High-resolution Magic Angle Sample Spinning Research Articles

Shear-Induced Structural and Functional Transformations of Poly(N-vinylcaprolactam) Microgels

We here performed an in-depth investigation of the behavior of microgels (μgels) and their associated physicochemical transformations under shear force. Thermo- and mechanoresponsive poly(N-vinylcaprolactam) (PVCL) μgels (d ∼ 400 nm) cross-linked with a force-responsive mechanofluorophore in different cross-linking degrees were synthesized and examined. Fluorescence spectroscopy (FS), confocal laser scanning microscopy (CLSM), dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryoTEM), high-resolution magic-angle sample spinning (HRMAS) nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) are used to characterize the μgels before, during, and after shearing with different shear rates and intensities. The obtained results suggest nonuniform structural features consisting of a softer outer “corona” and a harder particle “core” (cross-linker-rich). Upon shearing, the μgels rapidly lose their corona and the cores agglomerate altering μgel functionality. Surprisingly, μgels degrade promptly, even when subjected to low shear forces, such as the extrusion through a needle. This has potential implications for all applications in which shear forces in solution are expected, including extrusion, injection, and filtration processes involving colloidal μgel solutions as well as circulation within the bloodstream of living organisms.

Thermodynamic Parameters of Temperature-Induced Phase Transition for Brushes onto Nanoparticles: Hydrophilic versus Hydrophobic End-Groups Functionalization.

Quantification of the stimuli-responsive phase transition in polymers is topical and important for the understanding and development of novel stimuli-responsive materials. The temperature-induced phase transition of poly(N-isopropylacrylamide) (PNIPAm) with one thiol end group depends on the confinement-free polymer or polymer brush-on the molecular weight and on the nature of the second end. This paper describes the synthesis of heterotelechelic PNIPAm of different molecular weights with a thiol end group-that specifically binds to gold nanorods and a hydrophilic NIPAm end group by reversible addition-fragmentation chain-transfer polymerization. Proton high-resolution magic angle sample spinning NMR spectra are used as an indicator of the polymer chain conformations. The characteristics of phase transition given by the transition temperature, entropy, and width of transition are obtained by a two-state model. The dependence of thermodynamic parameters on molecular weight is compared for hydrophilic and hydrophobic end functional-free polymers and brushes.

Temperature‐Induced Phase Transition Characterization of Responsive Polymer Brushes Grafted onto Nanoparticles

Temperature‐induced phase transition parameters of responsive free polymer and brushes onto nanoparticles are measured using high‐resolution magic‐angle sample spinning (HRMAS) NMR spectroscopy. To this purpose, a two‐state statistical model of temperature dependence of thermodynamic observables is developed and applied to obtain parameters which characterize the process of temperature‐induced phase transition of stimuli‐sensitive polymers. In this investigation the thermodynamic observable is the integral intensity of the 1H HRMAS NMR spectrum peaks and the derived thermodynamic parameters are transition temperature and transition entropy. This approach is applied to investigate the dependence of temperature‐induced coil‐to‐globule transition of poly(N‐isopropylacrylamide), (PNIPAm), asymmetric end functionalized with benzyl and thiol groups (Bn–PNIPAm–SH) on molecular weight in the range 3600–30 000 g mol–1 in aqueous solutions. The characteristics of the phase transition represented by transition temperature, and transition entropy are compared to that of Bn–PNIPAm–SH brushes onto gold nanorods in the same range of molecular weight. The method used for measuring the characteristics of phase transition is based on transverse magnetization relaxation (T2) spin‐echo enhance editing of the integral intensities of the 1H HRMAS NMR spectra. This NMR observable reflects changes in transverse relaxation times as an indicative of the polymer chains conformations and dynamics reached in the process of temperature‐induced phase transition. image

Peptizing Mechanism at the Molecular Level of Laponite Nanoclay Gels.

In the presence of additives such as etidronic acid (1-hydroxyethane-1,1-diphosphonic acid, HEDP), a process of peptizing of Laponite clay gels takes place. The peptizing process at the molecular level was directly revealed by 31P and 1H high-resolution magic-angle sample spinning (HRMAS) NMR spectroscopy. Two NMR spectral components were detected and assigned to free etidronic acid and bound to the Laponite disk edges. Furthermore, with increase of temperature the ratio of bound-to-free etidronic acid increases. This thermal activation process could be explained by the increase in electrical polarization of the hydroxyl group at the edges and by the exfoliation of the tactoids that leads to more access to the additive molecules to the electrical charges of platelet edges. 31P HRNMR spectroscopy on sodium fluorohectorite with an aspect ratio of ∼750 shows a reduction of the bound etidronic acid molecules. Transmission electron microscopy (TEM), field-emission scanning microscopy (FESEM), UV-vis spectrophotometry, dynamic light scattering (DLS), and zeta potential results support the proposed peptizing mechanisms.

Aggregation behaviour of biohybrid microgels from elastin-like recombinamers.

Investigation of the aggregation behavior of biohybrid microgels, which can potentially be used as drug carriers, is an important topic, because aggregation not only causes loss of activity, but also toxicity and immunogenicity. To study this effect we synthesized microgels from elastin-like recombinamers (ELRs) using the miniemulsion technique. The existence of aggregation for such biohybrid microgels at different concentrations and temperatures was studied by different methods which include dynamic light scattering (DLS), (1)H high-resolution magic angle sample spinning (HRMAS) NMR spectroscopy, relaxometry and diffusometry. A hysteresis effect was detected in the process of aggregation by DLS as a function of temperature that strongly depends on ELR microgel concentration. The aggregation process was further quantitatively analyzed by the concentration dependence of the (1)H amino-acid residue chemical shifts and microgel diffusivity measured by NMR methods using the population balance kinetic aggregation model.

