ΔHf Values Research Articles

Conductometric study of hydroelectrochemical parameters for the interaction of cadmium bromide in lump and nano forms with Orange G dye

The hydroelectrochemical behaviour of cadmium bromide was investigated in the presence of the dye Orange G. This information can be used to develop conductometric sensors for detecting these substances, understand how they behave in aqueous solutions, and design effective procedures for removing the extremely toxic heavy cadmium ions from contaminated water sources. The hydroelectrochemical parameters for the interaction between lump and nanoCdBr2 with Orange G dye were investigated conductometrically in aqueous solutions at different temperatures. CdBr2 interacts with Orange G as a ligand, resulting in a decrease in conductivity. However, the interaction was more significant with nanoCdBr2, which showed a higher decrease in conductivity compared to lump CdBr2. Two stiochiometric complexes, 1:1 and 1:2, were produced; Kf and ΔGf are higher for 1:1 than for 1:2 (CdBr2/Orange G). With rising temperatures, the formation constants decreased, and the negative sign of ΔGf indicated the spontaneity of the reaction, which increased with rising temperatures. The negative values of (ΔHf) revealed the complexation's exothermic nature, whereas the positive entropy (ΔS) values confirmed that the complex formation depended on molecular entropy since the complex formation was favored by an increase in molecular disorder. The results of our investigation can be utilised to enhance comprehension of the behaviour of these materials in aqueous solutions and create efficient protocols for the removal of very toxic heavy metal cadmium ions from polluted water sources. We think that our study advances the discipline and offers a distinctive viewpoint on this subject.

Three-Dimensional Noncovalent Interaction Network within [NpO2Cl4]2- Coordination Compounds: Influence on Thermochemical and Vibrational Properties.

Noncovalent interactions (NCIs) can influence the stability and chemical properties of pentavalent and hexavalent actinyl (AnO2+/2+) compounds. In this work, the impact of NCIs (actinyl-hydrogen and actinyl-cation interactions) on the enthalpy of formation (ΔHf) and vibrational features was evaluated using Np(VI) tetrachloro compounds as the model system. We calculated the ΔHf values of these solid-state compounds through density functional theory+ thermodynamics (DFT+ T) and validated the results against experimental ΔHf values obtained through isothermal acid calorimetry. Three structural descriptors were evaluated to develop predictors for ΔHf, finding a strong link between ΔHf and hydrogen bond energy (EHtotal) for neptunyl-hydrogen interactions and total electrostatic attraction energy (Eelectrostatictotal) for neptunyl-cation interactions. Finally, we used Raman spectroscopy together with bond order analysis to probe Np=O bond perturbation due to NCIs. Our results showed a strong correlation between the degree of NCIs by axial oxygen and red-shifting of Np=O symmetrical stretch (ν1) wavenumbers and quantitatively demonstrated that NCIs can weaken the Np=O bond. These properties were then compared to those of related U(VI) and Np(V) phases to evaluate the effects of subtle differences in the NCIs and overall properties. In general, the outcomes of our study demonstrated the role of NCIs in stabilizing actinyl solid materials, which consequently governs their thermochemical behaviors and vibrational signatures.

Effect of chlorine substitution on the thermal stability of ferro-pargasite and thermochemical properties of ferro-chloro-hornblende

