Maurice O. Iwunze

Aqueous Photophysical Parameters of Congo Red

ABSTRACT Using steady-state fluorescence spectroscopy and UV-Vis absorbance spectrometry, the salient photophysical parameters of Congo red, a very important biological staining reagent, was determined. Its absorbance was observed at 497.0 nm; its molar absorptivity ϵ was determined as 6.26 × 104 M–cm. Its fluorescence, when excited at 330.0 nm, was observed at 417.0 nm. The quantum yield, ф, in aqueous solution was determined by two different methods—the relative, or comparative, method and the absolute method. Both methods gave the same value of 0.011. The room temperature fluorescence lifetime τo was determined as 2.8 ns using the Strickler–Berg equation.

Synthesis and characterization of fluoride fluorescent sensor

Due to the importance of fluoride in clinical treatment of osteoporosis and its toxicity from over accumulation in bones there is an increased interest in developing selective optical methods for the detection of fluoride anion. Anion recognition and sensing are of interest because of their importance in biological environmental assays and efforts are paid for developing sensitive methods. We synthesized salicylidene furfurylamine 1 and studied spectral properties. Compound 1 fluoresced strongly and the fluorescence was strongly enhanced in the presence of anions as fluoride at low concentrations. A substantially red-shifted emission in acetonitrile was observed. The excitation at 390 nm and the emission was observed at 469nm. Fluoride showed strong absorption and fluorescence enhancement with a significant Stokes shift. Acetate, dihydrogen phosphate, showed small effect, while chloride, bromide had no significant effect.

Characterization of fluorescent surfactant aggregates by fluorimetric and viscosimetric techniques

SummaryA combination of fluorimetric and viscosimetric methods was used to characterize N,N-dimethyl-N-2-(4-(t-butylphenoxy)ethoxy)ethyl-N-hexadecylammonium chloride (BDHC), a doubletailed surfactant with dissimilar tail groups.BDHC was observed to fluoresce at 315 nm when excited at 274 nm, a feature which could be utilized to determine its critical micelle concentration (CMC). A value of 3.98×10−5M was obtained and was observed to be slightly temperature dependent with aTmin of 25.35°C. Fluorescence quenching experiments using 4-nitroaniline as a quencher were performed in order to determine the aggregation number which was found to be 42.0. The hydrodynamic radius of 21.91 Å was obtained using data from viscosimetric experiments. These data, together with theTanford andEinstein-Stokes relationships, were used to determine the micellar structure (spherical) and the diffusion coefficient (D=0.97×10−6 cm2/s), respectively. The ΔG of micellization forBDHC was determined to be −34.9 kJ/mol.ZusammenfassungDie Verbindung N,N-Dimethyl-N-2-(4-(t-butylphenoxy)ethoxy)ethyl-N-hexadecylammoniumchlorid (BDHC), eine oberflächenaktive Substanz mit zwei unterschiedlichen Seitenketten, wurde mittels einer Kombination von fluorimetrischen und viskosimetrischen Methoden charakterisiert. Anregung bei 274 nm ruft eine Fluoreszenz bei 315 nm hervor; diese Eigenschaft wurde zur Bestimmung der kritischen Micellenkonzentration (CMC) herangezogen. Es wurde ein geringfügig temperaturabhängiger Wert von 3.98×10−5M gefunden (Tmin=25.35°C). Quenchexperimente mit 4-Nitroanilin ergaben eine Aggregationszahl von 42.0, viskosimetrische Untersuchungen einen hydrodynamischen Radius von 21.91 Å. Die erhaltenen Daten erlauben zusammen mit den Beziehungen nachTanford undEinstein-Stokes die Bestimmung der Micellenstruktur (sphärisch) und des Diffusionskoeffizienten (0.97×10−6 cm2/s). Das ΔG der Micellenbildung fürBDHC beträgt −34.9 kJ/mol.

Characterization of Cr-Curcumin Complex by Differential Pulse Voltammetry and UV-Vis Spectrophotometry

Differential Pulse Voltammetry (DPV) and UV-Vis techniques were used in characterizing the complexation of chromium with curcumin. It was observed that chromium complexed with curcumin in a 1 : 3 ratio. The experimental values that were used to calculate this ratio were independently determined by the two techniques used. The values obtained from each technique agree with each other reasonably well, within limits of experimental error. The stability constant or formation constant, , of the complex, , was determined using the Lingane equation and Gibb’s free energy of formation was calculated as −58.18 kJ.