Structural studies of poly(α-aminoisobutyric acid)

The electron-diffraction pattern of an oriented film of poly(α-aminoisobutyric acid) in the 3₁₀-helical conformation has been analyzed. The conformation was obtained by a linked-atom least-squares refinement of average values from crystal structures. Specimens treated with dichloracetic acid, to improve their crystallinity, conform to space group R3c with a = 21.8 Å, c = 5.95 Å. The structure contains channels that can accommodate molecules of dichloracetic acid. One molecule of acid per six residues fills the channels, and the R-factor then is 34% using 23 reflections. Ir evidence is presented to show that the acid may hydrogen bond to the peptide groups. Some reflections occasionally observed on the diffraction photographs are attributed to a 15/4 α-helix. The significance of the results is considered in relation to Aib-containing peptides.     

Crystal structure of zinc citrate

The crystal structure of zinc citrate [Zn(II) (C₆H₅O₇)₂·4NH₄⁺] shows isolated zinc ions octahedrally coordinated to two equivalent citrates via a central hydroxyl, central carboxyl, and one terminal carboxyl from each citrate. The clusters are linked through hydrogen bonds to ammonium ions in the lattice. The structure is distinctly different from that of other divalent cation triply ionized citrate complexes, which are polymeric. Crystal data : space group P2₁/C, a = 8.784(3) Å, b = 13.499(4) Å, c = 9.083(3) Å, β = 113.4°(1), V = 988(1) ų. Citrate has been identified as the low molecular weight ligand that complexes zinc in human milk; this may be of interest in relation to intestinal zinc absorption.     

The ionization behavior of bile acids in different aqueous environments

The ionization behavior of cholic acid, deoxycholic acid, and chenodeoxycholic acid in a variety of physiologically important molecular environments was studied using 13C NMR spectroscopy. The apparent pKa of the carboxyl group was determined from titration curves obtained from the dependence of the carboxyl carbon chemical shift on pH. Using 90% 13C isotopic substitution of the carboxyl carbon, a complete titration curve was obtained for cholate at a concentration below its critical micelle concentration and solubility limit in water. Incorporation of 12 mole % bile acid into mixed micelles with its taurine conjugate prevented precipitation of the unconjugated bile acid, and titration curves for cholic, deoxycholic, and chenodeoxycholic acids in the mixed micelles were obtained. The apparent pKa was also determined for 13C-enriched bile acids complexed with bovine serum albumin and in egg phosphatidylcholine vesicles. For monomers, micelles, and BSA complexes of all three bile acids and for deoxycholic and chenodeoxycholic acid in vesicles, one magnetic environment was observed. In contrast, two environments, both titratable, were detected for cholic acid in phosphatidylcholine vesicles. The apparent pKa's of the bile acids in the different environments ranged from 4.2 to 7.3. At pH 7.4, as monomers or bound to albumin, the bile acids were fully ionized, but when associated with phosphatidylcholine vesicles they were only partially ionized. In addition, aspects of the molecular motion and relative hydrophobicity of the bile acid carboxyl group in the environments studied were discerned from chemical shift, line-width, and lineshape data.     

Fluorescent probe and NMR studies of the aggregation of bile salts in aqueous solution

The binding of the fluorescent probes 1-anilino-8-naphthalene sulfonate and dansyl cadaverine to the sodium salts of cholic, deoxycholic and dehydrocholic acids has been investigated. Enhanced probe solubilisation accompanies aggregation. Monitoring of fluorescence intensities as a function of bile salt concentration permits the detection of primary micelle formation, as well as secondary association. The transition concentrations obtained by fluorescence are in good agreement with values determined for the critical micelle concentrations, by other methods. Differences in the behaviour of cholate and deoxycholate have been noted. Fluorescence polarisation studies of 1,6-diphenyl-1,3,5-hexatriene solubilised in bile salt micelles suggest a higher microviscosity for the interior of the deoxycholate micelle as compared to cholate. ¹H NMR studies of deoxycholate over the range 1–100 mg/ml suggest that micelle formation leads to a greater immobilisation of the C₁₈ and C₁₉ methyl groups as compared to the C₂₁ methyl group. Well resolved ¹³C resonances are observed for all three steroids even at high concentration. Both fluorescence and NMR studies confirm that dehydrocholate does not aggregate.     

