NOVEL TERAHERTZ PHOTOCONDUCTIVE ANTENNAS

The photoconductive (PC) antenna is a key device for the recent terahertz (THz) photonics based on laser-pumped generation and detection of THz radiation. In this paper we report on two new types of PC antennas: the Schottky PC antenna and the multi-contacts PC antenna. The former one is able to detect THz radiation intensity without the time-delay scan and useful for applications where spectroscopic information is not important, such as the THz intensity imaging. The latter one is useful for the polarization sensitive THz spectroscopy, such as the THz ellipsometry. The characteristic features of these new types of PC antennas are studied by using a THz time-domain spectroscopy system.     

Palladium‐Catalyzed Asymmetric C(sp3)−H Allylation of 2‐Alkylpyridines

The palladium‐catalyzed asymmetric side‐chain C(α)‐allylation of 2‐alkylpyridines, without using an external base, was developed. The high linear selectivities and enantioselectivities were achieved using new chiral diamidophosphite monodentate ligands. Given that the reaction conditions do not require an external base, this catalyst system enabled chemoselective C(α)‐allylation of 2‐alkylpyridines containing α‐carbonyl C?H bonds, which are more acidic than α‐pyridyl C?H bonds.     

Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient XAFS

The dynamics of the local electronic and geometric structures of WO₃ following photoexcitation were studied by femtosecond time‐resolved X‐ray absorption fine structure (XAFS) spectroscopy using an X‐ray free electron laser (XFEL). We found that the electronic state was the first to change followed by the local structure, which was affected within 200 ps of photoexcitation.     

Radical Polymerization of Vinyl Monomers in Porous Organic Cages

The radical polymerization of vinyl monomers was performed in a tetrahedral imine‐linked organic cage with extrinsic porosity (CC3). Because of its dynamic and responsive packing structure, CC3 endowed the polymerization with specific behaviors. The adsorption of styrene triggered a change in the CC3 assembly, resulting in a monomer arrangement that was suitable for polymerization within the host matrix. The polymerization reaction was strongly dependent on the crystallinity of CC3 and was promoted by amorphization of the host in a cooperative manner, which is not possible with conventional rigid porous materials. Furthermore, CC3 can recognize the polarity of substrates, and thus polar monomers, such as methyl methacrylate and acrylonitrile, could not induce the structural changes in CC3 that are required for polymerization. This monomer specificity governed by the flexibility of CC3 is useful to the prevent incorporation of unfavorable monomers into the polymeric products.     

Site‐Selective Tertiary Alkyl–Fluorine Bond Formation from α‐Bromoamides Using a Copper/CsF Catalyst System

A copper‐catalyzed site‐selective fluorination of α‐bromoamides possessing multiple reaction sites, such as primary and secondary alkyl?Br bonds, using inexpensive CsF is reported. Tertiary alkyl?F bonds, which are very difficult to synthesize, can be formed by this fluorination reaction with the aid of an amide group. Control experiments revealed that in situ generated CuF₂ is a key fluorinating reagent that reacts with the tertiary alkyl radicals generated by the reaction between an α‐bromocarbonyl compound and a copper(I) salt.     

Chemical derivatization of peptides containing phosphorylated serine/threonine for efficient ionization and quantification in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We describe a useful method for the efficient ionization and relative quantification of peptides containing serine/threonine phosphorylation sites. This method is based on beta-elimination of the phosphate group from serine/threonine phosphorylation sites under alkaline conditions, followed by Michael addition reaction with N-(2-mercaptoethyl)-6-methylnicotinamide (MEMN). As a result of the derivatization reaction, the negatively charged phosphate group is substituted with the nicotinoyl moiety to improve the ionization efficiency of the derivatized peptide. The combination of d(3)-labeled MEMN (d(3)-MEMN) and MEMN (d(0)-MEMN) generates a 3 Da mass difference between d(3)-MEMN-labeled and d(0)-MEMN-labeled peptides, which is a useful signature for the identification of peptides containing serine/threonine phosphorylation sites in the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrum. Moreover, the mass difference is useful for the quantitative analysis of serine/threonine phosphorylation in proteins. In this paper, we describe the synthesis of d(0)/d(3)-labeled MEMN and an application of our approach to model peptides and proteins.     

Organized monolayer of thermosensitive microgel beads prepared by double-template polymerization

A 2D close-packed array of thermosensitive microgel beads was prepared by the double-template polymerization method. First, a 2D colloidal crystal of silica beads with 10 microm diameter was obtained by the solvent evaporation method. This monolayer of colloidal crystals can serve as the first template for the preparation of macroporous polystyrene. The macroporous polystyrene trapping the crystalline order can be used as a negative template for fabricating gel beads arrays. A functional surface using thermosensitive poly(N-isopropylacrylamide) gel beads array was fabricated by the double-template polymerization method.     

Efficient identification and quantification of proteins using isotope-coded 1-(6-methylnicotinoyloxy)succinimides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We describe a convenient and useful method for the identification and relative quantification of proteins using light and heavy reagents, 1-(6-methylnicotinoyloxy)succinimides (6-CH(3)-Nic-NHS and 6-CD(3)-Nic-NHS, respectively). This method is based on the chemical derivatization of amino groups of tryptic peptides with these reagents, i.e., the basic moiety of the reagents thus incorporated into both the N-terminal amino group and the epsilon-amino group of the lysine residue would improve the ionization efficiency of tryptic peptides. An increase in protein sequence coverage is achieved by derivatization with these reagents or by combination of mass values before and after derivatization. Since a combination of 6-CH(3)-Nic-NHS and d(3)-labeled reagent (6-CD(3)-Nic-NHS) generates a 3 Da mass difference per reaction site, the d(3)-labeled reagent shifts the mass values of d(0)-labeled peptides according to the number of reactive amino groups in the peptides. In the case of tryptic peptides, the mass values of C-terminal arginine and lysine peptides are shifted by 3 and 6 Da, respectively. Further, the 3 Da mass difference between 6-CH(3)-Nic-NHS and 6-CD(3)-Nic-NHS offers a means for the relative quantification of protein by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.     

Numerical analysis of thermal lens effect for sensitive detection on microchips

Thermal lens microscope (TLM) is a sensitive detection method for nonfluorescent molecules and widely applied to detection in a capillary or on a microchip. In this paper, we developed a flexible design tool for TLM systems to meet various applications utilizing a microspace. The TL effect was modeled, including signal processing, and calculated by combining fluidic dynamics and wave optics software. The coincidence of the calculations and experiments was investigated by measuring the effects of optical path length or focus positions of the excitation beams on TL signals which are quite difficult to calculate by a conventional method. Good agreement was shown and the applicability of the TLM design tool was verified.     

Chemical synthesis of a glycoprotein having an intact human complex-type sialyloligosaccharide under the Boc and Fmoc synthetic strategies

The chemical synthesis of complex glycoproteins is an ongoing challenge in protein chemistry. We have examined the synthesis of a single glycoform of monocyte chemotactic protein-3 (MCP-3), a CC-chemokine that consists of 76 amino acids and one N-glycosylation site. A three-segment native chemical ligation strategy was employed using unprotected peptides and glycopeptide. Importantly, the synthesis required the development of methods for the generation of sialylglycopeptide-alphathioesters. For the sialylglycopeptide-alphathioester segment, we examined and successfully implemented approaches using Fmoc-SPPS and Boc-SPPS. To avoid use of hydrogen fluoride, the Boc approach utilized minimal side chain protection and direct thiolysis of the resin bound peptide. Using these strategies, we successfully synthesized a glycoprotein having an intact and homogeneous complex-type sialyloligosaccharide.