Chao Wang

Biosynthesis, characterization, and antimicrobial applications of silver nanoparticles

In the present study, the strain Brevibacterium frigoritolerans DC2 was explored for the efficient and extracellular synthesis of silver nanoparticles. These biosynthesized silver nanoparticles were characterized by ultraviolet-visible spectrophotometry, which detected the formation of silver nanoparticles in the reaction mixture and showed a maximum absorbance at 420 nm. In addition, field emission transmission electron microscopy revealed the spherical shape of the nanoparticles. The dynamic light scattering results indicated the average particle size of the product was 97 nm with a 0.191 polydispersity index. Furthermore, the product was analyzed by energy dispersive X-ray spectroscopy, X-ray diffraction, and elemental mapping, which displayed the presence of elemental silver in the product. Moreover, on a medical platform, the product was checked against pathogenic microorganisms including Vibrio parahaemolyticus, Salmonella enterica, Bacillus anthracis, Bacillus cereus, Escherichia coli, and Candida albicans. The nanoparticles demonstrated antimicrobial activity against all of these pathogenic microorganisms. Additionally, the silver nanoparticles were evaluated for their combined effects with the commercial antibiotics lincomycin, oleandomycin, vancomycin, novobiocin, penicillin G, and rifampicin against these pathogenic microorganisms. These results indicated that the combination of antibiotics with biosynthesized silver nanoparticles enhanced the antimicrobial effects of antibiotics. Therefore, the current study is a demonstration of an efficient biological synthesis of silver nanoparticles by B. frigoritolerans DC2 and its effect on the enhancement of the antmicrobial efficacy of well-known commercial antibiotics.

Enzymatic biotransformation of ginsenoside Rb1 to compound K by recombinant β-glucosidase from Microbacterium esteraromaticum.

We cloned and characterized a β-glucosidase (bgp3) gene from Microbacterium esteraromaticum isolated from ginseng field. The bgp3 gene consists of 2,271 bp encoding 756 amino acids which have homology to the glycosyl hydrolase family 3 protein domain. The molecular mass of purified Bgp3 was 80 kDa, as determined by SDS-PAGE. The enzyme (Bgp3) catalyzed the conversion of ginsenoside Rb1 to the more pharmacologically active minor ginsenoside Rd and compound K. The Bgp3 hydrolyzed the outer glucose moiety attached to the C-20 position of ginsenoside Rb1, followed by hydrolysis of the inner glucose moiety attached to the C-3 position. Using 0.1 mg mL(-1) enzyme in 20 mM sodium phosphate buffer at 40 °C and pH 7.0, 1.0 mg mL(-1) ginsenoside Rb1 was transformed into 0.46 mg mL(-1) compound K within 60 min with a corresponding molar conversion yield of 77%. Bgp3 hydrolyzed the ginsenoside Rb1 along the following pathway: Rb1 → Rd → compound K.

Unified failure criterion for asphalt binder under cyclic fatigue loading

Defining failure and developing a unified failure criterion for the fatigue testing of asphalt materials remain a challenge. This study seeks to develop a failure criterion for the fatigue testing of asphalt binders under cyclic loading in the dynamic shear rheometer. Newly developed pseudo-strain energy (PSE)-based failure analysis is introduced for both the time sweep fatigue test and the accelerated linear amplitude sweep (LAS) test (AASHTO TP101). The presented methodology builds upon recent advances in the simplified viscoelastic continuum damage (S-VECD) modelling of asphalt mixtures. Trends in stored PSE have been proven to be effective in defining failure for the LAS tests of asphalt binders. This new proposed failure definition is material-dependent and, thus, is effective in capturing the benefits of asphalt modification for binder fatigue resistance. In addition, it is found that a unique relationship that is independent of loading history exists between the PSE release rate and fatigue life. The fatigue life predictions using this relationship and the S-VECD model are in reasonable agreement with the laboratory-measured fatigue life data and also generally relate well with the field fatigue performance measured in the FHWA-ALF (Federal Highway Administration – Accelerated Loading Facility) pooled fund study.

Green synthesis of multifunctional silver and gold nanoparticles from the oriental herbal adaptogen: Siberian ginseng.

