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Synthesis, Characterisation and Antimicrobial Evaluation of Some New Heterocyclic Compounds Using Citric Acid as a Synthon.

Introduction

Substituted chromens were synthesised owing to their biological activities as antibacterial, anticoagulant, vasodilatory and hypothermal (Khodairy et al., 2001; El-saghier et al., 1983; Okumur et al., 1962). Also substituted 1, 3, 4-oxadiazoles, 1, 2, 4-triazoles and 1, 3, 4-thaiadiazoles are well known to possess biological activities, and have important uses in the agricultural, medical and industrial applications. Some substituted 1, 3, 4-oxadiazoles possess various biological activities as antibacterial agent(Arvind et al., 2011), antifungal and anti-inflammatory agents (Nargunf et al., 1994; Dutta et al.,1986), while substituted 1,3,4-thiadiazoles show wide range of biological activities such as antifungal and antiviral (Vashi et al., 1996), antibacterial and antimicrobial (Mohan et al., 2005; 2000; Srivastava et al., 2000). The substituted 1,2,4-triazoles and their derivatives have attracted global interest because of their pharmacological and therapeutic properties such as have moderate antimicrobial activity (Mani et al., 2015), antifungal (Reginaldo et al., 2012), antitubercular activity (Dinesh et al., 2015), and some of triazoles exhibited potent inhibition against AChE and BChE (Gaochan et al., 2018).

It was found that the 1, 3, 4-oxadiazoles, 1, 2, 4-triazoles and 1, 3, 4-thaiadiazoles are typically formed by forming suitable esters which were converted to the corresponding acid hydrazides by their reaction with hydrazine hydrate in ethanol. Acid hydrazide is served as key intermediate for the synthesis of the target heterocyclic compounds where the interest of many researchers is in organic chemistry. Several procedures were reported for the synthesis of substituted 1,3,4-oxadiazoles, 1,2,4-triazoles and 1,3,4-thaiadiazoles and review of some chemical research by Kuldipsinh et al. (2017); Almasirad et al. (2011); Jitendra et al. (2010) and Mihaela et al. (2009).

Materials and Methods

Melting point were determined in open capillary type on Stuart melting point SMP30. The FTIR spectra were recorded on FTIR-600 Bio Tec. Engineering Management Co. Ltd. (UK) using KBr disk. Nuclear Magnetic Resonance ([.sup.13]C & [.sup.1]H-NMR) spectra were recorded on Bruker DMX-500 NMR Spectrophotometer (300MHz); with TMS as internal standard, and DMSO-[d.sub.6] as solvents. UV spectra were recorded on Shimadzu UVNis using chloroform as a solvent.

2-(3-Oxo-3H-benzo[fJchromen-1-yl) acetic acid 1. (Manvar et al., 2008). A mixture of citric acid (l mol) and concentrated sulphuric acid (30 mL) was stirred for half an hour. Then the temperature was slowly raised during an interval of 15 min, soon the evolution of gas was reduced. Removed the flask from the bath, leave it aside until the reaction mixture became clear and free from carbon monoxide bubbles. Then cooled to (10 [degrees]C) in crushed ice. Then, a-naphthol (1 mol) was added drop wise and the reaction mixture was stirred at room temperature for about 48 h. The reaction mixture was then poured onto crushed ice, the solid precipitate was filtered off and dissolved in saturated sodium bicarbonate solution which on acidication and then recrystallization from ethanol gave the title compound as a brown powder (Yield: 60%; m.p. 201-203 [degrees]C).

Methyl 2-(3-oxo-3H-benzo[f]chromen-1-yl) acetate 2. (Manvar et al., 2008). The 2-(3-oxo-3H-benzo[f] chromen-1-yl) acetic acid 1 (1 mol) was dissolved in methanol (30 mL), and a few drops of sulphuric acid were added. The reaction mixture was refluxed for 3 h. After completion of the reaction, the solvent was evaporated and the resulting reaction mixture was extracted with ethyl acetate, washed with sodium bicarbonate and the solvent was removed in vacuum to give the compound 2 as a brown powder (Yield: 67%; m.p.: 112-114 [degrees]C).

