We considered it timely to test the applicability of transferable multipole pseudo-atoms for restoring inner-crystal electronic force density fields. The procedure was carried out on the crystal of ...1,3-bis(2-hydroxyethyl)-6-methyluracil, and some derived properties of the scalar potential and vector force fields were compared with those obtained from the experimental multipole model and from the aspherical pseudo-atom model with parameters fitted to the calculated structure factors. The procedure was shown to accurately replicate the general vector-field behavior, the peculiarities of the quantum potentials and the characteristics of the force-field pseudoatoms, such as charge, shape and volume, as well as to reproduce the relative arrangement of atomic and pseudoatomic zero-flux surfaces along internuclear regions. It was found that, in addition to the quantum-topological atoms, the force-field pseudoatoms are spatially reproduced within a single structural fragment and similar environment. In addition, the classical and nonclassical hydrogen bonds in the uracil derivative crystal, as well as the H...O, N...O and N...C interactions in the free π-stacked dimer of the uracil derivative molecules, were studied using the potential and force fields within the concepts of interatomic charge transfer and electron lone pair donation–acceptance. Remarkably, the nitrogen atoms in the N...O and N...C interactions behave rather like a Lewis base and an electron contributor. At the same time, the hydrogen atom in the H...O interaction, being a Lewis acid, also participates in the interatomic electron transfer by acting as a contributor. Thus, it has been argued that, when describing polar interatomic interactions within orbital-free considerations, it makes more physical sense to identify electronegative (electron occupier) and electropositive (electron contributor) atoms or subatomic fragments rather than nucleophilic and electrophilic sites.
Oxidation of petroleum asphaltenes by potassium iodide (KI) is described. Oxidation under mild conditions is shown to be accompanied by iodination of the asphaltene aromatic core. The inducing ...reaction is the oxidation of sulfide sulfur atoms in the asphaltenes with reduction of iodate anion to molecular iodine; the coupled reaction, electrophilic substitution. X-ray photoelectron spectroscopy detected an increase in the mass fraction of oxygen as compared with the initial sample and formation of C–I bonds. IR spectroscopy found that oxidation of the asphaltenes is accompanied by the formation of carboxyl and sulfoxide groups. Raman spectroscopy revealed a decrease in the size of the oxidized asphaltene molecules as compared to the native asphaltenes. X-ray powder diffraction analysis showed a decrease in the interplanar spacing of the asphaltene oxidation product that was due to ordering and a denser arrangement of the aliphatic fragments.
We confirm our previously formulated rule about the possibility of a spontaneous resolution of enantiomers of a series of 5-hydroxy-3-pyrrolin-2-one thioderivatives. Crystal packings of three racemic ...compounds are compared. A supramolecular associate of the same type (a hydrogen-bonded dimer) is found, which is differently packed in the 3D structure of the crystals.
The structure and magnetic properties of the single crystal of bis{1-4-(4-pentyloxybenzoyl-oxy)phenyl-1-amino-3-pentylprop-1-en-3-onate}copper(II), which shows nematic mesomorphism, were studied by ...X-ray diffraction and electron spin resonance spectroscopy.
Small (d
core
≈ 2–5 nm) well-dispersed gold nanoparticles (AuNPs) stabilized by amphiphilic octacarboxy-calix4resorcinarenes with different substituents on the lower rim—methyl (
С
1
–CR
), pentyl (
...С
5
–
CR
) and undecyl (
С
11
–
CR
)—in an aqueous solution were obtained. The nanoparticles were studied by spectrophotometry, transmission electron microscopy, FTIR-spectroscopy, dynamic light scattering, small angle X-ray scattering and X-ray powder diffraction. The influence of HAuCl
4
/macrocycle ratio during the synthesis on the nanoparticles size and aggregation only for weakly associated
С
1
–
CR
and
С
5
–
CR
was achieved. The self-association effect of
С
11
–
CR
on the nanoparticles stabilization is found. The existence of gold in the form of crystallites and their average sizes were defined. The average nanoparticle sizes were determined and the structure of macrocyclic shells on the surface of nanoparticles in an aqueous solution was proposed. The formation of cooperative calix4resorcinarene associates on the AuNPs surface due to the multiple supramolecular interactions leads to the creation of functional gold nanoparticles.
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•First colloidal PtNps using calixresorcinarenes as stabilizer were obtained.•PtNPs were characterized by spectrophotometry, IR, TEM, DLS, PXRD and SAXS.•PtNPs and AuNPs, capped by ...macrocycles, demonstrate high photocatalytic activity.•The interaction of colloidal PtNPs and AuNPs with organic photolinkers was studied.•First photocatalytic activity of obtained supramolecular nanoassociates was studied.
