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SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo589

nature geoscience | www.nature.com/naturegeoscience 1

1

Supplementary information for

Storage and bioavailability of molybdenum in soils

increased by organic matter complexation

Thomas Wichard 1,¶ , Bhoopesh Mishra 1,¶,*, Satish C.B. Myneni1, Jean-Philippe

Bellenger1 and Anne M.L. Kraepiel 1,2

Princeton University, Department of Geosciences1 and Chemistry Department2,

Guyot Hall, Princeton, NJ 08544, USA

¶ Joint first authorship

To whom correspondence should be addressed:

* email: [email protected]

Content:

1. Methods

2. Supporting Tables

3. Supporting Figures

4. Acknowledgements

5. References

2 nature geoscience | www.nature.com/naturegeoscience

SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo589

2

Methods

Chemicals.

Cysteine, malic acid (2-hydroxybutanedioic acid), tannic acid (C76H52O46) and sodium

molybdate were purchased from Sigma-Aldrich and used without further purification.

Azotochelin (L-LysineCAM) and azotobactin were prepared as previously

described15,20,30.

Collection and preparation of soil samples.

Mo-rich soil samples were collected from an exposed soil profile in the Red mountain of

the Coronado National Forest (AZ, USA) and directly analyzed using µXRF mapping

and µXANES spectroscopy.

Topsoil and subsoil samples were separated from a 0.5 m core collected from a hardwood

forest in central New Jersey (USA). For each sample, 1 g of the sieved soil was mixed

with 10 ml of a 0.2 mM aqueous solution of Na2MoO4. After 24 h, the soil suspension

was filtered (GF, pore size 0.45 µm, Whatman, UK), and the collected soil particles were

analyzed by XANES spectroscopy. Measurement of Mo concentration in the filtrate

showed that 31-43% of the added molybdate was bound to the soil particles.

Preparation of the leaf organic matter extract (LL).

Leaf litter from a mixed stand of maple and oak trees in the Pine Barrens (NJ, USA) was

collected, air-dried and ground with a mortar and pestle. The ground leaves were

extracted with distilled water (1:10 (w/w) dry leaf to water ratio) at 24̊ C for 24 h 31. The

resulting suspension was filtered through a glass fiber filter (GF, pore size 0.45 µm,



2

Methods

Chemicals.

Cysteine, malic acid (2-hydroxybutanedioic acid), tannic acid (C76H52O46) and sodium

molybdate were purchased from Sigma-Aldrich and used without further purification.

Azotochelin (L-LysineCAM) and azotobactin were prepared as previously

described15,20,30.

Collection and preparation of soil samples.

Mo-rich soil samples were collected from an exposed soil profile in the Red mountain of

the Coronado National Forest (AZ, USA) and directly analyzed using µXRF mapping

and µXANES spectroscopy.

Topsoil and subsoil samples were separated from a 0.5 m core collected from a hardwood

forest in central New Jersey (USA). For each sample, 1 g of the sieved soil was mixed

with 10 ml of a 0.2 mM aqueous solution of Na2MoO4. After 24 h, the soil suspension

was filtered (GF, pore size 0.45 µm, Whatman, UK), and the collected soil particles were

analyzed by XANES spectroscopy. Measurement of Mo concentration in the filtrate

showed that 31-43% of the added molybdate was bound to the soil particles.

Preparation of the leaf organic matter extract (LL).

Leaf litter from a mixed stand of maple and oak trees in the Pine Barrens (NJ, USA) was

collected, air-dried and ground with a mortar and pestle. The ground leaves were

extracted with distilled water (1:10 (w/w) dry leaf to water ratio) at 24̊ C for 24 h 31. The

resulting suspension was filtered through a glass fiber filter (GF, pore size 0.45 µm,

3

Whatman, UK) and the filtrate yielded the extract of leaf organic matter (leaf litter

extract, LL) that was subsequently frozen. In one experiment, a subsample of LL was

stored in the laboratory at 24̊ C for one month to evaluate the stability of the Mo -binding

groups over time. The polyphenol concentration of LL was estimated using the

colorimetric assay of Denis-Folin, and found to be equal to 1.3 × 10-2 M (expressed as

2,3-dihydroxybenzoic acid equivalents31,32). For XANES and EXAFS spectroscopy, LL

subsamples were spiked with an aqueous solution of Na2MoO4 to achieve a final Mo

concentration of 1 mM. To study the effect of pH on Mo binding to LL, the pH of the leaf

extract was adjusted with 0.1 N NaOH.

