Spin-lattice Relaxation Time In Rotating Frame Research Articles

Exploring Molecular Dynamics of Adsorbed CO2 Species in Amine-Modified Porous Silica by Solid-State NMR Relaxation.

Previous studies on CO2 adsorbents have mainly addressed the identification and quantification of adsorbed CO2 species in amine-modified porous materials. Investigation of molecular motion of CO2 species in confinement has not been explored in depth yet. This work entails a comprehensive study of molecular dynamics of the different CO2 species chemi- and physisorbed at amine-modified silica materials through the determination of the rotating frame spin–lattice relaxation times (T1ρ) by solid-state NMR. Rotational correlation times (τC) were also estimated using spin relaxation models based on the Bloch, Wangsness, and Redfield and the Bloembergen–Purcell–Pound theories. As expected, the τC values for the two physisorbed CO2 species are considerably shorter (32 and 20 μs) than for the three identified chemisorbed CO2 species (162, 62, and 123 μs). The differences in molecular dynamics between the different chemisorbed species correlate well with the structures previously proposed. In the case of the physisorbed CO2 species, the τC values of the CO2 species displaying faster molecular dynamics falls in the range of viscous liquids, whereas the species presenting slower dynamics exhibit T1ρ and τC values compatible with a CO2 layer of weakly interacting molecules with the silica surface. The values for chemical shift anisotropy (CSA) and 1H–13C heteronuclear dipolar couplings have also been estimated from T1ρ measurements, for each adsorbed CO2 species. The CSA tensor parameters obtained from fitting the relaxation data agree with the experimentally measured CSA values, thus showing that the theories are well suited to study CO2 dynamics in silica surfaces.

Structural Polymorphism of Alzheimer's β-Amyloid Fibrils as Controlled by an E22 Switch: A Solid-State NMR Study.

The amyloid-β (Aβ) peptide of Alzheimer's disease (AD) forms polymorphic fibrils on the micrometer and molecular scales. Various fibril growth conditions have been identified to cause polymorphism, but the intrinsic amino acid sequence basis for this polymorphism has been unclear. Several single-site mutations in the center of the Aβ sequence cause different disease phenotypes and fibrillization properties. The E22G (Arctic) mutant is found in familial AD and forms protofibrils more rapidly than wild-type Aβ. Here, we use solid-state NMR spectroscopy to investigate the structure, dynamics, hydration and morphology of Arctic E22G Aβ40 fibrils. (13)C, (15)N-labeled synthetic E22G Aβ40 peptides are studied and compared with wild-type and Osaka E22Δ Aβ40 fibrils. Under the same fibrillization conditions, Arctic Aβ40 exhibits a high degree of polymorphism, showing at least four sets of NMR chemical shifts for various residues, while the Osaka and wild-type Aβ40 fibrils show a single or a predominant set of chemical shifts. Thus, structural polymorphism is intrinsic to the Arctic E22G Aβ40 sequence. Chemical shifts and inter-residue contacts obtained from 2D correlation spectra indicate that one of the major Arctic conformers has surprisingly high structural similarity with wild-type Aβ42. (13)C-(1)H dipolar order parameters, (1)H rotating-frame spin-lattice relaxation times and water-to-protein spin diffusion experiments reveal substantial differences in the dynamics and hydration of Arctic, Osaka and wild-type Aβ40 fibrils. Together, these results strongly suggest that electrostatic interactions in the center of the Aβ peptide sequence play a crucial role in the three-dimensional fold of the fibrils, and by inference, fibril-induced neuronal toxicity and AD pathogenesis.

1H nuclear magnetic resonance study of hydrated water dynamics in perfluorosulfonic acid ionomer Nafion

We have studied the dynamics of hydrated water molecules in the proton exchange membrane of Nafion by means of high-resolution 1H nuclear magnetic resonance (NMR) measurements. “Bound” and “free” states of hydrated water clusters as well as the exchange protons were identified from the NMR chemical shift measurements, and their activation energies were obtained from the temperature-dependent laboratory- and rotating-frame spin-lattice relaxation measurements. Besides, a peculiar motional transition in the ultralow frequency region was observed at 373 K for the “free” hydrated water from the rotating-frame NMR spin-lattice relaxation time measurements.

