Synthesis and evaluation of chalcone derivatives as novel sunscreen agent

Article abstract of DOI:10.3390/molecules26092698

Ultraviolet (UV) irradiation is a serious problem for skin health thus the interest in the research to develop sunscreen agent has been increasing. Chalcone is a promising compound to be developed as its chromophore absorbs in the UV region. Therefore, in

Full text of DOI:10.3390/molecules26092698

molecules
Article
Synthesis and Evaluation of Chalcone Derivatives as Novel
Sunscreen Agent
Lucia Wiwid Wijayanti 1,2, Respati Tri Swasono 1, Wonkoo Lee 3 and Jumina Jumina 1,
*
1
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada,
Sekip Utara, Bulaksumur, Yogyakarta 55281, Indonesia; lwijayanti@usd.ac.id (L.W.W.);
respati@ugm.ac.id (R.T.S.)
Chemistry Education Department, Kampus III Paingan, Universitas Sanata Dharma,
Yogyakarta 55281, Indonesia
2
3
Department of Chemistry, Sogang University, Seoul 04107, Korea; wonkoo@sogang.ac.kr
Correspondence: jumina@ugm.ac.id
*
Abstract: Ultraviolet (UV) irradiation is a serious problem for skin health thus the interest in the
research to develop sunscreen agent has been increasing. Chalcone is a promising compound to
be developed as its chromophore absorbs in the UV region. Therefore, in the present work, we
synthesized eight chalcone derivatives through Claisen–Schmidt condensation at room temperature.
The evaluation of the optical properties of each chalcone derivatives in the UV region was conducted
through spectroscopic and computational studies. The synthesized chalcones were obtained in good
yields and they were active in the UV region. The results revealed that more methoxy substituents
to chalcone leads toward red shift. All chalcone derivatives have high molar absorptivity value
(21,000–56,000) demonstrating that they have the potential to be used as the sunscreen agent. The
cytotoxicity assay showed that chalcone derivatives were demonstrating low toxicity toward normal
human fibroblast cell, which is remarkable. Therefore, we concluded that the synthesized chalcones
in this work were potential to be developed as novel sunscreen agents in real application.
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Citation: Wijayanti, L.W.; Swasono,
R.T.; Lee, W.; Jumina, J. Synthesis and
Evaluation of Chalcone Derivatives
as Novel Sunscreen Agent. Molecules
2021, 26, 2698. https://doi.org/
10.3390/molecules26092698
Keywords: chalcone; synthesis; UV-activity; cytotoxicity; sunscreen
1. Introduction
Academic Editors: David Díez and
María Ángeles Castro
Sunlight provides many benefits for human health; however, sunlight can also gen-
erate negative effects. Several studies reported the adverse effects of ultraviolet (UV)
irradiation in sunlight exposure. One of the oxidative stress indicators, the concentration
of free radical in peripheral blood, was observed to be increasing in workers on Tuscany
Received: 8 April 2021
Accepted: 30 April 2021
Published: 4 May 2021
during the period of maximum solar UV irradiance [
Emerging and Newly Identified Health Risks (SCENIHR) found that UV irradiation is
a physical factor that initiates and promotes cancer disease [ ]. Research on TP53 muta-
tions provided strong evidence of a role for solar radiation in generating the etiology of
squamous cell carcinoma of the conjunctiva [ ]. UV irradiation is epidemiologically and
molecularly linked to the three types of skin cancer, basal cell carcinoma, squamous cell
carcinoma, and malignant melanoma diseases [ ]. Another study reported an increment
of reactive oxygen intermediates and inflammatory mediator due to UV-B light exposure
inducing oxidative stress in primary cultures of mouse keratinocytes [ ]. Mitochondrial
damage of human dermal cells was also observed after exposure to artificial sunlight [ ].
From in vitro and in vivo studies, UV–visible irradiation at boundary region (385–405 nm)
significantly damaged skin cells and formed dark cyclobutene-pyrimidine dimers [ ]. UV
irradiation also plays a direct mutational role in promoting melanoma and oncogene in-
duction as well as an indirect role through micro-environmental alterations in mouse [ ].
1]. The Scientific Committee on
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Copyright:
© 2021 by the authors.
6
Licensee MDPI, Basel, Switzerland.
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distributed under the terms and
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4.0/).
