amavadin and homologues as promoters of technological
TRANSCRIPT
1
Amavadin and homologues as promoters of technological
applications
Lúcia Dias, José Ferreira e José A.L. da Silva
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001
Lisboa, Portugal
Abstract
Study of the reaction of two complexes homologues of amavadin with the ligands, HIDA and HIDPA with
the following oxidants: persulfate, iodate, bromate, chlorate, periodate, perchlorate, hypochlorite, nitrite, tellurate
and bismuthate, by UV-Vis spectroscopy in the range 350-850 nm. The reaction of the complex with HIDA was
faster than with the other complex, but always with decomposition. The light increases for the complex with
HIDPA the rate of reaction, but with decomposition. In contrast, in the absence of light the complex is
regenerated. A kinetic study was separately carried out for the oxidation and reduction of the complex with HIDPA
with all oxidants, except hypochlorite, perchlorate, tellurate and bismuthate. A second order reaction was
determined for all cases excluding persulfate, zero order for reduction, and chlorate for both reactions. The rate
constants showed reduction is slower than the oxidation. The values for the oxidation are 1,15X10-6
M/s (chlorate)
4,87X10-2
L/mol.s (iodate) and 6,14X10-2
L/mol.s (persulfate) and for the reduction 3,64x10-7
M/s (persulfate),
1,35X10-6
M/s (chlorate), 1,97X10-2
L/mol.s (nitrite), 1,99X10-2
L / mol.s (iodate), 2,38X10-2
L / mol.s (bromate)
and 6,69X10-2
L/mol.s (periodate).
Keywords: Amavadin, oxidants, HIDPA, HIDA, light, kinetic
1. Introduction
Amavadin is a natural complex ion of
vanadium, isolated in 1972 by Bayer and
Kneifel from the fungus Amanita muscaria that
contains a heterogeneous distribution of
vanadium with higher concentration in the
base[1]. The same authors proposed a
structure as a complex of S,S-N-
hydroxyiminodiproprionic acid ( ) with
a vanadyl ion in a metal:ligand proportion of
1:2, this was later proved wrong by X-ray
scattering [2]. An alternative connection was
suggested based on Wienghardt once
hydroxylamines could coordinate laterally to
vanadium[3]. It was then proposed by Bayer
and co-workers a new structure in which
hydroxylamines are ionized and coordinated to
the metal (figure 1)[4]. The new structure was
confirmed by crystallographic studies of an
amavadin model, , and by
crystallographic studies and NMR of oxidized
and reduced species of amavadin[2].
Amavadin's structure was known in 1999 by
precipitation with calcium ion[5]. It is a
vanadium complex dianionic with symmetry,
distorted dodecahedral geometry and five
chiral centers, one in the metal and the other
four in the carbon atoms bonded to a nitrogen
atom and also exhibiting S stereochemistry
with two possible stereoisomer in the
ligands[6]. Some of its physico-chemical
properties are presented in table 1.
2
Figure 1: Amavadin[2]
Table 1: Amavadin physico-chemical properties[6,7]
Soluble in: Water, DMSO, DMF and acetone
Insoluble in: 1-propanol, 2-propanol, 1-butanol, diethyl ether, nitrobenzene, THF e toluene
ν ( = 985 [misinterpreted as ν (V=O)]
Stability constant log =23(1)
Redox Couple , E/V vs NHE: 0,27 (DMSO), 0,81 (water, pH 7)
) :(1 0,5)X
Studies have shown that amavadin can
electrocatalitically oxidize tiols with a carboxylic
or ester group [6]. It exhibits a Michaelis-
Menten mechanism with a formation of an
intermediary with the substrate[6]. It acts as
catalase after studies with releasing
[6]. Later using Ce4+
as oxidant it was proved
that amavadin models mediates the oxidation
of water[8]. Amavadin is a complex with
applications in industry and organic
synthesis[6]. The complex and its models can
be used as catalysts for hydroxylation,
oxygenation, peroxidative halogenation of
alkanes and benzene, peroxidative
oxygenation of benzene and mesitylene and
carboxilation of linear and cyclo alkanes.
Moreover, amavadin can participate in
oxidation of alcohols and cyanide addition to
aldehydes[6]. It can also be used as catalyst in
a new process of conversion of methane in
acetic acid with as oxidant and yields
between 20%-30% in the absence of CO or
[9]. Its biological function is still unknown
but it is probably related to redox properties as
an electron mediator[10]. The focus of this
work is the biological function of amavadin and
possible synthetic applications by analyzing its
oxidation and reduction (leading to the water
oxidation) with several oxidants.
