Energy Change Of Reaction Research Articles

Charge transfer regulates electrocatalytic CO2 reduction on one-dimensional carbon nanotube/boron nitride nanotube heterostructures

Driving the electrochemical carbon dioxide reduction reaction (CO2RR) to generate high-value chemicals is one of the effective solutions to promote carbon–neutral cycles. Herein, we use a heterostructure strategy to enhance the catalytic performance of single-atom catalysts (SACs) for CO2RR. A series of catalysts formed by doping some transition metal atoms (TM = Cr, Mn, Fe, Co, Ni, Cu) into heterostructures which include the single-wall carbon nanotube in boron nitride nanotube (CNT@BNNT) and the hybridization of carbon nanotube and boron nitride nanotube (CNT/BNNT) are respectively named as TM-CNT@BNNT and TM-CNT/BNNT, and their catalytic activity of CO2RR is systematically studied using density functional theory methods. After forming a heterostructure, the number of charges transferred from the metal center to the substrate and the d-band center will change, which will, to some extent, regulate the catalytic activity of the catalyst. Due to the effective activation of CO2 and significant inhibition ability of competitive hydrogen evolution reaction, nine catalysts are considered effective candidates for CO2RR. Finally, seven catalysts with high CO2RR activity are selected by calculating the Gibbs free energy. The moderate linear relations between charge transfer and adsorption energy of CO2/free energy change of reaction intermediates/limiting potential indicate that charge transfer can regulate activity to a certain extent. The improvement of CO2RR activity comes from the smaller charge transfer in the metal center, which is more likely to result in moderate binding strength between the catalyst and the key intermediate (*OH) to generate high catalytic performance.

Reaction thermodynamics as a constraint on piscine steroidogenesis flux distributions

While a considerable amount is known of the dynamics of piscine steroidogenesis during reproduction, the influence of thermodynamics constraints on its control has not been studied. In this manuscript, Gibbs free energy change of reactions was calculated for piscine steroidogenesis using the in silico eQuilibrator thermodynamics calculator. The analysis identified cytochrome P450 (cyp450) oxidoreductase reactions to have more negative Gibbs free energy changes relative to hydroxysteroid (HSD) and transferase reactions. In addition, a more favorable Gibbs free energy change was predicted for the Δ5 (cyp450 catalyzed) vs. Δ4 (HSD catalyzed) steroidogenesis branch-point, which converts pregnenolone to 17α-hydroxypregnenolone or progesterone respectively. Comparison of in silico predictions with in vivo experimentally measured flux across the Δ5 vs. Δ4 branch-point showed higher flux through the thermodynamically more favorable Δ5 pathway in reproducing or spawning vs. non-spawning fathead minnows (Pimephales promelas). However, the exposure of fish to endocrine stressors such as hypoxia or the synthetic estrogen 17α-ethinylestradiol (EE2), resulted in increased flux through both Δ5 and Δ4 pathways, indicating an adaptive response to increase steroidogenic redundancy. The correspondence of elevated flux through the Δ5 branch-point in spawning fish indicated the use of a thermodynamically favorable pathway to optimize steroid hormone productions during reproduction. We hypothesize that such selective use of a thermodynamically favorable steroidogenesis pathway may conserve reduced equivalents or transcriptional costs for investment to other biosynthetic or catabolic reactions to support reproduction. If generalizable, such an approach can provide novel insights into the structural principles and regulation of steroidogenesis or other metabolic pathways.

Identifying Noble Metal Catalysts for the Hydrogenation and Dehydrogenation of Dibenzyltoluene: A Combined Theoretical-Experimental Study.

