Novel spectrofluorimetric quantification of linagliptin in biological fluids exploiting its interaction with 4‐chloro‐7‐nitrobenzofurazan

Development and validation of an environmentally friendly fluorescence quenching method for linagliptin quantification using eosin Y: optimization via design of experiment and comparative greenness assessment

Diabetes management has increasingly relied on dipeptidyl peptidase-4 inhibitors like linagliptin, creating a need for environmentally sustainable analytical methods to replace conventional chromatographic techniques that often involve complex sample preparation, organic solvent usage, and expensive instrumentation. A sensitive and selective "turn-off" fluorescence quenching method was developed and validated for the determination of linagliptin using eosin Y as the fluorescent probe. The spectral characteristics and sensing mechanisms were investigated using Stern-Volmer analysis, Job's method, and thermodynamic studies, revealing a static quenching process driven by the formation of a non-fluorescent 1 : 1 linagliptin-eosin Y complex with a high Stern-Volmer constant (K sv = 6.46 × 105 M-1). The influencing factors, including pH, buffer volume, eosin Y concentration, and incubation time, were optimized using a Box-Behnken experimental design. A significant reduced quadratic regression model was established, and the optimal conditions were found to be pH 5.25, buffer volume of 1 mL, eosin Y volume of 1.25 mL, and an incubation time of 5 min based on desirability function analysis that maximizes the quenching efficiency. The developed method demonstrated linearity in the range of 0.1-3.0 μg mL-1 with a correlation coefficient of 0.9999, a limit of detection of 0.03 μg mL-1, and accuracy of 99.59 ± 1.360%, in accordance with ICH guidelines. Selectivity was confirmed by the lack of interference from common pharmaceutical excipients and endogenous plasma components. The eosin Y-based fluorescence quenching method was successfully applied for the determination of linagliptin in pharmaceutical dosage forms and spiked human plasma samples. Statistical comparison of the proposed method with the reported HPLC-UV method revealed comparable analytical performance as evident by non-significant differences in the accuracy and precision profiles as well as interval equivalence testing. Furthermore, a comprehensive assessment of the environmental impact and analytical practicality of the proposed method was conducted, confirming its "green" and "blue" analytical profile. These findings establish the eosin Y-based fluorescence quenching method as a viable and environmentally friendly alternative for the routine analysis of linagliptin in various pharmaceutical and bioanalytical applications shedding light on the potential of spectrofluorometric techniques in green analytical chemistry and bioanalysis.

Spectrofluorimetric Determination of 7-Aminoclonazepam, a Major Clonazepam Metabolite, in Human Urine: A Factorial Design of Experiment Approach to Optimize Method Development

Clonazepam, a high-potency benzodiazepine widely prescribed for seizure and panic disorders, carries a risk of abuse and dependency. This study developed a sensitive and selective spectrofluorimetric method for determining 7-aminoclonazepam, the major metabolite of clonazepam, in human urine. A 26-2 factorial design was employed to screen the optimal conditions for derivatization with NBD-Cl as the fluorescent label, considering factors such as pH, reagent volumes, temperature, and reaction time. A significant model was attained (p < 0.0001) revealing alkaline pH (9), elevated temperature (80°C), and high reagent concentrations as crucial for maximizing fluorescence intensity. The method demonstrated excellent linearity from 10 to 500 ng/mL (R2 = 0.9997), with limits of detection and quantitation of 3.3 and 10 ng/mL, respectively. Intra- and inter-day precision (% RSD) were less than 4%, and recoveries ranged from 97.59% to 106.12%. The method also showed no significant interference from endogenous compounds, pharmaceutical excipients, or the parent drug. Applicability of the method was validated in human subjects receiving clonazepam therapy; 7-aminoclonazepam was first detected after 12 h, peaked at 24 h (54.61 ± 9.870 ng/mL), and remained detectable up to 72 h post-dose, offering a simple, cost-effective spectrofluorimetric method for monitoring clonazepam metabolism in clinical and forensic settings.

