A New Flavone from Erythrina suberosa, its Biological Screening and Application as pH Indicator

A new flavone is isolated, characterized and its pH indicator property is studied for titration between strong/weak acids and bases. Flavone (Z)-3-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-5-(isopentyloxy)-7-methoxy-6-(2methylpent-1-en-1-yl) chromenylium chloride has been isolated by extracting ether and methanol. Compound is separated using column chromatography and identified with the help of spectroscopic techniques such as mass, 1HNMR, IR and UV. Compound is also screened for its antibacterial and anti-fungal activity from the flower extract of Erythrina suberosa. Activity of the isolated compound is observed for E Coli bacteria as a gram-negative organism. The compound shows significant color change in acidic and alkaline medium and its potential as pH indicator is encouraging.


Introduction
Researchers are more concerned about environmental pollution and climate change. They are working day and night to curb the pollution and decrease environmental pollution by developing methods and material which are less hazardous and biodegradable. Researchers are giving more emphasis on natural products as they are easily available, of low cost, bio-degradable and also have a wide range of biological and physiological activity.
Nowadays, researchers are isolating natural products from various parts of the plants [1][2][3]. Natural products are having fewer side effects therefore researchers are trying to find compounds with medicinal, bacteriological, antifungal, antibiotic, antitumor and anti-oxidant activities [4][5][6][7]. Some of the natural products show different colors at different pH, thus can be used as indicator. Colored or pigmented compounds impart color such as acylated or glycosidic flavones, isoflavones, flavonol, anthocyanin, anthraquionoids, indigoids, carotene etc present in flowers [8][9]. Degradation of the above compounds depends on isolation processes, storage and temperature. Due to hydrolysis at glycosidic bond these compounds loose color [10][11][12]. Flavones, flavonols and anthocyanin loose color due to thermal degradation to chalcones and coumarins. In view of this, herein we described for the first time isolation of flavone from erythrina suberosa, it's antibacterial and antifungal activities and application as pH indicator  [15][16]. Chemical method for detection of different natural products is done as per the procedure available in literature [17]. Isolated compound were identified using UV, mass, IR. and 1 HNMR data. On the basis of the above data structure of the compound is elucidated as (Z)-3-hydroxy-2-(4hydroxy-3-methoxyphenyl)-5-(isopentyloxy)-7methoxy-6-(2-methylpent-1-en-1yl)chromenylium chloride (Figure:1). The compound melts between 40 to 42 o C this might be due to partial degradation of the compound. The compound is also studied for its color change in acidic and alkaline media and show different colors in these medium. Titrations of different acids and bases with four different concentrations were studied. Absolute error, relative error and percentage errors are calculated for different set of titrations. Results for strong acid Vs Strong base (Table 1), weak acid Vs Strong base ( Table 2) strong acid Vs weak base (Table  3), weak acid Vs weak base (Table 4), strong acid Vs Strong base reverse titration (Table 5), and % OH and alkali error ( Table 6) suggest that compound is suitable to be used as pH indicator for acid-base titrations at various concentrations. Since the compound is biodegradable [18][19][20], it has advantage over synthetic and nonbiodegradable indicators used for titrations.

Microbial analysis
The compound is screened for biological activity. It is found be more active against gram negative bacteria E-coli with a zone diameter of 1 cm and staphylococcus aurena as a gram positive bacteria having a zone diameter of 0.5 cm. The compound found to be inactive against the fungal cultures used for the study i.e aspergillus niger and candida albicans.

Material and Methods
Flowers were collected about 5 Kg from Harsool nearby area of Aurangabad, identified as Erythrina suberosa. Petals were separated, dried in dark and macerated before extraction. All the chemicals used for present work were of analytical grade from SD-Fine chemicals Ltd and used without further purification otherwise mentioned. Solutions required during the study were prepared in glass double distilled water and standardized as per the standard procedures available in literature [13][14].

Conclusions
The compound isolated from erythrina suberosa showed different colour in acidic and alkaline medium which reveals that it can be used as pH indicator. This will help in reducing the use of synthetic dyes as pH indicators which are nonbio-degradable.