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L-Lysine on γ-alumina and kaolinite
Jan-Feb 2008
KEY FINDINGS
o No lysine observed on γ-alumina samples treated (and then washed to remove
pore water) with lysine solutions with an initial pH of 9.8.
o No lysine observed on γ-alumina samples treated (and then washed to remove
pore water) with lysine solutions with an initial pH of 6.3 and concentrations
ranging from 0.02 M – 0.001 M.
o Evidence of aliphatic carbon chain was found on the γ-alumina sample treated
with 0.05 M lysine at pH 6.3. No evidence of amino or carboxylate groups was
observed. This finding is consistent with incomplete exchange of pore water in
the washing cycle for this sample which was treated with the most concentrated
solution.
o Lysine was observed on kaolinite samples treated with 0.05 – 0.005 M solutions
(for both of the pH 9.8 and the pH 6.3 sets). The kaolinite samples were very
difficult to wash without large loss of solid and thus the observed lysine may be a
result of residual solution.
o The observed results are consistent with the strong ability of lysine to complex
with aluminum ions (particularly those with octahedral coordination) and to
extract them from mineral substrates.
ABSTRACT
The DRIFTS technique was successful in detecting lysine on the surface of γalumina and kaolinite, after treatment with solutions containing the amino acid (as
described previously in a May 2007 report. These preliminary investigations used
solutions with sufficient amino acid for multi-layer coverage of the mineral surface.
Samples were decanted but not washed and thus and some dry down of the organic
onto the surface occurred. The previous work was successful in showing that spectral
windows were available, on γ-alumina and on kaolinite, using the DRIFTS technique (as
developed at JLab Applied Science). The peaks observable in the spectral window
include peaks for carboxylate and amine and the hydrocarbon chain. The spectra
obtained for lysine was consistent with the work reported in the literature (for lysine
adsorption onto TiO2) using in situ ATR –IR spectroscopy. In this study conditions are
set for monolayer or less coverage and samples are washed, prior to drying so as to
remove residual treating solution. Investigations are carried out with solutions of pH 6.3
and of 9.3.
INVESTIGATION
The DRIFTS technique was successful in detecting lysine on the surface of γalumina and kaolinite, after treatment with solutions containing the amino acid. This has
been described in the May 2007 report “The use of DRIFTS to investigate the
adsorption of amino acids onto alumina and kaolinite – preliminary investigations”.
Samples were prepared such that the availability of amino acid in solution was sufficient
for multi-layer coverage of the mineral surface and some dry down of the organic onto
the surface occurred. The previous work showed that by using the DRIFTS technique
(as developed at JLab Applied Science) spectral windows, in the 1800 -1300 cm-1
region and in the 3400 -2800 cm-1 region, were available for the study of amino acids
on γ-alumina and on kaolinite. The peaks observable in the spectral window include
peaks for carboxylate and amine and the hydrocarbon chain. The spectra obtained for
lysine was consistent with the work reported in the literature (for lysine adsorption onto
TiO2) using in situ ATR –IR spectroscopyi,ii,iii .
Spectra obtained, in the initial study on kaolinite and on γ-alumina, are shown in
Figure 1.
12
11
10
9
8
7
KM 6
5
4
3
2
1
0
1606
1587
1636 adsorbed
water
1800
1700
1495
-NH2
1392
1407
1600
1500
1400
Wavenumbers (cm-1)
-COO1349; 1330
1300
Figure 1 Difference spectra (both full scale) of Lysine adsorbed onto minerals
(unwashed samples) (RED KW scale 0-12 KM) and (BLUE γ-alumina scale 0-3 KM).
In the previous study, L-lysine was observed on the surface of γ-alumina and on
kaolinite, after treatment with 0.02 M lysine (at pH 9.8, the pH obtained by dissolving the
lysine in 0.01 M HClO4, with no further manipulation). The samples were centrifuged to
remove excess solution but not washed, thus it was possible that deposition from
dry-down may have occurred. Further studies are now carried out with all samples
undergoing a washing cycle (as for studies with salicylic acid and myristic acid).
A dilution series was prepared for each of γ-alumina and kaolinite with two sets of pH
conditions used (4 sample sets in all);
o In the region of the iso-electric point of lysine, pH 9.8, such that the dominant
solution species is the uncharged but polarized Zwitter ion, and the surface
charge on the minerals is negative.
o A pH in the slightly acid to neutral region (pH 6.0-7.0) were the dominant solution
species is L+, (NH3+-(CH2)4-C(H)(NH3+)(COO-), exists in the region of pH 2.1 –
9.1 (the pKa of the α-amino group is 9.1 and L+). At this pH the surface charge of
γ-alumina is positive and that of the siloxane surface of kaolinite, negative.
