Nature of Interactions of Amino Acids with Bare Magnetite Nanoparticles
Supporting Information
Nature of Interactions of Amino Acids with Bare Magnetite Nanoparticles Sebastian P. Schwaminger,† Paula Fraga García,† Georg K. Merck,† Fabian A. Bodensteiner,† Stefan Heissler,‡ Sebastian Günther,§ Sonja Berensmeier*,† †
Bioseparation Engineering Group, Technische Universität München, Boltzmannstraße 15,
Garching D-85748, Germany ‡
Karlsruhe Institute of Technology, Institute of Functional Interfaces, Herrmann-von-
Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany §
Chemie Department, Technische Universität München, Lichtenbergstr. 4, Garching D-85748,
Germany
*E-mail address: [email protected]
S1
ATR-IR spectra
Intensity [a.u.]
a(NH3+)a(COO-)
s(COO-)
Glu pH 8 Glu pH 6 Glu pH 4 Mag-Glu
s(NH3+) (C=O)
(CH)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S1: IR spectra of 0.01 mol L-1 glutamic acid dissolved in water at different pH values (4, 6 and 8) and the magnetite glutamic acid mixture.
a(NH3+)a(COO-)
Intensity [a.u.]
s(COO-) (CH) s(NH3+)
Gly pH 8 Gly pH 6 Gly pH 4 Mag-Gly
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S2: IR spectra of 0.01 mol L-1 glycine dissolved in water at different pH values (4, 6 and 8) and the magnetite glycine mixture.
a(NH3+)a(COO-) (NH +) s 3 s(COO )
Intensity [a.u.]
-
(CH)
Lys pH 8 Lys pH 6 Lys pH 4 Mag-Lys
(C=O)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S3: IR spectra of 0.01 mol L-1 lysine dissolved in water at different pH values (4, 6 and 8) and the magnetite lysine mixture.
S2
a(NH3+)a(COO-)
Ser pH 8 Ser pH 6 Ser pH 4 Mag-Ser
Intensity [a.u.]
s(NH3+) s(COO-) (CH)
(OH)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S4: IR spectra of 0.01 mol L-1 serine dissolved in water at different pH values (4, 6 and 8) and the magnetite serine mixture.
a(NH3+)a(COO-)
Ala pH 8 Ala pH 6 Ala pH 4 Mag-Ala
Intensity [a.u.]
s(COO-) s(NH3+)
(CH)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S5: IR spectra of 0.01 mol L-1 alanine dissolved in water at different pH values (4, 6 and 8) and the magnetite alanine mixture.
a(NH3+)a(COO-)
s(COO-)
Intensity [a.u.]
s(NH3+)
(CH)
Cys pH 8 Cys pH 6 Cys pH 4 Mag-Cys Cystine
(C=O)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S6: IR spectra of 0.01 mol L-1 cysteine dissolved in water at different pH values (4, 6 and 8), the magnetite cysteine mixture and solid state cystine.
S3
a(NH3+)a(COO-)
His pH 8 His pH 6 His pH 4 Mag-His
s(COO-)
Intensity [a.u.]
s(NH3+)
(CH) Ring vibrations
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S7: IR spectra of 0.01 mol L-1 histidine dissolved in water at different pH values (4, 6 and 8) and the magnetite histidine mixture.
Absorbance [a.u.]
Blank Ala Cys Glu Gly His Lys Ser
3500
3000
2500
2000
1500
1000
500
-1
Wave Number [cm ]
Figure S8: Whole recorded IR spectra of magnetite and every magnetite amino acid mixture. X-ray Photoelectron spectroscopy 140000
Intensity [cps]
120000 100000 80000 60000 40000 20000 740
Mag-Ala Mag-Cys Mag-Glu Mag-Gly Mag-His Mag-Lys Mag-Ser Magnetite
735
730
725
720
715
710
705
Binding Energy [eV]
Figure S9: XP spectra in the Fe 2p region of magnetite and all the magnetite amino acid mixtures.
