Late-Stage Diversification of Tryptophan-Derived Biomolecules.

Gruß H, Sewald N. Late-Stage Diversification of Tryptophan-Derived Biomolecules. Chemistry - A European Journal. 2020;26(24):5328-5340.Pd-mediated reactions have emerged as a powerful tool for the site-selective and bioorthogonal late-stage diversification of amino acids, peptides and related compounds. Indole moieties of tryptophan derivatives are susceptible to C2 H-activation, whereas halogenated aromatic amino acids such as halophenylalanines or halotryptophans provide a broad spectrum of different functionalisations. The compatibility of transition-metal-catalysed cross-couplings with functional groups in peptides, other biologically active compounds and even proteins has been demonstrated. This Review primarily compiles the application of different cross-coupling reactions to modify halotryptophans, halotryptophan containing peptides or halogenated, biologically active compounds derived from tryptophan. Modern approaches use regio- and stereoselective biocatalytic strategies to generate halotryptophans and derivatives on a preparative scale. The combination of bio- and chemocatalysis in cascade reactions is given by the biocompatibility and bioorthogonality of Pd-mediated reactions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

A lattice dynamical treatment for the total potential energy of single-walled carbon nanotubes and its applications: relaxed equilibrium structure, elastic properties, and vibrational modes of ultra-narrow tubes

In this paper, we proposed a lattice dynamic treatment for the total potential energy for single-walled carbon nanotubes (SWCNT's) which is, apart from a parameter for the non-linear effects, extracted from the vibrational energy of the planar graphene sheet. Based upon the proposal, we investigated systematically the relaxed lattice configuration for narrow SWCNT's, the strain energy, the Young's modulus and Poisson ratio, and the lattice vibrational properties respected to the relaxed equilibrium tubule structure. Our calculated results for various physical quantities are nicely in consistency with existing experimental measurements. Particularly, we verified that the relaxation effect brings the bond length longer and the frequencies of various optical vibrational modes softer; Our calculation provides the evidence that the Young's modulus of armchair tube exceeds that of the planar graphene sheet, and the large diameter limits of the Young's modulus and Poisson ratio are in agreement with the experimental values of the graphite; The calculated radial breathing modes for the ultra narrow tubes with diameter range between 0.2 - 0.5 nm coincide the experimental results and the existing {\it ab initio} calculations with satisfaction; For narrow tubes of diameter 2 nm, the calculated frequencies of optical modes in tubule tangential plane as well as those of radial breathing modes are also in good agreement with the experimental measurement. In addition, our calculation shows that various physical quantities of relaxed SWCNT's can actually be expanded in terms of the chiral angle defined for the correspondent ideal SWCNT's.Comment: 9 pages, 7 figure

Doped carbon nanotubes as a model system of biased graphene

Albeit difficult to access experimentally, the density of states (DOS) is a key parameter in solid state systems which governs several important phenomena including transport, magnetism, thermal, and thermoelectric properties. We study DOS in an ensemble of potassium intercalated single-wall carbon nanotubes (SWCNT) and show using electron spin resonance spectroscopy that a sizeable number of electron states are present, which gives rise to a Fermi-liquid behavior in this material. A comparison between theoretical and the experimental DOS indicates that it does not display significant correlation effects, even though the pristine nanotube material shows a Luttinger-liquid behavior. We argue that the carbon nanotube ensemble essentially maps out the whole Brillouin zone of graphene thus it acts as a model system of biased graphene

van der Waals interaction in nanotube bundles : consequences on vibrational modes

We have developed a pair-potential approach for the evaluation of van der Waals interaction between carbon nanotubes in bundles. Starting from a continuum model, we show that the intertube modes range from $5 cm^{-1}$ to $60 cm^{-1}$. Using a non-orthogonal tight-binding approximation for describing the covalent intra-tube bonding in addition, we confirme a slight chiral dependance of the breathing mode frequency and we found that this breathing mode frequency increase by $\sim$ 10 % if the nanotube lie inside a bundle as compared to the isolated tube.Comment: 5 pages, 2 figure

Ab-initio structural, elastic, and vibrational properties of carbon nanotubes

A study based on ab initio calculations is presented on the estructural, elastic, and vibrational properties of single-wall carbon nanotubes with different radii and chiralities. We use SIESTA, an implementation of pseudopotential-density-functional theory which allows calculations on systems with a large number of atoms per cell. Different quantities like bond distances, Young moduli, Poisson ratio and the frequencies of different phonon branches are monitored versus tube radius. The validity of expectations based on graphite is explored down to small radii, where some deviations appear related to the curvature effects. For the phonon spectra, the results are compared with the predictions of the simple zone-folding approximation. Except for the known defficiencies of this approximation in the low-frequency vibrational regions, it offers quite accurate results, even for relatively small radii.Comment: 13 pages, 7 figures, submitted to Phys. Rev. B (11 Nov. 98

Density functional theory calculations of the carbon ELNES of small diameter armchair and zigzag nanotubes: core-hole, curvature and momentum transfer orientation effects

We perform density functional theory calculations on a series of armchair and zigzag nanotubes of diameters less than 1nm using the all-electron Full-Potential(-Linearised)-Augmented-Plane-Wave (FPLAPW) method. Emphasis is laid on the effects of curvature, the electron beam orientation and the inclusion of the core-hole on the carbon electron energy loss K-edge. The electron energy loss near-edge spectra of all the studied tubes show strong curvature effects compared to that of flat graphene. The curvature induced $\pi-\sigma$ hybridisation is shown to have a more drastic effect on the electronic properties of zigzag tubes than on those of armchair tubes. We show that the core-hole effect must be accounted for in order to correctly reproduce electron energy loss measurements. We also find that, the energy loss near edge spectra of these carbon systems are dominantly dipole selected and that they can be expressed simply as a proportionality with the local momentum projected density of states, thus portraying the weak energy dependence of the transition matrix elements. Compared to graphite, the ELNES of carbon nanotubes show a reduced anisotropy.Comment: 25 pages, 15 figures, revtex4 submitted for publication to Phys. Rev.

