Moduliranje i stabilizacija emulzija ulja u vodi pomoću fibroina svile

The purpose of this study is to prepare and characterize stable oil-in-water emulsions containing droplets coated with silk fibroin. Silk fibroin, a native edible fibrous protein originating from silkworm cocoons, was used to prepare 10 % (by mass) corn oil-in-water emulsions at ambient temperature (pH=7.0, 10 mM phosphate buffer). Emulsions with relatively small mean particle diameter (d32=0.47 μm) and extremely good creaming stability (>7 days) could be produced at silk fibroin concentration of 1 % (by mass). The influence of pH (2–8), thermal processing (60–90 °C, 20 min), and concentration of salt (c(NaCl)=0–250 mM) on the properties and stability of the emulsions was analyzed using ζ-potential, particle size, and creaming stability measurements. The isoelectric point of droplets stabilized with silk fibroin was pH~4. The emulsions were stable to droplet flocculation and creaming at any pH except intermediate value (pH=4.0) when stored at room temperature, which was attributed to their relatively low ζ-potential. Their ζ-potential went from around 25 to –35 mV as the pH was increased from 2 to 8. The emulsions were also stable to thermal treatment (60 and 90 °C for 20 min, pH=3 and 7), with a slight decrease in the magnitude of ζ-potential at temperatures exceeding 60 °C. The emulsions were unstable to aggregation and creaming even at relatively low salt concentrations (c(NaCl)=0–250 mM, pH=3 and 7) as a result of electrostatic screening effects. These results suggest that bulk oil stabilized with silk fibroin has improved physical stability and may provide a new way of creating functional oil products and delivery systems.Svrha je ovoga rada bila pripremiti i okarakterizirati stabilnu emulziju ulja u vodi, koja sadrži kapljice obložene fibroinom svile. Fibroin svile, prirodni jestivi vlaknasti protein dobiven iz čahura dudova svilca, upotrijebljen je za pripremu emulzije kukuruznog ulja u vodi (masenog udjela od 10 %) na sobnoj temperaturi (pH=7, 10 mM fosfatni pufer). Primjenom fibroina svile masene koncentracije od 1 % dobivene su emulzije relativno malog promjera čestica (d32=0,47 μm) i vrlo dobre stabilnosti (dulje od 7 dana). Ispitan je utjecaj pH-vrijednosti (pH=2–8), toplinske obrade (60–90 °C, 20 min) i koncentracije soli (c(NaCl)=0–250 mM) na svojstva i stabilnost emulzije (ζ-potencijal, veličina čestica i raslojavanje emulzije). Izoelektrična točka kapljica stabiliziranih pomoću fibroina svile postignuta je pri pH~4. Emulzije skladištene na sobnoj temperaturi bile su stabilne pri svim pH-vrijednostima, osim pri srednjoj (pH=4,0) kada su imale relativno nizak ζ-potencijal. Povećanjem pH-vrijednosti s 2 na 8 povećao se ζ-potencijal emulzija (s 25 na -35 mV). Uočena je stabilnost emulzija i nakon toplinske obrade (tijekom 20 minuta na 60 i 90 °C, pri pH=3 i 7), a pri temperaturama višim od 60 °C ζ-potencijal se neznatno smanjio. Zbog učinka elektrostatskog odbijanja emulzije su bile nestabilne čak i pri neznatnim koncentracijama soli (c(NaCl)=0-250 mM, pH=3 i 7). Rezultati upućuju na to da stabilizacija emulzija pomoću fibroina svile omogućuje proizvodnju funkcionalnih proizvoda na bazi ulja

Temperature dependence of circular DNA topological states

Circular double stranded DNA has different topological states which are defined by their linking numbers. Equilibrium distribution of linking numbers can be obtained by closing a linear DNA into a circle by ligase. Using Monte Carlo simulation, we predict the temperature dependence of the linking number distribution of small circular DNAs. Our predictions are based on flexible defect excitations resulted from local melting or unstacking of DNA base pairs. We found that the reduced bending rigidity alone can lead to measurable changes of the variance of linking number distribution of short circular DNAs. If the defect is accompanied by local unwinding, the effect becomes much more prominent. The predictions can be easily investigated in experiments, providing a new method to study the micromechanics of sharply bent DNAs and the thermal stability of specific DNA sequences. Furthermore, the predictions are directly applicable to the studies of binding of DNA distorting proteins that can locally reduce DNA rigidity, form DNA kinks, or introduce local unwinding.Comment: 15 pages in preprint format, 4 figure

Can Electric Field Induced Energy Gaps In Metallic Carbon Nanotubes?

