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Formation of molecular complexes and subsequent heterolytic halogen‐halogen bond splitting upon reactions of molecular Cl2 with nitrogen‐containing Lewis bases (LB) are computationally studied at M06‐2X/def2‐TZVPD and for selected compounds at CCSD(T)/aug‐cc‐pvtz//CCSD/aug‐cc‐pvtz levels of theory. Obtained results are compared with data for ICl and I2 molecules. Reaction pathways indicate, that in case of Cl2∙LB complexes the activation energies for the heterolytic Cl‐Cl bond splitting are lower than the activation energies of the homolytic splitting of Cl2 molecule into chlorine radicals. The heterolytic halogen splitting of molecular complexes of X2∙Py with formation of [XPy2]+…X3−$$ {\mathrm{X}}_3^{-} $$ contact ion pairs in the gas phase is slightly endothermic in case of Cl2 and I2, but slightly exothermic in the case of ICl. Formation of {[ClPy2]+…Cl3−$$ {\mathrm{Cl}}_3^{-} $$}2 dimers makes the overall process exothermic. Taking into account that polar solvents favor ionic species, generation of donor‐stabilized Cl+ in the presence of the Lewis bases is expected to be favorable. Thus, in polar solvents the oxidation pathway via donor‐stabilized Cl+ species is viable alternative to the homolytic Cl‐Cl bond breaking. [ABSTRACT FROM AUTHOR]

Existing metal-containing porous catalysts have inherent heterogeneity in metal species, rendering it difficult to compare reactivity across varied catalyst formulations without first developing active site quantification protocols. The supercages of faujasite zeolites (FAU) are large enough to confine metal phthalocyanines (MPCs), together serving as a well-defined active center for experimental and computational catalyst characterization. Deviations in zeolite synthesis conditions from prior literature were required to obtain phase-pure FAU. Metal perchloro-, perfluoro-, and perhydrogenated phthalocyanines (MPCCl16, MPCF16, and MPC; M = Cr, Mn, Fe, Co, Ni, Cu, and Zn) were encapsulated into FAU zeolites via hydrothermal synthesis (MPC@FAU) and deposited onto the external surfaces by postsynthetic deposition (MPC/FAU). These MPC@FAU catalysts were tested as catalysts for CO oxidation with dioxygen at 298 K and their reactivity compared to that of silica-supported PdAu nanoparticles and cobalt–nitrogen-doped carbon (Co–N–C). Initial CO2 site time yields were greater than the analogous metal-ion-exchanged zeolites (by ∼50×). However, this initial activity decreased with time on stream for all MPC samples tested, and the cause of this deactivation is explored herein. Stable CO2 formation rates with time on stream observed over PdAu/SiO2 and Co–N–C suggest that deactivation observed over MPC@FAU samples is distinct and not an artifact of the experimental apparatus. Density functional theory calculations suggest an O2-activation mechanism, aided by the coadsorption of CO on the pyrrole N of the MPC and an axial ligand that can provide additional electron density to reduce the barrier for O2 bond breaking; this reaction mechanism is distinct from that over structurally similar metal-nitrogen-doped carbons. Nevertheless, the reactivity of MPC@FAU catalysts for gas-phase CO oxidation with dioxygen at ambient temperature indicates that they may share similar functionality to metal–nitrogen-doped carbons and have the potential to serve as model catalysts for gas-phase chemistries. [ABSTRACT FROM AUTHOR]

Isostructural binuclear complexes [Ln2L2(hfac)6] (Ln = Eu, Tb; hfac– = hexafluoroacetylacetonate ion) are synthesized by the interaction of [Ln(hfac)3(H2O)2] with 3,6-bis(diphenylphosphinyl)pyridazine (L). According to the single-crystal XRD data, two Ln(hfac)3 moieties in the complexes are connected by two O,O´-bidentate-bridging ligands L, and the coordination polyhedron Ln@O8 has the geometry of a triangular dodecahedron. The Eu3+ and Tb3+ complexes exhibit characteristic lanthanide-centered photoluminescence in the solid state at 297 K with luminescence quantum yields of 31% and 2% and excited state lifetimes of 707 and 30 μs, respectively, thus indicating that luminescence sensitization by the ligand environment is more effective for Eu3+ than for Tb3+. [ABSTRACT FROM AUTHOR]

Densimetry is used to study the interaction between L-histidine (His) and nicotinic (NA), isonicotinic (INA), and picolinic acids (PA) in an aqueous buffer solution in the 288.15–313.15 K range of temperatures. Data on density are used to determine the apparent molar volumes and limiting apparent molar volumes of pyridine monocarboxylic acid (PyCOOH) isomers at infinite dilution, along with their temperature derivatives in a buffer solution containing the amino acid. Unlike the linear concentration dependences of the apparent molar volume of PyCOOH isomers in a buffer solution, the analogous dependences of ternary systems (PyCOOH–His–buffer) are nonlinear, indicating the formation of a molecular complex between the solutes. Limiting apparent molar expansibilities and their temperature derivatives are determined. Their values suggest that the ordering of the solvent grows in the series of isomers PA → NA → INA upon adding the amino acid to a buffer solution of PyCOOH. It is shown that the limiting apparent molar volumes of transferring PyCOOH from a buffer to a His-containing buffer solution have positive values and grow in the studied range of temperatures. The discussion of the results is based on the dominant types of molecular interactions between the solute and solvent using the Gurney model. [ABSTRACT FROM AUTHOR]

Theoretical investigation of thermodynamic stability and bonding features of possible isomers of the molecular and ionic complexes of pyridine with molecular iodine and iodine monochloride IX (X = I,Cl) is presented. M06‐2X DFT functional is found to provide bond distances and dissociation energies which are close to those obtained at high‐level ab initio CCSD(T)/aug‐cc‐pvtz//CCSD/aug‐cc‐pvtz benchmark computations for the most stable isomers, formed via donation of a lone pair of nitrogen atom of pyridine to the iodine atom. These isomers are by 23–33 kJ mol−1 (in case of I2) and by 39–56 kJ mol−1 (in case of ICl) more stable than other molecular complexes. T‐shaped π‐σ* bonded isomers turn out to be energetically comparable with van der Waals bound compounds. Among the ionic isomers, structures featuring [IPy2]+ cation with I3− or ICl2− counterions are more stable. Oligomerization favors ionic isomers starting from the tetrameric clusters of the composition (IX)4Py4. [ABSTRACT FROM AUTHOR]

