A Raman and UV-Vis study of catecholamines oxidized with Mn(III)

Article abstract of DOI:10.1016/S1386-1425(98)00164-4

A UV-Vis and Raman spectroscopy study of three aminochromes generated through Mn³⁺ oxidation of the dopamine, L-dopa and adrenaline molecules at physiological pH was performed. The UV-Vis spectra of the catecholamines oxidized using Mn³⁺ in buffer solution at pH 7.2 show a band at ca. 300 nm, formed by two transitions at 280 nm and 300 nm assigned to an L_a and L_b transition respectively, and other at ca. 470 nm assigned to an n-π* transition localized in the carbonyl group. This assignment is suggested by the UV-Vis and Raman spectra of ortho-aminoquinone generated by MnO₂ oxidation of a dopamine aqueous acidic solution. The resonance Raman spectra of the three chromes at buffer pH 7.2 show a very similar feature and the most intense bands are observed in the spectral range 1100-1800 cm^-1. The band around 1680 cm^-1 for the three compounds is assigned to a v(C=O) stretching vibration, 1630 cm^-1 to the v(C=C) ring mode, two bands at 1423, 1439 cm^-1; 1427, 1438 cm^-1 and 1456, 1475 cm^-1 are assigned to a v(C=N⁺) vibration, for aminochrome, dopachrome and adrenochrome, respectively. The excitation profiles for the most intense bands for aminochrome and adrenochrome were obtained. The band assigned to the v(C=N⁺) present a red shift with respect to the visible band peak, however the band in adrenochrome at 1475 cm^-1 shows a profile similar to v(C=O) and v(CC) modes that reflects the methyl group effect on mixing this mode more effectively with the v(CC) ring mode.

Full text of DOI:10.1016/S1386-1425(98)00164-4

Spectrochimica Acta Part A 55 (1999) 65–72
A Raman and UV-Vis study of catecholamines oxidized with
Mn(III)
W.J. Barreto a,*, S. Ponzoni b, P. Sassi c
a Uni6ersidade Estadual de Londrina, Departamento de Quimica, Campus Uni6ersita´rio, Centro de Cieˆncias Exatas,
Caixa Postal 6001, Londrina 86051-970, Brazil
b Uni6ersidade Estadual de Londrina, Departamento de Fisiologia, Londrina, Brazil
c Uni6ersita` degli Studi di Perugia, Dipartimento di Chimica, Perugia, Italy
Received 9 April 1998; accepted 30 April 1998
Abstract
A UV-Vis and Raman spectroscopy study of three aminochromes generated through Mn3+ oxidation of the
dopamine, -dopa and adrenaline molecules at physiological pH was performed. The UV-Vis spectra of the
L
catecholamines oxidized using Mn3+ in buffer solution at pH 7.2 show a band at ca. 300 nm, formed by two
transitions at 280 nm and 300 nm assigned to an La and Lb transition respectively, and other at ca. 470 nm assigned
to an n–y* transition localized in the carbonyl group. This assignment is suggested by the UV-Vis and Raman
spectra of ortho-aminoquinone generated by MnO2 oxidation of a dopamine aqueous acidic solution. The resonance
Raman spectra of the three chromes at buffer pH 7.2 show a very similar feature and the most intense bands are
observed in the spectral range 1100–1800 cm−1. The band around 1680 cm−1 for the three compounds is assigned
to a w(CꢀO) stretching vibration, 1630 cm−1 to the w(CꢀC) ring mode, two bands at 1423, 1439 cm−1; 1427, 1438
cm−1 and 1456, 1475 cm−1 are assigned to a w(CꢀN+) vibration, for aminochrome, dopachrome and adrenochrome,
respectively. The excitation profiles for the most intense bands for aminochrome and adrenochrome were obtained.
The band assigned to the w(CꢀN+) present a red shift with respect to the visible band peak, however the band in
adrenochrome at 1475 cm−1 shows a profile similar to w(CꢀO) and w(CC) modes that reflects the methyl group effect
on mixing this mode more effectively with the w(CC) ring mode. © 1999 Elsevier Science B.V. All rights reserved.
Keywords: Catecholamines; Manganese; Aminochromes; Resonance Raman
1. Introduction
nucleus due to death of more than 80% in the
dopamirnegic cells of the substantia nigra.
