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71.
Localized singlet diradicals (biradicals) are key intermediates in chemical reactions involving homolytic bond-cleavage and formation processes. The molecular structure and electronic structure had been historically elusive due to the short-lived character of the reactive intermediates. In the last 15 years, a significant development of singlet diradical chemistry was achieved after the pioneering findings of long-lived singlet diradicals. In this tutorial review, the recent development of localized singlet diradical chemistry is summarized and discussed. The following subjects are included (a) the mechanism by which the ground state spin-multiplicity of localized 1,3-diradicals is controlled; (b) the substituent and heteroatom effect on the most stable electronic configuration of the singlet 1,3-diradicals, type-1 versus type-2; (c) the molecular design for the long-lived singlet ground state diradicals; (d) the generation and characterization of the singlet diradicals; and (e) the future prospects. 相似文献
72.
Synchronized stereocontrol of two planar-chiral units was accomplished by using crystallization-induced asymmetric transformation (CIAT) of cyclophane-type bridged bisnicotinate derivatives 5b and 7. After screening various linkers, (S)-2-amino-1-butanol and (S)-tert-leucinol were found to be the most effective for CIAT of the corresponding bridged bisnicotinate 5b and 7, respectively, whose diastereomeric ratio finally reached 97% and 88%, respectively. 相似文献
73.
Soe Than Md. Mizanur Rahman Badal Shuhei Itoh Masaaki Mishima 《Journal of Physical Organic Chemistry》2010,23(5):411-417
The relative free energy changes (lanthanum cation basicity, LaCB[L2]) for the reaction [La(OMe)2]L ? La(OMe) + 2L were determined in the gas phase for m‐ and p‐substituted acetophenones based on the measurement of ligand exchange equilibria using an FT‐ICR mass spectrometer. The substituent effect on ΔLaCB[L2] of acetophenone is described in terms of the Yukawa–Tsuno equation, ΔG = ρ(σ° + r+ Δ σ ), with a ρ value of ?11.2 and an r+ value of 0.49. From this result, a ρ value of ?7.0 and an r+ value of 0.49 were estimated for the monomeric complex [LLa(OMe)] with the aid of theoretical calculations. This ρ value was found to be significantly smaller than that for protonation, and even smaller than Li+ basicity. Such a small ρ value has been attributed to the largely ionic (ion–dipole interaction) nature of the bonding interaction between La(OMe) and the carbonyl oxygen atom and, in part, to the long distance between La(OMe) and the substituent. Contrary to the ρ value, the r+ value is identical in both La(OMe) and Li+ basicities, suggesting that the r+ value of 0.49 can be regarded as a limiting one in a series of Lewis cation basicities of the acetophenone system, H+ (0.86) > Me3Si+ (0.75) > Me3Ge+ (0.71) > Cu+ (0.60) > Li+ = La(OMe) (0.49). Since the binding interaction between La(OMe) or Li+ and a neutral ligand is mostly electrostatic, the moderate r+ was interpreted to result from the redistribution of the induced positive charge within the acetophenone moiety upon binding with a metal ion rather than transfer of positive charge from a metal ion to the aromatic moiety. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
74.
Takashi Tanaka Teppei Ikeya Hajime Kamoshida Yusuke Suemoto Masaki Mishima Masahiro Shirakawa Peter Güntert Yutaka Ito 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(22):7362-7366
Proteins in living cells interact specifically or nonspecifically with an enormous number of biomolecules. To understand the behavior of proteins under intracellular crowding conditions, it is indispensable to observe their three‐dimensional (3D) structures at the atomic level in a physiologically natural environment. We demonstrate the first de novo protein structure determinations in eukaryotes with the sf9 cell/baculovirus system using NMR data from living cells exclusively. The method was applied to five proteins, rat calmodulin, human HRas, human ubiquitin, T. thermophilus HB8 TTHA1718, and Streptococcus protein G B1 domain. In all cases, we could obtain structural information from well‐resolved in‐cell 3D nuclear Overhauser effect spectroscopy (NOESY) data, suggesting that our method can be a standard tool for protein structure determinations in living eukaryotic cells. For three proteins, we achieved well‐converged 3D structures. Among these, the in‐cell structure of protein G B1 domain was most accurately determined, demonstrating that a helix‐loop region is tilted away from a β‐sheet compared to the conformation in diluted solution. 相似文献
75.
