Chloramination and bromamination of amino acids

Chloramination
Chl
i ti and
d bromamination
b
i ti off
amino acids
Virginie SIMON, Florence BERNE, Hervé GALLARD
Equipe Eau, Géochimie organique, Santé
1
Monochloramine
– Alternative of chlorine for the disinfection of drinking
water in some countries (e.g.
(e g United States,
States Canada,
Canada
Australia,…):
• More stable in water networks
• less DBPs formation compared to chlorine
– Allowed in France only for disinfection of cooling
water systems (e.g. nuclear power plant)
– Can be produced during the disinfection by chlorine of
waste waters or swimming pool waters by reactions
with nitrogen pollution
2
In presence of bromide: formation of different
haloamines (bromamines and bromochloroamines)
Br-
HOBr/BrOOrganic matter
HOCl/ClO-
NH4+/NH3
chloramines
haloamines
bromochloramines
bromamines
What is the reactivity of these haloamines
with organic compounds?
3
Compared to chlorine, only few data are available for
monochloramine on model compounds
– Kinetics
 amino acids (AA), amines and peptids
Snyder and Margerum, 1981; Issac and Morris,1983,…
 resorcinol
 tetracyclins
y
Cimetière et al., 2009
Wan et al., 2013
– DBP
 dimethylamine  NDMA
Choi and Valentine, 2002
 AA, peptides, purine and pyrimidine bases Yang et al., 2010
 DCAN and ClCN
 Amines, AA  THM, HAA and NDMA
Chang et al., 2011
 Pharmaceuticals and pesticides
Le Roux et al., 2011

NDMA, THM, HAN, HAA, HK, TCNM and AOX
 AA  TCNM and DCAN
Yang et al., 2012
4
No data is available for bromamines, studying the
reactivity
ti it off bromamines
b
i
with
ith model
d l compounds
d is
i
challenging because of their unstability.
The objective is to study the
chloramination and bromamination of
reactive biological compounds
- amino
i acids,
id peptids
tid and
d proteins
t i
- nitrogen containing nucleobases
5
Mechanism of the oxidation of amino acids
COOH
R
CH
N
+ oxidant
H
COOH
R
CH
N
H
First step is the formation
of the haloaminoacid and the
formation of the dihalogenated
species is not favored in excess
of aminoacid
+ oxidant
X
COOH
R
CH
X
N
H
X
- CO2
- CO2
- X-
- X-
NH
R
N
R
C
C
H
H
+ H2O
+ H2O
X
- HX
- H2O
- NH3
O
R
C
C
N
H
6
Protocol for kinetic study of
chloramination/bromamination of amino acids
Simulated pseudo-first order kinetic
Rate = k.[oxidant].[AA]
 In excess of oxidant,
AA should be analyzed after reduction of oxidant
but N-haloAA is also reduced into AA
 In excess of amino acid,
Oxidant and N-haloAA should be monitored by UV absorbance
but low extinction coefficients require the use of high reactant
concentrations involving fast reaction rates
7
Absorbance spectra for the chloramination of
an excess of glycine
Consumption of NH2Cl
Formation of the N-chloroglycine
for reaction time from 0 to 180 s
8
Interpretation of spectra
The absorbance is the sum of NH2Cl and N
N-Cl-AA
Cl AA absorbances.
