Size‐Dependent Thermochromism through Enhanced Electron–Phonon Coupling in 1 nm Quantum Dots

1 nm CuO quantum dots (QDs) were produced in size‐controlled super‐micropores of a silica matrix. The reversible color change of the QDs from pale blue to deep green was clearly observed in a wide temperature range from 298 to 673 K. This particular thermochromism is ascribed to an enhanced bandgap shift depending on temperature with a strong electron–phonon coupling in the confined space of the 1 nm QDs.     

Fine-tuning of radiolysis induced emission by variable substitution of donor-/acceptor-substituted tetrakis(arylethynyl)benzenes

Emission from charge recombination between radical cations and anions of various tetrakis(arylethynyl)benzenes (TAEBs) was measured during pulse radiolysis in benzene (Bz). The formation of TAEB in the excited singlet state ((1)TAEB*) can be attributed to the charge recombination between TAEB (*+) and TAEB (*-), which is initially generated from the radiolytic reaction. It was found that the charge recombination between TAEB (*+) and TAEB (*-) gave (1)TAEB* as the emissive species but not excimers because of the large repulsion between substituents caused by the rotation around C-C single bonds. Since donor-/acceptor-substituted TAEBs possess three types of charge-transfer pathways (linear-conjugated, cross-conjugated, and "bent"-conjugated pathways between the donor and acceptor substituents through the ethynyl linkage), the emission spectra of (1)TAEBs* with intramolecular charge transfer (ICT) character depend on the substitution pattern and the various types of donor and acceptor groups during pulse radiolysis. Through control of the substitution pattern (e.g., the position of the nitrogen atom within the pyridine ring or the number of acceptors per arene ring of the regioisomeric donor-/acceptor-substituted TAEBs with donating N, N-dibutylamino and accepting pyridine unit (N1-9) and those with donating N, N-dibutylamino and accepting one (F1-3), two trifluoromethyl (F4-6), or perfluorinated arene (F7-9) units), fine-tuning of radiolysis induced emission color can be achieved.     

Theoretical analysis of binding specificity of influenza viral hemagglutinin to avian and human receptors based on the fragment molecular orbital method

The hemagglutinin (HA) protein of the influenza virus binds to the host cell receptor in the early stage of viral infection. A change in binding specificity from avian 2-3 to human 2-6 receptor is essential for optimal human-to-human transmission and pandemics. Therefore, it is important to reveal the key factors governing the binding affinity of HA-receptor complex at the molecular level for the understanding and prediction of influenza pandemics. In this work, on the basis of ab initio fragment molecular orbital (FMO) method, we have carried out the interaction energy analysis of HA-receptor complexes to quantitatively elucidate the binding specificity of HAs to avian and human receptors. To discuss the binding property of influenza HA comprehensively, a number of HAs from human H1, swine H1, avian H3 and avian H5 viruses were analyzed. We performed detailed investigations about the interaction patterns of complexes of various HAs and receptor analogues, and revealed that intra-molecular interactions between conserved residues in HA play an important role for HA-receptor binding. These results may provide a hint to understand the role of conserved acidic residues at the receptor binding site which are destabilized by the electrostatic repulsion with sialic acid. The calculated binding energies and interaction patterns between receptor and HAs are consistent with the binding specificities of each HA and thus explain the receptor binding mechanism. The calculated results in the present analysis have provided a number of viewpoints regarding the models for the HA-receptor binding specificity associated with mutated residues. Examples include the role of Glu190 and Gln226 for the binding specificity of H5 HA. Since H5 HA has not yet been adapted to human receptor and the mechanism of the specificity change is unknown, this result is helpful for the prediction of the change in receptor specificity associated with forthcoming possible pandemics.     

Delocalization of positive charge in π-stacked multi-benzene rings in multilayered cyclophanes

In the present study, delocalization of a positive charge in π-stacked multi-benzene rings in multilayered para- and meta-cyclophanes, in which benzene rings are connected by propyl chains to form a chromophore array with the face-to-face structure, was investigated by means of transient absorption spectroscopy during the pulse radiolysis using dichloroethane as a solvent. The local excitation and charge resonance (CR) bands were successfully observed. It was revealed that the CR band shifted to the longer wavelength side with the number of the benzene rings. The stabilization energy estimated from the peak position of the CR band showed the efficient charge delocalization over the cyclophanes. Furthermore, the CR bands showed the slight spectral change attributable to the change in distribution of the conformers. The substantially long lifetime of the CR band can be explained on the basis of the smaller charge distribution on the outer layers of the multilayered cyclophanes.     

Sliding of water droplets on hydrophobic surfaces with various hydrophilic region sizes

Four patterned surfaces with hydrophilic areas of different sizes were prepared using photolithography with a smooth octadecyltrimethoxysilane (ODS) hydrophobic coating. The hydrophilic area in the surfaces was aligned hexagonally with a constant area fraction. The sliding angle and contact angle hysteresis of the water droplets increased concomitantly with increasing pattern size. The increase of the contact line distortion between defects at the receding side plays an important role in this trend. The droplet sliding velocity also increased concomitantly with increasing pattern size. This trend was simulated by a simple flow model. The contribution of the interface between the ODS region and the hydrophilic area was deduced from this trend. This study demonstrated the different size dependency of the chemical surface defects for sliding behavior between the critical moment at which a droplet slides down and the period when a droplet is sliding.     

