Investigating the Effect of Silver Nanoparticles on the Fluorescence Intensity of Bambuterol and its Active Metabolite Terbutaline Using FRET.

Silver nanoparticles (AgNPs) were found to significantly quench the fluorescence of bambuterol hydrochloride (BAM) and its active metabolite terbutaline sulfate (TER). The intrinsic fluorescence intensity of each of BAM (at 264/292 nm) and TER (at 276/306 nm) decreased by the gradual addition of AgNPs. Quenching of the steady state fluorescence of BAM and TER probably resulted from the energy transfer to the photo-excited state of AgNPs. The estimated Stern-Volmer quenching constant at several temperature settings proved that the quenching mechanism of the two drugs was dynamic quenching in case of BAM while it was static quenching in case of TER. The number of binding sites, binding constants, and corresponding thermodynamic parameters depending on the interaction system were estimated at 293, 313, and 333 °K and the results obtained were interpreted.

Insights for applying N,S-doped carbon dots as a fluorescent nanoprobe for estimation of some nitro-calcium channel blockers.

A facile and simple one-step hydrothermal approach was adopted for fabrication of N and S co-doped carbon quantum dots probe (NSCDs) by using thiosemicarbazide as a dopant and citric acid as a precursor. The prepared NSCDs with a high quantum yield of 0.58 were characterized using UV-visible spectroscopy, IR spectroscopy and high-resolution transmission electron microscopy. The as-obtained NSCDs could be deemed as an effective fluorescent nanosensor for the determination of some anti-hypertensive nitro-calcium channel blockers (Nitro-CCBs) including nicardipine (NIC), nifedipine (NIF) and nimodipine (NIM) whether in pure form or in their pharmaceutical formulations. Measurements of NSCD emission intensity were performed at 416 nm after being excited at 345 nm. Nitro-CCBs could induce quenching in the native fluorescence of NSCDs due to the inner filter effect and static quenching mechanism. The studied compounds were investigated within linear detection range of (10.0-100.0 µM) for NIC, (5.0-60.0 µM) for NIF and (5.0-60.0 µM) for NIM. Correlation coefficients are greater than or equal to 0.9998 and detection limits are ranged between 0.55 and 1.86 µM. The proposed method was extended to estimate the studied compounds in different pharmaceutical samples with high % recoveries ranging from (97.95 to 101.28%) and low % relative standard deviation values (less than 2%). Validation of the developed spectrofluorimetric method was done along with the International Council of Harmonization requirements.

Turn-off fluorescence of nitrogen and sulfur carbon quantum dots as effective fluorescent probes for determination of imatinib. Application to biological fluids.

Nitrogen and sulfur carbon quantum dots(N,S-CQDs) as effective fluorescent nanoprobes were synthesized through one-step-hydrothermal method using thiosemicarbazide (as nitrogen and sulfur source) and citric acid (as carbon source). The highly fluorescent N,S-CQDs were subjected to various characterization techniques. The fluorescence of the synthesized N,S-CQDs is characterized by maximum fluorescence emission at 415 nm after excitation at 345 nm and a high quantum yield of 0.58. The native N,S-CQDs fluorescence is quantitatively quenched upon addition of imatinib (IMA), so they are used for its spectrofluorimetric determination in its pharmaceutical formulations and biological fluids. Under optimal conditions, N,S-CQDs exhibited a "turn-off" fluorescence response to IMA over the range of 1.0 to 15.0 µg/mL with a limit of quantification of 0.42 µg/mL and a lower detection limit of 0.14 µg/mL. Stern-Volmer equation was used to study the mechanism of quenching and it was found to occur through static quenching mechanism. The method was extended to the in-vitro determination of the drug in spiked human urine and plasma samples and the percent recoveries were satisfactory.

First derivative synchronous fluorescence spectroscopy for the simultaneous determination of sulpiride and mebeverine hydrochloride in their combined tablets and application to real human plasma.

A rapid, simple and highly sensitive first derivative synchronous fluorometric method has been developed for the simultaneous analysis of binary mixture of sulpiride (SUL) and mebeverine hydrochloride (MEB). The method is based upon measurement of the synchronous fluorescence intensity of these drugs at ∆λ = 100 nm in water. The different experimental parameters affecting the fluorescence of the two drugs were carefully studied and optimized. The fluorescence-concentration plots were rectilinear over the range of 0.05-1 µg/mL and 0.2-3.2 µg/mL for SUL and MEB respectively with lower detection limits (LOD) of 0.006 and 0.01 µg/mL and quantification limits (LOQ) of 0.0.02 and 0.05 µg/mL for SUL and MEB, respectively. The proposed method was successfully applied for the determination of the two compounds in synthetic mixtures and in commercial tablets. The high sensitivity attained by the proposed method allowed the determination of both of SUL and MEB metabolite (veratic acid) in real human plasma samples applying second derivative synchronous fluorometric technique. The mean% recoveries (n = 3) for both MEB metabolite (veratic acid) and SUL were 99.82 ± 2.53 and 98.84 ± 6.20 for spiked human plasma respectively, while for real human plasma, the mean% recoveries (n = 3) were 91.49 ± 4.25 and 91.36 ± 8.46 respectively.

Spectrophotometric determination of fenoterol hydrobromide in pure form and dosage forms.

A sensitive and rapid spectrophotometric procedure has been investigated for the determination of fenoterol either per se or in pharmaceutical preparations. The proposed procedure is based on the reaction between the drug and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) at pH 7.2, using borate buffer, to produce a yellow adduct. The latter has maximum absorbance at 400 nm and obeys Beer's law within the concentration range 5-30 microg/ml. Regression analysis of the calibration data showed a good correlation coefficient (r=0.9996) with minimum detection limit of 0.24 microg/ml (6.2 x 10(-8) M). The proposed procedure has been successfully applied to the determination of this drug in its tablets and in syrup, the mean percent recoveries were 97.45+/-0.59 and 98.7+/-0.64%, respectively. The results obtained are in good agreement with those given using a reference method. The pharmaceutical additives other than active ingredient did not interfere. A proposal of the reaction pathway has been postulated.