absorbances The
unknown [NH2Cl] and [N-Cl-AA] can be calculated from the absorbance
at two different wavelengths
A (λ1) = l(ε1[NH2Cl] + ε’1[N-Cl-AA])
A (λ2) = l(ε2[NH2Cl] + ε’2[N-Cl-AA])

[NH2Cl]t =
[N-Cl-AA]t = [NH2Cl]0 – [NH2Cl]t
Extinction coefficients of N-Cl-AA were determined for complete consumption
of NH2Cl and considering [N
[N-Cl-AA]
Cl AA] = [NH2Cl]o
9
Material and methods: chloramination
– [NH2Cl] = 2 mM (molar N/Cl = 2)
prepared from chlorination of ammonium solution
–
–
–
–
–
[AA] = 40 mM
pH 8 with phosphate buffer 10 mM
T = 20°C
Vreactor = 0.6023 mL
Reaction time = 0.9
0 9 – 180 s for 0.2
0 2 – 40 mL/min
10
Kinetic results for the chloramination of
glycine
l i
Conditions: [AA]o from 40 mM to 200 mM, [NH2Cl]o = 2mM, pH 8,
phosphate buffer 10 mM, 20°C
11
Kinetic rate constants for the
chloramination of selected AA
Amino acids
diacid
dibasic
amide
hydroxylated
hydrophobic
Glutamic acid
Histidine
Arginine
Lysine
y
Glutamine
Serine
Threonine
Glycine
Valine
Leucine
Isoleucine
Alanine
k (M-1.s-1)
1 25 ± 0.11
1.25
0 11
2.13 ± 0.10
1.53 ± 0.05
1.09 ± 0.05
2.11 ± 0.11
1.94 ± 0.11
1.85 ± 0.07
1.22 ± 0.01
0.95 ± 0.01
0.92 ± 0.02
0 90 ± 0.04
0.90
0 04
0.71 ± 0.09
Snyder and Margerum (1981)
AA
k (M-1.s-1) at
25°C
Gly
1 52
1.52
Ala
0.55
Th
Thr
2
2.55
Rate constants vary from 0.71 to 2.13 M-1.s-1 and are 5 magnitude lower than with chlorine
Lower reactivity of non polar and hydrophobic amino acids
For dibasic amino acids, k increases with the number of nitrogen atoms in the side chain,
th hi
the
highest
h t rate
t constant
t t being
b i ffor hi
histidine
tidi with
ith th
the iimidazole
id
l group
12
Rate constants and pKa
2.5
AA with polar
uncharged side
chain
2
Gln
His
Ser
Thr
IIncreasing
i reactivity
ti it
of dibasic AA: lys < arg < his
k (M-1.s-1)
Arg
1.5
Gly
Glu
L
Lys
Val
1
Leu
Ile
Ala
0.5
AA with hydrophobic
side chains
0
8.5
8.7
8.9
9.1
9.3
pKa
9.5
9.7
9.9
13
Decomposition of the N-chloroamino acids
N-chloroisoleucine
decomposition from 0
to 8 hours
0
2
time (h)
4
6
8
0
-0.5
0.5
ln ((C/C0)
-1
-1.5
-2
2
y = -0.429x
R² = 0.9972
-2.5
-3
-3.5
First-order rate constants were determined from absorbance spectra
14
Kinetic rate constants for the decomposition of
N-chloroaminoacids
Diacid
Dib i
Dibasic
Amide
Hydroxylated
Hydrophobic
N-Cl-AA
N
Cl AA
k (h-1)
N-chloroglutamic acid
0.76 ± 0.02
N-chlorohistidine
0.36 ± 0.01
N hl
N-chloroarginine
i i
0 70 ± 0.01
0.70
0 01
Coker et al. (2008) : decomposition of N54.7 ± 1.4 chlororamino acids at pH 7.4 and 22°C :
 Half-time 37.5 ± 3.5 min for N115.9 ± 1.0
chloroglutamic acid and 61.2 ± 3.9 for N59 4 ± 0.4
59.4
0 4 chloroalanine.
N-chlorolysine
0.55 ± 0.01
76.0 ± 1.9
N-chloroglutamine
0.72 ± 0.02
58.0 ± 1.3
N-chloroserine
0.53 ± 0.01
78.2 ± 0.8
N-chlorothreonine
0.29 ± 0.01
145.3 ± 2.2
N-chlorovaline
0.23 ± 0.01
157.9 ± 2.4
N-chloroleucine
0.75 ± 0.02
55.8 ± 1.1
N-chloroisoleucine
0.43 ± 0.01
97.0 ± 1.0
N-chloroalanine
0.51 ± 0.01
81.6 ± 0.7
t1/2 (min)
Only the N-chloroglycine did not decay acccording to a first order kinetic
15
Material and method: bromamination
– [NH2Br] = 0.4 mM (molar N/Br = 100)
prepared from ozonation of bromide solution
–
–
–
–
–
[AA] = 4 mM
pH 8.5 borate buffer 10 mM
T = 20
20°C
C
Vreactor = 0.228 mL
Reaction time: 0.2 – 2.7 s for 5 – 60 mL/min
16
Disproportionation of NH2Br: the importance of salts
Lei
et
al.
