Biological interactions of fluorinated chalcones: Stimulation of tyrosinase activity and binding to bovine serum albumin

Article abstract of DOI:10.1016/j.jfluchem.2017.04.007

The evaluation of tyrosinase activity of CH, CH3F, CH4F, CH23F, CH25F, CH35F and CH2356F as well as of the interactions of CH and fluorinated chalcones CH3F, CH4F and CH2356F with bovine serum albumin (BSA) in a PBS buffer solution (pH?=?7.4), at 288?K, 2

Full text of DOI:10.1016/j.jfluchem.2017.04.007

Accepted Manuscript
Title: Biological interactions of fluorinated chalcones:
Stimulation of tyrosinase activity and binding to bovine serum
albumin
Author: Ot a´ vio Augusto Chaves Leonardo Santos de Barros
M a´ rcia C.C. de Oliveira Carlos Mauricio R. Sant’Anna
Aur e´ lio B.B. Ferreira Francisco Assis da Silva Dari
Cesarin-Sobrinho Jos e´ Carlos Netto-Ferreira
PII:
S0022-1139(17)30040-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2017.04.007
FLUOR 8972
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
26-1-2017
11-4-2017
24-4-2017
Please cite this article as: O.A. Chaves, L.S. Barros, M.C.C. de Oliveira, C.M.R.
Sant’Anna, A.B.B. Ferreira, F.A. Silva, D. Cesarin-Sobrinho, J.C. Netto-Ferreira,
Biological interactions of fluorinated chalcones: Stimulation of tyrosinase activity
and binding to bovine serum albumin, Journal of Fluorine Chemistry (2017),
http://dx.doi.org/10.1016/j.jfluchem.2017.04.007
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1
Biological interactions of fluorinated chalcones: stimulation of tyrosinase activity and
binding to bovine serum albumin.
1
,2
1
1
Otávio Augusto Chaves, Leonardo Santos de Barros, Márcia C.C. de Oliveira, Carlos Mauricio R.
1
1
1
1
Sant’Anna, Aurélio B. B. Ferreira, Francisco Assis da Silva, Dari Cesarin-Sobrinho, José Carlos Netto-
1
,
Ferreira, ∗
1
Departamento de Química, ICE, Universidade Federal Rural do Rio de Janeiro, Rodovia BR-465, Km 7, Seropédica/RJ, 23.890-000, Brazil.
Instituto Militar de Engenharia, Praça General Tibúrcio 80, Urca, Rio de Janeiro/RJ, 22290-270, Brazil.
2
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The evaluation of tyrosinase activity of CH, CH3F, CH4F, CH23F, CH25F, CH35F and
CH2356F as well as of the interactions of CH and fluorinated chalcones CH3F, CH4F and
CH2356F with bovine serum albumin (BSA) in a PBS buffer solution (pH = 7.4), at 288K, 293K
and 298K, were investigated by using spectroscopic techniques, zeta potential and
computational methods. Tyrosinase enzymatic activity was measured by UV-Vis spectrometry
of the oxidation of L-DOPA in the presence of the enzyme and chalcones: the unsubstituted
chalcone inhibits tyrosinase activity, whereas its fluorinated derivatives showed the opposite
effect, whose sample CH2356F showed the highest percentage activation. Studies of quenching
of the BSA fluorescence by CH, CH3F, CH4F and CH2356F show a combination of static and
dynamic quenching mechanisms. In addition FRET mechanism can occurs with high
Available online
5
−1
probability. For CH the binding constant (K
a
) is in the range of 10 M indicating a moderate
association between chalcone and BSA. On the other hand, for the fluorinated derivatives CH3F,
4
-1
a
CH4F and CH2356F K = 10 M , which indicates that the presence of fluorine atoms on the
Keywords:
Fluorinated chalcones
Tyrosinase
Bovine serum albumin
Spectroscopy
Molecular docking
chalcone structure decreases the binding ability. The thermodynamic parameters ∆Hº and ∆Sº
show that the BSA:CH association is enthalpically and entropically driven, whereas for
fluorinated derivatives it is only entropically driven. The negative ∆G° values found in all cases
are consistent with a spontaneous albumin:chalcone association. Circular dichroism and zeta
potential data show that the binding does not affect significantly the albumin structure. The
binding site study clearly indicates that the main binding pocket for the samples is the Trp-212-
containing binding site. The largest docking score values also suggest the same binding site.
Molecular docking results suggested that the presence of fluorine atoms decrease the number of
amino acid residues that can stabilize the interaction of the fluorinated chalcones with BSA. For
CH3F and CH2356F the type of interaction between the amino acid residues and ligand
structure did not change significantly.
©
2017 Elsevier B.V. All rights reserved.
—
——
∗
Corresponding author.
E-mail address: jcnetto.ufrrj@gmail.com (J.C. Netto-Ferreira).
Page 1 of 10

2
O.A. Chaves et al./ Journal of Fluorine Chemistry XXX (2017) XX-XX
1
. Introduction
of new possible tyrosinase activators based on fluorinated
chalcone derivatives (CH, CH3F, CH4F, CH23F, CH25F,
CH35F and CH2356F) as well as the investigation of the
mechanism by which the compounds CH, CH3F, CH4F and
CH2356F can be bio distributed in the bloodstream by interaction
with serum albumin. Spectroscopic techniques (fluorescence,
circular dichroism), zeta potential and a computational method
Chalcones constitute an important class of natural products
belonging to the flavonoid family. Chemically, chalcones are 1,
-diphenylprop-2-en-1-ones in which the two aromatic rings are
3
connected by a three carbon α, β-unsaturated carbonyl system. In
nature, chalcones are precursors in the biosynthesis of flavones,
flavanones, and chromanones, playing an important role in the
defense give protection against UV radiation, pathogens and
insects in plants [1]. Some natural and synthetic prenylated and
hydroxychalcones showed potential tyrosinase inhibitory activity.
Three chalcones derivatives, including licuraside, isoliquiritin,
and licochalcone A were isolated from the roots of the
Glycyrrhiza species and competitively inhibited the
monophenolase activity of mushroom tyrosinase [2], nevertheless
none of them are potential tyrosinase activators.
(molecular docking) were employed.