7
8
Therefore, the protection of human skin from direct exposure to UV irradiation shall be
carefully considered.
Molecules 2021, 26, 2698. https://doi.org/10.3390/molecules26092698
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 2698
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Sunscreen agents are critical products employed as photo-protectants against harm-ful
UV rays. Higher peoples’ awareness of the risk of continuous exposure to the sun and
its relation to cancer has increased the demand for effective sunscreen agents [9]. Clinical
results on erythema and HbO2 content indicated that better sunburn protection could be
achieved by using the SPF 100% sunscreen [10]. Following melanoma genetic assay on hu-
man population reported that daily routine usage of sun protection behavior within 2 years,
decreased the number of sunburn cases [11]. Inorganic sunscreens are materials that scatter
and reflect UV rays away from the protected area [9,12]. The most commonly used partic-
ulate sunscreens are titanium dioxide (TiO2) and zinc oxide (ZnO); however, their photo
corrosion property makes their application is limited [13]. Meanwhile, plant extracts have
been also evaluated as the subject of sunscreen studies [14–19]. However, their sunscreen
activities are not satisfying due to the low concentration of the extracted compounds.
On the other hand, organic sunscreens generally consist of aromatic compounds
linked with a carbonyl group. They are broadly classified into three categories based on
the range of protection; UV-B (290–320 nm) and UV-A (320–400 nm), and broad-spectrum
sunscreens that cover the entire spectrum (290–400 nm). The commonly used organic
sunscreen agents are para-aminobenzoic acid (PABA), benzophenones, and ethylhexyl-
methoxycinnamate derivatives [20
needs to be improved.
–22]. However, their efficacy as the sunscreen agent still
It is reported that the chalcone derivatives absorb light in the UV region. The UV
spectrum of chalcones consists of two essential absorption bands, i.e., band I and II as
ma-jor and minor bands, respectively. Band I of chalcones usually appears at 220–270 nm,
while band II appears at 340–390 nm. To be more specific, trans-Chalcones yield band I
and II near 230 and 300 nm, in which the intensity of band II is much stronger than band
I [23
–
26]. These bands are generated from n → π * and π → π * electronic transitions [25].
These electronic transitions offer a promising application as the sunscreen agent as chal-
cone derivatives can absorb the UV light before reaching the human skin. Furthermore,
sunscreen agent based on chalcone derivatives is possible to develop for large-scale com-
mercial production as chalcones can be easily synthesized by reacting benzaldehyde and
acetophenone derivatives through a Claisen-Schmidt condensation reaction under the
alkaline condition as shown in Scheme 1 [27–35].
Scheme 1. General reaction of chalcone synthesis.
2. Results and Discussion
2.1. Synthesis of Chalcone Derivatives
In this work, we synthesized eight chalcone derivatives and evaluated them as the sun-
screen agent (Figure 1). In this research, the synthesis of chalcone derivatives was carried by
using readily available starting materials, such as acetophenone, 4-methoxyacetophenone,
3,4,5-trimethoxyacetophenone, piperonal, 4-methoxybenzaldehyde (p-anisaldehyde), and
1-indole-3-carboxaldehyde (see Figure 1) in the one-pot reaction at room temperature,
which in turn considered to be efficient reactions. The Claisen-Schmidt condensation
reaction is a general organic reaction to obtain chalcone derivatives in medium to high
yield. During this reaction, the hydroxide base attracts
derivatives to form enolate anions (carbanions). The carbanion attacks the carbonyl of
benzaldehyde derivatives generating -hydroxy carbonyl intermediates. This intermediate
spontaneously produced chalcone under the acidic condition [26].
α-hydrogen from acetophenone
β

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Figure 1. Chemical structure of chalcones 1–8.
Because of that, the success of the reaction can be easily monitored from the disap-
pearance of C–H aldehyde and the appearance of the C=C alkene functional group. As an
example, the absorption signals at 2850 and 2750 cm−1 of C–H aldehyde were absent on
the FTIR spectrum of compound
on the FTIR spectrum of chalcone
1
. On the other hand, an absorption signal at 984 cm−1
1
was found due to the presence of C=C alkene in trans
geometry. From the 1H-NMR data, the C–H aldehyde signal at 9.79 ppm was absent in
the 1H-NMR spectrum of compound 1 while the protons of C=C trans were found at 7.39
and 7.72 ppm as doublet signals with the coupling constant of 15.6 Hz. Furthermore, the
13C-NMR data of chalcone
confirming that chalcone
1
shows carbon signals at 125.3 and 148.4 ppm for C=C trans
1
has been successfully synthesized. The other chalcone deriva-
tives have been also obtained in 62.0–98.0% yield. Afterward, the synthesized compounds
were evaluated through spectroscopic experiment as well as computational studies to know
their potential application as sunscreen agents.