Dual benefits of NBD-Cl fluorogenic action and sample pretreatment (SALLE) technology in the assessment of anticoagulant medication: Dabigatran in pharmaceutical capsules and plasma samples

Dabigatran (DBG), marketed as Pradaxa, is an anticoagulant medication prescribed for the treatment and mitigation of blood clots and to lower the risk of stroke in individuals with the heart condition known as atrial fibrillation. This medication is specifically indicated for preventing blood clots post hip or knee replacement surgeries and in patients with a prior history of clots. Compared to warfarin, dabigatran serves as a viable alternative that does not necessitate routine blood monitoring tests. The complimentary benefits associated with SALL (salting-out assisted liquid-liquid extraction) and the fluorogenic capabilities of benzofurazan. These methods were combined to provide an affordable and sensitive DBG assaying method. The spectral strength of the yellow luminous product was examined at 533.8 nm and by adjustment of a wavelength of 474.7 nm for excitation. To assess its linearity, the calibration chart was tested across a DBG concentration range of 30-500 ng/ml. Via accurate computation based on ICH, the detection limit (LD) was determined to be 9.5 ng/ml, and the strategy can quantify the DBG to a limit of 28 ng/ml. To ensure success, various crucial parameters for method implementation have been extensively studied and adapted. The validation of the strategy adhered to the policies outlined by ICH, affirming its precision in quantifying DBG in capsules. Furthermore, the inclusion of SALLE steps facilitated accurate monitoring of DBG in plasma samples, introducing a unique and advanced methodology for analyzing this compound in biological samples.

Development of fluorescence probe for spectrofluorimetric determination of viloxazine hydrochloride in pharmaceutical form and rat plasma; additional pharmacokinetic study

Attention deficit hyperactivity disorder (ADHD) is a neurological condition frequently identified in early childhood and frequently co-occurs with other neuropsychological disorders, particularly autism. Viloxazine hydrochloride, a non-stimulant medication, has recently gained approval for treating attention-deficit hyperactivity disorder. This paper describes the first spectrofluorimetric method for precisely measuring the content of viloxazine in pharmaceutical capsules and rat plasma. This method employed NBD-Cl (4-chloro-7-nitrobenzo-2-oxa-1,3-diazole) as a fluorescent probe, which transformed viloxazine in an alkaline environment into a remarkably sensitive fluorescent adduct. Upon excitation at 476 nm, this adduct becomes detectable at a wavelength of 536 nm. The method was validated using ICH criteria, revealing acceptable linearity across a concentration range of 200-2000 ng/ml and high sensitivity with LOD and LOQ values of 46.774 ng/ml and 141.741 ng/ml, respectively. This method was adeptly applied in a pharmacokinetic study of viloxazine in rat plasma following a single oral dose (10 mg/kg), yielding a mean peak plasma concentration (Cmax) of 1721 ng/ml, achieved within 1.5 h. Furthermore, the environmental impact of the technique was assessed using two greenness assessment tools, revealing a notable level of eco-friendliness and sustainability.

Development of sensitive spectrofluorometric approach based on formation of pyrrolidone derivative for determination of linagliptin through condensation reaction with ninhydrin and phenylacetaldehyde: Application to content uniformity and real plasma

The new drug linagliptin belongs to the class of dipeptidyl peptidase-4 enzyme inhibitors. Linagliptin is used to treat type 2 diabetes and is taken orally either alone or in combination with other drugs. In this instance, a new, simple, and economical technique for analyzing linagliptin was developed by the effective use of a pyrrolidone derivative. The primary amine group of linagliptin permits its condensation with ninhydrin (0.14% w/v) to produce a fluorescent product in the presence of phenylacetaldehyde (0.02% v/v). All experimental parameters were carefully examined and adjusted in order to monitor the generation of the pyrrolidone derivative at excitation and emission wavelengths of 385 and 475 nm, respectively. The calibration graph was made by plotting the intensity of the fluorescence in relation to linagliptin concentration. A significant linearity was found for values ranging from 20 to 460 ng/mL. The process's validity has been verified by a thorough assessment of the instructions provided by the International Conference on Harmonization (ICH). The results indicate excellent uniformity with a reference method, showing that there is no substantial difference in precision and accuracy. The proposed approach was utilized for determining linagliptin in real rat plasma successfully owing to its high sensitivity. Additionally, the proposed approach was evaluated using the Eco-Scale evaluation tool and showed a high degree of eco-friendliness (86/100).

4-Azido-7-nitrobenzoxadiazole as innovative clickable fluorescence probe for trace and selective quantification of ethinylestradiol in human plasma

