The investigation on the relative stability of different clusters of thiourea dioxide in water using gas phase quantum chemical calculations

The relative stability of different clusters of thiourea dioxide (TDO) in water is examined using gas phase quantum chemical calculations at the MP2 and B3LYP level with 6‐311++G(d,p) basis set. The possible equilibrium structures and other energetic and geometrical data of the thiourea dioxide clusters, TDO‐(H₂O)_n (n is the number of water molecules), are obtained. The calculation results show that a strong interaction exists between thiourea dioxide and water molecules, as indicated by the binding energies of the TDO clusters progressively increased by adding water molecules. PCM model is used to investigate solvent effect of TDO. We obtained a negative hydration energy of ?20.6 kcal mol^?1 and free‐energy change of ?21.0 kcal mol^?1 in hydration process. On the basis of increasing binding energies with adding water molecules and a negative hydration energy by PCM calculation, we conclude thiourea dioxide can dissolve in water molecules. Furthermore, the increases of the C? S bond distance by the addition of water molecules show that the strength of the C? S bonds is attenuated. We find that when the number of water molecules was up to 5, the C? S bonds of the clusters, TDO‐(H₂O)₅ and TDO‐(H₂O)₆ were ruptured. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical investigation of gas phase ethanol–(water)n (n = 1–5) clusters and comparison with gas phase pure water clusters (water)n (n = 2–6)

Various properties (such as optimal structures, structural parameters, hydrogen bonds, natural bond orbital charge distributions, binding energies, electron densities at hydrogen bond critical points, cooperative effects, and so on) of gas phase ethanol–(water)_n (n = 1–5) clusters with the change in the number of water molecules have been systematically explored at the MP2/aug‐cc‐pVTZ//MP2/6‐311++G(d,p) computational level. The study of optimal structures shows that the most stable ethanol‐water heterodimer is the one where exists one primary hydrogen bond (O? H…O) and one secondary hydrogen bond (C? H …O) simultaneously. The cyclic geometric pattern formed by the primary hydrogen bonds, where all the molecules are proton acceptor and proton donor simultaneously, is the most stable configuration for ethanol–(water)_n (n = 2–4) clusters, and a transition from two‐dimensional cyclic to three‐dimensional structures occurs at n = 5. At the same time, the cluster stability seems to correlate with the number of primary hydrogen bonds, because the secondary hydrogen bond was extremely weaker than the primary hydrogen bond. Furthermore, the comparison of cooperative effects between ethanol–water clusters and gas phase pure water clusters has been analyzed from two aspects. First of all, for the cyclic structure, the cooperative effect in the former is slightly stronger than that of the latter with the increasing of water molecules. Second, for the ethanol–(water)₅ and (water)₆ structure, the cooperative effect in the former is also correspondingly stronger than that of the latter except for the ethanol–(water)₅ book structure. © 2012 Wiley Periodicals, Inc.     

Global Minimum‐Energy Structure and Spectroscopic Properties of I2.−⋅n H2O Clusters: A Monte Carlo Simulated Annealing Study

The vibrational (IR and Raman) and photoelectron spectral properties of hydrated iodine‐dimer radical‐anion clusters, I₂^.? ? n H₂O (n=1–10), are presented. Several initial guess structures are considered for each size of cluster to locate the global minimum‐energy structure by applying a Monte Carlo simulated annealing procedure including spin–orbit interaction. In the Raman spectrum, hydration reduces the intensity of the I? I stretching band but enhances the intensity of the O? H stretching band of water. Raman spectra of more highly hydrated clusters appear to be simpler than the corresponding IR spectra. Vibrational bands due to simultaneous stretching vibrations of O? H bonds in a cyclic water network are observed for I₂^.? ? n H₂O clusters with n≥3. The vertical detachment energy (VDE) profile shows stepwise saturation that indicates closing of the geometrical shell in the hydrated clusters on addition of every four water molecules. The calculated VDE of finite‐size small hydrated clusters is extrapolated to evaluate the bulk VDE value of I₂^.? in aqueous solution as 7.6 eV at the CCSD(T) level of theory. Structure and spectroscopic properties of these hydrated clusters are compared with those of hydrated clusters of Cl₂^.? and Br₂^.?.     

