined the width of the extraaxial compartment in 82 normal newborn infants. Scanning technique was optimized for viewing the near field, and the extraaxial space was measured over the cerebral convexities. Correlation was made with demographic variables. Measurements varied from 0 to 3.3 mm (mean, 1.6 mm), with slight negative linear relationship to gestational age. We conclude that small amounts of extraaxial fluid, up to 3.3 mm in width on scans, are common and normal in newborn infants.     

Validation of a French version of an informant-based questionnaire as a screening test for Alzheimer's disease

BACKGROUND: Development of informant-based screening tests for dementia is an emerging field. The reliability and validity of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE), an instrument that screens for dementia in general, have been established. We conducted a study to validate a French version of the IQCODE as a screening test for Alzheimer's dementia in the elderly living in the community. METHOD: In the Canadian Study of Health and Aging, subjects were screened in their own homes using the modified Mini-Mental State Exam (3-MS). Those who screened positive, along with a sample of subjects who screened negative, were referred for a complete clinical examination. In Quebec, an informant was asked to complete the French version, IQCODE(F), at that time. Based on the final clinical diagnoses, performances of the IQCODE(F) and Mini-Mental State Examination (MMSE, converted from 3-MS) in screening for Alzheimer's disease were evaluated. RESULTS: Of the 237 subjects, the mean IQCODE (F) score was 3.4 (s.d. = 0.6), on a 5-point scale (1 = improvement in condition over the past 10 years, 5 = marked deterioration, 3 = no change). The mean MMSE score was 23.1 (s.d. = 4.5). The scores on the two scales were correlated (r = -0.44, P < 0.001). The IQCODE(F) scores were unrelated to education (r = -0.07, P > 0.3) in contrast to the MMSE scores (r = 0.28, P < 0.001). With respect to a diagnosis of probable Alzheimer's disease, the IQCODE(F) (cut-off point 3.6) had a sensitivity of 75% and a specificity of 95.6%. The sensitivity and specificity of the MMSE (cut-off point 23) were 70% and 82.3% respectively. CONCLUSION: The findings of the IQCODE(F) are consistent with those of the English version in correlation with the MMSE and apparent freedom from educational bias. The IQCODE is superior to the MMSE as a screening test for probable Alzheimer's disease in the elderly living in the community. It may be a useful addition to the screening tests already available, especially for the less well educated.