Abstract Substitution of chlorine for hydroxyls in calcium amphiboles has been widely documented but the effect of this substitution on thermal stability is not known. Experimental reversal data are presented here comparing the upper-thermal stability of amphiboles formed in the ferro-pargasite and ferro-chloro-pargasite bulk compositions. Experiments were made over the range of 550 – 900°C and 0.5 – 3 kbar at oxygen fugacities of log(fO2) of -0.3 to +0.5 relative to Co-CoO. Electron microprobe analysis of amphiboles made from the ferro-pargasite bulk composition were found to be ferro-pargasite, while those made from the ferro-chloro-pargasite bulk composition were low in A-site Na and Cl and were better classified as Cl-bearing ferro-ferri-hornblende. Although the differences between desired and observed amphibole compositions complicate the comparison of their thermal stabilities, it can be deduced that the Cl-bearing amphibole has a steeper dP/dT slope and, above 1 kbar, a lower thermal stability than ferro-pargasite. Thermodynamic analysis of the Cl-bearing amphibole was also done to extract thermochemical data for the Cl end-member amphibole ferro-chloro-hornblende (Ca2(Fe4Al)(AlSi7)O22Cl2 = Fe-Cl-Horn) that are consistent with the thermodynamic database of Holland and Powell (2011). Using an ideal-activity expression and estimated values for the heat capacity (CP = 1.106 + 8.9156 X 10-5(T, K) – 11,218.3/T2 – 5.9548/T0.5; kJ/K·mol) and volume (283.0 ± 1.5 cm3/mole) for Fe-Cl-Horn, the derived values for ΔHf° and S° are -10,842.6 ± 10.3 kJ/mol and 618.8 ± 11.1 J/K·mol, respectively. The implication of this work is that (a) chlorine appears to lower the thermal stability of a given calcium amphibole in contrast to the marked increase in thermal stabilities caused by fluorine, and (b) thermochemical data such as those derived in this study allow absolute concentrations of chloride salts to be calculated in metasomatic paleobrines, as illustrated for the Bamble sector of southern Norway reported in the literature.

Association thermodynamics parameters of nano vanadyl sulphate and its complexes with Orange G at different temperatures, docking versus Covid-19 and antioxidant behavior

Molecular thermodynamic association parameters for the bulk and nano-vanadyl sulfate were determined by the conductometry in aqueous solution at various temperatures. The thermodynamic parameters for complex formation 1:1, 1:2 (M/L) between bulk & nano vanadyl with Orange G were also determined by the conductivity measurements. From the interaction of the bulk & nano vanadyl sulfate (VOSO4) with Orange G, in the instance of the 1:1 complex as opposed to the 1:2 (VOSO4/Orange G) complex in water as the solvent, the estimated Kf and ΔGf were higher. When the temperature rises, the complex formation constants decrease. The molecular complexation's negative ΔGf values show that the production of molecular complexes is spontaneous and that it gets higher as the temperature rises. The molecular complexation is an endothermic and entropy-controlled reaction, which is supported by the negative values of ΔHf. Molecular docking of vanadyl sulfate versus 7 jwy of amino acid of covid-19 allows us to better understand the probable modes of engagement and binding affinities of the targeted molecule (vanadyl sulfate), that provide more clarity on how well the molecules exert bioactivity towards the target. The vanadyl sulfate show greater antioxidant behavior than the stander ascorbic acid with the same concentration. Also, the oxygen radicals ranging from 1.1 to 1.4 V which are reduced giving reduction peaks (broad) facilitating the use of vanadyl sulfate as a strong antioxidant solution.

Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non-Covalent Interactions in a Uranyl Tetrahalide Model System.

Together with the synthesis and experimental characterization of 14 hybrid materials containing [UO2 X4 ]2- (X=Cl- and Br- ) and organic cations, we report on novel methods for determining correlation trends in their formation enthalpy (ΔHf ) and observed vibrational signatures. ΔHf values were analyzed through isothermal acid calorimetry and a Density Functional Theory+Thermodynamics (DFT+T) approach with results showing good agreement between theory and experiment. Three factors (packing efficiency, cation protonation enthalpy, and hydrogen bonding energy [ ]) were assessed as descriptors for trends in ΔHf . Results demonstrated a strong correlation between and ΔHf , highlighting the importance of hydrogen bonding networks in determining the relative stability of solid-state hybrid materials. Lastly, we investigate how hydrogen bonding networks affect the vibrational characteristics of uranyl solid-state materials using experimental Raman and IR spectroscopy and theoretical bond orders and find that hydrogen bonding can red-shift U≡O stretching modes. Overall, the tightly integrated experimental and theoretical studies presented here bridge the trends in macroscopic thermodynamic energies and spectroscopic features with molecular-level details of the geometry and electronic structure. This modeling framework forms a basis for exploring 3D hydrogen bonding as a tunable design feature in the pursuit of supramolecular materials by rational design.

Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non‐Covalent Interactions in a Uranyl Tetrahalide Model System

AbstractTogether with the synthesis and experimental characterization of 14 hybrid materials containing [UO2X4]2− (X=Cl− and Br−) and organic cations, we report on novel methods for determining correlation trends in their formation enthalpy (ΔHf) and observed vibrational signatures. ΔHf values were analyzed through isothermal acid calorimetry and a Density Functional Theory+Thermodynamics (DFT+T) approach with results showing good agreement between theory and experiment. Three factors (packing efficiency, cation protonation enthalpy, and hydrogen bonding energy [ ]) were assessed as descriptors for trends in ΔHf. Results demonstrated a strong correlation between and ΔHf, highlighting the importance of hydrogen bonding networks in determining the relative stability of solid‐state hybrid materials. Lastly, we investigate how hydrogen bonding networks affect the vibrational characteristics of uranyl solid‐state materials using experimental Raman and IR spectroscopy and theoretical bond orders and find that hydrogen bonding can red‐shift U≡O stretching modes. Overall, the tightly integrated experimental and theoretical studies presented here bridge the trends in macroscopic thermodynamic energies and spectroscopic features with molecular‐level details of the geometry and electronic structure. This modeling framework forms a basis for exploring 3D hydrogen bonding as a tunable design feature in the pursuit of supramolecular materials by rational design.

The Potential Use of Cold-Pressed Coconut Oil By-Product as an Alternative Source in the Production of Plant-Based Drink and Plant-Based Low-Fat Ice Cream: The Rheological, Thermal, and Sensory Properties of Plant-Based Ice Cream.

This study aimed to investigate the potential use of cold-pressed coconut oil by-products (COB) as a low-cost alternative source for plant-based drink and ice cream production. Firstly, a plant-based drink was produced from cold-pressed coconut oil by-products (COB drink) and compared with a commercial coconut drink. The fat, protein, and zeta potential values of coconut drink obtained from COB were higher than those of the commercial samples. In addition, the particle size value of the drink obtained from COB was found to be lower than that of the commercial drink. In the second stage, full-fat and low-fat plant-based ice cream samples using COB drink were produced and compared to control ice cream samples (produced by the commercial coconut drink) in terms of rheological, sensorial, and thermal properties. Rheological analysis showed that all plant-based ice cream samples indicated pseudoplastic, solid-like, and recoverable characteristics. Low-fat commercial control ice cream samples (C1) indicated the lowest K value (9.05 Pasn), whereas the low-fat plant-based ice cream sample produced by the COB drink (COB-3) exhibited the highest K value (17.69 Pasn). ΔHf values of the plant-based ice cream samples varied from 144.70 J/g to 172.70 J/g. The low-fat COB ice cream stabilized with 3% COB and full-fat COB ice cream samples showed lower ΔHf values than control ice cream samples, indicating that the COB ice cream showed desired thermal properties. The COB drink may be utilized in plant-based ice cream without altering sensory qualities, and low-fat ice cream could be manufactured in the same manner to attain full-fat ice cream quality characteristics. The results of this study demonstrated that COB can be successfully used as an inexpensive raw material source in the production of full-fat and reduced-fat vegetable-based ice cream.

High-Accuracy Heats of Formation for Alkane Oxidation: From Small to Large via the Automated CBH-ANL Method.

