Analysis of medium-range order based on simulated segmented ring detector STEM-images: amorphous Si.

Properties of amorphous materials are connected to the local structure at the nanoscale, which is typically described in terms of short- and medium-range order (SRO, MRO). Variable resolution fluctuation electron microscopy (VR-FEM) is a sensitive method to characterize the underlying characteristic length scale of MRO of amorphous samples (Voyles, Gibson and Treacy, J. Electron Microsc. 49 (2000) 259). VR-FEM data was acquired using scanning transmission electron microscopy (STEM), collecting a large number of nano-beam diffraction patterns (NBDPs) with various probe sizes. Here we present an advanced method to accelerate the calculation of simulated FEM normalized variance profiles using a newly developed simulation and analysis approach with segmented ring detectors using the program STEMcl (Radek et al., Ultramicroscopy 188 (2018) 24). VR-FEM simulations are based on structures obtained from molecular dynamics (MD) simulations. A comparison between simulated and experimental VR-FEM profiles with respect to peak position, ratio and shape (and intensity) show good agreement. Moreover, a crystalline cluster of 1 nm in size was embedded into the MD box to test the validity of the paracrystalline approximation with the pair-persistence analysis suggested by Gibson et al. (Gibson, Treacy and Voyles, Ultramicroscopy 83 (2000) 169). The corresponding VR-FEM simulation and calculation of MROs yield close results to the size of the initially embedded crystalline cluster, which supports both the paracrystalline approach and the validity of the segmented detector simulation. Additionally, we conclude that continuous random network (CRN) amorphous silicon models contain a higher degree of MRO than experimentally expected.

Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements.

Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600° C. The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q=(2.70±0.11) eV and preexponential factor D_{0}=(5.5_{-3.7}^{+11.1})×10^{-2} cm^{2} s^{-1}. Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.025901).

Determination of biogenic amines in infusions of tea (Camellia sinensis) by HPLC after derivatization with 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl).

The reagent 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) was used for the pre-column derivatization of the biogenic amines (BAs) cadaverine (Cad), histamine (Him), octopamine (Ocp), phenylethylamine (Pea), putrescine (Put), spermidine (Spd), spermine (Spm), tyramine (Tym) and the internal standard 1,6-diaminohexane (Dhx). The resulting Fmoc-derivatives were resolved by high-performance liquid chromatography on a Superspher(©) C(18) column using a binary gradient generated from sodium acetate and acetonitrile. For quantification, the fluorescence of derivatives was used at 263 nm excitation and 313 nm emission wavelength. This approach was applied to free BAs extractable with boiling water from 14 black, 5 green, 1 Oolong, and 1 instant tea. Infusions were prepared by adding 35 ml boiling water to one gram of tea and extracted for 20 min. In the Oolong tea and two black teas, no BAs could be detected. Limits of detection were 0.07-1.0 pmol for BAs at signal-to-noise ratio 3:1. Besides most abundant Tym and Spm lower quantities of Pea, Put, and Spd were detected, albeit not in all teas. Quantities of Tym ranged from 16 to 431 µg Tym/L infusion (1.1-25.3 µg Tym/g tea) and 31 to 319 µg Spm/L infusion (1.5-16.9 µg Spm/g tea). In none of the teas, Him was detected. Owing to the low amounts of free BAs in tea infusions, no health risks are to be expected even on consumption of large quantities of tea as beverage.

Peptaibiomics: an advanced, rapid and selective analysis of peptaibiotics/peptaibols by SPE/LC-ES-MS.

"Proteomics" and "peptidomics" are used as technical terms to define the analysis and study of all proteins and peptides expressed in an organism or tissue. In analogy we propose the name peptaibiomics for the analysis of a group of fungal peptide antibiotics (peptaibiotics) containing the characteristic amino acid Aib (alpha-aminoisobutyric acid). In analogy to the peptidome the complete expression of peptaibiotics by fungal multienzyme complexes should be named the peptaibiome. Peptaibiotics are defined as peptides containing Aib and exerting a variety of bioactivities. They comprise the sub-groups of N-acetylated peptaibols, characterized also by a C-terminal amide-linked 2-amino alcohol, and lipopeptaibols having in place of an acetyl group a lipophilic fatty acid acyl group. Furthermore, lipoaminopeptides are also known with long-chain fatty acid on the N-termini, a lipoamino acid in position three and a strongly basic secondary or tertiary amine form a subgroup of mixed forms which could not be integrated in one of these three previously mentioned groups. Here we present a specific and rapid screening method on the peptaibiome applicable directly onto filamentous fungi cultured in a single Petri dish. The method comprises solid-phase extraction (SPE) of peptaibiotics followed by on-line reversed-phase HPLC coupled to an ion trap electrospray tandem mass spectrometer (ES-MS). The presence of these peptides is indicated by characteristic mass differences of Deltam = 85.1 Da representing Aib-residues which can be observed in the b-series of acylium fragment ions resulting from ES-MS. Partial sequences can be deduced from the data and compared with structures compiled in electronic peptaibol data bases. The judgement is possible whether or not structures are novel, already known or related to known structures. Suitability of the method is demonstrated with the analysis of strains of Trichoderma and its teleomorph Hypocrea. New sequences of peptaibiotics are presented and those being related to established 10- to 18-residue peptaibols trichovirin, trichogin and trichotoxin, which have been described in the literature.

