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81.
Dr. Sourav Sarkar Anushree Shil Suman Maity Dr. Yun Lim Jung Dr. Mingchong Dai Prof. Atanu Acharya Prof. Kyo Han Ahn 《Angewandte Chemie (International ed. in English)》2023,62(43):e202311168
Aryl alcohol-type or phenolic fluorophores offer diverse opportunities for developing bioimaging agents and fluorescence probes. Due to the inherently acidic hydroxyl functionality, phenolic fluorophores provide pH-dependent emission signals. Therefore, except for developing pH probes, the pH-dependent nature of phenolic fluorophores should be considered in bioimaging applications but has been neglected. Here we show that a simple structural remedy converts conventional phenolic fluorophores into pH-resistant derivatives, which also offer “medium-resistant” emission properties. The structural modification involves a single-step introduction of a hydrogen-bonding acceptor such as morpholine nearby the phenolic hydroxyl group, which also leads to emission bathochromic shift, increased Stokes shift, enhanced photo-stability and stronger emission for several dyes. The strategy greatly expands the current fluorophores’ repertoire for reliable bioimaging applications, as demonstrated here with ratiometric imaging of cells and tissues. 相似文献
82.
Herein, we report a detailed periodic DFT investigation of Mn(II)-based [(Mn4Cl)3(BTT)8]3− (BTT3−=1,3,5-benzenetristetrazolate) metal-organic framework (MOF) to explore various hydrogen binding pockets, nature of MOF…H2 interactions, magnetic coupling and, H2 uptake capacity. Earlier experiments found an uptake capacity of 6.9 wt % of H2, with the heat of adsorption estimated to be ∼10 kJ/mol, which is one among the highest for any MOFs reported. Our calculations unveil different binding sites with computed binding energy varying from −6 to −15 kJ/mol. The binding of H2 at the Mn2+ site is found to be the strongest (site I), with H2 found to bind Mn2+ ion in a η2 fashion with a distance of 2.27 Å and binding energy of −15.4 kJ/mol. The bonding analysis performed using NBO and AIM reveal a strong donation of σ (H2) to the dz2 orbital of the Mn2+ ion responsible for such large binding energy. The other binding pockets, such as −Cl (site II) and BTT ligands (site III and IV) were found to be weaker, with the binding energy decreasing in the order I>II>III>IV. The average binding energy computed for these four sites put together is 9.6 kJ/mol, which is in excellent agreement with the experimental value of ∼10 kJ/mol. We have expanded our calculations to compute binding energy for multiple sites simultaneously, and in this model, the binding energy per site was found to decrease as we increased the number of H2 molecules suggesting electronic and steric factors controlling the overall uptake capacity. The calculated adsorption isotherm using the GCMC method reproduces the experimental observations. Further, the magnetic coupling computed for the unbound MOF reveals moderate ferromagnetic and strong antiferromagnetic coupling within the tetrameric {Mn4} unit leading to a three-up-one-down spin configuration as the ground state. These were then coupled ferromagnetically to other tetrameric units in the MOF network. The magnetic coupling was found to alter only marginally upon gas binding, suggesting that both exchange interaction and the spin-states are unlikely to play a role in the H2 uptake. This is contrary to the O2 uptake studied lately, where strong dependence on exchange-coupling/spin state was witnessed, suggesting exchange-coupling/magnetic field dependent binding as a viable route for gas separation. 相似文献
83.
A p‐Hydroxyphenacyl–Benzothiazole–Chlorambucil Conjugate as a Real‐Time‐Monitoring Drug‐Delivery System Assisted by Excited‐State Intramolecular Proton Transfer 下载免费PDF全文
Shrabani Barman Sourav K. Mukhopadhyay Sandipan Biswas Surajit Nandi Moumita Gangopadhyay Satyahari Dey Anakuthil Anoop N. D. Pradeep Singh 《Angewandte Chemie (International ed. in English)》2016,55(13):4194-4198
Among the well‐known phototriggers, the p‐hydroxyphenacyl (pHP) group has consistently enabled the very fast, efficient, and high‐conversion release of active molecules. Despite this unique behavior, the pHP group has been ignored as a delivery agent, particularly in the area of theranostics, because of two major limitations: Its excitation wavelength is below 400 nm, and it is nonfluorescent. We have overcome these limitations by incorporating a 2‐(2′‐hydroxyphenyl)benzothiazole (HBT) appendage capable of rapid excited‐state intramolecular proton transfer (ESIPT). The ESIPT effect also provided two unique advantages: It assisted the deprotonation of the pHP group for faster release, and it was accompanied by a distinct fluorescence color change upon photorelease. In vitro studies showed that the p‐hydroxyphenacyl–benzothiazole–chlorambucil conjugate presents excellent properties, such as real‐time monitoring, photoregulated drug delivery, and biocompatibility. 相似文献
84.
