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Short communication
Synthesis, Characterization and Antimicrobial Activity of Long-Chain Hydrazones
Abdul Rauf,a* Mudasir R. Bandaya and Rayees H. Mattoob
aSection of Oils and Fats, Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India
bDepartment of Biochemistry, Aligarh Muslim University, Aligarh 202002, India
* Corresponding author: E-mail: abduloafchem@gmail.com Mob.: 0091-9412545345
Received: 19-11-2007
Abstract
Fatty acids containing hetero atoms are regarded as potential antimicrobial agents. Thus eight different hydrazones 2a–d and 3a–d were synthesized from four fatty acid hydrazides namely undecanoic hydrazide (1a), octadecanoic hydrazide (1b), 12-hydroxyoctadecanoic hydrazide (1c) and 9-hydroxyoctadecanoic hydrazide (1d) by condensing them with car-bonyl group of methyl acetoacetate and acetylacetone. The structural elucidation of these compounds is based on their spectral data (IR, 1H NMR, 13C NMR and MS). These compounds were also screened for their microbial activity against Escherichia coli, Staphylococcus aureus and Staphylococcus albus by cup-plate method at 100 µg/ml of DMF using chloromycetin as a standard drug.
Keywords: Fatty acid hydrazones, antimicrobial activity, IR, 1H NMR, 13C NMR, MS.
1. Introduction
The synthesis, structure and biological activity of some new hydrazones prepared from fatty acid hydrazides has been the focus of research. Different methods have been employed to synthesize different types of hydrazo-nes from different starting materials. Hydrazones have been found to possess many biological activities, e.g. anti-bacterial,1,2 anticonvulsant,3 anti-inflamatory,4 anti-proto-zoal,5 and antitubercular.6,7 The use of fatty acid substrates as starting materials has become significant because of their own biological activity.8,9 Thus carbonyl group of methyl acetoacetate and acetylacetone was employed to synthesize the hydrazones 2a–d and 3a–d from the aforementioned hydrazides 1a–d. These hydrazones were also screened for their antimicrobial activity and some of the synthesized compounds showed good antimicrobial activity against E. coli, S. aureus and S. albus.
2. Results and Discussion
Hydrazides were prepared by stirring and refluxing the fatty esters with hydrazine hydrate in ethanol in the
presence of air. Absence of peaks for olefinic protons (d 5.4–4.6) suggest that hydrogenation of double bond of the fatty acid chain has taken place. This indicates that hydra-zine hydrate can hydrogenate double bonds in the presence of air. Such findings are already reported in the literatu-re.10–12
The synthetic pathway followed for the synthesis of hydrazones is presented in the Scheme 1. Carbonyl group of methyl acetoacetate and acetylacetone has been employed to build the newly synthesized hydrazones from different fatty acid hydrazides. Reaction of undecanoic hydrazide with carbonyl group of methyl acetoacetate afforded hydrazone 2a. IR spectra of hydrazone 2a exhibited intensive bands at 3210, 1743 and 1660 cm–1 confirming the presence of NH, O=COCH3 and O=C–NH groups, respectively. 1H NMR was more informative. In addition to the peak of normal fatty acid chain, other characteristic signals were observed at d 10.35 (1H, NH), 3.66 (3H, OCH3), 2.30 (2H, t, J = 7.5 Hz, CH2–CONH), 2.01 (2H, s, CH2CO2CH3) and 1.56 (3H, s, N=C–CH3), confirming the structure of the hydrazone 2a. In 13C NMR signals at d 174.7 and 174.5 (COOCH3, CONH), 159.2 (C=N) and 25.0 (COCH3) also supported the structure. Similarly, hydrazones 2b–d were synthesized from hydrazides 1b–d by reacting them with methyl acetoace-
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Compounds
R
1a, 2a, 3a             CH3(CH2)9
1b, 2b, 3b            CH3(CH2)16
1c, 2c, 3c             CH3(CH2)5CHOH(CH2)10
1d 2d, 3d             CH3(CH2)8CHOH(CH2)7
Scheme 1: Synthesis of hydrazones from hydrazides.