It is generally challenging to obtain high-accuracy predictions for the heat of formation for species with more than a handful of heavy atoms, such as those of importance in standard combustion mechanisms. To this end, we construct the CBH-ANL approach and illustrate that, for a set of 194 alkane oxidation species, it can be used to produce ΔHf(0 K) values with 2σ uncertainties of 0.2-0.5 kcal mol-1. This set includes the alkanes, hydroperoxides, and alkyl, peroxy, and hydroperoxyalkyl radicals for 17 representative hydrocarbon fuels containing up to 10 heavy atoms with various degrees of branching in the alkane backbone. The CBH-ANL approach, automated in the QTC and AutoMech software suites, builds balanced chemical equations for the calculation of ΔHf(0 K), in which the reference species may be up to five heavy atoms. The high-level ANL0 and ANL1 reference ΔHf(0 K) values are further refined for even the largest of these reference species with a novel laddering approach. We perform a comprehensive quantification of the uncertainties for both the individual reference species (the largest of which is 0.15 kcal mol-1) and the propagation of those uncertainties when used in the calculation of ΔHf(0 K) for the 194 target species. We examine the sensitivity of the predicted ΔHf(0 K) values to (i) electronic energies from various methods, including ωB97X-D/cc-pVTZ, B2PLYP-D3/cc-pVTZ, CCSD(T)-F12b/cc-pVDZ-F12//B2PLYP-D3/cc-pVTZ, and CCSD(T)-F12b/cc-pVTZ-F12//B2PLYP-D3/cc-pVTZ; (ii) the zero-point vibrational energies (ZPVEs), where we consider harmonic ZPVEs as well as two scaling-based estimates of the anharmonic ZPVEs, all implemented for both ωB97X-D/cc-pVTZ and B2PLYP-D3/cc-pVTZ calculations; (iii) the particular CBH-ANL scheme employed; and (iv) the procedure for choosing the reference conformer for the analyses. The discussion concludes with a summary of the estimated overall uncertainty in the predictions and a validation of the predictions for the alkane subset.

Periodic Density Functional Theory Calculations of Uranyl Tetrachloride Compounds Engaged in Uranyl-Cation and Uranyl-Hydrogen Interactions: Electronic Structure, Vibrational, and Thermodynamic Analyses.

Solid-state uranyl hybrid structures are often formed through unique intermolecular interactions occurring between a molecular uranyl anion and a charge-balancing cation. In this work, solid-state structures of the uranyl tetrachloride anion engaged in uranyl-cation and uranyl-hydrogen interactions were studied using density functional theory (DFT). As most first-principles methods used for systems of this type focus primarily on the molecular structure, we present an extensive benchmarking study to understand the methods needed to accurately model the geometric properties of these systems. From there, the electronic and vibrational structures of the compounds were investigated through projected density of states and phonon analysis and compared to the experiment. Lastly, we present a DFT + thermodynamics approach to calculate the formation enthalpies (ΔHf) of these systems to directly relate to experimental values. Through this methodology, we were able to accurately capture trends observed in experimental results and saw good quantitative agreement in predicted ΔHf compared to the value calculated through referencing each structure to its standard state. Overall, results from this work will be used for future combined experimental and computational studies on both uranyl and neptunyl hybrid structures to delineate how varying intermolecular interaction strengths relates to the overall values of ΔHf.

Absolute Hydration Free Energy of Small Anions and the Aqueous pKa of Simple Acids.

Heats of formation and gas phase acidities for the simple acids and their deprotonated anions (A- = F-, Cl-, Br-, I-, OH-, SH-, SeH-, TeH-, OCl-, OBr-, and OI-) were calculated using the Feller-Peterson-Dixon (FPD) method with large basis sets including Douglass-Kroll scalar relativistic corrections. Hydration of the neutral and anionic species was predicted using the supermolecule-continuum approach, resulting in absolute hydration free energies that, when combined with calculated gas phase acidities, produce aqueous acidities and pKa values for these simple acids that are, in general, in excellent agreement with experimental literature values. Absolute hydration free energy values converged quickly in terms of the experimental values for neutral species, requiring only four explicit H2O molecules. HI is anomalous in that it fully dissociates ionically in a water tetramer and was treated without explicit water molecules. The hydration energies of anionic species converged more slowly and were modeled with up to 16 explicit H2O molecules. Calculated values for ΔHf and ΔGgas agree with experimental values within ca. 1.2 kcal/mol, and ΔGaq and ΔΔGhyd agree with experimental values within ca. 2 kcal/mol in most cases.

