Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 257–262
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Photo-physical behavior of some antitumor anthracycline in solvent media with different polarity M.S. Zakerhamidi a,⇑, M. Johari-Ahar b, S.M. Seyed Ahmadian c, R. Kian a,c a
Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz, Iran Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Science, Tabriz, Iran c Department of Chemistry, Faculty of Basic Sciences, Azarbaijan Shahid Madani University, BP 5375171379 Tabriz, Iran b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Self-aggregation of aglycone moiety
show main change in solvatochromism of anthracycline. Intramolecular charge-transfer takes place in all three anthracycline samples. Reorientation of doxorubicin and epirubicin molecular functions in polar environment increases. Idarubicin’s functional groups reorientation increases in hydrogen bond donor media.
a r t i c l e
i n f o
Article history: Received 22 January 2014 Received in revised form 30 March 2014 Accepted 7 April 2014 Available online 21 April 2014 Keywords: Anthracycline Stereoisomer Linear solvation energy relationship Solvent polarity scale Dipole moment Intramolecular hydrogen bonding
a b s t r a c t Absorption and emission spectra of three antitumour anthracyclines, with various substituent and stereoisomer groups, were studied in different solvents. The solute’s photo-physical behavior strongly depends on solvent–solute interactions and solvent’s nature. Solvatochromic method was used to investigate dipole moments of these materials in ground and excited states. Spectral variations were analyzed via means of linear solvation energy relationships concept, proposed by Kamlet and Taft. The results explain the nature of specific and non-specific solvent–solute interactions and functional groups’ reorientation of studied anthracyclines in different media. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Anthraquinones (AQ) are one of the largest and most important classes of organic compounds in nature [1]. Anthraquinones derivatives have several industrial, biological and pharmaceutical applications [1–9]. The hydroxy anthraquinone chromophore has ⇑ Corresponding author. Tel.: +98 411 3393003; fax: +98 411 3347050. E-mail address: [email protected] (M.S. Zakerhamidi). http://dx.doi.org/10.1016/j.saa.2014.04.048 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
biological activity in several antitumour anthracyclines [2–4]. Antitumour anthracycline is the most useful group of cytotoxic anticancer drugs, which are commonly used in cancer chemotherapy. They have anthraquinone skeleton and aglycone ring coupled with amino sugar. The disparate substitute in these materials creates unique properties, such as intercalate between DNA, interfering in transcription and replication [5–8]. The molecular activity and medicinal properties of anthracycline derivatives can be determined through stereoisomerism and
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substituting the hydrogen of aglycone ring by groups like alkyls, amines, hydroxyl, etc. The photo-physical behaviors of substituted anthracycline molecules in visible reign are controlled by anthraquinone skeleton. The substituted groups on anthraquinone chromophore can change photo-physical and interactional characters of anthracycline molecules. Along with the substitution effect, media effects can play significant roles in chemical and physical processes of anthraquinone in solutions [10–12]. Therefore, quantitative measurement of the antitumour anthracycline molecules, dipole moment variations and solvent–solute interactions is interesting, due to their therapeutic application [13]. The photo-physical and interactional behaviors of anthracycline arise from either specific (e.g., hydrogen bonding, proton transfer, intramolecular and intermolecular charge transfer (ICT)) or nonspecific (dielectric enrichment) interactions with media. Kamlet, Abboud and Taft’s implemented a multi-parameter polarity scale, for quantitative measurement of contribution assessment of different types of media–solute interactions [14– 16]. Media or solvent polarity scales [17,18] can evaluate the media effect in quantity. Spectroscopic solvent polarity scales have been derived from solvent-sensitive standard compounds, absorbing or emitting radiation in different spectral ranges, due to variation in their microenvironment polarity [18–23]. Media effect on the spectral features of solute molecule can be interpreted through means of linear solvation energy relationship (LSER), reported by Kamlet–Abboud–Taft equation [14].
t ¼ t0 þ s p þ b b þ a a
Table 1 Molecular structure of anthracycline compounds. Sample
Molecular weight (g/mol)
Doxorubicin
580.0
Epirubicin
580.0
Idarubicin
533.95
Structure
ð1Þ
where p is a measure of solvent dipolarity/polarizability [24], b is scale of solvent hydrogen bond acceptor (HBA) basicity [25], a is scale of solvent hydrogen bond donor (HBD) acidity [26] and t0 is a regression value for the solute property in reference solvent, cyclohexane, or in vacuum. Employing multi-linear regression analysis, the coefficients s, b and a in Eq. (1) can be obtained. These coefficients measure the relative susceptibilities of the solute property (spectral features in this work) to the indicated solvent characteristic. In this study, spectral features of three anthracyclines were studied in different solvents. The polarities of used solvents cover all application ranges of samples. Obtained results were used to estimate the ground and excited state dipole moments. Moreover, the solvatochromic activities of these anthracycline samples were evaluated quantitatively via multi-parameter solvent polarity scale. Dipole moment variation and solvatochromic behavior of the samples were elucidated as solvent–solute specific and/or non-specific interactions.
Table 2 Spectroscopic polarity parameters, physical properties and polarity functions of employed solvents [18]. Solvents
e
a
b
p
fBK(e, n)
gBK(n)
f(e, n) + 2g(n)
1,4-Dioxan 1-Butanol 2-Propanol Acetone Ethanol Methanol DMF DMSO Water
2.22 17.5 19.9 21.01 24.3 33.7 39.25 47.24 78.80
0.00 0.84 0.76 0.08 0.86 0.98 0.00 0.00 1.17
0.37 0.84 0.84 0.48 0.75 0.66 0.69 0.76 0.47
0.49 0.47 0.48 0.62 0.54 0.6 0.88 1.00 1.09
0.044 0.750 0.779 0.792 0.812 0.857 0.842 0.841 0.914
0.286 0.271 0.256 0.244 0.246 0.224 0.292 0.324 0.227
0.617 1.293 1.292 1.281 1.303 1.306 1.425 1.489 1.361
Experimental
Estimation of the dipole moment
Materials
The most common technique for determining dipole moment is based on the solvent spectral shift. In this method, employing the quantum mechanical second order perturbation theory and taking into account the Onsager model of reaction field for a polarizable dipole moment [27–29], leads to expressions for difference and ~ a and v ~f : sum of v
The three anthracycline solute samples was purchased from ALEXIS Biochemicals and used without further purification (Table 1). All the solvents used in the study were of highest available purity from Merck, and the spectroscopic solvent polarity parameters of them are given in Table 2.
v~ a v~ f
¼ m1 f ðe; nÞ þ const:
ð2Þ
Absorption and emission spectroscopy
v~ a þ v~ f
¼ m2 ½f ðe; nÞ þ 2gðnÞ þ const:
ð3Þ
Double beam Shimadzu UV-2450 Scan UV–visible spectrophotometer was used to record the absorption spectra over a wavelength range of 300–800 nm, which is combined with a cell temperature controller. Quartz cuvettes were used for measurements in solution via l 1 cm. Fluorescence of samples’ solutions was studied with a JASCO FP-6200, with standard Quartz cuvettes. The sample concentrations were chosen to be 1 105 M for all the samples.
