Gibbs Free Energy Of Reaction Research Articles

Mechanistic study of CO oxidation by N2O over Ag7Au6 cluster investigated by DFT methods

The potential of Ag7Au6 alloy nanocluster to be a catalyst for the oxidation of CO by N2O has been examined by density functional theory calculations. In the first mechanistic step, an N2O molecule decomposes at the Ag facet site of the Ag7Au6 cluster, yielding an N2 molecule and an Ag7Au6O intermediate. In the second step, the Ag7Au6‐O intermediate readily reacts with CO to form CO2. The product CO2 desorbs easily from the active Ag7Au6 site, thus avoiding catalyst poisoning. The potential energy surfaces of the doublet- and quartet-states have been systematically elucidated. There is no spin crossing found for the entire reaction and the results show that the reaction preferably follows the doublet state pathway. The activation Gibbs free energy barrier for the first and second steps are 24.6 and 10.6 kcal/mol, respectively, while the Gibbs free energy of the overall reaction is −81.2 kcal/mol. The results reveal that this catalyzed reaction is both thermodynamically and kinetically favorable. Therefore, the Ag7Au6 nanocluster is predicted to be a promising and highly active catalyst for conversion of CO and N2O pollutants to non-harmful products under ambient conditions.

Thermodynamic Research of S-H<sub>2</sub>O System in Sodium Aluminate Solution

There are many different types of valence of sufur in aluminate sodium solution during the process of the bauxite dissolution, which mainly including S2-, S22-, S, S2O32-, SO32-, SO42- and it may have an effect on the mineral dissolution process. Therefore, it is necessary that the thermodynamic properties of S-H2O system were investigated in sodium aluminate solution. In this paper, the reactions between different valence states of sulfur and lye (with or without oxygen participation) were studied in sodium aluminate solution. The thermodynamic software Factsage 7.0 was carried out to calculate the standard reaction Gibbs free energy (ΔGTθ). The results showed that S2- and SO42- are the most stability in terms of the autoreactive reaction of different valence states at 298-573 K, and that the stability of different valence states of sufur order is “S22- >(S2O32-, SO32-) >S”. At 523 K, SO32- is more stable than S2O32-. On the other hand, the low-valent sulfur was more likely to be oxidized into SO42- under oxidizing conditions at 298-573 K. Besides, it was also found that S22- is most susceptible to oxidation because of the lowest stability. Finally, the stability of the other valence states of sulfur under oxidizing conditions order is “SO32- >S2O32- >S2- >S”.

Study on the mechanism of deoxidization and purification for Li2BeF4 molten salt via graphite nanoparticles

Graphite nanoparticles originated from high purity graphite crucible were used for deoxidization and purification of Li2BeF4 molten salt containing a bit of (NH4)2BeF4 under high temperature vacuum condition. And the mechanism of deoxidization and purification via graphite nanoparticles was put forward based on analysis of sample characterization and chemical reaction Gibbs free energy calculation. The morphology, particle size, chemical composition and crystal structure of graphite nanoparticles in Li2BeF4 molten salt were characterized by High Resolution Transmission Electron Microscopy (HRTEM, SAED and EDS). Phase analysis, total oxygen content, full elemental and anion concentration for as-prepared Li2BeF4 products were studied by X-Ray Diffraction (XRD), LECO nitrogen-oxygen analyzer, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Ion Chromatography (IC), respectively. The results of sample characterization showed that graphite nanoparticles in Li2BeF4 molten salt were the poly-crystal round sheet shape with an average diameter of <100 nm. The concentration of total oxygen, sulfur and nickel in as-prepared Li2BeF4 molten salt after treatment were 548 ppm, <0.6 ppm and <0.4 ppm, respectively. Experiment and calculation all showed that SO42− and NO3− could react with carbon at 700 °C. And vacuum degassing play an excellent role in deoxidization and purification for Li2BeF4 molten salt via graphite nanoparticles.