Facet‐Dependent and Light‐Assisted Efficient Hydrogen Evolution from Ammonia Borane Using Gold–Palladium Core–Shell Nanocatalysts 下载免费PDF全文
Dr. Sourav Rej Chi‐Fu Hsia Tzu‐Yu Chen Fan‐Cheng Lin Prof. Jer‐Shing Huang Prof. Michael H. Huang 《Angewandte Chemie (International ed. in English)》2016,55(25):7222-7226
Au–Pd core–shell nanocrystals with tetrahexahedral (THH), cubic, and octahedral shapes and comparable sizes were synthesized. Similar‐sized Au and Pd cubes and octahedra were also prepared. These nanocrystals were used for the hydrogen‐evolution reaction (HER) from ammonia borane. Light irradiation can enhance the reaction rate for all the catalysts. In particular, Au–Pd THH exposing {730} facets showed the highest turnover frequency for hydrogen evolution under light with 3‐fold rate enhancement benefiting from lattice strain, modified surface electronic state, and a broader range of light absorption. Finite‐difference time‐domain (FDTD) simulations show a stronger electric field enhancement on Au–Pd core–shell THH than those on other Pd‐containing nanocrystals. Light‐assisted nitro reduction by ammonia borane on Au–Pd THH was also demonstrated. Au–Pd tetrahexahedra supported on activated carbon can act as a superior recyclable plasmonic photocatalyst for hydrogen evolution. 相似文献
85.
Synthesis of 3‐aminomethylidenechroman‐2‐carboxamides by a Sequential One‐pot Three Component Reaction and by Post‐Passerini Condensation Modification 下载免费PDF全文
Jaydip Ghosh Suman Kalyan Panja Sourav Maiti Pritam Biswas Tapas Sarkar Chandrakanta Bandyopadhyay 《Journal of heterocyclic chemistry》2016,53(2):449-456
3‐Arylaminomethylidenechroman‐2‐carboxamide has been synthesized by a one‐pot three component reaction among 3‐formylchromone, aromatic amine, and cyclohexyl isocyanide. 3‐(N‐alkylsubstitued/unsubstituted)aminomethylidenechroman‐2‐carboxamides were synthesized by heating Passerini products derived from chromone‐3‐carbaldehyde with different aliphatic primary amines. The products obtained from the reactions of aliphatic primary amines readily form chromeno[2,3‐c]pyrrole when heated in acetic acid. Bischromanones have also been synthesized using this methodology. 相似文献
86.
87.
In this critical review, we discuss switching of the light-powered bistable rotaxanes and catenanes and highlight the practical applications of some of these systems. Photoactive molecular and supramolecular machines are comprised of two parts-1) a switching element, based on noncovalent interactions within the recognition units, which is responsible for executing mechanical movement, and 2) a light-harvesting unit which utilizes light to control the competitive interactions between the recognition sites. We also survey another class of molecular devices, namely molecular rotary motors--i.e., those that behave like their macroscopic counterparts--in which photochemically and thermally induced mechanical movement relies on isomerizations of a pivotal C=C bond, leading to a rotation of the top propeller part with respect to the stationary bottom part of the helical shaped chiral molecule. (146 references.). 相似文献
88.
