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The Journal of Physical Chemistry. B Nov 2021The rates of protein (un)folding are often described as diffusion on the projection of a hyperdimensional energy landscape onto a few (ideally one) order parameters....
The rates of protein (un)folding are often described as diffusion on the projection of a hyperdimensional energy landscape onto a few (ideally one) order parameters. Testing such an approximation by experiment requires resolving the reactive transition paths of individual molecules, which is now becoming feasible with advanced single-molecule spectroscopic techniques. This has also sparked the interest of theorists in better understanding reactive transition paths. Here we focus on these issues aiming to establish (i) practical guidelines for the mechanistic interpretation of transition path times (TPT) and (ii) methods to extract the free energy surface and protein dynamics from the maximum likelihood analysis of photon trajectories (MLA-PT). We represent the (un)folding rates as diffusion on a 1D free energy surface with the FRET efficiency as a reaction coordinate proxy. We then perform diffusive kinetic simulations on surfaces with two minima and a barrier, but with different shapes (curvatures, barrier height, and symmetry), coupled to stochastic simulations of photon emissions that reproduce current SM-FRET experiments. From the analysis of transition paths, we find that the TPT is inversely proportional to the barrier height (difference in free energy between minimum and barrier top) for any given surface shape, and that dividing the TPT into climb and descent segments provides key information about the barrier's symmetry. We also find that the original MLA-PT procedure used to determine the TPT from experiments underestimates its value, particularly for the cases with smaller barriers (e.g., fast folders), and we suggest a simple strategy to correct for this bias. Importantly, we also demonstrate that photon trajectories contain enough information to extract the 1D free energy surface's shape and dynamics (if TPT is >4-5-fold longer than the interphoton time) using the MLA-PT directly implemented with a diffusive free energy surface model. When dealing with real (unknown) experimental data, the comparison between the likelihoods of the free energy surface and discrete kinetic three-state models can be used to evaluate the statistical significance of the estimated free energy surface.
Topics: Diffusion; Entropy; Kinetics; Photons; Protein Folding; Proteins; Thermodynamics
PubMed: 34735144
DOI: 10.1021/acs.jpcb.1c05401 -
American Journal of Public Health May 1993The purpose of this study was to estimate surface-specific rates of fall injuries on school playgrounds. Playground injuries related to falls from climbing equipment and...
The purpose of this study was to estimate surface-specific rates of fall injuries on school playgrounds. Playground injuries related to falls from climbing equipment and the surfaces involved were identified from injury reports for 1988 to 1990 from 157 Utah elementary schools. Enrollment data and playground inspections were used to estimate student-years spent over each surface. The fall injury rates per 10,000 student-years were asphalt, 44; grass, 12; mats, 16; gravel, 15; and sand, 7. These data did not show that impact-absorbing surfaces reduce fall injuries on playgrounds better than grass. Improved field studies are needed to guide policy decisions for playground surfacing.
Topics: Accidental Falls; Child; Child, Preschool; Female; Humans; Male; Play and Playthings; Schools; Utah; Wounds and Injuries
PubMed: 8484459
DOI: 10.2105/ajph.83.5.733 -
Colloids and Surfaces. B, Biointerfaces Nov 2014The present work aimed at studying the interaction between insulin and SiNP surfaced with mucoadhesive polymers (chitosan, sodium alginate or polyethylene glycol) and...
The present work aimed at studying the interaction between insulin and SiNP surfaced with mucoadhesive polymers (chitosan, sodium alginate or polyethylene glycol) and the evaluation of their biocompatibility with HepG2 and Caco-2 cell lines, which mimic in vivo the target of insulin-loaded nanoparticles upon oral administration. Thus, a systematic physicochemical study of the surface-modified insulin-silica nanoparticles (Ins-SiNP) using mucoadhesive polymers has been described. The surfacing of nanoparticle involved the coating of silica nanoparticles (SiNP) with different mucoadhesive polymers, to achieve high contact between the systems and the gut mucosa to enhance the oral insulin bioavailability. SiNP were prepared by a modified Stöber method at room temperature via hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Interaction between insulin and nanoparticles was assessed by differential scanning calorimetry (DSC), X-ray and Fourier-transform infrared (FTIR) studies. The high efficiency of nanoparticles' coating resulted in more stable system. FTIR spectra of insulin-loaded nanoparticles showed amide absorption bands which are characteristic of α-helix content. In general, all developed nanoparticles demonstrated high biocompatible, at the tested concentrations (50-500 μg/mL), revealing no or low toxicity in the two human cancer cell lines (HepG2 and Caco-2). In conclusion, the developed insulin-loaded SiNP surfaced with mucoadhesive polymers demonstrated its added value for oral administration of proteins.
Topics: Administration, Oral; Alginates; Caco-2 Cells; Cell Survival; Chitosan; Drug Carriers; Glucuronic Acid; Hep G2 Cells; Hexuronic Acids; Humans; Insulin; Nanoparticles; Polyethylene Glycols; Polymers; Silicon Dioxide
PubMed: 25466464
DOI: 10.1016/j.colsurfb.2014.10.047 -
Journal of Materials Chemistry. A Aug 2017Superhydrophobic surface simultaneously possessing exceptional stretchability, robustness, and non-fluorination is highly desirable in applications ranging from wearable...