tate and were characterized by their spectral data. Reaction of undecanoic hydrazide with carbonyl group of acetylacetone afforded the hydrazone 3a. Hydrazone 3a gave intensive IR bands at 3205, 1721 and 1664 cm–1, confirming the presence of NH, C=O and O=C–NH groups, respectively. The 1H NMR data gave characteristic peaks at d 10.33 (1H, NH), 2.30 (2H, t, J = 7.5 Hz, CH2–CONH), 2.04 (3H, s, CH3), 1.94 (2H, s, CH2–COCH3) and 1.56 (3H, s, N=C–CH3), confirming the structure. In 13C NMR signals at d 174.4 and 174.3 (COOCH3, CONH), 161.3 (C=N) and 29.2 (COCH3) also supported the structure. Similarly, hydrazones 3b–d were synthesized from hydrazides 1b–d by reacting them with acetylacetone and their structures were confirmed by the spectral data.
The hydrazones 2 and 3 were screened for their antibacterial activity against E. coli, S. aureus and S. albus by cup-plate method. It was observed that only C-11 hydra-zones 2a and 3a showed promising results. Whereas hydrazones 2c and 2d showed only moderate activity against E. coli and S. albus. Hydrazone 3d showed poor activity against E. coli and S. aureus.
3. Experimental
Undecanoic (purity 98%) and (Z)-9-octadecenoic (oleic acid, 97%) acids were purchased from Fluka Chemicals (Buchs, Switzerland). (Z)-12-Hydroxy-9-octade-cenoic (ricinolic acid, 98%) and (Z)-9-hydroxy-12-octa-decenoic (isoricinolic acid, 98%) were isolated from Rici-
nus communis and Wrightia tinctoria seed oils, respectively, following Gunstone’s partition procedure.13 Methyl acetoacetate, acetylacetone and hydrazine hydrate (80%) were purchased from Sd fine-chem (Mumbai, India). Thin layer chromatography was done on glass plates (20 × 5 cm) with a layer of silca gel G (Merck, Mumbai, India, 0.5 mm thickness). Mixture of petroleum ether-diethyl ether-acetic acid (80:20:1 v/v) was used as mobile phase. Column chromatography was carried out on silca gel (Merck, Mumbai, India, 60–120 mesh). 1H NMR were recorded at 300 MHz and 13C NMR were recorded at 75 MHz. Melting points were taken in open capillaries and are uncorrected.
General procedure for the preparation of fatty acid hydrazides 1. Methyl undecanoate (0.1 mmol) was reacted with hydrazine hydrate (0.25 mmol) while stirring and refluxing in ethanol for 5 h. The resulting solution was cooled and poured into crushed ice. The solid thus obtained was filtered and recrystalized from ethanol to afford the corresponding undecanoic hydrazide 1a. Similarly, octadecanoic hydrazide 1b, 12-hydroxyoctadecanoic hydrazide 1c and 9-hydroxyoctadecanoic hydrazide 1d were obtained from (Z)-9-octadecenoate, (Z)-12-hydroxy-9-octadecenoate and (Z)-9-hydroxy-12-octadecenoate, respectively.
Undecanoic hydrazide (1a). White crystals, yield 80%, m.p. 90–92 °C (lit. m.p. 93–94 °C).10 IR (KBr, cm–1) 3210–3080 (NH–NH2), 1660 (O=C–NH). 1H NMR (CDCl3) d 8.74 (1H, s, NH), 3.93 (2H, s, NH2), 2.57 (2H, t, J = 7.8 Hz, CH2–CONH), 1.55 (2H, m, CH2CH2–CO),
1.24 (14H, br. s, 7×CH2), 0.87 (3H, deg. t, CH3).
Octadecanoic hydrazide (1b). White powder, yield 85%, m.p. 110–112 °C (lit. m.p. 112–114 °C).10,14 IR (KBr, cm–1) 3218–3080 (NH–NH2), 1660 (O=C–NH). 1H NMR (CDCl3) d 8.85 (1H, s, NH), 3.98 (2H, s, NH2), 2.57 (2H, t, J = 7.8 Hz, CH2–CONH), 1.57 (2H, m, CH2CH2–CO),
1.25 (28H, br. s, 14×CH2), 0.87 (3H, deg. t, CH3).