Rotating-frame nuclear magnetic resonance study of the superprotonic conduction in LiH2PO4

The proton and phosphorus dynamics of the superprotonic conduction in the LiH2PO4 system has been studied by means of 1H and 31P NMR rotating-frame nuclear magnetic resonance (NMR). The temperature-dependent 1H NMR rotating-frame spin–lattice relaxation time measurements revealed in a sensitive manner the evolution of the microscopic environment and proton dynamics of the two distinct hydrogen-bond types in the system, which is quite compatible with the electrical conductivity and the impedance spectroscopy measurements. Besides, the proton dynamics was found to be coupled to the reorientational motion of the PO4 tetrahedra.

Modified lipid and protein dynamics in nanodiscs

For membrane protein studies, nanodiscs have been shown to hold great potential in terms of preparing soluble samples while maintaining a lipid environment. Here, we describe the differences in lipid order and protein dynamics in MSP1 nanodiscs compared to lamellar preparations by solid-state NMR. For DMPC, an increase of the dipolar C-H lipid acyl chain order parameters in nanodiscs is observed in both gel- and liquid crystalline phases. Incorporating proteorhodopsin in these nanodiscs resulted in a significantly longer rotating frame spin-lattice relaxation time for 13C leerzeichen and better cross polarisation efficiency due to restricted protein dynamics. A comparison of 13C–13C correlation spectra revealed no structural differences. The incorporation of proteorhodopsin into nanodiscs has been optimised with respect to detergent and to protein/scaffold protein/lipid stoichiometries. Its functional state was probed by time-resolved optical spectroscopy revealing only minor differences between lamellar and nanodisc preparations. Our observations show remarkable dynamic effects between membrane proteins, lipids and scaffold protein. The potential use of nanodiscs for solid-state NMR applications is discussed.

Multidimensional solid‐state NMR studies of the structure and dynamics of pectic polysaccharides in uniformly 13C‐labeled Arabidopsis primary cell walls

Plant cell wall (CW) polysaccharides are responsible for the mechanical strength and growth of plant cells; however, the high-resolution structure and dynamics of the CW polysaccharides are still poorly understood because of the insoluble nature of these molecules. Here, we use 2D and 3D magic-angle-spinning (MAS) solid-state NMR (SSNMR) to investigate the structural role of pectins in the plant CW. Intact and partially depectinated primary CWs of Arabidopsis thaliana were uniformly labeled with (13)C and their NMR spectra were compared. Recent (13)C resonance assignment of the major polysaccharides in Arabidopsis thaliana CWs allowed us to determine the effects of depectination on the intermolecular packing and dynamics of the remaining wall polysaccharides. 2D and 3D correlation spectra show the suppression of pectin signals, confirming partial pectin removal by chelating agents and sodium carbonate. Importantly, higher cross peaks are observed in 2D and 3D (13)C spectra of the depectinated CW, suggesting higher rigidity and denser packing of the remaining wall polysaccharides compared with the intact CW. (13)C spin-lattice relaxation times and (1)H rotating-frame spin-lattice relaxation times indicate that the polysaccharides are more rigid on both the nanosecond and microsecond timescales in the depectinated CW. Taken together, these results indicate that pectic polysaccharides are highly dynamic and endow the polysaccharide network of the primary CW with mobility and flexibility, which may be important for pectin functions. This study demonstrates the capability of multidimensional SSNMR to determine the intermolecular interactions and dynamic structures of complex plant materials under near-native conditions.

