Tautomerism in 11-hydroxyaklavinone: a DFT study.

The antharquinone-based chromophore of 11-hydroxyaklavinone is present in the structure of an anticancer agent, daunomycin. On the other hand, aklavinone is the parent aglycone of certain anthracycline antibiotics that possess anti-cancer activity too. The structures of aklavinone and its 11-hydroxy derivative have many -OH groups, and two keto groups which may take place in certain tautomeric equilibria. Of these tautomeric forms, presently the one involving the anthraquinone based tautomers of 11-hydroxyaklavinone has been investigated quantum chemically in the framework of the density functional theory at the levels of RB3LYP/6-31G(d) and RB3LYP/6-31G(d,p).

A model study on the possible effects of an external electrical field on enzymes having dinuclear iron cluster [2Fe-2S].

Hydrogenases which catalyze the H(2)↔ 2H(+) + 2e(-) reaction are metalloenzymes that can be divided into two classes, the NiFe and Fe enzymes, on the basis of their metal content. Iron-sulfur clusters [2Fe-2S] and [4Fe-4S] are common in ironhydrogenases. In the present model study, [2Fe-2S] cluster has been considered to visualize the effect of external electric field on various quantum chemical properties of it. In the model, all the cysteinyl residues are in the amide form. The PM3 type semiempirical calculations have been performed for the geometry optimization of the model structure in the absence and presence of the external field. Then, single point DFT calculations (B3LYP/6-31+G(d)) have been carried out. Depending on the direction of the field, the chemical reactivity of the model enzyme varies which suggests that an external electric field could, under proper conditions, improve the enzymatic hydrogen production.

Spectrophotometric and chromatographic determination of insensitive energetic materials: HNS and NTO, in the presence of sensitive nitro-explosives.

As there are no molecular spectroscopic determination methods for the most widely used insensitive energetic materials, 2,2',4,4',6,6'-hexanitrostilbene (HNS) and 3-nitro-1,2,4-triazole-5-one (NTO), in the presence of sensitive nitro-explosives, two novel spectrophotometric methods were developed. For HNS and TNT mixtures, both analytes react with dicyclohexylamine (DCHA) forming different colored charge-transfer complexes, which can be resolved by derivative spectroscopy. The spectrophotometric method for NTO measures the 416-nm absorbance of its yellow-colored Na(+)NTO(-) salt formed with NaOH. TNT, if present, is pre-extracted into IBMK as its Meisenheimer anion forming an ion-pair with the cationic surfactant cetyl pyridinium (CP(+)) in alkaline medium, whereas the unextracted NTO is determined in the aqueous phase. The molar absorptivity (ε, L mol(-1)cm(-1)) and limit of quantification (LOQ, mg L(-1)) are as follows: for HNS, ε=2.75 × 10(4) and LOQ=0.48 (in admixture with TNT); for NTO, ε=6.83 × 10(3) and LOQ=0.73. These methods were not affected from nitramines and nitrate esters in synthetic mixtures or composite explosives. The developed methods were statistically validated against HPLC, and the existing chromatographic method was modified so as to enable NTO determination in the presence of TNT. These simple, low-cost, and versatile methods can be used in criminology, remediation/monitoring of contaminated sites, and kinetic stability modeling of munitions containing desensitized energetic materials.

Desensitization of TNAZ via Molecular Structure Modification and Explosive Properties - A DFT Study.

TNAZ (1,3,3-trinitroazetidine) is a highly nitrated four membered nitrogen heterocyclic ring with greater performance when compared to melt castable explosive, TNT (trinitrotoluene). Desensitization of explosives is a significant area in military use. One current method is to use additives and coatings for explosives, as in the case of RDX. Another tactic would be to attempt small molecular level chemical changes in the explosive that bring the expected decrease in sensitivity without noteworthy loss in performance. TNAZ has three nitro groups. We thought that conversion of the nitro groups to nitroso and amine groups may decrease the sensitivity. We have correlated the bond dissociation energies with sensitivity and h50 values obtained from Keshavarz relations. We have also investigated chemical hardness and Mulliken electronegativities employing the frontier molecular orbitals. Furthermore, the explosive properties, i.e. detonation velocity (D), and detonation pressure (P) have been questioned by using both Kamlet-Jacobs equations and Keshavarz relations. Detonation products and power index values have also been calculated. We have proved that molecular modification is an operative method in desensitization of TNAZ.

