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    Wyświetlanie 1-6 z 6
    Tytuł:
    Application of fRMSDchiral for mathematical description of mutual position between stereoisomers
    Autorzy:
    Urniaz, Rafal Damian
    Powiązania:
    https://bibliotekanauki.pl/articles/748148.pdf
    Data publikacji:
    2015
    Wydawca:
    Polskie Towarzystwo Matematyczne
    Tematy:
    fragment-level RMSD
    chiral recognition
    bioinformatics
    molecular modeling
    fragment-level RMSD, związki chiralne, stereoselektywność, bioinformatyka, modelowanie molekularne
    Opis:
    The ability of biological systems to recognize and distinguish between compounds is crucial for living systems. A detailed study of this mechanism seems to be an important supplement for analysis of possible contact interactions between compounds and environment. This process could be characterized by variety of descriptors respond to compounds’ structural and physicochemical properties. Usually, the measure of variation in molecule positions in the three dimensional space is realized by the Root Mean Square Deviation (RMSD) calculation. Here, the traditional concept of RMSD was readjusted as fragment-level RMSD (fRMSD) and applied for mathematical description of stereoisomers’ role in the chiral recognition process.
    Źródło:
    Mathematica Applicanda; 2015, 43, 1
    1730-2668
    2299-4009
    Pojawia się w:
    Mathematica Applicanda
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spektrometria mas w rozróżnianiu związków chiralnych
    Chiral recognition by mass spectrometry
    Autorzy:
    Drabik, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/172040.pdf
    Data publikacji:
    2011
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    spektrometria mas
    rozróżnianie związków chiralnych
    związki chiralne
    oddziaływania typu gość-gospodarz
    metoda kinetyczna
    reakcje kompleksów jon–cząsteczka
    spektrometria ruchliwości jonów
    mass spectrometry
    chiral recognition
    kinetic method
    host–guest interaction
    ion-molecule reaction
    ion mobility spectrometry
    Opis:
    The phenomenon of optical activity was discovered by Louis Pasteur in 1848. Since this time, chirality of organic compounds observed in biological systems has became a central theme in scientific research. Synthesis and quantitation of enantiomerically pure compounds is important for a wide range of applications. Chirally pure compounds are required not only by pharmacology, but they are also of interest in cosmetic and food industry and many other applications. Similarity of enantiomers in their chemical and physical properties, except for optical rotation, makes their separation and detection very difficult. Until now, many methods have been used for the enantioselective discrimination of organic compounds, including nuclear magnetic resonance spectroscopy (NMR), circular dichroism (CD), capillary electrophoresis (CE) and chromatography (GC, HPLC), where an interference of a solvent cannot be excluded. Recent studies have shown that mass spectrometry (MS) is an alternative approach to traditional method for chiral recognition and determination of enantiomeric composition. Although, mass spectrometry has been considered as insensitive to chirality because enantiomers have the same mass and show identical mass spectra, it is now accepted as important tool for differentiating of enantiomeric compounds through their interactions with chiral reference molecules (Fig. 1). The ability to transfer diastereomeric non-covalent complexes between chiral selectors and analyte enantiomers, which differ in stability, into the gas-phase and measure such differences trough mass spectrometric ion abundances, has appeared with development of soft ionization techniques such electrospray ionization (ESI), fast atom bombardment (FAB) and matrix-assisted laser desorption/ionization (MALDI). Mass spectrometry-based methods for chiral recognition and quantitative determination of enantiomeric purity are attractive due to their speed, high sensitivity, low sample consumption, tolerance to impurities and ability to probe the analyte in a solvent free environment. Currently, there are four well-defined approaches for determining a measure of enantiomer discrimination, using either single-stage or tandem mass spectrometry. They can be classified into the following categories: (1) measurement of the relative abundance of diastereomeric complexes between chiral reference compound and the enantiomers (usually one isotopically labeled [10]), (2) enantioselective ion/molecule reaction between diastereomeric complexes and chiral or achiral reactants [11], (3) kinetic method [12] and (4) collision-induced dissociation (CID) of diastereomeric adducts in a tandem mass spectrometry (MS/MS) experiment [61, 62]. Over the past decade, new approaches to chiral separation and analysis of enantiomers have been introduced, where molecules are separated based on their mobility (ion mobility spectrometry) [66].