High-resolution solid-state NMR study of isotactic polypropylenes

The high-resolution solid-state 13 C NMR spectra were recorded for metallocene (m) and Ziegler-Natta (ZN) iso- tactic polypropylenes (iPP) in pelletized form using cross polarization (CP) and magic angle spinning (MAS) techniques within the temperature range of 20-160°C. Besides the CP MAS experiments also the MAS 13 C NMR spectra (without CP), MAS 1 H NMR spectra and rotating frame spin-lattice relaxation times T1 ( 13 C) were measured at elevated temperatures. With the rise of temperature the splitting of CH2, CH and CH3 signals into two components was detected in 13 C NMR spec- tra and assigned to amorphous and crystalline phases. The temperature dependences of chemical shifts and integral intensi- ties obtained from the deconvoluted spectra provided information on the main chain and CH3 groups motions in amorphous and crystalline regions of studied samples. While T1 ( 13 C) values show that the rate of segmental motion in amorphous regions in m-iPP and ZN-iPP is virtually the same, larger linewidths in 13 C and 1 H NMR spectra indicate somewhat larger restraints of the motion in amorphous regions of ZN-iPP.

Effect of Sugars on the Molecular Motion of Freeze-Dried Protein Formulations Reflected by NMR Relaxation Times

To relate NMR relaxation times to instability-related molecular motions of freeze-dried protein formulations and to examine the effect of sugars on these motions. Rotating-frame spin-lattice relaxation time (T(1ρ)) was determined for both protein and sugar carbons in freeze-dried lysozyme-sugar (trehalose, sucrose and isomaltose) formulations using solid-state (13)C NMR. The temperature dependence of T(1ρ) for the lysozyme carbonyl carbons in lysozyme with and without sugars was describable with a model that includes two different types of molecular motion with different correlation times (τ(c)) for the carbon with each τ(c) showing Arrhenius temperature dependence. Both relaxation modes have much smaller relaxation time constant (τ(c)) and temperature coefficient (Ea) than structural relaxation and may be classified as β-relaxation and γ-relaxation. The τ(c) and Ea for γ-relaxation were not affected by sugars, but those for β-relaxation were increased by sucrose, changed little by trehalose, and decreased by isomaltose, suggesting that the β-mobility of the lysozyme carbonyl carbons is decreased by sucrose and increased by isomaltose. T(1ρ) determined for the lysozyme carbonyl carbons can reflect the effect of sugars on molecular mobility in lysozyme. However, interpretation of relaxation time data is complex and may demand data over an extended temperature range.

Solid-State NMR Molecular Dynamics Characterization of aHighly Chlorine-Resistant Disulfonated Poly(arylene ether sulfone) Random Copolymer Blended with Poly(ethylene glycol) Oligomers for Reverse Osmosis Applications

We have investigated the dynamics-transport correlations of a chlorine-resistant polymeric system designed as a next-generation reverse osmosis (RO) membrane material by solid-state NMR spectroscopy. A random disulfonated poly(arylene ether sulfone) copolymer in the potassium salt (-SO(3)(-)K(+)) form (BPS-20K) was blended with poly(ethylene glycol)s (PEGs) for improving water permeability. Blended BPS-20K/PEG membranes maintained the intrinsic chlorine-resistant property of BPS-20K, with a somewhat reduced salt rejection. The dynamic characteristics of BPS-20K/PEG blends studied by the spin-lattice relaxation time (T(1)) and rotating frame spin-lattice relaxation time (T(1)ρ) indicated correlations with the observed water uptake and permeability. (1)H T(1) measured on the polymer's aromatic phenylene rings and (1)H T(1)ρ measured on the oxyethylene (-CH(2)CH(2)O-) units of PEG were sensitive to the morphological changes, due to the blending of PEGs, induced in the mixed matrices. Membranes made of BPS-20K/PEG blends, with a lower molecular weight and higher amount of PEGs, that exhibited higher water permeability also provided shorter (1)H T(1) and T(1)ρ relaxation times. PEGs behaved as a plasticizer in the BPS-20K matrix, providing shorter (1)H T(1) times and therefore shorter motional correlation times in the nanosecond regime. (1)H T(1)ρ data have indicated the formation of networks among different polymeric chains via K(+)-oxyethylene ion-dipole interactions. Other properties that exhibit ad hoc correlations with the observed T(1) and T(1)ρ times include density, glass transition temperature, and salt rejection. Additionally, the ring flip motions measured on the hydrophobic phenylene rings did not reveal any correlations to the molecular weight and amount of PEGs blended, suggesting that the blending of PEG molecules modifies only the ionic domains of the BPS-20K polymer matrix.

