Antioxidant activity of new aramide nanoparticles containing redox-active N-phthaloyl valine moieties in the hepatic cytochrome P450 system in male rats

Article abstract of DOI:10.3390/molecules17078255

We report the synthesis of aramide nanoparticles containing a chiral N-phthaloyl valine moiety and their antioxidant activities on hepatic contents of cytochrome P450, amidopyrene N-demethylase, aniline-4-hyroxylase and induced the hepatic content of cytochrome b5 and nicotinamide adenine dinucleotide phosphate (NADPH) cytochrome C-reductase. Polymers were obtained as well-separated spherical nanoparticles while highly aggregated particles via H-bonding organization of the aramide-containing pyridine led to a thin layer formation. The effects of the nanoparticles and CCl4 on enzyme activities and thiobarbituric acid reactive substances (TBARS) levels of male rat liver were studied. Pretreatments of rats with the polyamides prior to the administration of CCl4 decreased the hepatic content of the tested enzymes. Doses reduced the toxic effects exerted by (CCl3) upon the liver through inhibition of the cytochrome P450 system. Inhibition of such metabolizing enzymes could reduce the carcinogenic effects of chemical carcinogens.

Full text of DOI:10.3390/molecules17078255

Molecules 2012, 17, 8255-8275; doi:10.3390/molecules17078255
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Antioxidant Activity of New Aramide Nanoparticles Containing
Redox-Active N-phthaloyl Valine Moieties in the Hepatic
Cytochrome P450 System in Male Rats
Hammed H. A. M. Hassan 1,2,*, Sabah G. El-Banna 3, Amel F. Elhusseiny 1 and
El-Sayed M. E. Mansour 1
1
Department of Chemistry, Faculty of Science, Alexandria University, P. O. Box 2-Moharram Beck,
Alexandria 21598, Egypt
2
Department of Analytical and Pharmaceutical Chemistry, Faculty of Pharmacy, Pharos University,
Canal El Mahmoudia Street, Alexandria 21311, Egypt
3
Department of Environmental Studies, Institute of Graduate Studies and Research,
Alexandria University, Alexandria 21526, Egypt
* Author to whom correspondence should be addressed; E-Mails: hassan10@safwait.com or
hamed.hassan@upa.edu.eg; Tel.: +20-122-5888-595; Fax: +20-3391-1794.
Received: 23 April 2012; in revised form: 7 June 2012 / Accepted: 12 June 2012 /
Published: 10 July 2012
Abstract: We report the synthesis of aramide nanoparticles containing a chiral N-phthaloyl
valine moiety and their antioxidant activities on hepatic contents of cytochrome P450,
amidopyrene N-demethylase, aniline-4-hyroxylase and induced the hepatic content of
cytochrome b5 and nicotinamide adenine dinucleotide phosphate (NADPH) cytochrome
C-reductase. Polymers were obtained as well-separated spherical nanoparticles while
highly aggregated particles via H-bonding organization of the aramide-containing pyridine
led to a thin layer formation. The effects of the nanoparticles and CCl4 on enzyme activities
and thiobarbituric acid reactive substances (TBARS) levels of male rat liver were studied.
Pretreatments of rats with the polyamides prior to the administration of CCl4 decreased the
hepatic content of the tested enzymes. Doses reduced the toxic effects exerted by (•CCl3)
upon the liver through inhibition of the cytochrome P450 system. Inhibition of such
metabolizing enzymes could reduce the carcinogenic effects of chemical carcinogens.
Keywords: aramide nanoparticles; thermal analysis; valine; cytochrome P450 enzymes;
TBARS

Molecules 2012, 17
8256
1. Introduction
The liver plays a major role in regulating various physico-chemical functions of the body, including
synthesis, secretion and metabolism of xenobiotics. Liver diseases are amongst the most serious health
problems in the World today and their prevention and prevention options still remain limited despite
the tremendous advances in modern medicine. The liver, unique in its capacity for regeneration
following injury, may give rise to malignancy states of advanced fibrosis or cirrhosis [1,2]. Many
etiological factors may induce liver damage, including infectious agents and hepatotoxic chemicals.
Carbon tetrachloride (CCl4) is one of the most commonly used hepatotoxins for inducing liver injury
in experimental animal studies [3]. Various studies have demonstrated that CCl4 intoxication causes
free radical generation in the liver [4–6]. CCl4 intoxication in animals is an experimental model that
mimics oxidative stress in many physiological situations. The initial step in the tissue injury induced
by carbon tetrachloride is its cytochrome P450-mediated transfer of a single electron to the C–Cl bond,
giving a radical anion as a transient intermediate that eliminates chlorine to form a carbon centered
radical, the trichloromethyl radical (•CCl3) and chloride radical [7,8]. The trichloromethyl radical can
dismutate to chloroform, bind to macromolecules or attack polyenoic fatty acids in cellular
membranes. The double allylic hydrogen atoms in these acids are particularly susceptible to
abstraction by free radicals, giving chloroform and secondary lipid radicals which react rapidly with
molecular oxygen to form lipid peroxy radicals. The trichloromethyl radical can also react with oxygen
to form the peroxy trichloromethyl free radical (•CCl3O2), which is more reactive than the (•CCl3) and
produces similar kinds of damage.
Hepatic drug-metabolizing enzyme [9] is called mixed-function oxidase or monooxygenase and
contains many enzymes, including phase I enzymes such as cytochrome P-450, cytochrome b5 and
NADPH-cytochrome C reductase which metabolize most carcinogens and xenobiotics into less
and/or more active intermediates. In addition to the above enzymes agents involved in phase II drug
metabolism, e.g., glutathione and glutathione S-transeferase, as well as free radicals “detected as
thiobarbituric acid-reactive substances, TBARS”. It has been postulated that the rate-limiting step in
the oxidation of some xenobiotics may be due to the rate of reduction of cytochrome P450-substrate
complex which is dependent on the activation of NADPH- cytochrome C-reductase and of cytochrome
P450. NADPH-cytochrome C-reductase activity is a component of the microsomal mixed-function
oxidase system which catalyses hydroxylation reaction and this process are of a prime importance in
the metabolism of lipids, drugs and other foreign compounds. A wide variety of compounds have the
ability to increase or inhibit the drug metabolism by their effect on the activity of NADPH-cytochrome
C-reductase. The rate-limiting step in the activation and detoxification of toxic compounds is
dependent on the rate of reduction of cytochrome P-450-substerate complex, which in turn is
dependent on the activation and turnover rates of NADPH-cytochrome C-reductase, cytochrome b5
and on the total cytochrome P-450 content.
Antioxidants protect the human body against free radical attacks that may cause pathological
conditions. Various compounds with differential antioxidant properties are found in natural resources
which are considered to have high potential in the context of therapeutic approaches to encounter and
prevent free radical damage [10]. Many plants contain substantial amounts of antioxidants such as
vitamins C and E, carotenoids, flavonoids and tannins that can be utilized to scavenge excess free

