Transformations of citrate and Tween coated silver nanoparticles reacted with Na2S.

Silver nanoparticles (Ag NPs) are susceptible to transformations in environmental and biological media such as aggregation, oxidation, dissolution, chlorination, sulfidation, formation/replacement of surface coatings following interaction with natural organic matter (NOM). This paper investigates the impact of surface coating and Suwannee River fulvic acid (SRFA) on the transformations and behavior of Ag NPs (citrate coated and Tween coated; cit-Ag NPs and Tween-Ag NPs, respectively), following reaction with different concentrations of Na2S solution (as a source of sulfide species, H2S and HS(-)). These transformations and the dominant mechanisms of transformations were investigated using UV-vis and scanning transmission electron microscopy coupled with electron energy loss spectroscopy. Here, we have shown that Ag NP surface coating impacts their dissolution following dilution in ultrahigh purity water, with higher extent of dissolution of Tween-Ag NPs compared with cit-Ag NPs. Tween-Ag NPs are susceptible to dissolution following their sulfidation at low S/Ag molar ratio. Suwannee River fulvic acid (SRFA) slows down the dissolution of Tween-Ag NPs at low sulfide concentrations and reduces the aggregation of cit-Ag NP in the presence of sodium sulfide. Sulfidation appears to occur by direct interaction of sulfide species with Ag NPs rather than by indirect reaction of sulfide with dissolved Ag species subsequent to dissolution. Furthermore, the sulfidation process results in the formation of partially sulfidized Ag NPs containing unreacted (metallic) subgrains at the edge of the NPs for Tween-Ag NPs in the presence of high sulfide concentration (2000nM Na2S), which occurred to less extent at lower Na2S concentration for Tween-Ag NPs and at all concentrations of Na2S for cit-Ag NPs. Thus, sulfidized Ag NPs may preserve some of the properties of the Ag NPs such as their potential to shed Ag(+) ions and their toxic potential of Ag NPs.

Effect of monovalent and divalent cations, anions and fulvic acid on aggregation of citrate-coated silver nanoparticles.

The dynamic nature of nanoparticle (NP) aggregation behavior is of paramount interest to many current studies in environmental and toxicological nanoscience. The present study seeks to elucidate the influence that different electrolytes have on the aggregation of citrate-coated silver NPs (cit-AgNPs). The use of both UV-vis spectroscopy and dynamic light scattering (DLS, both z-average hydrodynamic diameter (z-dh) and size distribution analysis data) allowed improvement in the data quality and interpretation as compared to other studies using only DLS and reporting solely the z-dh, as the change in the z-dh can be related to analytical errors and uncertainties rather than only aggregation or dissolution of NPs. Divalent cations (CaCl2, Ca(NO3)2, CaSO4, MgCl2 and MgSO4) have stronger influence (ca. 50-65 fold) on aggregation of cit-AgNPs as compared to monovalent cations (NaCl, NaNO3, Na2SO4), as expected. For electrolytes with monovalent cations, there was no specific ion effect of nitrate and sulfate anions. However, the addition of chloride anions resulted in enhanced apparent aggregation, possibly due to the formation of AgCl NPs that sorb/attach to the surface of cit-AgNPs. Suwannee River fulvic acid enhances the stability of cit-AgNPs and shifts the critical coagulation concentrations to higher electrolyte concentrations for all types of electrolytes. Aggregation kinetics in the presence of mixture of monovalent and divalent cations is additive and controlled by the dominant cations. An empirical formula (αmixture=αNa+(50 to 65)Ca) is proposed that reproduces the effect of mixtures of electrolytes in the presence of humic substances and cations that can be used to help predict the aggregation behavior of cit-AgNPs in environmental and ecotoxicological media.

Early changes in the synapses of the neostriatum induced by perinatal asphyxia.

Perinatal asphyxia (PA) is a medical condition associated with a high short-term morbimortality and different long-term neurological diseases. In previous work we have observed at 6 months post-synaptic densities (PSDs) alterations compatible with neurodegeneration highly correlated with the increment in the ubiquitination. Although alterations in the synaptic organization and function have been related with neuronal death after hypoxia, little is known about the synaptic changes in young animals exposed to PA. The main aim of this work is to study the PSDs changes in striatum of 30-day-old rats subjected to PA. Using two-dimensional electron microscopic analyses of synapses staining with ethanolic phosphotungstic acid we observed an increment of PSD thickness in severe hypoxic rats. These data are consistent with the western blot analysis that showed an increment in ubiquitination levels in the synapses of severe hypoxic rat. We did observe any alterations neither in synaptic structure nor in ubiquitinization in mild asphyctic rats. These data suggest that hypoxia might cause early misfolding and aggregation of synaptic proteins in severe anoxic animas that could induce long-term neurodegeneration.

Fluorescent dual colour 2D-protein gel electrophoresis for rapid detection of differences in protein pattern with standard image analysis software.

