Molecular Mechanisms Underlying Detection Sensitivity in Nanoparticle-Assisted NMR Chemosensing.

Nanoparticle-assisted nuclear magnetic resonance (NMR) chemosensing exploits monolayer-protected nanoparticles as supramolecular hosts to detect small molecules in complex mixtures via nuclear Overhauser effect experiments with detection limits down to the micromolar range. Still, the structure-sensitivity relationships at the basis of such detection limits are little understood. In this work, we integrate NMR spectroscopy and atomistic molecular dynamics simulations to examine the covariates that affect the sensitivity of different NMR chemosensing experiments [saturation transfer difference (STD), water STD, and high-power water-mediated STD]. Our results show that the intensity of the observed signals correlates with the number and duration of the spin-spin interactions between the analytes and the nanoparticles and/or between the analytes and the nanoparticles' solvation molecules. In turn, these parameters depend on the location and dynamics of each analyte inside the monolayer. This insight will eventually facilitate the tailoring of experimental and computational setups to the analyte's chemistry, making NMR chemosensing an even more effective technique in practical use.

The long-term clinical course of moderate tricuspid regurgitation.

BACKGROUND: To evaluate the long-term clinical outcome of a cohort of patients suffering from moderate tricuspid regurgitation (TR), regardless of its etiology. METHODS: Clinical and echocardiographic follow-up were assessed in 250 patients diagnosed with moderate TR between January 2016 and July 2020. TR progression at follow-up was defined as TR grade increase to at least severe. The primary endpoint was all-cause death; secondary endpoints were cardiovascular (CV) death and the composite of heart failure (HF) hospitalization plus tricuspid valve (TV) intervention. RESULTS: After a median follow-up of 3.6 years, TR progression occurred in 84 patients (34%). At multivariate analyses, atrial fibrillation (AF, OR 1.81, CI 1.01-3.29, p = 0.045) and right ventricular end-diastolic diameter (RVEDD, OR 2.19, CI 1.26-3.78, p = 0.005) were independent predictors of TR progression. The primary endpoint occurred in 59 patients (24%) and was significantly more frequent in the group with TR progression (p = 0.009). At multivariate analyses, chronic kideney disease (OR 2.80, CI 1.30-6.03, p = 0.009), left ventricular ejection fraction (OR 0.97, CI 0.94-0.99, p = 0.041) and TR progression (OR 2.32, CI 1.31-4.12, p = 0.004) were independent predictors of the primary outcome. Moreover, both the secondary endpoints of CV death and HF hospitalization plus TV intervention were more frequent in the TR progression group (p = 0.001 and p < 0.001, respectively). CONCLUSIONS: Moderate TR progresses in a significant proportion of patients over a long-term follow-up, leading to a worse prognosis. TR progression is an independent determinant of hard clinical events and AF and RVEDD are associated with TR progression.

Preparation of ultrasmall cyclodextrin nanogels by an inverse emulsion method using a cationic surfactant.

Stable water-in-oil emulsion membranes can be prepared using [dilauryl(dimethyl)ammonium] bromide (DDAB), a cationic surfactant. We prepared ultrasmall cyclodextrin (γ-CyD) nanogels (γ-CyDngs) by forming ionic pairs between the secondary hydroxyl groups of γ-CyDs and DDAB. Fluorescence and NMR characterisation of the obtained γ-CyDngs revealed superior inclusion affinities compared with native γ-CyDs, beneficial for the solubilisation of hydrophobic compounds in water.

Selective NMR detection of N-methylated amines using cavitand-decorated silica nanoparticles as receptors.

We report a strategy for the realization of NMR chemosensors based on the spontaneous self-assembly of lower rim pyridinium-functionalized tetraphopshonate cavitands on commercial silica nanoparticles. These nanohybrids enable the selective detection of physiologically relevant N-methylated amines, with a limit of detection of 31 µM, via STD-based NMR experiments, achieving for the first time fine structural selectivity in nanoparticle-assisted NMR chemosensing.

Thiolated 2-Methyl-ß-Cyclodextrin as a Mucoadhesive Excipient for Poorly Soluble Drugs: Synthesis and Characterization.

