Correlation of Solubility of Bioactive Compound Reserpine in Eight

Jan 13, 2015 - Kayyali Chair for Pharmaceutical Industry, Department of Pharmaceutics, College of Pharmacy, King Saud University, P. O. Box 2457, Riya...
1 downloads 6 Views 387KB Size
Download PDF
Article pubs.acs.org/jced

Correlation of Solubility of Bioactive Compound Reserpine in Eight Green Solvents at (298.15 to 338.15) K Faiyaz Shakeel,*,†,‡ Nazrul Haq,†,‡ Nasir A. Siddiqui,§ Fars K. Alanazi,† and Ibrahim A. Alsarra†,‡ †

Kayyali Chair for Pharmaceutical Industry, Department of Pharmaceutics, College of Pharmacy, King Saud University, P. O. Box 2457, Riyadh 11451, Saudi Arabia ‡ Center of Excellence in Biotechnology Research, College of Science, King Saud University, P. O. Box 2460, Riyadh 11451, Saudi Arabia § Department of Pharmacognosy, College of Pharmacy, King Saud University, P. O. Box 2457, Riyadh 11451, Saudi Arabia S Supporting Information *

ABSTRACT: The solubility of reserpine in eight different green solvents, namely, water, ethanol, ethylene glycol (EG), ethyl acetate (EA), isopropanol (IPA), propylene glycol (PG), poly(ethylene glycol)-400 (PEG-400), and transcutol, was measured and correlated from (298.15 to 338.15) K using the shake flask method. The experimental solubilities were correlated with temperature-dependent Apelblat and ideal equations. For the Apelblat equation, the root-mean-square deviations (RMSD) and correlation coefficients (R2) were obtained as 0.005 to 0.053 and 0.9978 to 0.9999, respectively. For an ideal Apelblat equation, the RMSD and R2 were obtained as 0.005 to 0.018 and 0.9950 to 0.9990, respectively. The mole fraction solubility of reserpine was observed highest in PEG-400 (1.44·10−3 at 298.15 K) followed by transcutol, EG, PG, IPA, ethanol, and water from (298.15 to 338.15) K. However, the mass fraction solubility of reserpine was observed highest in EA (3.60·10−3 at 298.15 K). The dissolution enthalpy, Gibbs energy, and dissolution entropy were determined by van’t Hoff and Krug analysis, and results showed endothermic and spontaneous dissolution of reserpine in all green solvents investigated.

1. INTRODUCTION The IUPAC name of bioactive compound reserpine is 3,4,5trimethoxybenzoyl methyl reserpate (Figure 1).1 It occurs as a

of these bioactive compounds as they are associated with several regulatory and toxicity issues.10 Nevertheless, several nontoxic and environmentally benign solvents (green solvents) such as transcutol, β-cyclodextrin aqueous solution, ethanol, propylene glycol (PG), and poly(ethylene glycol)-400 (PEG400) have been investigated for solubilization and formulation development of various poorly water soluble bioactive compounds.10−12 Some approaches such as co-precipitation, solid dispersion, and co-solvency using N-methylpyrrolidone have been investigated for solubility/dissolution enhancement of reserpine.6,8,13−15 However, the temperature-dependent solubility data of bioactive compound reserpine in water, ethanol, ethylene glycol (EG), ethyl acetate (EA), isopropanol (IPA), PG, PEG-400, and transcutol have not been reported in the literature. The Apelblat equation is the commonly used semiempirical expression which is used to correlate the experimental solubilities with calculated ones and to evaluate the influence of temperature on the mole fraction solubility of the solute.16−18 An ideal equation is also a temperaturedependent equation.19 Therefore, in the present study, the solubilities of bioactive compound reserpine in various green solvents such as water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol were measured and correlated from (298.15 to 338.15) K at atmospheric pressure of 0.1 MPa using the shake

Figure 1. Molecular structure of reserpine.

white to off-white crystalline powder, and its molecular formula and molar mass are C33H40N2O9 and 608.68 g·mol−1, respectively.1−3 It is obtained from the dried roots of Rauwolf ia serpentia and therapeutically used as an antihypertensive and antipsychotic agent.4,5 According to the United States Pharmacopoeia (USP), it has been reported as practically insoluble (poorly soluble) in water, very slightly soluble in ethanol, and freely soluble in acetic acid.6 Poor water solubility of reserpine results in poor bioavailability, which is the major barrier for its formulation development.7,8 Bioactive compounds such as reserpine, diosmin, hesperidin, and silymarin are generally separated from their plant source using toxic solvents such as chloroform, methanol, and dichloromethane.9−11 These solvents are not recommended for formulation development © XXXX American Chemical Society