Structure and stability of thiourea with water, DFT and MP2 calculations

The relative stabilities of thiourea in water are investigated computationally by considering thiourea–water complexes containing up to 1–6 water molecules (CS(NH₂)₂(H₂O)_n=1–6) using density functional theory and MP2 ab initio molecular orbital theory. The results show that the thiourea complex is stable and has an unusually high affinity for incoming water molecules. The clusters are progressively stabilized by the addition of water molecules, as indicated by the increasing of the binding energy. The binding energy of the cluster to each H₂O molecule is about 33 kJ mol⁻¹ for n=1–5.The C–S bond, N–C bond distance, Mulliken populations and binding energy keep approximately constant as the clusters increase in size with an increasing number of H₂O molecules. As the solvation progresses, the C–S distance increases monotonically while the Mulliken populations on the C–S bond reduces monotonically with the addition of each H₂O molecule, indicating that the C–S bond of the thiourea unit in the clusters is de-stabilized with an increasing number of H₂O molecules. Charge transfers for the clusters are mainly found at N, S atoms of the thiourea.     

The Structural Features of the Hydrated Ferrous Ion Clusters: [Fe(H2O) n ]2+ (n?=?1–19)

The low-lying structures of the hydrated ferrous ion clusters [Fe(H₂O) _n ]²⁺ (n?=?1?C19) were extensively searched at the level of the density functional theory. The results show that the first hydration shell consists of six water molecules, and the second hydration shell contains seven water molecules. Furthermore, it is found that all the lowest-energy states of [Fe(H₂O) _n ]²⁺ (n?=?1?C19) clusters are spin quintet states. These lowest-energy states keep well even at finite temperatures. The analyses of the successive water binding energy and natural charges population on ferrous ion clearly show that the influence of ferrous ion on the surrounding water molecules goes beyond the second hydration shell.     

Crystallographic study of self‐organization in the solid state including quasi‐aromatic pseudo‐ring stacking interactions in 1‐benzoyl‐3‐(3,4‐dimethoxyphenyl)thiourea and 1‐benzoyl‐3‐(2‐hydroxypropyl)thiourea

1‐Benzoylthioureas contain both carbonyl and thiocarbonyl functional groups and are of interest for their biological activity, metal coordination ability and involvement in hydrogen‐bond formation. Two novel 1‐benzoylthiourea derivatives, namely 1‐benzoyl‐3‐(3,4‐dimethoxyphenyl)thiourea, C₁₆H₁₆N₂O₃S, (I), and 1‐benzoyl‐3‐(2‐hydroxypropyl)thiourea, C₁₁H₁₄N₂O₂S, (II), have been synthesized and characterized. Compound (I) crystallizes in the space group P , while (II) crystallizes in the space group P 2₁/c . In both structures, intramolecular N—H…O hydrogen bonding is present. The resulting six‐membered pseudo‐rings are quasi‐aromatic and, in each case, interact with phenyl rings via stacking‐type interactions. C—H…O, C—H…S and C—H…π interactions are also present. In (I), there is one molecule in the asymmetric unit. Pairs of molecules are connected via two intermolecular N—H…S hydrogen bonds, forming centrosymmetric dimers. In (II), there are two symmetry‐independent molecules that differ mainly in the relative orientations of the phenyl rings with respect to the thiourea cores. Additional strong hydrogen‐bond donor and acceptor –OH groups participate in the formation of intermolecular N—H…O and O—H…S hydrogen bonds that join molecules into chains extending in the [001] direction.     

