Nondestructive Quantification of Local Plasticizer Concentration in PVC by 1H NMR Relaxometry

The properties of plasticized poly(vinyl chloride) (PVC) , one of the most important polymers today, are strongly dictated by the concentration of plasticizer. Yet, it has been impossible to quantify this concentration at different positions inside a PVC product without its destruction because of a lack of suitable analytical methods. Thus, this paper introduces a simple, fast, and efficient way to determine truly nondestructively the concentration of plasticizer in PVC by single‐sided nuclear magnetic resonance (NMR). With the help of correlation curves between the concentration of plasticizer inside nonaged PVC samples and the corresponding volume‐averaged NMR parameters, single‐sided NMR allows the quantification of the local concentration of plasticizer in aged PVC plates at different depths by spatially resolved relaxation measurements. The presented approach represents a fundamental step toward in situ characterization of plasticized PVC.

     

High Relaxivity Supramolecular Adducts Between Human‐Liver Fatty‐Acid‐Binding Protein and Amphiphilic GdIII Complexes: Structural Basis for the Design of Intracellular Targeting MRI Probes

Gadolinium complexes linked to an apolar fragment are known to be efficiently internalized into various cell types, including hepatocytes. Two lipid‐functionalized gadolinium chelates have been investigated for the targeting of the human liver fatty acid binding protein (hL‐FABP) as a means of increasing the sensitivity and specificity of intracellular‐directed MRI probes. hL‐FABP, the most abundant cytosolic lipid binding protein in hepatocytes, displays the ability to interact with multiple ligands involved in lipid signaling and is believed to be an obligate carrier to escort lipidic drugs across the cell. The interaction modes of a fatty acid and a bile acid based gadolinium complex with hL‐FABP have been characterized by relaxometric and NMR experiments in solution with close‐to‐physiological protein concentrations. We have introduced the analysis of paramagnetic‐induced protein NMR signal intensity changes as a quantitative tool for the determination of binding stoichiometry and of precise metal‐ion‐center positioning in protein–ligand supramolecular adducts. A few additional NMR‐derived restraints were then sufficient to locate the ligand molecules in the protein binding sites by using a rapid data‐driven docking method. Relaxometric and ¹³C NMR competition experiments with oleate and the gadolinium complexes revealed the formation of heterotypic adducts, which indicates that the amphiphilic compounds may co‐exist in the protein cavity with physiological ligands. The differences in adduct formation between fatty acid and bile acid based complexes provide the basis for an improved molecular design of intracellular targeted probes.     

A multinuclear NMR relaxometry study of ternary adducts formed between heptadentate Gd(III) chelates and L-lactate

Dramatic relaxation enhancements of L-lactate resonances have been observed upon formation of ternary adducts with Gd(III) complexes of heptadentate DO3A and DO3A-like ligands (DO3A = 1,4,7,10-tetraazaciclododecane-1,4,7-triacetic acid). Detailed 1H and 17O NMR relaxometry investigations allow us to obtain structural, dynamic and thermodynamic information on the ternary complexes in which L-lactate acts as a bidentate ligand replacing two water molecules in the inner coordination sphere of the Gd(III) ion. It has been found that the exchange rate of the coordinated L-lactate is modulated by the structural and electronic properties of the parent Gd-heptacoordinated macrocyclic chelate. In addition to the characterisation of the relaxation behaviour of the 1H methyl resonance of L-lactate, this study has been extended to its 13C isomer (fully enriched at the three positions) and to the trifluoro-L-lactate. The obtained results may be relevant to the development of relaxation agents able to promote the relaxation enhancement of specific substrates detectable by in vivo magnetic resonance spectroscopy.     

Dual nuclear magnetic resonance for probing intrinsic bone structure and a potential gut–bone axis in ovariectomized rats

Currently, the existence of a gut–bone axis receives massive attention, and while sound premises and indirect proofs exist for the gut–bone axis concept, few studies have provided actual data linking the gut and bone physically. This study aimed to exploit the versatile nature of nuclear magnetic resonance (NMR) to link NMR relaxometry data on bone mineralization with NMR spectroscopic profiling of gut metabolites. For this purpose, sample material was obtained from a 6-week intervention study with ovariectomized (OVX) rats (n = 49) fed with seven different diets varying in calcium content (0.2–6.0 mg/kg) and prebiotic fiber content (0–5.0% w/w). This design ensured a span in (i) calcium available for bone mineralization and (ii) metabolic activity in the gut. After termination of the intervention, longitudinal (T₁), transverse (T₂) relaxation, and mechanical bone strength were measured on the excised femur bones. A PLS model with high predictability (Q² = 0.86, R² = 0.997) was demonstrated between T₂ decay curves and femur mechanical strength. Correlations were established between bone T₂ populations and gut short-chain fatty acids. In conclusion, the present dual NMR approach showed strong correlation between T₂ relaxation and mechanical strength of the bone, and when metabolic activity in the gut was modulated by inulin, the potential existence of a gut–bone axis was demonstrated.     

Capsaicin emulsions: Formulation and characterization

Oleoresin capsicum, the oil extract of chili pepper, is mainly composed of capsaicin. Capsaicin is a hydrophobic volatile compound exhibiting antimicrobial activity against various microorganisms. Capsaicin in the form of an emulsion-based carrier system could be a good alternative to enhance bioavailability and simultaneously to increase the shelf-life of food. In this study, capsaicin emulsions were formulated using three different surfactants (Tween 80, commercial soy lecithin, and sucrose monopalmitate/SMP). Effects of aqueous phase composition, pH, and heating the pre-homogenized dispersion were investigated. For characterization, NMR relaxometry, color, turbidity, and antioxidant activity experiments were conducted. Antimicrobial efficacies of the emulsions were also evaluated against Escherichia coli andStaphylococcus aureus. Mean particle sizes of emulsions with surfactants Tween 80, lecithin, and SMP were found to be 68.30, 582.63, and 50.10?nm, respectively. Lecithin-containing emulsions showed the highest antimicrobial activity against S. aureus with 4.60?log reduction, whereas the same effect was observed in Tween 80-containing emulsions against E. coli with 3.86 log reduction. Emulsions prepared with SMP showed the highest antioxidant activity with 0.482?mg DPPH/L emulsion. The formulated emulsions have the potential to be used in food industry as antimicrobial food grade solutions.     