2-(3-Oxo-3H-benzo[f]chromen-1yl)acetohydrazide 3. (Manvar et al., 2008). A mixture of (0.1 mol) ester 2, 86% hydrazine hydrate (10 mL) and methanol (40 mL) was refluxed with continuous stirring for about 3 h. After completion of the reaction, the reaction mixture was poured onto crushed ice, the separated solid product was filtered off, recrystallized from ethanol which furnished 2-(3-oxo-3H-benzo[f]chromen-1-yl) acetohydrazide 3 as a pale brown powder (Yield: 92%:m.p.: 119-120 [degrees]C).

1-((5-Mercapto-1,3,4-oxadiazol-2-yl)methyl)-3H-benzo[f]chromen-3-one 4. (Selvakumar et al., 2011) Hydrazide 3 (0.05 mol) was dissolved in potassium hydroxide solution (0.56 g/100 mL ethanol). To this solution carbon disulphide (6 mL, 0.1 mol) was added with shaking. The reaction mixture was refluxed for 24 h until the liberation of hydrogen sulphide was ceased. The solvent was evaporated under reduced pressure and the residue was poured into crushed ice; and acidified with dilute hydrochloride acid. The precipitate was filtered off and recrystallized from methanol which gave the compound 4 as a pale yellow powder (Yield: 42%; m.p. :132-134 [degrees]C).

Potassium2-(2-(3-oxo-3H-benzo[f]chromen-1-yl)acetyl)hydrazine-1-carbodithioate 5. (Yadav et al., 2016). Acid hydrazide 3 (0.05 mol) was dissolved in potassium hydroxide solution (0.56 g/100 mL ethanol). To this solution carbon disulphide (6 mL, 0.1 mol) was added with shaking, then continuously stirred for 24 h. The solvent was evaporated under reduced pressure and the residue was poured into crushed ice; and acidified with dilute hydrochloride acid. The precipitate was filtered off and recrystallized from methanol which gave the compound 5 as a pale yellow powder (Yield: 42%; m.p.: 132-134 [degrees]C).

1-((4-Amino-5-mercapto-4H-1,2,4-triazol-3-yl)methyl)-3H-benzo[f]chromen-3-one 6. Method-I. (Almasirad et al., 2007). To a suspension of compound 4 (0.14 mol) in ethanol (5 mL), hydrazine hydrate (0.28 mL) was added. The reaction mixture was refluxed for 24 h. After completion of the reaction, the reaction mixture was cooled and acidified with cold aqueous (3N) hydrochloric acid. The mixture was extracted with ether and the organic layer was washed with cold water dried over anhyd. sodium sulphate, filtered off, and the solvent was evaporated under reduced pressure. The residue was recrystallized from ethanol which furnished the compound 6 as a brown powder (Yield: 55%; m.p. :240-242 [degrees]C).

Method-II. (Yusra et al., 2015). A suspension of salt 5 (0.01 mol), hydrazine hydrate (0.02 mol) and water (50 mL) were refluxed for 6 h. The colour of the reaction mixture changed to green. The reaction mixture was cooled to room temperature: a brown solid was precipitated out by adding cold water (50 mL) followed by acidification with concentrated HCl. The precipitate was filtered off: washed with cold water, recrystallized from ethanol which furnished the desired compound 6 as a brown powder (Yield: 48%; m.p. :240-242 [degrees]C).

Preparation of 1-((5-amino-1,3,4-thiadiazol-2-yl)methyl)-3H-benzo[f]chromen-3-one 7. (Harika and Sudha, 2014). Thiosemicarbazide (0.025 mol) was suspended in a 1,4-dioxane (25 mL) and stirrers with the addition of 2-(3-oxo-3H-benzo[f]chromen-1-yl)acetic acid 1 (0.03 mol). The poly phosphoric acid was added at 0-5 [degrees]C. The reaction mixture was heated at 80-85 [degrees]C for about 6 h and then, left to room temperature. The solvent was evaporated; poured into crushed ice (50 mL) with vigorous stirring. Then, the reaction mixture was basified to pH-9 by the addition of 40% NaOH solution. The precipitate was filtered off: washed with cold water to remove all coloured impurities which gave the compound 7 as a pale yellow colour (Yield: 94%; m.p.:167-169 [degrees]C).