MATERIALS
L-Lysine H2N-(CH2)4-C(H)(NH2)COOH
o Molecular formula = C6H14N2O2;
o GMW = 146.18
Minerals
o γ-alumina, Science Minerals Corp, surface area (BET method) 51 m2/g
o kaolinite, Ward’s Natural Sci., Edgar, Florida deposit, surface area (BET method)
27 m2/g
METHOD
A Solution of 0.1 M NaClO4 was prepared using Milli-Q water (14.04 g/L) for use as a
high background strength medium for the lysine solutions. A stock solution of 0.05 M Llysine was prepared (1.829 g in 250 ml of 0.1 M NaClO4). Sets of dilution series were
prepared using the stock solution and 0.1 M NaClO4 for dilution. The pH of each solution
sample was adjusted before the addition of mineral
o sets Ai and Ki were adjusted to 9.8 ±0.1 (using NaOH)
o sets Aii and Kii were adjusted to 6.3 ±0.2 (using HClO4).
The solid to solution ratio for γ-alumina was 1g/20 ml to match that used in the previous
study (with samples unwashed after treatment) – in practice, 0.75 in 15 ml was used to
enable the use of the glass vial available. In the case of kaolinite, 1.5 g per 15 ml was
used such that an approximately equivalent surface area to solution was used for each
mineral.
The solutions were capped and placed on a shaker for 24 h. The solution was decanted
from the solid (after the solid was allowed to settle). Each sample was then washed
and decanted 3 X using Milli-Q water adjusted to either pH 9.8 or 6.3. Note that 0.1 M
NaClO4 was not used for the washing, to minimize the dry down of NaClO4.
Conc
M
0.05
0.02
0.01
0.005
0.002
0.001
0.000
Table 1: Summary of samples prepared
*molecules per nm2
Code
A = γ-alumina
K = kaolinite
i = pH 9.8
ii = pH 6.3
1
10 ± 1
A=12; K=11
2
5 ± 0.5
A=4.7; K=4.4
3
2 ± 0.5
A=2.4; K=2.2
4
1 ± 0.2
A=1.2; K=1.1
5
0.5 ± 0.1
A=0.47;K=0.44
6
0.2 ± 0.05
A=0.24; K=0.22
BLK
0.0
* Calculation of the number of molecules available per nm 2
Molecules/nm2 = vol(L) x conc (M) x 6.00 x 1023 / (wt (g) x area (m2/g) x 1018)
DRIFTS proceedure
System purged with dry air
Settings as in previous studies
RESULTS
Table 2: Sample table
γ-alumina
Initial pH
9.8
A1i
A2i
A3i
A4i
A5i
A5iR
A6i
BLK Ai
Final
pH
kaolinite
initial pH
9.8
K1i
K2i
Final
pH
9.7
9.1
10
5
K3i
K4i
8.8
8.4
K5i
K5iR
k6i
BLK Ki
7.7
7.8
7.6
5.7
9.5
9.3
9.3
9.0
8.4
8.7
8.2
7.9
max
molecules
/ nm2
10
5
2
1
0.5
0.5
0.2
0.0
lysine
Sample
observed Initial
pH 6.3
no
A1ii
no
A2ii
no
A3ii
no
A4ii
no
A5i
no
A5iiR
no
A6ii
no
BLK Aii
Final
pH
8.2
7.9
7.8
7.7
7.2
7.4
7.0
7.2
max
molecules
/ nm2
10
5
2
1
0.5
0.5
0.2
0.0
lysine
observed
?
Yes/
trace
yes
Yes
/trace
no
no
no
no
Final
pH
yes
yes
kaolinite
initial pH
6.3
K1ii
K2ii
8.0
7.8
10
5
2
1
yes
yes
K3ii
K4ii
7.3
6.7
2
1
0.5
0.5
0.2
0.0
no
no
no
no
K5ii
K5iiR
k6ii
BLK Kii
5.5
6.4
5.9
5.3
0.5
0.5
0.2
0.0
yes
no
no
no
no
no
no
no
Observed changes in pH.
Solutions with an initial pH of 9.8
Kaolinite & γ-alumina
o Biggest changes were observed with solutions with the least lysine, the greatest
being the blank.
o The observed changes were greater for kaolinite than for γ-alumina.
