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291.
P. S. Radhakrishnamurti H. P. Panda D. C. Pradhan 《Reaction Kinetics and Catalysis Letters》1986,31(1):79-84
Title reactions are acid catalyzed and strongly dependent on the permittivity of the medium. With Cr(VI) indene reacts faster than trans-stilbene, but with V(V), trans-stilbene reacts faster than indene. The mechanism is discussed.
. Cr(VI) , -, V(V) - , . , .相似文献
292.
Panda R Zhang Y McLauchlan CC Venkateswara Rao P Tiago de Oliveira FA Münck E Holm RH 《Journal of the American Chemical Society》2004,126(20):6448-6459
A method has been devised that creates a planar Ni(II) site from a tetrahedral site in a NiFe(3)S(4) cubane-type cluster. Reaction of [(Ph(3)P)NiFe(3)S(4)(LS(3))](2)(-) (2) with 1,2-bis(dimethylphosphino)ethane affords [(dmpe)NiFe(3)S(4)(LS(3))](2)(-) (3), isolated in ca. 45% yield as (Et(4)N)(2)[3a].2.5MeCN and (Et(4)N)(2)[3b].0.25MeCN, both of which occur in triclinic space group P. Each crystalline form contains two crystallographically inequivalent clusters with the same overall structure but slightly different dimensions. The cluster is bound by three thiolate terminal ligands to semirigid cavitand ligand LS(3). The NiFe(3)S(4) core contains three tetrahedral sites, one Fe(micro(3)-S)(3)(SR) and two Fe(micro(3)-S)(2)(micro(2)-S)(SR) with normal metric features, and one distorted square planar Ni(micro(3)-S)(2)P(2) site in a Ni(micro(3)-S)(2)Fe face with mean bond lengths Ni-P = 2.147(9) A and Ni-S = 2.29(2) A. The opposite Fe(2)(micro(3)-S)(micro(2)-S) face places the micro(2)-S atom at nonbonding and variable distances (2.60-2.90 A) above the nickel atom. Binding of the strong-field ligand dmpe results in a planar Ni(II) site and deconstruction of the full cubane geometry. The structure approximates that established crystallographically in the C-cluster of C. hydrogenoformans carbon monoxide dehydrogenase whose NiFe(4)S(4) core contains a planar NiS(4) site and three tetrahedral FeS(4) sites in a fragment that is bridged by sulfide atoms to an exo iron atom. M?ssbauer studies of polycrystalline samples containing both clusters 3a and 3b reveal the presence of at least two cluster types. The spectroscopically best defined cluster accounts for ca. 54% of total iron and exhibits hyperfine interactions quite similar to those reported for the S = (5)/(2) state of the protein-bound cubane-type cluster [ZnFe(3)S(4)](1+), whose M?ssbauer spectrum revealed the presence of a high-spin Fe(2+) site and a delocalized Fe(2.5+)Fe(2.5+) pair. Development of reactions leading to a planar nickel and a sulfide-bridged iron atom is requisite to attainment of a synthetic analogue of this complex protein-bound cluster. This work demonstrates a tetrahedral (2) --> planar (3) Ni(II) stereochemical conversion can be effected by binding of ligands that generate a sufficiently strong in-plane ligand field (dmpe = 1,2-bis(dimethylphosphino)ethane, LS(3) = 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3-)). 相似文献
293.
Bikash Kumar Panda 《Journal of organometallic chemistry》2005,690(13):3169-3175
The solution reaction of Ru(QL1)(PPh3)2(CO)Cl (3) and Os(QL1)(PPh3)2(CO)Br (4) with carbon monoxide at one atmosphere pressure has respectively afforded the orange acylruthenium system Ru(QL2)(PPh3)2(CO)Cl (5) and the yellow arylosmium dicarbonyl system Os(QL3)(PPh3)2(CO)2Br (6) in excellent yields. (QL1 is C6H2O-2-CHNHC6H4Q(p)-3-Me-5, QL2 is C6H2(CO-1)O-2-CHNHC6H4Q(p)-3-Me-5 and QL3 is C6H2OH-2-CHNC6H4Q(p)-3-Me-5 and Q is Me, OMe and Cl.) It is proposed that in the case of 3 a dicarbonyl complex similar to 6 is formed as an intermediate which rapidly undergoes aryl migration with concomitant phenolato coordination furnishing 5. The stability of 6 is consistent with the greatly diminished ability of osmium in promotion of migratory reactions. In the reaction 4 → 6 the Os-O(phenolato) bond is cleaved and the Schiff base moiety undergoes iminium-phenolato → imine-phenol tautomerization. The observed cis geometry of 6 may arise by a concerted route involving edge displacement of the halide ligand. The crystal and molecular structure of 5(Q = Cl) has revealed the presence of a distorted octahedral RuC2P2OCl coordination sphere and a highly planar acyl chelate ring characterized by a Ru-C distance of 2.013(4) Å. In the hydrogen bonded zwitterionic iminium-phenolato ring the N ? O distance is 2.561(6) Å. The acyl complexes of type 5 display an MLCT band near 500 nm which is absent in 6. The Schiff base CN stretch in 5 (∼1630 cm−1) is significantly higher than that in 6 (∼1600 cm−1) which displays two strong CO stretches near 2020 and 1940 cm−1 (cis-Os(CO)2 configuration). A single 31P NMR signal occurs in both 5 and 6 near 37 and −6 ppm, respectively (trans-M(PPh3)2 configuration). The voltammetric reduction potentials of the MIII/MII couple is observed near 1.0 and 0.8 V vs. SCE in 5 and 6, respectively. Both are significantly higher than those in parent complexes (3 and 4) due to stabilization of the bivalent state upon carbonylation. 相似文献
294.
