Minor Research Project
(Physics)
“ Investigation of Molecular Interactions in Liquid through
Microwave Spectroscopic Technique ”
File No. F.47-1254/09(WRO)
:- Submitted To :The Joint Secretary,
University Grants Commission’
Western Regional Office, Ganeshkhind,
PUNE
:- Submitted by :Shri A. R. Lathi
Associate Professor
Adarsh Education Society’s
Arts, Commerce & Science College Hingoli – 431513 (MH)
Title of the Research Project :“Investigation of Molecular Interactions in Liquid through
Microwave Spectroscopic Technique”
File No .
:- F.47– 1254/09 (WRO) Date 17 Nov. 2009
INDEX
Sr.No
Particulars
Page No.
1
Part - I – Introduction
3–9
2
Part – II - Theory of Dielectric
10 - 32
3
Part – III – Dielectric Relaxation Study of
Brucine – Methanol Solution
33-47
4
Part – IV - Dielectric Relaxation Study of
Caffeine – Water Solution
48-55
5
Part – V - Publications
56-63
PART - I
Introduction
1.1 Introduction
Dielectic relaxation study on liquids provides information regarding their
molecular behaviour and dynamics of the molecules involved at dipolar level.
Molecular Interaction in liquid can be studied by using Dielectric relaxation. In
present work, to understand the molecular behaviour of alkaloid solution, dielectric
study of this solution is carried out.
There are different spectroscopic technique to study dielectric properties of
liquid such as infrared, visible microwave and NMR technique . Dielectric study of
solutions of Alkaloids has great significance in understanding physical and chemical
behaviour. Due to molecular interaction in liquid system the physical parameters
changes.
These parameters can be studied by application of microwave using
frequency domain and time domain reflectometry (TDR) technique. We are using
time domain reflectometry technique and J Band Microwave bench to study
dielectric parameter , static dielectric constant (εo), relaxation time (τ)
and
thermodynamic parameters i.e. Enthalpy of activation ∆H, Entropy of activation
∆S.
Alkaloids are a group of naturally occurring chemical compounds that contain
mostly nitrogen atoms. The name alkaloid was introduced in 1819 by German
Chemist Carl Friedrich Willhelm Meibner.
The alkaloids content in plants is
usually within a few percent and is inhomogeneous over the plant tissues.
Depending on the type of plants, the maximum concentration is observed in the
leaves ( black henbane), fruits or seeds (Strychnine tree), root or bark. Furthermore,
different tissues of the same plants may contain different alkaloids . Alkaloids is
derived from the name “ vegetable alkali ” Alkaloids act on a diversity of metabolic
systems of human and other animals .
Some alkaloids are used as medicine.
Alkaloids have wide range of pharmacological activities such as stimulant activities
( e.g. Caffeine , Nicotine ), antimalarial ( e.g. quinine ),
anticancer ( e.g.
Homoharringtonine ) {1}. Some alkaloids are also useful in pesticides. So it is
great importance to study its physical parameters.
The interaction of molecules in liquid
can be studied by using several
methods such as light scattering {2},
NMR
spectroscopy {3-4},
dielectric
spectroscopy {5} and ultrasonic {6}.
Dielecteric spectroscopy is a important
method for study molecular interaction in liquid using time domain reflectometory (
TDR ) technique . We can obtain the information on the structural behaviour and
dynamic parameter of molecular liquids. Many alkaloid are insoluble in water, but
dissolves in organic solvents such as chloroform diethyl ether , methanol etc.
Alkaloids are separated from their mixtures using their solubility in certain solvents
and different reactivity with certain reagents or by distillation {7}. Extraction of
caffeine from coffee is an important industrial process and can be performed using a
number of different solvents.
Benzene , Chloroform, Trichloroethylene,
dichloromethane and ethylacetate have been used for the extraction of alkaloids.
At present , study on Caffeine and Brucine is in the pharmaceuticals area,
such as Effect of Brucine on human breast cancer cells, Mamatha, Serasanambati
etl. {8},
determination of Brucine in Herbal formulation by UV derivative
spectroscopy by Babu Ganesan etl. {9}.
Recent study suggests that no sex
differences in the pharmace kinetics of caffeine as measured in salivary
concentration of caffeine using high performance liquid chromatography {10, 11 }.
Solubility of caffeine in water, ethylacetate , chloroform and other solvents is
studied by A. Shalmashi etl. {12}. It has been shown in number of earlier studies
that caffeine
has
variety of roles on a molecular recognition of DNA by
intercalating drugs, Larsen R.W. etl. and Davis D.B. etl. {13, 14 }. Some of
alkaloids are toxic. Therefore while handling, precautions must be taken , such as
using mask , gloves etc. Yet dielectric study of Alkaloid solution is not carried out.
Due to great importance of alkaloid in pharmaceuticals, pesticides etc. dielectric
relaxation study of solution of Caffeine , Brucine is carried out.
1.2 Aims & Objective of the study :
To study molecular intraction the following objectives has been carried out
1.
To determine complex permittivity of i) Bruicine – methanol solution , ii)
Caffeine – water solution, using Time Domain Reflectometry Technique in the
frequency rang of 10 MHz to 30 GHz. The Frequency depend dielectric complex
permittivity data were fit to Havriliak – Negami equation using non linear least
square fit method.
ε* (ω) = ε∞ +
Where εo
ε0 −ε∞
[(1+𝑗𝜔 𝜏)1−𝛼 ]𝛽
is static dielectric constant , ε∞
is the dielectric constant at high
frequency τ is relaxation time in ϸs. α and β are distribution parameters . There are
three relaxation models of Havriliak - Negami equation. The Debye model (α=0
and β= 1)
suggests a single relaxation time , the Cole
– Cole
(0 ≤ α ≤ 1 and β = 1 ) and Cole – Davidson (α = 0 and 0 ≤ β ≤ 1) models both
suggests a distribution of relaxation times {15}.
2.
To determine Thermodynamic parameters
The Thermodynamic parameters such as Enthalpy of activation (∆H) and
Entropy of activation (∆S) are calculated using Erying equation {16}.
𝛕=
ℎ
𝑘𝑇
exp ( H - TΔS) / RT
Where τ is relaxation time in ϸs , T is temperature in Kelvin
and h is Plank’s
constant.
Enthalpy of activation (∆H), which gives information related to molecular
energy which is involved in relaxation process. The magnitude of Enthalpy of
activation (∆H) indicates the endothermic reaction or exothermic reaction.
References
[1]
Kittakorp P., Mahidol C., Ruchirawal S. (2014) curr top med. chem.