Parkinson’s disease is believed to be caused in
large measure by a reduction in level of a cate-
cholamine neurotransmitter, dopamine (4-(2-
aminoethyl)benzene-1,2-diol), in the caudade
Graham [1] performed spectrophotometric
studies on the pathways by which dopamine,
norepinephrine (4-(2-amino-1-hydroxyethyl)ben-
zene-1,2-diol) and adrenaline (4-[1-hydroxy-2-
(methylamino)ethyl]benzene-1,2-diol) can be oxi-
dized to aminochrome, noradrenochrome and
* Corresponding author. E-mail: barreto@uel.br
1386-1425/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved.
PII S1386-1425(98)00164-4

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W.J. Barreto et al. / Spectrochimica Acta Part A 55 (1999) 65–72
adrenochrome, through exposure to oxygen at
basic pH. He proposed that the oxidative process
that results in the production of superoxide radi-
cals also promotes the oxidation of the cate-
cholamines to quinone products. Such products
polymerize to form neuromelanin, which accu-
mulates progressively with time within the cyto-
plasm of the neuron. Then this oxidative
pathway produces potentially toxic products in
the cell. The proposed [1–3] oxidative mecha-
nism is shown in Fig. 1.
catecholamines while Mn3+ does so vigorously.
The resonance Raman spectra can provide im-
portant information about the nature of the
molecular electronic transitions. The resonance
Raman spectrum has the characteristic of pre-
senting a very selective feature because only a
few vibrational modes involved in electronic
transition are intensified.
Resonance Raman spectra of the amino-
chromes generated through periodate oxidation
of catecholamines, have been reported to have
been used as an analytical tool for trace level
quantitative determination [5–7]. Also SERRS
(Surface-enhanced resonance Raman scatter-
ing) [8] and NIR-SERS [9] have been suggested
as powerful tools for the quantitative determina-
tion of cathecolamines.
Archibald and Tyree [4] have shown that when
L
-dopa (3-hydroxytyrosine)in
a
physiological
buffer was mixed with Mn(III)-pyrophosphate
complex there was an immediate (B5 s) appear-
ance of visible color, easily discernible from the
Mn(III)-pyrophosphate color by its much greater
intensity and different visible maximum (476
nm). This final product also presents a band at
302 nm and is stable for at least several hours;
the author’s assignment was aminochrome, the
dehydro-indole-o-quinone derivative of dopa.
When Mn(III)-pyrophosphate was added to
buffered dopamine, the results were identical to
those with DL-dopa. The authors noted that if
the Mn3+ oxidized DL-dopa and dopamine were
left in aqueous solution, the solution blackened
over several hours, suggesting a slow melanin-
like polymerization of the quinones. Another ob-
servation was that Mn2+ does not react with the
In this article, continuing our studies on
quinone systems [10] and resonance Raman scat-
tering [11,12], we report a UV-Vis and Raman
spectroscopy study of three aminochromes gener-
ated through Mn3+ oxidation of the dopamine,
L-dopa and adrenaline molecules at physiological
pH. We also report the Raman and UV-Vis
spectra of the ortho-quinone derived from
adrenaline.
2. Experimental section
2.1. Reagents
Dopamine hydrochloride,
L-dopa-free and
adrenaline-free bases were supplied by the Sigma
(St. Louis, MO) and used without further purifi-
cation. The 0.01 M phosphate buffer solutions,
pH 7.2, were prepared using 0.1 M sodium hy-
droxide solution and 0.1 M KH2PO4 with further
dilution. Bi-distilled water was always used. The
Mn(III)-pyrophosphate complex in aqueous solu-
tion, pH 7, was prepared as reported [4] and is
stable for at least 6 months.
The ortho-quinones were prepared for the UV-
Vis spectra dissolving the MnO2 dust in stoichio-
metric quantities (2:1) to obtain a 5.00×10−4
M
aqueous solution of the catecholamines (pH 1).
Hydrochloric acid was used for acidification.
Fig. 1. The proposed oxidative pathway for dopamine.

