MOPAC Software Research Articles

Design, synthesis, explorations of DFT, PM6, molecular docking with SAR-CoV-2 Mpro and anticancer properties of novel indolo[2,3-c]isoquinoline analogues

A novel series of indolo[2,3-c]isoquinoline derivatives, coupled with pyrazole and pyrazolo[3,4-d]pyrimidinone rings bearing substituted Cl, OCH3, CH3, and H groups II, II(a-d), were successfully synthesized, exhibiting significant biological and pharmacological relevance. Computational chemistry using the semiempirical method PM6 via MOPAC software was employed to investigate their thermochemical properties. Compound IIIb displayed a lower heat formation (ΔHf) value of 68.89873 kcal/mole, indicating enhanced stability, whereas compound IId exhibited a higher ΔHf value of 151.32004 kcal/mole, suggesting lesser stability. Density functional theory (DFT) at B3LYP/def2-TZVP def2/J was utilized for analyzing electronic structures and geometric optimization. The HOMO-LUMO energy gap (ΔEg) followed an ascending order in the pyrimidinone>pyrazole series, with IIIb possessing the lowest energy gap (ΔEg = 2.994 eV) and IIc having the highest (ΔEg = 3.433 eV). Compound IIa displayed the highest electrophilicity index (χ = 3.540 eV) and exhibited potent anti-cancer activity, as observed in derivatives II and III(a-d). Additionally, compounds IIa, IIb, and IIc demonstrated promising interactions with amino acids of the SARS-CoV-2 main protease (PDB:7e18).

Investigation of the Adsorption Properties of Electrically Conductive Pyrolyzed Polyacrylonitrile Modified with Chromium (III) Oxide to Obtain Highly Efficient Gas Sensors

Introduction. Obtaining highly sensitive gas sensors is an urgent task, the solution to which will allow you to accurately and quickly assess changes in the air-gas composition of a given medium. Gas sensors based on metal-containing pyrolyzed polyacrylonitriles (Me-pPAN) are among the cheapest and most environmentally friendly gas-sensitive materials with a fast response. One of the types of sensor materials included in the Me-pPAN list is pyrolyzed polyacrylonitrile (pPAN) modified with a chromium (III) oxide molecule. The reasons for selective adsorption of pPAN and Me-pPAN to pollutant gases, which would allow controlling this process and obtaining sensory materials with increased sensitivity to gases, are not enough studied. Therefore, the aim of this work was to establish the main causes of selective adsorption of semiconductor electrically conductive films by modeling methods in the framework of molecular and quantum mechanics. Materials and Methods. The authors used modeling methods in the framework of molecular and quantum mechanics (MM2), the density functional theory (COSMO) method and the semi-empirical PM7 method in the MOPAC software package. Results. MM2 and PM7 methods were used to obtain models of adsorption complexes of "Cr-pPAN – gas-pollutant" systems. Thermodynamic parameters of the system were calculated for standard environmental conditions. The dependence of the adsorption of pollutant gases on the surface of Cr-pPAN on temperature has been established. Discussion and Conclusion. As a result of calculating the thermodynamic parameters of gas-pollutant–pPAN/Me-pPAN systems and obtaining positive values of Gibbs energies of these systems, it was confirmed that the adsorption of polluting gases on the surface of Cr-pPAN was not a spontaneous phenomenon and was effective at high temperatures. Considering that when chromium (III) oxide was introduced into the pPAN matrix, the charge on nitrogen atoms increased. It could be concluded that a chromium (III) oxide molecule had a positive effect on the semiconductor properties of pPAN. It was found that the adsorption of polluting gases (SO2 and NO2) was most likely on the surfaces of pPAN and Cr-pPAN. The results obtained in the work can be used to obtain gas-sensitive materials with specified metrological characteristics.