14(2) : 239 – 252
[2]
D. R. Jones and C. H. wang, J. Chem. Phys. 65 (5) , 1835 ( 1976)
[3]
M.C.lang, F. Laupretre, C. Noel and L. Monnerie , J.Chem. Soc. , Faraday
trans. 2, 75, 349 ( 1979)
[4]
H. Elmgren, J.Polym. Sci., Polym. Lett. Ed., 18,351 (1980)
[5]
Arivind V. Sarode and Ashok Kumbharkhane , J. Mole. Liq. 160,109 (2011)
[6]
I Alig, S.B. Grigor’ev, Manucarov Yus and S.A. Manucarova, Acat Polym.
37,698 (1986)
[7]
Grinkevich N.I. , Safromich L. N. ( 1983), The chemical analysis of Medical
plants : Proc. Allowance for pharmaceutical universities. M. pp – 134-36
[8]
Mamatha Serasanambati, Shanmuga Reddy Chilakapati, International
Journal of Drug Delivery 6 (2014) pp 133 – 139
[9]
Babu Ganesan, Perumal, Vijaya Baskaran Manickam, International journal of
pharm tech. research CODEN (USA) : IJPRIF , ISSN : 0974 – 4304. Vol. 2,
pp 1528 – 1532, April – June 2010.
[10] Rafeal S. Valencia M. , Rose M. Castano A. and Shiramani J. J92005), Sleep
medicine, Elsevier, p-1-2
[11] Dong C. ( 2002) , Spectrochimica Acta part A, Elsevier , Vol 59, p-1476.
[12] A. Shalmashi and F. Golmohmmad , “Latin American Applied Research”
Vol. 14 , pp 283 – 285 ( 2010)
[13] Larsen R.W., Jasuja R. etal , Bio Phy. J. Vol.70 (issue 1) Jan 1996 pp 443452
[14] Davis D.B., Veselkov D.A etal, Eur Bio. Phys. J. Vol.30 (issue5), Sept 2001,
pp 354 – 366
[15] S. Havriliak and S. Negami , J. Polym. Sci. C 4, 99, (1966)
[16] H. Erying , J. Chem. Phys. 4, 283(1926)
PART - II
Theory of Dielectric
Theory of Dielectric
2.1. The Electromagnetic Spectrum
In the electromagnetic spectrum, microwaves occur in a transitional region
between infrared and radiofrequency radiation, as shown in by Fig. 2.1. The
wavelengths are between 1 cm and 1 m and frequencies between 300 GHz and 300
MHz. The term ‘‘microwave’’ denotes the techniques and concepts used and a range
of frequencies. Microwaves may be transmitted through hollow metallic tubes and
may be focused into beams by the use of high-gain antennas.
Fig. 2.1 The Electromagnetic spectrum
Microwaves also change direction when traveling from one dielectric material
into another, similar to the way light rays are bent (refracted) when they passed from
air into water. Microwaves travel in the same manner as light waves; they are
reflected by metallic objects, absorbed by some dielectric materials and transmitted
without significant absorption through other dielectric materials. Water, carbon, and
foods with high water content are good microwave absorbers whereas ceramics and
most thermoplastic materials absorb microwaves only slightly.
2.2 Dielectric
Dielectric is a insulating material or a very poor conductor of electric current.
Dielectrics have no loosely bound electrons, and so no current flows through them.
When they are placed in an electric field, the positive and negative charges within
the dielectric are displaced minutely in opposite directions, which reduce the electric
field within the dielectric. Examples of dielectrics include glass, plastics, and
ceramics. The science of dielectrics, which has been pursued for well over one
hundred years, is one of the oldest branches of physics and has close links to
chemistry, materials, and electrical engineering [1].
The term dielectric was first coined by Faraday to suggest that there is
something analogous to current flow through a capacitor structure during the
charging process when current introduced at one plate (usually a metal) flows
through the insulator to charge another plate (usually a metal). The important
consequence of imposing a static external field across the capacitor is that the
positively and negatively charged species in the dielectric become polarized.
Charging occurs only as the field within the insulator is changing [1-3]. Maxwell
formulated equations for electromagnetic fields as they are generated from
displacement of electric charges and introduced dielectric and magnetic constants to
characterize different media. It is generally accepted that a dielectric reacts to an
electric field differently, compared to free space, because it contains charges that
can he displaced.
2.2.1 Polar and non-polar molecules
A polar molecule has a permanent electric dipole moment. The total amounts
of positive and negative charges on the molecule are equal, so the molecule is
electrically neutral. Distributions of the two kinds of charge are different, however,
so that the positive and negative charges are centered at points separated by a
distance of molecular dimensions forming an electric dipole.
A non-polar molecule is one that the electrons are distributed more
symmetrically and thus does not have an abundance of charges at the opposite sides.
The charges all cancel out each other. In non-polar dielectrics, molecules possess no
permanent dipole moment and the attractive energy between atoms or molecules is
provided by dispersion forces only. The magnitude of the dipole moment depends
on the size and symmetry of the molecule. Molecules with a center of symmetry, for
example methane, carbon tetrachloride, and benzene are apolar (zero dipole
moment) whereas molecules with no center of symmetry are polar.
2.3 Dipole moment
As above we have seen that polar molecules posses a permanent dipole
moment. Let us consider an electric dipole shown in Fig.2.2 having two charges, -q
and +q, e.s.u. charge per unit area of equal magnitude and opposite sign, separated
by distance ‘r’. The vector ‘r’ points from the negative to the positive charge, and
the electric dipole moment is,
(2.1)
Fig. 2.2 The direction of dipole moment.
The magnitude of the dipole moment depends on the size and symmetry of
the molecule. In a molecule ‘q’ is of the order of 10-10 e.s.u., while ‘q’ is of the
order of 10-8 cm. Therefore the unit of dipole moment is 10-18 e.s.u.cm and is
called as “Debye’ abbreviated as ‘D’. Molecules with center symmetry like
methane, carbon tetrachloride and benzene are non-polar whereas molecules with no
centre symmetry are polar.
2.3.1 Polarization
When the electric field is applied to the dielectric, the molecular charges get
displaced. The total charge passing through unit area within the dielectric,
perpendicular to the direction of applied field is called polarization [2]. In dielectric
materials different types of polarization may occur such as electronic polarization,
atomic, orientation and interfacial polarization
2.3.2 Polarization Mechanisms
The addition of an applied field to each of the situations shown on the left of
Fig. 2.3 will cause a displacement of charge and thus affect the dielectric constant
by effectively cancelling a part of the applied field.