W.J. Barreto et al. / Spectrochimica Acta Part A 55 (1999) 65–72
67
For Raman spectra the ortho-quinone samples
were prepared using a saturated acid solution of
the catecholamines and MnO2 was added until no
more reaction was observed. The adrenaline and
L
-dopa ortho-quinones are unstable in the laser
Fig. 2. A schematic structure of the compounds (trivial and
systematic name):(A) dopamine, (4-(2-aminoethyl)benzene-1,2-
diol), (B) adrenaline, (4-[1-hydroxy-2-(methylamino)ethyl]-
beam and decompose with time.
2.2. Raman measurements
benzene-1,2-diol), (C) L-dopa,(3-hydroxytyrosine).
A rotating cell was used to avoid sample de-
composition, and the laser beam emerged very
close to the glass wall to minimise reabsorption.
The compound stabilities were a critical problem
for the Raman resonance studies, even using a
laser power not exceeding 30 mW on the sample.
The chromes are intermediate compounds in the
course of the auto-oxidation processes (Fig. 1)
with a short lifetime which is no more than 60
min. When the chromes are irradiated with a
laser, their respective lifetimes are reduced and it
is impossible to measure the six spectra in a
sequence, since the total incidence time would be
ca. 2 h. To surmount this experimental problem
the original procedure of Raman resonance stud-
ies was developed but changing the samples after
each measurement.
For the dopachrome, the best spectrum was
obtained around the maximum absorption band,
and its resonance profile is not presented because
the signal/noise ratio was very low in 457 nm laser
excitation.
2.3. Raman instrumentation
The Raman spectra were obtained in a Jobin–
Yvon U1000 Raman spectrometer equipped with
a double monochromator and fitted with an RCA
high gain photomultiplier tube. The Raman spec-
tra were obtained using Ar+ ion laser lines (Ion
Laser Innova 400-Coherent), with a spectral reso-
lution of 7 cm−1. Spectra were acquired using the
Enhanced Prism Software 3.1 (Jobin Yvon Divi-
sion Instruments) and processed in Labcalc Arith-
metic A1.2 (Galactic Industries).
To obtain reproducible spectra it was necessary
to use a standard procedure in preparing the
samples. All solutions of dopamine,
adrenaline were freshly made and kept in the dark
until to be used. To 3 cm3 of the 5×10−4
L-dopa and
2.4. UV-Vis instrumentation
M
catecholamine solution, pH 7.2 and O2 free, was
added 250×10−6 dm3 of the 0.035 M Mn(III)-
pyrophosphate solution. The solution was bub-
bled with N2 for 4 min and centrifuged for 2 min
to precipitate the Mn(OH)2 produced by Mn(III)
reduction. After the spectrum acquisition using a
laser line, a new sample preparation was made for
the next laser line.
Good and reproducible spectra were obtained
for the aminochrome and adrenochrome using
this procedure for the laser lines at 514.5, 501.7,
496.5, 488.0, 476.0 and 457 nm. Two spectra were
obtained for each laser line and the intensities
were calculated measuring the band area and
dividing them by the sulphate standard area. Two
experiments were developed in duplicates and the
intensities presented correspond the average of
two measurements in each radiation excitation.
A DU-7500 Beckmann Spectrophotometer and
a Perkin–Elmer Lambda 5 were used to record
the ultra-violet and visible spectra.
3. Results and discussion
3.1. UV-Vis study
3.1.1. The catecholamines
In a 0.01 M phosphate buffer solution at pH
7.2 the three compounds show two bands in the
UV range: at 220 and 281 nm for dopamine, at
225 and 280 nm for adrenaline, at 222 and 282
nm for
ture for the compounds and the Fig. 3(a) the
spectra of the -dopa as exemple.
L-dopa. Fig. 2 present a schematic struc-
L

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W.J. Barreto et al. / Spectrochimica Acta Part A 55 (1999) 65–72
These electronic transitions are directly related
to those of the parent benzene molecule at 183,
203 and 253 nm. In benzene the first band is
assignable to a strong allowed y–y* (or Ba,b in
Platt’s notation) transition and the last two are
the weak symmetry-forbidden transitions La and
Lb.
We know that substitutions on the benzene ring
lower the symmetry and introduce some allowed
character into symmetry-forbidden transitions.