In this study, both practical and theoretical aspects of the solubility of edaravone (EDA) in Deep Eutectic Solvents (DESs) were considered. The solubility of edaravone in some media, including water, can be limited, which creates the need for new efficient and environmentally safe solvents. The solubility of EDA was measured spectrophotometrically and the complex intermolecular interactions within the systems were studied with the COSMO-RS framework. Of the four studied DES systems, three outperformed the most efficient classical organic solvent, namely dichloromethane, with the DES comprising choline chloride and triethylene glycol, acting as hydrogen bond donor (HBD), in a 1:2 molar proportion yielding the highest solubility of EDA. Interestingly, the addition of a specific amount of water further increased EDA solubility. Theoretical analysis revealed that in pure water or solutions with high water content, EDA stacking is responsible for self-aggregation and lower solubility. On the other hand, the presence of HBDs leads to the formation of intermolecular clusters with EDA, reducing self-aggregation. However, in the presence of a stoichiometric amount of water, a three-molecular EDA–HBD–water complex is formed, which explains why water can also act as a co-solvent. The high probability of formation of this type of complexes is related to the high affinity of the components, which exceeds all other possible complexes. [ABSTRACT FROM AUTHOR]

Quantum chemical computations at M06-2X/def2-TZVPD level of theory were employed to compute structural and thermodynamic properties of gaseous donor-acceptor complexes IX·LB [X = I, Cl; LB = trimethylamine, triethylamine, pyridine, 2-aminopyridine, 4,4′-bipyridine, pyrazine, 1,2-bis(4-pyridyl)ethylene, 1,2-bis(4-pyridyl)ethane]. Iodine monochloride is a stronger Lewis acid compared to the molecular iodine. With respect to homogeneous gas phase dissociation into components, the complex of ICl with triethylamine is the most stable and the complex of I2 with pyrazine is the least stable. It is shown that dissociation enthalpies do not correlate with proton affinity of the Lewis base, but there is a good correlation between dissociation enthalpies and I–X bond lengthening upon complex formation. This allows to estimate the stability of the complex based on its structural data. [ABSTRACT FROM AUTHOR]

New developments in the field of Lewis acidity are highlighted, with the focus of novel Lewis acids and Lewis superacids of group 2, 13, 14, and 15 elements. Several important basics, illustrated by modern examples (classification of Donor‐Acceptor (DA) complexes, amphoteric nature of any compound in terms of DA interactions, reorganization energies of main group Lewis acids and the role of the energies of frontier orbitals) are presented and discussed. It is emphasized that the Lewis acidity phenomena are general and play vital role in different areas of chemistry: from weak "atomophilic" interactions to the complexes of Lewis superacids. [ABSTRACT FROM AUTHOR]

In recent years, the non-covalent interactions between chalcogen centers have aroused substantial research interest because of their potential applications in organocatalysis, materials science, drug design, biological systems, crystal engineering, and molecular recognition. However, studies on π-hole-type chalcogen∙∙∙chalcogen interactions are scarcely reported in the literature. Herein, the π-hole-type intermolecular chalcogen∙∙∙chalcogen interactions in the model complexes formed between XO2 (X = S, Se, Te) and CH3YCH3 (Y = O, S, Se, Te) were systematically studied by using quantum chemical computations. The model complexes are stabilized via one primary X∙∙∙Y chalcogen bond (ChB) and the secondary C−H∙∙∙O hydrogen bonds. The binding energies of the studied complexes are in the range of −21.6~−60.4 kJ/mol. The X∙∙∙Y distances are significantly smaller than the sum of the van der Waals radii of the corresponding two atoms. The X∙∙∙Y ChBs in all the studied complexes except for the SO2∙∙∙CH3OCH3 complex are strong in strength and display a partial covalent character revealed by conducting the quantum theory of atoms in molecules (QTAIM), a non-covalent interaction plot (NCIplot), and natural bond orbital (NBO) analyses. The symmetry-adapted perturbation theory (SAPT) analysis discloses that the X∙∙∙Y ChBs are primarily dominated by the electrostatic component. [ABSTRACT FROM AUTHOR]

The quantum chemical simulation of complexes of the glycyl-L-glutamic acid anion and the - alanyl-L-tyrosine Ala-L-Tyr zwitterion with nucleic bases (uracyl and cytosine) is performed using the DFT/B97D method. The most energetically favorable configurations of the complexes are found. Changes in the peptide structure during the formation of the complexes are analyzed. It is shown that the complexes are stabilized by intermolecular hydrogen bonds. The stacking effect competing with the hydrogen bonding in the orientation of peptide ions in the complex is described. The topological analysis is carried out within which bond critical points and their parameters are studied and hydrogen bond energies are found in the complexes. [ABSTRACT FROM AUTHOR]

The advances made in the field of stimuli‐responsive catalysis during the last five years with a focus on the novel recently‐emerged directions and applications have been surveyed. Metal‐free catalysts and organometallic complexes, as well as biomimetic systems and extended structures, which display switchable catalytic activity for a variety of organic transformations, are discussed. Light‐activated systems comprised of photochromic molecules capable of modulating reaction rate, yield, or enantioselectivity based on geometric and electronic changes associated with photoisomerization are the focus of the detailed discussion. Alternative stimuli, including pH and temperature, which could be applied either alone or in combination with light, are also addressed. Recent advances clearly demonstrate that the capability to finely tune catalyst behavior via an external stimulus is a powerful tool that could alter the landscape of sustainable chemistry. [ABSTRACT FROM AUTHOR]

In this study, both practical and theoretical aspects of the solubility of edaravone (EDA) in Deep Eutectic Solvents (DESs) were considered. The solubility of edaravone in some media, including water, can be limited, which creates the need for new efficient and environmentally safe solvents. The solubility of EDA was measured spectrophotometrically and the complex intermolecular interactions within the systems were studied with the COSMO-RS framework. Of the four studied DES systems, three outperformed the most efficient classical organic solvent, namely dichloromethane, with the DES comprising choline chloride and triethylene glycol, acting as hydrogen bond donor (HBD), in a 1:2 molar proportion yielding the highest solubility of EDA. Interestingly, the addition of a specific amount of water further increased EDA solubility. Theoretical analysis revealed that in pure water or solutions with high water content, EDA stacking is responsible for self-aggregation and lower solubility. On the other hand, the presence of HBDs leads to the formation of intermolecular clusters with EDA, reducing self-aggregation. However, in the presence of a stoichiometric amount of water, a three-molecular EDA–HBD–water complex is formed, which explains why water can also act as a co-solvent. The high probability of formation of this type of complexes is related to the high affinity of the components, which exceeds all other possible complexes.

