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International Journal of Pharma and Bio Sciences V1(2)2010
MOLECULAR INTERACTION STUDY OF ANTIBIOTIC
DOXYCYCLINE HYCLATE WITH LINOLEIC ACID
1
www.ijpbs.net Medicinal Chemistry
C.ROUMANA*1AND G. VELRAJ1
1Department of Physics, Periyar University, Salem-11.
* Corresponding Author [email protected]
ABSTRACT Molecular Interaction of antibiotic Doxycycline hyclate with unsaturated fatty acid, the linoleic acid
have been investigated using dilute solution viscosity and ultrasonic techniques at ambient temperature
303 and the physiological temperatures 310 and 313K in the presence of solvent ethyl methyl ketone.
The temperatures 310 and 313K are favouring interaction between Doxycycline Hyclate and linoleic
acid. The interaction between the antibiotic and the linoleic acid is found on the basis of solute-solute
and solute-solvent interactions. Thus the antibiotic exhibits high structural specificity and the structure
of the drug play an important role in exhibiting liphophilic interactions.
KEYWORDS Interaction, Linoleic acid, antibiotic, viscosity, ultrasonic
INTRODUCTION
The growing interest in the study of molecular scale
interactions of drug with other biomolecules is due
to the fact that these interactions are the key to
understand the structural or characteristic property
of drug molecules. The non-newtonian Doxycycline
hyclate a member of tetracycline antibiotic family
exhibits metalloproteinase activity and shows
equilibrium between bioactive zwitterionic and non-
ionic conformation at physiological temperatures1.
In the presence of organic solvent Doxycycline
hyclate acquires non-ionic form which is suitable
for lipid solubility of the drug and penetrates the
cell membrane2. These interactions may leads to
antibiotic resistance and toxicity. Thus it is of
specific interaction type.
Therefore, the interaction between macromolecule
Doxycycline hyclate and the fatty acid, linoleic acid
may be attempted through dilute solution
viscometric technique and ultrasonic the effective
and established techniques to identify the solute-
solute and solute-solvent interactions in system.
Arun Kumar Misra et.al.,3 have attempted the
interactions of paracetamol with fatty acids through
viscometric technique. Conformity of
macromolecular interactions was reported by many
workers using ultrasonic technique4,5
. Varadarajalu
et.al.,4 and Singh and Singh
6 have suggested the use
of ultrasonic velocity and viscosity measurement
for investigating polymer interactions. In the
International Journal of Pharma and Bio Sciences V1(2)2010
www.ijpbs.net 2 Medicinal Chemistry
present study, the viscosity and ultrasonic
techniques were employed in Doxycycline hyclate /
Linoleic acid blends at the ambient temperature
303K and physiological temperature 310 and 313K.
MATERIALS AND METHODS
Doxycycline hyclate (Dox) (C22H24N2O8. HCl.1/2
C2H5OH.1/2H2O) of molecular weight 512.94
manufactured by Yangzhou huashu winsome
pharmacy Co.Ltd., China and supplied by Prime
Research laboratory (India) Pvt. Ltd., Chennai and
Linoleic acid of molecular weight 280.5
manufactured by merck specialities private Ltd.,
have been employed in the present study. 0.1%w/v
binary solutions of Doxycycline hyclate and
unsaturated linoleic acid (La) in ethyl methyl ketone
(EMK) were prepared. Using the binary solutions,
the blends of Dox/La of different compositions
were prepared. The relative viscosities were
measured using an Ubbelohde suspended level
viscometer for the binary solutions and blends of
Dox/La at temperatures 303K, 310K and 313K. The
Ultrasonic velocity measurements have been
performed by an ultrasonic interferometer operating
at frequency 2MHz and supplied by Mittal
enterprises New Delhi. The temperature is
maintained at 303K, 310K and 313K by a
thermostat, with a thermal stability of ±0.05°C. The
density of the solutions was measured using 10ml
standard specific gravity bottle.
THEORY
Viscometric Analysis
Based on additive law Huggin’s equation expresses
the specific viscosity (ηspe) as a function of
concentration if one of the components is alone in
solution,5
ηspe/C = [η] + KH [η]2 C -------- (1)
Where [η] is the intrinsic viscosity and K’ is the
Hugggin’s constant. If KH = b/[η]2, where b is the
interaction coefficient, then eq. (1) becomes
ηspe/C = [η] + bC ------------ (2)
Chee [7]
extended the Huggin’s equation for a
ternary system of solute A, solute B in common
solvent and gave the interaction parameter,
µ = ∆B / {[η]B - [η]A}2
---- (3)
Where [η]A and [η]B are the intrinsic viscosities for
the pure component solutions.
