imidazole and azo-based schiff bases ligands as highly...

Research ArticleImidazole and Azo-Based Schiff Bases Ligands as Highly ActiveAntifungal and Antioxidant Components

Siham Slassi12 Adeline Fix-Tailler3 Geacuterald Larcher3

Amina Amine 2 and Abdelkrim El-Ghayoury 1

1Universite drsquoAngers CNRS UMR 6200 Laboratoire MOLTECH-Anjou 2 bd Lavoisier 49045 Angers Cedex France2LCBAE Equipe Chimie Moleculaire et Molecules Bioactives Universite Moulay Ismail Faculte des Sciences Meknes Morocco3Universite drsquoAngers Groupe dEtude des Interactions Hote-Pathogene (GEIHP EA 3142) Institut de Biologie en Sante-IRISCHU 4 rue Larrey 49933 Angers Cedex France

Correspondence should be addressed to Amina Amine amine 7ayahoofrand Abdelkrim El-Ghayoury abdelkrimelghayouryuniv-angersfr

Received 12 October 2018 Accepted 4 November 2018 Published 3 January 2019

Academic Editor Jacek Skarzewski

Copyright copy 2019 Siham Slassi et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

We describe herein the synthesis full characterization and optical properties of four different ligands L1-L4 which associatean azo group an imidazole unit and a Schiff base fragment The UV-visible absorption bands are characteristic of 120587 997888rarr 120587lowastand 119899 997888rarr 120587lowast transitions with an additional charge transfer between the azobenzene moiety and the imino group Finally thedetermination of MIC

80values against pathogenic fungi such as S apiospermum A fumigatus and C albicans revealed that these

ligands have effective antifungal properties with highest activities (MIC80) on C albicans for the azole based ligands L1-L3 DPPH

radical scavenging of the studied ligands was also tested

1 Introduction

Imidazole derivatives constitute an important class of hete-rocycles being the core fragment of different natural prod-ucts and biological systems They occupy a unique placein the field of medicinal chemistry owing to their potentbiological activity [1] They are well known to possess manypharmacological properties and to play a very important rolein diverse biochemical processes [2 3] Many substitutedimidazoles display wide range of biological applications suchas antiprotozoal antifungal and antihypertensive agents [4ndash6] In addition imidazoles constitute an entire or partial partof the binding sites of various transition metal ions such asNi2+ Cu2+ or Zn2+ in a large number of metalloproteins andhave thus been utilized as effective ligands to chelate thesetransition metals For example imidazole based ligands havebeen used to afford tetranuclear copper(II) and nickel(II)metal complexes [7] copper(II) or zinc(II) coordinationpolymers [8] 1D coordination chains [9] tripodal metalcomplexes [10] andmany other complexes used for treatmentof Wilson and Menkes diseases [11] On the other hand

azobenzene [12 13] and its numerous derivatives are currentlyused as dyes and represent 60-70 of the world productionof ldquoabsorbing moleculesrdquo [14] They are known to possess aunique photoisomerization process which leads to two stablecis and trans geometries The trans-to-cis photoisomerizationoccurs by UV light irradiation while the reverse cis-to-transtakes place under blue light irradiation [15 16] This processis the key principle of various applications such as chemosen-sors [17] optical storage media [18] optical switches [19 20]nonlinear optics [21] as well as trigger for protein folding[22] Furthermore azo compounds have also a variety ofbiological activities including antibacterial [23] antifungal[24] pesticidal [25] antiviral and anti-inflammatory activi-ties [26] Schiff bases ligandswith chelating abilities have beenrecognized as privileged ligands to form stable complexeswith a large variety of transition metals [27] They havebeen used for example in metallo-ligand self-assembly togenerate discrete supramolecular assemblies such as metallo-supramolecular helicates [28ndash30] cages [31] and capsules[32] and have also been used with a variety of transitionmetals in catalysis [33 34] In addition Schiff base derivatives

HindawiHeteroatom ChemistryVolume 2019 Article ID 6862170 8 pageshttpsdoiorg10115520196862170

2 Heteroatom Chemistry

NN

NH2

NH2

N

N OH

N

N OHR

L1) R = H L2) R = o-CH3 L3) R = p-CH3

L1-L3

L4

MeOH

MeOH

NH2 OH

N

N+

CHO

NaNO2HCl

ROH

CHO

R

1

1

N

NN

N

0-5∘C

1a) R = H 1b) R = o-CH 1c) R =p-CH

Scheme 1 Synthesis of the azo-based salicylaldehydes (1a-c) and the ligands (L1-L4)

showed a variety of biological and pharmacological activitiesas antimicrobial [35] antidepressant [36] cytotoxic [37]analgesic [38] anti-HIV [39] antileishmanial [40] anticon-vulsant [41] fungicides [42] anti-inflammatory [43] andanticancer [44] In this present investigation work we areinterested by the combination of the azo group the imidazoleunit and the Schiff base fragment Thus we report hereinon the synthesis characterization and optical properties offour different Schiff bases ligands L1-L4 We also report thepossible use of such systems in biological applications inparticular due to their antifungal properties and antioxidantactivities Note that the X-ray crystal structure of ligand L2has been recently described by us [45]

2 Results and Discussions

21 Synthesis The synthesis of the Schiff bases was startedby the preparation of the azo-based salicylaldehyde (1a-c)[46] by a coupling reaction between 2-hydroxybenzaldehydeand the substituted anilines as it was previously reportedin the literature (Scheme 1) The resulting salicylaldehydes(1a-c) were subjected to condensation reaction with oneequivalent ofN-(3-Aminopropyl)imidazole or one equivalentof propylamine to afford in good yields the Schiff basesL1-L4

22 UV-Visible Absorption Spectroscopy Figure 1 shows thenormalized UV-visible absorption spectra of the Schiff basesligands L1-L4 that were recorded in dichloromethane solu-tion (sim2sdot10minus5M) at room temperature Ligands L1-L3 exhibittwo strong electronic absorption bands at around 120582 = 275nm and 350 nm while the two absorption bands of L4 are