A schematic representation of the real part of the dielectric constant is shown
in Figure 2.4. At high frequencies (>1014 Hz), the contribution comes solely from
electronic polarization, implying that only free electrons, as in metals, can respond
to the electric field. That is why metals are such good optical reflectors! Even the
various thermal and mechanical properties, such as thermal expansion, bulk
modulus, thermal conductivity, specific heat, and refractive index, are related to the
complex dielectric constant, because they depend on the arrangement and mutual
interaction of charges in the material.
Fig. 2.3 Schematic representation of the different polarization
mechanisms.
Fig. 2.4 Contributions to the frequency-dependent dielectric constant from the different charge
configurations.
Thus, the study of dielectrics is fundamental in nature and offers a unified
understanding of many other disciplines in materials science. In a given dielectric
material the total polarization, P, is the sum of the polarization resulting from each
mechanism,
P = Pelectronic + Pionic + Pdipolar + Pspace charge
(2.2)
2.3.3 Electronic Polarization
Electronic polarization is found in all materials. This mechanism arises from a
shift of the center of mass of the negative electron charge cloud surrounding the
positive atomic nucleus when an electric field is applied. Because electrons are very
light, they have a rapid response to the field changes. It is of the order of 10-15 sec.
which is comparable to time period optical frequencies.
2.3.4 Atomic Polarization
In
materials
where
molecules
of
different
atoms
with
different
electronegativities form the structure, atomic polarization can occur. The formation
of molecules of different types of atoms results in the displacement of their electron
clouds towards the stronger binding atom. The atoms acquire charges of opposite
polarity and application of applied field acting on these charges can change the
equilibrium positions of the atoms. Charge displacement occurs due to this
displacement of positive and negative atoms. It takes a short time of the order of 1013 to 10-12 sec. comparable to time period of infrared light. Atomic polarizations
differ from electronic polarizations in that they occur due to the relative motion of
atoms instead of a shift of the charge cloud surrounding atoms. Atomic and
electronic polarizations are referred to as instantaneous polarizations since they are
completely formed in a time that is very short with respect to the time needed to
apply fields electronically.
2.3.5 Orientation Polarization
As stated, the rearrangement of electrons when some molecules form can create a
dipole moment in the resulting molecule. When no electric field is present the
molecules are randomly orientated and no net charge exists in the material.
However, when a field is applied the dipoles will rotate canceling part of the applied
field and leading to an orientation polarization. It is a function of molecule size,
viscosity, temperature and excitation frequency of applied field. It takes 10-12 to
10-10 sec. comparable to time period of microwave region.
2.3.6 Interfacial Polarization
Electrically heterogeneous materials may experience interfacial polarization. In
these materials the motion of charge carriers may occur more easily through one
phase and therefore are constricted at phase boundaries. As a result charges build up
at interfaces and can be polarized in an applied field. This effect often depends
greatly on the conductivities of the phases present. All these polarization
mechanisms can exist in homogeneous pure materials, with the exception of
interfacial polarization which must contain either multiple phases or mixtures of
pure materials to exist.
2.4 Dielectric theories
The interaction between electromagnetic waves and matter is quantified by the two
complex physical quantities – the dielectric permittivity, ~, and the magnetic
susceptibility, ~µ. The electric components of electromagnetic waves can induce
currents of free charges (electric conduction that can be of electronic or ionic
origin). It can, however, also induce local reorganization of linked charges (dipolar
moments) while the magnetic component can induce structure in magnetic
moments. The local reorganization of linked and free charges is the physical origin
of polarization phenomena. The storage of electromagnetic energy within the
irradiated medium and the thermal conversion in relation to the frequency of the
electromagnetic stimulation appear as the two main points of polarization
phenomena induced by the interaction between electromagnetic waves and dielectric
media. These two main points of wave–matter interactions are expressed by the
complex formulation of the dielectric permittivity as described by,
() =  - j
(2.3)
where 0 is the dielectric permittivity of a vacuum,  and  are the real and
imaginary parts of the complex dielectric permittivity The storage of
electromagnetic energy is expressed by the real part whereas the thermal conversion
is proportional to the imaginary part. The dielectric constant or permittivity of a
material is a measure of the extent to which the electric charge distribution in the
material can be distorted or polarized by using electric field [4, 5].
The dielectric relaxation theories can be broadly divided into two parts (i)
theories of static permittivity and (ii) theories of dynamic permittivity. The polar
dielectric materials having permanent dipole moment, when placed in steady electric
field so that all types of polarization can maintain with it, the permittivity of
material under these condition is called as theories of static permittivity (ε 0). When
dielectric materials is placed in electric field varying with some frequency, then the
permittivity of the material change with change in frequency of applied field. This is
so because with increasing frequency molecular dipoles cannot orient faster with
applied field. Thus the permittivity of the material falls off with increasing
frequency of applied field. The frequency dependent permittivity of material is
called as dynamic permittivity. The different theories of static and dynamic
permittivity are given in the following sections.
2.4.1 Polarization and Storage of Electromagnetic Energy
Suppose that a charge ‘q’ e.s.u. per unit area is applied to a parallel plate having area
‘A’ and separated by a distance‘d’. If vacuum is present between the two plates then
electric field intensity ‘E’ is given by,
E vacuum = 4  q
(2.4)
If dielectric material of dielectric constant ‘ε’ is introduce between the plates then
the field is smaller by factor ‘ε’ because of the polarization so it becomes,
E=
4 q

(2.5)
The same drop in field strength might have been attributed to a reduction of the
surface charge density by the amount;
 1
P  q 1  
 
(2.6)
The surface charge density of these opposite sign charges on the surface of the
dielectrics is P and is known as the polarization; it is the total charge passing
through any unit area within the dielectric (parallel) to the plates.
The electric displacement D is defined in terms of the original applied charge
density:
D= 4πq
(2.7)
D=εE
(2.8)
If Eqn. (2.4) and (2.5) rearranged and simplified as,
From Eq. (2.4) q = εE/4π, if we put this value in Eq.(2.5) we get,
D = εE = E+4πP
(2.9)
And also we can write it as;
 1 
4P
E
(2.10)
The potential difference ‘V’ between the plates is simply
V 
E
d
(2.11)
and the total charge ‘Q’ is related to the capacitance C of the system by
Q=CV
(2.12)
Neglecting edge effects, the capacitance of a pair of parallel plates, each of area A
and containing materials of dielectric constant ‘’ is
C
A
4d
(2.13)
A measurement of this capacitance leads to a knowledge of the static
dielectric constant For a given substance the static dielectric constant is the ratio of
capacity of a condenser with that substance as the dielectric medium to the capacity
of the same condenser with a vacuum as the dielectric medium
0 
C
C0
(2.14)
The dielectric constant is a function of temperature and is a dimensionless quantity.
The polarization can therefore be regarded as the dipole moment per unit
volume.