THEORETICAL AND EXPERIMENTAL STUDIES OF ANTIOXIDANT PROPERTIES OF ANTIPYRINETHIOSEMICARBAZONE DERIVATIVES

Antipyrinethiosemicarbazone derivatives have been investigated as antioxidant in this work. The results of antioxidant activity coefficient (K) proved that all investigated compounds have good antioxidant activity. Investigation of the relation between antioxidant activity (K) and quantum-chemical parameters difference of heats of formation of a molecule and its cation radical ΔHf shows that the ΔHf values proportional with K values of investigated compounds.

Thermodynamic characterization of synthetic lead-arsenate apatites with different halogen substitutions

AbstractThermodynamic parameters have been measured for synthetic analogs of the mimetite-group minerals Pb5(AsO4)3X (X = OH, Cl, Br, I) belonging to the apatite supergroup. Phases precipitated from aqueous solutions under ambient conditions with well characterized structures and compositions were studied. For each phase, dissolution enthalpy was experimentally determined by oxide melt drop solution calorimetry in a molten solvent of sodium molybdate (3Na2O·4MoO3) at 976 K. The enthalpy of formation from the elements ΔHf,elo was calculated using thermochemical cycles and was −3030.6 ± 11.5, −3026.6 ± 15.8, −2967.6 ± 25.0, and −2993.1 ± 12.2 kJ/mol for Pb5.00(AsO4)3.00OH0.86(CO3)0.07, Pb5.00(AsO4)3.00Cl0.80(CO3)0.10, Pb5.00(AsO4)3.00Br0.80(CO3)0.10, and Pb5.00(AsO4)3.00I0.45OH0.35(CO3)0.10, respectively. These ΔHf,elo values exhibit typical trends for apatites: they increased (were less negative) with the increasing molar mass and ionic radius of X and decreased with the electronegativity and ionization energy of X. The compilation and comparison of data for Ca-, Pb-, P-, and As-apatites revealed correlations indicating that thermodynamic enthalpic stability is largely influenced by chemical factors (e.g., differences in electronegativities of the elements, ionization energy, or ionic characteristics of the bonds) and to a lesser extent by physical and geometric parameters in the crystal structure related to the mass and size of the X anion. Using the correlations, it was possible to estimate the value of hitherto unknown ΔHf,elo for Pb5(AsO4)3F, −3144.3 ± 66.5 kJ/mol. The observed relationships apply to the entire apatite supergroup and can be used to predict the values of ΔHf,elo for phases that have not been studied experimentally. The new data on environmentally significant phases will contribute to the modeling of mineral-water interactions, particularly for potential use in the remediation of soils and wastes contaminated with Pb and As and in the immobilization of radioactive waste containing I-129.

Lipase-Catalyzed Poly(glycerol-1,8-octanediol-sebacate): Biomaterial Engineering by Combining Compositional and Crosslinking Variables.