1-((5-((Substitutedbenzylidene)amino)-1,3,4-thiadiazol-2-yl)methyl)-3H-benzo[f]chromen-3-one8a-f. (Harika and Sudha, 2014): To (0.1 mol) of compound 7 in ethanol (25 mL), added benzaldehyde or substituted benzaldehyde (0.5 mol) and acetic anhydride (0.5 mL). The reaction mixture was refluxed for 10 h. The reaction mixture was cooled and poured with stirring onto crushed ice contained in a 500 mL beaker. The solid product was filtered off and dried, recrystallized from suitable solvent to give the compounds 8a-f. The physical and spectral data are listed in Tables 1 and 4, respectively.

2-((5-((3-Oxo-3H-benzo[fJchromen-1-yl)methyl)-1,3,4-thiadiazol-2-yl)imino)indolin-3-one 8 g. To a solution of compound 7 (0.1 mol) in ethanol (25 mL), added isatine (0.5 mol) and acetic anhydride (0.5 mL). The reaction mixture was refluxed for 12 h. After completion of the reaction, the reaction was cooled, poured with stirring onto crushed ice contained in a (500 mL) beaker. The solid product was filtered, dried and recrystallized from ethanol to give the compound 8g as a pale yellow (Yield: 72%); m.p.: 160-162 [degrees]C).

Results and Discussion

The synthesis of many heterocyclic system containing substituted 1,3,4-oxadiazoles,1,2,4-triazoles, 1,3,4-thaiadiazoles and 1,2,4-triazoles ring were achieved from reaction of citric acid with a-naphthol to give 2-(3-oxo-3H-benzo[f]chromen-1-yl) acetic acid 1 which on treatment with methanol, in the presence of few drops of sulphuric acid give ester 2 which were converted to the corresponding acid hydrazides 3 by their reaction with hydrazine hydrate in ethanol. The synthetic procedures adopted are illustrated in Scheme 1.

The IR spectra for compounds 1-3 showed characteristic absorption peak in the range of (1645-1692 [cm.sup.-1]) stretching for (C=O), at (1714-1726 [cm.sup.-1]) stretching group due to (C=O) group of lactones' ring. The[.sup.1]HNMR spectrum for compounds (1-3) showed significant peaks as the following singlet in the range (2.79-2.95 ppm) for (C[H.sub.2]) group, (6.32-6.45 ppm) due to (CH) group in the ring, also the aromatic part showed multiplet peaks in the range (7.18-8.22ppm). While [.sup.13]C-NMR spectra showed peaks for the carbon signal appeared at [delta] values as shown in Table 2. The UV spectra showed absorption peaks at [[lambda].sub.max] in the range (309-398 nm), (242-276 nm) due to (n [right arrow] [pi]*) and ([pi] [right arrow] [pi]*) electronic transitions, respectively.

Oxadiazole 4 was obtained by the reaction of acid hydrazide (Almasirad et al., 2011) with carbon disulphide in alkaline medium under reflux conditions. The mechanism of the reaction was accomplished by nucleophilic attack of nitrogen of hydrazide at the carbon atom of carbon disulphide to form the salts which undergoes intra nucleophilic attack of the oxygen of the carbonyl group on the carbon of C=S group followed by elimination of hydrogen sulphide to afford 1-((5-mercapto-1,3,4-oxadiazol-2-yl)methyl)-3H-benzo[f]chromen-3-one 4 (Ajllo et al., 1972). While the same reaction under the stirring at room temperature gave different potassium 2-(2-(3-oxo-3H-benzo[f]chromen-yl)acetyl) hydrazine-1-carbodithioate 5, which were converted to triazole 6 by reacting with hydrazine hydrate. Traizole 6 was obtained. Also, given by reaction of oxadiazole 4 with hydrazine hydrate as shown in Scheme 2.

The IR spectra for compounds 4-6 showed characteristic absorption peak in the range of (1646-1658 [cm.sup.-1]) stretching for (C=N), at (2332-2336 [cm.sup.-1]) due to (SH) group and at (1709-1718 [cm.sup.-1]) stretching group for (C=O) group of lactones' ring. The [.sup.1]H-NMR spectrum for compounds 4-6 showed significant peaks as the following singlet in the range (2.68-3.24 ppm) due to (C[H.sub.2]) group,(6,25-6.39 ppm) to (CH) group in the ring, while the aromatic part showed multiplet in the range (7.14-8.29 ppm), also the protons of (SH) group were appeared in the range (13.35-12.93 ppm). [.sup.13]C-NMR spectra showed peaks for the carbon signal appeared at [delta] values as shown in Table 2-3. The UV spectra showed absorption peaks at [[lambda].sub.max] (374-386 nm), (228-248 nm) for (n [right arrow] [pi]*) and ([pi] [right arrow] [pi]*) electronic transitions, respectively.

