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Struktura a nieelastyczne rozpraszanie neutronów przez kryształy molekularne z wiązaniami wodorowymi

Rok M., Bator G., Sobczyk L.

Wiadomości Chemiczne

2017

[Z] 71, 7-8

533--557

The molecular crystals, which are built of organic or organic-inorganic molecules, are characterized by the weak intermolecular interactions. From the viewpoint of the potential applications in electronics or optoelectronics the electric properties of the crystals are essential. In turn these properties are related to their crystal structure as well as the dynamics of the molecules in the solid state. The existence of the hydrogen bonds in the crystal structures, conventional and unconventional, is crucial from the viewpoint of the electric properties of the crystals. The dynamics of methyl groups present in the structure can be a measure of the molecular interactions in the crystals. In this work the dynamical properties, first of all taking into account the research results concerning the neutron scattering, will be discussed. The neutron technique is very effective as regards the methyl group dynamics investigations. The relationship between a formation of the conventional and unconventional hydrogen bonds and a tunneling of the methyl groups at low temperature will be discussed. The method of the interpretation of the INS spectra will be described taking into account the theoretical model, the parameters of which are fitted to the experimental data. The examples will regard the following molecular crystals: p-N,N’-1,10-tetraacethyldiaminodurene (TADD) (Figs. 2 and 4), 2,3,5,6-tetramethylpyrazine with chloranilic acid (TMP·CLA) (Figs. 5, 6 and 7), 2,3,5,6- tetramethylpyrazine with bromanilic acid (TMP·BRA) (Figs. 5 and 6) and the crystal of 3,4,7,8-tetramethylphenantroline (Me4phen) and its complex with picric acid (Me4phen·PIC) (Figs. 8 and 9). In this paper we have shown that the surrounding of the methyl group and its interactions with the adjacent molecules has a stronger effect than the changes in the electronic charge density in the molecule.

Efektywność grup donorowych nukleotydów w reakcjach z jonami metali w układach podwójnych i potrójnych z udziałem tetramin

Gąsowska A.

Wiadomości Chemiczne

2007

[Z] 61, 5-6

339-359

Nucleotides, being multifunctional ligands with donor nitrogen and oxygen atoms, take part in the majority of selective and specific processes occurring in nature [1-15]. It has been established that nucleotides react with the polyamines (biogenic amines) present in the living organisms and take part in genetic information transfer [16-24]. Nucleotides are composed of a purine or pyrimidine base, sugar residua and phosphate groups (Fig. 1) [25-27]. Each of the three components have potential centres of interaction with metal ions [28-29]. Because of the wide diversity of coordination possibilities there are often controversies as to the mode of coordination even in simple complexes with metal ions. Some authors claim that only nitrogen atoms of the nucleotide are effectively engaged in the metallation [30-43], while others maintain that it requires a combined engagement of nitrogen atoms and phosphate group [44-71]. There are also researchers who point to the involvement of only phosphate group of the nucleotide in the metallation [72-77]. The reaction of nucleotides with tetramines results in the formation of molecular complexes (Fig. 3) [78-88]. In the literature to date, there is no agreement as to the character of interactions and effectiveness of nucleotide donor groups in the formation of adducts with polyamines [80-82, 85-87, 89, 90]. According to some authors, the interaction between a nucleotide and polyamines in the metal-free systems has a noncovalent ion-ion or ion-dipole nature and the stability of molecular complexes is determined by the number of active centres in the reagents and the structural factor [80-84, 87]. According to other authors, it is a typical electrostatic interaction and the adduct stability is determined by the charge of the reagents [85, 89]. In the adducts formed by nucleotides with polyamines, the main interaction centres of a nucleotide are endocyclic nitrogen atoms and a phosphate group (the latter undergoes deprotonation already at a low pH), while in the case of tetramine the interaction centres are the NHx+ groups [77, 80-87, 89-91]. In the ternary systems of metal/nucleotide/tetramine, the following heteroligand molecular complexes are formed: MLźźźźźźHxL' (x = 4, HxL'-fully protonated polyamine) (Fig. 4) [80-82, 91, 94, 96], mixed protonated complexes MLHxL' (x = 1, 2, 3) (Fig. 5) [81, 82, 92, 96] and MLL' type complexes (Fig. 6) [81, 82, 91]. A significant influence of polyamines on the character of interactions of nucleotides with metal ions has been noted [80-82, 90-96]. In molecular complexes, the fully protonated polyamine is located in the outer coordination sphere. In the MLHxL' type complexes, the deprotonated nitrogen atoms of tetramine are involved in the coordination, while its protonated centres -NHx+ take part in noncovalent interactions that additionally stabilise the complex [81, 82, 92, 96, 97]. In the MLL' type complexes, oxygen atoms of nucleotide phosphate group and deprotonated nitrogen atoms of tetramine are in the inner coordination sphere, while nucleotide donor nitrogen atoms do not take part in the metallation [81, 82, 91].