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12-Hydroxyoctadecanoic hydrazide (1c). White crystals, yield 75%, m.p. 112–114 °C. IR (KBr, cm–1) 3327 (OH), 3278–3095 (NH–NH2), 1670 (O=C–NH). 1H NMR (CDCl3) d 8.70 (1H, s, NH), 4.11 (1H, m, CH–OH), 3.90 (2H, s, NH2), 3.66 (1H, br. s, OH), 2.57 (2H, t, J = 7.8 Hz, CH2–CONH), 1.61 (2H, m, CH2CH2–CO), 1.27 (26H, br. s, 13×CH2), 0.88 (3H, deg. t, CH3).
9-Hydroxyoctadecanoic hydrazide (1d). Off-white crystals, yield 70%, m.p. 112–114 °C. IR (KBr, cm–1) 3327 (OH), 3270–3095 (NH–NH2), 1669 (O=C–NH). 1H NMR (CDCl3) d 8.85 (1H, s, NH), 4.11 (1H, m, CH–OH), 3.90 (2H, s, NH2), 3.66 (1H, br. s, OH), 2.57 (2H, t, J = 7.8 Hz, CH2–CONH), 1.61 (2H, m, CH2CH2–CO), 1.27 (26H, br. s, 13×CH2), 0.88 (3H, deg. t, CH3).
General procedure for the preparation of hydrazones 2. Fatty acid hydrazide 1 (0.1 mmol) and methyl acetoace-tate (0.1 mmol) were refluxed in absolute ethanol (30 mL) for 3–4 h containing a few drops of HCl. The resulting solution was then concentrated and cooled. The solid thus separated was filtered and crystallized from ethanol, except for the oily compound 2a, which was chromatograp-hed on silica gel (60–120 mesh) using petrol ether-diethyl ether (98:2, v/v) as eluent.
Methyl 3-(2’-undecanoylhydrazono)butanoate (2a).
Oily, yield 86%. IR (neat, cm–1) 3210 (NH), 1743 (O=COCH3), 1660 (O=C–NH), 1449 (C=N). 1H NMR (CDCl3) d 10.35 (1H, s, NH, exchangeable with D2O), 3.66 (3H, s, OCH3), 2.30 (2H, t, J = 7.5 Hz, CH2–CONH), 2.01 (2H, s, CH2CO2CH3), 1.61 (2H, m, CH2CH2CO), 1.56 (3H, s, N=C–CH3), 1.26 (14H, br. s, 7×CH2), 0.87 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) d 174.7, 174.5, 159.2, 51.5, 34.2, 31.9, 29.8, 29.7, 29.5, 25.7, 25.0, 22.7, 14.2 (three signals are hidden). MS (FAB) m/z (%): 298 (M+, 3), 267 (50), 154 (100), 127 (25), 99 (20), 95 (45). Anal. Calcd for C16H30O3N2 (297.97): C, 64.40; H, 10.13; N, 9.39. Found: C, 64.18; H, 9.87; N, 9.08.
Methyl 3-(2’-octadecanoylhydrazono)butanoate (2b).
White powder, yield 78%, m.p. 45 °C. IR (KBr, cm–1) 3207 (NH), 1736 (O=COCH3), 1658 (O=C–NH), 1455 (C=N). 1H NMR (CDCl3) d 10.35 (1H, s, NH, exchangeable with D2O), 3.66 (3H, s, OCH3), 2.30 (2H, t, J = 7.8 Hz, CH2CONH), 1.94 (2H, s, CH2CO2CH3), 1.61 (2H, m, CH2CH2–CO), 1.59 (3H, s, N=C–CH3), 1.25 (28H, br. s, 14×CH2), 0.88 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) d 174.8, 174.4, 159.1, 51.6, 34.2, 31.9, 29.8, 29.7, 29.6, 29.5, 29.4, 25.7, 25.1, 22.7, 14.1 (eight signals are hidden). MS (FAB) m/z (%): 396 (M+, 3), 298 (100), 267 (30), 239 (12), 185 (7), 157 (10), 143 (50), 99 (35). Anal. Calcd for C23H44O3N2 (395.97): C, 69.65; H, 11.18; N, 7.06. Found: C, 69.59; H, 11.02; N, 6.98.