P=

V
or
µ=PV
(2.15)
The inner field ‘F’ is by considering a microscopic spherical region surrounding the
molecule, but large compared with it. The total internal field arises from the external
contribution, which is the external field inside the spherical region due to all sources
except the polarization inside this region. Electrostatic calculation [6] shows it to be
equal to E + 4πP/3, and therefore using Eq. (2.9)
F
(  2)
E
3
(2.16)
2.4.2 Debye theory of static permittivity
The dipole moment of a molecule is made up of a permanent and an induced
part. Atoms and molecules all posses a dipole polarizability ‘α’ which is the dipole
moment induced by a unit electric field for a number of atoms N in unit volume
Pinduced dipole = NαF =
N 0F
V
(2.17)
where ‘N0’ is the Avogadro constant and ‘V’ the molar volume. The permanent
dipole moment ‘µ’ is not present in atoms and is only present in some molecules,
including H2O. Debye was first to perform the calculation of polarization of system
of polar molecules, who started from the expression [5, 7-8].
Ppermanent dipole = N< cos >
(2.18)
where < cos > denotes the mean value of the cosine of the angle of inclination of a
dipole to the applied field. The moments are distributed about an applied field in
accordance with the Boltzmann’s law, from which Debye deuced that
< cos > = coth(
=L(
F
F
kT
kT
)
kT
F
)
(2.19)
(2.20)
This defines the Langevin function [9]. It approximates to
N0 2 F
Ppermanent dipole =
3VkT
(2.21)
The Debye equation for the static dielectric constant
 0  1 4N 0 
2 
 


0  2
3V 
3kT 
(2.22)
Limitations of Debye’s theory – the inadequacy of the Lorentz inner field results in
a failure of the Debye equation to reproduce static dielectric constants of dense
fluids.
For substances containing only non-polar molecules
 0  1 N 0

 0  2 3V
(2.23)
Above equation shows the Clausius-Mossotti formula for the dielectric
constant.
2.5 Dielectric Relaxation Behaviour
Dielectric relaxation occurs when; a dielectric material is polarized by the
externally applied alternating field. The decay in polarization is observed on
removal of the field. This depends on the internal structure of a molecule and on
molecular arrangement. The orientation polarization decay exponentially with time;
the characteristics time of this exponential decay is called relaxation time. This
phenomenon may occur as; at low frequencies, the dipoles can “follow” the field
and ε′ will be high. At high frequencies, the dipoles cannot follow the rapidly
changing field - and ε′ falls off. The resonance character of the attenuation (the
imaginary part of the complex permittivity) can be explained in a similar way.
Before the resonance the loss is increasing because the dipoles still can totally orient
when the electric field changes direction, so the loss is proportional to the
frequency. After resonance the frequency is so high that the dipoles do not have
enough time to orient, so there is less friction and less loss. The permittivity thus
acquires a complex characteristic.
 At low frequencies, the dipole rotation can follow the field easily; ε′ will be
high and ε″ will be low. As the frequency increases, the loss factor, ε″
increases as the dipoles rotate faster and faster.
 The loss factor ε″ peaks at the frequency 1/τ. Here, the dipoles are rotating as
fast as they can, and energy is transferred into the material and lost to the field
at the fastest possible rate.
 As the frequency increases further, the dipoles cannot follow the rapidly
changing field and both ε′ and ε″ fall off.
The complex permittivity ε* can be written as ε′- jε″, where ε′ is a real part
proportional to stored energy and ε″ is imaginary part and it is dielectric loss.
2.5.1 Relaxation time (τ)
Relaxation time describes the time required for dipoles to become oriented in
an electric field or the time needed for thermal agitation to disorient the dipoles after
the electric field is removed. Relaxation times Debye [8, 10] suggested that a
spherical or nearly spherical molecule could be treated as a sphere (radius r) rotating
in a continuous viscous medium of bulk viscosity h. The relaxation time is given by,
8r 3

2kT
(2.24)
2.5.2 Debye Model
The Debye model [8] could be built with these assumptions, and polarization
and permittivity become complex as described by Eq. (2.25) where n is the
refractive index and t the relaxation time,
 0  n2
   ' j "  n 
1   2 2
~
2
(2.25)
All polar substances have a characteristic time  called the relaxation time
(the characteristic time of reorientation of the dipolar moments in the electric field
direction). The refractive index corresponding to optical frequencies or very high
frequencies is given by,
   n2
whereas  s is the static permittivity or permittivity for static fields.
(2.26)
The real and imaginary parts of the dielectric permittivity of Debye’s model
are given by,
 0  n2
1   2 2
(2.27)
( 0  n 2 )
1   2 2
(2.28)
 '  
" 
Changes of  ' and  " with frequency are shown in Fig. 2.5. The frequency is
displayed on a logarithmic scale. The dielectric dispersion covers a wide range of
frequencies. The dielectric loss reaches its maximum given by,
 "max . 
 0  n2
2
(2.29)
This theory justifies the complex nature of the dielectric permittivity for
media with dielectric loss. The real part of the dielectric permittivity expresses the
orienting effect of electric field, with the component of polarization which follows
the electric field, whereas the other component of the polarization undergoes chaotic
motion leading to thermal dissipation of the electromagnetic energy.
Fig. 2.5 Debye relaxation is obtained by plotting the imaginary part against the real
part of complex permittivity for water at 300C.
Fig. 2.6 Cole-Cole Diagram of Debye Relaxation.
2.5.3 Cole - Cole Model
The Cole – Cole model [11] has been used successfully to describe the experimental
data for the dielectric constant of many materials as a function of frequency. The
complex permittivity may also be shown on a Cole-Cole diagram by plotting the
imaginary part ('') on the vertical axis and the real part (') on the horizontal axis
with frequency as the independent parameter (Fig. 2.6). A Cole-Cole diagram is, to
some extent, similar to the Smith chart. A material that has a single relaxation
frequency as exhibited by the Debye relation will appear as a semicircle with its
center lying on the horizontal '' = 0 axis and the peak of the loss factor occurring at
1/τ. A material with multiple relaxation frequencies will be a semicircle (symmetric
distribution) or an arc (nonsymmetrical distribution) with its centre lying below the
horizontal ''= 0 axis. The curve in Fig. 2.6 is a half circle with its centre on the xaxis and its radius
S 
2
. The maximum imaginary part of the dielectric constant 
max will be equal to the radius. The frequency moves counter clockwise on the
curve.
If the molecules are randomly oriented relative to the field, the corresponding
relaxation time is distributed between these two extreme cases. If f (τ) is the
distribution function of the relaxation time between τ and dτ, the corresponding Eq.

