Synthesis of novel fluorescent cyclohexenone derivatives and their partitioning study in ionic micellar media

Article abstract of DOI:10.1007/s10895-010-0657-6

An approach is demonstrated toward the synthesis of four novel cyclohexenone derivatives (CDs) via a convenient route of Michael addition of ethyl acetoacetate. The molecular structures of CDs were confirmed by means of FT-IR, ¹H NMR, EIMS, UV

Full text of DOI:10.1007/s10895-010-0657-6

J Fluoresc (2010) 20:1049–1059
DOI 10.1007/s10895-010-0657-6
ORIGINAL PAPER
Synthesis of Novel Fluorescent Cyclohexenone Derivatives
and their Partitioning Study in Ionic Micellar Media
Amir Badshah & Saleem Nawaz &
Muhammad Faizan Nazar & Syed Sakhawat Shah &
Aurangzeb Hasan
Received: 23 January 2010 /Accepted: 26 March 2010 /Published online: 6 May 2010
#
Springer Science+Business Media, LLC 2010
Abstract An approach is demonstrated toward the synthe-
sis of four novel cyclohexenone derivatives (CDs) via a
convenient route of Michael addition of ethyl acetoacetate.
The molecular structures of CDs were confirmed by means
Introduction
Consequently amplification of a large number of dyes and
specific probe molecules has rapidly opened the window for
luminescence probing techniques over the past three decades
[1]. The design of new fluorescent probe molecules is a
subject of intense research as they are valuable probes to
explore the structural as well as functional aspects of
biological systems [2]. Cyclic chalcones are carriers of
different types of biological activity [3, 4]. The motive for
their preparation is a variety of medical effects. Cyclo-
hexenone carboxylates have known to possess anti-cancer
[5], anti-HIV [6, 7], anti-fungal [8], anti-tumor [9, 10],
anticonvulsant [11, 12] and antitubercular [13] activity. A
series of novel compounds has been synthesized; known as
cyclohexenoic long chain fatty alcohols, which are used in
the treatment of neurological disorders [14]. From a chemical
point of view, an important feature of chalcones is the ability
to act as activated unsaturated systems in conjugated addition
reactions of carbanions in the presence of basic catalysts [15,
16]. This type of reaction may be exploited for the
preparation of 3,5-diaryl-6-carbethoxycyclohexenones via
Michael addition of ethyl acetoacetate. The mentioned
cyclohexenones are effective synthons in some projected
synthesis of benzoselenadiazoles and benzothiadiazoles [17],
spirocyclohexanones [18], carbazole derivatives [19], fused
isoxazoles and pyrazoles [20, 21].
1
of FT-IR, H NMR, EIMS, UV and also by X-ray single
crystal structure analysis. CDs are strongly fluorescent
compounds and their fluorescent spectra exhibits intense
violet fluorescence. To model the binding to biological
membranes the behavior of CDs in micellar solutions of a
cationic surfactant, cetyltrimethylammonium bromide
(CTAB) and an anionic surfactant, sodium dodecylsulfate
(SDS) has also been examined. The characteristics of
partition and binding interactions of CDs with CTAB and
SDS were investigated by UV-Visible and fluorescence
spectroscopic techniques. Higher values of all mentioned
interactions in case of CTAB, compared to SDS, indicate
that there are greater interactions between the CDs and
CTAB than with SDS.
.
Keywords Cyclohexenone derivatives
1
.
.
.
Ionic surfactants H NMR Fluorescence spectroscopy
Partition and binding interactions
The synthesis of 5-aryl-6-carbethoxy-2-cyclohexenone sub-
stituted in position 3 with a 2-furanyl moiety through the
Michael addition of ethyl acetoacetate to 3-aryl-1-(2-furanyl)-2-
propenones has already been briefly described [22]. This paper
presents the synthesis of some new 5-aryl-6-carbethoxy-3-(2-
furanyl)-2-cyclohexenone, whose various chemical functions
and optical properties commend them as valuable compounds
for applications in violet-light-emitting devices (light emitting
:
:
:
:
A. Badshah S. Nawaz M. F. Nazar (*) S. S. Shah A. Hasan
Department of Chemistry, Quaid-i-Azam University,
45320 Islamabad, Pakistan
e-mail: faizan_qau@yahoo.com
M. F. Nazar
School of Chemistry, University of Bristol,
Bristol BS8 1TS, UK

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J Fluoresc (2010) 20:1049–1059
laser, laser pointers, light-emitting diodes etc.) [23] or
fluorescent dyes. Herein we report the synthesis of cyclo-
hexenone derivatives and their photoluminescent properties.
