1. Novel Co-doped Polyaniline Fused Imidazole Copolymer represented by Formula I. Formula I

2. A process for preparing the Novel Co-doped Polyaniline Fused Imidazole Copolymer as claimed in claim 1, said process comprising: (vi) Dissolving aniline and imidazole in aqueous acidic media containing one or more dopant and co-dopant at a temp of 0-5°C, (vii) Adding an oxidizing agent to (i) at a temperature of 0-5°C under constant stirring to initiate polymerization, (viii) Filtering the reaction mass of step after 4-6 hours to obtain a precipitate, (ix) Washing the said precipitate with de-ionized water and alcohol to obtain a pure precipitate, and/or (x) Drying the pure precipitate to obtain the co-doped PANI-1H-imidazole copolymer.

3. The process as claimed in claim 1 wherein the dopant is an inorganic acid selected from hydrochloric acid, sulfuric acid and nitric acid.

4. The process as claimed in claim 1 wherein co-dopant is an organic acid selected from acetic acid, oxalic acid, citric acid, malic acid, formic acid, lactic acid, and maleic acid.

5. The process as claimed in claim 1 wherein oxidant is selected from hydrogen peroxide, ozone, sodium percarbonate, sodium permanganate, potassium permanganate, sodium perborate, sodium persulfate, potassium persulfate, ammonium persulfate.

6. The process as claimed in claim 1 wherein oxidant is ammonium persulfate.

7. The process as claimed in claim 1 wherein the dopant is nitric acid and co-dopant is oxalic acid.

8. An antimicrobial composition comprising the novel co-doped polyaniline fused imidazole copolymer as claimed in claim 1.

Description:Field of the invention
The present invention relates to Novel Co-doped Polyaniline Fused Imidazole (PANI-1H-Imidazole) Copolymer, their process of preparation and antimicrobial composition comprising the same.
Background of the invention:
The rise of infectious diseases and resistant pathogens have made it necessary for scientists to keep exploring new antimicrobials. In addition to small and large synthetic and semisynthetic molecules, polymers have been widely employed in the field of medicine and healthcare. Because of their low cytotoxicity and biocompatibility, polymeric materials have been the preferred material in biomedicine.
Modification of PANI such as by doping, changes the electronic, electrical, magnetic, optical and structural properties. This in turn effects the various physiochemical and biological properties of PANI.
The antibacterial properties of PANIs, PANI colloids, PANI doped with citric acid functionalized PANIs and aniline copolymers have been reported in the literature.
Bluma et al in Synthetic Metals Volume 266, August 2020, 116435 discloses Polyaniline co-doped with dodecyl benzene sulfonic acid and zwitterionic-based ionic liquids. It has been prepared by inverse emulsion polymerization.
Cheng et al in Journal of Polymer research, volume 24, article no 10 (2017) discloses polyaniline co-doped with nitric acid and dodecyl benzene sulfonic acid. It is directly prepared by the chemical oxidative polymerization of aniline in an aqueous solution. The co doping increases the electrical conductivity.
Mu et al in Adv. Mater. Res.2013; 650; 249–252 discloses Polyaniline (PANI) doped by natural acid such as citric acid, salicylic acid or rosin acid. or rosin acid) It was synthesized using aniline as monomer and ammonium peroxydisulfate ((NH4)2S2O8) as oxidant. The antibacterial activities of the PANI against Gram positive bacteria (Bacillus megatherium, Bacillus subtilis, Bacillus cereus and Staphylococcus aureus) and Gram negative bacteria (Bacillus coli) were investigated and it was shown that PANI doped by citric acid possessed the better antibacterial activity against the selected species of Gram positive bacteria and Gram negative bacteria than PANI doped by rosin acid. PANI doped by salicylic acid exhibited ascendant antibacterial activities against Gram positive bacteria, but it has little antibacterial activity against the Gram negative bacteria.
Dhivya et al. in Arabian Journal of Chemistry; 2019 discloses the antimicrobial activities of nanostructured polyanilines doped with aromatic nitro compounds. It discloses that Polyaniline (PANI) doped with nitro compounds such as 2,4,6-trinitrophenol i.e., picric acid, 3,5-dinitrobenzoic acid and hydrochloric acid in the emeraldine salt form was synthesized by chemical oxidative polymerization. Polyaniline emeraldine base (PANIEB) was prepared by dedoping polyaniline chloride (PANICl). The in vitro antimicrobial properties of the PANI against various gram-negative, gram-positive bacteria and fungus Candida albicans were evaluated using agar well diffusion method. The test results indicated that doped PANIs had enhanced antimicrobial efficacy compared to PANIEB.
Although, the literature is replete with doped PANI and their uses in various electrochemical and biological fields, still there is a need for efficient antimicrobials.
Object of the invention:
It is an object of the present invention to provide novel antimicrobial polymers based on polyaniline.
It is another object of the present invention to provide a process for the preparation of novel antimicrobial polymers based on polyaniline.
It is another object of the present invention to provide a process for the preparation of novel antimicrobial polymers based on polyaniline wherein the process provides the said compound in high yield and purity.

