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891.
Piyali De Dhurjati Prasad KumarAmit Kumar Mondal Pulak Chandra MandalSubrata Mukhopadhyay Rupendranath Banerjee 《Polyhedron》2010
In aqueous alkali, Fremy’s salt (potassium nitrosodisulfonate dimer), homolyses nearly exclusively to the monomer radical anion, nitrosodisulfonate (NDS). In this media, NDS almost quantitatively oxidizes benzyl alcohol (PhCH2OH) to benzaldehyde (PhCHO), itself being reduced to hydroxylamine disulfonate (HNDS). The reaction is very nearly first-order in [NDS], [alkanol] and in [OH−]. However, with progressive addition of HNDS, decay kinetics of NDS gradually deviates from first-order. Ultimately, with sufficient excess of HNDS, the reaction becomes second-order in [NDS]. The consumption ratio, (ΔPhCH2OH]/Δ[NDS]), is ∼2. PhCD2OH manifests a large primary kinetic isotope effect (kH/kD = 11.6). Substituted benzyl alcohols (RBzCH2OH) with R-groups withdrawing electron density from the O–H bond accelerated the reaction; those with R-groups donating electron density to the O–H bond retarded the reaction. The conversion of 2-propanol to 2-propanone is much slower compared to that of benzyl alcohol to benzaldehyde. An alpha-H atom transfer mechanism seems logical. 相似文献
892.
Mahendra Varne Vaishali Samant Dr. Jahur A. Mondal Dr. Sandip K. Nayak Dr. Hirendra N. Ghosh Dr. Dipak K. Palit Dr. 《Chemphyschem》2009,10(17):2979-2994
The dynamics of the excited states of 1‐aminofluoren‐9‐one (1AF) and 1‐(N,N‐dimethylamino)‐fluoren‐9‐one (1DMAF) are investigated by using steady‐state absorption and fluorescence as well as subpicosecond time‐resolved absorption spectroscopic techniques. Following photoexcitation of 1AF, which exists in the intramolecular hydrogen‐bonded form in aprotic solvents, the excited‐state intramolecular proton‐transfer reaction is the only relaxation process observed in the excited singlet (S1) state. However, in protic solvents, the intramolecular hydrogen bond is disrupted in the excited state and an intermolecular hydrogen bond is formed with the solvent leading to reorganization of the hydrogen‐bond network structure of the solvent. The latter takes place in the timescale of the process of solvation dynamics. In the case of 1DMAF, the main relaxation pathway for the locally excited singlet, S1(LE), or S1(ICT) state is the configurational relaxation, via nearly barrierless twisting of the dimethylamino group to form the twisted intramolecular charge‐transfer, S1(TICT), state. A crossing between the excited‐state and ground‐state potential energy curves is responsible for the fast, radiationless deactivation and nonemissive character of the S1(TICT) state in polar solvents, both aprotic and protic. However, in viscous but strong hydrogen‐bond‐donating solvents, such as ethylene glycol and glycerol, crossing between the potential energy surfaces for the ground electronic state and the hydrogen‐bonded complex formed between the S1(TICT) state and the solvent is possibly avoided and the hydrogen‐bonded complex is weakly emissive. 相似文献
893.
Himangshu Sharma Joyanta Mondal Ananyo K. Ghosh Ritesh Ranjan Pal Rajib Kumar Goswami 《Chemical science》2022,13(45):13403
Stereoselective total synthesis of the structurally intriguing polyketide natural product thailandamide lactone was accomplished, and done so using a convergent approach for the first time to the best of our knowledge. The key features of this synthesis included use of a Crimmins acetate aldol reaction, Evans methylation, Urpi acetal aldol reaction, Sharpless asymmetric epoxidation and subsequent γ-lactonization for the installation of six asymmetric centers and the use of the Negishi reaction, Julia-Kocienski olefination, cross metathesis, HWE olefination and intermolecular Heck coupling for construction of a variety of unsaturated linkages. Pd(i)-based Heck coupling was introduced, for the first time to the best of our knowledge, quite efficiently to couple the major eastern and sensitive western segments of the molecule. The antibacterial activity of thailandamide lactone was also evaluated.A convergent strategy for the total synthesis of the structurally intriguing polyketide natural product thailandamide lactone has been developed for the first time. The antibacterial activity of the molecule has also been disclosed. 相似文献
894.
Priyanka Chandrashekar Gopa Sardar Dr. Turbasu Sengupta Dr. Arthur C. Reber Dr. Pradip Kumar Mondal Prof. Dinesh Kabra Prof. Shiv N. Khanna Dr. Pravas Deria Prof. Sukhendu Mandal 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(6):e202317345
Silver cluster-based solids have garnered considerable attention owing to their tunable luminescence behavior. While surface modification has enabled the construction of stable silver clusters, controlling interactions among clusters at the molecular level has been challenging due to their tendency to aggregate. Judicious choice of stabilizing ligands becomes pivotal in crafting a desired assembly. However, detailed photophysical behavior as a function of their cluster packing remained unexplored. Here, we modulate the packing pattern of Ag12 clusters by varying the nitrogen-based ligand. CAM-1 formed through coordination of the tritopic linker molecule and NC-1 with monodentate pyridine ligand; established via non-covalent interactions. Both the assemblies show ligand-to-metal-metal charge transfer (LMMCT) based cluster-centered emission band(s). Temperature-dependent photoluminescence spectra exhibit blue shifts at higher temperatures, which is attributed to the extent of the thermal reverse population of the S1 state from the closely spaced T1 state. The difference in the energy gap (ΔEST) dictated by their assemblies played a pivotal role in the way that Ag12 cluster assembly in CAM-1 manifests a wider ΔEST and thus requires higher temperatures for reverse intersystem crossing (RISC) than assembly of NC-1. Such assembly-defined photoluminescence properties underscore the potential toolkit to design new cluster- assemblies with tailored optoelectronic properties. 相似文献
895.
