The porosity, acidity, and reactivity of dealuminated zeolite ZSM-5 at the single particle level: the influence of the zeolite architecture

A combination of atomic force microscopy (AFM), high‐resolution scanning electron microscopy (HR‐SEM), focused‐ion‐beam scanning electron microscopy (FIB‐SEM), X‐ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron‐based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM‐5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol‐to‐olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM‐5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM‐5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 5–50 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Brønsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.     

Electrophoretic characterization of posttranslational modifications of human parotid salivary alpha-amylase.

Human salivary alpha-amylase displays multiple bands upon native polyacrylamide gel electrophoresis. In fresh saliva, due to posttranslational modifications, a pattern of 5-6 isozymes is observed. The isozymes are designated 1-6, in the order of increasing anodal mobility. As a result of the development of a rapid and sensitive electrophoresis system, with markedly higher resolution than previously reported, we concluded that a previously proposed model (Karn et al., Biochem. Genet. 1973, 10, 341-350) is inadequate to explain the origin of the various bands. We propose an alternative model that fits in with our new and previously made observations. According to this model, band 2 is the primary gene product and band 1 is its glycosylated counterpart--with only one neutral oligosaccharide present on each molecule. Band 3 originates from band 1 by the transialidase-catalyzed incorporation of sialic acid into the biantennary chain. Bands 4 and 6 originate from bands 2 and 4, respectively, by deamidation; band 5 is the deamidation product of amylase with an acidic oligosaccharide (band 3). Only a minor part of band 3 consists of the deamidation product of band 1. Peptide Asn-Gly-Ser (residues 427-429) is the most probable candidate for glycosylation; literature data suggests that deamidation occurs in the stretch Glu-Asn-Gly-Lys-Asp (residues 364-368) and Asn-Gly-Asn-Cys (residues 474-477). Both glycosylation and deamidation might play a role in the clearance of amylase from the systemic circulation. The electrophoresis system described is a powerful tool to determine amylase isozyme distributions in health and disease, especially for the screening of alterations seen in ectopically produced amylase.     

Properties of Bangdiwala’s B

Advances in Data Analysis and Classification - Cohen’s kappa is the most widely used coefficient for assessing interobserver agreement on a nominal scale. An alternative coefficient for...     

Steering the Selectivity of Electrocatalytic Glucose Oxidation by the Pt Oxidation State

Electrocatalytic glucose oxidation can produce high value chemicals, but selectivity needs to be improved. Here we elucidate the role of the Pt oxidation state on the activity and selectivity of electrocatalytic oxidation of glucose with a new analytical approach, using high-pressure liquid chromatography and high-pressure anion exchange chromatography. It was found that the type of oxidation, i.e. dehydrogenation of primary and secondary alcohol groups or oxygen transfer to aldehyde groups, strongly depends on the Pt oxidation state. Pt⁰ has a 7-fold higher activity for dehydrogenation reactions than for oxidation reactions, while PtO_x is equally active for both reactions. Thus, Pt⁰ promotes glucose dialdehyde formation, while PtO_x favors gluconate formation. The successive dehydrogenation of gluconate is achieved selectively at the primary alcohol group by Pt⁰, while PtO_x also promotes the dehydrogenation of secondary alcohol groups, resulting in more complex reaction mixtures.     

A comparison of reliability coefficients for psychometric tests that consist of two parts

If a test consists of two parts the Spearman–Brown formula and Flanagan’s coefficient (Cronbach’s alpha) are standard tools for estimating the reliability. However, the coefficients may be inappropriate if their associated measurement models fail to hold. We study the robustness of reliability estimation in the two-part case to coefficient misspecification. We compare five reliability coefficients and study various conditions on the standard deviations and lengths of the parts. Various conditional upper bounds of the differences between the coefficients are derived. It is shown that the difference between the Spearman–Brown formula and Horst’s formula is negligible in many cases. We conclude that all five reliability coefficients can be used if there are only small or moderate differences between the standard deviations and the lengths of the parts.     

Efficient Intermolecular Charge Transport in Self-Assembled Fibers of Mono- and Bithiophene Bisurea Compounds

Hydrogen bonds between urea units allow self-organization of π systems in mono- and bithiophenes into fibers as shown schematically. In these fibers there is a surprisingly high mobility of charge carriers as determined by pulse-radiolysis time-resolved microwave conductivity measurements.