Rate Acceleration in Nucleophilic Alkylation of Carbonyl Compounds with a New Template Containing Two Metallic Centers

Two aluminum centers aligned in the same direction capture carbonyl groups in such a way that efficient alkyl transfer becomes possible from aluminum to the carbon atom. This occurs via a favorable cyclic six-membered transition state ( 1 ). Carbonyl compounds can now be alkylated with otherwise less reactive alkylmetal species.     

Estimation of sedimentation rates using 210Pb and 210Po at the coastal water of Sabah, Malaysia

Sediment cores were obtained from Teluk Brunei, Sipitang, Teluk Kimanis, Kota Kinabalu and Kuala Penyu at the coastal water of Sabah and analyzed for ²¹⁰Pb and ²¹⁰Po to estimate the sedimentation rates. The calculated sedimentation rates of ²¹⁰Pb and ²¹⁰Po varied from 0.003 to 0.049 cm/y and 0.74 to 8.77 cm/y, respectively. The highest sedimentation rates were determined for ²¹⁰Pb and ²¹⁰Po at stations located at Sipitang (mean: 0.027 cm/y) and Teluk Kimanis (mean: 5.53 cm/y), respectively. The sedimentation rate estimated for ²¹⁰Pb is not fully reliable because the activity of ²²⁶Ra was higher than that of ²¹⁰Pb and bioturbation was active at the sampling stations.     

Unveiling Latent Photoreactivity of Imines

Unlike carbonyl compounds, it has long been common understanding that excited imines show virtually no photoreactivity, and hence their properties and potential utility in chemical science remain largely unexplored. Now, a strategy is presented for eliciting latent photoreactivity of imines based on the introduction of a donor–acceptor (D‐A) structure to extend the lifetime of their photoexcited states. A series of spectroscopic analyses and density functional theory calculations reveal unique photophysical properties of the D‐A‐type imines. Furthermore, the reactivity of the D‐A‐type imines is demonstrated by using them as a photoredox catalyst for atom‐transfer radical addition. These findings illuminate a previously neglected chemical space in the field of photochemistry, which will be exploited by taking advantage of the inherent structural modularity of imines.     

New cytotoxic 14-membered macrolides from marine-derived fungus Aspergillus ostianus

Three new 14-membered macrolides, named aspergillides A, B, and C (1, 5, and 7), were isolated from marine-derived fungus Aspergillus ostianus strain 01F313, cultured in a medium composed of bromine-modified artificial seawater. The structures of the new compounds were determined by analyses of 1D and 2D NMR spectra. Their absolute configurations were elucidated by the modified Mosher's method and chemical conversions. The new compounds showed cytotoxic activity against mouse lymphocytic leukemia cells (L1210).     

Structural adjustment during intercalation of macrocyclic crown ether into LDH via swelling/restoration reaction: staging formation and mechanism insights

The structural control involving staging formation was studied in the nanocomposites of macrocyclic tetraazacrown ether carboxylic acid derivative (TECA) and layered double hydroxide (LDH) obtained by an osmotic swelling/restoration process. After NO(3)-type MgAl-LDH was osmotically swollen in formamide, TECA was added, leading to a restoration of the LDH sheets and formation of TECA-LDH nanocomposites. In the wet state, the structure of the composites was homogenous, and the basal spacings of ～2.0 or 1.8 nm were not changed by the water-washing process that removed formamide and caused the replacement of NO(3)(-) by CO(3)(2-). However, in the drying process, both the orientation of TECA in the interlayer and the formed staging structure varied with the TECA content. The TECA orientation changed from horizontal to tilted/twisted and finally to vertical with interlayer TECA density. The staging structure occurred for samples with both TECA and small inorganic guests coexisting in the interlayer. Third-staging, second-staging, and homogenous structures were observed at TECA/LDH weight ratios of low (0.125 and 0.25), medium (0.5) and large (1 and 2) values, respectively. The decrease of negative charge of TECA ions from -4 to -1 led to the co-existence of small ions (NO(3)(-)) with TECA in the gallery and the formation of a NO(3)(-)-containing staging structure, even at a high TECA/LDH ratio of 2. The study of the influence of CO(3)(2-) on the composite structure indicates that a TECA/CO(3)(2-) ion exchange progressed reversibly and the staging structure formed is thermodynamically stable, depending mainly on the chemical composition of the interlayer guests. The staging formation could be explained by the Daumas-Hérold model, which differs markedly from the Rüdorff model previously proposed for the LDH system. The treatment in formamide of the composite such as T2L+Na(2)CO(3) with staging structure shows that the transformation process is reversible, and these kinds of composites may be used as an adsorbent for some harmful organic solvents.