Molecules 2012, 17
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radicals from the human body [11]. The free radical scavenging potential of natural antioxidants varies
among diseases and types of antioxidant [12]. Nowadays, there is an increased interest in finding other
synthetic products for effective uptake of antioxidant compounds as an alternative source of
scavenging reactive oxygen species (ROS) which includes the superoxide anion O2, H2O2 and the
hydroxyl radical.
Aromatic polyamides have excellent thermal stability, good chemical resistance, mechanical
strength, and low dielectric constants [13,14]. They are used widely in the microelectronic, aviation,
liquid crystal display, and separation industries. However, aromatic polyamides are difficult to process
because they are insoluble in most organic solvents and do not flow below their decomposition
temperatures. The introduction of flexible chains into polyamide backbone [15], the use of meta-oriented
monomers [16–18], synthesis of polyamides with non coplanar units in the polymer chains [19], or
introduction of bulky side groups into the polymer chains, [20–23] resulted in a number of modified
polyamides. These modifications work by breaking chain symmetry and regularity and by destroying
hydrogen bonding, generally leading to better solubility and process-ability. The imine structure
on pyridines 1 can be oxidized by 30% aqueous H2O2 in acetic acid to form pyridine N-oxides 2,
Scheme 1 [24].
Scheme 1. Oxidation of pyridine to pyridine-N-oxide.
Based on this mechanism, we describe for the first time the synthesis and characterization of
nanoscale aramides containing N-phthaloyl valine moieties in the side chain by a precipitation
polymerization method [25–27]. Phthalimides are among the most useful organic compounds in
biology and synthetic chemistry [28]. The effects of the prepared aramides nanoparticles as
antioxidants on the hepatic content of cytochrome P450 and other dependent drug-metabolizing enzyme
activities were assessed.
2. Results and Discussion
The main objective of this work was to synthesize and characterize aramide nanoparticles
containing the chiral N-phthaloyl valine moieties and to assess them as antioxidants on the hepatic
content of cytochrome P450 and other dependent drug-metabolizing enzyme activities. Aromatic
polyamides are thermally stable polymers with an attractive combination of excellent chemical,
physical and mechanical properties [10]. One of the approaches to increase solubility and
processability without sacrificing their thermal stability is the introduction of asymmetric units into the
polymer backbone [29–31]. Introduction or the attachment of such pendent groups in the polymer main
chain imparts a significant increase in Tg by restricting the segmental mobility and providing a good
solubility as a result of decreased packing and crystallinity. Recent advances in asymmetric reactions

Molecules 2012, 17
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and catalysis as well as in chiral separations have afforded a rapid increase in the number of
commercially available optically active compounds and reagents [32,33] and the simplest method of
synthesizing optically active polymers involve the polymerization of optically active monomers.
2.1. Synthesis of Aramides Nanoparticles Containing N-Phthaloyl Valine Moieties
The known 2-phthalimidyl-3-methyl butyric acid chloride (4, Scheme 2) [34] was prepared by
heating equimolar ratios of S-valine (3) and phthalic anhydride in DMF, followed by refluxing of the
resulting crude material with thionyl chloride. Reaction of 4 with 5-aminoisophthalic acid (5) in
DMAc smoothly furnished the known 5-(2-phthalimidyl-3-methyl butanoylamino)isophthalic acid.
Heating the latter with thionyl chloride followed by co-evaporation of the product with n-hexane gave
the required diacid chloride 6 in good yield.
Scheme 2. Preparation of 5-(2-phthalimidyl-3-methylbutanoylamino)-isophthaloyl
chloride 6 from S-valine 3.
Reagents and conditions: (a) phthalic anhydride, DMF, reflux, 2 h; (b) SOCl2, reflux, 2 h; (c) DMAc, 80 °C.
Our attention focused next on the synthesis of new types of chiral aramide nanoparticles. Polymeric
aromatic nanoparticles can be prepared by either emulsion or interfacial polymerizations. Additionally,
a popular method used for polymeric nanoparticles preparation is solvent displacement, also referred
to as nanoprecipitation [35]. The basic principle of this technique is based on the interfacial deposition
of a polymer after displacement of a semipolar solvent, miscible with water, from a lipophilic solution.
Rapid diffusion of the solvent into the non-solvent phase results in a decrease of interfacial tension
between the two phases, which increases the surface area and leads to the formation of small droplets
of organic solvent. The key variables determining the success of the method and affecting the
physicochemical properties of nanoparticles are those associated with the conditions of adding the
organic phase to the aqueous phase, such as organic phase injection rate, aqueous phase agitation rate,
the method of organic phase addition and the organic phase to aqueous phase ratio. Likewise,
nanoparticle characteristics are influenced by the nature and concentration of their components [36,37].
The process of particle formation in the nanoprecipitation method comprises three stages: nucleation,
growth and aggregation. The rate of each step determines the particle size and the driving force of

Molecules 2012, 17
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these phenomena is the ratio of polymer concentration over the solubility of the polymer in the solvent
mixture. The separation between the nucleation and the growth stages is the key factor for uniform
particle formation [38].
The polyamides nanoparticles 9, 10 and the polyesteramide 12 (Scheme 3) were prepared by
ultrasonication of 0.5 mmol of m-phenylenediamine (7), 2,6-diaminopyridine (8) and m-aminophenol
(11), respectively, with 0.5 mmol of the acid chloride 6 in a total of 115 mL dioxane solution
containing distilled water (15 mL) (i.e., 50/15 mL dioxane-water v/v diamine solution and 50 mL
dioxane acid chloride solution) followed by centrifugal separation at 15,000 rpm for 30 min. Similarly,
polyamide nanoparticles 17–20 were obtained from the reaction of the acid chloride 6 with benzidine
(13), 4,4'-diaminodiphenylmethane (14), 4,4'-diaminodiphenylether (15) and 4,4'-diaminodiphenyl-
sulfone (16), respectively, under ultrasonication conditions (Scheme 4). Mixing 1,4-dioxane with H2O
was essential for many reasons, such as controlling the particle morphology, playing an important role
in determining the polarity of the reaction solution and as a reaction accelerator [24–27]. The polymer
structures 9, 10, 12 and 17–20 were confirmed by elemental analysis, IR and UV spectroscopy (Table 1).
Scheme 3. Chemical preparation of polyamide nanoparticles 9, 10 and the polyesteramide 12.
Reagents and conditions: (a) 90% dioxane/H2O, 20 min. Sonication at 42 KHz.
Scheme 4. Chemical preparation of polyamide nanoparticles 17–20.
Reagents and conditions: (a) 90% dioxane/H2O, 20 min. Sonication at 42 KHz.