A synergistic effect of cyclic ketals in compositions with lower alcohols has been revealed for the first time while adding those ketals to alcohol-containing gasoline. By using model oxidation reactions of ketals and their structural analogs, 1,3-benzodioxolanes, in protic media, the synergistic effect was rationalized assuming the formation of ketal–alcohol complexes possessing surfactant properties, which give rise to hydrated supramolecular structures around them. Deactivation of hot radicals with the transition from the explosive combustion mode to stationary combustion inside these structures is more effective than in the bulk medium. Such structuring effect is general for the behavior of ketals in hydrophobic–hydrophilic systems, including biological ones. This conclusion has been confirmed by studying the activity of cyclic ketals in compositions with antibacterial agents, as well as with alcohols and carboxylic acids. [ABSTRACT FROM AUTHOR]

The complex formation of uracil and cytosine with glycyl-L-glutamic acid (β-endorphin 30-31), γ-L-glutamyl-L-cysteinyl-glycine (glutathione reduced), α-L-alanyl-L-tyrosine, and α-L-alanyl-α-L-alanine in a buffered saline has been studied using dissolution calorimetry. The values of the reaction constant, the change in Gibbs energy, enthalpy, and entropy were obtained. It is shown that the ratio of the enthalpy and entropy factors depends on the charge of the peptide ion, and the number of H-bond acceptors in the peptide structure. The contributions of interaction between charged groups and polar fragments, hydrogen bonding, and stacking interaction are discussed, taking into account the effect of solvent reorganization around the reactant molecules. [ABSTRACT FROM AUTHOR]

Development of multifunctional electrocatalysts with high efficiency and stability is of great interest in recent energy conversion technologies. Herein, a novel heteroelectrocatalyst of molecular iron complex (FeMC)‐carbide MXene (Mo2TiC2Tx) uniformly embedded in a 3D graphene‐based hierarchical network (GrH) is rationally designed. The coexistence of FeMC and MXene with their unique interactions triggers optimum electronic properties, rich multiple active sites, and favorite free adsorption energy for excellent trifunctional catalytic activities. Meanwhile, the highly porous GrH effectively promotes a multichannel architecture for charge transfer and gas/ion diffusion to improve stability. Therefore, the FeMC–MXene/GrH results in superb performances towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in alkaline medium. The practical tests indicate that Zn/Al–air batteries derived from FeMC–MXene/GrH cathodic electrodes produce high power densities of 165.6 and 172.7 mW cm−2, respectively. Impressively, the liquid‐state Zn–air battery delivers excellent cycling stability of over 1100 h. In addition, the alkaline water electrolyzer induces a low cell voltage of 1.55 V at 10 mA cm−2 and 1.86 V at 0.4 A cm−2 in 30 wt.% KOH at 80 °C, surpassing recent reports. The achievements suggest an exciting multifunctional electrocatalyst for electrochemical energy applications. [ABSTRACT FROM AUTHOR]

Interactions of cationic and anionic chlorin photosensitizers (PSs) for photodynamic therapy with the potential delivery vehicle, the micellar surfactant Tween 80, were studied by spectrophotometric and fluorescence titration. The formation of PS—Tween 80 complexes in an aqueous solution was demonstrated. Two binding modes of the macrocycles to surfactant micelles, each with its own binding constant and stereochemistry of interactions, are observed in the spectrophotometric titration curves. Regardless of the sign and magnitude of the charge of the PS molecule, water-soluble chlorin macroheterocycles are located in the outer layer of the micelle surrounded by polar oxyethylene groups, into which hydrated iodide ions can penetrate. Cationic PSs were found to be, in general, more accessible to the quencher. [ABSTRACT FROM AUTHOR]

In recent years, the non-covalent interactions between chalcogen centers have aroused substantial research interest because of their potential applications in organocatalysis, materials science, drug design, biological systems, crystal engineering, and molecular recognition. However, studies on π-hole-type chalcogen∙∙∙chalcogen interactions are scarcely reported in the literature. Herein, the π-hole-type intermolecular chalcogen∙∙∙chalcogen interactions in the model complexes formed between XO2 (X = S, Se, Te) and CH3YCH3 (Y = O, S, Se, Te) were systematically studied by using quantum chemical computations. The model complexes are stabilized via one primary X∙∙∙Y chalcogen bond (ChB) and the secondary C−H∙∙∙O hydrogen bonds. The binding energies of the studied complexes are in the range of −21.6~−60.4 kJ/mol. The X∙∙∙Y distances are significantly smaller than the sum of the van der Waals radii of the corresponding two atoms. The X∙∙∙Y ChBs in all the studied complexes except for the SO2∙∙∙CH3OCH3 complex are strong in strength and display a partial covalent character revealed by conducting the quantum theory of atoms in molecules (QTAIM), a non-covalent interaction plot (NCIplot), and natural bond orbital (NBO) analyses. The symmetry-adapted perturbation theory (SAPT) analysis discloses that the X∙∙∙Y ChBs are primarily dominated by the electrostatic component.