Understanding Nitrilotris(methylenephosphonic acid) reactions with ferric hydroxide

Phosphonate compounds are used in a wide variety of industrial and agricultural applications, and are commonly found in surface and ground waters. Adsorption to ferric hydroxide can have a significant effect on the transport and fate of phosphonate compounds in the environment. This research used density functional theory modeling to investigate the adsorption mechanisms of nitrilotris(methylenephosphonic acid) (NTMP) on ferric hydroxide. Standard Gibbs free energies of reaction (ΔGro) and reaction activation barriers (Ea) were calculated for different possible adsorption mechanisms. Physical adsorption of NTMP to ferric hydroxide was promoted by negative charge assisted hydrogen bonding, and had ΔGro ranging from −2.7 to −7.4 kcal/mol. NTMP was found to form three different types of inner sphere complexes, monodentate, bidentate mononuclear and bidentate binuclear. For the monodentate complexes, ΔGro ranged from −8.0 to −13.7 kcal/mol, for the bidentate complexes ΔGro ranged from −15.3 to −28.9 kcal/mol. Complexation with Ca2+ decreased the energy for physical adsorption but increased the binding energies for mono- and bidentate complexes. Complexation with Ca2+ also allowed formation of a tridentate ternary surface complex, whereby the Ca2+ ion formed a bridge between three FeO− and three PO− groups. Physical adsorption had Ea = 0, but mono- and bidentate complex formation had Ea values ranging from 36 to 53 kcal/mol. Formation of tridentate ternary surface complexes involving Ca2+ had the lowest activation barriers of 8 and 10 kcal/mol. The different activation barriers for different modes of adsorption may explain previous experimental observations of unusual kinetic behavior for adsorption and desorption of NTMP.

Computational exploration of regioselectivity and atmospheric lifetime in NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3

The NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3 have been investigated by the BHandHLYP method in conjunction with the 6–311G(d,p) basis set. Thermodynamic and kinetic data are further refined using the comparatively accurate CCSD(T) method. According to the values of reaction enthalpies (ΔHr,298θ) and reaction Gibbs free energies (ΔGr,298θ) from CH3OCH2CH3 with NO3 system, we find that H-abstraction pathway from the α-CH2 group is more exothermic. It is further confirmed by the calculated CH bond dissociation energy of CH3OCH2CH3 molecule. All the rate constants, computed through means of canonical variational transition state with small-curvature tunneling correction, are fitted to the three-parameter expressions k1=1.54×10−23T3.34exp(−1035.53/T) and k2=3.55×10−26T4.31exp(−281.24/T)cm3molecule−1s−1 and branching ratios are computed over the temperature range 200–600K. The branching ratios are also discussed. The atmospheric lifetimes of CH3OCH3 and CH3OCH2CH3 determined by the NO3 radical are about 270 and 29days, respectively.

Experimental Study of Dissolution Kinetics of K-feldspar as a Function of Crystal Structure Anisotropy under Hydrothermal Conditions

We present the results of an experimental study of the effect of anisotropy on the kinetics of K-Feldspar dissolution under hydrothermal conditions as encountered in the Soultz-sous-Forêts enhanced geothermal system. We try to quantify the impact of K-feldspar anisotropy on dissolution rates in order to develop a more comprehensive model of the evolution of the reactive surface of silicate minerals in order to propose alternate kinetic rate laws to be implemented into water-rock interaction models and reactive transport codes. Our results evidence a relation between K-spar dissolution rate and the Gibbs free energy of reaction (ΔGr) which clearly differs from the transition state theory usually implemented into geochemical codes: it depends on the crystallographic orientation of K-spar mineral with significant differences between the different crystal faces. As for the far-from-equilibrium dissolution rate, this result highlights that using a unique theoretical rate law to describe dissolution rate as a function of ΔGr remains highly questionable. These results are very important for our challenge of understanding and modelling the dissolution mechanisms and they evidence that the dissolution anisotropy plays a fundamental role in these mechanisms.