Received: September 26, 2014 Accepted: December 24, 2014

A

DOI: 10.1021/je500893g J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Sample Table for Materials Used in the Experiment material

molecular formula

molecular mass (g mol−1)

purity (mass fraction)

purification method

analysis method

source

reserpine ethyl alcohol propylene glycol transcutol PEG-400 ethylene glycol ethyl acetate isopropyl alcohol

C33H40N2O9 C2H5OH C3H8O2 C6H14O3 H(OCH2CH2)nOH C2H6O2 C4H8O2 C3H8O

608.68 46.06 76.09 134.17 400.00 62.07 88.10 60.10

0.990 0.999 0.995 0.999 0.999 0.996 0.998 0.997

none none none none none none none none

HPLC GC GC GC GC GC GC GC

Sigma-Aldrich Sigma-Aldrich Fluka Chemicals Gattefosse Fluka Chemicals Winlab Laboratory Winlab Laboratory Winlab Laboratory

flask method. From solubility data, various thermodynamic parameters for reserpine dissolution were also determined using van’t Hoff and Krug analysis. The solubility data of this study could be useful in purification, recrystallization, separation/ extraction, and formulation development of reserpine.

in which m1 and m2 are the masses of reserpine (g) and respective green solvent (water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol) (g), respectively. M1 and M2 are the molecular masses of reserpine (g·mol−1) and respective green solvent (water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol), respectively.

2. EXPERIMENTAL METHODS 2.1. Materials. Reserpine and ethyl alcohol (IUPAC name: ethanol) were procured from Sigma-Aldrich (St. Louis, MO, USA). Transcutol (IUPAC name: diethylene glycol monoethyl ether) was obtained as a kind gift sample from Gattefosse (Lyon, France). EA (IUPAC name: ethyl acetate), EG (IUPAC name: ethane-1,2-diol), and IPA (IUPAC name: 2-propanol) were procured from Winlab Laboratory (Leicestershire, U.K.). PG (IUPAC name: propane-1,2-diol) and PEG-400 [IUPAC name: poly(oxyethene)] were procured from Fluka Chemicals (Busch, Switzerland). The water used in this study was highly pure deionized water which was collected from an ELGA purification unit (Wycombe, Bucks, U.K.) in the laboratory. The general properties, purities (mass fraction), method of purification, method of analysis, and sources of all materials are listed in Table 1. Because, all of these materials were procured with high purity, these materials were used without any further purification. 2.2. Measurement of Reserpine Solubility. The solubility of reserpine in eight different green solvents (water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol) was measured from (298.15 to 338.15) K at atmospheric pressure of 0.1 MPa using the shake flask method.20 The excess amount of reserpine was added in known amount (10 g) of each green solvent in triplicates. The sample mixtures were shaken in an isothermal shaker bath (Julabo, Allentown, PA, USA) at 100 rpm for the period of 72 h.10,11 The temperature was maintained with a thermostatic bath equipped with a water shaker bath. After 72 h, all of the sample mixtures were removed from the shaker and allowed to settle reserpine particles for 2 h.11,12 The supernatants from each sample were taken, diluted 100 times with a respective green solvent, and subjected for analysis of reserpine content using a UV−visible spectrophotometer at 268 nm.14 The proposed analytical method was observed linear in the concentration range of (1 to 50) μg·g−1 with correlation coefficient of 0.999 based on linear regression analysis of calibration data. The standard uncertainty for the temperatures u(T) was found to be ± 0.12 K. The relative standard uncertainty for solubility ur(xe) was recorded as 1.1 %. The experimental mole fraction solubility (xe) of bioactive compound reserpine in each green solvent was calculated using10,11 xe =