Raman spectra of hydrogen‐bonded water oligomers have been resolved from concentration‐dependent Raman spectra of tetrahydrofuran (THF)–water binary solutions with the use of multivariate curve resolution with alternating least‐squares (MCR‐ALS) analysis, assisted by hypothetical addition multivariate analysis with numerical differentiation (HAMAND) procedure. A total of 38 Raman spectra acquired in the broad spectral range of 700–3810 cm−1 were analyzed in a multistep procedure to explain the spectral variations in terms of four components: pure THF, Spectra A, Spectra B, and Spectra C. A four‐component MCR‐ALS analysis was performed with initial guesses by HAMAND analysis to refine the spectral components and determine their concentration dependence. Of the MCR‐ALS resolved three spectra, A was identified as THF(H2O), B as THF(H2O)2 with two hydrogens attached to THF, and C as THF(H2O)n having two or more linearly hydrogen‐bonded oligomers of water (n = 2–4). Observed spectral changes of the OH stretch vibrations of water and those of the C–C/C–O stretches of THF were well reproduced by quantum chemical calculations. Formation of hydrogen‐bonded water oligomers in THF–water complexes has thus been revealed. The present study provides a new insight into the basics of hydrogen bonding formation in aqueous systems. It also provides experimental methodology for extracting concentration‐dependent minor spectral components contained in complex condensed‐phase Raman spectra. [ABSTRACT FROM AUTHOR]

Many proteins form paralogous multimers - molecular complexes in which evolutionarily related proteins are arranged into specific quaternary structures. Little is known about the mechanisms by which they acquired their stoichiometry (the number of total subunits in the complex) and heterospecificity (the preference of subunits for their paralogs rather than other copies of the same protein). Here we use ancestral protein reconstruction and biochemical experiments to study historical increases in stoichiometry and specificity during the evolution of vertebrate hemoglobin (Hb), a α 2 β 2 heterotetramer that evolved from a homodimeric ancestor after a gene duplication. We show that the mechanisms for this evolutionary transition was simple. One hydrophobic substitution in subunit β after the gene duplication was sufficient to cause the ancestral dimer to homotetramerize with high affinity across a new interface. During this same interval, a single-residue deletion in subunit α at the older interface conferred specificity for the heterotetrameric form and the trans -orientation of subunits within it. These sudden transitions in stoichiometry and specificity were possible because the interfaces in Hb are isologous - involving the same surface patch on interacting subunits, rotated 180° relative to each other - but the symmetry is slightly imperfect. This architecture amplifies the impacts of individual mutations on stoichiometry and specificity, especially in higher-order complexes, and allows single substitutions to differentially affect heteromeric vs homomeric interactions. Many multimers are isologous, and symmetry in proteins is always imperfect; our findings therefore suggest that elaborate and specific molecular complexes may often evolve via simple genetic and physical mechanisms., Competing Interests: Competing Interest Statement: The authors declare no competing interests.

The complex formation of uracil and cytosine with glycyl-L-glutamic acid (β-endorphin 30-31), γ-L-glutamyl-L-cysteinyl-glycine (glutathione reduced), α-L-alanyl-L-tyrosine, and α-L-alanyl-α-L-alanine in a buffered saline has been studied using dissolution calorimetry. The values of the reaction constant, the change in Gibbs energy, enthalpy, and entropy were obtained. It is shown that the ratio of the enthalpy and entropy factors depends on the charge of the peptide ion, and the number of H-bond acceptors in the peptide structure. The contributions of interaction between charged groups and polar fragments, hydrogen bonding, and stacking interaction are discussed, taking into account the effect of solvent reorganization around the reactant molecules.

Abstract Before ‘cancer interception’ was first advocated, ‘interceptor molecules’ had been conceived as a sub-category of preventive agents that interfered with the earliest initiation steps in carcinogenesis. Three decades ago, a seminal review cataloged over fifty synthetic agents and natural products that were known or putative interceptor molecules. Chlorophylls and their derivatives garnered much interest based on the potent antimutagenic activity in the Salmonella assay, and the subsequent mechanistic work that provided proof-of-concept for direct molecular complexes with planar aromatic carcinogens. As the ‘interceptor molecule’ hypothesis evolved, mechanistic experiments and preclinical studies supported the view that chlorophylls can interact with environmental heterocyclic amines, aflatoxins, and polycyclic aromatic hydrocarbons to limit their uptake and bioavailability in vivo. Support also came from human translational studies involving ultralow dose detection in healthy volunteers, as well as intervention in at-risk subjects. Antimutagenic and antigenotoxic effects of natural and synthetic chlorophylls against small alkylating agents also highlighted the fact that non-interceptor mechanisms existed. This gave impetus to investigations broadly related to free radical scavenging, anti-inflammatory effects, immune modulation and photodynamic therapy. Therapeutic aspects of chlorophylls also were investigated, with evidence for cell cycle arrest and apoptosis in human cancer cells. As the science has evolved, new mechanistic leads continue to support the use and development of chlorophylls and their porphyrin derivatives for cancer interception, beyond the initial interest as interceptor molecules.

Six stationary points (three minima and three TS) in the thermal energy profile of octafluorocyclooctatetraene (F8‐COT) have been explored. The TSs corresponding to the inversion process of F8‐COT and its transformation in perfluoro bicyclo[2.2.2]octa‐2,5,7‐triene (F8‐BOT) and subsequent to perfluoro tetracyclo[4.2.0.02.02,8,05,7]octene (F8‐TCO) have been characterized. The results have been compared to the energy profile in the parent compound (cyclooctatetraene or COT). In addition, the effect of the formation of anion‐π complexes in the reaction profile has been explored. The results have been rationalized using the electrostatic potential of the isolated stationary points and thermodynamic cycles involving the complex formation in the minima and TS and the barriers in the isolated molecules. Moreover, the electron density has been analyzed with the AIM methodology. [ABSTRACT FROM AUTHOR]

The crystal structure of the silicon tetrafluoride molecular complex with 4-phenylpyridine SiF4·2ppy has been determined by X-ray diffraction analysis. Although 4-phenylpyridine has a higher proton affinity than pyridine, the Si–N bond length in crystalline SiF4·2Py is shorter by 0.03(2) Å than in SiF4·2ppy. The energies of donor-acceptor Si–N bonds in SiF4·2Py (220.6 kJ/mol) and SiF4·2ppy (225.0 kJ/mol) calculated by the M06-2X/def2-TZVP method agree with a slightly higher proton affinity of 4-phenylpyridine. [ABSTRACT FROM AUTHOR]