Chemical composition of the soils.

All soils were sieved, ground (fine grade) and dried at 90˚C for two days. Soil carbon and

nitrogen were measured on a 0.4 g subsample using a dry-combustion LECO analyzer

(LSU AgCenter, LA, USA). For determination of metal concentrations, about 50-100 mg

of dried leaf litter or soil samples were weighted and subsequently pre-digested in 8 ml of

nitric acid (68%, trace metal clean grade, Fisher Scientific, USA) for 24 h at 60˚C. The

samples were then digested in a MARS Xpress Microwave digester (CEM) and their

concentrations in Fe, and Mo were measured with an Inductively Coupled Plasma-Mass

Spectrometer (ICP-MS, Element2, Thermo Finnigan) at medium resolution.



4

Mo adsorption on iron oxides.

Goethite (α-FeOOH), hematite (α-Fe2O3) and ferrihydrite (Fe5HO8 ∙ 4H2O) were freshly

prepared according to established procedures33. The resulting iron oxides were collected

by filtration, rinsed with water and dried at 90°C.

To study Mo adsorption, 0.5 g of iron oxide was incubated in 10 ml of a 1.0 M aqueous

solution of Na2MoO4 at 24˚C for 24 h. The pH was adjusted to 4.5 ± 0.2 with 0.1 M HCl

and measured again after 24 h (∆pH = 0.05). The resulting solid was collected by

centrifugation, rinsed with 15 ml water and air-dried before analysis by XANES

spectroscopy.

Preparation of Mo-tannic acid complex.

Addition of an excess of an aqueous solution of Na2MoO4 (0.5 M final concentration) to

a 0.1 M solution of tannic acid in methanol resulted in the formation of a precipitate12,

which was filtered, washed and subsequently air-dried. Complete complexation of Mo by

tannic acid in the precipitate was demonstrated by EXAFS spectroscopy and ultraviolet-

visible spectroscopy.

Preparation of Mo-cysteine complexes.

Orange crystals of di−µ−oxo-bis-{oxo[cysteinato(2-)]aquo-molybdate (V)} trihydrate

were prepared from aqueous solutions of molybdenum(VI) and cysteine following

published procedures28,34 . The Mo(VI) complex forms first, and is reduced to Mo(V)

complexes over time in aqueous solution with an excess of cysteine35.



4

Mo adsorption on iron oxides.

Goethite (α-FeOOH), hematite (α-Fe2O3) and ferrihydrite (Fe5HO8 ∙ 4H2O) were freshly

prepared according to established procedures33. The resulting iron oxides were collected

by filtration, rinsed with water and dried at 90°C.

To study Mo adsorption, 0.5 g of iron oxide was incubated in 10 ml of a 1.0 M aqueous

solution of Na2MoO4 at 24˚C for 24 h. The pH was adjusted to 4.5 ± 0.2 with 0.1 M HCl

and measured again after 24 h (∆pH = 0.05). The resulting solid was collected by

centrifugation, rinsed with 15 ml water and air-dried before analysis by XANES

spectroscopy.

Preparation of Mo-tannic acid complex.

Addition of an excess of an aqueous solution of Na2MoO4 (0.5 M final concentration) to

a 0.1 M solution of tannic acid in methanol resulted in the formation of a precipitate12,

which was filtered, washed and subsequently air-dried. Complete complexation of Mo by

tannic acid in the precipitate was demonstrated by EXAFS spectroscopy and ultraviolet-

visible spectroscopy.

Preparation of Mo-cysteine complexes.

