Blue shift in X-H stretching frequency of molecules due to confinement

The effect of spatial confinement on the properties of isoelectronic molecules HF, H2O, NH3, and CH4 has been studied by encapsulating them in a C60 fullerene cage. Second-order M?ller-Plesset perturbation theoretical (MP2) calculations suggest that all the guest species are stable inside the fullerene cage. This stabilization arises from the dispersion interaction between the guest and the host. It is shown that the excitation energy (Esigma*-Esigma) for the X-H bond increases and that there is a blue shift in the stretching frequencies due to confinement.     

Simulation studies of protein folding/unfolding equilibrium under polar and nonpolar confinement

We study the equilibrium folding/unfolding thermodynamics of a small globular miniprotein, the Trp cage, that is confined to the interior of a 2 nm radius fullerene ball. The interactions of the fullerene surface are changed from nonpolar to polar to mimic the interior of the GroEL/ES chaperonin that assists proteins to fold in vivo. We find that nonpolar confinement stabilizes the folded state of the protein due to the effects of volume reduction that destabilize the unfolded state and also due to interactions with the fullerene surface. For the Trp cage, polar confinement has a net destabilizing effect that results from the stabilizing confinement and the competitive exclusion effect that keeps the protein away from the surface hydration shell and stronger interactions between charged side chains in the protein and the polar surface that compete against the formation of an ion pair that stabilizes the protein folded state. We show that confinement effects due to volume reduction can be overcome by sequence-specific interactions of the protein side chains with the encapsulating surface. This study shows that there is a complex balance among many competing effects that determine the mechanism of GroEL chaperonin in enhancing the folding rate of polypeptide inside its cavity.     

Ultrastable and Highly Catalytically Active N-Heterocyclic-Carbene-Stabilized Gold Nanoparticles in Confined Spaces

Controlling the size and surface functionalization of nanoparticles (NPs) can lead to improved properties and applicability. Herein, we demonstrate the efficiency of the metal-carbene template approach (MCTA) to synthesize highly robust and soluble three-dimensional polyimidazolium cages (PICs) of different sizes, each bearing numerous imidazolium groups, and use these as templates to synthesize and stabilize catalytically active, cavity-hosted, dispersed poly-N-heterocyclic carbene (NHC)-anchored gold NPs. Owing to the stabilization of the NHC ligands and the effective confinement of the cage cavities, the as-prepared poly-NHC-shell-encapsulated AuNPs displayed promising stability towards heat, pH, and chemical regents. Most notably, all the Au@PCCs (PCC=polycarbene cage) exhibited excellent catalytic activities in various chemical reactions, together with high stability and durability.     

Interaction Study of Guest with Host in Clathrate Hydrate

Lattice dynamical simulations of noble gas hydrate structuresⅠandⅡhave been performed. Potential energies were investigated to study the influence of guest species on the stability of the hydrate structure.Results show that when the diameter of inclusion molecules is between 3(?)and 4.2(?),such as Ar and Kr,the critical role of the 5~(12)cage in the stabilization of hydrates becomes effective.For Xe hydrates SⅠand SⅡ,with the help of lattice dynamical calcnlations,the modes attributions are identified directly.We proposed the resonant effect of the fingerprint frequency at about 7 meV and 10 meV which arise from the coupling of Xe molecules in the 5~(12)cage with the host lattice.     

Ultrastable and Highly Catalytically Active N‐Heterocyclic‐Carbene‐Stabilized Gold Nanoparticles in Confined Spaces

Controlling the size and surface functionalization of nanoparticles (NPs) can lead to improved properties and applicability. Herein, we demonstrate the efficiency of the metal‐carbene template approach (MCTA) to synthesize highly robust and soluble three‐dimensional polyimidazolium cages (PICs) of different sizes, each bearing numerous imidazolium groups, and use these as templates to synthesize and stabilize catalytically active, cavity‐hosted, dispersed poly‐N‐heterocyclic carbene (NHC)‐anchored gold NPs. Owing to the stabilization of the NHC ligands and the effective confinement of the cage cavities, the as‐prepared poly‐NHC‐shell‐encapsulated AuNPs displayed promising stability towards heat, pH, and chemical regents. Most notably, all the Au@PCCs (PCC=polycarbene cage) exhibited excellent catalytic activities in various chemical reactions, together with high stability and durability.     