S4
Fe-O O-H Cumulative Fit Ala Ref Glu Cys Ser Lys His Gly
100000
Intensity [cps]
80000 60000 40000 20000 0 526
528
530
532
534
536
Binding Energy [eV]
Figure S10: XP spectra in the O 1s region of magnetite and all the magnetite amino acid mixtures. The reference spectrum is deconvolved into a Fe-O and a surface hydroxyl (O-H) component. C-H C-N O-C=O Fit Ser
O-C=O
Lys Gly
Glu
C-H C-S C-N
C-H C-S C-N O-C=O Cumulative Fit His
O-C=O
Intensity [a.u.]
C-N
Intensity [a.u.]
C-H
Cys
Ala Ref
Ref 282
284
286
288
290
292
Binding Energy [eV]
282
284
286
288
290
292
Binding Energy [eV]
Figure S11: XP spectra in the C 1s region of magnetite and all the magnetite amino acid mixtures. The left figure shows the polar and the right figure the nonpolar amino acids incubated with magnetite. X-ray-Photoelectron Spectroscopy of amino acids The amino acids were pressed to pellets before being transferred into the XP analysis chamber. The pellet samples were examined under the same conditions as the magnetite powder samples. The fitting of spectra was processed according to procedure used for the powder samples. The COO peak (288.4 eV) was used as reference to compensate charging since no adventitious carbon could be detected for the amino acid samples.1
S5
Alanine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulaive Fit
404
402
400
398
396
Binding Energy [eV]
Figure S12: XP spectra in the N 1s region of an alanine powder pellet.
Cysteine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S13: XP spectra in the N 1s region of a cysteine powder pellet.
Cystine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S14: XP spectra in the N 1s region of a cystine powder pellet.
S6
Glutamic Acid Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S15: XP spectra in the N 1s region of a glutamic acid powder pellet.
Glycine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S16: XP spectra in the N 1s region of a glycine powder pellet.
Intensity [a.u.]
Histidine C-N-C C-(NH)-C + Hydrogen Bonds C-NH3+ Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S17: XP spectra in the N 1s region of a histidine powder pellet.
S7
Lysine C-NH2
Intensity [a.u.]
Hydrogen Bonds C-NH3+ Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S18: XP spectra in the N 1s region of a lysine powder pellet.
Serine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S19: XP spectra in the N 1s region of a serine powder pellet. Simultaneous Thermal Analysis Weightloss 16 amu 17 amu 18 amu 30 amu 44 amu
1.000
1E-11
Mass [-]
0.990 0.985 0.980 0.975 0.970
Ion current [A]
0.995
1E-12
0.965 200
400
600
800
Temperature [°C]
Figure S20: MS signals over temperature of the thermogravimetric measurements of blank magnetite in the temperature range of 40-880°C under nitrogen atmosphere.
S8
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu 42 amu 74 amu
1.00
1E-11
Ion current [A]
Mass [-]
0.99 0.98 0.97
1E-12
0.96 0.95 200
400
600
800
Temperature [°C]
Figure S21: MS signals over temperature of the thermogravimetric measurements of the magnetite alanine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
1.00 1E-10
0.98
Mass [-]
0.94 0.92
1E-11
0.90 0.88 0.86
1E-12
0.84 0.82 0.80 200
400
600
800
Temperature [°C]
Ion current [A]
0.96
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu 57 amu 59 amu 74 amu 76 amu 84 amu 101 amu
Figure S22: MS signals over temperature of the thermogravimetric measurements of the magnetite cysteine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
1.00 0.99
Mass [-]
0.98
1E-11
0.97 0.96 0.95
1E-12
Ion current [A]
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu 55 amu 74 amu
0.94 0.93 0.92 200
400
600
800
Temperature [°C]
Figure S23: MS signals over temperature of the thermogravimetric measurements of the magnetite glutamic acid mixture in the temperature range of 40-880°C under nitrogen atmosphere.