Молекулярное моделирование и экспериментальное подтверждение поиска средств коррекции токсического воздействия сероводорода

Mathematical modeling is a promising method enabling in silico calculations with subsequent suggestion of cell membrane protective agents used to reduce the consequences of exposure to hydrogen sulfide-containing gas in emergency situations. This study aimed to investigate the nature of interaction of hydrogen sulfide (H2S) and N-Acetyl-L-Cycteine (NAC) with the components of cell membranes. We built a mathematical model of interatomic interactions of cell membrane components with H2S and NAC (two separate models), then made the quantum-chemical calculations using our proprietary technique and set up GAMESS Z-matrices reflecting type and position of atoms in the molecules. The structure of the molecules was optimized with the help of MOPAC package built into ChemOffice. Lecithin-based liposomes in a sulfide solution (with Na2S being the donor of H and HS ions) were used as an experimental model of the biological membrane. Redox potential in mV was the comparison parameter in assessment of interaction of the H2S system components and NAC with phospholipid. The results include patterns showing the phospholipid reactive centers blocked by NAC under toxic exposure to H2S. Liposomal models of cell membranes were formed and redox parameters measured. Biological experiment confirmed the acceptable accuracy of the designed method of calculation of intermolecular interactions when used as a basis for further selection of agents capable of adjusting toxic doses of hydrogen sulfide. Membrane models of H2S interaction with protein and lecithin were visualized in silico and in vitro. The possibility of using NAC as an H2S inhibitor has been confirmed.

Support vector regression-based QSAR models for prediction of antioxidant activity of phenolic compounds

The Support vector regression (SVR) was used to investigate quantitative structure–activity relationships (QSAR) of 75 phenolic compounds with Trolox-equivalent antioxidant capacity (TEAC). Geometric structures were optimized at the EF level of the MOPAC software program. Using Pearson correlation coefficient analysis, four molecular descriptors [n(OH), Cosmo Area (CA), Core-Core Repulsion (CCR) and Final Heat of Formation (FHF)] were selected as independent variables. The QSAR model was developed from the training set consisting of 57 compounds and then used the leave-one-out cross-validation (LOOCV) correlation coefficient to evaluate the prediction ability of the QSAR model. Used Artificial neural network (ANN) and multiple linear regression (MLR) for comparing. The RMSE (root mean square error) values of LOOCV in SVR, ANN and MLR models were 0.44, 0.46 and 0.54. The RMSE values of prediction of external 18 compounds were 0.41, 0.39 and 0.54 for SVR, ANN and MLR models, respectively. The obtained result indicated that the SVR models exhibited excellent predicting performance and competent for predicting the TEAC of phenolic compounds.

Novel Aceclofenac Cocrystals with l-Cystine: Virtual Coformer Screening, Mechanochemical Synthesis, and Physicochemical Investigations.

Current work focuses on the improvement of the solubility and dissolution of ACF by the cocrystal approach. Aceclofenac (ACF) is one of the commonly used Nonsteroidal Anti-Inflammatory Drug (NSAID) representing a variety of therapeutic applications including management of pain, inflammation, rheumatoid arthritis, and osteoarthritis, etc. But very low solubility and dissolution rate of ACF compromise its therapeutic utility. Now a day's cocrystallization technique has emerged as a novel technique for modulation of the said problems. The Specific objectives of this research work were mechanochemical synthesis, characterization, and performance evaluation of aceclofenac cocrystal. ACF was screened with various pharmaceutically acceptable coformers (Selected from GRAS and EAFUS list) using MOPAC software and physical screening method to find out novel cocrystals of ACF with enhanced solubility and dissolution rate. Novel cocrystals (multi-component crystalline solid) of ACF with l-cystine were prepared by a neat grinding method and by liquid assisted grinding method. The synthesized cocrystals (ACF-l-CYS NG and ACF-l-CYS LAG) were characterized carefully by Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (IR), and Powder XRay Diffraction (PXRD) to verify the formation of the cocrystals. Pharmaceutically significant properties such as powder dissolution rate, solubility, and stability of the prepared cocrystals were evaluated. Compared to pure ACF, the prepared cocrystals showed superior solubility and dissolution rate. The prepared cocrystals were found to be stable and non-hygroscopic under study conditions. The cocrystallization technique was successfully utilized to increase the solubility and dissolution rate of aceclofenac.