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Table 1. Physical properties of polymers 9, 10, 12 and 17–20.
No. Yield
(%)
Unit
% C
(Exp.) (Exp.) (Exp.)
64.79 4.83 11.19
(64.31) (4.42) (11.38)
% H
% N
IR (KBr)
max
(nm)
265
a
M.Wt
ηinh
Formula
(υ cm−1)
9
88
81
86
C27H24N4O6
500
0.70
0.62
0.67
3464, 2968, 1768, 1712,
1608, 1549, 1488, 1450,
1386, 1334, 1248, 1115,
1071, 1017, 886, 686.
3448, 1768, 1712, 1608,
1554, 1488, 1450, 1387,
1333, 1245, 1115, 1071,
1016, 999, 959, 886, 868.
3423, 2966, 1769, 1713,
1656, 1605, 1548, 1494,
1451, 1385, 1354, 1335,
1255, 1174, 1157, 1117,
1077, 1016, 999,975, 888.
3457, 2967, 1769, 1713,
1652, 1597, 1523, 1502,
1467, 1447, 1415, 1385,
1331, 1116, 1070, 887.
3452, 2967, 1769, 1714,
1655, 1602, 1539, 1499,
1467, 1447, 1408, 1385,
1335, 1232, 1169, 1117,
1071, 1014, 876, 832.
3460, 1713, 1649, 1533,
1411, 1385, 1253, 1071,
720, 531.
300
10
12
C26H23N5O6
501
501
62.27
4.62
13.97
265
305
(62.63) (4.88) (13.54)
C27H23N3O7
64.67
4.62
8.38
265
296
(64.30) (4.22) (8.09)
17
18
90
84
C33H28N4O6
576
592
68.74
4.89
9.72
0.61
0.60
269
306
(69.01) (4.55) (9.37)
C33H28N4O7
66.88
4.76
9.45
268
292
(66.49) (4.41) (9.78)
19
20
88
86
C34H30N4O6
590
640
69.14
5.12
9.49
0.63
0.58
268
295
(70.45) (5.53) (9.81)
C33H28N4O8S
61.87
4.41
8.75
3468, 1770, 1714, 1674,
1593, 1529, 1447, 1394,
1320, 1252, 1148, 1106,
1071, 888, 836.
270
305
(62.34) (4.19) (8.42)
a The inherent viscosity of the polymers was measured at a concentration of 0.5 g/dL in DMSO at 30 C.
As judged by SEM photographs, (Figure 1), polyamides nanoparticles 9 and 10 were obtained with
average diameters of 106 nm, while polyesteramide nanoparticles 12 produced under the same reaction
conditions were obtained with larger diameters (190–300 nm). The average diameter of particles was
estimated from SEM images and selected at random. Noteworthy, the polymeric particles 9 and 12
were obtained as well-separated spherical nanoparticles while aggregated particles of the aramide-
containing pyridine 10 formed a thin layer. The formation of such a thin layer may be attributed to the
molecular self assembly via H-bond directed organization of molecular precursors [39]. Amides
embody self-complementary recognition groups defined by homomeric H-bond donor-acceptor pairs [40].

Molecules 2012, 17
Figure 1. SEM images of the aramides nanoparticles 9, 10, 12 and 17–20.
8261
Aramides containing pyridine assume extended helical secondary structures able to dimerize in
solution, undergoing dynamic exchange between single and double helical states. Internal H-bonding,
in the form of motifs A and B (Figure 2), induces curvature into the oligomer backbone [41,42].
Similarly, pyridine-containing polyamides 10 assemble through the action of H-bonds according to
motifs C or D (Figure 2). In addition, synthetic polymers may also assemble by virtue of homo- or
heteromeric association with other molecular strands to yield polymeric duplex or triplex ensembles.
In principle, H-bonding could occur in a frame-shifted sense, resulting in the formation of polymeric
aggregates. Although the H-bond donor acceptor sites of the composite strands are not in direct
juxtaposition, they nevertheless act in concert as a composite H-bonding recognition group. Single
strands that reside in well-defined conformations may adopt alternative forms upon complexation with
a complementary strand. Figure 2 represents the intramolecular hydrogen bonds in helical
conformations of pyridine-containing polymers and schematic representation of double helix made by
interaction of two helical monomers [43].

Molecules 2012, 17
Figure 2. Intramolecular hydrogen bonds in helical conformations of pyridine-containing
8262
polymers and schematic representation of double helix made by interactions of two
helical monomers.
Nanoparticles 17 and 20 were obtained with average diameters of 106 nm and 120 nm, respectively;
while nanoparticles 18 and 19 produced under these conditions have larger diameters (230–300 nm).
Noteworthy, addition of particular amount of water (15% v/v) to this reaction system is essential, not
only for the formation of spherical particles, but also to diminish the aggregation of these particles.
The tendency of spherical particles formation of such aramides may be correlated to the dispersion
stability of particles in the reaction solution or the precipitation mechanism of the particles. The
formation mechanism of polymers is related to the effect of water on the micelle structure. Micelles
grow in the presence of water to spherical micelles [25–27].

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2.2. Physical Properties of the Prepared Polymers
2.2.1. Solubility
The prepared pyridine-containing polymers 11–16 showed different solubility behaviors in different
organic solvents. Moderate to complete solubilities (5 wt% solid content) were observed in a variety of
hot aprotic solvents such as NMP, DMSO, DMAc and in hot conc.H2SO4, while they were insoluble in
boiling alcoholic solvents such as methanol, ethanol, propanol and ethylene glycol, in halogenated
solvents such as CHCl3, CCl4, CH2Cl2, ClCH2CH2Cl or in ethers such as Et2O, THF, 1,4-dioxane or
1,2-dimethoxyethane (DME).
2.2.2. Inherent Viscosity
The inherent viscosity of the polymers, as a suitable criterion for evaluation of molecular weight,
was measured at a concentration of 0.5 g/dL in DMSO at 30 °C. It was in the range of ηinh 0.57–0.70 dL/g
that showed moderate molecular weights (Table 1).
2.2.3. FTIR Spectroscopy
The FT-IR spectra of the polymers exhibited characteristic absorption bands at around 3,300 and
1,769, 1,712 and 1,650 cm−1 corresponding to the N–H and C=O stretching of amide groups,
respectively, while the bands at around υ 3,050, 2,960 and 1,600 cm−1 are due to H–Cstr and C–Cstr,
respectively. Table 1 compiles selected IR bands of the polymers 9, 10, 12 and 17–20.
2.2.4. Optical Properties
The optical properties of the prepared polymeric nanoparticles were investigated by UV-Vis
spectroscopy in DMSO with a polymer concentration of ~2 mg/10 mL (Table 1). All polyamides
exhibited maximum absorptions (λmax) around 300 nm and 265 nm due to the n–π* and π–π*
transitions, respectively.
2.2.5. Thermal Properties
The thermal properties of the prepared polymers were evaluated by differential thermo gravimetric
(DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) techniques.
Thermal data of the prepared polymers are complied in Table 2. Thermal results revealed that the
prepared polymers have high thermal stability. Structure-thermal property correlation based on
changing the diamine monomer, as a single structural modification, demonstrated an interesting
connection between a single change and the thermal properties. Polyamides 9, 10 and 17–20 exhibited
major degradation processes at 425 C leaving 41.40%, 41.81%, 32.00%, 53.18%, 59.02% and
47.71%, respectively, as char yields. Polyesteramide 12 exhibited less thermal behavior and showed a
major degradation step at 320 °C leaving 41.37% as residue. Char yield can be used as criteria for
evaluating limiting oxygen index (LOI) of the polymers in accordance with Van Krevelen and
Hoftyzer equation [44]. LOI = 17.5 + 0.4 CR where CR = chars yield. The LOI values of all polymers
calculated based on their char yield at 700 C was higher than 28. On the basis of LOI values, such

