Wideline Separation Research Articles

Understanding the molecular origin of the superior toughness of polyamide-6/polyketone blends by solid-state NMR spectroscopy

Polymer blending is a typical and conventional approach for integrating the excellent physical/chemical properties of individual polymer components. Specifically, the mechanical toughness and strength of polyamide-6 (PA6)/polyketone (PK) blend are substantially enhanced compared to either PA6 or PK individual component. Nevertheless, there are few atomic-level insights into such mechanical property enhancement. In this study, solid-state nuclear magnetic resonance (NMR) is utilized as a main tool to understand the molecular origin of the mechanical enhancement of PA6/PK blends. The proton relaxation times are used to evaluate the miscibility and domain sizes in PA6/PK blends, and to determine the crystallinity of each component, where both conventional DSC and WAXD experiments fail because of similar crystallization/melting behaviors of PA6 and PK components. 2D 1 H– 13 C WISE (wideline separation) and HETCOR (heteronuclear correlation) solid-state NMR spectroscopy were performed to further reveal the nano-heterogeneous structures and hydrogen bonding interactions in PA6/PK blend. With further combination with FTIR and SEM results, the previous characteristic morphological model for elucidating the toughening mechanism for PA6/PK blends is refuted, and it is proposed that the superior performance of PA6/PK blend is resulted from the synergistic effects of enhanced interfacial adhesion and interconnected interphase percolated in the bulk PA6/PK blends via hydrogen bonds. We envisage the detailed molecular level insights provided by solid-state NMR spectroscopy could assist in the bottom-up design of high performance polymer blend materials. • The locations of hydrogen bonding between PA6 and PK are precisely determined. • The strength of hydrogen bonding interactions is semi-quantitatively characterized. • A complementary approach for studying crystallization of polymer blends is provided. • Insights into the toughening mechanism via solid-state NMR techniques are obtained.

Tetracrystalline Tetrablock Quarterpolymers: Four Different Crystallites under the Same Roof.

Multicrystalline block polymers having three or more crystalline segments are essential materials for the advancement of physics in the field of crystallinity. The challenging synthesis of multicrystalline polymers has resulted in only a limited number of tricrystalline terpolymers having been reported to date. We report, for the first time, the synthesis of polyethylene-b-poly(ethylene oxide)-b-poly(ϵ-caprolactone)-b-poly(l-lactide) (PE-b-PEO-b-PCL-b-PLLA), a tetracrystalline tetrablock quarterpolymer, by combining polyhomologation, ring-opening polymerization, and an organic/metal "catalyst switch" strategy. 1 H NMR spectroscopy and gel-permeation chromatography confirmed the formation of the tetrablock quarterpolymer, while differential scanning calorimetry, X-ray diffraction, and wide-line separation solid-state NMR spectroscopy revealed the existence of four different crystalline domains.

Conformations and Intermolecular Interactions in Cellulose/Silk Fibroin Blend Films: A Solid-State NMR Perspective.

Fabricating materials with excellent mechanical performance from the natural renewable and degradable biopolymers has drawn significant attention in recent decades due to the environmental concerns and energy crisis. As two of the most promising substitutes of synthetic polymers, silk fibroin (SF), and cellulose, have been widely used in the field of textile, biomedicine, biotechnology, etc. Particularly, the cellulose/SF blend film exhibits better strength and toughness than that of regenerated cellulose film. Herein, this study is aimed to understand the molecular origin of the enhanced mechanical properties for the cellulose/SF blend film, using solid-state NMR as a main tool to investigate the conformational changes, intermolecular interactions between cellulose and SF and the water organization. It is found that the content of the β-sheet structure is increased in the cellulose/SF blend film with respect to the regenerated SF film, accompanied by the reduction of the content of random coil structures. In addition, the strong hydrogen bonding interaction between the SF and cellulose is clearly elucidated by the two-dimensional (2D) 1H-13C heteronuclear correlation (HETCOR) NMR experiments, demonstrating that the SF and cellulose are miscible at the molecular level. Moreover, it is also found that the -NH groups of SF prefer to form hydrogen bonds with the hydroxyl groups bonded to carbons C2 and C3 of cellulose, while the hydroxyl groups bonded to carbon C6 and the ether oxygen are less favorable for hydrogen bonding interactions with the -NH groups of SF. Interestingly, bound water is found to be present in the air-dried cellulose/SF blend film, which is predominantly associated with the cellulose backbones as determined by 2D 1H-13C wide-line-separation (WISE) experiments with spin diffusion. This clearly reveals the presence of nanoheterogeneity in the cellulose/SF blend film, although cellulose and SF are miscible at a molecular level. Without doubt, these in-depth atomic-level structural information could help reveal the molecular origin of the enhanced mechanical properties of the blend film, and thus to establish the structure-property relationship, which could further provide guidance for the fabrication of high performance biopolymer-based materials.