Hydrogen‐Bond Cooperative Effects in Small Cyclic Water Clusters as Revealed by the Interacting Quantum Atoms Approach

The cooperative effects of hydrogen bonding in small water clusters (H₂O)_n (n=3–6) have been studied by using the partition of the electronic energy in accordance with the interacting quantum atoms (IQA) approach. The IQA energy splitting is complemented by a topological analysis of the electron density (ρ( r )) compliant with the quantum theory of atoms‐in‐molecules (QTAIM) and the calculation of electrostatic interactions by using one‐ and two‐electron integrals, thereby avoiding convergence issues inherent to a multipolar expansion. The results show that the cooperative effects of hydrogen bonding in small water clusters arise from a compromise between: 1) the deformation energy (i.e., the energy necessary to modify the electron density and the configuration of the nuclei of the isolated water molecules to those within the water clusters), and 2) the interaction energy (E_int) of these contorted molecules in (H₂O)_n. Whereas the magnitude of both deformation and interaction energies is enhanced as water molecules are added to the system, the augmentation of the latter becomes dominant when the size of the cluster is increased. In addition, the electrostatic, classic, and exchange components of E_int for a pair of water molecules in the cluster (H₂O)_n?1 become more attractive when a new H₂O unit is incorporated to generate the system (H₂O)_n with the last‐mentioned contribution being consistently the most important part of E_int throughout the hydrogen bonds under consideration. This is opposed to the traditional view, which regards hydrogen bonding in water as an electrostatically driven interaction. Overall, the trends of the delocalization indices, δ(Ω,Ω′), the QTAIM atomic charges, the topology of ρ( r ), and the IQA results altogether show how polarization, charge transfer, electrostatics, and covalency contribute to the cooperative effects of hydrogen bonding in small water clusters. It is our hope that the analysis presented in this paper could offer insight into the different intra‐ and intermolecular interactions present in hydrogen‐bonded systems.     

Electrical field effects on dipole moment, structure and energetic of (H2O)n (2 n 15) cluster

The effect of an external electric field on water clusters of the (H₂O)_n type, with [1 n 15], in the ground state was analyzed at the B3LYP/cc-pVTZ level of theory. The calculations showed that an external electric field changes the number of hydrogen bonds, reduces the cluster sizes and increases the strength of the inter-cluster hydrogen bonds. The particular symmetry of the cluster and the null dipole moment in these specific configurations suggest that their stability can be associated with a perfect alignment of the water molecules, maximizing attractive electrostatic interactions caused by changes in the charge distribution of the clusters.     

A Biomimetic Catalytic Aerobic Functionalization of Phenols

The importance of aromatic C? O, C? N, and C? S bonds necessitates increasingly efficient strategies for their formation. Herein, we report a biomimetic approach that converts phenolic C? H bonds into C? O, C? N, and C? S bonds at the sole expense of reducing dioxygen (O₂) to water (H₂O). Our method hinges on a regio‐ and chemoselective copper‐catalyzed aerobic oxygenation to provide ortho‐quinones. ortho‐Quinones are versatile intermediates, whose direct catalytic aerobic synthesis from phenols enables a mild and efficient means of synthesizing polyfunctional aromatic rings.     

Collision-induced dissociation studies of protonated alcohol and alcohol—water clusters by atmospheric pressure ionization tandem mass spectrometry. 1?Methanol

Cluster size distribution and collision-induced dissociation (CID) studies of protonated methanol and protonated methanol—water clusters yield information on the structure and energetics of such ions. Ions were formed at atmospheric pressure in a corona discharge source, and were subjected to CID in the center quadrupole of a triple quadrupole mass spectrometer. Cluster ions containing up to 13 molecules of methanol and/or water were observed and examined using CID experiments. The CID of all (CH₃OH)_n · H₂O · H⁺ clusters, where n ? 8, showed that water loss was statistically favored over methanol loss and that the preferred dissociation channel involved loss of water with methanol molecules. These results support a model employing a chain of hydrogen-bonded solvent molecules rather than one in which fused rings of ligands surround a central hydronium ion. However, CID of larger clusters, where n ? 9, showed that loss of one methanol was equal to or less than loss of water, reflecting a change in structure.     

