Synthesis and evaluation of novel tetrapropoxycalix[4]arene enones and cinnamates for protection from ultraviolet radiation

Article abstract of DOI:10.1016/j.jphotobiol.2011.06.007

A series of novel calix[4]arene enones (5-7) and cinnamates (12-14) have been synthesized and evaluated for ensuring protection from ultraviolet radiation (UVR). Spectroscopic analyses has revealed that compound 6 absorbs ultraviolet radiations between 280 and 350 nm with an absorption maximum at 312 nm. Its molar absorption coefficient (ε) (>5 × 10⁴ M^-1 cm^-1) and bandwidth are larger than those for the commercially used sun protectants (oxybenzone (OB), 2-ethylhexyl 4-methoxycinnamate (OMC) and avobenzone). The in vitro Sun Protection Factor (SPF) measurement revealed an SPF of 5.2 at 2% concentration of 6 in home made emulsion formulations while combination of 2% each of 6 and OMC gave an SPF of 8.8. Lower sun protection seems to be compensated by significant protection from more harmful UVA radiations (UVA/UVB absorbance ratio of 0.62).

Full text of DOI:10.1016/j.jphotobiol.2011.06.007

Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology B: Biology
journal homepage: www.elsevier.com/locate/jphotobiol
Synthesis and evaluation of novel tetrapropoxycalix[4]arene enones
and cinnamates for protection from ultraviolet radiation
a
a
a
a
b
b
H.M. Chawla a, , Nalin Pant , Satish Kumar , Sarika Mrig , Bindu Srivastava , Naresh Kumar , D. StC. Black
⇑
a Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110 016, India
b School of Chemistry, University of New South Wales, UNSW, Sydney 2052, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel calix[4]arene enones (5–7) and cinnamates (12–14) have been synthesized and evalu-
ated for ensuring protection from ultraviolet radiation (UVR). Spectroscopic analyses has revealed that
compound 6 absorbs ultraviolet radiations between 280 and 350 nm with an absorption maximum at
Received 21 March 2011
Received in revised form 17 June 2011
Accepted 23 June 2011
312 nm. Its molar absorption coefficient (
e
) (>5 ꢀ 104 Mꢁ1 cmꢁ1) and bandwidth are larger than those
Available online 6 July 2011
for the commercially used sun protectants (oxybenzone (OB), 2-ethylhexyl 4-methoxycinnamate
(OMC) and avobenzone). The in vitro Sun Protection Factor (SPF) measurement revealed an SPF of 5.2
at 2% concentration of 6 in home made emulsion formulations while combination of 2% each of 6 and
OMC gave an SPF of 8.8. Lower sun protection seems to be compensated by significant protection from
more harmful UVA radiations (UVA/UVB absorbance ratio of 0.62).
Keywords:
Calix[4]arene
Arylenone
Cinnamate
UV-protectant
Ultraviolet radiation
Ó 2011 Published by Elsevier B.V.
1. Introduction
isomerization [19]. Rojanathanes et al. [20] have reported photo-
switchable calix[4]arene incorporating different regioisomers of
Calix[n]arenes (n = 4–20) are phenolic [1]n-metacyclophanes in
which phenolic units are interlinked through methylene bridges
[1]. They have attracted considerable attention due to their utility
in diverse areas [2,3], molecular separations [4,5] and sensing qual-
ities [6–8]. These applications primarily result from their stable
structure consisting of a distinct hydrophobic upper rim and a
hydrophilic lower rim besides their ability to generate a number
of structural and conformational isomers [9–11]. Calix[n]arenes
can be functionally modified via derivatization of the upper-rim
and the lower-rim [1,9]. Attaching substituents around the periph-
ery of the upper rim of calix[4]arenes enhances the accommoda-
tive ability of these molecules [1,9,12]. With podand arms
located close to the cavity, guest not only interact with the atoms
at the periphery but possibly could also enter the cavity to make
room for larger guest molecules and thus allowing opportunities
for enhanced ionic and molecular recognition via utilization of
external stimuli at the molecular level [1,9,12,13]. In this regard,
calix[4]arenes appended with photosensitive moieties at their
upper rim can provide light-triggered switches, ion-channel based
biosensors and photomodulated devices [14–18]. For example,
Vogtle et al. have reported the synthesis of photoresponsive doubly
azobenzene chain substituted at the lower-rim of calix[4]arenes
which undergo EZ photoisomerization and Z ? E thermal
stilbene and azobenzene. It has been observed that the stilbene
bridged derivative isomerized only under UV irradiation while
the azobenzene derivatives undergo thermal or photochemically
induced isomerization [20].
Since calixarenes are high melting stable compounds with good
chemical, radiation and thermal stability and relatively low toxic-
ity, it was envisaged that suitable calixarene derivatives would
either function as efficient sun-protectants to screen harmful ultra-
violet radiations themselves or they can be used as carrier mole-
cules to encapsulate established sun protectants.
As a part of above research objectives, we envisaged appropri-
ate modification of the calix[4]arene aryl groups to ensure strong
UVR absorption through introduction of the a,b-unsaturated ester
and enone groups on the upper rim of calix[4]arene annulus as
they are known to undergo light-induced reversible transforma-
tions. It was also anticipated that appropriate substitution at the
upper rim of calix[4]arene annulus would not only provide a new
class of UV-filters but would also promise a newer mechanism of
protection from harmful ultraviolet radiations through the syner-
gistic action of multiple chromophores and conformational motifs.
In this paper we present our preliminary results on novel sun
protectants in the hope to eventually obtain sunscreen formula-
tions with better efficacy, stability and compatibilities with or
without other additives commonly employed for the intended
application. They have a potential to be developed as designer sun-
screens [21,22], since rapid conformational transformations in
⇑
Corresponding author. Tel.: +91 11 26591517; fax: +91 11 26591502.
E-mail address: hmchawla@gmail.com (H.M. Chawla).
1011-1344/$ - see front matter Ó 2011 Published by Elsevier B.V.
doi:10.1016/j.jphotobiol.2011.06.007

26
H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
calix[n]arenes would allow dissipation of absorbed ultraviolet
radiation.
Consequently, we have introduced photosensitive enones and
cinnamates functionalities into the calixarene scaffold to yield
derivatives which are structurally akin to commercially used sun-
screen agent trans-2-ethylhexyl-4-methoxy cinnamate (t-EHMC).
The parent p-tert-butylcalix[4]arene 1 was synthesized from p-
tert-butyl phenol by a method reported by Gutsche et al. [23,24]
followed by its debutylation by using AlCl3/phenol under condi-
tions reported by us and others [2,25–29]. Since propyl groups
are known to immobilize the the calixarenes in a cone corforma-
tion, compound 2 was subjected to propylation under different
conditions. Treatment of compound 2 with propyl bromide in the
presence of K2CO3 gave the dipropyl calix[4]arene 4 while treat-
ment with NaH in anhydrous THF/DMF gave the corresponding tet-
rapropyl derivative 3 (Scheme 1). The propyloxy calixarenes 3–4
were subjected to cinamoylation under different reaction condi-
tions. For example, treatment of 3 with cinnamoyl chloride in the
presence of stannic chloride afforded the di-cinnamoyl- and tri-
cinnamoyl-tetrapropyloxycalix[4]arenes respectively. The treat-
ment of 4 with cinnamoyl chloride and borontrifluoride diethyl
etherate gave the mono-cinnamoyl dipropyloxycalix[4]arene 5.
