Download Effect of potassium nitrate on the optical and structural properties

International Journal of ChemTech Research
CODEN( USA): IJCRGG
ISSN : 0974-4290
Vol. 3, No.3, pp 1454-1461, July-Sept 2011
Effect of potassium nitrate on the optical and
structural properties
of L-Histidine Acetate single crystals
V. Renganayaki
PG Department of Physics, D G Vaishnav College, Arumbakkam,
Chennai- 600106,India.
Corres.author: [email protected]
Ph. 9445093284
Abstract: Single crystals of L-histidine acetate (LHA) with potassium nitrate have been grown successfully by slow
evaporation technique. The Fourier Transform Infrared spectral studies reveal the functional group identification for the
grown crystals. Absorption of these grown crystals was analyzed using UV Vis – NIR studies and the spectrum was
compared with that of pure LHA crystals. It was found that these crystals were more transparent in the UV Vis NIR
window. The presence of potassium in the crystal has been confirmed by mass spectrometry. The percentage
composition of potassium in L-histidine acetate with potassium nitrate was established by inductively coupled plasma
(ICP) technique.
Key words: LHA, potassium nitrate, FTIR, UV – Vis NIR, optical transmission.
INTRODUCTION
Non-linear optical (NLO) materials will be the
key elements for future photonic technologies based on
the fact that photons are capable of processing
information with the speed of light. Due to this fact,
the rapid development of optical communication
systems has led to a demand for non linear optical
materials of high structural and optical quality1, 2.
Amino acid families of crystals are under extensive
investigations in recent times owing to their favorable
NLO properties 3. Many number of natural amino acids
are individually exhibiting non linear optical properties
because they have a donor NH2 and acceptor COOH
and also inter molecular charge transfer is possible 4.
Earlier works have been reported on L-histidine
tetrafluroborate, L-histidinium dihydrogen phosphate,
L-histidine acetate and L-histidinium acetate
dihydrate5, 6 single crystals. Along these series, to
enhance the optical properties of L-HA, potassium
nitrate has been added and
semi-organic single
crystals are grown. In the present work, the synthesis
and growth of single crystals of L-HA with potassium
nitrate has been carried out. The grown crystals are
characterized by FTIR, optical transmission, Gas
chromatography-Mass spectroscopy (GCMS) and
inductively coupled plasma technique (ICP).
EXPERIMENTAL DETAILS
Synthesis and crystal growth
LHA with potassium nitrate was synthesized
from L–histidine (Merck–99.9%), acetic acid (Merck–
99.9%) and potassium nitrate (Merck–99%) taken in
equimolar ratio. The calculated amounts of the
reactants were thoroughly dissolved in doubly distilled
water and stirred well for about 12 h. This was then
filtered to remove suspended impurities and allowed to
crystallize. Seed crystals were formed due to
spontaneous nucleation. Optically transparent and
V. Renganayaki /Int.J. ChemTech Res.2011,3(3)
defect free seed crystals with perfect shape were
obtained with the pH value 5. The seeds were
suspended in the mother solution with nylon thread
and the growth was achieved by slow solvent
evaporation technique at a constant temperature of 305
K. In the present study, good optically transparent
crystal of dimension 12 × 4 × 4 mm3 was grown in a
period of 20 days. Figure 1 shows the photograph of
as grown crystals of LHA with potassium nitrate.
1455
function groups such as imidazoles, amino acids,
carboxylic acids etc. The frequency assignments are
presented in Table 1.
Characterization
A complete description of the physical and chemical
properties of a material of interest is termed as
characterization of that material. The assessment
techniques used for the study of the physical and
chemical properties of the grown single crystal help to
study the growth process and to improve the quality of
the crystal. Characterization of the crystal essentially
consists of determination of chemical composition,
structure, and study of its optical properties7. The
various functional groups present in the LHA crystal
were identified and confirmed by FT–IR study.
The spectrum was recorded in the range 4000–400 cm–
1
using Perkin Elmer (Model 66V) spectrometer by
KBr pellet technique. The UV–Vis –NIR analysis of
LHA with potassium nitrate was carried out between
200 and 2500 nm covering the entire near ultraviolet,
visible and near infrared regions, using the VARIAN
CARY
5E
model
spectrophotometer.
Gas
Chromatography-Mass Spectrometry is used to find
the existence of the reactants used in growing the
crystal. The mass spectrum for the grown crystal was
recorded in Sophisticated Analytical Instrumentation
Facility (SAIF), IIT, Madras, Chennai. Inductively
Coupled Plasma (ICP) test is to find the amount of
potassium entered into the grown crystal. The
percentage composition of potassium in L-histidine
acetate with potassium nitrate was established by
Perkin Elmer ICP technique at SAIF, IIT Madras,
Chennai.