Characterization of mixed micelles of phospholipids of various classes and a synthetic,homogeneous analogue of the nonionic detergent triton X-100 containing nine oxyethylene groups

The synthesis and high-pressure liquid chromatographic purification of the homogeneous nonionic surfactant $\text{p-}\text{(1,1,3,3-tetramethylbutyl)phenoxynonaoxyethylene}$ glycol (OPE-9) in quantities suitable for membrane solubilization studies is reported. Micelles of OPE-9 and mixed micelles of OPE-9 with dimyristoyl and dipalmitoyl phosphatidylcholine as well as phosphatidylserine, phosphatidylethanolamine, lysophosphatidylcholine, sphingomyelin, and palmitic acid were characterized by column chromatography on 6% agarose. It was found that at 28°C OPE-9 micelles have a Stokes' radius of 32 Å, giving a molecular weight for a spherical micelle of about half that of micelles of the polydisperse nonionic surfactant Triton X-100 under the same conditions. The micelle size is temperature dependent: at 40°C the OPE-9 micelles have a Stokes' radius of 44 Å, giving a molecular weight for a spherical micelle of about twice that of the OPE-9 micelles at 28°C. The size of the mixed micelles varies linearly (as measured by $\text{K}{}_{\mathrm{<mtext>av</mtext>}}$) with the mole fraction of phospholipid. The mixed micelle size was found to be relatively independent of the absolute concentration of surfactant over a four-fold range if the mole fraction of phospholipid is kept constant. The usefulness of the OPE-9/phospholipid mixed micelle system for lipolytic enzyme substrates and membrane-related studies is considered.     

Protein conformational landscapes: Energy minimization and clustering of a long molecular dynamics trajectory

Using energy minimization and cluster analysis, we have analyzed a 1020 ps molecular dynamics trajectory of solvated bovine pancreatic trypsin inhibitor. Elucidation of conformational sub states in this way both illustrates the degree of conformational convergence in the simulation and reduces the structural data to a tractable subset. The relative movement of structures upon energy minimization was used to estimate the sizes of features on the protein potential energy surface. The structures were analyzed using their pairwise root-mean-square C_α deviations, which gave a global measure of conformational changes that would not be apparent by monitoring single degrees of freedom. At time scales of 0.1 ps, energy minimization detected sharp transitions between energy minima separated by 0.1 Å rms deviation. Larger conformational clusters containing these smaller minima and separated by 0.25 Å were seen at 1 ps time scales. Both of these small features of the conformational landscape were characterized by movements in loop regions associated with small, correlated backbone dihedral angle shifts. On a nanosecond time scale, the main features of the protein energy landscape were clusters separated by over 0.7 Å rms deviation, with only seven of these sub states visited over the 1 ns trajectory. These substates, discernible both before and after energy minimization, differ mainly in a monotonic pivot of the loop residues 11–18 over the course of the simulation. This loop contains lysine 17, which specifically binds to trypsin in the active site. The trajectory did not return to previously visited clusters, indicating that this trajectory has not been shown to have completely sampled the conformational substates available to it. Because the apparent convergence to a single region of conformation space depends on both the time scale of observation and the size of the conformational features examined, convergence must be operationally defined within the context of the simulation. © 1995 Wiley-Liss, Inc.     

Metal-phenoxyalkanoic acid interactions. Part 15. The crystal structures of diaquabis(phenoxyacetato)cadmium(II) and catena-μ-[aquabis(phenoxyacetato-O)lead(II)-bis(phenoxyacetato)lead(II)]

