Reaction pathways and Sb(III) minerals formation during the reduction of Sb(V) by Rhodoferax ferrireducens strain YZ-1.

Antimony (Sb), a non-essential metalloid, can be released into the environment through various industrial activities. Sb(III) is considered more toxic than Sb(V), but Sb(III) can be immobilized through the precipitation of insoluble Sb2S3 or Sb2O3. In the subsurface, Sb redox chemistry is largely controlled by microorganisms; however, the exact mechanisms of Sb(V) reduction to Sb(III) are still unclear. In this study, a new strain of Sb(V)-reducing bacterium, designated as strain YZ-1, that can respire Sb(V) as a terminal electron acceptor was isolated from Sb-contaminated soils. 16S-rRNA gene sequencing of YZ-1 revealed high similarity to a known Fe(III)-reducer, Rhodoferax ferrireducens. XRD and XAFS analyses revealed that bioreduction of Sb(V) to Sb(III) proceed through a transition from amorphous valentinite to crystalline senarmontite (allotropes of Sb2O3). Genomic DNA sequencing found that YZ-1 possesses arsenic (As) metabolism genes, including As(V) reductase arsC. The qPCR analysis showed that arsC was highly expressed during Sb(V)-reduction by YZ-1, and thus is proposed as the potential Sb(V) reductase in YZ-1. This study provides new insight into the pathways and products of microbial Sb(V) reduction and demonstrates the potential of a newly isolated bacterium for Sb bioremediation.

Polyquaternium enhances the colloidal stability of chitosan-capped platinum nanoparticles and their antibacterial activity.

Here, for the first time, we have developed a novel green synthesis method where chitosan acts as a reducing agent and as a colloidal stabilizer, together with polyquaternium for the synthesis of platinum nanoparticles (PtNPs). It was observed that only chitosan-stabilized PtNPs (Ch@PtNPs) were stable up to pH 5, with a diameter of around 89 nm. The diameter of the Ch@PtNPs increased with the increase in pH, indicating the instability of Ch@PtNPs at neutral and alkaline mediums. However, when polyquaternium (PQ) (a cationic polymer) was added as a stabilizer along with chitosan, the diameter of chitosan/polyquaternium stabilized PtNPs (Ch/PQ@PtNPs), i.e. 87 nm, remained almost constant up to pH 9. Similarly, the pH-dependent decrease in the surface charge of Ch@PtNPs was also attenuated with the addition of polyquaternium. This indicates high colloidal stability of Ch/PQ@PtNPs in acidic, neutral, as well as alkaline mediums. It was observed that Ch/PQ@PtNPs exhibited high antibacterial activity againstStaphylococcus aureus, as compared to uncapped PtNPs and Ch@PtNPs. Thus, the addition of PQ increases the antibacterial properties of Ch/PQ@PtNPs againstStaphylococcus aureusby enhancing the stability of PtNPs at neutral pH.

Gelatin-loaded cubosomes stabilized with hydrophobically modified quaternized cellulose nanofiber and their pH-dependent release property.

Monoolein cubic phase immobilizing hydrophobically modified gelatin (HmGel) in its water channel was prepared by a melt-hydration method. The cubic phase was micronized into cubosomes by using hydrophobically modified quaternized cellulose nanofiber (HmQCNF) as a stabilizer. The phase transition temperature of the cubic phase was about 68-70 °C. Small angle X-ray diffraction revealed that HmGel-loaded cubosome stabilized with HmCNF was a diamond type of cubic phase. HmGel-loaded cubosomes stailized with HmQCNF were dependent on the pH value in terms of the release of their payload (i.e, methylene blue) much more strongly than HmGel-loaded cubosomes stabilized with Pluronic F127.

Distribution and speciation of Sb and toxic metal(loid)s near an antimony refinery and their effects on indigenous microorganisms.

Although several studies have investigated the effects of Sb contamination on surrounding environments and indigenous microorganisms, little is known about the effect of co-contamination of Sb and toxic metal(loid)s. In this study, the occurrence of Sb and other toxic metal(loid)s near an operating Sb refinery and near-field landfill site were investigated. Topsoil samples near the refinery had high Sb levels (∼3250 mg kg-1) but relatively low concentrations of other toxic metal(loid)s. However, several soil samples taken at greater depth from the near-field landfill site contained high concentrations of As and Pb, as well as extremely high Sb contents (∼21,400 mg kg-1). X-ray absorption fine structure analysis showed that Sb in the soils from both sites was present as Sb(V) in the form of tripuhyite (FeSbO4), a stable mineral. Three-dimensional principal coordinate analysis showed that microbial community compositions in samples with high toxic metal(loid)s concentrations were significantly different from other samples and had lower microbial populations (∼104 MPN g-1). Sequential extraction results revealed that Sb is present primarily in the stable residual fraction (∼99 %), suggesting low Sb bioavailability. However, microbial redundancy analysis suggested that the more easily extractable Pb might be the major factor controlling microbial community compositions at the site.

Rapid in-situ growth of gold nanoparticles on cationic cellulose nanofibrils: Recyclable nanozyme for the colorimetric glucose detection.

Novel microwave-assisted green in-situ synthesis of positively charged gold nanoparticles (AuNPs) supported by cationic cellulose nanofibrils (C.CNF) within 30 s and devoid of additional reducing agent is reported. Peroxidase activity of these positive AuNPs was studied and that appeared to be superior over its negative charged counterpart. Further the AuNPs@C.CNF is casted into a film which makes it reusable. Using TMB substrate, simple and sensitive colorimetric detection methods for H2O2 and glucose were established. Under optimal conditions, the linear ranges were found to be 0.5-30 µM and 1-60 µM, and the detection limits were 0.30 and 0.67 µM for H2O2 and glucose, respectively. The film was potentially reused for the detection of glucose up to five cycles without a decrease in the activity. Further, this technique was employed to quantify glucose in human serum samples, and the obtained results were comparable with those of the standard GOD-POD method.