2. Experimental section
2.1. Synthesis of proligands
The proligands, HIDPA, as a racemic
mixture (compare with figure 2a), and HIDA
(figure 2b), were synthesized according to
Bayer and Kneiffel[11] having been the zinc
salts of both previously prepared using the
procedure of those authors[11]. 1.2 g were
weighed and dissolved in ca. 20 mL of distilled
water and 1 mL of concentrated HCl until the
solution became transparent. The solution was
introduced in a exchange column
containing and washed with distilled water
(to retrieve excess acid and prevent the
formation of a salt with the eluent that could
contaminate the product) and then eluted with
a 0.2 M NaOH solution; the effluent was
collected in test tubes (each one with ca. 20
mL), the first eight were rejected once they do
not contain product. The content of the
selected tubes was transferred to a flask of
100 mL. Evaporation of the solvent was
achieved with a rotary evaporator at less than
40 ℃ in order to avoid decomposition of the
compounds, to a final volume of about 1 mL. In
both cases a white product by evaporation of
the solvent in a vacuum line was obtained.
Figure 2: a) S,S-HIDPA b)HIDA[6]
3
2.2. Preparation of vanadium
complexes
The complexes were prepared in situ with
0.01 M concentration in a volume of 4 mL from
0.0101 g (4X10-5
mol) vanadyl sulfate
pentahydrated and 0.0142 g (8X10-5
mol) of
HIDPA or 0.0119 g (8X10-5
mol) of HIDA, then
a bluish purple solution for the first one and to
the second more bluish, were formed,
respectively. The initial pH of the solutions was
ca. 1,72.
2.3. Sample preparation
Samples were prepared with deoxygenated
water (prepared from distilled water, typically
after at least three consecutive cycles under
vacuum and nitrogen atmosphere) in order that
the presence of molecular oxygen would result
from the oxidation of water and not from
dissolved in the solution. After preparation of
the solution of the complex an oxidant was
added to the solution (persulfate, iodate,
bromate, chlorate, periodate, perchlorate,
hypochlorite, nitrite, tellurate or bismuthate)
with a concentration of 0,005 M and 0,03 M, for
the last two.
In some of the studies light radiation was
avoided by covering the samples with
aluminum foil (designated by “covered” in
contrast with the “transparent” that was
uncovered).
The samples were analyzed by UV-Vis
spectroscopy using a Perkin-Elmer
spectrophotometer in the wavelength range of
350 to 850 nm. The spectra were run to red,
purple and blue solutions, resulting from
oxidation for the first two and decomposition
for the last one. The oxidation of water was
checked by the oxygen meter in SG9-SevenGo
solution calibrated with a saturated solution of
distilled water in air. The pH measurements
were performed with a Metrohm 827 pH lab.
2.4. Tests
Some tests were carried out to identify the
mechanism of the reactions. A test to
determine by forming barium carbonate
precipitate from the reaction of carbon dioxide
in a solution of 1 g of barium nitrate in 20 mL of
deoxygenated water. In another flask with a
solution of vanadium complex (0.01M)
containing 0.029 g HIDA and 0.0249 g of
oxovanadium(IV) sulfate pentahydrate, in 1 mL
of deoxygenated water to which was added
0.013 g of sodium nitrite. Both flasks were
connected and vacuum was done and the
system closed before starting reaction.
The formation of NO was tested in complex
solutions with 0.029 g (1,95X10-4
mol) HIDA
and 0.0249 g (1,95X10-4
mol) oxovanadium(IV)
sulfate pentahydrate in 1 mL of deoxygenated
water and 0.013 g (1,95X10-4
mol) of nitrite
and 0.04395 g (1,04X10-1
mol) of
(if this complex reacts with
NO the color of the solution changes from
yellow to red) in 20 mL of deoxygenated water.
Both solutions were in different flasks
connected by a tube and vacuum was done
before starting reaction.
To confirm the formation of was tested
by the formation of a yellow insoluble salt,
. First it was added the
solutions of the complex with both proligands,
0.0079 g (4X10-5
mol) of HIDPA, 0.00596 g
(4X10-5
mol) of HIDA, separately and 0.00506
g (2X10-5
mol) vanadyl sulfate pentahydrated
to 0.0034 g (4X10-5
mol) of the oxidant
4
potassium nitrite. A few hours later it was
added cobalt nitrate,0.000378 g (1,3X10-5
mol).