The use of two different fluorescent dyes in two-dimensional (2D) polyacrylamide gel electrophoresis was recently described and termed difference gel electrophoresis (DIGE). Thereby differences between protein samples could be accomplished by fluorescently tagging the samples with different dyes as well as co-separation and visualisation in a single gel. We adapted this method to the ampholyte technique, using newly available fluorescent dyes and three common image software systems for analysis. Working with protein lysates from tumour cell lines with defined added proteins we found that the technique is reproducible, sensitive and fast, because it circumvents the necessity of matching several 2D gels. This is mainly due to the fact that the generated images from the two different fluorescent channels could be superimposed by standard image analysis, so that changes in the protein pattern could be easily detected either by a different colour or by comparing grey values of corresponding spots. This method will be especially helpful in comparing proteins from normal and tumour tissue to highlight changes in genesis and progression in cancer.

Silencing of the Y-chromosomal gene tspy during murine evolution.

We have studied the process of tspy gene silencing in murine evolution. We have isolated functional tspy sequences from Apodemus agrarius, A. sylvaticus, A. flavicollis, and Mus platythrix (subgenus Pyromys) and nonfunctional tspy sequences from species of the subgenus Mus. We present two alternative models as to how tspy may have lost its function in the murine lineage.

A novel strategy to identify maternal and paternal inheritance in the mouse.

A novel strategy for identifying proteins which reveal maternal or paternal inheritance in the mouse is presented. Using two-dimensional electrophoresis we investigated protein expression patterns of adult liver and different embryonic and extraembryonic tissue in C57BL/6Crl and in DBA/2Crl mice, as well as in their reciprocal hybrids. We found three groups of protein spots which showed maternal or paternal inheritance of quantitative variations. These proteins were characterized by N-terminal or internal amino acid sequencing, by determination of the amino acid composition, by glycoprotein staining and RNA expression analysis. The three proteins identified were: alpha-enolase, cyclophilin and beta-group hemoglobins. The parental effects observed for alpha-enolase and cyclophilin were found to be due to parent-specific post-translational modifications of these proteins. For the beta-group hemoglobins our results suggested parental effects on the transcriptional level.

Adult phenotype in the mouse can be affected by epigenetic events in the early embryo.

Major epigenetic modifications apparently occur during early development in the mouse. The factors that induce such modifications are complex and may involve the various components of a zygote. We have started to explore whether changes in the nucleocytoplasmic composition brought about by micromanipulation can induce phenotypic effects through epigenetic modifications. Nucleocytoplasmic hybrids were therefore prepared by transplanting a female pronucleus into a recipient egg from a different genotype. As a result, the maternal genome was of a different genetic background as compared with the egg cytoplasm. Specifically, experimental zygotes had cytoplasm from the inbred strain C57BL/6, a maternal genome from DBA/2, and a paternal genome from C57BL/6 (termed BDB hybrids). The mirror-image combination, termed DBD, was also made. The reconstituted zygotes were transferred to recipients and allowed to develop to term. Mice born from manipulated zygotes showed transcriptional repression and DNA methylation of major urinary protein genes in their liver, as well as growth deficiency resulting in reduced adult body weight. No altered phenotype was observed in controls in which the maternal pronucleus was simply transplanted back into another zygote of the same genetic background. These results clearly demonstrate phenotypic as well as molecular effects on DNA methylation and expression of at least one gene. Phenotype was therefore no longer predicted by genotype as a result of epigenetic modifications in experimental embryos. What precisely triggers the phenotypic and epigenetic changes is unknown, but presumably, nucleocytoplasmic interactions in hybrid zygotes may be partly responsible.

Determination of antibodies to rubella virus with the disperse dye immunoassay (DIA) in comparison with an enzyme-linked immunosorbent assay (ELISA).

A disperse dye immunoassay (DIA) using Fantagen-dye sol particles as label was developed for the measurement of rubella antibodies in human serum specimen. The DIA has a sensitivity comparable to the hemagglutination-inhibition (HI) test, whereas the detection limit for a similar ELISA-system developed in parallel is lower by a factor of about two orders of magnitude. The results of testing 34 random serum specimens with the 3 different methods showed a significant correlation (v = 0.73 for DIA vs. ELISA). Titer rises in 10 paired sera (acute/convalescent) estimated with the DIA- and ELISA-methods were in good agreement with H1-results. Only two of the 10 pairs differed in titer rise by no more than one dilution step.

Aging changes in intracellular protein breakdown.

Using radioactively labelled cytosol proteins as substrates we were able to exclude the possible accumulation of any specific inhibitor for the lysosomal proteases in rat liver cytosol during the aging process. There were also no gross changes in the molecular weight patterns of these proteins during the aging process. The percentage of more hydrophobic proteins seems to be identical in both the "old" and "young" cytosol proteins. From immunological experiments we suppose a qualitative change in the composition of rat liver cytosol proteins or of their properties during the aging process.