Experimental study and quantum-chemical simulation of piroxicam adsorption on the coal sorbent from walnut shells

The aim of this work was to study the sorption of piroxicam on the surface of activated carbon obtained by heat treatment from walnut shells. The objects of study are piroxicam (a) and model clusters of the sorbent. The quantitative determination and study of the sorbability of piroxicam is based on photometric recording of spectra at λ 400 nm. The most complete sorption of piroxicam occurs at pH 6,8–7,3, where the maximum difference in the optical density of the solutions was observed before and after sorption, which indicates the formation of a stable state of piroxicam. The results obtained from three series before and after sorption were subjected to statistical processing. The dependences “sorption – equilibrium concentration” presented at various temperatures made it possible to attribute the obtained curves to the Langmuir solution. Based on the obtained thermodynamic indicators, the following conclusions can be made: the reaction proceeds spontaneously, exothermally. Saturation of the surface of activated carbon with a monomolecular layer of piroxicam does not depend much on temperature changes, which is confirmed by close values of thermodynamic parameters at three temperatures. Quantum chemical calculations of the starting materials and model adsorption complexes in the “piroxicam – activated carbon surface” system were performed using the GAMESS US and MOPAC software. As a result of the work done, it was found that activated carbon obtained by heat treatment of walnut shells is a good and quite promising material for concentrating piroxicam and other drugs with the aim of subsequent determination from water and various biological environments.

The geometric and electronic structures of AlnNam (n = 5, 6; n + m ≤ 10) clusters

The low-energy structures of Al5Nam (m=1–5) and Al6Nam (m=0–4) are searched by using the genetic algorithm combined with MOPAC package. The stabilities and the electronic structures are studied by density functional theory models and by first principle perturbation theory at MP4 level. The results show that the Na atoms are located at the outside of the clusters. Analysis on the density of states and the charge distribution indicate the sodium atoms transfer their 3s electrons to aluminum and exist as +1 cations. The molecular orbitals agree with the types predicted by the jellium model, and Al5Na5 and Al6Na2 show enhanced stabilities as the 20 valence electrons form closed electronic shells. However, the valence orbitals don’t encompass the Na+ cores. The electron localization function clearly demonstrates that the valence electrons reside at the outside of the Al3+ cores, and the Na+ cores are exposed at the outside of the valence electrons. All the results confirm that Aln moieties in the AlNa binary clusters form Zintl anions and the Na+ cations are ionically bonded to them. It suggests AlNa clusters can be used as building blocks to form cluster-assembled Zintl-phase materials.

Quantum chemical and thermodynamic calculations of fulvic and humic copper complexes in reactions of malachite and azurite formation

This article provides a thermodynamic evaluation of the reactions of humic and fulvic acids in the process of malachite and azurite mineralogenesis. Semi-empirical methods AM/1, MNDO, PM3, PM5, PM6 and PM7 were used to compute the heat of formation, enthalpy and entropy for thermodynamic calculations of the reactions performed on the basis of Hess's law. It is shown that methods PM6 and PM7 in the MOPAC software package provide good compliance with experimental and calculated heats of formation for copper complexes and alkaline earth metal complexes with organic acids. It is found that the malachite and azurite formation processes involving humus complexing substances are thermodynamically possible.

Accuracy comparison of several common implicit solvent models and their implementations in the context of protein-ligand binding

In this study several commonly used implicit solvent models are compared with respect to their accuracy of estimating solvation energies of small molecules and proteins, as well as desolvation penalty in protein-ligand binding. The test set consists of 19 small proteins, 104 small molecules, and 15 protein-ligand complexes. We compared predicted hydration energies of small molecules with their experimental values; the results of the solvation and desolvation energy calculations for small molecules, proteins and protein-ligand complexes in water were also compared with Thermodynamic Integration calculations based on TIP3P water model and Amber12 force field. The following implicit solvent (water) models considered here are: PCM (Polarized Continuum Model implemented in DISOLV and MCBHSOLV programs), GB (Generalized Born method implemented in DISOLV program, S-GB, and GBNSR6 stand-alone version), COSMO (COnductor-like Screening Model implemented in the DISOLV program and the MOPAC package) and the Poisson-Boltzmann model (implemented in the APBS program). Different parameterizations of the molecules were examined: we compared MMFF94 force field, Amber12 force field and the quantum-chemical semi-empirical PM7 method implemented in the MOPAC package. For small molecules, all of the implicit solvent models tested here yield high correlation coefficients (0.87–0.93) between the calculated solvation energies and the experimental values of hydration energies. For small molecules high correlation (0.82–0.97) with the explicit solvent energies is seen as well. On the other hand, estimated protein solvation energies and protein-ligand binding desolvation energies show substantial discrepancy (up to 10kcal/mol) with the explicit solvent reference. The correlation of polar protein solvation energies and protein-ligand desolvation energies with the corresponding explicit solvent results is 0.65–0.99 and 0.76–0.96 respectively, though this difference in correlations is caused more by different parameterization and less by methods and indicates the need for further improvement of implicit solvent models parameterization. Within the same parameterization, various implicit methods give practically the same correlation with results obtained in explicit solvent model for ligands and proteins: e.g. correlation values of polar ligand solvation energies and the corresponding energies in the frame of explicit solvent were 0.953–0.966 for the APBS program, the GBNSR6 program and all models used in the DISOLV program. The DISOLV program proved to be on a par with the other used programs in the case of proteins and ligands solvation energy calculation. However, the solution of the Poisson-Boltzmann equation (APBS program) and Generalized Born method (implemented in the GBNSR6 program) proved to be the most accurate in calculating the desolvation energies of complexes.