NiFe-LDHs催化氧气析出反应的密度泛函理论研究

本文采用第一性原理密度泛函理论研究了NiFe层状双氢氧化物析氧反应的机理，针对NiFe-LDHs (100)晶面暴露出来的不同金属作为催化反应的位点，计算了各基元反应的吉布斯自由能，推算出不同金属作为位点的过电位。Fe作为OER的催化位点过电位是0.703 eV，Ni作为OER的催化位点过电位是0.985 eV，通过比较过电位大小，发现0.703 eV更低一些，催化反应更容易实现。并且根据态密度图可以分析出Fe的电子传输能力更强。Fe原子作为OER催化位点的活性比Ni原子好。 In the work, First principles periodic Density functional theory (DFT) calculations were used to investigate the electrochemical oxygen evolution reaction (OER) on NiFe layered double hydrox-ide, NiFe-LDHs (100) surface were exposed different metals, Fe and Ni as the sites of catalytic re-action respectively. The Gibbs free energy of each elementary reaction was calculated and the overpotential of different metals was deduced. When Fe atoms as the OER catalytic sites, the overpotential is 0.703 eV, when Ni atoms as OER catalytic sites, the overpotential is 0.985 eV. By comparing the value of overpotential, catalytic reaction is easier to achieve when the overpoten-tial is 0.703 eV. According to the density of state, it can be concluded that the electron conductivity of Fe is stronger, so the effect of Fe atoms as the OER catalytic activity site is better than Ni atoms.

THERMODYNAMIC ANALYSIS OF INTERFACIAL REACTION SiN SiC/Mg MATRIX COMPOSITES

&lt;p class="AMSmaintext"&gt;Gibbs free energy of chemical reactions between SiC particles and the Mg matrix at the different temperature has been calculated based on the Gibbs-Helmholtz equation and thermodynamic equilibrium of chemical reactions. The thermodynamic stability of Al&lt;sub&gt;4&lt;/sub&gt;C&lt;sub&gt;3&lt;/sub&gt; and MgAl&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4 &lt;/sub&gt;in the interface was investigated. The results showed that when the activity of Si on interface is more than a critical value of A°si . A stable Al&lt;sub&gt;3&lt;/sub&gt;C&lt;sub&gt;4 &lt;/sub&gt;cannot formed when A si is more than A°si, which is not a constant, increasing with the temperature. The mass fraction and distribution of SiO&lt;sub&gt;2&lt;/sub&gt;in the interface have directly effects on the reactions of SiO&lt;sub&gt;2 &lt;/sub&gt;with Mg and Al. There is a critical value of A °Mg , A °Al and A 1Al , which increases with the temperature. When the mass fraction of Si in the interface is greater than a critical value, there is no interfacial reaction at a certain temperature. The interface reaction models have been proposed.&lt;/p&gt;

Thermodynamic Assessments and mechanically activated synthesis of ultrafine Cr2AlC MAX phase powders

This work attempts to produce ultrafine powders and studies the effect of mechanical activation on reaction kinetics and thermodynamics of Cr2AlC formation, which are essential to design the processing parameters. Cr2AlC formation was found to be exothermic in nature, which occurred as soon as Al started melting. Milling energies (1.6kJ/g and 3.2kJ/g after milling for 15h and 30h respectively) were found to enhance the reactivity of chromium carbide powders with Al, and lowered the activation energy of reaction significantly. The enthalpy of reaction was found to be changed from −53kJ/mol to −66kJ/mol and the change in Gibbs free energy of reaction was decreased from −107kJ/mol to −139kJ/mol, when milling duration was increased from 15h to 30h. Thus the mechanical activation provides more favorable condition for the conversion and nearly pure Cr2AlC powder with ultrafine (<400nm) size were produced at relatively lower temperature (at 800°C).

