Infrared and Raman spectroscopic studies ofl-valinel-valiniumperchlorate monohydrate
S. Pandiarajana,∗, M. Umadevib, R.K. Rajaramc, V. Ramakrishnana,1
a Laser Laboratory, Department of Microprocessor and Computer, School of Physics,Madurai Kamaraj University, Madurai 625021, India
b Department of Physics, Mother Teresa Women’s University, Kodaikanal 624102, Indiac Department of Physics, School of Physics, Madurai Kamaraj University, Madurai 625021, India
Received 1 January 2005; received in revised form 12 February 2005; accepted 14 February 2005
ound to be lowered corresponding to ClO2 group. The hydrogen bonds that prevail between amino acid residues, perchlorate anion aolecule influence the wave numbers of several stretching and deformation modes to deviate from the expected values.2005 Elsevier B.V. All rights reserved.
eywords: l-Valinel-valinium perchlorate monohydrate; Factor group analysis; FT-Raman spectrum; FT-IR spectrum; Hydrogen bonding; Group fr
. Introduction
Amino acids are popularly referred to as building blocksf protein. Proteins form the structural basis of chromo-omes through which our genetic information is passedrom parent to offspring. Valine (�-aminoisovalerate) isn essential amino acid and can be derived from ala-ine by the introduction of two methyl groups in placef two H-atoms of the methyl group present on�-carbontom. Valine, an essential amino acid, is hydrophobic, and
s usually found in the interior of proteins. Valine dif-ers from the threonine by replacement of the hydroxylroup with a methyl substituent. Valine is often referred tos one of the amino acids with hydrocarbon side chains,r as a branched chain amino acid. The branched chainmino acids are needed for the maintenance of muscle tis-ue and to preserve muscle stores of glycogen (a storage
∗ Corresponding author. Present address: Department of Physics, Devangarts College, Aruppukottai 626 101, India. Tel.: +91 4566223741.
form of carbohydrate that can be converted into ene[1].
When amino acids form salts with inorganic acids, tundergo conformational changes. Since the amino–inoracid complexes have small molecular structures, IR andman spectroscopic methods can be employed as a tool toout the interesting features, which are useful in understantheir various functional groups.
IR and Raman spectral studies have been made bishnan et al.[2] for few amino acids includingl-valine inzwitterionic form. Rajkumar and Ramakrishnan[3] have alsomade a comparative study ofl-valine nitrate andl-leucine ni-trate employing vibrational spectroscopy. SER spectralyses[4] of 19 l-amino acids (includingl-valine) adsorbeon electrochemically roughened silver surface have shstrong interaction with the silver surface through theirprotonated carboxylate group. In the case of two sucontaining amino acids (cysteine and methionine), the satom interacts with the surface. However, in all the studieamino acids, the protonated amino group does not showinteraction and appears relatively far from the silver surf
Co-corresponding author. Raman scattering study of synthetic polyl-valine[5] is also
S. Pandiarajan et al. / Spectrochimica Acta Part A 62 (2005) 630–636 631
very useful for identifying the absorption wave numbers ofside chain because of their existence even during polymer-ization. The vibrational spectral study of tril-valine selenate[6] enabled to define that crystal structure of the compound isformed by a selenate anion,l-valinium cations andl-valinezwitterion (in 1:2:1) interconnected by a system of hydro-gen bonds. In addition to this, the authors have noticed thelow temperature structural phase transition by the methodsof FT-IR spectroscopy and DSC measurements. IR and Ra-man spectral measurements were made for few hydrophobicamino acid chelates containingl-valine andl-norvaline[7].Inelastic Incoherent Neutron Scattering studies along withinfrared and Raman spectral studies onl- anddl-valine[8]is also immensely helpful in understanding vibrations below1800 cm−1. In the present investigation, the vibrational spec-troscopic study on crystals ofl-valinel-valinium perchloratemonohydrate has been undertaken[9].
−·H2O] were obtained bycrystallization at room temperature from an aqueous solutioncontainingl-valine and perchloric acid in a stoichiometricratio of 2:1 by the slow evaporation process. Needle shaped,t wereo
R)s . Thes ixedw
FRA1 AGl mWw er ther ed usingts froma sup-p cedb
3
emc -eT thea culei iona tal,o kingt lysis
Fig. 1. Structural formula ofl-valinel-valinium perchlorate monohydrate.