Wavelength (nm)L1L2

L3L4

Nor

mal

ized

abso

rban

ce

Figure 1 UV-visible absorption spectra of ligands L1-L4 (2sdot10minus5M)in dichloromethane at room temperature

blue shifted to 120582 = 262 nm and 335 nm These absorptionbands are assigned to 120587 997888rarr 120587lowast and 119899 997888rarr 120587lowast transitionsin the azobenzene moiety and the imidazole rings for L1-L3and in the azobenzene fragment for L4 In the visible regionthe four ligands show and additional broad absorption bandwhich might be assigned to a charge transfer band betweenthe azobenzene moiety and the imino group

Heteroatom Chemistry 3

Table 1 Antifungal activities determined on solid medium and expressed by the diameter of the growth inhibition zone (mm)

Compounds tested FungiS apiospermum A fumigatus C albicans

L1 32 28 17L2 19 13 145L3 21 33 145L4 165 12 125Miconazole 285 185 185

Table 2 Antifungal activities determined in liquid medium and expressed by aMIC80in 120583gmLminus1


L1 4 15 08L2 4 12 01L3 4 3 02L4 4 15 3Amphotericin B 4 8 1a MIC80 corresponds to the minimum inhibitory concentration of the compound that inhibits 80 of the fungal growth

23 Biological Activities

231 Antifungal Activity Antifungal activities of the ligandsL1 to L4 were evaluated on three important fungal speciespathogenic for humans Candida albicans Aspergillus fumi-gatus and Scedosporium apiospermum especially implicatedin patients with cystic fibrosis [47] First for a rapid anti-fungal screening we have used a disc diffusion method onsolid medium The results reported in Table 1 indicate thatconcerning C albicans we notice that the ligands L2 L3 andL4 exhibit an antifungal activity which is lower than the oneof the reference antifungal miconazole while ligand L1 showsan antifungal activity with the same order of magnitude tothe one of the reference miconazole Against S apiospermumall the ligands were active three of them showed activitiesaccording to this ascending order L4 lt L2 lt L3 but lowerthan the one of miconazole Once again L1 had a growthinhibition zone diameter (32 mm) superior to the one ofmiconazole (285 mm) The best antifungal activities againstA fumigatus were found for two ligands L1 and L3 whoseinhibition zone diameters of 28 and 33mm respectively weremuch superior to the one of miconazole (185 mm) A weakactivity on the growth of A fumigatus was observed with L2and L4 In all the tested fungi it appears clearly that ligand L1presents the best antifungal results which clearly indicate thatany additional substituent on the phenyl ring is not beneficialfor the antifungal activity

In liquid medium the antifungal activities measured intriplicate were confirmed (Table 2) Against S apiospermumthe four ligands had the same MIC

80(4 120583gmL) which was

equal to the one of the reference antifungal amphotericinB For A fumigatus as observed on solid medium L1 andL3 exerted significant antifungal activities (15 and 3 120583gmLrespectively) which were superior to the one of amphotericinB (8 120583gmL) It was also the case for L4 (15 120583gmL) incontrary to the result obtained on solid medium However in

correlation with the solid medium L2 had a weaker effect onthe growth ofA fumigatus in liquidmediumHigh antifungalactivities were detected againstC albicans for three ligands inopposite ascending order of theMIC

80values L1 (08 120583gmL)

lt L3 (02 120583gmL) lt L2 (01 120583gmL) All of these values werelower than the MIC

80value (1 120583gmL) of amphotericin B L4

had a weaker antifungal effect with aMIC80value three times

more the value of amphotericin B As for solid media L1 hadan excellent antifungal activity although it is less than L2 andL3 The fact that L4 shows a weak effect clearly indicates thatthe presence of the imidazole unit is of great importance forsuch biological activities

As previously described for thiosemicarbazone ligands[48] we noticed certain discordance for few results betweenthe solid and liquid media For example it was the case for L4against A fumigatus and S apiospermum But we can noticethat L4 has a structural formula very different from the otherthree ligands L1-L3 In fact the first three ligands containan imidazole ring which is absent in ligand L4 As the diskdiffusion method consists of test compounds in solid agarmedium we may hypothesize that steric hindrance andorlipophilic character of the molecules alter their diffusion insuchmedium All these effects favor the fungal growthTheseresults strengthen the interest of the broth microdilutionmethod for a large scale evaluation of compounds disk diffu-sion method being suitable for a rapid antifungal screening

The weaker antifungal activities of L4 observed againstC albicans may be explained by the lack of azole group inits formula This group found in antifungals used in therapyis known to interact with the lanosterol 14120572-demethylase(or CYP51A1) which is implicated in the biosynthesis ofthe ergosterol important component of the fungal plasmicmembrane Curiously in liquid medium L4 exerted a goodactivity against the other fungi S apiospermum and Afumigatus suggesting antifungal targets different from theergosterol synthesis As related in previous paper concerning


Table 3 The antioxidant activity of L1-L4 in DPPH

Compound Concentration (120583gml)10 50 100 200 400 600 IC50

L1 3912 4448 5162 6428 7629 8863 9598L2 4107 4383 5113 6314 7775 9107 9448L3 3587 461 5113 6461 8344 9155 9601L4 3360 3701 4983 7142 8327 8831 11639Ascorbic Acid 4918 5207 5531 6504 8234 9873 2588Blank - - - - - - -

thiosemicarbazones [48] there is the possibility that theactivity may be linked to the relative lipophilicity of themolecule that makes the penetration in the fungal cellthrough the cell membrane and finally its destabilizationeasier More generally for all the molecules tested we mayhypothesize that the capacity of these heterocyclic ligands tochelatemetal ionswhich are essentials in numerous biologicalprocesses may impact the physiology of the fungi [49 50]

Considering the need for new azole antifungals able toovercome the increase of life-threatening fungal infectionsand the emergence of resistant fungal isolates our new azoleligands may be worthy of interest to develop new therapeuticagents

232 Antioxidant Activity Antioxidants are important bio-active species since they are capable of capturing free radicalsresponsible for many diseases such as cancer [51] Due to themobility of a proton (OH NH ) in their structure they actby direct scavenging of reactive oxygen species (ROS)

