Binding of Scandium Ions to Metalloporphyrin–Flavin Complexes for Long‐Lived Charge Separation

A porphyrin–flavin‐linked dyad and its zinc and palladium complexes (MPor?Fl: 2 ?M, M=2 H, Zn, and Pd) were newly synthesized and the X‐ray crystal structure of 2 ?Pd was determined. The photodynamics of 2 ?M were examined by femto‐ and nanosecond laser flash photolysis measurements. Photoinduced electron transfer (ET) in 2 ?H₂ occurred from the singlet excited state of the porphyrin moiety (H₂Por) to the flavin (Fl) moiety to produce the singlet charge‐separated (CS) state ¹(H₂Por^.+?Fl^.?), which decayed through back ET (BET) to form ³[H₂Por]*?Fl with rate constants of 1.2×10¹⁰ and 1.2×10⁹ s^?1, respectively. Similarly, photoinduced ET in 2 ?Pd afforded the singlet CS state, which decayed through BET to form ³[PdPor]*?Fl with rate constants of 2.1×10¹¹ and 6.0×10¹⁰ s^?1, respectively. The rate constant of photoinduced ET and BET of 2 ?M were related to the ET and BET driving forces by using the Marcus theory of ET. One and two Sc³⁺ ions bind to the flavin moiety to form the Fl?Sc³⁺ and Fl?(Sc³⁺)₂ complexes with binding constants of K₁=2.2×10⁵ M ^?1 and K₂=1.8×10³ M ^?1, respectively. Other metal ions, such as Y³⁺, Zn²⁺, and Mg²⁺, form only 1:1 complexes with flavin. In contrast to 2 ?M and the 1:1 complexes with metal ions, which afforded the short‐lived singlet CS state, photoinduced ET in 2 ?Pd???Sc³⁺ complexes afforded the triplet CS state (³[PdPor^.+?Fl^.??(Sc³⁺)₂]), which exhibited a remarkably long lifetime of τ=110 ms (k_BET=9.1 s^?1).     

Synthesis and Structure of Hypervalent Iodine(III) Reagents Containing Phthalimidate and Application to Oxidative Amination Reactions

A new class of hypervalent iodine reagents containing phthalimidate was synthesized, and structurally characterized by X‐ray analysis. The benziodoxole‐based reagent displays satisfactory solubility in common organic solvents and is reasonably stable in solution as well as in the solid state. The reagent was used for the oxidative amination of the C(sp³)? H bond of N,N‐dimethylanilines. In addition, the reagent was also applicable to oxidative amination with rearrangement of trialkylamines as well as enamines that were prepared in situ from secondary amines and aldehydes.     

Ligand‐Controlled Synthesis of [3]‐ and [4]Cyclo‐9,9‐dimethyl‐2,7‐fluorenes through Triangle‐ and Square‐Shaped Platinum Intermediates

The syntheses of [3]‐ and [4]cyclo‐9,9‐dimethyl‐2,7‐fluorenes ([3] and [4]CFRs), cyclic trimer, and tetramers of 9,9‐dimethyl‐2,7‐fluorene (FR), respectively, were achieved by the platinum‐mediated assembly of FR units and subsequent reductive elimination of platinum. A triangle‐shaped tris‐platinum complex and a square‐shaped tetra‐platinum complex were obtained by changing the platinum ligand. The structure of the triangle complex was unambiguously determined by X‐ray crystallographic analysis. Reductive elimination of each complex gave [3] and [4]CFRs. Two rotamers of [3]CFR were sufficiently stable at room temperature and were separated by chromatography. The physical properties of the CFRs were also investigated theoretically and experimentally.     

Effect of ultrasonic frequency on polymerization of styrene under sonication

The effect of ultrasonic frequency on polymerization of styrene under sonication at 50 degrees C was studied at the frequencies of 23.4, 45.7, 92, 518 kHz and 1 MHz. Polymerization under sonication was carried out at the ultrasonic intensity that gives the same reaction rate of decomposition of porphyrin. The magnitude of the polymerization rate increases in the order of 92, 45.7 and 23.4 kHz. At the high frequencies of 518 kHz and 1 MHz, no polymerization was observed. These facts mean that there is an optimum frequency in the range from 92 to 518 kHz for effective polymerization. The average-number molecular weights at the sonication time of 3 h are 5.5 x 10(4), 8.0 x 10(4) and 11.5 x 10(4) for the irradiated frequencies of 92, 45.7 and 23.4 kHz, respectively. Sonication for 3 h at 92 kHz gives polystyrene with very high polydispersity, about 5.0, in comparison with the results obtained at 23.4 and 45.7 kHz. These observations indicate that polymerization under sonication is influenced by the irradiated frequency.     

Well-defined fluorescent particles of ZnS:Cu. 1. Preparation and effects of annealing

As an application of the gel-sol procedure for the synthesis of monodispersed particles in large quantities, uniform particles of ZnS:Cu were prepared by different methods from concentrated Zn-chelate solutions of nitrilotriatic acid (NTA) with thioacetamide (TAA), in which the dopant copper ion was introduced as a coexisting mixed chelate with Zn-NTA (Method A), a Cu-NTA complex in a separate solution continuously added to a system of Zn-NTA and TAA (Method B), or a Cu(NO3)2 solution infiltrated into a dry powder of ZnS prepared by Method A (Method C). All powders thus prepared were annealed before the test of fluorescent properties. The main roles of annealing were to remove the grain boundaries of such particles as nonradiative recombination centers of excited electrons and holes and to achieve uniform distribution of dopants. However, the initial intraparticle distribution of the dopant, controlled by the different methods, decisively affected the fluorescent particles, even after the conversion of the polycrystalline particles to single-crystal particles by annealing.     

Temperature dependence of microhardness of tetragonal hen-egg-white lysozyme single crystals

The mechanical properties of high-quality single crystals of tetragonal hen-egg-white lysozyme from hen egg white were investigated by the indentation method. The indentation marks were clearly observed on the crystal surface and elastic recovery did not occur. The micro-Vickers hardness of the crystals in the wet condition was observed to be 20?MPa at room temperature. To investigate deformation, the temperature dependence of the hardness was investigated from 278 to 308?K. The hardness strongly depended on the temperature above 290?K. From these results the deformation of lysozyme single crystals was explained in terms of dislocation mechanisms.     

Structural evolution of glutathionate-protected gold clusters studied by means of 197 Au Mössbauer spectroscopy

¹⁹⁷Au Mössbauer spectra of a series of glutathionate-protected gold clusters, Au _n (SG) _m , with n = 10 ? ~55, were re-analyzed to understand the structure evolution behavior. The numbers of gold atoms coordinated by different numbers (0, 1, and 2) of the GS ligands were successfully determined by assuming individual isomer shifts and quadrupole splittings for the three sites in Au₂₅(SG)₁₈ (Tsukuda et al., Chem Lett 40:1292, 2011). The analysis revealed the drastic structural evolution of Au _n (SG) _m in the range of n = 10 ? ~55. In Au₁₀(SG)₁₀, all the gold atoms are bonded to GS ligands, indicating –Au–S(G)– cyclic structures. A catenane structure was proposed for Au₁₀(SG)₁₀. At n = 25, a single Au atom without the GS ligation appeared, consistent with the formation of an icosahedral Au₁₃ core protected by six staples, –S(G)–[Au–S(G)–]₂. At n = 39, it is considered that Au₃₉(SG)₂₄ has a similar structure to that of Au₃₈(SC₂H₄Ph)₂₄ with face-fused bi-icosahedral Au₂₃ core.