Thermodynamic Destabilization Research Articles

Glycosylation May Reduce Protein Thermodynamic Stability by Inducing a Conformational Distortion.

Glycosylation plays not only a functional role but can also modify the biophysical properties of the modified protein. Usually, natural glycosylation results in protein stabilization; however, in vitro and in silico studies showed that sometimes glycosylation results in thermodynamic destabilization. Here, we applied coarse-grained and all-atom molecular dynamics simulations to understand the mechanism underlying the loss of stability of the MM1 protein by glycosylation. We show that the origin of the destabilization is a conformational distortion of the protein caused by the interaction of the monosaccharide with the protein surface. Though glycosylation creates new short-range glycan-protein interactions that stabilize the conjugated protein, it breaks long-range protein-protein interactions. This has a destabilizing effect because the probability of long- and short-range interactions forming differs between the folded and unfolded states. The destabilization originates not from simple loss of interactions but due to a trade-off between the short- and long-range interactions.

An integrative approach combining ion mobility mass spectrometry, X-ray crystallography, and nuclear magnetic resonance spectroscopy to study the conformational dynamics of α1 -antitrypsin upon ligand binding.

Native mass spectrometry (MS) methods permit the study of multiple protein species within solution equilibria, whereas ion mobility (IM)-MS can report on conformational behavior of specific states. We used IM-MS to study a conformationally labile protein (α1-antitrypsin) that undergoes pathological polymerization in the context of point mutations. The folded, native state of the Z-variant remains highly polymerogenic in physiological conditions despite only minor thermodynamic destabilization relative to the wild-type variant. Various data implicate kinetic instability (conformational lability within a native state ensemble) as the basis of Z α1-antitrypsin polymerogenicity. We show the ability of IM-MS to track such disease-relevant conformational behavior in detail by studying the effects of peptide binding on α1-antitrypsin conformation and dynamics. IM-MS is, therefore, an ideal platform for the screening of compounds that result in therapeutically beneficial kinetic stabilization of native α1-antitrypsin. Our findings are confirmed with high-resolution X-ray crystallographic and nuclear magnetic resonance spectroscopic studies of the same event, which together dissect structural changes from dynamic effects caused by peptide binding at a residue-specific level. IM-MS methods, therefore, have great potential for further study of biologically relevant thermodynamic and kinetic instability of proteins and provide rapid and multidimensional characterization of ligand interactions of therapeutic interest.PDB Code(s): 4PYW

Thermodynamic Protein Destabilization by GFP Tagging: A Case of Interdomain Allostery

The Engrailed Homeodomain (EnHD) transcription factor of Drosophila melanogaster was fused to the enhanced green fluorescent protein (eGFP) either at its C- or N-terminus via three- or ten-residue flexible linkers. Here, we show that EnHD undergoes destabilization upon fusing it to eGFP regardless of the linker length used and whether the tethering is to its N- or C-terminus. The destabilization is reflected in melting points that are lower by up to 9°C. Thermodynamic analysis and coarse-grained molecular dynamic simulations indicate that this destabilization is due to eGFP-promoted entropic stabilization of the denatured state ensemble of EnHD. Our results provide, therefore, an example for destabilizing interdomain allostery. They are also important given the widespread use of eGFP tagging in cell biology, as they indicate that such tagging can cause unintended protein destabilization and concomitant effects.

Hydrogen Desorption Kinetics in Metal Intercalated Fullerides

For different hydrogenated metal intercalated fullerides (Na10C60-H, Li12C60-H, and Li28C60-H) the activation energies for hydrogen desorption were determined by DSC. The Vyazovkin advanced method (VA) was used for the calculation of the reaction model free activation energy as a function of the extent of conversion a. Activation energies are highest for low a and decrease for increasing alpha, between around 200-145 and 245-175 kJ/mol for the Na and Li compounds, respectively. The decrease of activation energy as a function of the extent of conversion can be explained by an increasing charge transfer to the C60H36+y cage during desorption. Na intercalation leads to a significant thermodynamic destabilization for hydrogen desorption. Dehydrogenation enthalpies of 52 (Na10C60-H), 66 (Li12C60-H), and 69 kJ/mol H-2 (Li28C60-H) were determined. These values are lower compared to literature values for desorption of pure C60H36 (74 kJ/mol H-2). The onsets of hydrogen desorption are 185 degrees C (Na10C60-H), 260 degrees C (Li12C60-H), and 250 degrees C (Li28C60-H) compared to >400 degrees C for pure C60H36.