A Combined Experimental and Theoretical Electron Density Study of Intra‐ and Intermolecular Interactions in Thiourea S,S‐Dioxide

The thiourea S,S‐dioxide molecule is recognized as a zwitterion with a high dipole moment and an unusually long C? S bond. The molecule has a most interesting set of intermolecular interactions in the crystalline state—a relatively strong O???H? N hydrogen bond and very weak intermolecular C???S and N???O interactions. The molecule has C_s symmetry, and each oxygen atom is hydrogen‐bonded to two hydrogen atoms with O???H? N distances of 2.837 and 2.826 Å and angles of 176.61 and 158.38°. The electron density distribution is obtained both from Xray diffraction data at 110 K and from a periodic density functional theory (DFT) calculation. Bond characterization is made in terms of the analysis of topological properties. The covalent characters of the C? N, N? H, C? S, and S? O bonds are apparent, and the agreement on the topological properties between experiment and theory is adequate. The features of the Laplacian distributions, bond paths, and atomic domains are comparable. In a systematic approach, DFT calculations are performed based on a monomer, a dimer, a heptamer, and a crystal to see the effect on the electron density distribution due to the intermolecular interactions. The dipole moment of the molecule is enhanced in the solid state. The typical values of ρ_b and H_b of the hydrogen bonds and weak intermolecular C???S and N???O interactions are given. All the interactions are verified by the location of the bond critical point and its associated topological properties. The isovalue surface of Laplacian charge density and the detailed atomic graph around each atomic site reveal the shape of the valence‐shell charge concentration and provide a reasonable interpretation of the bonding of each atom.     

How Many Water Molecules Does it Take to Dissociate HCl?

The potential energy surfaces of the HCl(H₂O)_n (n is the number of water molecules) clusters are systematically explored using density functional theory and high‐level ab initio computations. On the basis of electronic energies, the number of water molecules needed for HCl dissociation is four as reported by some experimental groups. However, this number is five owing to the inclusion of entropic factors. Wiberg bond indices are calculated and analyzed, and the results provide a quadratic correlation and classification of clusters according to the nondissociated, partially dissociated, and fully dissociated character of the H?Cl bond. Our computations show that if temperature is not controlled during the experiment, the values obtained for the dipole moment (or for any measurable property) are susceptible to change, providing a different picture of the number of water molecules needed for HCl dissociation in a nanoscopic droplet.     

Structural and Infrared Spectroscopic Study on Solvation of Acetylene by Protonated Water Molecules

The effect of solvation on the conformation of acetylene has been studied by adding one water molecule at a time. Quantum chemical calculations of the H⁺(C₂H₂)(H₂O)_n (n=1-5) clusters indicate that the H₂O molecules prefer to form the OH…π interaction rather than the CH…O interaction. This solvation motif is different from that of neutral (C₂H₂)(H₂O)_n (n=1-4) clusters, in which the H₂O molecules prefer to form the CH…O and OH…C H-bonds. For the H⁺(C₂H₂)(H₂O)_n cationic clusters, the first solvation shell consists of one ring structure with two OH…π H-bonds and three water molecules, which is completed at n=4. Simulated infrared spectra reveal that vibrational frequencies of OH…π H-bonded O-H stretching afford a sensitive probe for exploring the solvation of acetylene by protonated water molecules. Infrared spectra of the H⁺(C₂H₂)(H₂O)_n(n=1-5) clusters could be readily measured by the infrared photodissociation technique and thus provide useful information for the understanding of solvation processes.     

X-Ray Diffraction Study on Manganese(II) Complexes with Thiophene-2-Carboxylate and Furan-3-Carboxylate Ligands

