Intermolecular Complexes Research Articles

In situ mechanical reinforcement of polymer hydrogels via metal-coordinated crosslink mineralization

Biological organic-inorganic materials remain a popular source of inspiration for bioinspired materials design and engineering. Inspired by the self-assembling metal-reinforced mussel holdfast threads, we tested if metal-coordinate polymer networks can be utilized as simple composite scaffolds for direct in situ crosslink mineralization. Starting with aqueous solutions of polymers end-functionalized with metal-coordinating ligands of catechol or histidine, here we show that inter-molecular metal-ion coordination complexes can serve as mineral nucleation sites, whereby significant mechanical reinforcement is achieved upon nanoscale particle growth directly at the metal-coordinate network crosslink sites.

Matrix isolation in laboratory astrochemistry: state-of-the-art, implications and perspective

Recent progress in observational astronomy and astrophysics has stimulated intensive laboratory studies aimed at elucidating the mechanisms of evolution of molecular matter in interstellar space and various space objects. One of the most intriguing and rapidly developing areas of these studies is the so-called “cold astrochemistry” devoted to the complex processes occurring in astrophysical ices. In this context, the matrix isolation technique (known for decades) is a very useful approach for both interpreting the results of astrophysical observations and verifying possible mechanisms of key astrochemical processes. This review outlines the most important results of recent studies using the matrix isolation technique. In fact, the results of these studies contribute to “cold” astrochemistry in two main aspects: (i) spectroscopy of astrochemically important molecules, ions and radicals stabilized in cryogenic matrices; (ii) experimental modeling of mechanisms of radiation-induced and “in dark” chemical reactions occurring in “cold” space environments (interstellar, cometary and planetary ices). In the first aspect, special attention is paid to new spectroscopic data obtained using various methods (electronic and vibrational absorption spectroscopy, electron paramagnetic resonance spectroscopy). In the second aspect, we consider the chemical effects resulting from both direct excitation of isolated molecules and the transfer of energy initially absorbed by the medium. Special attention has been paid to recent studies of spectroscopic characteristics and radiation-induced evolution of matrix-isolated weak intermolecular complexes, which can be considered “building blocks” for cold synthesis of complex molecules in the absence of diffusion mobility. In addition, we consider the use of matrix isolation for the studies of low-temperature chemical reactions “in dark” involving atoms and highly reactive intermediates, which can occur in cold space environments. In the final part, we briefly discuss the applicability of the results of matrix isolation experiments for interpretation of the mechanisms in molecular ices and highlight the prospects of this field. The review can also be useful for specialists in various aspects of chemistry and chemical physics (radiation chemistry, photochemistry, molecular spectroscopy, low-temperature chemistry).The bibliography includes 379 references.

Ethoxy-tethered calix[4]arenes containing P(III) substituents and trimethylsiloxy groups as building blocks in supramolecular chemistry; cis/trans intra- and intermolecular complexation of dichloroplatinum(II) fragments

p-tert-Butylcalix[4]arene 1 reacts with bromoethyl acetate and LiAlH4 to form the p-tert-butyl-tetrakis(2-hydroxyethoxy)calix[4]arene 8 bearing four ethyl-spacers at the lower rim of the calixarene. Reaction of 8 with Et2NSiMe3 leads to the tetrakis-substituted derivative 9. Treatment of 9 with PF2Cl gives the stable tetrakis-fluorophosphite 10, while the reaction with 2-chloro-1,3,5-trimethyl-1,3,5-triaza-2σ3λ3-phosphorin-4,6-dione furnishes the tetrakis-substituted molecule 11. When 11 was allowed to react with SO2Cl2, formation of the tetrakis(2-chloro)ethyl substituted calix[4]arene 13 was observed. All examined calixarene derivatives are exclusively obtained in the cone conformer. Reaction of 11 with dichloro(cyclooctadiene)platinum(II) leads to the symmetrically four-times bridged dimmer 15, which exhibits a trans orientation of the atoms surrounding the platinum(II) atom and involves all eight phosphorus atoms in the bridges. When 10 was treated with (COD)PtCl2, the cis intermolecular complex 16 was obtained.