Quantification of ethinylestradiol (EE) in biological matrices is challenging as it is a very potent drug with a very low Cmax (75 pg.ml-1 ). Despite the high sensitivity of fluorometric methods, the detection of EE was confined because its structure exhibited very limited fluorescence. Therefore, it must be derivatized first using a fluorogenic agent to produce a more potent fluorescence derivative to achieve the desired ultrasensitive bioanalysis. Here, for the first time, we proposed a promising click fluorescent probe, 4-azido-7-nitrobenzoxadiazole (NBD-AZ) to react with the alkyne group of EE, with the help of copper sulphate and l-ascorbic acid to give a highly fluorescent and stable 1,2,3-triazole derivative. Density functional theory calculation revealed how the triazole formation affects the quantum yield and fluorescence of click reaction product when compared with NBD-AZ. The resulting triazole exhibited a strong signal at a wavelength of 540 nm after excitation at 470 nm. Reaction parameters impacting the intensity of fluorescence were cautiously studied and optimized. The suggested approach has shown outstanding performance, high linearity (25-300 pg.ml-1 ) and a low detection limit of 7.5 pg.ml-1 . The enhanced sensitivity and selectivity were exploited for analyzing EE in plasma using liquid-liquid extraction for samples cleaning up without interference from any biological components and with a mean % recovery of 100.13 ± 0.39. Accuracy, sensitivity, selectivity, simplicity, and cost-effectiveness make this approach a convincing, promising, and appealing alternative to the reported analytical methods for EE bioanalysis in different matrices.

Facile decoration of one-pot fluorescence probe-patterned reaction for sensing and ultrasensitive determination of tradjenta, a new type 2 diabetes oral therapy

Type 2 diabetes can be cured by using tradjenta (also known as Linagliptin), a new therapeutic drug that is an inhibitor of the dipeptidyl peptidase-4 enzyme. Tradjenta is administered orally alone or in combination with metiguanide or empagliflozin. An easy and specific fluorimetric analysis of Tradjenta was developed and demonstrated in the present investigation. The Hantzsch reaction method, which generates a fluorescent dihydropyridine derivative, is the basis of this assay. In a Toerell-Stenhagen buffered solution, the unsubstituted amine group of Tradjenta interacted with 2,4-Pentadione/Oxomethane. Spectrofluorimetry was utilized for this investigation at an excitation/emission wavelength of 421/480 nm. When comparing the Tradjenta concentration to the tracked fluorimetric signal, the method revealed linearity over the concentration range of 0.05 to 1.2 µg/mL. By strictly altering system parameters and analyzing the validation factors following International Council for Harmonisation (ICH) requirements, the outcomes were achieved. Finally, the proposed approach was successfully applied to assay the drug not only in its raw form and prescribed formulations but also to evaluate the tablet's uniformity of content.

Application of isoindole fluorophore formation for determination of linagliptin in the sole and co-formulated tablets: Application for plasma assay and content uniformity testing

Linagliptin is a new medicament belonging to dipeptidyl peptidase-4 enzyme inhibitors group. The mentioned medication is used to cure type 2 diabetes and is taken orally as a monotherapy or in a co-formulation with metformin. or empagliflozin. Herein, a novel, straightforward, and cost-effective method for linagliptin assay was developed with a workable use of an isoindole derivative. The primary amine moiety present in linagliptin enables its condensation with o-phthalaldehyde to form a fluorescent product in the presence of a sulfhydryl group-containing compound (2-mercaptoethanol) 0.01 % V/V. The isoindole fluorophore yield was monitored at (λ_excitation 337.8 nm, λ_emission 434.3 nm) and all experimental variables were meticulously checked and adjusted. Fluorescence intensity versus linagliptin concentration was plotted to construct the calibration graph, and excellent linearity was achieved at values between 50 and 2000 ng/mL. The validity of the method was verified through a rigorous examination of the ICH guidelines. The method application was successful for linagliptin in different dosage forms, content uniformity study, and monitoring in spiked plasma. The devised technique was demonstrated to be a promising, easy, and quick alternate method for linagliptin assayin clinical study and quality control.

Thermodynamic and Computational (DFT) Study of Non-Covalent Interaction Mechanisms of Charge Transfer Complex of Linagliptin with 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and Chloranilic acid (CHA)

This study describes the non-covalent interactions of the charge transfer complex (CT), which was responsible for the synthesis of Linagliptin (LNG) with 2,3-Dichloro-5,6-Dicyano-1,4-benzoquinone (DDQ), or with Chloranilic acid (CHA) complexes in acetonitrile (MeCN) at temperatures of (25 ± 2 °C). Then, a UV–Vis spectrophotometer was utilized to identify Linagliptin (LNG) from these complexes. For the quantitative measurement of Linagliptin in bulk form, UV–Vis techniques have been developed and validated in accordance with ICH criteria for several aspects, including selectivity, linearity, accuracy, precision, LOD, LOQ, and robustness. The optimization of the complex synthesis was based on solvent polarization; the ratio of molecules in complexes; the association constant; and Gibbs energy (ΔG°). The experimental work is supported by the computational investigation of the complexes utilizing density functional theory as well as (QTAIM); (NCI) index; and (RDG). According to the optimized conditions, Beer’s law was observed between 2.5–100 and 5–100 µM with correlation coefficients of 1.9997 and 1.9998 for LGN-DDQ and LGN-CHA complexes, respectively. For LGN-DDQ and LGN-CHA complexes, the LOD and LOQ were (1.0844 and 1.4406 μM) and (3.2861 and 4.3655 μM), respectively. The approach was successfully used to measure LGN in its bulk form with high precision and accuracy.