2
. Experimental
2
.1. Materials
Bovine Serum Albumin, ibuprofen, warfarin, tyrosinase from
mushroom
dihydroxyphenyl)-propionic acid (L-DOPA), 2,2',2'',2'''-(ethane-
,2-diylbis(azanetriyl))-tetraacetic acid (EDTA), dimethyl
sulfoxide (DMSO), phosphate buffer (pH=7.4), benzaldehyde, 3-
fluorobenzaldehyde, 4-fluorobenzaldehyde and 2,3,5,6-
tetrafluorobenzaldehyde were purchased from Sigma-Aldrich
Chemical Company, St. Louis, USA. Ethanol
spectrophotometric grade) and acetophenone were obtained
lyophilized
enzyme,
(S)-2-amino-3-(3,4-
Tyrosinase is a multifunctional copper-containing oxidase,
which catalyzes the first two steps in mammalian melanogenesis.
Melanogenesis is the process that leads to the formation of
melanin, an important biological pigment for protection against
harmful effects of ultraviolet irradiation (UV) and responsible for
the skin color. When the concentration of modified melanin
increases it is possible to generate melanoma, which is one of the
most serious forms of skin cancer [3]. In order to reduce the
adverse effects of melanin formation, most industries are
interested on inhibitors of the enzyme tyrosinase. On the other
hand, tyrosinase activators with stimulatory effects on
melanogenesis are beneficial for the prevention of hair whitening
and treatment of the hypopigmentation [4]. Currently, there are
some treatments for hypopigmentation diseases, but these
treatments are usually long term, have poor efficacy and
sometimes produce severe side effects. Thus, the search for a
more efficacious and cost-effective therapy is necessary [3,4].
1
(
from Vetec Quimica Fina Ltda, R.J., Brazil and Carlo Erba, Val
de Reuil, France, respectively.
Chalcone (CH) and its fluorinated derivatives (CH3F, CH4F
and CH2356F) were synthesized by aldol condensation reaction
in basic medium [23]: in a 50 mL round bottom flask, an aqueous
-
3
-1
solution of KOH (10%, 2.60x10 gL ) was added to a solution
of ethanol–water (6:4 v/v, 10 ml). Benzaldehyde, or one of the
fluorinated benzaldehydes (5.20 mmol), and acetophenone (279
mg, 2.33mmol) were added in small portions. The reaction
mixture was stirred at low temperature (278K) for 24 h. A yellow
solid was formed for chalcone and a slightly yellow solid for the
fluorinated chalcones. The final mixture was neutralized with
hydrochloric acid (10%). The product was recrystallized three
times from ethanol. Spectroscopic and spectrometric properties
for all synthesized fluorinated chalcones are in full accord with
the proposed structures [24,25]. Recently, the synthesis and
characterization of the samples CH23F, CH25F and CH35F was
already described by our group [22].
One strategy in drug design is the replacement of hydrogen by
fluorine atoms, which can change significantly the
physicochemical and biological properties of
a
drug.
Incorporating fluorine to a molecule makes it more lipophilic, so
it can percolate through a membrane more readily and hence can
show a higher bioavailability [5]. For these reasons great efforts
have been placed on the development and evaluation of
biologically active fluorinated materials [6]. Recently, it has been
demonstrated that synthetic fluorine chalcone derivatives show
high biological activities, such as: analgesic [7], antioxidant [8],
monoamine oxidase-B inhibitor [9-11], antiviral, antiprotozoal
and insecticidal [12].
O
O
O
F
O
F
F
F
F
CH
CH3F
CH23F
CH25F
O
O
F
F
O
Over the past decade, numerous drug delivery systems have
been developed to improve the treatment of different diseases and
disorders. Albumin is the most abundant soluble endogenous
protein in blood plasma. It has been widely studied as a carrier
for drug delivery and has been employed as a non-immunogenic
delivery carrier in various disease therapies [13]. Human Serum
Albumin (HSA) is commonly substituted by Bovine Serum
Albumin (BSA) in laboratory experiments due to the higher
availability and lower cost of the later. The BSA binding capacity
is similar to that of HSA, due the76% identity and 88% similarity
in amino acid sequences [14]. The largest difference between the
two proteins is that HSA has only one tryptophan (Trp-214) in
subdomain IIA, whereas BSA has two tryptophan residues: one
on the surface of the protein in the subdomain IB (Trp-134) and
another in a hydrophobic region in the subdomain IIA (Trp-212)
F
F
F
F
F
CH4F
CH2356F
CH35F
Samples tested with BSA
Samples tested with tyrosinase
Fig. 1:Chemical structure for chalcone and its fluorinated
derivatives: (E)-3-(phenyl)-1-phenylprop-2-en-1-one (CH), (E)-
-(3-fluorophenyl)-1-phenylprop-2-en-1-one (CH3F), (E)-3-(4-
fluorophenyl)-1-phenylprop-2-en-1-one (CH4F), (E)-3-(2,3-
difluorophenyl)-1-phenylprop-2-en-1-one (CH23F), (E)-3-(2,5-
difluorophenyl)-1-phenylprop-2-en-1-one (CH25F), (E)-3-(3,5-
difluorophenyl)-1-phenylprop-2-en-1-one (CH35F) and (E)-1-
3
(
(
phenyl)-3-(2,3,5,6-tetrafluorophenyl)-prop-2-en-1-one
CH2356F).
[
15]. Since serum albumin:drug interactions affect significantly
the apparent distribution and elimination rate of drugs, the study
of interaction between BSA with ligands is extremely important.
2
2
.2. Apparatus and methods
The interaction between plasmatic albumins with chalcone
and some chalcone derivatives was already reported [16-21] and
recently our group was the first to investigate the binding ability
between BSA and di-fluorinated chalcones [22]. In view of the
above background, the goal of the present work is the evaluation
.2.1. Tyrosinase Enzyme Activity
The UV-Vis absorption for tyrosinase in the activity
measurements were performed on
a U V
Shimadz uP ag eV -2 oi sf 10

3
spectrophotometer UV Mini 1240 (Kyoto, Japan) at room
temperature. Tyrosinase inhibition activity was measured by the
method of Amorim et.al [26].
2.2.4. Circular dichroism spectra measurements
CD spectra were obtained using Jasco J-815
spectropolarimeter equipped with Jasco PFD-425S15F
a
a
thermostat system with 0.1 °C accuracy. All spectra were
recorded with appropriate background corrections. BSA
Firstly, (10 mM) stock solutions of CH, CH3F, CH4F and
CH2356F were prepared by dissolving each chalcone in DMSO.