Electronic structure, molecular interaction, and stability of the CH4-nH2O complex, for n = 1-21

Molecular calculations were carried out with four different methodologies to study the CH 4- nH 2O complex, for n = 1-21. The HF and MP2 methods used considered the O atom with pseudopotential to freeze the 1s shell. The other methodologies applied the Bhandhlyp and B3lyp exchange and correlation functionals. The optimized CH 4- nH 2O structures are reported, specifying the number and type of H 2O subunits (triangle, square, pentagon, etc.) that comprised the nH 2O counterpart cluster or cage, that interacted with the CH 4 molecule, and, in the latter case, that provided its confinement. Results are focused to understand the stability of the CH 4- nH 2O complex. The quality of the electron correlation effect, as well as the size of the nH 2O cage to confine the guest molecule, and the number and type of H 2O subunits comprising the nH 2O cluster or cage are the most important factors to provide the stability of the complex and also dictate the particular n value at which the CH 4 molecule confinement occurs. This number was 14 for the HF, Bhandhlyp, and B3Lyp methods and 16 for the MP2 method. The reported hydrate structures for n < 20 could be predictive for future experiments.     

Dispersion interactions govern the strong thermal stability of a protein

Rubredoxin from the hyperthermophile Pyrococcus furiosus (Pf Rd) is an extremely thermostable protein, which makes it an attractive subject of protein folding and stability studies. A fundamental question arises as to what the reason for such extreme stability is and how it can be elucidated from a complex set of interatomic interactions. We addressed this issue first theoretically through a computational analysis of the hydrophobic core of the protein and its mutants, including the interactions taking place inside the core. Here we show that a single mutation of one of phenylalanine's residues inside the protein's hydrophobic core results in a dramatic decrease in its thermal stability. The calculated unfolding Gibbs energy as well as the stabilization energy differences between a few core residues follows the same trend as the melting temperature of protein variants determined experimentally by microcalorimetry measurements. NMR spectroscopy experiments have shown that the only part of the protein affected by mutation is the reasonably rearranged hydrophobic core. It is hence concluded that stabilization energies, which are dominated by London dispersion, represent the main source of stability of this protein.     

Stereoelectronic tuning of the structure and stability of the trp cage miniprotein

Proline residues are critical structural elements in proteins, defining turns, loops, secondary structure boundaries, and polyproline helices. Control of proline conformation therefore may be used to define protein structure and stability. 4-Substituted proline derivatives may be used to control proline ring pucker, which correlates with protein main chain conformation. To examine the use of proline conformational restriction to tune globular protein stability, a series of peptides derived from the trp cage miniprotein was synthesized. Proline at residue 12 of the trp cage miniprotein, which adopts a Cgamma-exo ring pucker in the NMR structure, was replaced with 4-substituted proline derivatives, including 4R derivatives favoring a Cgamma-exo ring pucker and 4S derivatives favoring a Cgamma-endo ring pucker. Eight trp cage peptides were synthesized, five of which included residues that are not commercially available, without requiring any solution phase chemistry. Analysis of the trp cage peptides by circular dichroism and NMR indicated that the structure and stability of the trp cage miniprotein was controllable based on the conformational bias of the proline derivative. Replacement of Pro12 with 4S-substituted proline derivatives that favor the Cgamma-endo ring pucker destabilized the trp cage, while replacement of Pro12 with 4R-substituted proline derivatives that favor a Cgamma-exo ring pucker resulted in increased alpha-helicity and thermal stability of the trp cage. The most stable trp cage derivatives contained benzoates of 4R-hydroxyproline, which also exhibited the most pronounced stereoelectronic effects in TYProxN model peptides. Overall, the stability of the trp cage was tunable by over 50 degrees C depending on the identity of the proline side chain at residue 12.     

制备方法对锶改性氧化铝的高温热稳定性的影响

γ-Al2O3是一种常用的催化剂载体,但对于许多高温反应体系,如汽车尾气催化净化,其热稳定性在很大程度上制约了汽车催化剂的活性和稳定性.     

