organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 71| Part 6| June 2015| Pages o376-o377

Crystal structure of 2,4-di­amino-7-(hy­droxy­meth­yl)pteridin-1-ium nitrate

aDepartment of Chemistry, Government Arts College (Autonomous), Thanthonimalai, Karur 639 005, Tamil Nadu, India, and bSchool of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
*Correspondence e-mail: manavaibala@gmail.com

Edited by H. Stoeckli-Evans, University of Neuchâtel, Switzerland (Received 25 April 2015; accepted 28 April 2015; online 7 May 2015)

In the crystal of the title mol­ecular salt, C7H9N6O+·NO3, the cations and anions are linked via N—H⋯O and O—H⋯O hydrogen bonds, forming sheets parallel to (100). Within the sheets there are numerous hydrogen-bonding ring motifs.

1. Related literature

For background to and the biological activity of pteridine derivatives, see: Benkovic Annu (1980[Benkovic, S. J. (1980). Annu. Rev. Biochem. 49, 227-251.]); Blakeley (1969[Blakeley, L. (1969). In The Biochemistry of Folic Acid and Related Pteridines. New York: Elsevier.]); Van Beelen et al. (1984[Van Beelen, P., Van Neck, J. W., De Cock, R. M., Vogels, G. D., Guijt, W. & Haasnoot, C. A. G. (1984). Biochemistry, 23, 4448-4454.]); Dolphin (1980[Dolphin, D. (1980). Adv. Chem. Ser. 191, 65-87.]); Pfleiderer (1982[Pfleiderer, W. (1982). In Biochemical and Clinical Aspects of Pteridines, edited by H. Wachter, H. C. Curtius & W. Pfleiderer. Berlin: DeGruyter.]); Blakely & Cocco (1985[Blakely, R. L. & Cocco, L. (1985). Biochemistry, 24, 4702-4772.]); Pfleiderer & Taylor (1964[Pfleiderer, W. & Taylor, E. (1964). Editors. In Pteridine Chemistry. Oxford: Pergamon.]); Müller et al. (1991[Müller, M. M., Curtius, H. C., Herold, M. & Huber, C. H. (1991). Clin. Chim. Acta, 201, 1-16.]); Weinstock et al. (1968[Weinstock, J., Wilson, J. W., Wiebelhaus, V. D., Maass, A. R., Brennan, F. T. & Sosnowski, G. (1968). J. Med. Chem. 11, 573-579.]). For related structures, see: Kuyper (1990[Kuyper, L. F. (1990). Crystallographic and Modeling Methods in Molecular Designs, edited by C. E. Bugg & S. E. Ealick, pp. 56-79. New York: Springer Verlag.]); Schwalbe & Williams (1986[Schwalbe, C. H. & Williams, G. J. B. (1986). Acta Cryst. C42, 1254-1257.]); Robertson et al. (1998[Robertson, K. N., Bakshi, P. K., Lantos, S. D., Cameron, T. S. & Knop, O. (1998). Can. J. Chem. 76, 583-611.]). For hydrogen-bond motifs, see: Etter (1990[Etter, M. C. (1990). Acc. Chem. Res. 23, 120-126.]); Bernstein et al. (1995[Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555-1573.]); Allen et al. (1998[Allen, F. H., Shields, G. P., Taylor, R., Allen, F. H., Raithby, P. R., Shields, G. P. & Taylor, R. (1998). Chem. Commun. pp. 1043-1044.]).

[Scheme 1]

2. Experimental

2.1. Crystal data

  • C7H9N6O+·NO3

  • Mr = 255.21

  • Orthorhombic, C m c 21

  • a = 6.4060 (17) Å

  • b = 14.960 (6) Å

  • c = 10.867 (3) Å

  • V = 1041.4 (6) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.14 mm−1

  • T = 294 K

  • 0.27 × 0.10 × 0.07 mm

2.2. Data collection

  • Bruker SMART APEXII Duo CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Bruker, 2009[Bruker (2009). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.964, Tmax = 0.991

  • 2866 measured reflections

  • 862 independent reflections

  • 720 reflections with I > 2σ(I)