Orange crystals of di−µ−oxo-bis-{oxo[cysteinato(2-)]aquo-molybdate (V)} trihydrate

were prepared from aqueous solutions of molybdenum(VI) and cysteine following

published procedures28,34 . The Mo(VI) complex forms first, and is reduced to Mo(V)

complexes over time in aqueous solution with an excess of cysteine35.

5

Mo binding to tannic acid and azotobactin. Mo complexation by tannic acid was

verified by titrating a 5.88 × 10-5 M solution of tannic acid in 10 mM ammonium acetate

(pH = 6.6) with a 1.11 × 10-3 M solution of sodium molybdate and monitoring the

ultraviolet-visible absorbance of the solution. The formation of Mo-azotobactin in the

presence of tannic acid was investigated by adding a solution of Mo and tannic acid to a

solution of azotobactin and monitoring the solution fluorescence at λ = 487 nm over time

(excitation wavelength λ = 380 nm).

XANES and EXAFS measurements and data processing

XAFS spectroscopy was used to provide information about the type, number, and radial

distances of the atoms surrounding Mo. Mo K-edge (20000 eV) XAFS spectroscopy

measurements were performed at beamline X18B at the NSLS (Brookhaven National

Laboratory) and at beamlines 11-2 and 4-3 at the SSRL (Menlo Park). However, the data

presented here were collected at NSLS. At beamline X18B (NSLS), a channel cut Si

(111) crystal was used as monochromator. The higher harmonics were rejected by

detuning the monochromator crystal by 30%. The incident ionization chamber was filled

with 100% N2 gas. The transmitted and reference ion chambers were filled with 100% Ar

gas. The fluorescence detector in the Stern-Heald geometry36 was also filled with Ar gas.

Mo foil was used as a reference and for energy calibration.

Solutions and homogeneous pallet samples were loaded into a slotted Plexiglas holder,

covered with Kapton film, and transported immediately to the beamline for XAFS

measurements. Prepared samples were kept refrigerated before XAFS measurements,

which were performed within 2-3 days of sample preparation.



6

The data were analyzed using the methods described within the UWXAFS package37.

The background removal procedure is based on the AUTOBK method38 and implemented

by using the ATHENA interface to IFEFFIT39. The data sets were aligned and the

backgrounds were removed using ATHENA program. ATHENA was also used for

Linear Combination Fitting (LCF) of the unknown Mo samples to quantify the relative

contribution of different components in a given spectra. The fitting was done in the

normalized mu (E) space. Fitting range of -30 eV to +90 eV was used for proper

normalization of the XANES spectra. The input parameter to ATHENA that determines

the maximum frequency of the background, Rbkg, was set to 1.2 Å38. The data range used

for Fourier transforming the EXAFS χ(k) data was 3.0 – 10.5 Å-1 with a Hanning window

function and a delta k value of 1.0 Å-1 40. Simultaneous fitting with multiple k-weighting

(k1, k2, k3) was performed using the Fourier transformed χ(R) spectra. Fitting range was

1.2 – 4.0 Å. The simultaneous fitting approach reduces the possibility of obtaining

erroneous parameters due to correlations at any single k-weighting41

EXAFS data analysis is based on refining theoretical EXAFS spectra against the

experimental data. Models are constrained by use of crystalline model compounds with

well-characterized local structures. The crystallographic information of the standard

compounds were first transformed into a cluster of atoms by using the program

ATOMS42. Then FEFF843 was used to carry self-consistent quantum mechanical

calculations to simulate theoretical EXAFS spectra based on the cluster of atoms thus

obtained. Experimentally obtained EXAFS data on the standard compounds were fit to

these theoretically generated EXAFS spectra using the program FEFFIT39,40. We refined



6

The data were analyzed using the methods described within the UWXAFS package37.