Christian A. Gomez Dibyendu Mondal Qian Du Natalie Chan Jared C. Lewis 《Angewandte Chemie (International ed. in English)》2023,62(15):e202301370
FeII- and α-ketoglutarate-dependent halogenases and oxygenases can catalyze site-selective functionalization of C−H bonds via a variety of C−X bond forming reactions, but achieving high chemoselectivity for functionalization using non-native functional groups remains rare. The current study shows that directed evolution can be used to engineer variants of the dioxygenase SadX that address this challenge. Site-selective azidation of succinylated amino acids and a succinylated amine was achieved as a result of mutations throughout the SadX structure. The installed azide group was reduced to a primary amine, and the succinyl group required for azidation was enzymatically cleaved to provide the corresponding amine. These results provide a promising starting point for evolving additional SadX variants with activity on structurally distinct substrates and for enabling enzymatic C−H functionalization with other non-native functional groups. 相似文献
896.
Rahul Mondal Matthew J. Evans Thayalan Rajeshkumar Laurent Maron Cameron Jones 《Angewandte Chemie (International ed. in English)》2023,62(37):e202308347
The activation of dinitrogen (N2) by transition metals is central to the highly energy intensive, heterogeneous Haber–Bosch process. Considerable progress has been made towards more sustainable homogeneous activations of N2 with d- and f-block metals, though little success has been had with main group metals. Here we report that the reduction of a bulky magnesium(II) amide [(TCHPNON)Mg] (TCHPNON=4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) with 5 % w/w K/KI yields the magnesium-N2 complex [{K(TCHPNON)Mg}2(μ-N2)]. DFT calculations and experimental data show that the dinitrogen unit in the complex has been reduced to the N22− dianion, via a transient anionic magnesium(I) radical. The compound readily reductively activates CO, H2 and C2H4, in reactions in which it acts as a masked dimagnesium(I) diradical. 相似文献
897.
Fluorescence-based detection technique using coordination polymer has been considered an attractive alternative over conventional approaches. Herein, a new luminescent zinc(II) coordination polymer, [Zn(4-ABPT)(NIPA)(H2O)], SSICG-5 , is synthesized by using a Lewis acidic Zn(II) ion, aromatic nitro group containing ligand 5-nitroisophthalic acid (H2NIPA), and basic −NH2 rich ligand 3,5-di(pyridine-4-yl)-4H-1,2,4-triazol-4-amine (4-ABPT). SSICG-5 can detect Fe3+ and Cr2O72− selectively with a LOD of 0.16 μM and 1.94 μM, respectively. Additionally, carbon dioxide (CO2) fixation via one-pot CO2 cycloaddition reaction has significant importance for reduced waste formation, minimizing reaction time and lowering chemical usage. Zn metal centre of SSICG-5 possesses a replaceable coordinated water molecule. The active metal sites combined with the Lewis acidic and basic sites of the ligands make SSICG-5 an ideal bifunctional heterogeneous catalyst for efficient CO2 cycloaddition reaction under room temperature (RT), solvent-free conditions. Notably, SSICG-5 exhibits near quantitative conversion (turnover number (TON) of 198) of propylene oxide to its carbonate compound under mild reaction conditions. 相似文献
898.
Correction to: Non‑precious transition metal‑based counter electrodes for dye‑sensitized solar cells
Journal of Solid State Electrochemistry - 相似文献
899.
Surajit Mondal Supriti Dutta Santanu Mal Swapan K. Pati Sayan Bhattacharyya 《Angewandte Chemie (International ed. in English)》2023,62(18):e202301269
The immiscibility of crystallographic facets in multi-metallic catalysts plays a key role in driving the green H2 production by water electrolysis. The lattice mismatch between tetragonal In and face-centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close-packed (hcp) Ni is 49.8 %. Hence, in a series of Ni−In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18–20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni0 state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h−1 H2 is evolved at −385 mV with mass activity of 57.5 A g−1 at—400 mV, 200 h stability at −0.18 V versus reversible hydrogen electrode (RHE), and Pt-like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH− ions and the prevention of catalyst poisoning. 相似文献
900.
Dr. Shi Kuang Dr. Biyue Zhu Dr. Jing Zhang Fan Yang Dr. Bo Wu Dr. Weihua Ding Liuyue Yang Dr. Shiqian Shen Dr. Seven H. Liang Dr. Prasenjit Mondal Dr. Mohanraja Kumar Dr. Rudolph E. Tanzi Dr. Can Zhang Dr. Hui Chao Dr. Chongzhao Ran 《Angewandte Chemie (International ed. in English)》2023,62(45):e202312519
The development of Alzheimer's disease (AD) drugs has recently witnessed substantial achievement. To further enhance the pool of drug candidates, it is crucial to explore non-traditional therapeutic avenues. In this study, we present the use of a photolabile curcumin-diazirine analogue, CRANAD-147, to induce changes in properties, structures (sequences), and neurotoxicity of amyloid beta (Aβ) species both in cells and in vivo. This manipulation was achieved through irradiation with LED light or molecularly generated light, dubbed as “molecular light”, emitted by the chemiluminescence probe ADLumin-4. Next, aided by molecular chemiluminescence imaging, we demonstrated that the combination of CRANAD-147/LED or CRANAD-147/ADLumin-4 (molecular light) could effectively slow down the accumulation of Aβs in transgenic 5xFAD mice in vivo. Leveraging the remarkable tissue penetration capacity of molecular light, phototherapy employing the synergistic effect of a photolabile Aβ ligand and molecular light emerges as a promising alternative to conventional AD treatment interventions. 相似文献