DPPH (22 Dipheny-1-picrylhydrazyl) radical scaveng-ing capacities of the Schiff bases L1-L4 were evaluatedusingUV-visible spectroscopy at different concentrations andcompared to that of the well-known antioxidant ascorbicacid Data summarized in Table 3 show that all the testedcompounds exhibit an antioxidant activity although it is lessthan the ascorbic acid This promising activity is probablydue to the hydroxyl group that is commonly known to bethe active group for DPPH scavenging [52] Indeed severalstudies [53] have established the relation between antiradicalproperties and the ability to transfer the H-atom of the OHgroup from antioxidants to free radicals according to theproposed three steps mechanism drawn below [54]

RXH +DPPH∙ 997888rarr RXH∙+ +DPPHminus

RXH∙+ 997888rarr RX∙ +H+

DPPHminus +H+ 997888rarr DPPHH

(1)

We observed also that the tested ligands L1-L3 whichstructures differ only by the presence of a methyl groupgave similar inhibitory concentrations and that they are moreactive than the ligand L4 whose formula lacks the imidazolering This result led us to conclude that the presence of theimidazole ring significantly contributes to the bioactivity ofthe studied compounds

3 Experimental

31 General Methods and Materials All organic solventswere commercially available distilled and dried by appropri-ate methods1H and 13C NMR spectra were obtained from a Bruker

Avance DRX 300 spectrometer Chemical shifts are expressedin parts per million (ppm) downfield from external TMSPerkin Elmer spectrophotometer was used to record theUV-visible absorption spectra Mass spectra were mea-sured on Bruker Biflex-III TM IR spectra were measuredon a Bruker vertex 70 A Thermo-Scientific Flash 2000Analyzer was used to obtain (C H and N) elementalanalyses

32 Synthesis of the Precursors and the Ligands

321General Procedure for the Synthesis of 2-Hydroxy-5-((aryl)diazenyl)benzaldehyde A diazonium solution was preparedby dissolving 001 mol of amine in 8 mL of water and 5 mLof concentrated hydrochloric acid was cooled to 0∘C treatedwith 15 mL of aqueous 10 M sodium nitrate dropwise andstirred for 15 minThe resulting solution was added dropwiseto a solution of salicylaldehyde (001 mol) dissolved in 50mL of 10 aqueous sodium hydroxide After the resultingmixture had been stirred for an hour at 0-5∘C the precipitatewas filtered and the products were obtained by recrystallizedfrom ethanol

322 2-Hydroxy-5-(phenyldiazenyl)benzaldehyde (1a) Yield84 mp 128∘C 1H NMR (300MHz DMSO) 120575ppm 116(s1H) 104 (s1H) 822 (d 1H J = 3) 812 (q 1H J = 3)785(dd2H J = 6 J = 3) 770 (m 2H) 762 (m 1H) 722 (d 1HJ = 9)13C NMR (75 MHz DMSO) 120575ppm 1906 1633 15181448 1311 1296 1294 1238 12258 1223 1184 MALDITOFMS calcdmz = 22607 Da Foundmz = 22710 [M+1]+Selected IR bands (cmminus1) 318584 1960 1620 1570 1446 13011281 1154 1019 952 905 843 809 759 735 708 682 641

323 2-Hydroxy-5-(o-tolyldiazenyl)benzaldehyde (1b) Yield88 mp 130∘C 1H NMR (300 MHz DMSO) 120575ppm 1155(s 1H) 1040 (s1H) 821 (d 1H J = 3) 812 (dd1H J = 6 J =3) 759-745 (m 3H) 734 (m 1H) 724 (d 1H J = 9) 268 (s3H) 13C NMR (75 MHz DMSO) 120575ppm 1906 1631 14981453 1372 1314 1320 1294 1266 1241 1226 1184 1151171 MALDI TOF MS calcd mz = 24009 Da Found mz= 24110 [M+1]+ Selected IR bands (cmminus1) 3100 2928 1650


1621 1581 1486 1373 1277 1140 1094 1038 951 896 867 848834 766 735 697 643

324 2-Hydroxy-5-(p-tolyldiazenyl)benzaldehyde (1c) Yield89 mp 154∘C 1H NMR (300MHz DMSO) 120575ppm 1153(s 1H) 1039 (s1H) 819 (d 1H J = 3) 810 (dd 1H J = 6 J =3) 780 (d 2H J = 6) 742 (dd 2H J = 6 J = 3) 722 (d 1H J= 9) 242 (s 3H) 13C NMR (75 MHz DMSO) 120575ppm 19061631 1499 1448 1413 1299 1296 1235 1226 1224 1183210 MALDI TOF MS calcd mz = 24009 Da Found mz= 24110 [M+1]+ Selected IR bands (cmminus1) 3170 2866 16501602 1572 1477 1375 1275 1166 1105 1013 951 908 850 825777 763 739 725 688 614

325 General Procedure for the Synthesis of the Schiff BasesBased on Imidazole L1-L3 N-(3-Aminopropyl)imidazole(4mmol) was added to a methanol solution (30 mL) of2-Hydroxy-5-((aryl)diazenyl)benzaldehyde (4 mmol) Themixture was refluxed for 2 h and cooled to room temperatureThe solvent was removed on a rotatory evaporator and theorange products were rinsed and recrystallized with mixtureof methanol and etherThe products were obtained as orangecrystals

326 Schiff Base Ligand L1 Yield 84 mp 110∘C 1H NMR(300MHz DMSO) 120575ppm 865 (s 1H) 803 (d 1H J = 24)791(dd 1H J = 66 J = 24) 778 (dd 2H J = 72 J = 15)765 (s 1H) 755-75 (m 2H)746-748 (m1H) 72 (s 1H) 692-689 (m 2H) 404 (t 2H J = 69) 356 (t 2H J = 69)212 (qd 2H J = 69) 13C NMR (75 MHz DMSO) 120575ppm318 443 557 1180 1182 1187 1226 1271 1272 1310 13001371 1454 1526 1641 16591 MALDI TOF MS calcd mz= 33316 Da Found mz = 3344 [M+1]+ HR-MS(M) forC19H19N5O 3331589 found 3471589 Selected IR bands (cm-