The background removal procedure is based on the AUTOBK method38 and implemented

by using the ATHENA interface to IFEFFIT39. The data sets were aligned and the

backgrounds were removed using ATHENA program. ATHENA was also used for

Linear Combination Fitting (LCF) of the unknown Mo samples to quantify the relative

contribution of different components in a given spectra. The fitting was done in the

normalized mu (E) space. Fitting range of -30 eV to +90 eV was used for proper

normalization of the XANES spectra. The input parameter to ATHENA that determines

the maximum frequency of the background, Rbkg, was set to 1.2 Å38. The data range used

for Fourier transforming the EXAFS χ(k) data was 3.0 – 10.5 Å-1 with a Hanning window

function and a delta k value of 1.0 Å-1 40. Simultaneous fitting with multiple k-weighting

(k1, k2, k3) was performed using the Fourier transformed χ(R) spectra. Fitting range was

1.2 – 4.0 Å. The simultaneous fitting approach reduces the possibility of obtaining

erroneous parameters due to correlations at any single k-weighting41

EXAFS data analysis is based on refining theoretical EXAFS spectra against the

experimental data. Models are constrained by use of crystalline model compounds with

well-characterized local structures. The crystallographic information of the standard

compounds were first transformed into a cluster of atoms by using the program

ATOMS42. Then FEFF843 was used to carry self-consistent quantum mechanical

calculations to simulate theoretical EXAFS spectra based on the cluster of atoms thus

obtained. Experimentally obtained EXAFS data on the standard compounds were fit to

these theoretically generated EXAFS spectra using the program FEFFIT39,40. We refined

7

ab initio calculations on clusters of atoms derived from a known Mo-bis(catecholate)

crystal structure44 against the EXAFS data from Mo-azotochelin solution standards. The

best fit values of the path parameters obtained by independent modeling of the Mo-tannic

acid and Mo-LL samples at pH = 4.6, 6.1 and 7.5 were the same within uncertainties as

those obtained for the Mo-azotochelin standard. The sigma square (disorder factor) of the

Oax, Oeq, C and C-O and O-O signals (scattering paths) were thus set to be equal to the

ones obtained for the Mo-azotochelin standard reported in Table S2.

The value obtained for the EXAFS amplitude reduction factor for all standards was S02 =

0.9 ± 0.05 and this value was used in modelling the spectra from the unknown samples.

Statistically significantly lower R factor and 2νχ values were used as criteria for

improvement in the fit to justify the addition of an atomic shell to the model41.

XRF Mapping.

X-ray fluorescence (XRF) mapping was used to provide element specific information

about the spatial distribution of the atoms surrounding Mo. A Canberra 9-element Ge

Array detector was used for Mo XRF mapping at microscale using 5 x 5 micron beam.

Incident energy of X-ray was 21000 eV and a step size of 25 µm was used with 3 seconds

per pixel counting time. Soil samples were packed into a polycarbonate sample holder

and sealed with Kapton tape prior to transport to beamline X26A at the NSLS at

Brookhaven National Laboratory.



8

2. Tables

Table S1. Chemical composition of soil and leaf litter layer samples collected in Arizona

and New Jersey (USA).

Metal carbon %

nitrogen %

Fe%

Moppm

AZ top-soil 32.3 1.01 2.1 23.8AZ sub-soil

(30 cm depth) 0.95 0.072 6.3 63.2

Pine Barrens leaf litter 52.2 0.82 0.06 5.2NJ top-soil 9.1 0.64 3.0 16.7NJ sub-soil

(50 cm depth) 0.77 0.095 4.6 35.9



8

2. Tables

Table S1. Chemical composition of soil and leaf litter layer samples collected in Arizona

and New Jersey (USA).

Metal carbon %

nitrogen %

Fe%

Moppm

AZ top-soil 32.3 1.01 2.1 23.8AZ sub-soil

(30 cm depth) 0.95 0.072 6.3 63.2

Pine Barrens leaf litter 52.2 0.82 0.06 5.2NJ top-soil 9.1 0.64 3.0 16.7NJ sub-soil

(50 cm depth) 0.77 0.095 4.6 35.9

9

Tables S2. Chemical structure parameters of Mo in complexes with leaf litter extract

(LL) and tannic acid

shell Distance (Å) coordination

number

Debye-Waller

Factor (x 10-3 Å2)