f ( )d
1  j
0
 *       ( 0    ) 
(2.30)
Because this leads to circular arc centred below the axis, K.S. Cole and R. H. Cole
have proposed a modified form of Debye’s equation with a term ‘α’ characterizing
the flattening of the diagram. The Cole –Cole equation is [11]
 *      
0 
1
1   j 
with 0 ≤ α ≤ 1.
(2.31)
The value of ‘α’ has a tendency to increase with increasing number of internal
degrees of freedom in the molecules and with decreasing temperature [11]. The
value of ‘α’ increases with decreasing chain length, i.e. the distribution of relaxation
time tends toward symmetric distribution with decreasing chain length.
2.5.4 Cole-Davidson Model
Cole –Davidson model describes the asymmetric distribution of
relaxation times. The proposed Cole-Davidson equation is [12]
 *      
0  
[1  jw ]
(2.32)
which corresponds to relaxation time and gives rise to a skewed arc ε′ (ε''). When β
is close to unity this reduces to Debye’s model and for β less than unity an
asymmetric distribution of relaxation time is obtained.
2.5.5 The Havriliak-Negami Model
More recently Havariliak-Negami (HN) found that none of the above dielectric
functions was successful in giving the spectral response they had measured in a
number of polymetric materials. There are many examples of dielectric behaviors
which can not be explained by Cole-Cole and Davidson – Cole expressions, both of
which contain only one adjustable parameter to describe the shape of the plot (″vs.
′). Havariliak-Negami generalized the expression, consisting in a contribution of
both Cole-Cole and Davidson – Cole expression as given below [13].
 * ( )    
0  
[1  ( j )1 ]
(2.33)
It includes Cole-Cole model if  = 1, the Davidson –Cole model if =0 and if =0
and  = 1 it gives the Debye model.
2.6 Thermodynamic Parameters
Relaxation processes in dielectrics may be considered as the passing of a dipole
across a potential barrier that separates the minima of energy. Let ∆G denote the
difference in free enthalpy per mole of molecules, i.e. the difference of free enthalpy
between the excited and ground state. According to Eyring [15], k represents the
number of times per unit time a dipole acquires sufficient energy to pass across the
potential barrier from one equilibrium position to another. In such a case,
k
kT
  G 
exp 

h
 RT 
(2.34)
The microscopic relaxation time τ is related to k by k = 1/τ. In accordance with the
principles of thermodynamics [14] ∆G = ∆H – T∆S. Therefore the relaxation
process is as analogous to chemical rate process [15]. The temperature variation of
the inverse microscopic relaxation time will then be approximately exponential,
according to the equation:

kT
 H
exp 
h
 RT

  S 
 exp 


 RT 
(2.35)
where ∆H is molar enthalpy of activation, and ∆S is the molar entropy of activation.
Recasting the above equation we get
ln( T ) 
H S
h H

 ln 
A
RT RT
k RT
(2.36)
It follows from the equation that if ∆H and ∆S are independent of the temperature,
the plot of ln(τT) vs. 1/T is linear with negative slope. Using the tangent of the slope
of this function we can determine the height of the potential barrier ∆H.
References
[1] J. Daintith, "Biographical Encyclopedia of Scientists" CRC Press, ISBN
0750302879, page
943 (1994).
[2] C. P. Smyth, Dielectric behavior and structure, McGraw-Hill Book Co., New
York (1955).
[3] B. Tareev, Physics of Dielectric Material, Mir Publishers, Moscow (1975).
[4] N. E. Hill, W. E. Vaughan, A. H. Price and Davies, “Dielectric properties and
molecular behaviour” Van Neatrand Reinhold co., London (1970).
[5] J. B. Hasted, “Aqueous dielectric” Chapman and Hall Ltd., London (1973).
[6] S. G. Kukolich, J. Chem. Phys. 50 (1969) 3751-3755.
[7] A. Chelkowski, “Dielectric Physics” Elsevier scientific publishing company,
Amsterdam-Oxford-New York (1980).
[8] P. Debye, “Polar molecules”, Chemical catalog company, New York (1929).
[9] H. A. Lorentz, “Theory of Electrons”, Teutorver Verlogsellscharft, Leipzig,
306,1909.
[10] P. Debye, The collected papers of Peter J. W. Debye, Ed. Interscience
Publishers, New
York, USA, (1913).
[11] K. S. Cole, R. H. Cole, J. Chem. Phys. 9 (1941) 341.
[12] D. W. Davidson, R. H. Cole, J. Chem. Phys. 18 (1951) 1417-1422.
[13] S. Havriliak, S. Negami, J. Polym. Sci. 14 (1966) 99-117.
[14] J. Werle, Phenomenological Thermodynamics (in Polish),PWN, Warszawa
(1957).
[15] S. Glasstone, K. J. Laidler, H. Eyring, “The Theory of Rate Processes”,
McGraw-Hill, New York (1941).
PART – III
Dielectric Relaxation Study
Of Brucine – Methanol
Solution
3.1 Introduction :
2-3-Dimethoxystrichnine (Brucine) is an alkaloid of the strychnine type [1,2]. It
is found in bark and seeds of the strychnine tree (Strychno nux-vomica L). In bark
of this tree contains 2-3% of Brucine [3]. This alkaloid have been used for
therapeutic purpose in smaller doses, they should have a central stimulation effect
and improve circulation and muscle tone [4,5]. It is very poisonous Alkaloid. It
affects on all portion of central nervous system [6]. It is used in pesticides [7,8].
Brucine is primarily used in the regulation of high blood pressure and other
comparatively benign cardiac ailments.
The alkaloid brucine is isostructural to strychnine, with methoxy groups at the
aromatic ring rather than hydrogens. Both brucine and strychnine are commonly
used as agents for chiral resolution.
The separation of racemic mixtures by
alkaloids from the cinchona bark has been known since 1853, when its use as such
was reported by Pasteur. The ability of brucine, and to a lesser extent strychnine, to
function as resolving agents for amino acids was reported by Fisher in 1899.
Brucine and strychnine are basic and thus have a tendency to crystallise with acids.
The acid base reaction leaves the brucine protonated at the N(2) position. The
formation of diastereomeric salts has been reported for thousands of organic
compounds. The packing of brucine in corrugated (waving ) layers was an essential
aspect in the co-crystallisation of brucine, whereas strychnine was shown to
crystallise predominantly in bilayers.
Brucine is slightly soluble in water but dissolves readily in alcohols and
chloroform. It’s molecular formula is C23 H26 N2 O4 and molecular mass is 394.46
gm/mole. It’s molecular structure is shown in fig.3.1 [6].