This study examined poly(glycerol-1,8-octanediol-sebacate) (PGOS) copolymers with low-level substitution of O (1,8-octanediol) for G (glycerol) units (G/O ratios 0.5:0.5, 0.66:0.33, 0.75:0.25, 0.8:0.2, and 0.91:0.09) prepared in bulk by immobilized Candida antarctica Lipase B (N435) catalysis. The central question explored was the extent that exchanging less than half of poly(glycerol sebacate) (PGS) glycerol units with 1,8-octanediol can be used as a strategy to fine-tune biomaterial properties. Synthesized copolymers having G/O ratios of 0.66:0.33, 0.75:0.25, 0.8:0.2, and 0.91:0.09 have similar molecular weights, where Mw varied from 52,800 to 63,800 g/mol, Mn varied from 5100 to 6450 g/mol, and ĐM (molecular mass dispersity, Mw/Mn) values were also similar (8.4-11.4). All of the copolymers were branched, and dendritic glycerol units reached 11% for PGOS-0.91:0.09:1.0. Analysis of DSC second heating scans revealed that copolymers with higher 1,8-octanediol contents have relatively higher Tm and ΔHf values. Over the copolymer compositional range studied herein, Tm and ΔHf values varied from 5.3 to 21.1 °C and 8.0 to 23.1 J/g, respectively. Stress-strain curves of PGOS copolymers cured at 140 °C for 48 h exhibited either a unimodal, bimodal, or trimodal response to tensile loading. Varying G/O from 10:1 to 2:1 resulted in significant increases in the peak stress (0.26-4.01 MPa), preyield modulus (0.65-62.59 MPa), failure to strain (64-110%), and failure toughness (0.1-0.56 MPa). This demonstrates that altering the G/O ratio over a narrow compositional range provides biomaterials with widely different yet tunable mechanical properties. Further investigation of PGOS-0.75:0.25:1.0 films revealed that varying the cure conditions from 120 to 160 °C for periods of 24-72 h provides access to biomaterials with a failure strain range from 15 to 224% and Young's modulus from 1.17 to 10.85 MPa. Hence, using the dual variables of compositional variation and changes in cure conditions provides an exciting platform for PGS analogues to optimize material-tissue interactions. Increased contents of 1,8-octanediol slowed in vitro degradation. Slowed degradation of PGOS relative to PGS will be valuable for use in slower healing wounds.

Point defect formation near the epitaxial Ge(001) growth surface and the impact on phosphorus doping activation

First-principles calculations are used to systematically investigate the impact of surface effects on the energetic cost to incorporate point defects near the growing surface [Ge(001)] and its consequence on the dopant activation in P-doped Ge layers. We illustrate the formation enthalpy ΔHf for the incorporation of a mono-vacancy, which is the dominant point defect responsible for the electrically inactive dopant incorporation in P-doped Ge. The calculated values point toward a significant lowering of ΔHf near the growing surface in comparison to the bulk cubic Ge supercell. The impact of the surface almost vanishes beyond the sixth atomic monolayer located below the surface and the calculated ΔHf values overlap with the ones computed for a bulk cubic Ge supercell. For epitaxial Ge:P layers, grown at low growth temperatures (<450°C) using the deposition method such as the Chemical Vapor Deposition, the dopant-vacancy clusters are formed within the first few monolayers close to the growing surface. The low ΔHf values for the incorporation of a mono-vacancy near the growing surface suggest that the concentration of vacancies can be significantly enhanced with respect to the bulk Ge, which can subsequently trap more dopants and deactivate them at the surface itself. Our first-principles calculation results are in line with previously reported experimental positron annihilation spectroscopy analysis on Ge:P layers grown at 440 °C using GeH4 as gas precursor. At P concentrations above 1×1020cm−3, the mono-vacancy sized open-volume defects are passivated by at least three P atoms.

Polymerization during melting of ortho- and meta-silicates: Effects on Q species stability, heats of fusion, and redox state of mid-ocean range basalts (MORBs)