Formula I
It is an object of the present invention to provide novel antimicrobial polymers based on polyaniline which are suitable for use in pharmaceutical formulations.
Summary of the invention:
Accordingly, in one embodiment, the present invention provides novel co-doped polyaniline (PANI)-1H-imidazole copolymer.
In another embodiment, the present invention provides co-doped polyaniline (PANI)-1H-imidazole copolymer represented by formula I.
In another embodiment, the present invention provides co-doped polyaniline (PANI)-1H-imidazole copolymer wherein the said polymer is free of any impurity.
In another embodiment, the present invention provides co-doped polyaniline (PANI)-1H-imidazole copolymer wherein the said polymer is in the form of free flowing powder.
In another embodiment, the present invention provides antimicrobial composition comprising co-doped polyaniline (PANI)-1H-imidazole copolymer.
In another embodiment, the present invention provides a process for preparing co-doped polyaniline (PANI)-1H-imidazole copolymer represented by formula I said process comprising:
(i) Dissolving aniline and imidazole in aqueous acidic media containing one or more dopant and co-dopant at a temp of 0-5°C,
(ii) Adding an oxidizing agent to (i) at a temperature of 0-5°C under constant stirring to initiate polymerization,
(iii) Filtering the reaction mass of step after 4-6 hours to obtain a precipitate,
(iv) Washing the said precipitate with de-ionized water and alcohol to obtain a pure precipitate, and/or
(v) Drying the pure precipitate to obtain the co-doped PANI-1H-imidazole copolymer.

Brief description of drawings:
Figure 1 shows the graphical plot between (a) log10 ? vs 1000/T and (b) log10 s vs 1000/T of PANI and PANI-1H-Imidazole.

DETAILED DESCRIPTION OF THE INVENTION WITH NON-LIMITING EXAMPLES AND EMBODIMENTS

In the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be obvious to a person skilled in the art that the invention may be practiced with or without these specific details. In other instances, well known methods, procedures and components have not been described in details so as not to unnecessarily obscure aspects of the invention.

Furthermore, it will be clear that the invention is not limited to these alternatives only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art, without parting from the scope of the invention.

Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of elements or steps but not the exclusion of any other element or step or group of elements or steps.

The present invention provides novel co-doped polyaniline (PANI)-1H-imidazole copolymer. These copolymers are useful as antimicrobial compounds.

In another embodiment, the present invention provides co-doped polyaniline (PANI)-1H-imidazole copolymer represented by formula I.

Formula I

In another embodiment, the present invention provides co-doped polyaniline (PANI)-1H-imidazole copolymer wherein the said polymer is free of any impurity.
In another embodiment, the present invention provides co-doped polyaniline (PANI)-1H-imidazole copolymer wherein the said polymer is in the form of free-flowing powder. The free-flowing property of the powder provides better handling properties and makes it suitable for pharmaceutical compositions.
In one embodiment the present invention provides a process for preparing the co-doped PANI-1H-Imidazole as claimed in claim 1, said process comprising:
(i) Dissolving aniline and imidazole in aqueous acidic media containing one or more dopant and co-dopant at a temp of 0-5°C,
(ii) Adding an oxidizing agent to (i) at a temperature of 0-5°C under constant stirring to initiate polymerization,
(iii) Filtering the reaction mass of step after 4-6 hours to obtain a precipitate,
(iv) Washing the said precipitate with de-ionized water and alcohol to obtain a pure precipitate, and/or
(v) Drying the pure precipitate to obtain the co-doped PANI-1H-imidazole copolymer.
The dopant suitable for use in step (i) is an inorganic acid selected from hydrochloric acid, sulfuric acid and nitric acid.
The co-dopant suitable for use in step (i) is an organic acid selected from acetic acid, oxalic acid, citric acid, malic acid, formic acid, lactic acid, and maleic acid.
The oxidizing agent suitable for use in step (ii) is selected from hydrogen peroxide, ozone, sodium percarbonate, sodium permanganate, potassium permanganate, sodium perborate, sodium persulfate, potassium persulfate, ammonium persulfate.
Stirring at step (ii) is carried for 1-5 hours, preferably 1.2-2.5 hours.
In a preferred embodiment, the oxidizing agent is ammonium persulfate.
In a preferred embodiment the dopant is nitric acid and co-dopant is oxalic acid.
In yet another embodiment, the present invention provides an antimicrobial composition comprising Novel Co-doped Polyaniline Fused Imidazole Copolymer.
The antimicrobial composition can be in the form of tablets, capsules, pellets, granules. powders, coated granules, coated pellets etc. The preferred dosage form of the present invention is a tablet. The coated granules or pellets can be filled in capsules or compressed into a tablet.
The antimicrobial composition of the present invention is useful for the treatment of infections caused by both gram positive and gram-negative bacteria.
Gram positive bacteria are selected from but not limited to Staphylococcus aureus, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Enterococci, Corynebacterium diphtheriae and Bacillus anthracis
Gram negative bacteria are selected from but not limited to Escherichia coli, Vibrio cholerae, Bartonella henselae, Campylobacter, Legionella, Salmonella and Salmonella typhi.

