Journal of Chemical Sciences最新文献

The catalyst Y(NO₃)₃, 6H₂O exhibited remarkable activity in the aza-Michael addition of various aromatic and aliphatic amines with acrylonitrile at ambient temperature in a protic solvent. The method is selective for the monocyanoethylation of primary aromatic amines, aliphatic secondary amines, and sterically hindered aliphatic amines. Phenols and active methylene compounds do not undergo cyanoethylation. Thiophenol, in the presence of yttrium nitrate, promotes the polymerization of acrylonitrile. The water solubility and high catalyst stability make the process of removing the catalyst from the product easy. Direct aqueous workup of the reaction mixture could lead to the isolation of cyanoethylation products up to 99.9% purity.

Graphical Abstract

• Selective mono-cyanoethylation at the primary aromatic amine, especially electron-rich aromatic amines

• Excellent regio-selectivity in the presence of Carbon and Oxygen nucleophiles

• The reported condition could be used to polymerize acrylonitrile in the presence of thiophenol.

• Reaction is facile for electron-rich aromatic amine.

• Highly sensitive to the steric effect at the nitrogen center

State-average complete active space self-consistent field (SA-CASSCF) calculation followed by multi-reference configuration interaction (MRCI) treatment of low-lying states of BNB radical, cation as well as anion have been undertaken in order to estimate the non-adiabatic coupling terms (NACT) between different pairs of the low-lying states. Numerical values of NACT’s have been used to analyze the possibility of symmetry breaking of different states of the taken species.

Graphical Abstract

We employed the wavelength-interrogated surface plasmon resonance (SPR) method to characterize the real-time kinetics of urea-urease hydrolysis reaction in response to a CO₂-free N₂ environment and CO₂-enriched ambient reaction medium. We established that a simple label-free SPR probe could accurately extract kinetic parameters from the nature of the sharp jump of the SPR wavelength shift in the reaction profile. The kinetic analysis showed that CO₂ production increases with increasing reaction time irrespective of CO₂-free N₂ or CO₂-enriched reaction environment. We also explored the essential insights into the isotopic fractionations of ¹²CO₂, ¹³CO₂, ¹²C¹⁸O¹⁶O in the reaction medium utilizing integrated cavity output spectroscopy. The plasmonic system measured the reaction rate in the order of 10^-7 M/s for urea species in the presence of the urease enzyme. This study deepens our understanding of plasmonic-based enzymatic urea hydrolysis in real time and opens a new way to quantify chemical reaction kinetics for various other systems.

Graphical abstract

This is the first detailed experimental investigation of the real-time kinetics of urea-urease hydrolysis reaction exploiting wavelength-interrogated surface plasmon resonance method in response to produced CO₂ in the CO₂-free N₂ environment and CO₂-enriched ambient reaction medium utilizing integrated cavity output spectroscopy.

Two bis(dithiolene)nickel(II) complexes of the type [Ni(L)₂] [L = 1,2-di(4-chlorophenyl)ethene-1,2-dithiolate (1) and 1,2-di(4-bromophenyl)ethene-1,2-dithiolate (2)] have been synthesized and characterized by different chemical and physicochemical methods. 1 was characterized by different spectroscopic and spectrometric techniques. The molecular structure of 2 was derived from the single crystal X-ray diffraction. The electrochemical activities of both complexes were investigated by cyclic voltammetry. Both the complexes were found to exhibit intense near-infra-red (NIR) absorptions.

Graphical Abstract

Two isostructural bis(dithiolene)nickel(II) complexes of general formula [Ni(L)₂] [L = 1,2-di(4-chlorophenyl)ethene-1,2-dithiolate (1) and 1,2-di(4-bromophenyl)ethene-1,2-dithiolate (2)] have been synthesized and characterized by different chemical and physicochemical methods. 2 was crystallized, and its molecular structure was derived from the single crystal X-ray diffraction. In spite of several efforts, crystallization of 1 was not possible. 1 was characterized by several spectroscopic and spectrometric methods. Redox activities of ligands of both complexes were investigated by cyclic voltammetry. Both the complexes were found to exhibit intense near-infra-red (NIR) absorptions.

In this work, Nested Monte Carlo (NMC) simulation was done for symmetric and asymmetric ionic systems where the energy function is described by a combination of hard-sphere and Coulomb interaction (the primitive model). In the NMC method, Monte Carlo (MC) moves for the primary chain (where the energy function is the primitive model) is given by running a short MC trajectory using an auxiliary potential reducing the computational cost significantly. The Debye-Hückel (DH) potential was used as the auxiliary potential in our work. It is shown that with a careful choice of Debye length in the DH potential, and length of the short MC run in the auxiliary chain, the NMC method gives the same result as the more expensive MC simulation using full Ewald summation in the primitive model. Implementing the minimization of the Kullback–Leibler (KL) divergence between the pair-correlation function of the standard (without any auxiliary potential) MC simulation and NMC, a simple algorithm was also presented to develop good DH-like potentials to be used as auxiliary potentials in the nested MC run. Overall, this technique significantly reduces the Ewald summation technique's computational cost and can be applied to any atomic and molecular system with coulombic interaction in the potential energy function.