Alkenylation of calix[4]arene tetraether (3) has been achieved via
Wittig Olefination reaction which utilizes the tetraformyl calix[4]-
arene derivatives 8 as the substrate. The significance and general-
ity of the Wittig carbonyl olefination process in synthetic organic
chemistry has prompted us to investigate it for obtaining alkenyl
calix[4]arenes in their cone conformation (Scheme 2). Possible
depropylation of tetrapropyloxy calix[4]arene was not observed
during the reactions as determined by NMR experiments. The
synthesized calix[4]arene alkene esters and enones were purified
Scheme 2. Wittig Olefination reaction on formyl calix[4]arenes.
further by column chromatography and subjected to NMR analysis
which revealed them to be present in their cone conformation (see
experimental data).
2. Experimental
2.1. General
UV–visible spectra have been recorded on Lambda 35 UV/VIS
spectrometer (Perkin Elmer, Inc. USA) with 10 mm quartz cells.
The data was processed using UV WINLAB version 2.85.04 soft-
ware. FT-IR spectra have been recorded on a [5-DX] Nicolet FT-IR
spectrophotometer. 1H NMR and 13C NMR spectra were recorded
on a 300 MHz Bruker DPX 300 instrument at room temperature
in deuterated solvents using tetramethylsilane (TMS) as an internal
standard with the values of chemical shifts reported on a d scale.
FAB-mass spectra have been recorded on a JEOL SX 102/DA-6000
Mass Spectrometer. Melting points were recorded on an electric
melting-point apparatus (Toshniwal, India) and are uncorrected.
Analytical HPLC procedures were performed using a liquid chro-
matograph equipped with 2487 Dual k absorbance detector and
600 Controller (Waters, Milford, MA, USA). The column used for
the HPLC analysis was
a 5 l
SpherisorbÒ ODS2 column
(4.6 mm ꢀ 250 mm I.D., Waters Corp.) with an inline pre-filter.
Data processing was accomplished by using a personal computer
equipped with Empower™ personal software.
2-Ethylhexyl 4-methoxycinnamate (98%) and oxybenzone
(P96%) were purchased from Aldrich and Fluka respectively. Sam-
ple of Arlacel P 135, Arlamol M812 were procured from ICI India
Limited (Mumbai) and titanium dioxide from Whittaker Clark &
Daniel (supplied by Colorcon). HPLC-grade tetrahydrofuran was
purchased from E. Merck (India). Lewis acids (TiCl4, SnCl4, BBr3),
cinnamoyl chloride, sodium bicarbonate, potassium fluoride, so-
dium sulfate, citric acid, isopropyl palmitate and mineral oil were
Scheme 1. Synthetic route for the preparation of enone appended calix[4]arenes.

H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
27
obtained from Sigma Aldrich. Sunscreens (named in the text as A,
B, C, D, E, F and G) were commercial samples purchased from the
local markets. Other ingredients used in the preparation of emul-
sions were of high purity.
dH (ppm): 0.87 (m, 12H, CH3), 1.82 (m, 8H, CH2), 3.06 (dd, 4H,
J = 13.3 Hz, ArCH2Ar), 3.69 (m, 8H, OCH2), 4.32 (t, 4H, J = 10.3 Hz,
ArCH2Ar), 6.24 (d, J = 6.99 Hz, 2H, CH@CH + ArH), 6.53 (m, 7H,
ArH + CH@CH), 7.03 (s, 2H, ArH), 7.34 (m, 3H, ArH), 7.44 (m, 4H,
ArH). 13C NMR: (300 MHz, CDCl3): d 10.16, 10.41, 23.27, 29.67,
30.93, 77.42, 117.13, 121.79, 122.09, 122.03, 127.30, 127.85,
128.14, 128.65, 128.89, 129.48, 130.67, 133.71, 134.61, 135.27,
135.69, 137.96, 143.01, 146.90, 156.0.
2.2. Synthesis
p-tert-Butylcalix[4]arene 1 and its debutylated analog 2 were
synthesized by the method described in literature [23,24]. Calix[4]-
arene formylated derivative 8 was synthesized according to the
procedure reported by Chawla et al. [25,30]. The phosphonium
salts were prepared by refluxing stoichiometric amounts of tri-
phenylphosphine and alkyl halide in toluene for 30 min-1 h.
2.2.4. 5,11,17-tris(3-phenyl-2-propenoyl)-25,26,27,28-
tetrapropoxycalix[4]arene (6)
Calix[4]arene 3 (0.10 g, 0.17 mmol) was dissolved in 50 mL of
dry CHCl3. SnCl4 (0.31 mL, 1.689 mmol) and cinnamoyl chloride
(0.32 g, 1.94 mmol) were diluted with 5 mL of CHCl3 and the solu-
tion was added to the calixarene solution at room temperature.
Reaction mixture was stirred further for 15 h at room temperature
following which the product was obtained as above by precipita-
tion with CHCl3–MeOH to give a yellow precipitate of calixarene
6 (25% yield). m.p. 125 °C. FAB-MS m/z calcd. 982.48; found 982
[M+, 100%]; Anal. calcd. for C67H66O7: C 81.84, H 6.77; found: C
81.80, H 6.67; 1H NMR (300 MHz, CDCl3): dH (ppm): 0.87 (m,
12H, CH3), 1.82 (m, 8H, CH2), 3.06 (dd, 4H, J = 13.3 Hz, ArCH2Ar),
3.69 (m, 8H, OCH2), 4.32 (t, 4H, J = 10.3 Hz, ArCH2Ar), 6.13–7.44
(m, 30H, ArH + CH@CH). 13C NMR: (300 MHz, CDCl3): d 10.83,
10.91, 23.43, 29.77, 31.28, 78.45, 121.69, 122.26, 122.52, 125.56,
127.48, 128.11, 128.24, 128.31, 128.65, 128.90, 128.94, 129.44,
130.49, 132.53, 134.99, 136.13, 136.47, 137.10, 144.26.
2.2.1. 25,26,27,28-Tetrapropoxycalix[4]arene (3)
To a suspension of 5.8 g of NaH (0.15 mol) in 150 mL of anhy-
drous DMF was added 3.0 g of tetrahydroxycalix[4]arene
2
(7.1 mmol). After the mixture was stirred for 15 min at 70 °C, alkyl
halide (77 mmol) was added. The reaction mixture was stirred for
an additional 1 h at 70 °C, cooled to room temperature and then
quenched by dropwise addition of methanol. After removal of sol-
vent under reduced pressure, 150 mL of water was added followed
by stirring for 10 min. The crude product was washed with meth-
anol and recrystallized from acetone or chloroform and methanol
to give the calixarene 3, m.p. 192 °C. FAB-MS: m/z 592.80;
found = 593 [M+, 100%]; 1H NMR (300 MHz, CDCl3): dH (ppm):
0.96 (t, 12H, J = 7.6 Hz, CH3), 1.85 (m, 8H, OCH2CH2), 3.02 (d, 4H,
J = 13.3 Hz, ArCH2Ar), 3.81 (t, 4H, J = 6.6 Hz, OCH2), 4.42 (d, 4H,
J = 13.1 Hz, ArCH2Ar), 6.53 (m, 12H, ArH).
2.2.5. 5,17-Bis(3-phenyl-2-propenoyl)-25,27-dipropoxy calix[4]arene
(7)
2.2.2. 25,27-Bis-propyloxy-26,28-dihydroxy-calix[4]arene (4)
Calix[4]arene 4 (0.10 g, 0.17 mmol) was dissolved in 50 mL of
dry CHCl3. SnCl4 (0.31 mL, 1.69 mmol) and cinnamoyl chloride
(0.28 g, 1.69 mmol) were diluted with 5 mL of CHCl3 and the solu-
tion was added to the calixarene solution at room temperature.