Functionalized naphthalenediimide based supramolecular charge-transfer complexes via self-assembly and their photophysical properties

Two new intermolecular CT complexes having large Stokes shift (>170 nm) and significant fluorescence life-time (∼1.55 ns) have been prepared and exploited for cell imaging application.

Extremely superb efficiency and lifetime of deep blue phosphorescent OLEDs by introducing a hypsochromic emissive intermolecular complex (HEIC) with a negligibly small ΔEST and fast reverse intersystem crossing rate

Concept of a hypsochromic emissive intermolecular complex (HEIC) compared with the conventional exciplex and electroplex. A mixed host system with HEIC exhibits blue-shifted electroluminescence as well as photoluminescence.

In English

Nanocomposites based on biomolecules and highly dispersed silica are quite promising for use in many fields of biotechnology. There are many methods of obtaining such materials, in particular, adsorption from liquid or gas phases. Saccharides and their derivatives are present in the human body, they are involved in metabolic process, thus it is reasonable to use them while working with biomolecules. The work considers such disaccharides as sucrose, lactose and N-acetylneuraminic acid (NANA). Being a part of glycoproteins and glycolipids, NANA is also considered to be a carbohydrate. The main objective of the study was to study the ways of interaction of NANA on the disaccharide-modified silica surface. The methods of quantum chemistry have been used to find the probable structures of three-component adsorbtion complexes at molecular level and to clarify the mutual influence of these compounds in adsorbtion process. An analysis of the results of quantum chemical calculations shows that the adsorption of an anion of N-acetylneuraminic acid on silica surface is less likely than in its molecular form. Molecules of N-acetylneuraminic acid, disaccharides and silica form intermolecular complexes due to intermolecular hydrogen bonds between polar functional (mainly –OH) groups of the analytes. The sucrose dimer is 85.4 kJ/mol stronger than the lactose one. The sucrose molecule also forms a 38.1 kJ/mol stronger intermolecular complex with the N-acetylneuraminic acid molecule compared to a similar complex where lactose is used as a disaccharide. The highest energy (245.2 kJ/mol) is released when a silica cluster interacts with the intermolecular complex of N-acetylneuraminic acid and sucrose provided silica and the sucrose molecule are in a direct contact with each other. Therefore, as studies have shown, the adsorption of N-acetylneuraminic acid is possible if silica surface is pre-modified with disaccharides. The results of quantum chemical modeling confirm the obtained experimental data.

In Ukrainian

Quantum chemical modeling of orthophosphoric acid adsorption sites on the hydrated surface of anatase was performed by the method of density functional theory (exchange-correlation functional PBE0, basis set 6-31 G(d,p)). The influence of the aqueous medium was taken into account within the framework of the continual solvent model. The work uses a cluster approach. The anatase surface is simulated by a neutral Ti(OH)4(H2O)2 cluster. The results of analysis of the geometry and energy characteristics of all the calculated complexes show that the highest interaction energy is inherent to the intermolecular complex of orthophosphoric acid and hydrated surface of anatase, where the oxygen atom of the phosphoryl group (О=Р≡) forms a hydrogen bond with a hydrogen atom of the coordinated water molecule of Ti(OH)4(H2O)2 cluster and two hydrogen atoms of the hydroxyl groups of the orthophosphoric acid molecule form two hydrogen bonds with two oxygen atoms of the titanol groups. The formation energy effect of this complex is -134.0 kJ/mol. The formation energy effect of the complex with separated charges by the proton transfer from the molecule H3PO4 to the Ti(OH)4(H2O)2 cluster with the formation of dihydrogen phosphate anion and the protonated form of the titanol group (º) is -131.1 kJ/mol, so indicating less thermodynamic probability of such intermolecular interaction. The smallest thermodynamic probability (-123.9 kJ/mol) of complexation between orthophosphoric acid and hydrated anatase surface where a water molecule moves from the coordination sphere of the titanium atom. The calculation results indicate a possible adsorption of the H3PO4 molecule in an aqueous solution on the hydrated anatase surface. Taking into account the effect of the solvent within the polarization continuum insignificantly changes the adsorption energy, which is -44.5 kJ/mol; for vacuum conditions this value is -49.0 kJ/mol.

