Photochemistry and Photobiology, 2004, 80 317
a Bischoff Chromatography NC-04 column Ultrasep ES 100 RP, 18–6.0
lm (250 3 4.0 mm), at room temperature (258C). A Waters-Micromass
Qtof-Ultimaä API mass spectrometer was used in positive mode (ESIþ) to
identify the photodegradation products.
Chemical actinometer. Photochemical titration, for measurement of the
UV-B (290–320 nm) and UV-A (320–400 nm) light dose, was done
according to the polychromatic actinometric method of Allen et al. (12). It
is based on the photolysis of an aqueous 2-nitrobenzaldehyde solution for
which the quantum yield was established: it is of 0.5 from 290 to 400 nm
in solid, liquid and vapor phases. The 2-nitrobenzaldehyde actinometer
solution absorbs all photons between 290 and 400 nm. All the photons
having wavelengths in the 290–400 nm range convert 2-nitrobenzaldehyde
into 2-nitrosobenzoic acid with equivalent efficiency. Experiments were
conducted in a 1 cm quartz cell in which 2-nitrobenzaldehyde actinometer
solutions (0.1 M, EtOH–water 1:1) with NaOH (0.01 M) and phenolphtha-
lein indicator were illuminated using the xenon lamp at 16 mW cmꢀ2
(WG320 filter). The solution pH was noted as a function of illumination
time. When the desired dose of UV photons had been absorbed by the
actinometer solution, sufficient acid was formed to neutralize the added
NaOH, and then the pH fell rapidly.
Preparation of 1-(4-tert-butylphenyl)-2-decanyl-3-(49-methoxyphenyl)-
propane-1,3-dione (C10-DBM). According to the procedure described by
Clark and Miller (13,14) and Marzinzik and Felder (15), an aqueous
solution of tetra-n-butylammonium fluoride (0.017 mol) was added to BM-
DBM (0.010 mol). By heating this mixture to 808C, under reduced pressure
(evaporator) for 3 h, water escaped leaving an anhydrous yellow residue.
This residue was dissolved in THF (25 mL) and 1-bromodecane (0.030
mol) was added. Then, the mixture was stirred at 708C for 2 h. The solution
was evaporated, giving a yellow viscous residue. This was purified on silica
Figure 1. Structure of the two UV filters studied: BM-DBM and C10-
DBM (H and C are numbered for NMR assignments).
In this study, we present a new long-chain UV filter, the 1-(4-
tert-butylphenyl)-2-decanyl-3-(49-methoxyphenyl)-propane-1,3-
dione, called C10-DBM, derived from BM-DBM by grafting a
10-carbon aliphatic chain to the a-carbonyl position (Fig. 1). The
chain length was chosen to give amphiphilic properties to the
molecule. It is well known that such properties are obtained with
aliphatic chain lengths above eight carbons (11).
1
column with dichloromethane as eluent (42% yield). H NMR (400 MHz,
CDCl3), dppm, JHz: 8.00 (m, 2H, J 5 8.8; H6); 7.93 (m, 2H, J 5 8.4; H8);
7.46 (m, 2H, J 5 8.4; H9); 6.94 (m, 2H, J 5 8.8; H10); 5.11 (t, 1H, J 5 6.6;
H11); 3.87 (s, 3H, H12); 2.12 (m, 2H, H18); 1.34 (s, 9H, H14); 1.28 (m, 16H,
H16 and H17); 0.89 (t, 3H, J 5 6.7; H15). 13C NMR assignments were
ascertained with the help of 1H–1H COSY, 1H–13C HSQC and HMBC
spectra. 13C NMR (100 MHz, CDCl3), dppm: 196.1 (C2); 195.1 (C1); 163.9
(C3); 157.3 (C4); 133.9 (C5); 131.2 (C6); 129.5 (C7); 128.8 (C8); 125.9 (C9);
114.2 (C10); 57.7 (C11); 55.7 (C12); 35.3 (C13); 32.1–28.6 (C17); 31.2 (C14);
29.9 (C18); 22.9 (C16); 14.3 (C15). IR (KBr), mcmꢀ1 : 2924; 1692; 1663;
1602–1464; 1262; 1171; 844. Mass spectrometry (MS) (ES, MeOH,
positive mode) m/z 5 451 [MHþ]. Anal. Calcd for C30H42O3: C, 79.96; H,
9.39; O, 10.65%. Found: C, 80.07; H, 9.69; O, 10.87%.
First, we demonstrate that C10-DBM is a BM-DBM precursor.
