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    Wyświetlanie 1-3 z 3
    Tytuł:
    Średni ciężar cząsteczkowy chondrytu Jezersko (H4). Promień i objętość atomu i cząsteczki chondrytu
    Average molecular weight of Jezersko H4 chondrite. Radius and volume of atom and molecule of chondrite
    Autorzy:
    Szurgot, Marian
    Powiązania:
    https://bibliotekanauki.pl/articles/1033154.pdf
    Data publikacji:
    2020
    Wydawca:
    Polskie Towarzystwo Meteorytowe
    Tematy:
    Jezersko chondrite
    average molecular weight
    average radius of atom
    average radius of molecule
    Opis:
    Average molecular weight and average atomic number of molecule of Jezersko ordinary chondrite (H4 S2(3) W2, find in 1992 in Slovenia) have been calculated using literature data on chemical composition of the meteorite (Miler et al. 2014). It was shown that Jezersko’s = 55.58, = 27.21, and ratio / = 2.043 for composition without water. Jezersko’s silicates shown the values: = 54.08, = 21.77, and / = 2.484. Volume and radius of average Jezersko molecule, and of atom have been also determined. It was calculated that the average volume of Jezersko’s molecule Vmol = 2.515·10–29 m3, and average radius of Jezersko’s molecule Rmol = 181.5 pm. Average volume of the Jezersko’s atom Vatom = 1.117·10–29 m3, and average radius of Jezersko’s atom: Ratom = 138.5 pm. Ratio of average Jezersko’s volume of molecule to atom volume: 2.25, and ratio of radius of molecule to radius of atom: 1.31. Number of atoms in Jezersko meteorite average molecule Nmol = /Amean = /Zmean = 2.25, and for Jezersko’s silicates Nsimol = 2.48.
    Źródło:
    Acta Societatis Metheoriticae Polonorum; 2020, 11; 98-109
    2080-5497
    Pojawia się w:
    Acta Societatis Metheoriticae Polonorum
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Procedure for determination of the molecular weight of chitosan by viscometry
    Autorzy:
    Czechowska-Biskup, Renata
    Wach, Radosław A.
    Rosiak, Janusz M.
    Ulański, Piotr
    Powiązania:
    https://bibliotekanauki.pl/articles/1034447.pdf
    Data publikacji:
    2018
    Wydawca:
    Sieć Badawcza Łukasiewicz - Polskie Towarzystwo Chitynowe
    Tematy:
    Mark-Houwink equation
    capillary viscometry
    chitosan
    intrinsic viscosity
    viscosity-average molecular weight
    Opis:
    The aim of this publication is to facilitate the estimation of chitosan molecular weight (MW) in laboratories with no access to sophisticated analytical instruments, by applying the easily accessible and economical capillary viscometry. The procedure of viscosity-average molecular weight (Mv) determination is described in details. The examples provided encompass testing of the experimental procedure for determination of the Mv of chitosan with a low-molecular weight of 7.7 kDa and 88 kDa, after verification with a high-molecular weight polymer (477 kDa). The experimental work demonstrated the importance of the initial concentration of low-MW chitosan for the accurate determination of intrinsic viscosity and, as a consequence, the viscosity-average molecular weight.
    Źródło:
    Progress on Chemistry and Application of Chitin and its Derivatives; 2018, 23; 45-54
    1896-5644
    Pojawia się w:
    Progress on Chemistry and Application of Chitin and its Derivatives
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Równowagi asocjacyjne alkilopochodnych mocznika i tiomocznika
    Association equilibria of alkyl derivatives of urea and thiourea
    Autorzy:
    Rospenk, M.
    Koll, A.
    Obrzud, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/172815.pdf
    Data publikacji:
    2017
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    model samoasocjacji
    momenty dipolowe
    średnia masa cząsteczkowa
    obliczenia DFT
    pochodne mocznika i tiomocznika
    model of self-association
    dipole moments
    average molecular weight
    FTIR spectra
    DFT calculation
    derivatives of urea and thiourea
    Opis:
    The studies and comparison of a series of molecular mono- and di-substituted derivatives of urea and thiourea in solvents of increasing polarity are presented [1–4]. These substances are characterized by a high tendency to self-associate through the formation of intermolecular hydrogen bonds due to the presence in their structure both groups as donors (NH) as well as proton acceptors (C=O) or (C=S). Studies were performed by using IR spectroscopy, method of measuring the average molecular weight and the dipole moments. The experimental data were verified by DFT quantum chemical calculations with B3PW91 correlation functional. Simultaneous use of these techniques alowed establishing not only the efficiency of aggregation, but also the structure and polarity of formed aggregates. It was shown, that in solvents with weak acidic C-H groups the aggregation was strongly limited because of molecular interactions between solute and solvent. The theoretical DFT calculations which included the impact of the environment on the nature of interactions in the complex were carried out [e.g. Scheme 4.1.4]. A combination of geometry optimization in polarizable continuum model (PCM) with the connection of chloroform molecules (1,2-dichloroethane) with urea dimers enabled to obtain the expected theoretical simulation compliance with the experiment. The equilibrium constants were calculated on the basis of data obtained in two independent methods of measurement: IR spectroscopy and measurements of average molecular weights. Good agreement of experimental data of both research techniques were found up to concentration of 0.03 mol/dm3 [Fig. 2.5]. The type of associates have been assessed following the dipole moments measured as a function of concentration, and on the results of density-functional theory (DFT) calculations on the structure and energy of particular species. All of the urea derivatives demonstrated an increase in dipole moment with increased concentration, suggesting linear-type aggregation [Fig. 4.1.3]. Contrastingly, the dipole moments of the N,N-dimethylthiourea and mono-N-alkyl-substituted thioureas decreased with concentration and suggest that cyclic dimers or trimers are formed by C=S…(HR)2N-C=S interactions [Fig. 4.2.2]. The efficiency of self-aggregation was described by use of two equilibrium constants. The first constant, K1, was describing dimer formation and the second constant, K2, the subsequent multimer formation. In N,N’-thioureas aggregation was lower than for the related urea compounds [Table 4.1.1 and Table 4.2.1]. Differences between urea and thiourea derivatives result from the fact that the ureas are stronger bases and, therefore, more active in aggregation.
    Źródło:
    Wiadomości Chemiczne; 2017, 71, 7-8; 559-608
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-3 z 3

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