Fig. 3.1 Molecular Structure of Brucine
Few researcher were worked on Brucine in various subject area. Considering
solubility in methanol and molecular mass, a solution of different concentration of
Brucine in molar were prepared. Methanol is polar-protic Solvent.
we present the complex permittivity study of brucine – methanol solutions from
10MHz to 30 GHz using time domain reflectometry (TDR) technique for different
temperature and for different concentrations of Brucine. The Dielectric relaxation
behaviour of this solution is explained by Cole-Davidson model. The dielectric
parameters and activation enthalpy, activation entropy are reported.
3.2 Experimental Procedure :
Considering Solubility of Brucine in methanol and its molecular mass, solutions
of different concentration upto 0.5M of Brucine were prepared. The complex
permittivity of solution was observed in frequency range 10MHz to 30GHz at
different temperatures. Using TDR method static dielectric constant ε 0, relaxation
time 𝜏 and thermodynamic parameter i.e. Enthalpy of activation ∆𝐻 and Entropy of
activation ∆𝑆 are determined.
Using TDR, sampling oscilloscope monitors changes in step pulse after
reflection from the end of line. Reflected pulse without sample R1 (t) and with
sample Rx (t) were recorded in time window of 5ns and digitized in 2000 points.
The Fourier transformation of the pulses and data analysis were done earlier to
determine complex permittivity spectra 𝜺*(ω) using non linear least squares fit
method [9].
3.3 Data analysis :- These recorded pulses are added [q(t) = R1(t) + RX(t)] and
subtracted [p(t) = R1(t) - RX(t)]. Further the Fourier transformation of p(t) and q(t)
was obtained by summation and Samulon [10-11] methods respectively, for the
frequency range 10 MHz to 30 GHz. The complex reflection spectra were
determined as follows,
 c   p( ) 
 

 jd   q( ) 
  ( )  
(3.1)
where p( ) & q( ) are Fourier transforms of p(t) and q(t) respectively, c is the speed
of light,  is the angular frequency, d is the effective pin length and j=  1 . The
Complex permittivity spectra ε*() was obtained from reflection coefficient *()
by applying calibration method as described earlier [9].
The recorded pulses are as shown in figure 3.2 a,b,c,d
0.6
Voltage(V)
0.5
0.4
0.3
R1(t)
0.2
0.1
0
1
501
1001
1501
2001
No. of sampling points
Fig.3.2 (a) Reflected pulse without sample.
0.6
Voltage(V)
0.5
0.4
0.3
0.2
0.1
0
Rx(t)
Fig. 3.2(b) Reflected pulse with sample for 0.5M Brucine – Methanol solution
at 25°C.
0.07
0.06
Voltage(V)
0.05
0.04
0.03
R1(t)-Rx(t)
0.02
0.01
0
-0.01
0
500
1000
1500
2000
No. of sampling points
Fig. 3.2(c) sample pulse of
R1(t)-Rx(t) for
0.5M Brucine – Methanol solution at 25°C.
1.2
Voltage(V)
1
0.8
0.6
R1(t)+Rx(t)
0.4
0.2
0
1
501
1001
No. of sampling points
1501
2001
Fig. 3.2(d) sample pulse of R1(t)+Rx(t)for 0.5M Brucine – Methanol solution at 25°C.
3.4 RESULT AND DISCUSSION
The complex permittivity is given ε*(ω) = ε′ (ω) – jε′′ (ω) – (3.2) where ε′ (ω) is
real component which is known as electric dispersion and imaginary component
known as dielectric loss.
The complex frequency spectra for various molar
solutions of Brucine at 25°C is as shown in fig.3.3
Fig.3.3 Frequency dependence of the dielectric constant and loss for 2-3dimethoxystrychnine (Brucine) – Methanol at 250 C
Static dielectric constant and relaxation time
To determine static dielectric constant ε0, relaxation time 𝜏 and distribution
parameters (α and β), the complex permittivity ε*(ω) data were fitted by non linear
least square method to the Havriliak-Negami expression[12]
ε* (ω) = ε∞ +
ε0 −ε∞
[(1+𝑗𝜔 𝜏)1−𝛼 ]𝛽
(3.3)
Where ε∞ is permittivity at high frequency.
The Havriliak-Negami equation includes three relaxation models as limiting
forms. The Debye model (α = 0 and 𝛽 = 1) implies a single relaxation time while the
cole-cole model (0 ≤ α ≤ 1 and 𝛽 = 1), and Cole Davidson (α = 0 and 0 ≤ 𝛽 ≤ 1)
both suggest a distribution of relaxation times. The magnitudes of α and 𝛽 indicate
the width of distribution. This system could fit Cole-Davidson type dispersion
Hence α = 0 and 0 ≤ 𝛽 ≤ 1 and experiment values ε* (ω) were fitted to
ε* (ω) = ε∞ +
ε0 −ε∞
(1+𝑗𝜔 𝜏)𝛽
(3.4)
The dialectic relaxation parameters for different molar solution of Brucine and
for different temperatures are listed in Table. 3.1
Table .3.1
Dielectric relaxation parameters for molar solution of Brucine
at different temperatures.
Concentration
of Brucine in
Molar(M)
ε0
𝛕(Þs)
ε∞
0
0.64(3)
46.88(9)
0.05
30.52(3)
47.55(10) 3.63(1) 0.9524(0.1)
0.15
29.96(3)
48.7(10)
3.67 1) 0.9399(0.1)
0.25
29.15(3)
49.5(11)
3.69(1) 0.9303(0.1)
0.3
28.72(3)
50.43(11) 3.50(1) 0.9226(0.1)
0.35
28.2 (3)
51.26(12) 3.39(1) 0.9107(0.1)
0.4
27.68(3)
52.09(13) 3.56 1) 0.9084(0.1)
0.5
27.16(3)
53.95(16) 3.08 1) 0.8887(0.1)
0
31.66(3)
50.62 11) 4.08(1) 0.9604(0.1)
0.05
31.35(3)
51.02(11) 3.88(1) 0.9526(0.1)
0.15
30.92(3)
51.97 12) 4.05(1) 0.9407(0.1)
0.25
30.25(3)
52.91 11) 3.96(1) 0.9326(0.1)
0.3
29.58(3)
53.85(12) 3.90(1) 0.9256(0.1)
0.35
29.19(3)
54.63 14) 3.75(1) 0.9117(0.1)
0.4
28.61(3)
55.84 14) 3.68(1) 0.9090(0.1)
0.5
27.7(3)
57.06 16) 3.40(1) 0.8921(0.1)
β
250c
3.76(1) 0.9627(0.1)
200c
150c
0
33.06(3)
55.36 13) 4.69(1) 0.9595(0.1)
0.05
32.46(4)
55.11 14) 4.35(1) 0.9525(0.1)
0.15
31.81(3)
55.93 14) 4.42(1) 0.9424(0.1)
0.25
30.84(3)
56.25(14) 4.43(1) 0.9324(0.1)
0.3
30.36(3)
57.25 14) 4.22(1) 0.9268(0.1)
0.35
29.95(3)
57.69(15) 4.16(1) 0.9152(0.1)
0.4
29.29(4)
60 (13)
0.5
28.63(3)
62.31(17) 3.87(1) 0.8961(0.1)
4.11(1) 0.9051(0.1)
Note – Number in bracket denotes uncertainties in the last significant
digits obtained by least square fit method i.e. 28.63(3) means 28.63 +
− 0.03.