Coacervation of Elastin-Like Recombinamer Microgels.

The investigation of the coacervation (self-aggregation) behavior of biomicrogels which can potentially be used as drug carriers is an important topic, because self-aggregation can not only cause loss of activity, but also toxicity and immunogenicity. To study this effect microgels from elastin-like recombinamer are synthesized using miniemulsion technique. The existence of coacervation for such microgels, at different concentrations and temperatures, is studied and proved by cryo-field emission scanning clectron microscopy (cryo-FESEM), cryo-transmission electron microscopy (cryo-TEM), and by a novel (1) H high-resolution magic angle sample spinning (HRMAS), nuclear magnetic resonance (NMR) spectroscopy, and relaxometry methods. The findings by (1) H HRMAS NMR spectroscopy and relaxometry show simultaneous processes of volume phase temperature transition and coacervation with different sensitivity for hydrophobic and hydrophilic amino acid side-chains in the microgel. The coacervation process is more evidential by the behavior of glycine α-CH2 , (1) H NMR peak as compared to the proline β-CH2 .

Structural and interaction parameters of thermosensitive native α-elastin biohybrid microgel

The structural and water interaction parameters for native, α-elastin biohybrid microgel crosslinked with hydrophilic and hydrophobic crosslinkers are obtained from the volume phase transition temperature behaviour, 1H high-resolution magic-angle sample spinning transverse magnetization relaxation NMR, and modified Flory–Rehner swelling theory. Firstly, considering a homogeneous morphology the number of subchains in the biohybrid microgel, the residual water in deswollen state as a function of crosslink density and the temperature dependence of the Flory biopolymer–water interaction parameters are reported for the biohybrid microgels prepared with hydrophilic (PEG-DGE) and hydrophobic (BS3) crosslinkers. The Flory–Rehner classical approach is subsequently modified taking into account the heterogeneities observed by NMR transverse relaxation measurements. Two differently mobile regions are determined, a hydrophobic domain and a crosslinking domain with relative reduced mobility. For the first time, the influence of chain mobility on the Flory interaction parameter is investigated through a modified Flory state equation. The contributions of amino-acids located in the hydrophobic and crosslinking domains in the polypeptide sequence are separated while analyzing the biopolymer–water interaction.

Evaluation of High Resolution Magic-Angle Coil Spinning NMR Spectroscopy for Metabolic Profiling of Nanoliter Tissue Biopsies

High-resolution magic-angle sample spinning (HR-MAS) (1)H NMR spectroscopy of tissue biopsies combined with chemometric techniques has emerged as a valuable methodology for disease diagnosis and environmental assessments. However, the tissue mass required for such experiments is of the order of 10 mg, and this can compromise the metabolic evaluation because of tissue heterogeneity. Tissue availability is often a limitation for clinical studies due to histopathological requirements, which are currently the gold standard for diagnosis, for example, in the case of tumors. Here, we introduce the use of a rotating micro-NMR detector that optimizes the coil filling factor such that mass-limited samples can be measured. We show the results for measuring nanoliter volume tissue biopsies using a commercial HR-MAS probe for the first time. The method has been tested with bovine muscle and human gastric mucosal tumor tissue samples. The gain in mass sensitivity is approximate up to 17-fold, and the adequate spectral resolution (3 Hz) allows the measurement of the metabolite profiles in nanoliter volume samples, thereby limiting the ambiguity resulting from heterogeneous tissues; thus, the approach presents diagnostic potential for studies by metabonomics of mass-limited biopsies.

Disordered Pore Formation At Rigid/Fluid Boundary Zones As A New Mechanism For Peptide-Membrane Interaction With The Beta-sheeted Antimicrobial Peptide Cateslytin

The peptide cateslytin (RSMRLSFRARGYGFR) produced by enzymatic degradation of stress proteins is remarkably active against a large number of microorganisms including Plasmodium Falciparum responsible for Malaria. Its mode of action on membranes mimicking the external negatively charged membrane of these microorganisms has been studied by circular dichroism, infra-red (attenuated total reflection), high-resolution magic angle sample spinning and wide line solid state NMR, patch clamp and molecular dynamics. The peptide, which is unstructured in solution, adopts an aggregated beta sheet structure upon interacting with negatively charged membranes. Rigid membrane domains are formed upon interaction and separate from more fluid zwitterionic membrane zones. No macroscopic membrane lysis is observed, suggesting that crossing through membranes occurs at phase boundary defects. Patch clamp and all atom molecular dynamics of these zones indicate that disordered pores of ca. 10 Angstrom are formed by a mechanism that is analogous to molecular electroporation (Jean-Francois et al., Biochemistry & Biophysical J., 2008).View Large Image | View Hi-Res Image | Download PowerPoint Slide

MASS-NMR structural analysis of barium aluminofluorophosphate glasses with and without nitridation

The local structure of barium-aluminofluorophosphate (Ba–Al–P–O–F) glasses was investigated using high resolution magic-angle sample spinning nuclear magnetic resonance (MASS-NMR) spectroscopy. The 27Al spectra show three different aluminum environments [Al(4), Al(5), and Al(6)] in these glasses. Changes were observed due to the addition of fluorine and nitrogen. 31P results indicate only one type of phosphorus environment which shifts with fluorine additions. The 19F spectra suggest that fluorine has both Ba and Al as nearest neighbors.