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A New Mechanism of Stabilization of Large Decahedral Nanoparticles.

ABSTRACT: The stability of decahedral shaped nanoparticles depends upon size. Ino and Marks introduced new mechanisms for the stabilization of decahedra nanoparticles which involves the faceting and the formation of surfaces different of {111}. These mechanisms have relevance for small size nanoparticles; however, they do not explain, thoroughly, how decahedral particles can grow up to 300 nm or more. Here, we report new mechanisms that help stabilize very large decahedral. With the use of aberration corrected scanning transmission electron microscopy, we observed the formation of high index facets, determined to be of the {511} family, on all five sides of the particles. Surface dislocations strings are also observed. In addition, surface reconstruction of the {001} surfaces can also be observed in two different orientation: with hexagonal strings along the [110] and along the [410] directions.

SUBMITTER: Casillas G

PROVIDER: S-EPMC3353654 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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A New Mechanism of Stabilization of Large Decahedral Nanoparticles.

Casillas Gilberto G Velázquez-Salazar J Jesús JJ Jose-Yacaman Miguel M

The journal of physical chemistry. C, Nanomaterials and interfaces 20120331 15

The stability of decahedral shaped nanoparticles depends upon size. Ino and Marks introduced new mechanisms for the stabilization of decahedra nanoparticles which involves the faceting and the formation of surfaces different of {111}. These mechanisms have relevance for small size nanoparticles; however, they do not explain, thoroughly, how decahedral particles can grow up to 300 nm or more. Here, we report new mechanisms that help stabilize very large decahedral. With the use of aberration corr ...[more]

PMID: 22609961

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Project description:BackgroundThe FAbry STabilization indEX (FASTEX) is an innovative index allowing the assessment of clinical stability over time in Fabry disease patients. This index was developed in a population of 28 male patients with the classical form of Fabry disease.ObjectivesThe aim of the study was to test the accuracy of the FASTEX in evaluating Fabry disease stability in 132 male and female patients with classical and non-classical Fabry disease from nine Italian centres and it also aimed to define the sensitivity and specificity of this new tool. In particular, we aimed to investigate the correlation between the FASTEX and clinical judgement in a large-scale cohort of the study population.MethodsStatistical methods applied to this investigation included the calculation of accuracy, specificity and sensitivity, receiver operating characteristic (ROC) curves and Cohen's κ index related to the FASTEX and clinical judgement.ResultsThe patient population included 58 males (43.9%). The mean age of the overall population was 46.3 ± 15. 1 years (range 31.2-61.4). The median interval between the two multidisciplinary evaluations used for FASTEX calculation was 398 days. Since no gold standard method is available to define the overall clinical condition of Fabry patients over time, the results of the FASTEX were compared with clinical judgements given by the physicians involved in this study. In this way, the FASTEX classified 121 of 132 (92%) patients correctly. In particular, the FASTEX correctly identified 93% (41/44) of clinically 'unstable' and 91% (80/88) of clinically 'stable' patients. The area under the curve of the ROC related to the FASTEX index cut-off (20) was equal to 0.967, very close to its theoretical maximum (1), which means that it is an excellent test for classifying patients as 'stable' or 'unstable' compared with clinical judgement. In addition, the FASTEX cut-off >20 provides the most acceptable balance between sensitivity and specificity. The Cohen's κ index value obtained in our study was 0.82, showing a highly statistically significant P-value < 0.01 related to the agreement between the FASTEX and clinical judgement.ConclusionsThe FASTEX is demonstrated here to be a specific and sensitive tool. When applied to a large cohort of Fabry patients, it was shown to be a valid instrument in helping physicians to discriminate objectively the clinical stability of individual Fabry patients.

Project description:The impact of disulfide bonds on protein stability goes beyond simple equilibrium thermodynamics effects associated with the conformational entropy of the unfolded state. Indeed, disulfide crosslinks may play a role in the prevention of dysfunctional association and strongly affect the rates of irreversible enzyme inactivation, highly relevant in biotechnological applications. While these kinetic-stability effects remain poorly understood, by analogy with proposed mechanisms for processes of protein aggregation and fibrillogenesis, we propose that they may be determined by the properties of sparsely-populated, partially-unfolded intermediates. Here we report the successful design, on the basis of high temperature molecular-dynamics simulations, of six thermodynamically and kinetically stabilized variants of phytase from Citrobacter braakii (a biotechnologically important enzyme) with one, two or three engineered disulfides. Activity measurements and 3D crystal structure determination demonstrate that the engineered crosslinks do not cause dramatic alterations in the native structure. The inactivation kinetics for all the variants displays a strongly non-Arrhenius temperature dependence, with the time-scale for the irreversible denaturation process reaching a minimum at a given temperature within the range of the denaturation transition. We show this striking feature to be a signature of a key role played by a partially unfolded, intermediate state/ensemble. Energetic and mutational analyses confirm that the intermediate is highly unfolded (akin to a proposed critical intermediate in the misfolding of the prion protein), a result that explains the observed kinetic stabilization. Our results provide a rationale for the kinetic-stability consequences of disulfide-crosslink engineering and an experimental methodology to arrive at energetic/structural descriptions of the sparsely populated and elusive intermediates that play key roles in irreversible protein denaturation.

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A New Mechanism of Stabilization of Large Decahedral Nanoparticles.

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A New Mechanism of Stabilization of Large Decahedral Nanoparticles.

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