Variation of static dielectric constant with concentration of
Brucine in Molar at various temperature is shown in Fig.3.4
33.5
0
25 c
0
20 c
0
15 c
33.0
32.5
32.0
Dielectric Constant
31.5
31.0
30.5
30.0
29.5
29.0
28.5
28.0
27.5
27.0
0.0
0.1
0.2
0.3
0.4
0.5
Concentration of Brucine(Molar)
Fig.3.4 Dielectric constant versus Concentration of Brucine (molar)
And variation of relaxation time 𝛕 with concentration of Brucine
Relaxation Time
at various temperature is shown in fig.3.5
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
0
25 c
0
20 c
0
15 c
0.0
0.1
0.2
0.3
0.4
0.5
Concentration of Brucine(Molar)
Fig.3.5 Relaxation Time versus concentration of Brucine (molar)
It is noted that static dielectric constant ε0 decreases and relaxation time
increases with increasing concentration of Brucine. The static dielectric constant ε0
and relaxation time 𝛕 decreases as temperature increases. The relaxation time varies
from 46Þs to 62Þs within temperature range studied.
Determination of Enthalpy of activation H and entropy S.
The energy of activation of dielectric relaxation process can be calculated from
dielectric relaxation time using Erying equation [13].
The enthalpy of activation H and entropy of activation S are determined from
Erying rate equation.
𝛕=
ℎ
𝑘𝑇
exp ( H - TΔS) / RT
(4)
Where h is planck’s constant, k is Boltzmann’s constant T is absolute
temperature, 𝛕 is relaxation time and R is gas constant.
The temperature dependence of relaxation time describes by Arrehenius plot
of log (𝛕 T) versus 1000/T is shown in fig.3.6.
Fig.3.6 Arrehenius plot of Various molar Solutions
The values of H and S are reported in table.4.2
Table-4.2. Enthalpy and Entropy of activation for Brucine – Methanol solution
Concentration of
Enthalpy of
Entropy of
Brucine in Molar
Activation H (KJ
Activation S (J
mole-1)
mole-1 K-1)
M
9.431 (42)
0.2142 (0.1)
0.15 M
7.443 (26)
0.2072 (0.8)
0.3 M
6.61 (25)
0.2041 (0.8)
0.35 M
5.97 (13)
0.2018 (0.4)
0.4 M
7.64 (92)
0.2073 (0.3)
0.5 M
7.85 (12)
0.2077 (0.4)
0
Note – Number in bracket denotes uncertainties in the last significant digits
obtained by least square fit method i.e. 7.85(12) means 7.85 +
− 0.12.
When an amount for Brucine is added to methanol, H and S of Brucinemethanol solution decreases from pure methanol to minimum values at 0.35M. The
plot between concentration of Brucine verses enthalpy of activation is as shown in
figure 3.7 The decrease of activation enthalpy in solution can be attributed to
change in hydrogen bond strength or a decrease in average number of hydrogen
bonds. The entropy and enthalpy of activation ware determined using least square fit
method.
-1
Enthalpy Of Activation (kJ mole )
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
0.0
0.1
0.2
0.3
0.4
0.5
Concentration of Brucine (M)
Fig 3.7 The plot between concentration of brucine verses enthalpy of activation
4
CONCLUSION
Dielectric relaxation parameters and thermodynamic parameter and for
various concentration of
Brucine in methanol were studied.
Static dielectric
constant ε0 decreases with increasing concentration of Brucine and it decreases with
increase in temperatures. Relaxation time 𝛕 increases with increase in concentration
of Brucine and decreasing with increasing temperature shows interaction in
molecules. The values of enthalpy ∆H and entropy ΔS shows decrease in average
number of Hydrogen bonds.
References :
1)
K.W. Bentley, The chemistry of natural products : The alkaloids Vol. 1. P162 Interstice Publishers a division of John wiley sons, Inc, Newyork,
London, Sydney.
2)
G. Philippe, L. Angenot, M. Tits amd M. Fredrich. J – Toxicon 44 : 405 –
416 (2004)
3)
R. Sarvesvaran, Strychine Poisoning Case report Malays. J. Pathol, 14:3539 (1992)
4)
G. Jackson and G. Diggle. Strychine – containg tonics. Br. Med. J 2:176-177
(1973)
5)
R.C. Baselt, Disposition of Toxic Drugs and chemicals in man, 8 th ed.
Biomedical publication, foster city CA, 2008, PP 1448-1450
6)
Pradyot patnaik – A comprehensive guide to the Hazardous properties of
chemical substances p-224 – A John wiley & sons, INC publication .
7)
A. prakash and j rao, Botonical pesticides in Agriculture, CRC press, Boca
Raton, FL, 1997. P 357
8)
K. Dittrich, M.J. Bayer and L.A. Wanke. A case of fatal strychnine poisoning
J. Emerg. Med 1 : 327-330 (1984)
9)
A. C. Kumbharkhane, S.M.Puranik, & S. C. Mehrotra J. Chemical Society
Faraday Trans 87(10),1569 (1991)
10) Shannon C. E., Proc.IRE. 37 (1949) 10-21.
11) Samulon H. A., Proc.IRE. 39 (1951) 175-186..
12) S. Harilliak and S. Negami, J Polym. SC. 14-91 (1966)
13)
H. Erying, J. Chem. Phy. 4, 283 (1926).
PART - IV
Dielectric Relaxation
Study of Caffeine-water
Solution
4.1 Introduction
Caffeine is a bitter , white crystalline xanthine alkaloid that is a psychoactive
stimulant drug. Caffeine was discovered by a German chemist, Friedrich Ferdinand
Runge, in 1819. He coined the term kaffein, a chemical compound in coffee , which
in English became caffeine. Caffeine is found in varying quantities in the beans,
leaves and fruit of some plants, where it acts as a natural pesticide that paralyses
and kills certain insects feeding on the plants. It is most commonly consumed by
humans in infusions extracted from the bean of the coffee plant and the leaves of the
tea. Humans have consumed caffeine since the stone Age [1].