[11] of the title compound gives rise to 279 genuine normalmodes of vibration distributed asΓ = 140A + 139B. Theseare presented inTable 1. Both the A and B species are IRand Raman active, simultaneously[12].
The structural formula of thel-valine l-valinium per-chlorate monohydrate is depicted inFig. 1. The IR and Ra-man spectra recorded at room temperature are presented inFigs. 2 and 3, respectively. The IR and Raman data alongwith their proposed assignments are listed inTable 2. Invaline, the side chain contains isopropyl or gem-dimethylgroup being attached to the�-carbon atom. In the presentinvestigation, few functional groups associated with theamino acid residues have been discussed separately. They are–[NH3]+, –CH3, C O, COO−, C OH, O H, C H, C N,C (CH3)2, O C O, C C O, C C, and C C C C. The
e.
ransparent and colorless crystals of the title compoundbtained in fortnight duration.
A Bruker IFS 66V Fourier Transform Infrared (FT-Ipectrometer was employed to record the IR spectrumample for this measurement was finely ground and mith KBr.Raman spectral measurements were made with an
06 Raman module. An air-cooled diode pumped Nd:Yaser, operated at 1064 nm and a power output of 200as used as source. The spectrum was recorded ov
ange 3500–50 cm−1. For confirming the reliability of thata, Raman spectral measurements were also made
he facility developed in our laboratory[10]. The excitationource in the Raman measurement was 488 nm radiationSpectra Physics model 2020-04S argon-ion laser. To
ress the Rayleigh line, a suitable notch filter was plaefore the monochromator.
. Results and discussion
The title compoundl-valine l-valinium perchloratonohydrate, [(C5H11NO2)·(C5H12NO2)+·ClO4
−·H2O],rystallizes in the space groupP21 with monoclinic geomtry. The crystal has two formula units per unit cell[9].he X-ray investigation of the title crystal reveals thatsymmetric part of the unit cell contains a valine mole
n zwitterionic form, a valinium cation, a perchlorate annd a water molecule of crystallization. In the title crysne proton is shared between two valine groups ma
he total entity monoprotonated. The factor group ana
632 S. Pandiarajan et al. / Spectrochimica Acta Part A 62 (2005) 630–636
Table 1Factor group analysis ofl-valinel-valinium perchlorate monohydrate [(C5H11NO2)·(C5H12NO2)+·ClO4
−·H2O]
Mode and degrees of freedomfor each species
Molecular symmetry Site symmetry species C1 Factor group species C2
Space group:P21 = C22; Z = 2; ZB = 2
(C5H11NO2)·(C5H12NO2)+ Vibrational, 234 A 117 A, 117 B
Γ(C5H11NO2)·(C5H12NO2)+ = 117AIR,R + 117BIR,R
ClO4− Td C1 C2
Vibrational (intramolecular) 18 A1, E, 2F2 A 9A, 9BTranslational 6 F2 A 3A, 3BLibration 6 F1 A 3A, 3B
Γ intClO4
− + Γ transClO4
− + Γ rotClO4
− = 15AIR,R + 15BIR,R
H2O C2v C1 C2
Vibrational 6 2A1, B2 A 3A, 3B
Translational 6 A1, B1, B2 A 3A, 3BRotational 6 A2, B1, B2 A 3A, 3B
Γ intH2O + Γ trans
H2O + Γ rotH2O = 9AIR,R + 9BIR,R; Γacoustic= A + 2B; Γ total
crystal = Γ(C5H11NO2).(C5H12NO2)+ + Γ intClO4
− + Γ transClO4
− + Γ rotClO4
− + Γ intH2O + Γ trans
H2O + Γ rotH2O =
141A+ 141B;Γ intcrystal = Γ total
crystal− Γacoustic= 140AIR,R + 139BIR,R.
vibrational bands of these groups are expected to changein their intensity and position due to their crystalline en-vironment and the nature of the bonding. Removal of de-generacy is also expected in the case of perchlorate an-ion owing to positional disorder of some of the atoms, andthen to possible reduction in symmetry in the crystallinestate.
