SIA spotlight on Asia

There has been rapid development in science and technology in Asia in recent decades, including in the fields of surface and interface sciences. This has been facilitated by the sustained economic growth in the region, especially the growth of the semiconductor, electronic, chemical, coating and biomedical industries. Accompanying this growth is the increased use of more sophisticated analytical techniques, especially in the field of surface and interface analysis. This article reviews a selection of papers from Asia, published in major international journals in the last two years. Short reviews of each paper are presented in three sections: (i) Characterization and techniques, (ii) Materials and processing and (iii) Nanoscience and nanotechnology. Copyright © 2007 John Wiley & Sons, Ltd.     

Two-photon excited fluorescence of nitrogen-vacancy centers in proton-irradiated type Ib diamond

Two-photon fluorescence spectroscopy of negatively charged nitrogen-vacancy [(N-V)-] centers in type Ib diamond single crystals have been studied with a picosecond (7.5 ps) mode-locked Nd:YVO(4) laser operating at 1064 nm. The (N-V)- centers were produced by radiation damage of diamond using a 3 MeV proton beam, followed by thermal annealing at 800 degrees C. Prior to the irradiation treatment, infrared spectroscopy of the C-N vibrational modes at 1344 cm(-1) suggested a nitrogen content of 109 +/- 10 ppm. Irradiation and annealing of the specimen led to the emergence of a new absorption band peaking at approximately 560 nm. From a measurement of the integrated absorption intensity of the sharp zero-phonon line (637 nm) at liquid nitrogen temperature, we determined a (N-V)- density of (4.5 +/- 1.1) x 10(18) centers/cm3 (or 25 +/- 6 ppm) for the substrate irradiated at a dose of 1 x 1016) H(+)/cm(2). Such a high defect density allowed us to observe two-photon excited fluorescence and measure the corresponding fluorescence decay time. No significant difference in the spectral feature and fluorescence lifetime was observed between one-photon and two-photon excitations. Assuming that the fluorescence quantum yields are the same for both processes, a two-photon absorption cross section of sigma(TPA) = (0.45 +/- 0.23) x 10(-50) cm(4).s/photon at 1064 nm was determined for the (N-V)- center based on its one-photon absorption cross section of sigma(OPA) = (3.1 +/- 0.8) x 10(-17) cm2 at 532 nm. The material is highly photostable and shows no sign of photobleaching even under continuous two-photon excitation at a peak power density of 3 GW/cm(2) for 5 min.     

Pd(II) polymeric compounds directed by intermolecular C–H⋯X–C interactions (X = F,Cl): Suzuki–Miyaura cross-coupling catalytic activity by a novel N4-type saturated Pd complex

New palladium polymeric compounds containing novel tetradentate halogen-substituted 6Me₂bpX²⁻ ligands (6Me₂bpX²⁻ = 1,2-bis(6-methylpyridine-2-carboxamide) halobenzene dianion, X = F for 4, Cl for 5) were constructed by non-classical C–H?X–C interactions, and the novel catalyst 5 was used to carry out Suzuki coupling reactions with aryl iodides and aryl boronic acids under mild conditions.     

Epitaxially guided assembly of collagen layers on mica surfaces

Ordered assembly of collagen molecules on flat substrates has potential for various applications and serves as a model system for studying the assembly process. While previous studies demonstrated self-assembly of collagen on muscovite mica into highly ordered layers, the mechanism by which different conditions affect the resulting morphology remains to be elucidated. Using atomic force microscopy, we follow the assembly of collagen on muscovite mica at a concentration lower than the critical fibrillogenesis concentration in bulk. Initially, individual collagen molecules adsorb to mica and subsequently nucleate into fibrils possessing the 67 nm D-periodic bands. Emergence of fibrils aligned in parallel despite large interfibril distances agrees with an alignment mechanism guided by the underlying mica. The epitaxial growth was further confirmed by the formation of novel triangular networks of collagen fibrils on phlogopite mica, whose surface lattice is known to have a hexagonal symmetry, whereas the more widely used muscovite does not. Comparing collagen assembly on the two types of mica at different potassium concentrations revealed that potassium binds to the negatively charged mica surface and neutralizes it, thereby reducing the binding affinity of collagen and enhancing surface diffusion. These results suggest that collagen assembly on mica follows the surface adsorption, diffusion, nucleation, and growth pathway, where the growth direction is determined at the nucleation step. Comparison with other molecules that assemble similarly on mica supports generality of the proposed assembly mechanism, the knowledge of which will be useful for controlling the resulting surface morphologies.     