The formation of or was tested
taking into account the pH variation resulting of
amavadin oxidation reactions (complex with
proligand HIDPA) at a solution of complex with
the concentration of 0.01 M by periodate,
iodate, persulfate, nitrite and cerium in
proportions metal: oxidant, 7: 1, 5: 1, 2: 1, 3: 1
and 1: 1, respectively.
Extraction with 2 mL of dichloromethane of
solutions of complexes using bromate, iodate
and periodate as oxidants were carried out.
The organic solution would be pink in the
presence of iodine[12] and yellow with
bromine[13].
2.5. Kinetics
The kinetics of the complex with HIDPA was
studied with, iodate, periodate, bromate,
chlorate, persulfate and nitrite by running 15
spectra at every 10 minutes interval for two
cases (eq. 1 and 2) with Perkin-Elmer
spectrophotometer in the range 350-850 nm.
Equation 1
Equation 2
The rate constants and order of reaction
were determined according table 2, and
considered[14,15],
Equation 3
3. Results and Discussion
In most cases, after addition of the oxidant,
solutions changed color to red due to oxidation
of vanadium complexes and later returned to
the blue color (with variants). These reactions
followed the pattern observed for [6] and
[8] meaning the return to the blue color
would lead to the water oxidation. In the cases
presented, there are some differences in the
cases already studied, and sometimes
reactions are very slow and some dependents
of light radiation.
Examining Table 3 with the ligand HIDPA by
various oxidants, it is clear that with the
exception of perchlorate (fig.3) they all reacted
with the complex. Although the latter being a
strong oxidizing agent, that is known to their
lack of reactivity[16].
Figure 3: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
perchlorate(0,005M) covered(red) and transparent(blue).
Table 2: Absorbance vs time for the kinetics analyzed
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
Kinetic Concentration (M)[14] Absorbence[15]
0
1
2
5
With oxidants, iodate (fig.4), periodate (fig.5),
nitrite (fig.6) the solutions maintained under
light acquired a clear blue color probably
containing a vanadyl complex formed from
radical reactive species acting upon the
complex during the reduction of water.
Figure 4: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
iodate(0,005 M) covered(red) and transparent(blue).
Figure 5: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
periodate(0,005 M) covered(red) and transparent(blue).
Figure 6: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
nitrite(0,005 M) covered(red) and transparent(blue).
In a second study with nitrite with twice the
concentration and covered with yellow and red
filters, figure 7, there has been no different
behavior, having both solutions acquired the
initial color dark red and a final color light blue,
so it is possible that the concentration of nitrite
has no effect on the rate of the reaction.
Figure 7: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
nitrite(0,01 M) yellow and red filters.
In contrast, persulfate (fig.8) and
hypochlorite (fig.9) do not oxidize the complex
to red color (the five-vanadium oxidation state),
but only becomes purple in color, possibly a
reactive species. Additionally, the light does
not appear to have any effect on the rate of
reaction nor the final concentration of the
complex in solution.
Figure 8: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
persulfate(0,005 M) covered(red) and transparent(blue).
Figure 9: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
hypochlorite(0,005 M) covered(red) and transparent(blue).
For chlorate (fig.10) light has a different
effect. This was more prominent in the fact that
the solution alternatively changed color
between yellow and grey by the interaction
with light (in the presence and absence of light,
respectively).
Figure 10: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
chlorate covered(0,005 M)(red) and transparent(blue).
With tellurate (fig.10) and bismuthate (fig.11)
the results need additional studies, but a
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ (nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
0,000
0,100
0,200
0,300
350 450 550 650 750 850
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 450 550 650 750 850
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
6
dilution of complex was observed after
variation of the color of the solution over time.
Figure 11: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
tellurate(0,01 M) (blue).
Figure 12: Absorption spectra of [V(HIDPA)2 ]-2(0,01 M),
bismuthate (0,01M) (blue).
Table 3: Results for complex with HIDPA oxidation
Oxidants Covered Transparent
Bromate Initial color: Dark red Final Color: Violet blue In 6 days.
Initial color: Red Final Color: Violet blue In 2 hours.
Hipochlorite
It took 2 hours until purple. Initial color: Purple Final Color: Blue Violet In 6 days.
It took 2 hours to purple. Initial color: Purple Final Color: Blue Violet In 5 days or less.
Iodate
It took 1 day until dark red. Initial color: Dark red Final Color: Light blue In 21 days.
It took 1 day until dark red Initial color: Purple Final Color: Light blue In 3 days.
Perchlorate Reaction did not occur. Reaction did not occur.
Periodate Initial color: Dark red Final Color: Violet blue In 6 days.
Initial color: Dark red Final Color: Light blue In 1 day.
