2-Aminopyridine derivative as fluorescence ‘On–Off’ molecular switch for selective detection of Fe3+/Hg2+

2-Amino-6-methyl-4-phenyl-nicotinonitrile 1, a 2-aminopyridine-based fluorescent compound, was found to be a fluorescent chemosensor for the detection of Fe³⁺ and Hg²⁺ ions over a number of other metal ions. Compound 1 was synthesized in one step using a multicomponent reaction, and characterized using common spectroscopic tools. During Fe³⁺/Hg²⁺ sensing the compound 1 followed a ‘switch-off’ mechanism. Further, compound 1 could sense Fe³⁺ over Hg²⁺ by its distinct absorption and fluorescence quenching behaviors. 1:1 complex formation of 1 with Fe³⁺ and Hg²⁺ was clearly understood from Job’s plot. The present work brings additional evidence on the importance of multicomponent reactions which could lead to the development of fluorescence chemosensor in one step for the selective detection of biologically important metal ions.     

Origin of methyl torsional barrier in 1-methyl-2-(1H)-pyridone

The laser induced fluorescence excitation and single vibronic excitation dispersed fluorescence spectra have been studied for supersonic jet cooled 1-methyl-2(1h)-pyridone. The methyl torsional bands and some low frequency vibrational transitions were assigned for both ground and excited states. The torsional parameters V(3)=244 cm(-1) and V(6)=15 cm(-1) for the ground state and V(3)=164 cm(-1) and V(6)=40 cm(-1) for the excited state were obtained. To get the insight into the methyl torsional barrier, ab initio calculations were performed and compared with the experimental results. Origin of potential barrier was traced by partitioning the barrier energy into changes in bond-antibond interaction, structural, and steric energies accompanying methyl rotation using natural bond orbital analysis. The role of local interactions in ascertaining the barrier potential reveals that its nature cannot be understood without considering the molecular flexing. The hyperconjugation between CHsigma(*) and ring pi(*) observed in lowest unoccupied molecular orbital (LUMO) stabilizes the methyl group conformer that undergoes a 60 degrees rotation in the excited state with respect to that of the ground state, and it is the change in LUMO that plays important role in the excited state barrier formation.     

Hydrogen bond-induced vibronic mode mixing in benzoic acid dimer: a laser-induced fluorescence study

Laser-induced dispersed fluorescence spectra of benzoic acid dimer in the cold environment of supersonic jet expansion have been reinvestigated with improved spectral resolution of measurements. The spectra are analyzed with the aid of the normal mode vibrations of the dimer calculated by the ab initio quantum chemistry method at the DFT/B3LYP/6-311+G(*) (*) level of theory. The analysis reveals that the low-frequency intermolecular hydrogen bond modes are mixed extensively with the carboxyl as well as aromatic ring vibrations upon electronic excitation. The mode mixing is manifested as the complete loss of mirror symmetry relation between the fluorescence excitation and dispersed fluorescence spectra of the S(1) origin, and appearance of large number of cross-sequence transitions when the DF spectra are measured by exciting the low-energy vibrations near the S(1) origin. The cross-sequence bands are found in all the cases to be the combinations of two nontotally symmetric fundamentals consisting of one of the intermolecular hydrogen bond modes and the other from the aromatic ring and carboxyl group vibrations. The implications of this mode mixing on the excited state dynamics of the dimer are discussed.     

High-resolution ultraviolet spectroscopy of p-fluorostyrene-water: evidence for a sigma-type hydrogen-bonded dimer

Ab initio calculations predict four stable conformational structures of the singly hydrated cluster of p-fluorostyrene: two out of plane with pi- and two in plane with sigma-type intermolecular hydrogen bonding between p-fluorostyrene and water. We employed mass-selective resonance-enhanced two-photon ionization high-resolution (70-MHz FWHM laser bandwidth) spectroscopy to partially resolve the rotational structure of the 0(0) (0) origin band of the S(1) <--S(0) electronic transition. A computer-aided fit based on genetic algorithms was used to analyze the experimental high-resolution spectrum and to determine the observed conformational structure. The good agreement between the experimental and the simulated spectra of the 0(0) (0) band and the assignment of the other prominent bands as inter- and intramolecular vibrational progressions clearly demonstrates that the anti in-plane conformer is the most abundant one in the molecular beam. The existence of the sigma-type hydrogen bond between p-fluorostyrene and water manifests that the electron attracting effect of fluorine dominates over the releasing mesomeric effect of the vinyl group and thus a pi-type hydrogen bonding with the aromatic ring is not favored in this case.     

