Journal of Materials Science and Chemical Engineering, 2014, 2, 43-51
Published Online January 2014 (http://www.scirp.org/journal/msce)
http://dx.doi.org/10.4236/msce.2014.21008
OPEN ACCESS MSCE
An Interaction Study of Chloro and Alkyl Substituted
Benzylamine with DPPH● through UV
Spectrophotometric and Physicochemical Methods at
T = (298.15, 303.15 and 308.15) K
Rakesh Kumar Ameta, Man Singh*, B. S. Kitawat, R. K. Kale
School of Chemical Sciences, Central University of Gujarat, Gandhinagar, India
Received November 2013
ABSTRACT
Radical scavenging activity (RSA) of chloro and methyl substituted benzylamine derivatives (BADs) has been
studied using 1, 1-diphenyl-2-picrylhydrazyl free radical (DPPH•) through spectrophotometric and physico-
chemical techniques at T = (298.15, 303.15 and 308.15) K. New experimental data on the density, sound velocity,
isentropic and apparent molal compressibility of selected BADs + DPPH● solutions as a function of temperature
and concentration are reported. The results are discussed with regards to structure-activity relationship (SAR)
principles of BADs. The relative deviations in RSAs varied with structural potentials of BADs which were ana-
lyzed by making a comparative study for both the spectrophotometric and physicochemical results.
KEYWORDS
SAR; RSAs; BADs; Spectrophotometric; Physicochemical Data
1. Introduction
Free radicals in food, chemicals and even in living sys-
tems are produced by an oxidation process playing an
important role in processes of food spoilage, materials
degradation and many other modes of deactivation [1-4].
To prevent oxidation, several kinds of antioxidants
mainly organic compounds and other metal complexes
are being used for last few decades [5]. Recently, there
has been a growing interest regarding antioxidants usage
for medicinal purposes in the recent years [6]. Evidently,
it has also been suggested that antioxidants diminish the
jeopardy for chronic diseases like those of cancer and
heart disease [7]. In biological systems, highly reactive
free radicals and oxygen species are present which may
oxidize nucleic acids, proteins, lipids or DNA, and can
initiate degenerative disease [2-4,5]. To calculate their
efficiency in vitro, several methods are being used which
measure the RSA of antioxidants against free radicals
[8-10]. Among the several methods, a rapid, simple and
inexpensive method based on free radical DPPH scav-
enging effect is often used to quantify antioxidants in
complex biological systems reported in the recent years
[9]. Many inorganic metal complexes have been reported
for their antioxidant potential [11-16]. The RSAs of
metal complexes depend on the ligands which are at-
tached with the metal through coordination bonding and
pliancy of their functional groups [12,13]. Thus, the RSA
of metal complexes are highly affected with ligands and
also enhances the anticancer activity of the complexes
[14]. Recently, BADs as ligands have been used to pre-
pare anticancer complexes of platinum against solid tu-
mor, and also complexes have been shown impressive
antioxidant activities [17]. Since, BADs as ligands were
used in study reported by Ameta et al. [17], those have
great potential towards catalytic or biological applica-
tions [18]. Thus, with this in mind, the alkyl and chloro
substituted benzylamine as BADs (Table 1) are selected
for analysis of their antioxidant potential through in vitro
method. Generally, the interaction is always temperature
dependent and strength of interaction is determined with
the physicochemical properties of the compounds [19].
Thus, in present study, we determined RSAs of chosen
BADs at T = (298.15, 303.15 and 308.15) K, to bring to
the foreground some of these aspects, including the pe-
culiarities of the BADs. Thus, an input of physicochemi-
cal properties of BADs + DPPH● mixture such as density,
*Corresponding author.