FUNCTIONALIZATION OF THE SINGLE-WALLED CARBON NANOTUBES BY SULFUR DIOXIDE AND ELECTRIC FIELD EFFECT, A THEORETICAL STUDY ON THE MECHANISM

In this study, kinetics and mechanism of the sulfur dioxide adsorption on the single-walled carbon nanotubes (CNT) are investigated. Three single-walled carbon nanotubes, including the armchair (6,6), chiral (6,5) and zigzag (6,0) CNTs were chosen as the models and the different orientations of SO2 molecule relative to the CNT axis were considered. The B3LYP functional within the 6-31G(d) basis set was used for the theoretical calculations. For all orientations, reaction Gibbs free energies (ΔG˚) were calculated and the transition state structures were investigated for the spontaneous reactions. Chiral single-walled carbon nanotube (6,5) showed the least activation energy (11.72 kcal mol-1) while the armchair model showed the highest one (17.93 kcal mol-1). Natural bond orbital analysis showed that the electronic charge is transferred from CNT to sulfur dioxide. Topological analysis confirmed the C-S bond formation at the transition state. Density of states analysis showed that Fermi level energy is increased in armchair model. The application of the external electric field indicated that the CNTs stability and the functionalization energies are improved. Based on the obtained data, by using the electric field, it is possible to elevate the conductivity of CNT and the functionalization rate of SWCNT for industrial applications.

Effects of Global and Local Anharmonicities on the Thermodynamic Properties of Sulfuric Acid Monohydrate.

We use state-of-the-art electronic structure calculation methods and large basis sets to obtain reliable values for the thermodynamic properties of sulfuric acid monohydrate and study the effects of vibrational anharmonicity on these properties. We distinguish between two forms of vibrational anharmonicity: local anharmonicity, which refers to the anharmonicity of the vibrational modes of a given cluster conformer, and global anharmonicity, which originates from accounting for the presence of different conformers in the first place. In our most accurate approach, we solve the nuclear Schrödinger equation variationally for the intermolecular large-amplitude motions, thus quantum-mechanically accounting for the presence of higher-energy conformers for both reactants and products, while using the standard vibrational perturbational approach for the other vibrational modes. This results in a value of -11.0 kJ/mol for the reaction Gibbs free energy at 298.15 K. When standard vibrational perturbational approaches are employed, the effects of local anharmonicity depend heavily on the choice of the electronic structure calculation basis set. In fact, better results can often be achieved by combining a simple harmonic treatment for the vibrational partition function with a statistical mechanical accounting of global anharmonicity. Thus, we recommend that future studies that intend to include anharmonicity start by accounting for the presence of higher-energy conformers and only then consider whether local anharmonicity calculations are feasible and necessary.

Alkaline nanoparticle coatings improve resin bonding of 10-methacryloyloxydecyldihydrogenphosphate-conditioned zirconia.

Creating an alkaline environment prior to 10-methacryloyloxydecyldihydrogenphosphate (MDP) conditioning improves the resin bonding of zirconia. The present study evaluated the effects of four alkaline coatings with different water solubilities and pH values on resin bonding of MDP-conditioned zirconia. Two alkaline nanoparticle coatings were studied in particular. Thermodynamics calculations were performed to evaluate the strengths of MDP-tetragonal phase zirconia chemical bonds at different pH values. Zirconia surfaces with and without alkaline coatings were characterized by scanning electron microscope (SEM)/energy dispersive spectrometer and Fourier transform infrared spectroscopy; alkaline coatings included NaOH, Ca(OH)2, nano-MgO, and nano-Zr(OH)4. A shear bond strength (SBS) test was performed to evaluate the effects of the four alkaline coatings on bonding; the alkaline coatings were applied to the surfaces prior to conditioning the zirconia with MDP-containing primers. Gibbs free energies of the MDP-tetragonal zirconia crystal model coordination reaction in different pH environments were −583.892 (NaOH), −569.048 [Ca(OH)2], −547.393 (MgO), and −530.279 kJ/mol [Zr(OH)4]. Thermodynamic calculations indicated that the alkaline coatings improved bonding in the following order: NaOH > Ca(OH)2 > MgO > Zr(OH)4. Statistical analysis of SBS tests showed a different result. SBSs were significantly different in groups that had different alkaline coatings, but it was not influenced by different primers. All four alkaline coatings increased SBS compared to control groups. Of the four coatings, nano-Zr(OH)4 and -MgO showed higher SBS. Therefore, preparing nano-Zr(OH)4 or -MgO coatings prior to conditioning with MDP-containing primers may potentially improve resin bonding of zirconia in the clinic.