The perturbation is observable for tyrosine, with a
hydroxyl and a methylene substituent, where the
La and Lb have higher intensity and are red-
shifted relative to benzene: 193 nm for the y–y*
transition and 222–273 nm for the La–Lb transi-
tions, respectively. When the perturbation is
strong, like the tryptophan molecule with a
pyrrole ring fused onto the benzene ring, the two
bands La and Lb overlap in the 280 nm range and
the y–y* transition shifts to 218 nm [13].
Fig. 4. Acid-base equilibrium suggested for the aminochromes
in aqueous solutions at neutral pH where the dipolar ion (III)
is the predominant form. For aminochrome R1ꢀH2, R2ꢀH2
R3ꢀH2, adrenochrome R1ꢀOH, R2ꢀꢀCH3, R3ꢀH2 and do-
pachrome R1ꢀH2, R2ꢀH2, R3ꢀCOOH.
compared to the reagents. Fig. 3(b–g) show the
spectra obtained during the Mn3+ oxidation for
L-dopa. The same spectrum pattern was observed
for adrenaline and dopamine during the oxidation
processes. During the oxidation a band appears at
ca. 300 nm rising progressively in intensity until it
overlaps the band at 280 nm that clearly does not
change in intensity and finally results in a broad
band centered at 307 nm (for dopamine at 301 nm
and adrenaline, 303 nm). This broad and intense
band is formed by two transitions around the
peak at 300 nm. An intense band rises at 475 nm
Considering these arguments we may tenta-
tively assign the transitions at 220 and 280 nm in
catecholamines, with two hydroxyl and one
aliphatic group substituents, to a y–y* and an
La–Lb coincident transition, respectively.
for
L-dopa (for dopamine at 473 nm and
adrenaline at 478 nm), and is a characteristic
electronic transition of the chrome form.
3.1.2. The chromes
In aqueous solutions at neutral pH, the pre-
dominant chrome form would be the dipolar ion
III in acid-base equilibrium [1,14] (Fig. 4).
In order to make a tentative assignment of
these bands we refer to indole and indole-
derivates. First we will consider the band at 300
nm composed of two transitions. In tryptophan,
the La and Lb transitions overlap, the resulting
band having a maximum at 280 nm: since the
tryptophan molecule has a very similar structure
to the chromes, these latter are expected to show
the same effect. The details of the nature of La
and Lb can be understood using the indole
assignation.
The UV-Vis spectra of the catecholamines oxi-
dized using Mn3+ in buffer solution at pH 7.2
show marked modification in the visible region as
In a recent study on the electronic transitions of
indole and its methyl and methoxy derivatives
[15], the bands at 287 and 265 nm are assigned to
a 1Lb’1A1 and a 1La’1A1 transition, respec-
tively. The separation between these two transi-
tions is sensitive to the substitution site. The
presence of a substituent in position 3 lowers the
energy of the La transition whereas substitutions
Fig. 3. UV-Vis spectra of: (a) L
-dopa 9.6×10−5 M in 0.01 M
phosphate buffer pH 7.2; (b) (g) L-dopa oxidized during the
successive addition of a 0.035 M Mn3+-pyrophosphate solu-
tion to the (a) solution, until an excess of Mn3+ ion is present.

W.J. Barreto et al. / Spectrochimica Acta Part A 55 (1999) 65–72
69
for the three compounds. The most intense bands
are observed in the spectral range 1100–1800
cm−1. The in-plane-skeleton vibrations and the
carbonyl group vibration should fall within this
region.
in positions 5 and 6 lower the Lb transition energy.
In the chrome molecule positions 5 and 6 have a
carbonyl group, and thus a similar shift is expected.
Considering these observations we assigned the
band at 280 nm to the La transition and that at 300
nm to the Lb. Taking these arguments into consid-
eration, the carbonyl group substitution on indole
in positions 5 and 6 seems to be much more effective
in changing the La and Lb transitions in terms of
intensities and frequencies as compared with substi-
tution on position 3. This is the case of adrenaline
where position 3 is occupied by a hydroxyl group
and the same spectrum pattern is observable.