Effects of milk protein-polysaccharide interactions on the stability of ice cream mix model systems

Polysaccharides (PS) are commonly used as stabilizers in ice cream to improve the structural and textural properties. However, in emulsions, the polysaccharides can interact with the milk proteins, resulting in the thermodynamic destabilization of the emulsion systems. This paper focuses on the effect of the interactions between milk proteins and two gums (carboxymethylcellulose (CMC) and guar gum (GG)) on the stability of ice cream models consisting of 11% skimmed milk powder (SMP) and 10% coconut oil. Parameters such as interfacial tension, fluorescence spectroscopy, zeta-potential, surface adsorption, microstructure, creaming, and rheological properties were determined. Furthermore, the interactions between the proteins and PS attributed to the stability of the emulsions were characterized. The results indicated that the stability of ice cream model emulsions depended on the types and concentrations of polysaccharides. SMP/GG mixed emulsions were distinguished by a higher rate of creaming compared to SMP/CMC mixed models with the same levels of polysaccharides (except for 0.1%). Depletion flocculation was involved in the destabilization of the two SMP/PS emulsion systems. Lower creaming rates above the critical content of phase separation in the SMP/CMC mixed models were related to the attractive interactions between milk proteins and CMC and enhanced apparent viscosity compared to that of SMP/GG systems. These findings provided a theoretical basis for ice cream processing; however, further research is required due to the complex ingredients and reactions involved during ice cream processing.

Thermodynamic Destabilization of Magnesium Hydride Using Mg-Based Solid Solution Alloys

Thermodynamic destabilization of magnesium hydride is a difficult task that has challenged researchers of metal hydrides for decades. In this work, solid solution alloys of magnesium were exploited as a way to destabilize magnesium hydride thermodynamically. Various elements were alloyed with magnesium to form solid solutions, including: indium (In), aluminum (Al), gallium (Ga), and zinc (Zn). Thermodynamic properties of the reactions between the magnesium solid solution alloys and hydrogen were investigated. Equilibrium pressures were determined by pressure–composition–isothermal (PCI) measurements, showing that all the solid solution alloys that were investigated in this work have higher equilibrium hydrogen pressures than that of pure magnesium. Compared to magnesium hydride, the enthalpy (ΔH) of decomposition to form hydrogen and the magnesium alloy can be reduced from 78.60 kJ/(mol H2) to 69.04 kJ/(mol H2), and the temperature of 1 bar hydrogen pressure can be reduced to 262.33 °C, from 282.78 °C, fo...

Use of the Parcel Buoyancy Minimum (Bmin) to Diagnose Simulated Thermodynamic Destabilization. Part I: Methodology and Case Studies of MCS Initiation Environments

Abstract A method based on parcel theory is developed to quantify mesoscale physical processes responsible for the removal of inhibition energy for convection initiation (CI). Convection-permitting simulations of three mesoscale convective systems (MCSs) initiating in differing environments are then used to demonstrate the method and gain insights on different ways that mesoscale thermodynamic destabilization can occur. Central to the method is a thermodynamic quantity Bmin, which is the buoyancy minimum experienced by an air parcel lifted from a specified height. For the cases studied, vertical profiles of Bmin using air parcels originating at different heights are qualitatively similar to corresponding profiles of convective inhibition (CIN). Though it provides less complete information than CIN, an advantage of using Bmin is that it does not require vertical integration, which simplifies budget calculations that enable attribution of the thermodynamic destabilization to specific physical processes. For a specified air parcel, Bmin budgets require knowledge of atmospheric forcing at only the parcel origination level and some approximate level where Bmin occurs. In a case of simulated daytime surface-based CI, destabilization in the planetary boundary layer (PBL) results from a combination of surface fluxes and upward motion above the PBL. Upward motion effects dominate the destabilizing effects of horizontal advections in two different simulated elevated CI cases, where the destabilizing layer occurs from 1 to 2.5 km AGL. In an elevated case with strong warm advection, changes to the parcel at its origination level dominate the reduction of negative buoyancy, whereas for a case lacking warm advection, adiabatic temperature changes to the environment near the location of Bmin dominate.