COMPLEXATION OF PRAZIQUANTEL WITH α-, β- AND y-CYCLODEXTRINS IN AQUEOUS-ALCOHOLIC SOLUTIONS

Currently, the percentage of infections with invasive (parasitic) diseases is quite large; therefore, the treatment of helminthiases is an urgent problem in veterinary medicine. Parasitic worms inflict significant damage on animal husbandry, leading to the death of animals, shortage of meat, dairy products, and wool. The most common active ingredient in antihelmintics is praziquantel, which is well known as an effective broad-spectrum anthelmintic. At the same time, praziquantel has low solubility in water and a pronounced bitter taste, which represents a significant obstacle in developing liquid forms of drugs that are convenient for administration to animals. One way to solve these problems is the complexation of medicinal substances with various (natural and synthetic) compounds. In this regard, this paper aims to study the complexation of praziquantel with α-, β-, and -cyclodextrins in aqueous-alcoholic solutions. The studies were carried out by the method of ultraviolet spectroscopy. It was found that the addition of cyclodextrins to aqueous-alcoholic solutions of praziquantel leads to spectral changes indicating the presence of intermolecular interactions and complexation. The isomolar series method showed that in dilute solutions, praziquantel forms complex compounds with cyclodextrins 1:1, that is, one molecule of praziquantel falls on one molecule of α-, β- or y-cyclodextrin. The stability constants of the resulting complexes were calculated using the molar ratio method. It is shown that in the range of 296-316 K, the composition of complex compounds remains unchanged (1:1), and their stability decreases with increasing temperature. The study of the temperature dependences of the stability constants made it possible to determine the standard values of changes in the Gibbs energy, enthalpy, and complexation entropy.

Phototautomerism of Alloxazine in Acetic acid – Water solvent systems

The photophysics of Alloxazine was studied in Acetic acid – Water solvent systems which included neutral water (pH = 7), pure acetic acid, and their binary mixtures. Alloxazine was found to exhibit tautomerization into Isoalloxazine over a time-scale which depended on the nature of the solvent. While the process was too fast in neutral water to be detected with a ~100 ps time-resolution, it was drastically inhibited on addition of small quantities of acetic acid, displaying a remarkably long time-constant ~700 ps. However, further addition of acetic acid gradually decreased the time-constant, until it finally reached ~280 ps in pure acetic acid. Quantum chemical calculations indicated that the tautomerization occurred via Excited-state Double Proton Transfer (ESDPT) mechanism in cyclic intermolecular H-bonded complexes of Alloxazine with the solvent molecule (water or acetic acid). This involved reorganization of the H-bonded structures in the S1 energy surface, causing effective transfer of the N(1) bound proton of Alloxazine to its N(10) position, producing the Isoalloxazine tautomer. The H-bond reorganization of the complexes were strongly coupled with the solvation dynamics of the solvent concerned, and this helped to explain the large divergence of the tautomerization time-constants in the different solvents and solvent mixtures used in this study.

Gelation of commercial pea protein isolate: effect of microbial transglutaminase and thermal processing

Abstract In the studied commercial pea protein isolate (PPI) some physicochemical modifications are induced in the protein structure during its processing. That fact would result into a reduction of proteins techno-functional properties. It has been evidenced by Differential Scanning Calorimetry the protein denaturation what gives as a result poor gelling ability. Microbial transglutaminase (MTGase) was added at different concentrations to improve the gelation process at two different settings/thermal treatments to make suitable texture PPI gels as a base for various meat and/or seafood analogues. SDS-PAGE analysis indicated that MTGase activity was focused on the polymerization of vicilins and legumins resulting in the promotion of new intermolecular protein complexes (increase in β-sheet aggregates). Rheological data showed that at 23% PPI with 5 and 7 U/g protein of MTGase the gel strength increased in terms of breaking force and complex modulus. It also improved the conformational stability and flexibility of their gel networks. The results suggest that appropriate gels with 23% PPI could be obtained adding 5 U/g MTGase able to be used as meat and/or seafood analogues.