Each of these solutions was diluted in water in the proportion of
-
6
concentration was maintained constant at 1.00x10 M, and the
ligands concentrations were set at varying concentrations (0.39;
1
:5, obtaining a final solution of 2 mM concentration. For each
chalcone solution, 1.5 mL (30 µM) was mixed with L-DOPA
0.17 mM), EDTA (0.022 mM) and tyrosinase (50–100 units) in
-
5
0
.79; 1.57; 3.10x10 M) in 1:0, 1:4, 1:8, 1:16 and 1:32 molar
ratio BSA:ligand. The addition was done manually by using a 10
microliter syringe. CD spectra were measured in the range 200-
(
PBS (pH=7.4). When the tyrosinase solution was added to the
mixture, the absorbance was immediately measured at 475 nm
and the formation of dopachromone monitored during 30 min
2
60 nm, at 298K.
In order to estimate the percentage of the decrease in the α-
(Scheme 1).
helical content upon the ligand binding, the intensity of the CD
signal was expressed as mean residue ellipticity (MRE) which
can be defined according to Equation 2:
O
O
HO
HO
O
O
OH
O
2
/ tyrosinase
OH
NH
2
NH2
EDTA/PBS
θ
pH 7.4 t = 30 min
MRE =
(2)
L-DOPA
Dopaquinone
(10.n.l.CP )
Scheme 1: Oxidation L-Dopa to dopaquinone from tyrosinase
enzyme.
where θ is the observed CD (in milli-degrees), n is the number of
amino acid residues (583 for BSA) [27], l is the path length of the
-
6
cell (in cm) and C is the molar concentration of BSA (1.00x10
p
M). The α-helical content of free and bound with CH, CH3F,
CH4F and CH2356F was calculated from the molar residual
ellipticity (MRE) values at 208 (Eq. 3A) and 222 nm (Eq. 3B)
[28]:
The percent inhibition can be calculated using the Equation 1:
[
(B30 - B A30 A0)]
0) - (
-
Inhibitionor Activation% =
x 100 (1)
(
B30 -
)
0
B
(
- MRE208 - 4000
)
)
(3A)
(3B)
where B and B are the absorbance of L-DOPA + tyrosinase at t
α - helix % =
α - helix % =
x 100
x 100
0
30
(
33000- 4000
)
=
0 min and t = 30 min, respectively. A0 and A30 are the
absorbance of L-DOPA + tyrosinase + inhibitor at t = 0 min and t
30 min, respectively. All experiments were performed in
triplicate, and the results obtained were expressed as mean ± SD.
(
-
MRE222 -2340
=
30300
2
.2.5. Zeta potential measurements
The surface charge of BSA in the absence and in the presence
2
.2.2. Fluorescence experiments
Fluorescence measurements were performed on a Jasco Model
of CH, CH3F, CH4F and CH2356F was characterized in terms of
zeta potential (ZP) using a Brookhaven Instruments NanoBrook
ZetaPALS. All measurements were performed with 10 runs at
J-815 spectrofluorimeter equipped with a 1.0 cm quartz cell and a
Jasco PFD-425S15F thermostat system with 0.1°C accuracy. All
spectra were recorded with appropriate background corrections.
For this study the inner filter correction was not necessary
because at the maximum concentration used of CH, CH3F, CH4F
2
98K and results are reported in terms of ZP ± SD. The ZP was
-5
measured for BSA solution (1.00x10 M in PBS solution, pH =
.4) without the ligands and in the presence of each studied
7
-
6
compound – CH, CH3F, CH4F and CH2356F – at the maximum
and CH2356F (6.70x10 M) the UV-Vis absorption is less than
.1 u.a. at 280 nm and 345 nm (Fig. 1S in supplementary
-6
concentration used in the fluorescence experiments (6.70x10
0
M).
material). The excitation wavelength at 280 nm was selected for
the experiments, and fluorescence spectra were obtained in the
range of 300–440 nm at 288K, 293K and 298K. To a 3.0 mL
solution, containing an appropriate concentration of BSA
2
.2.6. Molecular docking studies
-
5
The crystallographic structure of BSA was obtained from the
(1.00x10 M) at pH 7.4, were added successive aliquots from an
Protein Data Bank (PDB) with access code 4F5S [29]. The CH,
CH3F, CH4F, and CH2356F structures were built and energy-
minimized with the Density Functional Theory (DFT), method
Becke-3-Lee Yang Parr (B3LYP) with the standard 6-31G* basis
set available in the Spartan'14 program (Wavefunction, Inc.).
ethanol stock solution of CH, CH3F, CH4F or CH2356F
-
3
(1.00x10 M). The addition of the ligands was done manually by
using a 10 microliter syringe, and varying concentrations of 0.85;
-
6
1
.60; 2.50; 3.30; 4.20; 5.10; 6.00 and 6.70x10 M. From the
fluorescence quenching results, the modified Stern-Volmer
binding constant (K ) values were obtained.
a
The docking study was performed with the GOLD 5.2
program (CCDC, Cambridge Crystallographic Data Centre).
Hydrogen atoms were added to the protein according to the data
inferred by the program on the ionization and tautomeric states
[30]. In order to identify the most probable binding site of the
ligands in BSA, a 10 Å radius spherical interaction cavity around
each tryptophan residue (Trp-134 and Trp-212) was defined, then
docking calculations with the ligands inside each of these sites
were carried out. The number of genetic operations (crossover,
migration, mutation) in each docking run used in the searching
procedure was set to 100,000. The program optimizes hydrogen-
bond geometries by rotating hydroxyl and amino groups of
2
.2.3. Competitive binding studies
Competitive binding studies were carried out using site probes
for the Trp-134 and Trp-212 containing binding sites (ibuprofen
and warfarin, respectively). BSA and site probes were used at a
-
5
fixed concentration (1.00x10 M), and fluorescence quenching
titration (with CH, CH3F, CH4F, CH2356F) was performed as
described previously in the fluorescence experiments.
Page 3 of 10
amino acid side chains. The scoring function used was

4
O.A. Chaves et al./ Journal of Fluorine Chemistry XXX (2017) XX-XX
'
ChemPLP', which is the default function of the GOLD 5.2
ligands are associated. The same evidence (red shift) was already
observed for chalcone [21], but for the di-fluorinated chalcones
there are no significant indications of perturbation in the
microenvironment around the tryptophan residue [22].
program [31]. The score of each pose identified was calculated as
the negative of the sum of a series of energy terms involved in
the protein-ligand interaction process, so that the more positive
the score, better is the interaction. The figures of the best score
poses were generated with the PyMOL program (DeLano
Scientific LLC).