Newly synthesised compounds 8a-f were characterised by the physical properties shown in Table 1. The synthetic strategy for the synthesis of imines 8a-g has been described in the Scheme 3, involves reaction of acid hydrazide 1 with thiosemicarbazide to give first on a product it is 1-((5-amino-1,3,4-thiadiazol-2-yl)methyl)-3H-benzo[f]chromen-3-one 7, which is considered as starting material for the synthesis of imines 8a-f and 8g by its reaction with substituted aldehydes or isatin as shown in Scheme 3. Thus treatment of thaidiazole 7 with substituted benzaldehyde and isatin gave the compounds 8a-f and 8g, respectively.

The IR spectra for compound 7 showed the following frequencies: 3100-3300 [cm.sup.-1] and 1560-1590 [cm.sup.-1] due to NH stretching and bending respectively, 1595-1600 [cm.sup.-1] for C=N stretching and 1723 [cm.sup.-1] due to (C=O) group of lactones' ring, also [.sup.1]H-NMR spectrum for this compound distinguish the appearance characteristic absorption peak in as the following singlet in 3.24 ppm due to (C[H.sub.2]) group,at 6.37 ppm for (CH) and doublet at 6.91 ppm due to (N[H.sub.2]) group, while the aromatic part showed multiplet in the range (7.34-8.19 ppm). The [.sup.13]C-NMR spectrum showed peaks for the carbon signal appeared at [delta] values as shown in the following signal: 45.19, 115.8, 116, 4, 122.2, 123.8, 126.3, 128.1, 128.7, 130.4, 131.4, 150.4, 155.3, 161.21, 168.3, 169.8.

The IR spectra for imine compounds 8a-g showed characteristic absorption peak in the range of (1588-1638 [cm.sup.-1]) stretching for (C=N), at (1695-1722 [cm.sup.-1]) stretching group for (C=O) group of lactones' ring. The [.sup.1]H-NMR spectra for compounds 8a-g showed signi-ficant peaks as the following singlet in the range (2.71-3.25 ppm) for (C[H.sub.2]) group, (6,22-6.39 ppm) due to (CH) group in the ring, also at the range (8.71-9.1 ppm) as singlet peak due to (CH=N) group. Which are characterised by the compounds 8a-f, while aromatic parts showed two types where multiple peaks were found at range (7.49-7.83 ppm). Return to the aromatic part which represents substituted aldehydes while the other aromatic part showed multiplet in the range (7.12-8.21 ppm) due to protons of chromens ring. [.sup.13]C-NMR spectra showed good peaks for the carbon signal appeared at [delta] values as shown in Table 4.

Biological activity. All the synthesised compounds were screened for in vitro antibacterial and antifungal activity by adopting the disc diffusion method. For antibacterial studies the microorganisms employed were Esherichia coli, Staphylococcus aureus, Micrococcus, Pseudomonas, Bacillus 11 and Bacillus 12. While for antifungal, Microsporum gypseum, Microsporum destortum and Trichophyton rubrum were used as microorganisms. Both antimicrobial studies were assessed by a minimum inhibitory concentration. From the obtained data, it is evident that compounds 8a and 8d possess a very good activity against bacteria strains like E. coli and Staphylococcus and the compounds 8e, 8f and 8g possess almost a significant activity against all fungi tested at 1 mg/mL and 2 mg/mL. The remaining compounds showed a moderate activity against other bacteria and fungi tested.

Conclusion

From the experiment it was concluded that the synthesis of 1,3,4-oxadiazoles, 1,2,4-triazoles and 1,3,4-thaiadiazoles were prepared on safe and simplicity with a good product yields, and some of them showed a good significance to moderate activity as antibacterial and antifungal agents.

Acknowledgement

We are grateful to Department of Chemistry, College of Science, Mosul University, for the facilities given to perform this work. Thanks are also due to Dr. Maha A. Al-Rejaboo, Department of Biology, College of Science, University of Mosul for the biological assays.

