Main Noncovalent Interactions Research Articles

Kohn-Sham fragment energy decomposition analysis.

We introduce the concept of Kohn-Sham fragment localized molecular orbitals (KS-FLMOs), which are Kohn-Sham molecular orbitals (MOs) localized in specific fragments constituting a generic molecular system. In detail, we minimize the local electronic energies of various fragments, while maximizing the repulsion between them, resulting in the effective localization of the MOs. We use the developed KS-FLMOs to propose a novel energy decomposition analysis, which we name Kohn-Sham fragment energy decomposition analysis, which allows for rationalizing the main non-covalent interactions occurring in interacting systems both in vacuo and in solution, providing physical insights into non-covalent interactions. The method is validated against state-of-the-art energy decomposition analysis techniques and with high-level calculations.

Highly Water-Stable Zinc Based Metal-Organic Framework: Antibacterial, Photocatalytic Degradation and Photoelectric Responses.

A reported water-stable Zn-MOF ([Zn(L)2(bpa)(H2O)2]·2H2O, H2L = 5-(2-cyanophenoxy) isophthalic acid has been prepared via a low-cost, general and efficient hydrothermal method. It is worth noting the structural features of Zn-MOF which exhibit the unsaturated metal site and the main non-covalent interactions including O⋯H, N⋯H and π-π stacking interactions, which lead to strong antibacterial and good tetracycline degradation ability. The average diameter of the Zn-MOF inhibition zone against Escherichia coli and Staphylococcus aureus was 12.22 mm and 10.10 mm, respectively. Further, the water-stable Zn-MOF can be employed as the effective photocatalyst for the photodegradation of tetracycline, achieving results of 67% within 50 min, and it has good cyclic stability. In addition, the photodegradation mechanism was studied using UV-vis diffuse reflection spectroscopy (UV-VIS DRS) and valence-band X-ray photoelectron spectroscopy (VB-XPS) combined with the ESR profile of Zn-MOF, which suggest that ·O2- is the main active species responsible for tetracycline photodegradation. Also, the photoelectric measurement results show that Zn-MOF has a good photocurrent generation performance under light. This provides us with a new perspective to investigate Zn-MOF materials as a suitable multifunctional platform for future environmental improvement applications.

EFFECTS OF COMPOSITION OF GLUTEN-FREE BINARY GELS ON THE RETENTION AND RELEASE OF AROMA COMPOUNDS

Background. Gluten-free binary gels (BGs) composed of polysaccharides and animal proteins appear to be food products of great practical importance due to the constantly increasing risk of coeliac disease. Moreover, understanding the factors influencing the stability of aroma compounds (ACs) is very important because consumer acceptance of food is mainly dependent on aroma. The objective of this research was to determine the thermodynamic and kinetic behavior of ACs in BGs prepared with starches varying in amylose content depending on the concentration of myofibrillar proteins (MPs). BGs were prepared with 8 % of waxy rice starch (WRS) or tapioca starch (TS) and MPs ranged from 2 to 12 %. BGs were aromatized with: 1-heptanol, nonanal, 2-butanone, ethyl acetate, s-(+)-carvone. The studies included measurements of: rheological properties of BGs, non-covalent interactions between myosin and ACs, retention and release of ACs and enthalpy of ACs vaporization (ΔHvap). Results and conclusions. The main non-covalent interactions between myosin and ACs were hydrogen bonds and hydrophobic interactions. Retention and release parameters, determined during refrigerated storage (12 days) were statistically significantly (p ≤ 0.05) dependent on: starch type, MPs concentration and physicochemical properties of ACs. The ACs release rate constants were statistically significantly (p ≤ 0.05) correlated with those of rheological parameters derived from first order kinetic equation. ΔHvap values found in TS-based BGs were generally lower (p ≤ 0.05) than in counterparts prepared using WRS. BGs with a relatively high protein content can be intended for direct consumption and as subsystems for other food products to increase ACs stability.

