Density functional theory of tautomerism and water-assisted proton transfer of glycoluril

Density functional theory and MP2 methods have been employed to study of proton transfer reaction in annular tautomerization of tetrahydroimidazo[4,5-d]imidazole-2,5(1H,3H)-dione (glycoluril). Ten different tautomers are possible for the tetrahydroimidazo[4,5-d]imidazole-2,5(1H,3H)-dione. For all molecules, the Gibbs free energy at 0 and 298 K was estimated. In addition variation of dipole moments and charges on atoms are studied in the gas phase and solution, the specific solvent effects with addition of one molecule of water near the electrophilic centers of tautomer and the NBO charges of atoms were investigated. NBO analysis shows that there is a strong interaction between nitrogen lone pairs and double bonds.     

Application of DFT and MP2 calculations on structural and water-assisted proton transfer in 3-amino-4-nitrofurazan

Density functional theory (DFT) and MP2 calculations have been employed to study of 3-amino-4-nitrofurazan molecule using the standard 6-311++G(d,p) basis set. The chemical properties of the 3-amino-4-nitrofurazan have been extensively studied. The geometries of molecules in the gas phase were optimized and compared with the crystallography of this substance. The results suggest that A form is the most stable form in the gas phase and it is the predominant tautomer in solution according to the DFT and MP2 calculations, respectively. In addition, variation of dipole moments in the gas phase, the specific solvent effects with addition of one molecule of water near the electrophilic centers of tautomers, the transition state of proton transfer assisted by a water molecule, the NBO charges of atoms and the potential energy surface were investigated. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are presented.     

Investigation of the Effect of Various Substituents on the Density of Tetrazolium Nitrate Salts as Green Energetic Materials

The substitution effect of various functional groups such as –NO₂, –CN, –N₃, –NF₂, and –NH₂ on the density of tetrazolium nitrate salts is investigated through multiple linear regression method. The methodology of this work introduces a new model, which related density of tetrazolium nitrate salts to the number of fluorine and nitrogen atoms, the presence of NF₂ groups, NO₂ groups, as well as CH₃ groups in the structural formula. The new reliable correlation shows that the NF₂ and NO₂ group can cause increasing the density of tetrazolium nitrate salts, especially NO₂, whereas the CH₃ group can decrease their density. The new proposed relationship has good reliability and predictability, so it can be used to design new rich nitrogen compounds based on tetrazolium nitrate salts as green energetic materials. These results are also tested for N,N′‐azo‐1,2,4‐triazolium nitrate salts, which is caused to derive another correlation. This correlation shows that the presence of NF₂ functional groups increases the density of N,N′‐azo‐1,2,4‐triazolium nitrate salts as well as the value of n_O/n_C.     

Structures,Unimolecular Fragmentations,and Reactivities of the Self‐Assembled Multimetallic/Peptide Complexes [Mnn(GlyGly‐H)2n−1]+ and [Mnn+1(GlyGly‐H)2n]2+

Complexes of Mn²⁺ with deprotonated GlyGly are investigated by sustained off‐resonance irradiation collision‐induced dissociation (SORI‐CID), infrared multiple‐photon dissociation spectroscopy, ion–molecule reactions, and computational methods. Singly [Mn_n(GlyGly‐H)_2n?1]⁺ and doubly [Mn_n+1(GlyGly‐H)_2n]²⁺ charged clusters are formed from aqueous solutions of MnCl₂ and GlyGly by electrospray ionization. The most intense ion produced was the singly charged [M₂(GlyGly‐H)₃]⁺ cluster. Singly charged clusters show extensive fragmentations of small neutral molecules such as water and carbon dioxide as well as dissociation pathways related to the loss of NH₂CHCO and GlyGly. For the doubly charged clusters, however, loss of GlyGly is observed as the main dissociation pathway. Structure elucidation of [Mn₃(GlyGly‐H)₄]²⁺ clusters has also been done by IRMPD spectroscopy as well as DFT calculations. It is shown that the lowest energy structure of the [Mn₃(GlyGly‐H)₄]²⁺ cluster is deprotonated at all carboxylic acid groups and metal ions are coordinated with carbonyl oxygen atoms, and that all amine nitrogen atoms are hydrogen bonded to the amide hydrogen. A comparison of the calculated high‐spin (sextet) and low‐spin (quartet) state structures of [Mn₃(GlyGly‐H)₄]²⁺ is provided. IRMPD spectroscopic results are in agreement with the lowest energy high‐spin structure computed. Also, the gas‐phase reactivity of these complexes towards neutral CO and water was investigated. The parent complexes did not add any water or CO, presumably due to saturation at the metal cation. However, once some of the ligand was removed via CO₂ laser IRMPD, water was seen to add to the complex. These results are consistent with high‐spin Mn²⁺ complexes.     

The convergence and stability analysis of the Jacobi collocation method for solving nonlinear fractional differential equations with integral boundary conditions

In this paper, we apply the Jacobi collocation method for solving nonlinear fractional differential equations with integral boundary conditions. Due to existence of integral boundary conditions, after reformulation of this equation in the integral form, the method is proposed for solving the obtained integral equation. Also, the convergence and stability analysis of the proposed method are studied in two main theorems. Furthermore, the optimum degree of convergence in the L₂ norm is obtained for this method. Furthermore, some numerical examples are presented in order to illustrate the performance of the presented method. Finally, an application of the model in control theory is introduced. Copyright © 2015 John Wiley & Sons, Ltd.     