S9
Weightloss 16 amu 17 amu 18 amu 30 amu 43 amu 44 amu
1.00
Mass [-]
1E-11 0.98 0.97 0.96
Ion current [A]
0.99
1E-12
0.95 0.94 200
400
600
800
Temperature [°C]
Figure S24: MS signals over temperature of the thermogravimetric measurements of the magnetite glycine acid mixture in the temperature range of 40-880°C under nitrogen atmosphere. Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu
1.00 0.99
1E-11
Mass [-]
0.97 0.96 0.95 0.94 0.93
1E-12
Ion current [A]
0.98
0.92 0.91 0.90 200
400
600
800
Temperature [°C]
Figure S25: MS signals over temperature of the thermogravimetric measurements of the magnetite histidine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
1.00 0.99
Mass [-]
0.98
1E-11
0.97 0.96 0.95 1E-12
0.94
Ion current [A]
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu
0.93 0.92 200
400
600
800
Temperature [°C]
Figure S26: MS signals over temperature of the thermogravimetric measurements of the magnetite lysine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
S10
0.99
1E-11
Mass [-]
0.98 0.97 0.96
1E-12
0.95
Ion current [A]
Weightloss 16 amu 17 amu 18 amu 30 amu 43 amu 44 amu
1.00
0.94 0.93 200
400
600
800
Temperature [°C]
Figure S27: MS signals over temperature of the thermogravimetric measurements of the magnetite serine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
Determination of the specific surface area by BET-isotherms The specific surface area was determined with a Gemini VII 2390 Surface Area Analyzer (Micromeritics Instrument Corporation, USA). Prior to analysis, the samples were dried in vacuum at 100°C and weighted. The measurement included a determination of the sample volume with the inert gas helium and the gas adsorption isotherm of nitrogen at 77 K. From
Adsorbed Quantity [mmol g-1]
the gas adsorption isotherms the specific surface area was determined by the BET-method.2
1.4 1.3 1.2 1.1 1.0 0.9 0.8
N2 adsorption isotherme
0.7 0.6 0.00
0.05
0.10
0.15
0.20
0.25
Relative Pressure [p p0-1]
Figure S28: Nitrogen adsorption isotherm on magnetite nanoparticles at 77 K.
Determination of the point of zero charge (PZC) of magnetite nanoparticles Potentiometric titrations were accomplished in an OptiMax™ reactor (Mettler-Toledo GmbH, Germany) from pH 4 to 10. The degassed magnetite suspensions were adjusted to a S11
concentration of 2 g L-1 which correlates to 203 m2 L-1 and equilibrated at a pH of 4 overnight. The whole titration was conducted under nitrogen atmosphere at 298.5 K with HCl and NaOH as titrand and a NaCl concentration of 100 mmol L-1 and 10 mmol L-1 respectively. The surface charge was calculated according to the procedure of Lützenkirchen et al.3
Magnetite (100 mM NaCl) Magnetite (10 mM NaCl)
Surface Charge [C m-2]
0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 3
4
5
6
7
8
9
10
11
pH
Figure S29: Determination of the point of zero charge of magnetite nanoparticles (2 g L-1) by potentiometric titration with NaOH.
Raman Spectroscopy A Senterra Raman spectrometer (Bruker Optics, Ettlingen, Germany) equipped with a 785 nm laser was used for the analysis of freeze-dried nanoparticles. Low laser powers were selected in order to prevent oxidation of samples. A baseline correction was accomplished with the software OPUS 7.2 for spectra measured by Raman spectroscopy using the concave rubber band method. The spectra were normalised with a maximum/minimum normalisation for comparison purposes.
S12
(S-S)
Mag Mag-Cys Cystine Cysteine
Intensity [a.u.]
(Fe-O)
1000 900
800
700
600
500
400
300
200
Wave Number [cm-1]
Figure S30: Raman spectra of the solid bodies; magnetite, magnetite cysteine mixtures, cystine and cysteine in the range of 400 to 1000 cm-1.
Intensity [a.u.]