TNB/TNCB cocrystal – an insensitive energetic cocrystal with low melting point

Effective cocrystallization technology plays a significant role in regulating the properties of existing explosives. A new energetic cocrystal consisting of TNB and TNCB in a 1:1 molar ratio was synthesized via slow evaporation of absolute alcohol. The crystal structure of TNB/TNCB cocrystal was verified by single crystal X-ray diffraction. Four main non-covalent interactions were conducive in building the TNB/TNCB cocrystal, including C–H—O, C–Cl—O, NO2—π and NO2—NO2 interactions. Through researching the different percentages of atom contacts, the NO2—π interaction is found to be the dominant non-covalent interaction. The melting points, impact sensitivities and detonation performances of cocrystal and coformers were measured and analyzed. The TNB/TNCB cocrystal was found to have a melting point of 100.2°C, which is between those of TNB (82.4°C) and TNCB (123.7°C). The cocrystal impact sensitivity (H50 = 97.5 cm) was superior to that of TNB (H50 = 59.6 cm) on account of the presence of insensitive TNCB (H50 = 118.9 cm), which is more insensitive than TNT (H50 = 83.5 cm, a common low-sensitive explosive). Moreover, the cocrystal detonation performance (detonation velocity: 7547 m/s, detonation pressure: 25.5 GPa) is also greater than that of TNT. Therefore, the TNB/TNCB cocrystal may be a promising future melt-cast carrier for insensitive melt-cast explosives.

Ordered Nanofibers Fabricated from Hierarchical Self-Assembling Processes of Designed α-Helical Peptides.

Peptide self-assembly is fast evolving into a powerful method for the development of bio-inspired nanomaterials with great potential for many applications, but it remains challenging to control the self-assembling processes and nanostrucutres because of the intricate interplay of various non-covalent interactions. A group of 28-residue α-helical peptides is designed including NN, NK, and HH that display distinct hierarchical events. The key of the design lies in the incorporation of two asparagine (Asn) or histidine (His) residues at the a positions of the second and fourth heptads, which allow one sequence to pack into homodimers with sticky ends through specific interhelical Asn-Asn or metal complexation interactions, followed by their longitudinal association into ordered nanofibers. This is in contrast to classical self-assembling helical peptide systems consisting of two complementary peptides. The collaborative roles played by the four main non-covalent interactions, including hydrogen-bonding, hydrophobic interactions, electrostatic interactions, and metal ion coordination, are well demonstrated during the hierarchical self-assembling processes of these peptides. Different nanostructures, for example, long and short nanofibers, thin and thick fibers, uniform metal ion-entrapped nanofibers, and polydisperse globular stacks, can be prepared by harnessing these interactions at different levels of hierarchy.

In silico decryption of serotonin-receptor binding: local non-covalent interactions and long-range conformational changes.

Serotonin–receptor binding is the key step in the process behind serotonin functionality, including several psychological and physiological behaviours. This study is focused on identifying the main non-covalent interactions controlling the stability of serotonin–receptor complexes as well as the main conformational changes in the receptor due to serotonin–receptor binding using classical molecular dynamics simulations and quantum chemical calculations. A qualitative analysis based on two order parameters ((i) the centre of mass distance and (ii) the angle between the surface normals of each aromatic residue and serotonin in the binding site) on the serotonin–receptor complex trajectory suggests that the T-type stacking interaction is predominant in the binding site. Quantum chemical calculations of the stacking interaction energy provide the quantitative contributions of important aromatic residues to the stabilization of the complex. Furthermore, a three body stacking interaction (named ‘L’-type) was observed and likely contributes to the stability of the complex. Direct and water-mediated hydrogen bonding between the residues in the binding site and serotonin contributes to the complex stability. Principal component analysis of the molecular dynamics simulation trajectory of the serotonin–receptor complex and the apo-receptor in water indicates that the whole receptor is significantly stabilized due to serotonin binding. An analysis based on the dynamic cross correlation function reflects the strong correlation between trans-membrane (TM)3, TM5, TM6 (containing residues responsible for the stacking interaction and hydrogen bonding) and mini-G0 which may participate in signal transduction leading to the functionality of serotonin.

Decavanadate Salts of Cytosine and Metformin: A Combined Experimental-Theoretical Study of Potential Metallodrugs Against Diabetes and Cancer.

