A comprehensive theoretical study was conducted on the thermal Curtius rearrangement of N,N-dimethylcarbamoyl azide in its syn and anti conformations, examining both concerted and stepwise pathways in the gas phase and various solvents. The syn conformer is consistently more stable than the anti conformer by 7.99-10.05 kcal mol-1 and rearranges via a single transition state along a concerted, exergonic pathway to form N,N-dimethylamino isocyanate. The anti conformer undergoes a two-step conversion through an intermediate, with an endergonic first step followed by an exergonic second step. In the gas phase, the concerted pathway dominates, proceeding 101-104 times faster than the stepwise mechanism, while in highly polar solvents the stepwise pathway becomes favored due to solvent effects on relative rates, with NBO analyses providing a rationale for the solvent-dependent rate variations. Potential energy profiles were analyzed at the B3LYP/6-311++G(2d,d,p) level within the electron localization function framework, combined with bonding evolution theory and Thom's catastrophe theory. The concerted pathway proceeds through eight structural stability domains (syn-DMCA:8-CF†TSC†F†E CC†-0:DMAI + N2), whereas the stepwise pathway involves five and eight domains in its first and second steps (anti-DMCA:5-C†CF†C†TS-0:NI + N2 and NI:8-FC†TSFEFCC†-0:DMAI), highlighting the role of the nitrene intermediate. Topological and electronic analyses reveal pronounced asynchronicity in both the concerted mechanism and the second step of the stepwise pathway.

Molecular geometries and 3D networks of two reported complexes with mixed ligands formulated as [Co(pydco)(bipy)(H2O)2] (1) and [Cu(Hpydco)(bipy)Cl] (2) (H2pydco = pyridine-N-oxide-2,5-dicarboxylic acid, bipy = 2,2′-bipyridine) were studied by density functional theory computations. The molecular units of each compound were optimized as neutral building blocks for their respective 3D networks (1-net and 2-net). Pertinent networks, in amount of or more than summation of binding energies of involved non-covalent forces, have been stabilized. Accordingly, the Grimme's D3 dispersion correction has been applied for accurate computation of those long-distance forces. Therefore, determination of binding energy of each involved non-covalent interaction has been calculated using B3LYP and Grimme’s DFT-D3 and QTAIM manners. The measured results of both methods interestingly are in good agreement.

An innovative and comprehensive theoretical investigation was conducted to examine the thermal Curtius rearrangement of malonyl azide in its syn-syn and syn-anti conformations, taking into account both the concerted and stepwise pathways. This study covered analyses performed in gaseous environments and a range of solvents. In both the gas phase and different solvents, the syn-syn conformation of malonyl azide proves to be more stable than the syn-anti conformation with a stability difference ranging from 4.15 to 4.99 kcal mol-1. It undergoes an exergonic concerted process with a single transition state, leading to the formation of syn-2-isocyanatoacetyl azide. Furthermore, syn-2-isocyanatoacetyl azide can be converted into methylene diisocyanate via a concerted pathway. In contrast, the rearrangement of the syn-anti conformation involves two transition states and an intermediate. The initial step is endergonic, followed by an exergonic subsequent step. The calculated Delta G values for the conversion of syn-syn-MA to syn-ICA and syn-ICA to MDI in the gas phase, determined at the CBS-QB3 level of theory, are -62.91 and -64.67 kcal mol-1, respectively. Meanwhile, the Gibbs free energies for the first and second steps of the rearrangement of syn-anti conformation are 10.51 and -77.98 kcal mol-1, respectively. Theoretical results indicate the dominance of the concerted pathway, surpassing the stepwise mechanism by roughly 104-106 and 104 times in both the gas phase and various solvents, respectively. Analyzing the electron localization function using the B3LYP/6-311++G(2d,d,p) level of theory unveils the catastrophe sequences for syn-syn malonyl azide and syn-2-isocyanatoacetyl azide structures, denoted as 8-CF dagger C dagger TSF dagger C dagger C dagger C and 9-CF dagger C dagger TSFC dagger FC dagger C-0, respectively. The Curtius rearrangement of the syn-syn malonyl azide conformer commences with the transformation of two valence bonding disynaptic attractors, where V1,2(N2,N3) merges into a single disynaptic attractor. This is followed by the division of the non-bonding monosynaptic attractor V(N1) into two non-bonding monosynaptic attractors. Subsequently, the N1-N2 bond breaks, eliminating a nitrogen molecule and altering the topological signature of C1-N1. This transformation leads to the consolidation of the pair of non-bonding monosynaptic attractors V1,2(N1) into a single non-bonding monosynaptic attractor V(N1). Then, the C1-C2 bond breaks, resulting in the formation of pseudo-radical centers on the C1 and C2 atoms. Following this, a transformation in the topological signature of C1-N1 occurs, leading to the elimination of pseudo-radical centers on the C1 atom and the formation of a C2-N1 bond. The results of ELF calculations indicate that the Curtius rearrangement of syn-ICA follows a method similar to that of syn-syn. The results indicate that the reaction follows a concerted mechanism but is highly asynchronous, with absolute asynchronicity indices of 0.801 and 0.763 for the Curtius rearrangement of syn-syn-MA and syn-ICA, respectively.