Pharmacologically active stem of the oriental herbal adaptogen, Siberian ginseng, was employed for the ecofriendly synthesis of Siberian ginseng silver nanoparticles (Sg-AgNPs) and Siberian ginseng gold nanoparticles (Sg-AuNPs). First, for metabolic characterization of the sample, liquid chromatography-tandem mass spectrometry analysis (indicated the presence of eleutherosides A and E), total phenol content, and total reducing sugar were analyzed. Second, the water extract of the sample mediated the biological synthesis of both Sg-AgNPs and Sg-AuNPs that were crystalline face-centered cubical structures with a Z-average hydrodynamic diameter of 126 and 189 nm, respectively. Moreover, Fourier transform infrared analysis indicated that proteins and aromatic hydrocarbons play a key role in the formation and stabilization of Sg-AgNPs, whereas phenolic compounds accounted for the synthesis and stability of Sg-AuNPs. 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MTT) assay determined that Sg-AgNPs conferred strong cytotoxicity against MCF7 (human breast cancer cell line) and was only slightly toxic to HaCaT (human keratinocyte cell line) at 10 µg⋅mL−1. However, Sg-AuNPs did not display cytotoxic effects against both of the cell lines. The disc diffusion assay indicated a dose-dependent increase in the zone of inhibition of Staphylococcus aureus (ATCC 6538), Bacillus anthracis (NCTC 10340), Vibrio parahaemolyticus (ATCC 33844), and Escherichia coli (BL21) treated with Sg-AgNPs, whereas Sg-AuNPs did not show inhibitory activity. In addition, the 2,2-diphenyl-1-picrylhydrazyl assay demonstrated that both Sg-AgNPs and Sg-AuNPs possess strong antioxidant activity. To the best of our knowledge, this is the first report unraveling the potential of Eleutherococcus senticosus for silver and gold nanoparticle synthesis along with its biological applications, which in turn would promote widespread usage of the endemic Siberian ginseng.

Coalescence of functional gold and monodisperse silver nanoparticles mediated by black Panax ginseng Meyer root extract

A rapid biological synthesis of multifunctional gold nanoparticle (AuNp) and monodisperse silver nanoparticle (AgNp) was achieved by an aqueous extract of black Panax ginseng Meyer root. The physicochemical transformation into black ginseng (BG) greatly enhanced the pharmacological activities of white ginseng and its minor ginsenoside content. The optimal temperature conditions and kinetics of bioreduction were investigated. Formation of BG-AuNps and BG-AgNps was verified by ultraviolet–visible spectrophotometry at 548 and 412 nm, respectively. The biosynthesized BG-AgNps were spherical and monodisperse with narrow distribution, while BG-AuNps were icosahedral-shaped and moderately polydisperse. Synthesized nanoparticles exhibited long-term stability in buffers of pH 7.0–8.0 and biological media (5% bovine serum albumin) at an ambient temperature and at 37°C. BG-AgNps showed effective antibacterial activity against Escherichia coli and Staphylococcus aureus. BG-AuNps and BG-AgNps demonstrated increased scavenging activity against 2,2-diphenyl-1-picrylhydrazyl free radicals. In addition, BG-AuNps and BG-AgNps were nontoxic to HaCaT and MCF-7 cells; the latter showed no cytotoxicity at concentrations lower than 10 µg/mL. At higher concentrations, BG-AgNps exhibited apparent apoptotic activity in MCF-7 breast cancer cell line through reactive oxygen species generation and nuclear fragmentation.

Application of Time-Temperature Superposition Principle on Fatigue Failure Analysis of Asphalt Binder

AbstractThe linear amplitude sweep (LAS) test has been proposed for fatigue specifications of asphalt binders. Recently, a newly developed fatigue failure definition and energy-based failure criterion have been proposed for improving the LAS procedure and data interpreting; however, these improvements only affect LAS data conducted at a constant temperature. This paper, therefore, discusses the loading temperature effects on LAS-based binder fatigue, damage evolution, and final fatigue failure occurrence. Experimental results indicate that both damage characteristic curves (DCCs) and the failure criterion derived from the simplified-viscoelastic continuum damage (S-VECD) model are strongly affected by the testing temperature. However, the temperature shift factors determined from the dynamic shear modulus testing within the linear viscoelastic domain have been proven to be effective in eliminating the temperature influence for both fatigue DCCs and the failure criterion. The validation on binder phase dem...

Refining the Calculation Method for Fatigue Failure Criterion of Asphalt Binder from Linear Amplitude Sweep Test

AbstractThe objective of this paper is to refine the calculation method for improving the regression accuracy of fatigue failure criterion of asphalt binder using the linear amplitude sweep (LAS) t...

A Study on the Welding Distortion Analysis According to Rib Height in Fillet Welding

Abstract The welding distortion is caused by welding heat in the structures which are widely used in shipbuilding and automotive industries, thus many researchers have proposed such methods to control the welding distortionthrough trials and numerical studies. The welding distortion has been the main cause of low productivity due to the structural strength degradation, apparent flaw, additional deformation caused by the process followed the current assembly step, and the increase of correction workload. The deformation of fillet welding is investigated in this study, and the influence of the rib height on the welding distortion is verified through the actual experiment. And the numerical analysis model using the FE software MSC.marc for analysis of welding distortion is proposed.Key Words : Welding distortion, Longitudinal bending, Angular distortion, Finite element analysis 1. 서 론 용접변형(welding distortion)은 용접에 의해 구조물에 발생되는 변형을 말하며, 이는 용접이 실시되는 다양한 산업전반의 구조물에서 필연적으로 발생하게 된다. 용접열에 의해 가열되는 용접부는 팽창하게 되고 열의 영향을 받지 않는 모재가 팽창하고 있는 용접부를 구속하게 되어 열응력이 발생한다. 이때 생성된 열응력이 항복응력을 초과하게 되면 가열 부위는 수축 항복이 일어난다. 따라서 용접이 끝나고 구조물이 냉각하게 되면 용접부는 원래의 길이보다 수축하게 되어 용접변형을 수반한다