1 ml of the soap solution was aseptically transferred into sterile petri plates. Into these plates, 20 ml of P.D.A. was poured and was mixed with soap solution by rotating the petri plates in clockwise and anticlockwise direction 3-4 times and was allowed to solidify. After the solidification of the above medium, single hypha / spore of test organism was aseptically transferred in the centre of the petri plates. The plates were incubated at 30 ^oC for 3 days. After the period of incubation, the plates were observed for the growth of fungus in different concentration of the soap solution used in the present study. The data were statistically analyzed according to the following formula [15Garg BS, Kumar DN. Spectral studies of complexes of nickel (II) with tetradentate schiff bases having N2O2 donor groups, Spectrochim. Acta 59A (2003): 229-234; https://DOI:10.1016/S1386-1425(02)00142-7].

% Inhibition = (C-T)*100/C

Where C = diameter of fungal colony in control plates after 3 days

T = diameter of fungal colony in test plate after 3 days

The detailed infrared spectral investigation reveals that there are marked differences between the spectra of pure copper soaps and pure ligand than those of the corresponding complexes (Table 2) The absorption bands observed in the region 2960-2950 cm^-1 and 2900-2950 cm^-1 respectively were assigned to the antisymmetric stretching for methyl group of the soap segment present in the complex. Symmetric stretching bands for methyl group has been assigned in the region 2820-2850 cm^-1. It has been observed that the absorption peaks, which are characteristics of the aliphatic portion of the soap molecules, remain unchanged on going while being transferred from soaps to the complexes. The absorption spectra in the region 710-725 cm^-1 may probably be due to the rocking vibration of a chain of methylene group –(CH₂)_n. The peaks in the region 1575-1590 cm^-1 and 1400-1410 cm^-1 are due to COO^-, C-O anti-symmetric and symmetric stretching, respectively [17Sharma AK, Sharma S, Sharma R. Thermal degradation of Cu (II) metallic soaps and their characterizations. A pharmaceutical application chronicles of pharmaceutical science 2017; 1(5): 312-19.].

The presence of bands in the region 810±20 cm^-1 was due to C-H deformation (in plane) present in the tri-substituted benzene ring of benzothiazole segment, where two hydrogens are adjacent [1,2,and 4 position]. In 2-amino-6-methyl benzothiazole, the C-H deformation vibration of –CH₃ group has been observed at 1477 cm^-1. C-N stretching (aryl tertiary) peaks was observed in the region 1360-1310 cm^-1. C=N stretching peaks in the region 1460-1430 cm^-1 was also observed. The C-S stretching bands present in the region of 700-600 cm^-1 also confirm the structure of the molecule. IR spectrum of the pure ligand 2-amino-6-R benzothiazole [R= -CH₃] contained peaks in the region 3450±15 cm^-1 due to symmetric N-H stretching, which shifted to 3400±20 cm^-1 on complexation, indicating the participation of the primary amino group in the chelation (Table 3) [18Sharma S, Sharma R, Heda LC, Sharma AK. Kinetic parameters and Photo Degradation studies of copper soap derived from soybean oil using ZnO as a photo catalyst in solid and solution phase. J Inst Chemists (India) 2017; 89(4): 119-36.].

The ¹H NMR spectra of the complexes were collected in C₆D₆ and examined to determine bonding and tautomerism present in the structure. A perusal of the spectra of the complexes shows aliphatic –CH₃ proton signal at δ - 0.9 and -CH₂ proton signal at δ - 1.2 of soap segment, indicating the presence of soap segment in the complex molecule.

Fig. (4) NMR spectra of ligand (2-amino-6-methyl benzothiazole).

A broadened peak has been observed in all the spectra of the complexes at δ 3.2 – 4.2 due to the presence of aromatic –NH₂ protons. In the given spectra of CC_prAMB (Fig. 4), the above peak was clear which indicates the coordination through the –NH₂ group of the benzothiazole segment to the metal atom of soap segment. The proton present in the nitrogen atom may undergo rapid, intermediate or slow exchange. The broadening of the observed peak is suggestive of a slow exchange because the electrical quadripole moment of the nitrogen nucleus induces a moderately efficient spin relaxation. A very weak signal was observed at δ - 8.5 in the spectra, which may be due to tautomerism present in the molecule of the complex similar to the pyrrole and indole. The triplets at δ 6.9 – 7.2 are may be due to tri-substituted aromatic protons of benzothiazole segment indicating that the environment of all the three protons is different. Another peak present at δ - 2.8 in the methyl substituted complex confirmed the presence of aromatic methyl group in the benzothiazole segment of the molecule suggesting a downfield shift [19Khan S, Sharma R, Sharma AK. Ultrasonic studies of Cu (II) Soap derived from seed oil of Pongamiapinnata(Karanj), in non-aqueous binary and ternary systems at 298.15K. Malasian J Chem 2017; 19(2): 99-110.].

Literature reveals that magnetic conductivity and spectral studies of complexes of some first-row transition elements with pyrazine carboxylic acid have been conducted , where it acts as a bidentate ligand through O and N donor atoms [20Bhutra R, Sharma R, Sharma AK. Comparative studies of treated & untreated oils as Cu (II) surfactants“ISBN978-3-659-83122-5 2017.].

Table 1
Analytical and physical data of the complexes.

Table 2
Infrared absorption spectral frequencies (cm^-1) of soap and ligands and their assignments.

Table 3
Infrared absorption spectral frequencies (cm^-1) of complexes and their assignments.