Density functional theory (DFT) calculations at the M06-2X/def2-TZVP level have been employed to investigate the atmospheric oxidation mechanism of anthracene (ANT) initiated by HO center dot. Direct hydrogen atom abstraction from the ANT using HO center dot takes place hardly at ambient conditions while addition of HO center dot to the C1, C2, and C4 sites are thermodynamically and kinetically more advantageous. The addition reactions are controlled by the aromaticity and the kinetic trends were justified by resonance stabilization energies. The rate constants were calculated by using the Rice-Ramsperger-Kassel-Marcus (RRKM) and canonical transition state theory (CTST) methods in conjugation with zero curvature tunneling (ZCT). The overall RRKM-bimolecular rate constant at ambient conditions is 6.72 x 10(-12) cm(3) molecule(-1) s(-1), is negatively dependent on the temperature and can be expressed as k(250-350)(1bar) = 3.92 x 10(-14) exp(1534.9/T). Contribution of the AD-C4 path in the overall reaction is about T70-80%, implying that the dependence of overall rate constant on pressure can be ignored. The kinetic data exhibit that the ANT is degraded during its long-range transport in the atmosphere and cannot be classified as persistent organic pollutants.

The conformational analysis of n-formyl-d-serine-d-alanine-NH2 dipeptide was studied using density functional theory methods at B3LYP, B3LYP‒D3, and M06‒2X levels using 6‒311 + G (d,p) basis set in the gas and water phases. 87 conformers of 243 stable ones were located and the rest of them were migrated to the more stable geometries. Migration pattern suggests the more stable dipeptide model bears serine in βL, γD, γL and the alanine in γL and γD configurations. The investigation of side‒chain‒backbone interactions revealed that the most stable conformer, γD–γL, is in the β‒turn region of Ramachandran map; therefore, serine-alanine dipeptide model should be adopted with a β‒turn conformation. Intramolecular hydrogen bonding in β‒turns consideration by QTAIM disclosed γD–γL includes three hydrogen bonds. The computed UV‒Vis spectrum alongside of NBO calculation showed the five main electronic transition bands derived of n → n* of intra‒ligand alanine moiety of dipeptide structure.

Abstract The conformational analysis of N-formyl-D-serine-D-alanine-NH2 dipeptide was comprehensively studied using the density functional theory methods in the gas and solution phases. The all-expected 35=243 stable conformers were explored, where 91 conformers were located, and the rest of them were migrated to the more stable geometries. Migration pattern suggests the more stable dipeptide model with the serine in βL, γD, γL and the alanine in γL and γD configurations. The investigation of side-chain–backbone interactions revealed that the most stable conformer, γD–γL, is in the β − turn region of the Ramachandran map; therefore, serine-alanine dipeptide model should be adopted with a β − turn conformation. QTAM consideration of the intramolecular hydrogen bonding in β-turns disclosed the highest stable conformer as γD–γL includes the three hydrogen bonds. The computed UV-Vis spectrum alongside of NBO calculation showed and explained the five main electronic transition bands derived of n→ n* of intra-ligand alanine moiety of dipeptide structure.

The complete theoretical study of thermal Curtius rearrangement of syn-syn and syn-anti conformers of oxalyl diazide, in the gas phase and in solution has been established for the first time. The inexplicit solvent effect was taken into account via the self-consistent reaction field (SCRF) method. The gas and solution phases of all optimized geometries of the mentioned conformers associated with the Curtius rearrangement along the concerted and stepwise pathways were reported using the polarized continuum model and non-electrostatic terms from the SMD universal solvation model. The Curtius rearrangement of syn-syn and syn-anti conformers was taken place via concerted and stepwise pathways, respectively. The syn-syn conformer of oxalyl diazide is more stable than the syn-anti conformer in the gas phase and solution, and rearranged to syn-carbonyl azide isocyanate via an exergonic concerted mechanism with a single transition state. Nevertheless, the rearrangement of syn-anti conformer occurred through the two transition states and an intermediate, which the first and second steps are endergonic and exergonic, respectively. Theoretical results point out that the concerted pathway is predominant with 102-106 and 104-105 times faster than the stepwise mechanism in gas phase and solution, respectively. Topological analysis of the electron localization function at the B3LYP/6-311++G (2d,d,p) level of theory indicate that the catastrophe sequence 1-6-C†TSC†F C†C-0 begins with the N4-N5 bond breaking, elimination of nitrogen molecule and increasing of non-bonding monosynaptic attractor on N4 atom, and then changing of topological signature of C2-N4 bond, breaking of C1-C2 bond, and formation of pseudo-radical centers on C1 and C2 atoms. Subsequently, annihilation of pseudo-radical centers on the C1 atom, change of topological signature of C2-N4 and formation of C1-N4 bond were executed. The obtained results of ELF calculations show that the reaction takes place via a concerted mechanism but highly asynchronous process.

