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  • 1
    In: Environmental Science: Nano, 2016, Vol.3(2), pp.418-433
    Description: Understanding of the interplay of generally known colloidal transformations under conditions of test media (TM) used during cultivation of organisms and biological effect (=ecotoxicological) studies is still limited, although this knowledge is required for an adequate interpretation of test outcomes and for a comparison among different studies. In this context, we investigated the aggregation and dissolution dynamics of citrate-stabilized silver nanoparticles (Ag NPs) by varying the composition of three TM (ASTM, SAM-5S, and R2A, used during bioassays with Daphnia magna , Gammarus fossarum , and bacterial biofilms, respectively) in the presence and absence of two types of natural organic matter (NOM), namely, Suwanee River humic acid (SRHA) and seaweed extract (SW). Each original test medium induced reaction-limited aggregation of Ag NPs, and aggregation increased from R2A to SAM-5S and ASTM. In addition to the differences in aggregation dynamics, the concentration and speciation of Ag( i ) differed between the three TM, whereby SAM-5S and ASTM are comparable with respect to the nature of the aggregation process but clearly differ from the R2A medium. Furthermore, Cl , mainly present in SAM-5S, induced NP stabilization. The release of silver ions from Ag NPs was controlled by the presence of NOM and organic constituents of TM and by interactions with Cl and Br . The degree of aggregation, formation of interparticle cationNOM bridges or stabilization was larger for Ca 2+ than for Mg 2+ due to the stronger ability of Ca 2+ to interact with citrate or NOM compared to Mg 2+ . These observations and the dependence of aggregation rates on the particle concentration renders the interpretation of doseresponse relationships challenging, but they may open perspectives for targeted ecotoxicological testing by modifications of TM composition.
    Keywords: Bacteria ; Media ; Stabilization ; Concentration (Composition) ; Silver ; Nanoparticles ; Dynamics ; Agglomeration ; Chemical and Electrochemical Properties (MD) ; Chemical and Electrochemical Properties (Ep) ; Chemical and Electrochemical Properties (Ed) ; Chemical and Electrochemical Properties (EC);
    ISSN: 2051-8153
    E-ISSN: 2051-8161
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  • 2
    In: Faraday Discussions of the Chemical Society, 1986, Vol.82, pp.275-305
    ISSN: 0301-7249
    Source: Royal Society of Chemistry
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  • 3
    In: Journal of the Chemical Society, Faraday Transactions, 1991, Vol.87(12), pp.1809-1814
    Description: The dissociation paths NH 3 → NH + H 2 have been investigated for the X 1 A ′ 1 , à 1 A ″ 2 and ã 3 A ″ 2 electronic states of ammonia. Depending on the point group used to describe the dissociation, the NH 3 electronic states correlate with different asymptotes: the electronic ground state with the a 1 Δ(NH)+ 1 Σ + g (H 2 ) and X 3 Σ – (NH)+ 3 Σ + u (H + H); the à 1 A ″ 2 state with a 1 Δ, b 1 Σ + , c 1 Π(NH)+ 1 Σ + g (H 2 ) and X 3 Σ – (NH)+ 3 Σ + u (H + H); the ã 3 A ″ 2 with X 3 Σ – (NH) and A 3 Π(NH)+ 1 Σ + g (H 2 ), respectively. Parts of these dissociative paths of the potential-energy functions have been mapped using CASSCF ab initio wavefunctions. In the C 2v structures the X 1 A ′ 1 state possesses a high barrier reaching into the energy region of the à 1 A ″ 2 and B 1 E″ states. No such barriers exist for the à 1 A ″ 2 and ã 1 A ″ 2 states. The X 1 A ′ 1 , à 1 A ″ 2 and the B 1 E″ states as well as the ã 3 A ″ 2 and b 3 E″ states of ammonia possess common conical intersections, leading to vibronic coupling effects among those states. The à 1 A ″ 2 dissociates mainly into NH 2 (X 2 B 1 )+ H, the ã 3 A ″ 2 state into NH(X 3 Σ – )+ H 2 (X 1 Σ + g ) products.
    ISSN: 0956-5000
    E-ISSN: 1364-5455
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  • 4
    In: Faraday Discussions of the Chemical Society, 1991, Vol.91, pp.111-172
    ISSN: 0301-7249
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  • 5
    Language: English
    In: Faraday Discuss. Chem. Soc., 1986, Vol.82(0), pp.275-305
    ISSN: 0301-7249
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