Glass transition of soft segments in phase-mixed poly(urethane urea) elastomers by time-domain 1H and 13C solid-state NMR

Abstract The glass transition processes of the soft-segments (SS) in a series of poly(urethane urea) (PUU) elastomers were studied by solid-state NMR. Two SS fractions, rigid (SSr) and mobile (SSm), can be discerned by time-domain wideline separation, 13C 1H dipolar dephasing, and frequency-switched Lee-Goldberg spin-locked T1ρ relaxation experiments. At increasing temperature, part of the SSr population turns into SSm, while the decay constants of both fractions only see moderate changes. The extent of the population exchange is greater for samples with more phase mixing. This population exchange can be interpreted as the glass transition in the SS-rich domains. Comparison between T1ρ relaxations on the xy plane and along the magic angle indicates that the domain sizes of SSr and SSm are likely less than 2–3 nm. SSr is not completely rigid, but possesses both a fast, anisotropic chain rotation associated with the β relaxation and a slower motion with more isotropic nature at ca. 105 s−1. It is predicted that at high strain rates, most of SSr and part of SSm would become rigid, resulting in dynamically induced strengthening and toughening.

Molecular interactions between green tea catechins and cheese fat studied by solid-state nuclear magnetic resonance spectroscopy

Molecular integrations between green tea catechins and milk fat globules in a cheese matrix were investigated using solid-state magic angle spinning nuclear magnetic resonance spectroscopy. Full-fat cheeses were manufactured containing free catechin or free green tea extract (GTE), and liposomal encapsulated catechin or liposomal encapsulated GTE. Molecular mobility of the carbon species in the cheeses was measured by a wide-line separation technique. The 1H evolution frequency profile of the 13C peak at 16ppm obtained for the control cheese and cheeses containing encapsulated polyphenols (catechin or GTE) were similar, however, the spectrum was narrower for cheeses containing free polyphenols. Differences in spectral width indicates changes in the molecular mobility of –-CH3– or –C–C–PO4– species through hydrophobic and/or cation–π associations between green tea catechins and cheese fat components. However, the similar spectral profile suggests that encapsulation protects cheese fat from interaction with catechins.

Investigation of sorbate-induced plasticization of Pahokee peat by solid-state NMR spectroscopy

Sorbate-induced swelling and plasticization of sorbent have been linked to sorption hysteresis of organic compounds in the natural organic matter of isolated humic acids, soils, and coals. The above processes, which have important implications for the fate and bioavailability of organic and inorganic contaminants, are mostly based on macroscopic changes and require molecular-level confirmation. This study aimed to investigate the presence or absence of sorbate-induced plasticization of Pahokee peat soil as a function of different sorbates. The plasticization of Pahokee peat soil was studied upon sorption of different proton-free solutes including C6D6, CDCl3, CCl4, C2Cl4, CBr4, C6D5Cl, and C5D5N, covering apolar and polar aromatic and aliphatic compounds. The swelling and plasticization of Pahokee peat soil were verified at the molecular level by 1H wideline and two-dimensional wideline separation (2D WISE) NMR. The use of 1H wideline shapes is the traditional technique for studying molecular dynamics but hampered by the lack of spectral resolution, with one dimension displaying 13C chemical shifts and the second showing 1H wideline shapes, is capable of providing information on molecular dynamics of specific functional groups. Our results showed that the segments of Pahokee peat soil sorbed with C6D6, C2Cl4, and C5D5N became more mobile, but the changes due to the plasticization were small. Both C6D6 and C5D5N selectively increased the mobility of specific components, C6D6 of the nonpolar alkyl domains, and C5D5N of both the nonpolar alkyl domains and aromatic components. Some liquid solutes at high concentrations (2–5 wt%) are capable of slightly “softening” natural organic matter of a soil, and this provides support for the hypothesis that natural organic matter in Pahokee peat soil is in a glassy state that is subject to plasticization.

