Modeling,Analysis, and Simulation of Biofilm Formation and Decay

In this article, we give a brief overview of our recent work on continuum mechanical modelling and simulation of microbial films. This comprises some classical tasks of applied mathematics such as computational fluid dynamics, analysis of partial differential equations, and mathematical biology.     

Thermal Control Using Far-Infrared Irradiation for Producing Deglycosylated Bioactive Compounds from Korean Ginseng Leaves

Although ginseng leaf is a good source of health-beneficial phytochemicals, such as polyphenols and ginsenosides, few studies have focused on the variation in compounds and bioactivities during leaf thermal processing. The efficiency of far-infrared irradiation (FIR) between 160 °C and 200 °C on the deglycosylation of bioactive compounds in ginseng leaves was analyzed. FIR treatment significantly increased the total polyphenol content (TPC) and kaempferol production from panasenoside conversion. The highest content or conversion ratio was observed at 180 °C (FIR-180). Major ginsenoside contents gradually decreased as the FIR temperature increased, while minor ginsenoside contents significantly increased. FIR exhibited high efficiency to produce dehydrated minor ginsenosides, of which F4, Rg6, Rh4, Rk3, Rk1, and Rg5 increased to their highest levels at FIR-190, by 278-, 149-, 176-, 275-, 64-, and 81-fold, respectively. Moreover, significantly increased antioxidant activities were also observed in FIR-treated leaves, particularly FIR-180, mainly due to the breakage of phenolic polymers to release antioxidants. These results suggest that FIR treatment is a rapid and efficient processing method for producing various health-beneficial bioactive compounds from ginseng leaves. After 30 min of treatment without leaf burning, FIR-190 was the optimum temperature for producing minor ginsenosides, whereas FIR-180 was the optimum temperature for producing polyphenols and kaempferol. In addition, the results suggested that the antioxidant benefits of ginseng leaves are mainly due to polyphenols rather than ginsenosides.     

Correlation between the bath composition and nanoporosity of DC-electrodeposited Ni-Fe alloy

The outstanding mechanical strength of as-deposited DC-electrodeposited nanocrystalline (nc) Ni-Fe alloys has been the subject of numerous researches in view of their scientific and practical interest. However, recent studies have reported a dramatic drop in ductility upon annealing above 350°C, associated with a concomitant abnormal rapid grain growth. The inherent cause has been ascribed to the presence of a detrimental product or by product in the bath, which affects either the microstructure or causes defects in the concentration and/or distribution of the as-deposited films. The present work has been inspired by the observed abnormal behaviour of annealed electrodeposited nc Ni-Fe alloy, which has here been addressed by considering the relationship between the composition of the bath (iron-chloride, nickel-sulphate solution, saccharin and ascorbic acid) and deposition defects (e.g. grain boundary pores) in the case of an nc Ni-Fe (Fe 48 wt%) alloy. The current investigations have included X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) in both as-deposited and post-annealed conditions (300°C–400°C). XPS depth profiling with Ar ion sputtering showed a significant amount of C and O impurities entrapped in the foils during deposition. As such impurities are often overlooked in common analytical techniques, new scenarios may need to be rationalised to explain the observed drop in tensile ductility of the as-deposited Ni-Fe alloys.     

Conjugated polymers for pure UV light emission: Poly(meta‐phenylenes)

We report the synthesis of a 3‐ethylhexyloxy substituted poly(meta‐phenylene), EHO‐PMP that shows absorption and solid state photoluminescence exclusively in the UV region of the electromagnetic spectrum with an emission maximum of 345 nm. Computational analysis of model oligomers by DFT methods indicates that EHO‐PMP is a wide bandgap polymer with the HOMO being localized on a dimeric (biphenyl) unit and with the LUMO being more delocalized. The energy of the LUMO, however, suggests that inefficient electron injection would occur from currently available cathode materials in standard light‐emitting device architectures, and this was observed experimentally. The computational results, coupled with experimental observation, lead us to believe that efficient electroluminescence from organic polymer UV emitters requires advances in electron transport layers and cathode materials. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Coherent electric field characterization of molecular chirality in the time domain

Intrinsic handedness encountered in molecular sciences plays an essential role in diverse physical, chemical and biological processes. Optical activity spectroscopy has enabled one to characterize such molecular handedness (chirality) and demonstrated its unique ability to provide stereo-specific structural insight into chiral molecular systems including biopolymers, chiral drugs, and superchiral materials. However, more extended applications including time-resolved studies have often been hindered by inherent limitations of conventional differential methods utilizing both left- and right-handed radiations. The latest methodological advance is heterodyned detection methods measuring wave interferences between signal and reference fields, which allowed direct characterizations of coherent chiroptical signals in a flash. With its ultimate sensitivity, the heterodyned chiroptical method promises to open new possibilities of transient electronic or vibrational optical activity measurements in the ultrafast time domain.     

