Determination of amantadine and rimantadine using a sensitive fluorescent probe

Prediction of binding affinity and enthalpy of CB7 with alkaloids by attach-pull-release molecular dynamics simulations study

Host-guest complex has attracted much attention because of their fantastic capability. Accurate prediction of their binding affinity and enthalpy is essential to the rational design of guest molecules. The attach-pull-release (APR) method proposed by Henriksen et al. (J. Chem. Theory Comput., 2015, 11:4377.) shows good prediction capability of binding affinity especially for host-guest system. In order to further evaluate the performance of APR method in practice, we have conducted the calculations on the macrocycle cucurbit [7]urils (CB7) encapsulated with four structurally similar alkaloids (berberine, coptisine, epiberberine and palmatine) with two force fields (GAFF and GAFF2) and three water models (TIP3P, SPC/E and OPC). Compared to the experimental data, the calculation by the combination of GAFF2 and SPC/E force field presents the best performance, of which the Pearson correlation coefficients (R2) is 0.95, and the root-mean-square-deviation is 3.04 kcal/mol. While the predictions from GAFF force field all overestimated the binding affinity, suggesting a systematic error may be involved. Comparison of calculation also indicates that the accuracy of prediction was susceptible to the combination of force field. Therefore, it would be necessary to repeat the simulation with different combination of force fields in practice.

Covalent cucurbit[7]uril-dye conjugates for sensing in aqueous saline media and biofluids

Non-covalent chemosensing ensembles of cucurbit[n]urils (CBn) have been widely used in proof-of-concept sensing applications, but they are prone to disintegrate in saline media, e.g. biological fluids. We show here that covalent cucurbit[7]uril-indicator dye conjugates are buffer- (10× PBS buffer) and saline-stable (up to 1.4 M NaCl) and allow for selective sensing of Parkinson's drug amantadine in human urine and saliva, where the analogous non-covalent CB7⊃dye complex is dysfunctional. The in-depth analysis of the covalent host-dye conjugates in the gas-phase, and deionized versus saline aqueous media revealed interesting structural, thermodynamic and kinetic effects that are of general interest for the design of CBn-based supramolecular chemosensors and systems. This work also introduces a novel high-affinity indicator dye for CB7 through which fundamental limitations of indicator displacement assays (IDA) were exposed, namely an impractical slow equilibration time. Unlike non-covalent CBn⊃dye reporter pairs, the conjugate chemosensors can also operate through a SN2-type guest-dye exchange mechanism, which shortens assay times and opens new avenues for tailoring analyte-selectivity.

Analysis of amantadine in Laminaria Japonica and seawater of Daqin Island by ultra high performance liquid chromatography with positive electrospray ionization tandem mass spectrometry

A sensitive and validated method for determination of amantadine in Laminaria Japonica and seawater was established using ultra high performance liquid chromatography with positive electrospray ionization tandem spectrometry (UHPLC-ESI-MS/MS). Laminaria Japonica was extracted with acetonitrile containing formic acid (1%), then purified with 10.0 g anhydrous sodium sulfate, 0.50 g C18 and 0.50 g PSA powder. Seawater added 10.0 mL 0.20 mol/L hydrochloric acid was purified with MCX solid phase extraction (SPE) cartridge. After extraction and purification, the supernatant of Laminaria Japonica and eluate of seawater were evaporated to nearly dry under a gentle stream of nitrogen at 40 °C. Acetonitrile-0.1% formic acid in water (3/7, v/v) was adjusted to 1.00 mL final volume. An aliquot (10 μL) was injected into the C18 column for separation with the mobile phase of acetonitrile and 0.1% formic acid in water at 0.25 mL·min-1. Calibration curves were linear ranged from 1.00 ng/mL to 20.0 ng/mL. Mean recoveries were 73.5% to 95.8%, and limit of detection (LOD) and quantification (LOQ) were 0.50 μg/kg and 1.00 μg/kg for Laminaria Japonica. Mean recoveries were 75.8% to 93.4%, and LOD and LOQ were 0.50 ng/L and 1.00 ng/L for seawater. Based on the method above, Laminaria Japonica and seawater in Daqin Island were analyzed in February to June continuously, lgBAF3.71 (bioaccumulation factor), indicating a bioenrichment effect.

A Highly Selective and Strong Anti-Interference Host-Guest Complex as Fluorescent Probe for Detection of Amantadine by Indicator Displacement Assay

Amantadine (AMA) and its derivatives are illicit veterinary drugs that are hard to detect at very low concentrations. Developing a fast, simple and highly sensitive method for the detection of AMA is highly in demand. Here, we designed an anthracyclic compound (ABAM) that binds to a cucurbit[7]uril (CB[7]) host with a high association constant of up to 8.7 × 10⁸ M⁻¹. The host-guest complex was then used as a fluorescent probe for the detection of AMA. Competition by AMA for occupying the cavity of CB[7] allows ABAM to release from the CB[7]-ABAM complex, causing significant fluorescence quenching of ABAM (indicator displacement assay, IDA). The linear range of the method is from 0.000188 to 0.375 μg/mL, and the detection limit can be as low as 6.5 × 10⁻⁵ μg/mL (0.35 nM). Most importantly, due to the high binding affinity between CB[7] and ABAM, this fluorescence host-guest system shows great anti-interference capacity. Thus, we are able to accurately determine the concentration of AMA in various samples, including pharmaceutical formulations.