The partitioning of cyclohexenone derivatives (CDs)
was also studied quantitatively between the micelles and
surrounding aqueous bulk. Conjugated cyclic enones react
smoothly in water with a variety of aldehydes (Baylis-
Hillman reaction) in the presence of surfactants above their
critical micelle concentrations [24]. Efficient removal and
sorption of 2-cyclohexenone to a benzyltrimethylammo-
nium cation has also been developed [25]. The additive
must partition to a well-defined and energetically favorable
environment, orientation, and conformation in the mem-
brane bilayers before diffusing into intrabilayer receptor
binding cell [26]. The physical behavior of the surfactant
micelles can be visualized as the construction of model
membrane to mimic a biological system. The experimental
model is useful for studying the interaction of biological
surfaces with solubilizate [27, 28].
Compound characterization techniques
Rf values were calculated by using precoated silica gel
aluminum backed plates Kiesel gel 60F254 Merck (Germany)
using ethylacetate : pet-ether (1:4) as developing solvents.
Melting points of the compounds were determined in open
capillaries using Gallenkamp melting point apparatus and are
uncorrected. The FTIR spectral data were recorded on Bio-
1
Rad Merlin Spectrophotometer using KBr discs. H NMR
spectra were recorded on Bruker (300 MHz) AM-250
spectrometer in CDCl3 solution using TMS as internal
standard. EIMS was recorded on Agilent mass spectrometer.
Purity of each compound was ascertained by thin layer
chromatography. The purification of synthesized com-
pounds was achieved mostly through recrystallization,
the use of solvent extraction, or by making preparative
thin layer chromatography or column chromatography
whenever required.
The aggregation behavior of surfactants-CDs in water
was elucidated using simple UV-visible spectroscopy,
differential UV-visible spectroscopy and Steady-state fluo-
rescence spectroscopy (SSFS). By employing the above
mentioned spectroscopic techniques, the micellar-water
partition coefficient (Kx), the standard free energy change
of solubilization (ΔGp), the additive-surfactant binding
constant (Kb), the binding energy (ΔGb), the number of
binding sites or binding capacity (nb) and the number of
additive molecules per micelle solution (n) have been
calculated at 25 °C. The results point toward a strong
partitioning of the cyclohexenone derivatives in favor of the
micellar pseudo-phase.
Steady-state fluorescence measurements
Steady-state fluorescence (SSF) was performed on a Perkin
Elmer LS 55 Luminescence Spectrometer with PC con-
trolled software FinWinLab. The Photo Multiplier tube
(PMT) voltage was kept at 665 V. The emission and
excitation slits were fixed at 6.0 nm each. The excitation
wavelength was taken as 331 nm. The scan range used was
from 350–600 nm. Polarizers were kept clear and no cutoff
was operating during the scan. The temperature of the cell
was fixed with the help of an external circulator water bath.
Spectrophotometric (UV-visible) measurements
Spectrophotometric measurements were performed on a
Perkin-Elmer Lambda 20 ultraviolet-visible spectrophotome-
ter with 1.0 cm quartz cells at a temperature of 25.0 0.1 °C.
Differential absorbance measurements were made in such a
way that additive solution of a particular concentration was
kept on the reference side and the surfactant-additive solution
on the sample side in the spectrophotometer.
Materials and methods
Reagents
The reagents; ethyl acetoacetate, 3-Bromobenzaldehyde, 2-
Chlorobenzaldehyde, 4-Ethoxybezaldehyde, 3-Methoxy-
benzaldehyde were purchased from Fluka (Germany). The
liquid reagents were distilled at their boiling points and the
solid reagents were characterized by recording their melting
points. No further purification was required. Sulphuric acid
and hydrochloric acid (37%) were obtained from Stedee
Ltd. The solvents chloroform, ethyl acetate, absolute
ethanol and pet ether were purchased from Sigma Aldrich
(Germany). All the solvents were used after necessary
purification and drying according to the standard proce-
dures. The dried solvents were stored over molecular sieves
(4Å). Sodium dodecylsulphate (SDS) was 99% pure and
was purchased from Fluka. Cetyltrimethylammonium bro-
mide (CTAB) was purchased from Sigma Chemical Co.
General synthetic methods
In view of the immense pharmacological and physiological
importance of cyclohexenone, the present work was
undertaken to synthesize this class of organic compounds
with variable substituents to diversify in the ring of the
chalcones. As such a variety of cyclohexenone derivatives
were obtained in moderate to good yields. The synthetic
strategy for the titled compounds is outlined in the
following Scheme 1.