R. K. AMETA ET AL. 44
speed of sound, isentropic and apparent molal com-
pressibility data could be found as useful materials in
understanding of the antioxidant mechanism and may
lead to develop new correlations or predictive models.
2. Experimental
2.1. Materials
Table 1 reports chemicals, used as received, and Milli-Q
water (Millipore SAS 67/20 Mosheim) of 10−7 S·cm−1
was used for solutions. Glassware were cleaned with
standard methods and dried to absolute dryness checked
with an anhydrous CuSO4. Few pinch of CuSO4 was
spreaded in flasks, beakers and others which did not
change color due to a level of absolute dryness and con-
sidered as a level of dryness.
2.2. Experimental Measurements
The antioxidant activities were assessed on a basis of free
radical scavenging effect of stable DPPH● with spectro-
photometric titration [17,20]. The 0.01% DPPH● stock
solution was prepared in ethanol/water (1:1) and for pre-
paring a sample solution, 5 mL DPPH● solution was
mixed with 5 mL BADs solutions followed by vigorous
shaking and incubated in dark. Before measuring ab-
sorbance, the sample solutions were incubated at chosen
temperature for an hour in dark. In measurement of ab-
sorption spectra, initially blank spectra for ethanol/water
were taken then spectrophotometric titration was per-
formed with chosen concentration of BADs. Absorbance
was measured at 517 nm with Spectro 2060 plus model
UV/V is spectrophotometer, and RSAs were determined
as a decrease in absorbance of DPPH●. Their densities
and sound velocities were measured by Anton Paar Den-
sity and Sound velocity meter DSA 5000 M with ±10−3
kg·m−3 accuracy [21]. For each measurement, the tube
was cleaned with acetone and dried by passing dry air
through the tube by inbuilt air pump. Results and discus-
sion
2.3. Spectrophotometric Study
Figure 1 contains absorption and scavenging activities
(%) of BADs at chosen temperature where the RSA was
determined as a result of decrease in absorbance of
DPPH● [17,20] calculated with following formula:
0
0
%
s
AA
Scavenging activityA





100 (1)
The AS is absorbance of DPPH● with BADs and A0 is
an absorbance of DPPH● without BADs. The data calcu-
lated for antioxidation are presented as means ± SD of
three determinations. The odd numbered electrons in free
DPPH● give a strong absorption maximum at 517 nm due
to availability of empty space in orbital for transition and
impart it a purple colored appearance which turns to yel-
low to form a reduced DPPH-H (Figure 1) [17,20,22,23].
The change in UV with position of them, the absorb-
ances have decreased in compare to the pure DPPH●.
Therefore, a sample amount can lower an initial absorb-
ance of DPPH● solution by 50% and has been chosen as
an endpoint in measuring antioxidant activity [20]. The
% RSAs of BADs have affected with concentration as
well as with temperature where BADs have shown their
RSAs as BADs303.15 K > BADs308.15 K > BADs298.15 K
for chosen concentrations (Table 2, Figure 2).
It inferred that at 303.15 and 298.15 K maximum and
minimum %RSA respectively, BADs are active to scav-
enge the free radicals. At 303.15 K the hydrogen donat-
ing activity is maximum which stabilized the free
Table 1. Benzylamine derivatives and scavenging agent
studied in this work.
Structure Name
NH
2
Phenylmethanamine
NH
2
Cl
(2-chlorophenyl)methanamine
NH
2
Cl
(3-chlorophenyl)methanamine
NH
2
Cl
(4-chlorophenyl)methanamine
HN CH
3
N methyl(phenyl)methanamine
NCH
3
H
3
C
N, N dimethyl(phenyl)methanamine
N
O
2
N
O
2
N
NO
2
NN
O
2
N
O
2
N
NO
2
N
-
+e
-
N
O
2
N
O
2
N
NO
2
N
RR
Figure 1. Mechanism of DPPH● free radical for antioxidant activity.
OPEN ACCESS MSCE