  • Rint = 0.028

2.3. Refinement

  • R[F2 > 2σ(F2)] = 0.030

  • wR(F2) = 0.074

  • S = 1.03

  • 862 reflections

  • 127 parameters

  • 1 restraint

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.09 e Å−3

  • Δρmin = −0.16 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N3—H1N3⋯O2 1.03 (5) 1.82 (5) 2.831 (5) 167 (4)
N6—H2N6⋯O4 0.98 (3) 2.06 (3) 3.019 (6) 167 (3)
O1—H1O1⋯O2i 0.95 (6) 1.93 (6) 2.846 (4) 163 (6)
N5—H1N5⋯O3ii 0.92 (4) 2.09 (4) 2.983 (6) 164 (4)
N5—H2N5⋯O1i 0.91 (5) 2.15 (5) 2.913 (5) 141 (4)
N6—H1N6⋯O3iii 0.78 (5) 2.35 (4) 3.015 (5) 145 (5)
N6—H1N6⋯O4iii 0.78 (5) 2.44 (5) 3.190 (6) 162 (5)
Symmetry codes: (i) [-x+1, -y+1, z+{\script{1\over 2}}]; (ii) x, y, z+1; (iii) [-x+1, -y, z+{\script{1\over 2}}].

Data collection: APEX2 (Bruker, 2009[Bruker (2009). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2009[Bruker (2009). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).

Supporting information


Structural commentary top

Pteridine derivatives are found as the core structure of folic acid flavin adenine dinucleotide (FAD) and function as cofactors for enzymes involved in hy­droxy­lation (Benkovic & Annu,1980) and methyl transfer (Blakeley, 1969; Van Beelen et al., 1984), as redox mediators (Dolphin, 1980) and as pigments for eyes and wings in certain insects (Pfleiderer, 1982). Variation of the substituents on the pteridine core of folates has provided synthetic anti­cancer drugs (Blakely & Cocco, 1985; Pfleiderer & Taylor, 1964). Pterdines are metabolites formed by a bicyclic pyrimidine-pyrazine moiety that occurs in a wide range of living systems and contributes in relevant biological functions (Muller et al., 1991). Pteridine derivatives have good diuretic activity and are also used as simple models for therapeutically valuable anti­folate drugs (Weinstock et al., 1968). In order to study potential hydrogen bonding inter­actions, the title compound was synthesized and we report herein on its crystal structure.

The title molecular salt, Fig. 1, consists of a 2,4-di­amino-7-(hy­droxy­methyl)­pteridinum cation and a nitrate anion. During the synthesis of the molecular salt a proton was transferred from the hydroxyl group of nitric acid to atom N3 of the pteridine ring. The pteridine ring system (C1—C7/N1—N6/O1) is planar with a maximum deviation of 0.001 (1) Å for all the non H atoms. The bond lengths and angles are close to those found for similar compounds, viz. 2,4-di­amino-6,7-di­methyl­pteridine hydro­chloride monohydrate (Schwalbe & Williams, 1986) and triamterenium tetra­phenyl­borate aceto­nitrile solvate (Robertson et al., 1998).

In the crystal, Fig. 2, the protonated N3 atom and the protonated 2-amino group (N6) are hydrogen-bonded to the nitrate O atoms (O2 and O4) via a pair of N3—H1N3···O2 and N6—H2N6···O4 hydrogen bonds, forming an R22(8) ring motif (Bernstein et al., 1995). This type of inter­action is similar to the carboxyl­ate-trimethoprim inter­action observed in the trimethoprim cation-di­hydro­folate redu­ctase complex (Kuyper, 1990) and to the cyclic hydrogen bonded motif observed in many organic crystal structures (Allen et al., 1998). An R12(4) ring motif indicates a bifurcated hydrogen bond formed by N6–H1N6 to the two acceptors (O3 and O4). The 4-amino group and the hydroxyl group form hydrogen bonds with the O atoms of the nitrate ion leading to an R33(8) ring. The three center and bifurcated hydrogen bonds and fork like inter­action form an R44(12) ring. Two R33(8) motifs and an R22(8) ring motif generate a new R32(18) ring motif. The above inter­actions lead to the formation a two dimensional network parallel to the bc plane (Table 1 and Fig. 2).

Synthesis and crystallization top

A few drops of nitric acid were added to a hot methanol solution (20 ml) of 2,4-di­amino-6-(hy­droxy­methyl)­pteridine (43 mg, Aldrich) which had been warmed over a heating magnetic stirrer hotplate for a few minutes. The resulting solution was allowed to cool slowly at room temperature and crystals of the title molecular salt appeared after a few days.