Furanyl-containing chalcone analog 1 (3 mmol) and
ethyl acetoacetate 2 (0.39 g, 0.40 mL, 3 mmol) were

J Fluoresc (2010) 20:1049–1059
1051
Scheme 1 General methodology for the synthesis of cyclohexenone derivatives
refluxed for 2 h in 10–15 mL ethanol in the presence of
0.5 mL 10% NaOH. The reaction mixture was then poured
with good stirring into 200 mL ice-cold water and kept at
room temperature until the reaction product separated as a
solid, which was filtered off and recrystallized from
ethanol.
the vinylic proton in the position C-3 of the cyclohexenone
rings, that occurs at approximately 6.61 ppm integrating for
one proton, and confirms that the intramolecular cyclo-
condensation subsequent to the Michael addition actually
took place. The signal due to the C-5 methylene protons
appeared as two doublets at 3.03 ppm and at 3.07 ppm
respectively thereby indicating that they are diastereo-
tropic protons. The signal due to C6-H appeared as a
multiplet centered at 2.83 ppm integrating for one
proton. The C1-H proton appeared as doublet at
3.73 ppm integrating for one proton. As for the protons
Results and discussion
Synthesis of cyclohexenone
1
in the aromatic region, the HNMR spectrum allowed the
The reaction of chalcones and their heterocyclic analogs
with ethyl acetoacetate in the presence of basic condition
underwent Michael addition followed by internal claisen
condensation to produce cyclohexenone, as outlined in
Scheme 1.
assignments of the protons in the furane ring at 6.53 ppm,
6.85 ppm and 7.23 ppm. The number of the other aromatic
protons of the aryl substituent in the C-6 of the cyclo-
hexenone ring that was integrated in the H NMR spectra
of compound (1FuE) was always in good agreement with
the factual one.
The mass spectrum of (1FuE) is also in accordance with
the proposed structure showed characteristic peaks; how-
ever, the molecular ion peak is absent. The fragment peak at
m/z 282 is due to the loss of ester moiety. The base peak
appeared at m/z 134 as a result of Retro-Diels-Alder fission
of cyclohexene ring. The peaks appeared at m/z 254 and
209 due to the loss of carbon monoxide molecule and then
side chain respectively.
To understand their real structures [29], the single crystal
of compound (1FuE) is determined by single-crystal X-ray
diffraction. The molecular structure and packing diagram
(Fig. 1) are discussed with their structural features, while
their selected bond lengths and bond angles are shown in
Table 1.
1
The organic compounds were separated out by pouring
the reaction mixture into water. All Compounds precipitat-
ed after being kept for several days. The solid products
were separated by filtration, dried and recrystallized from
ethanol. The yields of the cyclocondensation were good,
varying from 63 to 70%. Structural analysis of the newly
synthesized cyclohexenone was done by analytical and
spectral data. The IR spectra of these compounds revealed a
sharp strong absorption band around 1,730–1,740 cm−1 that
can be correlated with the presence of the ester function in
the structure of cyclohexenone. Furthermore, another sharp
strong absorption band at around 1,650–1,660 cm−1
assigned to the conjugated carbonyl group. The bands at
2,900–3,100 cm−1 accounted for the OH group due to enol
form and the hydrogen bonded carbonyl of ester group
appeared around 1,500–1,600 cm−1.
The synthetic procedure used for the synthesis of (1FuE)
was also used for the synthesis of other members of the
series. The molar ratio, physical, FTIR, 1H NMR and EIMS
data for these compounds are given below:
1
The H-NMR spectra substantiated the results of the IR
analysis. One of the representative compounds of cyclo-
hexenone series, ethyl 6-(4-ethoxyphenyl)-4-(furan-2-yl)-2-
oxocyclohex-3-ene-1-carboxylate (1FuE), has been
described here in detail. In the 1H-NMR spectrum of
(1FuE), the ethyl protons resonated as a triplet and a quartet
at 1.07 ppm 4.07 ppm integrating for three and two protons
respectively. The characteristic signal in the 1H NMR
spectrum of compound (1FuE) is however the singlet of
Ethyl-6-(3-bromophenyl)-4-(furan-2-yl)-2-oxocyclohex-3-
ene-1-carboxylate (1FuB) Golden solid, Yield 2.85 g
1
(63%); m.p.: 87–89 °C. H NMR (CDCl3, 300 MHz): δ
1.08 (t, J=7.2 Hz, 3H), 4.07 (q, J=7.2 Hz, 2H), 3.02 (dd,
J1=2.4 Hz, J2=17.0, 1H), 2.79–2.87 (m, 1H), 3.73 (dd J1=

1052
J Fluoresc (2010) 20:1049–1059
Fig. 1 X-ray Molecular structure of (1FuE). The displacement ellipsoids are drawn at the 40% probability level and the H atoms are shown as small spheres
of arbitrary radii, (b) The packing diagram of the (1FuE), viewed along the a-axis showing the weak hydrogen-bond and C—H π electron interactions
1
2.8 Hz, J2=6.70, 2H), 6.61 (s, 1H), 7.58 (d, J=1.8 Hz, 1H),
6.54 (dd J1=1.8 Hz, J2=3.3, 1H), 6.77 (d, J=3.6 Hz, 1H),
7.23–7.42 (m, 4H). IR (KBr, cm−1): 639, 1552, 1609, 1666,
1725, 2993. MS (EI): m/z (%) = 318(25), 134(100), 106
(20), 51(5), 39(4), 290(3), 209(2).