The pH of the most concentrated solution was as a result of lysine dissolution in water –
no extra OH- added.
Kaolinite
At high pH mineral oxides deprotonate, thus in an unbuffered system the pH will fall.
Aluminum cations may be dissolved from the surface (esp edges) See Chpt 5
.Chemistry of the solid water interface – Wener Stummiv
-Al3+ + 4OH- ↔ Al(OH)4Si4+ +4OH- ↔ Si(OH)4
The solution with the highest lysine concentration have the smallest pH change. This
could be due to
1. Buffering by the lysine L ↔ L+ + OH2. Adsorption of lysine onto cations thus protecting them from OH- (competitive
adsorption).
Γ-alumina samples
o All samples, showed an increase in pH, the blank being the least.
For the blank this is consistent with uptake of H+ by surface oxide groups.
The equilibrium L + H+ ↔ HL+ will also come into play when lysine is present.
Solutions with an initial pH of 6.3.
Γ-alumina samples
o The range of final pH values (7.2 (blank) – 8.2 (most conc solution))
o Increase in pH of the blank is due to adsorption of protons onto the surface
o Some contribution by the lysine in solution L + H+ ↔ HL+
The lysine extracts Al3+ from the mineral (forming a complex) Na ions would exchange
into the lattice but to maintain charge balance, protons would move into the lattice as
well, thus increasing pH.
Al3+ + 3L ↔ Al(L)33+
Kaolinite samples.
o The pH of the blank solution and the most dilute lysine solution increased. This is
consistent with the coordination of hydroxyl groups to surface cations, but it
should be noted that a change from 6.3 to 5.9 is very small in terms of the
change in hydrogen ion concentration. Calculation show a change of 7.5 x10 -7
moles per L in H+ which equates to 2 x 10-4 ions per nm2. Such a value is
consistent with adsorption of OH- to under coordinated edge or corner sites.
Al3+ + H2O → Al(OH)2+ + H+
o Samples treated with lysine conc > 0.005 M showed an increase in pH
The pH behavior can be explained by there being sufficient lysine to extract significant
Al from the surface of the kaolinite (as was the case with alumina), such that H+ moves
into the surface to counteract the charge imbalance from the Al3+ / Na+ exchange into
the lattice. This effect competes for the adsorption of OH- onto the kaolinite surface.
The process of removal of Al3+ may also promote the release of Si as H4SiO4
(especially from the edge surface of the particles). (Se STUMM iv chpt 5)
SiO44- + 4H+ ↔ H4SiO4
DRIFTS analysis
Regions examined
o 2000 – 1300 cm-1 (amino and carboxyl groups)
o 3000 – 2800 cm-1 (aliphatic chain -(CH2)4- )
Γ-alumina samples; Initial pH 9.8 (Figures 2 and 3)
KM
No lysine was detected on any of the samples
o In 2000 – 1300 cm-1 region
o In the 3000 – 2800 cm-1 region
1800
1700
1600
1500
1400
Wavenumbers (cm-1)
1300
Figure 2: Γ-alumina samples; Initial pH 9.8. Red curve is an unwashed sample 1-33
Lys (2005) all other curves are 2008 Ai series which have all been washed
0.05
KM
0.00
2980 2960 2940 2920 2900 2880 2860 2840 2820 2800
Wavenumbers (cm-1)
Figure 3: Comparison of set Ai samples after washing and drying with a sample (RED)
equivalent to A2i (treated with 0.02 M lysine solution) which was dried without washing
(3000 – 2800 cm-1 region for aliphatic chain).
Γ-alumina samples pH 6.3 (Figures 4,5,6)
No lysine was detected on any of the samples in 2000 – 1300 cm-1 region. In the 3000
– 2800 cm-1 region, signal for aliphatic carbon was observed on sample A1i, the
sample treated with 0.05 M lysine. Since this was the sample treated with the most
concentrated lysine solution it is possible that the washing was not sufficient to remove
all of the residual lysine.