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 2. The O– and N-bound H atoms were located in a difference Fourier map and freely refined (O–H = 0.94 (6) Å and N–H = 0.78 (5)– 1.03 (5) Å). The C-bound H atoms were positioned geometrically (C–H = 0.93–0.97 Å) and refined using a riding model with Uiso(H) = 1.2 Ueq(C).

Related literature top

For background to and the biological activity of pteridine derivatives, see: Benkovic Annu (1980); Blakeley (1969); Van Beelen et al. (1984); Dolphin (1980); Pfleiderer (1982); Blakely & Cocco (1985); Pfleiderer & Taylor (1964); Müller et al. (1991); Weinstock et al. (1968). For related structures, see: Kuyper (1990); Schwalbe & Williams (1986); Robertson et al. (1998). For hydrogen-bond motifs, see: Etter (1990); Bernstein et al. (1995); Allen et al. (1998).

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title salt, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The N-H···O hydrogen bonds are shown as dashed lines (see Table 1 for details).
[Figure 2] Fig. 2. A view along the a axis of the crystal packing of the title molecular salt. The N-H···O hydrogen bonds are shown as dashed lines (see Table 1 for details).
2,4-Diamino-7-(hydroxymethyl)pteridin-1-ium nitrate top
Crystal data top
C7H9N6O+·NO3F(000) = 528
Mr = 255.21Dx = 1.628 Mg m3
Orthorhombic, Cmc21Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C 2c -2Cell parameters from 1083 reflections
a = 6.4060 (17) Åθ = 2.7–24.6°
b = 14.960 (6) ŵ = 0.14 mm1
c = 10.867 (3) ÅT = 294 K
V = 1041.4 (6) Å3Block, bronze
Z = 40.27 × 0.10 × 0.07 mm
Data collection top
Bruker SMART APEXII Duo CCD area-detector
diffractometer
862 independent reflections
Radiation source: fine-focus sealed tube720 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.028
ϕ and ω scansθmax = 25.0°, θmin = 2.7°
Absorption correction: multi-scan
(SADABS; Bruker, 2009)
h = 57
Tmin = 0.964, Tmax = 0.991k = 1717
2866 measured reflectionsl = 812
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.030Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.074H atoms treated by a mixture of independent and constrained refinement
S = 1.03 w = 1/[σ2(Fo2) + (0.0382P)2 + 0.1935P]
where P = (Fo2 + 2Fc2)/3
862 reflections(Δ/σ)max < 0.001
127 parametersΔρmax = 0.09 e Å3
1 restraintΔρmin = 0.15 e Å3
Crystal data top
C7H9N6O+·NO3V = 1041.4 (6) Å3
Mr = 255.21Z = 4
Orthorhombic, Cmc21Mo Kα radiation
a = 6.4060 (17) ŵ = 0.14 mm1
b = 14.960 (6) ÅT = 294 K
c = 10.867 (3) Å0.27 × 0.10 × 0.07 mm
Data collection top
Bruker SMART APEXII Duo CCD area-detector
diffractometer
862 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2009)
720 reflections with I > 2σ(I)
Tmin = 0.964, Tmax = 0.991Rint = 0.028
2866 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0301 restraint
