Mass spectra of π-cyclopentadienyl-diene cobalt complexes

Many reports on the mass spectra of organotransition-metal complexes have appeared in recent years,¹ whilst there have only been a few reports on the mass spectra of transition metal olefin complexes, some metal carbonyl olefin complexes²³⁴ and π-cyclooctenyl-π-cyclooctadienyl cobalt.⁵ Recently fragmentation paths of π-cyclopentadienyl-cyclooctadiene rhodium were elucidated by King.⁶ The present authors found metastable ions in the mass spectra of π-cyclopentadienyl-diene cobalt complexes as well as in the mass spectra of π-cyclopentadienyl-diene rhodium complexes.⁷. In the present paper the authors wish to report the mass spectra of several π-cyclopentadienyl diene cobalt complexes.     

Geographical distribution of plutonium derived from the atomic bomb in the eastern area of Nagasaki

In order to know the distribution of plutonium derived from the Nagasaki atomic bomb, soil samples were measured to determine the ²⁴⁰Pu/²³⁹Pu isotope ratio of and concentrations of ^239+240Pu and ¹³⁷Cs. The ^239+240Pu concentrations in soils, except for Nishiyama area, were close to the average concentration of soil collected in Japan. In soils collected at the Nishiyama area and at the eastern area of Nagasaki Prefecture and at part of northern area in Kumamoto Prefecture, the ²⁴⁰Pu/²³⁹Pu ratios were lower than the global fallout values. This suggests that plutonium from the atomic bomb was deposited in the eastern area from the hypocenter reaching up to 100 km eastwards.     

Phase-separation and distribution of phenyl groups for PhTES-TEOS coatings prepared on polycarbonate substrate

Phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) coatings [xPhTES·(100 − x)TEOS (mol%)] (x = 0 − 80) were prepared on polycarbonate (PC) substrate, and adhesion, surface hardness and distribution of phenyl groups were studied. The coatings with more than 60 mol% of PhTES showed good adhesion (≈ 100%), and the pencil hardness of PC substrate (4B) improved to 2B or B after the coatings. Bulk gels with the same compositions were also prepared, and distribution of phenyl groups were estimated using fourier transform infrared (FT-IR) spectroscopy (KBr method for bulk gels and attenuated total reflection (ATR) method for coatings). A significant difference for the distribution of phenyl groups was clearly observed between bulk gels and coatings, suggesting PC substrate affects the distribution of phenyl groups in coatings. The adhesion and FTIR results revealed that there is an interaction caused by π-electrons between benzene rings on PC substrate and phenyl groups of PhTES-TEOS coatings. It was found that the adhesion was strongly correlated with the phenylsilsesquioxane networks formed around PC substrate side.     

Redox-responsive molecular switches based on azoterpyridine-bridged Ru/Os complexes

Three new terpyridine-based dinuclear complexes, [(tpy)Ru(azotpy)Ru(tpy)]4+ (tpy = 2,2':6',2'-terpyridine, azotpy = bis[2,6-bis(2-pyridyl)-4-pyridyl]diazene), [(tpy)Os(azotpy)Os(tpy)]4+, and [(tpy)Ru(azotpy)Os(tpy)]4+ were prepared and their electrochemical and photophysical properties investigated. The bridging ligand, azotpy, in these complexes is reduced at less negative potentials than the unsubstituted tpy ligand. These complexes exhibit absorption bands due to the metal-to-ligand charge-transfer transitions both to the unsubstituted tpy ligand and the bridging azotpy ligand, the latter absorption being observed at the lower energy side of the former. These observations are consistent with the lower lying pi* level of the azotpy ligand than that of the tpy ligand. These complexes are nonluminescent, since the excited electron is trapped in this lower lying pi* level of the azotpy ligand in the excited state. Reduction of this bridging ligand by constant potential electrolysis renders the shape of absorption spectra for these complexes nearly identical to those of the parent complexes, [M(tpy)2]2+ (M = Ru, Os). In this reduced state, the homodinuclear Os complex becomes luminescent at room temperature, whereas the homodinuclear Ru complex becomes luminescent at 77 K, thus establishing their photoswitching behavior. The reduced heterodinuclear complex exhibits luminescence from the Os center, which is sensitized by the Ru center in the same molecule as evidenced by the excitation spectra. Thus, the intramolecular energy transfer can be switched on and off by the redox reaction of the bridging component.     