(E)-3-(benzo[d][1,3]dioxol-5-yl)-1-phenylprop-2-en-1-one (1)
Yield 98.0%. Yellow solid. FTIR:
(C=O), 1486 & 1559 (aromatic C=C), 1105 (C–O–C), 984 (C=C trans). H-NMR (CDCl3)
ν
max/cm−1: 3030 (C–H sp2), 2922 (C–H sp3), 1658
1
δ/ppm: 6.04 (s, 2H, -OCH2O-), 6.86 (d, 1H, J = 8.00 Hz, Ar–H), 7.14 (d, 1H, J = 8.00 Hz,
Ar–H), 7.18 (s, 1H, Ar–H), 7.39 (d, 1H, J = 15.2 Hz, C=C trans), 7.50 (t, 2H, J = 8.00 Hz, Ar–H),
7.58 (t, 1H, J = 8.00 Hz, Ar–H), 7.72 (d, 1H, J = 15.6 Hz, C=C trans), 7.99 (d, 2H, J = 8 Hz,
Ar–H). 13C-NMR (CDCl3)
δ/ppm: 101.6 (-OCH2O-), 125.3 & 148.4 (C=C trans), 190.4 (C=O),
106.6, 108.7, 120.1, 128.4, 128.6, 129.3, 132.7, 138.4 (C aromatics). Mass spectrum (ESI): m/z
calcd. 252.26; found 253.08 [M+].
(E)-3-(4-methoxyphenyl)-1-phenylprop-2-en-1-one (2)
Yield 96.0%. Pale-yellow solid. FTIR:
1684 (C=O), 1511 (aromatic C=C), 1171 (C–O–C), 984 (C=C trans). H-NMR (CDCl3)
ν
max/cm−1: 3010 (C–H sp2), 2955 (C–H sp3),
1
δ/ppm:
3.86 (s, 3H, -OCH3), 6.95 (d, 2H, J = 8.4 Hz, Ar–H), 7.40 (d, 1H, J = 15.6 Hz, C=C trans),
7.51 (t, 2H, J = 7.6 Hz, Ar–H), 7.58 (q, 3H, J = 8.4 Hz, Ar–H), 7.81 (d, 1H, J = 15.6 Hz, C=C
trans), 8.02 (d, 2H, J = 7.6 Hz, Ar–H). 13C-NMR (CDCl3)
δ/ppm: 55.61 (-OCH3), 123.9 &
144.9 (C=C trans), 190.8 (C=O), 113.8, 114.5, 119.9, 127.8, 128.6, 128.7, 129.0, 130.4, 131.8,
132.7, 138.7 (C aromatics). Mass spectrum (ESI): m/z calcd. 238.28; found 239.08 [M+].

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(E)-3-(1H-indol-3-yl)-1-phenylprop-2-en-1-one (3)
Yield 62.0%. Light-brown solid. FTIR:
(C=O), 1516 & 1438 (aromatic C=C), 1105 (C–O–C), 994 (C=C trans). H-NMR (DMSO-d6)
ν
max/cm−1: 3165 (NH), 3039 (C–H sp2), 1625
1
δ
/ppm: 7.23 (m, 6H, -OCH3), 7.49 (d, 2H, J = 8.4 Hz, Ar–H), 8.09 (d, 2H, J = 8.4 Hz, Ar–H),
8.29 (s, 2H, Ar–H), 9.93 (s, 2H, Ar–H), 12.13 (s, 1H, NH). 13C-NMR (DMSO-d6)
δ/ppm:
112.8 & 124.6 (C=C indole), 123.9 & 138.9 (C=C trans), 185.4 (C=O), 118.6, 121.2, 121.3, 122.6,
137.5 (C aromatics). Mass spectrum (ESI): m/z calcd. 247.29; found 248.16 [M+].