The crystal structures of the cadmium(II) and lead(II) complexes of phenoxyacetic acid (PAH) have been determined by single crystal X-ray diffraction techniques. The cadmium complex, [Cd(PA)₂(H₂O)₂] (1), space group C2, with Z = 2 in a cell of dimensions, a = 11.801(2), b = 5.484(1), c = 13.431(3) Å, β = 100.87(2)°, possesses a distorted trapezoidal bipyramidal coordination around the metal atom, involving two water oxygens [2.210(5) Å] and four carboxyl oxygens from two symmetrical bidentate phenoxyacetate ligands [2.363(4), 2.365(4) Å] with Cd lying on the crystallographic two- fold axis. The lead complex, [Pb₂(PA)₄(H₂O)]_n(2) is triclinic, space group P$\text{1}$, Z = 2, with a cell of dimensions, a = 10.135(4), b = 10.675(3), c = 19.285(9) Å, α = 114.66(3), β = 91.94(3) and γ = 114.99(3)°. (2) is a two-dimensional polymer with a repeating dimer sub-unit. The first lead [Pb(1)] has an irregular MO₈ coordination [2.34?2.96(2) Å: mean, 2.63(2) Å] involving the water molecule, two oxygens from an asymmetric bidentate carboxylate group, two from a bidentate chelate [O(ether), O(carboxylate)] group and three from bridging oxygens, one of which also provides a polymer link to another symmetry generated lead. The second lead [Pb(2)] is irregular seven-coordinate [PbO, 2.48?2.73(2) Å: mean, 2.61(2) Å] with three bonds from the bridging groups, two from an unsymmetrical bidentate carboxylate (O, O′) group and one from a second carboxyl group which also bridges two Pb(2) centres in the polymer.     

X-Ray Studies on Crystalline Complexes Involving Amino Acids and Peptides XXXI. Effect of Chirality on Ionization State,Stoichiometry and Aggregation in the Complexes of Oxalic Acid with L-and DL-histidine

Abstract

Crystals of the oxalic acid complex of L-histidine (orthorhombic P2₁2₁2₁; a=5.535(4), b=6.809(4), c=26.878(3) Å) R= 3.6% for 1188 observed reflections) contain histidine molecules and semi-oxalate ions in the 1:1 ratio, while the ratio is 1:2 in the crystals of the DL-histidine complex (monoclinic P2₁ lc; a=6.750(7), b=10.139(2), c=19.352(2) Å, β= 90.8°; R= 3.7% for 3176 observed reflections). The histidine molecule in the latter has an unusual ionization state with positively charged amino and imidazole groups and a neutral carboxyl group. The molecule has the sterically least favourable allowed conformation with the side chain imidazole ring staggered between the α-amino and the α- carboxyl (carboxylate) groups, in both the structures. The unlike molecules aggregate into separate alternating layers in both of them. There are elements of similarity in the aggregation patterns in the semi-oxalate layers in the two complexes, but the patterns in the amino acid layers are entirely different. Interestingly, the crystal structure of L-histidine semi-oxalate has broad similarities with that of DL-histidine glycolate, demonstrating how broad features of aggregation could be retained inspite of changes in chirality and composition. The unusual ionization state of the amino acid molecule in the DL-histidine complex is reflected in a hitherto unobserved aggregation pattern in its crystal structure.     

A critical survey of average distances between catalytic carboxyl groups in glycoside hydrolases

Published X‐ray crystallographic structures for glycoside hydrolases (GHs) from 39 different families are surveyed according to some rigorous selection criteria, and the distances separating 208 pairs of catalytic carboxyl groups (20 α‐retaining, 87 β‐retaining, 38 α‐inverting, and 63 β‐inverting) are analyzed. First, the average of all four inter‐carboxyl O^…O distances for each pair is determined; second, the mean of all the pair‐averages within each GH family is determined; third, means are determined for groups of GH families. No significant differences are found for free structures compared with those complexed with a ligand in the active site of the enzyme, nor for α‐GHs as compared with β‐GHs. The mean and standard deviation (1σ) of the unimodal distribution of average O^…O distances for all families of inverting GHs is 8 ± 2Å, with a very wide range from 5Å (GH82) to nearly 13Å (GH46). The distribution of average O^…O distances for all families of retaining GHs appears to be bimodal: the means and standard deviations of the two groups are 4.8 ± 0.3Å and 6.4 ± 0.6Å. These average values are more representative, and more likely to be meaningful, than the often‐quoted literature values, which are based on a very small sample of structures. The newly‐updated average values proposed here may alter perceptions about what separations between catalytic residues are “normal” or “abnormal” for GHs. Proteins 2014; 82:1747–1755. © 2014 Wiley Periodicals, Inc.     