Biogenic Synthesis of Silver Nanoparticles with High Antimicrobial and Catalytic Activities using Sheng Di Huang (Rehmannia glutinosa)

Silver nanoparticles (AgNPs) are widely sought after for a variety of biomedical and environmental applications due to their antimicrobial and catalytic properties. We present here a green and simple synthesis of AgNPs utilizing traditional Chinese medicinal herbs. The screening of 20 aqueous herb extracts shows that Sheng Di Huang (Rehmannia glutinosa) had the most promising potential in producing AgNPs of 30±6 nm, with narrow size distribution and high crystallinity. The antimicrobial activities of these AgNPs conducted on E. coli cells were found to be superior in comparison to poly(vinylpyrrolidone)-capped AgNPs synthesized using common chemical method. Additionally, the AgNPs obtained possess excellent catalytic performance in the reduction of 4-nitrophenol to 4-aminophenol. We compared the phytochemical and FTIR spectral analyses of the herb extract before and after synthesis, in order to elucidate the phytochemicals responsible for the reduction of Ag⁺ ions and the capping of the AgNPs produced.     

Online Flowing Colloidosomes for Sequential Multi-analyte High-Throughput SERS Analysis

3D plasmonic colloidosomes are superior SERS sensors owing to their high sensitivity and excellent tolerance to laser misalignment. Herein, we incorporate plasmonic colloidosomes in a microfluidic channel for online SERS detection. Our method resolves the poor signal reproducibility and inter-sample contamination in the existing online SERS platforms. Our flow system offers rapid and continuous online detection of 20 samples in less than 5 min with excellent signal reproducibility. The isolated colloidosomes prevent cross-sample and channel contamination, allowing accurate quantification of samples over a concentration range of five orders of magnitude. Our system demonstrates high-resolution multiplex detection with fully preserved signal and Raman features of individual analytes in a mixture. High-throughput multi-assay analysis is performed, which highlights that our system is capable of rapid identification and quantification of a sequence of samples containing various analytes and concentrations.     

Harnessing Endogenous Formate for Antibacterial Prodrug Activation by in cellulo Ruthenium‐Mediated Transfer Hydrogenation Reaction

The abundance and evolving pathogenic behavior of bacterial microorganisms give rise to antibiotic tolerance and resistance which pose a danger to global public health. New therapeutic strategies are needed to keep pace with this growing threat. We propose a novel approach for targeting bacteria by harnessing formate, a cell metabolite found only in particular bacterial species, to activate an antibacterial prodrug and selectively inhibit their growth. This strategy is premised on transfer hydrogenation reaction on a biorthogonal substrate utilizing native formate as the hydride source as a means of uncaging an antibacterial prodrug. Using coordination‐directed 3‐component assembly to prepare a library of 768 unique Ru–Arene Schiff‐base complexes, we identified several candidates that efficiently reduced sulfonyl azide functional group in the presence of formate. This strategy paves the way for a new approach of targeted antibacterial therapy by exploiting unique bacterial metabolites.     

Synthesis of backbone modified cyclic peptides bearing dipicolylamino sidearms

Three analogues of the Lissoclinum class of cyclic peptides, bearing dipicolylamino functionalised side chains, have been synthesised using a stepwise approach followed by macrocyclisation. Attempts to incorporate dipicolylamino functionalised side chains prior to peptide synthesis resulted in epimerisation, but this was overcome by functionalising the ornithine side chains with dipicolylamino groups after the macrocyclisation reaction.