Molecules 2012, 17
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macromolecules can be classified as self-extinguishing polymers. Polyamide 9 exhibited three
endothermic decomposition peaks at 320 °C, 425 °C and 525 °C, respectively, which clearly
demonstrated the highest thermal stability compared to analogues 10 and 12 in which both
demonstrated one endothermic peak at 425 °C and 320 °C, respectively. Interestingly, thermal
analyses of polyamides series 17–20 demonstrated similar thermal stability up to 700 °C due to the
increase of the aromatic character and/or the presence of strong polar groups such as sulfonyl and ether
linkages. Polyamides 18 and 19 exhibited two similar endothermic decomposition peaks at 200 °C and
425 °C while the analogue 20 demonstrated only one major endothermic peak at 425 °C.
Table 2. Thermoanalytical and the kinetic parameters of polymers 9, 10, 12 and 17–20.
Cpd.
No.
9
TG
(C)
200–700
Residue
% Wt
loss
58.60
41.40
A (S−1)
× 10−4
0.47
0.72
1.40
c
Stage
LOI a
T b
Ea
H* c
S* c
G* c
I
II
320
425
525
425
6.72
22.34
86.16
19.62
1.78
16.53
79.52
17.04
−329.1
−327.0
−322.3
−317.2
199.9
244.7
336.6
184.9
34.1
34.2
41.1
30.3
10
12
17
I
II
I
II
I
200–700
Residue
200–700
Residue
200–700
Residue
58.19
41.81
58.63
41.37
68.00
32.00
1.97
320
200
82.97
74.79
320 182.96
425 49.09
200 143.60
3.72
78.20
−311.8
256.8
5.18
1.49
3.11
1.81
3.53
1.44
2.05
8.40
70.85
178.02
43.28
139.66
84.88
48.40
36.74
128.06
−317.7
−309.0
−314.9
−316.1
−313.7
−322.3
−318.3
−310.8
221.1
361.6
263.1
289.2
303.8
200.8
257.3
345.0
II
18
19
20
I
II
I
II
I
200–700
Residue
200–700
Residue
200–700
Residue
46.82
53.18
40.98
59.02
52.29
47.71
38.8
41.1
36.6
425
200
425
90.69
52.34
42.50
425 133.87
II
a Limiting oxygen index; b The peak temperature from the DTG charts; c Values are in kj/mole.
The thermodynamic parameters of decomposition processes of polymers, namely, activation energy
(Ea), enthalpy (ΔH*), entropy (ΔS*), and Gibbs free energy change of (ΔG*) were evaluated
graphically by employing the Coats-Redfern method [45]. This method, reviewed by Johnson and
Gallagher [46] as an integral method assuming various orders of reaction and comparing the linearity
in each case to select the correct order by using equations (i) and (ii):
(i)
(ii)
where α is the fraction of sample decomposed at time t, T is the derivative peak temperature, A is the
frequency factor, Ea is the activation energy, R is the gas constant, θ is the heating rate, and
(1 − (2RT/Ea))  1. A plot of log [−log (1 − a)/T2] versus 1/T gives a slope from which the Ea was
calculated and A (Arrhenius factor) was determined from the intercept. The correlation coefficient R

Molecules 2012, 17
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was computed by using the least square method for the above equations. The values of R2 were nearer
to unity in most cases. Linear curves were drawn for different values of n equal 0, 0.33, 0.5, 0.66 and
1. The values of n, which gave the best fit, were chosen as the order parameter for the decomposition
stage of interest. The entropy of activation was calculated [47] using equation (iii):
(iii)
where h and k stand for the Plank and Boltzmann constants, respectively, and T is the peak temperature
from the DTG curve. The enthalpy of activation H* and the free energy of activation ΔG* are
calculated using equations (iv) and (v), respectively.
H* = Ea  RT
(iv)
(v)
G* = H*  TS*
The kinetic data obtained from the nonisothermal decomposition of the prepared polymers 9, 10, 12
and 17–20 are given in Table 2. Activation energy values (Ea) of polyamides 9 demonstrated higher Ea
values compared to their analogues 12 and 10, respectively. Activation energy values (Ea) of other
polyamides were in the order 17  18  20  19, respectively, and thus indicating different degradation
mechanism in all compounds. From the Ea values, one can conclude that the water molecules are easily
eliminated from all ligands and the energies of activation for the second stages of decomposition are
higher than that of the first stage. According to the kinetic data obtained from DTG curves all
polymers have negative entropy (S*), which indicates ordered systems and more ordered activated
states that may be possible through the chemosorption of other light decomposition products [48]. The
positive sign of the free energy of decomposition (ΔG*) of the investigated polymers indicated that the
free energy of the final residue is higher than that of the initial compound and all the decomposition
steps are non-spontaneous processes. Additionally, kinetic parameters showed that activation energies
of decomposition, and hence the rate of decomposition, and the enthalpy (H*) the polymers follow
the sequence 9 > 12  10 and 17 > 18  20  19, respectively, and the positive values of H* means
that the decomposition processes are endothermic.
2.3. Biochemical Findings
The effects of the prepared aramide nanoparticles and carbon tetrachloride on drug metabolizing
enzyme activities, and TBARS levels of male rat liver are presented in Figure 3. Intraperitoneal
administration of CCl4 (1 mL/kg) insignificantly affects the hepatic content for microsomal protein, the
same trend was observed in 10, 17 and 20. Pretreatment of rats with 17–20 prior to the administration
of CCl4 significantly increased the hepatic content of microsomal protein by 7%, 21%, 15% and 34%,
respectively, compared to the control group. The opposite trend was observed in rats pretreated with 9,
10 and 12, where this content significantly decreased by −46%, −19% and −16%, respectively,
compared to the control group. The hepatic content of cytochrome b5 in rats treated with CCl4 was
unchanged. Pretreatment of rats with 9, 10, 12, 18 and 20 prior to the administration of CCl4 induced
cytochrome b5. Cytochrome P450 was significantly induced by CCl4 treatment, however, 18–20
reduced P450 content by −3%, −28% and −22%, respectively, compared to the control group. Liver

Molecules 2012, 17
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GST activity was significantly reduced by CCl4 treatment; meanwhile, polyamides induced GST
activity compared to the control group. The activity of amidopyrene N-demethylase, aniline 4-
hyroxylase and TBARS levels significantly induced in CCl4 group by 4%, 17% and 27%, respectively,
compared to the control group while treatment with polyamides reduced the alteration caused by CCl4.
The opposite trend was observed for NADPH cytochrome C-reductase.
Figure 3. Effect of polyamides and carbon tetrachloride on drug metabolizing enzyme
activities, and TBARS levels of male rat liver.
Values are expressed as Mean ± SEM; n = 6 for each treatment group; Hepatic microsomal protein
content was expressed as mg protein/g liver, cytochrome b5 and cytochrome P450 contents were
expressed as nmol cytochrome/mg microsomal protein, glutathione S-transferase activity was
expressed as units/mg protein, NADPH cytochrome C reductase activity was expressed as nmol
cytochrome C reductase/mg protein/min, amidopyrene N-demethylase in liver microsomes was
expressed as μmol/min × kg liver sample, aniline-4-hydroxylase was expressed as μmol/min/mg
protein, and thiobarbituric acid reactive substances (TBARS) were expressed as μmol TBARS/g
tissue; a p < 0.05 in comparison to Control; × p < 0.05 in comparison between CCl4 and
CCl4 + polyamide.