Cytosine, a DNA and RNA building-block, and Metformin, the most widely prescribed drug for the treatment of Type 2 Diabetes mellitus were made to react separately with ammonium or sodium metavanadates in acidic aqueous solutions to obtain two polyoxovanadate salts with a 6:1 ratio of cation-anion. Thus, compounds [HCyt]6[V10O28]·4H2O, 1 and [HMetf]6[V10O28]·6H2O, 2 (where HCyt = Cytosinium cation, [C4H6N3O]+ and HMetf = Metforminium cation, [C4H12N5]+) were obtained and characterized by elemental analysis, single crystal X-ray diffraction, vibrational spectroscopy (IR and Raman), solution 51V-NMR, thermogravimetric analysis (TGA-DTGA), as well as, theoretical methods. Both compounds crystallized in Pspace group with Z' = 1/2, where the anionic charge of the centrosymmetric ion [V10O28]6− is balanced by six Cytosinium and six Metforminium counterions, respectively. Compound 1 is stabilized by π-π stacking interactions coming from the aromatic rings of HCyt cations, as denoted by close contacts of 3.63 Å. On the other hand, guanidinium moieties from the non-planar HMetf in Compound 2 interact with decavanadate μ2-O atoms via N−H···O hydrogen bonds. The vibrational spectroscopic data of both IR and Raman spectra show that the dominant bands in the 1000-450 cm−1 range are due to the symmetric and asymmetric ν(V−O) vibrational modes. In solution, 51V-NMR experiments of both compounds show that polyoxovanadate species are progressively transformed into the monomeric, dimeric and tetrameric oxovanadates. The thermal stability behavior suggests a similar molecular mechanism regarding the loss of water molecules and the decomposition of the organic counterions. Yet, no changes were observed in the TGA range of 540–580°C due to the stability of the [V10O28]6− fragment. Dispersion-corrected density functional theory (DFT-D) calculations were carried out to model the compounds in aqueous phase using a polarized continuum model calculation. Optimized structures were obtained and the main non-covalent interactions were characterized. Biological activities of these compounds are also under investigation. The combination of two therapeutic agents opens up a window toward the generation of potential metalopharmaceuticals with new and exciting pharmacological properties.

Noncovalent cation-π interactions--their role in nature

Non-covalent interactions play an extremely important role in organisms. The main non-covalent interactions in nature are: ion-ion interactions, dipole-dipole interactions, hydrogen bonds, and van der Waals interactions. A new kind of intermolecular interactions--cation-π interactions--is gaining increasing attention. These interactions occur between a cation and a π system. The main contributors to cation-π interactions are electrostatic, polarization and, to a lesser extent, dispersion interactions. At first, cation-π interactions were studied in a gas phase, with metal cation-aromatic system complexes. The characteristics of these complexes are as follows: an increase of cation atomic number leads to a decrease of interaction energy, and an increase of cation charge leads to an increase of interaction energy. Aromatic amino acids bind with metal cations mainly through interactions with their main chain. Nevertheless, cation-π interaction with a hydrophobic side chain significantly enhances binding energy. In water solutions most cations preferentially interact with water molecules rather than aromatic systems. Cation-π interactions occur in environments with lower accessibility to a polar solvent. Cation-π interactions can have a stabilizing role on the secondary, tertiary and quaternary structure of proteins. These interactions play an important role in substrate or ligand binding sites in many proteins, which should be taken into consideration when the screening of effective inhibitors for these proteins is carried out. Cation-π interactions are abundant and play an important role in many biological processes.

New terpyridine-(β-diketonate)-copper(II) complex. Structure and magnetism

Over the last decade the design and synthesis of metal-organic compounds with fascinating structural properties and potential applications as functional materials has been a major challenge in various fields of research.1Strategies for preparing these compounds are based on the careful selection of the constituent building blocks. 4'-(substituted)-4,2':6',4''-terpyridine ligands are considered versatile building blocks for the assembly of coordination polymers and networks with useful solid-state properties, such as magnetism, luminescence, redox activity, etc.2The divergent arrangements of N-donor atoms and the attachment of aryl substituents into the 4'-position of 4,2':6',4''-terpyridine allow to bridge two or more metal centers, giving rise to molecular assemblies of 1, 2 or 3 dimensions.3Our line of interest is the obtainment of compounds with emergent magnetic properties. Herein we present a copper complex surveying the new 4'-(quinolin-4-yl)-4,2':6',4''-terpyridine ligand (L), and formulated as [Cu(C5H1F6O2)2(C25H16N4·CHCl3)]n which was produced from the reaction of two equivalents of L with Cu(hfac)2, (hfac=hexafluoroacetylacetonate). The copper ion in trans-{CuN2(hfac)2} has an octahedral environment. The nitrogen atoms of the terminal pyridine rings coordinate to the paramagnetic centres, while the central ring remains uncoordinated. The linkage of the resulting polyhedra gives raise to an undulating 1D polymeric structure. Within these chains there are two main non-covalent interactions: π-stacking between the quinoline substituents and the pyridine rings and CH···F interactions due to CF3group of the hfac ligand. There are also weak CH···N, CH···π and π-π intermolecular interactions linking the L and CHCl3groups, which give stability to the crystal structure. Finally, we performed magnetic measurements, in order to determine the magnetic behaviour of our system. Acknowledgments: FONDECYT 1130433 project, CIPA of University of Concepción, LIA-MIF 836