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Surface reactions on mineral particles controlling the hydrolysis of glucose phosphates
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phosphorus (P) is an essential nutrient. A significant amount of soil P may be in the form of organophosphates. Due to the size of these compounds, hydrolysis is often required before P can be assimilated by organisms. Hydrolysis may be mediated by mineral surfaces, or catalyzed by extra cellular enzymes. Since both organophosphates and enzymes have a strong affinity for environmental particles, a study of the hydrolysis of organophosphates must focus on reactions at the water/particle interface. This thesis is a summary of four papers, discussing the adsorption, desorption, and abiotic and enzymatic hydrolysis of glucose-1-phosphate (G1P) and glucose-6-phosphate (G6P) in aqueous goethite suspensions. A new technique for simultaneous infrared and potentiometric titrations (SIPT) allowed in-situ measurements of the interfacial reactions. It was found that glucose phosphates form pH-dependent inner sphere complexes on goethite, which coordinate in a monodentate fashion, and are stabilized by hydrogen bonding. Desorption involves a change in speciation of the surface complexes, illustrating the difficulty in determining desorption rates for individual complexes. The surface mediated hydrolysis is primarily base catalyzed for G1P, and acid catalyzed for G6P. The difference is partly due to electronic factors, and partly to differences in glucose group/goethite interactions. Considerably more extensive is the hydrolysis catalyzed by an acid phosphatase (AcPase). The rate of the enzymatic hydrolysis are strongly dependent on the glucose phosphate surface coverage, showing that surface properties affect the adsorption mode of enzymes, and thus their catalytic activity. In solution, AcPase showed a greater specificity towards G6P, but this specificity was partly lost after adsorption onto goethite.

Place, publisher, year, edition, pages
Umeå: Kemiska institutionen, Umeå universitet , 2011.
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:umu:diva-46578ISBN: 978-91-7459-270-2 (print)OAI: oai:DiVA.org:umu-46578DiVA: diva2:439068
Public defence
2011-09-30, KBC-huset, KB3A9, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-09-09 Created: 2011-09-06 Last updated: 2011-09-06Bibliographically approved
List of papers
1. Adsorption, desorption, and surface-promoted hydrolysis of Glucose-1-phosphate in Aqueous Goethite (α-FeOOH) Suspensions
Open this publication in new window or tab >>Adsorption, desorption, and surface-promoted hydrolysis of Glucose-1-phosphate in Aqueous Goethite (α-FeOOH) Suspensions
2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 24, 18760-18770 p.Article in journal (Refereed) Published
Abstract [en]

Adsorption, desorption, and precipitation reactions at environmental interfaces govern the fate of phosphorus in terrestrial and aquatic environments. Typically, a substantial part of the total pool of phosphorus consists of organophosphate, and in this study we have focused on the interactions between glucose-1-phosphate (G1P) and goethite (α-FeOOH) particles. The adsorption and surface-promoted hydrolysis reactions have been studied at room temperature as a function of pH, time, and total concentration of G1P by means of quantitative batch experiments in combination with infrared spectroscopy. A novel simultaneous infrared and potentiometric titration (SIPT) technique has also been used to study the rates and mechanisms of desorption of the surface complexes. The results have shown that G1P adsorption occurs over a wide pH interval and at pH values above the isoelectric point of goethite (IEP(goethite) = 9.4), indicating a comparatively strong interaction with the particle surfaces. As evidenced by IR spectroscopy, G1P formed pH-dependent surface complexes on goethite, and investigations of both adsorption and desorption processes were consistent with a model including three types of surface complexes. These complexes interact monodentately with surface Fe but differ in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The apparent desorption rates were shown to be influenced by reaction pathways that include interconversion of surface species, which highlights the difficulty in determining the intrinsic desorption rates of individual surface complexes. Desorption results have also indicated that the molecular structures of surface complexes and the surface charge are two important determinants of G1P desorption rates. Finally, this study has shown that surface-promoted hydrolysis of G1P by goethite is base-catalyzed but that the extent of hydrolysis was small.