Graphical abstract

Nested Monte Carlo (NMC) simulations for symmetric and asymmetric ionic systems are performed, where Monte Carlo (MC) moves for the primary chain are given by running a short MC trajectory using an auxiliary potential. Excellent agreement has been shown between the pair correlation functions calculated from NMC, and standard Ewald simulations.

In this work, we performed high-level quantum chemical calculations to understand the comparative efficiency of Ti₃C₂ and oxygen-functionalized Ti₃C₂ (Ti₃C₂O₂) clusters for the catalytic conversion of N₂ to NH₃. The global minima structures of N₂-free and N₂-adsorbed cluster were predicted using the ABC algorithm. Accordingly, N₂ can be adsorbed on Ti atoms in a side-on fashion. Binding energy, Wiberg bond index, and Bader charge analyses suggest that the N₂-binding ability of the Ti₃C₂O₂ cluster is far better than that of the Ti₃C₂ cluster. Relative free energy diagrams indicate that cluster-catalyzed NH₃ synthesis prefers to follow the distal pathway. The calculation of the energetic span model concludes that catalytic conversion of N₂ to NH₃ on Ti₃C₂O₂ possesses a lower effective activation barrier than that on the Ti₃C₂ cluster, which implies that the Ti₃C₂O₂ is a more efficient catalyst than Ti₃C₂ for the synthesis of NH₃. Moreover, from the comparison with other metal clusters like V₃C₂O₂ and Nb₃C₂O₂, we find that although the latter cluster possesses comparatively less energy span N₂-philicity of Ti₃C₂O₂ is found to be far higher than that of Nb₃C₂O₂ cluster. Thus, the present study will provide a molecular-level understanding of improved N₂ reduction efficiency of the Ti₃C₂ cluster through O-functionalization.

Graphical Abstract

Herein, we have performed quantum chemical calculations to understand the comparative efficiency of Ti₃C₂ and oxygen-functionalized Ti₃C₂ (Ti₃C₂O₂) clusters for the catalytic conversion of N₂ to NH₃. We found that oxygen functionalization can dramatically enhance the N₂ reduction efficiency of the Ti₃C₂ cluster.

Acetone photochemistry upon excitation by vacuum ultraviolet (VUV) radiation of photon energy 7.75 eV has been investigated under a cryogenic condition of an argon matrix (8 K) and also by shining the molecule seeded in an effusive beam of argon prior to matrix deposition on a pre-cooled KBr window, where the photo-products get trapped in the argon matrix. Product analysis by infrared spectroscopy reveals appearance of the characteristic enolic O-H stretching fundamental at 3622 cm^-1 and other bands in the infrared fingerprint region, including C=C stretching only in the gas phase. The findings reveal the opening of a new isomerization reaction channel of acetone over the popular Norrish type-I α-CC bond cleavage upon VUV excitation to high-lying Rydberg states.

Graphical abstract:

SYNOPSIS Photochemical transformation of acetone upon excitation by vacuum ultraviolet radiation of photon energy 7.75 eV is reported under a cryogenic condition of an argon matrix (8 K). Infrared spectroscopic analysis of the products reveals that acetone isomerizes to the enolic form, 1-propene-2-ol, upon excitation to the high-lying Rydberg states.

Developing fluorescence probes with a turn-on model for picric acid (PA) detection is a challenge due to its fluorescence quenching property. In this work, a novel multi-branched triphenylamine Schiff base derivative (TPAS) was designed, synthesized, and characterized. TPAS performed well in PA detection, exhibiting weak emission in organic solvents and aqueous environments. However, bright fluorescence was observed in the aqueous solution of TPAS after adding PA. Moreover, the response of TPAS to PA was not affected by the other nitroaromatic compounds and had a limit of detection of 43 nM, which was lower than most of the reported PA probes. According to the mechanism study, the increased fluorescence was caused by the PA-induced hydrolysis of the Schiff base to the highly emissive amino precursor. This work provides new insights into designing novel PA probes with a turn-on model.

Graphical abstract

A novel multi-branched triphenylamine Schiff base derivative (TPAS) was used for picric acid turn-on sensing with a lower limit of detection by inducing the hydrolysis of the Schiff base to the highly emissive amino precursor.