Search results for "Effects"

The influence of solvent on conformational properties of peptides with Aib residue—a DFT study

2017

The conformational propensities of the Aib residue on the example of two model peptides Ac-Aib-NHMe (1) and Ac-Aib-NMe2 (2), were studied by B3LYP and M06-2X functionals, in the gas phase and in the polar solvents. To verify the reliability of selected functionals, we also performed MP2 calculations for the tested molecules in vacuum. Polarizable continuum models (PCM and SMD) were used to estimate the solvent effect. Ramachandran maps were calculated to find all energy minima. Noncovalent intramolecular interactions due to hydrogen-bonds and dipole attractions between carbonyl groups are responsible for the relative stabilities of the conformers. In order to verify the theoretical results,…

Efficient Resolution of Menthylamine with Inexpensive (R,R)-Tartaric Acid by Dielectrically Controlled Resolution (DCR)

2013

A practical procedure for the resolution of menthylamine 2 with (R,R)-tartaric acid [(R,R)-3] as resolving agent is presented. Variation of the solvent system allows both enantiomers of 2 to be selectively crystallized. Performing the resolution in methanol containing 6 % water leads to (–)-2·(R,R)-3·MeOH. The other, less-soluble diastereomeric salt is obtained by applying a solvent system consisting of methanol with 19 % water with a yield of 14 %. Subsequent basic workup with aqueous sodium hydroxide gave the free menthylamine compounds. Further workup of the mother liquors and an additional recrystallization step allowed the (–)-2·(R,R)-3·MeOH salt to be obtained in an overall yield of 2…

Solvent dependent photochemical reactivity of 3-allyloxy-1,2,4-oxadiazoles

2009

Structural study of oxalamide compounds: 1H, 13C, and DFT calculations

2011

Abstract The conformational properties of some N-alkyl, N,N′-dialky, and tetraalkyloxalamides have been investigated, in vacuo and in solvent using DFT methods at the B3LYP/6-31G∗∗ computational level. Special emphasis has been given on oxalamides with substituents of the type –CH2CH2OH. In oxalamides with the N–H group (N-alkyl and N,N′-dialky), the most stable conformations are those in which the oxalamide moiety adopts a planar s-trans arrangement and the amide bonds are trans. A different situation appears in the case of tetraalkyloxalamides, in which the oxalamide moiety always adopts a skewed arrangement and there are conformations with similar energy. A careful study of 13C and 1H NM…

Polymerisation von methylmethacrylat mit alkaliorganischen verbindungen. Über die stereospezifische polymerisation mit alkaliorganischen verbindungen…

1962

Methylmethacrylat kann durch alkalimetallorganische Verbindungen zu Produkten mit sehr verschiedener sterischer Struktur polymerisiert werden. Es wird der Einflus des Kations des Initiators, des Losungsmittels und der Temperatur auf die Taktizitat der Polymeren untersucht. In apolaren Losungsmitteln entstehen vornehmlich isotaktische Polymerisate, wobei der Anteil an isotaktischen Verknupfungen in den mit lithiumorganischen Verbindungen hergestellten Produkten am hochsten ist und mit natrium- und kaliumorganischen Initiatoren in dieser Reihenfolge abfallt. In polaren Losungsmitteln entstehen hauptsachlich syndiotaktische Polymere, wobei Lithiumalkyle die hochste Zahl syndiotaktischer Verknu…

Heterogeneous Gold Catalyst: Synthesis, Characterization, and Application in 1,4-Addition of Boronic Acids to Enones

2015

The new 1 wt % Au/TiO2–UVM-7 catalyst was prepared and fully characterized. This heterogeneous catalyst proved to be active, selective and recyclable for the unprecedented gold-catalyzed 1,4-addition of various functionalized arylboronic acids to 2-cyclohexen-1-one and other selected enones using toluene as a solvent. The gold-based catalyst was recycled two times and played an active role in this reaction, and the nature of the solvent determined a remarkable change in the products’ selectivities.

Field-practice study of sorafenib therapy for hepatocellular carcinoma: a prospective multicenter study in Italy

2011

A multicenter randomized controlled trial established sorafenib as a standard of care for patients with advanced hepatocellular carcinoma (HCC). Because the study was prematurely interrupted due to survival benefits in the sorafenib arm, we conducted an observational study to adequately assess risks and benefits of this regimen in field practice. Starting in 2008, all clinically compensated patients with advanced HCC and those with an intermediate HCC who were unfit or failed to respond to ablative therapies were consecutively evaluated in six liver centers in Italy, for tolerability as well as radiologic and survival response to 800-mg/d sorafenib therapy. Treatment was down-dosed or inter…

Towards a multilingual database of sound effects

One of the most significant linguistic and technical challenges applied to subtitling for the deaf and hard of hearing persons (SDH) is the linguistic description of sound encapsulated within the space of subtitles. This subtitle typology is crucial to hearing impaired audiences, since its main purpose is to improve the level of comprehension and appreciation of the plot, character development and, in general, of the nuances of audiovisual products. The scope of this study is to investigate the possibilities and the applications of a multilingual database of sound effects. Such database will combine the most recent technologies in Respeaking, viewed as “the production of subtitles by means …

The Impact of Shadowing and the Severity of Fading on the First and Second Order Statistics of the Capacity of OSTBC MIMO Nakagami-Lognormal Channels

2011

Published version of an article in Wireless Personal Communications (2011), 1-16. Also available from the publisher at http://dx.doi.org/10.1007/s11277-011-0275-x This article presents a thorough statistical analysis of the capacity of orthogonal space-time block coded (OSTBC) multiple-input multiple-output (MIMO) Nakagami- lognormal (NLN) channels. The NLN channel model allows to study the joint effects of fast fading and shadowing on the statistical properties of the channel capacity. We have derived exact analytical expressions for the probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades (ADF) of the capacity…

A Computational Study of Two-State Conformational Changes in 16-Electron [CpW(NO)(L)] Complexes (L=PH3, CO, CH2, HCCH, H2CCH2)

1999

International audience; High-spin and low-spin [CpW(NO) (L)] complexes are calculated to be remarkably close in energy. Several critical conformational changes in the singlet compounds are predicted to proceed more readily by spin crossover to the triplet hypersurface. The relationships between spin state, π bonding, ligand orientation, and geometry at W are explored.