2.0
1.5
1.0
0.5
2.0
1.5
1.0
0.5
(A)
(B)
2
293K
298K
88K
1.8
1.6
288K
293K
298K
2
.5
2.0
1.4
1.5
1.2
2
.0x10
-6
4.0x10
-6
6.0x10
-6
3
. Results and discussion
-6
4.0x10
-6
6.0x10
-6
[CH3F] (M)
2.0x10
[
CH] (M)
3
.1. Tyrosinase Enzyme Activity
In the literature mono-, di-, tri- and tetra-hydroxy as well as
methoxy chalcones, such as flavokawain A and flavokawain B,
showed inhibition of tyrosinase activity [32,33], however there
are no reports on the effect of the presence of fluorine atoms in
the chalcone moiety upon the tyrosinase activity. Since several
polyphenols are considered as affecting tyrosinase, their activity
as inhibitor or activator will depend on the presence and position
of additional chemical groups in the polyphenol moiety. In other
words, the presence of electron donor groups such as methoxy,
hydroxyl and amine groups suggests that compounds containing
these groups can act as a potential tyrosinase activator [32,33].
inhibition percentage of chalcone (CH) was less than 1% at the
maximum concentration tested (30 µM), indicating that this
compound is not a good tyrosinase inhibitor [33]. On the other
hand, upon fluorine substitution chalcone was able to activate the
catalytic L-DOPA oxidation by the tyrosinase enzyme by 2.31%
300
350
400
450
500
300
350
400
450
500
Wavelength (nm)
Wavelength (nm)
2
.0
2.0
1.5
1.0
0.5
(
C)
288K
293K
298K
(D)
288K
1.8
1.4
293K
298K
1.5
1.5
1.2
1.2
1.0
2
.0x10-6
4.0x10
-
6
6.0x10
-
6
1.0
2.0x10-6
4.0x10-6
6.0x10-6
[CH4F] (M)
[CH2356F] (M)
0.5
3
00
350
400
450
500
300
350
400
450
500
Wavelength (nm)
Wavelength (nm)
Fig. 2. Fluorescence emission spectra for free BSA and its
quenching by CH (A), CH3F (B), CH4F (C) and CH2356F (D) at
298K. Inset: Stern–Volmer plots for the BSA:fluorinated
chalcones interactions in pH = 7.4 at 288K, 293K and 298K.
(CH3F), 4.62% (CH4F), 8.97% (CH23F), 6.92% (CH25F),
7
.21% (CH35F) and 14.1% (CH2356F), respectively. These
-
5
results indicate that the presence of the electronegative fluorine
atom in the chalcone moiety probably can increase the catalytic
capacity of the enzyme on the substrate L-DOPA. It is worth to
note that the increase in the number of fluorine atoms in the
chalcone structure leads to an increase on the enzyme activity.
This is probably due the presence of one to four highly
electronegative fluorine atoms that are able to decrease the
binding ability of chalcone to the binuclear copper of the enzyme
active center [3]. An alternative explanation for the tyrosinase
activation can be found in the work of Solomon, Lerch and
coworkers [34], which showed that copper atoms have to be in
the Cu(I) state to enable molecular oxygen to bind in preparation
for an efficient monooxygenase activity. Therefore, the activation
of the tyrosinase function requires a reduction reaction of the
copper atoms. A way this can be brought about is the use of a
reducing agent such as ascorbate. As the studied compounds
CH3F, CH4F and CH2356F activated the tyrosinase enzyme,
probably these compounds can act as a potential reducing agent,
leading Cu(II) to its reduced form Cu(I) [35]. Although the
fluorinated chalcone derivatives showed some tyrosinase
activation, this activation is much weaker when compared to
other molecules described in the literature, for example
xanthenediones derivatives (4-methoxybenzyl xanthenedione -
[BSA] = 1.00x10 M, [CH] = [CH3F] = [CH4F] = [CH2356F] =
-6
0.85; 1.60; 2.50; 3.30; 4.20; 5.10; 6.00 and 6.70x10 M, λ
=
exc
280 nm.
Fluorescence quenching mechanisms can be divided into two
groups: static and dynamic quenching. In order to differentiate
between these two quenching mechanisms in the interaction of
CH, CH3F, CH4F and CH2356F with BSA, temperature-
dependent fluorescence spectral experiments were conducted at
2
88K, 293K and 298K and the data were analyzed with the
classical Stern–Volmer equation (eq. 4) [40]:
KSV
F0
(A)
(B) kq =
(4)
=
1+kqτ0
[Q
]
=1+KSV
[Q]
τ0
F
where F and F represent the fluorescence intensity values of the
protein sample in the absence and in the presence of the
quencher, respectively; [Q] is the CH, CH3F, CH4F or CH2356F
concentration, KSV is the Stern-Volmer quenching constant, k is
the bimolecular quenching constant and τ is the lifetime of the
0
q
0
-8
fluorophore (tryptophan residue, 10 s) [41] in the absence of
1
73%) [36] and fatty acids (oleic acid – 126%) [37].
quencher.
As can be seen in Table 1, the k values are higher than the
q
9
-1 -1
limiting diffusion rate constant in water (kdiff ≈ 5x10 M s at
3
.2. Fluorescence quenching studies
2
98K) [42], indicating that the main fluorescence quenching
Intrinsic fluorescence quenching of protein was used to
mechanism is static and probably originates from a ground-state
association between the fluorophore and the ligands [39].
However, since the KSV values (Table 1) increase with increasing
temperature and the Stern–Volmer plots shown as insets in Fig.2
are not totally linear, the interaction mechanism between BSA
and CH, CH3F, CH4F and CH2356F is not typically of a static
type, probably having a significant contribution from dynamic
quenching [43,44]. This is probably due the fact that at high
concentrations significant amounts of quencher molecules are
already in close proximity to the fluorophore. The same trend
was observed for interaction between BSA with di-fluorinated
retrieve many drug-protein binding information. Upon excitation
at the wavelength of 280 nm, the two tryptophan residues (Trp-
1
34 and Trp-212) in the BSA structure contribute significantly to
the fluorescence emission [38]. As depicted in Fig. 2, the
addition of CH, CH3F, CH4F and CH2356F to a BSA solution
affects its fluorescence intensity, suggesting that the ligands are
interacting next to the Trp-134 and/or Trp-212 residue [39]. The
slight red shift observed in the maximum of the fluorescence
emission for BSA with successive additions of CH and CH4F
suggests an increase in the hydrophobicity of the
microenvironment around the tryptophan residue to which the
Page 4 of 10
chalcones [21], but for chalcone the dynamic fluorescence

5
quenching mechanism does not have influence in the binding
process [22].