Superhydrophobic surface simultaneously possessing exceptional stretchability, robustness, and non-fluorination is highly desirable in applications ranging from wearable devices to artificial skins. While conventional superhydrophobic surfaces typically feature stretchability, robustness, or non-fluorination individually, co-existence of all these features still remains a great challenge. Here we report a multi-performance superhydrophobic surface achieved through incorporating hydrophilic micro-sized particles with pre-stretched silicone elastomer. The commercial silicone elastomer (Ecoflex) endowed the resulting surface with high stretchability; the densely packed micro-sized particles in multi-layers contributed to the preservation of the large surface roughness even under large strains; and the physical encapsulation of the microparticles by silicone elastomer due to the capillary dragging effect and the chemical interaction between the hydrophilic silica and the elastomer gave rise to the robust and non-fluorinated superhydrophobicity. It was demonstrated that the as-prepared fluorine-free surface could preserve the superhydrophobicity under repeated stretching-relaxing cycles. Most importantly, the surface's superhydrophobicity can be well maintained after severe rubbing process, indicating wear-resistance. Our novel superhydrophobic surface integrating multiple key properties, i.e. stretchability, robustness, and non-fluorination, is expected to provide unique advantages for a wide range of applications in biomedicine, energy, and electronics.
PubMed: 29062483
DOI: 10.1039/C6TA11133E -
Journal of the American Chemical Society Jul 2016Electronic traps at the inorganic-organic interface of colloidal quantum dots (QDs) are detrimental to their luminescent properties. Several types of interface traps...
Electronic traps at the inorganic-organic interface of colloidal quantum dots (QDs) are detrimental to their luminescent properties. Several types of interface traps were identified for single-crystalline CdSe/CdS core/shell QDs, which were all found to be extrinsic to either the core/shell structure or their optical performance. The electron traps-presumably excess or unpassivated Cd surface sites-are shallow ones and could be readily isolated from the electron wave function of the excitons with more than ∼2 monolayers of CdS shell. There were two identifiable deep hole traps within the bandgap of the QDs, i.e., the surface adsorbed H2S and unpassivated surface S sites. The surface adsorbed H2S could be removed by either degassing processes or photochemical decomposition of H2S without damaging the QDs. The unpassivated surface S sites could be removed by surface treatment with cadmium carboxylates. Understanding of the surface traps enabled establishment of new phosphine-free synthetic schemes for either single-precursor or successive-ion-layer-adsorption-and-reaction approach, which yielded CdSe/CdS core/shell QDs with near-unity photoluminescence quantum yield and monoexponential photoluminescence decay dynamics with 2-10 monolayers of CdS shell.
PubMed: 27312799
DOI: 10.1021/jacs.6b02909 -
Materials (Basel, Switzerland) Feb 2019In this study, two kinds of copper micro-patterned surfaces with different heights were fabricated by using a powder injection molding (PIM) process. The micro-pattern's...
In this study, two kinds of copper micro-patterned surfaces with different heights were fabricated by using a powder injection molding (PIM) process. The micro-pattern's size was 100 μm, and the gap size was 50 μm. The short micro-pattern's height was 100 μm, and the height of the tall one was 380 μm. A copper powder and wax-polymer-based binder system was used to fabricate the micro-patterned surfaces. The critical heat flux (CHF) and heat transfer coefficient (HTC) during pool-boiling tests were measured with the micro-patterned surfaces and a reference plain copper surface. The CHF of short and tall micro-patterned surfaces were 1434 and 1444 kW/m², respectively, and the plain copper surface's CHF was 1191 kW/m². The HTC of the plain copper surface and the PIM surface with short and tall micro-patterned surfaces were similar in value up to a heat flux 1000 kW/m². Beyond that value, the plain surface quickly reached its CHF, while the HTC of the short micro-patterned surface achieved higher values than that of the tall micro-patterned surface. At CHF, the maximum values of HTC for the short micro-pattern, tall micro-pattern, and the plain copper surface were 68, 58, and 57 kW/m² K.
PubMed: 30736470
DOI: 10.3390/ma12030507 -
The Journal of Chemical Physics Aug 2014Despite its importance in atmospheric science, much remains unknown about the microscopic mechanism of heterogeneous ice nucleation. In this work, we perform hybrid...
Despite its importance in atmospheric science, much remains unknown about the microscopic mechanism of heterogeneous ice nucleation. In this work, we perform hybrid Monte Carlo simulations of the heterogeneous nucleation of ice on a range of generic surfaces, both flat and structured, in order to probe the underlying factors affecting the nucleation process. The structured surfaces we study comprise one basal plane bilayer of ice with varying lattice parameters and interaction strengths. We show that what determines the propensity for nucleation is not just the surface attraction, but also the orientational ordering imposed on liquid water near a surface. In particular, varying the ratio of the surface's attraction and orientational ordering can change the mechanism by which nucleation occurs: ice can nucleate on the structured surface even when the orientational ordering imposed by the surface is weak, as the water molecules that interact strongly with the surface are themselves a good template for further growth. We also show that lattice matching is important for heterogeneous nucleation on the structured surface we study. We rationalise these brute-force simulation results by explicitly calculating the interfacial free energies of ice and liquid water in contact with the nucleating surface and their variation with surface interaction parameters.