The J-coupling Restrained Molecular Mechanics (JrMM) Protocol - An Efficient Alternative for Deriving DNA Endocyclic Torsion Angle Constraints Part II: Experimental Application of the JrMM Protocol

Abstract

The J-coupling restrained molecular mechanics (JrMM) protocol, which correlates deoxyribose endocyclic torsion angles and vicinal proton-proton torsion angle φ_{1′ 2′} in Part I of this study, is demonstrated to be a viable alternative to efficiently derive the endocyclic torsion angle constraints for the determination of the solution structures of DNA molecules. Extensive testing demonstrating the validity of the JrMM-derived torsion angle constraints in the restrained molecular dynamics and energy minimization structural refinement processes is performed theoretically using an energy-minimized B-DNA model and experimentally using a DNA hexamer d(CGTACG)₂. The results show that only a 0.2 Å difference exists between the RMSD values of the refined structures using the ideal and the JrMM-derived endocyclic torsion angle constraints. The JrMM-derived torsion angles are also determined to be in good agreement with the torsion angles derived through the use of the vicinal J-derived torsion angles. These results show that through the use of reliably measured J_{1′ 2′} values and computer simulation method, the endocyclic torsion angle constraints can be derived reliably and efficiently. Thus the JrMM method serves as an alternative strategy to generate endocyclic torsion angle constraints for the determination of the solution structures of DNA molecules.     

Topography of cyclodextrin inclusion complexes : Part I. Classification of crystallographic data of α-cyclodextrin inclusion complexes

The crystallographic and stoichiometric data obtained for 17 different inclusion complexes of α-cyclodextrin are reported. The cell dimensions and space-group symmetries reflect the packing arrangement of the torus-shaped host molecules and are largely determined by the size and ionic character of the guest molecules.In the series acetic acid, propionic acid, butyric acid, valeric acid, the first three complexes with α-cyclodextrin crystallize in a cage-type structure with space group P2₁2₁2₁, which is characteristic or small, non-ionic guest molecules. The valeric acid molecule seems to be too long to be accommodated in a cage structure; thus, the α-cyclodextrin molecules are arranged such that a structure consisting of parallel channels is formed. This packing is typical for the inclusion of long, thin, or ionic guest molecules. A third class of complexes with structures differing from the two described was also observed.A correlation exists between the type of inclusion complex and the volume required for a complex molecule: 1200–≈ 1400 ų for molecular guests, and 1400–1500 ų for ionic guests.     

DNA,oligosaccharides, and mononucleotides stimulate oligomerization of human lactoferrin

Using small‐angle X‐ray scattering (SAXS), light scattering (LS), and soft laser ablation we have shown that lactoferrin (LF) in solution at neutral pH is oligomerized in the absence of salt or at physiological salt concentrations. The level of oligomerization depends on the concentration of LF, KCl or NaCl, and on the duration of the protein storage in solution. At the concentrations comparable with those in human milk (1 ÷ 6 mg/ml), the average radius of gyration (R_g) values of LF can attain 400 ÷ 480 Å´, while fresh solution of previously lyophylized LF demonstrate a lower average R_g (50 ÷ 100 Å´), and R_g value characterizing the LF monomer formed at 1 M NaCl is 26.7 Å´. The addition of oligonucleotides, oligosaccharides, or mononucleotides to LF in the presence or in the absence of KCl with different level of initial oligomerization accelerates the oligomerization rate and increases the R_g values up to ～600 ÷ 700 Å´, which correspond to associates containing ten or more protein molecules. During gel filtration on Sepharose 4B, high‐degree LF oligomers dissociate nearly completely forming different degraded complexes, but in some cases it is possible to reveal small amount of a decamer. A possible role for oligomerization of LF, a highly polyfunctional protein, for its different biological activities is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

A hypothetical complex between crystalline flavocytochrome b2 and Cytochrome c

Flavocytochrome b₂ and cytochrome c are physiological electron transfer partners in yeast mitochondria. The formation of a stable complex between them has been demonstrated both in solution and in the crystalline state. On the basis of the three-dimensional structures, using molecular modeling and energy minimization, we have generated a hypothetical model for the interaction of these redox partners in the crystal lattice. General criteria such as good charge and surface complementarity, plausible orientation, and separation distance of the prosthetic groups, as well as more specific criteria such as the stoichiometry determined in the crystal, and the involvement of both domains and of more than one subunit of flavocytochrome b₂ led us to discriminate between several possible interaction sites. In the hypothetical model we present, four cytochrome c molecules interact with a tetramer of flavocytochrome b₂. The b₂ and c hemes are coplanar, with an edge-to-edge distance of 14 Å. the contact surface area is ca. 800 Ų. Several electrostatic interactions involving the flavin and the heme domains of flavocytochrome b₂ stabilize the binding of cytochrome c. © 1993 Wiley-Liss, Inc.     