4. Amino acid residues
4.1. Vibrations of carboxyl group
The backbone geometries such as CO bond distances(1.225 and 1.268A) and O C C angles (116.7 and 119.3◦) ofone amino acid residue suggest the presence of valine havingdeprotonated carboxylate group. However, these geometriesfor another residue [CO 1.197 and 1.305A, and O C C 112and 122◦] indicate the presence of valinium cation contain-ing protonated carboxyl group[9]. The carbonyl-stretchingmode generally lies within the range 1755–1730 cm−1 forsalts of�-amino acids. In the present investigation, a strongpeak is observed at 1726 cm−1 in the infrared spectrum. Thisband shows the presence of CO bond in the amino acid.Also a shoulder IR band was identified∼1707 cm−1, andi anda s ares d ini gena
wT yn[ and
1574 cm−1 have been assigned to asymmetric stretching vi-bration of the carboxylate ion. These two bands are due to de-viation of resonant C O bond distances. Symmetric COO−stretching vibrations fall in the CH3 deformation region. Soit cannot be assigned unambiguosly and consequently, reporton these are not always consistent. However, in the presentcase, the medium IR peak that arises at 1399 cm−1 revealsthe COO− symmetric stretch. These are the characteristic ab-sorption bands of an ionized carboxylate group. These wavenumbers of the stretching mode have shifted towards thelower region because of the involvement of COO− group inthe hydrogen bonding. Also the characteristic wave numbersfor the rocking, wagging and scissoring modes are expectedat 502, 577 and 665 cm−1, respectively[13], and they havebeen identified.
Two bands arising from CO stretching and OH bend-ing appear in the spectra of carboxylic acids near 1320–1210and 1440–1395 cm−1, respectively. Both these bands in-volve some interaction between CO stretching and in-planeC O H deformation[14,15]. In the present study, the bandsat 1283 and 1429 cm−1 in both spectra are assigned to thesaid combination mode. These values agree well with the as-signments of Krishnan et al.[2] for amino acids containingCOOH group. A broad medium intensity band expected at960–875 cm−1 is due to the OH out-of-plane deformationm ei them ase,a eRp um-b ongO andaa
t is due to the interaction between the carboxyl groupmino group of valinium residues. These wave numberomewhat lower, since the carbonyl oxygen is involve
ntermolecular hydrogen bonding with one of the hydrotoms of the−[NH3]+ moiety.
Carboxylate group has two strongly coupled CO bondsith bond strengths intermediate between CO and C O.his deprotonated carboxylate group COO− absorbs stronglear 1600–1570 cm−1 and weakly near 1415–1400 cm−1
13]. In the present case, the medium IR bands at 1589
ode[13]. Bands involving X H bending usually increasn wave numbers on formation of hydrogen bonding, and
agnitude of shift is notably smaller. In the present cshoulder band at 970 cm−1 in IR and a medium intensaman band at 998 cm−1 are attributed to the OH out-of-lane deformation mode. The up shifting of the wave ner is due to involvement of the carboxyl group in a str− H · · · O hydrogen bond. In amino acids a strong IR b
t 1220–1190 cm−1 arises from CC( O) O stretching[14],nd it has been identified at 1207 cm−1.