The ESR spectra of the complexes synthesized by us were recorded on X-band at frequency 9.07 GHz under the magnetic field strength of 2000±4000 and 3000±2000 gauss at room temperature. The value of ESR parameters for all the complexes is given in Table 4. A perusal of Table 4 shows that the values of g, g_II, are greater than the value of g₀ ii.e. 2.0027. This indicates that the distortion from the regular octahedron has taken place in the shape of the complex. Also the trend g_II> for all the complexes indicates that the unpaired electron is most likely in d_x2-y2 orbital of Cu (II) giving ²B_1g as the ground state. This fact supports that complexes possess elongated octahedral geometry. It is well known that g_II is a moderately sensitive function for indicating covalency. Thus, the values of g_II are suggestive of the covalent character of metal-ligand bond [21Saxena M, Sharma R, Sharma AK. Micellar Features of Cu (II) surfactants derived from edible oils 2017., 22Mishra AP, Mishra RK, Shrivastava SP. Structural and antimicrobial studies of coordination compounds of VO(II), Co(II), Ni(II) and Cu(II) with some Schiff bases involving 2-amino-4-chlorophenol, J Serb Chem Soc 2009; 79: 523-35]. Earlier magnetic studies, about copper (II) soaps confirm the binuclear configuration in the solid state. However, the low values of the magnetic moments for copper ion present in copper (II) soaps in non-aqueous solvent like alcohol and hydrocarbon confirm that the binuclear configuration exists in the soap solutions and the dispersion unit is a binuclear molecule having the structure proposed in Figs. (5-7) [23Raval JP, Desai KG, Desai KR. Microwave synthesis, characterization and antimicrobial study of new pyrazolyl-oxopropyl-quinazolin-4(3H)-one derivatives. J Saudi Chem Soc 2011; 16(4): 387-93.
[http://dx.doi.org/10.1016/j.jscs.2011.02.003] , 24Chandra S, Jain D, Sharma AK, Sharma P. Coordination modes of a schiff base pentadentate derivative of 4-aminoantipyrine with cobalt(II), nickel(II) and copper(II) metal ions: synthesis, spectroscopic and antimicrobial studies. Molecules 2009; 14(1): 174-90.
[http://dx.doi.org/10.3390/molecules14010174] [PMID: 19127246] ].

Table 4
ESR spectral values of complexes.

Fig. (5) ESR spectra of complex CCplAMB.

Fig. (6) ESR spectra of complex CCprAMB.

Fig. (7) ESR spectra of complex CLrtlAMB.

The antifungal activities of the pure ligands, pure soaps and their corresponding complexes have been evaluated by testing against Alternaria-alternata [25Sharma AK, Saxena M, Sharma R. Acoustic studies of copper soap- urea complexes derived from groundnut and seasam oils. J Phy Studies 2017; 21(4): 4601-6.-26Sharma AK, Saxena M, Sharma R. Ultrasonic studies of Cu (II) Soaps derived from Groundnut and Sesame oils. Tenside Surf Det 2017; 55(2): 127-34.
[http://dx.doi.org/10.3139/113.110544] ] at a different concentration by Agar plate technique. A perusal of Fig. (8) reveals that all complexes show higher activity than pure soaps and ligands suggesting that complexes are more powerful antifungal agents and benzothiazole and other N, S, O etc [27Khan S, Sharma R, Sharma AK. (2018) Acoustic studies and other acoustic parameters of Cu(II) Soap derived from non- edible Neem oil (Azadirectaindica), in Non-aqueous media at 298.15 Acta. Ac united Ac 2018; 104: 277-283. DOI 10.3813/AAA.919170., 28Bhutra R, Sharma R, Sharma AK. Synthesis, Characterization and fungicidal activities of Cu (II) surfactants derived from groundnut and mustard oils treated at high temperatures. J Inst Chemists (India) 2018; 90(3): 66-80.]. containing compounds are able to enhance the performance of copper soaps. The organic compounds containing amino group play an important role in biology, as it constitutes the repeating unit of the polypeptide macromolecules. These results show that the Cu (II) soap-complexes of ligands are much more toxic than the ligands themselves [29Tank P, Sharma R, Sharma AK. Micellar features and various interactions of copper soap complexes derived from edible mustard oil in benzene at 303.15 K Curr. Phy Chem 2018; 8(1): 46-57.]. The enhanced activity of newly synthesized complexes as compared to those of the ligand can possibly be explained on the basis of chelate formation, the presence of donor atoms, basicity as well as the structural compatibility with molecular nature of the toxic moiety [30Bhutra R, Sharma R, Sharma AK. Fungicidal activities of Cu (II) soaps derived from various oils treated at high temperature for biomedical use. SAJ Biotechnol 2018; 5(103): 1-6.]. The enhanced biological activity of complexes is in accordance with the chelation theory. The results of ANOVA [31Sharma A K, Sharma R, Saxena M. (2018) Biomedical and antifungal application of Cu(II) soaps and its urea complexes derived from various oils. Open access J Trans Med res 2(2) 40-43.] for the antifungal activities for all soaps complexes are shown in Table 5. The predicted R² was obserbed to be in reasonable agreement and closer to1.0. This confirms that the experimental data are satisfactory. The descriptive statics results shown in Table 6 confirm the satisfactory results in triplet [32Sharma AK, Sharma R, Gangwal A. Biomedical and fungicidal application of copper surfactants derived from pure fatty acid, Organic & Medicinal Chem. 2018 IJ 5(5): OMCIJ.MS.ID.555680, 1-4].

Fig. (8) Antifungal activity of ligand soap and complex (methyl) for fungi Alternaria Alternata.

Table 5
Descriptive statics results for antifungal activities of Cu (II) soaps and its complexes.

Table 6
ANOVA results for antifungal activities of Cu (II) soaps and its complexes.