A Nine‐Coordinated ZrIV Complex and a Self‐Assembling System Obtained from a Proton Transfer Compound Containing 2,6‐Pyridinedicarboxylate and 2,6‐Pyridinediammonium; Synthesis and X‐ray Crystal Structure

Starting with a zirconium salt and LH₂ , (pydaH₂)²⁺(pydc)^2?, (pyda=2, 6‐pyridinediamine; pydcH₂=2,6‐pyridinedicarboxylic acid), as a 1:1 proton transfer self‐associated compound, two different compounds were resulted. One of them is a new complex of Zr^IV with a flat pyridine containing ligand and structure of (pydaH)₂[Zr(pydc)₃] · 5H₂O (1) and the other, (pydaH)⁺(NO₃)^? (2) is an ion pair with no zirconium ion. The zirconium(IV) complex (1) is crystallized in triclinic system with space group and Z = 2, the crystallographic parameters are: a = 10.612(5) Å, b = 10.617(5) Å, c = 16.815(8) Å, α = 103.654(9)°, β = 95.821(9)°, γ = 98.891(9)° and R‐value for 16767 collected reflections is 0.0592. The ion pair (2) has crystals of monoclinic system with P2₁ space group and Z = 2. Its crystallographic parameters are: a = 3.6227(11) Å, b = 10.034(4) Å, c = 10.296(4) Å, β = 93.422(9)° and R‐value for 4031 collected reflections is 0.0521. The two compounds were characterized with elemental analysis, ESI/MS, NMR and IR spectroscopy.     

Oxalic Acid: An Efficient and Cost-Effective Organic Catalyst for the Friedländer Quinoline Synthesis under Solvent-Free Conditions

Summary. Oxalic acid is used as an efficient catalyst in the condensation of 2-aminoaryl ketones with carbonyl compounds leading to the formation of quinolines in excellent yields under solvent-free conditions. This methodology offers significant improvements for the synthesis of quinolines with regard to the yield of products, simplicity in operation, inexpensive reagents, and green aspects by avoiding toxic catalysts and solvents.     

Sulfate-selective PVC membrane electrode based on a strontium Schiff's base complex

A strontium Schiff's base complex (SS) can be used as a suitable ionophore to prepare a sulfate-selective PVC-based membrane electrode. The use of oleic acid (OA) and hexadecyltrimethylammonium bromide (HTAB), as additives, and nitrobenzen (NB), dibutyl phthalate (DBP) and benzyl acetate (BA) as solvent mediators, were investigated. The best performance was observed with a membrane composition PVC: NB: SS: HTAB of 30%: 62%: 5%: 3% ratio. The resulting sensor works well over a wide concentration range (1.0 x 10(-2)-1.0 x 10(-6) M) with a Nernstian slope of -29.2 mV per decade of sulfate activity over a pH range 4.0-7.0. The limit of detection of the electrode is 5 x 10(-7) M. The proposed sensor shows excellent discriminating ability toward SO4(2-) ions with regard to many anions. It has a fast response time of about 15 s. The membrane electrode was used to the determination of zinc in zinc sulfate tablets. The sensor was also used as an indicator electrode in the potentiometric titration of SO4(2-) against barium ion.     

Complex Formation of 1,10-Dibenzyl-1,10-diaza-18-crown-6 with Ni2+, Cu2+, Ag+ and Cd2+ Metal Cations in Acetonitrile–dimethylformamide Binary Solutions

Conductance measurements are reported for nickel(II), cupper(II), silver(I) and cadmium(II), salts in acetonitrile (AN)–dimethylformamide (DMF) binary solvents containing macrocyclic ligand, 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBDA18C6) at different temperatures. The changes in molar conductance caused by addition of DBDA18C6 to solutions were analyzed by non-linear least squares to give stability constants of 1:1 metal cation–DBDA18C6 complexes. The results show that the stabilities of the complexes are sensitive to solvent composition and in some cases the sequence of stabilities is changed with changing the composition of the mixed solvents. The values of thermodynamic quantities (ΔH°c and ΔS°c) for formation of DBDA18C6-Ni²⁺, DBDA18C6-Cu²⁺, DBDA18C6-Ag⁺ and DBDA18C6-Cd²⁺ complexes were obtained from temperature dependence of the stability constants and the results show that the values of ΔH°c and ΔS°c for these complexes are sensitive to the nature and composition of AN–DMF binary solutions, but they do not vary monotonically with the solvent composition.     

Thermal and photochemical isomerization of exocyclic 1,3-dienes: 1,1-diphenyl-3,4-bis(trimethylsilylmethylene)-1-silacyclopentane s-cis(E,E)

This paper describes the photochemical and the thermal isomerization of s-cis(E,E) 1,1-diphenly-3,4-bis(trimethylsilylmethylene)-1-silacyclopentane (1a). Under thermal conditions a 1,3-sigmatropic of the methylene hydrogen occurs, yielding the s-trans isomer (1b). The photochemical irradiation of (1a) at 300 nm for 1 h in deoxygenated benzene gives the corresponding s-cis(E,Z) isomer (1c) and then the s-cis(Z,Z) isomer (1d) after prolonged irradiation (3 h). There was no evidence for the formation of the corresponding cyclobutene resulting from the ring closure of the exocylic diene.