When Density Functional Approximations Meet Iron Oxides.

Three density functional approximations (DFAs), PBE, PBE+U, and Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE), were employed to investigate the geometric, electronic, magnetic, and thermodynamic properties of four iron oxides, namely, α-FeOOH, α-Fe2O3, Fe3O4, and FeO. Comparing our calculated results with available experimental data, we found that HSE (a = 0.15) (containing 15% "screened" Hartree-Fock exchange) can provide reliable values of lattice constants, Fe magnetic moments, band gaps, and formation energies of all four iron oxides, while standard HSE (a = 0.25) seriously overestimates the band gaps and formation energies. For PBE+U, a suitable U value can give quite good results for the electronic properties of each iron oxide, but it is challenging to accurately get other properties of the four iron oxides using the same U value. Subsequently, we calculated the Gibbs free energies of transformation reactions among iron oxides using the HSE (a = 0.15) functional and plotted the equilibrium phase diagrams of the iron oxide system under various conditions, which provide reliable theoretical insight into the phase transformations of iron oxides.

A study of B12N12 nanocage as potential sensor for detection and reduction of 2,3,7,8-tetrachlorodibenzodioxin

The adsorption of the 2,3,7,8-tetrachlorodibenzodioxin (TCDD) molecule on the B12N12 nanocage (B12N12-NC) was studied by M06-2X/6-31++G** method. There are three sites for TCDD adsorption on B12N12-NC. The B–B atom pair in six-membered rings (B(6MR)–B(6MR)) of B12N12-NC is the preferable adsorption site. When TCDD approaches the B12N12 nanocage, electronic exchange between them occurs, and TCDD is converted to 3,4-dichlorophenol, 3-chloroprop-2-en-1-ol, and 1-chloroprop-1-ene. The HOMO/LUMO energy, energy gaps (Eg), thermodynamic properties, and structural deformation are calculated by DFT methods. The lowest value of Eg (3.796 eV) was obtained for TS-3 (the first transition state of conversion of intermediate 3,4-dichlorophenol to 3-chloroprop-2-en-1-ol and 1-chloroprop-1-ene). The Gibbs free energy and heat of reactions are negative; therefore, these reactions are favorable and spontaneous and make B12N12-NC suitable as nanosensor for TCDD detection and reduction.

Versatile Reactivity and Theoretical Evaluation of Mono- and Dinuclear Oxidovanadium(V) Compounds of Aroylazines: Electrogeneration of Mixed-Valence Divanadium(IV,V) Complexes.

