Photoinduced Electron Transfer from Oligothiophenes/Polythiophene to Fullerenes (C₆₀/C₇₀) in Solution: Comprehensive Study by Nanosecond Laser Flash Photolysis Method

Photoinduced electron-transfer processes from oligothiophenes (nT)/polythiophene (poly-T) to fullerenes (C60/C70) have been studied by the nanosecond laser flash photolysis method, observing the transient absorption spectra in the visible and near-IR regions. When fullerene was selectively photoexcited in polar solvents, electron transfer from nT to the excited triplet state of fullerene was confirmed. The electron-transfer rate constants increased with the number of repeating unit (n) of nT. On the other hand, the efficiency of electron transfer showed a maximal value at n = 4; for n > 4, electron-transfer efficiency of nT decreased, indicating contribution of other processes such as energy transfer. By the photoexcitation of nT in polar solvent, both electron and energy transfer processes were observed for 4T and 6T. In the case of 3T, energy transfer occurred predominantly even in polar solvent. In nonpolar solvent, energy transfer was a predominant deactivation process. Electron-transfer efficiencies among these oligothiophenes and polythiophene were explained on the basis of free-energy changes for the electron transfers and triplet energy levels of nT

Dot-matrix analysis between three haplotypes of MHC class II region.

<p>Diagonal lines indicate regions where contiguous sequences align.</p

Structure and Polymorphism of the Major Histocompatibility Complex Class II Region in the Japanese Crested Ibis, <i>Nipponia nippon</i>

<div><p>The major histocompatibility complex (MHC) is a highly polymorphic genomic region that plays a central role in the immune system. Despite its functional consistency, the genomic structure of the MHC differs substantially among organisms. In birds, the MHC-B structures of Galliformes, including chickens, have been well characterized, but information about other avian MHCs remains sparse. The Japanese Crested Ibis (<i>Nipponia nippon</i>, Pelecaniformes) is an internationally conserved, critically threatened species. The current Japanese population of <i>N. nippon</i> originates from only five founders; thus, understanding the genetic diversity among these founders is critical for effective population management. Because of its high polymorphism and importance for disease resistance and other functions, the MHC has been an important focus in the conservation of endangered species. Here, we report the structure and polymorphism of the Japanese Crested Ibis MHC class II region. Screening of genomic libraries allowed the construction of three contigs representing different haplotypes of MHC class II regions. Characterization of genomic clones revealed that the MHC class II genomic structure of <i>N. nippon</i> was largely different from that of chicken. A pair of MHC-IIA and -IIB genes was arranged head-to-head between the <i>COL11A2</i> and <i>BRD2</i> genes. Gene order in <i>N. nippon</i> was more similar to that in humans than to that in chicken. The three haplotypes contained one to three copies of MHC-IIA/IIB gene pairs. Genotyping of the MHC class II region detected only three haplotypes among the five founders, suggesting that the genetic diversity of the current Japanese Crested Ibis population is extremely low. The structure of the MHC class II region presented here provides valuable insight for future studies on the evolution of the avian MHC and for conservation of the Japanese Crested Ibis.</p></div

Genomic organization of the Japanese Crested Ibis MHC class II region.

<p>Three contigs representing different haplotypes were constructed. <i>Collagen-type XI α-2</i> (<i>COL11A2</i>), MHC-IIA (<i>α</i>), MHC-IIB (<i>β</i>) and <i>bromodomain-containing 2</i> (<i>BRD2</i>) genes and their orientations are indicated. Locus names are indicated below the MHC-IIA and -IIB genes. The types of MHC-IIB exon 2 sequences (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108506#pone-0108506-t001" target="_blank">Table 1</a>) are shown below the locus names. B, K, P, S, Sc, and X represent restriction sites used for subcloning of <i>Bam</i>HI, <i>Kpn</i>I, <i>Pst</i>I, <i>Sal</i>I, <i>Sac</i>I, and <i>Xho</i>I, respectively. Solid bars below the map represent locations of isolated lambda phage clones. The bidirectional arrow above <i>DAB2</i> in haplotype 3 indicates the first amplified MHC-IIB fragment.</p

Digestion profiles of 279 bp of the MHC-IIB exon 2 sequence.