Furan ring oxidation strategy for the synthesis of macrosphelides A and B

By using the convenient protocol for conversion of 2-substituted furans into 4-oxo-2-alkenoic acids ((i) NBS, (ii) NaClO(2)), macrosphelide B (2) was synthesized from furyl alcohol 5 (>98% ee) and acid 6 (99% ee). The protocol was first applied to the PMB ether of 5 to afford acid 13b. On the other hand, DCC condensation of acid 6 with 5 gave 16 after deprotection of the TBS group. Condensation was again carried out between 13b and 16 to furnish the key ketone 17, which upon reduction with Zn(BH(4))(2) afforded anti alcohol 18 stereoselectively (15:1). After protection/deprotection steps, the furan 18 was converted to seco acid 3 by using the furan oxidation protocol mentioned above, and lactonization of 3 with Cl(3)C(6)H(2)COCl, Et(3)N, and DMAP afforded 22 (MOM ether of 2), which upon deprotection with TFA produced 2. Transformation of 22 to macrosphelide A (1) was then investigated. Although the chelation-controlled reduction of 22 should afford the desired anti alcohol 24, Zn(BH(4))(2) at <-90 degrees C gave a 2 approximately 1:1 mixture of anti/syn alcohols. On the contrary, reduction with NaBH(4) in MeOH at -15 degrees C produced the syn isomer 23 with >10:1 diastereoselectivity. Mitsunobu inversion of the resulting C(14)-hydroxyl group and deprotection of the MOM group with TFA afforded 1. Similarly, reduction of 2 with NaBH(4) afforded the C(14)-epimer of 1 stereoselectively. The observed stereoselectivity in the reductions of 22 and 2 could be explained on the basis of computer-assisted calculation, which showed presence of the low-energy conformers responsible for the stereoselective reduction. In addition, conversion of 2 to 1 was established, for the first time.     

Structure and Dynamics in the Nucleosome Revealed by Solid‐State NMR

Eukaryotic chromatin structure and dynamics play key roles in genomic regulation. In the current study, the secondary structure and intramolecular dynamics of human histone H4 (hH4) in the nucleosome core particle (NCP) and in a nucleosome array are determined by solid‐state NMR (SSNMR). Secondary structure elements are successfully localized in the hH4 in the NCP precipitated with Mg²⁺. In particular, dynamics on nanosecond to microsecond and microsecond to millisecond timescales are elucidated, revealing diverse internal motions in the hH4 protein. Relatively higher flexibility is observed for residues participating in the regulation of chromatin mobility and DNA accessibility. Furthermore, our study reveals that hH4 in the nucleosome array adopts the same structure and show similar internal dynamics as that in the NCP assembly while exhibiting relatively restricted motions in several regions consisting of residues in the N‐terminus, Loop 1, and the α3 helix region.     

Phosphine‐Catalyzed anti‐Carboboration of Alkynoates with 9‐BBN‐Based 1,1‐Diborylalkanes: Synthesis and Use of Multisubstituted γ‐Borylallylboranes

Trialkylphosphine organocatalysis has enabled the regioselective anti‐carboboration of alkynoates with 9‐BBN‐based 1,1‐diborylalkanes to produce secondary allylboranes with β‐alkoxycarbonyl and γ‐boryl substituents. The utility of the densely functionalized allylboranes was demonstrated by the highly diastereoselective allylation of N‐(trimethylsilyl)aldimines to produce homoallylamines containing tertiary allylborane and acrylate moieties.     

Direct Participation of a Peripheral Side Chain of a Corrin Ring in Coenzyme B12 Catalysis

The crystal structures of the B₁₂‐dependent isomerases (eliminating) diol dehydratase and ethanolamine ammonia‐lyase complexed with adenosylcobalamin were solved with and without substrates. The structures revealed that the peripheral a‐acetamide side chain of the corrin ring directly interacts with the adenosyl group to maintain the group in the catalytic position, and that this side chain swings between the original and catalytic positions in a synchronized manner with the radical shuttling between the coenzyme and substrate/product. Mutations involving key residues that cooperatively participate in the positioning of the adenosyl group, directly or indirectly through the interaction with the a‐side chain, decreased the turnover rate and increased the relative rate of irreversible inactivation caused by undesirable side reactions. These findings guide the engineering of enzymes for improved catalysis and producing useful chemicals by utilizing the high reactivity of radical species.