Mo-LL pH 6.1Mo-Oax 1.72 ± 0.01 2.04 ± 0.15 3.2*Mo-Oeq 1.99 ± 0.01 3.85 ± 0.36 8.0*Mo....C 2.93 ± 0.02 3.64 ± 0.62 4.0*Mo-S 2.45 ± 0.02 0.48 ± 0.10 5.8#

Mo....C-O 3.23 ± 0.03 4.0* 4.5*Mo....O-O 3.98 ± 0.03 4.0* 4.4*

Mo-azotochelin pH 6.1Mo-Oax 1.72 ± 0.01 2.14 ± 0.10 3.2 ± 0.8Mo-Oeq 2.01 ± 0.01 4.21 ± 0.35 8.0 ± 2.0Mo....C 2.95 ± 0.02 4.10 ± 0.40 4.0 ± 1.5

Mo....C-O 3.23 ± 0.03 4.0* 4.5 ± 1.5Mo....O-O 3.98 ± 0.03 4.0* 4.4 ± 1.2

Mo-LL pH 4.6 (¶)Mo-Oax 1.72 ± 0.01 2.04 ± 0.15 3.2*Mo-Oeq 1.99 ± 0.01 3.05 ± 0.32 8.0*Mo....C 2.93 ± 0.02 2.82 ± 0.32 4.0*Mo-S 2.45 ± 0.02 0.60 ± 0.12 5.8#

Mo....C-O 3.23 ± 0.03 4.0* 4.5*Mo....O-O 3.98 ± 0.03 4.0* 4.4*

Mo-LL pH 7.5Mo-Oax 1.72 ± 0.01 2.04 ± 0.15 3.2*Mo-Oeq 1.99 ± 0.01 3.85 ± 0.46 8.0*Mo....C 2.93 ± 0.02 3.14 ± 0.55 4.0*Mo-S 2.45 ± 0.02 0.67 ± 0.16 5.8#

Mo....C-O 3.23 ± 0.03 4.0* 4.5*Mo....O-O 3.98 ± 0.03 4.0* 4.4*

Mo-Tannic AcidMo-Oax 1.73 ± 0.01 2.24 ± 0.15 3.2*Mo-Oeq 2.05 ± 0.01 3.46 ± 0.38 8.0*Mo....C 2.94 ± 0.02 3.04 ± 0.42 4.0*

Mo....C-O 3.25 ± 0.03 4.0* 4.5*Mo....O-O 3.97 ± 0.03 4.0* 4.4*

¶Mo(VI) polymerization in the sample was ruled out by the lack of Mo-Mo peak in the EXAFS Fourier transform spectrum45.* set to the best fit value of the azotochelin standard# set to the best fit value of the Mo-cysteine standard



10

Figure S1 Linear Combination Fitting (LCF) of Mo K-edge XANES spectra of soil samples.

a, and b, Mo-spiked soil samples (hardwood forest, NJ, USA). c, Mo-spiked leaf litter extract

(Mo-LL, Pine Barrens, NJ, USA).

20000 20020 20040 20060 20080 20100

0.0

0.3

0.6

0.9

1.2a

Norm

alize

d Ab

sorb

ance

µ(E)

x Top-soil

Mo-top soil, pH 5.7 LCF Mo-geothite, pH 5.4 Mo-LL, 5.3 residue

E (eV)

20000 20020 20040 20060 20080 20100

0.0

0.3

0.6

0.9

1.2b

Norm

alize

d Ab

sorb

ance

µ(E)

x Sub-soil

Mo-top soil, pH 5.7 LCF

Mo-ferrihydrite, pH 4.4 Mo-geothite, pH 5.4 Mo-LL, pH 5.3 residue

E (eV)

20000 20020 20040 20060 20080 20100

0.0

0.3

0.6

0.9

1.2

c

Norm

alize

d Ab

sorb

ance

µ(E)

x Leaf leachates

Mo-LL, pH 6.1 LCF Mo-azotochelin, pH 6.1 Mo-cysteine, crystaline Residue

E (eV)



10

Figure S1 Linear Combination Fitting (LCF) of Mo K-edge XANES spectra of soil samples.

a, and b, Mo-spiked soil samples (hardwood forest, NJ, USA). c, Mo-spiked leaf litter extract

(Mo-LL, Pine Barrens, NJ, USA).