m1/M1 m1/M1 + m2 /M 2

3. RESULTS AND DISCUSSION 3.1. Solubility Data of Reserpine. The solubilities (both the mole fraction and mass fraction [we]) of reserpine in the eight different green solvents from (298.15 to 338.15) K at atmospheric pressure of 0.1 MPa are presented in Table 2. The temperature-dependent solubility data of crystalline reserpine in water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol are not available in the literature. Nevertheless, it has been reported as practically insoluble in water and very slightly soluble in ethanol at room temperature according to the USP.6 In the present study, the mass fraction solubility of crystalline reserpine in water and ethanol was observed as 3.28·10−5 at 298.15 K and 1.21·10−4 at 298.15 K, respectively. According to these data, crystalline reserpine is practically insoluble in water and very slightly soluble in ethanol. Therefore, our results were in good agreement with USP. In general, the values of xe and we were found to be increasing with an increase in temperature in all green solvents investigated. The xe values of crystalline reserpine were observed highest in PEG-400 (1.44·10−3 at 298.15 K) followed by transcutol (7.69·10−4 at 298.15 K), EA (5.21·10−4 at 298.15 K), EG (5.30·10−5 at 298.15 K), PG (2.88· 10−5 at 298.15 K), IPA (2.43·10−5 at 298.15 K), ethanol (9.16· 10−6 at 298.15 K), and water (9.71·10−7 at 298.15 K) from (298.15 to 338.15) K (Table 2). However, the we values of crystalline reserpine were observed highest in EA (3.60·10−3 at 298.15 K), followed by transcutol (3.48·10−3 at 298.15 K), PEG-400 (2.20·10−3 at 298.15 K), EG (5.20·10−4 at 298.15 K), IPA (2.46·10−4 at 298.15 K), PG (2.30·10−4 at 298.15 K), ethanol (1.21·10−4 at 298.15 K), and water (3.28·10−5 at 298.15 K) from (298.15 to 338.15) K. The relative standard uncertainty in xe and we was observed as 1.1 % and 1.2 %, respectively. The we values of crystalline reserpine in EA, transcutol, and PEG-400 were not significantly different. However, the xe values of crystalline reserpine in PEG-400 were significantly different from other green solvents. This observation was probably due to higher molar mass of PEG-400 as compared to other green solvents. 3.2. Correlation of Experimental Solubilities with the Apelblat Equation. The Apelblat equation was used to correlate experimental solubilities of crystalline reserpine with calculated ones.16−18 The temperature-dependent solubility of crystalline reserpine can be calculated using eq 2 according to this model:16,17

(1) B

DOI: 10.1021/je500893g J. Chem. Eng. Data XXXX, XXX, XXX−XXX

(0.92)·10−5 (0.50)·10−4 (0.55)·10−4 (0.28)·10−3 (0.27)·10−3 (0.38)·10−3 (0.25)·10−4 (0.28)·10−3 7.60 3.34 4.40 7.20 7.30 1.40 6.15 7.20

The standard uncertainties, u, are u(T) = 0.12 K, u(m) = 0.1 %, u(p) = 0.0003 MPa, and ur(xe) = 1.1 %.

ln x = a +

⎛ x − xe ⎞2 ⎤ ⎟⎥ ∑⎜ x ⎝ e ⎠ ⎥ ⎦ N i=1

1/2

(3)

b T

(4)

in which x is the solubility of crystalline reserpine calculated by an ideal equation. The parameters a and b are the ideal equation parameters which were determined by plotting ln xe against 1/T. For an ideal equation, the RMSD values were also calculated using eq 3. For an ideal equation, the values of a, b, R2, RMSD, and SE in all green solvents are presented in Table 4. The RMSD values in different green solvents were obtained as 0.005 to 0.018 (Table 4). The highest value of RMSD was observed in transcutol followed by PEG-400, EA, water, ethanol, EG, IPA, and PG. The SE values for an ideal model were observed in the range of 0.008 to 0.022. The R2 values for crystalline reserpine in all green solvents were observed in the range of 0.9950 to 0.9990. The data of R2, RMSD, and SE again indicated good curve fitting of experimental solubilities with an ideal equation. 3.4. Thermodynamic Parameters for Reserpine Dissolution (van’t Hoff and Krug Analysis). The dissolution enthalpy (ΔH°) for crystalline reserpine in water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol was determined by van’t Hoff analysis.21,22 According to van’t Hoff analysis, the ΔH° values for dissolution behavior of crystalline reserpine can be calculated at mean harmonic temperature (Thm was 317.52 K in this study) using