The decomposition of aluminum hydride complexes with trimethylamine and N-heterocyclic carbene—1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene was studied by a static tensimetric method with a membrane null-manometer. The AlH3·NMe3 complex passes into vapor in the form of monomeric molecules and in unsaturated vapor slowly decomposes at 70‒80°С into solid aluminum, gaseous trimethylamine, and hydrogen. The decomposition is accompanied by an induction period, the duration of which decreases as temperature increases. The AlH3 complex with carbene slowly decomposes at 170‒200°С with a rate practically independent of temperature. [ABSTRACT FROM AUTHOR]

Theoretical investigation of thermodynamic stability and bonding features of possible isomers of the molecular and ionic complexes of pyridine with molecular iodine and iodine monochloride IX (X = I,Cl) is presented. M06-2X DFT functional is found to provide bond distances and dissociation energies which are close to those obtained at high-level ab initio CCSD(T)/aug-cc-pvtz//CCSD/aug-cc-pvtz benchmark computations for the most stable isomers, formed via donation of a lone pair of nitrogen atom of pyridine to the iodine atom. These isomers are by 23-33 kJ mol -1 (in case of I 2 ) and by 39-56 kJ mol -1 (in case of ICl) more stable than other molecular complexes. T-shaped π-σ* bonded isomers turn out to be energetically comparable with van der Waals bound compounds. Among the ionic isomers, structures featuring [IPy 2 ] + cation with I 3 - or ICl 2 - counterions are more stable. Oligomerization favors ionic isomers starting from the tetrameric clusters of the composition (IX) 4 Py 4 ., (© 2024 Wiley Periodicals LLC.)

Energetic effects of solvation of SbF5, SbCl5, and 21 group 13 Lewis acids (LA) and their molecular complexes with acetonitrile and pyridine are evaluated using SMD approach. Compared to the gas phase, solvation increases the stability of boron‐ and aluminum‐containing complexes but decreases the stability of gallium and indium‐containing homologs due to larger solation energies of free LA. New Lewis acidity scales, based on the Gibbs energy of dissociation of the molecular complexes LA·pyridine and LA·acetonitrile in the gas phase, in benzene and acetonitrile solutions, are proposed. [ABSTRACT FROM AUTHOR]

The phosphorescence of oxygen in the liquid phase and in tetrachloromethane solution is studied under direct optical excitation by a light-emitting diode array at a wavelength of 765 nm. The intensity of observed oxygen phosphorescence at a wavelength of 1270 nm excited at a wavelength of 765 nm is compared with the phosphorescence intensity in the case of excitation at other wavelengths partially or completely coinciding with the absorption lines of molecular oxygen complexes. [ABSTRACT FROM AUTHOR]

Before 'cancer interception' was first advocated, 'interceptor molecules' had been conceived as a sub-category of preventive agents that interfered with the earliest initiation steps in carcinogenesis. Three decades ago, a seminal review cataloged over fifty synthetic agents and natural products that were known or putative interceptor molecules. Chlorophylls and their derivatives garnered much interest based on the potent antimutagenic activity in the Salmonella assay, and the subsequent mechanistic work that provided proof-of-concept for direct molecular complexes with planar aromatic carcinogens. As the 'interceptor molecule' hypothesis evolved, mechanistic experiments and preclinical studies supported the view that chlorophylls can interact with environmental heterocyclic amines, aflatoxins, and polycyclic aromatic hydrocarbons to limit their uptake and bioavailability in vivo. Support also came from human translational studies involving ultralow dose detection in healthy volunteers, as well as intervention in at-risk subjects. Antimutagenic and antigenotoxic effects of natural and synthetic chlorophylls against small alkylating agents also highlighted the fact that non-interceptor mechanisms existed. This gave impetus to investigations broadly related to free radical scavenging, anti-inflammatory effects, immune modulation and photodynamic therapy. Therapeutic aspects of chlorophylls also were investigated, with evidence for cell cycle arrest and apoptosis in human cancer cells. As the science has evolved, new mechanistic leads continue to support the use and development of chlorophylls and their porphyrin derivatives for cancer interception, beyond the initial interest as interceptor molecules. [ABSTRACT FROM AUTHOR]

The provitamin A activity of β-carotene is of primary interest to address one of the world’s major malnutrition concerns. β carotene is a fat-soluble compound and its bioavailability from natural sources is very poor. Hence, studies have been focused on the development of specific core/shell micro- or nano-structures that encapsulate β-carotene in order to allow its dispersion in liquid systems and improve its bioavailability. One key objective when developing these structures is also to accomplish β-carotene stability. The aim of this review is to collect kinetic data (rate constants, activation energy) on the degradation of encapsulated β-carotene in order to derive knowledge on the possibility for these systems to be scaled-up to the industrial production of functional foods. Results showed that most of the nano- and micro-structures designed for β-carotene encapsulation and dispersion in the water phase provide better protection with respect to a natural matrix, such as carrot juice, increasing the β-carotene half-life from about 30 d to more than 100 d at room temperature. One promising approach to increase β-carotene stability was found to be the use of wall material, surfactants, or co-encapsulated compounds with antioxidant activity. Moreover, a successful approach was the design of structures, where the core is partially or fully solidified; alternatively, either the core or the interface or the outer phase are gelled. The data collected could serve as a basis for the rational design of structures for β-carotene encapsulation, where new ingredients, especially the extraordinary natural array of hydrocolloids, are applied.

