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51.
In Silico Olefin Metathesis with Ru‐Based Catalysts Containing N‐Heterocyclic Carbenes Bearing C60 Fullerenes 下载免费PDF全文
Juan Pablo Martínez Dr. Sai Vikrama Chaitanya Vummaleti Dr. Laura Falivene Prof. Dr. Steven P. Nolan Prof. Dr. Luigi Cavallo Prof. Dr. Miquel Solà Dr. Albert Poater 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6617-6623
Density functional theory calculations have been used to explore the potential of Ru‐based complexes with 1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene (SIMes) ligand backbone ( A ) being modified in silico by the insertion of a C60 molecule ( B and C ), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A , B , and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron‐withdrawing N‐heterocyclic carbene improves the performance of unannulated complex A . The efficiency of complex B is only surpassed by complex A when the backbone of the N‐heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic‐donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A . Overall, this study indicates that such Ru‐based complexes B and C might have the potential to be effective olefin metathesis catalysts. 相似文献
52.
Sreeruttun RK Ramasami P Wannere CS Paul A Schleyer PV Schaefer Iii HF 《The Journal of organic chemistry》2005,70(22):8676-8686
[reaction: see text] The adiabatic electron affinity (EA(ad)) of the CH(3)-C[triple bond]C(*) radical [experiment = 2.718 +/- 0.008 eV] and the gas-phase basicity of the CH(3)-C[triple bond]C:(-) anion [experiment = 373.4 +/- 2 kcal/mol] have been compared with those of their fluorine derivatives. The latter are studied using theoretical methods. It is found that there are large effects on the electron affinities and gas-phase basicities as the H atoms of the alpha-CH(3) group in the propynyl system are substituted by F atoms. The predicted electron affinities are 3.31 eV (FCH(2)-C[triple bond]C(*)), 3.86 eV (F(2)CH-C[triple bond]C(*)), and 4.24 eV (F(3)C-C[triple bond]C(*)), and the predicted gas-phase basicities of the fluorocarbanion derivatives are 366.4 kcal/mol (FCH(2)-C[triple bond]C:(-)), 356.6 kcal/mol (F(2)CH-C[triple bond]C:(-)), and 349.8 kcal/mol (F(3)C-C[triple bond]C:(-)). It is concluded that the electron affinities of fluoropropynyl radicals increase and the gas-phase basicities decrease as F atoms sequentially replace H atoms of the alpha-CH(3) in the propynyl system. The propargyl radicals, lower in energy than the isomeric propynyl radicals, are also examined and their electron affinities are predicted to be 0.98 eV ((*)CH(2)-C[triple bond]CH), 1.18 eV ((*)CFH-C[triple bond]CH), 1.32 eV ((*)CF(2)-C[triple bond] CH), 1.71 eV ((*)CH(2)-C[triple bond]CF), 2.05 eV ((*)CFH-C[triple bond]CF), and 2.23 eV ((*)CF(2)-C[triple bond]CF). 相似文献
53.
Wannere CS Corminboeuf C Wang ZX Wodrich MD King RB Schleyer PV 《Journal of the American Chemical Society》2005,127(15):5701-5705
Quantitative evidence for the existence of aromaticity involving the d orbitals of transition metals is provided for the first time. The doubly bridged square planar (D(4)(h)()) coinage metal clusters (M(4)Li(2), M = Cu (1), Ag (2), and Au (3)) are characterized as aromatic by their substantial nucleus independent chemical shifts (NICS) values in the centers (-14.5, -14.1, and -18.6, respectively). Nevertheless, the participation of p orbitals in the bonding (and cyclic electron delocalization) of 1-3 is negligible. Instead, these clusters benefit strongly from the delocalization of d and to some extent s orbitals. The same conclusion applies to Tsipis and Tsipis' H-bridged D(4)(h)() Cu(4)H(4) ring (4). Canonical MO-NICS analysis of structures 1-3 shows the total diatropic d orbital contributions to the total NICS to be substantial, although the individual contributions of the five sets of filled d orbitals vary. The d orbital aromaticity of Cu(4)Li(2) also is indicated by its atomization energy, 243.2 kcal/mol, which is larger than Boldyrev's doubly (sigma and pi) aromatic Al(4)Li(2) (215.9 kcal/mol). 相似文献
54.
Diethyl ethoxymethylenemalonate was used for the novel synthesis of the triheterocyclic 3-carbethoxy-9,ll-disubstituted-4-oxo-4H-pyrido[3,2-e]pyrimido[1,2-c]pyrimidines from 4-aminopyrido[2,3-d]pyrim-idines via thermal cyclization of the intermediate ethyl 2-carbethoxy-3-[5,7-disubstituted-4-amino-pyrido[2,3-d]pyrimidin-4-yl]acrylates. The alkaline hydrolysis of 3-carbethoxy-4-oxo-4H-pyrido[3,2-e]-pyrimido[1,2-c]pyrimidines was performed to give corresponding acid derivatives. 相似文献
55.