Application of molecular modeling to urokinase inhibitors development.

Urokinase-type plasminogen activator (uPA) plays an important role in the regulation of diverse physiologic and pathologic processes. Experimental research has shown that elevated uPA expression is associated with cancer progression, metastasis, and shortened survival in patients, whereas suppression of proteolytic activity of uPA leads to evident decrease of metastasis. Therefore, uPA has been considered as a promising molecular target for development of anticancer drugs. The present study sets out to develop the new selective uPA inhibitors using computer-aided structural based drug design methods. Investigation involves the following stages: computer modeling of the protein active site, development and validation of computer molecular modeling methods: docking (SOL program), postprocessing (DISCORE program), direct generalized docking (FLM program), and the application of the quantum chemical calculations (MOPAC package), search of uPA inhibitors among molecules from databases of ready-made compounds to find new uPA inhibitors, and design of new chemical structures and their optimization and experimental examination. On the basis of known uPA inhibitors and modeling results, 18 new compounds have been designed, calculated using programs mentioned above, synthesized, and tested in vitro. Eight of them display inhibitory activity and two of them display activity about 10 μM.

7-hydroxy-3-(1-hydroxyethyl)-5-methoxy-3-4-dimethylisobenzofuran-a(3H)-one and 4, 8-dihydroxy-6-methoxy-3,4,5-trimethyIisochroman-1-one using MOPAC Software

A benzofuranone type of compound known as 7-hydroxy-3-(1-hydroxyethyl)-5methoxy-3,4-dimethylisobenzofuran-1 (3H)-one (1) and 4,8-dihydroxy-6-methoxy-3,4,5trimethylisochroman-l-one (2) were studied for the molecular modeling using MOPAC. Compound 1 was originally isolated from the fungus Leptosphaeria sp. KTC 727. Initial Nuclear Magnetic Resonance (NMR) analyses using I H, 13C, Correlation Spectroscopy (COSY), Heteronuclear Multiple Quantum Coherence (HMQC), Heteronuclear Multiple Bond Coherence (HMBC) and Mass Spectrometry (MS) suggested 1 and 2 as the candidate planar structures. Succeeding chemical experiments confirmed it to be 1 and not 2. This study provided new confirmatory evidence about the exclusion of 2 as possible candidate compound via theoretical computation approach using MOPAC software.

Quantum chemical studies of novel 2′-4′ conformationally restricted antisense monomers

The principle of antisense technologies is based on the specific inhibition of unwanted gene expression by blocking mRNA activity. A rapid increase in the number of antisense molecules in clinical trials was observed. The 2′-O-methoxyethyl modification (MOE) showed a good safety profile with limited binding affinity, whereas locked nucleic acid (LNA) showed high potency by exhibiting strong binding affinity and high toxicity. The novel 2′-4′ conformationally restricted nucleoside analogue has the structural features of both MOE (second generation) and LNA (third generation). It is possible to acquire the positive features of both MOE and LNA and show high potency without an increase in the hepatotoxicity. Structural insight at the monomer level can be useful in understanding the function of the modification and designing derivatives of these molecules. Therefore, the quantum chemical studies of the antisense nucleoside modifications like MOE, LNA, and two stereo isomers of constrained MOE (cMOE) were performed at the monomer level. The conformational preferences of these antisense monomers were studied using a multidimensional conformational search. The semiempirical method PM6 of the MOPAC software was used for the conformational search. Three structures were chosen based upon energy criteria after the conformational search for all the monomers. Full geometry optimization calculations were done on the three structures (most stable, alternate stable, start structures) of all the monomers using the Hartree–Fock method. This was followed by single-point density functional theory (DFT) calculations in gas phase and solvent phase using the B3LYP/6-311G** basis set. Quantum chemical descriptors were derived for the stable geometries of all these monomers. Structural properties and reactivity descriptors of all four antisense modifications in the gas phase and the solvent phase were also studied. The results suggest that LNA is more reactive, that is, highly toxic in nature and with a good binding affinity, while MOE is less reactive, that is, less toxic with weak binding affinity. These results agree with the experimental findings. Properties of 2′-4′ conformationally restricted modifications (ScMOE and RcMOE) showed better stability than MOE and less reactivity than LNA. Therefore, these cMOEs may show less toxicity with high binding affinity toward the target, as shown in the experiments. Study at the monomer level would help in understanding the conformational flexibility available with all modifications, along with various reactivity descriptors, which may help guide the design of new modifications. This study attempts to find an indirect relationship between the quantum chemical descriptors and the experimental data, which may be useful in designing new molecules or modifications tuned for specific requirements of antisense molecules. © 2013 Wiley Periodicals, Inc.