Dynamics of liquid benzene: a cage analysis

Dynamics of single molecules in liquids, inspected in the picosecond time scale by means of spectroscopic measurements or molecular-dynamics (MD) simulations, reveals a complex behavior which can be addressed as due to local confinement (cage). This work is devoted to the analysis of cage structures in liquid benzene, obtained from MD simulations. According to a paradigm proposed for previous analysis of atomic and molecular liquids [see, for example, A. Polimeno, G. J. Moro, and J. H. Freed, J. Chem. Phys. 102, 8094 (1995)], the istantaneous cage structure is specified by the frame of axes which identifies the molecular configuration at the closest minimum on the potential-energy landscape. In addition, the modeling of the interaction potential between probe molecule and molecular environment, based on symmetry considerations, and its parametrization from the MD trajectories, allows the estimation of the structural parameters which quantify the strength of molecular confinement. Roto-translational dynamics of probe and related cage with respect to a laboratory frame, dynamics of the probe within the cage (vibrations, librations, re-orientational motions), and the restructuring processes of the cage itself are analyzed in terms of selected time self-correlation functions. A time-scale separation between the processes is established. Moreover, by exploiting the evidence of fast vibrational motions of the probe with respect to the cage center, an orientational effective potential is derived to describe the caging in the time scale longer than approximately 0.2 ps.     

Effects of lipid confinement on insulin stability and amyloid formation

We report on a study of insulin incorporation into cubic phases of mono-olein (MO), using synchrotron small-angle X-ray scattering and FT-IR spectroscopy. We studied the thermal stability and aggregation scenario of insulin as a function of protein concentration in the narrow water channels of the cubic lipid matrix and compared it with data for insulin unfolding and fibrillation in bulk water solutions. The concomitant effect of insulin entrapment on the structure and phase behavior of the lipid matrix itself was also examined. We show that the protein's unfolding behavior and stability are influenced by confinement due to geometrical limitations, and vice versa, the topological properties of the lipid matrix change as well. The addition of insulin already at concentrations as low as 0.1 wt % significantly alters the phase behavior of MO. Surprisingly, new cubic structures are induced by insulin incorporation into the lipid matrix. When insulin begins to partially unfold at higher temperatures, the structure of the new cubic phase changes and finally disappears around 60 degrees C, where the aggregation process sets in. The aggregation in cubo proceeds much faster and leads to the formation of medium-sized oligomers or clusters, while the formation of large fibrillar agglomerates, as observed for bulk insulin aggregation, is largely prohibited. Hence, the results yield valuable information about the use of cubic mesoporous lipid systems as a medium for long-term storage of insulin and aggregation-prone proteins in general. Furthermore, the results provide new insights into the effects of soft-matter confinement on protein aggregation and fibrillation, a situation usually met in natural cell environments.     

Electrothermal atomization of arsenic,antimony and thallium using a graphite atomizer with refractory metal platforms

The electrothermal atomization of the volatile elements arsenic, antimony and thallium from a refractory metal platform consisting of a tungsten coil and/or a refractory metal foil with the dimensions of a conventional graphite platform was studied. Several combinations of refractory metal platforms were investigated, as follows: W platform; Ta platform; W coil; W coil on a W platform and W coil on a Ta platform. The best combination for these elements as regards both thermal stabilization and sensitivity is the W coil on a Ta platform. Thermal stabilization is also achieved with a W coil on a W platform. The presence of Pd-containing chemical modifier favors the thermal stabilization of the analytes. The sufficient amount is 2 micrograms of Pd. The maximal temperatures of pyrolysis are higher (arsenic, antimony) or equal (thallium) to those when using different chemical modifiers, added as solutions. It may be concluded, that the refractory metal platforms act as "built-in modifiers". They are suitable for the determination of arsenic, antimony and thallium in samples of complex matrix composition where high thermal stability of the analytes during the pyrolysis step is required.     