We present a comprehensive theoretical and experimental investigation of the hydrogenation and dehydrogenation of dibenzyltoluene (DBT) using Pd-, Pt-, Ru-, and Rh-supported metal catalysts to identify the optimal catalysts for hydrogen storage and release processes. Our results demonstrated significant variation in the catalytic activity of the metal catalysts. 5 wt % Rh/Al2O3 and 5 wt % Pt/Al2O3 showed the highest activity for hydrogenation and dehydrogenation with the highest selectivity and turnover frequency (TOF), respectively. Conversely, 5 wt % Pd/Al2O3 and 5 wt % Ru/Al2O3 exhibited lower catalytic activity toward full hydrogenation and dehydrogenation. Rh/Al2O3 showed the best catalytic hydrogenation activity with a TOF of 26.49 h-1 and a hydrogenation degree of 92.69% in 2 h, while Pt/Al2O3 exhibited the best catalytic dehydrogenation activity with a released H2 volume of 3755 mL, a dehydrogenation degree of 78.23%, and a TOF of 39.56 h-1 in 2 h. Additionally, we estimated the activation energies for hydrogenation and dehydrogenation to be 67.20 and 82.78 kJ/mol, respectively. Notably, the produced hydrogen gas was of high purity and suitable for use in fuel cells. Density functional theory (DFT) calculations were used to analyze the adsorption structure and reaction energy changes of all intermediate products of DBT on the surface of the chosen catalysts. Our research provides valuable insights into developing efficient catalysts for liquid organic hydrogen carriers.

Silica particles convert thiol-containing molecules to disulfides

Synthetic amorphous silica is a common food additive and a popular cosmetic ingredient. Mesoporous silica particles are also widely studied for their potential use in drug delivery and imaging applications because of their unique properties, such as tunable pore sizes, large surfaces areas, and assumed biocompatibility. Such a nanomaterial, when consisting of pure silicon dioxide, is generally considered to be chemically inert, but in this study, we showed that oxidation yields for different compounds were facilitated by simply incubating aqueous solutions with pure silica particles. Three thiol-containing molecules, L-cysteine, glutathione, and D-penicillamine, were studied separately, and it was found that more than 95% of oxidation happened after incubating any of these compounds with mesoporous silica particles in the dark for a day at room temperature. Oxidation increased over incubation time, and more oxidation was found for particles having larger surface areas. For nonporous silica particles at submicron ranges, yields of oxidation were different based on the structures of molecules, correlating with steric hindrance while accessing surfaces. We propose that the silyloxy radical (SiO•) on silica surfaces is what facilitates oxidation. Density functional theory calculations were conducted for total energy changes for reactions between different aqueous species and silicon dioxide surfaces. These calculations identified two most plausible pathways of the lowest energy to generate SiO• radicals from water radical cations H2O•+ and hydroxyl radicals •OH, previously known to exist at water interfaces.

In-situ phase evolution of multi-component boride to high-entropy ceramic upon ultra-high temperature ablation

Multi-component boride (Hf0.5Zr0.5)B2-SmB6-ErB4-YB6 (HZRB) utilized as a coating on SiC-coated carbon/carbon (C/C) composite was prepared by supersonic atmosphere plasma spraying. In-situ phase evolution of HZRB into (Hf0.2Zr0.2Sm0.2Er0.2Y0.2)O2-δ high-entropy oxide (HEO) was investigated after oxyacetylene ablation for 120 s. The first-principles calculations were applied to analyze the in-situ formation mechanism of HEO. The mixing Gibbs free energy change (∆Gmix) of HEO was calculated to be negative at 2573 K, indicating that the HEO can be generated upon the ablation temperature. Due to the lower Gibbs free energy change of reaction (∆RGm), (Hf0.5Zr0.5)B2 will be oxidized to generate HfO2 firstly, and other elements dissolved into the HfO2 lattice to form HEO. The solution energies of Zr, Sm, Er and Y atoms are − 0.01, 6.28, 8.55 and 4.46 eV/atom, and corresponding solution reactions possess negative ∆RGm, indicating the possible solution sequence of these elements is Zr > Y > Sm > Er.