Place, publisher, year, edition, pages
Americal Chemical Society, 2010
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-46540 (URN)10.1021/la1026152 (DOI)000285217700029 ()21087005 (PubMedID)
Available from: 2011-09-06 Created: 2011-09-05 Last updated: 2017-12-08Bibliographically approved
2. Enzymatic hydrolysis of organic phosphates adsorbed on mineral surfaces
Open this publication in new window or tab >>Enzymatic hydrolysis of organic phosphates adsorbed on mineral surfaces
2012 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, 285-291 p.Article in journal (Refereed) Published
Abstract [en]

Esters of phosphoric acid constitute a sizable fraction of the total phosphorus supply in the environment and thus play an important role in the global phosphorus cycle. Enzymatic hydrolysis of these esters to produce orthophosphate is often a required reaction preceding phosphorus uptake by plants and microorganisms. Generally, adsorption to environmental particles is assumed to limit this process. Here we show, however, that the rate of enzymatic hydrolysis of glucose-1-phosphate (G1P) adsorbed on goethite by acid phosphatase (AcPase) can be of the same order of magnitude as in aqueous solution. The surface process releases carbon to the solution whereas orthophosphate remains adsorbed on goethite. This hydrolysis reaction is strictly an interfacial process governed by the properties of the interface. A high surface concentration of substrate mediates the formation of a catalytically active layer of AcPase, and although adsorption likely reduces the catalytic efficiency of the enzyme, this reduction is almost balanced by the fact that enzyme and substrate are concentrated at the mineral surfaces. Our results suggest that mineral surfaces with appropriate surface properties can be very effective in concentrating substrates and enzymes thereby creating microchemical environments of high enzymatic activity. Hence, also strongly adsorbed molecules in soils and aquatic environments may be subjected to biodegradation by extracellular enzymes.

National Category
Other Basic Medicine
Identifiers
urn:nbn:se:umu:diva-46541 (URN)10.1021/es2028422 (DOI)
Available from: 2011-09-05 Created: 2011-09-05 Last updated: 2017-12-08Bibliographically approved
3. Abiotic and enzymatic hydrolysis of glucose-6-phosphate on Goethite Particles
Open this publication in new window or tab >>Abiotic and enzymatic hydrolysis of glucose-6-phosphate on Goethite Particles
(English)Manuscript (preprint) (Other academic)
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:umu:diva-46554 (URN)
Available from: 2011-09-06 Created: 2011-09-05 Last updated: 2011-09-06Bibliographically approved
4. Adsorption mechanisms of glucose in aqueous goethite suspensions
Open this publication in new window or tab >>Adsorption mechanisms of glucose in aqueous goethite suspensions
2011 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 353, no 1, 263-268 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption of glucose and polysaccharides onto solid surfaces is important in several areas of science and engineering including soil chemistry and mineral processing. In this work we have studied the adsorption of D-glucose at the water-goethite (α-FeOOH) interface as a function of pH using batch adsorption measurements and a simultaneous infrared and potentiometric technique. Molecular orbital calculations were also performed in order to support interpretations of the infrared spectroscopic data. Infrared spectroscopy has shown that glucose adsorbs at the water-goethite interface with an intact ring structure and that the β-form is favored relative to the α isomer. The collective spectroscopic and macroscopic results were fully consistent with an adsorption mechanism where glucose interacts with goethite surface sites via hydrogen bonding interactions. Specific infrared peak shifts indicated that glucose primarily acts as a hydrogen bond donor and that it interacts with acceptor sites that become increasingly more prevalent as the surface is deprotonated. These results are in general agreement with the acid/base model for mono- and polysaccharide interactions at metal oxide surfaces, but contradict the inner sphere hypothesis that was proposed based on ex situ spectroscopic measurements.

Place, publisher, year, edition, pages
Elsevier Inc, 2011
Keyword
glucose, adsorption, infrared spectroscopy, hydrogen bonding
Identifiers
urn:nbn:se:umu:diva-37777 (URN)10.1016/j.jcis.2010.09.023 (DOI)20933242 (PubMedID)
Available from: 2010-11-12 Created: 2010-11-12 Last updated: 2017-12-12Bibliographically approved

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