where
m1 ¼
2ðle lg Þ2 hca 2
m2 ¼
3
l2e l2g hca
3
ð4Þ
ð5Þ
259
1 aa3
2
ð6Þ
n2 1 2n2 þ1
ð7Þ
n2 1 2n2 þ1
In these relations, e denotes the dielectric permittivity and n is the refractive index. a and a represent the spherical cavity radius of the solute and average polarizability, respectively. For an isotropic polarizability of the solute, the condition 2aa3 ¼ 1 is usually satisfied [30–32] and the following relations were obtained by Bakhshiev:
2n2 þ 1 fBK ðe; nÞ ¼ 2 n þ2
e 1 n2 1 e þ 2 n2 þ 2
" # 3 n4 1 g BK ðnÞ ¼ 2 ðn2 þ 2Þ2
" # m m hca3 1=2 2 1 2 2m1
" # m þ m hca3 1=2 2 1 2 2m1
le ¼ le ¼
m1 þ m2 l ðm1 m2 Þ m1 m2 g
450
500
550 λ (nm)
600
(b) 1,2,3,4,5,6,7,8,9
5,4,2,1,9,3,6,8,7
ð8Þ
ð9Þ
Considering that, the symmetry of the investigated solute molecule does not change during the electronic transition and the ground and excited state dipole moments are parallel, based on the Eqs. (4) and (5) one obtains [32]:
lg ¼
0 400
ð10Þ
0 400
450
500
550
600
650
1-Methanol 2-Acetone 3-Water 4-Ethanol 5-2-Propanol 6-1,4-Dioxane 7-DMSO 8-DMF 9-1-Butanol
650
0 700
Fluorescence (a.u)
1 aa2
n2 1 2n2 þ1
1-1,4-Dioxane 2-Methanol 3-Acetone 4-Ethanol 5-2-Propanol 6-DMF 7-DMSO 8-Water
0 700
λ (nm)
ð11Þ
(c) 1,2,3,4,5,6,7,8
1-Methanol 2-Acetone 3-Ethanol 4-1-Butanol 5-2-Propanol 6-Water 7-DMF 8-DMSO
8,2,3,5,1,4,6,7
ð12Þ
h is the Plank’s constant and c is the velocity of light in vacuum. le and lg are the dipole moments in the excited and ground states, respectively. Onsager cavity radii (a) for investigated samples were determined theoretically according to their optimized geometry [33]. Results and discussion The solvent effect on the absorption and emission spectra The absorption spectra of anthracycline samples show different active bands. Previously, some researchers reported a spectral bands assignment at 290 and 480 nm. There is a general agreement that anthracycline derivatives are relevant two allowed 1A ? 1La and 1A ? 1Lb p–p transitions, polarized along the short and long axis, respectively [34,35]. The 1A ? 1Lb transitions appear about 480–500 nm in these materials. Also, some formally forbidden transitions appeared in 320–400 nm [13,35]. In this study, we focus on the p–p transitions bands in absorption and fluorescence spectra. The visible absorption and fluorescence spectra of the anthracycline samples (5 105 M) were obtained at room temperature (22 °C) in different organic solvents (Fig. 1). Spectral data are also summarized in Table 3. The spectral data show shifts in absorption and emission spectra of investigated samples depend on the solvent polarity. All the investigated anthracycline samples show small bathochromic shifts in the absorption and fluorescence band
0 400
450
500
550 λ (nm)
600
650
Fluorescence (a.u)
n 1 2n 2 þ1 e1 1 2aa3 2eþ1
4,1,2,5,3,8,6,7
Absorbance
gðnÞ ¼
n2 1 2n2 þ1
2
e1 2eþ1
1,2,3,4,5,6,7,8
Absorbance
f ðe; nÞ ¼ 1 2aa3
(a)
Absorbance
Parameters m1 and m2 for difference and sum of wave numbers, which are linear functions of solvent polarity functions f(e, n) and g(n), can be determined from slopes of the straight lines. The solvent polarity parameters f(e, n) and g(n) are as followed:
Fluorescence (a.u)
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 257–262
0 700
Fig. 1. Absorption and fluorescence spectra of studied group of anthracycline samples in selected solvents with different polarities: (a) Doxorubicin, (b) Epirubicin and (c) Idarubicin.
with an increase in solvent polarity. It suggests that strong intramolecular interaction exist in chromophore part of anthracycline and it reduces the interactions between samples and solvent. Furthermore, the small bathochromic shifts of anthracyclines in polar solvents with hydrogen-bond donor and accepter abilities indicate that hydrogen bonding between solvent molecules and anthracycline samples cannot efficiently break the existing intramolecular hydrogen bonding between CO and neighboring OH groups in anthraquinone chromophore part. Similar behavior has been found for 1-hydroxyanthraquinone [36], 1-hydroxynaphthaquinone [37], and anthraquinone [38]. However, the emission spectra’s bathochromic shift expresses that the intermolecular interactions between the solvent molecules and anthracycline
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samples established excited state. For investigating the nature and degree of specific and non-specific interactions’ contributions in anthracyclines’ spectra shifts multi-parameter solvent polarity scale was used. Correlation with multi-parameter solvent polarity scale The effects of solvent polarity and hydrogen bonding on the spectroscopic behaviors of anthracycline samples are interpreted by means of the linear solvation energy relationship concept using Eq. (1). Multi linear analysis was employed to characterize solvent contributions into spectral features of the studied samples, according to Kamlet–Abboud–Taft polarity scales. Multiple linear analysis of absorption, fluorescence and stokes shift data, with multiparameter polarity scales, show satisfying correlation for the selected collection of solvents. Results of the multiple linear regressions are presented in Table 4. To make the data in Table 4 reasonable and comparable, we have transformed the values in Table 4 into contribution percentages of different polarity parameters (Table 5). It should be noted that, if the interaction only occurs in the excited state, this interaction shows a major effect in the fluorescence spectra. However, if the interaction occurs in the ground state, change in the absorption spectrum is expected [39]. The first step in explanation of the obtained data is establishing the relation between active molecular functional groups in anthracycline samples and solvation parameters. As it can be seen from Table 1, all anthracycline samples have similar active functional groups. It should be noted that the anthraquinone skeleton of samples and substituted groups participating in the chromophore’s p–p resonance electron show a band in absorption and fluorescence in visible range. In addition, another molecular part such as aglycone moiety’s steric hindrance effect on chromophore’s skeleton indirectly controls the samples spectroscopic behavior. Epirubicin is a stereoisomer of doxorubicin, so it can be expected that theses samples show same activity in solvation. However, in idarubicin the lack of attached methoxy group, to
