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Kinetics of L-Tryptophan Oxidation in Acidic Medium using TMGCC:
A Comprehensive Study
Pooja Mahawar, Anushka Jangid, Yadvendra Singh, D. K. Mahawar, Ammilal Rao*
Department of Chemistry, University of Rajasthan, Jaipur, Rajasthan, India
*Corresponding Author
DOI:
https://doi.org/10.51584/IJRIAS.2025.10100000144
Received: 01 November 2025; Accepted: 07 November 2025; Published: 18 November 2025
ABSTRACT
Kinetics for the oxidation of L-tryptophan in a sulphuric acid medium by 1,1,3,3, -tetramethylguanidinium
chlorochromate [TMGCC] has been investigated. The results of the experiment suggest that the intermediate
complex formed between the protonated L-tryptophan and TMGCC, then decomposes in the rate-determining step
to give the reaction products. The final oxidation products received were identified as indole-3-acetaldehyde, NH
4
+
,
and CO
2
. First-order dependence on TMGCC, and a fractional order dependence on L-tryptophan have been found
for the reaction. The thermodynamic parameters such as activation energy, entropy, and free energy were evaluated
accordingly. A suitable mechanism has been proposed for the reaction.
Keywords: Tryptophan, Kinetics, Oxidation, Mechanisms.
INTRODUCTION
L-Tryptophan (L-Trp), an essential amino acid, plays a vital role in various biological processes, including protein
synthesis and the production of neurotransmitters such as serotonin. Its oxidation is of considerable interest not only
due to its physiological significance but also because it can lead to the formation of various bioactive compounds,
some of which may have implications in human health and disease.
The study of L-Tryptophan oxidation is crucial for understanding its reactivity and the subsequent effects on
biological systems [1-5]. In acidic media, L-Tryptophan undergoes oxidation through various pathways, leading to
the formation of oxidized products that can impact its biological functions. The kinetics of this oxidation process
are influenced by multiple factors, including pH, temperature, and the presence of catalysts. Understanding these
kinetics is essential for both theoretical insights into amino acid reactivity and practical applications in
pharmaceutical and biotechnological fields. The findings of this study will contribute to a deeper comprehension of
L-Tryptophan's behaviour in oxidative environments, highlighting its significance in both health and disease
contexts.
1,1,3,3,-tetramethylguanidinium chlorochromate (TMGCC) has garnered attention for its effectiveness in
facilitating chemical reactions, including oxidation processes [6]. Their unique properties make them suitable for
investigating the kinetics of L-Tryptophan oxidation under acidic conditions. This research article aims to explore
the kinetics of L-Tryptophan oxidation in acidic media using TMGCC as a catalyst.
MATERIALS AND METHODS
Materials
The chemicals used in the research work are of high purity grade. TMGCC was freshly prepared before carrying out
the experiment work in the laboratory as reported [6], and a check of purity was ascertained by an iodometric method
[7]. L-tryptophan was used directly as received from Merck. Standard methods were used for the purification of
solvents [8].
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Product analysis:
In the oxidation of L- tryptophan by TMGCC, the final product is the carbonyl compound, and it was tested by 2,4
DNP test [9] by the addition of 2,4- dinitrophenylhydrazine to the mixture, which gave a yellow precipitate, thus
confirming quantitatively the presence of the carbonyl compound. The product mainly identified was indole-
3acetaldehyde as tested by the spot test [10]. Cr (IV) was identified using the iodometric method. The by-products
formed during the reaction were identified as carbon dioxide gas and ammonium ion, where the carbon dioxide gas
was tested by limewater, and ammonium ion got tested using Nessler’s reagent [11]. Other oxidation products having
similarities with different experimental conditions have been received as mentioned in previous studies [12– 16].