Study of stretched polypropylene fibres by [formula omitted] pulsed and CW NMR spectroscopy

A set of stretched isotactic polypropylene fibres prepared with the draw ratio λ = 4 at four different stretching temperatures was investigated by H 1 pulsed relaxation NMR methods and CW NMR spectroscopy. We have studied the influence of the stretching temperature and draw ratio upon the changes of structure and molecular mobility. Some information on the influence of these conditions was obtained from CW NMR measurements by means of the temperature dependences of second moment M 2 and decomposition of NMR spectra into elementary components corresponding to the chains with different mobility. H 1 CW NMR spectra were measured at two (14.1 and 10.5 MHz) Larmor frequencies in the temperature range 200–420 K. An analysis of the experimental data shows that the stretching of the fibres at different temperature results in a change of molecular mobility. Spin-lattice relaxation times in laboratory ( T 1 ) and rotating ( T 1 ρ ) frames were also measured on the set of the fibres in the temperature range 239–423 K at 30 MHz Larmor frequency employing a home made pulse spectrometer. In the rotating frame spin-lattice relaxation time measurements in the temperature range above 278 K three relaxation times T 1 ρ have been observed. The minima of the temperature dependences of the observed relaxation times reflect an α -relaxation process in crystalline regions and β -relaxation process related to a double glass transition in the non-crystalline regions of the studied fibres.

Synthesis, infrared stealth and corrosion resistance of organically modified silicate–polyaniline/carbon black hybrid coatings

Hybrid coatings based on organically modified silicate–polyaniline/carbon black (Ormosil-PANI/CB) were synthesized through a sol–gel technique with different carbon black (10–30 wt%) and PANI/CB (10–30 wt%) contents. These hybrid films were deposited via spin coating onto an aluminum alloy in order to improve the corrosion protection and to act as infrared stealth coatings. The effects induced by the PANI/CB composites on the chain dynamic, thermal properties, infrared stealth, and anticorrosion performances of the coated samples were investigated. The rotating-frame spin–lattice relaxation times and scale of the spin–diffusion path length indicated that the configuration of the hybrid films was highly cross-linked and dense. Thermal properties of these Ormosil-PANI/CB hybrids have been improved over the pure Ormosil analyzed by thermal gravimetric analysis (TGA). The thermal extinction of the hybrid coatings increased with the increase in the carbon black and PANI/CB content. Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

A Solid-State NMR Study of Phase Structure, Molecular Interactions, and Mobility in Blends of Citric Acid and Paracetamol

Citric acid anhydrate (CAA) and paracetamol (PARA), prepared as crystalline physical mixtures and as amorphous blends, were studied using 13C solid-state cross polarization magic angle spinning (CPMAS) NMR. Amorphous blends showed significant line broadening from the conformational distribution as compared to the crystalline samples. Also, chemical shift variations were observed between crystalline and amorphous blends, which were attributed to differences in intermolecular interactions. Averaging of proton rotating-frame spin-lattice relaxation times (T1ρ) probed via different 13C sites in the amorphous blends confirmed molecular level mixing. For some, initially amorphous, sample compositions the onset of crystallization was evident directly from spectra and from the significantly longer T1ρ relaxations. Thus, crystallization caused phase separation with properties of the two phases resembling those of pure CAA and PARA, respectively. 13C spectra of amorphous 50/50 (w/w, %) CAA/PARA recorded from above the glass transition temperature broadened as the temperature increased to a maximum at T≈Tg + 33K. This was the result of a dynamic interference between the line narrowing techniques being applied and the time scale of molecular reorientation in the miscible melt. The derived average correlation time was found to correspond well with previous results from melt rheology. We conclude that the underlying reasons for physical instability (i.e., crystallization from the miscible melt, including molecular interactions and dynamics) of this class of amorphous binary mixtures can be effectively evaluated using NMR spectroscopy. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1862-1870, 2009