1) 3104 2946 1630 1584 1497 1480 1437 1383 1350 12751250 1195 977 926 906 852 837 769 745 665 641 AnalCalc for C

19H19N5OC 6845H 574N 2101 Found

C 6825 H 579 N 2082

327 Schiff Base Ligand L2 Yield 79 mp 82∘C 1H MR(300MHzDMSO) 120575ppm 865 (s1H) 801 (d1H J = 24) 791(dd1H J = 66 J = 24) 765 (s 1H) 752 (dd 1H J = 78 J = 15)735-734 (m1H) 733 (dd 1H J = 76 J = 15) 728-725 (m1H)720 (s1H) 693-690 (m 2H) 401 (t 2H J = 72) 355 (t2H J= 69) 261 (s 3H) 210 (qd 2H J = 69) 13CNMR (75 MHzDMSO) 120575ppm 176 317 442 537 1154 1176 1198 12011265 1270 1304 1308 1317 1372 1378 1441 1504 16681686 MALDI TOF MS calcd mz = 34717 Da Found mz =3484 [M+1]+ HR-MS(M) for C20H21N5O 3471746 found3471745 Selected IR bands (cm-1) 3136 2941 1621 1567 14861381 1308 1274 1146 1095 1031 961 906 830 748 703 670Anal Calc for C

20H21N5O C 6914 H 609 N 2016

Found C 6884 H 613 N 1995

328 Schiff Base Ligand L3 Yield 82 mp 95∘C 1H MR(300MHzDMSO) 120575ppm 863 (s1H) 799 (d1HJ = 27) 788(dd 1H J = 66 J = 24) 771 (d 2H J = 81) 765 (s 1H)732 (d 2H J = 81) 719 (s 1H) 690-700 (m 2H) 404 (t2H J = 72) 355 (t 2H J = 66) 234 (s3H) 213 (qd 2H

J = 69) 13C NMR (75 MHz DMSO) 120575ppm 215 318 443557 1179 1182 1187 1226 1269 1271 1298 1299 1371 14111455 1507 1638 1660 MALDI TOF MS calcd mz = 34717Da Foundmz = 3484 [M+1]+ HR-MS(M) for C

20H21N5O

3471746 found 3471745 Selected IR bands (cmminus1) 3105 29431634 1580 1485 1445 1377 1283 1229 1107 999 959 905 851756 689 662 Anal Calc for C

20H21N5O C 6914 H 609

N 2016 Found C 6923 H 601 N 2007

329 Schiff Base Ligand L4 Propylamine (4 mmol) wasadded to a methanol solution (30 mL) of 2-Hydroxy-5-(o-tolyldiazenyl)benzaldehyde (4 mmol) The mixture wasrefluxed for 2h and cooled to room temperature The solventwas removed on a rotatory evaporator and the orange productsolid was recrystallized with mixture of methanol and etherProduct was obtained as orange crystals Yield 90 1HNMR(300MHzDMSO) 120575ppm 1HNMR(300MHzDMSO)120575ppm 1442 (s1H) 845 (s 1H) 802 (dd 1H J = 24 J= 9) 792 (d 1H J = 24) 765-763 (m 1H) 737-733 (m2H) 732-727 (m 1H) 709 (d 1H J = 9) 365 (t 2H J =6) 274 (s 3H) 18 (m 2H) 106 (t 3H J = 9) 13CNMR(75 MHz DMSO) 120575ppm 112 171 232 565 11504 11641206 1260 1265 1300 1311 1312 1366 1429 1500 16581707 MALDI TOF MS calcd mz = 28115 Da Found mz =2824 [M+1]+ HR-MS(M) for C

17H19N3O 2811528 found

2811522 Selected IR bands (cmminus1) 3115 2956 1640 16121510 1478 1461 1434 139666 1366 1301 1258 1237 1201 11691151 1115 1027 944 914 887 836 761 750 715 678 628 AnalCalc for C17H19N3OC 7257H 681N 1494 FoundC 7246 H 681 N 1474

3210 Microorganisms Antifungal activity was assayed onhuman pathogenic fungi including Candida albicans (ATCC1066) Aspergillus fumigatus (CBS 11326) and Scedosporiumapiospermum (IHEM 15115) The yeast was obtained fromthe American Type Culture Collection (ATCC ManassasVA USA) and the opportunistic molds were furnished forA fumigatus by the Centraalbureau voor Schimmelcultures(CBS Delft Netherlands) and for S apiospermum by theInstitute of Hygiene and Epidemiology-Mycology sectionInstitute of Public Health (IHEM Brussels Belgium) All thestrains were maintained on yeast extract-peptone-dextroseagar (YPDA) plates which contained 005 chloramphenicolat 37∘C during an incubation time of 48 h for yeast 72 h forA fumigatus and 7 days for S apiospermum

3211 Determination of Antifungal Activity Disk DiffusionMethod on SolidMedium Antifungal activities of the differentligands were evaluated using a disk diffusion method adaptedfrom routinely antifungal tests [55] Casitone agar plates of90 mm diameter were used for the experiences Antifungalinocula were prepared for yeast by suspending one colony in10 mL of sterile distilled water For the filamentous fungi themycelium was recovered by scrapping the YPDA plates with10 mL of sterile distilled water Conidia were then harvestedfrom the suspension after a centrifugation at 1500 g for 5minThe supernatant was then adjusted by spectrophotometry at630 nm to an absorbance of 01 Casitone Petri dishes wereflooded with 10 mL of the spore suspensions Excess of the


suspension was eliminated and the Petri dishes were dried 10min at 37∘C

Compounds were dissolved in DMSO at a final concen-tration of 10 mgmL and 25 120583L aliquots were applied on12 mm diameter paper disks (rf 06234304 Prolabo 33173Gradigan France) Then disks were deposited in the centerof the casitone agar plates previously inoculated by fungalsuspensions

After an incubation time of 48 h for C albicans 72 hfor A fumigatus and 7 days for S apiospermum at 37∘Cdiameters of the growth inhibition zones were measuredGrowth control was performed using filter paper disks soakedwith an equal volume of respectively drug-free solvent(DMSO) and positive control was made with miconazole(Neosensitabs tablets Rosco Diagnostic Denmark)