On the Dual Mode of Aldol Cyclization of Bicyclo-[4.3.1] Decane-3,8-Dione: A Novel,Efficient Entry into the Isotwistanone System

Isotwistanones have been highlighted since their use in the sesquiterpene syntheses.¹ Begley and coworkers reported a new access to this system via the postulated aldol cyclization of bicyclo [4.3.1]decane-2, 7-dione.² We have found another novel path of a similar mode.     

DNA Damage and Apoptosis Induced by Photosensitization of 5,10,15,20-Tetrakis (N-methyl-4-pyridyl)-21H,23H-porphyrin via Singlet Oxygen Generation

Cancer photodynamic therapy (PDT) requires photosensitizers that efficiently and selectively destroy tumor cells. We investigated 5,10,15,20-tetrakis ( N -methyl-4-pyridyl)-21 H ,23 H -porphyrin (TMPyP) as a potential cancer treatment. Confocal fluorescence microscopy showed that TMPyP was localized in the nuclei, whereas 5-aminolevulinic acid (ALA)-derived protoporphyrin IX (PPIX) was localized diffusely in the cytoplasm of human leukemia (HL-60) cells. In HL-60 cells under UVA irradiation, TMPyP effectively induced apoptosis. Moreover, 8-oxo-7,8-dihydro-2'-deoxyguanosine, an oxidative product of 2'-deoxyguanosine, was accumulated in the DNA of cells treated with photoirradiated TMPyP, whereas only small amounts were observed in ALA-treated cells in the presence of UVA light. TMPyP and UVA caused extensive damage at every guanine residue in DNA fragments obtained from the human p 53 tumor suppressor gene and the c-Ha- ras -1 proto-oncogene, whereas PPIX induced little DNA damage under these conditions. Electron spin resonance spectroscopy using a singlet oxygen (¹O₂) probe and D₂O showed that photoexcited TMPyP generated ¹O₂. These results suggest that photoexcited TMPyP reacts with oxygen to generate ¹O₂, which in turn, oxidizes guanine residues. Taken together, the results demonstrated that TMPyP was localized in the nucleus where it was photosensitized to induce DNA damage, suggesting that TMPyP may have clinical utility as a nucleus-targeted PDT.     

Temperature-driven oxygenation rate control by polymeric photosensitizer

A polymeric photosensitizer, poly(NIPAM-co-BP), consisting of N-isopropylacrylamide (NIPAM) and benzophenone (BP) units, demonstrates a temperature-controlled oxygenation activity in water. The system promotes a heat-induced oxygenation enhancement at <17 degrees C and suppression at >22 degrees C. This unprecedented photo-oxygenation activity is triggered by a heat-induced phase transition of the polymer from coil to micelle, and then to globule state, cleverly controlling the stability and diffusion of singlet oxygen and the location of substrate.     

Photoinduced intramolecular electron-transfer reactions of reconstituted met- and zinc-myoglobins appending acridine and methylacridinium ion as DNA-binders

Three types of reconstituted met- and zinc-myoglobin (metMb and ZnMb) dyads, ZnMbAc(4)Me+, ZnMbAc(6)Me+, and metMbAc(6) have been prepared by incorporating chemically modified metalloporphyrin cofactor appending an acridine (Ac) or a methylacridinium ion ([AcMe]+) into apo-Mb. In the bimolecular system between ZnMb and [AcMe]+, the photoexcited triplet state of ZnMb, 3(ZnMb)*, was successfully quenched by [AcMe]+ to form the radical pair of ZnMb cation (ZnMb*+) and reduced methylacridine ([AcMe]*), followed by a thermal back ET reaction. The rate constants for the intermolecular quenching ET (kq) and the back ET reaction (kb) at 25 degrees C were successfully obtained as kq = (8.8 +/- 0.4) x 10(7) M(-1) s(-1) and kb = (1.2 +/- 0.1) x 10(8) M(-1) s(-1), respectively. On the other hand, in case of the intramolecular photoinduced ET reactions of ZnMbAc(4)Me+ and ZnMbAc(6)Me+ dyads, the first-order quenching rate constants (kET) of 3(ZnMb)* by [AcMe]+ moiety were determined to be kET = 2.6 x 10(3) and 2.5 x 10(3) s(-1), respectively. When such ET occurs along the alkyl spacer via through-bond mechanism at the surface of Mb, the obtained kET is reasonable to provide decay constant of beta (1.0-1.3 A(-1)). Upon photoirradiation of [AcMe]+ moiety, kinetic studies also presented the intramolecular quenching reactions from the excited singlet state, 1([AcMe]+)*, whose likely process is the photoinduced energy-transfer reaction. For metMbAc(6) dyad, steady-state fluorescence was almost quenched, while the signal around 440 nm gradually appeared in the presence of various concentrations of DNA. Our study implies that synthetic manipulation at the Mb surface, by using an artificial DNA-binder coupled with photoinduced reaction, may provide valuable information to construct new Mb-DNA complex and sensitive fluorescent for DNA.