We have explored the structural and energetic properties of a series of RMX3‐NH3 (M=Si, Ge; X=F, Cl; R=CH3, C6H5) complexes using density functional theory and low‐temperature infrared spectroscopy. In the minimum‐energy structures, the NH3 binds axially to the metal, opposite a halogen, while the organic group resides in an equatorial site. Remarkably, the primary mode of interaction in several of these systems seems to be hydrogen bonding (C‐H‐‐N) rather than a tetrel (N→M) interaction. This is particularly clear for the RMCl3‐NH3 complexes, and analyses of the charge distributions of the acid fragment corroborate this assessment. We also identified a set of metastable geometries in which the ammonia binds opposite the organic substituent in an axial orientation. Acid fragment charge analyses also provide a clear rationale as to why these configurations are less stable than the minimum‐energy structures. Matrix‐isolation infrared spectra provide clear evidence for the occurrence of the minimum‐energy form of CH3SiCl3–NH3, but analogous results for CH3GeCl3–NH3 are less conclusive. Computational scans of the M‐N distance potentials for CH3SiCl3–NH3 and CH3GeCl3–NH3, both in the gas phase and bulk dielectric media, reveal a great deal of anharmonicity and a propensity for condensed‐phase structural change. [ABSTRACT FROM AUTHOR]

Driven by the many potential applications as molecular catalyst for a range of metal‐promoted transformations, the quest for well‐defined, soluble and reactive complexes of barium has attracted substantial interest in the past decade. While it has long been overlooked, barium is now one of the hotly debated metals in main group chemistry. The present review surveys the main achievements of the last 10 years in the molecular chemistry of barium, presenting along the way the key synthetic strategies that have been implemented successfully to address the specificities of barium chemistry. This includes ligand design and non‐covalent interactions. The performances of barium complexes as homogeneous catalysts for the most prominent reactions mediated by alkaline‐earth metals (hydroelementations and heterodehydrocouplings) are reviewed in conjunction with those obtained with somewhat more common calcium or strontium catalysts. [ABSTRACT FROM AUTHOR]

Diadamantyl ether (DAE, C20H30O) represents a good model to study the interplay between London dispersion and hydrogen‐bond interactions. By using broadband rotational spectroscopy, an accurate experimental structure of the diadamantyl ether monomer is obtained and its aggregates with water and a variety of aliphatic alcohols of increasing size are analyzed. In the monomer, C−H⋅⋅⋅H−C London dispersion attractions between the two adamantyl subunits further stabilize its structure. Water and the alcohol partners bind to diadamantyl ether through hydrogen bonding and non‐covalent Owater/alcohol⋅⋅⋅H−CDAE and C−Halcohol⋅⋅⋅H−CDAE interactions. Electrostatic contributions drive the stabilization of all the complexes, whereas London dispersion interactions become more pronounced with increasing size of the alcohol. Complexes with dominant dispersion contributions are significantly higher in energy and were not observed in the experiment. The results presented herein shed light on the first steps of microsolvation and aggregation of molecular complexes with London dispersion energy donor (DED) groups and the kind of interactions that control them. [ABSTRACT FROM AUTHOR]

The properties of the hydrogen-bonded complexes of chloroform and bromoform with ammonia, water, hydrogen fluoride, phosphine, hydrogen sulphide and hydrogen chloride were studied by means of ab initio calculations. The properties of interest were the molecular structures, the interaction energies, the vibrational spectra and the nature of the orbital interactions involved in the formation of the complexes. Of particular interest was the determination of whether the various interactions exhibited red-shifted or blue-shifted hydrogen bond behaviour. The complexes optimized in three distinct structural models, singly bonded, cyclic and cage. The interaction energies, in the main, varied systematically with changes of the haloform and of the partner molecules. Changes of the CH or YH (Y = N, O, F, P, S and Cl) bond lengths correlated in most cases with the interaction energies, subject to some inconsistencies, with opposite behaviour being shown by the two sets. Similarly, the CH and YH stretching wavenumber shifts also displayed a dependence on the interaction energies, tracking with the bond length changes. Based on the diagnostic utility of these structural and spectroscopic properties, the complexes were found to be almost exclusively red-shifted, for binding through both the CH and YH groups. The orbital interactions responsible for the stability of the complexes were determined to be donation from a Y atom lone pair orbital of the partner molecule to a CH σ antibonding orbital and from a X lone pair orbital (X = Cl and Br) of the haloform to a YH σ antibonding orbital. [ABSTRACT FROM AUTHOR]

The non-covalent assemblies among multiple non-identical metal complexes have scopes to develop a new subject area. There are infinite numbers of ways for different combinations among inorganic neutral or ionic complexes. Each partnering species of those molecular complexes would also have diversities by changing metal ions, ligands, oxidation states of metal ions, and coordination numbers. Keeping a view of the emergence of framework materials and self-assembled nano-structures of metal complexes, the non-covalently linked assemblies of inorganic molecular complexes would have scopes for new nano-dimensional materials. This account provides a systematic description of the different inorganic molecular complexes for a concerted effort to develop a new area that would have importance in applied materials. [ABSTRACT FROM AUTHOR]

The possibility of the formation of practically nonvolatile molecular complexes between the components of mixture and the separating agent of various compositions has been shown using the benzene–heptane–N-methylpyrrolidone system as an example. When modeling the vapor–liquid phase equilibrium, as a rule, the real structure of the solution is not taken into account, assuming the monomolecular structure of the substances contained in the solution. This significantly affects the real values ​​of coefficients of relative volatility, leading to the appearance of concentration inversion. The values ​​of fractions of substances in a monomolecular form are experimentally determined. [ABSTRACT FROM AUTHOR]

Phosphorescence of liquid oxygen under excitation at cooperative transitions of О2–О2 molecular oxygen complexes is studied using direct optical excitation by LED arrays emitting in the near-UV and visible spectral regions at wavelengths partially or completely coinciding with the absorption lines of the molecular complexes. [ABSTRACT FROM AUTHOR]

Molecular structure of crystalline complex SbCl5 • Py was determined for the first time and the structure of the complex SbCl5 • AN was refined by means of single crystal X-ray diffraction analysis. It is shown that donor-acceptor Sb–N bond lengths for these complexes are equal within the experimental error. Quantum chemical calculations of the complexes in the gas phase reveal that the energies of the donor-acceptor bond Sb–N are 88 and 180 kJ mol−1 for SbCl5 • AN and SbCl5 • Py, respectively. It is established that the length of the donor-acceptor bond Sb–N in the crystal cannot serve as a measure of its strength. [ABSTRACT FROM AUTHOR]