(E)-3-(benzo[d][1,3]dioxol-5-yl)-1-(4-methoxyphenyl)prop-2-en-1-one (4)
Yield 94.0%. Light-yellow solid. FTIR:
1652 (C=O), 1581 & 1496 (aromatic C=C), 1235 (C–O–C), 992 (C=C trans). H-NMR (CDCl3)
ν
max/cm−1: 3063 (C–H sp2), 2965 (C–H sp3),
1
δ/ppm: 3.89 (s, 3H, -OCH3), 6.03 (s, 2H, J = 7.15 Hz, -OCH2O-), 6.86 (d, 1H, J = 8.00 Hz,
Ar–H), 6.98 (t, 2H, J = 7.2 Hz, Ar–H), 7.12 (d, 1H, J = 6.8 Hz, Ar–H), 7.17 (s, 1H, Ar–H), 7.41
(d, 1H, J = 15.2 Hz, C=C trans), 7.75 (d, 1H, J = 15.2 Hz, C=C trans), 8.02 (m, 2H, Ar–H).
13C-NMR (CDCl3)
δ/ppm: 55.63 (-OCH3), 101.7 (-OCH2O-), 125.9 & 148.2 (C=C trans),
187.3 (C=O), 106.9, 108.6, 114, 119.9 129.4, 130.6, 130.9, 143.3, 149.5, 163.2 (C aromatics).
Mass spectrum (ESI): m/z calcd. 282.29; found 283.18 [M+].
(E)-1,3-bis(4-methoxyphenyl)prop-2-en-1-one (5)
Yield 95.0%. Pale-yellow solid. FTIR: ν
max/cm−1: 3070 (C–H sp2), 2966 (C–H sp3),
1654 (C=O), 1591 & 1589 (aromatic C=C), 1165 (C–O–C), 985 (C=C trans). 1H-NMR
(CDCl3) δ/ppm: 3.86 (s, 3H, -OCH3), 3.89 (s, 3H, -OCH3), 6.97 (m, 4H, Ar–H), 7.45 (d, 1H,
J = 15.6 Hz, C=C trans), 7.61 (d, 2H, J = 8.8 Hz, Ar–H), 7.85 (d, 1H, J = 15.6 Hz, C=C trans),
8.05 (d, 2H, J = 7.6 Hz, Ar–H). 13C-NMR (CDCl3)
δ/ppm: 55.37 & 55.46 (-OCH3), 127.7
& 143.7 (C=C trans), 188.7 (C=O), 113.7, 114.3, 119.5, 130.1, 130.7, 131.3, 161.5, 163.2 (C
aromatics). Mass spectrum (ESI): m/z calcd. 268.31; found 269.16 [M+].
(E)-3-(1H-indol-3-yl)-1-(4-methoxyphenyl)prop-2-en-1-one (6)
Yield 65.0%. Yellow solid. FTIR:
ν
max/cm−1: 3165 (NH), 3040 (C–H sp2), 2928 (C–H
sp3), 1628 (C=O), 1519 (aromatic C=C), 1119 (C–O–C), 982 (C=C trans). H-NMR (DMSO)
1
δ
/ppm: 2.45 (s, 3H, -OCH3), 6.52 (d, 3H, J = 8.00 Hz, Ar–H), 7.23 (m, 6H), 8.09 (d, 2H,
J = 7.24 Hz), 8.28 (s, 3H, Ar–H), 9.93 (s, 3H, Ar–H). 13C-NMR (DMSO)
δ/ppm: 30.73
(-OCH3), 118.2 & 124.1 (C=C indole), 123.5 & 138.5 (C=C trans), 185.0 (C=O), 120.8, 122.2,
137.1 (C aromatics). Mass spectrum (ESI): m/z calcd. 277.32; found 279.16 [M+].
(E)-3-(benzo[d][1,3]dioxol-5-yl)-1-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (7)
Yield 98.0%. Yellow solid. FTIR:
(C=O), 1574 & 1491 (aromatic C=C), 1118 (C–O–C), 991 (C=C trans). H-NMR (CDCl3)
ν
max/cm−1: 3012 (C–H sp2), 2934 (C–H sp3), 1654
1
δ
/ppm: 3.93 (m, 12H, -OCH3), 6.04 (s, 2H, -OCH2-), 6.87 (d, 1H, J = 8.00 Hz, Ar–H),
7.15 (d, 1H, J = 8.00 Hz), 7.18 (s, 1H, Ar–H), 7.30 (d, 1H, J = 15.2 Hz, C=C trans), 7.77
(d, 1H, J = 15.2 Hz, C=C trans). 13C-NMR (CDCl3)
/ppm: 56.34 & 60.96 (-OCH3), 101.6
δ
(-OCH2O-) 125.3 & 148.4 (C=C trans), 189.1 (C=O), 105.9, 106.6, 108.7, 119.65, 129.3, 133.7,
142.3, 144.6, 149.9, 153.1 (C aromatics). Mass spectrum (ESI): m/z calcd. 342.34; found
343.16 [M+].
