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51.
Shubham Vyas Jacek Kubicki Hoi Ling Luk Yunlong Zhang Nina P. Gritsan Christopher M. Hadad Matthew S. Platz 《Journal of Physical Organic Chemistry》2012,25(8):693-703
The photochemistry of pivaloyl, benzoyl, 4‐phenylbenzoyl, and 2‐anthroyl azides has been studied using femtosecond (fs) time‐resolved infrared (TRIR) and UV–vis spectroscopy and interpreted with the aid of computational chemistry. Density functional theory calculations revealed a significant difference in the nature of the lowest singlet excited state for these carbonyl azides. The lowest singlet excited states (S1) of p‐phenylbenzoyl and 2‐anthroyl azides are (π,π*) in nature, while the pivaloyl and benzoyl azides S1 states involve (n,π*) excitations. Nevertheless, for all acyl azides studied here, a similar, and intense, IR band at about 2100 cm?1 has been detected in the ultrafast TRIR experiments following 270 nm excitation. These bands were shifted to lower energy by about 100 cm?1 relative to the N3 stretching mode for the ground states of these azides. These 2100 cm?1 vibrational bands were assigned to the S1 states of acyl azides in agreement with density functional theory calculations. The decay of the acyl azide S1 states was described by bi‐exponential functions. The fast component was attributed to the decay of the hot S1 state and the longer component to the decay of the thermally relaxed S1 state. A strong and broad transient absorption in the 350–650 nm spectral range was observed in the fs UV–vis experiments for p‐phenylbenzoyl and 2‐anthroyl azides. The carrier of this absorption also decayed bi‐exponentially, and the time constants were in excellent agreement with those found in the fs TRIR experiments. The slow component of the S1 state decay was found to be dependent on the solvent polarity. When the lifetime of the acyl azide S1 state is substantially longer than the time constant for vibrational cooling of nascent (hot) isocyanate, the correlation between the S1 decay and isocyanate formation was clear. The 270 nm excitation populates the Sn (n ≥ 2) states of these acyl azides. It was established that a hot nitrene is produced more efficiently from both the Sn and hot S1 states than from the relaxed S1 state of these acyl azides. Thus, time‐resolved study provides direct experimental evidence that the S1 state is the precursor of nitrene only when the S1 state is pumped directly and when the S1 state lifetime is longer than the time constant of vibrational cooling of the newborn nitrene. All of these results are consistent with the data obtained recently for 2‐napththoyl azide. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
52.
Sivaramakrishnan Muthukrishnan Vivekanand S. Shete Toby T. Sanan Shubham Vyas Shameema Oottikkal Lauren M. Porter Thomas J. Magliery Christopher M. Hadad 《Journal of Physical Organic Chemistry》2012,25(12):1247-1260
We designed, synthesized, and screened a library of analogs of the organophosphate pesticide metabolite paraoxon against a recombinant variant of human serum paraoxonase‐1. Alterations of both the aryloxy leaving group and the retained alkyl chains of paraoxon analogs resulted in substantial changes to binding and hydrolysis, as measured directly by spectrophotometric methods or in competition experiments with paraoxon. Increases or decreases in the steric bulk of the retained groups generally reduced the rate of hydrolysis, while modifications of the leaving group modulated both binding and turnover. Studies on the hydrolysis of phosphoryl azide analogs as well as amino‐modified paraoxon analogs, the former being developed as photoaffinity labels, found enhanced tolerance of structural modifications when compared with O‐alkyl‐substituted molecules. Results from computational modeling predict a predominant active site binding mode for these molecules, which is consistent with several proposed catalytic mechanisms in the literature and from which a molecular‐level explanation of the experimental trends is attempted. Overall, the results of this study suggest that while paraoxonase‐1 is a promiscuous enzyme, there are substantial constraints in the active site pocket, which may relate to both the leaving group and the retained portion of paraoxon analogs. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
53.
Neeraj Soni Shivendra Singh Shubham Sharma Gayatri Batra Kush Kaushik Chethana Rao Navneet C. Verma Bhaskar Mondal Aditya Yadav Chayan K. Nandi 《Chemical science》2021,12(10):3615
The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.Herein we unveil the presence of a molecular fluorophore quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA) in a colossal amount in red emissive CNDs synthesized from o-phenylenediamine, a well-known precursor molecule used for CND synthesis. 相似文献
54.
Malcolm H. Chisholm Christopher M. Hadad Katja Heinze Klaus Hempel Namrata Singh Shubham Vyas 《Journal of Cluster Science》2008,19(1):209-218
The homoleptic compound Ru(II)(L)2 where L = 4′-carboxylato-2,2′:6′,2″-terpyridine was employed as a bridge to link two [Mo2(O2CBu
t
)3]+ units in the formation of the title complex: [Mo2(O2CBu
t
)3]2-μ-Ru(II)L2] (2+) [BF4−]2, which has been characterized by 1H-NMR, UV–vis and emission spectroscopy, MALDI-TOF-MS and cyclic voltammetry. The electronic structure of the complex has
been investigated by density functional theory employing Turbomole on the model complex cation [Mo2(O2CH)3]2-μ-(Ru(II)L2)2+. The intense blue color of the cation arises from M2 δ to bridge/terpyridine charge transfer.
This paper is dedicated to Prof. F. A. Cotton in memoriam. 相似文献
55.