Kao YT Saxena C He TF Guo L Wang L Sancar A Zhong D 《Journal of the American Chemical Society》2008,130(39):13132-13139
We report here our systematic studies of excited-state dynamics of two common flavin molecules, FMN and FAD, in five redox states--oxidized form, neutral and anionic semiquinones, and neutral and anionic fully reduced hydroquinones--in solution and in inert protein environments with femtosecond resolution. Using protein environments, we were able to stabilize two semiquinone radicals and thus observed their weak emission spectra. Significantly, we observed a strong correlation between their excited-state dynamics and the planarity of their flavin isoalloxazine ring. For a bent ring structure, we observed ultrafast dynamics from a few to hundreds of picoseconds and strong excitation-wavelength dependence of emission spectra, indicating deactivation during relaxation. A butterfly bending motion is invoked to get access to conical intersection(s) to facilitate deactivation. These states include the anionic semiquinone radical and fully reduced neutral and anionic hydroquinones in solution. In a planar configuration, flavins have a long lifetime of nanoseconds, except for the stacked conformation of FAD, where intramolecular electron transfer between the ring and the adenine moiety in 5-9 ps as well as subsequent charge recombination in 30-40 ps were observed. These observed distinct dynamics, controlled by the flavin ring flexibility, are fundamental to flavoenzyme's functions, as observed in photolyase with a planar structure to lengthen the lifetime to maximize DNA repair efficiency and in insect type 1 cryptochrome with a flexible structure to vary the excited-state deactivation to modulate the functional channel. 相似文献
56.
Krishnaprasad Madica Krishna Chaitanya Nadimpally Gangadhar J. Sanjayan 《Tetrahedron letters》2017,58(16):1568-1571
Rapastinel (GLYX-13) is a C-amidated tetrapeptide drug under clinical development for adjunctive treatment of major depressive disorder (MDD). Rapastinel features two consecutive proline residues centered at the peptide sequence (Thr-Pro-Pro-Thr-NH2), which are detrimental to its biological activity. In this communication, we report the synthesis of very close structural analogues of rapastinel comprising silaproline (Sip) as proline surrogate. By virtue of its enhanced lipophilicity and metabolic stability, Sip introduction in the native rapastinel sequence is expected to improve its pharmacokinetic profiles. 相似文献
57.
Dr. Sai Vikrama Chaitanya Vummaleti Dr. Davide Branduardi Dr. Matteo Masetti Dr. Marco De Vivo Prof. Roberto Motterlini Prof. Andrea Cavalli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(30):9267-9275
We used density functional theory to investigate the capacity for carbon monoxide (CO) release of five newly synthesized manganese‐containing CO‐releasing molecules (CO‐RMs), namely CORM‐368 ( 1 ), CORM‐401 ( 2 ), CORM‐371 ( 3 ), CORM‐409 ( 4 ), and CORM‐313 ( 5 ). The results correctly discriminated good CO releasers ( 1 and 2 ) from a compound unable to release CO ( 5 ). The predicted Mn? CO bond dissociation energies were well correlated (R2≈0.9) with myoglobin (Mb) assay experiments, which quantified the formation of MbCO, and thus the amount of CO released by the CO‐RMs. The nature of the Mn? CO bond was characterized by natural bond orbital (NBO) analysis. This allowed us to identify the key donor–acceptor interactions in the CO‐RMs, and to evaluate the Mn? CO bond stabilization energies. According to the NBO calculations, the charge transfer is the major source of Mn? CO bond stabilization for this series. On the basis of the nature of the experimental buffers, we then analyzed the nucleophilic attack of putative ligands (L′=HPO42?, H2PO4?, H2O, and Cl?) at the metal vacant site through the ligand‐exchange reaction energies. The analysis revealed that different L′‐exchange reactions were spontaneous in all the CO‐RMs. Finally, the calculated second dissociation energies could explain the stoichiometry obtained with the Mb assay experiments. 相似文献
58.
Umesh Fegade Shivaji Tayade G. Krishna Chaitanya Sanjay Attarde Anil Kuwar 《Journal of fluorescence》2014,24(3):675-681
The noncyclic 2,2′-[ethane-1,2-diylbis (iminomethanediyl)]diphenol (4) fluorescent receptor bearing two amine and hydroxyl groups have been designed and investigated for their binding properties towards various cations. The fluorescent spectral measurements revealed that receptor 4 is a selective fluorescent sensor for Fe3+ ions but not for metal ions such as Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Pb2+ and Bi3+. The binding ability was confirmed with spectroscopic methods and density functional theory calculation (DFT). This straightforward and cost effective receptor provides rapid detection of Fe3+ ions at concentrations as low as 2.5 μM and expected to be useful to design efficient chemically and biological sensor. 相似文献
59.
J. Scott Edgar Graham Milne Dr. Yiqiong Zhao Dr. Chaitanya P. Pabbati David S. W. Lim Dr. Daniel T. Chiu Prof. 《Angewandte Chemie (International ed. in English)》2009,48(15):2719-2722
Not merely a drop in the ocean : The integration of capillary electrophoresis (CE) with droplet generation driven by electroosmotic flow enabled the compartimentalization of molecular components separated by CE in a series of droplets (see picture; the green bars represent the separated analytes). The droplet‐confined bands can be docked and studied on a chip.
60.
In the capacitated facility location problem with hard capacities, we are given a set of facilities, ${\mathcal{F}}$ , and a set of clients ${\mathcal{D}}$ in a common metric space. Each facility i has a facility opening cost f i and capacity u i that specifies the maximum number of clients that may be assigned to this facility. We want to open some facilities from the set ${\mathcal{F}}$ and assign each client to an open facility so that at most u i clients are assigned to any open facility i. The cost of assigning client j to facility i is given by the distance c ij , and our goal is to minimize the sum of the facility opening costs and the client assignment costs. The only known approximation algorithms that deliver solutions within a constant factor of optimal for this NP-hard problem are based on local search techniques. It is an open problem to devise an approximation algorithm for this problem based on a linear programming lower bound (or indeed, to prove a constant integrality gap for any LP relaxation). We make progress on this question by giving a 5-approximation algorithm for the special case in which all of the facility costs are equal, by rounding the optimal solution to the standard LP relaxation. One notable aspect of our algorithm is that it relies on partitioning the input into a collection of single-demand capacitated facility location problems, approximately solving them, and then combining these solutions in a natural way. 相似文献