anthraquinone skeleton, and displacement of –OH in hydroxyacetyl part with –CH3 can cause different behavior in guest–host interaction as compared to epirubicin and doxorubicin. From the data represented in Tables 4 and 5, solvent hydrogenbond acceptor ability and dipolarity/polarizability show significant role in bathochromic shifts of anthracycline samples in absorption bands. In other words, self-aggregation of aglycone moiety in idarubicin and epirubicin increases samples hydrogen-bond donor ability and dipolarity, respectively. But, three-dimensional orientations of self-aggregated aglycone in doxorubicin increases dipolarity effect higher than hydrogen-bond donor ability in solvent media. Furthermore, hydrogen-bond acceptor ability and dipolarity/polarizability coefficient signs in absorption are negative. These negative signs indicate that these solvent parameters decrease ground state stability [39]. Existence of methoxy group attached to anthraquinone skeleton of epirubicin and doxorubicin causes their fluorescence data to show same performance in solvents. Solvents dipolarity/polarizability and hydrogen bond acceptor ability are effective parameters for increasing excited state’s stability of epirubicin and doxorubicin (negative solvation coefficient signs in fluorescence illustrates that these solvent parameters increase excited state’s stability [39]). Also, solvent’s hydrogen-bond donor ability show inverse effect as solvent dipolarity/polarizability and hydrogen bond acceptor ability in these samples. In idarubicin, solvents hydrogen-bond acceptor and hydrogen bond donor ability show important role in propelling of fluorescence spectral band’s position. Solvent dipolarity/polarizability and hydrogen bond acceptor ability reduce excited state’s stability of idarubicin. The solvent effect on the molecular reorientation of anthracycline samples can be checked through correlation between solvent polarity parameters and Stokes shifts. Stokes shifts value of epirubicin and doxorubicin rises by increasing the solvent dipolarity/ polarizability. Furthermore, solvent’s hydrogen bond acceptor and donor ability decrease molecular reorientation of epirubicin and doxorubicin in solvent media. Idarubicin’s Stokes shift in solvent enhances by solvent hydrogen bond donor ability and
Table 3 Absorption and fluorescence spectral data of anthracycline samples in various solvents. Solvent
(Abs)kmax (nm)
(Fluo)kmax (nm)
ma mf (cm1)
ma + mf (cm1)
Doxorubicin 1,4-Dioxane Acetone 2-Propanol Ethanol Methanol DMF DMSO Water
495.00 495.60 496.97 496.18 495.30 497.15 497.34 497.80
583.60 584.20 583.90 583.40 583.60 587.30 587.30 585.70
37337.04 37294.99 37248.16 37294.87 37324.81 37141.73 37134.04 37161.98
3066.99 3060.14 2995.72 3013.08 3054.76 3087.58 3079.90 3014.80
Epirubicin 1,4-Dioxane 1-Butanol Acetone 2-Propanol Ethanol Methanol DMF DMSO Water
496.70 497.87 495.90 496.45 496.21 495.16 497.56 497.40 496.20
587.10 584.60 584.00 583.30 583.40 584.50 587.30 587.70 586.30
37165.75 37191.28 37288.64 37286.85 37293.66 37304.13 37125.15 37120.03 37209.28
3100.00 2979.85 3042.07 2999.18 3011.86 3086.85 3071.01 3089.06 3097.05
Idarubicin 1-Butanol Acetone 2-Propanol Ethanol Methanol DMF DMSO Water
484.34 482.65 484.34 483.88 482.00 485.00 485.82 484.71
560.00 556.50 557.50 557.5 558.50 562.00 554.00 560.00
38503.80 38688.40 38583.87 38603.50 38651.99 38412.15 38634.30 38488.04
2789.51 2749.50 2709.43 2729.06 2841.78 2824.96 2533.21 2773.75
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v0 (103 cm1)
a (103 cm1)
b (103 cm1)
s (103 cm1)
R2
Doxorubicin Absorbance Fluorescence Stokes shift
20.303 (±0.027) 17.245 (±0.013) 3.048 (±.018)
0.024 (±0.012) +0.035 (±0.006) 0.067 (±0.008)
0.106 (±0.033) 0.073 (±0.016) 0.021 (±0.022)
0.122 (±0.023) 0.163 (±0.011) +0.051 (±0.015)
0.94 0.99 0.96
Epirubicin Absorbance Fluorescence Stokes shift
20.282 (±0.060) 17.295 (±0.064) 3.075 (±0.040)
+0.033 (±0.015) +0.025 (±0.017) 0.027 (±0.017)
0.135 (±0.061) 0.112 (±0.062) 0.136 (±0.046)
0.089 (±0.036) 0.201 (±0.038) +0.107 (±0.032)
0.85 0.91 0.89
Idarubicin Absorbance Fluorescence Stokes shift
20.950 (±0.014) 17.868 (±0.045) 3.101 (±0.120)
0.006 (±0.004) 0.117 (±0.013) +0.145 (±0.036)
0.253 (±0.014) +0.181 (±0.046) 0.388 (±0.117)
0.176 (±0.008) +0.041 (±0.028) 0.280 (±0.074)
0.99 0.98 0.95
Table 5 Percentage contribution of solvatochromic parameters for absorbance, fluorescence and Stokes’ shift of anthracycline compounds. Anthracycline compounds Absorbance Doxorubicin Epirubicin Idarubicin Fluorescence Doxorubicin Epirubicin Idarubicin Stokes’shift Doxorubicin Epirubicin Idarubicin
Pa (%) 10 13 2
Pb (%) 42 52 58
(a) 375000.76
Pp (%)
0.78
0.8
0.82
0.86
3100
37400
48 35 40
0.84
R² = 0.75
3000
37300 2900 37200
13 8 34 48 10 18
27 33 53 15 50 48
60 59 13
R² = 0.82
37100 1.25
37 40 34
(b)
0.72
1.3
1.35
0.77
1.4
0.82
2800 1.5
1.45
0.87
0.92
3200
37550
diminishes with augmentation of solvent’s dipolarity/polarizability and hydrogen bond acceptor ability. Lack of methoxy group in idarubicin’s anthraquinone skeleton, increases the local dipolarity in self-aggregated aglycone part. Decreasing hydrogen acceptor group and existing polar self-aggregated part in one side of the molecular structure of idarubicin causes the solvent’s dipolarity/polarizability and hydrogen bond acceptor ability to decrease molecular reorientation and ground and excited state’s stability of idarubicin.
3100
R² = 0.84
37450 3000
37350
2900
37250 37150
2800
R² = 0.83
37050 1.25
1.3
0.76
0.78
1.35
1.4
2700 1.5
1.45
Estimation of ground state and excited state dipole moment In order to get a detailed examination of the solvent effect, one must estimate solute molecules’ dipole moments in solvent media. To estimate the ground and excited state’s dipole moments of anthracycline samples, first the solvent polarity functions, f(e, n) and f(e, n) + 2g(n), were calculated and presented in Table 1. Then, ~a v ~ f Þ and ðv ~a þ v ~ f Þ of these linear correlation of spectral shifts ðv matters against the polarity functions f(e, n) and f(e, n) + 2g(n), respectively, were used (Fig. 2). The data were fit into a straight line, using linear curve fitting approach. The slopes of these lines were taken as m1 and m2. Afterwards, the ground and excited state dipole moments were calculated using Eqs. (10) and (11). The results are summarized in Table 6, that show greater dipole moments in excited state (le) as compared to ground state (lg), in all studied samples. Increase in dipole moments of excited state demonstrates that these compounds are more polar in excited state. The observed variations in the dipole moment values depend on the possible resonance structures, the stereochemical hindrance in possible resonance structures of solute in different solvent media and interactions between solvent and solute molecules.