Ms. S. Singh C. R. Panda V. Chakravortty K. C. Dash 《Journal of Radioanalytical and Nuclear Chemistry》1988,120(1):65-73
Solvent extractions of thorium(IV) and uranium(VI) by a commercially available chelating extractant LIX-26 (an alkylated 8-hydroxyquinoline) or 8-hydroxyquinoline, benzoic or salicylic acid, dipentyl sulphoxide (DPSO) and their mixtures with butanol as modifier in benzene/methylisobutyl ketone (MIBK) as the diluent have been studied. Extraction of uranium(VI) by 10% LIX-26 and 10% butanol in benzene becomes quantitative at pH 5.0. The pH 0.5 values for the extraction of thorium(IV) and uranium(VI) are 4.95 and 3.35, respectively. Quantitative extraction of thorium(IV) by the mixture of 0.1 M oxine and 0.1 M salicylic acid in methylisobutyl ketone was observed at pH 5.0. The influence of concentration of various anions on the extraction of Th4+ by mixtures of LIX-26 and benzoic acid has been studied. Studies on extraction of thorium(IV) and uranium(VI) by mixtures of LIX-26 (HQ) and DPSO show that the extracted species are possibly of the type [ThQ2/DPSO/2/SCN/2] and [UO2Q2/DPSO/], respectively. 相似文献
295.
The azopyrimidine and azoimidazole ligands (general abbreviations, RL) used in the present work are 2-(p-R-C6H4NN)C4H3N2, RLpm (R=H, Cl) and 2-(p-R-C6H4NN)-1-(Me)C3H2N2, RLim (R=Me, Cl), respectively. The reaction of Re(CO)5Cl with a slight excess of RL in boiling benzene has furnished blue-violet complexes of type Re(CO)3Cl(RL) which have been spectrally characterized. In Re(CO)3Cl(HLpm) and Re(CO)3Cl(ClLim) the Re-Nh, Re-Na distances are 2.173(6), 2.136(6) Å and 2.150(5), 2.166(5) Å, respectively (Nh and Na are heterocyclic and azo N atoms, respectively). Their N-N lengths (1.271(8), 1.281(7) Å) implicate relatively weak Re-azo(π*) back-bonding. In the lattice of Re(CO)3Cl(HLpm), pair-wise C-H?O hydrogen bonding between symmetry related molecules is present (C?O; 3.264(9) Å, H?O; 2.460(10) Å; C-H?O; 130.6(5)°). The lattice of Re(CO)3Cl(ClLim) also consists of centrosymmetric dimers held by aromatic π-π stacking between parallely placed pendant aryl rings (centroid?centroid distance, 3.781(9) Å). Extended Hückel calculations reveal that the LUMO of Re(CO)3Cl(RL) is ∼60% azo in character. One-electron quasireversible electrochemical reduction occurs near −0.1 and −0.4 V vs. SCE in the cases of Re(CO)3Cl(RLpm) and Re(CO)3Cl(RLim), respectively. The redox orbital is believed to be to the above noted LUMO. Electrogenerated Re(CO)3Cl(RL−) underwent spontaneous solvolytic chloride displacement in MeCN furnishing Re(CO)3(MeCN)(RL−) which has been isolated. The latter in turn reacted with imidazole and triphenyl phosphine furnishing Re(CO)3(C3H4N2)(RL−) and Re(CO)3(PPh3)(RL−), respectively. The pattern of carbonyl stretching frequencies of these radical anion complexes is similar to that of Re(CO)3Cl(RL) but for shifts to lower frequencies by 10-40 cm−1. All the three radical anion systems are one-electron paramagnets (1.7-1.8 μB). The unpaired electron is primarily localized in a predominantly azo-π* orbital. A small metal contribution (185, 187Re, I=5/2) is present and both Re(CO)3(MeCN)(RL−) and Re(CO)3(C3H4N2)(RL−) display six-line EPR spectra (A∼28 G). The line shapes and intensities are characteristic of the presence of g-strain. In the case of Re(CO)3(PPh3)(RL−) seven nearly equispaced lines are observed due to virtually equal coupling with metal and 31P (I=1/2) nuclei. The g values of the radical species span the range 2.0033-2.0066. 相似文献
296.