Reaction mixture was stirred further for 15 h at room temperature
following which the product was obtained as above by precipitation
with CHCl3–MeOH to give a yellow precipitate of calixarene 7 (45%
yield). m.p. 120 °C. FAB-MS: m/z calcd. 768.93; found 769 [M+,
100%]; Anal. calcd. for C52H48O6: C 81.22, H 6.29; found: C 81.21,
To a suspension of tetrahydroxycalix[4]arene 2 (3.0 g, 7.1 mmol)
in CH3CN (200 mL) were added 1-bromopropane (2.56 g,
28.2 mmol) and K2CO3 (3.9 g, 28.2 mmol) and the reaction mixture
was refluxed with stirring for 24 h. The solvent was evaporated, the
residue taken up with CH2Cl2 (100 mL), and the organic phase sep-
arated and washed twice with HCl (10%) and then with water. Evap-
oration of the organic phase afforded
a solid which when
recrystallized (CH2Cl2–MeOH) gave diether calixarene 4 as white
crystals (87% yield). m.p. 268–270 °C. FAB-MS: m/z 508.65;
found = 508 [M+, 100%]; 1H NMR (300 MHz, CDCl3): dH (ppm):
1.31 (t, 6H, J = 7.3 Hz, CH3), 2.07 (quintet, 4H, OCH2CH2CH3), 3.37
(d, 4H, J = 13.1 Hz, ArCH2Ar), 3.97 (t, 4H, J = 6.5 Hz, OCH2), 4.32 (d,
4H, J = 13.2 Hz, ArCH2Ar), 6.74 (t, 2H, J = 7.1 Hz, ArH), 6.64 (t, 2H,
J = 7.0 Hz, ArH), 6.92 (d, 4H, J = 7.2 Hz, ArH), 7.05 (d, 4H, J = 7.7 Hz,
ArH), 8.61 (s, 2H, D2O exch. OH), 13C NMR (CDCl3, d): 153.3, 151.9,
133.4, 128.9, 128.4, 128.1, 125.2, 78.2, 31.4, 23.4, 10.8.
H
6.30; 1H NMR (300 MHz, CDCl3): dH (ppm): 1.32 (t, 6H,
J = 7.41 Hz, CH3), 2.06 (m, 4H, CH2), 3.50 (d, 4H, J = 13 Hz, ArCH2Ar),
4.01 (t, 4H, J = 5.88 Hz, OCH2), 4.31 (d, 4H, J = 13.02 Hz, ArCH2Ar),
6.81 (d, 2H, J = 7.5 Hz, CH@CH), 6.99 (d, 2H, J = 7.5 Hz, CH@CH),
7.41 (m, 10H, ArH (enone ring)), 7.57 (m, 2H, ArH), 7.65 (m, 4H,
ArH), 7.85 (s, 4H, ArH), 9.12 (s, 4H, OH). 13C NMR: (300 MHz, CDCl3):
d 10.86, 23.45, 29.77, 31.39, 78.48, 1222.23, 125.535, 128.28,
128.85, 129.81, 130.14, 132.60, 143.52, 146.74, 151.70, 158.38.
2.2.3. 5-Mono(3-phenyl-2-propenoyl)-25,26,27,28-tetrapropoxycalix
[4]arene (5)
2.2.6. General procedure for Wittig Olefination reaction
A mixture of phosphonium salt (stoichiometric amount) and NaH
(6.99 mmol) in 20 mL of CH2Cl2 was refluxed for 30 min. This was
followed by addition of 25,26,27,28-tetrapropoxycalix[4]arene
(0.1 g, 0.17 mmol) in THF (50 mL) to the above mixture. The reaction
mixture was refluxed and monitored by TLC. On completion of the
reaction, the reaction was quenched with 20 mL of 1% HCl solution
in water and stirred for 1 h. The organic layer was extracted with
CH2Cl2 (2 ꢀ 50 mL) and washed with water thrice. The combined
CH2Cl2 layers were dried over anhydrous Na2SO4 and evaporated
under reduced pressure to yield an oily residue which was subjected
to purification by column chromatography on silica gel.
Calix[4]arene 4 (0.1 g, 0.169 mmol) was dissolved in 50 mL of
dry CHCl3. BF3ꢂEt2O (0.42 mL, 3.37 mmol) and cinnamoyl chloride
(0.31 g, 1.86 mmol) were diluted with 5 mL of CHCl3 and the solu-
tion was added to the calixarene solution at room temperature.
Reaction mixture was stirred further for 72 h at room temperature.
A saturated solution of NaHCO3 and KF was added and the mixture
was stirred for 30 min. The biphasic mixture was decanted into a
separatory funnel and the organic layer was separated. The organic
layer was washed with saturated mixture of NaHCO3 and KF thrice
followed by washing with distilled water. The solution was dried
over Na2SO4 and the solvent was removed in vacuo to obtain the
oily product. Precipitation with CHCl3–MeOH allowed the isolation
of a pale yellow precipitate of calixarene 5 (63% yield). m.p. 165 °C.
FAB-MS: m/z calcd. 722.95; found 723 [M+]; Anal. calcd. for
2.2.7. Synthesis of 5-ethenyl-11,17,23-triformyl-25,26,27,28-
tetrapropoxy calix[4]arene (9)
The reaction procedure described above was followed by using
C
49H54O5: C 81.41, H 7.53; found: C 81.43, H 7.57; IR (KBr,
calix[4]arene
8 (0.10 g, 0.17 mmol) and methylidenetriphenyl
cmꢁ1): 1690 cmꢁ1 c@c); 1H NMR (300 MHz, CDCl3):
(m
c@o), 1634 (
m
phosphorane ylide (0.07 g, 0.17 mmol) affording a white solid

28
H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
(0.046 g, 44% yield); m.p. 163–164 °C; Anal. calcd. for C45H50O7: C
76.90, H 7.17; Found: C 76.91, H 7.18; FAB-MS: m/z calcd.
702.87; Found 703 [M+, 100%]; 1H NMR (300 MHz, CDCl3): dH
(ppm): 0.99 (m, 12H, J = 3.5 Hz, CH3), 1.87 (m, 8H, J = 6.78 Hz,
ACH2CH3), 3.12 (m, 4H, ArCH2Ar), 3.89 (m, 8H, AOCH2), 4.37 (m,
4H, ArCH2Ar), 4.98 (d, H, J = 17.5 Hz, @CH2), 5.30 (d, H,
J = 17.5 Hz, @CH2), 6.28 (m, H, CH@CH2), 6.61, 6.65, 7.15, 7.19 (s,
8H, ArH), 9.61 (s, 3H, CHO). 13C NMR: (300 MHz, CDCl3): d 10.16,
10.41, 23.27, 29.67, 30.93, 77.42, 117.13, 121.79, 122.09, 122.03,
127.30, 127.85, 128.14, 128.65, 128.89, 129.48, 130.67, 133.71,
134.61, 135.27, 135.69, 137.96, 143.01, 146.90, 156.0.