(70%); m.p.: 114–116 °C. H NMR (CDCl3, 300 MHz): δ
1.07 (t, J=7.2 Hz, 3H), 4.07 (q, J=6.9 Hz, 2H), 3.03 (dd,
J1=3.0 Hz, J2=18.0, 1H), 2.72–2.81 (m, 1H), 3.72 (dd J1=
2.7 Hz, J2=6.75, 2H), 6.60 (s, 1H), 7.57 (d, J=1.5 Hz, 1H),
6.53 (dd J1=1.8 Hz, J2=3.4, 1H), 6.75 (d, J=3.6 Hz, 1H),
6.85 (dd J1=2.1 Hz, J2=6.6, 2H), 7.23 (dd J1=3.0 Hz, J2=
6.6, 2H), 1.43 (t, J=7.2 Hz, 3H), 4.09 (q, J=7.1 Hz, 2H).
IR (KBr, cm−1): 1038, 1510, 1604, 1657, 1729, 2977. MS
(EI): m/z (%) = 282(33), 134(100), 106(10), 51(6), 39(5),
254(12), 209(2), 119(60), 91(10), 65(3).
Ethyl-6-(2-chlorophenyl)-4-(furan-2-yl)-2-oxocyclohex-3-
ene-1-carboxylate (1FuC) Beige solid, Yield 3.1 g (67%);
1
m.p.: 116–118 °C. H NMR (CDCl3, 300 MHz): δ 1.07 (t,
J=7.1 Hz, 3H), 4.07 (q, J=7.1 Hz, 2H), 3.08 (dd, J1=
2.6 Hz, J2=17.5, 1H), 2.75–2.82 (m, 1H), 3.79 (dd J1=
2.9 Hz, J2=6.9, 2H), 6.62 (s, 1H), 7.58 (d, J=1.5 Hz, 1H),
6.54 (dd J1=1.8 Hz, J2=3.3, 1H), 6.78 (d, J=3.8 Hz, 1H),
7.20–7.44 (m, 4H). IR (KBr, cm−1): 750, 1512, 1600, 1652,
1736, 2978. MS (EI): m/z (%) = 272(33), 134(100), 106
(20), 51(7), 39(5), 244(2), 209(2).
Ethyl 6-(3-methoxyphenyl)-4-(furan-2-yl)-2-oxocyclohex-3-
ene-1-carboxylate (1FuM) Orange solid, Yield 3.0 g
(65%); m.p.: 82–84 °C. H NMR (CDCl3, 300 MHz): δ
1
1.07 (t, J=7.0 Hz, 3H), 4.09 (q, J=6.9 Hz, 2H), 3.00 (dd,
J1=2.7 Hz, J2=17.0, 1H), 2.81–2.87 (m, 1H), 3.74 (dd J1=
2.8 Hz, J2=6.2, 2H), 6.60 (s, 1H), 7.57 (d, J=1.7 Hz, 1H),
6.53 (dd J1=1.8 Hz, J2=3.4, 1H), 6.77 (d, J=3.6 Hz, 1H),
6.99–7.25 (m, 4H), 3.81 (s, 3H). IR (KBr, cm−1): 1050,
1523, 1603, 1658, 1729, 2980. MS (EI): m/z (%) = 268(30),
134(100), 106(5), 51(4), 39(4), 240(5), 209(3), 119(12), 91
(10), 65(3).
Ethyl 6-(4-ethoxyphenyl)-4-(furan-2-yl)-2-oxocyclohex-3-
ene-1-carboxylate (1FuE) Bright yellow solid, Yield 3.3 g
Table 1 Selected bond lengths (Å) and angles (deg) for compound
1FuE
On the basis of the aforementioned results the structures
of cyclohexenone derivatives are as follows (Table 2):
Bond lengths
O1—C1
1.353 (2)
O1—C4
1.3642 (16)
1.1949 (18)
1.4449 (18)
1.4164 (17)
1.5090 (19)
O2—C7
1.2186 (17)
1.3157 (18)
1.3616 (15)
1.4367 (19)
1.5095 (17)
O3—C11
O4—C12
O5—C20
C8—C11
O4—C11
Absorption and emission spectra of cyclohexenone
derivatives
O5—C17
C4—C5
C9—C14
The UV-Visible absorption spectra and fluorescence emis-
sion spectra of cyclohexenone derivatives are shown in
Fig. 2. The absorptions of cyclohexenone derivatives were
located at 331 nm. Their excitation wavelengths were all
fixed at 331 nm. It is found that their intensity of
fluorescence differs from each other but shows the same
emission maximum (λem) of 412 nm in the violet region.