Kinetic Measurements
The concerned investigations were performed on kinetics under the usual pseudo-first-order conditions by keeping
the concentration of L-tryptophan at more than the concentration of TMGCC. The temperature of the reaction was
controlled at 25
0
C with an accuracy of ±0.2
0
C. The TMGCC solution and a mixture having tryptophan and sulphuric
acid, both were thermostated separately for almost 2 hours. The above-mentioned solutions were allowed to mix
and then they were transferred to the cell and then subsequent 3 to 4 experimental readings were collected. The rate
of consumption of Cr (VI) was checked by decrease in absorption using a spectrophotometer at its absorption
maximum, k
max
= 350 nm, where Cr (VI) absorbs to a noticeably greater value as compared to any other reactants
and products, as the function of time and it was thus verified using UV-Vis spectrophotometer having cell at constant
temperature. For pseudo-first order rate constant, the k
obs
was assessed using a gradient between ln(A) and time
from the following equation given below:
log
e
(A
t
- A
∞
) = log
e
( A
0
- A
∞
) – K
obs
.T (1)
{A
t
is the absorbance of the reaction mixture measured at time t. and
A
∞
is the absorbance of the mixture measured at equilibrium.}
A
∞
was measured as soon as the reaction got completed. Then the k
2
(second order rate constant), was evaluated
using the relation given below:
k
2
= k
obs
/[L- tryptophan]
RESULTS AND DISCUSSION
Stoichiometry
Stoichiometry of reaction between the L- tryptophan and TMGCC in sulphuric acid medium was found in the ratio
of 1:1. TMGCC underwent two-electron change and with the earlier observations it is in accord with structurally
similar other halo-chromates.
The overall equation for the L-tryptophan’s oxidation by TMGCC in H
2
SO
4
(acidic medium) can be represented as
follows:
L-tryptophan + TMGCC H
+
Indole-3- acetaldehyde + Cr(IV) + NH
4
+
+ CO
2
(2)
H2O
Order of Reaction
The reaction order(n) was calculated using the slope of the plots between logk
obs
and log(concentration) by changing
the concentrations(C) of substrate and acid, and making other conditions constant. The [TMGCC] was varied by
keeping others at a fixed concentration. The pseudo-first-order rate constant, k
obs
, was calculated using gradient
from ln(A) versus time plots. It was confirmed from the above data that the reaction is of order first with respect to
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[TMGCC]. The k
obs
was also calculated at diverse initial concentrations of the tryptophan by keeping concentrations
of others constant. A linear plot of k
obs
against [L-tryptophan] indicated that the reaction’s order was less than one
with respect to [L-tryptophan] and its intercept was positive.
Rate-laws:
A typical kinetic run proved that the reactions with respect to TMGCC are of first order Figure 1. The pseudo-
firstorder rate constant, k
obs
is not dependent on the initial concentration of TMGCC. A linear plot of 1/k
obs
against
1/[ L- tryptophan] obtained with the intercept on the y-axis, with r > 0.995 and to further prove this fact
MichaelisMenten reaction was applied to the L- tryptophan (Trp), leading to the generalization of the following
reaction mechanisms 3 & 4 obtained, where the depiction of the following rate law is shown by equation 5 as
follows:
K,H
+
Try + TMGCC[Complex] (3)
(4)
[Complex]Products
(5)
Rate = k
2
[Try] [TMGCC] / ( 1 + K [Try])
FIGURE 1: Oxidation of Tryptophan by TMGCC: A typical kinetic run
FIGURE 2: Oxidation of Tryptophan by TMGCC: A double reciprocal plot Test for free radicals:
S
l
o
w
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The polymerization test was employed to check the presence of the free radical species formed during the reaction.
It was performed by taking a known quantity of acrylonitrile with the mixture of the reaction and was thus kept for
approximately 3 hours. Mixture’s dilution using methanol did not resulted in any white precipitate, which supported
the absence of free radicals in the reaction mixture. Further, it was reinforced by the fact that the reaction’s rate does
not change with the addition of acrylonitrile Table 1. This completely ruled out the prospect of oxidation of only a
single electron giving rise to the involvement of free radicals.