Caffeine (1,3,7,-trimethyl xanthine) [C8H10N4O2] is alkaloid, which is
naturally found in coffee, tea, cola etc. Caffeine comes under group of purine
alkaloids and nitrogen containing substance [2, 3]. The molecular structure of
caffeine is shown in Fig. 4.1. Caffeine is colourless compound which crystallises in
silky needles and it is weak base and forms salts with strong acids which easily
decomposed by water. Caffeine used as nerve and heart stimulant as a medicine [4].
Caffeine is extracted from tea with water – saturated solvent [2]. Solubility of
caffeine in water is 2.17 gm. / 100ml. Solubility in water is temperature dependant,
as temperature increases solubility increases [5].Analytical and some physical
properties of caffeine was studied [6].
Figure 4.1
In this chapter the temperature dependant dielectric relaxation studies of caffeine-water
mixture for different molar fraction of caffeine in the frequency range of 10 MHz to 30
GHz using pico-second is given. Time Domain Reflectometry technique. The static
dielectric constant, relaxation time, high frequency permittivity has been determined.
From deielctric parameters the thermodynamics parameters are obtained. On the basis of
these parameters, intermolecular interaction and dynamics of molecules at molecular level
are discussed.
4.2. Experimental
:- Considering solubility and molecular mass solution of
different concentration were prepared.
Using TDR, Sampling oscilloscope
monitors changes in step pulse after reflection from the end of line. Reflected pulse
without sample R1 (t) and with sample Rx (t) were recorded in time window of 5ns
and digitized in 2000 points. The Fourier transformation of the pulses and data
analysis were done earlier to determine complex permittivity spectra 𝜺*(ω) using
non linear least squares fit method [7].
4.3 Data Analysis :These recorded pulses are added [q(t) = R1(t) + RX(t)] and subtracted [p(t) =
R1(t) - RX(t)]. Further the Fourier transformation of p(t) and q(t) was obtained by
summation and Samulon [8-9] methods respectively, for the frequency range 10
MHz to 30 GHz. The complex reflection spectra were determined as follows,
 c   p( ) 
 

 jd   q( ) 
  ( )  
(4.1)
where p( ) & q( ) are Fourier transforms of p(t) and q(t) respectively, c is the speed
of light,  is the angular frequency, d is the effective pin length and j=  1 . The
Complex permittivity spectra ε*() was obtained from reflection coefficient *()
by applying calibration method as described earlier [7]. The dielectric permittivity ε′
and dielectric loss ε″ for 0.06M, 0.1M and water mixtures at 25˚C is shown in
Fig.4.2.
.
Figure 4.2
The temperature dependent dielectric relaxation parameters for caffeine–water
mixtures with molar fraction of caffeine are listed in Table 4.1. The errors in these
parameters have been given in the brackets which shows an uncertainty in the last
significant digits e.g. the static dielectric constant of 0.1M 72.70(6) means 72.70 ± 0.06.
The decrease in dielectric constant of the solution with increasing caffeine
concentration and systematic change in the dielectric parameters of the solution can be
explained on the basis of molecular interactions. The dielectric properties will get
affected by temperature for all molar concentration. This is due to the effect of
temperature on polarization mechanism and charge mobility. Similar behavior observed
from the Table 4.1, the values of ε0 and τ
temperature.
Table 4.1
(a) Water
are decreasing with an increasing
The Temperature dependent dielectric constant for different solution is given in figure
Dielectric Constant
4.3 below .
0M
0.06M
0.1M
82.5
82.0
81.5
81.0
80.5
80.0
79.5
79.0
78.5
78.0
77.5
77.0
76.5
76.0
75.5
75.0
74.5
74.0
73.5
73.0
72.5
14
16
18
20
22
24
26
0
Temperature( C)
Figure 4.3 Dielectric constant verses temperature
4.4 Thermodynamic Parameters The thermodynamic parameters evaluated using
Eyring equation is as follows [10,11] τ = (h/KT) exp (ΔH/RT) exp (-ΔS/R) (3) where
ΔS is the entropy of activation, ΔH is the activation energy in kJ/mol. τ is the relaxation
time in ps and T is the temperature in K and h is the Plank's constant. The result in
values of activation energy are obtained by least square fit method are reported in Table
4.2.
Table 4.2: Thermodynamic Parameters for caffeine–water mixtures
Molar
Conc. of
caffeine
Water
.06M
0.1M
ΔH(kJ
mole-1)
ΔS (Jmole1k-1)
17.62(15)
3.60(34)
2.80(70)
0.249(1)
0.208(1)
0.205(2)
The temperature dependence of relaxation time described by Arrhenius plot shown in
Fig. 4.4. Activation energy (ΔH) for water, 0.06M and 0.1M is positive. This indicates
endothermic reaction in entire concentrations
Figure 4.4
4.5 Conclusion
The dielectric permittivity spectra of Caffeine (1,3,7,- treimethyl xanthine) in aqueous
solution have been studied using time domain reflectometry technique in frequency
range 10 MHz to 30 GHz at 15°C, 20°C and 25°C. With increase caffeine
concentration, the dielectric constant decreases which can be explained on the basis of
molecular interaction.
References
[1] “ A brief history of drugs ; from the stone age to the stoned age “ Escohotado
Antonio; Ken Symington, park street press ISBN 0-89281-826 -3 ( 1999)
[2] The chemistry of Natural Products – alkaloids Vol. – I, by K. W. Bentley, Inter
Science Publishers, New York, London, Sydney.
[3] The World of caffeine – Bennett Alan Weinberg Bonnie K. Bealer, Routledge Pub.
New York. & London.
[4] Organic Chemistry Natural products Vol. – I O. P. Agrawal, Krishna
Prakashan,Meerut.
[5] A. Shalmashi, F. Golmohammad – Latin American applied research – 401 283285(2010)
[6] Francis Agyemang – Yeboah, Sulvester raw oppong, research sign post – 2013
27-37 ISBN 978-81-308-0521-4
[7] A. C. Kumbharkhane, S.M.Puranik, & S. C. Mehrotra J. Chemical Society
Faraday Trans 87(10),1569 (1991)
[8] Shannon C. E., Proc.IRE. 37 (1949) 10-21.
[9] Samulon H. A., Proc.IRE. 39 (1951) 175-186.
[10] H. Erying, J. Chem. Phy. 4 – 283(1926)
[11] H. C. Chaudhary, A. Chaudhary and S. C. Mehrotra J. korean chem. Soc. 52, 4
(2008)
PART - V
Publications