Methyl 3-[2’-(12-hydroxyoctadecanoylhydrazono)]bu-tanoate (2c). Off-white powder, yield 75%, m.p. 47 °C. IR (KBr, cm1) 3321 (OH), 3212 (NH), 1737 (O=COCH3), 1660 (O=C-NH), 1458 (C=N). 1H NMR (CDCl3) ô 10.34 (1H, s, NH, exchangeable with D2O), 3.98 (1H, m, CH–OH), 3.66 (3H, s, OCH3), 3.58 (1H, br. s, OH, exchangeable with D2O), 2.30 (2H, t, J = 7.5 Hz, CH2CONH), 1.91 (2H, s, CH2CO2CH3), 1.61 (2H, m, CH2CH2-CO), 1.59 (3H, s, N=C-CH3), 1.27 (26H, br. s, 13×CH2), 0.88 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) ô 174.44, 174.40, 159.2, 72.1, 51.5, 37.6, 34.2, 31.9, 29.8, 29.7, 29.57, 29.55, 29.5, 29.2, 25.7, 25.0, 22. 8, 14.2 (five signals are hidden). MS (FAB) m/z (%): 412 (M+, 2), 299 (25), 297 (100), 283 (30), 265 (70), 199 (10), 154 (75), 98 (15). Anal. Calcd for C23H44O4N2 (411.96): C, 66.95; H, 10.75; N, 6.79. Found: C, 66.91; H, 10.55; N, 6.67.
Methyl 3-[2’-(9-hydroxyoctadecanoylhydrazono)]bu-tanoate (2d). White powder, yield 75%, m.p. 43 °C. IR (KBr, cm–1) 3327 (OH), 3214 (NH), 1737 (O=COCH3), 1658 (O=C-NH), 1459 (C=N); 1H NMR (CDCl3) ô 10.35 (1H, s, NH, exchangeable with D2O), 4.11 (1H, m, CH–OH), 3.66 (3H, s, OCH3), 3.58 (1H, br. s, OH, exchangeable with D2O), 2.30 (2H, t, J = 7.5 Hz, CH2CONH), 1.91 (2H, s, CH2CO2CH3), 1.61 (2H, m, CH2CH2CO), 1.55 (3H, s, N=C-CH3), 1.25 (26H, br. s, 13×CH2), 0.88 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) ô 174.5, 174.4, 159.2, 72.0, 51.6, 37.6, 37.5, 34.1, 31.9, 29.7, 29.6, 29.53, 29.50, 29.4, 29.2, 25.7, 25.0, 22.7, 14.1 (four signals are hidden). MS (FAB) m/z (%): 412 (M+, 4), 313 (30), 299 (100), 267 (20), 265 (70), 199 (10), 143 (10), 126 (25), 98 (15). Anal. Calcd for C23H44O4N2 (411.96): C, 66.95; H, 10.75; N, 6.79. Found: C, 66.87; H, 10.52; N, 6.63.
General procedure for preparation of hydrazides 3.
Fatty acid hydrazide 1 (0.1 mmol) and acetylacetone (0.1 mmol) were refluxed in absolute ethanol (30 mL) for 4 h containing a few drops of HCl. The resulting solution was then concentrated and cooled at room temperature. The solid thus separated was filtered and crystallized from ethanol, except for the oily compound 3a, which was chro-matographed on silica gel (60-120 mesh) using petrol et-her-diethyl ether (96:4, v/v) as eluent.