Abstract

Mn(II) cations in the crystals of trisaquobis(μ-thiophen-2-carboxylato-O,O′)(thiophen-2-carboxylato-O)manganese(II) monohydrate are bridged by oxygen atoms donated by bidentate carboxylic groups of two thiophen-2-carboxylate ligands. In addition, each Mn(II) ion is coordinated by an oxygen atom of a monodentate carboxylic group of this ligand and three oxygen atoms of water molecules. The coordination around the Mn(II) cation is octahedral. The bridging of the ligands results in molecular ribbons propagating in the c-direction of the crystal held together by C?H…O hydrogen bonds. The crystal structure of diaquobis(μ-furan-3-carboxylato-O,O′)di(μ-furan-3-carboxylato-O,O)(μ-aqua-O)manganese(II) consists of dinuclear structural units. In each molecule Mn(II) cations are O,O′ bridged by oxygen atoms of bidentate carboxylic groups of two furan-3-carboxylate ligands and have a water located between the Mn cations. The units are O,O′ bridged to Mn(II) ions located in adjacent units by bidentate oxygen atoms, forming molecular ribbons extending in the c-direction. Octahedral coordination around each Mn(II) ion is completed by two water molecules. The octahedra around two adjacent metal ions in the unit share a common apex - the bridging oxygen atom of the water molecule. The ribbons are held together by C?H…O hydrogen bonds between furan ring oxygen atoms and the carbon atoms of adjacent furan rings.     

Effect of microhydration on the atmospherically important metastable carbonyl sulfide anion: Structure,energetic, and infrared study

Structure, energetics, and vibrational frequency of the microhydrated carbonyl sulfide anion [OCS^?? (H₂O)_n (n = 1–6)] have been explored by the systematic ab initio study to have a comprehensive understanding about the hydration‐induced stabilization phenomenon of OCS^?. Water binds with the OCS^? in single hydrogen‐bonded (SHB) or double hydrogen‐bonded (DHB) fashion with O? H S and O? H O contacts. Maximum five water molecules can stay in a cyclic water network of these hydrated clusters forming interwater hydrogen bonding (IHB) with each other and out of this, maximum of two water molecules can bind directly to the OCS^? in (DHB) arrangement. The stabilization energy values of OCS^?? (H₂O)_n depict that ion–water interaction is significant up to four water molecules and beyond that OCS^? is stabilized by IHB between the water molecules. The CO stretching frequency of OCS^? gets red shifted, whereas CS stretching frequency gets blue shifted on hydration. Charge analysis of hydrated clusters of OCS^? indicates that negative charge moves toward oxygen from sulfur on hydration. © 2015 Wiley Periodicals, Inc.     

Structures and isomerization of neutral and zwitterion serine–water clusters: Computational study

Calculations are presented for the structure and the isomerization reaction of various conformers of the bare serine, neutral serine–(H₂O)_n and serine zwitterion–(H₂O)_n (n = 1, 2) clusters. The effects of binding water molecules on the relative stability and the isomerization processes are examined. Hydrogen bonding between serine and the water molecule(s) may significantly affect the relative stability of conformers of the neutral serine–(H₂O)_n (n = 1, 2) clusters. The sidechain (OH group) in serine is found to have a profound effect on the structure and isomerization of serine–(H₂O)_n (n = 1, 2) clusters. Conformers with the hydrogen bonding between water and the hydroxyl group of serine are predicted. A detailed analysis is presented of the isomerization (proton transfer) pathways between the neutral serine–(H₂O)₂ and serine zwitterion–(H₂O)₂ clusters by carrying out the intrinsic reaction coordinate analysis. At least two water molecules need to bind to produce the stable serine zwitterion–water cluster in the gas phase. The isomerization for the serine–(H₂O)₂ cluster proceeds by the concerted double and triple proton transfer mechanism occurring via the binding water molecules, or via the hydroxyl group. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Hydrogen bonding interaction between 1,4‐dioxane and water

This work reports an interaction of 1,4‐dioxane with one, two, and three water molecules using the density functional theory method at B3LYP/6‐311++G* level. Different conformers were studied and the most stable conformer of 1,4‐dioxane‐(water)_n (n = 1–3) complex has total energies ?384.1964038, ?460.6570694, and ?537.1032381 hartrees with one, two, and three water molecules, respectively. Corresponding binding energy (BE) for these three most stable structures is 6.23, 16.73, and 18.11 kcal/mol. The hydrogen bonding results in red shift in O? O stretching and C? C stretching modes of 1,4‐dioxane for the most stable conformer of 1,4‐dioxane with one, two, and three water molecules whereas there was a blue shift in C? O symmetric stretching and C? O asymmetric stretching modes of 1,4‐dioxane. The hydrogen bonding results in large red shift in bending mode of water and large blue shift in symmetric stretching and asymmetric stretching mode of water. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Density functional theoretical study of pKa of RCOOH (RH,CH3, and C2H5) using the combination of the extended clusters‐continuum model