S. Pandiarajan et al. / Spectrochimica Acta Part A 62 (2005) 630–636 633
Table 2Observed wave numbers (ν) for the vibrational spectra ofl-valinel-valiniumperchlorate monohydrate
Infraredν
(cm−1)Ramanν(cm−1)
Assignment
3438 sh 3281 w OH str (H2O)3083 s br 3078 w –[NH3]+ asym str3014 s br 3020 w –[NH3]+ sym str; (C)O H str2988 s br 2977 v s CH3 asym str
2935 v s CH3 asym str2900 sh 2902 s CH3 sym str2866 sh 2875 s CH3 sym str2633–1927 Overtone and combination
bands1726 v s
}C=O str
1707 sh 1707 w1661 sh 1670 w –[NH3]+ asym def
1625 w H2O sym def1611 s 1601 w –[NH3]+ sym def1589 m
}COO− asym str
1574 m1509 s C N asym str1480 v s 1470 s
}CH3 asym def
1452 sh 1438 s1429 m C O str + O H i.p. def1399 m COO− sym str; CH3 sym def1379 m 1383 w CH3 sym def1338 s 1343 m C� H def1320 sh 1331 m C� H def1283 s 1289 w CO str + O H i.p. def1207 vs C C(=O) O str1144 vs 1134 m ClO2* asym str; –[NH3]+ rock
–C�–(CH3)2 asym str; CH3rock + C–C str of isopropylgroup
1108 sh 1108 br ClO2 asym str1093 br vs ClO2 sym str; C–C–N asym str
1063 m C-N sym str1026 m –C�–(CH3)2 sym str970 sh 998 m O–H o.p. def939 m 935 v v s ClO2* sym str919 sh CH3 rock + C–C str of iso-
propyl group868 s 875 m C–C–N sym str810 s 818 s C–C str of isopropyl group781 m
}C–C skeletal stretch768 m
754 m 750 m730 m 736 s H2O rock;635 sh ClO2 sym def; COO− sci627 v s 627 s ClO2 rock572 s ClO2 rock.; COO− wag.; H2O
wag.537 m C–C=O i.p.def.
515 w COO− rock.481 m ClO2
* sym def; –[NH3]+ tor457 m 460 s ClO4− tor422 w 406 m C–C–C–C in phase def
The aliphatic monocarboxylic acids attached to�-carbonatom usually exhibit three strong bands nearly 655, 635 and620 cm−1, and they are not found to be well resolved be-tween 655 and 610 cm−1, owing to the in-plane vibration ofthe O C O group[16]. These wave numbers of the in-planedeformation mode are not identified distinctly in both thespectra, since the degenerate bending modes of the COO−ion will also lie in the same region. A strong band that arisesbetween 555 and 520 cm−1 is attributed to the in-plane vibra-tion of the C C O group, and it is identified at 537 cm−1 as amedium band in the IR spectrum. These discussions confirmthat one amino acid residue is in the zwitterionic form whilethe other is in the cationic form.
4.2. Vibrations of –[NH3]+ group
It is known that the –[NH3]+ group exhibits pyramidalstructure in its free state. Therefore, the –[NH3]+ assumes C3v
symmetry whose normal modes of vibrations areν1 (A1), ν2(A1), ν3 (E) andν4 (E). All of them are both IR and Ramanactive with the asymmetric stretching and bending modesbeing doubly degenerate[17].
Aliphatic primary amines salts are characterized bystrong absorption between 3200 and 2800 cm−1 due to theasymmetric and symmetric –[NH3]+ stretching. Also the–[NH ]+ asymmetric and symmetric deformation wave num-b1 gp erf eRte e– trics di anc
eara s as as nda or-mt .Ro d tor inoaar nd-i etrics -d
rdi-n andp dro-g ave
3ers are expected to fall in the regions 1660–1610 cm−1 and550–1485 cm−1, respectively[14]. For amino acids havinrotonated amino group, the NH stretching wave numb
or the –[NH3]+ group (near 2970 cm−1) is obscured in thaman by more intense CH stretching vibrations[13]. In
he present study, the IR band at 3083 cm−1 in broad strongnvelop in the 3000–3100 cm−1 region is assigned to th[NH3]+ asymmetric stretching vibration. The symmetretching mode associated with –[NH3]+ group is observe
n IR at 3014 cm−1 in the same envelop, while its Ramounterpart appears as a weak band at 3020 cm−1.
The asymmetric deformation band will normally apps a weak band. In the IR spectrum, this mode appearhoulder at 1661 cm−1, while the corresponding Raman bappears at 1670 cm−1 as a weak one. The symmetric defation mode produces a strong band at 1611 cm−1 in IR, and
he Raman band appears at 1601 cm−1 with a weak intensityegarding the bending vibrations of –[NH3]+ moiety, it isf interest to look for the bands which could be ascribeocking and torsional modes. Correlations with other amcids allow us to assign a strong IR band at 1144 cm−1 andmedium intense Raman band at 1134 cm−1 to –[NH3]+
ocking vibration. For molecules involved in hydrogen bong, rocking modes are most sensitive than the asymmtretching mode[18]. The –[NH3]+ torsional vibration is inicated by the band at 481 cm−1 in the IR spectrum.