Molecular structure and local dynamic in impact polypropylene copolymers studied by preparative TREF, solid state NMR spectroscopy, and SFM microscopy

The phase morphology in impact polypropylene was studied by size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and solid-state nuclear magnetic resonance (NMR). The characterizations of the raw copolymer materials indicate the presence of amorphous and crystalline phases. In order to gain more comprehensive insight in the microstructure of these materials, four different subsamples were prepared by Temperature Rising Elution Fractionation (TREF) and subsequently analyzed by DSC, SEC, analytical TREF and solid state NMR measurements. Fraction 1 consisted of non-crystalline ethylene–propylene random copolymer (EPR). Fraction 2 was composed of intermediate ethylene and propylene segments with different length and capabilities to crystallize. In fraction 3, long propylene segments were the dominating contribution, although some amorphous and crystalline ethylene sequences were detected, which are probably incorporated into the polypropylene main chains, since no soluble component was detected by analytical TREF. Finally, isotactic polypropylene (iPP) was determined to be the unique component of fraction 4. The local molecular mobility in the different phases was analyzed using 2D Wide Line Separation (WISE) NMR, while 13C detected spin diffusion experiments helped to elucidate local morphologies. Scanning Force Microscopy (SFM) studies of the impact polypropylene revealed a semicrystalline iPP matrix with dispersed softer regions, which involve not only soft amorphous elastomeric EPR components, but additional nano-domains with semi-crystalline properties different from the iPP matrix. Combining the SFM and solid state NMR results, a phase model for the EPR regions dispersed in the iPP matrix is proposed.

Probing the nanostructure, interfacial interaction, and dynamics of chitosan-based nanoparticles by multiscale solid-state NMR.

Chitosan-based nanoparticles (NPs) are widely used in drug and gene delivery, therapy, and medical imaging, but a molecular-level understanding of the internal morphology and nanostructure size, interface, and dynamics, which is critical for building fundamental knowledge for the precise design and efficient biological application of the NPs, remains a great challenge. Therefore, the availability of a multiscale (0.1-100 nm) and nondestructive analytical technique for examining such NPs is of great importance for nanotechnology. Herein, we present a new multiscale solid-state NMR approach to achieve this goal for the investigation of chitosan-poly(N-3-acrylamidophenylboronic acid) NPs. First, a recently developed (13)C multiple cross-polarization magic-angle spinning (MAS) method enabled fast quantitative determination of the NPs' composition and detection of conformational changes in chitosan. Then, using an improved (1)H spin-diffusion method with (13)C detection and theoretical simulations, the internal morphology and nanostructure size were quantitatively determined. The interfacial coordinated interaction between chitosan and phenylboronic acid was revealed by one-dimensional MAS and two-dimensional (2D) triple-quantum MAS (11)B NMR. Finally, dynamic-editing (13)C MAS and 2D (13)C-(1)H wide-line separation experiments provided details regarding the componential dynamics of the NPs in the solid and swollen states. On the basis of these NMR results, a model of the unique nanostructure, interfacial interaction, and componential dynamics of the NPs was proposed.

Phase-mixing and molecular dynamics in poly(urethane urea) elastomers by solid-state NMR

The dynamical heterogeneity in a series of 4,4′-dicyclohexylmethane diisocyanate-diethyltoluenediamine-poly(tetramethylene oxide) based poly(urethane urea) (PUU) elastomers was studied by solid-state nuclear magnetic resonance (NMR) methods. Extensive phase mixing was evidenced by the 1H wideline signal, which can be approximately fitted by a single exponential model. 13C T1 relaxation time measurements indicate that the hard segments (HS) exhibit some small-amplitude mobility, likely “activated” by neighboring soft segments (SS). Fitting of the time-domain wideline separation (TD-WISE) data was employed to characterize the extent of phase mixing, which revealed that a PUU elastomer contains four fractions: rigid-HS, mobile-HS, rigid-SS, and mobile-SS regions. For a variety of SS MWs, the dynamics and relative portions of rigid vs. mobile fractions among HS were substantially similar, while those for the SS exhibit large contrast. Furthermore, the dynamics in the rigid-SS fraction is at least an order of magnitude slower than that in mobile-SS for all PUUs. Greater phase-mixing substantially lowers the SS mobility, facilitating SS to undergo glass transition at high strain rates, thus can be key to enhancing dynamic mechanical strengthening.