a

338.15 K

(2)

in which N is the number of experimental data points. The correlation and curve fitting between xe and x in water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol from (298.15 to 338.15) K as a function of temperature are presented in Supporting Information (SI) Figure S1. The correlation between xe and x in all of these green solvents as a function of Tref/T are presented in SI Figure S2. The values of A, B, C, correlation coefficients (R2), RMSD, and standard errors of coefficients (SE) in water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol are presented in Table 3. The RMSD values in different green solvents were observed in the range of 0.005 to 0.053 (Table 3). The highest value of RMSD was observed in ethanol followed by IPA, transcutol, water, PEG-400, EG, EA, and PG. The SE values were observed in the range of 0.002 to 0.019. The R2 values for crystalline reserpine in all green solvents were observed in the range of 0.9978 to 0.9999. The data of R2, RMSD, and SE indicated good curve fitting of experimental solubilities of crystalline reserpine with the modified Apelblat model. 3.3. Correlation of Experimental Solubilities with an Ideal Equation. An ideal equation was also used to correlate experimental solubilities of crystalline reserpine with calculated ones.19 For an ideal solution, the temperature-dependent solubility of crystalline reserpine can be calculated using

5.31 2.10 3.20 4.30 5.00 9.10 4.07 5.00

328.15 K

(0.90)·10−5 (0.42)·10−4 (0.52)·10−4 (0.25)·10−3 (0.24)·10−3 (0.35)·10−3 (0.22)·10−4 (0.21)·10−3 (0.84)·10−5 (0.40)·10−4 (0.50)·10−4 (0.23)·10−3 (0.21)·10−3 (0.34)·10−4 (0.18)·10−4 (0.16)·10−3

6.42 2.74 3.70 5.70 6.20 1.12 5.01 6.00

⎡ 1 RMSD = ⎢ ⎢⎣ N

(0.81)·10−5 (0.35)·10−4 (0.45)·10−4 (0.16)·10−3 (0.16)·10−3 (0.31)·10−4 (0.12)·10−4 (0.13)·10−3

318.15 K

B + C ln(T ) T

in which x is the calculated solubility of crystalline reserpine and T is absolute temperature (K). The parameters A, B, and C are the modified Apelblat parameters which were determined by multivariate nonlinear regression analysis of xe.11 In order to correlate xe with x, the root-mean-square deviations (RMSD) were calculated using11

4.24 1.65 2.70 3.12 4.10 6.90 3.20 4.20

308.15 K

ln x = A +

(0.70)·10−5 (0.30)·10−4 (0.40)·10−4 (0.18)·10−3 (0.14)·10−3 (0.30)·10−4 (0.09)·10−4 (0.10)·10−3

298.15 K

Article

3.28 1.21 2.30 2.20 3.48 5.20 2.46 3.60 (0.04)·10−6 (0.03)·10−5 (0.01)·10−5 (0.00)·10−3 (0.08)·10−3 (0.04)·10−4 (0.06)·10−5 (0.04)·10−3

338.15 K

2.25 2.53 5.50 4.70 1.61 1.43 6.07 1.04 (0.05)·10−6 (0.05)·10−5 (0.02)·10−5 (0.00)·10−3 (0.07)·10−3 (0.03)·10−4 (0.05)·10−5 (0.05)·10−4

328.15 K

1.90 2.07 4.63 3.73 1.37 1.14 4.95 8.68 (0.07)·10−6 (0.06)·10−5 (0.01)·10−5 (0.00)·10−3 (0.06)·10−3 (0.04)·10−5 (0.04)·10−5 (0.06)·10−4

318.15 K

1.57 1.59 4.00 2.81 1.10 9.28 4.02 7.23 (0.09)·10−6 (0.07)·10−5 (0.01)·10−5 (0.00)·10−3 (0.05)·10−4 (0.02)·10−5 (0.03)·10−5 (0.04)·10−4

308.15 K

1.25 1.25 3.38 2.06 9.06 7.04 3.16 6.08 (0.20)·10−7 (0.08)·10−6 (0.02)·10−5 (0.00)·10−3 (0.03)·10−4 (0.01)·10−5 (0.02)·10−5 (0.03)·10−4 9.71 9.16 2.88 1.44 7.69 5.30 2.43 5.21