In the –[NH3]+ group each of the hydrogen atoms cooate with O atoms of the carboxyl group of amino aciderchlorate group through hydrogen bonding. These hyen bonds are responsible for the lowering of stretching w
634 S. Pandiarajan et al. / Spectrochimica Acta Part A 62 (2005) 630–636
numbers and the shift of bending wave numbers to higher val-ues than the expected range. This is due to weakening of NHbonds.
4.3. Vibrations of methyl group
The side chain of valine has two methyl groups attachedto the C� atom. The CH3 stretching and deformation vibra-tions are more or less localized, and give rise to good groupfrequencies. The positions of the CH stretching vibrationsare among the most stable in the spectrum. Since theCH3group also exhibit C3v symmetry, the vibrations of CH3group also correspond to –[NH3]+ vibrations.
In aliphatic compounds, the asymmetric and symmetricCH3 stretching vibrations absorb near 2960 and 2870 cm−1,
respectively. Additional CH3 bands are also seen in somecompounds near 2934 and 2912 cm−1 [19]. These predic-tions hold good in the present study. The strong broad bandat 2988 cm−1 in IR is attributed to asymmetricCH3 stretch-ing vibration, while its Raman counterpart splits into two dis-tinct bands at 2977 and 2935 cm−1. Similarly, correspondingto symmetric stretching mode two strong bands are observedat 2902 and 2875 cm−1 in Raman spectrum, and the corre-sponding IR bands appear as shoulder peaks at 2900 and2866 cm−1. Splitting of these stretching modes are due topresence of two independentCH groups in the amino acidr s arerv
the band that has to appear at 1124 cm−1 corresponding tothe asymmetric stretching mode ofC� (CH3)2 group ismasked in IR spectrum by the strong broad band of ClO2asymmetric stretching mode. These assignments agree withthe vibrational study of polyl-valine [5]. It is known thatthe bands that arise at 1170, 1140 and 920 cm−1 are dueto mixing of C C stretching modes in the isopropyl groupwith the methyl rocking mode[3]. In the present case thesemixing modes are identified due to the bands at 1144 and919 cm−1 in IR spectrum. The band at 1170 cm−1 is maskedby the band due to –[NH3]+ rocking mode. These assign-ments agree well with the bands obtained forl-valine nitratecrystal[3].
4.4. Vibrations of C C N group
The absorption bands corresponding to CC N group vi-brations have been identified. These bands arise from CNand C C stretching vibrations and are observed in the wavenumber range 1150–850 cm−1 [19,20]. The strong IR bandat 868 cm−1 and medium intense Raman band at 875 cm−1
are ascribed to the CC N symmetric stretching vibrations.The broad strong band at 1093 cm−1 is attributed to theC C N asymmetric stretching vibration. The medium inten-sity Raman peak at 1063 cm−1 is assigned to CN symmetrics g IRc de-g gen-em7 ei havea
4
ionsi vingz dt log-i ules,w hanN
sa em ndedt g2 iblef
epa-r ) hy-d haino ren as2 ely.
3esidues. As expected, the symmetric stretching bandelatively less intense than the asymmetricCH3 stretchingibrations.
In aliphatic compounds containing only oneCH3 group,he asymmetric and symmetric deformation modes abearly 1465 and 1378 cm−1, respectively. The configuration
hat have two methyl groups attached to the same catom, as in isopropyl or gem-dimethyl group, exhibit a bt 1465 cm−1. In the present study, the IR bands at 1480 c−1
strong) and 1452 cm−1 (shoulder) and their correspondiaman bands at 1470 and 1438 cm−1 are attributed to thsymmetric deformation mode of isopropyl group. Appnce of these bands is due to presence of two indepeCH3 groups in the amino acid residues in slightly diffnt environments. The symmetric deformation mode ofropyl group normally exhibits relatively two weak band385 and 1368 cm−1. They are due to the interaction betweydrogen atoms in two different methyl groups depenpon whether they are moving either closer or away fach other’s way[19]. In the IR spectrum these bands
dentified at 1399 and 1379 cm−1. The weak bands resultinrom methyl rocking vibrations in isopropyl group appn the range 922–919 cm−1 [14]. The band for rocking vration of isopropyl group is identified at 919 cm−1 (shoul-er) in the IR spectrum. The medium intensity peaks340 cm−1 in both the spectra are ascribed to the defor
ion of the C� H group while the peak at 1320 cm−1 (shoul-er) in IR and 1331 cm−1 in Raman are assigned to C� Hroup. IR line at 1026 cm−1 is a consequence of the symmic stretching motion of the C� (CH3)2 group. However
t
tretching vibrations. However the much-expected stronounterpart is not found distinctly as it overlaps with theenerate stretching mode of the anion due to lifting of deracy. The strong peak at 1509 cm−1 is due to C N antisym-etric stretching vibration. The wave numbers at∼810 and68 cm−1 are attributed to CC stretching vibrations. Th
n-phase and out-of-phase vibrations of skeletal carbonlso been identified.