Bond angles
C6—C5—C4
C11—C8—C7
C14—C9—C10
O5—C17—C16
C19—C14—C9
121.59 (12)
111.43 (11)
114.30 (10)
116.00 (11)
122.46 (11)
C6—C5—C10
C11—C8—C9
C14—C9—C8
O5—C17—C18
C15—C14—C9
121.65 (12)
110.98 (11)
112.04 (10)
124.71 (11)
120.24 (11)

J Fluoresc (2010) 20:1049–1059
1053
Table 2 Structures and Rf values of cyclohexenone derivatives
Molecular
Formula
Molecular
Weight
Compound
Structure
aRf Values x 100
O
O
O
1FuB
C19H17BrO4
389
67
O
Br
O
O
O
1FuC
1FuE
1FuM
C19H17ClO4
C21H22O5
C20H20O5
344.8
354.4
340.4
62
57
54
O
Cl
O
O
O
O
OC2H5
O
O
O
O
OCH3
aSolvent for Rf values = Pet-ether:ethylacetae (4:1)
Interactions of cyclohexenone derivatives with ionic
surfactants
enter into the micelle. Although the additive molecules are
incorporated in the micelles, their chromophores are still
oriented near the surface and hence absorb light more
favorably than in the aqueous bulk solution [30]. The
micellar interior is a nonpolar moiety where the aqueous
bulk is a polar. So the hydrophobic 1FuE molecules prefer
to reside inside or near the nonpolar core of the micelle.
After micelle formation the absorbance of the system
become constant on further addition of surfactants (Inset
of Fig. 3).
CDs-micelle interaction is better explained by quantify-
ing their magnitude through the elucidation of additive-
micelle partition coefficient (Kx), the standard free energy
of solubilization (ΔGp) of the additive in micelles, the
additive-surfactant binding constant (Kb), the binding
energy (ΔGb), the number of binding sites or binding
capacity (nb) and the number of additive molecules in a
micelle solution (n). In case where interactions of the
molecule with its surrounding environment are intrinsically
related to spectral characteristics, their changes can be used
for the determination of corresponding partition coefficients
and approximate numbers of dye molecules per micelle.
UV visible absorption spectroscopy
Simple absorption spectra of cyclohexenone derivatives
(CDs) with varying concentration of surfactants (SDS and
CTAB) give some useful information about the interaction
of CDs and the surfactant. Figure 3 shows the simple
absorbance spectra of one of the representative compound
of cyclohexenone series (1FuE) with varying concentration
of surfactants i.e. SDS (0.006 mol.dm−3 to 0.02 mol.dm−3)
and CTAB (0.0006 mol.dm−3 to 0.002 mol.dm−3). The
absorbance of 1FuE increases with increasing concentration
of surfactants. The interaction between additive and the
surfactants below CMC allow the additive to absorb light
more favorably; hence absorbance is enhanced in the sub-
micellar region. The leveling off the curve above CMC
shows the maximum solubilization of additive molecules
within the micelle.
The increase in absorbance at micellar concentration is
due to the tendency of hydrophobic additive molecules to

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J Fluoresc (2010) 20:1049–1059
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
350
300
250
200
150
100
50
1FuB
1FuC
1FuE
1FuM
a
b
1FuB
1FuC
1FuE
1FuM
0
350
250
300
350
400
450
500
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
Fig. 2 Spectra of aqueous solution (3% ethanol) of cyclohexenone derivatives with the concentration of 3×10−5 M; a The normalized absorption
spectra b The emission spectra
The approximate number of additive molecules incorpo-
rated into a single micelle (n) is calculated by using the
following relations [30, 31]. Results of all the cyclo-
hexenone derivatives (CDs) are shown in Table 3.