Isolation and characterization of iridium(III) and iridium(V) complexes of 2-(arylazo)pyridine and studies of amine fusion reactions at the coordinated diazo-ligand

The reaction of IrCl3.3H2O with 2-(arylazo)pyridine (HL1) in boiling methanol has afforded [Ir(III)Cl2(L1)(HL1)](1) and [Ir(V)Cl4(HL1)]Cl (2). In complex , one of the two ligands [L1]- is orthometallated via coordination of an ortho-carbon of the aryl ring of [L1]- and one of the two azo nitrogens to form a five-membered chelate. X-Ray crystal structures of the two representative complexes, viz. 1a and 2a, have been solved. Notably, the Ir-N length (2.140(3) A)trans to the Ir-C bond in 1a is appreciably longer than the other three Ir-N lengths present in the same molecule. The N-N lengths in these two compounds lie close to that observed in the uncoordinated ligand. Thorough NMR studies were made to authenticate the carbon-bonded structure of compound 1a. In its 13C NMR spectrum, the resonance near delta 148 is assigned to the carbon bonded to the iridium metal center. UV-visible spectra along with the redox properties of these complexes are reported. The iridium(V) complex, 2 showed a reversible response near 1.40 V, presumably due to the iridium(V)-iridium(VI) couple. Several reductive responses at cathodic potentials, due to ligand reductions, were also observed. Metal promoted aromatic ring amination reactions at the coordinated HL1 ligand in complexes 1 and 2 were investigated. The products were characterized using X-ray diffraction.     

Higher Dimensional Cosmology with Some Dark Energy Models in Emergent, Logamediate and Intermediate Scenarios of the Universe

We have considered N-dimensional Einstein field equations in which four-dimensional space-time is described by a FRW metric and that of extra dimensions by an Euclidean metric. We have chosen the exponential forms of scale factors a and d numbers of b in such a way that there is no singularity for evolution of the higher dimensional Universe. We have supposed that the Universe is filled with K-essence, Tachyonic, Normal Scalar Field and DBI-essence. Here we have found the nature of potential of different scalar field and graphically analyzed the potentials and the fields for three scenario namely Emergent Scenario, Logamediate Scenario and Intermediate Scenario. Also graphically we have depicted the geometrical parameters named statefinder parameters and slow-roll parameters in the higher dimensional cosmology with the above mentioned scenarios.     

Microwave-assisted synthesis of benzo[4,5]imidazo[1,2-a]pyrimidines and pyrano[4,3-b]pyrans catalyzed by L-glutamine functionalized magnetic nanoparticles in water:ethanol mixture

In this work, we report an effective, one-pot syntheses of benzo[4,5]imidazo[1,2-a]pyrimidine and pyrano[4,3-b]pyran derivatives using L-glutamine functionalized nanoparticles (Fe₃O₄@SiO₂@L-glutamine NPs) under microwave irradiation. The organo-nanocatalyst underwent characterization through diverse techniques, including FT-IR, p-XRD, SEM, TEM, EDX, XPS, TGA, and VSM. Microwave irradiation and multicomponent reactions synergistically yield excellent product yields (≈80%–95%) in shorter reaction times (≈6–15 min) with a broader substrate scope. The organo-nanocatalyst displays notable catalytic efficacy, evidenced by high turnover numbers (TON) and turnover frequencies (TOF) across syntheses. This innovative protocol showcases exceptional efficiency, cost-effectiveness, and environmental friendliness, with advantages like minimal reaction conditions, easy catalytic recovery, recyclability, operational simplicity, and the use of eco-friendly solvents.     

Observational Data Fitting to Constrain Variable Modified Chaplygin Gas in the Background of Horava-Lifshitz Gravity

FRW universe in Horava-Lifshitz (HL) gravity model filled with a combination of dark matter and dark energy in the form of variable modified Chaplygin gas (VMCG) is considered. The permitted values of the VMCG parameters are determined by the recent astrophysical and cosmological observational data. Here we present the Hubble parameter in terms of the observable parameters Ω _{d m0}, Ω _{v m c g0}, H ₀, redshift z and other parameters like α, A, γ and n. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the χ ² test. The best-fit values of the parameters are obtained by 66 %, 90 % and 99 % confidence levels. Next due to joint analysis with BAO and CMB observations, we have also obtained the bounds of the parameters (A, γ) by fixing some other parameters α and n. The best fit value of distance modulus μ(z) is obtained for the VMCG model in HL gravity, and it is concluded that our model is perfectly consistent with the union2 sample data.