DNA-Templated Synthesis of Perylenediimide Stacks Utilizing Abasic Sites as Binding Pockets and Reactive Sites.

DNA is considered to be a promising biomolecule as a template and scaffold for arranging and organizing functional molecules on the nanoscale. The construction and evaluation of DNAs containing multiple functional molecules that are useful for optoelectronic devices and sensors has been studied. In this paper we report the efficient incorporation of perylenediimide (PDI) units into DNA by using abasic sites both as binding sites and as reactive sites and the construction of PDI stacks within the DNA structure, accomplished through the preorganization of the PDI units in the hydrophobic pocket within the DNA. Our approach could become a valuable method for construction of DNA/chromophore hybrid structures potentially useful for the design of DNA-based devices and biosensors.

Photocurrent generation through charge-transfer processes in noncovalent perylenediimide/DNA complexes.

The charge-transfer process in noncovalent perylenediimide (PDI)/DNA complexes has been investigated by using nanosecond laser flash photolysis (LFP) and photocurrent measurements. The PDI/DNA complexes were prepared by inclusion of cationic PDI molecules into the artificial cavities created inside DNA. The LFP experiments showed that placement of the PDI chromophore at a specific site and included within the base stack of DNA led to the efficient generation of a charge-separated state with a long lifetime by photoexcitation. When two PDI chromophores were separately placed at different positions in DNA, the yield of the charge-separated state with a long lifetime was dependent upon the number of A-T base pairs between the PDIs, which was explained by electron hopping from one PDI to another. Photocurrent generation of the DNA-modified electrodes with the complex was also dependent upon the arrangement of the PDI chromophores. A good correlation was obtained between observed charge separation and photocurrent generation on the PDI/DNA-modified electrodes, which demonstrated the importance of the defined arrangement and assembly of organic chromophores in DNA for efficient charge separation and transfer in multichromophore arrays.

Photocurrent generation enhanced by charge delocalization over stacked perylenediimide chromophores assembled within DNA.

We now report the photocurrent generation and charge transfer dynamics of stacked perylenediimide (PDI) molecules within a π-stack array of DNA. The cofacially stacked PDI dimer and trimer were found to strongly enhance the photocurrent generation compared to an isolated PDI monomer. Femtosecond time-resolved transient absorption experiments revealed that the excitation of the stacked PDI dimer and trimer provided the broad transient absorption band, which was attributed to the charge delocalization of a negative charge over the PDI chromophores. The lifetime of the charge delocalization of the PDI dimer and trimer (nearly 1 ns) was much longer than that of the charge separated state of the PDI monomer. A comparison between the photocurrent measurements and time-resolved transient absorption measurements demonstrated that the cofacially stacked structure could possibly lead to the charge delocalization and increase the lifetime of the charge-separated state that is essential to enhancing the photocurrent generation.

Cationic perylenediimide as a specific fluorescent binder to mismatch containing DNA.

Small ligand molecules, which can recognize thermodynamically unstable site within DNA, such as mismatch base pair, abasic site, and single-bulge, have attracted much attention because of their potential diagnostics and biological applications. In this paper, we describe the binding of cationic perylenediimide (cPDI) molecules to thymine-containing mismatch base pair in DNA and the formation of cPDI dimer at the mismatch site. The cPDI dimer exhibits a characteristic excimer emission at 650nm. For T/T mismatch containing DNA, the switching behavior from the PDI dimer (650nm) to the monomer (550nm) emission in specific response to Hg(2+) ion was observed.

Determination of molybdenum in foods and human milk, and an estimate of average molybdenum intake in the Japanese population.

To evaluate the molybdenum (Mo) status in the Japanese population, the Mo content in various foods and human milk was determined using inductively coupled plasma mass spectrometry (ICP-MS) and the average Mo intake was estimated. The difference in Mo content among food groups was marked; Mo levels in several plant foods such as cereals were more than 0.5 g/g while those in most animal foods were less than 0.1 microg/g. In particular, Mo contents in several samples of seeds and pulses were more than mixeo 1 mirog/g. The variation in Mo contents in each type of cereal was also conspicuous. Based on the present quantification of Mo in foods and the recent National Nutrition Survey in Japan, the average Mo intake of the Japanese population was estimated as 225 microg/d/capita. The principal Mo source in the Japanese diet was rice followed by soybean products, and approximately 90% of the Mo intake was derived from plant foods. Seventeen human milk samples were collected from 3 healthy mothers once or twice a month from 96 to 327 d after delivery. The median and range of Mo in human milk samples were 4.5 ng/mL and 2.0 to 8.8 ng/mL, respectively. Mo levels in Japanese formula milk were 2 to 3 ng/mL. Based on the Mo levels in human milk and formula milk, the Mo intake of Japanese infants was estimated to be 2 to 4 microg/d/capita.