0.040
KM
0.030
0.020
0.010
0.000
3000
2950
2900
2850
Wavenumbers (cm-1)
2800
Figure 4 : Set Ai, γ-alumina samples pH 6.3 . Samples treated & washed; A1i - 0.05 M
(black); A6i- 0.02 M (pink)
0.045
0.040
0.035
0.030
K0.025
0.020
0.015
0.010
0.005
0.000
3000
2950
2900
2850
Wavenumbers (cm-1)
2800
Figure 5: Set Ai, γ-alumina samples pH 6.3 . A1ii cf A6ii
KM
9
6
3
1
1800
1700
1600
1500
Wavenumbers (cm-1)
1400
Figure 6: Set Ai, γ-alumina samples pH 6.3 . 1800 – 1300 cm-1 region; spectrum
observed on an unwashed sample compared with the sample set treated at pH 6.3;
Discussion of the interaction of aluminum ions with lysine
Lysine forms a strong complex with aluminum ions which can result in
o Stopping the exchange of Al3+ into a resin (as does EDTA)
o Lysine solutions extract Al3+ from exchange resins and from glass containers
(resulting contamination of pharmaceutical products).
Articlev
Denise Bohrer, Paulo Cícero do Nascimento, Patrícia Martins and Regina Binotto
“Availability of aluminum from glass and an Al form ion exchanger in the presence of
complexing agents and amino acids” Analytica Chimica Acta Vol 459 -2 May 2002
P267-276
Extract from paper
Al present in glass are supposed to replace the silicon in the silicate tetrahedra network. This is possible
because of size similarities (rSi4+=0.50 Å, rAl3+=0.55 Å). Because of the difference in oxidation number,
replacement of Si4+ by Al3+ raises the anion oxidation state by one unit and requires the presence of
either a balancing cation (Na+) or a further isomorphous replacement of one cation by another of higher
positive charge (Na+ by Ca2+). However, whereas silicon is always 4-coordinate toward oxygen, Al may
be either 4 or 6-coordinate [44]. An AlO4 group would be the structural analog of an SiO4 group, but an
AlO6 group would not. As Al is added as Al2O3 to the glass mass, the 6-coordinate Al must be converted
into the 4-coordinate ion. It is only possible when Na2O is also present. It furnishes the polarizable O2−
ions that allow the change in the coordination of the Al ions and the necessary Na+ in order to balance
the charge [45]. When Al replaces Si in the glass network, it acts as a network former and is rigidly tied
into the lattice. If, however, the AlO6 group is not able to be converted into the AlO4 group, Al remains 6coordinate and acts as a network modifier, that has the role of balancing the charge of terminal oxygen
ions (oxygen of one tetrahedron not linked to another). Network modifiers only balance the charges and
this site can be occupied by any cation. Network modifiers can be replaced by other cations in an
exchange procedure and this is the fundamental principle of the glass electrode [45 and 46]. Al is
considered a network former and therefore not exchangeable, however based on anomalies in viscosity,
expansion coefficient and electric properties of glass some authors consider that Al can exist in glass as
6-coordinate. Yoldas [47] considers that only above a critical concentration, Al ion exists as [AlO4]−,
below this, it exists as [AlO6]−. Because the AlO6 octahederon is convered into a AlO4 tetrahedron in the
glass mass only in the presence of Na2O (or other alkali metal oxide) and this oxide is randomly
distributed in the glass structure [48], it is possible that most but not all of the Al ions are converted into
the 4-coordinate tetrahedron. Only the existence of 6-coordinate residual ions, occupying network
modifier sites, could justify how, amino acid solutions that do not interact with glass themselves, would be
able to withdraw Al3+ from glass.
Conclusions from the investigation from the γ-alumina treated samples.
Some interaction of γ-alumina with hydroxide (note the change in pH of the blank from
9.8 to 7.9).
Al2O3(s) + 3H2O → 2Al(OH)3(s)
Al(OH)3(s) + OH- + 2H2O → Al(OH)4(H2O)2The presence of lysine countered this change in pH – with the most concentrated lysine
solution restricting the change from 9.8 to 9.5. It is hypothesized that the lysine
extracted Al3+ from the mineral surface, into solution. In the washing process any lysine
coordinated with the surface was removed.
In set Aii (pH 6.3) all solutions (including the blank) showed an increase in pH
o Blank - uptake of H+ onto surface sites – to take the alumina closer to its isoelectric point
Kaolinite samples treated with lysine solutions
In the case of the kaolinite samples, the suspensions took over 1 day to settle. Traces
of lysine was detected and samples treated with solutions treated with ≥ 1 molecule of
lysine / nm2. This was true for both set of samples (with basic (Figure X1) and slightly
acidic (Figure X2) initial pH.)
pH 9.8 lysine solution (Figures 7, 8, 9, 10, 11, 12 )
1349 CH2
KM
1636 ads water
Peak also in
the blank
1606 -COO
1495 NH2
1407 -COO
Wavenumbers (cm-1)
Figure 7: Kaolinite samples treated with 0.02 M lysine solution at pH 9.8. The red curve
is an unwashed sample and the green curve a washed sample.