Effect of the conserved oligosaccharides of recombinant monoclonal antibodies on the separation by protein A and protein G chromatography

Glycosylation of the conserved asparagine residue in CH2 domains of IgG molecules is an important post-translational modification. The presence of oligosaccharides is critical for structure, stability and biological function of IgG antibodies. Effect of the glycosylation states of recombinant monoclonal antibodies on protein A and protein G chromatography was evaluated. Antibodies lacking oligosaccharides eluted later from protein A and earlier from protein G columns than antibodies with oligosaccharides using a gradient of decreasing pH. Interestingly, different types of oligosaccharides also affected the elution of the antibodies. Antibodies with high mannose type oligosaccharides were enriched in later eluting fractions from protein A and earlier eluting fractions from protein G. While antibodies with more mature oligosaccharides, such as core fucosylated biantennary complex oligosaccharides with zero (Gal 0), one (Gal 1) or two (Gal 2) terminal galactoses, were enriched in earlier eluting fractions from protein A and in the later eluting fractions from protein G. However, analysis by enzyme-linked immunosorbent assay (ELISA) revealed that antibody binding affinity to protein A and protein G was not affected by the absence or presence of oligosaccharides. It was thus concluded that the elution difference of antibodies with or without oligosaccharides and antibodies with different types of oligosaccharides were due to differential structural changes around the CH2–CH3 domain interface under the low pH conditions used for protein A and protein G chromatography.     

Thermolysis of Neopentylcobalamin Analogs Complexed to Haptocorrin: Side Chain Entropy and Activation of Organocobalamins for Carbon-Cobalt Bond Homolysis

The kinetics of the thermal Co-C bond homolysis of the complexes of a vitamin B(12) binding protein (haptocorrin) with a series of analogs of neopentylcobalamin modified in side chain structure have been studied. The analogs include the C13 epimer in which the e propionamide side chain adopts an "upwardly" axial conformation and a series of c side chain-modified analogs, including the c-monocarboxylate, the c-N-methylamide, the c-N,N-dimethylamide, and the c-N-isopropylamide. Activation parameters for the thermal homolysis of these complexes show that the previously observed stabilization of alkylcobalamins by haptocorrin is due to both enthalpic and entropic factors. With the exception of that for the analog having the bulkiest c side chain substituent, neopentylcobalamin-c-N-isopropylamide, the enthalpies of activation are independent of analog structure, but the entropies of activation increase with the steric bulk of the c side chain and with the number of "upwardly" projecting side chains, as previously observed for protein-free neopentylcobalamin and its analogs. The results are discussed in terms of the solvent cage effect on Co-C bond homolysis and the importance of corrin ring side chain thermal motions to the entropy of activation for this reaction.     

Thermal stability limits of proteins in solution and adsorbed on a hydrophobic surface

A coarse-grained Monte Carlo simulation is used to study thermal denaturation of small proteins in an infinitely dilute solution and adsorbed on a flat hydrophobic surface. Intermolecular interactions are modeled using the Miyazawa-Jernigan (MJ) knowledge-based potential for implicit solvent with the BULDG hydrophobicity scale. We analyze the thermal behavior of lysozyme for its prevalence of α-helices, fibronectin for its prevalence of β-sheets, and a short single helical peptide. Protein dimensions and contact maps are studied in detail before and during isothermal adsorption and heating. The MJ potential is shown to correctly predict the native conformation in solution under standard conditions, and the anticipated thermal stabilization of adsorbed proteins is observed when compared with heating in solution. The helix of the peptide is found to be much less stable thermally than the helices of lysozyme, reinforcing the importance of long-range forces in defining the protein structure. Contact map analysis of the adsorbed proteins shows correlation between the hydrophobicity of the secondary structure and their thermal stability on the surface.     

质子交换膜燃料电池铂电催化剂稳定策略

质子交换膜燃料电池使用寿命低是制约其商业化应用的主要瓶颈. 其中,影响质子交换膜燃料电池寿命的一个主要因素是其所广泛使用的贵金属铂基电催化剂在燃料电池苛刻的运行环境下（如可变电压、强酸性、气液两相流等）容易发生降解,导致电催化剂性能衰减,从而降低了质子交换膜燃料电池的使用寿命. 因此,如何保持铂基电催化剂的电化学稳定性已成为质子交换膜燃料电池稳定性研究中的重大科学问题. 本论文基于作者在该领域的长期研究成果,评述了应用于质子交换膜燃料电池的铂电催化剂稳定性的研究进展. 重点关注了能够大幅改善铂催化剂电化学稳定性的策略,包括聚合物稳定策略、多孔碳封装/限域稳定策略以及载体稳定策略,并对这些铂催化剂稳定策略所面临的挑战进行了展望.     

