Search

A bifunctional, microporous ZnII metal-organic framework, [Zn2(NH2BDC)2(dpNDI)] n (MOF 1) (where, NH2BDC=2-aminoterephthalic acid, dpNDI= N, N′-di(4-pyridyl)-1,4,5,8-naphthalenediimide) has been synthesized solvothermally. MOF 1 shows an interesting two-fold interpenetrated, 3D pillar-layered framework structure composed of two types of 1D channels with dimensions of approximately 2.99×3.58 Å and 4.58×5.38 Å decorated with pendent −NH2 groups. Owing to the presence of a basic functionalized pore surface, MOF 1 exhibits selective adsorption of CO2 with high value of heat of adsorption ( Qst=46.5 kJ mol−1) which is further supported by theoretically calculated binding energy of 48.4 kJ mol−1. Interestingly, the value of Qst observed for MOF 1 is about 10 kJ mol−1 higher than that of analogues MOF with the benzene-1,4-dicarboxylic acid (BDC) ligand, which establishes the critical role of the −NH2 group for CO2 capture. Moreover, MOF 1 exhibits highly selective and sensitive sensing of the nitroaromatic compound (NAC), 2,4,6-trinitrophenol (TNP) over other competing NACs through a luminescence quenching mechanism. The observed selectivity for TNP over other nitrophenols has been correlated to stronger hydrogen bonding interaction of TNP with the basic −NH2 group of MOF 1, which is revealed from DFT calculations. To the best of our knowledge, MOF 1 is the first example of an interpenetrated ZnII-MOF exhibiting selective adsorption of CO2 as well as efficient aqueous-phase sensing of TNP; investigated through combined experimental and theoretical studies. [ABSTRACT FROM AUTHOR]

In this article, we put forward a resolution to the prolonged ambiguity in energy band gaps between theory and experiments of fabricated graphene nanoribbons (GNRs). Band structure calculations using density functional theory are performed on oxygen-passivated GNR supercells of customized edge configurations without disturbing the inherent sp² hybridization of carbon atoms. Direct band gaps are observed for both zigzag and armchair GNRs, consistent with the experimental reports. In addition, we provide an explanation of the experimentally observed scattered band gap values of GNRs as a function of width in a crystallographic orientation on the basis of edge configurations. We conclude that edge configurations of GNRs significantly contribute to band gap formation in addition to its width for a given crystallographic orientation and will play a crucial role in band gap engineering of GNRs for future research on fabrication of nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Photoredox catalysis provides a green and sustainable alternative for C-H activation of organic molecules that eludes harsh conditions and use of transition metals. The photocatalytic C-N borylation and C-H arylation mostly depend on the ruthenium and iridium complexes or eosin Y and the use of porphyrin catalysts is still in infancy. A series of novel 21-thiaporphyrins (A 2 B 2 and A 3 B type) were synthesized having carbazole/phenothiazine moieties at their meso-positions and screened as catalysts for C-N borylation and C-H arylation. This paper demonstrates the 21-thiaporphyrin catalyzed C-N borylation and het-arylation of anilines under visible light. The method utilizes only 0.1 mol % of 21-thiaporphyrin catalyst under blue light for the direct C-N borylation and het-arylation reactions. A variety of substituted anilines were used as source for expensive and unstable aryl diazonium salts in the reactions. The heterobiaryls and aryl boronic esters were obtained in decent yields (up to 88 %). Versatility of the 21-thiaporphyrin catalyst was tested by thiolation and selenylation of anilines under similar conditions. Mechanistic insight was obtained from DFT studies, suggesting that 21-thiaporphyrin undergo an oxidative quenching pathway. The photoredox process catalyzed by 21-thiaporphyrins offers a mild, efficient and metal-free alternative for the formation of C-C, C-S, and C-Se bonds in aryl compounds; it can also be extended to borylation reaction., (© 2024 Wiley-VCH GmbH.)

The rotational dynamics of isocyanogen (CNCN) is studied for its collision with para (p-) and ortho (o-) hydrogen (H2) in the temperature range of 1-100 K. These temperatures correspond to the cold dense molecular clouds in the interstellar medium where molecular hydrogen is the primary collider. An ab initio 4D potential energy surface (PES) is constructed keeping the two molecules under rigid rotor approximation. The PES is generated using the CCSD(T)-F12b/AVTZ level of theory. The 4D PES is further fitted into a neural network (NN) model, which can augment the surface and account for missing data points within spectroscopic accuracy. This NN-fitted PES is then expanded over a bispherical harmonics function to get radial terms, which are expressed into analytic functions. Thereafter, the cross sections (σ) are computed for rotational transitions of CNCN (j → j') using the close-coupling and centrifugal sudden methods for both p-H2 (jc = 0) and o-H2 (jc = 1) collision till 194 cm-1. In addition, p-H2 (jc = 0, 2) cross sections are also computed using the centrifugal sudden approximation method. The collisional rates are achieved by taking the Boltzmann distribution of σ over the translational energy of H2 till 100 K. Finally, the CNCN-H2 rates are compared to CNCN-He and NCCN-H2 collisional rates. Comparing even and odd transitions for the CNCN-H2 rates show a propensity toward higher rates for even transitions especially for o-H2 collisions considering low-order transitions., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