2.2.12. Synthesis of 5,11,17,23-tetrakis(2-ethoxycarbonyl)ethenyl-
25,26,27,28-tetrapropoxy calix[4]arene (14)
The reaction procedure described above was followed by using
calix[4]arene 8 (0.10 g, 0.17 mmol) and (ethoxycarbonylmethyl)-
triphenylphosphonium bromide (0.29 g, 0.67 mmol) affording a
white solid (0.06 g, 35% yield); m.p. 165–166 °C; Anal. calcd. for
C60H72O12: C 73.15, H 7.37; found: C 73.35, H 7.18; FAB-MS: m/z
calcd. 985.21; found 986 [M+, 100%]; 1H NMR (300 MHz, CDCl3):
dH (ppm): 0.99 (m, 12H, CH3), 1.32 (m, 12H, AOCH2CH3), 1.89 (m,
8H, ACH2CH3), 3.14 (d, 4H, J = 13.3 Hz, ArCH2Ar), 3.87 (m, 8H,
ACOOCH2CH3), 4.23 (m, 8H, AOCH2), 4.40 (d, 4H, J = 12.9 Hz,
ArCH2Ar), 6.05 (d, 4H, J = 15.96 Hz, @CH), 6.80 (s, 8H, ArH), 7.32
(d, 4H, J = 15.93 Hz, CH@).
2.2.8. Synthesis of 5,11-bisethenyl-17,23,-diformyl-25,26,27,28-
tetrapropoxy calix[4]arene (10)
The reaction procedure described above was followed by using
2.2.13. Synthesis of 5,11,17,23-tetrakis(2-phenyl)ethenyl-25,26,27,28-
tetrapropoxy calix[4]arene (15)
calix[4]arene
8 (0.10 g, 0.17 mmol) and methylidenetriphenyl
phosphorane ylide (0.20 g, 0.51 mmol) affording a white solid
(0.04 g, 35% yield); m.p. 178 °C; Anal. calcd. for C46H52O6: C 78.83,
H 7.48; found: C 78.89, H 7.50; FAB-MS: m/z calcd. 700.90; Found
701 [M+, 100%]; 1H NMR (300 MHz, CDCl3): dH (ppm): 0.99 (m,
12H, CH3), 1.87 (m, 8H, ACH2CH3), 3.12 (m, 4H, ArCH2Ar), 3.8 (m,
8H, AOCH2), 4.37 (m, 4H, ArCH2Ar), 4.98 (d, 2H, J = 10.7 Hz,
@CH2), 5.5 (d, 2H, J = 17.7 Hz, @CH2), 6.28 (m, 2H, CH@CH2), 6.61,
6.65, 7.15, 7.19 (s, 8H, ArH), 9.56 and 9.61 (s, 2H, CHO).
The reaction procedure described above was followed by using
calix[4]arene
8 (0.10 g, 0.17 mmol) and benzylidenetriphenyl
phosphorane ylide (0.29 g, 0.675 mmol) affording a white solid
mixture of cis and trans isomer (44% yield); m.p. >250 °C; Anal.
calcd. for C72H72O4: C 86.36, H 7.25; Found: C 86.45, H 7.23;
FAB-MS m/z calcd. 1001.34, Found 1002 [M+, 100%]; 1H NMR
(300 MHz, CDCl3): dH (ppm): 1.12 (t, 6H, J = 7.4 Hz), 2.05–1.70
(m, 8H), 3.15 (d, 4H, J = 13.3 Hz), 3.66 (t, 4H, J = 7.0 Hz), 4.02 (t,
4H, J = 7.9 Hz), 6.95 (d, 4H, J = 16.3 Hz), 7.13 (d, 4H, J = 16.3 Hz),
7.15–7.35 (m, 20H, ArH), 7.43 (s, 8H, J = 7.0 Hz, ArH), 13C NMR d
10.8, 23.4, 31.1, 77.6, 122.2, 126.2, 126.9, 127.7, 128.6, 129.0,
133.6, 136.6, 137.8, 155.6, 157.7.
2.2.9. Synthesis of 5,11,17,23-tetrakis(ethenyl)-25,26,27,28-
tetrapropoxy calix[4]arene (11)
The reaction procedure described above was followed by using
calix[4]arene
8 (0.10 g, 0.17 mmol) and methylidenetriphenyl
phosphorane ylide (0.68 g, 1.69 mmol) affording a white solid
2.3. UV spectroscopy
(0.059 g, 53% yield); m.p. 350 °C (decomp.); Anal. calcd. for
C48H56O4: C 82.72, H 8.10; found: C 82.73, H 8.09; FAB-MS: m/z
kmax, e and UV specific extinction values of synthesized calixare-
calcd. 696.96; found 697 [M+, 100%]; 1H NMR (300 MHz, CDCl3):
dH (ppm): 0.95 (m, 12H, J = 7.0 Hz, CH3), 1.86 (m, 8H, ACH2CH3),
3.1 (m, 4H, ArCH2Ar), 3.81 (t, 8H, J = 6.8 Hz, AOCH2), 4.38 (m, 4H,
ArCH2Ar), 4.93 (d, 2H, J = 10.7 Hz, @CH2), 5.32 (d, 2H, J = 17.4 Hz,
@CH2), 6.34 (m, 4H, CH@CH2), 7.25 (s, 8H, ArH). 13C NMR
(75 MHz, CDCl3): 10.3, 23.1, 31.0, 76.7, 111.3, 126.1, 131.6, 134.8,
137.0, 156.5.
nes and reference UV filters were determined as follows: three
solutions of 5, 6, 7, 12, 13 and 14 in the concentration range
10ꢁ4–10ꢁ5 M were prepared in chloroform. Similarly, three differ-
ent molar concentrations of reference UV filters (OMC, OB and avo-
benzone) were also prepared in this range and their absorbance (A)
was recorded at respective peak wavelengths (kmax) using quartz
cuvettes of 1 cm path length (L). A plot of A versus molar concen-
tration at kmax was prepared and
e value was obtained from the
2.2.10. Synthesis of 5-(2-ethoxycarbonyl)ethenyl-11,17,23-triformyl-
25,26,27,28-tetrapropoxy calix[4]arene (12)
The reaction procedure described above was followed by using
calix[4]arene 8 (0.10 g, 0.17 mmol) and (ethoxycarbonylmethyl)-
triphenylphosphonium bromide (0.07 g, 0.169 mmol) affording a
white solid (0.02 g, 18% yield); m.p. 232–236 °C; Anal. calcd. for
slope of straight line. The UV specific extinction (E1%,1cm) was eval-
uated by using stock solutions of 1 mg mLꢁ1 which were prepared
for the reference and calixarene UV filters by appropriate dilution
to obtain a 10 ppm solution. Absorbance of all the solutions was re-
corded at their kmax using quartz cuvettes of 1 cm path length to
give E1%, 1cm values.
C
48H54O9: C 74.39, H 7.02; found: C 74.40, H 7.0; FAB-MS: m/z
To obtain the absorption in the UVA to UVB regions for OMC,
OB, avobenzone and 6, UV specific extinction spectrum obtained
above in chloroform were used and the mean absorbance values
were calculated separately in the UVB (290–320 nm) and UVA
(320–400 nm) regions of the spectrum. The total area under the
curve in individual UVB and UVA regions was also obtained arith-
metically by using the UVWINLAB software. These were then used
to calculate the UVA/UVB ratio in terms of absorbance as well area
under the curve.
calcd. 774.94; found 775 [M+, 100%]; 1H NMR (300 MHz, CDCl3):
dH (ppm): 0.78 (m, 12H, CH3), 0.92 (m, 3H, OCH2CH3), 1.82 (m,
8H, ACH2CH3), 3.17 (m, 4H, ArCH2Ar), 3.84 (m, 2H, ACOOCH2),
4.19 (m, 8H, AOCH2), 4.37 (m, 4H, ArCH2Ar), 6.02 (m, H, @CH),
6.69 (d, H, J = 15.9 Hz, CH@), 7.02, 7.09 and 7.15 (s, 8H, ArH),
9.48 and 9.55 (s, 3H, CHO).