Brain strokes are widely spread all over the world and are among the most dangerous for the population. Often it leads to death, complete or partial loss of ability to work. The correction of imbalance of Excitatory and inhibitory neurotransmitter systems by activation of natural inhibitory processes is a promising direction of primary neuroprotection in cerebral ischemia. Particular attention is drawn to the natural inhibitory neurotransmitter – glycine and its role in the mechanisms of acute cerebral ischemia. There are data on the ability of the thiotriazoline antioxidant to potentiate the therapeutic effect of neurometabolic cerebroprotectors. Therefore, the creation of new combined preparation based on glycine with thiotriazoline is important today. Objective: to study the structure, and estimate the energy of formation and geometric characteristics of the intermolecular hydrogen bonds for complexes which are formed with glycine, 3-methyl-1,2,4-triazolyl-5-thioacetate (MTTA) and morpholine. Method of calculation. The initial approximation to the structure of the complexes was obtained with the help of molecular docking procedure using the AutoDock Vina program. The resulting three-component complexes were preliminarily optimized by the semiempirical PM7 method, taking into account the outward influences, which was simulated by the COSMO method. The calculations were carried out using the MOPAC2012 program. The complexes were optimized using the density functional method with the empirical dispersion correction B97-D3/SVP+COSMO (Water) using geometric correction for the incompleteness of the gCP basic set. A more accurate calculation of the solvation energy was carried out by SMD method. Calculations by the density functional method were carried out using the ORCA 3.0.3 program. The energy of formation of complexes in solution was calculated as the difference between the free Gibbs energies of the solvated complex and its individual solvated components. Results and its discussion. Quantum-chemical modeling of the complexes of thiatriazoline and glycine has showed the possibility of the formation of multiple hydrogen bonds in them. The results of calculations show that the multiplicity of charge-enhanced donor and acceptor sites for hydrogen bonding leads to the formation of complexes that are different in structure but close in energy formation. Conclusions. The conducted quantum-chemical study of system has shown the possibility of formation of three-component complexes with low stability in infinitely diluted solutions. The glycine molecule tends to form not only intermolecular hydrogen bonds, but also a charge-enhanced intramolecular hydrogen bond. It can be expected that in real solutions the enhancement of intermolecular interactions can lead to an increase in the stability of the complexes.

Quantum chemical calculations of molecular complexes formed by ammonia and methanide (electron pair donor) with HCl and ClF molecules (acceptor) at different mutual orientations are performed by the MP2 method of second-order Møller–Plesset perturbation theory using Dunning's correlation-consistent aug-cc-pVTZ basis set, augmented by diffuse functions. An elongation in the covalent bond of the acceptor and a red shift in the corresponding IR band are observed for all complexes. NBO analysis and topological analysis of electron density are performed and maps of electron density shift upon complexation are plotted. The structure of the transition state for interconversion of NH3···HCl and NH3···ClH complexes corresponding to minima on the potential energy surface is calculated. The transition between configurations is accompanied by evolution of the intermolecular bond path with the N···H contact critical point being replaced by the critical point for the N···Cl contact. Calculated data supplemented by a comparative analysis of potential interaction curves indicate a similar nature of intermolecular binding in the H3N and HCl complexes with different orientations of monomers. [ABSTRACT FROM AUTHOR]

Noncovalent interactions are important in determining structures and properties of molecular complexes and biological molecules, and for understanding adsorption processes in chemistry and biological science, and are still challenging to conventional density functional theories. In this work, the recently developed Tao-Mo (TM) meta-GGA (generalized gradient approximation) functional is combined with the D3 scheme of long-range van der Waals (vdW) interaction correction and the parameters of damping function are optimized with the S66 × 8 set. The resulting TM-D3 method is applied to the medium-sized molecular set S22 and large size molecular complexes set L7 to calculate intramolecular interaction energies. The TM-D3 method produces the best accuracy for the S22 set with a MAE of 0.2 kcal/mol, improving upon the PBE-D3 (MAE = 0.5 kcal/mol), PBE0-D3 (MAE = 0.5 kcal/mol), TPSS-D3 (MAE = 0.4 kcal/mol), M06L (MAE = 0.8 kcal/mol), and SCAN-D3 (MAE = 0.4 kcal/mol) methods. For the large size set L7, the TM-D3 (MAE = 2.1 kcal/mol) also performs better than the PBE-D3 (MAE = 2.6 kcal/mol), SCAN-D3 (2.5 kcal/mol) and M06L (3.0 kcal/mol), but not accurate than the PBE0-D3 (MAE = 0.8 kcal/mol) and TPSS-D3 (MAE = 1.1 kcal/mol). However, overall, the TM-D3 method performs very well with an error of 2.7% of mean binding of the S22 set and an error of 12.6% of the mean binding of the L7 set for the two typical and important medium and large size molecular complex sets. The success of the dispersion-corrected TM functional benefits from the ability of the plain TM functional to capture the short-range vdW interaction or extend the short-range interaction to the middle range, and the right coupling between the TM and the long-range vdW correction D3 scheme, leading to the improved description of noncovalent interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of co-pigments on the stability of Rhododendron arboreum anthocyanin were studied. • The interaction mechanism between co-pigments and anthocyanins was explored. • Structural simulation and steered molecular dynamics showed naringin as most favourable co-pigment. The impact of intermolecular copigmentation between five phenolic acids, two flavonoid and three amino acids with R. arboreum anthocyanins (ANS) and its isolated cyanidin-3- O -monoglycosides were investigated through experimental and theoretical approach. On addition of different copigments, phenolic acid induced strong hyperchromic (0.26–0.55 nm) and bathochromic shift (6.6–14.2 nm). The color intensity and stability of ANS with, storage at 4 °C & 25 °C, sunlight, oxidation and heat were evaluated by chromaticity, anthocyanin content, kinetic and structural simulation analysis. The strongest copigmentation reaction was observed with narningin (NA) and also showed high thermostability and highest half-life i.e. 3.39 h-1.24 h at 90–160 °C. The cyanidin-3- O -monoglycosides were analysed for their copigmentation effect and observations revealed that NA displayed best copigmentation effect to cyanidin-3- O -arabinoside (B) followed by cyanidin-3- O -galactoside (A), and cyanidin-3- O -rhamnoside (C). Additionally, structural simulation and steered molecular dynamics insights NA is the most favourable co-pigment involving π-π stacking and H-bonding. [ABSTRACT FROM AUTHOR]