Hydroperoxide and carboxyl groups preferential location in oxidized biomembranes experimentally determined by small angle X-ray scattering: Implications in membrane structure

We report small angle X-ray scattering (SAXS) data from large unilamellar vesicles as model membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocoline (POPC) and two oxidized species, namely its hydroperoxidized form POPC-OOH and 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC) lipid that has a carboxyl group at the end of its truncated sn-2 chain. The replacement of POPC by either POPC-OOH (POPC-OOH_xPOPC_1−x) or PazePC (PazePC_xPOPC_1−x), with oxidized lipid molar ratio x varying from 0.00 up to 1.00, permits to experimentally inspect changes in the membrane structural properties due to oxidation. The volume fraction distribution of each lipid chemical group along the bilayer is determined. The results quantify that 95% of the hydroperoxide group lies in the membrane polar moiety, near the carbonyl and phosphate groups, whereas just 5% of OOH group experiences the polar/apolar interface, for all values of x studied. In the case of PazePC up to x = 0.33, a bimodal distribution of the carboxyl group in the interior and polar regions of the lipid membrane is obtained, probably due to a dynamic movement of the shortened alkyl chain towards the water interface. The mean molecular area A gradually increases from 65.4 ± 0.4 Ų for POPC bilayers to 78 ± 2 Ų for pure POPC-OOH bilayers, whereas POPC-OOH membrane thickness resulted to be 20% thinner than the non-oxidized POPC membrane. For PazePC up to x = 0.33, A increases to 67 ± 2 Ų with 10% of membrane thinning. The SAXS results thus demonstrate how the lipid oxidation progress affects the membrane structural features, thus paving the way to better understand membrane damage under oxidative stress.     

The isolation of a soluble type III collagen precursor from rat skin

A soluble form of type III collagen has been isolated from the 1.0 M NaCl neutral salt soluble extract of rat skin. This component has a molecular weight of 350,000 and is converted by reduction and alkylation to three identical α-chains with molecular weight 118,000. Segment-long-spacing precipitates produced from the renatured disulfide-linked component are about 300 Å longer than collagen with extensions at both the amino and carboxyl terminal ends. Pepsin treatment removes both amino and carboxyl terminal extensions. These and radioisotope incorporation data lead to the conclusion that this component is a precursor of the [αl(III)₃] collagen.     

Cholic acid changes defense response to oxidative stress in soybean induced by <Emphasis Type="Italic">Aspergillus niger</Emphasis>

The oxidative stress and antioxidant systems in soybean leaves and roots infected with plant pathogen Aspergillus niger were studied following treatment with different concentrations of cholic acid. Several oxidative stress parameters were analyzed: production of superoxide (O₂ ^·−) and hydroxyl radicals (^·OH), lipid peroxidation (LP), and superoxide dismutase (SOD; EC 1.15.1.1) activity, as well as the content of reduced glutathione (GSH). Results showed that inoculation with A. niger led to the increase of O₂ ^·− production and GSH quantities in leaves and ^·OH in roots. The highest activity of SOD occured in infected plants treated with cholic acid in concentrations of 40 and 60 mg L⁻¹ which ultimately led to a decrease in O₂ ^·− production. Inoculation with Aspergillus in combination with elevated cholic acid concentrations also increased ^·OH production which is correlated with increased LP. These results may support the idea of using cholic acid as an elicitor to trigger hypersensitive response in plant cells. Use of cholic acid may also actively contribute to soybean plants defense response against pathogen attack.     

