Spectroscopic investigation (IR and NMR) and HOMO-LUMO analysis of aromatic imines using theoretical approach

In this work, the theoretical studies on the structure, FT-IR, NMR, and UV–Vis spectroscopy of (E)-N-benzylidenebenzenamine (A1) and (E)-N-(2, 4′-dichlorobenzylidene) propan-1-amine (A2) are presented. The optimized structure of the molecules, NMR and UV–Vis spectra analysis were determined by the Density Functional Theory (DFT) method using B3LYP/6-311G (d, p) basis set. For FT-IR analysis, both the HF and DFT methods were used in order to determine their accuracy and reliability in theoretical calculations. The computed result of DFT calculations in comparison with the experimental results showed that the DFT method gives a more accurate prediction. The infrared (IR) spectra for the imine molecules have been recorded in the region of 500–4000 cm^?1. The gauge-independent atomic orbital (GIAO) method has been used to evaluate the ¹³C and ¹H nuclear magnetic resonance (NMR) chemical shifts of the molecules. The computed results of NMR spectra of the molecules was found to be in good agreement with the experimental data. The UV–Vis spectra of the molecules were computed to determine the HOMO-LUMO energies in order to gain insight into their electronic properties. Mulliken population analysis on atomic charges of the molecules was also calculated using the HF (Hartree-Fock) and B3LYP method. All the computed results indicated that the B3LYP method provides satisfactory results and, therefore, can be employed to support experimental data. It also demonstrated a reliable approach towards characterization of molecules in chemical science.     

Rational design, synthesis, and spectroscopic and photophysical properties of a visible-light-excitable, ratiometric, fluorescent near-neutral pH indicator based on BODIPY

A visible-light-excitable, ratiometric, brightly fluorescent pH indicator for measurements in the pH range 5-7 has been designed and synthesized by conjugatively linking the BODIPY fluorophore at the 3-position to the pH-sensitive ligand imidazole through an ethenyl bridge. The probe is available as cell membrane permeable methyl ester 8-(4-carbomethoxyphenyl)-4,4-difluoro-3-[2-(1H-imidazol-4-yl)ethenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (I) and corresponding water-soluble sodium carboxylate, sodium 8-(4-carboxylatophenyl)-4,4-difluoro-3-[2-(1H-imidazol-4-yl)ethenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (II). The fluorescence quantum yield Φ(f) of ester I is very high (0.8-1.0) in the organic solvents tested. The fluorescence lifetime (ca. 4 ns) of I in organic solvents with varying polarity/polarizability (from cyclohexane to acetonitrile) is independent of the solvent with a fluorescence rate constant k(f) of 2.4×10(8) s(-1). Probe I is readily loaded in the cytosol of live cells, where its high fluorescence intensity remains nearly constant over an extended time period. Water-soluble indicator II exhibits two acid-base equilibria in aqueous solution, characterized by pK(a) values of 6.0 and 12.6. The Φ(f) value of II in aqueous solution is high: 0.6 for the cationic and anionic forms of the imidazole ligand, and 0.8 for neutral imidazole. On protonation-deprotonation in the near-neutral pH range, UV/Vis absorption and fluorescence spectral shifts along with isosbestic and pseudo-isoemissive points are observed. This dual-excitation and dual-emission pH indicator emits intense green-yellow fluorescence at lower pH and intense orange fluorescence at higher pH. The influence of ionic strength and buffer concentration on the absorbance and steady-state fluorescence of II has also been investigated. The apparent pK(a) of the near-neutral acid-base equilibrium determined by spectrophotometric and fluorometric titration is nearly independent of the added buffer and salt concentration. In aqueous solution in the absence of buffer and in the pH range 5.20-7.45, dual exponential fluorescence decays are obtained with decay time τ(1)=4.3 ns for the cationic and τ(2)=3.3 ns for the neutral form of II. The excited-state proton exchange of II at near-neutral pH becomes reversible on addition of phosphate (H(2)PO(4)(-)/HPO(4)(2-)) buffer, and a pH-dependent change of the fluorescence decay times is induced. Global compartmental analysis of fluorescence decay traces collected as a function of pH and phosphate buffer concentration was used to recover values of the deactivation rate constants of the excited cationic (k(01)=2.4×10(8) s(-1)) and neutral (k(02)=3.0×10(8) s(-1)) forms of II.     