2H double quantum filtered (DQF) NMR spectroscopy of the nucleus pulposus tissues of the intervertebral disc

Deuterium (2H) double-quantum filtered (DQF) NMR spectroscopy of nucleus pulposus (NP) tissues from human intervertebral discs is reported. The DQF spectral intensities, DQ build-up rates, and DQF-detected rotating-frame spin-lattice relaxation times are sensitive to the degree of hydration of the NP tissue, and display a monotonous correlation with age between 15 and 80 years. The implications of this work are that the changes in water dynamics as detected via DQF NMR spectroscopy may be used as a probe of tissue degeneration in NP, particularly in the early stages of degeneration to which most standard NMR methods are not sensitive.

Significance of Local Mobility in Aggregation of β-Galactosidase Lyophilized with Trehalose, Sucrose or Stachyose

The purpose of this study is to compare the effects of global mobility, as reflected by glass transition temperature (T(g)) and local mobility, as reflected by rotating-frame spin-lattice relaxation time (T(1rho)) on aggregation during storage of lyophilized beta-galactosidase (beta-GA). The storage stability of beta-GA lyophilized with sucrose, trehalose or stachyose was investigated at 12% relative humidity and various temperatures (40-90 degrees C). beta-GA aggregation was monitored by size exclusion chromatography (SEC). Furthermore, the T(1rho) of the beta-GA carbonyl carbon was measured by (13)C solid-state NMR, and T(g) was measured by modulated temperature differential scanning calorimetry. Changes in protein structure during freeze drying were measured by solid-state FT-IR. The aggregation rate of beta-GA in lyophilized formulations exhibited a change in slope at around T(g), indicating the effect of molecular mobility on the aggregation rate. Although the T(g) rank order of beta-GA formulations was sucrose < trehalose < stachyose, the rank order of beta-GA aggregation rate at temperatures below and above T(g) was also sucrose < trehalose < stachyose, thus suggesting that beta-GA aggregation rate is not related to (T-T(g)). The local mobility of beta-GA, as determined by the T(1rho) of the beta-GA carbonyl carbon, was more markedly decreased by the addition of sucrose than by the addition of stachyose. The effect of trehalose on T(1rho) was intermediate when compared to those for sucrose and stachyose. These findings suggest that beta-GA aggregation rate is primarily related to local mobility. Significant differences in the second derivative FT-IR spectra were not observed between the excipients, and the differences in beta-GA aggregation rate observed between the excipients could not be attributed to differences in protein secondary structure. The aggregation rate of beta-GA in lyophilized formulations unexpectedly correlated with the local mobility of beta-GA, as indicated by T(1rho), rather than with (T-T(g)). Sucrose exhibited the most intense stabilizing effect due to the most intense ability to inhibit local protein mobility during storage.

Characterization and corrosion resistance of organically modified silicate–NiZn ferrite/polyaniline hybrid coatings on aluminum alloys

Hybrid coatings based on organically modified silicate (Ormosil)–NiZn ferrite/polyaniline (10–30 wt.%) were synthesized through a sol–gel technique. Tetraethylenepentamine, 3-glycidoxypropyltrimethoxysilane, tetraethoxysilane and Ni 0.5Zn 0.5Fe 2O 4/polyaniline were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the NiZn ferrite/polyaniline content on the chain dynamics, ferromagnetic behavior and corrosion performances of the coated samples were investigated. The rotating-frame spin–lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly cross-linked, dense and adhered to the aluminum alloy substrates. The magnetic properties of the resulting hybrids showed super-paramagnetic behavior, such as zero coercive force (coercivity = 0 G) and a low blocking temperatures (45 K). Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