Examples:

Example 1: Preparation of the co-doped PANI polymer
Aniline and imidazole were dissolved in an aqueous acidic medium containing 1.0 M nitric acid (HNO3) as a dopant and 1.0 M oxalic acid (C2H2O4) as a co-dopant while stirring in an ice bath. 1.0 M ammonium persulfate (NH4)2S2O8, was added dropwise to the acidified solution containing aniline at 0 °C under constant stirring (3 hours) to initiate polymerization. After 5 h, a dark colour precipitate was obtained through filtration and washed with distilled deionized water and ethanol until the filtrate was colorless to ensure the complete removal of any impurities and unreacted reagents. After washing and drying, it was found that the pure PANI-1H-Imidazole copolymer produced with this process was dark green. It was oven-dried for 24 hours at 60-70°C to get a free-flowing powder of the polyaniline-1H-imidazole copolymer. The final compound was characterized by
Example 2: Antimicrobial activity of PANI-1H-Imidazole
The antibacterial activity of the PANI-1H-Imidazole was tested against both gram-negative bacteria Escherichia coli (E. coli) and gram-positive Staphylococcus Aureus (S. aureus) and measured in terms of IC50, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The IC50 was found to be 10 µg/mL against E. coli and 0.75 µg/mL against S. aureus respectively. In addition, the MIC was found to be 1 µg/mL and 0.5 µg/mL against E. coli and S. aureus respectively whereas the MBC was found as 100 µg/mL and 80 µg/mL against E. coli and S. aureus respectively. As a result, the synthesized co-doped PANI-1H-Imidazole has higher antibacterial activity than pure polyaniline (PANI) (Table 1, Figure 1).
Table 1. Antibacterial activity of PANI, and PANI-1H-Imidazole
E. coli
Sr. No. Name of Composites MIC
(µg/mL) IC50 (µg/mL) MBC (µg/mL)
1. PANI 10 50 150
2. PANI-1H-Imidazole 1 10 100
S. aureus
3. PANI 4 10 120
4. PANI-1H-Imidazole 0.50 0.75 80

Example 3: Conductivity measurement of PANI-1H-Imidazole
The imidazole-substituted polyanilines have been prepared by substitution of imidazole moieties on the polyaniline backbone. Structural analysis indicated that the interactions of polyaniline with imidazole moieties occur at the nitrogen atom of imine groups on polymeric chain backbones which led to the increase of delocalization of conjugated electrons and ordered arrays of polymer chains. An enhancement of conductivity has been observed by the substitution of imidazole moieties on the polyaniline backbone. The conductivity has been reported 1.941 x 10-5 S/cm for the PANI and 2.008 x 10-4 S/cm for PANI-1H-Imidazole. As a result, the synthesized co-doped PANI-1H-Imidazole has higher conductivity than pure PANI. Plotted graphs of resistivity (a) log10 ? vs 1000/T and conductivity (b) log10 s vs 1000/T of PANI and PANI-1H-Imidazole are shown in Figure 2. The slope (m) and conductivity of) are shown in Table 2.
Table 2: Conductivity and slope of PANI and modified polyaniline (PANI-1H-Imidazole
Sr. No. Name of Composites Slope (m) Band Gap (Eg)
Conductivity (S/cm)
1. PANI 0.311 0.617 1.941 x 10-5
2. PANI-1H-Imidazole 3.213 0.638 2.008 x 10-4

, Claims:We claim:
1. Novel Co-doped Polyaniline Fused Imidazole Copolymer represented by Formula I.

Formula I
2. A process for preparing the Novel Co-doped Polyaniline Fused Imidazole Copolymer as claimed in claim 1, said process comprising:
(vi) Dissolving aniline and imidazole in aqueous acidic media containing one or more dopant and co-dopant at a temp of 0-5°C,
(vii) Adding an oxidizing agent to (i) at a temperature of 0-5°C under constant stirring to initiate polymerization,
(viii) Filtering the reaction mass of step after 4-6 hours to obtain a precipitate,
(ix) Washing the said precipitate with de-ionized water and alcohol to obtain a pure precipitate, and/or
(x) Drying the pure precipitate to obtain the co-doped PANI-1H-imidazole copolymer.
3. The process as claimed in claim 1 wherein the dopant is an inorganic acid selected from hydrochloric acid, sulfuric acid and nitric acid.
4. The process as claimed in claim 1 wherein co-dopant is an organic acid selected from acetic acid, oxalic acid, citric acid, malic acid, formic acid, lactic acid, and maleic acid.
5. The process as claimed in claim 1 wherein oxidant is selected from hydrogen peroxide, ozone, sodium percarbonate, sodium permanganate, potassium permanganate, sodium perborate, sodium persulfate, potassium persulfate, ammonium persulfate.
6. The process as claimed in claim 1 wherein oxidant is ammonium persulfate.
7. The process as claimed in claim 1 wherein the dopant is nitric acid and co-dopant is oxalic acid.
8. An antimicrobial composition comprising the novel co-doped polyaniline fused imidazole copolymer as claimed in claim 1.