RESULTS AND DISCUSSION
FTIR Analysis
Vibrational spectroscopy is useful in the
identification of functional groups. Molecular
vibrational information can be obtained from the
absorption or emission of infrared radiation and also
from the inelastic scattering of light. Infrared radiation,
when incident upon matter is capable of giving indirect
but very valuable information on molecular structure.
The middle IR spectrum of L-histidine acetate with
potassium nitrate is shown in Figure 2. Band
assignments have been made in analogy with various
Figure 1–Photograph of as grown crystal of LHA
with potassium nitrate
V. Renganayaki /Int.J. ChemTech Res.2011,3(3)
Figure 2– FTIR spectrum of LHA with potassium nitrate single crystal
Table 1 FTIR frequency assignment for LHA with potassium nitrate
FTIR frequency(cm-1)
3009 (s)
2624 (vs)
1634 (vs)
1591 (ms)
1568 (ms)
1497 (vs)
1342 (vs)
1414 (vs)
1314 (ms)
1270 (ms)
1250–1000 (ms)
836 (m)
776 (m)
731 (w)
656(m)
537 (m)
432 (w)
Band Assignment
NH3+ asymmetric stretching
NH3+ symmetric stretching
C=N stretching
–COO– asymmetric stretching
NH3+ asymmetric bending
N=C=N stretching
NH3+ symmetric bending
–COO– symmetric stretching / – NO3
stretching
–CH2 deformation
NH3+ rocking
–COO– vibrations
NO group bending
In plane bending of –COO–
NO group bending
N–H bending
Out of plane bending of –COO–
N–H bending
vs- very strong, s-strong , m-medium, ms–medium strong, w-weak
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V. Renganayaki /Int.J. ChemTech Res.2011,3(3)
(i) Imidazoles
Azoles generally have three or four bands in the
region 1670-1320cm-1 due to C=C and C=N stretching
vibration. The intensities of these bands depend on the
nature and position of the substituent and on the
position and nature of the ring hetero atoms 8. In the
FTIR spectrum, the band observed at 1591cm-1 is
assigned to ring C=C stretching while the band at 1634
cm-1 is assigned to C=N stretching. The band at 1464
cm-1 is due to N=C-N stretching present in the ring. 4mono substituted imidazoles show two strong bands at
670-625 cm-1 and 635-605 cm-1. They also show two
bands of medium intensity at 445-335 cm-1 and 360325 cm-1. The first of these two bands is due to out-ofplane bending of the –N-H group 9. In accordance with
the reference cited above, the band at 656 cm-1 is
assigned to the in-plane bending of the –N-H- group
and the peak at 432cm-1 is due to out of plane bending
of –N-H group. It is known that hetero aromatic
compounds show generally bands due to C=C in-plane
vibrations at about 1580, 1490, 1400 cm-1. So the
bands observed at 1498cm-1 and 1416cm-1 are
assigned to C=C in plane vibrations.
(ii) NH3+ Vibrations
Amino acids are amine derivatives of carboxylic acids
10, 11
. Amino acids may be found in three forms, viz.
free acid, salt of the acid and the amine hydro halide.
Amino acids show a broad absorption of medium
intensity in the region 3200-3000 cm-1 due to
asymmetric –NH3+ stretching vibrations. Weak bands
due to symmetric stretching vibrations of the –NH3+
group
are
observed
near
2600-2100cm-1
12
.Accordingly, the bands at 3009 cm-1 and 2624 cm-1
are assigned to asymmetric and symmetric stretching
vibrations of the –NH3+ group respectively. A fairly
strong –NH3+ deformation band is observed at 15501485 cm-1 and a weaker band at 1660-1590cm-1.
Therefore the bands observed at 1568cm-1 and
1342cm-1 are assigned asymmetric and symmetric –
NH3+ deformations respectively. The band at 1271cm-1
of medium intensity is assigned to NH 3+ rocking. In
the case of amino acid hydro halides, in addition to the
–NH3+ stretching and deformation absorption bands, a
series of weak, fairly broad bands are observed in the
region 3000-2500 cm–1 13. In the FTIR spectrum of
LHA with potassium nitrate, a definite broad band is
seen in the above said region.
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(iii) Carboxyl Bands
In the FTIR spectrum, it is seen that the broad
bands in the higher energy side is not extended above
3300cm-1, which confirms the unprotonated nature of
the carboxyl group. The broad band also suggests that
the major contributing lattice force for the ions in the
crystals is due to the hydrogen bonding between –
NH3+ sites with the acetate ion CH3COO‾. A strong
band which is due to CO2– or C-C-N group
deformation vibrations and occurs at 560-500cm-1 in
amino acids14.In the present FTIR spectrum of LHA
with potassium nitrate, the band at 537 cm-1 is due to
CO2– deformation vibrations.