298.15 K GS

water ethanol PG PEG-400 transcutol EG IPA EA

we xe

Table 2. Experimental Mole Fraction Solubilities (xe) and Mass Fraction Solubilities (we) of Crystalline Reserpine in Eight Different Green Solvents (GS) at Temperatures T = (298.15 to 338.15) K and Pressure p = 0.1 MPaa (Values in Parentheses Are Standard Deviations)

Journal of Chemical & Engineering Data

C

DOI: 10.1021/je500893g J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 3. Apelblat Parameters (A, B, and C)a along with R2, RMSD, and Standard Errors of Coefficient (SE) for Crystalline Reserpine in Eight Different Green Solvents (GS) A

GS water ethanol PG PEG-400 transcutol EG IPA EA a

107.09 82.10 −74.99 136.94 −98.81 74.05 43.06 −138.36

B −7453.81 −6551.86 1658.10 −9250.60 2690.83 −6029.76 −4455.98 4657.01

(8.72) (5.89) (12.13) (11.41) (10.57) (8.66) (1.79) (14.55)

C −16.83 −12.58 10.35 −19.73 14.49 −11.17 −6.79 20.21

(409.18) (274.77) (113.04) (104.50) (309.79) (228.51) (381.45) (282.82)

(1.29) (4.12) (2.45) (3.16) (1.43) (2.19) (1.78) (2.15)

R2

RMSD

SE

0.9999 0.9992 0.9994 0.9999 0.9978 0.9994 0.9998 0.9998

0.044 0.053 0.005 0.042 0.048 0.031 0.053 0.029

0.002 0.015 0.008 0.005 0.019 0.013 0.005 0.004

The values in parentheses are standard errors of coefficients.

Table 4. Ideal Equation Parameters (a and b)a along with R2, RMSD, and SE for Crystalline Reserpine in Eight Different Green Solvents (GS) a

GS −6.72 −2.98 −5.01 3.52 −0.79 −1.48 −2.89 −1.70

water ethanol PG PEG-400 transcutol EG IPA EA a

b −2117.00 −2563.00 −1624.00 −2996.00 −1906.00 −2489.00 −2302.00 −1752.00

(0.18) (0.18) (0.13) (0.22) (0.22) (0.16) (0.08) (0.22)

(58.81) (59.54) (41.49) (70.42) (71.53) (52.16) (27.20) (70.44)

R2

RMSD

SE

0.9970 0.9980 0.9980 0.9980 0.9950 0.9980 0.9990 0.9950

0.014 0.014 0.005 0.017 0.018 0.012 0.006 0.017

0.018 0.018 0.013 0.022 0.019 0.022 0.008 0.022

The values in parentheses are standard errors of coefficients.

Table 5. Thermodynamic Parameters and R2 Values at Mean Harmonic Temperature of 317.52 K for Dissolution of Crystalline Reserpine in Eight Different Green Solvents (These Values Obtained from van’t Hoff and Krug Analysis)a

a

parameters

water

ethanol

PG

PEG-400

transcutol

EG

ΔH°(/kJ·mol−1) ΔG°/(kJ·mol−1) ΔS°/(J mol−1·K−1) R2

17.61 (0.28) 35.34 (0.41) −55.84 (0.24) 0.997 (0.01)

21.32 (0.32) 29.19 (0.35) −24.79 (0.26) 0.998 (0.01)

13.51 (0.12) 26.71 (0.22) −41.67 (0.15) 0.999 (0.01)

24.92 (0.37) 15.59 (0.10) 29.37 (0.33) 0.998 (0.02)

15.86 (0.31) 17.95 (0.14) −6.58 (0.05) 0.995 (0.02)

20.71 (0.42) 24.61 (0.43) −12.29 (0.08) 0.998 (0.01)

IPA

EA

19.15 (0.35) 14.58 (0.29) 26.78 (0.40) 19.05 (0.23) −23.97 (0.10) −14.11 (0.12) 0.999 (0.00) 0.995 (0.02)

The values in parentheses represent the estimated errors.