Modeling of 2-Pyridin-3-yl-Benzo[d][1,3]Oxazin-4-one Derivatives by Several Conformational Searching Tools and Molecular Docking

Neutrophil elastase, a serine proteinase from the chymotrypsin family, has been the object of comprehensive experimental and theoretical studies to develop efficient human neutrophil elastase inhibitors. The serine protease has been linked to the pathology of a variety of inflammatory diseases, making it an attractive target for the development of anti-inflammatory compounds. In this work, we have built a common binding model of the 2-pyridin-3-yl-benzo[d][1,3]oxazin-4-one derivatives into the human neutrophil elastase binding site. This was accomplished through a comparative conformational analysis (using OMEGA, HYPERCHEM, and MOPAC software) of 2-pyridin-3-yl-benzo[d][1,3]oxazin-4-one inhibitors followed by rigid and flexible molecular docking (by the FRED and GLIDE programs) into the target protein. We conclude that OMEGA software generates the most representative conformers to model the protein-ligand interactions.

Theoretical study of the properties of adsorbed oxygen complexes on a Si(100) surface

The results from quantum-chemical calculations of the properties of adsorbed oxygen complexes on a Si(100) surface are presented. Semi-empirical MNDO quantum-chemical modeling, implemented in the MOPAC software package, is used to model the physicochemical properties and estimate the energy parameters. The dependences of the total energy of the silicon cluster-oxygen system are calculated in dependence on the location of oxygen in the Si(100) surface layer, and the geometrical and electron characteristics of the equilibrium states of a cluster with adsorbed oxygen.

N-octanol-water partition coefficients (log KOW) of 399 congeners of polychlorinated azoxybenzenes (PCAOBs) determined by QSPR- and ANN-based approach

Polychlorinated azoxybenzenes (PCAOBs) theoretically consist of 798 congeners with 399 in cis and 399 in trans configuration. PCAOBs in trans configuration are largerly planar compounds and some are highly toxic and environmentally relevant compared to cis congeners. Trans-PCAOBs can be found as by-side products in 3,4-dichloroaniline and some herbicides. To fulfill gaps in physical and chemical properties of PCAOBs, the values of log Kow were determined for 399 congeners of t-CAOB using a computational approach. We used the semi-empirical RM1 in MOPAC and DFT B3LYP in Gaussian 03 methods, artificial neural net (ANN) predictions, and the standardized variables with and without the normal varimax rotation. The models created predicted the values of log KOW of all 399 chlorinated derivatives of trans-azoxybenzenes (C-t-AOBs). The values of log KOW of C-t-AOBs varied between 5.08 and 5.42 for Mono-, 5.16 and 5.96 for Di-, 5.79 and 6.73 for Tri-, 6.26 and 7.18 for Tetra-, 6.65 and 7.54 for Penta-, 7.13 and 7.94 for Hexa-, 7.20 and 8.20 for Hepta-, 7.96 and 8.32 for Octa-, 8.32 and 8.43 for Nonachloro-t-AOBs and 8.55 and 8.97 for Decachloro-t-AOB. These log KOW values were similar per chloro-t-AOB congener and independent of the calculation method. C-t-AOBs have log KOW values above 4.5, and what relates to contaminants of low or very low envionmentally mobility but a high predilection to the soil and sediment particles and with potential for bioaccumulation. The models that used the standardized variables had smallest errors and higher correlation coefficients compared to the models that based on the normal varimax rotation of standardized structural descriptors. In light of these data, the semi-empirical RM1 calculations in MOPAC software and followed by ANN were a much less time consuming and less expensive compared to the DFT B3LYP method.