Experimental investigation and validation on the effect of nickel addition on properties of the pressureless sintered boron carbide composites using machine learning models

This research work aims to investigate the effect of a low amount of nickel (<0.6 wt%) on the properties of the boron carbide. The samples are synthesized through pressureless sintering at 2150 °C under an argon atmosphere (1 bar). Firstly, the thermodynamic simulation is carried out using the HSC software to determine the free energy change of reactions and their viability. The prepared samples are analyzed by employing various characterization techniques such as XRD, FESEM, and EDS. It is concluded that the presence of nickel (i.e., a low melting point than the boron carbide) results in the formation of the liquid phase during the sintering process. Thus, the sinterability of the samples is significantly enhanced. Moreover, the optimum sample is obtained by adding the 4 wt% of nickel in boron carbide. The maximum density, hardness, elastic modulus, and fracture toughness for the sample containing 4 wt% nickel are obtained as 91.00%, 21.83 GPa, 374.45 GPa, and 3.11 MPa m0.5, respectively. Furthermore, machine learning (ML) techniques (i.e., M5P tree model, random tree, REPTree (Reduced-Error Pruning), and artificial neural network (ANN)) are also utilized to check the adequacy of the results. It is concluded that the maximum value of CC, i.e., 0.9929, is obtained for the REPTree technique with a minimum value of MAE (i.e., 0.0869) and RMSE (i.e., 0.0968). It is observed that the ML technique showed the validation of experimental results.

DGPredictor: Automated fragmentation method for metabolic reaction free energy prediction and de novo pathway design.

Group contribution (GC) methods are conventionally used in thermodynamics analysis of metabolic pathways to estimate the standard Gibbs energy change (ΔrG'o) of enzymatic reactions from limited experimental measurements. However, these methods are limited by their dependence on manually curated groups and inability to capture stereochemical information, leading to low reaction coverage. Herein, we introduce an automated molecular fingerprint-based thermodynamic analysis tool called dGPredictor that enables the consideration of stereochemistry within metabolite structures and thus increases reaction coverage. dGPredictor has comparable prediction accuracy compared to existing GC methods and can capture Gibbs energy changes for isomerase and transferase reactions, which exhibit no overall group changes. We also demonstrate dGPredictor's ability to predict the Gibbs energy change for novel reactions and seamless integration within de novo metabolic pathway design tools such as novoStoic for safeguarding against the inclusion of reaction steps with infeasible directionalities. To facilitate easy access to dGPredictor, we developed a graphical user interface to predict the standard Gibbs energy change for reactions at various pH and ionic strengths. The tool allows customized user input of known metabolites as KEGG IDs and novel metabolites as InChI strings (https://github.com/maranasgroup/dGPredictor).

Effect of the particle size on the reactivity of MgO-Al2O3 hydrating mixtures: A long-term kinetic investigation of hydrotalcite synthesis

Hydrotalcite-like compounds (HTlc) are commonly known anionic clay that may potentially be used as hydraulic binder component for refractory materials, ion exchangers, catalyst or carrier of bioactive molecules. According to current state of knowledge LDH (Layered Double Hydroxides) can be synthesized using various methods including mechanochemical synthesis, hydrothermal precipitation, sol–gel syntheses and coprecipitation method. Research on the synthesis of hydrotalcite in the mixture of oxide powders of Al2O3 and MgO cured under specific conditions is particularly important in case of the determination of the relationship between the type (susceptibility to hydration, grain size and specific surface area) of initial powders and reaction kinetics. As a result, the hydration of an equimolar mixture of magnesium and alumina oxides nano- or micro-powders has been proven to be an effective low temperature method of synthesis well crystallized MgAl LDH with highly ordered structures. This investigations clearly show that the kinetics of hydration is influenced only by properties of aluminium oxide as initial powder. The synthesis of Mg6Al2CO3(OH)16∙4H2O as a result of hydration is associated with composite matrix formation which firstly consist of partly reacted initial powders bonded by hydration products. The synthesis of Mg6Al2CO3(OH)16∙4H2O was discussed in terms of molar Gibbs free energy change of reactions within the MgO-Al2O3-CO2-H2O system. The calculated formation Gibbs energy was negative, when Mg(OH)2 was formed as an intermediate product. The standard Gibbs free energies of hydrotalcite formation was estimated based on the simple mechanical mixture model that treats Mg6Al2CO3(OH)16∙4H2O as mixtures of simple oxides. Thermodynamic calculations were performed assuming an equilibrium state between aqueous solutions and corresponding precipitates after synthesis.

