Spectral correlations and antimicrobial activities of some 1-pyrenyl chalcones

A series of 1-pyrenyl chalcones have been synthesized by Crossed-Aldol condensation of 1-acetylpyrene and substituted benzaldehydes. The purities of these chalcones have been checked by their physical constants, UV, IR, NMR and MASS spectral data. The spectral data of these chalcones have been correlated with Hammett sigma constants, F and R parameters using single and multi-linear regression analysis. From the results of statistical analysis, the effect of substituents on the spectral group frequencies have been discussed. The anti-microbial activities of these chalcones have been evaluated using Bauer-Kirby method.


1. General
All chemicals used were purchased from Sigma-Aldrich and E-Merck chemical companies. Melting points of all chalcones were determined in open glass capillaries on Mettler FP51 melting point apparatus and are uncorrected. The ELICO BL 222 ultraviolet spectrophotometer was utilized for recording the absorption maxima (λmax, nm), of all chalcones in spectral grade methanol. Infrared spectra (KBr, 4000-400 cm -1 ) were recorded AVATAR-300 Fourier transform spectrophotometer. Bruker AV400 NMR spectrometer was used for recording NMR spectra operating at 400 MHz for 1 H spectra and 125.46 MHz for 13 C spectra in CDCl 3 solvent using TMS as internal standard. Mass spectra of all chalcones were recorded on SHIMADZU spectrometer using chemical ionization technique.

Synthesis of Chalcones
All substituted styryl-1-pyrenyl chalcones were synthesized by procedure published in literature. An equi-molar quantities of 1-acetylpyrene (2 mmol) and substituted benzaldehydes (2 mmol), Fly-ash(0.5 g) with 20 mL of water [19,31] (Scheme 1) were refluxed for 4h. and the completion of the reaction was monitored by thin layer chromatography. After completion of the reaction, the solid product was separated by filtration. Further the product was purified by column chromatography using dichloromethane and ethyl acetate mixture as eluent. The physical constants, analytical and mass fragments were presented in Table 1.

RESULTS AND DISCUSSION
In the present study the authors have studied the effects of substituents on the spectral data such as ultraviolet absorption maxima (λmax, nm), infrared spectral carbonyl and deformation modes (ν, cm -1 ), the chemical shifts (δ, ppm) of α,β protons, and carbonyl carbons of synthesized 1pyrrenyl chalcones with Hammett substituent constants, F and R parameters using single and multilinear regression analysis for predicting the reactivity on the group frequencies.

1. UV spectral study
The measured ultraviolet absorption maxima (λmax, nm) of all 1-pyrenyl chalcones were tabulated in Table 2. These values are correlated [1, 2, 6, 10, 19, 21, 23-25, 28, 32] with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis. While seeking Hammett correlation, involving UV absorption maximum values, the form of the Hammett equation employed is as given in equation.
The results of statistical analysis are presented in Table 3. From the Table 3, the correlation of absorption maxima (λmax, nm) with F parameter is satisfactory. The remaining Hammett substituent constants and R parameter were failing in correlation.
International Letters of Chemistry, Physics and Astronomy Vol. 10   This is due to the inductive and resonance effects of substituents incapable for predicting the reactivity on the absorption and is associated with the resonance conjugated structure as shown in Fig. 1. In single parameter correlation, the Hammett substituents constants not obeyed in the regression.
While seeking these parameters in multi-regression, with F and R Swain-Lupton's [33] constants, they gave satisfactory correlations. The multi correlation equations are given in 2 and 3.

2. IR spectral study
The synthesized chalcones in the present study are shown in Scheme 1. The carbonyl stretching frequencies (cm -1 ) of s-cis and s-trans of isomers are tabulated in in Table 2 and the corresponding conformers are shown in Fig. 2. Hammett substituent constants and Swain-Lupton constants [33]. In this correlation the structure parameter Hammett equation employed is as shown in the following equation: Where υ is the carbonyl frequencies of substituted system and υ 0 is the corresponding quantity of unsubstitued system; σ is a Hammett substituent constant, which in principle is characteristics of the substituent and ρ is a reaction constant which is depend upon the nature of the reaction.
The results of statistical analysis [1, 2, 6, 10, 19, 21, 23-25, 28, 32] were shown in Table 3, From table 3, The resonance component only correlated satisfactorily with CO s-cis conformers stretches. The remaining Hammett substituent constants and F parameters were fail in correlation. The Hammett σ and F parameters gave satisfactory correlation with CO s-cis conformers stretches. The remaining Hammett substituent constants and R parameters were fail in correlation. This is due to the reasons stated in earlier and associated with the resonance conjugative structure shown in Fig.  1.
The correlation of CH ip modes with Hammett σ R and R parameters gave satisfactory correlation. The remaining The remaining Hammett substituent constants and F parameters were fail in correlation. The Hammett σ constants correlated satisfactorily with CH op modes of all chalcones. The remaining Hammett substituent constants, F and R parameters gave poor correlation. This failure in correlation is due to the incapability of polar and inductive effects of the substituents and associated with the resonance conjugative structure as shown in Fig. 1.
The Hammett σ and σ+ constants gave satisfactory correlation with CH=CH op modes. The inductive, resonance and field components of the substituents are failed in correlation. The Hammett σ, σ+ and σ R constants were satisfactorily correlated with C=C op modes. The inductive components of the substituents, F and R parameters failed in correlation. This is due to the reasons stated earlier and associated with the resonance conjugative structure as shown in Fig. 1.
Some of the single parameter correlations with Hammett substituent constants were not obeyed in the regression. While seeking these parameters in multi-regression, with F and R Swain-Lupton's constants [33], they gave satisfactory correlations with the infrared red group frequencies.
The multi correlation equations are given in 5 -16.  Then the discs with 5mm diameter made up of Whatmann No.1 filter paper, impregnated with the solution of the compound were placed on the medium using sterile foreceps. The plates were incubated for 24 hours at 37 °C by keeping the plates upside down to prevent the collection of water droplets over the medium. After 24 hours, the plates were visually examined and the diameter values of the zone of inhibition were measured. Triplicate results were recorded by repeating the same procedure. The antibacterial effect of the styryl 1-pyrenyl ketones is shown in Fig. 3   The test solution was prepared by dissolving 15 mg of the Chalcone in 1mL of DMSO solvent. The medium was allowed to solidify and kept for 24 hours. Then the plates were visually examined and the diameter values of zone of inhibition were measured. Triplicate results were recorded by repeating the same procedure. The antifungal effect of the styryl 1-pyrene ketones is shown in Fig. 5 for Plates (1)(2)(3)(4)(5)(6). Analysis of the zone of inhibition as given Table 5

CONCLUSIONS
A series of 1-pyrenyl chalcones have been synthesized by Crossed-Aldol condensation. The spectral data of these chalcones have been correlated with Hammett sigma constants, F and R parameters using single and multi-linear regression analysis. From the results of statistical analysis, the effects of substituents on the spectral group frequencies have been discussed. The antimicrobial activities of these chalcones have been studied International Letters of Chemistry, Physics and Astronomy Vol. 10 35