The synthesis of colloidal platinum nanoparticles (PtNPs) (dcore≈1-40 nm) in an aqueous solution was carried out using amido(dimethyl)amino- and carboxy- calix4resorcinarenes with alkyl substituents on the lower rim as stabilizer. The nanoparticles were characterized by spectrophotometry, IR, TEM, DLS, PXRD and SAXS. It was shown that PtNPs and gold nanoparticles (AuNPs) obtained, stabilized by calix4resorcinarenes, demonstrate the photocatalytic activity in the photodegradation of methyl orange and rhodamine B toxic dyes under visible light irradiation. The rate constants of catalytic reaction (K1, min−1) and activity of nanocatalysts (K2, min−1 mol−1) were calculated. It was found that size of metal core, structure of macrocycle stabilizing the surface of metal nanoparticles, its ability to form self-associates and bind dye molecules define the rate of dye photodegradation reaction. The study of the interaction of PtNPs and AuNPs capped with amidoamine macrocycles with organic photolinkers by spectrophotometry and fluorescence showed the binding of photolinkers by macrocycles, PtNPs and AuNPs. The photocatalytic activity of obtained cooperative nanoassociates was studied. The addition of photolinkers leads to both an increase and a decrease in the reaction rate, depending on the structure of linker and macrocycle. An increase in the reaction rate occurs due to the formation of photoactive supramolecular nanoassociates and the additional photosensitizing action of the photolinker on the surface of a metal nanoparticle. Such hybrid nanocatalysts based on metal nanoparticle and calixresorcinarenes have the potential to be used in the field of effective photodegradation of toxic water pollutants.
The crystal structures of 3-chloro-5-hydroxy-1-(4-methylbenzyl)-4-4-phenyl-1H-1,2,3-triazole-1-yl-1,5-dihydro-2Н-pyrrol-2-one
rac
-
1
and ...1-benzyl-3-chloro-5-hydroxy-4-4-phenyl-1H-1,2,3-triazole-1-yl-1,5-dihydro-2Н-pyrrol-2-one
rac
-
2
are studied. The reproducibility of a same-type homochiral chain in both chiral and racemic crystals is found. Molecular conformations, secondary interactions additionally cross-linking the chain, and π…π contacts between the cyclic molecular moieties are analyzed.
Two packing polymorphs of 5-hydroxy-1-(4-methylbenzyl)-3-chloro-4-(4-chlorophenyl)sulfanyl-1,5-dihydro-2
H
-pyrrol-2-one are studied by single-crystal and powder X-ray diffraction, IR spectroscopy, ...and differential scanning calorimetry. Classical hydrogen bonds and CL…O interactions have the fundamental importance for the formation of the supramolecular motif that is identical in both modifications. The difference relates to the packing of 2D layers which is “parallel” in the triclinic modification and of the “herringbone” type in the monoclinic modification. It is shown that close similarity between structural organizations of crystal lattices, which is typical of packing polymorphs, can be accompanied by significant differences between their energies as well as by a high potential barrier upon the transition from the metastable polymorph to its stable form.
New uncharged conjugates of 6-methyluracil derivatives with imidazole-2-aldoxime and 1,2,4-triazole-3-hydroxamic acid units were synthesized and studied as reactivators of organophosphate-inhibited ...cholinesterase. Using paraoxon (POX) as a model organophosphate, it was shown that 6-methyluracil derivatives linked with hydroxamic acid are able to reactivate POX-inhibited human acetylcholinesterase (AChE) in vitro. The reactivating efficacy of one compound (5b) is lower than that of pyridinium-2-aldoxime (2-PAM). Meanwhile, unlike 2-PAM, in vivo study showed that the lead compound 5b is able: (1) to reactivate POX-inhibited AChE in the brain; (2) to decrease death of neurons and, (3) to prevent memory impairment in rat model of POX-induced neurodegeneration.
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•Synthesis of conjugates of 6-methyluracil with imidazole and 1,2,4-triazole as uncharged reactivators of phosphylated AChE.•Uracil derivative decreased death of neurons and prevented memory impairment in rat model of POX-induced neurodegeneration.•6-Methyluracil based reactivators deliver the reactive group to the phosphylated adduct in the active site of inhibited AChE.•Uracil ring serves as an anchor in the acetylcholinesterase peripheral anionic site.
This article accompanies the award of the Struchkov Prize to Robert Fayzullin. It is part of a collection of articles from the IUCr 2023 Congress in Melbourne, Australia, and commemorates the 75th ...anniversary of the IUCr. We considered it timely to test the applicability of transferable multipole pseudo-atoms for restoring inner-crystal electronic force density fields. The procedure was carried out on the crystal of 1,3-bis(2-hydroxyethyl)-6-methyluracil, and some derived properties of the scalar potential and vector force fields were compared with those obtained from the experimental multipole model and from the aspherical pseudo-atom model with parameters fitted to the calculated structure factors. The procedure was shown to accurately replicate the general vector-field behavior, the peculiarities of the quantum potentials and the characteristics of the force-field pseudoatoms, such as charge, shape and volume, as well as to reproduce the relative arrangement of atomic and pseudoatomic zero-flux surfaces along internuclear regions. It was found that, in addition to the quantum-topological atoms, the force-field pseudoatoms are spatially reproduced within a single structural fragment and similar environment. In addition, the classical and nonclassical hydrogen bonds in the uracil derivative crystal, as well as the H⋯O, N⋯O and N⋯C interactions in the free π-stacked dimer of the uracil derivative molecules, were studied using the potential and force fields within the concepts of interatomic charge transfer and electron lone pair donation–acceptance. Remarkably, the nitrogen atoms in the N⋯O and N⋯C interactions behave rather like a Lewis base and an electron contributor. At the same time, the hydrogen atom in the H⋯O interaction, being a Lewis acid, also participates in the interatomic electron transfer by acting as a contributor. Thus, it has been argued that, when describing polar interatomic interactions within orbital-free considerations, it makes more physical sense to identify electronegative (electron occupier) and electropositive (electron contributor) atoms or subatomic fragments rather than nucleophilic and electrophilic sites.