KM
1750
Wavenumbers (cm-1)
Figure 8: Ki series initial pH 9.8: Red 0.05 M; Blue 0.02 M; Black 0.01; Aqua 0.005;
Green 0.002; Pink 0.001
KM
1800
1750
1700
1650
1600
1550
1500
Wavenumbers (cm-1)
1450
1400
Figure 9: Kaolinite samples K1i and K2i treated with lysine solution with an
initial pH of 9.8. BLUE: blank (0-5 KM); RED K1i (0-3 KM) and GREEN K2i (0-2
KM): difference spectra of kaolinite exposed to 10 and 5 molecules / nm2
respectively. All spectra shown full scale
Note: in Figure 9:
o 1636 cm-1 water
o Broad pk centered on 1600 combination of
o Antisymmetric carboxylate stretch
o 1620 anti sym deformation of proximal and distal NH3+
KM
Wavenumbers (cm-1)
2800
Figure 10: 3000 – 2700 cm-1 region – all spectra are on a common scale. Aliphatic
carbon shows clearly on samples K1i & K2i but perhaps a hint on all samples.
Red K1i; yellow K2i; blue K3i; black K4i; pink K5i; green K6i.
Not clearly resolved over the noise in the signal for samples 4-6
KM
-0.000
-0.005
-0.010
-0.015
2900
Wavenumbers (cm-1)
Figure 11: 3000 – 2700 cm-1 region - all shown full scale.
Samples K1i (red); K2i (gold); K3i (blue)
KM
3300
3100
Wavenumbers (cm-1)
Figure 12: Sample K1i (Blue); Blank (pink); Difference spectrum for K1i (Red )
PEAKS (figure 12
o 3264 ? NH3+ stretch
o 3190 ? NH3+ stretch
o 2947 CH stretching of methylene groups
o 2868 CH stretching of methylene groups
Spectra of kaolinite samples (Kii) treated with initial pH 6.3 (Figures 13, 14)
5.0
4.5
4.0
3.5
3.0
KM
2.5
2.0
1.5
1.0
0.5
0.0
1800
1750
1700
1650
1600
1550
1500
Wavenumbers (cm-1)
1450
1400
Figure 13: Kaolinite samples treated with lysine solution with an initial pH of 6.3. RED:
blank (0-5 KM); Aqua and GREEN (0-3.5 KM); Grey and BLUE (0-1.25 KM): difference
spectra of kaolinite exposed to from 10 to 1 molecules / nm 2. All spectra shown full
scale.
KM
3300
3000
Wavenumbers (cm-1)
Figure 14: K1ii – Red difference spectrum cf blank (clue)
PEAKS
o 3264 ? NH3+ stretch
o 3190 ? NH3+ stretch
o 2974
o 2947 CH stretching of methylene groups
o 2870 CH stretching of methylene groups
Conclusions
Investigation of γ-alumina treated with lysine showed no organic remained on the
mineral surface after washing. This is not to say that no interaction occurred. Al ions on
the surface of the alumina intact strongly with lysine and are extracted into solution. The
washing step removes the soluble lysine –Al complex.
The kaolinite samples settled very slowly and it was difficult to decant solution from the
solid. To confirm the presence of lysine on kaolinite samples treated with solutions
>0.0005 M concentration in lysine, the experiments would have to be redone and the
kaolinite vacuum filtered (or centrifuged) and then washed 3 times (with filtration each
time).
i
Roddick-Lanzilotta, A. D. & McQuillan, A. J. (2000) Journal of Colloid and Interface Science, 227, 48-54.
ii
Bellamy L.J., The Infrared spectra of complex molecules. Third Edition, Wiley, New York.
iii
Brian Smith, B. (1999) Infrared Spectral Interpretation; a systematic approach. CRC Press LLC., Boca
Raton, London, New York, Washington DC.
iv
Werner Stumm (1992) Chemistry of the Solid-Water Interface. Wiley-Interscience, New York,
Chichester, Brisbane, Toronto, Singapore.
v
Denise Bohrer, Paulo Cícero do Nascimento, Patrícia Martins and Regina Binotto (2002) “Availability of
aluminum from glass and an Al form ion exchanger in the presence of complexing agents and amino
acids” Analytica Chimica Acta Vol 459 -2 May 2002 P267-276