.5. Hydrogen bonding
Hydrogen bonds are very important dipole interactn stabilizing the protein structures. In amino acids hawitterionic form, the –[NH3]+ moiety is a good donor anhe carboxylate group is an excellent acceptor. In biocal crystals, hydrogen bonds link the adjacent molechere O–H· · ·O hydrogen bonds are relatively stronger t–H· · ·O bonds.Emsley et al. [21] relate the O· · ·O bond distance
nd their strengths. In thel-valine l-valinium perchloratonohydrate crystal, two amino acid molecules are bo
hrough O–H· · ·O hydrogen bonds with O· · ·O distance bein.562A, which is a strong hydrogen bond. This is respons
or the strong broad IR band centered around 3020 cm−1.In the present crystal two amino acid molecules in s
ate cases are involved in straight (S2) and zigzag (Z1rogen bonded sequences, giving rise to infinitely long cf N–H· · ·O hydrogen bonds[9]. The above said bonds aormal hydrogen bonds since the N· · ·O distances remain.727 and 2.886A in the former and latter cases, respectiv
S. Pandiarajan et al. / Spectrochimica Acta Part A 62 (2005) 630–636 635
These bonds also contribute to the broadness of strong bandcentered∼3020 cm−1 in IR.
The three dimensional network of hydrogen bonds thatprevail in the crystal structure influence the various vibra-tional modes of –[NH3]+, COO−, COOH, and ClO4− groups.In the overall vibrational band assignments, the lowering ofstretching wave numbers and the shift of deformation modesto higher wave numbers from the free ion values are due tothe N–H· · ·O and O–H· · ·O hydrogen bonds.
4.6. Vibrations of ClO4− anion
Several investigators have studied Raman and IR spectraof perchlorate ion. The ClO4− ion adopts a regular tetrahe-dral structure and has nine different vibrational degrees offreedom [Γ = A1 + E + 2F2]. The symmetrical stretching andbending modes (A1 and E) are only Raman active while theasymmetric stretching and bending modes (F2) are both IRand Raman active[22]. These normal modes of vibrationsare expected to occur at 928 cm−1 (νsym), 459 cm−1 (δsym),1119 cm−1 (νasym) and 625 cm−1 (δasym), respectively.
X-ray study of the crystal shows that out of the four Oatoms of the perchlorate, two are in positional disorder. Suchdisorder is possibly due to the onset of rotational disorder ofthe perchlorate ion. This disorder also brings about consider-able variations in the ClO bond distances and the tetrahedrals rso
in Raman. The shoulder band at 635 cm−1 in IR identifies thesymmetric deformation. Also the symmetric stretching modegives rise to a strong band at 935 cm−1 in Raman and the cor-responding IR band is obtained at 939 cm−1 with mediumintensity. Moreover, the symmetric deformation mode of co-ordinated ClO2 group is reflected in both spectra by a bandnearly at 481 cm−1. Also the bands at 627 and 572 cm−1 havebeen identified to two rocking modes. The ClO4
− torsionmode appears as a strong band at 460 cm−1 in the Ramanand 457 cm−1 in IR with medium intensity. The activationof this IR inactive mode may be due to crystalline environ-ment. These assignments are in close agreement with thatof d-phenylglycinium perchlorate[18] andl-phenylalaninel-phenylalaninium perchlorate[24] crystals.