Halogen Bonding in the Complexes of Brominated Electrophiles with Chloride Anions: From a Weak Supramolecular Interaction to a Covalent Br–Cl Bond

The wide-range variation of the strength of halogen bonds (XB) not only facilitates a variety of applications of this interaction, but it also allows examining the relation (and interconversion) between supramolecular and covalent bonding. Herein, the Br…Cl halogen bonding in a series of complexes of bromosubstituted electrophiles (R-Br) with chloride anions were examined via X-ray crystallographic and computational methods. Six co-crystals showing such bonding were prepared by evaporation of solutions of R-Br and tetra-n-propylammonium chloride or using Cl− anions released in the nucleophilic reaction of 1,4-diazabicyclo[2.2.2]octane with dichloromethane in the presence of R-Br. The co-crystal comprised networks formed by 3:3 or 2:2 halogen bonding between R-Br and Cl−, with the XB lengths varying from 3.0 Å to 3.25 Å. Analysis of the crystallographic database revealed examples of associations with substantially longer and shorter Br…Cl separations. DFT computations of an extended series of R–Br…Cl− complexes confirmed that the judicious choice of brominated electrophile allows varying halogen Br…Cl bond strength and length gradually from the values common for the weak intermolecular complexes to that approaching a fully developed covalent bond. This continuity of halogen bond strength in the experimental (solid-state) and calculated associations indicates a fundamental link between the covalent and supramolecular bonding.

Clarifying the effect of moisture absorption and high-temperature thermal aging on structure and properties of polyimide film at molecular dynamic level

A series of pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) polyimide (PI) films with different moisture content were experimentally prepared and corresponding PI/H2O composite models were constructed and analyzed based on molecular dynamic (MD) simulation. The elongation at break increased from 47.2% to 59.7% when the moisture content of the PI film reached 2%, which was attributed to the presence of water molecules that increased the mobility of molecular chains. The fractional free volume and XRD patterns of the composite models illustrated that the average packing distance of PI chains increased with moisture absorption and weakened intermolecular charge-transfer complex formation, therefore endowing the wet PI films better transmittance. The thermal decomposition mechanism of PMDA/ODA, 3,3′,4,4′-biphenyldianhydride (BPDA)/ODA and BPDA/p-phenylene diamine (PDA) based PI films were also investigated by thermogravimetric-infrared radiation (TG-IR) and MD simulation. The IR spectra of gas products indicated that the thermal decomposition of PI mainly generated CO2, CO, NH3 and HCN, and the PI with different chemical structures had the same thermal decomposition products. The MD results showed that the C–O bond in the ODA structural unit was broken first during the thermal decomposition, which could well explain that the BPDA/PDA exhibited better thermal stability compared with PMDA/ODA and BPDA/ODA. This work paved the way for the investigation of the macromolecular structural evolution of PI materials during moisture absorption and thermal aging process.

Therapeutic Approach against 2019-nCoV by Inhibition of ACE-2 Receptor.

The continued spread of 2019-nCoV has prompted widespread concern around the world. WHO formally named COVID-19 and International Committee on Taxonomy called it Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). Due to this viral attack, the whole world is in lockdown. Presently, there is no effective way to control it, except social distancing and hygienic activity. World class scientists and researchers are trying to make vaccine and discover the medicine against the control and cure to this deadly viral disease. Our aim to presenting this article is kick-off deadly viral disease i.e COVID-19 by an easy way with minimum intervention and effort. Different ayurvedic therapeutic agents (Curcuma Longa L, Green tea and Piper nigrum) inhabit entry of virus in host cell, transmission of pathogen and improve the immunity. Curcumin and piperine (1-piperoylpiperidine) interact to each other and form a π—π intermolecular complex which enhance the bioavailability of curcumin by inhibition of glucuronidation of curcumin in liver. Both the molecules curcumin and catechin get bound directly to receptors binding domain of S-protein and ACE-2 receptors of host cell, due to which these molecules inhibit the entry of virus in host cell i. e. animal survives from being infected.