Use of the Parcel Buoyancy Minimum (Bmin) to Diagnose Simulated Thermodynamic Destabilization. Part II: Composite Analysis of Mature MCS Environments

Abstract Herein, the parcel buoyancy minimum (Bmin) defined in Part I of this two-part paper is used to examine physical processes influencing thermodynamic destabilization in environments of mature simulated mesoscale convective systems (MCSs). These convection-permitting simulations consist of twelve 24-h forecasts during two 6-day periods characterized by two different commonly occurring warm-season weather regimes that support MCSs over the central United States. A composite analysis of 22 MCS environments is performed where cases are stratified into surface-based (SB), elevated squall (ES), and elevated nonsquall (ENS) categories. A gradual reduction of lower-tropospheric Bmin to values indicative of small convection inhibition, occurring over horizontal scales >100 km from the MCS leading edge, is a common aspect of each category. These negative buoyancy decreases are most pronounced for the ES and ENS environments, in which convective available potential energy (CAPE) is greatest for air parcels originating above the surface. The implication is that the vertical structure of the mesoscale environment plays a key role in the evolution and sustenance of convection long after convection initiation and internal MCS circulations develop, particularly in elevated systems. Budgets of Bmin forcing are computed for the nocturnally maturing ES and ENS composites. Though warm advection occurs through the entire 1.5-km-deep layer comprising the vertical intersection of the largest environmental CAPE and smallest environmental Bmin magnitude, the net effect of terms involving vertical motion dominate the destabilization in both composites. These effects include humidity increases in air parcels due to vertical moisture advection and the adiabatic cooling of the environment above.

Non-natural G-quadruplex in a non-natural environment

The biocompatibility as well as the sustainability of a deep eutectic solvent makes it a good substitute for aqueous media in studying biomolecules. Understanding the structure and stability of natural and non-natural G-quadruplexes in aqueous and highly viscous media will be useful in biological and nanodevice applications. We report the synthesis and conformational analysis of a model G-rich oligonucleotide G3T3 and non-natural G-rich sequences Pyr1-Pyr3 in aqueous and highly viscous media. Progressive increases in the loop replacement with a non-natural pyrene linker leads to a systematic increase of the thermal denaturation temperature of the modified G-rich oligonucleotides Pyr1-Pyr3 in 10 mM cacodylate buffer (pH 7.2) containing 100 mM KCl, as monitored using UV-Vis spectroscopy. A circular dichroism signal clearly revealed the formation of a predominantly anti-parallel vs. parallel conformation in the natural G-rich oligonucleotide G3T3 as well as the non-natural G-rich oligonucleotides Pyr1-Pyr3 in 10 mM cacodylate buffer (pH 7.2) containing 100 mM KCl. On the other hand, we observed thermodynamic destabilization of G-rich oligonucleotides in a deep eutectic solvent (DES; 1 : 2 choline chloride-urea) containing 100 mm KCl with an increase in loop replacements. Interestingly, we observed an exclusively parallel G-quadruplex conformation in the case of G3T3 in DES containing 100 mm KCl. While pyrene containing G-rich oligonucleotides Pyr1-Pyr3 exhibited a predominantly parallel vs. anti-parallel G-quadruplex conformation in DES containing 100 mM KCl.

Improved Dehydrogenation and Rehydrogenation Properties of LiBH<sub>4</sub> by Nanosized Ni Addition

The complex hydride LiBH4, with a hydrogen density of 18.5 mass%, has been attracting significant interests for hydrogen storage, while suffers from its high dehydrogenation and rehydrogenation temperature. In this work, we systematically investigated the improvement effects of nanosized Ni on the dehydrogenation and rehydrogenation reactions of LiBH4 using thermogravimetry, quadrupole mass spectrometry and pressure-composition-isotherm analyses. Nanosized Ni was homogeneously dispersed on the surface of LiBH4 after ball milling. The dehydrogenation peak temperature of LiBH4 was reduced from 743 to 696 K with addition of 25 mass% Ni. First, LiBH4 tended to react with Ni to form Ni4B3, which suggests the thermodynamic destabilization effect of Ni. Then, the in-situ formed Ni4B3 was suggested to play a catalytic role on the dehydrogenation of the unreacted LiBH4. Moreover, the rehydrogenation content of LiBH4 was improved from 4.3 to 10.8 mass% by addition of 25 mass% Ni, suggesting the significant improvement effect of Ni4B3 on the rehydrogenation.