N'-(4-Oxopentane-2-ylidene)undecanohydrazide (3a). Oily, yield 80%. IR (KBr, cm–1) 3205 (NH), 1721 (C=O), 1664 (O=C-NH), 1446 (C=N). 1H NMR (CDCl3) ô 10.33 (1H, s, NH, exchangeable with D2O), 2.30 (2H, t, J = 7.8 Hz, CH2CONH), 2.04 (3H, s, CH3), 1.94 (2H, s, CH2COCH3), 1.61 (2H, m, CH2CH2CO), 1.56 (3H, s, N=C-CH3), 1.25 (14H, br s, 7×CH2), 0.87 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) ô 174.4, 174.3, 161.3, 74.1, 51.4, 32.0, 29.7, 29.6, 29.4, 29.2, 25.1, 22.8, 14.1 (three signals are hidden). MS (FAB) m/z (%): 282 (M+, 3), 281 (65), 267 (40), 239 (15), 169 (10), 141 (10), 137
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(100). Anal. Calcd for C16H30O2N2 (281.98): C, 68.04; H, 10.71; N, 9.92. Found: C, 67.84; H, 10.37; N, 9.71.
N´-(4-Oxopentane-2-ylidene)octadecanohydrazide (3b). White crystals, yield 70%, m.p. 43 °C. IR (KBr, cm–1) 3207 (NH), 1723 (C=O), 1662 (O=C–NH), 1443 (C=N). 1H NMR (CDCl3) d 10.33 (1H, s, NH, exchangeable with D2O), 2.30 (2H, t, J = 7.8 Hz, CH2CONH), 2.04 (3H, s, CH3), 1.94 (2H, s, CH2COCH3), 1.64 (2H, m, CH2CH2CO), 1.59 (3H, s, N=C–CH3), 1.25 (28H, br s, 14×CH2), 0.88 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) d 174.38, 174.36, 161.3, 51.4, 34.2, 32.1, 29.8, 29.63, 29.58, 29.52, 29.47, 29.41, 29.3, 25.1, 22.7, 14.1 (seven signals are hidden). MS (FAB) m/z (%): 282 (M+, 4), 281 (65), 267 (40), 239 (15), 169 (10), 141 (10), 137 (100). Anal. Calcd for C23H44O2N2 (379.98): C, 72.58; H, 11.65; N, 7.36. Found: C, 72.51; H, 11.44; N, 7.23.
12-Hydroxy-N´-(4-oxopentane-2-ylidene)octadeca-nohydrazide (3c). Off-white powder, yield 70%, m.p. 44 °C. IR (KBr, cm–1) 3327 (OH), 3205 (NH), 1719 (C=O), 1658 (O=C–NH), 1452 (C=N). 1H NMR (CDCl3) d 10.35 (1H, s, NH, exchangeable with D2O), 4.13 (1H, m, CH–OH), 3.58 (1H, br. s, OH, exchangeable with D2O), 2.32 (2H, t, J = 7.5 Hz, CH2CONH), 2.04 (3H, s, CH3), 1.91 (2H, s, CH2COCH3), 1.64 (2H, m, CH2CH2CO), 1.59 (3H, s, N=C–CH3), 1.25 (26H, br. s, 13×CH2), 0.88 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) d 174.36, 174.34, 161.3, 72.1, 51.4, 37.6, 37.5, 34.1, 32.0, 29.7, 29.6, 29.5, 29.4, 29.3, 25.1, 22.7, 14.2 (six signals are hidden). MS (FAB) m/z (%): 396 (M+, 4), 313 (10), 297 (100), 281 (20), 267 (10), 199 (7), 171 (15), 154 (90), 140 (9), 112 (8), 98 (20). Anal. Calcd for C23H44O3N2 (395.97): C, 69.65; H, 11.18; N, 7.06. Found: C, 69.57; H, 10.98; N, 6.96.
9-Hydroxy-N´-(4-oxopentane-2-ylidene)octadecanohy-drazide (3d). White powder, yield 75%, m.p. 42 °C. IR (KBr, cm–1) 3325 (OH), 3208 (NH), 1724 (C=O), 1660 (O=C–NH), 1455 (C=N). 1H NMR (CDCl3) d 10.35 (1H, s, NH, exchangeable with D2O), 4.11 (1H, m, CH–OH), 3.58 (1H, br. s, OH, exchangeable with D2O), 2.30 (2H, t, J = 7.5 Hz, CH2CONH), 2.04 (3H, s, CH3), 1.90 (2H, s, CH2COCH3), 1.61 (2H, m, CH2CH2CO), 1.55 (3H, s, N=C–CH3), 1.25 (26H, br. s, 13×CH2), 0.88 (3H, deg. t, terminal CH3). 13C NMR (CDCl3) d 174.37, 174.34, 161.3, 72.0, 51.4, 37.6, 37.5, 34.2, 32.0, 29.7, 29.63, 29.55, 29.50, 29.46, 29.42, 29.3, 25.0, 22.8, 14.2 (four signals are hidden). MS (FAB) m/z (%): 396 (M+, 5), 363 (7), 297 (100), 267 (30), 199 (10), 185 (10), 140 (15), 115 (8), 98 (20). Anal. Calcd for C23H44O3N2 (395.97): C, 69.65; H, 11.18; N, 7.06. Found: C, 69.55; H, 10.95; N, 6.92.
