The current–voltage characteristics of Schottky barrier diodes formed on GaN(0001) free-standing substrates with net donor concentrations of 7.6×1015–1.4×1017 cm-3 are discussed. The substrates were grown by hydride vapor phase epitaxy. Ni Schottky contacts were directly formed on chemical–mechanical-polished Ga-polar faces of the substrates. Nearly ideal characteristics for both directions were obtained. The ideality factors for forward characteristics are 1.02–1.05, very close to unity. The reverse characteristics agree well with calculations based on thermionic-field emission theory without any fitting parameter.

Complex formation between pyrazine derivatives and dimeric self-assembly of αααα-isomer of meso-tetrakis(2-carboxy-4-nonylphenyl)porphyrin Zn complex (1·Zn) was investigated. Thermal atropisomerization of 1·Zn in a nonpolar solvent such as toluene gives the αααα-atropisomer exclusively. Vapor pressure osmometry for the resultant αααα-atropisomer solubilized in CHCl3 shows molecular weight of 2650 ± 200, indicating formation of dimeric self-assembly of 1·Zn. 1H NMR and UV/vis titration experiments for this dimeric assembly with pyrazine derivatives show highly specific 1:2 complex formation of pyrazine and 1·Zn. The equilibrium constants for 1·Zn dimer/pyrazine complex formation are estimated to be over 107 M-1. The most characteristic feature of the present ternary system, (1·Zn)2 ·pyrazine, is that the pyrazine derivative, having a large side moiety such as benzoyl group, can coordinate two zinc atoms inside the dimer cavity by sticking the side moiety out of a window formed between hydrogen-bond pillars of the complex.

DNA replication is a key step in initiating cell proliferation. Loading hexameric complexes of minichromosome maintenance (MCM) helicase onto DNA replication origins during the G1 phase is essential for initiating DNA replication. Here, we examined MCM hexamer states during the cell cycle in human hTERT-RPE1 cells using multicolor immunofluorescence-based, single-cell plot analysis, and biochemical size fractionation. Experiments involving cell-cycle arrest at the G1 phase and release from the arrest revealed that a double MCM hexamer was formed via a single hexamer during G1 progression. A single MCM hexamer was recruited to chromatin in the early G1 phase. Another single hexamer was recruited to form a double hexamer in the late G1 phase. We further examined relationship between the MCM hexamer states and the methylation levels at lysine 20 of histone H4 (H4K20) and found that the double MCM hexamer state was correlated with di/trimethyl-H4K20 (H4K20me2/3). Inhibiting the conversion from monomethyl-H4K20 (H4K20me1) to H4K20me2/3 retained the cells in the single MCM hexamer state. Non-proliferative cells, including confluent cells or Cdk4/6 inhibitor-treated cells, also remained halted in the single MCM hexamer state. We propose that the single MCM hexamer state is a halting step in the determination of cell cycle progression.

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