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    Wyświetlanie 1-4 z 4
    Tytuł:
    Proces samo-dysproporcjowania enancjomerów podczas chromatografii kolumnowej
    Self-disproportionation of enantiomers via column chromatography
    Autorzy:
    Wzorek, Alicja
    Kwiatkowska, Magdalena
    Urbaniak, Mariusz
    Gawdzik, Barbara
    Powiązania:
    https://bibliotekanauki.pl/articles/27310046.pdf
    Data publikacji:
    2023
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    chiralność
    chromatografia
    asocjacja
    enancjomeryczne wzbogacanie
    oddziaływania międzycząsteczkowe
    chirality
    chromatography
    association
    enantiomeric enrichment
    intermolecular interactions
    Opis:
    The review is devoted to self-disproportionation of enantiomers (SDE) phenomenon which has been observed for many different classes of chiral organic compounds. The SDE phenomenon occurs when the fractionation of an enantioenriched sample due the application of a physicochemical process under achiral conditions results in the variation of the proportion of the enantiomers present across the fractions, though the overall composition in terms of the sample ee remains unchanged. The SDE process can be considered in terms of separating the excess enantiomer from the racemate. The basic terminology related to SDE was described. The formation of the SDE under chromatographic conditions is the result of an association process occurring in a solution of a chiral, non-racemic compound. Information on preferred interactions leading to homo-/heterochiral supramolecules can be provided by quantum chemical calculations, NMR spectroscopy and comparison of crystal structures of the racemic and enantiomeric crystals. Several examples of the chromatographic experiments with different classes of compounds were given in two purposes 1) to highlight the possibility of application SDE during column chromatography as the method for enantiopurification of the chiral, non-racemic compounds; 2) to demonstrate that a standard workup (chromatographic purification, evaporation) can alter the stereochemical outcome of asymmetric reactions.
    Źródło:
    Wiadomości Chemiczne; 2023, 77, 5-6; 425--448
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Wpływ anestetyków wziewnych na modelową błonę biologiczną
    Influence of inhalation anesthetics on a model biological membrane
    Autorzy:
    Horochowska, Martyna
    Cieślik-Boczula, Katarzyna
    Rospenk, Maria
    Powiązania:
    https://bibliotekanauki.pl/articles/171702.pdf
    Data publikacji:
    2019
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    anestetyki wziewne
    anestezja
    słabe oddziaływania międzycząsteczkowe
    błona lipidowa
    inhalation anesthetics
    anesthesia
    weak intermolecular interactions
    lipid membrane
    Opis:
    General anesthesia is defined as impairment of the central nervous system (UON) caused by intravenous or volatile anesthetics. The state of loss of consciousness or even amnesia and the disappearance of perception into external stimuli is achieved by the use of a large group of chemical compounds. The use of nitrous oxide in 1844 revolutionized surgery and medicine at that time. From that moment, anesthesiology develops dynamically, allowing more and more complex procedures. Despite more than 170 years of history of anesthesia, understanding the mechanism of reversible loss of awareness and sensitivity to pain caused by the action of general anesthetics is one of the greatest challenges of modern pharmacology and neuroscience. Incredibly high diversity of anesthetics, including both noble gases and complex steroids, combined with human sensation makes the above problem extremely difficult to solve. The reversibility of the anesthesia phenomenon suggests that the analyzed phenomenon is based on disturbance of weak intermolecular interactions, such as hydrogen bond or van der Walls forces. Anesthetic molecules may bind directly to the hydrophobic region of protein, which causes its conformational changes or disturb ion channel activity by anesthetic-induced perturbations of lipid bilayers. The mechanism of anesthesia is thus very often attributed to both protein and lipid membrane targets. The influence of anesthetic molecules on biomolecular systems can be studied successfully using many different physico-chemical methods, such as, infrared, fluorescence or nuclear magnetic resonance spectroscopy. Vibrational circular dichroism as well as differential scanning calorimetry can also be used.
