Dentin interaction with universal adhesive containing isopropanol solvent studied by solid-state NMR spectroscopy.

OBJECTIVE: This study investigated the chemical and structural changes in the mineral phase and collagen of dentin during application of a mild universal adhesive. Particular attention was paid to the role of isopropanol and changes in water molecules. METHODS: In vitro application of the mild universal adhesive on dentin with two established etching modes (self-etch and etch-and-rinse) was studied using solid state nuclear magnetic resonance spectroscopy. RESULTS: It was evidenced that the etch-and-rinse mode leads to a decrease of the inorganic apatite and a reorganization of the residual mineral phase with a low amount of adhesive phosphate monoesters calcium salt formed, compared to the self-etch mode. In contrast, the adhesive interacts very similarly to the level of dentin collagen in both protocols, with a strong decrease in the amount of the free water molecules induced by the presence of isopropanol as the adhesive solvent, but without significant changes in the initial collagen structure. For both modes, the adhesive acrylates monomers remain mobile and can infiltrate the collagen. SIGNIFICANCE: Understanding the molecular interactions between dentin and adhesive solutions is a major challenge for designing products that lead to the formation of ideal dentin resin hybrid layer. Notably, one point considered essential is the presence of unbound water which, over time, is associated with a hydrolytic degradation of the organic matrix. Isopropanol, as an adhesive solvent, leads to a decrease in the amount of the less stable water molecules while the water molecules strongly attached to the collagen are retained, thus preserving the collagen structure.

Characterization of hydrogenated dentin components by advanced 1H solid-state NMR experiments.

Collecting information about molecular organisation on biological materials such as bone and dentin represents a major challenge in attaining a better understanding of their mechanical properties. To that end, solid state Nuclear Magnetic Resonance (ssNMR) spectroscopic study is an appropriate strategy to provide atomic structural details on these amorphous composite materials. However, species like water molecules and hydroxyl groups are usually observed through 1H magic angle spinning (MAS) ssNMR that suffers from poor resolution due to strong signal overlapping, making their identification difficult. This paper proposes a set of ssNMR experiments for 1H characterization of the main components of human dentin, based on homo- and hetero-nuclear dipolar couplings and composed mostly of fast 1D experiments. The 1H assignment is assisted by straightforward sample modifications: vacuum drying, deuterium exchange and demineralization. These experiments allow the hydrogen signal edition of dentin species like water molecules, HPO42- and OH- groups, depending on their localization (bound to the organic phase, linked to apatite or at the interface) and their dynamic behaviour. This ssNMR toolbox has the potential to provide important structural and dynamic information on chemical and physical modifications of biomaterials. STATEMENT OF SIGNIFICANCE: Molecular characterisation of apatitic biomaterials by biophysical techniques is extremely difficult due to their complex and amorphous nature. It is, however, crucial to obtain such information if we want to understand their mechanical properties in relation to their physical state, for example their hydration levels. In this article we used a set of solid state NMR experiments and sample modifications to distinguish 1H signal of human dentin components with a particular attention to water molecules, known for their major role in biomaterial structuring.

Molecular weights of cyclic and hollow clusters measured by DOSY NMR spectroscopy.

The Stokes-Einstein expression of the diffusion coefficient as a function of the hydrodynamic radius of the diffusing object does not explicitly carry the mass dependency of the object. It is possible to correlate the translational self-diffusion coefficients D with the molecular weight M for an ensemble of cyclic or hollow clusters ranging from about 200 to 30,000 g x mol(-1). From this correlation, the mass of a cluster can be deduced from its diffusion coefficient. Consistency of diffusion as a power law of mass and Stokes-Einstein formulation is completely fulfilled with the selected compounds of this contribution.

NMR measure of translational diffusion and fractal dimension. Application to molecular mass measurement.

Experimental NMR diffusion measure on polymers and on globular proteins are presented. These results, complemented with results found in the literature, enable a general description of effective fractal dimension for objects such as small organic molecules, sugars, polymers, DNA, and proteins. Results are compared to computational simulations as well as to theoretical values. A global picture of the diffusion phenomenon emerges from this description. A power law relating molecular mass with diffusion coefficients is described and found to be valid over 4 orders of magnitude. From this law, the fractal dimension of the molecular family can be measured, with experimental values ranging from 1.41 to 2.56 in full agreement with theoretical approaches. Finally, a method for evaluating the molecular mass of unknown solutes is described and implemented as a Web page.

Two-dimensional DOSY experiment with Excitation Sculpting water suppression for the analysis of natural and biological media.

The Bipolar Pulse Pair Stimulated Echo NMR pulse sequence was modified to blend the original Excitation Sculpting water signal suppression. The sequence is a powerful tool to generate rapidly, with a good spectrum quality, bidimensional DOSY experiments without solvent signal, thus allowing the analysis of complex mixtures such as plant extracts or biofluids. The sequence has also been successfully implemented for a protein at very-low concentration in interaction with a small ligand, namely the salivary IB5 protein binding the polyphenol epigallocatechine gallate. The artifacts created by this sequence can be observed, checked and removed thanks to NPK and NMRnotebook softwares to give a perfect bidimensional DOSY spectrum.