⎞ ⎛ ∂ ln x ΔH ° ⎟ =− ⎜ R ⎝ ∂(1/T − 1/Thm) ⎠ P

The ΔH° values for the dissolution of crystalline reserpine were observed as positive values in all green solvents, indicating an endothermic dissolution of crystalline reserpine in all green solvents investigated. The ΔH° values for the dissolution of crystalline reserpine in water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol were observed as 17.61 kJ·mol−1, 21.32 kJ·mol−1, 20.71 kJ·mol−1, 14.58 kJ·mol−1, 19.15 kJ·mol−1, 13.51 kJ·mol−1, 24.92 kJ·mol−1, and 15.86 kJ·mol−1, respectively. The ΔG° values for the dissolution of crystalline reserpine were also observed as positive values in all green solvents investigated, indicating spontaneous dissolution of crystalline reserpine in all green solvents investigated. The ΔG° values for the dissolution of crystalline reserpine in water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol were observed to be 35.34 kJ·mol−1, 29.19 kJ·mol−1, 24.61 kJ·mol−1, 19.05 kJ·mol−1, 26.78 kJ·mol−1, 26.71 kJ·mol−1, 15.59 kJ·mol−1, and 17.95 kJ·mol−1, respectively. The ΔS° values for the dissolution of crystalline reserpine in most of the green solvents (except PEG-400) were observed as negative values, indicating that the dissolution of crystalline reserpine was not an entropydriven process in most of the green solvents investigated. The ΔG° values for the dissolution of crystalline reserpine in ethanol, EG, EA, IPA, PG, PEG-400, and transcutol were significantly reduced as compared to water. These results indicated that relatively low energy is required for the solubilization

(5)

in which R is the universal gas constant. The graphs were plotted between ln xe and 1/T − 1/Thm according to eq 5. These van’t Hoff plots were observed to be linear with R2 values in the range of 0.995 to 0.999 (SI Figure S3). The ΔH° values of crystalline reserpine in eight different green solvents were determined from the slope of each van’t Hoff plot. The Gibbs free energy (ΔG°) for the dissolution of crystalline reserpine in eight different green solvents was determined at Thm using Krug analysis with the help of23 ΔG° = −RThm × intercept

(6)

in which the intercept was determined from the van’t Hoff plots of crystalline reserpine presented in SI Figure S3. Finally, the dissolution entropy (ΔS°) for crystalline reserpine in the eight different green solvents was calculated using ΔS° =

ΔH ° − ΔG° Thm

(7)

The values of ΔH°, ΔG°, ΔS°, and R for the dissolution of crystalline reserpine in the eight different green solvents are presented in Table 5. 2

D

DOI: 10.1021/je500893g J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 6. Thermodynamic Parameters (ΔH° and ΔS°) and R2 Values Obtained by the Lorimer and Cohen-Adad Treatise for Dissolution of Crystalline Reserpine in Eight Different Green Solventsa

a

parameters

water

ethanol

PG

PEG-400

transcutol

EG

ΔH°/(kJ·mol−1) ΔS°/(J·mol−1·K−1) R2

17.60 (0.48) −55.91 (1.53) 0.997 (0.01)

20.60 (0.49) −24.85 (1.55) 0.998 (0.01)

13.50 (0.34) −41.71 (1.08) 0.999 (0.01)

24.90 (0.58) 29.30 (1.84) 0.998 (0.02)

15.84 (0.59) −6.62 (1.87) 0.995 (0.02)

20.69 (0.43) −12.34 (1.36) 0.998 (0.01)

IPA

EA

19.14 (0.22) 14.56 (0.58) −24.06 (0.70) −14.15 (1.84) 0.999 (0.00) 0.995 (0.02)

The values in parentheses represent the estimated errors.

plots of experimental solubilities of crystalline reserpine in different solvents. This material is available free of charge via the Internet at http://pubs.acs.org.

of crystalline reserpine in ethanol, EG, EA, IPA, PG, PEG-400, and transcutol as compared to water. The positive values of ΔH° and ΔG° for the dissolution of crystalline reserpine were probably due to the stronger interactions between reserpine molecules and the solvent molecules as compared to those between the solvent−solvent and reserpine−reserpine molecules.11,12 3.5. Calculation of Thermodynamic Parameters by Lorimer and Cohen-Adad equation. The ΔH° and ΔS° values for reserpine dissolution were also calculated using the two-parameters-based Lorimer and Cohen-Adad equation.24 According to this equation, the ΔH° values were calculated using ΔH ° = A1 RTref

■

Corresponding Author

*Phone: +966-537507318. E-mail: [email protected]. Funding

We extend our appreciation to the Kayyali Chair for Pharmaceutical Industry for supporting this project (Grant no. FN-2015). Notes

The authors declare no competing financial interest.