Abstract29Si NMR and Raman spectroscopic studies demonstrate that fusion of crystalline orthosilicates and metasilicates produces melts more polymerized than their precursor crystals. Forsterite, for example, consists of 100% Q0 species, whereas its melt consists of ~50 mol% of Q1 species (Q = a Si tetrahedron and the superscript indicates the number of bridging oxygen atoms in the tetrahedron). Polymerization during melting can be rationalized from an energetics perspective. Si-NBO-M moieties of Q species are more susceptible to librational, rotational, and vibrational modes than are Si-BO-Si moieties (NBO = non-bridging oxygen; BO = bridging oxygen; M = counter cation). Thermal agitation activates these additional modes, thus increasing the CP and free energy of melts. The reaction of Qn to Qn+1 species during melting eliminates Si-NBO-M moieties and produces Si-O-Si moieties that are less susceptible to the additional modes, thereby minimizing the CP of melts. By decreasing the abundances of Q0, Q1, and Q2 species in favor of Q3 and Q4 species, melts become more stable. In the absence of polymerization, melting temperatures of minerals would be appreciably greater than observed.Polymerization involves formation of Si-O bonds, which are strongly endothermic (Si-O bond dissociation is ~798 kJ/mol). The large heats of fusion (ΔHf) of orthosilicates result primarily from polymerization reactions during melting (ΔHf of forsterite, fayalite, and tephroite are ~142, ~92, and ~90 kJ/mol). The fusion of metasilicates and sorosilicates (e.g., pyroxenes and melilites) involves endothermic polymerization and exothermic depolymerization reactions, although the former dominates. These reactions tend to negate each other during melting, yielding less positive ΔHf values than observed for orthosilicate fusion (e.g., ΔHf of enstatite, diopside, pseudowollastonite, and åkermanite are ~73, ~69, ~57, and ~62 kJ/mol). Where polymerization and depolymerization reactions are absent ΔHf is low and is due mostly to disordering during melting (e.g., ΔHf of cristobalite iŝ8.9 kJ/mol).Experimental evidence indicates that ferric iron is present as a negatively charged oxy-anionic complex in melts (e.g., [FeO2]1–) so that oxidation of Fe2+ should proceed according to: 4Femelt2+ + 1O2 + 6Omelt2−→4[FeO2]melt1−.Free oxygen (O2–), a by-product of polymerization reactions, drives the reaction to the right. Midocean ridge basalts (MORBs) consequently should be more oxidized than their source (e.g., lherzolites) or their residues (e.g., harzburgites). Extraction of melt from the upper mantle and deposition in the crust should produce a crust more oxidized than its upper mantle source. Production of O2– during melting and its presence in alkali-rich magmas also explains the alkali-ferric iron effect.

Self-Consistent Component Increment Theory for Predicting Enthalpy of Formation.

The gas-phase enthalpy of formation (ΔHf) plays a fundamental role in predicting reaction thermodynamics and constructing kinetic models. With advances in computational power and method development, chemically accurate quantum chemistry methods that can predict ΔHf values for small molecules are available; however, large molecules are still out of reach. Increment theories provide a means of extending the prediction capability of high-level methods by decomposing the molecular ΔHf into the additive contributions from individual atoms, bonds, groups, or components. Here, we introduce a novel component increment theory, topology-automated force-field interaction component increment theory (TCIT), in which all component contributions are derived exclusively from Gaussian-4 (G4) results for algorithmically generated model compounds. In a benchmark evaluation of noncyclic compounds from the Pedley, Naylor, and Kline experimental ΔHf dataset, TCIT exhibits consistently lower signed and absolute errors compared with the conventional Benson group increment theory (BGIT). These results pave the way for future extensions of TCIT to ring-containing, ionic, and radical species for which experimental data scarcity currently limits the application of BGIT.

Theoretical study on the heat of formation of some polycyclic aromatic hydrocarbons

This paper reports the results on how structural details govern the heat of formation (ΔHf) of the catacondensed benzenoid hydrocarbons, a wide subclass of polycyclic aromatic hydrocarbons. To accomplish this goal, the influence of the molecular size (expressed through the number of six-membered rings, NR), number of bays (NB), number of coves (NC), number of fjords (NF), and molecular branching (expressed through the number of B3-type rings, NB3), as well as the position of the latter four structural features in a molecule were inspected. To obtain the ΔHf values, the semiempirical PM7 method was applied, and it showed good agreement with the existing experimental results. These structural properties affect ΔHf of these compounds differently. The strongest effect on ΔHf has NR, and it was found that ΔHf increases with increasing NR. ΔHf also increases with increasing NB3. However, when the molecular branching is moved across the molecule, it was found that ΔHf decreases, as it moves to the middle of a molecule. ΔHf of the examined compounds decreases with increasing NB, NC, and NF, and as the bay, cove, and fjord move to the middle of a molecule. When NB, NC, and NF take large values, this decrease slows down.