(E)-3-(4-methoxyphenyl)-1-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (8)
Yield 71.0%. Pale-yellow solid. FTIR:
1654 (C=O), 1568 & 1506 (aromatic C=C), 1119 (C–O–C), 978 (C=C trans). 1H-NMR
(CDCl3) /ppm: 3.86 (s, 3H, -OCH3), 3.94 (s, 3H, -OCH3), 3.95 (s, 6H, -OCH3), 6.96 (d, 2H,
J = 8.80 Hz, Ar–H), 7.25 (d, 2H, Ar–H), 7.38 (d, 2H, J = 15.6 Hz, C=C trans), 7.63 (d, 2H,
J = 8.80 Hz, Ar–H), 7.82 (d, 1H J = 15.2 Hz, C=C trans). 13C-NMR (CDCl3)
/ppm: 55.24,
ν
max/cm−1: 3006 (C–H sp2), 2942 (C–H sp3),
δ
δ
56.17 & 60.79 (-OCH3), 127.4 & 142. (C=C trans), 189.1 (C=O), 105.5, 105.7, 108.7, 114.2,
119.2, 130.5, 133.6, 144.5, 152.9, 161.5 (C aromatics). Mass spectrum (ESI): m/z calcd. 328.4;
found 329.25 [M+].

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2.2. UV Absorbance Profile of Chalcone Derivatives
UV spectroscopy measurement of chalcone derivatives
1
–8
was conducted in order to
characterize their optical properties in the UV region (200–400 nm), such as cut off wave-
length (λcut off), maximum wavelength ( max), and molar extinction coefficient ( ). Table 1
also lists the λcut off of chalcone derivatives . The result of λcut off measurement showed
λ
ε
1–8
that the empirical λcut off was obtained in a smaller wavelength region in comparison to
that of theoretical prediction. This difference is possibly attributed to solvent interference
in the experimental and computational studies.
Table 1. Comparison of empirical experimental and theoretical data of UV–vis absorbance profile of chalcones 1–8.
Experimental
Theoretical
Chalcone
−1
−1
−1
−1
λ
(nm)
ε (L mol cm
)
λcut off (nm)
λ
(nm)
max
ε (L mol cm
)
λcut off (nm)
max
269
363
-
-
405
277
866
192
397
160
473
211
302
152
241
156
262
185
286
153
497
34,720
56,400
47,500
33,840
46,400
21,400
21,600
32,080
27,627
45,473
31,282
25,753
49,405
29,139
23,529
38,716
1
2
3
4
5
6
7
8
426
306
406
-
326
-
415
-
398
-
506
221
276
209
323
235
253
166
190
171
196
199
213
183
319
352
265
299
258
363
258
349
259
299
258
367
257
355
324
-
418
-
405
Figure 2 shows that more methoxy substitutions to the chalcones lead to the shift
toward higher wavelength. These results suggested that the presence of the methoxy
group as an electron-donating group stabilized the electron delocalization in the chalcone
structure. This phenomenon in experimental is consistent with the results of computational
study (see Figure 3 and Table 1).
Figure 2. Experimental UV–vis spectra of synthesized chalcone derivatives 1–8.

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Figure 3.
Theoretical UV–vis spectra of synthesized chalcone derivatives
1
–8
from the
computational study.
The
ε value of chalcone derivatives 1–8 was obtained in high molar absorptivity
value (21,000–56,000). Again, this fact is consistent with the result of the predicted molar
extinction coefficient using theoretical computation which showed that the molar extinction
coefficient of chalcone derivatives
phenomenon is possibly attributed to
gave high absorptivity in the UV region. It is promising that chalcone derivatives
the potential to be used as sunscreen agent. The and values of compound
max = 340 nm, = 19,000 in CHCl3)
1–
8
π
was obtained in the range of 20,000–48,000. This
* excitation thus that chalcone derivatives
have
(Table 1
–π
1–8
1–8
2
λ
max
ε
in DMSO) is different from the previously reported (
λ
ε
due to different solvent media or as known as the solvatochromic effect [36].