wR(F2) = 0.074H atoms treated by a mixture of independent and constrained refinement
S = 1.03Δρmax = 0.09 e Å3
862 reflectionsΔρmin = 0.15 e Å3
127 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.50000.63088 (17)0.8666 (3)0.0557 (8)
O20.50000.2129 (2)0.5161 (3)0.0585 (9)
O30.50000.12875 (19)0.3553 (3)0.0584 (9)
O40.50000.06903 (19)0.5342 (3)0.0608 (9)
N10.50000.4061 (2)0.9909 (3)0.0415 (9)
N20.50000.1632 (3)0.9791 (4)0.0451 (9)
N30.50000.2207 (2)0.7764 (3)0.0447 (9)
N40.50000.3731 (2)0.7360 (4)0.0499 (10)
N50.50000.2581 (3)1.1464 (4)0.0524 (10)
H1N50.50000.210 (3)1.199 (4)0.042 (13)*
H2N50.50000.312 (3)1.185 (5)0.062 (14)*
N60.50000.0703 (3)0.8120 (4)0.0546 (11)
H1N60.50000.028 (3)0.854 (5)0.056 (15)*
H2N60.50000.060 (2)0.723 (3)0.020 (9)*
N70.50000.1359 (2)0.4687 (4)0.0448 (9)
C10.50000.5648 (3)0.9606 (5)0.0467 (11)
H1A0.37760.57261.01200.056*0.50
H1B0.62240.57261.01200.056*0.50
C20.50000.4726 (2)0.9092 (4)0.0390 (10)
C30.50000.3228 (3)0.9449 (4)0.0384 (11)
C40.50000.2451 (2)1.0250 (4)0.0401 (10)
C50.50000.1519 (2)0.8573 (5)0.0408 (11)
C60.50000.3074 (2)0.8204 (5)0.0391 (10)
C70.50000.4546 (3)0.7834 (4)0.0498 (13)
H7A0.50000.50280.72930.060*
H1O10.50000.689 (4)0.901 (6)0.072 (14)*
H1N30.50000.208 (3)0.683 (5)0.046 (11)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0954 (19)0.0284 (13)0.0435 (17)0.0000.0000.0045 (16)
O20.090 (2)0.0310 (14)0.054 (2)0.0000.0000.0078 (16)
O30.096 (2)0.0401 (17)0.039 (2)0.0000.0000.0029 (17)
O40.093 (2)0.0323 (15)0.057 (2)0.0000.0000.0045 (15)
N10.0534 (19)0.0299 (17)0.041 (2)0.0000.0000.0027 (15)
N20.062 (2)0.0276 (17)0.046 (2)0.0000.0000.0055 (15)
N30.068 (2)0.0304 (18)0.035 (2)0.0000.0000.0005 (14)
N40.082 (3)0.0300 (15)0.038 (2)0.0000.0000.0011 (17)
N50.086 (2)0.035 (2)0.036 (2)0.0000.0000.0041 (18)
N60.082 (3)0.0308 (18)0.051 (3)0.0000.0000.001 (2)
N70.058 (2)0.036 (2)0.040 (2)0.0000.0000.0012 (17)
C10.069 (3)0.034 (2)0.037 (2)0.0000.0000.0015 (19)
C20.056 (2)0.032 (2)0.029 (2)0.0000.0000.0006 (18)
C30.046 (2)0.027 (2)0.041 (3)0.0000.0000.0013 (15)
C40.049 (2)0.032 (2)0.040 (3)0.0000.0000.007 (2)
C50.049 (2)0.029 (2)0.044 (3)0.0000.0000.006 (2)
C60.050 (2)0.0322 (19)0.035 (2)0.0000.0000.0005 (18)
C70.075 (3)0.036 (2)0.038 (3)0.0000.0000.003 (2)
Geometric parameters (Å, º) top
O1—C11.422 (6)N5—C41.333 (7)
O1—H1O10.94 (6)N5—H1N50.92 (5)
O2—N71.262 (5)N5—H2N50.91 (5)
O3—N71.237 (5)N6—C51.317 (5)
O4—N71.228 (5)N6—H1N60.78 (5)
N1—C21.334 (5)N6—H2N60.98 (4)
N1—C31.342 (5)C1—C21.487 (6)
N2—C41.322 (5)C1—H1A0.9700
N2—C51.334 (7)C1—H1B0.9700
N3—C51.353 (6)C2—C71.394 (5)
N3—C61.383 (5)C3—C61.372 (6)
N3—H1N31.03 (5)C3—C41.454 (5)
N4—C71.323 (5)C7—H7A0.9300
N4—C61.344 (6)
C1—O1—H1O1111 (4)C2—C1—H1B109.2
C2—N1—C3116.4 (4)H1A—C1—H1B107.9