Thiolated cyclodextrins are structurally simple mucoadhesive macromolecules, which are able to host drugs and increase their apparent water solubility, as well as interact with the mucus layer prolonging drug residence time on the site of absorption. The aim of this study was to synthesize through green microwave-assisted process a freely soluble thiolated 2-methyl-ß-cyclodextrin (MßCD-SH). Its inclusion complex properties with dexamethasone (Dex), a poor water soluble drug, and mucoadhesive characteristics were also determined. The product was deeply characterized through NMR spectroscopy (2D COSY, 2D HSQC, 1D/2D TOCSY, and 1D ROESY), showing a thiolation degree of 67%, a selective thiolation on the C6 residues and a monomeric structure. The association constant of MßCD and MßCD-SH with Dex resulted in 2514.3 ± 32.3 M-1 and 2147.0 ± 69.3 M-1, respectively, indicating that both CDs were able to host the drug. Microrheological analysis of mucin in the presence of MBCD-SH showed an increase of complex viscosity, G' and G″, due to disulphide bond formation. The cytotoxicity screening on fibroblast BALB/3T3 clone A31 cells indicated an IC50 of 27.7 mg/mL and 30.0 mg/mL, for MßCD and MßCD-SH, respectively. Finally, MßCD-SH was able to self-assemble in water into nanometric structures, both in the presence and absence of the complexed drug.

NMR Investigation of the Supramolecular Complex Formed by a Phenylboronic Acid-Ferrocene Electroactive Probe and Native or Derivatized ß-Cyclodextrin.

Specifically designed electrochemical sensors are standing out as alternatives to enzyme-based biosensors for the sensing of metabolites. In our previous works, we developed a new electrochemical assay based on cyclodextrin supramolecular complexes. A ferrocene moiety (Fc) was chemically modified by phenylboronic acid (4-Fc-PB) and combined with two different kinds of cyclodextrins (CDs): ß-CD and ß-CD modified by a dipicolylamine group (dpa-p-HB-ß-CDs) for the sensing of fructose and adenosine-triphosphate (ATP), respectively. The aim of the present work is to better comprehend the features underlining the aforementioned complex formation. For the first time, a study about inclusion phenomena between the 4-Fc-PB electroactive probe with ß-CD and with dpa-p-HB-ß-CD was performed by using nuclear magnetic resonance (NMR) analysis. In particular, we focused on providing insights on the interaction involved and on the calculation of the binding constant of 4-Fc-PB/ß-CD supramolecular complex, and elucidation about a drift in the time observed during the control experiments of the electrochemical measurements for the 4-Fc-PB/dpa-p-HB-ß-CD supramolecular complex. In this sense, this paper represents a step further in the explanation of the electrochemical results obtained, pointing out the nature of the interactions present both in the formation of the inclusions and in the sensing with the analytes.

Hydrolysis and Enantiodiscrimination of (R)- and (S)-Oxazepam Hemisuccinate by Methylated ß-Cyclodextrins: An NMR Investigation.

Partially and exhaustively methylated ß-cyclodextrins [(2-methyl)-ß-CD (MCD), heptakis-(2,6-di-O-methyl)-ß-CD (DIMEB), and heptakis-(2,3,6-tri-O-methyl)-ß-CD (TRIMEB)] have been compared in the hydrolysis and enantiodiscrimination of benzodiazepine derivative (R)- or (S)-oxazepam hemisuccinate (OXEMIS), using nuclear magnetic resonance (NMR) spectroscopy as an investigation tool. After 6 h, MCD induced an 11% hydrolysis of OXEMIS, remarkably lower in comparison with underivatized ß-CD (48%), whereas no hydrolysis was detected in the presence of DIMEB or TRIMEB after 24 h. DIMEB showed greater ability to differentiate OXEMIS enantiomers in comparison to TRIMEB, by contrast MCD did not produce any splitting of racemic OXEMIS resonances. Both enantiomers of OXEMIS underwent deep inclusion of their phenyl pendant into cyclodextrins cavities from their wider rims, but tighter complexes were formed by DIMEB with respect to TRIMEB.

Nanoparticles Based on Quaternary Ammonium Chitosan-methyl-ß-cyclodextrin Conjugate for the Neuropeptide Dalargin Delivery to the Central Nervous System: An In Vitro Study.

Peptide oral administration is a hard goal to reach, especially if the brain is the target site. The purpose of the present study was to set up a vehicle apt to promote oral absorption of the neuropeptide dalargin (DAL), allowing it to cross the intestinal mucosal barrier, resist enzymatic degradation, and transport drugs to the brain after crossing the blood-brain barrier. Therefore, a chitosan quaternary ammonium derivative was synthesized and conjugated with methyl-ß-cyclodextrin to prepare DAL-medicated nanoparticles (DAL-NP). DAL-NP particle size was 227.7 nm, zeta potential +8.60 mV, encapsulation efficiency 89%. DAL-NP protected DAL from degradation by chymotrypsin or pancreatin and tripled DAL degradation time compared to non-encapsulated DAL. Use of DAL-NP was safe for either Caco-2 or bEnd.3 cells, with the latter selected as a blood-brain barrier model. DAL-NP could also cross either the Caco-2 or bEnd.3 monolayer by the transepithelial route. The results suggest a potential DAL-NP ability to transport to the brain a DAL dose fraction administered orally, although in vivo experiments will be needed to confirm the present data obtained in vitro.