A new four dimensional (4D) ab initio potential energy surface (PES) is generated for the collision of C 4 ( 3 Σ g - ) with H 2 ( 1 Σ g ), considering both molecules as rigid rotors. A supervised neural network model is created to augment the ab initio PES and to get the missing data points. Furthermore, space fixed expansion of the augmented PES is carried out using a least squares fit over two spherical harmonics terms, resulting in radial coefficients ( λ 1 , λ 2 , and λ ). The centre of symmetry in both C 4 and H 2 forces λ 1 and λ 2 to have even values, respectively. Moreover, the rotational states of C 4 are only populated by odd levels due to its ground state triplet symmetry and the nuclear spin ( I = 0) of 12 C. The cross-sections and rate coefficients with para and ortho H 2 partners are studied for various odd state transitions, where the rate coefficients of the ortho are 10-20% higher than those of the latter. The de-excitation rates obtained by the para H 2 collisions are also compared to those of He and are found to be ∼1.7-2.8 times the He rates, across various order transitions. The simple scaling of He rates using a factor of 1.38 proves insufficient to describe para H 2 rates. Therefore, these results show the importance of explicitly studying H 2 as an important colliding partner, governing the kinetics of various rotational processes in the interstellar space.

The selective carbon capture and utilization (CCU) as a one-carbon (C1) feedstock offers dual advantages for mitigating the rising atmospheric CO 2 content and producing fine chemicals/fuels. In this context, herein, we report the application of a porous bipyridine-functionalized, pyrene-based covalent organic framework (Pybpy-COF) for the stable anchoring of catalytic Ag(0) nanoparticles (NPs) and its catalytic investigation for fixation of CO 2 to commodity chemicals at ambient conditions. Notably, Ag@Pybpy-COF showed excellent catalytic activity for the carboxylation of various terminal alkynes to corresponding alkynyl carboxylic acids/phenylpropiolic acids via C-H bond activation under atmospheric pressure conditions. Besides, carboxylative cyclization of various propargylic amines with CO 2 to generate 2-oxazolidinones, an important class of antibiotics, has also been achieved under mild conditions. This significant catalytic activity of Ag@Pybpy-COF with wide functional group tolerance is rendered by the presence of highly exposed, alkynophilic Ag(0) catalytic sites decorated on the pore walls of high surface area (787 m 2 g -1 ) Pybpy-COF. Further, density functional theory calculations unveiled the detailed mechanistic path of the Ag@Pybpy-COF-catalyzed transformation of CO 2 to alkynyl carboxylic acids and 2-oxazolidinones. Moreover, the catalyst showed high recyclability for several cycles of reuse without significant loss in its catalytic activity and structural rigidity. This work demonstrates the promising application of Pybpy-COF for stable anchoring of Ag NPs for successful transformation of CO 2 to valuable commodity chemicals at ambient conditions.

The objective of this study is to enhance our understanding of the existence of molecules in interstellar space by determining the collisional rate coefficients with the most prevalent species. The study examines the impact of para -H 2 collisions, specifically when it is in its ground vibrational state with a nuclear spin of para -H 2 , i.e. , j p orientations. Using the CCSD(T)-F12a approach and aug-cc-pVTZ basis sets, the 2 orientations. Using the CCSD(T)-F12a approach and aug-cc-pVTZ basis sets, the ab initio 4DPES for the CNNC-H 2 van der Waals system is calculated. The CNNC- para -H 2 4DPES attains a global minimum of 221.38 cm -1 at the CNNC and H 2 center of mass distance ( R ) of 3.1 Å. The method of close coupling calculations is employed for the purpose of calculating the cross-sectional data of CNNC with para -H 2 ( j p = 0), for total energies up to 1000 cm -1 . Rate coefficients are computed over the temperature range of 1 K to 100 K. Propensity suggests that even Δ j transitions are strongly preferred. The rate coefficients for CNNC-H 2 are determined to be 0.90-2.95 times those of CNNC-He, which implies it is not reliable to estimate the H 2 rate coefficients by multiplying the rate coefficients for CNNC-He collision with a scaling factor of 1.38.