surfactant concentration and N is the mean aggregation
number of micelles at CMC in water. The normal CMCs of
the CTAB and SDS are 0.9 mM and 8.2 mM respectively
[32]. Cm is the concentration of solubilized additive, which
is determined, as [33]:
Cm
n ¼
ð1Þ
Ao ꢀ A
M
Cm ¼
ð3Þ
"o ꢀ "m
and
Here Ao is the absorbance of additive solution in the
absence of surfactant, A is the absorbance at any point in the
presence of surfactant above the CMC, εo is calculated from
Ao, and εm is determined at higher surfactant concentration
above the CMC when the absorbance of the additive-
Cs ꢀ CMC
M ¼
ð2Þ
N
Here Cm is the concentration of additive solubilized in
the micelle, M is the micelle concentration, Cs is the total
0.40
1.2
1.2
0.38
a
b
0.36
1.0
0.34
0.35
1.0
0.8
0.32
0.30
0.6
0.4
0.30
0.25
0.20
0.15
0.10
0.28
6.0x10-4
0.8
9.0x10-4
1.2x10-3
1.5x10-3
-3
1.8x10-3
2.1x1 0-3
0.2
6.0x10-3
9.0x10-3
1.2x10-2
1.5x10-2
-3
1.8x10-2
2.1x10-2
[CTAB] mol dm
[SDS] mol dm
0.6
0.4
0.2
0.0
250
300
350
Wavelength (nm)
400
450
250
300
350
Wavelength (nm)
400
450
Fig. 3 Simple absorbance spectra of 1FuE with varying concentration
of surfactants in aqueous solution at 25 °C, a CTAB b SDS. Arrow
indicates change in absorbance of 1FuE with increasing surfactants
concentration. Inset: Relation between absorbance of (Surfactants +
additive) and concentration of surfactants

J Fluoresc (2010) 20:1049–1059
1055
Table 3 Calculation of n, Kc,
Kx and ΔGp for cyclohexenone
derivatives in micellar solution
of ionic surfactants
Surfactant
Compound
n=Cm/M
Kc (dm3mol−1
)
Kx
ΔGp (kJ/mol)
CTAB
1FuB
1FuC
1FuE
1FuM
1FuB
1FuC
1FuE
1FuM
4
6
6
5
1
1
1
1
2.50×103
4.21×103
4.88×103
3.60×103
3.73×102
5.19×102
7.21×102
4.16×102
1.39×105
2.34×105
2.71×105
2.00×105
2.07×104
2.88×104
4.01×104
2.31×104
−29.34
−30.63
−30.99
−30.24
−24.62
−25.44
−26.26
−24.89
SDS
surfactant solution becomes almost constant. The micellar
aggregation number used for CTAB is 80 and for SDS it is
70 [34]. For a particular concentration of CTAB (Cs), higher
value of ‘n’ shows the more hydrophobicity of CDs in
aqueous solution than for SDS.
nonpolar central region and the relatively polar interfacial
region of the micelles [35, 36]. The partitioning of the
additive molecules in water micelle system is calculated
using equation proposed by Kawamura et al. [37]. The
equation is given as:
1
1
1
À
Á
¼
þ
ð4Þ
Differential absorbance spectra of 1FUE with CTAB
KcΔA Ca þ Cmo
ΔA
ΔA
1
1
s
Differential spectroscopy technique was utilized to study the
partitioning of cyclohexenone derivatives from aqueous to the
micellar environment. Partition coefficient (Kx) results are
intrinsically valuable providing essential data relating to the
interactions of organic solubilizate with the surfactant
micelles and the locus of solubilizate within the micelles.
Figure 4 shows the differential absorption spectra of the
additive (1FuE) in presence of various concentrations of
surfactants (CTAB and SDS) independently at 25 °C. No shift
in the peaks was observed. The mounting value of ΔA with
increasing surfactant concentration can be seen in connection
to the increase in 1FuE molecules solubilized by the micelles.
Solubilized additive molecules thus distribute them-
selves according to their polarity between the highly
Where Ca is the additive concentration, Csmo represents
Cs-CMC0 (CMC0 is the CMC of surfactant in water), ΔA∞ is
the differential absorbance at the infinity of CsꢁKc can be
obtained through intercept and slope values of the straight
ꢀÀ
Á
line plot of 1/ΔA against 1 Ca þ Csmo , as shown in Fig. 5.
The value of Kc is given in Table 3.
The dimensionless partition coefficient Kx is related to
Kc as Kx ¼ Kcꢁnw, where nw is the number of moles of
water per dm3 (55.55 mol dm−3), and is reported in Table 3.