(c)
0.8
0.82
0.84
0.86
2900
38950 2800
R² = 0.91
38800 2700 38650 2600 38500
38350 1.25
R² = 0.90
2500 2400
1.28
1.31
1.34
1.37
1.4
1.43
~a v ~ f with fBK(e, n) ( ) and variation v ~a þ v ~ f with Fig. 2. The variation of v fBK(e, n) + 2gBK(n) ( ) for (a) Doxorubicin, (b) Epirubicin and (c) Idarubicin.
The large change in dipole moments of studied anthracycline samples in ground and excited states suggests that intramolecular
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Table 6 Dipole moments, cavity radius of anthracycline samples.
a
Anthracycline compounds
Radius (Å)
lg (D)
le (D)
Ra
Doxorubicin Epirubicin Idarubicin
7 7 7
1.2 1.3 1.4
7.2 6.6 8.9
0.75 0.83 0.90
R-square (COD).
noted that, drug-related possible freedom of interaction is controlled by their effective functional groups’ reorientation and functional groups’ reorientation are directly related to Stokes shifts. Doxorubicin and epirubicin, in media with hydrogen bond acceptor or donor ability, show low reorientation. But, polar and hydrogen bond acceptor media show prevention of reorientation for idarubicin. References
charge-transfer takes place in all three samples, in solvents. Increase of singlet excited state’s dipole moments, as compare to ground state, in doxorubicin is about 6.1 D, for epirubicin is about 5.2 D and in idarubicin this increment is about 7.5 D. Doxorubicin and epirubicin are stereoisomer, thus it can be expected that the ground and excited states’ dipole moments have same values in solvation. However, the stereochemical hindrance increases self-aggregation of aglycone part, and therefore reduces the solvation effect on stability of resonance structures of anthraquinone skeleton in doxorubicin upon excitation, and so increases excited state’s dipole moment compared to epirubicin. But, in idarubicin the lack of methoxy attached group to anthraquinone skeleton and displacement of –OH in hydroxyacetyl part with –CH3 cause local dipolarity enhancement in one side of it. Ground and excited states dipole moments of idarubicin in solvent media increase as compared to other samples. Conclusions The results show that the solvent effect on absorption and emission spectra of investigated anthracycline samples strongly depend on the strong intramolecular hydrogen bonding and stereochemical modifying effect in possible resonance structures of them. The solvatochromic behaviors of anthracycline samples are controlled by molecular functional groups interactions with solvation factors. Solvent dipolarity/polarizability and hydrogen bond acceptor ability show effective effect in ground state of anthracycline samples. Same as ground state of epirubicin and doxorubicin, excited state of them are affected by solvent dipolarity/polarizability and hydrogen bond acceptor ability. The idarubicin’s excited state is effectively modified by solvents’ hydrogen-bond acceptor and hydrogen bond donor ability. The obtained dipole moments from solvent perturbation method indicate that, for all samples the excited state dipole moment (le) is greater than ground state dipole moment (lg). Also, intramolecular charge-transfer takes place in all of them, in solvents. Idarubicin local dipolarity increases ground and excited states dipole moments as compared to other samples. In addition, doxorubicin and epirubicin show same values for ground and excited states’ dipole moments in solvents. Finally, the obtained results suggest doxorubicin interacts with polar environment and is absorbed in these media. Also, reorientation of doxorubicin molecular functions in these media increases. Idarubicin and epirubicin interact with hydrogen bond acceptor environment and are attracted in these media. Furthermore, epirubicin’s reorientation functional groups, same as doxorubicin, increases in polar media, but idarubicin’s functional groups’ reorientation increases in hydrogen bond donor media. It should be
[1] R. Siva, Curr. Sci. Ind. 92 (2007) 916–925. [2] P. Ghosh, G. Poornima Devi, R. Priy, A. Amrita, A. Sivaramakrishna, S. Babu, R. Siva, Appl. Biochem. Biotechnol. 170 (2013) 1127–1137. [3] I. Brigger, C. Dubernet, P. Couvreur, Adv. Drug Deliv. Rev. 54 (2002) 631–651. [4] L. Joguet, I. Sondi, E. Matijevic, J. Colloid Interface Sci. 251 (2002) 284–287. [5] A. Dimacro, F. Arcamone, F. Zunino, Daunomycin (Daunorubicin) and Adriamycin and Structural Analogues, Biological Activity and Mechanism of Action Antimicrobial and Antitumor Agents, Springer Verlag, Berlin, 1975. [6] S. Neidle, Prog. Med. Chem. 16 (1979) 151–221. [7] S.T. Crooke, S.D. Reich, Anthracyclines Current Status and New Developments, Academic Press, New York, 1980. [8] M.A. Viswamitra, O. Kennard, P.G. Jones, G.M. Sheldrick, S. Salisbury, L. Falvello, Z. Shakked, Nature 273 (1978) 687–688. [9] M.P. Marzocchi, A.R. Mantini, M. Casu, G. Smulevich, J. Chem. Phys. 108 (1998) 534–549. [10] C. Milliani, A. Romani, G. Favaro, J. Phys. Org. Chem. 13 (2000) 141–150. [11] V. Sasirekha, P. Vanelle, T. Terme, V. Ramakrishnan, Spectrochim. Acta A 71 (2008) 766–772. [12] M.S. Zakerhamidi, A. Ghanadzadeh, M. Moghadam, Spectrochim. Acta A 79 (2011) 74–81. [13] I. Manet, F. Manoli, B. Zambelli, G. Andreano, A. Masi, L. Cellai, S. Ottani, G. Marconia, S. Monti, Photochem. Photobiol. Sci. 10 (2011) 1326–1337. [14] M.J. Kamlet, J.M. Abboud, R.W. Taft, Prog. Phys. Org. Chem. 13 (1981) 485–630. [15] A.F. Lagalante, R.L. Hall, T.J. Bruno, J. Phys. Chem. B 102 (1998) 6601–6604. [16] R.J. Sindreu, M.L. Moyá, F.S. Burgos, A.G. González, J. Solution Chem. 25 (1996) 89–293. [17] M.A. Kessler, O.S. Wolfbeis, Spectrochim. Acta A 47 (1991) 187–192. [18] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, third ed., Wiley-VCH, Weinheim, 2003. [19] C. Reichardt, Angew. Chem. 91 (1979) 119–131. [20] E.M. Kosower, An Introduction to Physical Organic Chemistry, Wiley, New York, 1968. [21] M.J. Kamlet, J.M. Abboud, M.H. Abraham, R.W. Taft, J. Org. Chem. 48 (1983) 2877–2887. [22] J.A. Hirsch, Concepts in Theoretical Organic Chemistry, Allyn and Bacon, Boston, 1974. pp. 207–260. [23] V. Gutmann, The Donor–Acceptor Approach to Molecular Interactions, Plenum Publ. Corp., New York, 1978. [24] J.M. Abboud, M.J. Kamlet, R.W. Taft, J. Am. Chem. Soc. 99 (1977) 8325–8327. [25] M.J. Kamlet, R.W. Taft, J. Am. Chem. Soc. 98 (1976) 377–383. [26] M.J. Kamlet, R.W. Taft, J. Chem. Soc., Perkin Trans. 2 (1979) 349–356. [27] L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621–627. [28] A. Kawski, Z. Naturforsch. 57a (2002) 255–262. [29] A. Kawski, Prog. Photochem. Photophys., vol. 5, CRC Press, Boston, 1992. [30] N.G. Baksiev, OPT Skeptrosk. 16 (1964) 821–832. [31] A. Kawski, Acta Phys. Polym. 25 (1964) 285–290. 479. [32] J.R. Mannekutla, B.G. Mulimani, S.R. Inamdar, Spectrochim. Acta A 69 (2008) 419–426. [33] J. Kabatc, B.O. smiałowski, J. Paczkowski, Spectrochim. Acta A 63 (2006) 524– 531. [34] M.M.L. Fiallo, H. Tayeb, A. Suarato, A. Garnier-Suillerot, J. Pharm. Sci. 87 (1998) 967–975. [35] B. Samori, A. Rossi, I.D. Pellerano, G. Marconi, L. Valentini, B. Gioia, A. Vigevani, J. Chem. Soc., Perkin Trans. 2 (1987) 1419–1426. [36] P.F. Barbara, P.K. Walsh, L.E. Brus, J. Phys. Chem. 93 (1993) 29–34. [37] D.K. Palit, T. Mukherjee, J.P. Mittal, J. Ind. Chem. Soc. 43 (1986) 35–42. [38] M.S. Zakerhamidi, A. Ghanadzadeh, M. Moghadam, Spectrochim. Acta A 79 (2011) 74–81. [39] M.S. Zakerhamidi, K. Nejati, Sh. Golghasemi Sorkhabi, M. Saati, J. Mol. Liq. 180 (2013) 225–234.