Mag Cystine Mag-Cys Cysteine
3500
3000
2500
(Fe-O)
2000
1500
1000
(S-S)
500
Wave Number [cm-1]
Figure S31: Whole recorded Raman spectra of the solid bodies; magnetite, magnetite cysteine mixture, solid state cystine and cysteine.
Elemental analysis Table S1: Measured elemental compositions (C, H, N and S) of blank particles and particle amino acid mixtures. The residual weight was contributed to iron and oxygen. Mag-Ala Mag-Cys Mag-Glu Mag-Gly Mag-His Mag-Lys Mag-Ser Blank
Carbon [%] 0.45 3.26 1.42 0.59 1.80 1.32 0.95 0.10
Hydrogen [%] 0.35 0.73 0.36 0.34 0.39 0.46 0.39 0.32
Nitrogen [%] 0.17 1.30 0.39 0.27 1.04 0.50 0.39 0.00
Sulfur [%] 0.00 2.83 0.00 0.00 0.00 0.00 0.00 0.00
other (Fe, O) [%] 99.03 91.89 97.83 98.80 96.77 97.72 98.27 99.58
Calculation of residue loading for Elemental Analysis S13
Load q can be determined by the following equation with xN and xAA Fe,O being the nitrogen content and the magnetite content (Fe, O) respectively and as molar mass of nitrogen. The blank value xAA Fe,O is used to correct the ratio of nitrogen to magnetite, f resembles a stoichiometric nitrogen factor (2 for lysine, 3 for histidine, 1 for other amino acids) and MN is the molar mass of nitrogen (14 g mol-1). q=
xN AA xFe,O ∙MN ∙f xBlank Fe,O
Calculation of residue loading for STA Load q can be calculated by the dimensionless weightloss mWL which is the difference between the final weight of the blank and the coated samples, the mass loss due to oxidization of amino acid mOx and the molar mass of the corresponding amino acid. The mass loss due to oxidation of amino acids is approximated with use of factor f which depends on the nitrogen/sulfur atoms (count 1) and the noncarboxylic carbon atoms (count 0.5) of the corresponding amino acid and the molar mass of oxygen MO .
q=
(mWL -mOx )∙ (1+
(mWL -mOx ) (mend +mOx ))
MAA
mWL =(mend (Blank)-mend (AA)) mOx =
f∙MO ∙mWL MAA +f∙MO
Calculation of surface coverage The surface coverage θ can be calculated with the loads q of the different methods applied, the Avogadro constant NA and the specific surface area of particles sMNP . θ=
(qSTA +qEle +qXPS )∙NA 3∙sMNP S14
Table S2: Calculated surface coverages for different amino acids. Amino Acid
Coverage
Cysteine Glutamic Acid Serine Histidine Glycine Lysine Alanine
[molecules nm-2] 5.53 1.84 1.61 1.55 1.27 1.16 0.66
Intensity [a.u.]
Ser-S Ser Lys-S Lys His-S His Gly-S Gly Glu-S Glu Cys-S Cys Ala-S Ala 1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S31: Solid state spectra of amino acids in comparison with spectra of amino acids adsorbed on magnetite nanoparticles.
References (1) Zubavichus, Y.; Fuchs, O.; Weinhardt, L.; Heske, C.; Umbach, E.; Denlinger, J. D.; Grunze, M. Soft X-Ray-Induced Decomposition of Amino Acids: An XPS, Mass Spectrometry, and NEXAFS Study. Radiat. Res. 2004, 161, 346–358. (2) Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of Gases in Multimolecular Layers. J. Am. Chem. Soc. 1938, 60, 309–319. (3) Lützenkirchen, J.; Preočanin, T.; Kovačević, D.; Tomišić, V.; Lövgren, L.; Kallay, N. Potentiometric Titrations as a Tool for Surface Charge Determination. Croat. Chem. Acta 2012, 85, 391–417.