Decomposition pathway and kinetic analysis of perfluoroketone C5F10O

Recently, perfluoroketone C5F10O has been seen as a promising alternative gas for sulphur hexafluoride (SF6), of which the global warming potential (GWP) is extremely high. C5F10O has a good insulation property and the GWP value is only 1, thus can be used as insulation medium in gas-insulated switchgears. In this study, the decomposition pathway of C5F10O and the recombination processes of free radicals are firstly explored. Secondly, the rate constants of the reactions are calculated based on the variational transition state theory, which then are fitted in the NIST form. The results not only provide the basic data for the chemical kinetics calculations, but also supplementary data for the NIST database. Finally, the chemical kinetic calculations are performed to study the decomposition characteristics at 400 °C and 700 °C. Only 4% C5F10O decomposes at 400 °C, while 96% decomposes at 700 °C. The stable products like CO, C2F4, C2F6, C3F6 are formed. The mole fraction of CF4 is above 10–10 at 400 °C. A certain amount of C2F2 is produced at 700 °C. Besides, precise chemical kinetic composition results at steady state during the thermal decomposition of C5F10O are obtained. By analyzing the energy change of reactions, the formation of products is explained theoretically. The results not only reveal the decomposition mechanism of C5F10O and recombination mechanism of the stable products, but also provide the guidance for electrical engineering.

Evaluation of reaction spontaneity for acidic and reductive dissolutions of corrosion metal oxides using HyBRID chemical decontamination

Complete sets of reaction mechanisms are proposed in the acidic and reductive dissolution of magnetite, nickel ferrite, and chromite using the HyBRID (Hydrazine Based Reductive metal Ion Decontamination) process for the decontamination of a primary coolant system of nuclear power plant. Hydrazine participated in the reaction pathway of reducing ferric ions to ferrous ions and simultaneously regenerating oxidized cupric ions into cuprous ions. The data of the heat capacity, the heat of formation, the entropy of formation, and the Gibbs energy of formation for all chemical species and ions were collected from the HSC Chemistry 9 database. The enthalpy, entropy, and Gibbs energy changes of reactions were calculated in the temperature range of 298.15–373.15 K for individual reactions. The degree of spontaneity decreased with the increase of the temperature. The reaction spontaneity was significantly enhanced by addition of hydrazine and slightly increased by further addition of copper sulfate.

Design of amino-functionalized chelated macroporous copolymer [poly(GMA-EDGMA)] for the sorption of Cu (II) ions

Polymer-based, highly porous nanocomposites with functionalized ligands attached to the core structure are extremely efficient in the detection, removal and recovery of metals through the process of sorption. Quantumchemical models could be helpful for sorption process analyses. The sorption of Cu(II) ions by amino-functionalized chelating macroporous copolymers poly(GMA-co-EGDMA)-amine and sorption selectivity of the subject copolymers, ethylenediamine (en), diethylenetriamine (dien) and triethylenetetramine (trien), were successfully modelled by quantum chemical calculations. Considering the crystal structures from CSD and experimental conditions during the formation of metal complexes, the most frequent mononuclear complexes are those with the tetradentate teta ligand, while binuclear complexes are formed when the metal ion is in large excess. Although the en-copolymer was the most effective functionalized one, higher maximum sorption capacities (Qmax) were observed for the dien- and trien-copolymers, due to their abilities to form binuclear complexes. The enthalpy term has the greatest contribution to the total Gibbs energy change of reaction for the formation of mononuclear Cu(II) complexes (?Gaq), while the solvation energy of the reaction has the greatest contribution in the formation of binuclear complexes. The results of the study indicate that small amines with the ability to form binuclear complex are the best choice for functionalization of the considered copolymer.