2-Methyl-ß-cyclodextrin grafted ammonium chitosan: synergistic effects of cyclodextrin host and polymer backbone in the interaction with amphiphilic prednisolone phosphate salt as revealed by NMR spectroscopy.

Reduced molecular weight chitosan was quaternized with 2-chloro-N,N-diethylethylamine to obtain a water soluble derivative (N+-rCh). Methylated-ß-cyclodextrin (MCD), with 0.5 molar substitution, was covalently linked to N+-rCh through 1,6-hexamethylene diisocyanate spacer to give the derivatized ammonium chitosan N+-rCh-MCD. To shed light on the role of the cyclodextrin pendant in guiding binding interactions with amphiphilic active ingredients, corticosteroid prednisolone phosphate salt (PN) was considered. The deep inclusion of PN into cyclodextrin in PN/MCD model system was pointed out by analysis of 1H NMR complexation shifts, 1D ROESY spectra, and diffusion measurements (DOSY). By using proton selective relaxation rates measurements as investigation tool, the superior affinity of N+-rCh-MCD towards PN was demonstrated in comparison with parent ammonium chitosan N+-rCh.

Improvement of Peptide Affinity and Stability by Complexing to Cyclodextrin-Grafted Ammonium Chitosan.

Cyclodextrin-grafted polymers are attractive biomaterials that could bring together the host-guest complexing capability of pristine cyclodextrin and the pharmaceutical features of the polymeric backbone. The present paper is aimed at characterizing the potential application of ammonium-chitosan grafted with 2-methyl-ß-cyclodextrin (N+-rCh-MCD) as the functional macromolecular complexing agent for the oral administration of the neuropeptide dalargin (DAL). Specific NMR characterization procedures, along with UV and fluorescence techniques, as well as biological in vitro assessments have been performed. The results indicate that N+-rCh-MCD forms water-soluble complexes with DAL, with a prevalent involvement of Tyr or Phe over Leu and Ala residues. The association constant of DAL with the polymeric derivative is one order of magnitude higher than that with the pristine cyclodextrin (Ka: 2600 M-1 and 120 M-1, respectively). Additionally, N+-rCh-MCD shields DAL from enzymatic degradation in gastrointestinal in vitro models with a three-fold time delay, suggesting a future pharmaceutical exploitation of the polymeric derivative. Therefore, the greater affinity of N+-rCh-MCD for DAL and its protective effect against enzymatic hydrolysis can be attributed to the synergistic cooperation between cyclodextrin and the polymer, which is realized only when the former is covalently linked to the latter.

Binding and mucoadhesion of sulfurated derivatives of quaternary ammonium-chitosans and their nanoaggregates: An NMR investigation.

The effect of insertion of SH and S-protected groups on the binding and mucoadhesion properties of quaternary ammonium-chitosans and their nanoparticulate forms has been investigated by NMR spectroscopy. Diclofenac sodium salt has been assumed as low molecular weight probe to detect the different binding behaviour of polymeric materials; mucin from bovine submaxillary glands was selected as the model protein for differentiating their mucoadhesion. NMR proton selective relaxation rates of the probe molecule were remarkably sensitive to the presence of very low amounts of sulfurated moieties. Impact of supramolecular aggregation in nanostructured species was demonstrated as well as the relevance of S-protection.

Fitting Corrections to an RNA Force Field Using Experimental Data.

Empirical force fields for biomolecular systems are usually derived from quantum chemistry calculations and validated against experimental data. We here show how it is possible to refine the full dihedral-angle potential of the Amber RNA force field by using solution NMR data as well as stability of known structural motifs. The procedure can be used to mix multiple systems and heterogeneous experimental information and crucially depends on a regularization term chosen with a cross-validation procedure. By fitting corrections to the dihedral angles on the order of less than 1 kJ/mol per angle, it is possible to increase the stability of difficult-to-fold RNA tetraloops by more than 1 order of magnitude.

Mechanistic insight into the formation of colloidal WS2 nanoflakes in hot alkylamine media.