The accurate pK_a determinations for three carboxylic acids have been investigated using the combination of the extended clusters‐continuum model at B3LYP/6‐31+g(d,p) and B3LYP/6‐311++g(d,p) levels. To take into account of the effect of the water combined with carboxylic acids in different positions, eleven molecular clusters were considered. Among these clusters, the one involving the carboxylic acid wrapped up with water molecules and saturated with hydrogen bonds (four hydrogen bonds around ? COOH) leads to the best B3LYP pK_a results compared to the experimental data. For those clusters saturated with hydrogen bonds, when n = 3 (the number of water molecules), the average absolute errors between the calculated pK_a results and experimental data of these three carboxylic acids were 0.19 (0.23) and 0.12 (0.22) pK_a at B3LYP/6‐31+g(d,p)//PCM (IEFPCM) and B3LYP/6‐311++g(d,p)//PCM (IEFPCM) levels, respectively; when n = 4, they are 0.53 (1.23) and 1.09 (1.03) pK_a, respectively. On the basis of the above results, the molecular cluster saturated with four hydrogen bonds formed by three waters and one carboxylic acid molecule was the chief existence in the carboxylic acid solution. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Study of water clusters in the n = 2–34 size regime, based on the ABEEM/MM model

Various properties of water clusters in the n = 2–34 size regime with the change of cluster size have been systemically explored based on the newly developed flexible-body and charge-fluctuating ABEEM/MM water potential model. The ABEEM/MM water model is to take ABEEM charges of all atoms, bonds, and lone-pairs of water molecules into the intermolecular electrostatic interaction term in molecular mechanics. The computed correlating properties characterizing water clusters (H₂O) _n (n = 2–34) include optimal structures, structural parameters, ABEEM charge distributions, binding energies, hydrogen bonds, dipole moments, and so on. The study of optimal structures shows that the ABEEM/MM model can correctly predict the following important structural features, such as the transition from two-dimensional (from dimer to pentamer) to three-dimensional (for clusters larger than the hexamer) structures at hexamer region, the transition from cubes to cages at dodecamer (H₂O)₁₂, the transition from all-surface (all water molecules on the surface of the cluster) to one water-centered (one water molecule at the center of the cluster, fully solvated) structures at (H₂O)₁₇, the transition from one to two internal molecules in the cage at (H₂O)₃₃, and so on. The first three structural transitions are in good agreement with those obtained from previous work, while the fourth transition is different from that identified by Hartke. Subsequently, a systematic investigation of structural parameters, ABEEM charges, energetic properties, and dipole moments of water clusters with increasing cluster size can provide important reference for describing the objective trait of hydrogen bonds in water cluster system, and also provide a strong impetus toward understanding how the water clusters approach the bulk limit.     

α‐Halogenoacetanilides as Hydrogen‐Bonding Organocatalysts that Activate Carbonyl Bonds: Fluorine versus Chlorine and Bromine

α‐Halogenoacetanilides (X=F, Cl, Br) were examined as H‐bonding organocatalysts designed for the double activation of C?O bonds through NH and CH donor groups. Depending on the halide substituents, the double H‐bond involved a nonconventional C?H???O interaction with either a H?CX_n (n=1–2, X=Cl, Br) or a H?C_Ar bond (X=F), as shown in the solid‐state crystal structures and by molecular modeling. In addition, the catalytic properties of α‐halogenoacetanilides were evaluated in the ring‐opening polymerization of lactide, in the presence of a tertiary amine as cocatalyst. The α‐dichloro‐ and α‐dibromoacetanilides containing electron‐deficient aromatic groups afforded the most attractive double H‐bonding properties towards C?O bonds, with a N?H???O???H?CX₂ interaction.