Microdilutions Method in Liquid Medium Antifungaltests were performed by following the guidelines of theClinical Laboratory Standards Institute (CLSI) correspond-ing for yeasts to the reference method M27-A3 [56] andfor filamentous fungi to the M38-A2 reference method [57]Briefly the fungal suspensions were prepared in RPMI-1640culture medium (Sigma) added with 2 mM of L-glutaminebuffered with 0165 M of morpholine propane-sulfonic acid(MOPS) and adjusted spectrophotometrically at 630 nmto final inocula concentrations of 05 to 25 x 103 colony-forming units (CFU) per mL for C albicans and 05 to 50x 104CFU per mL for A fumigatus and S apiospermumBroth microdilution tests were performed using sterile 96-wells flat-shaped microtitre plates Each well was inocu-lated with 195 120583L of the corresponding fungal workingsuspension

Serial twofold dilutions of ligand weremade inDMSO 40times the strength of the final drug concentration (10-00025mgmLminus1) and were dispensed in triplicate at a volumeof 5 120583L per well Final concentrations for the drugs werefrom 25000 to 0061 120583gmLminus1 According to this procedurethe final concentration of DMSO solvent was lower than25 which did not affect significantly the growth of anyfungus After a 48 h incubation time for the yeast 72 h forA fumigatus and 7 days for S apiospermum at 37∘C thespectrophotometric reading of each well was performed at630 nm with a Dynatech Laboratories MRXTC automaticplate spectrophotometric reader The minimum inhibitoryconcentration of the compound that inhibits 80 (MIC

80)

of the fungal growth was calculated from the turbidimetricdata compared to that of the DMSO-free control as thelowest compound concentration giving rise to an inhibitionof growth equal or greater than 80 of the compound-freecontrol

3212 Antioxidant Activity DPPH free radical scavengingassays were performed according to the procedure describedby Blois et al [58] A DPPH solution was prepared bydissolving 2 mg DPPH in 100 mL of methanol and then250 120583L of this solution was mixed with 50 120583L of differentconcentrations of compounds L1-L4 dissolved in methanolAfter 30min incubation in the dark and at room temperaturethe absorbance was read against a blank at 517 nm Inhibition

of free radical (DPPH) in percentage (I) was calculated asfollows

119868 = (1198600 minus 119860i1198600) times 100 (2)

where A0 is the absorbance of the control (containing allreagents except the test compound) and Ai is the absorbanceof the tested sample

IC50 values were also defined as the concentration ofthe sample that causes 50 of DPPH radicals inhibitionThese values were calculated from the plot of inhibitionpercentages against sample concentration Ascorbic acid wasused as a positive control Each measurement was performedin triplicate

4 Conclusion

In this paper we describe the synthesis full characterizationand optical properties of four different Schiff bases ligandsL1-L4which associate an azo group an imidazole unit and aSchiff base fragmentThe antifungal activities of the preparedligands were evaluated and the results indicate two maintendency (a) the presence of an azole group in this ligandsis of great importance for the biological activities since L1-L3exhibit higher growth inhibition zone diameters against thestudied S spiospermum A fumigatus and C albicans fungiand lower MIC

80values for C albicans as compared with

the azole free ligand L4 (b) the presence of an additionalsubstituent on the phenyl ring of the azo group lowers theMIC80

activity of the ligands Note that L1-L3 azole basedligands show excellent MIC

80values against C albicans with

concentrations as low as 01 120583gmL which is ten times lowerthan the reference concentration (1 120583gmL) In additionthe four ligands show a significant antioxidant activity Allthese findings clearly indicate the great potential of thesenew azole ligands as valuable candidates for developing newtherapeutic agents The complexation ability of these novelSchiff bases ligands towards transition metal cations suchas Cu(II) Fe(II) Co(II) as well as their correspondingbiological activities is in progress

Data Availability

The experimental data used to support the findings of thisstudy are included within the article

Conflicts of Interest

The authors declare that they have no conflicts of interest

References

[1] A Puratchikody and M Doble ldquoAntinociceptive and antiin-flammatory activities and QSAR studies on 2-substituted-45-diphenyl-1H-imidazolesrdquo Bioorganic amp Medicinal Chemistryvol 15 p 1083 2007

[2] K Shalini P K Sharma and N Kumar ldquoImidazole and itsbiological activities a reviewrdquoDer Chemica Sinica vol 1 p 362010


[3] H Bhawar N Dighe P Shinde R Lawre and S Bhawar AsianJournal of Pharmacy and Technology vol 4 p 189 2014

[4] F Bellina SCauteruccio andRRossi ldquoSynthesis andbiologicalactivity of vicinal diaryl-substituted 1H-imidazolesrdquo Tetrahe-dron vol 63 no 22 pp 4571ndash4624 2007

[5] R Di Santo A Tafi R Costi et al ldquoAntifungal agents11 N-substituted derivatives of 1-[(aryl)(4-aryl-1H- pyrrol-3-yl)methyl]-1H-imidazole Synthesis anti-Candida activity andQSAR studiesrdquo Journal of Medicinal Chemistry vol 48 no 16pp 5140ndash5153 2005

[6] S Dutta ldquoSynthesis and anthelmintic activity of some novel 2-substituted-45-diphenyl imidazolesrdquo Acta Pharmaceutica vol60 p 229 2010

[7] S Mukherjee T Weyhermuller E Bill and P ChaudhurildquoTetranuclear copper(II) and nickel(II) complexes incorporat-ing a new imidazole-containing ligandrdquo European Journal ofInorganic Chemistry p 4209 2004

[8] R Singh M Ahmad and P K Bharadwaj ldquoCoordinationpolymers of copper and zinc ions with a linear linker havingimidazole at each end and an azo moiety in the middle pedalmotion gas adsorption and emission studiesrdquo Crystal Growthamp Design vol 12 p 5025 2012

[9] C Y Chen P Y Cheng H H Wu and H M Lee ldquoCon-formational effect of 26-bis(imidazol-1-yl)pyridine on the self-assembly of 1D coordination chains spontaneous resolutionsupramolecular isomerism and structural transformationrdquoInorganic Chemistry vol 46 p 5691 2007