Velocity of detonation-a mathematical model.

Based on the principles of conservation of energy and momentum, a mathematical formula has been derived for the squares of detonation velocities of a large set of explosives. The equation is a function of the total energy and molecular weight of an explosive compound considered. A regressed equation has been obtained for a pool of explosives of various types including nitramines, aliphatic and aromatic nitro compounds. Also another regressed equation for nitramines only is given. For the regression, the total energies are obtained using DFT (UB3LYP/6-31G(d)). The regression statistics are given and discussed.

Tunneling effect and impact sensitivity of certain explosives.

Certain set of benzenoid nitro compounds are considered for DFT calculations at the level of B3LYP/6-31G(d). The output data are statistically analyzed in order to get some correlations between the various quantum chemical properties and the impact sensitivities of the compounds considered. Two regression equations are given. All the analyses indicate that the impact sensitivity values of these structures are highly dependent on the lowest unoccupied molecular orbital energy and partially dependent on the highest occupied molecular orbital energy which is the indication of occurrence of tunneling from ground state to excited state(s) during the explosion initiated by an impact.

Contemplation on spark sensitivity of certain nitramine type explosives.

Spark sensitivity of explosives is an important subject. Presently, some correlations are sought between the spark sensitivity and certain molecular orbital characteristics of some nitramine type explosives. For that purpose certain semi-empirical and DFT calculations have been carried out. Investigations have revealed that the nitramines considered undergo decomposition in the electric field mainly via their anionic states.

A DFT study on nitrotriazines.

In this study, all possible mono-, di- and tri-nitro-substituted triazine compounds have been considered as potential candidates for high-energy density materials (HEDMs) by using quantum chemical treatment. Geometric and electronic structures, thermodynamic properties and detonation performances of these nitro-substituted triazines have been systematically studied using density functional theory (DFT, B3LYP) at the level of 6-31G(d,p), 6-31+G(d,p), 6-311G(d,p), 6-311+G(d,p) and cc-pVDZ basis sets. Moreover, thermal stabilities have been evaluated from the homolytic bond dissociation energies (BDEs). Detailed molecular orbital (MO) investigation has been performed on these potential HEDMs. According to the results of the calculations, mono-, di- and tri-nitro-substituted derivatives of symmetric 1,3,5-triazine have been found to be more stable than their 1,2,3 and 1,2,4 counterparts.

A theoretical study on vomitoxin and its tautomers.

In the present work, the structural and electronic properties of vomitoxin (deoxynivalenol, a mycotoxin) and all of its possible tautomers have been investigated by the application of B3LYP/6-31G(d,p) type quantum chemical calculations. According to the results of the calculations, tautomer V(4) has been found to be the most stable one among all the structures both in the gas and aqueous phases. The calculations also indicated that, vomitoxin and V(2) possess the deepest and the highest lying HOMO levels, respectively. Hence, V(2) is to be more susceptible to oxidations than the others. On the other hand, V(5)(S) and vomitoxin have the lowest and the next lowest LUMO energies, respectively. Whereas, V(1) and V(2) possess quite highly lying (within the group) LUMO energy levels which result in comparatively unfavorable reduction potentials. Some important geometrical and physicochemical properties and the calculated IR spectra of the systems have also been reported in the study.

Computational studies on nitratoethylnitramine (NENA), its tautomers and charged forms.