References

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Moayed Salim Al-Gwady, Salim Jasim Mohammed (*) and Attalla Mohammed Sheat

Department of Chemistry, College of Science, University of Mosul, Iraq

(received October 19, 2017; revised April 16, 2018; accepted April 23, 2018)

Author for correspondence: E-mail: dr_salimjasim@yahoo.com
Table 1. Physical data for compounds 8a-f

Comp.                 M.P.          Yield               Cryst.
no.    R              ([degrees]C)  (%)    Colour       solvent

a      H              185-187       39     Yellow       Ethanol
b      2-OH           153-155       42     Brown        Methanol
c      4-C[H.sub.3]   186-188       49     Brown        Ethanol
d      4-OC[H.sub.3]  197-199       60     Pale yellow  Acetone
e      2-C[O.sub.2]H  181-183       55     Brown        Methanol
f      CH=CH          184-186       35     Yellow       Ethanol

Table 2. Spectral data for compounds (1-3)

Comp.  U.V. CH[Cl.sub.3]         FTIR (KBr) [gamma][cm.sup.-1]
no.    [[lambda].sub.max] nm     C=O      C=O   Other
       (n [right arrow] [pi]*)   lactone
       [pi] [right arrow] [pi]*  ring

1.     (266) 377                 1724     1692  3345 OH-
2.     (276) 398                 1726     1685  -
3.     (242) 309                 1714     1645  3228, NH
                                                3365,N[H.sub.2]

Comp.  [.sup.1]H-NMR [delta] (ppm)  [.sup.1]C-NMR ([delta], ppm)
no.    DMSO-[d.sub.6]               DMSO-[d.sub.6]

1.     2.95(bs,2H,C[H.sub.2]),      37.2,112.6,115.8,116.8,122.612,6.4,
       6.42(s,1H, HC),              126.9,128.5,128.8,130.2,13,1.9155.7,
       7.24-8.22(m,6H,ArH),         160.9,171.3
       12.31(s,1H,OH)
2.     3.65(s,3H,C[H.sub.3]),       34.9,51.8,115.7,116,6,122.4,12,3.5,
       2.85(bs,2H,C[H.sub.2]),      126.9,128.4,128.8,130.2,13,2.1,
       6.35(s,1H, HC),              150.6,161.1,168.3
       7.18-8.17(m,6H,ArH),
3.     2.79 (bs,2H,C[H.sub.2]),     45.7,112.7,115.6,116.4,122.5,126.7,
       6.32(s,1H, HC),7.36-8.18     128.3,128.8,130.2,131.9,151.2,144.1,
       (m,6H,ArH),9.14(s,1H,NH),    161.1,170,4
       4.28(d,2H,N[H.sub.2])

Table 3. Spectral data for compounds (4-6)

Comp.  U.V. CH[Cl.sub.3]         FTIR (KBr) [gamma][cm.sup.-1]
no.    [[lambda].sub.max] nm     C=O      S=H   C=N
       (n [right arrow] [pi]*)   lactone
       [pi] [right arrow] [pi]*  ring

4.     (228) 374                 1718     2336  1646
5.     (248) 379                 1709     -     -
6.     (236) 386                 1712     2332  1658

Comp.  [.sup.1]H-NMR [delta] (ppm)  [.sup.1]C-NMR ([delta], ppm)
no.    DMSO-[d.sub.6]               DMSO-[d.sub.6]

4.     3.24(bs,2H,C[H.sub.2]),      37.2,112.6,115.8,116.8,122.612,6.4,
       6.25(s,1H, HC),7.34-8.09     126.9,128.5,128.8,130.2,13,1.9155.7,
       (m,6H,ArH),13.35(s,1H,SH)    160.9,171.3
5.     2.68(bs,2H,C[H.sub.2]),      45.9,115.6,116,4,122.2,123.8,126.4,
       6.39(s,1H, HC),7.14-8.21     128.1,128.7,130.4,131.8,150.4,
       11.05(s,1H,NH)               (m,6H,ArH),7.71(s,1H,NH),
                                    155.4,161.1,169.8,203.5.
6.     3.19(bs,2H,C[H.sub.2]),6.26  34.2,112.5,115.4,116.1,122.4,126.3,
       (s,1H, HC),7.33-8.14         128.6,128.8,130.3,131.7,150.2,
       (m,6H,ArH).4.8               154.1,160.1
       (d,2H,N[H.sub.2]),
       12.93(s,1H,SH).