Radiation-induced transformations of HCN⋯C2H2, HCN⋯C2H4 and HCN⋯C2H6 complexes in noble gas matrices: Synthesis of C3HxN molecules in cryogenic media

The nitrogen containing molecules of general structure C3HxN are important astrochemical species, which occur in interstellar and other extraterrestrial media. In this work, we have first demonstrated the formation of a number of nitriles and isonitriles (C2H3CN, C2H3NC and C2H5NC) through a direct radiation-induced synthesis from the matrix isolated intermolecular complexes HCN⋯C2Hn (n = 2, 4, 6) at 6 K. The deposited matrices Ng/HCN/C2Hn (Ng = Ar, Kr or Xe) were irradiated with X-rays and the formation of products was monitored by FTIR spectroscopy. In addition to synthetic products (C3HxN molecules), irradiation results in dehydrogenation of the initial complexes and their isomerization to the corresponding HNC⋯C2Hn complexes. The formation of propionitrile (C2H5CN) also cannot be excluded, although this molecule was not detected experimentally, possibly due to its poor IR absorption coefficients. Cyanoacetylene (HC3N) is accumulated with an induction period and becomes predominating at high absorbed doses, which points to its formation from the radiation-induced decomposition of the primary products. The obtained results suggest new possible routes for formation of nitriles, isonitriles and cyanoacetylene in complex astrochemical ices.

Solid Dispersions of Medamine and Albendazole with Water-Soluble Polymers: Preparation and Properties

Solid dispersions of medamine and albendazole with water-soluble polymers (PVP, arabinogalactan) were obtained by mechanochemical technology to increase the aqueous solubility of poorly soluble anthelmintic drug substances. An analysis of solid dispersions of drug–polymer systems showed that their solubilities depended on the nature of both the drug and polymer. The aqueous solubilities of medamine and albendazole could be increased by greater than 50 and 27 times, respectively, by varying the joint processing time with the polymers. An analysis of IR spectra and a comparison of them with published data suggested that intermolecular complexes were formed in these systems. Innovative anthelmintic drugs with increased solubility for medicine and veterinary medicine could be created by using the proposed mechanochemical technology for obtaining solid dispersions. The resulting solid dispersions had several advantages over conventional dosage forms, in particular, they were obtained in one stage, their preparation did not require excipients (dispersants, surfactants, wetting agents, etc.), and they were more conveniently used and inexpensively priced.

Probing the Molecular Interactions of Chitosan Films in Acidic Solutions with Different Salt Ions

Understanding the interaction mechanisms of chitosan films plays a central role in a wide range of its applications, such as bioadhesive, drug delivery, wound healing, tissue engineering, and wastewater treatment for heavy metal ions. Here, we investigated the molecular interactions between chitosan films in acidic solutions with different salt ions using a surface forces apparatus (SFA). The results showed that chitosan can be adsorbed to mica surfaces by electrostatic interaction under acidic conditions. The force measurements demonstrated that the interactions depend on the salt types, concentrations, and contact time. With the addition of 1 mM LaCl3 and NaCl into the acetic acid (HAc) buffer solution, the cohesion between chitosan films enhanced by about 45% and 20%, respectively, after a contact time of 60 min. The enhanced cohesion induced by the combination of partly intermolecular complexation formation in a bridge model and conformation adjustment of chitosan under contact time in 1 mM LaCl3 solution. However, the cohesion reduced rapidly and even disappeared when the salt concentration increased to 10 mM and 100 mM. We proposed that the cross-linked structures of chitosan mainly contribute to the significant reduction of chitosan cohesion in LaCl3 solution. In comparison, the decrease in cohesion capacity in NaCl solution mainly results from the enhanced hydration effect. Our findings may provide insights into the interaction mechanisms of chitosan films under nanoconfinement in acidic conditions and suggestions for the development of chitosan-based materials.