Modulation of lymphocyte phenotype and function by immunoglobulins.

BACKGROUND: Immunoglobulins have immune-modulating capacities and are used for the treatment of different dermatological diseases. They have also been reported for the treatment of severe atopic dermatitis (AD). OBJECTIVES: To determine the effects of immunoglobulins on the phenotype and function of peripheral T and B lymphocytes from patients with AD in comparison with healthy donors (HD) as controls. METHODS: We studied lymphocyte activation and T-cell cytokine production from 12 patients with AD and 10 HD by multicolour flow cytometric analysis in the presence of immunoglobulins. RESULTS: Immunoglobulins significantly inhibited T-cell activation (CD69), by 71% (AD) and by 62% (HD). Production of interferon-gamma and interleukin-4 was also significantly inhibited, by 44%/24% (AD) and 38%/10% (HD), respectively. In addition, CD86 expression on B lymphocytes was downregulated by 30% in AD and by 29% in HD, whereas CD23 expression was decreased without reaching statistical significance. CONCLUSIONS: Our data demonstrate that, in vitro, immunoglobulins modulate the activation and cytokine production of peripheral blood lymphocytes from both HD and patients with AD.

Single-electron-phonon interaction in a suspended quantum dot phonon cavity.

An electron-phonon cavity consisting of a quantum dot embedded in a freestanding GaAs/AlGaAs membrane is characterized using Coulomb blockade measurements at low temperatures. We find a complete suppression of single electron tunneling around zero bias leading to the formation of an energy gap in the transport spectrum. The observed effect is induced by the excitation of a localized phonon mode confined in the cavity. This phonon blockade of transport is lifted at discrete magnetic fields where higher electronic states with nonzero angular momentum are brought into resonance with the phonon energy.

Saccharide induced racemization of amino acids in the course of the Maillard reaction.

The formation of D-amino acids on heating aqueous solutions of protein L-amino acids at pH 2.5 and pH 7.0 together with glucose, fructose or saccharose was investigated by enantioselective gas chromatography. The saccharide induced partial racemization (epimerisation) of L-amino acids is attributed to the Maillard reaction.

Liquid chromatographic determination of biogenic amines in fermented foods after derivatization with 3,5-dinitrobenzoyl chloride.

The reagent 3,5-dinitrobenzoyl chloride (DNBZ-Cl) was tested for pre-column derivatization of biogenic amines (BAs). Samples were derivatized within 3 min in 1 M NaOH at ambient temperature by adding 2-propanole and 50 mM DNBZ-Cl in acetonitrile. The reaction was terminated by addition of 2 M HCl. For high-performance liquid chromatography an encapsulated stationary reversed-phase and gradient elution using a ternary gradient system were used. The DNBZ derivatives were quantified by their UV-absorption at 260 nm. The structures of the derivatives were elucidated using coupling of HPLC with electrospray ionization mass spectrometry. Detection limits of BAs were approximately 124-864 microg l(-1) (injected amounts 203-1410 pg) at a signal-to-noise ratio of 3:1. The coefficients of determination were 0.989-0.996, with the exceptions of cadaverine (0.976) and serotonin (0.965). The method was applied to the quantitative determination of agmatine, cadaverine, histamine, octopamine, 2-phenylethylamine, putrescine, serotonin, spermidine, spermine, tryptamine and tyramine, in fermented cabbage juices, soy sauces, Misos (soy pastes), fermented fish sauces, and anchovy paste.

Structures of trichovirins II, peptaibol antibiotics from the mold Trichoderma viride NRRL 5243.