The substituted hydrazones H2L(1-4) (L(1-4) = dibasic tridentate ONO(2-) donor ligands) obtained by the condensation of 2-hydroxy-1-naphthaldehyde and 2-aminobenzoylhydrazine (H2hnal-abhz) (H2L(1)) , 2-hydroxy-1-naphthaldehyde and 2-hydroxybenzoylhydrazine (H2hnal-hbhz) (H2L(2)), 2-hydroxy-1-acetonaphthone and benzoylhydrazine (H2han-bhz) (H2L(3)), or 2-hydroxy-1-acetonaphthone and 2-aminobenzoylhydrazine (H2han-abhz) (H2L(4)) are prepared and characterized. Reaction of ammonium vanadate with the appropriate H2L(1-4) results in the formation of oxidoethoxidovanadium(V) [V(V)O(OEt)(L(1-4))] (1-4) complexes. All compounds are characterized in the solid state and in solution by spectroscopic techniques (IR, UV-vis, (1)H, (13)C, and (51)V NMR, and electrospray ionization mass spectrometry). Single-crystal X-ray diffraction analysis of 1, 3, and 4 confirms the coordination of the corresponding ligands in the dianionic (ONO(2-)) enolate tautomeric form. In solution, the structurally characterized [V(V)O(OEt)(L)] compounds transform into the monooxido-bridged divanadium(V,V) [(V(V)OL)2-μ-O] complexes, with the processes being studied by IR and (1)H, (13)C, and (51)V NMR. The density functional theory (DFT) calculated Gibbs free energy of reaction 2[V(V)O(OEt)(L(4))] + H2O ⇆ [(V(V)OL(4))2-μ-O] + 2EtOH is only 2-3 kcal mol(-1), indicating that the dinuclear complexes may form in a significant amount. The electrochemical behavior of the complexes is investigated by cyclic voltammetry, with the V(V)-V(IV) E1/2(red) values being in the range 0.27-0.44 V (vs SCE). Upon controlled potential electrolysis, the corresponding (L)(O)V(IV)-O-V(V)(O)(L) mixed-valence species are obtained upon partial reduction of the [(V(V)OL)2-μ-O] complexes formed in solution, and some spectroscopic characteristics of these dinuclear mixed-valence complexes are investigated using DFT calculations and by electron paramagnetic resonance (EPR), with the formation of V(IV)-O-V(V) species being confirmed by the observation of a 15-line pattern in the EPR spectra at room temperature.

Computational electrochemistry of doped graphene as electrocatalytic material in fuel cells

AbstractIn this work, we present an overview on how density functional theory calculations can be used to design novel electrocatalytic materials for fuel cells. In particular, we focus the attention on non‐metal doped graphene systems, which were reported to present excellent performances as electrocatalysts for the oxygen reduction reaction (ORR) at the cathodic electrode of fuel cells and are, thus, considered promising substitutes of platinum or platinum alloys electrodes. The methodology, originally proposed by Nørskov et al. (J. Phys. Chem. B 2004, 108, 17886) for electrochemical processes at metal electrodes, is revisited and applied specifically to doped graphene. Finite molecular models of graphene are found to perform as well as periodic models for localized properties or reactions. Therefore, the sophisticated molecular quantum mechanics methodologies can be safely used to compute reliable Gibbs free energies of reaction in an aqueous environment for the various steps of reduction (at the cathode) or of oxidation (at the anode). Details of the reaction mechanisms and accurate cell onset‐ or over‐potentials can be derived from the Gibbs free energy diagrams. The latter are computational quantities which can be directly compared to experimentally obtained cell overpotentials. Modeling electrocatalysis at fuel cells is, thus, an extremely powerful and convenient tool to improve our understanding of how fuel cells work and to design novel potentially active electrocatalytic materials. In this work, we present two specific applications of B‐doped graphene, as electrocatalysts for the ORR at a half‐cell cathode and for the methanol oxidation reaction (MOR) at a half‐cell anode.

Thermal dissociation in terms of the second law of chemical thermodynamics

Starting from the relationship between Gibbs free energy and equilibrium constant of a chemical reaction (ECCR) and taking into account its temperature dependence according to Kirchhoff, Eq. (12), we arrive at the three-parametric Eq. (26). In going this way, we employ the relationship between the ECCR and the degree of conversion of the solid phase using Eqs. (20) and (21). We find that there is a compensating effect between the coefficients of the equation (i.e., \(a_{1} , a_{2}\)) in the form of a linear equation, which has been attributed to the enthalpy–entropy compensation. According to current state of knowledge, this result applies both to the chemical reactions resulting in individual chemical bond formation as well as in thermal decomposition. When the heat capacity of such chemical reactions decreases linearly along with temperature, it can adopt the value of the (arithmetic mean) average, and the negative sign determines the elements of the functional equations valid for theoretical (Eq. 26) and experimentally fit (Eq. 32) states. For calcite, several possibilities arising from equilibrium changes in the conversion rate vs. temperature are compared by taking into account the CDV L’vov theory.