Table 4. Spectral data for compounds (8a-g)

Comp.  U.V. CH[Cl.sub.3]         FTIR (KBr) [gamma][cm.sup.-1]
no.    [[lambda].sub.max] nm     C=O   C=N   ArCH
       (n [right arrow] [pi]*)
       [pi] [right arrow] [pi]*

a      (297) 359                 1703  1611  3058
b      (301) 369                 1711  1633  3054
c      (287) 388                 1695  1597  3062
d      (276) 391                 1722  1608  3065
e      (304) 412                 1705  1594  2073
f      (298) 365                 1721  1638  3053
g      (258) 366                 1698  1588  3059

Comp.  [.sup.1]H-NMR [delta] (ppm)  [.sup.1]C-NMR ([delta], ppm)
no.    DMSO-[d.sub.6]               DMSO-[d.sub.6]

a      3.15(bs,2H,C[H.sub.2]),6.32  36.8,112.4,115.8,116.8,122.7,126.2,
       (s,1H,HC),7.65-7.78          126.9,128.5,128.4,130.5,131.9,155.7,
       (m,4H,ArH),7.26-8.12         160.9,160.5,161.3,167.9,168.5
       (m,6H,ArH),9.07
       (s,1H,CH=N)
b      2.85(bs,2H,C[H.sub.2]),6.35  39.7,112.4,117,6,120.4,121.7,126.2,
       (s,1H,HC),7.62-7.73          128.1,128.8,131.3,132.2,150.3,
       (m,4H,ArH),7.12-8.20         168.2,161.1,168.3
       (m,6H,ArH),9.1
       (s,1H,CH=N),11.2(s,1H,OH)
c      2.45(s,3H,C[H.sub.3]),2.75   45..4,112.7,115.6,116.4,122.5,126.7,
       (bs,2H,C[H.sub.2]),6.37      128.3,128.8,130.2,131.9,151.1,
       (s,1H,HC),7.49-7.71          160.3,160.7,161.4,168.2
       (m,4H,ArH),7.36-8.18
       (m,6H,ArH),8,86(s,1H,CH=N)
d      3.82(s,3H,OC[H.sub.3]),2.71  39.5,55.7,112.1,114.5,115.6,116.7,
       (bs,2H,C[H.sub.2]),6.31      122.4,123.9,126.7,128.5128.7,130.2,
       (s,1H,HC),7.54-7.68          130.5,131.3,132.4,150.3,150.4,
       (m,4H,ArH),7.32-8.16         160.5,160.9,162.4,168.4.
       (m,6H,ArH),8,96(s,1H,CH=N)
e      3.23(bs,2H,C[H.sub.2]),6.39  39.2,112.8,115,6,116.2,120.6,121.7,
       (s,1H,HC),7.61-7.77          126.8,128.1,128.8,131.3,132.2,150.3,
       (m,4H,ArH),7.23-8.19         155.8,168.2,161.1,167.3,168.2
       (m,6H,ArH),8.99(s,1H,CH=N),
       13.15(s,1H,OH)
f      2.88(bs,2H,C[H.sub.2]),      41.1,113.4,117.1,118.9,122.3,126.8,
       6.25(s,1H,HC),6.85           128.1,128.8,131.3,132.3,150.3,155.5,
       (s,1H,=CH)6.93               68.2,160.7,167.6,168.2.,170.6
       (s1H,CH-triazole),7.24
       (s,IH,-CH=)7.52-7.83
       (m,4H,ArH),7.14-8.21
       (m,6H,ArH),8.71(s,1H,CH=N)
g      3.25(bs,2H,C[H.sub.2]),6.22  39.9,112.2.112.6,114.1,115.2,116.7,
       (s,1H, HC),6.92-7.74         122.4,123.6,124.2,126.3,128.4,128.8,
       (m,4H,ArH of isatin ring)    130.2,131.4,135.5,150.5,151.7,155.5,
       7.29-8.17(m,6H,ArH),10.75    156.4,160.7,168.3,187.4
       (s1H,NH)
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Author:Al-Gwady, Moayed Salim; Mohammed, Salim Jasim; Sheat, Attalla Mohammed
Publication:Pakistan Journal of Scientific and Industrial Research Series A: Physical Sciences
Article Type:Report
Date:May 1, 2018
Words:4602
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