Theoretical conformational analysis of N–formyl–L–serine–L–alanine–NH2 dipeptide model was investigated using B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) calculations. In this research, 243 total possible conformations of the dipeptide model were optimized including 87 stable conformers and the other disappeared ones migrated to more stable geometries. Migration pattern suggests more stability of the dipeptide model with the serine (ser) in βL, γL, and γD and the alanine (ala) in γD and γL configurations, along with 26 of the found conformers having β-turn structures. Our calculations reveal that the most stable conformer, γL+γD, is in β-turn region of Ramachandran map; therefore, serine-alanine (ser-ala) dipeptide model should be adopted with a β-turn conformation. The atoms in molecules (AIM) topological analysis was carried out to characterize the nature of the intramolecular hydrogen bonding in β-turn structures. The γL+γD, including three hydrogen bonds, has the highest stability, while αLaγL as the most unstable β-turn conformer bears two and one hydrogen bonds at the B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) levels of theory, respectively.

Fluoxetine is used as an effective antidepressant in psychopharmacology. As a pharmaceutical and personal care product (PPCP) found in superficial waters, fluoxetine influences the wildlife that inhabit these waters. This study was conducted to determine the fluoxetine concentration even in trace quantity in the hospital wastewater, using a solid-phase microextraction (SPME) silica fiber layered with single-walled carbon nanotubes (SWCNTs). An instrumental setup including off-line SPME, which uses a simple carbon nanotube (CNT) to bond capillary column combined with fluorescence spectrometry, was arranged as a sensitive method for the quantification of fluoxetine in real sample. A one at-a-time optimization strategy was applied for optimizing extraction parameters such as extraction time, stirring rate, desorption time, pH, and salt effect on the extraction, preconcentration and determination of fluoxetine in aqueous samples. The advantages of the developed method were: being simple to use with shorter amounts of time for analysis, lower equipment costs, thermal stability of fiber, and high relative recovery in contrast to conventional methods of analysis. Linear ranges were within 0.1-30 µg/L and the detection limit for the fluoxetine was 1×10-4 µg/L.

Fluoxetine (N-methyl-c-[4-phenoxy] benzenepropanamine) (FLU) is the parent drug of the selective serotonin reuptake inhibitor (SSRI) antidepressant class, which has emerged as a major therapeutic advance in psychopharmacology. It has been approved worldwide in the therapy of major depression and has also demonstrated to be effective in the treatment of other syndromes, such as bulimia nervosa, panic fits and obsessive-compulsive disorder. An instrumental setup including off-line solid phase microextraction coupled to fluorescence spectrometry has been constructed to improve the sensitivity for quantification of fluoxetine in real samples. The method was applied to analysis of spiked wastewater samples with the recovery 90.17%. This research provides an overview of the new developments in material and format technology that improve the extraction of semi-polar compounds in several extraction techniques. It mainly includes a solid-phase microextraction, that uses a simple carbon nanotube bonded silica fiber. The influences of microextraction conditions such as pH, ageing time, salt effect, performance and desorption conditions were investigated. It is a promising pre-treatment method for the fast, trace analysis in many complicated matrixes such as aqueous and biological samples. The method has a high enrichment factor and excellent selective cleanup of sample. Reasonable relative recovery was also obtained. The linear calibration curves was obtained in the range of0.1-10 mu g.L-1. We used the method to pre-concentration and clean up fluoxetine from real samples.

An ab initio and density functional theory (DFT) study on conformational analysis of tripeptide model HCO-GLY-L-ILE-GLY-NH2 is presented. The tripeptide was scanned around initial, central, and final residues, separately while for every scanning procedure the two other residues had been kept in the beta conformation and side chain (SC) dihedral angles were maintained on the gauche-(g(-)) state (chi(1), chi(2) = -60). Conformers (beta(L), gamma(L), gamma(D), alpha(D), epsilon(D)), (beta(L), gamma(L), gamma(D)), and (beta(L), gamma(L), gamma(D), epsilon(L)) were found through scanning of the tripeptide around initial, central, and the last amino acids, respectively. The geometry optimization and frequency calculation were performed at the HF/ 6-31G(d) and B3LYP/ 6-31G(d) levels of theory. In followings, comparison of the calculated thermodynamic data presents. beta(L)beta(L)beta(L) as the most stable conformer among the tripeptide minima on Ramachandran map.