Effects of Chemical Modification on the Molecular Dynamics of Complex Polyrotaxanes Investigated by Solid-State NMR

The chemical modification of the pendant hydroxyl functional groups on cyclodextrins (CDs) significantly suppresses the hydrogen-bonding interactions between the cyclodextrin molecules and leads to the unique viscoelastic properties of hydroxypropylated polyrotaxane (HyPR) [Inomata et al. Macromolecules 2010, 43, 4660–4666]. HyPR consists of poly(ethylene glycol) (PEG) and α-CDs that are partially modified with a hydroxypropyl (Hy) group, setting them apart from other polyrotaxanes (PRs). The molecular dynamics of PR and HyPR with 25% (HyPR25) and 78% (HyPR78) modification ratios were investigated using various solid-state NMR techniques. Two-dimensional 1H–13C wide-line separation (WISE) NMR spectra of three samples demonstrated that the PEG chains provide two components of the restricted and the near-isotropic components in a fast motion limit at 329 K. The fraction of restricted dynamics of the threaded PEG chains was found to depend on the chemical modification ratio. In addition, WISE experiments pro...

Synthesis and characterization of novel polyampholyte and polyelectrolyte polymers containing imidazole, triazole or pyrazole

Novel soluble and non-soluble polymers based on methacrylic acid, ethylene glycol diglycidyl ether and pyrazole, triazole or imidazole were obtained by a one-spot synthetic strategy. The new materials were characterized by spectroscopic techniques (FT-IR, and solution- and solid-state NMR). Evidence on the covalent binding of the different heterocycles to the non-soluble matrix was given by the unequivocal assignment of the 13C solid-state NMR spectra. Proton relaxation times in the rotating frame and two-dimensional wideline separation (1H-13C WISE) NMR spectra were used to assess their molecular dynamics. The higher synthetic yield of polyampholytes bearing triazole or pyrazole correlated with a lower molecular motion and a higher cross-linking degree. The polyelectrolyte effect of these materials was exhaustively explored through the acid-base properties, swelling and zeta potential. The quaternization of heterocyclic residues, responsible for adsorptive properties, was studied taking into account that these materials are attractive for analytical, environmental and biotechnological processes.

Structural characterization of gilsonite bitumen by advanced nuclear magnetic resonance spectroscopy and ultrahigh resolution mass spectrometry revealing pyrrolic and aromatic rings substituted with aliphatic chains

Gilsonite, a naturally occurring asphaltite bitumen, consists of a complex mixture of organic compounds. In the present study, advanced one and two dimensional solid state and solution 1H, 13C and 15N nuclear magnetic resonance (NMR) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) were employed to investigate its composition and structure. 13C NMR yielded a carbon aromaticity of 27%. Aromatic moieties in gilsonite were primarily single rings or small clusters of fused rings. Half of the aromatic carbons of gilsonite can be accounted for by pyrroles. 15N and 13C cross polarization-magic angle spinning (CP-MAS) NMR showed that most nitrogen in gilsonite was pyrrolic. The aromatic rings were heavily substituted with alkyl chains, as evidenced by 1H13C correlation spectra. Advanced solid state NMR spectral editing techniques clearly identified specific functional groups such as CCH3, CCH2, and CCH2 (exomethylene). 1H13C wideline separation (WISE) NMR helped identify mobile and non-protonated alkyl carbons. FT-ICR-MS indicated that ∼64% of calculated formulae generated by ESI were aliphatic, while only about 0.8–2.5% of formulae contained possible aromatic rings. All of the assigned formulae contained at least one heteroatom (N, O or S), indicating that ionization by ESI was selective for the polar fraction of gilsonite and potentially less reflective of the overall chemical character of gilsonite than NMR spectroscopy. By combining the information obtained from advanced NMR and ultrahigh resolution MS we propose a structural model for gilsonite as a mixture of many pyrrolic and a few fused aromatic rings highly substituted with and connected by mobile aliphatic chains.