R. K. AMETA ET AL. 45
Table 2. Absorbance and scavenging activities of BADs at T = (298.15, 303.15 and 308.15).
Absorbance % Scavenging activity
BADs mM 298.15 K 303.15 K 308.15 K 298.15 K 303.15 K 308.15 K
BA 10 0.494 0.370 0.453 52.68 62.66 60.26
20 0.517 0.387 0.474 50.48 60.95 58.43
30 0.518 0.398 0.483 50.38 59.84 57.25
40 0.426 0.320 0.396 59.20 67.71 65.63
50 0.553 0.470 0.529 47.03 52.57 49.52
2CBA 10 0.537 0.431 0.506 48.56 56.51 53.71
20 0.558 0.464 0.520 46.55 53.18 50.16
30 0.697 0.577 0.665 33.24 41.78 38.02
40 0.561 0.439 0.529 46.26 55.70 52.85
50 0.523 0.429 0.496 49.90 56.71 53.92
3CBA 10 0.459 0.357 0.426 56.03 63.98 61.65
20 0.521 0.402 0.481 50.10 59.43 56.82
30 0.512 0.411 0.479 50.96 58.53 55.85
40 0.561 0.459 0.530 46.26 53.68 50.70
50 0.590 0.501 0.563 43.49 49.45 46.19
4CBA 10 0.520 0.425 0.487 50.19 57.11 54.35
20 0.554 0.470 0.530 46.93 52.57 49.52
30 0.548 0.467 0.521 47.51 52.88 49.84
40 0.509 0.409 0.477 51.25 58.73 56.07
50 0.533 0.451 0.501 48.95 54.49 51.56
MBA 10 0.486 0.386 0.453 53.45 61.05 58.54
20 0.501 0.394 0.464 52.01 60.24 57.68
30 0.547 0.434 0.513 47.61 56.21 53.38
40 0.591 0.491 0.562 43.39 50.45 47.26
50 0.610 0.540 0.596 41.57 45.51 42.00
MMBA 10 0.502 0.394 0.477 51.92 60.24 57.68
20 0.526 0.441 0.476 49.62 55.50 52.63
30 0.540 0.462 0.498 48.28 53.38 50.38
40 0.505 0.393 0.515 51.63 60.34 57.79
50 0.500 0.399 0.467 52.11 59.74 57.14
DPPH 0.01% 1.044 0.991 0.931 - - -
Estimated uncertainties in absorbance and %scavenging activities were less than ±1 × 10−3 and ±0.01 respectively. The uncertainties in temperature are
±0.01˚C.
OPEN ACCESS MSCE

R. K. AMETA ET AL.
OPEN ACCESS MSCE
46
Figure 2. % Scavenging activities of BADs at T = (298.15, 303.15 and 308.15) K where (A), (B), (C), (D), (E) and (F) are stand
for BA, 2CBA, 3CBA, 4CBA, MBA and MMBA.
radicals while at 298.15 K it is minimum, may be, due to
temperature dependent structural changes create such
environment. For comparing individual % RSAs, their
values were compared with each other and found as
2CBA > 3CBA > 4CBA > BA and MMBA > MBA at all
T = (298.15, 303.15 and 308.15) K. It inferred that the
2CBA is highly effective to scavenge the free radicals
due to negative inductive effect of chlorine with an in-
crease in hydrogen donating ability which stabilized the
free radicals. But in case of 3CBA and 4CBA the posi-
tion of chlorine in BA has changed where the negative
inductive effect works as 2C > 3C > 4C, therefore, 2CBA
showed higher scavenging effect and BA showed mini-
mum. In comparison of MMBA and MBA, since positive
inductive effect increases electron density on nitrogen,
therefore, two methyl group of MMBA increased much
electron density on nitrogen than one methyl group of
MBA that increased hydrogen donation ability more.
Thus, MMBA showed higher RSA than MBA.
2.4. Physicochemical Study
Both BADs and DPPH molecules have hydrophilic and
phobic parts, therefore their molecular interactions are
analyzed with physicochemical properties (PCPs). Hence,
density, apparent molal volume and sound velocity as
PCPs for BADs solutions with DPPH● at T = (298.15,
303.15 and 308.15) K, have been critically analyzed. For
example, the density decreased on an increase in tem-
perature and concentration of BADs + DPPH● solutions
except MMBA + DPPH● solution but increased from
pure DPPH●. For instance, the density for 10 mM of BA

R. K. AMETA ET AL. 47
increased by 0.948391 g/cm3 from 0.933242 g/cm3 (pure
DPPH●) at 298.15 K while it decreased by 0.945097 and
0.944585 g/cm3 for 20 mM at 303.15 K respectively.
Densities decreased with the concentration and tempera-
ture for BADs except MMBA, due to interaction with
DPPH● which has produced a lower denser medium
where positions of chlorine on BA were critical. Also
due to negative and positive inductive effects of chlorine
and methyl groups respectively, made -NH bond weaker
in BADs. In case of MMBA, density increased with
concentration while decreased with temperatures, it was
may be that two methyl groups created a compact envi-
ronment which made the medium strong denser. Their
limiting values (ρ0) where the structural contribution was
found maximum for BA with trend as ρ0
BA > ρ0 3CBA >
ρ0
MBA > ρ0 2CBA > ρ0 4CBA > ρ0 MMBA at chosen temperatures
(Figure 3 and Table 3).
Thus, the substitution of chloro or methyl groups has
decreased interaction of BADs with DPPH● due to weak-
er intermolecular forces. Apart from density, the apparent
molal volume, 0V2
*#, was calculated as below.
*# 0
2
0
1000 ..
M
Vm