The bands at 480 nm can be assigned to an n–y*
transition localized in the carbonyl group where the
ring pyrrole formation caused a delocalization
effect over the indole structure, lowering the tran-
sition energy, and consequentely leading to a red
shift for this transition. This assignment is sug-
gested by the spectrum of ortho-aminoquinone
(Fig. 5) generated by MnO2 oxidation of a do-
pamine aqueous acidic solution (Fig. 6)
A close analysis of the spectra as functions of
time allows us to see an intense band at 225 nm and
a weak band at 280 nm (Fig. 5(a)). After a few
minutes a shoulder at 293 nm rises gradually until
it has the same intensity as the 280 nm band, and
an intense band at 386 nm appears (Fig. 5(b–e)).
The band at 225 nm can be assigned to a y–y*
transition and the 293 nm band to the overlapped
La and Lb transitions. The band in the visible
region, 395 nm, is n–y* transition due to the
carbonyl group attached to benzene ring, and is a
characteristic band for the identification of the
ortho-quinone family [16]. This band disappears
when the solution is neutralized to pH 7. At this
pH the aminochrome is readily formed by a nucle-
ophilic nitrogen attack on the benzene ring result-
ing in an indole-like structure [17].
3.2. Raman study
3.2.1. The Raman spectra
The resonance Raman spectra of the three
chromes at buffer pH 7.2 show a very similar
feature (Fig. 7).
Fig. 5. (a) UV-Vis spectrum of 1×10−4 M dopamine solution
prepared in 30% HCl. (b–e) UV-Vis spectra of the ortho-
aminoquinone generation at time by the oxidation with excess
of MnO2 dust added to the solution (a).
Table 1 gives the observed wavenumber (cm−1
)

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W.J. Barreto et al. / Spectrochimica Acta Part A 55 (1999) 65–72
Table 1
Raman shift (w (cm−1)) of adrenochrome, dopachrome and
aminochrome principal bands and a tentative assignment
Mode
Adreno- Dopa-
Amino-
Fig. 6. The proposed mechanism of the dopamine oxidation
with MnO2 at pH 0–1.
chrome
chrome chrome
~ Ring
349
387
~ Ring
~ Ring
~ Ring
~ Ring
~ Ring
~ Ring
w(CC)
W12 or w(CH)
W7 or w(CH):w(CC)
W6.or.w(CꢀN+):w(C–H)
W5 or w(CꢀN+):w(C–H)
W1 or w(CC)
w(CꢀO)
416
457
465
598
621
660
669
1178
1385
1456
1475
1627
1686
431
526
533
404
427
462
The band around 1680 cm−1 for the three
compounds is assigned to a w(CꢀO) stretching
vibration. This band is obviously absent before
the oxidation with the Mn3+ ion in the dopamine
for exemple (Fig. 8(b)), but is observed in this
same region in the ortho-aminoquinone spectrum
(Fig. 8(a)). The evidence for ortho-quinone forma-
tion is the absence of the intense Raman band at
ca. 1290 cm−1 assigned to w(C–OH) stretching.
624
658
665
1175
1343
1427
1438
1632
1679
1178
1345
1423
1439
1632
1680
An intense band is observable at ca. 1630 cm−1
,
and is assigned to the w(CꢀC) stretching vibration
of the benzene ring. In the ortho-aminoquinone
this band is also observable in the oxidized as well
as in the unoxidazed form. The bending mode of
water, at ca. 1640 cm−1, also lies between these
two bands and is the origin of the broad feature
in this region.
Obervations: ~ are ring or CH out-of-plane modes [19,20], W
nomenclature from Maruyama and Takeuchi [18] and Ra-
haman and Korenkiewicz [19].
seem to arise from similar vibrations. In tryp-
tophan there can be observed three bands in this
region denominated W4, W5 and W6 (in Takeuchi
notation [18]) at 1487, 1458 and 1424 cm−1 re-
spectively. The vibrations W5 and W6 are basi-
The spectral range 1400–1500 cm−1 causes
greater difficulties for assignments. In do-
pachrome, aminochrome and adrenochrome, two
bands are present at 1427, 1438 cm−1, 1423, 1439
cm−1 and 1456, 1475 cm−1 respectively, and
Fig. 7. The resonance Raman spectra of: (a) adrenaline (b)
dopamine (c)
L
-dopa, 5×10−4 M in phosphate buffer pH 7.2
Fig. 8. Raman spectra using capillary and the laser radiation
of u=514.5 nm for: (a) ortho-aminoquinone in 30% HCl
solution with 70 mW laser power, (b) saturated dopamine
solution in phosphate buffer pH 7.2 with 30 mW laser power.
using u=514.5 nm laser radiation and 30mW of power laser
on the sample. The band indicated with a plus (+) is the ca.
