Search

This study is aimed to shed light on the electronic absorption and emission spectra of DBDMA (2-(1-(difluoroboraneyl)-1,2-dihydroquinolin-2-yl)-2-(1-methylquinoxalin-2-ylidene) acetonitrile) in different solvents. Both types of spectra were obtained theoretically and produced experimentally in different solvents. The photostability of dye was tested, and its energy transfer behavior in the presence of oxygen and hydrated copper sulfate quenchers was investigated. We also gave a qualitative estimation of the effect of acidic media on the absorption and emission spectra. There is good compatibility between the calculated and measured values of many photophysical parameters. DBDMA has a low chemical quantum yield in solvents of different polarities, and the fluorescence quantum yield is high enough, which confirms, together with the low values of the excited state lifetime, its efficiency as laser emitting dye in the range of wavelength emission maxima. The rigidity of the DBDMA molecule is the main reason for the photochemical stability and the absence of a considerable shift as a result of the change in the polarity of the solvents. Geometries of ground and excited states were optimized using the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT), respectively. Upon using the TD-DFT method, the UV-Vis absorption and emission spectra of the DBDMA molecule in different solvents were illustrated. A slight change is observed in the position of the maximum emission and absorption wavelength with the change of the solvent due to the rigidity of the compound. There was no apparent effect of quenching by oxygen. Besides, no intersystem crossing (ISC) was observed for the excited state of the DBDMA as a result of aeration of a solution with O2 for 20 min, which was an explanation of the stability of peak emission intensity of dye after exposure to oxygen gas. The energy transfer rate constant has been calculated as well.

A closed-vessel microwave digestion method was developed for the simultaneous determination of macro, micro, and toxic elements (Mg, K, Ca, Al, Mn, Fe, Cu, Zn, Se, Rb, V, Cd, and As) in wheat by inductively coupled plasma mass spectrometry (ICP-MS). A two-level factorial design with four variables was employed to determine the optimal conditions for the significant parameters. The optimal conditions for microwave digestion of ground wheat samples were found to be 0.5 g of the sample, 9 mL of 8 mol/L HNO3, and 3 mL of 33% H2O2 at 210°C. The analytical method was validated, and the accuracy of the method was then evaluated through analysis of wheat flour-certified standard reference materials (NIST SRM 1567b). The validated procedure was subsequently applied to the analysis of 12 wheat samples sourced from local farms in the Al-Qassim region and a further six samples purchased from the Al-Qassim markets, covering six imported brands common in Saudi Arabia. The results of the study showed that the level of minerals in wheat grown in desert areas is higher than in other areas. The concentrations of macroelements and microelements in the Al-Qassim samples exceeded those of the imported samples by 12.41% and those of the samples from other countries by 33.90%. The results were also evaluated using multivariate analysis techniques: principal component analysis (PCA) and hierarchical cluster analysis (HCA).

A new coumarin derivative, (E)-3-(3-(4-(dimethylamino) phenyl) acrylo-yl)-4-hydroxy-2H-chromen-2-one (3), was synthesized by the condensation of 3-acetyl-4-hydroxycoumarin (1) with 4-N,N-dimethylaminobenzaldehyde (2) in the presence of piperidine in ethanol. The structure of the synthesized compound was characterized using spectroscopic data (IR and 1H NMR) and elemental analysis. The antimicrobial properties and acetylcholinesterase inhibition activity (AChEI) of coumarin 3 were investigated, with the highest observed AChEI activity providing 48.25% inhibition. The electronic absorption and emission spectra revealed that 3 exists as two, main keto-enol tautomers. The ratios of these tautomers in both protic and aprotic solvents with different polarities and dielectric constants were calculated. The fluorescence of coumarin 3 was enhanced upon increasing the medium viscosity, which was due to the resultant molecular rigidity. This criterion was further investigated using DNA, whereby 3 showed enhanced fluorescence upon its uptake in DNA grooves and was therefore tested as a novel DNA fluorescent stain.