Synthesis and characterization of a new hyperbranched organic–inorganic solid polymer electrolyte with cyanuric chloride as a core element

A new hyperbranched organic–inorganic hybrid electrolyte based on the use of 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride, CC) as the coupling core to couple with oligo(oxyalkylene)-amines, followed by condensation with (3-glycidoxypropyl)-trimethoxysilane (GLYMO) and complexed with LiClO 4, has been prepared and characterized. The Vogel–Tamman–Fulcher (VTF) like conductivity behavior is observed in the present organic–inorganic hybrid electrolytes with a maximum ionic conductivity value of 4.4 × 10 −5 S cm −1 at 30 °C. Multinuclear NMR techniques are used to provide a microscopic view for the specific interaction between the polymer chains and Li + cations and their dynamic behaviors. The results of 2D 1H– 13C wide-line separation (WISE) and 7Li static line NMR width measurements divulge that the mobility of the 7Li cations is strongly related to a dynamic environment created by the polymer motion in the amorphous phase. The combined results of conductivity and 7Li pulse-gradient spin-echo (PGSE) NMR self-diffusion coefficient measurements reveal that the conductivity enhancement at low salt concentrations is mainly caused by the high mobility of the lithium cations.

Optimized NMR spectroscopic strategy to characterize water dynamics in soil samples

1H wideline NMR spectra of soil samples offer the possibility to analyze soil material based on their proton mobility. Care has to be taken to remove unwanted signal contributions from the probe background. We demonstrate that unstructured wideline spectra can be analyzed quantitatively by a combination of a Gaussian line for rigid and a Lorentzian line for mobile protons. This is used to study effects of hydrogen-bonded water networks upon heat treatment for a series of different soil samples with varying water content as a contribution to study physical aging of soil organic matter (SOM). Results are combined with 1H projections from 13C 2D WISE (wideline separation) experiments representing solely the broad Gaussian line. Furthermore, for the first time applied to soils, 1H structural information from soil samples is obtained from 2D PMLG phase modulated Lee–Goldburg measurements under magic angle spinning (MAS). Low water contents improve the resolution of main functional groups significantly.

Effect of Encapsulating a Pseudo-Decapeptide Containing Arginine on PLGA: A Solid-State NMR Study

The effects of incorporating an amorphous decapeptide in PLGA on the cooperative and local motions of the polymer chains have been evaluated. Whereas assessment of the bulk properties is used traditionally for studies of host-guest interactions, there are only rare examples where molecular-level understanding of such amorphous host-guest systems has been sought. Moreover, addressing the mechanism of interactions and stabilisation of a drug in a polymeric network is a key factor for the achievement of reproducibility of the formulations and ultimately the preparation of composites able to deliver drugs with consistency. We present a methodology combining the study of the dynamics by solid-state NMR and the characterisation of the bulk properties to address and localise the presence of interactions in PLGA/guest composites. The results (estimation of relaxation times, 2D wideline separation and T(g) measurements) suggested (1) the existence of a drug-polymer solid solution and (2) significant changes in the local dynamics of both the drug and the polymer in their composites depending on the loading level. The changes in the local dynamics as well as in the cooperative motions of the polymer chains in the composites were attributed to the formation of guest-polymer interactions. Differentiation of the affinity of glycolide or lactide units for interactions was also apparent.

Evidence of formation of site-selective inclusion complexation between β-cyclodextrin and poly(ethylene oxide)-block-poly(propylene oxide)- block-poly(ethylene oxide) copolymers

A series of inclusion complexes of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO) with beta-cyclodextrin (beta-CD) was prepared. Their formation, structure, and dynamics were investigated by solution two-dimensional rotating-frame Overhauser effect spectroscopy (2D ROESY) and one-dimensional (1D) and 2D solid-state (13)C NMR. The inclusion complexes between the PEO-b-PPO-b-PEO copolymers and the beta-CDs were formed in aqueous solution and detected by 2D ROESY. The high efficiency of cross polarization and spin diffusion experiments in (13)C solid-state NMR showed that the mobility of the PPO blocks dramatically decreases after beta-CD complexation, indicating that they are selectively incorporated onto the PPO blocks. The hydrophobic cavities of beta-CD restrict the PPO block mobility, which is evidence of the formation of inclusion complexes in the solid state. The 2D wide-line separation NMR experiments suggested that beta-CDs only thread onto the PPO blocks while forming the inclusion complexes. The stoichiometry of inclusion complexes was studied using (1)H NMR, and a 3:1 (PO unit to beta-CD) was found for all inclusion complexes, which indicated that the number of threaded beta-CDs was only dependent on the molecular weight of the PPO blocks. 1D wide angle x-ray diffraction studies demonstrated that the beta-CD in the inclusion complex formed a channel-like structure that is different from the pure beta-CD crystal structure.