S15
Nature of Interactions of Amino Acids with Bare Magnetite Nanoparticles Sebastian P. Schwaminger,† Paula Fraga García,† Georg K. Merck,† Fabian A. Bodensteiner,† Stefan Heissler,‡ Sebastian Günther,§ Sonja Berensmeier*,† †
Bioseparation Engineering Group, Technische Universität München, Boltzmannstraße 15,
Garching D-85748, Germany ‡
Karlsruhe Institute of Technology, Institute of Functional Interfaces, Herrmann-von-
Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany §
Chemie Department, Technische Universität München, Lichtenbergstr. 4, Garching D-85748,
Germany
*E-mail address: [email protected]
S1
ATR-IR spectra
Intensity [a.u.]
a(NH3+)a(COO-)
s(COO-)
Glu pH 8 Glu pH 6 Glu pH 4 Mag-Glu
s(NH3+) (C=O)
(CH)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S1: IR spectra of 0.01 mol L-1 glutamic acid dissolved in water at different pH values (4, 6 and 8) and the magnetite glutamic acid mixture.
a(NH3+)a(COO-)
Intensity [a.u.]
s(COO-) (CH) s(NH3+)
Gly pH 8 Gly pH 6 Gly pH 4 Mag-Gly
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S2: IR spectra of 0.01 mol L-1 glycine dissolved in water at different pH values (4, 6 and 8) and the magnetite glycine mixture.
a(NH3+)a(COO-) (NH +) s 3 s(COO )
Intensity [a.u.]
-
(CH)
Lys pH 8 Lys pH 6 Lys pH 4 Mag-Lys
(C=O)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S3: IR spectra of 0.01 mol L-1 lysine dissolved in water at different pH values (4, 6 and 8) and the magnetite lysine mixture.
S2
a(NH3+)a(COO-)
Ser pH 8 Ser pH 6 Ser pH 4 Mag-Ser
Intensity [a.u.]
s(NH3+) s(COO-) (CH)
(OH)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S4: IR spectra of 0.01 mol L-1 serine dissolved in water at different pH values (4, 6 and 8) and the magnetite serine mixture.
a(NH3+)a(COO-)
Ala pH 8 Ala pH 6 Ala pH 4 Mag-Ala
Intensity [a.u.]
s(COO-) s(NH3+)
(CH)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S5: IR spectra of 0.01 mol L-1 alanine dissolved in water at different pH values (4, 6 and 8) and the magnetite alanine mixture.
a(NH3+)a(COO-)
s(COO-)
Intensity [a.u.]
s(NH3+)
(CH)
Cys pH 8 Cys pH 6 Cys pH 4 Mag-Cys Cystine
(C=O)
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S6: IR spectra of 0.01 mol L-1 cysteine dissolved in water at different pH values (4, 6 and 8), the magnetite cysteine mixture and solid state cystine.
S3
a(NH3+)a(COO-)
His pH 8 His pH 6 His pH 4 Mag-His
s(COO-)
Intensity [a.u.]
s(NH3+)
(CH) Ring vibrations
1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S7: IR spectra of 0.01 mol L-1 histidine dissolved in water at different pH values (4, 6 and 8) and the magnetite histidine mixture.
Absorbance [a.u.]
Blank Ala Cys Glu Gly His Lys Ser
3500
3000
2500
2000
1500
1000
500
-1
Wave Number [cm ]
Figure S8: Whole recorded IR spectra of magnetite and every magnetite amino acid mixture. X-ray Photoelectron spectroscopy 140000
Intensity [cps]
120000 100000 80000 60000 40000 20000 740
Mag-Ala Mag-Cys Mag-Glu Mag-Gly Mag-His Mag-Lys Mag-Ser Magnetite
735
730
725
720
715
710
705
Binding Energy [eV]
Figure S9: XP spectra in the Fe 2p region of magnetite and all the magnetite amino acid mixtures.