Molecules 2012, 17
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A protein involved in the architecture and also in the physiology of the cell seems to occupy a key
role in the cell metabolism [49]. In the present study the induction in protein levels in rats pretreated
with polyamides 17–20 prior to the administration of CCl4 indicates an acceleration of protein
anabolism during CCl4 intoxication. This induction may be one of the defense mechanism of the
experimental animals against oxidative stress induced by CCl4 intoxication. The rate-limiting step in
the activation and detoxification of toxic compounds is dependent on the rate of reduction of
cytochrome P450-substrate complex, which in turn is dependent on the activation and turnover rates of
NADPH cytochrome C-reductase, cytochrome b5 and on the total cytochrome P450 content [50].
Administration of polyamides as repeated dose prior to the administration of CCl4 was found to
increase the hepatic content of cytochrome b5 and NADPH cytochrome C-reductase activity. This
induction could be one of the defense mechanisms of the experimental animals to increase the rate of
reduction of cytochrome P450-substrate complex because the total hepatic content of cytochrome P450
decreased in these groups.
Pretreatment of rats with polyamides prior to the administration of CCl4 was found to decrease the
activity of amidopyrene N-demethylase. Inhibition of cytochrome P450 content and amidopyrene
N-demethylase activity may play a significant role in the reduction of tumorgenicity and
carcinogenicity of N-nitroso compounds [51]. CCl4 induced liver aniline 4-hydroxylase activity. On
the other hand, polyamides ameliorate the action of CCl4. In accordance with the present study it has
been found that the activity of aryl hydrocarbon hyroxylase (AHH) was decreased after pretreatment of
rats with repeated doses of garlic and other free radical producer (CCl4) as a single dose.
Lipid peroxidation is one of the principal causes of CCl4-induced liver injuries mediated by free
radical derivatives of CCl4. The antioxidative activity of some substances and inhibition of free radical
generation is important in protecting the liver [52] from CCl4 induced damage. CCl4 increased TBARS
level after single dose treatment, the recovery in TBARS level due to pretreatment of rats with
polyamides could be one of the protective mechanisms against the toxicity caused by CCl4 and
probably other compounds.
3. Experimental
3.1. Materials
S-Valine, 5-aminoisophthalic acid, m-phenylenediamine, m-aminophenol, 2,6-diaminopyridine,
4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylether, 4,4'-diaminodiphenylmethane, benzidine (all
Aldrich, Taufkirchen, Germany), and the solvents 1,4-dioxane (Aldrich), N,N-dimethylacetamide
(DMAc, Aldrich), 1-methyl-2-pyrrolidone (NMP) (Fluka), dimethylsulfoxide (DMSO, Aldrich) were
used as purchased without purification. Carbon tetrachloride was obtained from Merck (Darmstadt,
Germany). Reduced glutathione (GSH), 1-chloro-2,4-dinitrobenzene (CDNB), reduced nicotinamide
adenine dinucleotide phosphate (NADPH), amidopyrene, cytochrome C, thiobarbituric acid and all
other chemicals were purchased from Sigma Chemical Company (St. Louis, MO, USA). Use of carbon
tetrachloride was approved by the Animal Care Committee and met all guidelines for its use.

Molecules 2012, 17
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3.2. Measurements
Infrared spectra (IR, KBr pellets; 3 mm thickness) were recorded on a Perkin-Elmer FTIR 1650
Infrared Spectrophotometer. All spectra were recorded within the wave number range of
500–4,000 cm−1 at 25 C. Absorption spectra were measured with a UV 500 UV-vis spectrometer at
room temperature (rt) in DMSO with a polymer concentration of 2 mg/10 mL. Differential thermo
gravimetric (DTG) analyses were carried out in the temperature range from 20 C to 400 C in a
stream of nitrogen atmosphere by Shimadzu DTG 60H thermal analyzer. The experimental conditions
were: Platinum crucible, nitrogen atmosphere with a 30 mL/min flow rate and a heating rate 10 C/min.
Differential scanning calorimetry (DSC-TGA) analyses were carried out using SDT-Q600-V20.5-
Build-15 at the Institute of Graduate Studies and Research, Alexandria University. Inherent viscosities
(ηinh) were measured at a concentration of 0.5 g/dL in DMSO at 30 C by using an Ubbelohde
viscometer. Elemental analyses were performed at the Microanalytical Unit, Cairo University. The
morphologies of polymer nanoparticles were observed by Scanning Electron Microscope (SEM)
(JEOL-JSM5300), at the E-Microscope Unit; Faculty of Science, Alexandria University. The samples
were sonicated in de-ionized water for 5 min and deposited onto cover glass and allowed to air-dry and
sputter-coated with gold prior to examination. Biological studies were performed at the department of
environmental studies, Institute of Graduate Studies and Research, Alexandria University.
3.3. Synthesis of 2-Phthalimidyl-3-methyl Butyric Acid Chloride (4) [19]
A mixture of phthalic anhydride (3.00 g, 20.27 mmol) and S-valine (3, 2.61 g, 22.30 mmol) in DMF
(30 mL) was stirred under reflux for 1 h. The solvent was removed under reduced pressure and to the
residue a cold mixture of water (50 mL) and concentrated hydrochloric acid (5 mL) was added. The
solution was then stirred for 2 h. A white precipitate was formed, filtered off and dried, to give 4.0 g
(85% yield) of the known 2-phthalimidyl-3-methyl butyric acid, m.p. 112–113 °C.
Suspension of compound 2-phthalimidyl-3-methyl butyric acid (4.0 g, 16.91 mmol) in SOCl2
(30 mL) was refluxed on boiling water bath. After 10 minutes, a clear solution was obtained and
heating was continued for additional 2 h. Excess of the solvent was removed under vacuum and
n-hexane (20 mL) was added. The resulting white solid was collected by filtration and dried in vacuo
to give 4.0 g (93% yield) of 4, m.p. 82–83 °C.
3.4. Synthesis of 5-(2-Phthalimidyl-3-methyl butanoylamino)isophthaloyl Chloride (6)
Into a 25 mL round-bottomed flask fitted with a magnetic stirrer was placed a solution of 5-amino-
isophthalic acid (5, 2.72 g, 15.02 mmol) in DMAc (25 mL). While stirring, a solution of the acid
chloride 4 (4.0 g 15.06 mmol) in DMAc (25 mL) was added dropwise and the mixture was stirred for
10 h (overnight) at room temperature. Triethylamine (TEA, 0.52 mL) was added to this mixture and
heated at 80 °C for an additional 4 h. The solution was poured into a mixture of water (250 mL) and
concentrated hydrochloric acid (5 mL). The white precipitate was collected by filtration and washed
thoroughly with water and dried in a vacuum oven at 60 °C for 10 h, to give 3.5 g of the corresponding
diacid (56.8% yield), m.p. >250 °C. A suspension of the resulting diacid (2.00 g, 4.87 mmol) in SOCl2
(20 mL) was refluxed on a boiling water bath. After 30 minutes, a clear solution was obtained and