Effect of curvature on C–F bonding in fluorinated carbons: from fullerene and derivatives to graphite

The effect of the curvature of the carbon lattice is discussed taking into account NMR data on various fluorinated carbons including C(60) fullerenes, single, double and multiwall carbon nanotubes. Graphite fluorides and highly fluorinated fullerenes are used as limit model compounds for planar and spherical geometries, respectively. The curvature results in a weakening of the C-F bonding covalence. First of all, various highly fluorinated fullerenes with increasing F/C molar ratio were prepared by treatment with pure gaseous fluorine. A preliminary study using XRD, EPR and IR spectroscopy confirms that the highest fluorination level can be reached either at 133 or at 300 degrees C. In order to extract the correlation between fluorine and carbon atoms and the C-F bond length, specific sequences such as solid echo, two-dimensional (19)F -->(13)C cross polarization wide-line separation and inverse (19)F -->(13)C cross polarization were also used for fluorinated C(60).

Wideline Separation (WISE) NMR of Native Elastin

Native elastin is an insoluble, amorphous (noncrystalline) protein with significant hydrophobic character. As its name suggests, the elasticity of blood vessels and other tissue types in vertebrates originates from this protein. We have previously shown that there is significant structural heterogeneity in this protein and its mimetics, and our earlier data indicated that its dynamic profile includes motions under multiple time scales. To examine this picture further, we use WIdeline SEparation (WISE) NMR experiments to characterize the natural-abundance 13C populations of unenriched elastin in fully hydrated and lyophilized states. The hydrated elastin has only one peak in the indirect dimension, reflective of significant motional narrowing. In contrast, the lyophilized elastin has a broad feature, indicating limited or no motion. In addition, however, our results indicate that a faster motion is also present, even in the absence of the water. The details of the line fitting and the possible implications...

A highly conductive organic–inorganic hybrid electrolyte based on co-condensation of di-ureasil and ethylene glycol-containing alkoxysilane

Organic–inorganic hybrid electrolytes based on di-ureasil backbone structures by reacting poly(propylene glycol)- block-poly(ethylene glycol)- block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2000) with 3-(triethoxysilyl)propyl isocyanate (ICPTES), followed by co-condensation with methoxy(polyethylenoxy)propyl trimethoxysilane (MPEOP) in the presence of LiClO 4 were prepared and characterized by a variety of techniques. The hybrid electrolytes showed good resistance to crystallization and excellent conductivity for use in lithium-ion batteries, as determined by differential scanning calorimetry (DSC) and impedance measurements, respectively. The temperature dependence of the ionic conductivity exhibited a VTF (Vogel–Tamman–Fulcher)-like behavior for all the compositions studied and a maximum ionic conductivity value of 6.9 × 10 −5 S cm −1, a relatively high value for solid polymer electrolytes, was achieved at 30 °C for the hybrid electrolyte with a [O]/[Li] ratio of 16. A microscopic view of the dynamic behavior of the polymer chains ( 13C) and the ionic species ( 7Li) was provided by the 1H and 7Li line widths measured from 2D 1H– 13C WISE (Wideline Separation) and variable temperature 7Li static NMR, respectively, to elucidate the influence of the mobility of the polymer chains and the charge carriers on the observed ionic conductivity. The present salt-free hybrid electrolyte after plasticization with 1 M LiClO 4 in EC/PC solution exhibited a swelling ratio of 275% and reached an ionic conductivity value up to 8.3 × 10 −3 S cm −1 at 30 °C, which make it a good candidate for the further development of advanced rechargeable lithium-ion batteries.

Solid-State NMR Investigation of Major and Minor Ampullate Spider Silk in the Native and Hydrated States

Silks spun from the major (Ma) and minor (Mi) ampullate glands by the spider Nephila clavipes respond to water differently. Specifically, Ma silk supercontracts (shrinks 40-50% in length) while Mi silk does not contract at all when hydrated with water. In the present study, 1H --> 13C cross polarization magic angle spinning (CP-MAS), 13C MAS NMR collected with dipolar decoupling, and two-dimensional wide-line separation spectra are presented on Mi silk in its native and hydrated state and comparisons are made to Ma silk. This combination of NMR data demonstrates that water plasticizes Mi and Ma silk similarly, with an increase in chain dynamics observed in regions containing Gly, Glu, Ser, Tyr, Leu, and a fraction of Ala when the Mi silk is hydrated. Resonances that correspond to the poly(Ala) and poly(Gly Ala) motifs of Ma and Mi silk are predominately rigid indicating that water does not penetrate these beta-sheet domains.