On the relationship between the energy characteristics of the isodesmic reactions of polychlorinated dioxins and their toxicity

Thermodynamic functions (ΔGf and ΔHf) of clorinated dibenzo-p-dioxins (ClnDD) with n = 0–8 were calculated at the DFT level of theory using the B3LYP functional and extended 6–31** basis sets and used to analyze possible relationship of the structures and energy characteristics of these compounds with their toxicity. A new sequence of successive isodesmic reactions, which makes it possible to calculate chemical potentials μG and μH from the ΔGf and ΔHf values, has been proposed. In the framework of this approach, satisfactory linear correlations between the chemical potentials μ and the logarithms of toxicity of the corresponding polychlorodioxins were obtained for the first time.

IR spectroscopy as a source of data on bond strengths

The aim of this work is the estimation of double bond strength, namely CO bonds in ketones and aldehydes and CC bonds in various compounds. By the breaking of these bonds one or both fragments formed are carbenes, for which experimental data on the enthalpies of formation (ΔHf298) are scarce. Thus for the estimation of ΔHf298 of the corresponding carbenes, the empirical equations were proposed based on different approximations. In addition, a quantum chemical calculations of the ΔHf298 values of carbenes were performed, and the data obtained were compared with experimental values and the results of earlier calculations.Equations for the calculation of CO bond strengths of different ketones and aldehydes from the corresponding stretching frequencies ν(CO) were derived. Using the proposed equations, the strengths of CO bonds of 25 ketones and 12 conjugated aldehydes, as well as CC bonds of 13 hydrocarbons and 7 conjugated aldehydes were estimated for the first time. Linear correlations of CC and CO bond strengths with the bond lengths were established, and the equations permitting the estimation of the double bond strengths and lengths with acceptable accuracy were obtained. Also, the strength of central CC bond of stilbene was calculated for the first time. The uncertainty of the strengths of double bonds obtained may be regarded as accurate ±10–15 kJ/mol.

On the formation of solid solutions with blödite- and kröhnkite-type structures

In this contribution, we provide experimental results on the synthesis and some properties (structural, spectroscopic and thermal) of limited solid solutions Na2Ni1−xCux(SO4)2·4H2O (0 < x ≤ 0.17). Based on different experimental methods—vibrational spectroscopy (infrared and Raman), X-ray powder diffraction at ambient and elevated temperature, electron paramagnetic resonance spectroscopy (EPR) and TG–DTA–DSC methods, it has been established that the copper ions are included in the nickel blodite-type structure up to about 17 mol%. However, the nickel ions are not able to accept the coordination environment of the copper ions in the strongly distorted [Cu(H2O)2O4] clusters due to the Jahn–Teller effect, thus resulting in the crystallization of a krohnkite free from nickel ions. The X-ray powder diffraction data show that the included copper ions do not influence considerably on the lattice parameters of the blodite matrix owing probably to the buffer effect of the sodium ions and hydrogen bonds. The vibrational spectra are interpreted in the light of their crystal structures. The TG and DTA methods combined with X-ray powder diffraction at elevated temperature reveal that the dehydration of Na2Ni(SO4)2·4H2O and Na2Ni1−xCux(SO4)2·4H2O solid solutions occurs stepwise, thus forming dihydrates and anhydrous compounds—Na2Ni(SO4)2 and Na2Ni1−xCux(SO4)2 of the same structures. It has been found that the increased amount of copper ions causes increasing in the values of ΔH deh and decreasing in the values of ΔH f of the solid solutions. EPR spectra of the solid solutions are presented and compared to that of Na2Zn0.86Cu0.14(SO4)2·4H2O.