S4
Fe-O O-H Cumulative Fit Ala Ref Glu Cys Ser Lys His Gly
100000
Intensity [cps]
80000 60000 40000 20000 0 526
528
530
532
534
536
Binding Energy [eV]
Figure S10: XP spectra in the O 1s region of magnetite and all the magnetite amino acid mixtures. The reference spectrum is deconvolved into a Fe-O and a surface hydroxyl (O-H) component. C-H C-N O-C=O Fit Ser
O-C=O
Lys Gly
Glu
C-H C-S C-N
C-H C-S C-N O-C=O Cumulative Fit His
O-C=O
Intensity [a.u.]
C-N
Intensity [a.u.]
C-H
Cys
Ala Ref
Ref 282
284
286
288
290
292
Binding Energy [eV]
282
284
286
288
290
292
Binding Energy [eV]
Figure S11: XP spectra in the C 1s region of magnetite and all the magnetite amino acid mixtures. The left figure shows the polar and the right figure the nonpolar amino acids incubated with magnetite. X-ray-Photoelectron Spectroscopy of amino acids The amino acids were pressed to pellets before being transferred into the XP analysis chamber. The pellet samples were examined under the same conditions as the magnetite powder samples. The fitting of spectra was processed according to procedure used for the powder samples. The COO peak (288.4 eV) was used as reference to compensate charging since no adventitious carbon could be detected for the amino acid samples.1
S5
Alanine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulaive Fit
404
402
400
398
396
Binding Energy [eV]
Figure S12: XP spectra in the N 1s region of an alanine powder pellet.
Cysteine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S13: XP spectra in the N 1s region of a cysteine powder pellet.
Cystine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S14: XP spectra in the N 1s region of a cystine powder pellet.
S6
Glutamic Acid Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S15: XP spectra in the N 1s region of a glutamic acid powder pellet.
Glycine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S16: XP spectra in the N 1s region of a glycine powder pellet.
Intensity [a.u.]
Histidine C-N-C C-(NH)-C + Hydrogen Bonds C-NH3+ Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S17: XP spectra in the N 1s region of a histidine powder pellet.
S7
Lysine C-NH2
Intensity [a.u.]
Hydrogen Bonds C-NH3+ Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S18: XP spectra in the N 1s region of a lysine powder pellet.
Serine Hydrogen Bonds C-NH3+
Intensity [a.u.]
Cumulative Fit
404
402
400
398
396
Binding Energy [eV]
Figure S19: XP spectra in the N 1s region of a serine powder pellet. Simultaneous Thermal Analysis Weightloss 16 amu 17 amu 18 amu 30 amu 44 amu
1.000
1E-11
Mass [-]
0.990 0.985 0.980 0.975 0.970
Ion current [A]
0.995
1E-12
0.965 200
400
600
800
Temperature [°C]
Figure S20: MS signals over temperature of the thermogravimetric measurements of blank magnetite in the temperature range of 40-880°C under nitrogen atmosphere.
S8
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu 42 amu 74 amu
1.00
1E-11
Ion current [A]
Mass [-]
0.99 0.98 0.97
1E-12
0.96 0.95 200
400
600
800
Temperature [°C]
Figure S21: MS signals over temperature of the thermogravimetric measurements of the magnetite alanine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
1.00 1E-10
0.98
Mass [-]
0.94 0.92
1E-11
0.90 0.88 0.86
1E-12
0.84 0.82 0.80 200
400
600
800
Temperature [°C]
Ion current [A]
0.96
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu 57 amu 59 amu 74 amu 76 amu 84 amu 101 amu
Figure S22: MS signals over temperature of the thermogravimetric measurements of the magnetite cysteine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
1.00 0.99
Mass [-]
0.98
1E-11
0.97 0.96 0.95
1E-12
Ion current [A]
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu 55 amu 74 amu
0.94 0.93 0.92 200
400
600
800
Temperature [°C]
Figure S23: MS signals over temperature of the thermogravimetric measurements of the magnetite glutamic acid mixture in the temperature range of 40-880°C under nitrogen atmosphere.