A Quantitative Relaxometric Version of the ELISA Test for the Measurement of Cell Surface Biomarkers

Quantitative measurement of marker expression in diseased cells is still a topic of considerable interest and different methodologies are currently under intense scrutiny. This work aims at developing an in vitro diagnostic method based on the release of paramagnetic species from relaxometrically “silent” liposomes operated by the action of a phospholipase A₂ (PLA₂) previously targeted to the epitope of interest. The released paramagnetic species causes an increase of the longitudinal water proton relaxation rate proportional to the number of PLA₂ bound to the cell outer surface. The sensitivity of the herein proposed method, named R‐ELISA, was attempted in the detection of folate receptor expression on human ovarian cancer cells by functionalizing PLA₂ with folic acid. Receptor/cell number of 8.3×10⁵ has been measured on IGROV‐1 cells. The R‐ELISA assay can detect nanomolar cell suspension receptor concentrations and has been validated by well‐established spectrofluorimetric procedures.     

Effect of magnetic pore surface coating on the NMR relaxation and diffusion signal in quartz sand

Magnetic impurities are ubiquitous in natural porous media such as sand and soil. They generate internal magnetic field gradients because of increased magnetic susceptibility differences between solid and liquid phase in the pore space and because of the presence of magnetic centers. These internal gradients accelerate NMR relaxation rates and thus might limit the possibility of pore space characterization using NMR. In this study, we investigate the effects of coating the surface of natural sands by the antiferromagnetic iron oxyhydroxide goethite on NMR relaxation and diffusion properties. We found a non‐quadratic dependence of the relaxation time distributions on the echo time indicating that the relaxation experiments were not performed in the fast diffusion limit, while the weak dependence on the external magnetic field strength is explained by the preponderance of the surface relaxation over the effect of diffusion in internal gradients. The surface to volume ratio of the pore space, determined by NMR diffusimetry ((S/V)_NMR) remains approximately constant, whereas the same quantity, determined from gas adsorption ((S/V)_BET) increases proportional to the coating density. This is because gas adsorption measures surface roughness on sub‐nanometer scale, whereas NMR diffusimetry averages over structures smaller than few microns. This has consequences for the calculation of the surface relaxivities. The usage of the (S/V)_NMR leads to constant values, whereas the usage of (S/V)_BET leads to apparently decreasing relaxivities with increasing coating, which is unrealistic. Copyright © 2016 John Wiley & Sons, Ltd.     

Differences in Dynamics between Crosslinked and Non‐Crosslinked Hyaluronates Measured by using Fast Field‐Cycling Relaxometry

The dynamic properties of water molecules in gels containing linear and crosslinked hyaluronic acid polymers are investigated by using an integrated approach that includes relaxometry, solid‐state NMR spectroscopy, and scanning electron microscopy. A model‐free analysis of field‐dependent nuclear relaxation is applied to obtain information on mobility and the population of different pools of water molecules in the gels. Differences between linear and crosslinked hyaluronic acid polymers are observed, indicating that crosslinking increases both the fraction and the correlation time of water molecules with slow dynamics.     

Phase Behavior in Blends of Ethylene Oxide–Propylene Oxide Copolymer and Poly(ether sulfone) Studied by Modulated-Temperature DSC and NMR Relaxometry

The state diagram of a blend consisting of a copolymer containing ethylene oxide and propylene oxide, P(EO-ran-PO), and poly(ether sulfone), PES, is constructed by using modulated-temperature differential scanning calorimetry (MTDSC), T₂ NMR relaxometry, and light scattering. The apparent heat capacity signal in MTDSC is used for the characterization of polymer miscibility and morphology development. T₂ NMR relaxometry is used to detect the onset of phase separation, which is in good agreement with the onset of phase separation in the apparent heat capacity from MTDSC and the cloud-point temperature as determined from light scattering. The coexistence curve can be constructed from T₂ values at various temperatures by using a few blends with well-chosen compositions. These T₂ values also allow the detection of the boundary between the demixing zones with and without interference of partial vitrification and are in good agreement with stepwise quasi-isothermal MTDSC heat capacity measurements. Important interphases are detected in the heterogeneous P(EO-ran-PO)/PES blends.     

The segmental and global dynamics in lamellar microphase-separated poly(styrene-b-isoprene) diblock copolymer studied by H NMR and dielectric spectroscopy

The nuclear magnetic resonance (NMR) and dielectric spectroscopy (DS) methods were used to investigate the segmental and global dynamics in lamellar microphase separated poly(styrene-b-isoprene) (SI) diblock copolymer. For the first time, the susceptibility representation of the NMR relaxation data is applied to the analysis of the molecular dynamics in complex polymer systems like the diblock copolymer. This approach in combination with the frequency-temperature superposition (FTS) allows one to compare directly the NMR and DS data in an extended frequency range providing a unique comprehensive picture of various relaxation processes present in the system studied. The findings of these investigations include structural relaxations of the polyisoprene (PI) and the polystyrene (PS) blocks, a normal mode relaxation of the PI block, and an extra low frequency interfacial relaxation. Special attention has been devoted to influence of the copolymer morphology on the segmental and global dynamics in PI.