2.3. Cytotoxicity Assay
Figure 4 shows the cytotoxicity assay of a series chalcone 1–8. Cytotoxicity was
tested by WST assay toward normal human fibroblast cells (HDFn). In the WST assay, the
quantity of formazan (presumably directly proportional to the number of viable cells) is
measured by recording changes in absorbance using a plate reading spectrophotometer.
Viable cells with active metabolism convert tetrazolium compound into purple-colored
formazan product. When cells died, they lose the ability to convert tetrazolium compound
into formazan, thus color formation serves as a useful and convenient marker of only the
viable cells. WST reagents were reported as one of the more recently developed tetrazolium
reagents that can be reduced by viable cells to generate formazan products that are directly
soluble in cell culture medium. These improved tetrazolium reagents eliminate a liquid
handling step during the assay procedure because the second addition of reagent to the
assay plate is not needed to solubilize formazan precipitates, thus making the protocols
more convenient [37].
Cell viability was expressed as percentage of the control. Values are mean
deviation (SD) of three separate experiments, with three wells each. The result showed that
the percentages of living human fibroblast cell were higher than 50% under treatment of
±
standard
50 ppm of chalcones. Chalcones
100% of the percentage of living cells) from the cytotoxicity assay. All compounds
and have one methoxy functional groups showing that chalcones having one methoxy
group are not toxic for human fibroblast cells.
2, 3, 4, and 6 are the most promising candidates (about
2, 3, 4,
6

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Figure 4. Cell viability (%) upon treatment with chalcone (1–8) in concentration of 50 ppm.
3. Materials and Methods
3.1. Materials
Chemical reagents in this work are KOH, acetophenone, 4-methoxyacetophenone,
3,4,5-trimethoxyacetophenone, piperonal (3,4-(methylenedioxy)benzaldehyde), 4-methoxy-
benzaldehyde (p-anisaldehyde), 1-indole-3-carboxaldehyde, dimethyl sulfoxide (DMSO),
ethanol, methanol, dichloromethane, ethyl acetate, and n-hexane. All reagents and solvents
were commercially available in pro analytical grade.
For the cytotoxicity assay, the cells and reagents used were Human Neonatal Dermal
Fibroblasts (HDFn, PCS-201-010, American Type Culture Collection (ATCC), Manassas,
VA, USA), WST reagent EZ-CYTOX (from DoGenBio Co., Ltd., Seoul, Republic of Korea),
96-well plate, Dulbecco’s modified Eagle’s medium (DMEM), Fetal Bovine Serum (FBS),
and antibiotics (penicillin and streptomycin).
3.2. Instruments Analysis
1
The H- and 13C-NMR spectra of synthesized compounds were recorded using
NMR spectroscopy (Varian-NMR VNMRS-400) 400 MHz (1H) and 100 MHz (13C) spec-
trometers) in CDCl3 and DMSO-d6 with TMS as the internal standard. FTIR spectra
of synthesized compounds were recorded using an FTIR spectrophotometer Shimadzu
Spirit. The purity and mass spectra of the synthesized products were characterized by
liquid-chromatography-mass spectrometer (ESI-Iontrap Mass Spectrometer LTQ XL model,
Thermo Fischer Scientific, San Jose, CA, USA). Reaction and purity test were monitored
through a thin-layer chromatography (TLC) on aluminum sheets silica gel 60 F254 plates
(Merck) with an UV lamp (Camag, Muttenz, Switzerland) at 254 nm as a detecting unit
(eluent: n-hexane/ethyl acetate in 2:4 ratio). The UV spectra were measured by double
beam UV–vis spectrophotometer Shimadzu UV 1800 (Shimadzu Corp., Kyoto, Japan).