S9
Weightloss 16 amu 17 amu 18 amu 30 amu 43 amu 44 amu
1.00
Mass [-]
1E-11 0.98 0.97 0.96
Ion current [A]
0.99
1E-12
0.95 0.94 200
400
600
800
Temperature [°C]
Figure S24: MS signals over temperature of the thermogravimetric measurements of the magnetite glycine acid mixture in the temperature range of 40-880°C under nitrogen atmosphere. Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu
1.00 0.99
1E-11
Mass [-]
0.97 0.96 0.95 0.94 0.93
1E-12
Ion current [A]
0.98
0.92 0.91 0.90 200
400
600
800
Temperature [°C]
Figure S25: MS signals over temperature of the thermogravimetric measurements of the magnetite histidine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
1.00 0.99
Mass [-]
0.98
1E-11
0.97 0.96 0.95 1E-12
0.94
Ion current [A]
Weightloss 16 amu 17 amu 18 amu 30 amu 41 amu 43 amu 44 amu
0.93 0.92 200
400
600
800
Temperature [°C]
Figure S26: MS signals over temperature of the thermogravimetric measurements of the magnetite lysine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
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0.99
1E-11
Mass [-]
0.98 0.97 0.96
1E-12
0.95
Ion current [A]
Weightloss 16 amu 17 amu 18 amu 30 amu 43 amu 44 amu
1.00
0.94 0.93 200
400
600
800
Temperature [°C]
Figure S27: MS signals over temperature of the thermogravimetric measurements of the magnetite serine mixture in the temperature range of 40-880°C under nitrogen atmosphere.
Determination of the specific surface area by BET-isotherms The specific surface area was determined with a Gemini VII 2390 Surface Area Analyzer (Micromeritics Instrument Corporation, USA). Prior to analysis, the samples were dried in vacuum at 100°C and weighted. The measurement included a determination of the sample volume with the inert gas helium and the gas adsorption isotherm of nitrogen at 77 K. From
Adsorbed Quantity [mmol g-1]
the gas adsorption isotherms the specific surface area was determined by the BET-method.2
1.4 1.3 1.2 1.1 1.0 0.9 0.8
N2 adsorption isotherme
0.7 0.6 0.00
0.05
0.10
0.15
0.20
0.25
Relative Pressure [p p0-1]
Figure S28: Nitrogen adsorption isotherm on magnetite nanoparticles at 77 K.
Determination of the point of zero charge (PZC) of magnetite nanoparticles Potentiometric titrations were accomplished in an OptiMax™ reactor (Mettler-Toledo GmbH, Germany) from pH 4 to 10. The degassed magnetite suspensions were adjusted to a S11
concentration of 2 g L-1 which correlates to 203 m2 L-1 and equilibrated at a pH of 4 overnight. The whole titration was conducted under nitrogen atmosphere at 298.5 K with HCl and NaOH as titrand and a NaCl concentration of 100 mmol L-1 and 10 mmol L-1 respectively. The surface charge was calculated according to the procedure of Lützenkirchen et al.3
Magnetite (100 mM NaCl) Magnetite (10 mM NaCl)
Surface Charge [C m-2]
0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 3
4
5
6
7
8
9
10
11
pH
Figure S29: Determination of the point of zero charge of magnetite nanoparticles (2 g L-1) by potentiometric titration with NaOH.
Raman Spectroscopy A Senterra Raman spectrometer (Bruker Optics, Ettlingen, Germany) equipped with a 785 nm laser was used for the analysis of freeze-dried nanoparticles. Low laser powers were selected in order to prevent oxidation of samples. A baseline correction was accomplished with the software OPUS 7.2 for spectra measured by Raman spectroscopy using the concave rubber band method. The spectra were normalised with a maximum/minimum normalisation for comparison purposes.
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(S-S)
Mag Mag-Cys Cystine Cysteine
Intensity [a.u.]
(Fe-O)
1000 900
800
700
600
500
400
300
200
Wave Number [cm-1]
Figure S30: Raman spectra of the solid bodies; magnetite, magnetite cysteine mixtures, cystine and cysteine in the range of 400 to 1000 cm-1.
Intensity [a.u.]