PubMed: 25173015
DOI: 10.1063/1.4892804 -
International Journal of Molecular... Aug 2021Polyetheretherketone (PEEK), due to its excellent mechanical and physico-chemical parameters, is an attractive substitute for hard tissues in orthopedic applications....
Polyetheretherketone (PEEK), due to its excellent mechanical and physico-chemical parameters, is an attractive substitute for hard tissues in orthopedic applications. However, PEEK is hydrophobic and lacks surface-active functional groups promoting cell adhesion. Therefore, the PEEK surface must be modified in order to improve its cytocompatibility. In this work, extreme ultraviolet (EUV) radiation and two low-temperature, EUV induced, oxygen and nitrogen plasmas were used for surface modification of polyetheretherketone. Polymer samples were irradiated with 100, 150, and 200 pulses at a 10 Hz repetition rate. The physical and chemical properties of EUV and plasma modified PEEK surfaces, such as changes of the surface topography, chemical composition, and wettability, were examined using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and goniometry. The human osteoblast-like MG63 cells were used for the analysis of cell viability and cell adhesion on all modified PEEK surfaces. EUV radiation and two types of plasma treatment led to significant changes in surface topography of PEEK, increasing surface roughness and formation of conical structures. Additionally, significant changes in the chemical composition were found and were manifested with the appearance of new functional groups, incorporation of nitrogen atoms up to ~12.3 at.% (when modified in the presence of nitrogen), and doubling the oxygen content up to ~25.7 at.% (when modified in the presence of oxygen), compared to non-modified PEEK. All chemically and physically changed surfaces demonstrated cyto-compatible and non-cytotoxic properties, an enhancement of MG63 cell adhesion was also observed.
Topics: Benzophenones; Biocompatible Materials; Cell Adhesion; Cell Line; Humans; Nitrogen; Osteoblasts; Oxygen; Plasma Gases; Polymers; Surface Properties; Ultraviolet Rays
PubMed: 34445159
DOI: 10.3390/ijms22168455 -
Biophysical Chemistry Sep 1997Electric light scattering measurements of thylakoid membranes from wild type and two mutant forms (JB67 and LK3) of Arabidopsis thaliana have shown that application of...
Electric light scattering measurements of thylakoid membranes from wild type and two mutant forms (JB67 and LK3) of Arabidopsis thaliana have shown that application of external electric pulses induces electric dipole moments of different origin. The asymmetric surface charge distribution and electric polarizability are significantly altered by the lipid modification. Mild trypsin treatment of Arabidopsis thylakoids leading to digestion of small polypeptides from the light-harvesting chlorophyll a/b protein complex of photosystem II (LHCP II) gives evidence for a lower content of LHCP II in the mutant forms. The results demonstrate the significance of the level of thylakoid lipid unsaturation in determining the surface charge distribution through changes either in the pigment-protein content and membrane appression induced by the lipid modification or in the exposure of charged polypeptides on the thylakoid membrane surface(s) arising from alteration of the lipid geometry.
Topics: Arabidopsis; Cell Membrane; Electrophysiology; Light; Membrane Lipids; Mutation; Scattering, Radiation; Surface Properties; Trypsin
PubMed: 9397528
DOI: 10.1016/s0301-4622(97)00042-2 -
The Anatomical Record Jun 1978The present paper deals with a scanning electron microscopic investigation which was undertaken in order to make a direct study of geometrical conformations of...
The present paper deals with a scanning electron microscopic investigation which was undertaken in order to make a direct study of geometrical conformations of thymocytes, to determine the effect of external mechanical forces and finally to analyse the relation of the cell surface morphology to the differentiation and release of thymocytes into circulation. Thymocytes in situ revealed a striking polyhedral configuration with distinct edges and angles that permit a close orientation of cells in a minimum space. This conformation is probably acquired under the influence of forces in the microenvironment of the cells. The immature thymocytes in the cortex were smooth surfaced and constituted a homogenous population with regards to surface morphology except for slight variations in the size and angles of varoius facets of the polyhedra. A minority of the cell population occupying the medulla, however, exhibited a departure in possessing surface undulations and stubby protuberances. Thymocytes isolated in suspension and those in postcapillary venules of thymus did not show the polyhedral shape characteristic of the cells in thymic tissue. They were always rounded, with their surfaces often exhibiting undulations or microvilli. The variations observed in situ are discussed in light of external mechanical forces, cell surface characteristics and the inherent properties of differentiating thymocytes.
Topics: Animals; Capillaries; Cortisone; Mice; Microscopy, Electron, Scanning; Rats; T-Lymphocytes; Thymus Gland
PubMed: 307348
DOI: 10.1002/ar.1091910206