TABLE 1: Effect of variation of [TMGCC)], [Trp], on the observed rate constant in the oxidation of L-tryptophan
by TMGCC in sulphuric acid solutions at 298K.
[TMGCC]
(mol/dm
3
)
[H
+
]
(mol/dm
3
)
104 kobs
(1/s)
1.0
0.10
2.50
1.0
0.10
3.14
1.0
0.10
4.60
1.0
0.10
6.40
1.0
0.10
8.30
1.0
0.10
9.50
0.3
0.10
4.80
0.5
0.10
4.70
0.8
0.10
4.67
1.0
0.10
4.60
2.0
0.10
4.90
1.0
0.10
6.47*
*Contained Acrylonitrile (0.001 mol/dm
3
)
Effect of temperature:
The influence of temperature on the reaction rate was examined at four different temperatures, namely 288, 298,
308, and 318 K, while maintaining constant conditions for all other variables except the concentration of sulfuric
acid. The results indicated that the rate of reaction increases with rising temperature, demonstrating a direct
relationship between temperature and reaction rate. The kinetic data obtained at these temperatures were used to
calculate the values of formation constant (K)
and rate constant (k
2
).
Thermodynamic Parameters:
The thermodynamic parameters for the complex formation and the activation parameters of the decomposition of
the Trp-TMGCC complexes had been calculated using K
and k
2
values at various temperatures.
The data obtained for formation constant, thermodynamic parameters, rate constant, and activation parameters are
depicted in Tables 2 and 5.
TABLE 2: Formation constant for the Trp-TMGCC complexes.
K (dm
3
/mol)
288 K
298 K
308 K
318 K
20.5
17.4
14.2
10.9
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TABLE 3: Thermodynamic Parameters for formation of Trp -TMGCC complexes.
−
(kJ/mol)
−S
(J/mol K)
−G
(kJ/mol)
10.2 ± 0.3
± 8 ± 2
4.5 ± 0.3
TABLE 4: Rate constants (k
2
) for the decomposition of the Trp-TMGCC complexes.
10
4
k
2
(dm
3
/mol s) at
288 K
298 K
308 K
318 K
4.81
10.2
21.8
48.5
TABLE 5: Activation Parameters for the oxidation of Tryptophan by TMGCC.

(kJ/mol)
−S
#
(J/mol K)
G
#
(kJ/mol)
31.8 ± 0.8
44 ± 3
43.2 ± 0.8
Effect of Acidity:
As reported in the literature survey that the amino acid exists as zwitter ion at pH of 7 and predominantly tends to
protonate at pH <7. The employment of a high concentration of hydrogen ions during the reaction and also the
observed augmentation of reaction’s rate on increasing acid’s concentration recommended the protonation of
Ltryptophan in the step before equilibrium, whereas the protonated form (Trp
+
) appeared as reactive in the slow
step.
Varying the concentration of acid and keeping others constant, found that the concentration of acid was seen to
catalyze the rate of reaction. It was indicated by Table 6, that the process of oxidation was catalyzed by acid.
TABLE 6: Dependence of reaction rate on hydrogen ion concentration at 298K.
[TMGCC]
(mol/dm
3
)
10
3
[Trp]
(mol/dm
3
)
[H
+
]
(mol/dm
3
)
104 kobs
(1/s)
1.0
0.10
0.02
1.25
1.0
0.10
0.03
1.90
1.0
0.10
0.04
2.58
1.0
0.10
0.06
3.70
1.0
0.10
0.10
6.46
1.0
0.10
0.20
12.3
Solvent effect:
The effect of the solvent can be described in terms of solvation, as solvent plays an important role during reactions.
Here, L-tryptophan’s oxidation has been considered in various types of solvents. In all of the selected solvents, the
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same type of kinetics has been observed, and the values of second-order rate constants, k
2
, have been presented in
Table 7.
TABLE 7: Effect of solvent at 298K.