(iv) C-H Vibrations
The C-H stretching vibrations of −CH2 group
produce the characteristic peak at 2941 cm-1. The peak
at 2875cm-1 is assigned to C-H stretching vibrations. In
amino acids, the –CH2 deformation occurs in the
range 1340-1315 cm-1 which is of medium intensity.
Hence the peak at 1314 cm-1 is assigned to –CH2
deformation vibrations.
(v) Carboxylate Anion
The carboxylate ion give rise to bands near 1650-1550
cm-1 due to asymmetrical stretching and a weaker band
due to symmetrical stretching near 1400 cm-1.The
intense peaks at 1591 and 1414 cm–1 are assigned to
the asymmetrical and symmetrical stretching modes of
–COO–, respectively. This observation clearly
indicates the protonation of amine nitrogen lone pair
rather than the carboxylate group by acetic acid. Due
to the in plane and out-of- plane deformation
vibrations of carboxylate ion, medium-to-strong bands
are observed in the region 780-400 cm-1 15. The band at
776 cm-1 is assigned to in-plane vibrations of C=O
bond.
(vi) Nitrate Vibrations
In organic nitrate salts, there is a sharp weak
medium band in the region 860-800 cm-1 due to
bending vibration of N-O group. The band at 836 cm-1
denotes the characteristic sharp weak to medium band.
Also a weak band in the region of 740-725 cm-1
corresponds to bending vibrations. In the spectrum, the
band at 731cm-1 represents bending vibration of N-O
group.
V. Renganayaki /Int.J. ChemTech Res.2011,3(3)
Figure 3–UV–Vis–NIR spectrum of LHA with potassium nitrate single crystal
Figure 4– Comparative UV–Vis –NIR spectrum
(1) LHA with potassium nitrate
(2) Pure LHA
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V. Renganayaki /Int.J. ChemTech Res.2011,3(3)
1459
Figure 5 – GC MSof LHA with potassium nitrate
UV–Vis–NIR transmission spectral studies
Single crystals are mainly used in optical
applications and hence the optical transmission studies
play a vital role in identifying the potential of crystal
to be a NLO material. It can be concluded that only
when the optical transmission spectrum of the crystal
has a wide range of transparency window, without any
absorption at the fundamental and second harmonic
wavelengths, preferably when the lower limit of the
transparency window is well below the 300 nm limits,
its applications to the optoelectronic field is more. The
crystal becomes a suitable NLO material. The UV-VisNIR spectrum of LHA with potassium nitrate is shown
in Figure 3. It is seen from the spectrum that the
percentage of transmission is high in the wavelength
range 600–2200 nm. Due to the effect of potassium
nitrate on the LHA, the grown crystal has become
more transparent in UV-Vis- NIR window. This is
shown in the comparison spectrum in Figure 4. The
pure LHA crystal has the percentage of transmission
high in the wavelength range 950–1600 nm and the
value is only 60%. The effect of potassium nitrate on
LHA crystal is that the optical transparency has
enhanced to 100% and there is no appreciable
absorption of light from UV region to infra red region
suggesting the adaptability of the crystal for NLO
applications.
Mass Spectroscopic studies
The mass spectrograph of grown LHA with
potassium nitrate crystal is presented in the Figure 5.
From the spectrum the presence of constituent
compounds such as acetic acid, L-histidine and
potassium nitrate are traced from the peaks formed.
The peaks are corresponding to the molecular weight
of the added samples. The main observation in GC-MS
technique is the presence of potassium nitrate in the as
grown crystal.
Elemental analysis
The primary goal of ICP is to get elements to
emit characteristic wavelength specific light which can
then be measured. The percentage of potassium in the
crystal as obtained by ICP is provided in Table 2.
V. Renganayaki /Int.J. ChemTech Res.2011,3(3)
Table 2 ICP test of LHA with potassium nitrate
Sample Id
Analyte
Sample weight
K 766.490
1460
Mean
333.5 mg/L
.02176 g
The percentage of weight has been calculated from the formula,
Wt% =
ppm (mg/l)*volume in ml* dilution factor*10-4
-----------------------------------------------------Weight of the sample (g)
Applying the formula, the amount of potassium is
found to be 38.31%. From ICP technique, it is evident
that potassium is present in the crystal and has entered
the lattice of the crystal.
Non–linear optical study
Powder SHG test offers the possibility of
assessing the non–linearity of new materials. Kurtz
and Perry proposed a powder SHG method for
comprehensive analysis of the second order non–
linearity. The SHG of the LHA with potassium nitrate
crystal has been confirmed by Kurtz SHG test. The
crystal was illuminated by spectra physics Quanta ray
Nd:YAG laser using the first harmonic output of 1064
nm, with a pulse width of 8 ns. The emission of green
radiation from the crystal confirms the second
harmonic generation in the crystal.
CONCLUSION
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