Spectral correlation analysis and antimicrobial activities of some 2,4-dimethoxy phenyl chalcones

A series of 2,4-dimethoxy phenyl chalcones have been synthesized by Crossed-Aldol condensation of 2,4-dimethoxy phenyl and various 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 effects 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 ultraviolet spectrophotometer was utilized for recording the absorption maxima (λmax, nm), of all chalcones in spectral grade solvent. Infrared spectra (KBr, 4000-400cm -1 ) were recorded AVATAR-300 Fourier transform spectrophotometer. BRUKER AVANCE III-500MHz NMR spectrometer was used for recording NMR spectra operating at 500MHz 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.

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 2,4-dimethoxy phenyl chalcones with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis for predicting the reactivity on the group frequencies.
The results of statistical analysis are presented in Table 3. From the Table 3, the correlation of absorption maxima (λmax, nm) with σ and σ + parameter is satisfactory. The remaining Hammett substituent constants, F and R parameter were failing in correlation. This

50
ILCPA Volume 23 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 [37] constants, they gave satisfactory correlations. The multi correlation equations are given in (2) Table 3. Results of statistical analysis of ultraviolet absorption maxima (λmax, nm), infrared absorptions (ν, cm -1 ) and NMR chemical shifts (δ, ppm) of substituted styryl 2,4-dimethoxy phenyl ketones with Hammett σ, σ + ,σ I , σ R and F and R parameters.

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 Table 2 and the corresponding conformers are shown in Fig. 2. The stretching frequencies for carbonyl absorption are assigned based on the assignments made by Hays and Timmons [2] for s-cis and s-trans conformers at 1690 and 1670 cm -1 , respectively. The assigned infrared COs-cis and s-trans conformers have been correlated with Hammett substituent constants and Swain-Lupton constants [37]. In this correlation the structure parameter Hammett equation employed is as shown in the following equation: ν = ρσ + ν 0 … (4)

International Letters of Chemistry, Physics and Astronomy Vol. 23
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][24][25]28,37] 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 failing in correlation. The Hammett σ I and F parameters gave satisfactory correlation with CO s-trans conformers stretches. The remaining Hammett substituent constants and R parameters were failing 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 and σ + constant gave satisfactory correlation. The remaining Hammett substituent constants, F and R parameters were failing in correlation. The Hammett σ and 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 remaining Hammett substituent constants and F and R parameter failed in correlation due to the inductive, resonance and field components of the substituents. The Hammett σ R constants, F and R were satisfactorily correlated with C=C op modes. The inductive components of the substituents σ, σ + and σ I constants 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 [37], they gave satisfactory correlations with the infrared red group frequencies. The multi correlation equations are given in (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16).
The remaining Hammett substituent constant σ I and F parameter were failing in correlations due to the inductive and field effects of the substituents. Hammett σ+ constant only one gave satisfactory correlation with H β chemical shifts (δ, ppm). The remaining Hammett substituent constants and parameter failure in correlation for both chemical shifts are the reasons stated earlier and associated with the resonance -conjugated structure 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 [37] constants, they gave satisfactory correlations with the chemical shifts of (δ, ppm ) Hα and Hβ. The multi correlation equations are given in (17)(18)(19)(20).  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 2,4-dimethoxy phenyl ketones is shown in Fig. 3 for Plates (1)- (10). Analysis of the zone of inhibition as given Table 4 and the Clustered column Chart Fig. 4, reveals that all the substituents except 4-NO 2 and 2-Cl have shown moderate antibacterial activity against all the bacterial species, under investigation. Table 4. Antibacterial activity of substituted styryl 2,4-dimethoxy phenyl ketones. have shown inactive for the above two fungal species. The parent compound (H), 2-Cl, 4-Cl and 4-F substituted compound has shown equal activity against fungal species T. viride. Fig. 5. Antifungal activities substituted styryl 2,4-dimethoxy phenyl ketones. Table 5. Antifungal activity of substituted styryl 2,4-dimethoxy phenyl ketones.

CONCLUSIONS
A series of 2,4-dimethoxy phenyl 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 anti-microbial activities of these chalcones have been studied.