DFT Studies of SN2 Dechlorination of Polychlorinated Biphenyls.

Nucleophilic dechlorination of all 209 PCBs congeners by ethylene glycol anion has been studied theoretically at the DFT level. The obtained Gibbs free energies of activation are in the range 7-22 kcal/mol. The reaction Gibbs free energies indicate that all reactions are virtually irreversible. Due to geometric constrains these reactions undergo rather untypical attack with attacking oxygen atom being nearly perpendicular to the attacked C-Cl bond. The most prone to substitution are chlorine atoms that occupy ortho- (2, 2', 6, 6') positions. These results provide extensive information on the PEG/KOH dependent PCBs degradation. They can also be used in further developments of reaction class transition state theory (RC-TST) for description of complex reactive systems encountered for example in combustion processes.

English

The self-association of amoxicillin (AMX) and its hetero-association with biologically active compound, chlorogenic acid (CGA) were investigated at room temperature (295°K). The dimerization constant of amoxicillin and thiamine (THIA) analyzed using the dimer model at the wavelength of 278 and 256 nm were found to be and , respectively. The hetero-association constant of amoxicillin and chlorogenic acid analyzed using Benesi-Hildebrand approach were . Thermodynamic parameters such as Gibbs free energy, enthalpy and entropy of dimerization reactions for the self-association and hetero-association of the compounds were also investigated using Vant’s Hoff equation at the temperature ranges (295 to 305°K). The change of enthalpy calculated for amoxicillin, thiamine and the complexes of amoxicillin-chlorogenic acid are 34.73±2.17, 54.1±4.585, and 6.988±0.493 at the temperature of 305°K, respectively. The values of change in enthalpy and entropy indicate that the hydrophobic interaction play the major role in the interaction between the molecules. Key words: Amoxicillin, thiamine, chlorogenic acid, UV-Vis spectroscopy, thermodynamic, self-association, hetero-association.

Strong Hydrogen Bonded Molecular Interactions between Atmospheric Diamines and Sulfuric Acid

We investigate the molecular interaction between methyl-substituted N,N,N',N'-ethylenediamines, propane-1,3-diamine, butane-1,4-diamine, and sulfuric acid using computational methods. Molecular structure of the diamines and their dimer clusters with sulfuric acid is studied using three density functional theory methods (PW91, M06-2X, and ωB97X-D) with the 6-31++G(d,p) basis set. A high level explicitly correlated CCSD(T)-F12a/VDZ-F12 method is used to obtain accurate binding energies. The reaction Gibbs free energies are evaluated and compared with values for reactions involving ammonia and atmospherically relevant monoamines (methylamine, dimethylamine, and trimethylamine). We find that the complex formation between sulfuric acid and the studied diamines provides similar or more favorable reaction free energies than dimethylamine. Diamines that contain one or more secondary amino groups are found to stabilize sulfuric acid complexes more efficiently. Elongating the carbon backbone from ethylenediamine to propane-1,3-diamine or butane-1,4-diamine further stabilizes the complex formation with sulfuric acid by up to 4.3 kcal/mol. Dimethyl-substituted butane-1,4-diamine yields a staggering formation free energy of -19.1 kcal/mol for the clustering with sulfuric acid, indicating that such diamines could potentially be a key species in the initial step in the formation of new particles. For studying larger clusters consisting of a diamine molecule with up to four sulfuric acid molecules, we benchmark and utilize a domain local pair natural orbital coupled cluster (DLPNO-CCSD(T)) method. We find that a single diamine is capable of efficiently stabilizing sulfuric acid clusters with up to four acid molecules, whereas monoamines such as dimethylamine are capable of stabilizing at most 2-3 sulfuric acid molecules.