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Photo-physical behavior of some antitumor anthracycline in solvent media with different polarity M.S. Zakerhamidi a,⇑, M. Johari-Ahar b, S.M. Seyed Ahmadian c, R. Kian a,c a
Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz, Iran Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Science, Tabriz, Iran c Department of Chemistry, Faculty of Basic Sciences, Azarbaijan Shahid Madani University, BP 5375171379 Tabriz, Iran b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Self-aggregation of aglycone moiety
show main change in solvatochromism of anthracycline. Intramolecular charge-transfer takes place in all three anthracycline samples. Reorientation of doxorubicin and epirubicin molecular functions in polar environment increases. Idarubicin’s functional groups reorientation increases in hydrogen bond donor media.
a r t i c l e
i n f o
Article history: Received 22 January 2014 Received in revised form 30 March 2014 Accepted 7 April 2014 Available online 21 April 2014 Keywords: Anthracycline Stereoisomer Linear solvation energy relationship Solvent polarity scale Dipole moment Intramolecular hydrogen bonding
a b s t r a c t Absorption and emission spectra of three antitumour anthracyclines, with various substituent and stereoisomer groups, were studied in different solvents. The solute’s photo-physical behavior strongly depends on solvent–solute interactions and solvent’s nature. Solvatochromic method was used to investigate dipole moments of these materials in ground and excited states. Spectral variations were analyzed via means of linear solvation energy relationships concept, proposed by Kamlet and Taft. The results explain the nature of specific and non-specific solvent–solute interactions and functional groups’ reorientation of studied anthracyclines in different media. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Anthraquinones (AQ) are one of the largest and most important classes of organic compounds in nature [1]. Anthraquinones derivatives have several industrial, biological and pharmaceutical applications [1–9]. The hydroxy anthraquinone chromophore has ⇑ Corresponding author. Tel.: +98 411 3393003; fax: +98 411 3347050. E-mail address: [email protected] (M.S. Zakerhamidi). http://dx.doi.org/10.1016/j.saa.2014.04.048 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
biological activity in several antitumour anthracyclines [2–4]. Antitumour anthracycline is the most useful group of cytotoxic anticancer drugs, which are commonly used in cancer chemotherapy. They have anthraquinone skeleton and aglycone ring coupled with amino sugar. The disparate substitute in these materials creates unique properties, such as intercalate between DNA, interfering in transcription and replication [5–8]. The molecular activity and medicinal properties of anthracycline derivatives can be determined through stereoisomerism and
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substituting the hydrogen of aglycone ring by groups like alkyls, amines, hydroxyl, etc. The photo-physical behaviors of substituted anthracycline molecules in visible reign are controlled by anthraquinone skeleton. The substituted groups on anthraquinone chromophore can change photo-physical and interactional characters of anthracycline molecules. Along with the substitution effect, media effects can play significant roles in chemical and physical processes of anthraquinone in solutions [10–12]. Therefore, quantitative measurement of the antitumour anthracycline molecules, dipole moment variations and solvent–solute interactions is interesting, due to their therapeutic application [13]. The photo-physical and interactional behaviors of anthracycline arise from either specific (e.g., hydrogen bonding, proton transfer, intramolecular and intermolecular charge transfer (ICT)) or nonspecific (dielectric enrichment) interactions with media. Kamlet, Abboud and Taft’s implemented a multi-parameter polarity scale, for quantitative measurement of contribution assessment of different types of media–solute interactions [14– 16]. Media or solvent polarity scales [17,18] can evaluate the media effect in quantity. Spectroscopic solvent polarity scales have been derived from solvent-sensitive standard compounds, absorbing or emitting radiation in different spectral ranges, due to variation in their microenvironment polarity [18–23]. Media effect on the spectral features of solute molecule can be interpreted through means of linear solvation energy relationship (LSER), reported by Kamlet–Abboud–Taft equation [14].
t ¼ t0 þ s p þ b b þ a a
Table 1 Molecular structure of anthracycline compounds. Sample
Molecular weight (g/mol)
Doxorubicin
580.0
Epirubicin
580.0
Idarubicin
533.95
Structure
ð1Þ
where p is a measure of solvent dipolarity/polarizability [24], b is scale of solvent hydrogen bond acceptor (HBA) basicity [25], a is scale of solvent hydrogen bond donor (HBD) acidity [26] and t0 is a regression value for the solute property in reference solvent, cyclohexane, or in vacuum. Employing multi-linear regression analysis, the coefficients s, b and a in Eq. (1) can be obtained. These coefficients measure the relative susceptibilities of the solute property (spectral features in this work) to the indicated solvent characteristic. In this study, spectral features of three anthracyclines were studied in different solvents. The polarities of used solvents cover all application ranges of samples. Obtained results were used to estimate the ground and excited state dipole moments. Moreover, the solvatochromic activities of these anthracycline samples were evaluated quantitatively via multi-parameter solvent polarity scale. Dipole moment variation and solvatochromic behavior of the samples were elucidated as solvent–solute specific and/or non-specific interactions.