Finding an ideal bioorthogonal reaction that responds to a wide range of biological queries and applications is of great interest in biomedical applications. Rapid diazaborine (DAB) formation in water by the reactions of ortho-carbonyl phenylboronic acid with α-nucleophiles is an attractive conjugation module. Nevertheless, these conjugation reactions demand to satisfy stringent criteria for bioorthogonal applications. Here we show that widely used sulfonyl hydrazide (SHz) offers a stable DAB conjugate by combining with ortho-carbonyl phenylboronic acid at physiological pH, competent for an optimal biorthogonal reaction. Remarkably, the reaction conversion is quantitative and rapid (k 2 >10 3  M -1  s -1 ) at low micromolar concentrations, and it preserves comparable efficacy in a complex biological milieu. DFT calculations support that SHz facilitates DAB formation via the most stable hydrazone intermediate and the lowest energy transition state compared to other biocompatible α-nucleophiles. This conjugation is extremely efficient on living cell surfaces, enabling compelling pretargeted imaging and peptide delivery. We anticipate this work will permit addressing a wide range of cell biology queries and drug discovery platforms exploiting commercially available sulfonyl hydrazide fluorophores and derivatives., (© 2023 Wiley-VCH GmbH.)

Boron-pnictogen (BX; X = N, P, As, Sb) materials, in most cases, share structural characteristics with the aesthetically pleasing architectures of carbon allotropes. Recently, a two-dimensional (2D) metallic carbon allotrope (biphenylene) has been synthesized using experimental methods. In the present study, we have examined the structural stabilities, mechanical properties, and electronic fingerprints of biphenylene analogs of boron-pnictogen (bp-BX) monolayers using state-of-the-art electronic structure theory. We have validated the dynamical stability using phonon band dispersion analysis and thermal stabilities using ab initio molecular dynamics studies. The bp-BX monolayers exhibit a positive (bp-BN) and negative (bp-BP, bp-BAs, bp-BSb) Poisson's ratio with anisotropic mechanical properties in the 2D plane. Electronic structure studies unveil that the bp-BX monolayers show semiconducting properties with an energy gap of 4.50, 1.30, 2.28 and 1.24 eV for X = N, P, As and Sb, respectively. Computed band edge positions, lighter charge carriers and optimally separated hole and electron regions indicate that the bp-BX monolayers can serve as potential candidates for the metal-free water dissociation reaction using photocatalysis.

Lignin-derived aryl ethers and vanillin are essential platform chemicals that fulfil the demands for renewable aromatic compounds. Herein, an efficient heterogeneous catalyst is reported for reforming vanillin via a selective hydrodeoxygenation route to 2-methoxy-4-methyl phenol (MMP), a precursor to medicinal, food, and petrochemical industries. A series of MoCoO x @C catalysts were synthesized by decorating the Co-BTC MOF with different contents of MoO 3 rods, followed by carbonization. Among these catalysts, MoCoO x @C-2 afforded ∼99% vanillin conversion and ∼99% MMP selectivity at 150 °C in 1.5 h in an aqueous medium. In contrast, CoO x @C afforded ∼75% vanillin conversion and ∼85% MMP selectivity. Detailed catalyst characterization revealed that CoO x and Co 2 Mo 3 O 8 were the active species contributing to the higher activity of MoCoO x @C-2. The excellent H 2 -adsorption characteristics and acidity of MoCoO x @C-2 were beneficial to the hydrodeoxygenation of vanillin and other homologous compounds. The DFT adsorption energy calculations suggested the favourable interactions of vanillin and vanillyl alcohol with the Co 2 Mo 3 O 8 sites in MoCoO x @C-2. The catalyst could be efficiently recycled 5 times, with a negligible loss in activity after the 5th cycle. These findings provide a systematic explication of the active sites of the mixed metal oxide-based MoCoO x @C-2 catalyst for the selective hydrodeoxygenation of vanillin to MMP, which is important for the academic and industrial catalysis community.

Collisional cross-sections of inelastic rotational excitations of CN in its ground electronic state (X 2 Σ + ) by H + scattering are studied by the exact quantum mechanical close-coupling (CC) method at very low collision energies (0-600 cm -1 ) relevant to interstellar atmospheres. Ab initio rigid rotor potential energy surface computed at MRCI/ cc - p VTZ level of accuracy has been employed. Rate coefficients for the rotational excitations have also been calculated. The obtained results are compared with previous theoretical calculations and analyzed whether proton collisions could be significant sources for rotationally excited CN as a possible source for cosmic microwave background of about 3 K from the interstellar media., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Anusuri, Dhilip Kumar and Kumar.)