An energetic material, nitratoethylnitramine (NENA), its tautomers and also its charged forms are considered quantum chemically, using various basis sets at the levels of ab initio and density functional theories (DFT). NENA has been found to be sensitive to negative charge development, resulting in rupture of ONO(2) bond. Also conformational and molecular dynamics (MD) studies have been performed on NENA. Various geometrical parameters, energies and infrared spectra have been obtained and discussed. Also, calculations indicate that s-cis conformation of NENA is slightly more stable than the s-trans and the tautomers of it have very comparable total energy values to NENA. On the other hand, on the basis of homolytic bond dissociation energies (BDE) for ONO(2) bond in the structures, it is clear that the presence of the tautomers in the bulk of NENA somewhat should decrease its sensitivity.

Quantum chemical treatment of nivalenol and its tautomers.

Nivalenol, a highly poisonous mycotoxin, and its possible tautomers have been considered theoretically by RHF/6-31G/d,p) and B3LYP/6-31G(d,p) calculations together with a semi-empirical PM3 method. The calculations revealed that some of the tautomers are more stable and exothermic than nivalenol. The calculated IR spectra as well as some geometrical and physicochemical properties of the structures considered have been presented.

Quantum chemical treatment of cyanogen azide and its univalent and divalent ionic forms.

An explosive material, cyanogen azide (CN4) and its univalent and divalent anionic and cationic forms have been studied quantum chemically by using different theoretical approaches. In this study, the structures considered have been screened for their relative stabilities. Also, they have been investigated whether the charged forms play a role in the usual explosion process or any electrical charging during storage cause explosion. Various quantum chemical properties are obtained and discussed. It has been found that the univalent cation and anion and divalent cation formations do not cause much change in the molecular structure as compared to the neutral cyanogen azide molecule, whereas the divalent anionic form exhibits drastic changes in the geometry, resulting in bond cleavage to eliminate nitrogen molecule.

A novel synthesis of bromobenzenes using molecular bromine.

Certain substituted bromobenzenes have been synthesized in acceptable yields using a novel Sandmeyer type reaction. The reactions are relatively quick and possibly proceed via a radical mechanism.

Sodium, ammonium, calcium, and magnesium forms of zeolite Y for the adsorption of glucose and fructose from aqueous solutions.

The kinetics of adsorption by sodium, ammonium, calcium and magnesium forms of zeolite Y from aqueous solutions containing 25% w/v of either one or an equimolar mixture of glucose (G) and fructose (F) have been studied batch-wise at 50 degrees C. The adsorption of aqueous pure G was fast, while that of aqueous pure F depended on the cationic form, approaching that of G on the Mg-Y, and slowing down in the sequence of Mg2+ > NH4+ > Ca2+ > Na+ of the cations. The adsorption behavior from solutions containing both G and F indicated significant hindering effects of F on G on Na-Y. Na-Y and Mg-Y did not exhibit rate-based selectivity, while Ca-Y an NH4-Y adsorbed G faster than F. Addition of CaCl2 to the mixture of Ca-Y and aqueous solution of G and F improved the separation, by hindering the adsorption of F. Addition of NH4Cl to the mixture of the sugar solution and NH4-Y, on the other hand, had a negative effect on the separation. NH4-Y was found to be desorbing about 30% of the adsorbed sugars and this value was found to be around 50% for Ca-Y. Re-adsorption experiments resulted in similar or somewhat higher percentages of amounts adsorbed compared to adsorption on fresh samples. Both NH4-Y and Ca-Y were found to be re-adsorbing around 50% of the sugars they adsorbed on fresh samples.

Quantum chemical study on 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) and some of its constitutional isomers.