Solvents
K (dm
3
/mol)
k
2
(1/s)
Chloroform
16.8
3.06
1,2-dichloroethane
17.2
3.62
DCM
16.6
3.52
DMSO
17.4
10.8
Acetophenone
17.0
3.25
DMF
17.5
5.78
Butanone
16.7
2.38
Nitrobenzene
17.1
4.27
Benzene
16.5
1.20
Cyclohexane
17.3
0.13
Toluene
16.3
0.90
Acetophenone
17.6
5.02
Tetrahydrofuran
18.0
1.60
tert-Butyl alcohol
16.7
1.27
1,4-Dioxane
16.9
1.71
1,2-Dimethoxyethane
17.8
0.85
Acetic acid
16.6
0.60
Ethyl acetate
17.7
1.30
Carbon disulfide
17.5
0.45
Kamlet presented equation [17] for the rate constant in terms of linear solvation energy relationship, which has been
given below Equation 6 where the π, α, β (solvatochromic parameters) are characteristic of various solvents.
log k
2
= A
0
+ pπ + aα + bβ (6)
Here π indicates the polarity of solvent (a measure of the ability of solvent to stabilize a charge or dipole due to its
dielectric effect), β indicates the hydrogen bond acceptor basicity (the ability of solvent to donate an electron pair
or in a hydrogen bond to accept a proton) and α indicates the hydrogen bond donor acidity (where solvent either
donate a proton or accept electron pair in hydrogen bond which is in between solute to solvent) and A
0
is the term
of intercept. Here the coefficient of determination (r
2
), standard deviation (SD), and Exner’s statistical parameter
[18], (ψ) has been used to correlate analyses. Results thus obtained from biparametric equation 6 has been given by
the following equations 7-10:
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log k
2
= -4.81 + (1.62 ± 0.19) п – (0.13 ± 0.14) α + (0.18 ± 0.14) ß (7)
r
2
= 0.8652, SD = 0.17, n = 18, ψ = 0.40 log k
2
= -4.54 + (1.70 ± 0.18) п –
(0.13 ± 0.16) ß (8) r
2
= 0.8474, SD = 0.18, n = 18, ψ
= 0.41
log k
2
= -4.50 + (1.70 ± 0.17) п (9)
r
2
= 0.8474, SD = 0.18, n = 18, ψ = 0.41
log k
2
= -4.38 + (0.43 ± 0.35) ß (10)
r
2
= 0.0840, SD = 0.45, n = 18, ψ = 0.98 here, the number of data points considered in
the analysis has been represented by ‘n’.
The Swain equation has also been used for the solvent effect examination. Swain equation [19] has given following
data on concept of cation-anion solvation:
log k
2
= aA + bB + C (11)
In equation (11), the anion-solvating power of solvent A has been indicated by ‘A’, the cation-solvating power
indicated by ‘B’, and ‘C’ is the term of intercept. Solvent polarity is indicated by (A+B). Equation 11 has been used
to analysis rates in various solvents.
log k
2
= (0.63 ± 0.02) A + (1.72 ± 0.01) B – 4.74 (12) r
2
= 0.9997, SD = 0.01, n = 19, ψ = 0.01.
log k
2
= (0.38 ± 0.58) A – 3.54 (13)
r
2
= 0.0274, SD = 0.47, n = 19, ψ = 1.00
log k
2
= (1.67 ± 0.12) B – 4.50 (14)
r
2
= 0.9279, SD = 0.12, n = 19, ψ = 0.26
log k
2
= 1.36 ± 0.16 (A + B) – 4.70 (15)
r
2
= 0.8458, SD = 0.18, n = 19, ψ = 0.41
Swain’s equation 12 correlation for rates of oxidation of tryptophan in diverse solvents has given brilliant results. In
equation 14 only ‘B’ parameter gives a major contribution. In equation 15 the term (A+B) shows the solvent polarity
parameter and also contributed for about 84% of the data.
Reaction Mechanism:
We investigated the mechanism of L-tryptophan oxidation by chlorochromate (CrO
3
Cl⁻) using density functional
theory (DFT).