    Źródło:
    Wiadomości Chemiczne; 2011, 65, 7-8; 609-649
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Atroposelektywna synteza naturalnych chiralnych osiowo związków biarylowych. Część 1
    Atroposelective synthesis of natural axially chiral biaryl compounds. Part 1
    Autorzy:
    Kołodziejska, R.
    Tafelska-Kaczmarek, A.
    Studzińska, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/171903.pdf
    Data publikacji:
    2017
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    naturalne chiralne osiowo związki biarylowe
    mostkowane biaryle
    otwarto-łańcuchowe biaryle
    atropoizomeryzacja
    atroposelektywna synteza
    chiralne osiowo biaryle
    natural axially chiral biaryl compounds
    bridged biaryls
    unbridged biaryls
    atropoisomerization
    atroposelective synthesis
    axially chiral biaryls
    Opis:
    In early twentieth century, it was already known that chemical compounds might be chiral without containing the chiral atoms. The presence of the stereogenic center is a sufficient but not necessary condition that the molecule appears in two forms which are mirror images. In certain cases, the limit of free rotation in the molecule may result in asymmetry, e.g. inhibition of rotation around single bond leads to axial isomers. This is the kind of conformational isomerism, which according to the nomenclature is called atropisomerism [1, 2]. The most often optically active molecules without stereogenic atoms, possessing an axial chirality are biaryls, which are commonly found in nature. In most cases, pharmacological activity of biaryls is associated with the presence of axial chirality (Figs 1, 2; Scheme 1) [1–14]. Generally chiral biaryls are divided into bridged biaryls (Scheme 4–6) [15–24], and biaryls, which do not contain the additional ring (Scheme 2, 3) [25–33]. The thermal stability of both enantiomeric/diastereomeric forms is an essential precondition for atropisomerism. For a given temperature, conformationally stable isomers may coexist when their a half-life is at least 1000 s, which gives the minimum energy barrier of 93 kJ mol–1 at 300 K. Chiral biaryls can be achieved by either desymmetrization of stable but achiral biaryls by modifying one of the groups on the aromatic moiety (Scheme 7–9) [1, 34, 35], or by dynamic kinetic resolution of racemic mixtures of the conformationally unstable chiral substrates. The synthesis of the chirally stable biaryls from the chiral labile substrates is most frequently the result of the extra substituent addition (Scheme 10) [36], and formation or cleavage of a bridge (Scheme 11–16) [37–54]. The axially chiral biaryls can also be obtained in the atroposelective transformation of the alkyl substituent of the arene ring into a second aromatic ring in the presence of an organometallic catalyst (Scheme 17, 18) [55, 56].
    Źródło:
    Wiadomości Chemiczne; 2017, 71, 3-4; 177-197
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Wykorzystanie pochodnych butano-2,3-diacetali w syntezie naturalnych związków optycznie czynnych
    Application of butane-2,3-diacetals in the synthesis of optically active natural products
    Autorzy:
    Wacławczyk-Biedroń, W.
    Drop, A.
    Frąckowiak-Wojtasek, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/142635.pdf
    Data publikacji:
    2014
    Wydawca:
    Stowarzyszenie Inżynierów i Techników Przemysłu Chemicznego. Zakład Wydawniczy CHEMPRESS-SITPChem
    Tematy:
    związki naturalne
    butano-2,3-diacetale
    chiralne bloki budulcowe
    natural compounds
    butane-2,3-diacetals
    chiral building blocks
    Opis:
    Butanodiacetale (BDA) są stabilnymi, optycznie czynnymi blokami budulcowymi wykorzystywanymi w syntezie produktów naturalnych. Otrzymać je można na drodze syntezy z tanich substratów: D-mannitolu, kwasu L-askorbinowego, L-winianu dimetylowego, oraz D-winianu dimetylowego. Usztywniona struktura butanodiacetali daje możliwość zastosowania ich w syntezie asymetrycznej. Przedstawiono przegląd literaturowy dotyczący syntezy butanodiacetali oraz ich zastosowania do syntezy małocząsteczkowych i wielkocząsteczkowych naturalnych związków optycznie czynnych.
    Butane diacetals (BDAs) are stable, optically active building blocks used in the synthesis of natural products. They can be synthesized from cheap substrates such as: D-mannitol, L-ascorbic acid, dimethyl L-tartrate and dimethyl D-tartrate. The rigid structure of butane diacetals makes possible their application in asymmetric synthesis. The article presents literature review on synthesis of butane diacetals and their application in the synthesis of natural small and large optically active compounds.