Presently, certain isomeric compounds of NTO and their tautomers have been investigated by performing density functional theory (DFT) calculations at B3LYP/6-31G(d,p) and ROB3P86/6-311G(d,p) levels and also ab initio calculations at RHF/6-311G(d,p) level. The optimized geometries, vibrational frequencies, electronic structures and some thermodynamical values for the presently considered NTO isomers have been obtained in their ground states. Also, detonation performances were evaluated by the Kammlet-Jacobs equations, based on the calculated densities and heat of formation values. The homolytic bond dissociation energies (BDEs) (at ROB3P86/6-311G(d,p) level) of NNO(2) and CNO(2) for the molecules were calculated. Moreover, aromatic character of NTO and its isomers and tautomers were investigated by performing NICS calculations using the gauge invariant atomic orbital (GIAO) approach at the B3LYP/6-31G(d,p) and B3LYP/cc-pVDZ levels.

Ab initio and DFT study on 1,4-dinitroglycoluril configurational isomers: cis-DINGU and trans-DINGU.

cis-1,4-Dinitroglycoluril (1,4-dinitrotetrahydroimidazo[4,5-d]imidazole-2,5-(1H,3H)-dione, C(4)H(4)N(6)O(6), known as DINGU in the literature) is an important explosive regarded as one of the potential ingredients for LOVA (low vulnerability ammunition) applications. However, there is no study concerning trans-DINGU, to the best of our knowledge. Thus, in the present study the structural and electronic properties of the configurational isomers of DINGU (cis- and trans-isomers) have been investigated by performing density functional theory (DFT) calculations at B3LYP/6-31G(d,p), UB3LYP/6-31G(d,p) levels and also ab initio calculations at RHF/6-31G(d,p) and UHF/6-31G(d,p) levels. The optimized geometries, vibrational frequencies, electronic structures, and some thermodynamical values for the presently considered DINGU isomers have been obtained in their ground states. Comparing the calculated energy data (total electronic energy, heat of formation values and homolytic bond dissociation values of N-NO(2)) and the calculated bond lengths, cis-DINGU was found to be a more stable molecule than the trans-isomer.

Ab initio and DFT studies on nitrosoguanidine tautomers.

Isolated nitrosoguanidine tautomers have been subjected to 6-31G(d,p), 6-31G(d,p) /(MP2), B3LYP/6-311G(d,p) and B3LYP/6-311++G(d,p) type quantum chemical analyses in the gas phase. The geometrical features and energetics of some conformers of the tautomers are reported. The nitrosimine form has the highest stability than the others and the diazoic acid form is the least stable one. The nitrosoimine form has the highest HOMO and LUMO energies. Whereas, the nitrosamine form possesses the lowest HOMO and the diazoic acid form has the lowest LUMO energies.

Density functional theory calculations for [C(2)H(4)N(2)O(6)]((n)) (n=0, +1, -1).

The structural and electronic properties of neutral and mono ionic structures of isolated ethylene glycol dinitrate (EGDN) [C(2)H(4)N(2)O(6)]((n)) (n=0, +1, -1) have been investigated by performing density functional theory calculations at B3LYP level. The optimum geometry, vibrational frequencies, electronic structure and some thermo dynamical values of the structures considered have been obtained in their ground states. The calculations reveal that as the charge develops the bond lengths and angles change. In the anionic case charge accumulation causes NO(2) elimination as a result of esteric O-N bond cleavage.

An ab initio study on ethylenedinitramine and its monovalent ions.

An explosive material, ethylenedinitramine (EDNA), its mono and di aci forms, as well as its monovalent cation and anion forms have been considered for 6-31G (UHF) type ab initio quantum chemical treatment in order to investigate the stability of EDNA in the neutral form and when charges develop on it exposed to electrical fields during the storage, handling or explosion process. The calculations indicate stable species. The aci forms are less stable than EDNA itself and the anion form is more stable than the neutral and cation forms. Although, the charge development is accompanied by some elongation or contraction of bonds and deviation of bond angles also as compared to the neutral state, no bond rapture occurs.

The syntheses of some novel (naphthalen-1-yl-selenyl)acetic acid derivatives.

Some new (naphthalen-1-yl-selenyl)acetic acids derivatives 7a-d have been synthesized by two different methods, using naphthylselenols or naphthylselenocyanates. The structures of the products were investigated by spectroscopic methods.