0
0
∆H
∆S
lnK = -
+
a
(6)
RT
R
The tryptophan residues in albumin are not all equally
accessible to quenchers; if part of those fluorophores cannot be
affected by quenchers, a modified Stern-Volmer equation can be
used (Equation 5) [45]:
where T is the temperature (288K, 293K and 298K) and R is the
−
1
−1
gas constant (8.3145Jmol K ). Values for the Gibbs free energy
°
change (∆G ) for the binding interaction was subsequently
°
°
F0
1
1
obtained by fitting the ∆H and ∆S values into the eq. 7 [48]:
=
+
(5)
F0 -F f[Q]Ka
f
0
0
0
∆
G =
∆
H -T
∆S
(7)
where F and F are the steady-state fluorescence intensities in the
0
absence and presence of quencher, respectively; Ka is the
modified Stern-Volmer binding constant; ƒ is the fraction of the
initial fluorescence intensity that corresponds to a fluorophore
that is accessible to the quencher (f ≈ 1.0) and [Q] is the quencher
°
The negative ∆G <0 values show a spontaneous binding process
for BSA:CH, BSA:CH3F, BSA:CH4F and BSA:CH2356F. For
°
°
the fluorinated chalcones, ∆H >0 and ∆S >0 suggest that the
binding ability is entropically driven and the enthalpy change is
unfavorable, but due to the higher contribution of entropy,
(CH, CH3F, CH4F or CH2356F) concentration. The modified
Stern-Volmer plot is represented as Fig. 2S in supplementary
°
°
°
material. As can be seen in Table 1, the K values for fluorinated
∆G <0. On the other hand, for chalcone, ∆H <0 and ∆S >0
indicating that the BSA:CH association is both entropically and
enthalpically driven, suggesting that the presence of fluorine
atoms in the chalcone moiety affects the thermodynamic
parameters of interaction, decreasing the binding ability. The
main interaction forces between molecules and proteins may
include hydrogen bonds, electrostatic, van der Waals and
hydrophobic interactions [49]. According to Ross and
Subramanian [50], the positive enthalpy and entropy change
values for fluorinated chalcones derivatives suggest the dominant
influence of hydrogen bonding and/or hydrophobic forces in the
binding process. On the other hand, for chalcone, the negative
enthalpy and positive entropy change values suggest,
respectively, electrostatic and hydrophobic interactions as
binding forces. A comparison between the binding ability for
CH3F, CH4F and CH2356F and chalcone [21], as well as di-
fluorinated chalcones [22] and a quinoline appended chalcone
derivative [16] shows the same thermodynamic trends, i.e the
binding process is enthalpically unfavorable.
a
4
-1
chalcones derivatives are in the range of 10 M , indicating a
moderate binding affinity in BSA:CH3F, BSA:CH4F and
BSA:CH2356F [22,46]. On the other hand, for chalcone the Ka
values are one order of magnitude higher than for the fluorinated
derivatives, suggesting that the presence of fluorine atoms in the
chalcone moiety decreases the binding ability. However, a
comparison between K values for CH3F and CH4F (Table 1)
a
clearly shows that the fluorine atom location on the phenyl ring
did not result in any difference on the binding ability. The
increase in the K values with the increasing of temperature is
a
due the greater mobility in the protein cavity at 298K, facilitating
the approach of quencher to fluorophore in the required
conformation for the binding process.
°
The thermodynamic parameters (∆H , enthalpy change and
°
∆
S , entropy change) associated with the binding ability between
BSA:CH, BSA:CH3F, BSA:CH4F and BSA:CH2356F were
obtained from van’t Hoff plots (insets in Fig.2S in supplementary
material) applying eq. 6 [47]:
Table 1
The Stern–Volmer quenching constant (K ), bimolecular quenching rate constant (k ), modified Stern-Volmer binding constant (K ),
SV
q
a
enthalpy change (∆H°), entropy change (∆S°) and Gibbs’ free energy change (∆G°) values for the interaction BSA:CH, BSA:CH3F,
BSA:CH4F and BSA:CH2356F at 288K, 293K and 298K.
-1
-1 -1
2
-1
2
-1
-1 -1
-1
2
Sample
T (K)
88
293
K
SV (M )
k
q
(M s )
r
K
a
(M )
r
∆H° (kJmol )
∆S° (kJmol K )
∆G° (kJmol )
r
5
5
5
5
5
5
5
5
5
4
4
4
13
5
5
5
4
4
4
4
4
4
4
4
4
2
(2.67±0.11)x10
(2.70±0.10)x10
(2.78±0.12)x10
(1.33±0.04)x10
(1.35±0.04)x10
(1.36±0.04)x10
(1.37±0.05)x10
(1.38±0.04)x10
(1.39±0.04)x10
(6.17±0.09)x10
(6.34±0.04)x10
(6.69±0.07)x10
2.67x10
2.70x10
2.78x10
1.33x10
1.35x10
1.36x10
1.37x10
1.38x10
1.39x10
6.17x10
6.34x10
6.69x10
0.9878 (1.14±0.09)x10
0.9899 (1.13±0.10)x10
0.9870 (1.12±0.09)x10
0.9944 (5.27±0.07)x10
0.9941 (5.60±0.05)x10
0.9949 (6.06±0.08)x10
0.9922 (6.21±0.04)x10
0.9947 (6.40±0.05)x10
0.9954 (6.63±0.08)x10
0.9985 (4.26±0.09)x10
0.9997 (4.85±0.08)x10
0.9992 (5.39±0.06)x10
0.9980
0.9977
0.9978
0.9987
0.9992
0.9984
0.9991
0.9990
0.9979
0.9983
0.9984
0.9991
-27.2
-27.6
-28.1
-21.8
-22.4
-22.9
-23.5
-24.0
-24.5
-25.5
-26.3
-27.0
13
13
13
13
13
13
13
13
12
12
12
CH
-0.811
9.87
0.0916
0.110
0.9721
0.9853
0.9925
0.9967
2
2
98
88
CH3F
CH4F
293
2
2
98
88
293
4.71
0.0980
0.147
2
2
98
88
CH2356F
293
98
16.8
2
3
.3. Energy transfer from BSA to fluorinated chalcones
Fluorescence resonance energy transfer (FRET) is an
electronic excitation energy of a donor chromophore (Tryptophan
in BSA) is transferred to an acceptor molecule (chalcone and its
fluorinated derivatives) nearby by a dipole-dipole interaction
electrodynamic phenomenon that occurs between a donor
molecule in its excited state and an acceptor molecule in the
ground state. Non-radiative energy transfer occurs when the
[
51]. The energy transfer efficiency (E) can be given by the
equations 8A and 8B [52].