The standard free energy change of the transfer (ΔGp) of
additive from bulk water to micelle can be calculated using
the following relation:
ΔGp ¼ ꢀRT ln Kx
ð5Þ
a
b
0.20
0.6
0.4
0.15
0.10
0.05
0.00
-0.05
0.2
0.0
-0.2
250
300
350
400
450
250
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Fig. 4 Differential absorbance spectra of 1FuE with changing concentration of surfactants. a CTAB, b SDS

1056
J Fluoresc (2010) 20:1049–1059
a
b
8
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1FuB
1FuC
1FuE
1FuM
1FuB
1FuC
1FuE
1FuM
6
4
2
0
0.9
1.2
1.5
1.8
2.1
2.4
10
15
20
25
30
35
(Ca+Csmo -1 x 102dm3mol-1
)
(Ca+Cs )
mo -1 x 102dm3mol-1
Fig. 5 Plot of inverse of differential absorbance (1/ΔA) vs. (Ca+Csmo −1
)
of all the cyclohexenone derivatives and concentration of surfactants, a
CTAB, b SDS
Here T is absolute temperature and R is the gas constant.
The values of Kc, Kx and ΔGp of all the cyclohexenones
derivatives (CDs) are reported in Table 3. The negative ΔGp
value implies that the process of the additives partition is a
spontaneous one [38]. This can be justified due to the
hydrophobic nature of the cyclohexenone derivatives.
Different parameters obtained from spectroscopic measure-
ments indicate enhanced solubility of the cyclohexenones
derivatives in the micellar region. The increases in Kx values
with hydrophobicity of additive molecules indicate that
mainly the hydrophobic interactions between the additives
and the micelles control the solubilization. From the high
negative value of ΔGp it can be concluded that although some
interaction with the polar surface of the micelle is possible but
the most favored place is toward the micellar core.
Steady-state fluorescence spectroscopy study
Fluorescence emission spectroscopy is utilized to study the
interaction of cyclohexenone derivatives (CDs) with ionic
surfactants. Fluorescence measurements can give some
information on the binding of additive molecules to the
a
b
350
350
(1)
(1)
300
300
250
250
(2)
(2)
200
150
100
50
200
150
100
50
0
0
350
400
450
500
550
600
350
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
Fig. 6 Fluorescence emission spectra of 1FuE at varying concentration of surfactants; a CTAB, b SDS. (1) Fluorescence intensity of pure 1FuE,
(2) Arrow indicates that fluorescence intensity of 1FuE increases with decreasing surfactants concentration

J Fluoresc (2010) 20:1049–1059
1057
2.5
2.2
1.9
1.6
1.3
1
4
1FuB
1FuC
1FuE
1FuM
1FuB
1FuC
1FuE
1FuM
3.5
3
2.5
2
1.5
(b)
(a)
1
0.009
0.011
0.013
[SDS] mol dm-3
0.015
0.017
0.019
0.0009 0.0011 0.0013
0.0015 0.0017 0.0019
[CTAB] mol dm-3
Fig. 7 Stern-Volmer plot for the binding of all the cyclohexenone derivatives with surfactants; a CTAB, b SDS
surfactants, such as the binding constants and the number of
binding sites [39]. Fluorescence intensity of a compound can
be decreased by a variety of molecular interactions, viz.,
excited-state reactions, molecular rearrangements, energy
transfer, ground state complex formation and collisional
quenching. Such a decrease in intensity is called quenching
[40]. Fluorescence spectra of cyclohexenone derivatives
(CDs) in the presence of different amounts of surfactants
(CTAB and SDS) were recorded in the range of 350–600 nm
upon excitation at 331 nm.
constant and [Cs] is the concentration of surfactants (CTAB
and SDS) independently. Stern-Volmer plot (Io/I versus
[Cs]) for all the cyclohexenone derivatives (Fig. 7) revealed
the quenching type, may be static or dynamic, since the
characteristic Stern-Volmer plot of combined quenching
(both static and dynamic) is an upward curve (as in the
Fig. 7). The values of Ksv of all the cyclohexenones
derivatives (CDs) are shown in Table 4.
Analysis of binding equilibria
CTAB and SDS both caused a concentration-dependent
quenching of the intrinsic fluorescence of cyclohexenone
derivatives (CDs). Figure 6 indicated that there were
interactions between 1FuE and surfactants and the binding
resulted in a non-fluorescent complex without changing the
emission maximum.
The above results indicate that both surfactants (CTAB and
SDS) act as a quencher in its interaction with cyclo-
hexenone derivatives. The binding constant and binding
affinities were calculated using following equation [41]:
log ½ðIo ꢀ IÞ=Iꢂ ¼ log Kb þ nb log ½Csꢂ
ð7Þ
The fluorescence quenching data was analyzed by the
Stern-Volmer equation:
Where Kb is binding constant and nb is number of
binding sites or binding capacity. Io and I represent the
fluorescence intensities of the cyclohexenone derivatives in
the absence and presence of surfactants, respectively.
Plotting log [(Io-I)/I] versus log [Cs] gives rise to nb (from
slope) and log Kb (from intercept) as shown in Fig. 8.