    Źródło:
    Wiadomości Chemiczne; 2019, 73, 3-4; 263-285
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Badania rozkładu gęstości elektronowej w kryształach, czyli jak zobaczyć szczegóły struktury elektronowej cząsteczek
    Electron density distribution in crystals or how to see the details of the electronic structure of molecules
    Autorzy:
    Kubicki, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/171566.pdf
    Data publikacji:
    2014
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    rozkład gęstości elektronowej
    model multipolowy
    oddziaływania międzycząsteczkowe
    pochodne 4-nitroimidazolu
    electron density distribution
    multipolar model
    intermolecular interactions
    4-nitroimidazole derivatives
    Opis:
    X-ray structural analysis might be regarded as a method of visualizing molecules as they appear in the crystals. The model, which is conventionally and universally used in this method, the Independent Atom Model (IAM) assumes that the electron density distribution, which scatters the X-rays is built of the spherically-symmetrical, neutral atoms. This model is responsible for the unprecedented success of X-ray structural analysis, which reflects in about one million crystal structures (i.e. the sets coordinates of the atoms constituting the molecules) deposited in the various databanks (cf. Fig. 1), and in the speed and accuracy which the method has reached. In principle, in few hours one can get the complete information about the crystal structure. But this success is accompanied by negligence of the scientific virtue hidden beyond the IAM. In fact, it was known from the very beginning of the X-ray diffraction studies by von Laue and Braggs, that some fine details of the electron density distribution should be available. The technological advance (four-circle diffractometers, powerful X-ray sources, fast computers etc.) caused that in 1960’s the time was ripe for the development of the experimental studies of details of electron density distribution in the crystals, beyond the IAM. The early experiments by Coppens and co-workers proved that this information – about the electron density transferred to the covalent bonds, lone pairs, even intermolecular interactions – can actually be obtained and analyzed (Fig. 2). The need for the model which could be used in the least-squares procedure led to the formulation of so-called pseudoatom models, including the most popular till now, Hansen-Coppens model (eq. 2) in which the aspherical part is described in terms of real spherical harmonics. In this paper, the basics of the electron density studies is described in some detail, including the step-by-step description of a typical procedure from the experiment to the final steps of refinement. An example of the analysis of the high-resolution structure of 1,2-dimethyl-4-nitro-5-morpholine-imidazole hydrate is used to show an application of this method in studying the intermolecular interactions, including weak C-H···O and C-H···N hydrogen bonds. It is shown that the multipolar model is able to deliver more informations than the promolecular model with spherically symmetrical electron distributions.
    Źródło:
    Wiadomości Chemiczne; 2014, 68, 5-6; 403-427
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Elektrooptyczny efekt Kerra w chemii
    Electrooptic Kerr effect in chemistry
    Autorzy:
    Prezhdo, O.
    Olan, K.
    Zubkowa, W.
    Preżdo, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/171825.pdf
    Data publikacji:
    2011
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    elektrooptyczny efekt Kerra
    analiza konformacyjna
    wewnątrzcząsteczkowe oddziaływania
    oddziaływania wewnątrzcząsteczkowe
    oddziaływania międzycząsteczkowe
    polaryzowalność
    moment dipolowy
    stała Kerra
    electro-optical Kerr effect
    conformational analysis
    intra-molecular interactions
    intermolecular interactions
    polarizability
    dipole moment
    Kerr constant
    Opis:
    The electro-optical Kerr effect finds wide application in conformational analysis of molecules and molecular aggregates [1–5], particularly in cases where the standard X-ray and NMR techniques cannot be used. For instance, NMR allows to establish conformations of linear and cyclic unsaturated organic compounds. However, it is less effective in an analysis of molecular complexes, particularly of those that have several rotational symmetry axes. In such cases a combination of techniques based on molecular dipole moments, electro-optical Kerr effect, optical Kerr effect, IR spectroscopy, and Rayleigh scattering can be applied [6]. The foundations of conformational analysis of molecular complexes using several complementary physical approaches are developed in Ref. [7]. The electro-optical methods are particularly useful for an investigation of intramolecular interactions [8–18]. The strength, direction and other details of intramolecular interactions can be determined by analyzing the deviations of the experimental molar Kerr constant (mK) from its value calculated according to the tensor-additive scheme that operates with polarizability tensors of molecular cores and functional groups [19, 20]. For instance, using this approach it has been shown that weakening of conjugation in an electron donor-acceptor chain can lead to flattening of the molecular structure [21]. The Kerr constant is also very sensitive to intermolecular interactions [22–29]. In order to assess quantitatively an extent of the solvent effect on the mK values, both molecular and continuum models of solution structure have been used [30, 31]. The mK values are greatly affected by the mutual orientation of solvent and solute molecules, which interact by dispersive, inductive and dipole-dipole forces [32]. Hydrogen and donor-acceptor bonding have an even stronger influence on the mK values [33]. The equimolar mixtures approach developed in Ref. [34] allows to determine the molar Kerr constant (mK), dipole moment (m), equilibrium constant (K) and, ultimately, structure of a molecular complex based on measurements of the Kerr constant (B), dielectric permittivity (e), density (d) and refractive index (n) of a series of dilute solutions of the complex. Future trends in the development of the electro-optical methods in chemistry are discussed. Theories that relate the electric-optic proprieties of molecules with their reactivity are particularly important. Such theories should be able to predict the changes in the polarizabilities and dipole moments of bonds, molecules and molecular aggregates during the course of chemical reactions.
    Źródło:
    Wiadomości Chemiczne; 2011, 65, 1-2; 1-31
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
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