Shubham Sharma Virender Singh Vaishali Rakesh Kumar Rahul Jamra Naveen Banyal Jyoti 《Journal of heterocyclic chemistry》2024,61(2):232-284
The synthesis of pyrazole derivative using α,β-unsaturated carbonyl compounds has attracted increasing attention of the synthetic organic chemist community. Interestingly, the simplicity of the synthetic method, high reactivity, and ease of incorporating diversity into the desired prototype have contributed a lot toward the exploration of α,β-unsaturated carbonyl compounds by various research groups. Due to the tremendous pharmacological significance of pyrazole derivatives, their synthesis has been one of the leading research frontiers in recent years. As prime examples, sildenafil, zometapin, Celebrex, and rimonabant have been successfully commercialized in the market to treat various life-challenging diseases. Considering the great profile of α,β-unsaturated carbonyl compound in the synthesis of biologically active pyrazole derivatives, this review incorporates contemporary literature (2011–2022) on the synthesis of pyrazole and its derivatives using α,β-unsaturated carbonyl compound as a starting precursor. 相似文献
56.
In this paper, the cosmological model of the Universe has been presented in gravity and the parameters are constrained from the cosmological data sets. At the beginning, a well motivated form of has been employed, where α, β, and n are model parameters. The Hubble parameter is obtained in redshift with some algebraic manipulation from the considered form of . Then it is parameterized with the recent data and data using Markov chain Monte Carlo analysis. The obtained model parameter values are validated with the baryon acoustic oscillation data set. A parametrization of the cosmographic parameters shows the early deceleration and late time acceleration with the transition at . The diagnostics gives positive slope which shows that the model is in the phantom phase. Also the current age of the Universe has been obtained as, . Based on the present analysis, it indicates that the gravity may provide an alternative to dark energy for addressing the current cosmic acceleration. 相似文献
57.
Shubham Som Avantika Hasija Deepak Chopra 《Acta Crystallographica. Section C, Structural Chemistry》2023,79(10):399-408
Mechanochemical synthesis via grinding of trimesic acid (TA, C9H6O6) and 4-chlorophenyl diphenyl phosphate (4CDP, C18H14ClO4P) (liquid at room temperature) in a 1:1 ratio resulted in the formation of an inclusion type of cocrystal. The crystallization of this phase via slow evaporation at low temperature (276–277 K) from methanol resulted in a rare `stairstep morphology' during the process of crystal growth. This morphology was not observed after crystallization of the compound from other solvents like toluene, dichloromethane, acetone, hexane and isooctane, and hence this was characteristically observed in methanol only. The characterization from single-crystal X-ray diffraction revealed the formation of a cocrystal with five molecules of TA and two molecules of 4CDP in the asymmetric unit. The trimesic acid molecules form hydrogen-bonded dimers resulting in hexagonal rings, and these rings are stacked through π–π intermolecular interactions to make a hexagonal honeycomb-like structure. The phosphate molecules, 4CDP, were found to be trapped as guests in these hexagonal channels. The similarity in the packing of trimesic acid is compared in the cocrystal and the free acid quantitatively viaXpac analysis, which establishes the relationship of a `2D supramolecular construct' between them. This signifies a unique type of arrangement in which the voids created by the trimesic acid moiety do not undergo distortion by the inclusion of the guest molecules. The quantitative analysis of the intermolecular interactions using Hirshfeld surfaces and fingerprint plots deciphers the role of both strong O—H…O hydrogen bonds and weak intermolecular interactions in the crystal packing. 相似文献
58.
Dr. Shubham Dutta Prof. Dr. Akhila K. Sahoo 《Angewandte Chemie (International ed. in English)》2023,62(12):e202300610
A Pd-catalyzed three-component syn-1,2-arylmethylation of internal alkynes (ynamides/yne-acetates/alkynes) is described. The readily available and bench stable coupling partners iodo-arenes, and methyl boronic acid are successfully used in this coupling strategy to access the methyl-containing tetra-substituted olefins; the scope is broad showing excellent functional-group tolerance. Notably, the transformation is regio- as well as stereoselective. The biologically relevant motifs (BRM) bearing iodo-arenes and ynamides are also used for the late-stage syn-1,2-arylmethylation of alkynes. Aryl-alkylation, aryl-trideuteriomethylation, alkynyl-methylation, and alkenyl-methylation of ynamides are also presented. The Me-substituted alkenes are further transformed into synthetically important β-amino-indenones and α-fluoro-α′-methyl ketones. 相似文献
59.
Kyungsene Lee Brandon Davis Xuelin Wang Shubham Mirg Connie Wen Dr. Lidya Abune Dr. Benjamin E. Peterson Dr. Li Han Haoyang Chen Prof. Hongjun Wang Prof. Spencer E. Szczesny Prof. Yuguo Lei Prof. Sri-Rajasekhar Kothapalli Prof. Yong Wang 《Angewandte Chemie (International ed. in English)》2023,62(31):e202306583
Cell encapsulation has been studied for various applications ranging from cell transplantation to biological production. However, current encapsulation technologies focus on cell protection rather than cell regulation that is essential to most if not all cell-based applications. Here we report a method for cell nanoencapsulation and regulation using an ultrathin biomimetic extracellular matrix as a cell nanocapsule to carry nanoparticles (CN2). This method allows high-capacity nanoparticle retention at the vicinity of cell surfaces. The encapsulated cells maintain high viability and normal metabolism. When gold nanoparticles (AuNPs) are used as a model to decorate the nanocapsule, light irradiation transiently increases the temperature, leading to the activation of the heat shock protein 70 (HSP70) promoter and the regulation of reporter gene expression. As the biomimetic nanocapsule can be decorated with any or multiple NPs, CN2 is a promising platform for advancing cell-based applications. 相似文献