((2004):
)
fast
disproportionation of NH2Br with
phosphate and carbonate buffers
respectively 3.4x105 M-2.s-1 and
540 M-22.ss-11 at pH 7.2
7 2 and 9.4
94
2 NH2Br
NHBr2 + NH3
Fast disproportionation in presence of 10 mM phosphate buffer or acetate :
respectively 57 and 53% degradation in 1h
Borate buffer has no impact and disproportionation is only 17% in 1h
17
Kinetic results for the bromamination of
Li l
L-isoleucine
i
Consumption of NH2Br
0
ln (C/C
C0)
Formation of the
N-bromoisoleucine
for reaction time from 0
to 2.7 s
0
-0.1
-0.2
-0.3
04
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
reaction time (s)
1
2
3
y = -0.2906x
0.2906x
R² = 0.9801
18
Kinetic rate constants for the bromamination
of amino acids
amino acids
amide
hydrophobic
k (M-1.s-1)
Glutamine
658.5
Glycine
367.9
isoleucine
alanine
138.1
131.7
Bromamination rate c
constants (M
M-1.s-1)
700
y = 394.12x - 162.74
R² = 0.9689
0 9689
600
500
400
300
200
100
0
0
0.5
1
1.5
Chloramination rate constants
2
2.5
(M-1.s-1)
About 400-fold higher rate constants for bromamination compared to
p
to 1000-fold between bromination and
monochloramination ((compared
chlorination kinetics)
Monobromamination of AA follows the same order as monochloramination
kala < kile < kgly< kgln
19
Decomposition of N-bromoamino acids
0
N-bromoisoleucine
decomposition from 0 to
1 hour
time (min)
20
40
60
0
ln (C/C0)
-0.2
02
-0.4
-0.6
0.6
-0.8
y = -0.0233x
-0 0233x
R² = 0.9913
-1
-1.2
-1.4
First-order rate constants were determined from absorbance spectra
20
Rate constants for the decomposition of
N bromoaminoacids
N-bromoaminoacids
N-Br-AA
k (min-1)
t1/2 (min)
N-bromoisoleucine
0.0223
31.08
N-bromoglutamine
0.0337
20.57
N-bromothreonine
0.0143
48.47
Nb
N-bromoalanine
l i
0 0262
0.0262
26 46
26.46
N-bromoglycine
0.0022
315.07
N-BR-AA deco
N
omposition ra
ate
constants (h-1)
2.5
y = 3.1497x
3 1497 - 0.0385
0 0385
R² = 0.9991
2
1.5
1
0.5
0
0
0.2
0.4
0.6
0.8
N-Cl-AA decomposition rate constants (h-1)
Rate constants for decomposition of
N-chloroaminoacids
N
chloroaminoacids are linearly correlated
N-bromoaminoacids
and
Decomposition of N-bromoamino acids are 3–fold faster than for
chloroamino acids
21
Conclusions
– Rate constants of monochloramination of amino acids range
f
from
0 71 M-11.s-11 for
0.71
f alanine
l i to
t 2.13
2 13 M-11.s-11 for
f histidine
hi tidi
– Rate constants for monobromamination are 400-fold higher
compared
p
to monochloramination and range
g from 132 M-1.s-1 for
alanine to 659 M-1.s-1 for glutamine
– Th
The N-chloroamino
N hl
i acids
id and
d N-bromoamino
Nb
i acids
id are unstable
t bl
in aqueous solution
– The decomposition of N-bromoamino acids are 3–fold faster
than for chloroamino acids
22
Perspectives
– reactivity of NHBrCl
– Comparison between bromamination and chloramination for the
formation of disinfection by-products such as aldehydes,
trihalomethanes, halonitromethanes…
– Same study with other reactive biological molecules (peptides,
(peptides
purine and pyrimidine base, hormones…)
23
Thank y
you for yyour attention
24

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