Nanoconfinement significantly improves the thermodynamics and kinetics of co-infiltrated 2LiBH4–LiAlH4 composites: Stable reversibility of hydrogen absorption/resorption

A uniformly distributed composite of 2LiBH4–LiAlH4 was successfully nanoconfined in mesoporous carbon scaffolds by using the solvent-mediated infiltration technique. The onset dehydrogenation temperatures of LiAlH4 and LiBH4 in the infiltrated 2LiBH4–LiAlH4 composite are decreased to ∼80 and ∼230°C, respectively, and are 40 and 145°C lower for their post-milled counterparts. Isothermal measurements reveal that ∼10wt.% H2 could be released from the nanoconfined 2LiBH4–LiAlH4 composite at 300°C within 300min, while less than 4wt.% H2 was released with respect to the post-milled mixture, even at 350°C. Moreover, by taking advantage of both nanoconfinement and thermodynamic destabilization, the release of toxic diborane from LiBH4 was successfully suppressed. The dehydrogenation mechanism reveals that, under the structure-directing effects of carbon supports, the decomposition of the well-distributed 2LiBH4–LiAlH4 composite favors the formation of AlB2 instead of the thermodynamically stable Li2B12H12, which has been verified to play a crucial role in enhancing the hydrogenation of the 2LiBH4–LiAlH4 composite. In combination with the extra LiH supplied by the in situ decomposition of nanoconfined LiAlH4, the thus-tailored thermodynamics and kinetics of the 2LiBH4–LiAlH4 composite endow it with significantly advanced reversible hydrogen storage properties, with a stable reversibility without apparent degradation after seven dehydrogenation/rehydrogenation cycles.

Euler buckling and nonlinear kinking of double-stranded DNA

The bending stiffness of double-stranded DNA (dsDNA) at high curvatures is fundamental to its biological activity, yet this regime has been difficult to probe experimentally, and literature results have not been consistent. We created a ‘molecular vise’ in which base-pairing interactions generated a compressive force on sub-persistence length segments of dsDNA. Short dsDNA strands (<41 base pairs) resisted this force and remained straight; longer strands became bent, a phenomenon called ‘Euler buckling’. We monitored the buckling transition via Förster Resonance Energy Transfer (FRET) between appended fluorophores. For low-to-moderate concentrations of monovalent salt (up to ∼150 mM), our results are in quantitative agreement with the worm-like chain (WLC) model of DNA elasticity, without the need to invoke any ‘kinked’ states. Greater concentrations of monovalent salts or 1 mM Mg2+ induced an apparent softening of the dsDNA, which was best accounted for by a kink in the region of highest curvature. We tested the effects of all single-nucleotide mismatches on the DNA bending. Remarkably, the propensity to kink correlated with the thermodynamic destabilization of the mismatched DNA relative the perfectly complementary strand, suggesting that the kinked state is locally melted. The molecular vise is exquisitely sensitive to the sequence-dependent linear and nonlinear elastic properties of dsDNA.

Structural and Thermodynamic Insight into Escherichia coli UvrABC-Mediated Incision of Cluster Diacetylaminofluorene Adducts on the NarI Sequence

Cluster DNA damage refers to two or more lesions in a single turn of the DNA helix. Such clustering may occur with bulky DNA lesions, which may be responsible for their sequence-dependent repair and mutational outcomes. Here we prepared three 16-mer cluster duplexes in which two fluoroacetylaminofluorene adducts (dG-FAAF) are separated by zero, one, and two nucleotides in the Escherichia coli NarI mutational hot spot (5'-CTCTCG1G2CG3CCATCAC-3'): 5'-CG1*G2*CG3CC-3', 5'-CG1G2*CG3*CC-3', and 5'-CG1*G2CG3*CC-3' (G* = dG-FAAF), respectively. We conducted spectroscopic, thermodynamic, and molecular dynamics studies of these di-FAAF duplexes, and the results were compared with those of the corresponding mono-FAAF adducts in the same NarI sequence [Jain, V., et al. (2012) Nucleic Acids Res. 40, 3939-3951]. Our nucleotide excision repair results showed the diadducts were more reparable than the corresponding monoadducts. Moreover, we observed dramatic flanking base sequence effects on their repair efficiency in the following order: NarI-G2G3 > NarI-G1G3 > NarI-G1G2. The nuclear magnetic resonance, circular dichroism, ultraviolet melting, and molecular dynamics simulation results revealed that in contrast to the monoadducts, diadducts produced a synergistic effect on duplex destabilization. In addition, dG-FAAF at G2G3 and G1G3 destacks the neighboring bases, with greater destabilization occurring with the former. Overall, the results indicate the importance of base stacking and related thermal and thermodynamic destabilization in the repair of bulky cluster arylamine DNA adducts.