Electronegativity Seen as the Ground-State Average Valence Electron Binding Energy.

We introduce a new electronegativity scale for atoms, based consistently on ground-state energies of valence electrons. The scale is closely related to (yet different from) L. C. Allen's, which is based on configuration energies. Using a combination of literature experimental values for ground-state energies and ab initio-calculated energies where experimental data are missing, we are able to provide electronegativities for elements 1-96. The values are slightly smaller than Allen's original scale, but correlate well with Allen's and others. Outliers in agreement with other scales are oxygen and fluorine, now somewhat less electronegative, but in better agreement with their chemistry with the noble gas elements. Group 11 and 12 electronegativities emerge as high, although Au less so than in other scales. Our scale also gives relatively high electronegativities for Mn, Co, Ni, Zn, Tc, Cd, Hg (affected by choice of valence state), and Gd. The new electronegativities provide hints for new alloy/compound design, and a framework is in place to analyze those energy changes in reactions in which electronegativity changes may not be controlling.

Thermochemical Measurements of Cation Exchange in CdSe Nanocrystals Using Isothermal Titration Calorimetry.

Among the various reported post synthetic modifications of colloidal nanocrystals, cation exchange (CE) is one of the most promising and versatile approaches for the synthesis of nanostructures that cannot be directly synthesized from their constitutive precursors. Numerous studies have reported on the qualitative analysis of these reactions, but rigorous quantitative study of the thermodynamics of CE in colloidal nanoparticles is still lacking. We demonstrate using isothermal titration calorimetry (ITC), the thermodynamics of the CE between cadmium selenide (CdSe) nanocrystals and silver in solution can be quantified. We survey the influence of CdSe nanocrystal diameter, capping ligands and temperature on the thermodynamics of the exchange reaction. Results obtained from ITC provide a detailed description of overall thermodynamic parameters-equilibrium constant ( K eq), enthalpy (Δ H), entropy (Δ S) and stoichiometry ( n)-of the exchange reaction. We compared the free energy change of reaction (Δ G) between CdSe and Ag+ obtained directly from ITC for both CdSe bulk and nanoparticles with values calculated from previously reported methods. While the calculated value is closer to the experimentally obtained Δ G rxn for bulk particles, nanocrystals show an additional Gibbs free energy stabilization of ∼-14 kJ/mol Se. We discuss a thermochemical cycle elucidating the steps involved in the overall cation exchange process. This work demonstrates the application of ITC to probe the thermochemistry of nanoscale transformations under relevant solution conditions.

The synergy effect and reaction pathway in the oxygen reduction reaction on the sulfur and nitrogen dual doped graphene catalyst

The first-principle calculations are performed to explore the synergy effects between two dopants (N, S) and the detailed reaction pathway of oxygen reduction reaction (ORR) on the graphene catalysts. The co-doping N and S induces the significant spin density and has a strong chemical bonding with oxygen molecule which is not observed on the mono-doped cases. Three different reaction pathways are revealed from the calculations. Due to the large barrier of the OO breaking, the hydrogenation of the adsorbed oxygen molecule is kinetically more favorable. The free energy change of reaction under different electrode potential is also evaluated.

How computational methods and relativistic effects influence the study of chemical reactions involving Ru-NO complexes?

Two treatments of relativistic effects, namely effective core potentials (ECP) and all-electron scalar relativistic effects (DKH2), are used to obtain geometries and chemical reaction energies for a series of ruthenium complexes in B3LYP/def2-TZVP calculations. Specifically, the reaction energies of reduction (A-F), isomerization (G-I), and Cl- negative trans influence in relation to NH3 (J-L) are considered. The ECP and DKH2 approaches provided geometric parameters close to experimental data and the same ordering for energy changes of reactions A-L. From geometries optimized with ECP, the electronic energies are also determined by means of the same ECP and basis set combined with the computational methods: MP2, M06, BP86, and its derivatives, so as B2PLYP, LC-wPBE, and CCSD(T) (reference method). For reactions A-I, B2PLYP provides the best agreement with CCSD(T) results. Additionally, B3LYP gave the smallest error for the energies of reactions J-L. © 2017 Wiley Periodicals, Inc.