An electrochemical molecularly imprinted sensor based on CuBi2O4/rGO@MoS2 nanocomposite and its utilization for highly selective and sensitive for linagliptin assay

The molecularly imprinted polymers (MIP) is an outstanding electrochemical tool that demonstrates good chemical sensitivity and stability. These main advantages, coupled with the material's vast microfabrication flexibility, make molecularly imprinted sensors an attractive sensing device. Herein, it was aimed to develop a state-of-art molecularly imprinted sensor based on CuBi₂O₄/rGO@MoS₂ nanocomposite to be utilized for the detection of linagliptin (LNG), a novel hypoglycemic drug. The electrochemical characterizations of linagliptin on the surface of the modified electrode was examined via cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Several characterization methods including transmission electron microscope (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and Energy-dispersive X-ray spectroscopy(EDX), were utilized for electrode characterization. The LNG imprinted voltammetric sensor was developed in 80.0 mM phenol containing 20.0 mM LNG. CuBi₂O₄/rGO@MoS₂ nanocomposite on LNG imprinted screen-printed carbon electrode (SPCE) (MIP/CuBi₂O₄/rGO@MoS₂ nanocomposite/SCPE) exhibited a linear relationship between peak current and LNG concentration in the range 0.07-0.5 nM with a detection limit of 0.057 nM. In the existence of interfering substances, an LNG imprinted electrode was utilized to analyze urine, human plasma, and tablet samples with adequate selectivity. The developed sensor was also illustrated for stability, repeatability, reproducibility, and reusability.

Electrochemical Detection of Linagliptin and its Interaction with DNA

Objectives

Linagliptin (Lin) is a drug used in treatment of type 2 diabetes mellitus. In this study, the electrochemical detection of Lin and its interaction with DNA was analyzed for the first time using voltammetric methods by measuring the oxidation currents of the adenine bases of DNA before and after the interaction. In addition, the electrochemical properties of the Lin were studied.

Materials and Methods

The interaction between Lin and DNA was evaluated using differential pulse voltammetry. A three-electrode system comprising of a pencil graphite electrode as the working electrode, reference electrode (Ag/AgCl), and platinum wire as the auxiliary electrode was used in the electrochemical studies. Experimental conditions, such as the concentration, pH of the supporting electrolyte, and immobilization time were optimized to obtain maximum analytical signals.

Results

The adenine bases of DNA were evaluated as an analytical signal obtained at approximately +1.2 V vs. Ag/AgCl. After the Lin-DNA interaction, the oxidation currents of adenine decreased as proof of interaction. No reports have been published on Lin interacting with DNA. Based on our results, a diffusion-controlled irreversible redox process involving independent oxidation was revealed for Lin. Under optimum conditions, the detection limit was 6.7 µg/mL for DNA and 21.5 µg/mL for Lin. Based on the observations, Lin has a toxic effect on DNA.

Conclusion

We successfully demonstrated that Lin interacts with DNA, and its influence on DNA could play a vital role in the medical effect of the drug.

Development and Validation of Two New Methods for the Determination of Rilmenidine in Bulk and Pharmaceutical Preparation

In the present study, two new methods were developed and validated for the determination of rilmenidine in bulk and pharmaceutical preparation. Both methods are based on a derivatization reaction using 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) as a fluorogenic substance. The drug reagent derivatives were formed by the reaction of rilmenidine with NBD-Cl at pH 9.0 at 70°C for 40 min. The reaction mixtures were analyzed by spectrofluorimetry in the first method and high performance liquid chromatography (HPLC) in the second method. Derivatives were determined at λex 493 nm and at λem 536 nm in the spectrofluorimetric method. The separation was performed place on a Phenomenex, C18 column (250 × 4.6 mm, 5 μm i.d) using a mobile phase comprising 0.2% formic acid and acetonitrile gradient elution mode in the HPLC method. Analytes were detected by a fluorescence detector at the same wavelength. The methods were validated for limit of quantitation, linearity, robustness, recovery, limit of detection, precision and accuracy. Calibration curves for the first and second methods were found to be linear in the range of 2.0-12.0 and 250-2000 ng/mL, respectively. Detection limits for the spectrofluorimetric and HPLC methods were calculated as 0.16 and 18.28 ng/mL, respectively. The validated methods were applied successfully to the determination of rilmenidine in bulk and pharmaceutical preparation.