Jirarut Wongkongkatep

Bacteria Interface Pickering Emulsions Stabilized by Self-assembled Bacteria–Chitosan Network

An oil-in-water Pickering emulsion stabilized by biobased material based on a bacteria-chitosan network (BCN) was developed for the first time in this study. The formation of self-assembled BCN was possible due to the electrostatic interaction between negatively charged bacterial cells and polycationic chitosan. The BCN was proven to stabilize the tetradecane/water interface, promoting formation of highly stable oil-in-water emulsion (o/w emulsion). We characterized and visualized the BCN stabilized o/w emulsions by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). Due to the sustainability and low environmental impact of chitosan, the BCN-based emulsions open up opportunities for the development of an environmental friendly new interface material as well as the novel type of microreactor utilizing bacterial cells network.

Lipase-catalyzed synthesis of hydrophobically modified dextrans: Activity and regioselectivity of lipase from Candida rugosa

Vinyl decanoate-modified dextran macromolecules (DexT40-VD) were synthesized in dimethyl sulfoxide at 50°C using lipase AY from Candida rugosa for catalyzing transesterification between polysaccharide and vinyl fatty esters. The extent of dextran modification (quantified by the molar ratio of attached alkyl tails to sugar repeat units) with native-, pH-adjusted-, 18-crown-6 ether pretreated pH-adjusted-, and stepwise addition of pretreated lipase AY yielded <3%, 49%, 64% and 96% modified dextran respectively. Lipase AY accelerated the transesterification of DexT40 from 2- to 63-fold higher than the non-catalyzed system. This procedure was extended to other acyl donors showing that modification pattern exhibited regioselectivity depending on acyl donor structure. Regioselectivity equaled between 2- and 3-OH with saturated fatty acyl donors. The 2-OH was favored for unsaturated fatty acyl donors, while sterically hindered acyl donors oriented modification toward 3-OH position. DexT40-VD at 96% modification was a water-insoluble polymer forming 150nm diameter nanoparticles in water which can be used as drug carrier systems.

Coordination ligand exchange of a xanthene probe–Ce(III) complex for selective fluorescence sensing of inorganic pyrophosphate

A fluorescence sensing system for inorganic pyrophosphate based on ligand exchange of the Ce(III) complex of a xanthene-type probe is developed. This sensing system is successfully applied to the fluorescence detection of polymerase-catalyzed DNA amplification using loop-mediated isothermal amplification.

Arsenic Uptake by Native Fern Species in Thailand: Effect of Chelating Agents on Hyperaccumulation of Arsenic by Pityrogramma calomelanos

Abstract Nineteen native fern species collected from an area in Thailand with high arsenic concentration in soil and in ground water as a result of tin mining was screened for elevated arsenic concentration in fronds. Two species of fern were found to contain elevated arsenic in their fronds in nature: Pityrogramma calomelanos (108–1156 µg g−1 dried weight) and Pteris vittata (79 µg g−1 dried weight). Under hydroponic culture Pityrogramma calomelanos (a silver back fern) accumulated arsenic in its shoot at rate of 4616 µg g−1 (dried weight). The accumulation of arsenic in Pityrogramma calomelanos shoot doubled with the addition of an EDTA (Ethelenediamine tetraacetic acid) chelating agent. The highest accumulation occurred 6 weeks after exposure to 10 mg L−1 arsenic as disodium hydrogen arsenate. The addition of another chelating agent, DMSA (Dimercaptosuccinic acid), resulted in a 5-fold decrease in arsenic concentration in the Pityrogramma calomelanos shoot compared to control after 6 weeks of exposure to arsenic. The contrasting effect of the EDTA and DMSA chelating agent was attributed to the strong binding of the thiol group to arsenic ion. This study indicated that Pityrogramma calomelanos uptake and translocate arsenic in the form of arsenate and arsenite rather than the As–DMSA complex. Using phytoextraction efficiency calculations, it was determined that Pityrogramma calomelanos gave the highest arsenic phytoextraction efficiency at 6 weeks after exposure to arsenic in the EDTA treatment, with an efficiency of 77.8 mg As based on whole plant biomass.

Fluorescence Sensing of Inorganic Phosphate and Pyrophosphate Using Small Molecular Sensors and Their Applications

The aim of this contribution is to provide an introduction and a brief summary of the principle of fluorescence molecular sensors specific to inorganic phosphate (Pi) and inorganic pyrophosphate (PPi) as well as their applications. In our introduction we describe the impact of both Pi and PPi in the living organism and in the environment, followed by a description of the principle of fluorescence molecular sensors and the sensing mechanism in solution. We then focus on exciting research which has emerged in recent years on the development of fluorescent sensors specific to Pi and PPi, categorized by chemical interactions between the sensor and the target molecule, such as hydrogen bonding, coordination chemistry, displacement assay, aggregation induced emission or quenching, and chemical reactions.

Turning hydrophilic bacteria into biorenewable hydrophobic material with potential antimicrobial activity via interaction with chitosan

Alteration of a bacteriocin-producing hydrophilic bacterium, Lactococcus lactis IO-1, into a hydrophobic material with potential antimicrobial activity using chitosan was investigated and compared with five other bacterial species with industrial importance. The negatively charged bacterial cells were neutralized by positively charged chitosan, resulting in a significant increase in the hydrophobicity of the bacterial cell surface. The largest Gram-positive B. megaterium ATCC 14581 showed a moderate response to chitosan while the smaller E. coli DH5α, L. lactis IO-1 and P. putida F1 exhibited a significant response to an increase in chitosan concentration. Because L. lactis IO-1 is a good source for natural peptide lantibiotic that is highly effective against several strains of food spoilage organisms and pathogens, hydrophobic material derived from L. lactis IO-1 and chitosan is a promising novel material with antimicrobial activity for the food and pharmaceutical industries.

Hydroxypropyl methylcellulose enhances the stability of o/w Pickering emulsions stabilized with chitosan and the whole cells of Lactococcus lactis IO-1

Hydroxypropyl methylcellulose (HPMC) was used as a co-emulsifier with chitosan and the whole cells of bacteriocin-producing Lactococcus lactis IO-1 (L. lactis IO-1) for the preparation of bacteria interface Pickering emulsion. The obtained emulsion exhibited a high stability against centrifugation force, ionic strength and low temperature, with the whole cells of L. lactis IO-1 located at the oil/water interface. Because L.lactis IO-1 was found to produce peptide lantibiotic against several strains of Gram-positive food pathogen, the highly stable emulsion demonstrated in this study exhibited high potential as an antimicrobial emulsion with several health benefits of chitosan and HPLC useful for food industry.