QSARs on human carbonic anhydrase VA and VB inhibitors of some new not yet synthesized, substituted aromatic/heterocyclic sulphonamides as anti-obesity agent

This paper presents result of quantitative structure–activity relationships (QSAR) study realized with the PRECLAV, omega, brood and MOPAC software. The dependent property is the inhibitory activity against human carbonic anhydrase mitochondrial isoforms VA and VB. The calibration set includes 17 aromatic/heterocyclic sulphonamides incorporating phenacetyl, pyridylacetyl and thienylacetyl tails with three clinically used CA inhibitors namely AZA, TPM and ZNS molecules. The prediction set contains 24 others not yet synthesized substituted aromatic/heterocyclic sulphonamides having unknown observed values of activity. In the presence of prediction set, the predictive quality of QSAR of hCA VA (r2 = 0.9789, F = 418.115, r2CV = 0.9689) and hCA VB (r2 = 0.9768; F = 379.717; r2CV = 0.9637) is large. The obtained models suggest a slightly different inhibition mechanism for the two isoforms. Large percentage, in weight, of CONH molecular fragments seems to be favourable to inhibitory activity of both VA and VB.

QSPR probing of Na+ complexation with 15-crown-5 ethers derivatives using artificial neural network and multiple linear regression

A quantitative structure–property relationship (QSPR) study is performed to develop a model, relating to Na+ complex stability constant (log K) and the structure of 74 derivatives of 1,4,7,10,13-pentaoxacyclo-pentadecane ethers (15C5). Stepwise Multiple Linear Regression (SMLR) and Artificial Neural Network (ANN) methods have been exploited as linear and nonlinear methods, respectively to build the QSPR model. MOPAC software embedded in ChemOffice 2004 package was used for the minimizing energy using semi-empirical AM1 method. The optimum structures have been applied to generate more than 50 descriptors using available servers in ChemOffice 2004. The five most important constitutional, steric, electronic, thermodynamic and molecular descriptors were selected using the common preselection method combined by SMLR method. SMLR and ANN models were constructed based on the five selected descriptors. Both proposed models efficiently predict log K of 15C5 complexes. However, the results of ANN were more effective respect to SMLR model. This phenomenon reveals that log K of 15C5 complexes have a deviation from linear behavior related to the selected descriptors.

Quantitative Structure-Reduction Potential Relationship Study of Some Quinones in Five Solvents

The reduction half-wave potentials of nine quinones in five solvents are predicted by a statistically validated quantitative structure–reduction potential relationship modeling approach. The multiple linear regressions obtained were constructed based on a variety of electronic molecular descriptors calculated by the MOPAC software along with some solvent characteristics as independent variables. Reduction half-wave potentials of quinones were considered as dependent variables. The best of the selected descriptors that appear in the model are the minimum charge of the oxygen atom on the carbonyl group, Guttmann acceptor number of the solvent, final heat of formation, dipole moment of the solvent, and the lowest unoccupied molecular orbital (LUMO) energy. The model was validated by the leave-one-out cross validation method. The statistical parameters derived from this test were R 2=0.976, Q 2=0.970 and SPREES = 0.052, which indicate the suitability of the constructed model.

Enthalpies of formation of nitro-, nitroxy-, and nitrosoadamantanes

The enthalpies of formation of nitro-, nitroso-, and nitroxyadamantanes were calculated using semiempirical quantum-chemical PM3, MINDO, AM1, and MNDO methods incorporated into MOPAC software package. The best correlation with the experimental data was obtained with the results of PM3 calculations. Using the corresponding linear regression equation, the enthalpies of formation of 22 adamantane derivatives having nitro-, nitroso-, and nitroxy groups were calculated.

Enthalpy of formation of adamantane alkyl derivatives

The enthalpies of formation of adamantane alkyl derivatives were calculated by the semiempirical quantum chemical methods PM3, MINDO, AM1 and MNDO of the MOPAC software package. Comparison of the calculated values with the experimental data showed that the best correlation gave the PM3 method. Using this method and linear regression equation derived by us we calculated enthalpies of formation of twenty-two alkyl derivatives of adamantane.