Page 5 of 10

6
O.A. Chaves et al./ Journal of Fluorine Chemistry XXX (2017) XX-XX
The modified Stern-Volmer binding constant (K ) for
BSA:CH, BSA:CH3F, BSA:CH4F and BSA:CH2356F (Table 3
and Fig. 4S in supplementary material) decreased in presence of
both warfarin and ibuprofen at 298K. But the larger decrease in
a
6
6
0
F
R0
R .
(
1- E
)
6
(A) E =1−
=
(B) r =
(8)
6
0
6
F0 R + r
E
K values in the presence of warfarin is a clear indication that
a
where r is the distance between acceptor and donor; R is the
critical distance for transfer efficiency of 50%, which can be
determined by equation 9:
0
CH, CH3F, CH4F and CH2356F bind preferentially to the same
site where warfarin binds (subdomain IIA, Trp-212-containing
binding site) [55]. A similar observation had already been
reported for the case of the interaction between chalcone (CH)
and BSA [21].
6
0
-25
2
-4
R = 8.8x10 K n ΦJ
(9)
Table 3
Modified Stern-Volmer binding constant (Ka) values for
BSA:CH, BSA:CH3F, BSA:CH4F and BSA:CH2356F in the
presence of the site markers ibuprofen and warfarin at 298K and
pH = 7.4.
2
2
where K is the spatial orientation factor of the dipole (K =2/3), n
is the refractive index of the medium (n=1.336), φ is the
fluorescence quantum yield of the donor (BSA) in the absence of
acceptors (CH, CH3F, CH4F and CH2356F) (φ = 0.15) [53] and
J is the overlap integral between the emission spectrum of the
donor and the absorption spectrum of the acceptor; J can be
calculated by equation 10 [51]:
-
1
2
-1
2
Samples
K
a
(M )
r
K
a
(M )
r
Presence of
Ibuprofen
Presence of
warfarin
∞
4
4
4
4
4
4
4
4
4
CH
CH3F
(7.82±0.07)x10
(5.95±0.05)x10
(5.68±0.06)x10
(5.25±0.15)x10
0.9982
0.9994
0.9992
0.9945
(4.94±0.10)x10
(5.30±0.09)x10
(4.69±0.07)x10
(4.97±0.17)x10
0.9977
0.9982
0.9991
0.9950
4
F
(
∞
λ
)
ε
(
λ
)
λ dλ
(
)
(
)
∫
∑
F
λ
ε
λ
λ ∆λ
0
(10)
J =
=
∑
F (λ) ∆λ
F (λ) dλ
CH4F
∫
0
CH2356F
where F(λ) is the fluorescence intensity of the donor at
wavelength λ to λ + ∆λ and ε(λ) is the molar absorptivity of the
acceptor at wavelength λ.
3
.5. Perturbation on the secondary structure of the BSA upon
Figure 3S in supplementary material shows the spectral
overlap between the fluorescence emission spectrum of BSA and
the absorption spectrum of CH, CH3F, CH4F and CH2356F,
indicating that there is a reasonable probability of an energy
transfer process from BSA to chalcone or its fluorinated
derivatives [53]. The calculated values for the distances between
BSA (as donor) and each of the chalcones (as acceptors) (r)
shown in Table 2 is between 2 and 8 nm, in full agreement with
the rule 0.5R < r < 1.5R , confirming the high probability of
ligand binding
Circular dichroism (CD) plays an important role in the study
of protein folding because it allows the characterization of the
secondary structure of proteins in native, unfolded and partially
folded states [56]. Figure 3 shows the CD spectra for free BSA
and for BSA upon the addition of the ligands in different
concentrations. The CD spectra indicate negative bands at 208
nm and 222 nm, that corresponds to π-π* and n-π* transitions,
respectively. These electronic transitions are characteristic of the
peptide bond in the native α-helical protein [40]. The CD spectra
of BSA in presence and absence of chalcone and its derivatives
were observed to be similar in shape and peak position (208 nm
and 222 nm), indicating that the structure of BSA was also
predominantly α-helical even after binding with any of these
ligands [57].
0
0
occurrence of energy transfer between albumin and CH, CH3F,
CH4F or CH2356F [15]. The same probability was detected for
chalcone [21] and the other fluorinated chalcones derivatives
[
22].
Table 2
Energy transfer parameters for the association BSA:CH,
BSA:CH3F, BSA:CH4F and BSA:CH2356F at 298K.
-
13
3
-1
Ligand
CH
J (x10 cm Lmol )
E (%)
59.0
58.5
55.6
52.3
R
0
(nm)
r (nm)
2.90
3.49
3.50
3.32
31.5
6.10
9.40
4.60
3.09
2.99
3.22
2.85
CH3F
CH4F
CH2356F
3
.4. Binding site study
BSA has two tryptophan-containing binding sites, one
containing the Trp-134 and the other the Trp-212 residue. In
order to experimentally define the drug binding site on this
protein, competitive displacement experiments were carried out
for each quencher, using warfarin as a characteristic marker for
subdomain IIA (Trp-212-containing binding site) and ibuprofen
for subdomain IB (Trp-134-containing binding site) [54].
0
0
-20
(A)
(B)
BSA 1:0
BSA 1:0
-
20
BSA:CH 1:4
BSA:CH 1:8
BSA:CH 1:16
BSA:CH 1:32
BSA:CH3F 1:4
BSA:CH3F 1:8
BSA:CH3F 1:16
BSA:CH3F 1:32
-
40
-40
-60
-60
-80
-80
Page 6 of 10
-
100
-100
-120
-120
200
210
220
230
240
250
200
210
220
230
240
250

7
These results clearly indicate that there is no significant structural
change on the protein surface upon the addition of chalcone or its
fluorinated derivatives.
Table 5
Zeta Potential (ζ), conductance and current for free BSA and
BSA:CH, BSA:CH3F, BSA:CH4F, BSA:CH2356F at 298K in
PBS solution (pH = 7.4).