Developing convenient and reliable synthetic methodologies for solution processable 2D layered ultrathin nanostructures with lateral size control is one of the major challenges for practical applications. In this study, a rational understanding a long-chain amphiphilic surfactant assisted non-hydrolytic synthesis that is able to generate dimension-controllable 2D-WS2 nanocrystal flakes in a single-step protocol is proposed. The evolution of the starting soft organic-inorganic lamellar template into ultrathin few-layer 2D-WS2 nanostructures with lateral size modulation over a range between 3 and 30 nm is monitored. The initial formation of WS2 nanoseeds occurs in a self-assembled sacrificial precursor source, acting as a template, where larger two-dimensional nanostructures can grow without undergoing significant thickness variation. Overall, the chemical nature and steric hindrance of the alkylamines are essential to modulate the reactivity of such WS2 nanoclusters, which correlate with the lateral size of the resulting nanoflakes.

Determination of Structural Ensembles of Proteins: Restraining vs Reweighting.

The conformational fluctuations of proteins can be described using structural ensembles. To address the challenge of determining these ensembles accurately, a wide range of strategies have recently been proposed to combine molecular dynamics simulations with experimental data. Quite generally, there are two ways of implementing this type of approach, either by applying structural restraints during a simulation, or by reweighting a posteriori the conformations from an a priori ensemble. It is not yet clear, however, whether these two approaches can offer ensembles of equivalent quality. The advantages of the reweighting method are that it can involve any type of starting simulation and that it enables the integration of experimental data after the simulations are run. A disadvantage, however, is that this procedure may be inaccurate when the a priori ensemble is of poor quality. Here, our goal is to systematically compare the restraining and reweighting approaches and to explore the conditions required for the reweighted ensembles to be accurate. Our results indicate that the reweighting approach is computationally efficient and can perform as well as the restraining approach when the a priori sampling is already relatively accurate. More generally, to enable an effective use of the reweighting approach by avoiding the pitfalls of poor sampling, we suggest metrics for the quality control of the reweighted ensembles.

Impact of mucoadhesive polymeric nanoparticulate systems on oral bioavailability of a macromolecular model drug.

Nanoparticles (NP) only different in mucoadhesivity are compared for impact on drug oral bioavailability. Two polymeric NP types based on quaternary ammonium-chitosan (NP QA-Ch) and S-protected thiolated derivative thereof (NP QA-Ch-S-pro), respectively, containing the macromolecular drug model, FD4, were prepared by crosslinking each polymer with reduced MW hyaluronic acid. The structure of basic polymers was determined by H1NMR analysis. NP were similar in size (371 ±â€¯38 vs. 376 ±â€¯82 nm); polydispersity index (0.39 ±â€¯0.08 vs. 0.41 ±â€¯0.10); zeta potential (13.4 ±â€¯0.9 vs. 11.9 ±â€¯1.2 mV); reversible interactions with drug (bound drug, 67 vs. 66%); encapsulation efficiency (23 ±â€¯5 vs. 23 ±â€¯8%); release properties (15% released in 15 h in both cases); and apparent permeation across excised rat intestine (Papp, 8.8 ±â€¯0.8 vs. 10 ±â€¯1 cm/s). Then the differences in NP transport ratio through mucus (TR, 0.75 vs. 0.37) and adhesion to excised rat intestinal mucosa (adsorbed fraction, 23 ±â€¯3 vs. 45 ±â€¯2%) were ascribed to higher mucoadhesivity of NP QA-Ch-S-pro compared to NP QA-Ch. This directly influenced drug oral bioavailability in rats (Tmax, 1 vs. 2 h; AUC, 1.7 ±â€¯0.3 vs. 2.9 ±â€¯0.4 µg/mL min, for NP QA-Ch and NP QA-Ch-S-pro, respectively). Mucoadhesivity increases drug bioavailability by retaining NP at its absorption site and opposing its transit down the GI tract. Data on drug accumulation in rat liver allows the assertion that NP is absorbed by transcytosis across intestinal epithelium and transported from blood into liver by Kuppfer cells.

Combining Simulations and Solution Experiments as a Paradigm for RNA Force Field Refinement.

Recent computational efforts have shown that the current potential energy models used in molecular dynamics are not accurate enough to describe the conformational ensemble of RNA oligomers and suggest that molecular dynamics should be complemented with experimental data. We here propose a scheme based on the maximum entropy principle to combine simulations with bulk experiments. In the proposed scheme, the noise arising from both the measurements and the forward models used to back-calculate the experimental observables is explicitly taken into account. The method is tested on RNA nucleosides and is then used to construct chemically consistent corrections to the Amber RNA force field that allow a large set of experimental data on nucleosides and dinucleosides to be correctly reproduced. The transferability of these corrections is assessed against independent data on tetranucleotides and displays a previously unreported agreement with experiments. This procedure can be applied to enforce multiple experimental data on multiple systems in a self-consistent framework, thus suggesting a new paradigm for force field refinement.