Highly porous, polyhedral metal-organic frameworks (MOFs) of Co(II)/Ni(II), {[M 6 (TATAB) 4 (DABCO) 3 (H 2 O) 3 ]·12DMF·9H 2 O} n (where M = Co(II) (1)/Ni(II) (2), H 3 TATAB = 4,4',4″- s-triazine-1,3,5-triyl-tri- p-aminobenzoic acid, and DABCO = 1,4-diazabicyclo[2.2.2]octane) have been synthesized solvothermally. Both MOFs 1 and 2 show a 2-fold interpenetrated 3D framework structure composed of dual-walled cages of dimension ∼ 30 Å functionalized with a high density of Lewis acidic Co(II)/Ni(II) metal sites and basic -NH- groups. Interestingly, MOF 1 shows selective adsorption of CO 2 with high heat of adsorption ( Q st ) value of 39.7 kJ/mol that is further supported by theoretical studies with computed binding energy (BE) of 41.17 kJ/mol. The presence of the high density of both Lewis acidic and basic sites make MOFs 1/2 ideal candidate materials to carry out co-catalyst-free cycloaddition of CO 2 to epoxides. Consequently, MOFs 1/2 act as excellent recyclable catalysts for cycloaddition of CO 2 to epoxides for high-yield synthesis of cyclic carbonates under co-catalyst-free mild conditions of 1 bar of CO 2 . Further, MOF 1 was recycled for five successive cycles without substantial loss in catalytic activity. Herein, rational design of rare examples of 3D polyhedral MOFs composed of Lewis acidic and basic sites exhibiting efficient co-catalyst-free conversion of CO 2 has been demonstrated.

A bifunctional, microporous Zn II metal-organic framework, [Zn 2 (NH 2 BDC) 2 (dpNDI)] n (MOF1) (where, NH 2 BDC=2-aminoterephthalic acid, dpNDI=N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) has been synthesized solvothermally. MOF1 shows an interesting two-fold interpenetrated, 3D pillar-layered framework structure composed of two types of 1D channels with dimensions of approximately 2.99×3.58 Å and 4.58×5.38 Å decorated with pendent -NH 2 groups. Owing to the presence of a basic functionalized pore surface, MOF1 exhibits selective adsorption of CO 2 with high value of heat of adsorption (Q st =46.5 kJ mol -1 ) which is further supported by theoretically calculated binding energy of 48.4 kJ mol -1 . Interestingly, the value of Q st observed for MOF1 is about 10 kJ mol -1 higher than that of analogues MOF with the benzene-1,4-dicarboxylic acid (BDC) ligand, which establishes the critical role of the -NH 2 group for CO 2 capture. Moreover, MOF1 exhibits highly selective and sensitive sensing of the nitroaromatic compound (NAC), 2,4,6-trinitrophenol (TNP) over other competing NACs through a luminescence quenching mechanism. The observed selectivity for TNP over other nitrophenols has been correlated to stronger hydrogen bonding interaction of TNP with the basic -NH 2 group of MOF1, which is revealed from DFT calculations. To the best of our knowledge, MOF1 is the first example of an interpenetrated Zn II -MOF exhibiting selective adsorption of CO 2 as well as efficient aqueous-phase sensing of TNP; investigated through combined experimental and theoretical studies., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Proton and hydrogen atom time-of-flight spectra in collision energy range of E(trans) = 9.5-30 eV show that the endoergic charge transfer process in the H+ + CO system is almost an order of magnitude less probable than the elastic scattering [G. Niedner-Schatteburg and J. P. Toennies, Adv. Chem. Phys. LXXXII, 553 (1992)]. Ab initio computations at the multireference configuration interaction level have been performed to obtain the ground- and several low-lying excited electronic state potential energy curves in three different molecular orientations namely, H+ approaching the O-end and the C-end (collinear), and H+ approaching the CO molecule in perpendicular configuration with fixed CO internuclear distance. Nonadiabatic coupling terms between the ground electronic state (H+ + CO) and the three low-lying excited electronic states (H + CO+) have been computed and the corresponding diabatic potentials have been obtained. A time-dependent wavepacket dynamics study is modeled first involving only the ground and the first excited states and then involving the ground and the three lowest excited states at the collision energy of 9.5 eV. The overall charge transfer probability have been found to be approximately 20%-30% which is in qualitative agreement with the experimental findings.