2.2.11. Synthesis of 5,11,17-tris(2-ethoxycarbonyl)ethenyl-23-formyl-
25,26,27,28-tetrapropoxy calix[4]arene (13)
The reaction procedure described above was followed by using
calix[4]arene 8 (0.10 g, 0.17 mmol) and (ethoxycarbonylmethyl)-
triphenylphosphonium bromide (0.29 g, 0.67 mmol) affording a
white solid (0.034 g, 23% yield); m.p. 140–142 °C; Anal. calcd. for
2.4. HPLC analysis
HPLC analysis of 6 was done on a reverse-phase ODS2 column
by using THF (100% v/v) as mobile phase at a constant flow-rate of
1.0 mL minꢁ1 in isocratic mode at ambient temperature with the
C
56H66O11: C 73.5, H 7.27; found: C 73.52, H 7.25; FAB-MS: m/z
calcd. 915.12; Found 915 [M+, 100%]; 1H NMR (300 MHz, CDCl3):
dH (ppm): 0.78 (m, 12H, CH3), 0.92 (m, 9H, OCH2CH3), 1.81 (m,
8H, ACH2CH3), 3.15 (m, 4H, ArCH2Ar), 3.80 (m, 6H, ACOOCH2),
4.16 (m, 8H, AOCH2), 4.37 (m, 4H, ArCH2Ar), 6.05 (m, 3H, @CH),
6.55–7.38 (m, 12H, ArH + CH@), 9.43 (s, H, CHO).
detector wavelength set at 312 nm. Stock solution (250 l )
g mLꢁ1
was prepared by dissolving accurately weighed 6 in chloroform.
Three working standards were made by dilution of stock solutions
with chloroform and subsequent dilutions were done to prepare
standard solutions of concentration 1.0–10 l
g mLꢁ1 which were

H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
29
injected (20
matograms were recorded. All the samples were filtered through
0.45 m membrane filter before injection for HPLC profiling.
lL) onto the HPLC system in triplicates and chro-
3. Results and discussion
l
3.1. Characterization of calixarene derivatives
The synthesized calix[4]arenes were characterized by IR, NMR
and mass spectrometry. For example, 5 revealed strong absorp-
tions at 1690 cmꢁ1 and 1634 cmꢁ1 which could be ascribed to
the carbonyl and the C@C functions. The appearance of a doublet
of doublet at d 3.06 and a triplet at d 4.32 for the CH2 protons
was also consistent with its cone conformation (Fig. 1). The aro-
matic protons appeared as three multiplets (d 6.24, 6.53 and
7.34), a singlet and a doublet at d 7.03 and 6.24 respectively. Inte-
gration for 18 protons revealed that the 3-phenyl-2-propenoyl unit
(cinnamoyl group) has been introduced at one of the para aromatic
positions in 5. The doublets at d 6.24 and d 6.53 could be attributed
to the olefinic protons. However, it was determined that the aro-
matic signals merged with the protons of the olefinic moiety there-
by making elucidation of the exact stereochemistry little more
difficult by conventional techniques. 2D NMR experiments (COSY
and NOESY) were thus performed to understand the exact stereo-
chemistry around the olefinic double bond (Fig. 2). These tech-
niques were able to confirm the identification of olefinic protons.
Compound 5 showed a molecular ion peak at m/z 723 [M+] in its
FAB-MS spectrum thereby confirming the introduction of one en-
one moiety.
2.5. Preparation of O/W emulsion-based formulations
Several oil in water (O/W) emulsions were made in the labora-
tory by using varying proportions of 6 and OMC. Arlacel P 135 (2%)
was used as a polymeric emulsifier while isopropyl palmitate
(9.5%) and mineral oil (7.0%) were used as primary emollients.
Arlamol M812 (4%) was used as the solubilizer for 6. Citric acid
was used for final adjustment of pH of the formulation. The formu-
lation samples were stored in airtight glass containers until used.
pH of the formulated emulsions was determined at room
temperature.
2.6. Procedure used for determination of in vitro Sun Protection Factor
(SPF)
Of the various in vitro techniques that have been developed for
evaluation of Sun Protection Factor (SPF) [31–36], the SPF values of
calixarene analog 6 in emulsion was determined by using the
method proposed by Walters et al. that assumes a simplified rela-
tionship between absorbance and SPF [37].
ꢀ
ꢁ
The 1H NMR spectrum of 6 (Fig. 1) revealed the appearance of a
doublet of doublet at d 3.06 and a triplet at d 4.32 in the methylene
bridge región again consistent with a cone conformation. The aro-
matic region of the spectrum revealed a complex pattern of reso-
nances integrating for 30 protons indicating the introduction of
three cinnamoyl groups at the upper rim. While NMR spectrum
for compound 6 was similar to the other compounds of the series,
the FAB-MS spectrum of 6 showed the appearance of a molecular
ion peak at m/z 982 [M+] to confirm that it is a tricinnamoyl
derivative.
1
SPF
A ¼ ꢁlog10
¼ log10SPF
A standard calibration plot using different sunscreen products
with labeled SPF ranging from 5 to 34 was prepared as follows:
about 0.050 0.005 g of each of the formulated sunscreens was
weighed and 50.0 mL of distilled water was added to it and stirred
until the formulation was uniformly suspended in water. To
1.00 mL of the resultant mixture, 9.00 mL of 1-propanol was added
and stirred to produce a clear solution. A maximum in absorbance
was determined at 312 nm for the sunscreen solutions [38]. The
absorbance at 312 nm by a sample of 0.05 g was plotted versus
log10(SPF) on a semilog paper. In vitro SPF of eight different formu-
lations (F1–F8) prepared that (contained 6 in combination with
OMC and TiO2) were determined by interpolation from the calibra-
tion plot after preparation of sample solutions from different O/W
emulsion formulations.
It was also observed that compound 6 readily got photoisomer-
ized around the double bond on exposure to UV radiations. Such
quick isomerization gave credence to the anticipated utility of
the calixarene enone system for development of novel materials
for protection from UVR.
The 1H NMR spectrum of 7 revealed the introduction of two cin-
namoyl groups at the para positions of the phenolic rings and not
para to the propyl ether aromatic rings.
2.7. Procedure for photo-irradiation
In order to assess the UV-protection properties of the
synthesized calixarenes, they were purified by using high perfor-
mance liquid chromatography and the purified derivatives were
subjected to irradiation by UVA and UVB light. Rigorous purifica-
tion and isomerization experiments and the broad band width
(280–350 nm) reveal that compound 6 was suitable for further
investigations for sun-screen formulations and was therefore fur-
ther work was done on 6.
Irradiation experiments on 6 were performed by using LZC-4
(Dual irradiation model) photo reactor (Luzchem Research, Inc.
Canada) equipped with 14 lamps located at the top and sides. Solu-
tions of calixarene 6 were prepared in the concentration range of
5–100 l
g mLꢁ1 in chloroform and the samples were placed in
quartz tubes. All the experiments were carried out at room tem-
perature (25–28 °C). The temperature in the irradiation chamber
was determined to be approximately 3–4 °C above room tempera-
ture. Separate UV-B and UV-A lamps were used for irradiation with
specific UV-B and UV-A incident radiations. The energy distribu-
tion at the target sample was 35,337 and 52,670 mW mꢁ2 (Techni-
cal bulletin, Luzchem, Canada) in UV-B (281–315 nm) and UV-A
(316–400 nm) regions respectively in case of individual [39] as
against irradiance of about 60,000 mW mꢁ2 for natural sunlight
on a sunny day and 10 mW mꢁ2 on a cloudy day [40]. Out of the
total 14 lamps, eight of them on the side walls of the chamber were
switched on during each experiment. Solutions of 6 were subjected
to photo irradiation for following time points: 0 min, 1 min, 5 min,
10 min, 15 min, 20 min, 25 min, 30 min and 1 h. UV spectrum was
recorded after each exposure using chloroform as the blank.