Table 2 Spectroscopic polarity parameters, physical properties and polarity functions of employed solvents [18]. Solvents
e
a
b
p
fBK(e, n)
gBK(n)
f(e, n) + 2g(n)
1,4-Dioxan 1-Butanol 2-Propanol Acetone Ethanol Methanol DMF DMSO Water
2.22 17.5 19.9 21.01 24.3 33.7 39.25 47.24 78.80
0.00 0.84 0.76 0.08 0.86 0.98 0.00 0.00 1.17
0.37 0.84 0.84 0.48 0.75 0.66 0.69 0.76 0.47
0.49 0.47 0.48 0.62 0.54 0.6 0.88 1.00 1.09
0.044 0.750 0.779 0.792 0.812 0.857 0.842 0.841 0.914
0.286 0.271 0.256 0.244 0.246 0.224 0.292 0.324 0.227
0.617 1.293 1.292 1.281 1.303 1.306 1.425 1.489 1.361
Experimental
Estimation of the dipole moment
Materials
The most common technique for determining dipole moment is based on the solvent spectral shift. In this method, employing the quantum mechanical second order perturbation theory and taking into account the Onsager model of reaction field for a polarizable dipole moment [27–29], leads to expressions for difference and ~ a and v ~f : sum of v
The three anthracycline solute samples was purchased from ALEXIS Biochemicals and used without further purification (Table 1). All the solvents used in the study were of highest available purity from Merck, and the spectroscopic solvent polarity parameters of them are given in Table 2.
v~ a v~ f
¼ m1 f ðe; nÞ þ const:
ð2Þ
Absorption and emission spectroscopy
v~ a þ v~ f
¼ m2 ½f ðe; nÞ þ 2gðnÞ þ const:
ð3Þ
Double beam Shimadzu UV-2450 Scan UV–visible spectrophotometer was used to record the absorption spectra over a wavelength range of 300–800 nm, which is combined with a cell temperature controller. Quartz cuvettes were used for measurements in solution via l 1 cm. Fluorescence of samples’ solutions was studied with a JASCO FP-6200, with standard Quartz cuvettes. The sample concentrations were chosen to be 1 105 M for all the samples.
where
m1 ¼
2ðle lg Þ2 hca 2
m2 ¼
3
l2e l2g hca
3
ð4Þ
ð5Þ
259
1 aa3
2
ð6Þ
n2 1 2n2 þ1
ð7Þ
n2 1 2n2 þ1
In these relations, e denotes the dielectric permittivity and n is the refractive index. a and a represent the spherical cavity radius of the solute and average polarizability, respectively. For an isotropic polarizability of the solute, the condition 2aa3 ¼ 1 is usually satisfied [30–32] and the following relations were obtained by Bakhshiev:
2n2 þ 1 fBK ðe; nÞ ¼ 2 n þ2
e 1 n2 1 e þ 2 n2 þ 2
" # 3 n4 1 g BK ðnÞ ¼ 2 ðn2 þ 2Þ2
" # m m hca3 1=2 2 1 2 2m1
" # m þ m hca3 1=2 2 1 2 2m1
le ¼ le ¼
m1 þ m2 l ðm1 m2 Þ m1 m2 g
450
500
550 λ (nm)
600
(b) 1,2,3,4,5,6,7,8,9
5,4,2,1,9,3,6,8,7
ð8Þ
ð9Þ
Considering that, the symmetry of the investigated solute molecule does not change during the electronic transition and the ground and excited state dipole moments are parallel, based on the Eqs. (4) and (5) one obtains [32]:
lg ¼
0 400
ð10Þ
0 400
450
500
550
600
650
1-Methanol 2-Acetone 3-Water 4-Ethanol 5-2-Propanol 6-1,4-Dioxane 7-DMSO 8-DMF 9-1-Butanol
650
0 700
Fluorescence (a.u)
1 aa2
n2 1 2n2 þ1
1-1,4-Dioxane 2-Methanol 3-Acetone 4-Ethanol 5-2-Propanol 6-DMF 7-DMSO 8-Water
0 700
λ (nm)
ð11Þ
(c) 1,2,3,4,5,6,7,8
1-Methanol 2-Acetone 3-Ethanol 4-1-Butanol 5-2-Propanol 6-Water 7-DMF 8-DMSO
8,2,3,5,1,4,6,7
ð12Þ
h is the Plank’s constant and c is the velocity of light in vacuum. le and lg are the dipole moments in the excited and ground states, respectively. Onsager cavity radii (a) for investigated samples were determined theoretically according to their optimized geometry [33]. Results and discussion The solvent effect on the absorption and emission spectra The absorption spectra of anthracycline samples show different active bands. Previously, some researchers reported a spectral bands assignment at 290 and 480 nm. There is a general agreement that anthracycline derivatives are relevant two allowed 1A ? 1La and 1A ? 1Lb p–p transitions, polarized along the short and long axis, respectively [34,35]. The 1A ? 1Lb transitions appear about 480–500 nm in these materials. Also, some formally forbidden transitions appeared in 320–400 nm [13,35]. In this study, we focus on the p–p transitions bands in absorption and fluorescence spectra. The visible absorption and fluorescence spectra of the anthracycline samples (5 105 M) were obtained at room temperature (22 °C) in different organic solvents (Fig. 1). Spectral data are also summarized in Table 3. The spectral data show shifts in absorption and emission spectra of investigated samples depend on the solvent polarity. All the investigated anthracycline samples show small bathochromic shifts in the absorption and fluorescence band
0 400
450
500
550 λ (nm)
600
650
Fluorescence (a.u)
n 1 2n 2 þ1 e1 1 2aa3 2eþ1
4,1,2,5,3,8,6,7
Absorbance
gðnÞ ¼
n2 1 2n2 þ1
2
e1 2eþ1
1,2,3,4,5,6,7,8
Absorbance
f ðe; nÞ ¼ 1 2aa3
(a)
Absorbance
Parameters m1 and m2 for difference and sum of wave numbers, which are linear functions of solvent polarity functions f(e, n) and g(n), can be determined from slopes of the straight lines. The solvent polarity parameters f(e, n) and g(n) are as followed:
Fluorescence (a.u)
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 257–262
0 700
Fig. 1. Absorption and fluorescence spectra of studied group of anthracycline samples in selected solvents with different polarities: (a) Doxorubicin, (b) Epirubicin and (c) Idarubicin.