3.3. General Procedure Synthesis of Chalcone Derivatives
The cold solution of 0.893 g KOH (0.01 mol) in 6.5 mL of distilled water was added
dropwise into a solution of 3.65 mmol of acetophenone derivatives in 3 mL of ethanol. A
total of 3.65 mmol of benzaldehyde derivatives in 3 mL of ethanol was then introduced
into the mixture and the mixture was stirred at room temperature. The mixture was
then cooled in an ice bath. The formed solid product was filtered, recrystallized from
methanol, and dried. The purity and product characterizations were performed using TLC
(dichloromethane:n-hexane = 4:1), FTIR spectrometry, MS, 1H-, and 13C-NMR.

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3.4. Determination of the UV–Vis Absorbance Profile of Chalcone Derivatives
The UV–vis spectroscopy measurement was recorded using a UV–vis spectrophotome-
ter to obtain the absorbance profile including λcut off max, and values. The optimization
of concentration was conducted by preparing three concentrations of each synthesized
compound in 25
100, 25 10−2, and 25 10−4 mM. The UV–vis spectra of these three
,
λ
ε
×
×
×
samples of each synthesized compound were recorded in the range of 200–400 nm using a
1 cm quartz cuvette with DMSO as the blank solution. The concentration that produced a
smooth line curve was selected for further measurement and calculation of λcut off
and ε values. The ε value was determined by Equation (1).
,
λ
max
,
A = l × ε × c
(1)
where, A= absorbance, l = length of cuvette,
c = concentration (M).
ε
= molar absorptivity (M−1 cm−1),
3.5. Computational Study
For UV spectrum analysis, Gaussian09 was chosen to perform a geometry optimization
of chalcones molecule with time dependent-density functional theory (TD-DFT) method
for accurate calculation of ground and excitation state. This method was supported with
6-31G(d,p)/PBEPBE basis set, additional orbital (d,p) for extra polarization function to
increase
λ
max
by 1. Microsolvation was performed with chalcones and DMSO as solute
and solvent, respectively. The solvent effect played an important role in spectra absorption
of chalcone, so the type of solvent is crucial. Polarizable continuum model (PCM) was
chosen to deal with the solvent effect where solvent makes a cavity for the solute to take
the position. The bandgap, HOMO and LUMO energies were determined to predict
chalcones conductivity.
3.6. Cytotoxicity Assay
Primary human dermal fibroblast neonatal (HDFn) cells were grown in DMEM con-
taining 10% FBS and 1% antibiotics (penicillin and streptomycin). The cells were incubated
in a humidified (95% air and 5% CO2) incubator at 37 ◦C. Cells were cultured to the con-
fluence of 80–90% then seeded into a 96-well plate. After 24 h, the cells attached to the
bottom of the wells and treated with the chalcone derivative. The WST reagent diluted
with DMEM were added after the 24 h of treatment. After additional 2 h, the absorbance
was measured at 450 nm. Each assay contained control and solvent control. The control
contained cells in media and the solvent control contained the volume of solvent used.
Cell viability was expressed as percentage of the control. Values are mean
deviation (SD) of three separate experiments, with three wells each. The method design is
an adaptation from previously reported studies [38,39].
±
standard
4. Conclusions
The synthesis of eight chalcone derivatives has been successfully conducted at room
temperature in 62.0–98.0% yields. All compounds were found to be active in the UV
region. Chalcone derivatives with and without methoxy functional group absorb light at
the UV region, in which more methoxy substituents leads to the red shift. All chalcone
derivatives have high molar absorptivity value (21,000–56,000) demonstrating that they
have the potential to be used as sunscreen agent. The cytotoxicity evaluation showed
that chalcone derivatives have low toxicity toward normal human fibroblast cell, which is
remarkable. In conclusion, the synthesized compounds have potential to be developed as
novel sunscreen agents.
Author Contributions: Conceptualization: L.W.W. and J.J.; methodology, formal analysis, investiga-
tion, writing—original draft preparation: L.W.W.; writing—review and editing: L.W.W., R.T.S., W.L.
and J.J.; supervision: R.T.S., W.L. and J.J. All authors have read and agreed to the published version
of the manuscript.

Molecules 2021, 26, 2698
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Funding: This research was funded by Indonesia Endowment Fund for Education (LPDP-BUDIDN).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available on request from the
corresponding author.
Acknowledgments: The author would like to thank the Department of Chemistry, Universitas
Gadjah Mada, Department of Chemistry, Sogang University, and Indonesia Endowment Fund for
Education (LPDP-BUDIDN) for providing funds and facilities for this research.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of all compounds are available from the authors upon the reasonable request.
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