The structure of horse methaemoglobin at 2-0 A resolution

The structure of horse methaemoglobin has been redetermined by phase extension and refinement. This has improved our knowledge of the haem geometry and the stereochemistry of the interfaces between the subunits, and confirmed the disorder of the C-terminal residues. Using new four-circle diffractometer data between the limiting spheres of radius 10 and 2.0 Å^?1, the co-ordinates determined by Perutz et al. (1968a,b) were subjected to successive cycles of real-space refinement into electron density maps calculated with observed ¦F¦ values and phases derived from the latest refined model, until the reliability index had dropped from an initial value of 0.45 to 0.23. The positions of the iron atoms relative to the planes of the porphyrin rings were refined separately, and checked by Fourier syntheses based on anomalous scattering and by difference Fourier syntheses calculated with coefficients from which the iron contributions had been removed. The general root-mean-squared error in atomic positions is 0.32 Å; the probable error in the displacement of the iron atoms from the porphyrin planes is 0.06 Å. The difference Fourier synthesis, obtained after refinement of the protein was complete, showed 41 bound water molecules per asymmetric unit and also revealed five errors in amino acid sequence, one of which was confirmed chemically.The secondary structures of the subunits are stabilized by hydrogen bonds formed by main-chain NH and CO groups either with each other or with nearby polar side-chains. There are few internal hydrogen bonds linking the various chain segments; many of the external polar side-chains help to stabilize the tertiary structure by forming hydrogen bonds with each other or through bound water molecules. Several of the helical segments are irregular and the terminal residues are disordered. The contacts between the subunits are more polar than the earlier 2.8 Å map had led us to believe, because it had failed to show up the 15 bound water molecules at the α₁β₁ and the four at the α₁β₂ contact. Their inclusion has raised the number of hydrogen bonds between neighbouring subunits at α₁β₁ from five to 17 or possibly 19, and at α₁β₂ from two to six or possibly seven. The remaining 22 water molecules are distributed over the internal cavity and the molecular surface; most of them make hydrogen bonds with at least two polar groups of the protein. Despite several amino acid differences, the structure of the α₁β₁ contact, including the bound water, is the same as in human deoxyhaemoglobin (Fermi, 1975).     

Experimental and theoretical investigation of the molecular and electronic structure of 5-(4-aminophenyl)-4-(3-methyl-3-phenylcyclobutyl)thiazol-2-amine

The title molecule, 5-(4-aminophenyl)-4-(3-methyl-3-phenylcyclobutyl)thiazol-2-amine (C₂₀H₂₁N₃S), was prepared and characterized by ¹H-NMR, ¹³C-NMR, IR and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/c with a?=?9.4350(5) Å, b?=?11.2796(6) Å, c?=?18.4170(8) Å and β?=?113.378(3)°. In addition to the molecular geometry from X-ray experiment, the molecular geometry, vibrational frequencies, gauge including atomic orbital (GIAO) ¹H- and ¹³C-NMR chemical shift values and atomic charges distribution of the title compound in the ground state have been calculated using the Hartree–Fock (HF) and density functional method (DFT) (B3LYP) with 6-31G(d) basis set. To determine conformational flexibility, molecular energy profile of the title compound was obtained by semi-empirical (AM1) calculations with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 10°. Besides, frontier molecular orbitals (FMO) analysis was performed by the B3LYP/6-31G(d) method.     

An experimental and theoretical approach to the molecular structure of 2-{4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]thiazol-2-yl}isoindoline-1,3-dione

The title compound, 2-{4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]thiazol-2-yl}isoindoline-1,3-dione (C₂₄H₂₂N₂O₂S), was synthesized and characterized by IR-NMR spectroscopy and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/c with a?=?19.7799(13) Å, b?=?6.7473(4) Å, c?=?15.7259(9) Å and β?=?103.416(5)°. In addition, the molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) ¹H and ¹³C chemical shift values of the title compound in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (DFT/B3LYP) with 6–31G(d), 6–31 + G(d,p) and LANL2DZ basis sets, and compared with the experimental data. To determine conformational flexibility, molecular energy profile of the title compound was obtained by semi-empirical (AM1) calculations with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 5°. Besides, molecular electrostatic potential, frontier molecular orbitals (FMO) analysis and thermodynamic properties of the title compound were investigated by theoretical calculations.