Photoresponsive Molecular Memory Films Composed of Sequentially Assembled Heterolayers Containing Ruthenium Complexes

Photoresponsive molecular memory films were fabricated by a layer‐by‐layer (LbL) assembling of two dinuclear Ru complexes with tetrapodal phosphonate anchors, containing either 2,3,5,6‐tetra(2‐pyridyl)pyrazine or 1,2,4,5‐tetra(2‐pyridyl)benzene as a bridging ligand (Ru‐NP and Ru‐CP, respectively), using zirconium phosphonate to link the layers. Various types of multilayer homo‐ and heterostructures were constructed. In the multilayer heterofilms such as ITO||(Ru‐NP)_m|(Ru‐CP)_n, the difference in redox potentials between Ru‐NP and Ru‐CP layers was approximately 0.7 V, which induced a potential gradient determined by the sequence of the layers. In the ITO||(Ru‐NP)_m|(Ru‐CP)_n multilayer heterofilms, the direct electron transfer (ET) from the outer Ru‐CP layers to the ITO were observed to be blocked for m>2, and charge trapping in the outer Ru‐CP layers became evident from the appearance of an intervalence charge transfer (IVCT) band at 1140 nm from the formation of the mixed‐valent state of Ru‐CP units, resulting from the reductive ET mediation of the inner Ru‐NP layers. Therefore, the charging/discharging (“1”and “0”) states in the outer Ru‐CP layers could be addressed and interconverted by applying potential pulses between ?0.5 and +0.7 V. The two states could be read out by the direction of the photocurrent (anodic or cathodic). The molecular heterolayer films thus represent a typical example of a photoresponsive memory device; that is, the writing process may be achieved by the applied potential (?0.5 or +0.7 V), while the readout process is achieved by measuring the direction of the photocurrent (anodic or cathodic). Sequence‐sensitive multilayer heterofilms, using redox‐active complexes as building blocks, thus demonstrate great potential for the design of molecular functional devices.     

An improved chemiluminescence-based liposome immunoassay involving apoenzyme

An improved liposome immunoassay system (LIS) combining the chemiluminescence-based LIS with an apoenzyme reactivation immunoassay system (ARIS) was developed. A low-molecular-weight co-factor, FAD (flavin adenine dinucleotide), was incorporated into liposomes instead of the high-molecular-weight enzyme GOD (glucose oxidase). FAD released from liposomes by cytolysin-hapten conjugates bound to Apo-GOD and regenerated GOD. The system allowed detection of 10 pM digoxin, the model analyte and was linear over 10 pM to 13 nM digoxin. This sensitivity was about 300 times higher than that of the homogeneous system using GOD-containing liposomes and 30 times higher than that of the heterogeneous system which we reported previously. The time required for incubation during the detection of digoxin was reduced from 20 to 3 h.     

Highly E-selective and effective synthesis of antiarthritic drug candidate S-2474 using quinone methide derivatives.

We have developed an efficient and E-selective synthesis of an antiarthritic drug candidate (E)-(5)-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2-ethyl-1,2-isothiazolidine-1,1-dioxide (S-2474; 1), in which alpha-methoxy-p-quinone methide is used as a key intermediate. alpha-Methoxy-p-quinone methide was revealed to be an equivalent to a p-hydroxy protected benzaldehyde. It reacts smoothly with alpha-sulfonyl carbanion to give 1,6-addition intermediates, which can be further processed to provide S-2474 directly in the presence of a base. This procedure gives S-2474 as an almost single isomer on the benzylidene double bond in excellent yield and thus is a very practical method adaptable to large-scale synthesis. The detailed mechanistic aspects are studied and discussed.     

Theoretical study of trans-metalation process in palladium-catalyzed borylation of iodobenzene with diboron

Trans-metalation process in the palladium-catalyzed borylation of iodobenzene with diboron was theoretically investigated with the DFT method. Palladium(II) hydroxo phenyl complex, Pd(OH)(Ph)(PH(3))(2), and the fluoro analogue easily undergo the trans-metalation with diboron, B(2)(eg)(2) (eg = -OCH(2)CH(2)O-), to afford Pd(Ph)(Beg)(PH(3))(HO-Beg) and Pd(Ph)(Beg)(PH(3))(F-Beg), respectively, where B(2)(eg)(2) is adopted as a model of bis(pinacolato)diboron used experimentally. The electron re-distribution in the trans-metalation clearly indicates that the B-B bond scission occurs in a heterolytic manner. In the chloro analogue, PdCl(Ph)(PH(3))(2), however, the trans-metalation occurs in a homolytic manner with much difficulty, which is consistent with the experimental result. The significant differences between the chloro complex and the other hydroxo and fluoro complexes are easily interpreted in terms that hydroxo and fluoro ligands can form strongly bonding interaction with B(2)(eg)(2) but the chloro ligand cannot.