Microcalorimetric study of thermal unfolding of lysozyme in water/glycerol mixtures: an analysis by solvent exchange model

Folded protein stabilization or destabilization induced by cosolvent in mixed aqueous solutions has been studied by differential scanning microcalorimetry and related to difference in preferential solvation of native and denatured states. In particular, the thermal denaturation of a model system formed by lysozyme dissolved in water in the presence of the stabilizing cosolvent glycerol has been considered. Transition temperatures and enthalpies, heat capacity, and standard free energy changes have been determined when applying a two-state denaturation model to microcalorimetric data. Thermodynamic parameters show an unexpected, not linear, trend as a function of solvent composition; in particular, the lysozyme thermodynamic stability shows a maximum centered at water molar fraction of about 0.6. Using a thermodynamic hydration model based on the exchange equilibrium between glycerol and water molecules from the protein solvation layer to the bulk, the contribution of protein-solvent interactions to the unfolding free energy and the changes of this contribution with solvent composition have been derived. The preferential solvation data indicate that lysozyme unfolding involves an increase in the solvation surface, with a small reduction of the protein-preferential hydration. Moreover, the derived changes in the excess solvation numbers at denaturation show that only few solvent molecules are responsible for the variation of lysozyme stability in relation to the solvent composition.     

Vibrational dynamics of a glass forming liquid in nanoscopic confinement as probed by inelastic neutron scattering

In this article we present incoherent inelastic neutron scattering results, as a function of temperature, on the vibrational dynamics of a glass-forming liquid, namely propylene glycol, confined to the 26 Å pores of a controlled porous glass. The aim is to elucidate the effects induced by surface interactions (chemical traps) and geometrical restrictions (physical traps) on the fast microscopic dynamics of hydrogen-bonded liquids. The most prominent effect is the appearance of the ‘boson peak’ in the vibrational spectra. It is ascribed to an excess density of vibrational states due to quasilocalized collective atomic vibrations induced by confinement. A destructuring effect on the transient aggregates with the highest degree of connectivity, promoted by PG in the bulk phase, is hypothesized under confinement as a consequence of interactions, via hydrogen bond, between the hydroxyl groups (OH) of the PG molecule and the active silanol groups (Si–OH) on the surface of the porous glass.

Interfacial and/or finite-size effects are also found to give rise to a destructuring effect, under confinement, of the disordered Longitudinal Acoustic Mode, together with a broadening of the highest frequency torsional vibration and a stabilization, vs. T, of the internal CCO bending vibration.     

DNA aptamer folding on gold nanoparticles: from colloid chemistry to biosensors

We have investigated the effect of the folding of DNA aptamers on the colloidal stability of gold nanoparticles (AuNPs) to which an aptamer is tethered. On the basis of the studies of two different aptamers (adenosine aptamer and K+ aptamer), we discovered a unique colloidal stabilization effect associated with aptamer folding: AuNPs to which folded aptamer structures are attached are more stable toward salt-induced aggregation than those tethered to unfolded aptamers. This colloidal stabilization effect is more significant when a DNA spacer was incorporated between AuNP and the aptamer or when lower aptamer surface graft densities were used. The conformation that aptamers adopt on the surface appears to be a key factor that determines the relative stability of different AuNPs. Dynamic light scattering experiments revealed that the sizes of AuNPs modified with folded aptamers were larger than those of AuNPs modified with unfolded (but largely collapsed) aptamers in salt solution. From both the electrostatic and steric stabilization points of view, the folded aptamers that are more extended from the surface have a higher stabilization effect on AuNP than the unfolded aptamers. On the basis of this unique phenomenon, colorimetric biosensors have been developed for the detection of adenosine, K+, adenosine deaminase, and its inhibitors. Moreover, distinct AuNP aggregation and redispersion stages can be readily operated by controlling aptamer folding and unfolding states with the addition of adenosine and adenosine deaminase.