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    Wyświetlanie 1-8 z 8
    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:
    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
    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:
    Wiązania chalkogenowe : początki oraz znaczenie w układach biologicznych
    Chalcogen bonds : origins and importance in biological systems
    Autorzy:
    Bucka, Alicja
    Dopieralski, Przemysław
    Powiązania:
    https://bibliotekanauki.pl/articles/172608.pdf
    Data publikacji:
    2020
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    wiązanie chalkogenowe
    niekowalencyjne odziaływania międzycząsteczkowe
    niekowalencyjne odziaływania wewnątrzcząsteczkowe
    „dziura” sigma
    chalcogen bond
    intra and intermolecular Noncovalent Interactions
    sigma hole
    Opis:
    The chalcogen bond is analogous to the halogen and hydrogen bond and it produces favorable interactions between 16th group of elements, that play a role in catalysis, medical chemistry, design of materials and biological processes. In the solid state, the chalcogen bond was used to build nano-sized structures and in solution is responsible mainly for intramolecular interactions, which stabilize the structures of intermediates and reagents. Recently, chalcogen bonds have been increasingly used in the recognition and transport of anions and in organic synthesis.
    Źródło:
    Wiadomości Chemiczne; 2020, 74, 9-10; 663-686
    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:
    Budowa i funkcje układów białkowo-lipidowych
    Structure and function of protein-lipid systems
    Autorzy:
    Litwińczuk-Mammadova, A.
    Cieślik-Boczula, K.
    Rospenk, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/972303.pdf
    Data publikacji:
    2016
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    odziaływania białko-lipid
    liposomy DPPC
    przejścia fazowe
    α-laktoalbumina
    kompleks HAMLET/BAMLET
    stopiona globula
    lipid-protein interactions
    DPPC liposomes
    phase transitions
    α-lactalbumin
    complex HAMLET/BAMLET
    molten globule state
    Opis:
    Biomembranes play many structural and functional roles in both prokaryotic and eukaryotic cells [10]. They define compartments, the communication between the inside and outside of the cell. The main components of biomembranes are lipids and proteins, which form protein-lipid bilayer systems [10]. A structure and physicochemical properties of protein-lipid membranes, which determines biological activities of biomembranes, are strongly dependent on interactions between lipid and protein components and external agents such as a temperature, pH, and a membrane hydration [4]. A lipid bilayer matrix serves as a perfect environment for membrane proteins (Fig. 1), and it assures activities of these proteins. Because biomembranes are composed of many different groups of lipids and proteins and have a complex structure, it is difficult to study in details their physicochemical properties using physicochemical methods. For these reason, lipid membranes of liposomes are used in many scientific laboratories for studding processes associated with a lipid phase transition, a membrane hydration, or protein-membrane interactions. The structure of liposomes (Fig. 5), and an influence of pH and an ionic strength on a lipid bilayer structure are discussed in the presented work. The role of membrane proteins in determination of biological activities of biomembranes is highlighted. A high variety of a structure and an enzymatic activity of membrane proteins is responsible for a high diversity of biological functions of cell membranes [2]. α-Lactalbumin (α-LA) is a peripheral membrane protein (Figs 8 and 9), its biological function is strongly related to its conformational structure and interaction with lipid membranes [49]. The complex of α-LA in a molten globule conformational state with oleic acid, termed as a HAMLET complex, are disused in a context of its anti-tumor activity.
    Źródło:
    Wiadomości Chemiczne; 2016, 70, 11-12; 723-746
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Badanie struktury i dynamiki N-terminalnych sekwencji dermorfiny i ich analogów z wykorzystaniem spektroskopii NMR w ciele stałym i rentgenografii
    Studies on the structure and dynamics of N-terminal sequences of dermorphin and their analogs by means of solid state NMR spectroscopy and XRD
    Autorzy:
    Trzeciak-Karlikowska, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/171648.pdf
    Data publikacji:
    2012
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    peptydy opioidowe
    oddziaływania CH-pi
    dynamika molekularna
    oddziaływanie peptyd–fosfolipid
    spektroskopia NMR
    1H Ultra Fast MAS NMR
    PISEMA MAS
    PILGRIM
    XRD
    opioid peptides
    CH-pi interactions
    molecular dynamics
    peptide–phospholipid interaction
    NMR spectroscopy
    Opis:
    Deltorphin I (Tyr-d-Ala-Phe-Asp-Val-Val-Gly-NH_2) and dermorphin (Tyr-d-Ala-Phe- -Gly-Tyr-Pro-Ser-NH_2) are natural opioid peptides that have been isolated from the skin of South American frogs [1]. The presence of d-amino acid is crucial for their biological activity. The synthetic analogs of given heptapeptides containing l-alanine are not analgesics [2]. Analysis of the influence of stereochemistry on molecular packing, dynamics and biological functions of neuropeptides is still important for receptor studies and practical applications (e.g. design of new selective pain killers). Presented research is focused on the structure and dynamics of two N-terminal sequences of dermorphin: tripeptide Tyr-d-Ala-Phe 1, tetrapeptide Tyr-D-Ala-Phe-Gly 2, and their analogs with l-alanine: Tyr-Ala-Phe 3 and Tyr-Ala-Phe-Gly 4, using solid state NMR and X-ray diffraction. This study clearly demonstrates that 1 and 2 crystallized under different conditions to form exclusively one structure [3, 4]. In contrast, tripeptide and tetrapeptide with l-Ala in the sequence very easily form different crystal modifications. Tyr-Ala-Phe 3 crystallizes into two forms: 3a and 3b [5], while Tyr-Ala-Phe-Gly 4 gives three modifications: 4a, 4b and 4c [4]. It seems that one of the factors, which can be important in the preorganization mechanism anticipating the formation of crystals, is the intramolecular CH-đ interaction between aromatic rings of tyrosine and/or phenylalanine and the methyl group of alanine. Such interaction is possible only for d-Ala residue. For l-Ala in the peptide sequence, the methyl group is aligned on the opposite side with respect at least to one of the aromatic groups. It can be further speculated that such internal CH-π contacts can also occur during the interaction of ligand–receptor, making the message sequence of opioid peptides more rigid and finally selective. By employing different NMR experiments (e.g. PISEMA MAS and PILGRIM) it was proven that the main skeleton of analyzed peptides is rigid, whereas significant differences in the molecular motion of the aromatic residues were observed [4, 6]. Solid state 2H NMR spectroscopy of samples with deuterium labeled aromatic rings: Tyrd4-d-Ala-Phe 5, Tyr-d-Ala-Phed5 6, Tyrd4-Ala-Phe 7, Tyr-Ala-Phe^d5 8 was used to analyze the geometry and time scale of the molecular motion. At ambient temperature, the tyrosine ring of sample 5 is rigid and in the sample 6 the phenylalanine ring undergoes a "π -flip". The tyrosine rings of form I of 7 and 8 are static, while the phenylalanine rings of form II of 7 and 8 undergo a fast regime exchange [6]. Variable temperature 2H measurements proved that the tyrosine and phenylalanine rings of two forms of compounds 7 and 8 became more mobile with increasing temperature. In contrast, the aromatic rings of samples 5 and 6 preserve their dynamics regime (static tyrosine and "π -flip" phenylalanine) in a large range of temperatures [6]. The analysis of 13C, 15N labeled tetrapeptide Tyr-D-Ala-Phe-Gly 2’-phospholipid membrane interactions suggests that peptide 2’ is aligned on the surface of the membrane (RFDR MAS) and the sandwich-like π -CH_3-π arrangement of the pharmacophore is preserved (DARR) [7].
    Źródło:
    Wiadomości Chemiczne; 2012, 66, 9-10; 867-891
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Konformacje pierścienia monosacharydowego
    Monosaccharide ring conformations
    Autorzy:
    Stępień, Ł.
    Liberek, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/172490.pdf
    Data publikacji:
    2012
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    konformacja
    pseudorotacja
    ekwatorialna orientacja
    oddziaływania 1,3-diaksjalne
    efekt anomeryczny
    efekt allilowy
    winylowy efekt anomeryczny
    stała sprzężenia
    conformation
    pseudorotation
    equatorial orientation
    1,3-diaxial interactions
    anomeric effect
    allylic effect
    vinylogous anomeric effect
    coupling constant
    Opis:
    Conformational studies of the pyranose and furanose rings are important and have been carried out for years. Knowledge of the conformation of monosaccharide is essential for understanding its physical, chemical and biological properties. Additionally, conformation of the sugar ring plays a crucial role in the stereochemistry of the reaction in which it participates. This paper provides a basic knowledge concerning the conformational preferences of a monosaccharide ring. The pyranose ring conformations are defined with reference to a cyclohexane ring [1–3]. Factors influencing stability of the pyranose chair conformation are discussed: the 1,3-diaxial interactions [4–6] and anomeric effect [7–10]. It is shown how to estimate the relative stabilities of the two chair conformations on the basis of the Angyal destabilizing factors [11, 12]. It is also demonstrated how to use the NMR spectroscopy for conformational analysis [13–23]. Conformations of the unsaturated pyranose rings are defined and studied mainly on the glycals [24–29], the monosaccharides with a double bond between the C1 and C2 carbon atoms. Factors influencing stability of the unsaturated pyranose ring are disscused: the allylic effect [30] also named the vinylogous anomeric effect [31–34], and quasi 1,3-diaxial interactions [35, 36]. Finally, the furanose ring conformations and pseudorotational itinerary for a d-aldofuranose ring are presented [37]. Two parameters defining the furanose ring conformation are introduced: the amplitude of pseudorotation [38, 39], named also the maximum torsion angle [4] and pseudorotational phase angle [4]. The possible ways to study the conformation of the furanose ring are disscused [40–44].
    Źródło:
    Wiadomości Chemiczne; 2012, 66, 1-2; 67-92
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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