20000 20020 20040 20060 20080 20100

0.0

0.3

0.6

0.9

1.2a

Norm

alize

d Ab

sorb

ance

µ(E)

x Top-soil

Mo-top soil, pH 5.7 LCF Mo-geothite, pH 5.4 Mo-LL, 5.3 residue

E (eV)

20000 20020 20040 20060 20080 20100

0.0

0.3

0.6

0.9

1.2b

Norm

alize

d Ab

sorb

ance

µ(E)

x Sub-soil

Mo-top soil, pH 5.7 LCF

Mo-ferrihydrite, pH 4.4 Mo-geothite, pH 5.4 Mo-LL, pH 5.3 residue

E (eV)

20000 20020 20040 20060 20080 20100

0.0

0.3

0.6

0.9

1.2

c

Norm

alize

d Ab

sorb

ance

µ(E)

x Leaf leachates

Mo-LL, pH 6.1 LCF Mo-azotochelin, pH 6.1 Mo-cysteine, crystaline Residue

E (eV)

11

Figure S2. Linear Combination Fitting of the XANES spectrum of the Mo-spiked leaf

litter extract (Mo-LL, Pine Barrens, NJ, USA) at pH = 9.

20000 20020 20040 20060 20080 20100

0.0

0.3

0.6

0.9

1.2 Leaf LeachatespH 9.0

Norm

alize

d Ab

sorb

ance

µ(E)

x

Mo-LL, pH 9.0 LCF

Mo-azotochelin, pH 6.1 Molybdate, pH 5.8 residue

E (eV)



12

Figure S3. Ultraviolet-visible difference spectra of Mo-LL (black) and Mo-tannic acid

(blue) at pH 6.6. The difference spectrum of Mo-LL is obtained by subtracting the

spectrum of the leaf litter extract (LL) from that of the Mo-LL solution, prepared by

adding 1.0 mM molybdate to (LL). The difference spectrum of Mo-tannic acid is

obtained in a similar fashion by subtracting the spectrum of tannic acid from that of the

Mo-tannic acid solution. The spectrum of the 1:1 Mo-azotochelin complex at pH 6.6 (red)

is shown for comparison.

300 400 500 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

Abso

rban

ce (U

)

Wavelength (nm)



12

Figure S3. Ultraviolet-visible difference spectra of Mo-LL (black) and Mo-tannic acid

(blue) at pH 6.6. The difference spectrum of Mo-LL is obtained by subtracting the

spectrum of the leaf litter extract (LL) from that of the Mo-LL solution, prepared by

adding 1.0 mM molybdate to (LL). The difference spectrum of Mo-tannic acid is

obtained in a similar fashion by subtracting the spectrum of tannic acid from that of the

Mo-tannic acid solution. The spectrum of the 1:1 Mo-azotochelin complex at pH 6.6 (red)

is shown for comparison.

300 400 500 6000.0

0.1

0.2

0.3

0.4

0.5

0.6

Abso

rban

ce (U

)

Wavelength (nm)

13

Figure S4. k2 Weighed χ(k) data (black lines) and fit (red circles) for Mo K-edge EXAFS

of Mo-LL and Mo-azotochelin at different pH values.

4 6 8 10-1

0

1

2

3

4

Mo-LL (pH 7.5)

Mo-Azotochelin (pH 6.1)

Mo-LL (pH 6.1)

Mo-LL (pH 4.6)

k2 * χ(

k) (Å

-3)

k (Å-1)



14

4. Acknowledgments

Total nitrogen and carbon content analysis were performed by Jim Wang from the LSU

AgCenter, Baton Rouge, LA. µXRF and µXANES were performed at Beamline X26A,

National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. X26A is

supported by the Department of Energy (DOE) - Geosciences (DE-FG02-92ER14244 to

The University of Chicago - CARS) and DOE - Office of Biological and Environmental

Research, Environmental Remediation Sciences Div. (DE-FC09-96-SR18546 to the

University of Kentucky). Use of the NSLS was supported by DOE under Contract No.