 




(2)
m and M are molality and molecular weight of BADs
while ρ0 and ρ are densities of pure DPPH● and BADs +
DPPH● solutions respectively. The 0V2
*# data explained
molecular interactions that elucidated a net concentration
effect of BADs with DPPH● interactions. Analysis of
0V2
*# data has inferred strength of interactions where all
BADs + DPPH● systems showed negative 0V2
*# values
except at few concentrations, due to stronger interaction
of DPPH● + BADs molecules occupied less space and
caused high internal pressure. Figure 4 shows a variation
in 0V2
*# where it increased with concentration and de-
creased (except MMBA) with temperature and negative
0V2
*# inferred a contraction produced on interaction be-
tween BADs and DPPH● molecules.
Figure 3. Densities of BADs + DPPH interacting mixture at T = (298.15, 303.15 and 308.15) K.
OPEN ACCESS MSCE

R. K. AMETA ET AL. 48
Table 3. Limiting values of density, ρ0, apparent molal volume, 0V2
*#, and apparent molal compressibility, ϕKo
s, at (298.15,
3.03.15 and 308.15) K.
298.15 K 303.15 K 308.15 K
0ρ/(g.c-m3)
BA 0.951254 0.945803 0.942177
2CBA 0.940925 0.936063 0.931200
3CBA 0.947944 0.944745 0.940597
4CBA 0.938524 0.934772 0.931098
MBA 0.944669 0.942429 0.939571
MMBA 0.933718 0.926986 0.926605
0V2*# /(m3mol−1)
BA −2611.55 −2324.69 −2337.75
2CBA −928.77 −535.91 −220.82
3CBA −2160.22 −1999.25 −1947.71
4CBA −595.37 −349.40 −270.15
MBA −2183.13 −2032.88 −2025.95
MMBA 2 .84 184.74 146.85
ϕKos,/(m2 N−1)
BA −0.0062 −0.0060 −0.0062
2CBA −0.0029 −0.0024 −0.0016
3CBA −0.0060 −0.0058 −0.0087
4CBA −0.0023 −0.0020 −0.0019
MBA −0.0057 −0.0059 −0.0063
MMBA −0.0006 −0.0007 0
In case of MMBA, the 0V2
*# values decreased with
concentration and increased with temperature towards
positive values, it may be that both methyl groups have
positive inductive effect, and combining positive induc-
tive effect of both methyl groups of MMBA created
much electron density on nitrogen as well as indirectly
on hydrogen of -NH bond. Therefore a stronger interac-
tion developed between MMBA and DPPH molecules.
The structural contribution of BADs to this contraction
have studied with a comparative analysis of their limiting
values (Table 3) found as
0 *#0 *#0 *#0 *#
22 2322
0*# 0*#
24 2
B
AMBA CBA
CBA MMBA
VV VV
VV
 

CBA
Since, negative 0V2
*# values due to solutions of BADs
in a given amount of DPPH● have a smaller volume than
the same amount of pure DPPH● inferred that, the struc-
tural contraction is stronger for BA and weaker for
MMBA. The physical reason is that nearby DPPH●
molecules are strongly attracted to their molecules so that
they occupied less space. With the increasing concentra-
tion, the 0V2
*# values have increased (Table 3), which
showed that BADs molecules occupy more space on in-
teraction with DPPH● while in case of MMBA it is re-
versed. The interaction between BADs molecules and
DPPH● is also determined with their sound velocities
data and its derivatives where it decreased with concen-
tration as well as with temperatures. Due to two kinds of
interaction such as hydrophobic-hydrophobic and hy-
drophilic-hydrophilic interaction of BADs and DPPH●
molecules develop different zone of interactions which
heterogenised the interaction system. And as a result of
internal pressure developed that determined with speed
of sound data for gaining information about interaction
of BADs and DPPH● Equation (3). n is number of mole-
cules, V2
*# is apparent molal volume and T for specific
temp.
OPEN ACCESS MSCE

R. K. AMETA ET AL. 49
Figure 4. Apparent molal volumes of BADs + DPPH interacting mixture at T = (298.15, 303.15 and 308.15) K.
int *#
2
()
T
n
PV  (3)
2
1
su