The 1H NMR spectrum of 11 obtained by the reaction of methyl
phosphonium bromide ylide and tetraformyl calix[4]arene 8 re-
vealed the disappearance of aldehydic protons and appearance of
a pair of doublets at d 4.93 (4H) and 5.32 (4H) and a multiplet at
d 6.34 (4H) in its 1H NMR. These signals could be ascribed to vinylic
protons revealing that the ethenyl groups had been introduced at
all the four para positions of the calix[4]arene annulus. 1H NMR
characterization of 9 and 10 revealed the introduction of olefinic
group at one and two para positions respectively. The calix[4]arene
derivative 10 revealed the presence of multiplets at d 3.1 and 4.38
for methylene bridge protons in its 1H NMR spectrum that indi-
cated that two ethenyl groups in 10 are introduced on proximal
aromatic rings at the upper rim of calix[4]arenes (Fig. S1, Supple-
mentary information).

30
H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
CH3
ArH +CH=CH
CH2
ArCH2Ar
OCH2
ArCH2Ar
Fig. 1. 1H NMR spectra of 5,11,17-tris(3-phenyl-2-propenoyl)-25,26,27,28-tetrapropoxycalix[4]arene (6).
Fig. 2. (a) COSY and (b) NOESY spectra of 5,11,17-tris(3-phenyl-2-propenoyl)-25,26,27,28-tetrapropoxycalix[4]arene (6).
Fig. 3. Extinction curves of (
) 6, (
) OMC, (
) OB and (
) avobenzone in chloroform.
The 1H NMR spectrum of the calix[4]arene 14 derived from the
reaction of ethyl bromoacetate ylide and formyl calix[4]arene (10),
exhibited two well resolved doublets. One of the doublets centered
at d 7.32 (J = 15.96 Hz; 4H) to the left of phenyl resonance (at d

H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
31
Table 1
UV spectral analysis of calix[4]arenes (5–7) and reference UV filters.
Table 3
In vitro SPF analysis of formulation batches (F1–F8) prepared during the study.
a
a
Compound
kmax
E1%,1cm
ea (Mꢁ1 cmꢁ1
)
Absorbance
Emulsion formulation
Active components
Calculated SPFa
5
6
7
12
13
14
OB
312
312
300
273
295
294
287
356
310
584.50
666.10
612.50
–
508.50
541.00
686.45
1213.70
1058.90
19,187
59,541
23,125
–
14,256
19,141
15,150
39,470
31,670
UVB, UVA II
UVB, UVA II
UVB
–
UVB
UVB
UVB, UVA II
UVA I
F1
F2
F3
F4
F5
F6
F7
F8
2% 6
2% OMC
2% 6 + 2% OMC
4% OMC
2% 6 + 4% OMC
4% TiO2
5.2 0.25
6.4 0.18
8.8 0.45
8.4 0.19
10.8 0.54
5.2 0.40
5.6 0.49
6.8 0.51
2% 6 + 4% TiO2
2% OMC + 4% TiO2
Avobenzone
OMC
UVB
a
Each value is mean SD of three determinations.
a
Chloroform.
larger chemical shift as it would be in the deshielding area of the
anisotropic field of the aromatic ring (Fig. S2, Supplementary infor-
mation). All the products obtained were identified as cone con-
formers through the analysis of its 13C NMR spectra.
Table 2
Absorbance in the UVA/UVB regions of 6, OMC, OB and avobenzone.
UV filter
Mean absorbance
(5 nm interval)
Total area
UVA/UVB ratio
3.2. Comparison of UV spectra of calixarenes (5–7 and 12–14), OMC,
UVB
UVA
UVB
UVA
Absorbance Area
OB and avobenzone
region
(280–
region
(320–
region
(280–
region
(320–
320 nm) 400 nm) 320 nm) 400 nm)
The UV spectral behavior in relation to the absorption maxi-
mum and absorption range in the UV region from 280 to 400 nm
was examined for all the calix[4]arene analogs selected for the
study. The enone-appended calixarenes 5–7 and unsaturated ester
appended calixarenes 12–14 were found to absorb between 280–
350 nm in the UV region (Figs. 3 and S3). For example, 7 showed
an absorption maximum at 300 nm while 5 and 6 exhibited
absorption máxima at 312 nm. A comparison of the extinction
curves of 6 and reference UV filters (Fig. 3) in chloroform indicated
that 6 showed E1%,1cm of 666 compared to 686 for OB, 1058 for OMC
and 1213 for avobenzone. The results obtained indicated that
although the UV specific extinction coefficient of 6 was lower than
OMC and avobenzone, it was comparable to that of OB.
6
OB
OMC
0.5722
0.5151
0.9431
0.1903
0.1943
0.1328
0.7350
23.2571 14.5743 0.33
20.7463 15.4336 0.37
38.7465 9.0016 0.14
13.0260 61.3280 2.19
0.62
0.74
0.23
4.70
Avobenzone 0.3349
6.80) and other at d 6.05 (J = 15.93 Hz; 4H) to the right of the phe-
nyl resonance in the aromatic region. These signals were attributed
to the ethylenic protons of the trans isomer. Vinyl proton attached
to the carbon bearing the phenyl ring could be assigned to the
It was determined that 6 had a very high molar extinction coef-
0.56
> 5 ꢀ 104) than those of 5 and 7 as well as commercial UV
(a)
ficient (
e
0.50
filters like OMC, OB and avobenzone when examined under identi-
cal conditions (Table 1). Therefore 6 was subjected to detailed
evaluation.
Amongst the olefinic calixarene analogs studied, 14 showed a
good extinction in the UVB region but was not subjected to further
studies due to its susceptibility to degradation in solution on expo-
sure to UV light (Fig. S4, Supplementary information). Calixarene
analog 12 did not absorb in the desirable UV region and therefore
not studied further.
0 min
1 min
5 min
10 min
15 min
20 min
25 min
30 min
1 hour
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
A
3.3. Comparison of UVA/UVB protection ratio of 6 with OMC, OB and
avobenzone
235
250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400
nm
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
(b)
A comparison of the extinction spectrum of 6 in the UVA and
UVB regions with those of OMC, OB and avobenzone was done
0 min
1 min
5 min
10 min
15 min
20 min
25 min
30 min
1 hour
A
240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400
nm
Fig. 4. Time-dependent absorption spectra of 6 in chloroform (8
exposure to (a) UVB and (b) UVA range of radiations on UV photo reactor.
l
g mLꢁ1) after
Fig. 5. HPLC analysis of 100 l
g mLꢁ1 solution of calixarene 6.

32
H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
Table 4
Quantitative results for HPLC assay of calix[4]arene 6.
Retention time
(min)
Linear range
g mLꢁ1
Intercept (ꢀ102)
r2
Slope (log plot)
1.04 (0.019)
Sensitivityꢃ (L mgꢁ ꢀ 104)
LODꢃꢃ (mg Lꢁ1 ꢀ 10ꢁ4
)
LOQꢃꢃꢃ
(
l
)
zzz(mg Lꢁ1 ꢀ 10ꢁ4
)
2.93 (0.004)
1.0–10.0
0.0 (0.0)
0.9993 (0.001)
10.70 (0.015)
17.36 (0.471)
52.63 (0.284)
*
**
Slope of the calibration curve.
Calculated as per equation; LOD = 3.3Sx/y/b; where Sx/y is the standard deviation and b is the slope of the unweigted least square calibrated plot.