DE-AC02-98CH10886.



14

4. Acknowledgments

Total nitrogen and carbon content analysis were performed by Jim Wang from the LSU

AgCenter, Baton Rouge, LA. µXRF and µXANES were performed at Beamline X26A,

National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. X26A is

supported by the Department of Energy (DOE) - Geosciences (DE-FG02-92ER14244 to

The University of Chicago - CARS) and DOE - Office of Biological and Environmental

Research, Environmental Remediation Sciences Div. (DE-FC09-96-SR18546 to the

University of Kentucky). Use of the NSLS was supported by DOE under Contract No.

DE-AC02-98CH10886.

15

5. References

31 Kuiters, A. T. & Sarink, H. M. Leaching of phenolic compounds from leaf and

needle litter of several deciduous and coniferous trees. Soil Biol. Biochem. 18, 475-

480 (1986).

32 Sasaki, A., Shikenya, S., Takeda, K. & Nakatsubo, T. Dissolved organic matter

originating from the riparian shrub Salix gracilistyla. J. For. Res. 12, 68-74 (2007).

33 Schwertmann, U. & Cornell, R. M. Iron oxides in the laboratory: preparation and

characterisation. (VCH, 1991).

34 Kay, A. & Mitchell, P. C. Complexes of molybdenum-(V) and -(VI) with L-cysteine

and related compounds and their reactions with hydrogen sulphide. J. Chem. Soc.,

Inorg. Phys. Theo. 14, 2421-2428 (1970).

35 Cavaleiro, A., Dejesus, J. D. P., Gil, V. M. S., Gillard, R. D. & Williams, P. A.

Molybdenum(VI) complexation by amino acids. 2. species in aqueous solutions of

(R)-cysteine and sodium molybdate or tungstate. Inorg. Chim. Acta 172, 25-33

(1990).

36 Stern, E. A. & Heald, S. M. X-ray filter assembly for fluorescence measurements of

X-ray absorption fine structure. Rev. Sci. Instrum. 50, 1579-1582 (1979).

37 Stern, E. A., Newville, M., Ravel, B., Yacoby, Y. & Haskel, D. The UWXAFS

analysis package - philosophy and details. Physica B-Condensed Matter 209, 117-

120 (1995).

38 Newville, M., Livins, P., Yacoby, Y., Rehr, J. J. & Stern, E. A. Near edge X-ray

absorption fine structure of Pb - a comparison of theory and experiment. Phys. Rev. B

47, 14126-14131 (1993).



16

39 Newville, M. IFEFFIT: interactive XAFS analysis and FEFF fitting. J. Synch. Rad. 8,

322-324 (2001).

40 Newville, M. EXAFS analysis using FEFF and FEFFIT. J. Synch. Rad. 8, 96-100

(2001).

41 Kelly, S. D. et al. X-ray absorption fine structure determination of pH-dependent U-

bacterial cell wall interactions. Geochim. Cosmochim. Acta 66, 3855-3871 (2002).

42 Ravel, B. & Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for

X-ray absorption spectroscopy using IFEFFIT. J. Synch. Rad. 12, 537-541 (2005).

43 Ankudinov, A. L., Ravel, B., Rehr, J. J. & Conradson, S. D. Real-space multiple-

scattering calculation and interpretation of x-ray-absorption near-edge structure.

Physical Review B 58, 7565-7576 (1998).

44 Tkachev, V. V. & Atovmyan, L. O. Crustal and molecular structure of potassium

Dioxodipyrocatechuatemolybdate dihydrate. Sov. J. Coord. Chem. (Engl. Transl.) 1,

715-720 (1975).

45 Cruywagen, J. J. Protonation, oligomerization, and condensation reactions of

vanadate(V), molybdate(VI), and tungstate(VI). Adv. Inorg. Chem. 49, 127-182

(2000).

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