990 cm−1 sulphate internal standard.

W.J. Barreto et al. / Spectrochimica Acta Part A 55 (1999) 65–72
71
It is a very interesting fact that in the 700–1100
cm−1 region, enhanced Raman bands are not
present. In this range one expects there to appear
the more intense Raman band at 789 cm−1, (do-
pamine in aqueous solution) and 800 cm−1
(adrenaline in acid aqueous solution). This band
is also observable as the most intense line of the
indole Raman spectrum at 758 cm−1 (liquid). In
tryptophan this band appears strongly enhanced
at 762 cm−1 in the resonance Raman spectrum
which is excited in the Ba,b transition (218 nm).
cally ring skeleton displacements and involve hy-
drogen motions together with a substantial NH
bending contribution. The W4 band due to a CH
bending vibration disappears from the 1490 cm−1
region under deuteration and appears around 820
cm−1 [18].This observation supports the assign-
ment of the two aminochrome bands in this re-
gion as W6 and W5 vibrations. Morris [5] assigned
these two bands to a w(CꢀN+) or a w(CꢀN+ –C)
vibration. In the adrenochrome molecule these
frequencies show a shift to higher wavenumbers
not observable in the other two chromes. This
shift is due to the interaction of the methyl group
motions with the w(CN) mode when it is attached
to the nitrogen atom.
This effect is also observed in the adrenalin-
copper complex [19]. The Raman spectrum of this
compound shows three bands in this region at
1480, 1460 and 1435 cm−1 assigned to the w(CN),
w(H3C–N)as and w(H3C–N)s modes respectively.
The band at 1480 cm-1 assigned to a w(CN)
stretching, appears at 1435 cm−1 in the copper
noradrenaline complex where no such interaction
can take place since the complex has no methyl
group. This frequency shift is also observed for
the amide II’ mode at 1450 cm−1 in deuterated
N-methylacetamide and at a much lower fre-
quency (1338 cm−1) for diformylhydrazine which
has no methyl groups [20].
The bands in the 1300–1380 cm−1 region are
difficult to assign. In indole and tryptophan [21]
only one fundamental, w14 [22] (or W7 in Takeuchi
notation) is expected in this range and is described
as a i(CH) mode with little w(CC) contribution
from the pyrrole ring. The bands present at 1385,
1343 and 1345 cm−1, in adrenochrome, do-
pachrome and aminochrome respectively, seem to
have the same origin.
For the three compounds the band at ca. 1170
cm−1 is probably the w18 mode at 1203 cm−1 in
the indole molecule, described as a benzene ring
deformation and pyrrole-benzene w(CC) stretch-
ing. The predominance of the benzene ring defor-
mation in the mode composition may explain the
small frequency shift between the compounds and
the lack of dependence under the pyrrole ring
substitutions.
Fig. 9. Resonance Raman profile of 5×10−4
M of:
aminochrome (A) and adrenochrome (B) in 0.01 M phosphate
buffer pH 7.2 solution using the exciting radiation, 514.5,
501.7, 496.5, 488.0, 476.0 and 457.9 nm. To avoid the decom-
position 30 mW laser power was used, and each value is the
average of two measurements. The band resolution was ca. 7
cm−1. The sulphate band at ca. 990 cm−1 was used as
internal standard (Ir/Is).

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W.J. Barreto et al. / Spectrochimica Acta Part A 55 (1999) 65–72
between the carbonyl group (w(CO) enhanced)
and the pyrrole ring (w(CN+) enhanced).
This band is assigned to the benzene and pyrrole
ring-breathing in-phase mode [13].
In the 300–600 cm−1 range bands are observed
that are assigned in the indole molecule, via a
normal coordinate analysis, to ring out-of-plane
bending modes [22].
Acknowledgements
The CO− stretching mode, falling around 1260
cm−1 in anionic adrenaline, is observed in
W.J.B. thanks CAPES for a Research Fellow-
ship and to Professor R.S. Cataliotti for his hospi-
tality in the Physical Chemistry Laboratory at
Perugia University.
adrenochrome as a very weak band at 1215 cm−1
.