Then, a kinetic model for the photochemistry of C10-DBM is
proposed.
MATERIALS AND METHODS
Preparation of samples for HPLC and MS analyses. BM-DBM and
C10-DBM solutions in acetonitrile were irradiated at 20 mW cmꢀ2 for 6 h.
The solutions were stirred magnetically. A solution aliquot (200 lL) was
taken every 10 min for HPLC and every 30 min for MS analysis. Separation
of C10-DBM and BM-DBM was obtained under the isocratic conditions
H2O–CH3CN (10–90% vol/vol) at flow rate 1.5 mL minꢀ1, the injection
volume was 10 lL. An external calibration was achieved with an automatic
injector. A solution of 1-decene in acetonitrile was used to determine its
retention time under these conditions. MS analyses (ESIþ) were done by
adding 0.1% formic acid in aliquots, with a capillary voltage of 3 kV and
a cone voltage of 65 V. The source temperature was 808C.
Chemicals. Tetra-n-butylammonium fluoride, 75% wt/wt aqueous solution,
1-bromodecane 98% and 2-nitrobenzaldehyde 98% were obtained from
Avocado (Heysham, Lancashire, UK). BM-DBM (Parsol 1789) was
obtained from Givaudan-Roure (Geneva, Switzerland). Dichloromethane,
hexane and acetonitrile (high-performance liquid chromatography [HPLC]
grade) and NaOH (analytical grade) were obtained from SDS (Peypin,
France). Absolute ethanol for analysis was obtained from Prolabo
(Fontenay sous Bois, France) and tetrahydrofuran (THF) from Carlo
ERBA RPE (Val de Reuil, France). 1-Decene 96% was obtained from
Sigma (St. Louis, MO). Silica gel (0.063–0.200 mm) was obtained from
Merck (Darmstadt, Germany). To determine the pH, Hydrion Brilliant Dip
Stik (pH range 6.5–13.00) from Sigma–Aldrich (Steinheim, Germany) and
phenolphthalein, 0.5% (EtOH) from Alfa Aesar (Karlsruhe, Germany) were
used.
Kinetic experiments. A C10-DBM solution in hexane (3.9 3 10ꢀ5 M)
was irradiated at 16 mW cmꢀ2 (WG320 filter) for 180 min. The solution
was stirred magnetically. UV spectra were recorded every 10 min.
Irradiation was stopped and absorbance recorded as soon as possible to
avoid artifacts due to the occurrence of thermal relaxation. At the end of
irradiation, the solution was kept at room temperature. Thermal relaxation
was studied by recording UV spectra every 10 min (for 230 min) and then
every 60 min over the subsequent hours.
Instruments. Proton nuclear magnetic resonance (1H NMR), carbon
nuclear magnetic resonance (13C NMR), 1H–1H Correlation Spectroscopy
(1H–1H COSY), 1H–13
C Heteronuclear Simple Quantum Correlation
(1H–13C HSQC) and 1H–13C Heteronulcear Multiple Bond Correlation
(HMBC) spectra were obtained with a Bruker ARX-400 MHz. Infrared
spectra were recorded with a Perkin–Elmer FT-IR 1760 X and UV spectra
with a HP 8452A Diode Array Spectrometer. Irradiance measurements were
recorded with a UV meter 70380 from Oriel Instruments (response between
280 and 400 nm with maximum sensitivity at 370 nm, Oriel Comp.,
Stratford, CT). Irradiation was carried out using a 150 W xenon lamp; the
lamp output was sent through a water filter (5 cm path length) to remove
most of the IR radiations. An optical filter WG320 (Oriel Corporation,
Stratford, CT) of 3 mm removed wavelengths below 290 nm (actinometric
and kinetics experiments). The output of the irradiation system was focused
onto the face of a 1 cm quartz cell. Samples were stirred while being
illuminated. HPLC analyses were performed with a Waters Alliance 2695
RESULTS
UV absorption characteristics
The absorption spectrum of BM-DBM in acetonitrile at room
temperature presents two characteristic bands. The first absorption
band, with a wavelength of maximum absorbance (kmax) at 357
nm, has a large molar absorption coefficient of 33 000 Mꢀ1 cmꢀ1
and can be assigned to a p–p* transition of the chelated enol form
(in the C5O conjugated ethylene system) (8,16). The second, with
apparatus, with a Photodiode Array Detector. UV absorbance was
monitored at 192 nm by millennium 4.0 software. HPLC separation used