C4—N2—C5119.5 (4)N1—C2—C7120.6 (3)
C5—N3—C6119.3 (4)N1—C2—C1116.2 (4)
C5—N3—H1N3120 (2)C7—C2—C1123.3 (3)
C6—N3—H1N3121 (2)N1—C3—C6121.6 (4)
C7—N4—C6114.1 (5)N1—C3—C4121.3 (4)
C4—N5—H1N5120 (3)C6—C3—C4117.2 (4)
C4—N5—H2N5126 (3)N2—C4—N5120.6 (3)
H1N5—N5—H2N5114 (4)N2—C4—C3121.0 (5)
C5—N6—H1N6122 (4)N5—C4—C3118.4 (4)
C5—N6—H2N6121 (2)N6—C5—N2119.3 (4)
H1N6—N6—H2N6117 (4)N6—C5—N3117.5 (5)
O4—N7—O3120.5 (4)N2—C5—N3123.2 (4)
O4—N7—O2120.4 (4)N4—C6—C3123.4 (4)
O3—N7—O2119.0 (4)N4—C6—N3116.8 (4)
O1—C1—C2112.0 (4)C3—C6—N3119.9 (4)
O1—C1—H1A109.2N4—C7—C2124.1 (4)
C2—C1—H1A109.2N4—C7—H7A118.0
O1—C1—H1B109.2C2—C7—H7A118.0
C3—N1—C2—C70.000 (2)C6—N3—C5—N6180.000 (1)
C3—N1—C2—C1180.000 (2)C6—N3—C5—N20.000 (2)
O1—C1—C2—N1180.000 (2)C7—N4—C6—C30.000 (2)
O1—C1—C2—C70.000 (2)C7—N4—C6—N3180.000 (1)
C2—N1—C3—C60.000 (2)N1—C3—C6—N40.000 (2)
C2—N1—C3—C4180.000 (2)C4—C3—C6—N4180.000 (2)
C5—N2—C4—N5180.000 (2)N1—C3—C6—N3180.000 (2)
C5—N2—C4—C30.000 (2)C4—C3—C6—N30.000 (2)
N1—C3—C4—N2180.000 (2)C5—N3—C6—N4180.000 (1)
C6—C3—C4—N20.000 (2)C5—N3—C6—C30.000 (2)
N1—C3—C4—N50.000 (2)C6—N4—C7—C20.000 (2)
C6—C3—C4—N5180.000 (2)N1—C2—C7—N40.000 (2)
C4—N2—C5—N6180.000 (2)C1—C2—C7—N4180.000 (2)
C4—N2—C5—N30.000 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H1N3···O21.03 (5)1.82 (5)2.831 (5)167 (4)
N6—H2N6···O40.98 (3)2.06 (3)3.019 (6)167 (3)
O1—H1O1···O2i0.95 (6)1.93 (6)2.846 (4)163 (6)
N5—H1N5···O3ii0.92 (4)2.09 (4)2.983 (6)164 (4)
N5—H2N5···O1i0.91 (5)2.15 (5)2.913 (5)141 (4)
N6—H1N6···O3iii0.78 (5)2.35 (4)3.015 (5)145 (5)
N6—H1N6···O4iii0.78 (5)2.44 (5)3.190 (6)162 (5)
Symmetry codes: (i) x+1, y+1, z+1/2; (ii) x, y, z+1; (iii) x+1, y, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H1N3···O21.03 (5)1.82 (5)2.831 (5)167 (4)
N6—H2N6···O40.98 (3)2.06 (3)3.019 (6)167 (3)
O1—H1O1···O2i0.95 (6)1.93 (6)2.846 (4)163 (6)
N5—H1N5···O3ii0.92 (4)2.09 (4)2.983 (6)164 (4)
N5—H2N5···O1i0.91 (5)2.15 (5)2.913 (5)141 (4)
N6—H1N6···O3iii0.78 (5)2.35 (4)3.015 (5)145 (5)
N6—H1N6···O4iii0.78 (5)2.44 (5)3.190 (6)162 (5)
Symmetry codes: (i) x+1, y+1, z+1/2; (ii) x, y, z+1; (iii) x+1, y, z+1/2.
 

Footnotes

Thomson Reuters ResearcherID: A-5599-2009.

Acknowledgements

PS and KB thank the Department of Science and Technology (DST-SERB), grant No. SB/FT/CS–058/2013, New Delhi, India, for financial support. KT thanks the Academy of Sciences for the Developing World and USM for the TWAS–USM fellowship. The authors also thank the Malaysian Government and Universiti Sains Malaysia (USM) for the research facilities and a USM Short Term Grant, No. 304/PFIZIK/6312078, to conduct this work.

References

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Volume 71| Part 6| June 2015| Pages o376-o377
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