Dr. Piyush K. Jain Vyas Ramanan Dr. Arnout G. Schepers Nisha S. Dalvie Apekshya Panda Dr. Heather E. Fleming Prof. Sangeeta N. Bhatia 《Angewandte Chemie (International ed. in English)》2016,55(40):12440-12444
The ability to remotely trigger CRISPR/Cas9 activity would enable new strategies to study cellular events with greater precision and complexity. In this work, we have developed a method to photocage the activity of the guide RNA called “CRISPR‐plus” (CRISPR‐precise light‐mediated unveiling of sgRNAs). The photoactivation capability of our CRISPR‐plus method is compatible with the simultaneous targeting of multiple DNA sequences and supports numerous modifications that can enable guide RNA labeling for use in imaging and mechanistic investigations. 相似文献
297.
298.
Visible‐Light‐Induced Efficient Selective Oxidation of Nonactivated Alcohols over {001}‐Faceted TiO2 with Molecular Oxygen 下载免费PDF全文
Dr. Raji Vadakkekara Abul Kalam Biswas Tapan Sahoo Dr. Provas Pal Dr. Bishwajit Ganguly Dr. Subhash Chandra Ghosh Dr. Asit Baran Panda 《化学:亚洲杂志》2016,11(21):3084-3089
In the presence of molecular oxygen, a {001}‐faceted nanocrystalline anatase TiO2 catalyst enabled the selective oxidation of nonactivated aliphatic alcohols to the corresponding aldehydes or ketones under visible light. The reaction shows excellent conversion and selectivity towards the formation of the carbonyl products without over‐oxidation to the corresponding carboxylic acids. The exceptional reactivity of the catalyst is possibly due to the absorption of visible light originating from a stronger interaction of alcohol with the {001} facet, which facilitates the modification of the band structure of TiO2, thus facilitating the photogenerated hole transfer and subsequent oxidation processes. The experimental results have also been corroborated by first‐principles quantum chemical DFT calculations. 相似文献
299.
Tushar Ranjan Panda Manikandan M Shreyas P. Vaidya Sushanta Chhatar Suman Sinha Megha Mehrotra Sourav Chakraborty Shubhankar Gadre Prakash Duari Pritha Ray Malay Patra 《Angewandte Chemie (International ed. in English)》2023,62(38):e202303958
Even in the modern era of precision medicine and immunotherapy, chemotherapy with platinum (Pt) drugs remains among the most commonly prescribed medications against a variety of cancers. Unfortunately, the broad applicability of these blockbuster Pt drugs is severely limited by intrinsic and/or acquired resistance, and high systemic toxicity. Considering the strong interconnection between kinetic lability and undesired shortcomings of clinical Pt drugs, we rationally designed kinetically inert organometallic Pt based anticancer agents with a novel mechanism of action. Using a combination of in vitro and in vivo assays, we demonstrated that the development of a remarkably efficacious but kinetically inert Pt anticancer agent is feasible. Along with exerting promising antitumor efficacy in Pt-sensitive as well as Pt-resistant tumors in vivo, our best candidate has the ability to mitigate the nephrotoxicity issue associated with cisplatin. In addition to demonstrating, for the first time, the power of kinetic inertness in improving the therapeutic benefits of Pt based anticancer therapy, we describe the detailed mechanism of action of our best kinetically inert antitumor agent. This study will certainly pave the way for designing the next generation of anticancer drugs for effective treatment of various cancers. 相似文献
300.
Tanmoy Mandal Abhishek Kumar Jatin Panda Tapas Kumar Dutta Joyanta Choudhury 《Angewandte Chemie (International ed. in English)》2023,62(50):e202314451
In recent times, heterogenization of homogeneous molecular catalysts onto various porous solid support structures has attracted significant research focus as a method for combining the advantages of both homogeneous as well as heterogeneous catalysis. The design of highly efficient, structurally robust and reusable heterogenized single-site catalysts for the CO2 hydrogenation reaction is a critical challenge that needs to be accomplished to implement a sustainable and practical CO2-looped renewable energy cycle. This study demonstrated a heterogenized catalyst [Ir-HCP-(B/TPM)] containing a molecular Ir-abnormal N-heterocyclic carbene (Ir-aNHC) catalyst self-supported by hierarchical porous hyper-crosslinked polymer (HCP), in catalytic hydrogenation of CO2 to inorganic formate (HCO2−) salt that is a prospective candidate for direct formate fuel cells (DFFC). By employing this unique and first approach of utilizing a directly knitted HCP-based organometallic single-site catalyst for CO2-to-HCO2− in aqueous medium, extremely high activity with a single-run turnover number (TON) up to 50816 was achieved which is the highest so far considering all the heterogeneous catalysts for this reaction in water. Additionally, the catalyst featured excellent reusability furnishing a cumulative TON of 285400 in 10 cycles with just 1.6 % loss in activity per cycle. Overall, the new catalyst displayed attributes that are important for developing tangible catalysts for practical applications. 相似文献