All quantum chemical calculations were performed with the ORCA program package. Geometry optimizations and
harmonic frequency calculations were carried out at the B3LYP-D3(BJ)/def2-TZVP level with the corresponding
def2/J auxiliary basis set. Solvent effects were included via the CPCM (water) continuum model. Dispersion was
accounted for using Grimme’s D3(BJ) correction. For each optimized structure, vibrational frequency analysis was
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used to confirm minima (no imaginary frequencies) or first-order saddle points (one imaginary frequency). Thermal
corrections to 298.15 K were extracted from the frequency calculations and added to electronic energies to obtain
Gibbs free energies (G).
Protonation at the amino group (Trp-NH
3
⁺) is predicted to be energetically favoured, relative to the neutral form
under CPCM(water), consistent with the strongly acidic experimental conditions. We find that protonation of
Ltryptophan (Trp⁺) and explicit acid stabilization produces a strongly bound reactant complex (ΔG_bind = [~-159
kJ·mol⁻¹]; and that the computed transition state for the crucial electron/proton transfer lies at ΔG‡ = [34 kJ·mol⁻¹]
above the reactants. Coordinates, ORCA input files and vibrational data are provided in the Supporting Information.
TABLE 8: Gibbs free energies of different systems at B3LYP/def2-TZVP level.
System
G_Hartree
G_kJ/mol
Trp+
-686.5792617
-1802613.591
Oxidant
-1730.542348
-4543538.278
Intermediate complex
-2417.182253
-6346311.088
TS
-2417.10879
-6346118.209
Iminium Cation
-496.8138325
-1304384.528
CO
2
-188.5979943
-495163.9625
CrO(OH)
2
-1271.334364
-3337887.89
HCl
-460.7780322
-1209772.548
NH4+
-56.98969338
-149626.4183
H
2
O
-76.42312664
-200648.89
Indole-3- acetaldehyde
-516.2655171
-1355454.919
FIGURE 3: Free energy profile for the oxidation of L-tryptophan to indole-3-acetaldehyde, showing
calculated relative gibbs free energies (ΔG, in kJ·mol⁻¹) of intermediates and transition states along the
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reaction pathway. All energies were obtained at the DFT level using the B3LYP functional with the def2TZVP
basis set. Atom color scheme: carbon = grey, nitrogen = blue, chromium = sky blue, oxygen = red, hydrogen
= white, chlorine = green.
FIGURE 4: Optimized structures of (A) reactants (trp+ and oxidant), (B) transition state and (C) iminium cation.
All energies were obtained at the DFT level using the B3LYP functional with the def2-TZVP basis set. Atom colour
scheme: carbon = grey, nitrogen = blue, chromium = sky blue, oxygen = red, hydrogen = white, chlorine = green.
TABLE 9: Selected structural parameters of the reactant (R), transition state (TS), and product (P) for the oxidation
of L-tryptophan. Bond lengths are given in Å and bond angles in degrees (°).