Free radical scavenging and COX-2 inhibition by simple colon metabolites of polyphenols: A theoretical approach

Free radical scavenging and inhibitory potency against cyclooxygenase-2 (COX-2) by two abundant colon metabolites of polyphenols, i.e., 3-hydroxyphenylacetic acid (3-HPAA) and 4-hydroxyphenylpropionic acid (4-HPPA) were theoretically studied. Different free radical scavenging mechanisms are investigated in water and pentyl ethanoate as a solvent. By considering electronic properties of scavenged free radicals, hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms are found to be thermodynamically probable and competitive processes in both media. The Gibbs free energy change for reaction of inactivation of free radicals indicates 3-HPAA and 4-HPPA as potent scavengers. Their reactivity toward free radicals was predicted to decrease as follows: hydroxyl>>alkoxyls>phenoxyl≈peroxyls>>superoxide. Shown free radical scavenging potency of 3-HPAA and 4-HPPA along with their high μM concentration produced by microbial colon degradation of polyphenols could enable at least in situ inactivation of free radicals. Docking analysis with structural forms of 3-HPAA and 4-HPPA indicates dianionic ligands as potent inhibitors of COX-2, an inducible enzyme involved in colon carcinogenesis. Obtained results suggest that suppressing levels of free radicals and COX-2 could be achieved by 3-HPAA and 4-HPPA indicating that these compounds may contribute to reduced risk of colon cancer development.

Free radical scavenging potency of quercetin catecholic colonic metabolites: Thermodynamics of 2H+/2e− processes

Reaction energetics of the double (2H+/2e−), i.e., the first 1H+/1e− (catechol→ phenoxyl radical) and the second 1H+/1e− (phenoxyl radical→ quinone) free radical scavenging mechanisms of quercetin and its six colonic catecholic metabolites (caffeic acid, hydrocaffeic acid, homoprotocatechuic acid, protocatechuic acid, 4-methylcatechol, and catechol) were computationally studied using density functional theory, with the aim to estimate the antiradical potency of these molecules. We found that second hydrogen atom transfer (HAT) and second sequential proton loss electron transfer (SPLET) mechanisms are less energy demanding than the first ones indicating 2H+/2e− processes as inherent to catechol moiety. The Gibbs free energy change for reactions of inactivation of selected free radicals indicate that catecholic colonic metabolites constitute an efficient group of more potent scavengers than quercetin itself, able to deactivate various free radicals, under different biological conditions. They could be responsible for the health benefits associated with regular intake of flavonoid-rich diet.

Shifts in Rumen Fermentation and Microbiota Are Associated with Dissolved Ruminal Hydrogen Concentrations in Lactating Dairy Cows Fed Different Types of Carbohydrates

Background: Different carbohydrates ingested greatly influence rumen fermentation and microbiota and gaseous methane emissions. Dissolved hydrogen concentration is related to rumen fermentation and methane production.Objectives: We tested the hypothesis that carbohydrates ingested greatly alter the rumen environment in dairy cows, and that dissolved hydrogen concentration is associated with these changes in rumen fermentation and microbiota.Methods: Twenty-eight lactating Chinese Holstein dairy cows [aged 4–5 y, body weight 480 ± 37 kg (mean ± SD)] were used in a randomized complete block design to investigate effects of 4 diets differing in forage content (45% compared with 35%) and source (rice straw compared with a mixture of rice straw and corn silage) on feed intake, rumen fermentation, and microbial populations.Results: Feed intake (10.7–12.6 kg/d) and fiber degradation (0.584–0.692) greatly differed (P ≤ 0.05) between cows fed the 4 diets, leading to large differences (P ≤ 0.05) in gaseous methane yield (27.2–37.3 g/kg organic matter digested), dissolved hydrogen (0.258–1.64 μmol/L), rumen fermentation products, and microbiota. Ruminal dissolved hydrogen was negatively correlated (r < −0.40; P < 0.05) with molar proportion of acetate, numbers of fungi, abundance of Fibrobacter succinogenes, and methane yield, but positively correlated (r > 0.40; P < 0.05) with molar proportions of propionate and n-butyrate, numbers of methanogens, and abundance of Selenomonas ruminantium and Prevotella spp. Ruminal dissolved hydrogen was positively correlated (r = 0.93; P < 0.001) with Gibbs free energy changes of reactions producing greater acetate and hydrogen, but not correlated with those reactions producing more propionate without hydrogen.Conclusions: Changes in fermentation pathways from acetate toward propionate production and in microbiota from fibrolytic toward amylolytic species were closely associated with ruminal dissolved hydrogen in lactating dairy cows. An unresolved paradox was that greater dissolved hydrogen was associated with greater numbers of methanogens but with lower gaseous methane emissions.

