Abstract

We systematically quantified surface complexation of Np(V) onto whole cells, cell wall, and extracellular polymeric substances (EPS) of Shewanella alga strain BrY. We first performed acid and base titrations and used the mathematical model FITEQL to estimate the concentrations and deprotonation constants of specific surface functional groups. Deprotonation constants most likely corresponded to a carboxyl group not associated with amino acids (pK a ∼ 5), a phosphoryl site (pKa ∼ 7.2), and an amine site (pKa > 10). We then carried out batch sorption experiments with Np(V) and each of the S. alga components as a function of pH. Since significant Np(V) sorption was observed on S. alga whole cells and its components in the pH range 2-5, we assumed the existence of a fourth site: a low-pKa carboxyl site (pKa ∼ 2.4) that is associated with amino acids. We used the SPECIATE submodel of the biogeochemical model CCBATCH to compute the stability constants for Np(V) complexation to each surface functional group. The stability constants were similar for each functional group on S. alga bacterial whole cells, cell walls, and EPS, and they explain the complicated sorption patterns when they are combined with the aqueous-phase speciation of Np(V). For pH < 8, the aquo NpO2 + species was the dominant form of Np(V), and its log K values for the low-pKa carboxyl, mid-pKa carboxyl, and phosphoryl groups were 1.8, 1.8, and 2.5-3.1, respectively. For pH greater than 8, the key surface ligand was amine >XNH3 +, which complexed with NpO2(CO3)3 5-. The log K for NpO 2(CO3)3 5- complexed onto the amine groups was 3.1-3.9. All of the log K values are similar to those of Np(V) complexes with aqueous carboxyl and N-containing carboxyl ligands. These results help quantify the role of surface complexation in defining actinide- microbiological interactions in the subsurface.

Original languageEnglish (US)
Pages (from-to)4930-4935
Number of pages6
JournalEnvironmental Science and Technology
Volume44
Issue number13
DOIs
StatePublished - Jul 1 2010

Fingerprint

cells and cell components
Neptunium
neptunium
Algae
Complexation
complexation
experimental study
alga
Functional groups
functional group
Sorption
Deprotonation
sorption
modeling
Amines
amino acid
Actinoid Series Elements
Cells
Amino Acids
actinide

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

Cite this

Surface complexation of neptunium(V) onto whole cells and cell components of shewanella alga : Modeling and experimental study. / Deo, Randhir P.; Songkasiri, Warinthorn; Rittmann, Bruce; Reed, Donald T.

In: Environmental Science and Technology, Vol. 44, No. 13, 01.07.2010, p. 4930-4935.

Research output: Contribution to journalArticle

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abstract = "We systematically quantified surface complexation of Np(V) onto whole cells, cell wall, and extracellular polymeric substances (EPS) of Shewanella alga strain BrY. We first performed acid and base titrations and used the mathematical model FITEQL to estimate the concentrations and deprotonation constants of specific surface functional groups. Deprotonation constants most likely corresponded to a carboxyl group not associated with amino acids (pK a ∼ 5), a phosphoryl site (pKa ∼ 7.2), and an amine site (pKa > 10). We then carried out batch sorption experiments with Np(V) and each of the S. alga components as a function of pH. Since significant Np(V) sorption was observed on S. alga whole cells and its components in the pH range 2-5, we assumed the existence of a fourth site: a low-pKa carboxyl site (pKa ∼ 2.4) that is associated with amino acids. We used the SPECIATE submodel of the biogeochemical model CCBATCH to compute the stability constants for Np(V) complexation to each surface functional group. The stability constants were similar for each functional group on S. alga bacterial whole cells, cell walls, and EPS, and they explain the complicated sorption patterns when they are combined with the aqueous-phase speciation of Np(V). For pH < 8, the aquo NpO2 + species was the dominant form of Np(V), and its log K values for the low-pKa carboxyl, mid-pKa carboxyl, and phosphoryl groups were 1.8, 1.8, and 2.5-3.1, respectively. For pH greater than 8, the key surface ligand was amine >XNH3 +, which complexed with NpO2(CO3)3 5-. The log K for NpO 2(CO3)3 5- complexed onto the amine groups was 3.1-3.9. All of the log K values are similar to those of Np(V) complexes with aqueous carboxyl and N-containing carboxyl ligands. These results help quantify the role of surface complexation in defining actinide- microbiological interactions in the subsurface.",
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T1 - Surface complexation of neptunium(V) onto whole cells and cell components of shewanella alga

T2 - Modeling and experimental study

AU - Deo, Randhir P.

AU - Songkasiri, Warinthorn

AU - Rittmann, Bruce

AU - Reed, Donald T.

PY - 2010/7/1

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N2 - We systematically quantified surface complexation of Np(V) onto whole cells, cell wall, and extracellular polymeric substances (EPS) of Shewanella alga strain BrY. We first performed acid and base titrations and used the mathematical model FITEQL to estimate the concentrations and deprotonation constants of specific surface functional groups. Deprotonation constants most likely corresponded to a carboxyl group not associated with amino acids (pK a ∼ 5), a phosphoryl site (pKa ∼ 7.2), and an amine site (pKa > 10). We then carried out batch sorption experiments with Np(V) and each of the S. alga components as a function of pH. Since significant Np(V) sorption was observed on S. alga whole cells and its components in the pH range 2-5, we assumed the existence of a fourth site: a low-pKa carboxyl site (pKa ∼ 2.4) that is associated with amino acids. We used the SPECIATE submodel of the biogeochemical model CCBATCH to compute the stability constants for Np(V) complexation to each surface functional group. The stability constants were similar for each functional group on S. alga bacterial whole cells, cell walls, and EPS, and they explain the complicated sorption patterns when they are combined with the aqueous-phase speciation of Np(V). For pH < 8, the aquo NpO2 + species was the dominant form of Np(V), and its log K values for the low-pKa carboxyl, mid-pKa carboxyl, and phosphoryl groups were 1.8, 1.8, and 2.5-3.1, respectively. For pH greater than 8, the key surface ligand was amine >XNH3 +, which complexed with NpO2(CO3)3 5-. The log K for NpO 2(CO3)3 5- complexed onto the amine groups was 3.1-3.9. All of the log K values are similar to those of Np(V) complexes with aqueous carboxyl and N-containing carboxyl ligands. These results help quantify the role of surface complexation in defining actinide- microbiological interactions in the subsurface.

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