4.7. Vibrations of water molecule
The water molecule has C2v symmetry with normal modes2A1 (ν1 andν2) and B2 (ν3) that are both infrared and Ramanactive. In the crystalline state,ν1, ν2, andν3 modes are ex-pected to occur at about 3400, 1620 and 3220 cm−1, respec-tively. In the present crystal, a shoulder band at 3438 cm−1
in the IR spectrum is attributed to the symmetric stretchingmodeν1 of the water molecule. The corresponding Ramanband is so weak that it is hardly noticeable. The intense broadband due to NH and O H stretching modes masks the bandd ers ode( andba re-c( thef en duet ule.T beeni
5
l iousc . Theo culesi nicf estst uceda aterm enti orkb culel tionm
ymmetry of the molecule[9]. The two O atoms with minoite-occupation factor are removed in theFig. 1for the clarityf the picture.
If the perchlorate group occupies a position in the cal lattice where two of its oxygen atoms are involvedartial covalent bond formation to a cation, or, more pbly, to two separate cations, the symmetry of the percate group is lowered to C2v [22]. In the present investigion two oxygen atoms of the perchlorate ion are disordelso, the anion acts as a bridge between amino acidater molecules through hydrogen bonding, where thehlorate oxygen atoms are involved as acceptors. A
ook at the hydrogen bonding pattern reveals that theon is acting as a bidendate ligand through two of their oen atoms, and it seems that the symmetry of the perate group has been lowered corresponding to ClO2 group.his leads to the lifting of degeneracy of E and F mof perchlorate group. In this circumstance the vibratioodes are redistributed asΓ = 4A1 + A2 + 2B1 + 2B2. The
asym species (F2) splits into three occurring at 1038 cm−1
A1), 1125 cm−1 (B1) and 1170 cm−1 (B2) while theνsympecies (A1) generally occurs at 928 cm−1. TheνasymspeciesF2) also has its degeneracy removed, and the waveers are expected to occur 635 (A1), 617 (B1) and 623 (B2),hile theδsym species (E) breaks up into two bands ne60 cm−1(A1, A2). The A2 species is only Raman active a
he remaining other species are both IR and Raman a22,23].
The asymmetric stretching mode (F2) splits into three1108, 1144, 1093 cm−1) in IR and two (1108, 1134 cm−1)
ue to asymmetric stretching mode (ν3) that lies in the samegion. The very weak band around 1625 cm−1 in Ramanpectrum is assigned to the symmetric deformation mν2) of the water molecule. The shift in the stretchingending wave numbers indicates the presence of N–H· · ·OWnd OW–H· · ·O hydrogen bonds, which account for appiable distortion in the water molecule. The HO H angle98◦) of the water molecule, which is much deviated fromree molecule value 120◦, also confirms this. In the low wavumber region, lattice water exhibits vibrational modes
o restricted rotations and oscillations of the water moleche bands due to the rocking and wagging modes have
dentified.
. Conclusion
Infrared and Raman spectra were recorded forl-valine-valinium perchlorate monohydrate crystals and varharacteristic group frequencies have been assignedbserved bands show that one of the amino acid mole
s in the zwitterionic form and the other is in the catioorm. The removal of degeneracy of perchlorate ion sugghat the symmetry of the perchlorate ion has been rednd the corresponding bands are identified. The wolecule is considerably distorted due to its involvem
n the hydrogen bonding. The hydrogen-bonding netwetween amino acid, perchlorate anion and water mole
eads to shifting of several stretching and deformaodes.
636 S. Pandiarajan et al. / Spectrochimica Acta Part A 62 (2005) 630–636
Acknowledgements
The authors are grateful to DST, Government of India,New Delhi, for establishing the laser laboratory, and also tothe UGC, Government of India, New Delhi, for having rec-ognized our group (V.R.) activities as the thrust area of re-search in DRS-phase II and COSIST programs in the Schoolof Physics, and also for having provided assistance to laserlaboratory. One of the authors (S.Pandiarajan) is indebted tothe UGC, Government of India, New Delhi for the award ofteacher fellowship under the Faculty Improvement Program,and the Management and the Principal of Devanga Arts Col-lege, Aruppukottai, India, for their assistance and support.The financial assistance received from DST, Government ofIndia, New Delhi to one of us (V.R.) in the form of a researchproject is acknowledged.
References
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