Theory of coherent phonons in carbon nanotubes and graphene nanoribbons

We survey our recent theoretical studies on the generation and detection of coherent radial breathing mode (RBM) phonons in single-walled carbon nanotubes and coherent radial breathing like mode (RBLM) phonons in graphene nanoribbons. We present a microscopic theory for the electronic states, phonon modes, optical matrix elements and electronﾖphonon interaction matrix elements that allows us to calculate the coherent phonon spectrum. An extended tight-binding (ETB) model has been used for the electronic structure and a valence force field (VFF) model has been used for the phonon modes. The coherent phonon amplitudes satisfy a driven oscillator equation with the driving term depending on the photoexcited carrier density. We discuss the dependence of the coherent phonon spectrum on the nanotube chirality and type, and also on the graphene nanoribbon mod number and class (armchair versus zigzag). We compare these results with a simpler effective mass theory where reasonable agreement with the main features of the coherent phonon spectrum is found. In particular, the effective mass theory helps us to understand the initial phase of the coherent phonon oscillations for a given nanotube chirality and type. We compare these results to two different experiments for nanotubes: (i) micelle suspended tubes and (ii) aligned nanotube films. In the case of graphene nanoribbons, there are no experimental observations to date. We also discuss, based on the evaluation of the electronﾖphonon interaction matrix elements, the initial phase of the coherent phonon amplitude and its dependence on the chirality and type. Finally, we discuss previously unpublished results for coherent phonon amplitudes in zigzag nanoribbons obtained using an effective mass theory

A felső és alsó endoszkópiák indikációja, a diagnózisok megoszlása és minőségi mutatók 2010–2011-ben a Semmelweis Egyetem I. Belgyógyászati Klinikáján

Absztrakt: Bevezetés és célkitűzés: A Semmelweis Egyetem I. Belgyógyászati Klinikájának endoszkópos laboratóriumában vizsgálták a felső és alsó endoszkópiák indikációit, a diagnózisok megoszlását indikációk szerint, valamint a kolonoszkópiák minőségi mutatóit. Módszer: 2010. január 1. és 2011. december 31. között 2987 beteg felső és alsó endoszkópos vizsgálatának adatait elemezték (férfi/nő: 1361/1626, átlagéletkor: 60,7 év, SD: 16,7 év) a fekvő- és járóbeteg-megjelenések riportjaiból. Eredmények: A felső endoszkópiák során a jóindulatú fekélybetegség, nyelőcső-varicositas, gyomorpolip és gyomorrák előfordulási gyakorisága 10,8%, 4,5%, 6,1% és 2,9% volt. Az alsó endoszkópos vizsgálatok vastagbélpolipot, diverticulosist, daganatot és gyulladásos bélbetegséget 29,9%, 22,4%, 6,9% és 9,7%-ban írtak le. A betegek 26,3%-át vizsgálták okkult/manifeszt GI-vérzés indikációjával. A vérzés indikációjával vizsgált betegek idősebbek voltak (p<0,01), több volt a férfi (p<0,001, OR: 1,64), gyakrabban szedtek acenocoumarol- vagy heparinkészítményeket (p<0,001), gyakoribb volt a jóindulatú fekélybetegség (p<0,001, OR: 2,83) és nyelőcső-varicositas (p<0,001, OR: 2,79), a gasztroszkópiák, valamint a kolonoszkópiák során a colorectalis daganat (p<0,001, OR: 3,27). A kolonoszkópiák 81%-a volt komplett. Az inkomplett vizsgálat hátterében elégtelen előkészítés (38,2%), technikai nehézség (25,1%) és daganat miatti szűkület (20,5%) állt. Következtetés: A diagnózisok megoszlása és a minőségi mutatók (adenomatalálat, komplettálási arány) megfeleltek az adott populációban várhatónak. Orv. Hetil., 2016, 157(52), 2074–2081. | Abstract: Introduction and aim: The aim was to assess the incidence of endoscopic findings based on the indication of the procedures in upper/lower endoscopies, and measuring quality indicators of colonoscopies at the 1st Department of Medicine, Semmelweis University, Budapest. Method: Data of 2987 patients (male/female:1361/1626, mean age: 60.7 years(y), SD: 16.7y) between 01.01.2010 and 31.12.2011 were analyzed. Both inpatient and outpatient records were collected. Results: Incidence of peptic ulcer disease, esophageal varices, gastric polyps and gastric cancer were 10.8%, 4.5%, 6.1%, 2.9% in upper endoscopies, respectively. In colonoscopies colorectal polyps, diverticulosis, colorectal cancer and IBD were found in 29.9%, 22.4%, 6.9%, 9.7%, respectively. In patients having upper endoscopy with GI bleeding indication, older age (p<0.001), male gender (p<0.001, OR: 1.64), acenocoumarol/heparin use (p<0,001, peptic ulcers and esophageal varices were more frequent (p<0.001, OR: 2.83 and p<0.001, OR: 2.79), while in colonoscopies colorectal cancer had higher incidence (p<0.001, OR:3.27). 81% of colonoscopies were complete. Causes of incomplete procedures were ineffective bowel preparation (38.2%), technical difficulties (25.1%) and strictures (20.5%). Conclusion: The endoscopic findings and quality indicators (adenoma detection rate, coecal intubation rate) were in line with that reported in published series. Orv. Hetil., 2016, 157(52), 2074–2081