From the culture broth of the mold Trichoderma viride NRRL 5243 a mixture of polypeptides, named trichovirins (TV), could be isolated and purified by chromatography on XAD-2 adsorber resin and Sephadex LH-20 gel. Chromatography on silica gel using chloroform/methanol 8:2 as eluent provided a mixture of peptides named TV I. Subsequent elution with chloroform/methanol 1:1 yielded a second group of peptides named TV II. That group could be separated into individual components by repetitive HPLC on an octadecylsilyl and a fluorocarbon stationary phase. The sequences of 12 peptides of TV II could be determined by electrospray ionization tandem mass spectrometry of isolated peptides and gas chromatography-mass spectrometry of methanolysates. The N-termini of the 18-mer peptides are acetylated and the C-termini consist of leucinol. Owing to the presence of alpha-aminoisobutyric acid (Aib) residues and the bactericidal and hemolytic activity, the peptides belong to the family of peptaibol antibiotics.

Asbestos-induced lung epithelial permeability: potential role of nonoxidant pathways.

Asbestos fibers are an important cause of lung fibrosis; however, the biological mechanisms are incompletely understood. The lung epithelium serves an important barrier function in the lung, and disrupting the epithelial barrier can contribute to lung fibrosis. Lung epithelial permeability is increased in patients with asbestosis, and asbestos fibers increase permeability across cultured human lung epithelium. However, the mechanism of this increased permeability is not known. Many of the biological effects of asbestos are postulated to be due to its ability to generate oxidants, and oxidants are known to increase epithelial permeability. However, we previously reported that altering the iron content of asbestos (important in oxidant generation) had no effect on its ability to increase permeability. For that reason, we undertook these studies to determine whether asbestos increases epithelial permeability through nonoxidant pathways. Both extracellular (H2O2) and intracellular (menadione) oxidants increase paracellular permeability across human lung epithelial monolayers. Extracellular catalase but not superoxide dismutase prevented increased permeability after both oxidant exposures. However, catalase offered no protection from asbestos-induced permeability. We next depleted the cells of glutathione or catalase to determine whether depleting normal cellular antioxidants would increase the sensitivity to asbestos. Permeability was the same in control cells and in cells depleted of these antioxidants. In addition to generating oxidants, asbestos also activates signal transduction pathways. Blocking protein kinase C activation did not prevent asbestos-induced permeability; however, blocking tyrosine kinase with tyrophostin A25 did prevent asbestos-induced permeability, and blocking tyrosine phosphatase with sodium vanadate enhanced the effect of asbestos. These data demonstrate that asbestos may increase epithelial permeability through nonoxidant pathways that involve tyrosine kinase activation. This model offers an important system for studying pathways involved in regulating lung epithelial permeability.

The chondromucosal sleeve for the secondary correction of the unilateral cleft lip nasal deformity.

We present a new procedure for the secondary correction of the cleft lower lateral cartilage in the unilateral cleft lip nose deformity. A chondromucosal sleeve based entirely on mucosa is combined with an open rhinoplasty to facilitate a medial to lateral rotation of the cleft lower lateral cartilage. In 52 patients, we have found that this technique improved the results of the deformity and is more successful than lateral to medial rotation procedures alone. The chondromucosal sleeve adds to the medial to lateral rotation techniques the ability to obtain a controllable and reproducible result.

Liquid chromatographic resolution of the isomers of tipredane and phenylthioproline using urea-solubilized beta-cyclodextrin in the mobile phase.

Two LC assays were developed using urea-solubilized beta-cyclodextrin (beta-CD) as a mobile phase additive in combination with reversed-phase columns. A methylsilane column gave optimal resolution of the steroid tipredane from its epimer. An investigation of the effects of beta-CD concentration, column temperature, column type, and addition of ethanol on the chromatographic separation is detailed. The enantiomer and diastereoisomers of L-cis-phenylthioproline were best resolved by urea-solubilized beta-cyclodextrin and a trimethylsilane column. The elution order of L-cis-phenylthioproline relative to its stereoisomers was reversed after adding ethanol to the beta-CD containing mobile phase or by changing from a beta-CD to an acetylated beta-CD column. The resolution factors for these separations obtained using the beta-CD mobile phase were larger than those obtained using beta-CD columns. Mobile phases containing up to 0.15 M beta-CD and 8 M urea were investigated. The separation of these isomers are dramatically affected by column polarity.

High-performance liquid chromatography of the drug fosenopril.