3. 1. Antibacterial Activity
The in vitro antibacterial activity was carried out against E. coli, S. aureus and S. albus. These strains were
streaked on nutrient agar plates separately and grown overnight. Single-well isolated colonies of each type of bacteria were incubated in separate nutrient mediums for 16 h at 37 °C for the experiment. To determine the zone of inhibition cup-plate method was employed.15 In this technique bacteria liquid culture of each type grown in log phase was added aseptically to the autoclaved LB agar medium maintained at 45 °C, mixed well and poured immediately into sterile Petri dishes separately. After solidification, wells of about 6 mm were cut into agar plates aseptically.
Solution of 100 µg/ml of each hydrazone was prepared in DMF. Standard antibiotic chloromycetin was screened under similar conditions. 100 µl of these solutions were added to each well and incubated at 37 °C. One of the wells was used as control by adding 100 µg/ml of DMF. Zone of inhibition was measured in mm after 24 h and compared with the standard drug. Results of antibacterial screening are reported in Table 1.
Table 1. Response of various micro-organism to the new hydrazo-nes 2 and 3 in vitro (culture).
	Diameter of zone	of inhibition	
Hydrazone	E. coli	S. aureus	S. albus
2a	(+ + +)	(+ + +)	(+ + +)
2b	(-)	(-)	(-)
2c	(+ +)	(-)	(+ +)
2d	(+ + )	(-)	(+ +)
3a	(+ + +)	( + + +)	(+ + +)
3b	(-)	(-)	(-)
3c	(-)	(-)	(-)
3d	(+)	(+)	(-)
Chloromycetin	(+ + + +)	(+ + + +)	(+ + + +)
DMF used as the control.
Concentration used = 100 µg/ml of DMF.
Symbols: low activity (1–5mm) (+); moderate activity (6–10 mm)
(+ +); high activity (11–15 mm) (+ + +); very high activity (15–20
mm) (+ + + +); no activity (–)
4. Conclusion
To the best of our knowledge, hydrazones have been for the first time synthesized from fatty acids. Results obtained from the antibacterial activity show that some of the synthesized hydrazones, especially C-11 derivatives, i.e. hydrazones 2a and 3a, may be considered promising for development of new antibacterial agents after performing the significant toxicity tests.
5. Acknowledgement
We are grateful to chairman Department of Chemistry for providing necessary research facilities and to SAIF (CDRI, Lucknow) for spectral analysis.
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Povzetek
Ma{~obne kisline, ki vsebujejo hetero atome, imajo potencialno vlogo kot antimikrobne u~inkovine. S kondenazacijo s karbonilno skupino metil acetoacetata in acetilacetona smo iz {tirih razli~nih hidrazidov ma{~obnih kislin (in sicer undekanoil hidrazi-da (1a), oktadekanoil hidrazida (1b), 12-hidroksioktadekanoil hidrazida (1c) and 9-hidroksioktadekanoil hidrazida (1d)) sintetizirali osem razli~nih hidrazonov 2a–d in 3a–d. Strukturo produktov smo ugotovili s pomo~jo spektroskopskih podatkov (IR, 1H NMR, 13C NMR in MS). Raziskali smo tudi njihovo aktivnost proti mikrobom Escherichia coli, Staphylococcus au-reus in Staphylococcus albus s pomo~jo plo{~ne metode pri koncentraciji 100 µg/ml v DMF z uporabo kloromicetina kot standarda.
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