Calculated as per equation; LQD = 10Sx/y/b; Sx/y and b are defined above.
***
by determining their UVA/UVB ratios which was calculated arith-
metically from the mean absorbance and total areas under the
absorption curves in individual UVB and UVA regions. It has been
determined that the UVA/UVB ratio was 0.62 for 6 (Table 2) indi-
cating that it is predominantly a UVB absorber with sufficient effi-
ciency for offering pretection from UVA.
The in vitro SPF analysis of F1–F8 indicated that 6 has a syner-
gistic effect on boosting the SPF of OMC. For example, 2% of 6
and 2% of OMC combined in the formulation (F3) has a higher
SPF than 4% OMC alone (formulation F4). On the other hand, there
was no boosting effect on the SPF of TiO2 because 4% titanium
dioxide when combined with 2% 6, showed insignificant increment
in the SPF of 6 from 5.2 to 5.6.
3.4. Spectral changes in 6, OB and OMC on photo-irradiation with UVB
and UVA light
3.6. HPLC analysis of 6
The photostability of 6 was examined for both UVB and UVA
light by recording the temporal changes in the UV absorption spec-
trum in neat chloroform due to the insolubility of calix[4]arenes in
water. It was found that when 6 was subjected to UV-B radiations,
there was nearly 65% loss of absorption of 6 after 30 min of expo-
sure as indicated by a time-dependant spectrum showing shift in
the spectral band position with an isosbestic point at 278 nm.
When subjected to UVA radiations, about 70% loss of UV absorp-
tion after 30 min of exposure was noted with the time-dependant
spectrum showing a shift in the spectral band position with an
isosbestic point appearing at 272 nm (Fig. 4).
These results indicated that 6 undergoes a change in its absorp-
tion profile on exposure to both UVA and UVB light. Both octyl-
methoxycinnamate (OMC) and oxybenzone (OB) were also
quantitatively analyzed simultaneously in the mixture with other
excipients in the commercial sunscreen formulation through sec-
ond order derivative spectrophotometry allowed their determina-
tion without matrix interferences (Fig. S5, Supplementary
information). While zero-order calibration methods provided a
higher content for both the UV filters, second-order calibration
(D2 values; derivative mode for OB and derivative + peak mode
for OMC) resulted in values that were in agreement with the la-
beled content of commercial sunscreens, reported earlier for
OMC by us [41] and others [42,43].
Compound 6 was purified by column chromatography to give
sample which gave a sharp peak at a retention time of
2.414 min in its chromatogram when examined by high perfor-
mance liquid chromatography on a reverse-phase ODS2 column
using THF (100%) as the mobile phase and UV detection at
312 nm (Fig. 5).
a
A calibration curve of concentration of 6 versus the peak area
could be prepared in the concentration range of 1.0–10.0 l
g mLꢁ1
to derive an equation through linear unweighted regression analy-
sis. The linearity of the concentration versus the peak area plot was
ensured by a log area versus log C diagram where the slope was
determined to be one throughout the whole concentration range
examined. The quantitative results for HPLC assay of 6 are summa-
rized in Table 4.
The HPLC analysis of 13 and 14 was also examined by high per-
formance liquid chromatography on a reverse-phase ODS2 column
using THF:acetonitrile:triethylamine (89:10:1) as the mobile phase
at flow rate 0.4 mL minꢁ1 and UV detection at 295 nm. The chro-
matogram revealed that 13 eluted at a characterstic sharp peak
at 6.06 min (Fig. S6) while 14 eluted at 6.07 min (Fig. S7).
4. Conclusion
In conclusion, we have observed that of the three synthesized
calix[4]arene enones, 6 effectively assimilate the properties of pho-
3.5. Evaluation of in vitro Sun Protection Factor of 6 in combination
with OMC and TiO2
tosensitive cinnamates and show
a significant absorption
(e
> 5 ꢀ 104) in the UVB (280–320 nm) and UVA II (320–340 nm)
To test the protection offered by 6 in the UVB region, its in vitro
Sun Protection Factor was determined for different formulations
made from 6, OMC and OB. Accordingly, several formulations
(F1–F8) were made by combining 6 with UVB absorber (OMC)
and physical sunscreen (titanium dioxide). Absorbance of sun-
screen formulations available in the market was determined at
312 nm and corrected to a weight of 0.050 g. A calibration plot
was prepared between the corrected absorbance and the labeled
SPF value and the following equation was determined.
region of the ultraviolet spectrum. The calix[4]arene enone 6 has
specific extinction coefficient and the ratio of absorbance in the
UVA to UVB regions similar to commercially used mixed UV filter
oxybenzone. 6 exhibits an SPF boosting effect to OMC in emulsion
formulations.
Acknowledgements
The authors gratefully acknowledge financial support received
from the Department of Science and Technology (Govt. of India),
Ministry of Environment and Forests, Ministry of Food Processing
Industries, Ministry of Rural Development and CSIR, New Delhi.
SM thanks the Indian Institute of Technology for a senior research
fellowship. HMC thanks the University of New South Wales, Syd-
ney for a Visiting Research Fellowship under International Re-
search Workshop (2009–2012).
log10SPF ¼ 0:980ðAbsÞ þ 0:5051
SPF represents the Sun Protection Factor and Abs denotes the
absorbance of diluted sunscreen solution. The slope of least-
squares line fitted to the data was 0.980 and the intercept was
0.5051. The SPFs of 6, OMC and TiO2 were determined after sample
preparation from the formulations (F1–F8) and recording the
absorbance at 312 nm (Table 3).

H.M. Chawla et al. / Journal of Photochemistry and Photobiology B: Biology 105 (2011) 25–33
33
[21] E. Westhof, Water and Biological Macromolecules, CRC Press, Boca Raton, FL,
1993.
Appendix A. Supplementary material
[22] M. Pojarova, G.S. Ananchenko, K.A. Udachin, M. Daroszewska, F. Perret, A.W.
Coleman, J.A. Ripmeester, Solid lipid nanoparticles of p-hexanoyl calix[4]arene
as a controlling agent in the photochemistry of a sunscreen blocker, Chem.
Mater. 18 (2006) 5817–5819.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotobiol.2011.06.007.
[23] C.D. Gutsche, M. Iqbal, P-tert-Butylcalix[4]arene, Org. Synth. 68 (1990) 234.
[24] C.D. Gutsche, J.A. Levine, Calixarenes 6. Synthesis of
a functionalizable
References
calix[4]arene in a conformationally rigid cone conformation, J. Am. Chem.
Soc. 104 (1982) 2652–2653.
[25] H.M. Chawla, N. Pant, B. Srivastava, Regioselective ipso formylation of para-
tert-butylcalix[4]arene, Tetrahedron Lett. 46 (2005) 7259–7262.
[26] S. Kumar, R. Varadarajan, H.M. Chawla, G. Hundal, M.S. Hundal, Preparation of
p-nitrocalix[n]arene methyl ethers via ipso-nitration and crystal structure of
tetramethoxytetra-p-nitrocalix[4]arene, Tetrahedron 60 (2004) 1001–1005.
[27] S. Kumar, H.M. Chawla, R. Varadarajan, A convenient single step synthesis of p-
thiomethylmethylcalixarenes and metal ion extraction studies, Tetrahedron
59 (2003) 7481–7484.
[1] C.D. Gutsche, Calixarenes Revisited, Royal Society of Chemistry, UK, 1998.
[2] A. Casnati, R. Ungaro, Z. Asfari, J. Vicens, Calixarenes Kluwer Academic,
Dordrecht, Holland, 2001.
[3] Z. Asfari, V. Böhmer, J. Harrowfield, J. Vicens, Calixarenes 2001, Kluwer
Academic Pub, Dordrecht, Holland, 2001.