Nitrite Initial color: Dark red FinalColor: Violet blue In 7 days.
Initial color: Dark red Final Color: Light blue In 3 days.
Chlorate
It took 6 hours to purple and 1 day until red Initial color: Red Final Color: Light violet In 11 days.
It took 6 hours to purple and 1 day until red Initial color: Red Final Color: Light grey blue In 8 days.
Persulfate
It took 1 day until pink purple. Initial color:Pink Purple Final Color: Violet In 3 days.
It took 1 day until purple. Initial color: Purple Final Color: Violet In 3 days.
Telurate Initial color: Blue violet Final Color: Light violet In 6 days.
Bismuthate Initial color: Dark red Final Color: Blue In 7 days.
For the oxidation of the complex with ligand
HIDA, the results are summarized in table 4. It
can be seen that the reaction is much faster
compared to the previous ligand, (the
difference between them is just that the latter
has methyl groups in the carbon adjacent to
the carboxyl groups), and the radiation light
has no effect on the oxidation of the complex,
with decomposition of the vanadium complex
for all cases except hypochlorite,
persulfate(fig.13) and perchlorate (fig.14).
Figure 13: Absorption spectra of [V(HIDA)2 ]-2(0,01 M),
persulfate(0,005 M) covered(red) and transparent(blue).
Figure 14: Absorption spectra of [V(HIDA)2 ]-2(0,01M),
perchlorate(0,005 M) covered(red) and transparent(blue).
The absence of total regeneration of the
complex and a blue solution probably indicates
the formation of a vanadyl complex. Despite no
release was detected, the solution color
and the differences between the initial and
final spectrum, taking into account the results
obtained previously [6,8], the breakdown of the
complex should have occurred. The reaction
between the complex and oxidant nitrite
showed the higher decomposition of all cases
(fig.15).
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 450 550 650 750 850
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
7
Figure 15: Absorption spectra of [V(HIDA)2 ]-2(0,01 M),
nitrite(0,005 M) covered(red) and transparent(blue).
In respect of the complex with the ligand
HIDA, there were also no changes in the
behavior of the complex with yellow, red, green
and blue filters, taking solutions the initial color
clear purple and final color light blue at the end
of the same time, one day, Figure 16.
Figure 16: Absorption spectra of [V(HIDA)2 ]-2(0,01 M),
nitrite(0,01 M) yellow, red, green and blue filters.
The possible reduction of nitrite species are
the gases NO, , e , suggesting that
this oxidant originates , as final product,
given that the tests of NO and were
negative and the protons consumed on global
reaction in comparison with cerium(IV),
persulfate, iodate, and periodate. Nitrite is
used by some living organisms in the enzyme
nitrite redutase [17] in that the final product is
NO. If nitrite is used as a substrate by some
fungi Amanita, amavadina participates in its
reduction (metabolic pH is different from tested
in this work, which is very acidic, but in some
conditions protein medium can simulate low
pH) and leads to reduction, a new
contribution to the biogeochemical cycle of
nitrogen would be known. It also should be
noted that the production of by living
organisms is known [18], but involving other
substrate.
With bismuthate with the complex with HIDA
(fig.17) the results also need additional studies
to clarify the different behavior with the other
complex (compare with fig. 12), where the final
spectrum has higher absorbance at all
wavelength in contrast with the other cases.
Figure 17: Absorption spectra of [V(HIDA)2 ]-2(0,01 M),
bismutate (0,01M) (blue).
Table 4: Results for complex with HIDA oxidation
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 550 750
A
λ(nm)
0,000
0,100
0,200
0,300
350 550 750
A
λ(nm)
0 0,05
0,1 0,15
0,2 0,25
0,3 0,35
350 450 550 650 750 850
A
λ(nm)
Oxidants Covered Transparent
Bromate
Initial color: Purple Final Color: Light blue violet In 3 days.
Initial color: Purple Final Color: Light blue grey In 2 days.
Hipochlorite — Reaction did not occur
Iodate
Initial color: Light purple Final Color: Light blue grey In 3 days.
Initial color: Light purple Final Color: Light blue grey In 1 day.
Perchlorate Reaction did not occur.
Reaction did not occur.
Periodate
Initial color: Light orange Final Color: Light blue grey In 3 days.
Initial color: Light orange Final Color: Light blue grey In 1 day.
Nitrite
Initial color: Light purple Final Color: Blue In 1 day.
Initial color: Light purple Final Color: Almost colorless In 1 day.
Chlorate
Initial color: Blue violet Final Color: Light blue violet In 2 days.