Crystal Structures of (2-oxo-2H-Quinaxalin-1-yl)-acetic Acid and its Cobalt and Nickel Complexes and Their Comparison with (1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-acetic Acid

Abstract The crystal structures of (2-oxo-2H-quinaxalin-1-yl)-acetic acid and its cobalt and nickel complexes are determined. The (2-oxo-2H-quinaxalin-1-yl)-acetic acid (1) crystallizes in orthorhombic, Pbca, a = 12.8571(11) ?, b = 9.4267(8) ?, c = 15.0095(13) ?, the cobalt complex of (2-oxo-2H-quinaxalin-1-yl)-acetic acid (2) crystallizes as dihydrate in triclinic, P-1 space group with a = 4.81150(10) ?, b = 11.8631(2) ?, c = 12.4867(3) ?, α = 71.7800(10)°, β = 79.2490(10)°, γ = 84.9020(10)° whereas the nickel complex of (2-oxo-2H-quinaxalin-1-yl)-acetic acid (3) crystallizes in monoclinic, P2₁/c space group with a = 14.9210(5) ?, b = 4.81730(10) ?, c = 15.7672(5) ?. and β = 99.823(2)°. The crystal structure of the ligand and the complexes are compared with structures of (1,3-dioxo-1,3-dihydro-isoindol-2-yl)-acetic acid and its cobalt and nickel complexes. Index Abstract The crystal structures of (2-oxo-2H-quinaxalin-1-yl)-acetic acid and its nickel and cobalt complexes are compared with (1,3-dioxo-1,3-dihydro-isoindol-2-yl)-acetic acid and its corresponding complexes with nickel(II) and cobalt(II).      

Interaction of Polystyryl Radical with Tris Azido-Iron(III) Complex

The polymerization of styrene initiated by 2,2′-azobisisobutyro-nitrile (AIBN) had been studied in N, N-dimethylformamide (DMF) at 60°C in presence of tris azido-iron(III) complex. The complex was prepared in situ by mixing solid sodium azide with hexakis(N, N-dimethylformamide)iron(m) perchlorate, [Fe(DMF)₆] (ClO₄)₃, in the ratio 3:1. The nature of the complex formed was established by Job's method. The equilibrium constant for Fe³⁺ + 3N₃ ^? ? Fe(N₃)₃ determined by the limiting logarithmic method is 6.14 ± 10⁶ liter³/mole³. The velocity constant for the polystyryl radical towards the complex is 3.13 ± 10⁴ liter/mole-sec.     

Metallacycles of cadmium, mercury dicarboxylates

A series of linear coordination polymers, metallacycles of cadmium(II) and mercury(II) of flexible carboxylic acid ligands, RCH{3-CH(3)-,5-CH(3)-,6-(-OCH(2)CO(2)H)C(6)H(2)}(2), (when R = C(6)H(5), (H(2)L(1)); 2-NO(2)C(6)H(4)- (H(2)L(2)) and 3-NO(2)C(6)H(4)- (H(2)L(3))) are synthesized and characterized. [CdL(1) (py)(3)](n)·3nH(2)O (py = pyridine) is a linear coordination polymer, whereas [CdL(2)(py)(CH(3)OH)](2)·CH(3)OH is a dinuclear complex of cadmium with a Cd(2)O(2) type of core. The latter is obtained from reaction of cadmium(II) acetate with H(2)L(2) in methanol followed by reaction with pyridine. A similar reaction of cadmium(II) acetate with H(2)L(2) in dimethylformamide results in the formation of a cadmium metallacycle, namely [CdL(2) (py)(2)(H(2)O)](2)·H(2)O. The H(2)L(3) reacted with cadmium(II) acetate in the presence of pyridine to form a metallacycle [CdL(3)(py)(2)(H(2)O)](2)·3H(2)O. The ligand H(2)L(2) form mercury(II) metallacycle [HgL(2)(4-mepy)(2)](2) in the presence of 4-methylpyridine (4-mepy) and the ligand H(2)L(3) forms metallacycle [HgL(3)(3-mepy)(2)](2)·DMF in the presence of 3-methylpyridine (3-mepy). The potassium salts of H(2)L(1) and H(2)L(2) were found to be coordination polymers and these potassium coordination polymers were structurally characterized.     