The blend is miscible if µ ≥ 0 and immiscible when
µ < 0.
Sun. et. al.,8 Suggested a new criterion, ‘α’
Km in the Huggin’s coefficient for the blends.
According to Sun. et. al’s for a ternary system, there
are three types of interaction that might contribute
to the value of Km: long-range hydrodynamic
interaction of pairs of single molecules given by
Km1; the formation of double molecules given by
Km2; and intermolecular attraction or repulsion
given by Km3. Thus, the overall Km turns out to be
Km = Km1 + Km2 +Km3 ----------(4)
In the absence of strong special interactions that would encourage aggregation, and at
sufficiently low concentrations, the second term Km2 can be neglected. Reabbrevating, Km3 as α and
rearranging the final equation then yields. α = Km – Km1 ----------------(5)
2 22 2
2
2A A B B A B A BA B A Bm
A BA B
K W K W K K W WK
W W
-------------------------(6)
Km is the experimentally obtained Huggins constant. The parameter α indicates the nature and
strength of the intermolecular interaction (α>0, attraction; α<0, repulsion). The sign of the parameter
α can be used to predict the solute-solute interaction, when α≥0 and α<0 indicates blend-solvent
interaction.
Jiang and Han9 revised Sun’s criterion by substituting an expression for total interaction
existing in the system Km, illustrated as in equation (7).
2 22 2
2
2A A B B AB A BA B A Bm
A BA B
K W K W K W WK
W W
-----------------------(7)
Then the new criterion β for the resultant interaction
International Journal of Pharma and Bio Sciences V1(2)2010
www.ijpbs.net 3 Medicinal Chemistry
2
2 A BA B
A BA B
K W W
W W
-----------------------------------(8)
Where 1
2AB AA BBK K K K
The criteria β≥0 indicates solute-solute interactions and β<0 is for blend-solvent interactions.
Ultrasonics Studies
Ultrasonic velocity (u) and density (ρ) are the observed parameters. These parameters were
employed to calculate the parameters,
Adiabatic Compressibility β = 1/uρ m2/N --------- (1)
and Free length Lf = K √β Å -----------(2)
Where, k = 93.875 + 0.345* T *10^-8,
T = absolute temperature.
RESULTS AND DISCUSSIONS
Viscosity technique
The Huggin’s plots of ηspe/C versus concentration C for 0.1%w/v solutions of Doxycycline Hyclate,
and Linoleic acid and for the blends of Dox/La at compositions for temperatures 303, 310 and 313K
were drawn and shown in graphs 1, 2 and 3 respectively.
Graph 1 Graph 2 Huggins plot at 303K Huggins plot at 310K
The plot is used to find the interaction parameter
and intrinsic viscosity at 310K
The plot is used to find the interaction parameter
and intrinsic viscosity at 303K
International Journal of Pharma and Bio Sciences V1(2)2010
www.ijpbs.net 4 Medicinal Chemistry
Graph 3
Huggins plots at 313K
The values of viscometric parameters the, interaction parameter b, intrinsic viscosity [η] and the
Huggin’s constant KH for 0.1%w/v binary solutions at temperature 303K, 310K and 313K are
summarized in Table 1. The values of the derived, the chee7 parameter µ, the Sun.et.al,
8 parameter α
and the improved parameter β for the blends of Dox/La at 303, 310 and 313K are summarized in the
Table 2.
Table 1.
The values of b, [η], KH of 0.1% solutions of Doxycycline hyclate and
Linoleic acid in common solvent ethyl methyl ketone at 303, 310 and 313K
Temperature 303K 310K 313K
solutions [η]
dl/g b KH
[η]
dl/g b KH
[η]
dl/g b KH
0.1%
Doxycycline
hyclate
0.119 30.823 2191.31 1.565 -44.94 -18.34 1.342 -31.76 -17.63
0.1%
Linoleic acid 0.352 24.992 201.59 0.228 9.923 191.21 0.69 -21.47 -45.09
The plot is used to find the interaction parameter b and
intrinsic viscosity at 313K
International Journal of Pharma and Bio Sciences V1(2)2010
www.ijpbs.net 5 Medicinal Chemistry
The intrinsic viscosity [η] and the interaction parameter b of 0.1% solution of Doxycycline
hyclate and linoleic acid are positive at 303K. The positive value of b suggests the interaction
between the groups that are present in the system. The positive value of [η] indicates the solubility of
the solute components10
. At temperatures 310 and 313K, [η] remains positive but the interaction
parameter b negative suggesting the dominance of solute-solvent interactions.