with an increase in solvent polarity. It suggests that strong intramolecular interaction exist in chromophore part of anthracycline and it reduces the interactions between samples and solvent. Furthermore, the small bathochromic shifts of anthracyclines in polar solvents with hydrogen-bond donor and accepter abilities indicate that hydrogen bonding between solvent molecules and anthracycline samples cannot efficiently break the existing intramolecular hydrogen bonding between CO and neighboring OH groups in anthraquinone chromophore part. Similar behavior has been found for 1-hydroxyanthraquinone [36], 1-hydroxynaphthaquinone [37], and anthraquinone [38]. However, the emission spectra’s bathochromic shift expresses that the intermolecular interactions between the solvent molecules and anthracycline
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samples established excited state. For investigating the nature and degree of specific and non-specific interactions’ contributions in anthracyclines’ spectra shifts multi-parameter solvent polarity scale was used. Correlation with multi-parameter solvent polarity scale The effects of solvent polarity and hydrogen bonding on the spectroscopic behaviors of anthracycline samples are interpreted by means of the linear solvation energy relationship concept using Eq. (1). Multi linear analysis was employed to characterize solvent contributions into spectral features of the studied samples, according to Kamlet–Abboud–Taft polarity scales. Multiple linear analysis of absorption, fluorescence and stokes shift data, with multiparameter polarity scales, show satisfying correlation for the selected collection of solvents. Results of the multiple linear regressions are presented in Table 4. To make the data in Table 4 reasonable and comparable, we have transformed the values in Table 4 into contribution percentages of different polarity parameters (Table 5). It should be noted that, if the interaction only occurs in the excited state, this interaction shows a major effect in the fluorescence spectra. However, if the interaction occurs in the ground state, change in the absorption spectrum is expected [39]. The first step in explanation of the obtained data is establishing the relation between active molecular functional groups in anthracycline samples and solvation parameters. As it can be seen from Table 1, all anthracycline samples have similar active functional groups. It should be noted that the anthraquinone skeleton of samples and substituted groups participating in the chromophore’s p–p resonance electron show a band in absorption and fluorescence in visible range. In addition, another molecular part such as aglycone moiety’s steric hindrance effect on chromophore’s skeleton indirectly controls the samples spectroscopic behavior. Epirubicin is a stereoisomer of doxorubicin, so it can be expected that theses samples show same activity in solvation. However, in idarubicin the lack of attached methoxy group, to
anthraquinone skeleton, and displacement of –OH in hydroxyacetyl part with –CH3 can cause different behavior in guest–host interaction as compared to epirubicin and doxorubicin. From the data represented in Tables 4 and 5, solvent hydrogenbond acceptor ability and dipolarity/polarizability show significant role in bathochromic shifts of anthracycline samples in absorption bands. In other words, self-aggregation of aglycone moiety in idarubicin and epirubicin increases samples hydrogen-bond donor ability and dipolarity, respectively. But, three-dimensional orientations of self-aggregated aglycone in doxorubicin increases dipolarity effect higher than hydrogen-bond donor ability in solvent media. Furthermore, hydrogen-bond acceptor ability and dipolarity/polarizability coefficient signs in absorption are negative. These negative signs indicate that these solvent parameters decrease ground state stability [39]. Existence of methoxy group attached to anthraquinone skeleton of epirubicin and doxorubicin causes their fluorescence data to show same performance in solvents. Solvents dipolarity/polarizability and hydrogen bond acceptor ability are effective parameters for increasing excited state’s stability of epirubicin and doxorubicin (negative solvation coefficient signs in fluorescence illustrates that these solvent parameters increase excited state’s stability [39]). Also, solvent’s hydrogen-bond donor ability show inverse effect as solvent dipolarity/polarizability and hydrogen bond acceptor ability in these samples. In idarubicin, solvents hydrogen-bond acceptor and hydrogen bond donor ability show important role in propelling of fluorescence spectral band’s position. Solvent dipolarity/polarizability and hydrogen bond acceptor ability reduce excited state’s stability of idarubicin. The solvent effect on the molecular reorientation of anthracycline samples can be checked through correlation between solvent polarity parameters and Stokes shifts. Stokes shifts value of epirubicin and doxorubicin rises by increasing the solvent dipolarity/ polarizability. Furthermore, solvent’s hydrogen bond acceptor and donor ability decrease molecular reorientation of epirubicin and doxorubicin in solvent media. Idarubicin’s Stokes shift in solvent enhances by solvent hydrogen bond donor ability and
Table 3 Absorption and fluorescence spectral data of anthracycline samples in various solvents. Solvent
(Abs)kmax (nm)
(Fluo)kmax (nm)
ma mf (cm1)
ma + mf (cm1)
Doxorubicin 1,4-Dioxane Acetone 2-Propanol Ethanol Methanol DMF DMSO Water
495.00 495.60 496.97 496.18 495.30 497.15 497.34 497.80
583.60 584.20 583.90 583.40 583.60 587.30 587.30 585.70
37337.04 37294.99 37248.16 37294.87 37324.81 37141.73 37134.04 37161.98
3066.99 3060.14 2995.72 3013.08 3054.76 3087.58 3079.90 3014.80
Epirubicin 1,4-Dioxane 1-Butanol Acetone 2-Propanol Ethanol Methanol DMF DMSO Water
496.70 497.87 495.90 496.45 496.21 495.16 497.56 497.40 496.20
587.10 584.60 584.00 583.30 583.40 584.50 587.30 587.70 586.30
37165.75 37191.28 37288.64 37286.85 37293.66 37304.13 37125.15 37120.03 37209.28
3100.00 2979.85 3042.07 2999.18 3011.86 3086.85 3071.01 3089.06 3097.05
Idarubicin 1-Butanol Acetone 2-Propanol Ethanol Methanol DMF DMSO Water
484.34 482.65 484.34 483.88 482.00 485.00 485.82 484.71
560.00 556.50 557.50 557.5 558.50 562.00 554.00 560.00
38503.80 38688.40 38583.87 38603.50 38651.99 38412.15 38634.30 38488.04
2789.51 2749.50 2709.43 2729.06 2841.78 2824.96 2533.21 2773.75
261
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 257–262 Table 4 Regression fits to solvatochromic parameters for absorbance, fluorescence and stokes’ shift of anthracycline samples. Samples
v0 (103 cm1)
a (103 cm1)
b (103 cm1)
s (103 cm1)
R2
Doxorubicin Absorbance Fluorescence Stokes shift
20.303 (±0.027) 17.245 (±0.013) 3.048 (±.018)
0.024 (±0.012) +0.035 (±0.006) 0.067 (±0.008)
0.106 (±0.033) 0.073 (±0.016) 0.021 (±0.022)
0.122 (±0.023) 0.163 (±0.011) +0.051 (±0.015)
0.94 0.99 0.96
Epirubicin Absorbance Fluorescence Stokes shift
20.282 (±0.060) 17.295 (±0.064) 3.075 (±0.040)
+0.033 (±0.015) +0.025 (±0.017) 0.027 (±0.017)
0.135 (±0.061) 0.112 (±0.062) 0.136 (±0.046)
0.089 (±0.036) 0.201 (±0.038) +0.107 (±0.032)
0.85 0.91 0.89
Idarubicin Absorbance Fluorescence Stokes shift
20.950 (±0.014) 17.868 (±0.045) 3.101 (±0.120)
0.006 (±0.004) 0.117 (±0.013) +0.145 (±0.036)
0.253 (±0.014) +0.181 (±0.046) 0.388 (±0.117)
0.176 (±0.008) +0.041 (±0.028) 0.280 (±0.074)
0.99 0.98 0.95
Table 5 Percentage contribution of solvatochromic parameters for absorbance, fluorescence and Stokes’ shift of anthracycline compounds. Anthracycline compounds Absorbance Doxorubicin Epirubicin Idarubicin Fluorescence Doxorubicin Epirubicin Idarubicin Stokes’shift Doxorubicin Epirubicin Idarubicin
Pa (%) 10 13 2
Pb (%) 42 52 58
(a) 375000.76
Pp (%)
0.78
0.8
0.82
0.86
3100
37400
48 35 40
0.84
R² = 0.75
3000
37300 2900 37200
13 8 34 48 10 18
27 33 53 15 50 48
60 59 13
R² = 0.82
37100 1.25
37 40 34
(b)
0.72
1.3
1.35
0.77
1.4
0.82
2800 1.5
1.45
0.87
0.92
3200
37550
diminishes with augmentation of solvent’s dipolarity/polarizability and hydrogen bond acceptor ability. Lack of methoxy group in idarubicin’s anthraquinone skeleton, increases the local dipolarity in self-aggregated aglycone part. Decreasing hydrogen acceptor group and existing polar self-aggregated part in one side of the molecular structure of idarubicin causes the solvent’s dipolarity/polarizability and hydrogen bond acceptor ability to decrease molecular reorientation and ground and excited state’s stability of idarubicin.