Reactants (trp+ and Oxidant)
TS
Product
N1-C2
1.494
Cr2-O1
1.595
N1-C2
1.494
C14-C16
1.408
N1-H24
1.024
Cr2-O3
1.596
N1-H24
1.024
C14-C12
1.385
N1-H25
1.024
Cr2-O4
1.595
N1-H25
1.024
C14-H15
1.083
N1-H28
1.022
Cr2-Cl5
2.215
N1-H28
1.024
C16-C18
1.386
C2-C3
1.517
O1-Cr2-O3
111.4
C2-C3
1.507
C16-H17
1.083
C2-C6
1.542
O1-Cr2-O4
111.4
C2-C6
1.546
C10-C18
1.394
C2-H26
1.089
O1-Cr2-Cl5
107.2
C2-H26
1.088
C18-H19
1.083
C3-O4
1.207
O3-Cr2-O4
111.3
C3-O4
1.197
C10-C11
1.42
C3-O5
1.33
O3-Cr2-O5
108
C3-O5
1.367
C10-N8
1.376
O5-H27
0.974
O4-Cr2-Cl5
107.4
O5-H27
0.978
C11-C12
1.402
C6-H7
1.089
O5-Cr31
1.769
C11-C6
1.439
C6-H8
1.093
C6-H7
1.089
C12-H13
1.083
C6-C9
1.495
C6-H8
1.093
C6-C7
1.373
C9-C10
1.374
C6-C9
1.493
C6-C3
1.491
C9-C14
1.44
C9-C10
1.373
C7-N8
1.371
C10-N11
1.372
C9-C14
1.439
C7-H20
1.078
C10-H23
1.078
C10-N11
1.372
N8-H9
1.007
N11-H12
1.007
C10-H23
1.078
C3-C2
1.479
N11-C13
1.374
N11-H12
1.007
C3-H5
1.098
C13-C14
1.422
N11-C13
1.374
C3-H4
1.097
C13-C21
1.394
C13-C14
1.422
C2-N1
1.275
C14-C15
1.403
C13-C21
1.394
C2-H23
1.085
C15-H16
1.084
C14-C15
1.403
N1-H21
1.018
C15-C17
1.385
C15-H16
1.084
N1-H22
1.014
C17-H18
1.083
C15-C17
1.385
C16-C14-C12
121.2
C17-C19
1.407
C17-H18
1.083
C16-C14-H15
119.2
C19-H20
1.083
C17-C19
1.407
C14-C16-C18
121.3
C19-C21
1.386
C19-H20
1.083
C14-C16-H17
119.3
C21-H22
1.083
C19-C21
1.386
C12-C14-H15
119.7
C2-N1-H24
110.1
C21-H22
1.083
C14-C12-C11
118.8
C2-N1-H25
111.2
Cr31-O29
1.605
C14-C12-H13
120.6
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C2-N1-H28
111.8
Cr31-O30
1.604
C18-C16-H17
119.4
N1-C2-C3
107.9
Cr31-Cl32
2.61
C16-C18-C10
117.4
N1-C2-C6
110.6
Cr31-O33
1.626
C16-C18-H19
121.4
N1-C2-H26
107
C2-N1-H24
110.2
C10-C18-H19
121.1
H24-N1-H25
108.2
C2-N1-H25
111.6
C18-C10-C11
122.1
H24-N1-H28
107.8
C2-N1-H28
112.1
C18-C10-N8
130.6
H25-N1-H28
107.5
N1-C2-C3
107.8
C11-C10-N8
107.3
C3-C2-C6
112
N1-C2-C6
110.8
C10-C11-C12
119.1
C3-C2-H26
109.5
N1-C2-H26
107.3
C10-C11-C6
106.7
C2-C3-O4
123.8
H24-N1-H25
108
C10-N8-C7
109.5
C2-C3-O5
111
H24-N1-H28
107.2
C10-N8-H9
125.5
C6-C2-H26
109.7
H25-N1-H28
107.7
C12-C11-C6
134.1
C2-C6-H7
106.5
C3-C2-C6
111.9
C11-C12-H13
120.6
C2-C6-H8
108.7
C3-C2-H26
108.9
C11-C6-C7
106.7
C2-C6-C9
112.5
C2-C3-O4
125.6
C11-C6-C3
126.6
O4-C3-O5
125.2
C2-C3-O5
112.8
C7-C6-C3
126.7
C3-O5-H27
109.5
C6-C2-H26
110
C6-C7-N8
109.7
H7-C6-H8
107.4
C2-C6-H7
107.1
C6-C7-H20
129.4
H7-C6-C9
110.9
C2-C6-H8
108.4
C6-C3-C2
115.8
H8-C6-C9
110.7
C2-C6-C9
111.9
C6-C3-H5
112.3
C6-C9-C10
126.6
O4-C3-O5
121.6
C6-C3-H4
112
C6-C9-C14
126.9
C3-O5-H27
109.1
N8-C7-H20
120.9
C10-C9-C14
106.5
C3-O5-Cr31
138.2
C7-N8-H9
124.9
C9-C10-N11
109.9
H27-O5-Cr31
110.7
C2-C3-H5
105.8
C9-C10-H23
129.5
O5-Cr31-O29
97.7
C2-C3-H4
105.7
C9-C14-C13
106.9
O5-Cr31-O30
97
C3-C2-N1
123.4
C9-C14-C15
134.2
O5-Cr31-Cl32
174.8
C3-C2-H23
119.3
N11-C10-H23
120.7
O5-Cr31-O33
90.2
H5-C3-H4
104.3
C10-N11-H12
124.9
H7-C6-H8
107.5
N1-C2-H23
117.3
H7-C6-C9
110.1
C2-N1-H21
120.6
H8-C6-C9
111.6
C2-N1-H22
121.7