Substituent effect on the dynamics of the inclusion complex formation between protoberberine alkaloids and cucurbit[7]uril

The dynamics and activation parameters of alkaloid entry into and exit from cucurbit[7]uril significantly depend on the substitution pattern.

A supramolecular indicator displacement assay for acetyl amantadine, a proxy biomarker for spermidine/spermine N1-acetyltransferase (SSAT) activity

Acetyl amantadine (AcAm) is produced from amantadine (Am) in vivo upon catalysis by spermidine/spermine N1-acetyl transferase (SSAT). SSAT is a biomarker for multiple aggressive cancers, and the analysis of AcAm in urine has been promoted as a proxy measure for the early detection of cancer. We report here the development and optimization of cucurbit[7]uril–dye pair based indicator displacement assay (IDA) for the detection of AcAm in solution. In deionized water, using Rhodamine B as the dye, the limit of detection of AcAm was 0.087 μM with a linear response range from 0 to 1 μM. Using berberine as the dye, the limit of detection was 0.077 μM with the same range of linear response. Our efforts and difficulties in translating this assay to function in human urine are also described. We achieve a partial response of the berberine IDA to the presence of AcAm in urine that has undergone a simple PD-10 desalting step.

Combination of homogenous liquid–liquid extraction and dispersive liquid–liquid microextraction for extraction and preconcentration of amantadine from biological samples followed by its indirect determination by flame atomic absorption spectrometry

A new and simple procedure has been developed for the indirect determination of amantadine in biological samples.

Rapid and sensitive determination of clenbuterol in porcine muscle and swine urine using a fluorescent probe

The feed additive Clenbuterol hydrochloric acid (CLB) is non-fluorescent, thus it is difficult to quantify through direct fluorescent method. Palmatine (PAL) can react with cucurbit[7]uril (CB[7]) to form stable complexes as a fluorescent probe. Significant quenching of the fluorescence intensity of the CB[7]-PAL complex was observed with the addition of CLB. Based on the significant quenching of the supramolecular complex fluorescence intensity, a novel spectrofluorimetric method with high convenience, selectivity and sensitivity was developed for the determination of CLB. The fluorescence quenching values (ΔF) showed good linear relationship with CLB concentrations from 0.011 μg mL(-1) to 4.2 μg mL(-1) with a detection limit 0.004 μg mL(-1). In this research, an ultrasound treatment replaced the former time-consuming shake method to form stable complexes. The proposed spectrofluorimetric method had been successfully applied to the determination of CLB in porcine muscle and swine urine with good precision and accuracy. The competing reaction and the supramolecular interaction mechanisms between the CLB and PAL as they fight for occupancy of the CB[7] cavity were studied using spectrofluorimetry, (1)H NMR, and molecular modeling calculations. Interestingly, results indicate that two stable CB[7]-CLB complexes were formed.

Supramolecular interaction of labetalol with cucurbit[7]uril for its sensitive fluorescence detection

The supramolecular interaction between labetalol and cucurbit[7]uril is studied for simple and sensitive fluorescence detection of labetalol through its competitive interaction with berberine, palmatine or coptisine for occupancy of the cucurbit[7]uril cavity.

Unraveling the coptisine–ctDNA binding mechanism by multispectroscopic, electrochemical and molecular docking methods

This study provides evidences of coptisine–DNA intercalation, which may help to develop new efficient, safe probes for the fluorometric detection of DNA instead of traditional toxic and carcinogenic probes.

Solvatochromic study of highly fluorescent alkylated isocyanonaphthalenes, their π-stacking, hydrogen-bonding complexation, and quenching with pyridine

Mono- and dialkylated derivatives of 1-amino-5-isocyanonaphthalene (ICAN) were studied as new members of a multifunctional, easy-to-prepare fluorophore family, which showed excellent solvatochromic properties. The monoallyl derivative and the starting ICAN exhibited strong fluorescence quenching in the presence of small amounts of pyridine. The formation of a hydrogen-bonded ground-state pyridine complex was detected; however, analysis of quantum chemical calculations suggested the presence of an additional π-stacked pyridine complex. The Stern-Volmer plot of the quenching process exhibited a downward curvature and after reaching a minimum the fluorescence intensity increased back to a significant level at high pyridine concentrations. Significant fluorescence was observed even in pure pyridine. A new mechanism and a simple mathematical equation were derived to explain the downward curvature and the remaining fluorescence by the formation of a fluorescent π-stacked complex.

Determination of the purity of pharmaceutical reference materials by 1H NMR using the standardless PULCON methodology

A fast and reliable nuclear magnetic resonance spectroscopic method for quantitative determination (qNMR) of targeted molecules in reference materials has been established using the ERETIC2 methodology (electronic reference to access in vivo concentrations) based on the PULCON principle (pulse length based concentration determination). The developed approach was validated for the analysis of pharmaceutical samples in the context of official medicines control, including ibandronic acid, amantadine, ambroxol and lercanidipine. The PULCON recoveries were above 94.3% and coefficients of variation (CVs) obtained by quantification of different targeted resonances ranged between 0.7% and 2.8%, demonstrating that the qNMR method is a precise tool for rapid quantification (approximately 15min) of reference materials and medicinal products. Generally, the values were within specification (certified values) provided by the manufactures. The results were in agreement with NMR quantification using an internal standard and validated reference HPLC analysis. The PULCON method was found to be a practical alternative with competitive precision and accuracy to the classical internal reference method and it proved to be applicable to different solvent conditions. The method can be recommended for routine use in medicines control laboratories, especially when the availability and costs of reference compounds are problematic.