[10] G Brewer M J Olida A M Schmiedekamp C Viragh andP Y Zavalij ldquoA DFT computational study of spin crossover iniron(iii) and iron(ii) tripodal imidazole complexes A compar-ison of experiment with calculationsrdquo Journal of the ChemicalSociety Dalton Transactions no 47 pp 5617ndash5629 2006

[11] B Sharkar ldquoTreatment of Wilson and Menkes diseasesrdquo Chem-ical Reviews vol 99 p 2535 1999

[12] G S Hartley ldquoThe cis-form of azobenzenerdquoNature vol 140 p281 1937

[13] G S Hartley ldquoThe cis-form of azobenzene and the velocity ofthe thermal cis997888rarrtrans-conversion of azobenzene and somederivativesrdquo Journal of the Chemical Society vol 633 1938

[14] H Zollinger Color Chemistry Syntheses Properties and Appli-cations of Organic Dyes and Pigments Wiley-VCH WeinheimGermany 3rd edition 2003

[15] N Tamai and H Miyasaka ldquoUltrafast dynamics of pho-tochromic systemsrdquo Chemical Reviews vol 100 p 1875 2000

[16] T Schultz J Quenneville B Levine et al ldquoMechanism anddynamics of azobenzene photoisomerizationrdquo Journal of theAmericanChemical Society vol 125 no 27 pp 8098-8099 2003

[17] A G Cheelham M G Hutchings T D W Claridge andH L Anderson ldquoEnzymatic synthesis and photoswitchableenzymatic cleavage of a peptide-linked rotaxanerdquo AngewandteChemie International Edition vol 45 p 1596 2006

[18] R Fernandez J A Ramos L Esposito A Tercjak and IMondragon ldquoReversible optical storage properties of nanos-tructured epoxy-based thermosets modified with azobenzeneunitsrdquoMacromolecules vol 44 no 24 pp 9738ndash9746 2011

[19] H Nishihara ldquoCombination of redox- and photochemistryof azo-conjugated metal complexesrdquo Coordination ChemistryReviews vol 249 p 1468 2005

[20] A Bianchi E Delgado-Pinar E Garcıa-Espana C GiorgiaF Pina and E Garcıa-Espana ldquoHighlights of metal ion-basedphotochemical switchesrdquo Coord Chem Rev vol 260 p 1562014

[21] A Natansohn and P Rochon ldquoPhotoinduced motions in azo-containing polymersrdquo Chemical Reviews vol 102 p 4139 2002

[22] S Sporlein H Carstens H Satzger et al ldquoUltrafast spectro-scopy reveals subnanosecondpeptide conformational dynamicsand validates molecular dynamics simulationrdquo Proceedings ofthe National Acadamyof Sciences of the United States of Americavol 99 no 12 pp 7998ndash8002 2002

[23] S Concilio P Iannelli L Sessa et al ldquoBiodegradable antimi-crobial films based on poly(lactic acid) matrices and active azocompoundsrdquo Journal of Applied Polymer Science vol 132 no 33p 42357 2015

[24] S Piotto S Concilio L Sessa et al ldquoNovel antimicrobialpolymer films active against bacteria and fungirdquo PolymerComposites vol 34 no 9 pp 1489ndash1492 2013

[25] S Piotto S Concilio L Sessa et al ldquoSmall azobenzene deriva-tives active against bacteria and fungirdquo European Journal ofMedicinal Chemistry vol 68 p 178 2001

[26] M Huang S Wu J Wang et al ldquoBiological study of naphtha-lene derivatives with antiinflammatory activitiesrdquo Drug Devel-opment Research vol 60 p 261 2003

[27] A CormaHGarcıa F X Llabres and I Xamena ldquoEngineeringmetal organic frameworks for heterogeneous catalysisrdquo Chemi-cal Reviews vol 110 p 4606 2010

[28] R Ziessel A Harriman A El-Ghayoury et al ldquoFirst assemblyof copper(I) naphthyridine-based helicatesrdquo New Journal ofChemistry vol 24 no 10 pp 729ndash732 2000

[29] M C Young A M Johnson A S Gamboa and R J HooleyldquoAchiral endohedral functionality provides stereochemical con-trol in Fe(II)-based self-assembliesrdquoChemical Communicationsvol 49 p 1627 2013

[30] S E Howson A Bolhuis V Brabec et al ldquoOptically purewater-stable metallo-helical ldquoflexicaterdquo assemblies with antibi-otic activityrdquo Nature Chemistry vol 4 p 31 2012

[31] J L Bolliger A M Belenguer and J R Nitschke ldquoEnantiopurewater-soluble [Fe

4L6] cages hostndashguest chemistry and catalytic

activityrdquo Angewandte Chemie International Edition vol 52 p7958 2013

[32] R A Bilbeisi T K Ronson and J RNitschke ldquoA self-assembled[FeII12L12] capsule with an icosahedral frameworkrdquo Ange-

wandte Chemie International Edition vol 52 p 9027 2013[33] J Cloete and S F Mapolie ldquoFunctionalized pyridinylndashimine

complexes of palladium as catalyst precursors for ethylenepolymerizationrdquo Journal ofMolecular Catalysis A Chemical vol243 p 221 2006

[34] P Shejwalkar N P Rath and E B Bauer ldquoNew iron(II) 120572-iminopyridine complexes and their catalytic activity in the oxi-dation of activatedmethylene groups and secondary alcohols toketonesrdquo Dalton Transactions vol 40 p 7617 2011

[35] N Mishra K Poonia S K Soni and D Kumar ldquoSynthesischaracterization and antimicrobial activity of Schiff base Ce(III)complexesrdquo Polyhedron vol 120 pp 60ndash68 2016

[36] A B Thomas R K Nanda L P Kothapalli and S C HamaneldquoSynthesis and biological evaluation of Schiff rsquos bases and 2-azetidinones of isonocotinyl hydrazone as potential antidepres-sant and nootropic agentsrdquoArabian Journal of Chemistry vol 9p S79 2016