Io=I ¼ 1 þ Ksv½Csꢂ
ð6Þ
Where Io and I are the steady-state fluorescence
intensities in the absence and presence of quencher
(surfactants), respectively, Ksv the Stern-Volmer quenching
Table 4 Calculation of nb, Kb,
Surfactant
Compound
nb
log Kb
Kb (dm3mol−1
)
ΔGb (kJ/mol)
Ksv (dm3mol−1
)
Ksv and ΔGb for cyclohexenone
derivatives in micellar solution
of ionic surfactants
CTAB
1FuB
1FuC
1FuE
1FuM
1FuB
1FuC
1FuE
1FuM
1.66
1.63
1.64
1.67
1.36
1.39
1.43
1.44
4.51
4.74
4.85
4.60
2.45
2.51
2.52
2.48
3.24×104
5.49×104
7.08×104
3.98×104
2.82×102
3.24×102
3.31×102
3.02×102
−25.73
−27.04
−27.67
−26.24
−13.98
−14.32
−14.38
−14.15
4.21×102
11.40×102
12.75×102
5.27×102
4.84×101
5.91×101
6.38×101
5.38×101
SDS

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J Fluoresc (2010) 20:1049–1059
a
b
0.4
0.2
0.0
0.30
0.15
1FuB
1FuC
1FuE
1FuM
1FuB
1FuC
1FuE
1FuM
0.00
-0.15
-0.30
-0.45
-0.2
-0.4
-0.6
-2.05
-2.00
-1.95
-1.90
-1.85
-1.80
-1.75
-1.70
-3.00
-2.95
-2.90
-2.85
-2.80
-2.75
-2.70
log [SDS]
log [CTAB]
Fig. 8 The plot for binding constant and binding sites of all cyclohexenone derivatives with surfactants; a CTAB, b SDS
The binding constant (Kb) thus obtained was used to
calculate the standard free energy change ΔGb of the additive
binding to surfactants from the following relationship:
membrane solubilization properties and in drug delivery
events are expected. This present work has also
provided a good example about how to increase the
solubility of water-insoluble drugs, to enhance their
loading efficiency and to optimize the dispersion in
drug carriers. Demanding effort has been made to
differentiate assemblies such as micelles, vesicles, lip-
osomes, microemulsions, polymers, and biological mem-
branes over the past decades. Cyclohexenone derivatives
are carriers of different types of biological activity.
Their partitioning study of solubilized system can
provide a useful insight into the process of solubiliza-
tion, which is applicable to the general problem of
membrane solubilization properties and in drug delivery
to quantify the degree of drug-micelle interaction.
The interaction of reported cyclohexenone with ionic
surfactants was investigated by UV-Visible and fluores-
cence spectroscopic techniques. Fluorescence intensity of
cyclohexenone derivatives at 412 nm dropped regularly
with the increasing concentrations of the surfactants
resulted in a non-fluorescent complex without changing
the emission maximum. Higher values of binding
constant, quenching constant, numbers of binding sites
and binding energy in case of CTAB, compared to SDS,
indicate that there are more interactions between the
cyclohexenone derivatives and CTAB than with SDS. It
is clear from the discussion above that the cyclohex-
enone partitions strongly into the nonpolar environment.
The results obtained from both UV-Visible and fluores-
cence spectroscopies support each other.
ΔGb ¼ ꢀRT ln Kb
ð8Þ
The values of binding constant Kb, binding energy
ΔGb and binding capacity nb thus determined were listed
in Table 4. The values of Kb are comparable. High values
of Kb indicate that the interactions between cyclohexenone
derivatives and CTAB are strong compared to SDS.
From the result it is also clear that all the four
compounds showed almost similar results in both cases
of SDS and CTAB. This may be due to the fact that the
substituents present are away from the binding sites and
affect the interactions very little. The smaller nb values
of SDS, compared to CTAB, indicate that there are less
binding sites available for it to bind cyclohexenone
derivatives. This may be due to the fact that the SDS
micellar surface is negatively charged and that of CTAB is
positively charged while there is an electron system in the
cyclohexenone derivatives. So in the case of CTAB there
may be more electrostatic interactions present, compared
to SDS, besides hydrophobic interactions.
Conclusion
The present work has described the synthesis and
photoluminescent properties of a new fluorescent series
of cyclohexenone derivatives. These compounds could
function as environment sensitive fluorescent probes and
their expanded applications to biological samples for
Acknowledgements Authors express gratitude the Quaid-i-Azam
University for provision of lab facility and gratefully acknowledge the
Higher Education Commission of Pakistan for sponsorship.

J Fluoresc (2010) 20:1049–1059
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