Summary of ISO/TC 201 International Standard ISO 18516:2019 Surface chemical analysis—Determination of lateral resolution and sharpness in beam-based methods with a range from nanometres to micrometres and its implementation for imaging laboratory X-ray photoelectron spectrometers (XPS)

ISO 18516:2019 Surface chemical analysis—Determination of lateral resolution and sharpness in beam-based methods with a range from nanometres to micrometres revises ISO 18516:2006 Surface chemical analysis—Auger electron spectroscopy and X-ray photoelectron spectroscopy—Determination of lateral resolution. It implements three different methods delivering parameters useful to express the lateral resolution: (1) the straight edge method, (2) the narrow line method and (3) the grating method. The theoretical background of these methods is introduced in ISO/TR 19319:2013 Surface chemical analysis—Fundamental approaches to determination of lateral resolution and sharpness in beam-based methods. The revised International Standard ISO 18516 delivers standardized procedures for the determination of the (1) effective lateral resolution by imaging of square-wave gratings, the (2) lateral resolution expressed as the parameter D_12–88 characterizing the steepness of the sigmoidal edge spread function (ESF) determined by imaging a straight edge and (3) the lateral resolution expressed as the full width of half maximum of the line spread function (LSF), w_LSF, determined by imaging a narrow line. The last method also delivers information on the shape of the LSF, which characterizes an individual imaging instrument. Finally, the implementation of all three standardized methods in the field of imaging laboratory X-ray photoelectron spectroscopy (XPS) is shortly presented. This part of the letter is based on the use of a new test sample developed at ETH Zurich, Switzerland. This test sample displays a micrometre scaled pattern motivated by the resolving power of recent imaging XPS instruments.     

Fluorescence and liquid room-temperature phosphorescence of the aluminium-ferron chelate in vesicles

In order to evaluate the analytical potential of vesicles for enhancing the room-temperature luminescence of metal chelates, the photoluminescence emission of the aluminium-ferron complex in vesicular solutions was examined. The presence of vesicles of didodecyldimethylammonium bromide produced a six-fold enhancement in the fluorescence intensity of the metal chelate. Vesicles also proved to be efficient stabilizers to obtain analytically useful liquid room-temperature phosphorescence for aluminium. Optimum experimental conditions and luminescence characteristics of the aluminium complex in the presence of vesicles are described and compared with those obtained for the same chelate in micellar media. As a result, a vesicle-enhanced fluorimetric procedure is proposed which has been successfully applied to the determination of low levels of aluminium in milk powders.     

Modeling H-bonding and solvent effects in the alkylation of pyrimidine bases by a prototype quinone methide: a DFT study

Nucleophilicity of NH(2), N3, and O(2) centers of cytosine toward a model quinone methide (o-QM) as alkylating agent has been studied using DFT computational analysis [at the B3LYP/6-311+G(d,p) level]. Specific and bulk effects of water (by C-PCM model) on the alkylation pathways have been evaluated by analyzing both unassisted and water-assisted reaction mechanisms. An ancillary water molecule, H-bonded to the alkylating agent, may interact monofunctionally with the o-QM oxygen atom (passive mechanisms) or may participate bifunctionally in cyclic hydrogen-bonded structures as a proton shuttle (active mechanisms). A comparison of the unassisted with the water-assisted reaction mechanisms has been made on the basis of activation Gibbs free energies (DeltaG(++)). The gas-phase alkylation reaction at N3 does proceed through a passive mechanism that is preferred over both the active (by -6.3 kcal mol(-1)) and the unassisted process. In contrast, in the gas phase, the active assisted processes at NH(2) and O(2) centers are both favored over their unassisted counterparts by -4.0 and -2.2 kcal mol(-1), respectively. The catalytic effect of a water molecule, in gas phase, reduces the gap between the TSs of the O(2) and NH(2) reaction pathways, but the former remains more stable. Water bulk effect significantly modifies the relative importance of the unassisted and water-assisted alkylation mechanisms, favoring the former, in comparison to the gas-phase reactions. In particular, the unassisted alkylation becomes the preferred mechanism for the reaction at both the exocyclic (NH(2)) and the heterocyclic (N3) nitrogen atoms. By contrast, alkylation at the cytosine oxygen atom is a water-catalyzed process, since in water the active water-assisted mechanism is still favored. As far as competition, among all the possible mechanisms, our calculations unambiguously suggest that the most nucleophilic site both in gas phase (naked reagents: N3 > O(2) >or= NH(2)) and in water solution (solvated reagents: N3 > NH(2) > O(2)) is the heterocyclic nitrogen atom (N3) (DeltaG(++)(gas) = +7.1 kcal mol(-1), and DeltaG(++)(solv) = +13.7 kcal mol(-1)). Our investigation explains the high reactivity and selectivity of the cytosine moiety toward o-QM-like structures both in deoxymononucleoside and in a single-stranded DNA, on the basis of strong H-bonding interactions between reactants and solvent bulk effect. It also offers two general reactivity models in water, uncatalyzed and active water-catalyzed mechanisms (for nitrogen and oxygen nucleophiles, respectively), which should provide a general tool for the planning of nucleic acid modification.     

Neuraminic Acid Derivatives as Anti-Influenza Drugs

Influenza types A and B both cause serious disease in man; vaccines are in use but must be reformulated each year in response to antigenic variation and are frequently ineffective against new influenza variants. Influenza viruses are enveloped RNA viruses which contain two major surface glycoproteins: hemagglutinin (HA) and neuraminidase (NA, EC 3.2.1.18). These proteins are essential for infection and offer potential targets for antiviral drug development. Based upon the knowledge of the most important steps of the whole interaction between virus and host cell, the main purpose of our research was to find a sialic acid analogue for increasing the affinity of the sialic acid cell receptor analogue to the principal binding site of HA. A series of sialic acid analogues were prepared and their structures were designed with the goal to have molecules able to saturate the HA receptor and thereby be potentially useful as anti-influenza drugs.     