<p>Digestion profiles of 279 bp of the MHC-IIB exon 2 sequence.</p

Detection of MHC class II gene regions by Southern blotting.

<p>Genomic DNA from five founders (A–E) was digested with <i>Bam</i>HI and <i>Eco</i>RI and hybridized with a mixture of three probes (MHC IIA exon 3, MHC IIB exon 2, and MHC IIB exon 3). Three bands of approximately 8, 13, and 18 kb represented HP1, HP2, and HP3, respectively.</p

Genotyping of MHC class II gene regions by PCR-RFLP.

<p>A 279-bp fragment of MHC IIB exon 2 was amplified from five founder genomes (A–E). PCR products were digested with <i>Pst</i>I, <i>Rsa</i>I, or <i>Sal</i>I and digested fragments were analyzed by 3% agarose gel. Non-digested fragments with <i>Rsa</i>I, <i>Pst</i>I-digested fragments, and <i>Sal</i>I-digested fragments represented type II (<i>DAB1*01</i> in HP1), type IV (<i>DAB1*02</i> in HP2), and type III (<i>DAB1*03</i> in HP3), respectively (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108506#pone-0108506-t001" target="_blank">Table 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108506#pone-0108506-g001" target="_blank">Figure 1</a>).</p

Maximum-likelihood tree with MHC-IIB exon 2 or partial exon 3 sequences from <i>Nipponia nippon</i> and other bird species.

<p>The best-fitting nucleotide substitution model for each codon position was evaluated using Find Best DNA/Protein Models (ML) in MEGA version 5.2 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108506#pone.0108506-Tamura1" target="_blank">[28]</a> according to the Akaike information criterion. (A) The tree of exon 2 was constructed by using a Kimura 2-parameter model with gamma distribution in MEGA. (B) The tree of partial exon 3 was constructed by using a Tamura 3-parameter model with gamma distribution in MEGA. Bird species used for the analyses were shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108506#pone.0108506.s005" target="_blank">Table S3</a>. In both analyses, bootstrap values were evaluated with 1000 replications. Bootstrap values>60 are shown in this tree. Branch lengths represent the number of changes per site.</p

Alignment of predicted amino acid sequences of six MHC class IIB alleles from three haplotypes.

<p>Duck (Anpl-IIb) and chicken (Gaga-BLB1) amino acid sequences are provided for reference. The first amino acid of the β1 domain was designated as position 1. Identity with the <i>Nini-DAB1*01</i> sequence is indicated with a dot. Gaps are indicated by dashes. Asterisks above the sequence of the β1 domain indicate peptide-binding residues <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108506#pone.0108506-Brown1" target="_blank">[40]</a>.</p

Visible Light and Hydroxynaphthylbenzimidazoline Promoted Transition-Metal-Catalyst-Free Desulfonylation of <i>N-</i>Sulfonylamides and <i>N-</i>Sulfonylamines

A visible light promoted process for desulfonylation of <i>N-</i>sulfonylamides and -amines has been developed, in which 1,3-dimethyl-2-hydroxynaphthyl­benzimidazoline (HONap-BIH) serves as a light absorbing, electron and hydrogen atom donor, and a household white light-emitting diode serves as a light source. The process transforms various <i>N-</i>sulfonylamide and -amine substrates to desulfonylated products in moderate to excellent yields. The observation that the fluorescence of 1-methyl-2-naphthoxy anion is efficiently quenched by the substrates suggests that the mechanism for the photoinduced desulfonylation reaction begins with photoexcitation of the naphthoxide chromophore in HONap-BIH, which generates an excited species via intramolecular proton transfer between the HONap and BIH moieties. This process triggers single electron transfer to the substrate, which promotes loss of the sulfonyl group to form the free amide or amine. The results of studies employing radical probe substrates as well as DFT calculations suggest that selective nitrogen–sulfur bond cleavage of the substrate radical anion generates either a pair of an amide or amine anion and a sulfonyl radical or that of an amidyl or aminyl radical and sulfinate anion, depending on the nature of the <i>N-</i>substituent on the substrate. An intermolecular version of this protocol, in which 1-methyl-2-naphthol and 1,3-dimethyl-2-phenyl­benzimidazoline are used concomitantly, was also examined