■

(8)

The ΔS° values for reserpine dissolution were calculated using ΔS° − = A0 R

REFERENCES

(1) Iqbal, M.; Alam, A.; Wani, T. A.; Khalil, N. Y. Simultaneous determination of reserpine, rescinnamine and yohimbine in human plasma by ultraperformance liquid chromatography tandem mass spectrometry. J. Anal. Methods Chem. 2013, 2013, No. E940861. (2) Srivastava, A.; Tripathi, A. K.; Pandey, R.; Verma, R. K.; Gupta, M. M. Quantitative determination of reserpine, ajmaline and ajmalicine in Rauwolf ia serpentina by reversed-phase high performance liquid chromatography. J. Chromatogr. Sci. 2006, 44, 557−560. (3) Cieri, U. R. Determination of reserpine and rescinnamine in Rauwolf ia serpentina powders and tablets: Collaborative study. J. AOAC Int. 1998, 81, 373−380. (4) Mashour, N. H.; Lin, G. I.; Frishman, W. H. Herbal medicine for the treatment of cardiovascular disease: Clinical considerations. Arch. Int. Med. 1998, 158, 2225−2234. (5) Dey, A.; De, J. N. Ethnobotanical aspects of Rauwolf ia serpentina (L). Benth. Ex. Kurz. in India, Nepal and Bangladesh. J. Med. Plant Res. 2011, 5, 144−150. (6) Reserpine; United States Pharmacopoeia: Rockville, MD, USA, 2012; Vol. 35, p 1142. (7) Gibaldi, M.; Feldman, S.; Bates, T. R. Correlation of pharmacological activity and dissolution rates of reserpine-desoxycholic acid dispersions. J. Pharm. Sci. 1968, 57, 708−709. (8) Stupak, E. I.; Rosenberg, H. A.; Bates, T. R. Biopharmaceutical and physicochemical studies on reserpine-polyvinylpyrrolidone coprecipitates. J. Pharmacokinet. Biopharm. 1974, 2, 511−524. (9) Jassbi, A. R.; Miri, R.; Asadollahi, M.; Javanmardi, N.; Firuzi, O. Cytotoxic, antioxidant and antimicrobial effects of nine species of woundwort (Stachys) plants. Pharm. Biol. 2014, 52, 62−67. (10) Shakeel, F.; Anwer, M. K.; Shazly, G. A.; Jamil, S. Measurement and correlation of solubility of bioactive compound silymarin in five different green solvents at 298.15 to 333.15 K. J. Mol. Liq. 2014, 195, 255−258. (11) Anwer, M. K.; Al-Shdefat, R.; Jamil, S.; Alam, P.; Abdel-Kader, M. S.; Shakeel, F. Solubility prediction of bioactive compound hesperidin in six pure solvents at (298.15 to 333.15) K. J. Chem. Eng. Data 2014, 59, 2065−2069. (12) Anwer, M. K.; Jamil, S.; Ansari, M. J.; Al-Shdefat, R.; Ali, B. E.; Ganaie, M. A.; Abdel-Kader, M. S.; Shakeel, F. Water soluble binary and ternary complexes of diosmin with β-cyclodextrin: spectroscopic characterization, release studies and antioxidant activity. J. Mol. Liq. 2014, 199, 35−41.

(9)

In eqs 8 and 9 A0 and A1 are equation parameters which were determined by plotting −ln xe against Tref/T (SI Figure S2). The values of ΔH°, ΔS°, and R2 calculated by Lorimer and Cohen-Adad equation are presented in Table 6. The values of ΔH° and ΔS° were not significantly changed when compared with those calculated by van’t Hoff analysis as shown in Tables 5 and 6. The dissolution of crystalline reserpine was observed endothermic and spontaneous in all green solvents investigated.