THE ACTIVITY OF INTERMOLECULAR HYDROGEN COMPLEXES OF QUERCETIN WITH GLUCOSE IN REAC-TIONS WITH COTTON OIL PEROXY RADICALS

The presence of a strong synergistic effect of the binary quercetin–glucose composition in the reaction with peroxyl radicals generated during the auto- and initiated oxidation of cottonseed oil was established. The highest antiradical activity showed the synergistic compositions at a ratio of 60 : 40%. The established synergism refers to the type when products, formed during reaction, interacts with peroxy radicals more effectively than the original individual substances. Such products may be intermolecular hydrogen-bonded complexes of quercetin and glucose, the existence of such complexes confirmed by NMR spectroscopy. DFT method showed that the most stable is the donor H-complex, where quercetin acts as a hydrogen donor. A quantitative measure of the electron-donating properties of H complexes – the ionization potential – was calculated in the gas phase. The ionization potential of the donor complex is lower so its reducing ability in reaction with radicals is higher than that of the monomeric antioxidant.This can explain the presence of the maximum synergistic effect in the quercetin-glucose mixture at the ratio of 60 : 40%, when, probably, the proportion of donor H-complexes in the reaction mixture is maximum. Obtained results make it possible to carry out a targeted search for effective antioxidant synergistic flavonoid–carbohydrate compositions in plant extracts.

Studies on the solid–liquid equilibria and intermolecular interactions Urea binary mixtures with Sulfanilamide and Sulfacetamide

The binary phase diagrams of Sulfanilamide-Urea (SN-U) and Sulfacetamide-Urea (SC-U) were measured using differential scanning calorimetry technique (DSC). Both examined mixtures were found to form simple binary eutectics. The limited miscibility in the solid state observed by DSC, proving inability of co-crystallization in new multi-molecular form, was also confirmed using PXRD and FTIR-ATR measurements of solid dispersions obtained via liquid assisted co-grinding. The lack of intermolecular complex formation in the crystals does not imply the lack of interactions in the liquid state. Detailed characteristics of potential homo- and hetero-molecular pairs were offered using ab initio and the first principle quantum chemistry computations. The obtained results happened to be strongly dependent on the applied level of theory. The importance of including the zero point energy contributions and electron correlation corrections was emphasized. It was found that the mole fraction of hetero-complexes with urea is the highest among all other constituents of studied systems at their eutectic points. Finally, the importance of intermolecular interaction leading to complexes formation in the liquid state at saturated position was documented by computed values of solvation Gibbs free energy. Based on computed trends it was inferred that the eutectic mixtures can be interpreted as such equilibria for which mutual solvation of all components is maximized.

In Ukrainian

Nowadays, it is relevant to study the processes that occur at the boundary of biomolecule (cell)-nanoparticle phase distribution. There is a growing interest in studying the interaction of ultrafine silica (UFC) with saccharides, in particular glucose and fructose, as well as with N-acetylneuraminic acid (NANA) (which is а part of the body’s cell membrane), for further creation of nanocomposites with biomolecules to use in biological systems. Using the density functional theory method (DFT) within the polarization continuum model (PCM), the interaction peculiarities of monosaccharides with silica surface were examined and the influence of the NANA molecule on this process was determined. The results of the analysis of quantum chemical calculations indicate that glucose and fructose can be used as modifiers for NANA adsorption. The molecules of these carbohydrates are related to silica surface and form a complex with N-acetylneuraminic acid. It is found that hydrogen bonds between hydroxyl groups of carbohydrates and silanol groups of the UFC surface play a major part in the formation of intermolecular complexes. The calculations show that the adsorption of monosaccharides on silica surface is possible considering their location, and it also depends on how to carry out the adsorption. That is, whether the adsorption of saccharides and then of NANA, or the adsorption from monosaccharides-NANA solution on silica surface is sequential.

Diels‐Alder reaction rate in the solid state and the evidence of the location of molecular complexes between the reagents on the reaction pathway

AbstractThe rate of reactions in the solid phase with uniform grinding of crystals of dienes, anthracene, and 9,10‐dimethylanthracene, with dienophiles, tetracyanoethylene, N‐phenylmaleimide, and 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione, has been studied. It was shown that, despite the high difference in the reaction rates in solution, the rates of these reactions in the solid phase are much closer. For anthracene‐tetracyanoethylene and 9,10‐dimethylanthracene‐tetracyanoethylene pairs, it was concluded that their intermolecular complexes are on the reaction pathway.