[37] E S Aazam and W A El-Said ldquoSynthesis of coppernickelnanoparticles using newly synthesized Schiff-base metals com-plexes and their cytotoxicitycatalytic activitiesrdquo BioorganicChemistry vol 57 pp 5ndash12 2014


[38] S Murtaza M S Akhtar F Kanwal A Abbas S Ashiq andS Shamim ldquoSynthesis and biological evaluation of schiff basesof 4-aminophenazone as an anti-inflammatory analgesic andantipyretic agentrdquo Journal of Saudi Chemical Society vol 21 pS359 2017

[39] P Zhan X Liu J Zhu et al ldquoSynthesis and biological evaluationof imidazole thioacetanilides as novel non-nucleoside HIV-1 reverse transcriptase inhibitorsrdquo Bioorganic amp MedicinalChemistry vol 17 p 5775 2009

[40] N Suleymanoglu R Ustabas S Direkel Y B Alpaslan and YUnver ldquo124-triazole derivative with Schiff base thiol-thionetautomerism DFT study and antileishmanial activityrdquo Journalof Molecular Structure vol 1150 pp 82ndash87 2017

[41] N Karali and A Gursoy ldquoSynthesis and anticonvulsant activityof some new thiosemicarbazone and 4-thiazolidone derivativesbearing an isatin moietyrdquo Farmaco vol 49 p 819 1994

[42] E Gungor S Celen D Azaaz and H Kara ldquoTwo tridentateSchiff base ligands and their mononuclear cobalt (III) com-plexes Synthesis characterization antibacterial and antifungalactivitiesrdquo Spectrochimica Acta Part A Molecular and Biomolec-ular Spectroscopy vol 94 pp 216ndash221 2012

[43] A M Alafeefy M A Bakht M A Ganie N Ansari NN El-Sayed and A S Awaad ldquoSynthesis analgesic anti-inflammatory and anti-ulcerogenic activities of certain novelSchiff rsquos bases as fenamate isosteresrdquo Bioorganic amp MedicinalChemistry Letters vol 25 no 2 pp 179ndash183 2015

[44] Z D Mou N Deng F Zhang J Zhang J Cen and X ZhangldquordquoHalf-sandwichrdquo Schiff-base Ir(III) complexes as anticanceragentsrdquo European Journal of Medicinal Chemistry vol 138 pp72ndash82 2017

[45] S Slassi M Aarjane A Amine H Zouihri and K Yamnildquo2-((E)-[3-(1H-Imidazol-1-yl)propyl]iminomethyl)-4-[(E)-(2-methylphenyl)diazenyl]phenolrdquo IUCrData vol 2 2017x171477

[46] R Botros US Patent 1977 4051119[47] M Pihet J Carrere B Cimon et al ldquoOccurrence and relevance

of filamentous fungi in respiratory secretions of patients withcystic fibrosismdasha reviewrdquo Medical Mycology vol 47 no 4 pp387ndash397 2009

[48] K Alomar A Landreau M Allain G Bouet and G LarcherldquoSynthesis structure and antifungal activity of thiophene-23-dicarboxaldehyde bis(thiosemicarbazone) and nickel(II) cop-per(II) and cadmium(II) complexes Unsymmetrical coordina-tionmode of nickel complexrdquo Journal of Inorganic Biochemistryvol 126 pp 76ndash83 2013

[49] P I S Maia F R Pavan C Q F Leite et al Metal Ions inBiology and Medicine and Aqueous Chemistry and Biochemistryof Silicon John Libbey Eurotext Paris France 2011 164

[50] K Alomar V Gaumet M Allain G Bouet and A LandreauldquoSynthesis crystal structure characterisation and antifungalactivity of 3-thiophene aldehyde semicarbazone (3STCH) 23-thiophene dicarboxaldehyde bis(semicarbazone) (23BSTCH

2)

and their nickel (II) complexesrdquo Journal of Inorganic Biochem-istry vol 115 pp 36ndash43 2012

[51] P L de Sa D A D Junior A S Porcacchia et al ldquoThe Roles ofROS in CancerHeterogeneity andTherapyrdquoOxidative Medicineand Cellular Longevity vol 2017 Article ID 2467940 12 pages2017

[52] W Brand-Williams M E Cuverlier C Berset and C FoodldquoUse of a free radical method to evaluate antioxidant activityrdquoScience and technology vol 28 p 25 1995

[53] D Amic V Stepamic B Lucic et al ldquoPM6 study of freeradical scavenging mechanisms of flavonoids why does OndashHbond dissociation enthalpy effectively represent free radicalscavenging activityrdquo Journal of Molecular Modeling vol 9 p2593 2013

[54] M C Foti C Daquino and C Geraci ldquoElectron-transferreaction of cinnamic acids and their methyl esters with theDPPH() radical in alcoholic solutionsrdquo The Journal of OrganicChemistry vol 69 p 2309 2004

[55] A L Barry and D Brown ldquoFluconazole disk diffusion proce-dure for determining susceptibility of Candida speciesrdquo Journalof Clinical Microbiology vol 34 pp 2154ndash2157 1996

[56] CLS Institute Reference Method for Broth Dilution AntifungalSusceptibility Testing of Yeasts Clinical Laboratory StandardInstitute M27-A3Wayne 2008

[57] Institute CLS ldquoReferenceMethod for BrothDilutionAntifungalSusceptibility Testing of Filamentous Fungi M38-A2rdquo WaynePA Clinical Laboratory Standard Institute 2008

[58] M S Blois ldquoAntioxidant determinations by the use of a stablefree radicalrdquo Nature vol 181 p 1119 1958

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018


International Journal ofInternational Journal ofPhotoenergy


Journal of

Chemistry


Advances inPhysical Chemistry

Hindawiwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2018

Bioinorganic Chemistry and ApplicationsHindawiwwwhindawicom Volume 2018

SpectroscopyInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Medicinal ChemistryInternational Journal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Applied ChemistryJournal of