Mag Cystine Mag-Cys Cysteine
3500
3000
2500
(Fe-O)
2000
1500
1000
(S-S)
500
Wave Number [cm-1]
Figure S31: Whole recorded Raman spectra of the solid bodies; magnetite, magnetite cysteine mixture, solid state cystine and cysteine.
Elemental analysis Table S1: Measured elemental compositions (C, H, N and S) of blank particles and particle amino acid mixtures. The residual weight was contributed to iron and oxygen. Mag-Ala Mag-Cys Mag-Glu Mag-Gly Mag-His Mag-Lys Mag-Ser Blank
Carbon [%] 0.45 3.26 1.42 0.59 1.80 1.32 0.95 0.10
Hydrogen [%] 0.35 0.73 0.36 0.34 0.39 0.46 0.39 0.32
Nitrogen [%] 0.17 1.30 0.39 0.27 1.04 0.50 0.39 0.00
Sulfur [%] 0.00 2.83 0.00 0.00 0.00 0.00 0.00 0.00
other (Fe, O) [%] 99.03 91.89 97.83 98.80 96.77 97.72 98.27 99.58
Calculation of residue loading for Elemental Analysis S13
Load q can be determined by the following equation with xN and xAA Fe,O being the nitrogen content and the magnetite content (Fe, O) respectively and as molar mass of nitrogen. The blank value xAA Fe,O is used to correct the ratio of nitrogen to magnetite, f resembles a stoichiometric nitrogen factor (2 for lysine, 3 for histidine, 1 for other amino acids) and MN is the molar mass of nitrogen (14 g mol-1). q=
xN AA xFe,O ∙MN ∙f xBlank Fe,O
Calculation of residue loading for STA Load q can be calculated by the dimensionless weightloss mWL which is the difference between the final weight of the blank and the coated samples, the mass loss due to oxidization of amino acid mOx and the molar mass of the corresponding amino acid. The mass loss due to oxidation of amino acids is approximated with use of factor f which depends on the nitrogen/sulfur atoms (count 1) and the noncarboxylic carbon atoms (count 0.5) of the corresponding amino acid and the molar mass of oxygen MO .
q=
(mWL -mOx )∙ (1+
(mWL -mOx ) (mend +mOx ))
MAA
mWL =(mend (Blank)-mend (AA)) mOx =
f∙MO ∙mWL MAA +f∙MO
Calculation of surface coverage The surface coverage θ can be calculated with the loads q of the different methods applied, the Avogadro constant NA and the specific surface area of particles sMNP . θ=
(qSTA +qEle +qXPS )∙NA 3∙sMNP S14
Table S2: Calculated surface coverages for different amino acids. Amino Acid
Coverage
Cysteine Glutamic Acid Serine Histidine Glycine Lysine Alanine
[molecules nm-2] 5.53 1.84 1.61 1.55 1.27 1.16 0.66
Intensity [a.u.]
Ser-S Ser Lys-S Lys His-S His Gly-S Gly Glu-S Glu Cys-S Cys Ala-S Ala 1800 1700 1600 1500 1400 1300 1200 1100 1000
Wave Number [cm-1]
Figure S31: Solid state spectra of amino acids in comparison with spectra of amino acids adsorbed on magnetite nanoparticles.
References (1) Zubavichus, Y.; Fuchs, O.; Weinhardt, L.; Heske, C.; Umbach, E.; Denlinger, J. D.; Grunze, M. Soft X-Ray-Induced Decomposition of Amino Acids: An XPS, Mass Spectrometry, and NEXAFS Study. Radiat. Res. 2004, 161, 346–358. (2) Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of Gases in Multimolecular Layers. J. Am. Chem. Soc. 1938, 60, 309–319. (3) Lützenkirchen, J.; Preočanin, T.; Kovačević, D.; Tomišić, V.; Lövgren, L.; Kallay, N. Potentiometric Titrations as a Tool for Surface Charge Determination. Croat. Chem. Acta 2012, 85, 391–417.
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