 (4)
The density and sound velocity data were fitted in
Newton-Laplace equation to get isentropic compressi-
bilities, K
s, as Equation (4). The ρ is density and u is
sound velocity of the BADs + DPPH● solutions. The Ks
values for BADs + DPPH●, are positive at all tempera-
tures and attributed to a breaking or stretching of interac-
tion bonds in a self-associated DPPH●. It inferred that Ks
have increased when BADs molecules interacted to
DPPH●. In general, the isentropic compressibility in-
creases with an increase in temperature at a fixed com-
position due to an increase in thermal agitation which
makes the solution more compressible [19]. In the pre-
sent study, Ks increased with an increase in temperature
and decreased with an increase in concentration of BADs
for BADs + DPPH● system. The KS of the BADs+
DPPH● mixture is found lower than pure DPPH● solution,
it may be due to presence of BADs, the interaction of
DPPH● molecules has broken which led to development
of weaker BADs-DPPH● interaction than DPPH●-DPPH●.
Therefore, the compactness decreased and a system
compressed lesser. Since, the interaction of BADs with
DPPH● varied with different BADs which has analyzed
with density, isentropic apparent molal volume and com-
pressibility. For checking compressibility at the molecu-
lar level, the apparent molal compressibility, ϕKs are cal-
culated with equation as under.
0
0
0
00
1000 ()(
.
S
SSS
)
M
m





OPEN ACCESS MSCE

R. K. AMETA ET AL. 50
The m and M are molality of solution and molecular
weight of taken BADs. The ρ, ρ0
and Ks, 0Ks, are density
and isentropic compressibility of BADs + DPPH● solu-
tion and pure DPPH● solution respectively. Table 3 re-
ports the values of ϕKs are negative indicate stronger in-
teraction between BADs and DPPH● at structural or mo-
lecular level. The increase in ϕKs primarily explains that
changes with structure lead to change in ultrasonic veloc-
ity as well as a definite contraction upon mixing which in
turn dependent on the structural contributing strength.
The increase in ϕKs value indicates a dominant contribu-
tion from structure-breaking effect in BADs + DPPH● by
the stronger intermolecular force. Since, DPPH● mole-
cules have cohesive forces between self-associated
DPPH● molecules and when interacted with BADs, this
cohesivity is disrupted to make the interaction bond, thus,
friccohesity is a real model of structure breaker effect in
BADs-DPPH● by molecular forces. The breaking of in-
termolecular interaction of DPPH● molecules induced by
different BADs is reflected by ϕKs values. The overall
structural contribution of BADs is measured by regress-
ing the ϕK
s
values where the trend of ϕKs is found as ϕKs 0
BA >
ϕKs 0 3CBA > ϕKs 0 MBA > ϕKs 0
2CBA >
ϕKs 0
4CBA >
ϕKs 0
MMBA for chosen temperatures (Figure 5 and Table 3).
The BA due to absence of any functional group on ben-
zene ring showed higher ϕKs
0than others like chloro and
methyl groups attached benzene ring such as 2CBA,
3CBA, 4CBA, MBA and MMBA. Since, two methyl
groups on the nitrogen of MMBA occupy a certain
amount of space, and on interaction they come too close
together with an associated cost in energy due to over-
lapping electron clouds. Thus, the presence of two
methyl groups on nitrogen in MMBA developed steric
hindrance to interact with DPPH● molecules with lower
ϕKs
0among all the BADs. It also showed an effect of
functional group on the compressibility at the molecular
level which can be categorized as -3Cl > -2Cl > -4Cl and
–CH3 > -(CH3)2.
Figure 5. Apparent molal compressibilities of BADs + DPPH interacting mixture at T = (298.15, 303.15 and 308.15) K.
OPEN ACCESS MSCE

R. K. AMETA ET AL. 51
3. Conclusion
This study defined the SAR of chloro and methyl substi-
tuted BADs by analyzing their antioxidant activities
thermodynamically using DPPH* scavenging effect
through spectrophotometric and physicochemical meth-
ods. The chloro substituted BADs showed higher anti-
oxidant activities than methyl where position of chloro
and methyl substitute affected antioxidant activity as
2CBA > 3CBA > 4CBA and MMBA > MBA respec-
tively, which inferred that their SAR varied with chloro
and methyl groups. These thermodynamic physico-
chemical results may be of significance in evolving a
mechanism for effective biodegradable agents, bioreme-
diation, drug efficacy and protein interacting capacity.
Acknowledgements
Authors are highly thankful to Central University of Gu-
jarat, Gandhinagar for financial, infrastructural support
and experimental facilities.
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