Molecules 2012, 17
8269
heating was continued for additional 4 h. Excess of the solvent was removed under vacuum and
n-hexane (20 mL) was added. The white solid was collected by filtration and dried in vacuo to give
2.00 g (92% yield) of 6 as a yellow solid, m.p. 128–129 °C.
3.5. Polymer Particles Synthesis (General Method)
The diacid chloride 6 (0.5 mmol) and the appropriate diamine 7, 8, 13–16 or m-aminophenol 11
(0.5 mmol) were each dissolved in dioxane (50 mL). Distilled water (15 mL) was added to the solution
of the diamine followed by the addition of the entire acid chloride solution at once. The resulted turbid
solution was ultrasonicated at 42 KHz in a water bath for a period of 30 min. The polymer colloidal
solution was extracted by centrifugal separation for 15 min. at 15,000 rpm and the resulted precipitate
were carefully washed with methanol and water to purify the product of any unreacted monomer. The
polymer samples were then dried at 100 C for 10 h then kept in a vacuum desiccator.
3.6. Biological Studies
The cytochrome P450 enzymes are responsible for the oxidation of xenobiotic chemicals including
drugs, pesticides and carcinogens. These enzymes include cytochrome P450, cytochrome b5, NADPH
cytochrome C-reductase, amidopyrene N-demethylase and aniline 4-hyroxylase (phase I). In addition
to the above enzymes, agents involved in phase II drug metabolism e.g. glutathione S-transferase
(GST) as well as free radicals, detected as thiobarbituric acid-reactive substances (TBARS). Changes
in the activities of these enzymes were studies in the liver microsomes of rats treated with antioxidant
(polyamides) as repeated doses prior to the administration of a single dose of carbon tetrachloride
(CCl4).
3.6.1. Animals and Treatments
Ninety six male Sprague Dawley rats, six weeks old weighing 100–120 g were obtained from the
National Research Institute, Cairo, Egypt and acclimatized for two weeks prior to the experiments. They
were assigned to 16 groups and housed at Universal galvanized wire cages at room temperature
(22–25 °C) and in a photoperiod of 14 h light/10 h dark per day. Animals received standard laboratory
balanced commercial diet and water ad libitum.
3.6.2. Experimental Design
Animals were randomly allocated into 16 groups (six rats/group) and treated as follows: group (1)
served as a control and was given deuterated dimethyl sulphoxide (DMSO-d6) at the same volume as
the vehicle (ip), in order to standardize the stress stimulation due to the capture and medicine
application; group (2) received a single injection of CCl4 in corn oil (ip) at dose level of 1 mL/kg [53]
during the last two weeks (i.e., day 15), groups from 3 to 16 were treated with the polyamides (ip) for
two weeks (three times a week; 25 mg/kg ) and then groups 4, 6, 8, 10, 12, 14, 16 were administered
CCl4 during the last two weeks. After 4 days of CCl4 injection, the samples were collected.

Molecules 2012, 17
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3.6.3. Tissue Preparations and Assays
3.6.3.1. Preparation of Liver Microsomes
Rats were fasted 24 h prior to each designated time point and then sacrificed by cervical
dislocation. The abdominal cavity was opened immediately, the liver was removed, washed with cold
0.1 mol phosphate buffer, pH 7.4, weighed and chilled on ice. All the following procedures were
carried out under cold conditions. A 33% (W/V) crude homogenate was prepared in 0.1 mol phosphate
buffer, pH 7.4 by homogenization with a Teflon pestle, using five strokes. The crude homogenate was
then centrifuged at 11,000 ×g for 20 min at 4 °C to remove the intact cells, nuclei and mitochondria.
The supernatant solution was subsequently centrifuged at 105,000 ×g for 60 min at 4 °C to sediment
the microsomal pellet. The pellet was re-suspended in 0.1 mol phosphate buffer, pH 7.4, kept in an ice
bath and used as the enzyme source.
3.6.3.2. Protein Determination
The protein concentration of the hepatic microsomal fractions was determined by the method of
Lowery et al. [54].
3.6.4. Enzyme Assays
Liver microsomal cytochrome P450 and b5 were determined according to Omura and Sato [55],
using a molar extinction coefficient 91 cm−1 m mol−1 for P450 and 185 cm−1 m mol−1 for cytochrome b5.
The activity of microsomal NADPH-cytochrome-C-reductase was assayed according to the method of
Williams and Kamin [56]. The rate of reduction of cytochrome C was measured at zero and 30 seconds
after the addition of NADPH at wavelength 550 ηm. The activity of this enzyme was calculated by
using an extinction coefficient of 21 cm−1 m mol−1.
Glutathione-S-transferase activity was assayed according to the method of Habig et al. [57]. A unit
of enzyme activity is defined as the amount of enzyme that catalyzes the formation of 1 μmol of
1-chloro-2,4-dinitrobenzene (CDNB) conjugate/mg protein/min under the assay conditions. The
CDNB conjugate was measured spectrophotometrically at 340 ηm. Calculations were made using a
molar extinction coefficient of 9.6 cm−1 m mol−1.
The activity of amidopyrene N-demethylase was measured according to Nash [58]. The method is
based on measurement of the concentration of formaldehyde produced by oxidative N-demethylation
of amidopyrene in microsomes. Formaldehyde was determined spectrophotometrically from changes
in the color intensity of the supernatant at 412 ηm. The enzymatic activity was then expressed as μmol
of formaldehyde/min × kg liver sample.
The activity of aniline 4-hydroxylase was measured according to Kato and Gillette [59]. The color
developed was measured spectrophotometrically at 630 ηm.
Thiobarbituric acid reactive substances (TBARS) were measured according to the method described
by Tapel and Zalkin [60]. The color intensity of the TBARS reactants was measured at 532 ηm and a
molar extinction coefficient of 156,000 cm−1 mol−1 was used for calculation of the concentration.

Molecules 2012, 17
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3.6.5. Statistical Analyses
Mean and standard error values were determined for all the parameters and the results were
expressed as mean ± standard error for six rats in each group. The data were analyzed using a one-way
analysis of variance (ANOVA). The student-Newman-keuls test was used to compare the treated and
control groups and the significance is given as p < 0.05.
3.6.6. Clinical Findings
No clinical sings of CCl4 poisoning were evident among rats of the treatment groups. Farther, no
mortality occurred in any of the treatment groups during the experimental period.
4. Conclusions
New nanoscale chiral aramides containing N-phthaloyl valine moieties in the side chain were
successfully prepared and characterized. Polyamide nanoparticles 9 and 10, derived from
m-phenylenediamine and 2,6-diaminopyridine, respectively, were obtained with average diameters of
106 nm, while polyesteramide nanoparticles 12, derived from m-aminophenol, produced under the
same reaction conditions were obtained with larger diameters (200 nm). Polymeric particles 9 and 12
were obtained as well-separated spherical nanoparticles while aggregated particles of the aramide-
containing pyridine 10 form a thin layer. The formation of such thin layer is attributed to the molecular
self assembly via H-bond directed organization of molecular precursors. Based on the flexible linkage
type, the average diameters of the nanoparticles-containing methylene 18, ether 19 and sulfone 20
linkage were 260 nm and 120 nm, respectively, as judged by SEM photographs. The inherent
viscosities of the nanoparticles were in the range of 0.58–0.70 dL/g and the particles exhibited similar
solubility behaviors in different organic solvents. The structures were carefully characterized by
different techniques such as IR, UV, elemental analyses. The thermal properties were evaluated by
TG/DTG and DSC techniques and results revealed that the prepared polymers have high thermal
stability. Structure-thermal property correlation based on changing the diamine monomer, as a single
structural modification, is also studied. The limiting oxygen index (LOI) values of polymers calculated
based on their char yield at 700 C clearly revealed that the reported macromolecules can be classified
as self-extinguishing polymers.
The effects of the aramide nanoparticles and carbon tetrachloride on drug metabolizing enzyme
activities and TBARS levels of male rat liver were studied. Pretreatments of rats with repeated doses
of the polyamides prior to the administration of CCl4 not only decreased the hepatic content of
cytochrome P450, amidopyrene N-demethylase, aniline-4-hyroxylase, but also induced of the hepatic
content of cytochrome b5 and NADPH cytochrome C-reductase. Repeated doses of the tested
compounds could reduce the toxic effects exerted by CCl4 upon the liver, and probably other organs,
through inhibition of cytochrome P450 system that activates CCl4 into its active metabolite,
trichloromethyl radical. Moreover, inhibition of cytochrome P450 system could also reduce the toxic
and carcinogenic effects of chemical carcinogens.