3100
R² = 0.84
37450 3000
37350
2900
37250 37150
2800
R² = 0.83
37050 1.25
1.3
0.76
0.78
1.35
1.4
2700 1.5
1.45
Estimation of ground state and excited state dipole moment In order to get a detailed examination of the solvent effect, one must estimate solute molecules’ dipole moments in solvent media. To estimate the ground and excited state’s dipole moments of anthracycline samples, first the solvent polarity functions, f(e, n) and f(e, n) + 2g(n), were calculated and presented in Table 1. Then, ~a v ~ f Þ and ðv ~a þ v ~ f Þ of these linear correlation of spectral shifts ðv matters against the polarity functions f(e, n) and f(e, n) + 2g(n), respectively, were used (Fig. 2). The data were fit into a straight line, using linear curve fitting approach. The slopes of these lines were taken as m1 and m2. Afterwards, the ground and excited state dipole moments were calculated using Eqs. (10) and (11). The results are summarized in Table 6, that show greater dipole moments in excited state (le) as compared to ground state (lg), in all studied samples. Increase in dipole moments of excited state demonstrates that these compounds are more polar in excited state. The observed variations in the dipole moment values depend on the possible resonance structures, the stereochemical hindrance in possible resonance structures of solute in different solvent media and interactions between solvent and solute molecules.
(c)
0.8
0.82
0.84
0.86
2900
38950 2800
R² = 0.91
38800 2700 38650 2600 38500
38350 1.25
R² = 0.90
2500 2400
1.28
1.31
1.34
1.37
1.4
1.43
~a v ~ f with fBK(e, n) ( ) and variation v ~a þ v ~ f with Fig. 2. The variation of v fBK(e, n) + 2gBK(n) ( ) for (a) Doxorubicin, (b) Epirubicin and (c) Idarubicin.
The large change in dipole moments of studied anthracycline samples in ground and excited states suggests that intramolecular
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Table 6 Dipole moments, cavity radius of anthracycline samples.
a
Anthracycline compounds
Radius (Å)
lg (D)
le (D)
Ra
Doxorubicin Epirubicin Idarubicin
7 7 7
1.2 1.3 1.4
7.2 6.6 8.9
0.75 0.83 0.90
R-square (COD).
noted that, drug-related possible freedom of interaction is controlled by their effective functional groups’ reorientation and functional groups’ reorientation are directly related to Stokes shifts. Doxorubicin and epirubicin, in media with hydrogen bond acceptor or donor ability, show low reorientation. But, polar and hydrogen bond acceptor media show prevention of reorientation for idarubicin. References
charge-transfer takes place in all three samples, in solvents. Increase of singlet excited state’s dipole moments, as compare to ground state, in doxorubicin is about 6.1 D, for epirubicin is about 5.2 D and in idarubicin this increment is about 7.5 D. Doxorubicin and epirubicin are stereoisomer, thus it can be expected that the ground and excited states’ dipole moments have same values in solvation. However, the stereochemical hindrance increases self-aggregation of aglycone part, and therefore reduces the solvation effect on stability of resonance structures of anthraquinone skeleton in doxorubicin upon excitation, and so increases excited state’s dipole moment compared to epirubicin. But, in idarubicin the lack of methoxy attached group to anthraquinone skeleton and displacement of –OH in hydroxyacetyl part with –CH3 cause local dipolarity enhancement in one side of it. Ground and excited states dipole moments of idarubicin in solvent media increase as compared to other samples. Conclusions The results show that the solvent effect on absorption and emission spectra of investigated anthracycline samples strongly depend on the strong intramolecular hydrogen bonding and stereochemical modifying effect in possible resonance structures of them. The solvatochromic behaviors of anthracycline samples are controlled by molecular functional groups interactions with solvation factors. Solvent dipolarity/polarizability and hydrogen bond acceptor ability show effective effect in ground state of anthracycline samples. Same as ground state of epirubicin and doxorubicin, excited state of them are affected by solvent dipolarity/polarizability and hydrogen bond acceptor ability. The idarubicin’s excited state is effectively modified by solvents’ hydrogen-bond acceptor and hydrogen bond donor ability. The obtained dipole moments from solvent perturbation method indicate that, for all samples the excited state dipole moment (le) is greater than ground state dipole moment (lg). Also, intramolecular charge-transfer takes place in all of them, in solvents. Idarubicin local dipolarity increases ground and excited states dipole moments as compared to other samples. In addition, doxorubicin and epirubicin show same values for ground and excited states’ dipole moments in solvents. Finally, the obtained results suggest doxorubicin interacts with polar environment and is absorbed in these media. Also, reorientation of doxorubicin molecular functions in these media increases. Idarubicin and epirubicin interact with hydrogen bond acceptor environment and are attracted in these media. Furthermore, epirubicin’s reorientation functional groups, same as doxorubicin, increases in polar media, but idarubicin’s functional groups’ reorientation increases in hydrogen bond donor media. It should be
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