    Źródło:
    Chemik; 2014, 68, 4; 304-311
    0009-2886
    Pojawia się w:
    Chemik
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Asymetryczne przeniesienie wodoru do ketonów katalizowane związkami Rutenu(II) i Rodu(III)
    Asymmetric transfer hydrogenation of ketones catalyzed by Ruthenium(II) and Rhodium(III) complexes
    Autorzy:
    Karczmarska-Wódzka, A.
    Kołodziejska, R.
    Studzińska, R.
    Wróblewski, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/172550.pdf
    Data publikacji:
    2012
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    transfer wodoru asymetryczny
    związki kompleksowe Ru(II) i Rh(III)
    chiralne ligandy
    prochiralne związki karbonylowe
    asymmetric transfer hydrogenation
    Ru(II) and Rh(III) complexes
    chiral ligands
    prochiral carbonyl compounds
    Opis:
    Asymmetric hydrogen transfer (ATH) is one of the methods of stereoselective reduction of prochiral carbonyl compounds (Scheme 6). Complexes of the platinum group metals (Noyori catalysts) are the most common catalysts for AT H reactions. The specific structure of the Noyori catalyst allows to activate two hydrogen atoms. These atoms are transferred from donor to acceptor in the form of hydride ion and proton (Scheme 1). Depending on the used catalyst the transfer hydrogenation of ketons can proceed by direct and indirect transfer mechanism. The direct hydride transfer from a donor to an acceptor proceeds via a six-membered transition state (3) (Scheme 2). The indirect hydride transfer proceeds through the formation of an intermediate metal hydride. A monohydride (HLnMH) and or a dihydride (LnMH2) can be formed depending on the catalyst that is used (Scheme 3). In the monohydride route, the reduction proceeds in the inner sphere of the metal (four-membered transition state (4)) or in the outer sphere of the metal (six-membered transition state (5)) (Scheme 4). The proposed reduction of carbonyl compounds in the AT H reaction by Noyori catalysts uses the mechanism of the hydride ion and proton transfer from the donor to the catalyst and the formation of the monohydride. In the indirect transfer hydrogenation the hydride ion and proton are transferred from the monohydride to the acceptor (Scheme 5, 7). AT H reactions that lead to chiral alcohols are conducted in organic solvents or in water. Hydrogen donors most often used in organic solvent reactions are propan-2-ol or an azeotropic mixture of formic acid and triethylamine (Tab. 1, 6). Sodium formate is usually used as hydrogen donor in the reactions conducted in water. Yield and enantioselectivity of the reaction depend on many factors the most important of which are: the structure of a substrate, hydrogen donor and solvent that were used, the reaction time, substrate concentration, and the S/C ratio [2]. In the case of asymmetric reduction conducted in water the solvent pH is also of great importance [3, 7, 8]. An optimal pH range depends on the type of a catalyst [7, 8]. AT H reactions conducted in water are distinguished by a shorter reaction time and higher enantioselectivity than the reactions conducted in organic solvents. In addition, catalysts used in the AT H reactions are more stable in water allowing reuse of the catalyst without loss of its activity. This paper presented examples of the use of specific catalysts in asymmetric reactions of hydrogen transfer. In particular, I drew attention to the reactions running in the aquatic environment due to the above-mentioned advantages of this solvent. The authors focused specifically on bifunctional catalysts based on Ru(II) and Rh(III) on the account of wide usage of the catalysts of that type in AT H reactions in water and their good performance [8, 9, 15, 16, 17, 19, 20, 21, 22]. p-Cymene is the most common aromatic ligand in catalysts based on Ru(II) while in the case of catalysts with Rh(III) the most common is anionic pentamethylcyclopentadienyl ligand. In both cases the second most common ligands are diamines or amino alcohols (Scheme 8). There are better performance and enantioselectivity when diamines are used as ligands. Attempts to replace diamines and amino alcohols by Schiff bases (Scheme 13) in the catalysts containing Rh(III) proved poor results due to a very low enantioselectivity of conducted reactions (Tab. 7).
    Źródło:
    Wiadomości Chemiczne; 2012, 66, 3-4; 273-295
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-6 z 6

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