Three new organic–inorganic hybrid materials based on two important heteropolyoxometalates namely Preyssler (=K12.5H1.5[Na(H2O)P5W30O110]·35H2O) and Wells–Dawson (=K6[P2W18O62]·10H2O) anions, namely, (Hpro)9(Hleu)3K2[Na(H2O)P5W30O110]·25H2O (1), (Hpro)4(Hasp)[HP2W18O62]·20H2O (2), and (Hpro)11K3[Na(H2O)P5W30O110]·18H2O (3) where pro, leu, and asp are proline, leucine, and asparagine, respectively, were prepared and identified by elemental analysis, infrared and proton nuclear magnetic resonance spectroscopies, and thermogravimetric analysis. The hybrid materials are made up of positively charged amino acids, [Na(H2O)P5W30O110]14− and [P2W18O62]6− anions, and H2O molecules of crystallization. These constituents’ fragments held together into a three-dimensional supermolecular network through non-covalent interactions. The protonation constants of the amino acids used, and Preyssler and Wells–Dawson species in all possible protonated forms, the equilibrium constants for binary systems of proline–asparagine and proline–leucine, and the stoichiometry and stability constants of the corresponding binary and ternary hybrids with Preyssler and Wells–Dawson heteropolyoxometalates in aqueous solution were investigated by potentiometric pH titration method. The stoichiometries of the most hybrid species in solution were compared with the corresponding hybrids in the solid phase, in detail.

3-Amino-1-phenyl-2-buten-1-one (APBO) was synthesized by amination of benzoylacetone (BA) and its structure was studied by X-ray crystallographic method. The geometry of APBO was also optimized by means of density functional theory (DFT) and ab initio calculations and the results were compared with the X-ray crystallographic data. The vibrational fundamentals predicted within harmonic model, calculated at the B3LYP/6-311++G**, and by anharmonic model, calculated at the B3LYP/6-31G** level, display excellent agreement with the measured data. The proposed assignments are further confirmed by observing the deuterium isotopic shifts of different bands through predictions by the same theoretical method. The theoretical results obtained for APBO were compared with those of 4-amino-3-penten-2-one (APO).

•“A” and “C” are the most and the least stable tautomers, respectively.•The rate constants for interconversions highly decrease in solution.•The interconversion barrier heights in presence of two water molecules are very low.

Betamethasone sodium phosphate ( BMNaP ) has been employed as an electroactive material in the design of an ion-selective electrode ( ISE ). The electrode incorporates PVC membrane with betamethasone sodium phosphate-lidocaine ion pair complex. The influences of membrane composition, temperature, pH of the test solution, and the interfering ions on the electrode performance were investigated. The sensor exhibits a Nernstian response for betamethasone sodium phosphate ions over a relatively wide concentration range (1.0 × 10 −1 to 1.0 × 10 −5 M) with a slope of 28.4 ± 0.9 mV per decade at 25°C. It can be used in the pH range 4.0–10.0. The isothermal temperature coefficient of this electrode amounted to −0.0008 V/°C. The membrane sensor was successfully applied to the determination of betamethasone sodium phosphate in pharmaceutical products.

A complete conformational analysis of the keto and enol forms of ethyl benzoylacetate (EBA), a β-ketoester, was carried out by ab initio calculations, at the density functional theory (DFT) level. The relative stabilities of cis-enol and keto forms were calculated in the gas phase and in solution. The intramolecular hydrogen bond characters of the most stable enol forms of EBA are discussed and compared with those of benzoylacetone (BA).Harmonic vibrational frequencies and 1H and 13C NMR chemical shifts of the most stable enol and keto forms were also calculated at the B3LYP/6-311++G** level and compared with the experimental data.

This paper is a descriptive report focusing on the trends of complex formation of palladium(II) and 4-2-(pyridyl azo)-resorcinol in different media under optimized conditions by using Uv/vis. spectrophotometric technique. All the affecting chemical variables have been investigated. At first, by application of job and mole ratio methods the stoichiometric M:L ratio was confirmed to be 1:1. By calculation the mean molar absorptivity coefficient and equilibrium concentration of complex, its stability constants were determined over a wide range of ionic strengths in presence of KCl as the background salt. The results showed the thermodynamically endurance of the complex and applicability of utilization of organic solvents. Satisfactory agreement between experimental and theoretical formation constants verifies the accuracy of the proposed method.