[4] P. Kandwal, P.K. Mohapatra, S.A. Ansari, V.K. Manchanda, Selective caesium
transport using hollow fibre-supported liquid membrane containing
calix[4]arene-bis-naphthocrown-6 as the carrier extractant, Radiochim. Acta
98 (2010) 493–498.
[28] S. Kumar, H.M. Chawla, R. Varadarajan,
A single step preparation of p-
sulphonated calixarenes, Ind. J. Chem. Sect. B – Org. Chem. Incl. Med. Chem. 42
(2003) 2863–2865.
[29] S. Kumar, N.D. Kurur, H.M. Chawla, R. Varadarajan, A convenient one pot one
step synthesis of p-nitrocalixarenes via ipsonitration, Synth. Commun. 31
(2001) 775–779.
[5] D.R. Raut, P.K. Mohapatra, V.K. Manchanda, Cs(I) extraction/transport studies
using irradiated calix [4]-bis 2,3-naphtho-crown-6, Desalin. Water Treat. 12
(2009) 52–56.
[6] H.M. Chawla, R. Shrivastava, Synthesis of novel cone-configurated hexa-tert-
butyl-trimethoxy-calix[6]arenes bearing tris(bipyridyl) pendants and their use
in recognition and ionic speciation, J. Incl. Phenom. Macrocycl. Chem. 64
(2009) 255–263.
[30] V. Arora, H.M. Chawla, A. Santra, Synthesis of selectively formylated calixarene
ethers, Tetrahedron 58 (2002) 5591–5597.
[31] J. de Souza Mansur, M.N.R. Breder, M.C. dAscenção Mansur, R.D. Azulay,
Determinação do fator de proteção solar por espectrofotometria, An. Bras.
Dermatol. 61 (1986) 121–124.
[7] H.M. Chawla, S.N. Sahu, R. Shrivastava, Synthesis and binding characteristics of
novel calix[4]arene(amidocrown) diquinones, Can. J. Chem. – Rev. Can. Chim.
87 (2009) 523–531.
[32] V.C. Gordan, Evaluation du facteur de protection solaire, Parfum. Cosmet.
Arom. Paris 112 (1993) 62–65.
[33] C. Walters, A. Keeney, C.T. Wigal, C.R. Johnston, R.D. Cornelius, The
spectrophotometric analysis and modeling of sunscreens, J. Chem. Educ. 74
(1997) 99–102.
[34] E.R.M. Kedor-Hackmann, C. Universitária, Determination of sun protection
factor (SPF) of sunscreens by ultraviolet spectrophotometry, Braz. J. Pharm. Sci.
40 (2004) 381–385.
[8] G. Montavon, U. Repinc, C. Apostolidis, F. Bruchertseifer, K. Abbas, A.
Morgenstern, Investigation of para-sulfonatocalix[n]arenes [n = 6, 8] as
potential chelates for 230U, Dalton Trans. 39 (2010) 1366–1374.
[9] H.M. Chawla, N. Pant, S. Kumar, N. Kumar, D.S.C. Black, Chemical Sensors:
Fundamentals of Sensing Material, Momentum Press, New York, 2010.
[10] M. Iqbal, T. Mangiafico, C.D. Gutsche, Calixarenes 21. The conformations and
structures of the products of aroylation of the calix[4]arenes, Tetrahedron 43
(1987) 4917–4930.
[35] E.A. Dutra, E.O. Costa, Determination of sun protection factor (SPF) of
sunscreens by ultraviolet spectrophotometry, Rev. Bras. Cienc. Farm. 40
(2004) 381–385.
[11] C.D. Gutsche, B. Dhawan, J.A. Levine, H.N. Kwang, L.J. Bauer, Calixarenes. 9.
Conformational isomers of the ethers and esters of calix[4]arenes, Tetrahedron
39 (1983) 409–426.
[36] M. Pissavini, L. Ferrero, V. Alard, U. Heinrich, H. Tronnier, D. Kockott, D. Lutz, V.
Tournier, M. Zambonin, M. Meloni, Determination of the in vitro SPF, Cosmet.
Toiletries 118 (2003) 63–72.
[37] C. Walters, A. Keeney, C.T. Wigal, C.R. Johnston, R.D. Cornelius, The
Spectrophotometric Analysis and Modeling of Sunscreens J. Chem. Edu. 78
(2001) 1388.
[38] M.R. Davis, M.N. Quigley, Liquid chromatographic determination of UV
absorbers in sunscreens, J. Chem. Educ. 72 (1995) 279–281.
[39] Technical release Luzchem exposure standard: les-uva-01, 21 June 2004,
Luzchem.
[12] J. Rebek, Host-guest chemistry of calixarene capsules, Chem. Commun. (2000)
637–643.
[13] Y. Kubo, S.Y. Maeda, S. Tokita, M. Kubo, Colorimetric chiral recognition by a
molecular sensor, Nature (London) 382 (1996) 522–524.
[14] G. Deng, T. Sakaki, Y. Kawahara, S. Shinkai, Tunable chemical sensors: light-
switched ion selective electrodes on the basis of
calix[4]arene, Supramol. Chem. 2 (1993) 71–76.
a photoresponsive
[15] H. Suenaga, K. Nakashima, O. Hamachi, S. Shinkai, Pyrenylboronic acid as a
novel entry for photochemical DNA cleavage, Tetrahedron Lett. 38 (1997)
2479–2482.
[40] H. Hidaka, H. Kubota, M. Graätzel, E. Pelizzetti, N. Serpone, Photodegradation
of surfactants II: degradation of sodium dodecylbenzene sulphonate catalysed
by titanium dioxide particles, J. Photochem. 35 (1986) 219–230.
[41] H.M. Chawla, S. Mrig, Simultaneous quantitative estimation of oxybenzone
and 2-ethylhexyl-4-methoxycinnamate in sunscreen formulations by second
order derivative spectrophotometry, J. Anal. Chem. 64 (2009) 585–592.
[42] S.P. Huong, V. Andrieu, J.P. Reynier, E. Rocher, J.D. Fourneron, The
photoisomerization of the sunscreen ethylhexyl p-methoxy cinnamate and
its influence on the sun protection factor, J. Photochem. Photobiol. A 186
(2007) 65–70.
[16] U.E. Spichiger, Chemical Sensors and Biosensors for Medical and Biological
Applications, Wiley-VCH, Weinheim, 1998.
[17] W. Czarnik Anthony, Fluorescent chemosensors of ion and molecule
recognition, in: Interfacial Design and Chemical Sensing, American Chemical
Society, 1994, pp. 314–323.
[18] B.L. Feringa, R.A. van Delden, M.K.J. ter Wiel, Chiroptical Molecular Switches,
Wiley-VCH Verlag GmbH, 2001.
[19] F. Vogtle, D. Udelhofen, S. Abramson, B. Fuchs, Photoresponsive lower-rim
azobenzene substituted and bridged calix[4]arenes, J. Photochem. Photobiol. A
– Chem. 131 (2000) 41–48.
[43] S. Pattanaargson, T. Munhapol, P. Hirunsupachot, P. Luangthongaram,
Photoisomerization of octyl methoxycinnamate, J. Photochem. Photobiol. A –
Chem. 161 (2004) 269–274.
[20] M. Sukwattanasinitt, R. Rojanathanes, T. Tuntulani, Y. Sritana-Anant, V.
Ruangpornvisuti,
Synthesis
of
stilbene
crown
ether
p-tert-
butylcalix[4]arenes, Tetrahedron Lett. 42 (2001) 5291–5293.