Sample
BSA
ζ (mV)
Conductance (µS)
28063
Current (mA)
150
-7.50±2.08
-8.15±2.77
-8.35±2.22
-10.80±1.18
-7.92±1.86
-10.79±1.95
-8.68±2.09
-10.75±2.04
BSA:CH
BSA
25615
145
27636
149
Fig. 3. Circular dichroism spectra for free BSA and BSA:CH (A),
BSA:CH3F
BSA
28004
150
BSA:CH3F (B), BSA:CH4F (C) and BSA:CH2356F (D) at 298K.
27245
147
-
6
[
BSA] = 1.00x10 M and pH = 7.4.
BSA:CH4F
BSA
26930
145
As can be seen in Table 4, for pure BSA the α-helix %
29236
150
decreased with 4.00%, 4.20%, 1.60%, 3.20% at 208 nm and
.70%, 2.90%, 2.10% and 2.30% at 222 nm after the addition of
2
BSA:CH2356F
29328
150
the maximum concentration of CH, CH3F, CH4F and CH2356F,
respectively, at 298K, indicating again that these ligands do not
affect significantly the hydrogen bond networks of the secondary
structure of BSA. There is a report in the literature which
indicates that the parent chalcone (CH) does affect the secondary
structure of the protein in 13.1% at 208 nm and 298K [21]. On
the other hand, the same trend observed for CH3F, CH4F and
CH2356F was observed for other fluorinated chalcone
derivatives previously published in the literature [22].
3.7. Molecular docking studies
Molecular docking was used to allow a closer look at ligand-
protein interactions and site specific binding amino acid residues.
The BSA structure consists of 583 amino acids with only two
tryptophan residues (Trp-134 and Trp-212). Trp-134 is located
on the surface of the molecule (subdomain IB) and Trp-212 is
located into a hydrophobic pocket (subdomain IIA) [57].
Docking score values show that CH, CH3F, CH4F and CH2356F
interact more favorably in the Trp-212-containing site (Table 6),
in accordance with the competition studies with site markers
warfarin and ibuprofen (Table 3).
Table 4
Content of α-helix % on the secondary structure of BSA upon
interaction with CH, CH3F, CH4F and CH2356F in pH = 7.4 at
2
1
98K in the molar ratio BSA:ligand of 1:0, 1:4, 1:8, 1:16 and
-6
:32. [BSA] = 1.00x10 M, [CH] = [CH3F] = [CH4F] =
Table 6
-
5
[
CH2356F] = 0.39; 0.79; 1.57 and 3.10x10 M.
Best scores (ChemPLP) for CH, CH3F, CH4F and CH2356F in
the BSA Trp-134- and Trp-212-containing binding sites.
CH
CH3F
208
CH4F
208
CH2356F
2
08
222
51.0
50.6
50.1
49.5
48.3
222
51.3
50.8
50.3
49.6
48.4
222
51.9
51.7
51.3
50.8
49.8
208
222
52.8
52.4
52.1
51.6
50.5
Sample
CH
Docking score Trp-134 site
Docking score Trp-212 site
1
1
1
:0
:4
:8
52.7
51.9
50.3
49.9
48.7
52.8
52.1
51.1
50.2
48.6
52.9
52.3
51.7
51.5
51.3
54.1
53.4
53.2
52.0
50.9
45.8
46.9
44.0
46.0
51.7
50.7
49.3
50.0
CH3F
CH4F
1
:16
:32
CH2356F
1
The thermodynamic parameters (Table 1) show that the
association between BSA and all chalcone derivatives is
thermodynamically favorable, with a favorable entropic term
contributing the most part of it. In fact, the enthalpy term is
unfavorable for all fluorinated derivatives; only for chalcone this
term is favorable. This is indicative that for all compounds
hydrophobic interactions play the major role during the
interaction, whereas for chalcone there could be also the
favorable influence of interactions between polar groups, such as
hydrogen bonds.
3
.6. Zeta potential studies
Zeta potential (ZP, ζ) is an useful and feasible parameter to
characterize the surface charge properties of proteins. Changes in
the ZP for a protein can imply in conformational changes on the
protein structure, surface modifications, aggregation of macro-
molecule and/or unfolding/denaturation processes. Therefore, ZP
of a protein can be used as an indicator of protein stability upon
ligand binding [58].
Table 5 shows the ZP for BSA in the absence and in the
presence of each fluorinated chalcone studied in the present
work. The ZP values of BSA before and after addition of the
fluorinated chalcones CH, CH3F, CH4F and CH2356F are the
same inside the experimental error of the measurements [59].
The docking results, however, show some additional details
about the interaction between the ligands and BSA. As depicted
in Fig. 4, CH, CH3F, CH4F and CH2356F have different
distributions in the electrostatic potential map, resulting in some
differences on the binding ability. Thus, the carbonyl group of
Page 7 of 10

8
O.A. Chaves et al./ Journal of Fluorine Chemistry XXX (2017) XX-XX
the CH structure can form a hydrogen bond with the indole group
of Trp-212 residue with a distance of 1.96 Å, whereas the
cinnamoyl group of the ligand is located in a hydrophobic region
of the protein, interacting with Leu-197, Ala-209, Val-342, Leu-
their number, decreases the participation of amino acid residues
in the stabilization of the complex formation.
3
46, Leu-480 and Val-481 (Fig. 5A). The molecular docking
results is also indicative that the aromatic ring attached to the
carbonyl group of the CH structure can interact via electrostatic
forces with the positively-charged guanidinium groups of Arg-
Fig. 4. Electrostatic potential map, dipole vector, dipole moment
and Milliken charge (MC) for CH, CH3F, CH4F and CH2356F.
The structures were built and energy-minimized with Density
Functional Theory (DFT), method Becke-3-Lee Yang Parr
1
94 and Arg-217 residues.
Figure 5B suggests that the oxygen of the carbonyl group of
CH3F is hydrogen bonded with the peptidic NH hydrogen of the
Val-342 residue with a distance of 2.06 Å, whereas the aromatic
ring connected to the carbonyl group can interact with the
hydrophobic Ala-341 and Pro-446 residues. A T-stacking
interaction was detected between the cinnamoyl group of this
ligand and the Trp-212 residue, with a distance of 2.21 Å, and the
presence of a fluorine atom in the meta position of the aromatic
ring results in a region that can interact via electrostatic forces
with the guanidinium group of the Arg-194 residue. On the other
hand, the presence of a fluorine atom in the para position of the
aromatic ring (Fig. 5C) results in an inversion of the ligand inside
the binding site, and the fluorine-substituted ring is now involved
in hydrophobic interactions with Ala-341 and Val-342, whereas
the guanidinium group of Arg-194 interacts via electrostatic
forces with the electron-rich aromatic ring attached to the
carbonyl group. At same time, a T-stacking interaction was
detected between this aromatic ring and the Trp-212 residue. The
oxygen of the carbonyl group of CH4F is hydrogen bonded to the
Arg-217 side chain with a distance of 2.10 Å.