Infrared stealth and anticorrosion performances of organically modified silicate-NiZn ferrite/polyaniline hybrid coatings

Hybrid coatings based on organically modified silicate-Ni0.5Zn0.5Fe2O4/polyaniline were synthesized through a sol–gel technique with different NiZn ferrite/polyaniline weight ratio (1/1, 1/2, 1/5). These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection and to act as infrared stealth coatings. The effects induced by the NiZn ferrite/polyaniline hybrids on the chain dynamic, ferromagnetic behavior, infrared stealth, and anticorrosion performances of the coated samples were investigated. The rotating-frame spin-lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly cross-linked and dense. The thermal extinction of the hybrid coatings increased with the increase in the polyaniline content. Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 926–935, 2008

Thermal stability and corrosion resistance of polysiloxane coatings on 2024-T3 and 6061-T6 aluminum alloy

Hybrid coatings based on polydimethylsiloxane-cured organically modified silicate were synthesized through a sol–gel technique. Amino-terminated siloxane, 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the different molar ratio of silane on the chain dynamics, thermal stability and corrosion performance of the coated samples were investigated. The rotating-frame spin-lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly crosslinked and dense. The thermal stability and the apparent activation energy, evaluated by van Krevelen's method, of the hybrid coatings depended on the molar ratio of silane. Potentiodynamic analysis revealed that the hybrid films provided good barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

Synthesis and characterization of organically modified silicate/NiZn ferrite hybrid coatings

Hybrid coatings based on organically modified silicate (Ormosil)/Ni 0.5Zn 0.5Fe 2O 4 (10–30 wt.%) were synthesized through a sol–gel technique. Tetraethylenepentamine, 3-glycidoxypropyltrimethoxysilane, tetraethoxysilane and Ni 0.5Zn 0.5Fe 2O 4 were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy in order to improve the corrosion protection and to act as infrared stealth coatings. The effects induced by the NiZn ferrite content on the chain dynamic, ferromagnetic behavior, infrared stealth and corrosion performances of the coated samples were investigated. The rotating-frame spin–lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly cross-linked, dense and adhered to the aluminum alloy substrates. The magnetic properties of the resulting hybrids showed super-paramagnetic behavior, such as zero coercive force (coercivity = 0 G) and a low blocking temperature (∼75 K). The thermal extinction of the hybrid coatings increased with the increase in the NiZn ferrite content. Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

Synthesis and characterization of polydimethylsiloxane-cured organically modified silicate hybrid coatings

Hybrid coatings based on polydimethylsiloxane-cured organically modified silicate were synthesized through a sol–gel technique. Amino-terminated siloxane, 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the different chain lengths of siloxane on the chain dynamics, thermal stability and corrosion performance of the coated samples were investigated. The rotating-frame spin–lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly crosslinked, dense and adhered to the aluminum alloy substrates. The thermal stability and the apparent activation energy, evaluated by van Krevelen's method, of the hybrid coatings depended on the siloxane chain length. Potentiodynamic analysis revealed that the hybrid films provided exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.

Domain size and thermal stability of amine-cured hybrid films as corrosion resistance treatments for aluminum alloy

Amine-cured Ormosil coatings were prepared from tetraethylenepentamine (TEPA), 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) by sol–gel method. These Ormosil films were deposited by spin coated on aluminum alloy to improve the corrosion protection. The effect of the concentration of curing agent TEPA on the chain dynamic, domain size, thermal stability and corrosion performance of coated samples was investigated. The rotating frame spin–lattice relaxation times (T1ρH) and scale of the spin-diffusion path length (L) indicated that the configuration of the Ormosil films was highly crosslinked and dense and adhered to the aluminum alloy (AA) substrates. The thermal stability and the apparent activation energy (Ea), evaluated by van Krevelen’s method, of the TEPA-cured GPTMS–TEOS Ormosils decreased with increasing TEPA content. Potentiodynamic and salt-spray analysis revealed that the Ormosil films provided exceptional barrier and corrosion protection in comparison with untreated AA substrates.