Spontaneous Translocation of Antitumor Oxaliplatin, its Enantiomeric Analogue, and Cisplatin from One Strand to Another in Double-Helical DNA

Oxaliplatin and cisplatin belong to the class of platinum-based anticancer agents. Formation of DNA adducts by these complexes and the consequences for its structure and function, is the mechanistic paradigm by which these drugs exert their antitumor activity. We show that employing short oligonucleotide duplexes containing single, site-specific 1,3-intrastrand cross-links of oxaliplatin, its enantiomeric analogue, or cisplatin and by using gel electrophoresis that under physiological conditions the coordination bonds between platinum and the N7 position of guanine residues involved in the cross-links of the Pt(II) complexes can be cleaved. This cleavage may lead to linkage isomerization reactions between these metallodrugs and double-helical DNA. For instance, approximately 25 % 1,3-intrastrand cross-links of the platinum complexes isomerized after 192 h (at 310 K in 200 mM NaClO4). Differential scanning calorimetry of duplexes containing single, site-specific cross-links of oxaliplatin, its enantiomeric analogue, and cisplatin reveals that one of the driving forces that leads to the lability of DNA cross-links of these metallodrugs is a difference between the thermodynamic destabilization induced by the cross-link and by the adduct into which it could isomerize. The rearrangements may proceed in the way that cross-links originally formed in one strand of the DNA can spontaneously translocate from one DNA strand to its complementary counterpart, which may evoke walking of the platinum complex on DNA molecule. In addition, the differences in the kinetics of the rearrangement reactions and the thermodynamic destabilization of DNA observed for adducts of oxaliplatin and its enantiomeric analogue confirm that the chirality at the carrier 1,2-diaminocyclohexane ligand can considerably affect structural and other physical properties of DNA adducts and consequently their biological effects. In aggregate, interesting generalization of the results described in this work might be that the migration of oxaliplatin, its enantiomeric analogue, or cisplatin from one strand to another in double-helical DNA controlled by energetic signatures of these agents might contribute to a better understanding of their cytotoxic and mutagenic potential.

Effect of Signal Peptide on Stability and Folding of Escherichia coli Thioredoxin

The signal peptide plays a key role in targeting and membrane insertion of secretory and membrane proteins in both prokaryotes and eukaryotes. In E. coli, recombinant proteins can be targeted to the periplasmic space by fusing naturally occurring signal sequences to their N-terminus. The model protein thioredoxin was fused at its N-terminus with malE and pelB signal sequences. While WT and the pelB fusion are soluble when expressed, the malE fusion was targeted to inclusion bodies and was refolded in vitro to yield a monomeric product with identical secondary structure to WT thioredoxin. The purified recombinant proteins were studied with respect to their thermodynamic stability, aggregation propensity and activity, and compared with wild type thioredoxin, without a signal sequence. The presence of signal sequences leads to thermodynamic destabilization, reduces the activity and increases the aggregation propensity, with malE having much larger effects than pelB. These studies show that besides acting as address labels, signal sequences can modulate protein stability and aggregation in a sequence dependent manner.

Using only the very accurately known experimental enthalpy of hydrogenation of ethylene as a reference standard in the atomization method

Theoretical Gn model chemistries yield slightly different values for the enthalpy of formation of the hydrogen molecule from the constituent protons and electrons. For example, the G3 model yields −1.92 kJ mol−1 at 298 K, which differs from zero by an acceptably small amount. However, using this G3 value for a stepwise series of hydrogenations of polyunsaturated molecules multiplies the error, e.g., by five times for the hydrogenation of naphthalene. For polyunsaturates, this can produce errors considerably greater than experimental uncertainties. We calculate enthalpies of hydrogenation by referring the calculated values to the accurately known experimental enthalpy of hydrogenation of ethylene. This approach is simpler than the atomization method that depends on several experimental enthalpies of formation of the constituent atoms of the target molecules. This method yields enthalpies of hydrogenation and of formation in excellent agreement with experiment for many polyunsaturated compounds and lends confidence to results obtained for others, for which no accurate experimental values exist or are disparate, for example azulene. Some new and surprising results are that the formally conjugated triple bonds of cyanoacetylene do not lead to stabilization, but to destabilization by 10.2 kJ mol−1. The conjugated triple bonds of cyanogen cause thermodynamic destabilization by 47.5 kJ mol−1. Stabilization by conjugation in acrylonitrile is near zero. The remarkable endothermic monohydrogenation of benzene (25 kJ mol−1), first noted by Kistiakowsky, is also found in toluene and naphthalene, leading to stability of the reactant relative to the product of ~30 and 22 kJ mol−1, respectively.