While the blocking barrier (Ueff) and blocking temperature (TB) for “Dysprocenium” SIMs have been increased beyond liquid N2 temperature, device fabrication of these molecules remains a challenge as low-coordinate Ln3+ complexes are very unstable. Encapsulating the lanthanide ion inside a cage such as a fullerene (called endohedral metallofullerene or EMF) opens up a new avenue leading to several Ln@EMF SMMs. The ab initio CASSCF calculations play a pivotal role in identifying target metal ions and suitable cages in this area. Encouraged by our earlier prediction on Ln2@C79N, which was verified by experiments, here we have undertaken a search to enhance the exchange coupling in this class of molecules beyond the highest reported value. Using DFT and ab initio calculations, we have studied a series of Gd2@C2n (30 ≤ 2n ≤ 80), where an antiferromagnetic JGd⋯Gd of −43 cm−1 was found for a stable Gd2@C38-D3h cage. This extremely large and exceptionally rare 4f⋯4f interaction results from a direct overlap of 4f orbitals due to the confinement effect. In larger cages such as Gd2@C60 and Gd2@C80, the formation of two centre-one-electron (2c-1e−) Gd–Gd bonds is perceived. This results in a radical formation in the fullerene cage leading to its instability. To avoid this, we have studied heterofullerenes where one of the carbon atoms is replaced by a nitrogen atom. Specifically, we have studied Ln2@C59N and Ln2@C79N, where strong delocalisation of the electron yields a mixed valence-like behaviour. This suggests a double-exchange (B) is operational, and CASSCF calculations yield a B value of 434.8 cm−1 and resultant JGd–rad of 869.5 cm−1 for the Gd2@C59N complex. These parameters are found to be two times larger than the world-record J reported for Gd2@C79N. Further ab initio calculations reveal an unprecedented Ucal of 1183 and 1501 cm−1 for Dy2@C59N and Tb2@C59N, respectively. Thus, this study offers strong exchange coupling as criteria for new generation SMMs as the existing idea of enhancing the blocking barrier via crystal field modulation has reached its saturation point.Using ab initio calculations, we have made some robust predictions towards lanthanofullerene SMMs exhibiting remarkable characteristics. 相似文献
89.
Peter Bartner Birendra N. Pramanik Anil K. Saksena Yan-Hui Liu Pradip R. Das Olga Sarre Ashit K. Ganguly 《Journal of the American Society for Mass Spectrometry》1997,8(11):1134-1140
The structural characterization of a new oligosaccharide antibiotic, Everninomicin-6 (EV-6), is described. Detailed fast-atom bombardment mass spectrometry (FAB-MS) studies along with NMR and chemical degradation methods were conducted to elucidate the structure of EV-6. The effects of the use of various matrices, including salt addition, on the quality of the FAB-MS were explored. The use of 3-nitro benzyl alcohol, dimethyl sulfoxide (DMSO), and NaCl produced the best results: an intense sodiated molecular ion plus structurely informative fragmentation. FAB-MS yields information providing the complete sugar sequence information for everninomicins, which is quite valuable to the elucidation of the structure of this complex oligosaccharide antibiotic. In addition, the results of accurate mass work with the molecular ion are consistent with the assigned structure. The use of electrospray ionization mass spectrometry (ESI-MS) and ESI-MS/MS for the study of EV-6 was investigated and was found to produce an abundant molecular ion with limited structural information. These results revealed that EV-6 resembled EV-D quite closely except for the absence of the nitrosugar and the replacement on ring g of the -CH2OCH3 group with a -CH2OH group. 相似文献
90.
Dr. Milan Pramanik Michael G. Guerzoni Dr. Emma Richards Prof. Dr. Rebecca L. Melen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(9):e202316461
The development of new methods for enantioselective reactions that generate stereogenic centres within molecules are a cornerstone of organic synthesis. Typically, metal catalysts bearing chiral ligands as well as chiral organocatalysts have been employed for the enantioselective synthesis of organic compounds. In this review, we highlight the recent advances in main group catalysis for enantioselective reactions using the p-block elements (boron, aluminium, phosphorus, bismuth) as a complementary and sustainable approach to generate chiral molecules. Several of these catalysts benefit in terms of high abundance, low toxicity, high selectivity, and excellent reactivity. This minireview summarises the utilisation of chiral p-block element catalysts for asymmetric reactions to generate value-added compounds. 相似文献