Molecules 2012, 17
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References
1. Malhi, H.; Gores, G. Cellular and molecular mechanisms of liver injury. Gastroenterology 2008,
134, 1641–1654.
2. Tacke, F.; Luedde, T.; Trautwein, C. Inflammatory pathways in liver homeostasis and liver injury.
Clin. Rev. Allergy Immunol. 2009, 36, 4–12.
3. Johnston, D.E.; Kroening, C. Mechanism of early carbon tetrachloride toxicity in cultured rat
hepatocytes. Pharmacol. Toxicol. 1998, 83, 231–239.
4. Rechnagel, R.O.; Glende, E.A.; Dolak, J.A.; Waller, R.L. Mechanisms of carbon tetrachloride
toxicity. J. Pharmacol. Exp. Ther. 1989, 43, 139–154.
5. Kumar, G.; Banu, G.S.; Pandian, M.R. Evaluation of the antioxidant activity of Trianthema
portulacastrum L. Ind. J. Pharmacol. 2005, 37, 331–333.
6. Khan, M.R.; Ahmed, D. Protective effects of Digera muricata (L.) Mart. On testis against
oxidative stress of carbon tetrachloride in rat. Food Chem. Toxicol. 2009, 47, 1393–1399.
7. Slater, T.F. Free radical mechanisms in tissue injury. Biochem. J. 1984, 222, 1–15.
8. Halliwell, B.; Gutteridge, J. Oxygen toxicity, oxygen radicals, transition metals and disease.
Biochem. J. 1984, 219, 1–14.
9. Mohutsky, M.A.; Romeike, A.; Meador, V.; Lee, W.M.; Fowler, J.; Francke-Carroll, S. Hepatic
Drug-Metabolizing Enzyme Induction and Implications for Preclinical and Clinical Risk
Assessment. Toxicol. Pathol. 2010, 38, 799–809.
10. Khan, R.A.; Khan, M.R.; Sahreen, S. Evaluation of Launaea procumbens use in renal disorders:
aratmodel. J. ethnopharmacol. 2010, 128, 452–461.
11. Afolayan, A.J.; Jimoh, F.O. Nutritional quality of some wild leafy vegetables in South Africa.
Int. J. Food Sci. Nutr. 2008, 60, 424–431.
12. Sahreen, S.; Khan, M.R.; Khan, R.A. Evaluation of antioxidant activities of various solvent
extracts of Carissa opaca fruits. Food Chem. 2010, 122, 1205–1211.
13. Cassidy, P.E. Thermally Stable Polymers: Syntheses and Properties; Marcel Dekker: New York,
NY, USA, 1980, p. 179.
14. Preston, J. Aromatic Polyamides. In Encyclopedia of Polymer Science and Engineering;
Mark, H.F., Bikales, N.M., Overberger, C.C., Menges, G., Eds.; Wiley-Interscience: New York,
NY, USA, 1989; Volume 11, p. 381.
15. Mallakour, S.; Kowsari, E. Synthesis and characterization of new optically active
poly(amide-imide)s containing epiclon and L-methionine moieties in the main chain. Polym. Adv.
Technol. 2005, 16, 732–737.
16. Liaw, D.J.; Liaw, B.Y. Synthesis and characterization of new polyamide imides containing
pendent adamantyl groups. Polymer 2001, 42, 839–845.
17. Nakata, S.; Brisson, J.J. Preparation of aromatic copolyamides containing regularly placed
1,6-hexamethylenediamine units. J. Polym. Sci. A Polym. Chem. 1997, 35, 2379–2386.
18. Pal, R.R.; Patil, P.S.; Salunkhe, M.M.; Maldar, N.M.; Wadgaonkar, P.P. Synthesis,
characterization and constitutional isomerism study of new aromatic polyamides containing
pendant groups based on asymmetrically substituted meta-phenylene diamines. Eur. Polym. J.
2009, 45, 953–959.

Molecules 2012, 17
8273
19. Liaw, D.J.; Hsu, P.N.; Liaw, B.Y. Synthesis and characterization of novel polyamide-imides
containing noncoplanar 2,2'-dimethyl-4,4'-biphenylene unit. J. Polym. Sci. A Polym. Chem. 2001,
39, 63–70.
20. Hsiao, S.H.; Chang, Y.H. New soluble aromatic polyamides containing ether linkages and
laterally attached p-terphenyls. Eur. Polym. J. 2004, 40, 1749–1757.
21. Ayala, V.; Maya, E.M.; Garcia, J.M.; de la Campa, J.G.; Lozano, A.E.; de Abajo, J. Synthesis,
characterization, and water sorption properties of new aromatic polyamides containing
benzimidazole and ethylene oxide moieties. J. Polym. Sci. A Polym. Chem. 2005, 43, 112–121.
22. Hsiao, S.H.; Yang, C.P.; Chen, C.W.; Liou, G.S. Synthesis and properties of novel
poly(amide-imide)s containing pendent diphenylamino groups. Eur. Polym. J. 2005, 41, 511–517.
23. Sava, I.; Bruma, M. Aromatic polyamides containing pendent acetoxybenzamide groups.
Macromol. Symp. 2006, 239, 36–42.
24. Donnici, C.L.; Filho, D.H.M.; Moreira, L.L.C.; dos Reis, G.T.; Cordeiro, E.S.; de Oliveira,
I.F.M.; Carvalhoa, S.; Paniagob, E.B. Synthesis of the novel 4,4'- and 6,6'-dihydroxamic-2,2'-
bipyridines and improved routes to 4,4'- and 6,6'-substituted 2,2'-bipyridines and mono-Noxide-
2,2'-bipyridine. J. Braz. Chem. Soc. 1998, 9, 455–460.
25. Hassan, H.H.A.M.; Elhusseiny, A.F.; Sweyllam, A.M. Polyamides nanoparticles containing
flexible linkages and their copper complexes with novel dielectric properties: Structure-property
relationship. J. Mol. Str. 2011, 1001, 89–103.
26. Hassan, H.H.A.M.; Elhusseiny, A.F.; Sweyllam, A.M. Synthesis and properties of narrow-sized
spherical aramides nanoparticles containing pyridine and their copper (II) complexes.
J. Macromol. Sci. Part A 2011, 48, 73–89.
27. Hassan, H.H.A.M.; Elhusseiny, A.F.; Sweyllam, A.M. Synthesis of novel semiconducting
aromatic polyesteramids containing pyridine: Characterization of nanometer-sized rod-like
analogues and their copper (II) complexes. J. Macromol. Sci. Part A 2010, 47, 521–533.
28. Casimir, J.R.; Guichard, G.; Briand, J.P. Methyl 2-((succinimidooxy) carbonyl)benzoate (MSB):
A new, efficient reagent for N phthaloylation of amino acid and peptide derivatives. J. Org. Chem.
2002, 67, 3764–3768.
29. In, I.; Kim, S.Y. Soluble wholly aromatic polyamides containing unsymmetrical pyridyl ether
linkages. Polymer 2006, 47, 547–552.
30. Yang, C.P.; Chen, R.S.; Chen, C.D. Synthesis and properties of organosoluble poly(amide-
imide)s with propeller-shaped 1,1,1-triphenylethane units in the main chain. J. Polym. Sci. Part A
Polym. Chem. 2001, 39, 775–787.
31. Hsiao, S.H.; Chen, C.W.; Liou, G.S. Novel aromatic polyamides bearing pendent diphenylamino
or carbazolyl groups. J. Polym. Sci. A Polym. Chem. 2004, 42, 3302–3313.
32. Okamoto, Y. Chiral polymers. Prog. Polym. Sci. 2000, 25, 159–162.
33. Wulff, G. Main-chain chirality and optical activity in polymers consisting of C–C chains.
Angew. Chem. Int. Ed. Engl. 1989, 28, 21–37.
34. Mallakpour, S.; Kolahdoozan, M. Synthesis and Properties of Thermally Stable and Optically
Active Novel Wholly Aromatic Polyesters Containing Chiral Pendent Group. Eur. Polym. J.
2007, 43, 3344–3354.