4. CONCLUSION The solubilities of crystalline reserpine in eight different green solvents, namely, water, ethanol, EG, EA, IPA, PG, PEG-400, and transcutol were measured from (298.15 to 338.15) K and atmospheric pressure of 0.1 MPa using the shake flask method. The solubility of crystalline reserpine was found to increase nonlinearly with an increase in temperature in all green solvents investigated. The mole fraction solubility of crystalline reserpine was found to be highest in PEG 400 followed by transcutol, EA, EG, PG, IPA, ethanol, and water. However, the mass fraction solubility of crystalline reserpine was observed highest in EA, followed by transcutol, PEG-400, EG, IPA, PG, ethanol, and water. The experimental solubilities were correlated well with the Apelblat and ideal equations in all green solvents from (298.15 to 338.15) K. Dissolution thermodynamics studies showed endothermic and spontaneous dissolution of crystalline reserpine in all green solvents investigated.

■

AUTHOR INFORMATION

ASSOCIATED CONTENT

S Supporting Information *

Figures showing fitting of ln xe of crystalline reserpine in different solvents, −ln xe as a function of Tref/T, and van’t Hoff E

DOI: 10.1021/je500893g J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

(13) Stoll, R. G.; Bates, T. R.; Nieforth, K. A.; Swarbrick, J. Some physical factors affecting the enhanced blepharoptotic activity orally administered reserpine-cholanic acid coprecipitates. J. Pharm. Sci. 1969, 58, 1457−1459. (14) Stupak, E. I.; Bates, T. R. Enhanced absorption and dissolution of reserpine from reserpine-polyvinypyrrolidone coprecipitates. J. Pharm. Sci. 1972, 61, 400−403. (15) Tarantino, R.; Bishop, E.; Chen, F. C.; Iqbal, K.; Malick, A. W. N-Methyl-2-pyrrolidone as a cosolvent: Relationship of cosolvent effect with solute polarity and the presence of proton-donating groups on model drug compounds. J. Pharm. Sci. 1994, 83, 1213−1216. (16) Apelblat, A.; Manzurola, E. Solubilities of L-aspartic, DLaspartic, DL-glutamic, p-hydroxybenzoic, o-anisic, p-anisic, and itaconic acids in water from T = 278 to 345 K. J. Chem. Thermodyn. 1997, 29, 1527−1533. (17) Apelblat, A.; Manzurola, E. Solubilities of o-acetylsalicylic, 4aminosalicylic, 3,5-dinitrosalicylic and p-toluic acid and magnesiumDL-aspartate in water from T = (278 to 348) K. J. Chem. Thermodyn. 1999, 31, 85−91. (18) Manzurola, E.; Apelblat, A. Solubilities of L-glutamic acid, 3nitrobenzoic acid, acetylsalicylic, p-toluic acid, calcium-L-lactate, calcium gluconate, magnesium-DL-aspartate, and magnesium-L-lactate in water. J. Chem. Thermodyn. 2002, 34, 1127−1136. (19) Liu, J. Q.; Chen, S. Y.; Ji, B. Solubility and thermodynamic functions of isatin in pure solvents. J. Chem. Eng. Data 2014, 59, 3407−3414. (20) Higuchi, T.; Connors, K. A. Phase-solubility techniques. Adv. Anal. Chem. Instrum. 1965, 4, 117−122. (21) Ruidiaz, M. A.; Delgado, D. R.; Martínez, F.; Marcus, Y. Solubility and preferential solvation of indomethacin in 1,4-dioxane + water solvent mixtures. Fluid Phase Equilib. 2010, 299, 259−265. (22) Holguín, A. R.; Rodríguez, G. A.; Cristancho, D. M.; Delgado, D. R.; Martínez, F. Solution thermodynamics of indomethacin in propylene glycol + water mixtures. Fluid Phase Equilib. 2012, 314, 134−139. (23) Krug, R. R.; Hunter, W. G.; Grieger, R. A. Enthalpy-entropy compensation. 2. Separation of the chemical from the statistic effect. J. Phys. Chem. 1976, 80, 2341−2351. (24) Lorimer, J. W.; Cohen-Adad, R. Temperature and pressure dependence of the standard Gibbs energy of solution. In Experimental determination of solubilities; Hefter, G. T., Tomkins, R. P. T., Eds.; John Wiley & Sons: Chichester, U.K., 2003; Vol. 6, pp 19−26.

F

DOI: 10.1021/je500893g J. Chem. Eng. Data XXXX, XXX, XXX−XXX