C6-C9-C10
125.7
H21-N1-H22
117.8
C6-C9-C14
127.6
C10-C9-C14
106.7
C9-C10-N11
109.8
C9-C10-H23
129.2
C9-C14-C13
106.8
C9-C14-C15
134.4
N11-C10-H23
121
C10-N11-H12
125
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue X October 2025
Page 1610
www.rsisinternational.org
A possible mechanism for the oxidation of L-tryptophan with TMGCC in sulphuric acid media can be given on
the basis of other previously reported mechanisms [20]. The absence of free radical in the respective test ruled
out any possibility of intermediate Cr (V) species in the concerned reaction involving Cr (VI) as an oxidant,
which involved one-electron transfer.
The existence of Amino acids in the form of zwitter ions is known [21, 22]. Mainly, they tend to protonate in
acidic medium which is in accordance with below equilibria:
Try + H
+
Try
+
(16)
Also, the fractional-second order rate constant for the concentration of hydrogen ions was elucidated on basis
of polar nature of both TMGCC and Trptophan in acidic media as they are more reactive species which have a
major impact in the kinetics of redox reactions.
The 1:1 stoichiometry for TMGCC and L-tryptophan reaction in H
2
SO
4
media, i.e., 1 Trp:1 TMGCC, with a
fractional-first order dependence on [Trp] and a first order dependence on [TMGCC)]. The formation of
complex before the slow step supported fractional order dependence of tryptophan concentration.
The mechanism for the oxidation of Tryptophan by TMGCC in H
2
SO
4
medium may be suggested by Scheme
1, which involves a complex formation with a fast step between the protonated Tryptophan and TMGCC,
leading to the formation of an intermediate complex. Further decomposition of the intermediate complex during
the slow step, with successive fast steps, gave the final products of oxidation.
O O O
OH
N
2
NH + NH
H
Tryptophan (Trp) Zwitter ion Protonated Tryptophan
(Trp
+
)
N
H
3
+
N
H
O
H
N
H
3
O
-
H
+
K
1
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue X October 2025
Page 1611
www.rsisinternational.org
k1 Slow
H
H
O
+ Cl
-
O
(H3C)
2
N N(CH
3
)
2
+ NH
4
+
N + H
H
Iminium Cation Indole-3-acetaldehyde
Scheme 1: Mechanism for L-tryptophan’s oxidation by TMGCC in H
2
SO
4
medium.
CONCLUSION
The kinetics of the L- tryptophan’s oxidation by TMGCC was studied in H
2
SO
4
medium, which proceeded
through a complex formation. It showed a stoichiometry of 1:1, i.e. a single mole of tryptophan was used with
one mole of TMGCC. The reaction is of first order with respect to TMGCC, fractional order with respect to
tryptophan, and fractional second order with respect to acid. The final products of the oxidation of tryptophan
were recognized as indole-3- acetaldehyde, NH
4
+
ion with CO
2
.
ACKNOWLEDGEMENT
Grateful to the Head of the Department, Chemistry (University of Rajasthan), for providing the required and
needed facilities for conducting the research work smoothly and efficiently.
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