Biochemistry Research International


Enzyme Research


Journal of

SpectroscopyAnalytical ChemistryInternational Journal of


MaterialsJournal of



BioMed Research International Electrochemistry

International Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom


NN

NH2

NH2

N

N OH

N

N OHR

L1) R = H L2) R = o-CH3 L3) R = p-CH3

L1-L3

L4

MeOH

MeOH

NH2 OH

N

N+

CHO

NaNO2HCl

ROH

CHO

R

1

1

N

NN

N

0-5∘C

1a) R = H 1b) R = o-CH 1c) R =p-CH

Scheme 1 Synthesis of the azo-based salicylaldehydes (1a-c) and the ligands (L1-L4)

showed a variety of biological and pharmacological activitiesas antimicrobial [35] antidepressant [36] cytotoxic [37]analgesic [38] anti-HIV [39] antileishmanial [40] anticon-vulsant [41] fungicides [42] anti-inflammatory [43] andanticancer [44] In this present investigation work we areinterested by the combination of the azo group the imidazoleunit and the Schiff base fragment Thus we report hereinon the synthesis characterization and optical properties offour different Schiff bases ligands L1-L4 We also report thepossible use of such systems in biological applications inparticular due to their antifungal properties and antioxidantactivities Note that the X-ray crystal structure of ligand L2has been recently described by us [45]

2 Results and Discussions

21 Synthesis The synthesis of the Schiff bases was startedby the preparation of the azo-based salicylaldehyde (1a-c)[46] by a coupling reaction between 2-hydroxybenzaldehydeand the substituted anilines as it was previously reportedin the literature (Scheme 1) The resulting salicylaldehydes(1a-c) were subjected to condensation reaction with oneequivalent ofN-(3-Aminopropyl)imidazole or one equivalentof propylamine to afford in good yields the Schiff basesL1-L4

22 UV-Visible Absorption Spectroscopy Figure 1 shows thenormalized UV-visible absorption spectra of the Schiff basesligands L1-L4 that were recorded in dichloromethane solu-tion (sim2sdot10minus5M) at room temperature Ligands L1-L3 exhibittwo strong electronic absorption bands at around 120582 = 275nm and 350 nm while the two absorption bands of L4 are

Wavelength (nm)L1L2

L3L4

Nor

mal

ized

abso

rban

ce

Figure 1 UV-visible absorption spectra of ligands L1-L4 (2sdot10minus5M)in dichloromethane at room temperature

blue shifted to 120582 = 262 nm and 335 nm These absorptionbands are assigned to 120587 997888rarr 120587lowast and 119899 997888rarr 120587lowast transitionsin the azobenzene moiety and the imidazole rings for L1-L3and in the azobenzene fragment for L4 In the visible regionthe four ligands show and additional broad absorption bandwhich might be assigned to a charge transfer band betweenthe azobenzene moiety and the imino group




L1 32 28 17L2 19 13 145L3 21 33 145L4 165 12 125Miconazole 285 185 185










80values L1 (08 120583gmL)


















(1)


3 Experimental








1621 1581 1486 1373 1277 1140 1094 1038 951 896 867 848834 766 735 697 643




1) 3104 2946 1630 1584 1497 1480 1437 1383 1350 12751250 1195 977 926 906 852 837 769 745 665 641 AnalCalc for C

19H19N5OC 6845H 574N 2101 Found

C 6825 H 579 N 2082


20H21N5O C 6914 H 609 N 2016

Found C 6884 H 613 N 1995



20H21N5O


20H21N5O C 6914 H 609

N 2016 Found C 6923 H 601 N 2007


17H19N3O 2811528 found










80)




119868 = (1198600 minus 119860i1198600) times 100 (2)



4 Conclusion







Data Availability




References
























































2)















Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls







L1 32 28 17L2 19 13 145L3 21 33 145L4 165 12 125Miconazole 285 185 185










80values L1 (08 120583gmL)


















(1)


3 Experimental








1621 1581 1486 1373 1277 1140 1094 1038 951 896 867 848834 766 735 697 643




1) 3104 2946 1630 1584 1497 1480 1437 1383 1350 12751250 1195 977 926 906 852 837 769 745 665 641 AnalCalc for C

19H19N5OC 6845H 574N 2101 Found

C 6825 H 579 N 2082


20H21N5O C 6914 H 609 N 2016

Found C 6884 H 613 N 1995



20H21N5O


20H21N5O C 6914 H 609

N 2016 Found C 6923 H 601 N 2007


17H19N3O 2811528 found










80)




119868 = (1198600 minus 119860i1198600) times 100 (2)



4 Conclusion







Data Availability




References
























































2)















Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls















(1)


3 Experimental








1621 1581 1486 1373 1277 1140 1094 1038 951 896 867 848834 766 735 697 643




1) 3104 2946 1630 1584 1497 1480 1437 1383 1350 12751250 1195 977 926 906 852 837 769 745 665 641 AnalCalc for C

19H19N5OC 6845H 574N 2101 Found

C 6825 H 579 N 2082


20H21N5O C 6914 H 609 N 2016

Found C 6884 H 613 N 1995



20H21N5O


20H21N5O C 6914 H 609

N 2016 Found C 6923 H 601 N 2007


17H19N3O 2811528 found










80)




119868 = (1198600 minus 119860i1198600) times 100 (2)



4 Conclusion







Data Availability




References
























































2)















Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls





1621 1581 1486 1373 1277 1140 1094 1038 951 896 867 848834 766 735 697 643




1) 3104 2946 1630 1584 1497 1480 1437 1383 1350 12751250 1195 977 926 906 852 837 769 745 665 641 AnalCalc for C

19H19N5OC 6845H 574N 2101 Found

C 6825 H 579 N 2082


20H21N5O C 6914 H 609 N 2016

Found C 6884 H 613 N 1995



20H21N5O


20H21N5O C 6914 H 609

N 2016 Found C 6923 H 601 N 2007


17H19N3O 2811528 found










80)




119868 = (1198600 minus 119860i1198600) times 100 (2)



4 Conclusion







Data Availability




References
























































2)















Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls










80)




119868 = (1198600 minus 119860i1198600) times 100 (2)



4 Conclusion







Data Availability




References
























































2)















Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls

























































2)















Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls









Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




imidazole and azo-based schiff bases ligands as highly...

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