High-performance liquid chromatography was used to determine the purity and impurities of fosinopril, an angiotensin-converting enzyme inhibitor used to treat hypertension. Purity values are determined using a silica column and usually are above 99%. All known possible impurities, including stereoisomeric impurities, can be resolved and quantified by injecting solutions of fosinopril onto three separate columns; silica, strong anion exchange and phenyl. Typical impurity contents total 0.5%. Validation data and a study of properties of fosinopril in solution is included.

Inter-laboratory transfer of HPLC methods: problems and solutions.

As high-performance liquid chromatography (HPLC), the premier analytical technique in the pharmaceutical industry, becomes more ubiquitous, methods are more frequently being transferred from one laboratory to another. This review will discuss sources of failures to reproduce HPLC procedures, ranging from sample handling and preparation, through mobile phase, injector, column, detector and data manipulation problems. Also to be considered will be the precautions that should be taken, when initially developing a method, to obviate future problems. These precautions include using stable, well-defined analytical columns, buffered mobile phases, low wavelengths (or a mass-sensitive detector) and internal tests for accuracy; based on the author's experiences. Since the laboratory that originally developed the procedure has the moral obligation and, perhaps, the regulatory responsibility to "guarantee" that the method will perform successfully elsewhere, a series of increasingly comprehensive steps will be given, based on practice, to be followed by the laboratory that could not reproduce the procedure. Also to be discussed are approaches for treating methods that were initially successful but have slowly deteriorated and now fail, and several examples of procedures that were not reproducible in some other laboratories.

Induction of tryptophan degradation in vitro and in vivo: a gamma-interferon-stimulated activity.

Human recombinant gamma interferon (rHuIFN-gamma) was found to induce tryptophan degradation in vitro in human cell cultures and in vivo in participants in phase I clinical trials. When human lung fibroblasts were treated with various concentrations of rHuIFN-gamma, they degraded tryptophan in a dose- and time-dependent manner. No tryptophan degradation was observed when cells were incubated in growth medium alone or in medium supplemented with human recombinant beta-interferon (rHuIFN-beta ser). Similarly human bladder carcinoma cells were induced to catabolize tryptophan after incubation with rHuIFN-gamma, but no activity was observed in untreated cells or cells treated with either rHuIFN-beta ser or human naturally produced alpha-interferon (HuIFN-alpha). When tryptophan plasma levels were measured in cancer patients who had received i.v. bolus injections of rHuIFN-gamma as part of a phase I clinical trial, decreased tryptophan levels were observed when compared with pretreatment values or values obtained from individuals who had received i.v. injections of HuIFN-alpha. Urine analyses were suggestive that plasma tryptophan degradation occurred via the kynurenine catabolic pathway in individuals who received rHuIFN-gamma. We conclude that tryptophan degradation is an activity induced in vitro and in vivo in response to exogenous IFN-gamma but not to IFN-alpha or IFN-beta. Tryptophan degradation may play an important role in the mechanism of antiproliferative, immunologic, and clinical side effects of IFN-gamma.

Analysis of captopril and hydrochlorothiazide combination tablet formulations by liquid chromatography.

A reverse-phase, high-performance liquid chromatographic (HPLC) procedure was developed for the simultaneous assay of captopril and hydrochlorothiazide in a combination tablet formulation. Gradient elution was used to quantify these two drugs, as well as the oxidized form of captopril, the disulfide. Tablets were extracted with methanol and, after centrifugation, were chromatographed. Initially, a methanol-0.05% aqueous phosphoric acid (25:75, v/v) solution was pumped at 2 mL/min into a phenyl column. After 8 min, the flow rate was increased to 4.5 mL/min and the methanol content of the mobile phase was increased to 45% to elute the disulfide. Detection was at 210 nm. Linearity and repeatability of all constituents were satisfactory. The hydrolytic degradation product of hydrochlorothiazide, 4-amino-6-chloro-1,3-benzene disulfonamide (also called the disulfonamide ), could be resolved in test solutions but was not visible in chromatograms of tablets carried through the gradient procedure even after storage at elevated temperatures for prolonged time periods prior to assay. The method can be automated.

High-performance liquid chromatographic analysis of nadolol and bendroflumethiazide combination tablet formulations.

A reverse-phase high-performance liquid chromatographic (HPLC) method was developed for the simultaneous assay of nadolol and bendroflumethiazide in tablet formulations. The tablets were extracted with methanol and, after centrifugation, were chromatographed. A phenyl column was used with a mobile phase of aqueous acetate buffer with sodium chloride-methanol (60:40); detection was at 270 nm. Linearity of both drugs was satisfactory. The procedure can be automated and also applied to bendroflumethiazide formulations and bulk material.