A STUDY ON THE SOLUBILITY OF FRANGULA EMODIN
Martina Mizzi, Deborah Duca and Claude Farrugia
Department of Chemistry, University of Malta, Msida MSD2080, Malta
Introduction
Methodology
Emodin (1,3,8‐trihydroxy‐6‐methyl‐anthraquinone) is a kind
of anthraquinone derived from Frangula alnus.1 This research
study describes how its solubility varies in acetonitrile,
methanol, ethanol and sodium hydroxide. The physico‐
chemical properties of emodin were also analysed through
particle size, bulk density, tapped density, angle of repose and
wettability measurements.
The project consisted of conducting solubility and absorption
studies for solutions of emodin containing varying organic
concentrations for each solvent using water as an aqueous
component. A linearity study was performed for the solution of
percentage organic concentrations that showed the highest
solubility for emodin in each solvent. The method was then
validated according to the International Conference on
Harmonisation guidelines and the parameters of linearity,
repeatability and range were assessed. The second part
consisted of analysing powder properties of emodin by testing
its wettability, particle size, density, tapped density and angle of
repose.
Figure 1 Chemical structure of anthraquinones and positions of substituents.
Results
3
2.5
(ii)
2.0
Absorbance (AU)
Absorbance (AU)
(i)
2
1
Geometric mean diameter (µm)
Bulk Density (gcm‐3)
0.195 ± 0.030
Tapped Density (gcm‐3)
0.255 ± 0.005
Angle of repose (o)
12.078 ± 0.421
Full Linearity Range
15
1.5
Reduced Linearity Range
1.0
Table 2 Powder properties results
0.5
0
0.0
0.5
1.0
0.0
0.0
1.5
0.05
0.5
Concentration (mg/mL)
1.0
1.5
(i)
Concentration (mg/mL)
0.08
(ii)
0.04
0.06
Absorbancce (AU)
(iv)
2
1
6
Full Linearity Range
Reduced
Linearity Range
4
0.03
2
2
Mass squared (g )
8
(iii)
Mass squared (g )
M
3
Absorban
nce (AU)
316.5
0.02
0.01
0.04
0.02
Full Linearity Range
0.00
0.00
Reduced Linearity Range
2
0
200
400
600
800
1000
0
200
Time (s)
1.0
1.5
2.0
2.5
Concentration (mg/mL)
Figure 2
0.5
1.0
1.5
Coefficient (R2)
600
800
1000
(iii)
Concentration (mg/mL)
0.06
Linearity plots for emodin in (i) 100% ethanol, (ii) 90% acetonitrile, (iii) 100% methanol and (iv) 2M sodium hydroxide at 325 nm
Correlation 400
Time (s)
0.08
2
0.5
0
0.0
Mass squared (g )
0
0.0
0.04
0.02
0.00
Residual System Overall % Range
sum of precision precision 0
200
400
600
800
1000
Time (s)
squares
% RSD
% RSD
90% acetonitrile
0.9992
0.001577
0.720
9.165
10 – 600
100 % ethanol
0.9994
0.005870
0.104
2.317
10 – 300
100% methanol
2M sodium y
hydroxide
0.9963
0.012990
0.113
1.512
10 – 200
50 – 400
0.9998
0.001399
0.097
11.365
Table 1 Validation parameters of linearity, repeatability and range for solvents showing the best solubility in emodin
Figure 3 Wettability plots for (i) 90% acetonitrile, (ii) 100 % ethanol and (iii) 100% methanol
T1(s)
Gradient (g2/s)
90 % Acetonitrile
3.578 ± 0.0497
0.0078
100 % Ethanol
6.488 ± 0.0427
0.0086
100 % Methanol
100 % Methanol
5 998 ± 0.0590
5.998 ±
0 0590
0 0097
0.0097
Table 3 Inflection point and gradient results from step‐wise regression analysis of wettability plots
Conclusions
References
Emodin was found to be best soluble in 90% acetonitrile,
100% ethanol, 100% methanol, 2M sodium hydroxide, and
their linearity studies showed optimal solubility in the ranges
of 0.05 mg/mL and 0.8 mg/mL, 0.05 mg/mL and 1.5 mg/mL,
0.05 mg/mL and 1.1 mg/mL, and 0.025 mg/mL and 0.2
mg/mL respectively. Emodin ‘s powder properties indicated
excellent flow properties. The fastest rate and extent of
wettability were found in 100% methanol and 100% ethanol.
[1] Dave, H.; Ledwani, L. A review on anthraquinones isolated
from Cassia species and their applications. Indian Journal of
Natural Products and Resources 2012, 3, 291‐319
Acknowledgements
This project was supported by a research grant from the
University of Malta.