Loading device effect on protein unfolding mechanics

Single-molecule mechanical manipulation has enabled quantitative understanding of not only the kinetics of both bond rupture and protein unfolding, but also the free energy landscape of chemical bond and/or protein folding. Despite recent studies reporting the role of loading device in bond rupture, a loading device effect on protein unfolding mechanics has not been well studied. In this work, we have studied the effect of loading-device stiffness on the kinetics of both bond rupture and protein unfolding mechanics using Brownian dynamics simulations. It is shown that bond rupture forces are dependent on not only loading rate but also the stiffness of loading device, and that protein unfolding mechanics is highly correlated with the stiffness of loading device. Our study sheds light on the importance of loading device effect on the mechanically induced bond ruptures and protein unfolding.     

A simple, fast, and easy assay for transition metal-catalyzed coupling reactions using a paper-based colorimetric iodide sensor

A paper-based colorimetric iodide sensor (PBCIS) that consists of filter paper treated with starch and an oxidant is developed. It has been employed as a protocol to obtain the extent of conversion of aryl iodides in C-C, C-N, C-O and C-S bond formations, including polymer-supported Heck reactions, by transition metal catalysts such as palladium, nickel and copper.     

A bi-ligand co-functionalized gold nanoparticles-based calcium ion probe and its application to the detection of calcium ions in serum

In this study, the use of bi-ligand co-functionalized gold nanoparticles in a highly selective and sensitive colorimetric probe for Ca(2+) ions is demonstrated and this probe also determined the concentrations of Ca(2+) ions in serum samples.     

Preparation of highly ordered TiO2 nanotubes on Ti-foil for dye-sensitized solar cells

TiO₂ nanotube arrays were grown on Ti foil in mixed electrolyte by the anodizing process. TiO₂ nanotube arrays were immersed in the TiCl₄ solution to improve the photocurrent by enhanced charge transfer between TiO₂ and dye molecules on the activity surface. Internal resistance of dye-sensitized solar cells (DSSC) was measured by impedance spectroscopy measurements. Backside illuminated DSSC with TiCl₄-treated TiO₂ nanotubes exhibited a conversion efficiency of 1.45% and showed improved electron transfer.     

Directing Foldamer Self-Assembly with a Cyclopropanoyl Cap

The rational design of self-assembling organic materials is extremely challenging due to the difficulty in precisely predicting solid-state architectures from first principles, especially if synthons are conformationally flexible. A tractable model system to study self-assembly was constructed by appending cyclopropanoyl caps to the N termini of helical α/β-peptide foldamers, designed to form both N−H⋅⋅⋅O and C^α−H⋅⋅⋅O hydrogen bonds, which then rapidly self-assembled to form foldectures (foldamer architectures). Through a combined analytical and computational investigation, cyclopropanoyl capping was observed to markedly enhance self-assembly in recalcitrant substrates and direct the formation of a single intermolecular N−H⋅⋅⋅O/C^α−H⋅⋅⋅O bonding motif in single crystals, regardless of peptide sequence or foldamer conformation. In contrast to previous studies, foldamer constituents of single crystals and foldectures assumed different secondary structures and different molecular packing modes, despite a conserved N−H⋅⋅⋅O/C^α−H⋅⋅⋅O bonding motif. DFT calculations validated the experimental results by showing that the N−H⋅⋅⋅O/C^α−H⋅⋅⋅O interaction created by the cap was sufficiently attractive to influence self-assembly. This versatile strategy to harness secondary noncovalent interactions in the rational design of self-assembling organic materials will allow for the exploration of new substrates and speed up the development of novel applications within this increasingly important class of materials.