3.2.2. The excitation profiles
The excitation profiles for the most intense
bands of aminochrome and adrenochrome are
displayed in Fig. 9(a, b). The profiles obtained for
dopachrome are not sufficiently reproducible. For
the two compounds the bands assigned to w(CꢀO)
and w(CꢀC) modes show the same profile pattern,
with a maximum at ca. 470 nm. The band as-
signed to the w(CꢀN+) mode at 1456 cm−1 in
adrenochrome and at 1423 cm−1 aminochrome
present a red shift with respect to the visible band
peak; however the band in adrenochrome at 1475
cm−1 shows a profile similar to w(CꢀO) and
w(CC) modes.
References
[1] D.G. Graham, Mol. Pharmacol. 14 (1978) 633.
[2] R.A. Heacock, Advan. Heterocycl. Chem. 5 (1965) 205.
[3] E. Herlinger, R. F. Jameson, W. Linert, J. Chem. Soc.
Perkin Trans. 2 (1995) 259.
[4] F.S. Archibald, C. Tyree, Arch. Biochem. Biophys. 256
(2) (1987) 638.
[5] M.D. Morris, Anal. Chem. 47 (14) (1975) 2453.
[6] M.S. Rahaman, M.D. Morris, Talanta 23 (1976) 65.
[7] C.-Y Chen, M.D. Morris, J. Chromatogr. 540 (1991) 355.
[8] W.K. Kowalchyk, K.L. Davis, M.D. Morris, Spec-
trochim. Acta Part A 51A (1) (1995) 145.
[9] K. Kneipp, Y. Wang, R.R. Dasari, M.S. Feld, Spec-
trochim. Acta Part A 51A (3) (1995) 481.
This differences can be understood as the result
of a usual Franck–Condon mechanism where, in
this case, the modes with a strong w(CN) contri-
bution have a B term (B=Franck–Condon dis-
placement) higher as compared with the other
modes, and exhibit an expected red shift. The
profile of the vibration at 1475 cm−1 in
adrenochrome probably reflects the methyl group
effect on mixing this mode more effectively with
the w(CC) ring mode.
The absence of the enhanced bands in the 700–
1100 cm−1 range, where the intense breathing
ring vibrations present in tryptophan are ex-
pected, indicates a different origin for this chro-
mophore. This mode in tryptophan can be
expected to exhibit a strong Franck–Condon ac-
tivity in the allowed y–y* transition. It is evident
that in the n–y* transition the same activity is not
allowed and the molecule in the dipolar ion form
presents a more localized chromophore, possibly
[10] W.J. Barreto, D.A.M. Zaia, L.F.C. de Oliveira, Spec-
trochim. Acta Part A 50A (6) (1994) 1031.
[11] M.C.C. Ribeiro, W.J. Barreto, P.S. Santos, J. Raman
Spectrosc. 25 (1994) 923.
[12] P. Sassi, M.L. Ceccarini, R.S. Cataliotti, Ber. Bunsen.
Phys. Chem. 99 (1995) 779.
[13] R.P. Rava, T.G. Spiro, J. Phys. Chem. 89 (1985) 1856.
[14] R.T. Borchardt, E.E. Smissman, D. Nerland, J R. Reid,
J. Med. Chem. 19 (1976) 30.
[15] B. Albinsson, B. Norde´n, J. Phys. Chem. 96 (1992) 6204.
[16] F. Zhang, G. Dryhurst, Bioorganic Chem. 21 (1993) 392.
[17] J.D. Bu’Lock, J. Harley-Mason, J. Chem. Soc. (1951)
712.
[18] T. Maruyama, H. Takeuchi, J. Raman Spectrosc. 26
(1995) 319.
[19] M.S. Rahaman, S.M. Korenkiewicz, Can. J. Chem. 54
(24) (1976) 3815.
[20] T. Miyazawa, T. Shimanouchi, S.-I. Mizushima, J. Chem.
Phys. 29 (3) (1958) 611.
[21] I. Harada, H. Takeuchi, in: R.J.H. Clark, R.E. Hester
(Eds.), Spectroscopy of Biological Systems: Chapter 3,
Wiley, Chichester, 1982, p. 117.
[22] M. Majoube, G. Vergoten, J. Raman Spectrosc. 23 (1992)
431.
.
.