(
B3LYP) with the standard 6-31G* basis set, available in the
Spartan'14 program (Wavefunction, Inc.). Elements colors:
carbon, oxygen, fluorine and hydrogen are represented in black,
red, yellow and white, respectively.
Finally, Fig. 5D indicates that the presence of four fluorine
atoms in the aromatic ring of CH2356F results in practically the
same binding profile as CH3F regarding the cinnamoyl group.
The Trp-212 residue interacts via T-stacking with a distance of
2
.40 Å, the guanidinium groups of Arg-194 and Arg-217 residues
interacts via electrostatic forces and the oxygen of the carbonyl
group of CH2356F is hydrogen bonding with the peptidic NH
hydrogen of the Val-342 residue with a distance of 2.00 Å,
whereas the aromatic ring connected to the carbonyl group can
interact with the hydrophobic Ala-341 and Pro-446 residues.
Fig. 5. Representation of the main amino acids residues that
interacts with CH (A), CH3F (B), CH4F (C) and CH2356F (D) in
the Trp-212-containing binding site (ChemPLP function). The
ligands are represented in pink, green color is the BSA structure,
selected hydrophobic and hydrophilic amino acids residues are
represented in beige and yellow, respectively.
Overall, the computational results suggest that chalcone can
interact with a larger number of amino acid residues than its
fluorinated derivatives. Fluorinated chalcones (CH2356F and
CH3F) did not show a significant change in the type of
interaction between the amino acid residues and the ligand
structure.
4. Conclusions
In the literature, there are no reports at a molecular level
explanation on the chalcone binding [21], but the molecular
docking results for di-fluorinated chalcone derivatives showed
that the Trp-212 residue is the main chemical group stabilizing
the complex formation between BSA and CH25F or CH35F (for
CH23F there is also a high contribution from Ser-343) [22]. For
the investigated fluorinated chalcones derivatives (CH3F, CH4F
and CH2356F) the molecular docking results suggest that the
presence of fluorine atoms in the chalcone moiety, regardless of
The literature shows that polyhydroxylated chalcones can
inhibit the tyrosinase enzymatic activity and the present work
reports that fluorinated derivatives have the opposite effect. Thus,
they can accelerate the production of melanin and can have a
potential use to be explored against localized depigmentation
processes. Chalcone and its fluorinated derivatives show a
combination of static and dynamic quenching mechanisms on
BSA fluorescence. In addition FRET mechanism can occurs with
high probability. For CH the K values are higher than for CH3F,
a
CH4F and CH2356F, indicating that the presence of fluorine
atoms decrease the binding ability to albumin. This evidence can
be confirmed from the more favorable thermodynamic
parameters for CH than for the fluorinated chalcones. In all cases
the binding is spontaneous (∆G°<0) and does not affect
significantly the secondary structure of the protein. The zeta
potential results suggest that the studied compounds do not affect
significantly the structure and potential surface of the protein.
The binding site study clearly indicated that the main binding
pocket for the samples is Trp-212-containing binding site. The
Page 8 of 10

9
2
2
2. L.S. Barros, O.A. Chaves, E. Schaeffer, C.M.R. Sant’'Anna,
A.B.B. Ferreira, D. Cesarin-Sobrinho, F.A. Silva, J.C. Netto-
Ferreira. J. Fluorine Chem. 190 (2016) 81-88.
3. E.P. Kohler, H.M. Chadwell, Org. Synth. Coll.; John Wiley: New
York, 1932, Vol I, p. 78.
largest docking score values also suggest the same binding site.
Molecular docking results suggested that CH can interact with a
larger number of amino acid residues than its fluorinated
derivatives, explaining the more favorable experimental enthalpy
change value (∆H<0) for the former.
24. D. Cesarin-Sobrinho, J.C. Netto-Ferreira, Quim. Nova, 24 (2001)
04-611.
5. D. Cesarin-Sobrinho, J.C. Netto-Ferreira, Quim. Nova, 25 (2002)
2-68.
6
2
2
2
2
6
6. A.P.O. Amorim, M. C.C. de Oiveira, T. A. Amorim, A.
Echevarria, Antioxidants. 2 (2013) 90-99.
7. X. Ma, J. Yan, K. Xu, L.Guo, H. Li. Bioorg. Chem. 66 (2016)
102-110.
8. A. Rogozea, I. Matei, I.M. Turcu, G. Ionita, V.E. Sahini, A.
Salifoglou, J. Phys. Chem. B. 116 (2012) 14245-14253.
9. A. Bujacz, Acta Cryst. D68 (2012) 1278-1289.
0. G. Jones, P. Willett, R.C. Glen, A.R. Leach, R. Taylor, J. Mol.
Biol. 267 (1997) 727-748.
Acknowledgements
The authors gratefully acknowledge the financial support from
the Brazilian agencies: Coordenação de Aperfeiçoamento de
Pessoal de Nível Superior (CAPES), Conselho Nacional de
2
3
Desenvolvimento Científico
Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro
FAPERJ). A special acknowledgement is given to M.Sc. Paloma
Wetler Meireles and Prof. Dr. Lucio Mendes Cabral from
Laboratório de Tecnologia Industrial Farmacêutica
LabTIF/UFRJ) for making available the zeta potential facilities
e
Tecnológico (CNPq) and
(
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Page 9 of 10

10
O.A. Chaves et al./ Journal of Fluorine Chemistry XXX (2017) XX-XX
Graphical Abstract - Synopsis
Fluorinated chalcone derivatives are tyrosinase
activators. Thus, they might accelerate the
production of melanin, having a potential use to be
explored
against
localized
depigmentation
processes. The presence of fluorine atoms decreases
the binding ability to albumin. This evidence can be
confirmed from the more favorable thermodynamic
parameters for chalcone than for the fluorinated
derivatives. The binding does not affect
significantly the secondary structure of the protein.
The main binding pocket for the samples is site I.
Molecular docking results suggested that CH can
interact with a larger number of amino acid
residues than its fluorinated derivatives, explaining
the more favorable experimental enthalpy change
value (∆H<0).
Graphical Abstract
Page 10 of 10