Molecules 2012, 17
8274
35. Fessi, H.; Puisieux, F.; Devissaguet, J.P.; Ammoury, N.; Benita, S. Nano-capsule formation by
interfacial deposition following solvent displacement. Int. J. Pharm. 1989, 55, R1–R4.
36. Limayem, I.; Charcosset, C.; Sfar, S.; Fessi, H. Preparation and characterization of spironolactone-
loaded nanocapsules for paediatric use. Int. J. Pharm. 2006, 325, 124–131.
37. Ferranti, V.; Marchais, H.; Chabenat, C.; Orecchioni, A.M.; Lafont, O. Caprolactone nanocapsules:
Incorporation efficiency and in vitro release profiles. Int. J. Pharm. 1999, 193, 107–111.
38. Lince, F.; Marchisio, D.L.; Barresi, A.A. Strategies to control the particle size distribution of
poly-caprolactone nanoparticles for pharmaceutical application. J. Colloid. Interface Sci. 2008,
322, 505–515.
39. Archer, E.A.; Gong, H.; Krische, M.J. Hydrogen bonding in Noncovalent Synthesis: Selectivity
and Directional Organization of Molecular Strands. Tetrahedron 2001, 57, 1139–1159.
40. Krische, M.J.; Lehn, J.M. Utilization of persistent hydrogen-bonding motifs in the self-assembly
of supramolecular architectures. Struct. Bond 2000, 94, 3–30.
41. Nowick, J.S. Chemical models of protein β-sheets. Acc. Chem. Res. 1999, 32, 287–296.
42. Zhu, J.; Parra, R.D.; Zeng, H.; Skrzypczak-Jankun, E.; Zeng, X.C.; Gong, B. New class of folding
oligomers: Crescent oligoamides. J. Am. Chem. Soc. 2000, 122, 4219–4220.
43. Berl, V.; Huc, I.; Khoury, R.G.; Krische, M.J.; Lehn, J.M. Formation and interconversion of
artificial single and double stranded helices. Nature 2000, 407, 720–723.
44. van Krevelen, D.W.; Hoftyzer, P.J. Properties of Polymers; Elsevier Scientific Publishing;
Amsterdam, The Netherlands, 1976.
45. Coats, A.W.; Redfern, J.P. Kinetic parameters from thermogravimetric data. Nature 1961, 201,
68–69.
46. Johnson, D.W.; Gallagher, P.K. Comparison of dynamic with isothermal techniques for the study
of solid sate decomposition kinetics. J. Phys. Chem. 1972, 76, 1474–1479.
47. Glasstone, S. Textbook of Physical Chemistry; Macmillan: Bombay, India, 1974.
48. Frost, A.A.; Pearson, R.G. Kinetics and Mechanisms; Wiley: New York, NY, USA, 1961.
49. Yeragi, S.G.; Rana, A.M.; Koli, V.A. Effect of pesticides on protein metabolism of Mudskipper
Boleophthalmus Dussumieri. J. Ecotoxicol. Env. Monitor 2003, 13, 211–214.
50. Delvi, R.R. Alterations in hepatic phase I and phase II biotransformation enzymes by garlic oil in
rats. Toxicol. Lett. 1992, 60, 299–305.
51. Sheweita, S.; Abd El-Gaber, M.; Bastawy, M. Carbon tetrachloride changes the activity of
cytochrome P450 system in the liver of male rats: role of antioxidants. Toxicology 2001, 169, 83–92.
52. Ozturk, I.C.; Ozturk, F.; Gul, M.; Ates, B.; Cetin, A. Protective effects of ascorbic acid on
hepatotoxicity and oxidative stress caused by carbon tetrachloride in the liver of Westar rats.
Cell Biochem. Funct. 2009, 27, 309–315.
53. Bashandy, S.A.; Al Wasel, S.H. Carbon tetrachloride-induced hepatotoxicity and nephrotoxicity
in rats: Protective role of vitamin C. J. Pharmacol. Toxicol. 2011, 6, 283–292.
54. Lowery, O.H.; Rosebrough, N.J.; Farr, A.L.; Randhll, R.J. Protein measurement with the Folin-
phenol reagent. Protein measurement with the Folin-phenol reagent. J. Biol. Chem. 1951, 193,
265–275.
55. Omura, T.; Sato, R. The carbon monoxide binding pigment of liver microsomes. Ι. Evidence for
its hematoprotein nature. J. Biol. Chem. 1964, 239, 2370–2378.

Molecules 2012, 17
8275
56. Williams, C.H.; Kamin, H. Microsomal triphosphopyridine nucleotide-cytochrome-C reductase of
liver. J. Biol. Chem. 1962, 237, 587–595.
57. Habig, W.; Pabst, M.; Jakoby, W. Glutathione-S-transferases. The first enzymatic step in
mercapturic acid formation. J. Biol. Chem. 1974, 249, 7130–7139.
58. Nash, T. The colorimetric estimation of formaldehyde by means of Hantzsch reactions. Biochem. J.
1953, 55, 416–421.
59. Kato, R.; Gillette, J.R. Effects of starvation on NADPH-dependent enzymes in liver microsomes
of male and female rats. J. Pharmacol. Exp. Ther. 1965, 150, 279–284.
60. Tapel, A.L.; Zalkin, H. Inhibition of lipid peroxidation in mitochondria by vitamin E.
Arch. Biochem. Biophys. 1959, 80, 333–336.
Sample Availability: Samples of the prepared polymers 9, 10, 12, 17–20 are available from authors.
© 2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).