Theoretical Calculation of Thermodynamic and Kinetic Quantities for 1,3 Dipolar Cycloaddition Reactions Between Nitrile Sulfides R–CNS (R = H, CH3, Ph and Ph(CH3)3) with 7–10 Membered Simple Cycloalkynes

The 1,3-dipolar cycloaddition reactions also known as the Huisgen cycloaddition are one of the most widely used and versatile preparative methods in hetrocyclic chemistry. In this study, the reactivity and strain energy effect of the simple cycloalkynes with substituted Nitrile sulfides R–CNS (R = H, CH3, Ph and Ph(CH3)3) will be discussed in light of computational studies using DFT methods (B3LYP/6-31G*). The investigation of the structured properties, theoretical thermodynamic and kinetic data of the reactions in 298 K will be presented. The results show increase in the ∆G* by increasing the ring size and decreasing the strain energy of cycloalkynes. Also, the rate constants and the free energy changes in reactions increase as the size of the ring decreases. The relationships of the deviation of the internal bond angle (DIBA, in degrees), π-strain (Sπ) (in kcal mol−1), the bond angle of Csp3–C ≡ C (θo) and ΔG#(kcal mol−1) for the series of cycloalkynes I-1 to I-4 have investigated.

The stable polyiodides: Experimental and theoretical studies of formation mechanism

The structures of polyiodides have been extensively studied for long time, but it was rarely involved of the mechanism of polyiodide species formation in preparation. The tetraethylammonium polyiodides were chosen as model chemicals and prepared with different molar ratios of reactants in ethanol solvent, the products were analyzed by titration, Raman spectra and TGA/DTG/DSC analysis, with the increase of the molar ratios of reactants, the iodine contents of the products reached a constant value. Finally, only two stable structures, Et4NI3 (1, space group Cmca) and Et4NI7 (2, space group Cmca), were isolated by recrystallization of slow evaporating solvent(s). The thermal analysis of tetraethylammonium polyiodides showed that all tetraethylammonium polyiodides lost I2 together to become Et4NI3 firstly and then continue to decompose. The decomposition of Et4NI3 was not a simple process which Et4NI3 lost one iodine molecule and then became Et4NI. In addition, the thermodynamical properties of species (I2 and Et4NIx, x=1, 3, 5, 7) and the molar standard Gibbs free energy changes of reactions (ΔrGmθ), as well as the mechanism of tetraethylammonium polyiodides formation were interpreted by density functional theory (DFT) calculations. The calculations show that the solvent effects have impact on the reactions. Accordingly, a comparative study was carried out on the solid phase synthesis of Et4NI5 at 80°C and at molten state. Furthermore, the solid synthesis of Et4NI5 was characterized by variable temperature (−25°C∼150°C) Raman Spectrometer. The polyiodide components interconversion showed the discrete I5- could be formed in molten state. In short, what species of polyiodides crystallized from reactions in solutions are decided by the synergy between ΔrGm of reactions and Coulombic interactions etc. of polyiodide crystals.