Exploration of single molecule events in a haloperoxidase and its biomimic: localization of halogenation activity

In situ observation of single oxidation/halogenation events by catalytically generated hypobromite species using single molecule fluorescence microscopy allows monitoring of the diffusion behavior of these halonium species from the catalyst into the bulk solution. The fluororgenic probe specifically reacts with hypohalites, yielding fluorescein that can be detected with single molecule sensitivity. It was found for two investigated catalysts (Curvularia verruculosa enzymes and tungstate-exchanged LDH crystals) that in steady-state conditions hypobromite is able to diffuse over 800 nm in the bulk solution before it oxidizes organic substrates.     

4-amino- and 4-nitrodipicolinatovanadium(V) complexes and their hydroxylamido derivatives: synthesis, aqueous, and solid-state properties

A number of 4-substituted, dipicolinatodioxovanadium(V) complexes and their hydroxylamido derivatives were synthesized to characterize the solid state and solution properties of five- and seven-coordinate vanadium(V) complexes. The X-ray crystal structures of Na[VO2dipic-NH2].2H2O (2) and K[VO2dipic-NO2] (3) show the vanadium adopting a distorted, trigonal-bipyramidal coordination environment similar to the parent coordination complex, [VO2dipic]- (1), reported previously as the Cs+ salt. The observed differences in the chemical shifts of the complexes both in the 1H (ca. 0.7-1.4 ppm) and 51V (ca. 1-11 ppm) NMR spectra were consistent with the electron-donating or electron-withdrawing properties of the substituent groups, respectively. Stoichiometric addition of a series of hydroxylamine ligands (H2NOH, MeHNOH, Me2NOH, and Et2NOH) to complexes 1-3 led to the formation of seven-coordinate vanadium(V) complexes. The X-ray crystal structure of [VO(dipic)(Me2NO)(H2O)].0.5H2O (1c) was found to be similar to the previously characterized complexes [VO(dipic)(H2NO)(H2O)] (1a) and [VO(dipic)(OO-tBu)(H2O)]. While only slight differences in the 1H NMR spectra were observed upon addition of the hydroxylamido ligand, the signals in the 51V NMR spectra change by up to 100 ppm. The addition of the hydroxylamido ligand increased the complex stability of complexes 2 and 3. Evidence for a nonstoichiometric redox reaction was found for the monoalkyl hydroxylamine ligand. The reaction of an unsaturated five-coordinate species with a hydroxylamine to form a seven-coordinate vanadium complex will, in general, dramatically increase the amounts of the vanadium compound that remain intact at pH values near neutral.     

Non-isothermal decomposition kinetics of in-chain functionalized poly(MMA-co-ethylene)

Journal of Thermal Analysis and Calorimetry - Efficient incorporation of polar monomers in polyolefin can lead to many desirable properties in the parent chain. Herein, we report the synthesis of...     

Nickel,copper and zinc complexes of (2-methoxycarbonylmethylimino-5-methyl-thiazol-3-yl)-acetic acid

An ester of an imine containing dicarboxylic acid (2-methoxycarbonylmethylimino-5-methyl-thiazol-3-yl)-acetic acid methyl ester was prepared by the reaction of methylbromoacetate with 5-methyl-thiazol-2-ylamine. Base hydrolysis of this ester with sodium hydroxide gives the corresponding disodium salt of the diacid. The disodium salt of (2-methoxycarbonylmethylimino-5-methyl-thiazol-3-yl)-acetic acid (Na₂L) forms a mononuclear hexacoordinated complex [Ni(L)(H₂O)₃]2H₂O] with nickel, whereas it forms a pentacoordinated coordination polymer with zinc, having the composition {[Zn(L)(H₂O)₂]4H₂O}_n. A copper complex containing L and pyridine (py), with the composition [CuL(py)(H₂O)₂], has also been synthesized and characterized.     

On some of Ramanujan's Schläfli-type “mixed” modular equations

We give elementary proofs of seven Schläfli-type “mixed” modular equations recorded by Ramanujan on p. 86 of his first notebook. Previously, these equations were proved by Berndt by using the theory of modular forms. In the process, we also found three new Schläfli-type mixed modular equations of the same nature.