[Display omitted] • Changes in the volumetric properties upon a solute – co-solute interaction. • Complexation of uracil with +GlyTyr− zwitter ions and +GlyGlu2− anions. • Rearrangement of the hydration shell of uracil when interacting with peptides. Interactions between uracil (Ura) and peptides, glycyl-L-tyrosine (Gly-Tyr) and glycyl-L-glutamic acid (Gly-Glu), in a phosphate-buffered saline (pH = 7.4) were studied in temperature range of 288–313 K by a densimetry method. Using the obtained density data, the apparent molar volumes of Ura, standard apparent molar volumes at infinite dilution and their derivatives with respect to temperature have been calculated. The concentration dependences of the apparent molar volume of uracil have a maximum, the position of which characterizes the 1:1 stoichiometry in the resulting uracil:peptide complexes. The standard apparent molar volume of neutral uracil increases upon complexation with charged peptide particles, such as +GlyTyr− zwitterions and +GlyGlu2− anions. The effects of Ura concentration and temperature on the volume properties were discussed in terms of predominant types of molecular interactions (hydrophilic, hydrophobic, ionic and zwitterionic) on the basis of co-spheres overlap model. The positive values of the second derivative of the standard apparent molar volume of uracil with respect to temperature at constant pressure indicate an increase in the ordering of the solvent in the environment of uracil with the addition of peptides, which may be associated with the blocking of its polar groups due to hydrogen bonding with the peptides. The addition of the more hydrophobic peptide, glycyl-tyrosine, which takes the zwitterionic form in solution, has a stronger structuring effect compared to the more hydrophilic anions of glycyl-glutamic acid. [ABSTRACT FROM AUTHOR]

Modern single molecule fluorescence microscopy offers new, highly quantitative ways for studying the systems biology of cells while keeping the cells healthy and alive in their natural environment. In this context, a quantum optical technique, photon antibunching, has found a small niche in the continuously growing applications of single molecule techniques to characterize small molecular complexes. Here, we review some of the most recent applications of photon antibunching in biophotonics research, and we provide a guide for how to conduct photon antibunching experiments at the single molecule level by applying techniques borrowed from time-correlated single photon counting (TCSPC). We provide a number of new examples for applications of photon antibunching to the study of multichromophoric, molecules and small molecular complexes.

We have investigated with the pulsed ESR technique at X- and Q-band frequencies the coherence and relaxation of Cu spins S = 1/2 in single crystals of diamagnetically diluted mononuclear [n-Bu4N]2[Cu(opba)] (1%) in the host lattice of [n-Bu4N]2[Ni(opba)] (99%, opba = o-phenylenebis(oxamato)) and of diamagnetically diluted mononuclear [n-Bu4N]2[Cu(opbon-Pr2)] (1%) in the host lattice of [n-Bu4N]2[Ni(opbon-Pr2)] (99%, opbon-Pr2 = o-phenylenebis(N(propyl)oxamidato)). For that we have measured the electron spin dephasing time Tm at different temperatures with the two-pulse primary echo and with the special Carr–Purcell–Meiboom–Gill (CPMG) multiple microwave pulse sequence. Application of the CPMG protocol has led to a substantial increase of the spin coherence lifetime in both complexes as compared to the primary echo results. It shows the efficiency of the suppression of the electron spin decoherence channel in the studied complexes arising due to spectral diffusion induced by a random modulation of the hyperfine interaction with the nuclear spins. We argue that this method can be used as a test for the relevance of the spectral diffusion for the electron spin decoherence. Our results have revealed a prominent role of the opba4– and opbon-Pr24– ligands for the dephasing of the Cu spins. The presence of additional 14N nuclei and protons in [Cu(opbon-Pr2)]2– as compared to [Cu(opba)]2– yields significantly shorter Tm times. Such a detrimental effect of the opbon-Pr24− ligands has to be considered when discussing a potential application of the Cu(II)−(bis)oxamato and Cu(II)−(bis)oxamidato complexes as building blocks of more complex molecular structures in prototype spintronic devices. Furthermore, in our work we propose an improved CPMG pulse protocol that enables elimination of unwanted echoes that inevitably appear in the case of inhomogeneously broadened ESR spectra due to the selective excitation of electron spins.

Brain vascular diseases are one of the leading causes of morbidity, mortality and disability of population in the industrialized countries of the world. An important element of this problem’s solution is the creation of new highly effective and safe drugs, which would lead to mortality reduction, to increase in life expectancy and quality of life. Therefore it is interesting to create a new combined drug based on L-arginine and thiotriazolin. Purpose of the study: to consider the possible structure and energy characteristics of complexes formed by L-arginine, 3-methyl-1,2,4-triazolyl-5-thioacetate (MTTA) and morpholine. Calculation method. The initial approximation to the complex geometry was obtained using molecular docking with the help of AutoDock Vina program. The obtained ternary complexes were pre-optimized by semi-empirical PM7 method with modeling the impact of the environment by COSMO method. The calculations were carried out using MOPAC2012 program. Then they were optimized by B97-D3/SVP + COSMO (Water) dispersion-corrected DFT-D with geometrical spreading correction on insufficiency of gCP basis set. A more accurate calculation of the solvation energy was conducted by SMD. The calculations by density functional method were carried out using the ORCA 3.0.3 software. Energy complex formation in solution was calculated as the difference of the Gibbs free energy of the solvated complex and its individual components. Results. Quantum chemical calculations show, that thiotriazolin and L-arginine are able to form ternary complexes, where molecules are linked by multiple hydrogen bonds. The calculation data suggest, that studied complexes are thermodynamically unstable in solution. The energies of them are positive, but rather low despite charge gain of a number of intermolecular hydrogen bonds. Finding. Based on the results of the conducted quantum-chemical study of a three components system (MTTA, morpholine, and L-arginine) it is possible to show the possibility to form ternary complexes with low stability in infinite dilute solutions. It should be noted that two negative charges are always localized in formed complexes on the deprotonated carboxyl groups. The positive charges are located either on the guanidine moiety and the a-amino group of L-arginine, or on the guanidine moiety of L-arginine and protonated molecule of morpholine. It can be expected that the strengthening of intermolecular interactions in the real solutions may result in increased stability of the complexes.