A natural bond orbital analysis of aryl‐substituted polyfluorinated carbanions: negative hyperconjugation
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Masahiko Suenaga Kazuhide Nakata José‐Luis M. Abboud Masaaki Mishima 《Journal of Physical Organic Chemistry》2018,31(1)
Aryl‐substituted polyfluorinated carbanions, ArCHRf? where Rf = CF3 ( 1 ), C2F5 ( 2 ), i‐C3F7 ( 3 ), and t‐C4F9 ( 4 ), were analyzed by means of the natural bond orbital (NBO) theory at the B3LYP/6‐311+G(d,p) computational level. A lone pair NBO at the formal anionic center carbon (Cα) was not found in the Lewis structure. Instead, significant donor/acceptor NBO interactions between π(Cα‐C1) and σ*(Cβ‐F) or σ*(Cβ‐Cγ) were observed for 1 , 2 , 3a (strong electron‐withdrawing substituent, from p‐CF3 to p‐NO2), and 4 . Their second‐order donor/acceptor perturbation interaction energy, E(2), values decreased with the increase of the stability of carbanions. A larger E(2) value corresponds to longer Cβ‐F and Cβ‐Cγ bonds and a shorter Cα‐Cβ bond, indicating that the E(2) values can be associated with the negative hyperconjugation of the Cβ‐F and Cβ‐Cγ bonds. In accordance with this, the E(2) values for π(Cα‐C1) → σ*(Cβ‐F) were linearly correlated with the ΔGoβ‐F values (an empirical measure of β‐fluorine negative hyperconjugation obtained from an increased acidity). In 3b (weak electron‐withdrawing substituents, from H to m‐NO2) very large E(2) values for LP(Fβ) → π*(Cα‐Cβ) were obtained. This was attributed to the Cβ‐F bond cleavage and the Cα‐Cβ double bond formation in the Lewis structure that is caused by the extremely strong negative hyperconjugation of the Cβ‐F bond. 相似文献
76.
77.
Hongwei Liu Takeshi Fujiwara Yuri Mishima Takeshi Shida Hisayoshi Kobayashi Michio Namikoshi 《Tetrahedron》2005,61(36):8611-8615
Three new polysulfur alkaloids, lissoclibadins 1 (1)-3 (3), were isolated from the ascidian Lissoclinum sp. (cf. L. badium Monniot, F. and Monniot, C., 1996). The structures of 1-3 were assigned on the basis of their spectral data, and the computational modeling study was utilized for 1. Compound 1 had a trimeric structure of three identical aromatic anime moieties connected through two sulfide and a disulfide bonds. Compounds 2 and 3 were dimeric structures of the same unit as that of 1 connected through a sulfide and disulfide bonds (2) and two sulfide bonds (3). Compounds 1 and 2 inhibited the growth of the marine bacterium Ruegeria atlantica (15.2 mm at 20 μg/disk and 12.2 mm at 5 μg/disk, respectively) and 2 showed antifungal activity to Mucor hiemalis (13.8 mm at 50 μg/disk). Compounds 1-3 were cytotoxic against HL-60 (IC50=0.37, 0.21, and 5.5 μM, respectively). 相似文献
78.
K Kanao M Honda S Ishihara H Moriuma T Mishima M Tomonobu N Usami B Kishino H Itatani H Morii 《Radioisotopes》1988,37(7):402-405
Two-site immunoradiometric assay for human parathyrin (PTH1-84) is specific for the intact, secreted, biologically active 84 amino peptide. This system incorporates two-different polyclonal antibodies to human intact PTH and has several technical advantages for use. This assay could detect a wide range of PTH in patients with hypo-, hyperparathyroidism, chronic renal failure and hypercalcemia with malignancy, especially distinguishing the level of human intact PTH in hypoparathyroidism from in normal. 相似文献
79.
Hioki H Yoshio S Motosue M Oshita Y Nakamura Y Mishima D Fukuyama Y Kodama M Ueda K Katsu T 《Organic letters》2004,6(6):961-964
[structure: see text] Enantioselective synthesis of eurylene, 14-deacetyl eurylene, and their 11-epimers was achieved. The characteristic structural feature of these compounds is two tetrahydrofuran (THF) rings substituted in different stereochemistry. The synthetic approach involves nonstereoselective THF ring formation to afford both segments from a common precursor. We also investigated their ionophoric nature and cytotoxicity. The complexation of these compounds with K(+) might be related to their cytotoxic activity. 相似文献
80.