Electrochemical hydriding of Mg–Ni–Mm (Mm = mischmetal) alloys as an effective method for hydrogen storage

In this work, the electrochemical hydriding method was used for storing hydrogen in four binary Mg–Ni (Ni content from 15 to 34 wt.%) alloys and one ternary Mg–26Ni–12Mm alloy. Both the as-cast and powdered alloys were hydrided in a 6 M KOH solution at 80 °C for 120–480 min. The structures and phase compositions of the alloys, both before and after hydriding, were studied using optical and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. Differential scanning calorimetry and mass spectrometry were used to study the dehydriding process. In the case of as-cast alloys, the best combination of hydriding parameters (maximum hydrogen concentration on surface; depth of hydrogen penetration) was achieved in the Mg–26Ni alloy. In the case of powdered alloys, the Mg–34Ni alloy absorbed the highest amount of hydrogen, nearly 4.5 wt.%. The only hydride formed during hydriding was the MgH2 hydride. The results of the mass spectrometry analysis reveal a significant thermodynamic destabilization of magnesium hydride due to Ni and Mm. The decomposition temperature of MgH2 was reduced by more than 200 °C. The results are discussed in relation to the electronic structure and atomic size of the alloying elements and the structural variations in the alloys.

Metathesis Reaction-Induced Significant Improvement in Hydrogen Storage Properties of the KF-Added Mg(NH2)2–2LiH System

The hydrogen storage properties and mechanisms of the Mg(NH2)2–2LiH system with potassium halides (KF, KCl, KBr, and KI) were investigated and discussed. The results show that the KF-added sample exhibits superior hydrogen storage properties as ∼5.0 wt % of hydrogen can be reversibly stored in the 0.08KF-added sample via a two-stage reaction with an onset dehydrogenation temperature of 80 °C. However, hydrogen storage behaviors of the samples with KCl, KBr, and KI remain almost unchanged. The fact that KF can readily react with LiH to convert to KH and LiF due to the favorable thermodynamics during ball milling should be the primary reason for its significant effects, as the presence of KH provides a synergetic thermodynamic and kinetic destabilization in the hydrogen storage reaction of the Mg(NH2)2–2LiH system by declining the activation energy of the first-step dehydrogenation as a catalyst and reducing the desorption enthalpy change of the second step as a reactant. The understanding on the role playe...

Carbon nanomaterial-assisted morphological tuning for thermodynamic and kinetic destabilization in sodium alanates

In the present work, we develop an effective strategy, i.e., carbon nanomaterial-assisted morphological tuning, for both thermodynamic and kinetic destabilization in complex hydrides based on the interaction between the complex anion and the carbon matrix. The NaAlH4/carbon nanomaterials of graphene nanosheets (GNs), fullerene (C60) and mesoporous carbon (MC) were selected as model systems for illustrating the positive effect of carbon nanomaterial-assisted morphological tuning. It is demonstrated that through the dissolution–recrystallization process, the morphologies of NaAlH4 can be altered from the scale-like continuous structure for the GN-assisted sample, to flower-like structures with diameters ranging from 5 to 10 μm for the C60-assisted sample and to uniform particles with an average diameter of about 2 μm for the MC-assisted sample. Correspondingly, the onset temperature for dehydrogenation of NaAlH4 is reduced to about 188, 185 and 160 °C for the samples assisted with GNs, C60 and MC, respectively, much lower than 210 °C for the pristine sample. A remarkable reduction in activation energy for three-step dehydrogenation is also obtained in NaAlH4/carbon nanomaterial composites relative to the pristine sample, and the improved efficiency of carbon nanomaterials for kinetics is found to be in the order of MC > C60 > GNs. These positive improvements can be attributed to both the particle refinement and interaction between NaAlH4 and the carbon nanomaterial that are in intimate contact with each other, which are not only evidenced by FE-SEM observation, but also supported by 27Al solid-state NMR characterization.

Thermodynamically destabilized hydride formation in “bulk” Mg–AlTi multilayers for hydrogen storage

Thermodynamic destabilization of MgH2 formation through interfacial interactions in free-standing Mg-AlTi multilayers of overall "bulk" (0.5 μm) dimensions with a hydrogen capacity of up to 5.5 wt% is demonstrated. The interfacial energies of Mg-AlTi and Mg-Ti (examined as a baseline) are calculated to be 0.81 and 0.44 J m(-2). The enhanced interfacial energy of AlTi opens the possibility of creating ultrathin alloy interlayers that provide further thermodynamic improvements in metal hydrides.