Synthesis and properties of aromatic polyamides with oligobenzamide pendent groups. I. Poly-5-(4-benzoylamino-1-benzoylamino)isophthalamides

A series of polyisophthalamides having pendent oligomeric benzamide groups were prepared by the Yamazaki reaction from common aromatic diamines and 5-(4-benzoylamino-1-benzoylamino)isophthalic acid. The latter was synthesized from 5-aminoisophthalic acid in a three-step synthesis by successive incorporation of benzamido groups. The new polymers were characterized by NMR, DSC, TGA, and WAXD and the properties were compared to those of corresponding unsubstituted polyisophthalamides. All of the polymers were essentially amorphous and their T_gs were about 20°C higher than the reference polymers. Initial thermal decomposition temperatures ranged from 375 to 420°C. All of the polymers were soluble in aprotic polar solvents without added salts. Properties of particular note were: the water uptake, which was particularly high, ranging from 7.5 to 18.2%, and the temporary insolubilization in concentrated sulfuric acid of films of the polymers heated for a short time to ≥ 200°C. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of halogen‐containing poly(ether ketone ketone)s

A series of novel poly(ether ketone ketone)s (PEKKs) were synthesized from diphenyl ether and isophthaloyl chloride derivatives such as 5‐halo‐ and 5‐tert‐butyl‐isophthaloyl chloride. The aromatic electrophilic substitution route to polyketones was a convenient route for the preparation of the polymers in high yields via precipitation polycondensation at a low temperature with aluminum trichloride as a catalyst. High molecular weight PEKKs were achieved with number‐average molecular weights of 15,000–100,000 g/mol for polymers that showed good solubility in organic solvents. The presence of substituents greatly modified the spectroscopic features in comparison with those of unsubstituted isophthaloyl poly(ether ketone ketone)s, particularly for the series containing halogens, for which significant variations of the chemical shifts in both ¹H and ¹³C NMR spectra were observed; these shifts could be related to the nature of the halogen. Thermal properties were also affected by the presence of pendent substituents, with clear enhancements of the glass‐transition temperatures, which could be ascribed to the nature and bulkiness of the substituents. Thermogravimetric analyses showed that the new polymers had good thermal resistance, although an important drop in thermal resistance was observed for polymers bearing large halogen atoms, such as bromine and iodine. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2601–2608, 2002     

Phosphorescence detection in flowing systems: selective determination of aluminium by flow-injection liquid room-temperature phosphorimetry

The concept of the micelle stabilized liquid room-temperature phosphorescence (MS-LRTP) was applied to the determination of a metal (aluminium) in a flowing system. A three-line flow-injection manifold was developed and various parameters were optimized. A linear calibration graph was obtained for 0–4 μg ml^?1 aluminium. The limit of detection was 50 ng ml^?1 and the relative standard deviations for 0.1 and 1.0 μg ml^?1 aluminium were 2.7 and 1.3% respectively. The proposed procedure is fairly selective. More than 20 common ions studied did not interfere with the determination of aluminium or could be masked by appropriate reagents. The flow-injection method proposed was applied without any preliminary separation to the determination of aluminium in simulated synthetic samples in water and in clinical samples of particular importance in the control of aluminium toxicity in renal failure patients.     

Chemiluminescence Triggered by Hydrolase Activity in a Horseradish Peroxidase/H2O2-Coupled Assay*

2-Methyl-1-propenyl acetate (MPA) was hydrolyzed by wheat lipase, pancreatic lipase, hydrolases and lipopro-tein lipase from serum in a reaction that produces 2-methyl-1-propenol. The latter was subsequently oxidized by horseradish peroxidase (HRP)/H₂O₂/O₂ yielding triplet acetone that emits visible light. The integrated light emission was proportional to the units of lipase or volume of serum present. When pancreatic lipase was assayed, light emission was observed in the presence of bile salt as surfactant and chlorophyll a as light sensitizer. The potential application of this reaction in determinations of hydrolase/Iipase activities is discussed.     

A comprehensive procedure based on gas chromatography–isotope ratio mass spectrometry following high performance liquid chromatography purification for the analysis of underivatized testosterone and its analogues in human urine

The confirmation by GC/C/IRMS of the exogenous origin of pseudo-endogenous steroids from human urine samples requires extracts of adequate purity. A strategy based on HPLC sample purification prior to the GC/C/IRMS analysis of human urinary endogenous androgens (i.e. testosterone, androsterone and/or androstenediols), is presented. A method without any additional derivatization step is proposed, allowing to simplify the urine pretreatment procedure, leading to extracts free of interferences permitting precise and accurate IRMS analysis, without the need of correcting the measured delta values for the contribution of the derivatizing agent. The HPLC extracts were adequately combined to both reduce the number of GC/C/IRMS runs and to have appropriate endogenous reference compounds (ERC; i.e. pregnanediol, 11-keto-etiocholanolone) on each GC–IRMS run. The purity of the extracts was assessed by their parallel analysis by gas chromatography coupled to mass spectrometry, with GC conditions identical to those of the GC/C/IRMS assay. The method has been validated according to ISO17025 requirements (within assay precision below 0.3 ‰ ¹³C delta units and between assay precision below 0.6 ‰ ¹³C delta units for most of the compounds investigated) fulfilling the World Anti-Doping Agency requirements.