Table 2. The values of µ, α and β parameters at 303, 310 and 313K
At 303K, the parameters α and β are negative at all compositions. These parameters claim
blend-solvent interactions as per the criteria. The above discussed positive and negative values of α, β
and µ are in agreement with the reported observations 11, 12
.
At 310K and 313K the parameters α and β are positive at all compositions and indicates the
solute-solute interaction of Dox/La. The chee parameter µ exhibits the contradictory results with α
and β at all temperatures and compositions. Similar contradictory behavior of µ is common and
available in literature.8
Compositions
Doxy :
linoleic acid
303K 310K 313K
µ α β µ α β µ α β
9:1 169.380 -1475.137 -238.93 -12.401 76.297 1.15 2.499 10.199 0.08
8:2 449.780 -1060.558 -313.81 -6.684 42.960 0.34 30.453 9.680 0.32
7:3 370.197 -792.566 -316.44 -7.360 92.518 6.27 -4.854 10.046 1.04
6:4 125.068 -594.145 -279.41 -12.401 128.007 15.33 -4.955 19.417 5.57
5:5 212.776 -475.761 -240.47 -12.738 259.404 51.11 -22.066 22.541 8.92
4:6 59.132 -358.636 -184.52 -7.544 51.003 8.15 -37.136 4.830 2.29
3:7 -161.824 -322.746 -143.75 -12.447 191.422 67.04 -1.119 17.174 9.93
2:8 -89.560 -218.900 -86.48 6.079 298.533 139.58 -5.901 28.158 15.27
1:9 -218.535 -216.280 -44.82 -6.301 270.841 150.06 -23.306 46.231 16.75
International Journal of Pharma and Bio Sciences V1(2)2010
www.ijpbs.net 6 Medicinal Chemistry
The behavior of free length with compositions at 303 K The behavior of free length with compositions at 310
K and 313K.
Ultrasonic technique
In order to further confirm the identified solute-solute interactions, the behavior of (u), (κ)
and (Lf) of Doxy/La blend solutions are depicted in graphs 4, 5, 6 and 7 respectively for the
temperatures 303K, 310K and 313K.
Graph 4 Graph 5
Behaviour of ultrasonic velocity and compressibility Behaviour of ultrasonic velocity and compressibility
Graph 6 Graph 7
Behaviour of free length Behaviour of free length
The behavior of ultrasonic velocity and adiabatic
compressibility with compositions at 303 K.
The behavior of ultrasonic velocity and adiabatic
compressibility with compositions at 310 K and 313 K.
International Journal of Pharma and Bio Sciences V1(2)2010
www.ijpbs.net 7 Medicinal Chemistry
From the behaviours of the parameters it is clearly evident that the variation is non-linear at
303K and indicates solute-solvent interactions in the blend. The criterion of linear behavior in u, κ
and Lf in the blend of Dox/La at temperatures 310 and 313K and establishes solute-solute interaction
between Dox and La. These observations are in agreement with the results obtained through dilute
solution viscometric technique. Varadarajulu et. al. 4 Singh and Singh et. al.,
6 somanathan et. al.,
13
Paladhi and Singh, 14
Murali mohan et.al.,15
have employed the Viscometric and Ultrasonic
techniques to identify the solute-solute and solute-solvent interactions in the polymer blends and
established the criteria.
The Doxycycline exhibits liphophilicity with non-ionic nature. The non-ionic confirmation of
Doxycycline hyclate predominates in organic solvent which provides a suitable structure for linoleic
acid to interact.
Figure 1: Stucture of Linoleic acid
Figure 2: Structure of Doxycycline Hyclate
The structure of Linoleic acid and
Doxycyline hyclate are shown in figure 1 and 2
respectively. The Linoleic acid interaction through
ester carbonyl C=O at hydroxyl of Doxycycline
hyclate at C3 through a dipole-dipole interaction
which makes the Doxycycline hyclate as an inactive
non-ionic molecule.
CONCLUSIONS In the present investigation the dilute
solution viscosity and ultrasonics successfully have
investigated the molecular interactions between
Doxycycline hyclate and linoleic acid. At
physiological temperature 310 and 313K the
interactions are favoured between Doxycycline and
Linoleic acid and these interactions are absent at
room temperatures. These molecular interactions are
at the physiological temperatures might leads to the
formation of antibiotic resistance and toxicity.
International Journal of Pharma and Bio Sciences V1(2)2010
www.ijpbs.net 8 Medicinal Chemistry
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