Initial color: Blue violet Final Color: Light blue violet In 2 days.
Persulfate Reaction did not occur.
Reaction did not occur.
Telurate Reaction did not occur.
Bismuthate
Initial color: Blue Final Color: Light violet In 2 days.
8
The kinetics results are presented in table 5.
The rate constants showed reduction as the
slow reaction step. Considering all the data
iodate was the slowest reaction and especially
compared to periodate, although both are
reduced to iodine. The low value for the
reduction step using iodate is probably from
the strong character of its conjugate acid, iodic
acid, pKa = 0.75, being anionic form in initial
conditions (pH = 1.72). This species and the
complex are anions preventing the reaction
that occurs slowly. The reduction and the
oxidation step are both of second order
(fig.18), however persulfate showed zero order
for reduction (fig.19) and chlorate zero-order
for the oxidation (fig.20) and reduction, the only
example in cases studied and indicate a
concentration of the complex independent of
the rate reaction, and as such is the slowest
reaction after with iodate.
Figure 18: Kinetics for the reaction between complex with HIDPA and persulfate (0.005 M). R2 = 0.989.
Figure 19: Kinetics for the reaction between complex with HIDPA and persulfate (0.005 M) using the equation 6. R2 =
0.9997.
Figure 20: Kinetics for the reaction between complex with HIDPA and the chlorate (0.005 M). R2 = 0.979.
The isosbestic point was not well-defined
in the reduction of the complex for all oxidants
studied, example of chlorate (fig.21) unlike in
oxidation (fig.22), in which the point is between
675-680 nm. The absence of isosbestic point
may indicate that a secondary reaction occur
leading to the partial decomposition of the
complex.
Figure 21: Absorption spectrum in the visible region for the reaction with chlorate in 15 tests with 10-minute interval.
b = 1 cm.
Figure 22: Absorption spectrum in the visible region for the
reaction with chlorate in 15 tests with 10-minute interval.
b = 1 cm.
4
5
6
7
8
0 2000 4000 6000 8000 10000
1/A
t(s) 750 nm 775 nm 800 nm
0,3
0,31
0,32
0,33
0,34
0 5000 10000
A
t(s)
545 nm 554 nm 520 nm
0,15
0,17
0,19
0,21
0 2000 4000 6000
A
t(s)
750 nm 775 nm 800 nm
0,1
0,2
0,3
0,4
0,5
350 550 750
A
λ(nm)
0
0,2
0,4
0,6
0,8
1
1,2
350 550 750
A
λ(nm)
9
Table 5: Results for the kinetics
Oxidant Oxidation Reduction
Order k I.P. (nm) Order k I.P. (nm)
Iodate Second 4,87X10
-2
L.Mol-1
.s-1
680 Second
1,99X10-2
L.Mol
-1.s
-1
Indefined
Periodate Second 6,69X10
-2
L.Mol-1
.s-1
Indefined
Bromate Second 2,38X10
-2
L.Mol-1
.s-1
Indefined
Chlorate Zero 1,15X10
-6
M/s 675 Zero
1,35X10-6
M/s
Indefined
Persulfate Second 6,14X10
-2
L.Mol-1
.s-1
675 Zero
3,64X10-7
M/s
Indefined
Nitrite Second 1,97X10
-2
L.Mol-1
.s-1
Indefined
4. Conclusion
These results can inspire new
methodologies of synthesis, for example
halogenated organic compounds (which have
a high added value), as well as on amavadin
as mediator of water oxidation that has a
singular mechanism based on changing metal
oxidation in one unit and is a mononuclear
system[8]. Moreover, the behavior with respect
to chlorate with complex with HIDPA, may
allow specific sensors. It is noted that in our
research we found nothing comparable in the
literature for chlorate as oxidant.
Finally, these results reveal new information
about the biological role of amavadin despite
these experiments were carried out at different
pH than the biological ones. Hence its reaction
with nitrite (a biological metabolite) supports a
possible role to this vanadium
metallobiomolecule.
5. Acknowledgements
LD would like to thank family and friends.
6. Nomenclature
A-Absorbance
C-Concentration
Calc-Calculated
DMSO-Dimethylsulfoxide
DMF-Dimethylformamide
Exp-Experimental
HIDPA- N-hydroxyiminodipropionic acid
HIDA-N-hydroxyiminodiacetic acid
IV-Infra-Red
NHE-Normal Hydrogen Electrode
NMR-Nuclear Magnetic Ressonance
THF-Tetrahydrofuran
UV-Vis-Ultraviolet-Visible
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10
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