The low-energy electronic structure of metallic single-walled carbon nanotube (SWNT) in an external electric field perpendicular to the tube axis is investigated. Based on tight-binding approximation, a field-induced energy gap is found in all (n, n) SWNTs, and the gap shows strong dependence on the electric field and the size of the tubes. We numerically find a universal scaling that the gap is a function of the electric field and the radius of SWNTs, and the results are testified by the second-order perturbation theory in weak field limit. Our calculation shows the field required to induce a 0.1 ${\rm eV}$ gap in metallic SWNTs can be easily reached under the current experimental conditions. It indicates a kind of possibility to apply nanotubes to electric signal-controlled nanoscale switching devices

Dynamic disorder in receptor-ligand forced dissociation experiments

Recently experiments showed that some biological noncovalent bonds increase their lifetimes when they are stretched by an external force, and their lifetimes will decrease when the force increases further. Several specific quantitative models have been proposed to explain the intriguing transitions from the "catch-bond" to the "slip-bond". Different from the previous efforts, in this work we propose that the dynamic disorder of the force-dependent dissociation rate can account for the counterintuitive behaviors of the bonds. A Gaussian stochastic rate model is used to quantitatively describe the transitions observed recently in the single bond P-selctin glycoprotein ligand 1(PSGL-1)$-$P-selectin force rupture experiment [Marshall, {\it et al.}, (2003) Nature {\bf 423}, 190-193]. Our model agrees well to the experimental data. We conclude that the catch bonds could arise from the stronger positive correlation between the height of the intrinsic energy barrier and the distance from the bound state to the barrier; classical pathway scenario or {\it a priori} catch bond assumption is not essential.Comment: 4 pages, 2 figure

Magnetoelectrically driven catalytic degradation of organics

Here, we report the catalytic degradation of organic compounds by exploiting the magnetoelectric (ME) nature of cobalt ferrite-bismuth ferrite (CFO-BFO) core-shell nanoparticles. The combination of magnetostrictive CFO with the multiferroic BFO gives rise to a magnetoelectric engine that purifies water under wireless magnetic fields via advanced oxidation processes, without involvement of any sacrificial molecules or co-catalysts. Magnetostrictive CoFe2O4 nanoparticles are fabricated using hydrothermal synthesis, followed by sol-gel synthesis to create the multiferroic BiFeO3 shell. We perform theoretical modeling to study the magnetic field induced polarization on the surface of magnetoelectric nanoparticles. The results obtained from these simulations are consistent with the experimental findings of the piezo-force microscopy analysis, where we observe changes in the piezoresponse of the nanoparticles under magnetic fields. Next, we investigate the magnetoelectric effect induced catalytic degradation of organic pollutants under AC magnetic fields and obtained 97% removal efficiency for synthetic dyes and over 85% removal efficiency for routinely used pharmaceuticals. Additionally, we perform trapping experiments to elucidate the mechanism behind the magnetic field induced catalytic degradation of organic pollutants by using scavengers for each of the reactive species. Our results indicate that hydroxyl and superoxide radicals are the main reactive species in the magnetoelectrically induced catalytic degradation of organic compounds

The structure relaxation of carbon nanotube

A simple macroscopic continuum elasticity theory (CET) is used to calculate the structure relaxation of single-wall carbon nanotube (SWNT), an analytic formula is obtained. We also expand an atomic scale three-parameter empirical model [ T. Lenosky {\emph et al.} Nature 355, 333(1992)] in order to correctly describe the bond-length change effects. The structure relaxation of SWNT expected by the model is good in agreement with our CET results, and very well consistent with the previous calculation from a first principles local density function approximation. Using the expanded Lenosky model, we calculate the strain energy of bending tube. The obtained results are good in agreement with the previous theoretical expectation. It shows the model may be a good simple replacement of some more sophisticated methods on determining carbon networks deformations.Comment: 9 pages, 4 eps figure

Intraoperative device closure of atrial septal defects with inferior vena cava rim deficiency: A safe alternative to surgical repair

ObjectiveOur objective was to evaluate the safety and feasibility of intraoperative device closure of atrial septal defects with inferior vena cava rim deficiency.MethodsFrom January 2005 to December 2008, we enrolled 65 patients who had a secundum atrial septal defect with inferior vena cava rim deficiency closure in our institution. Patients were divided into 2 groups: 35 patients in group I underwent intraoperative device closure with a right lateral minithoracotomy and 30 in group II underwent open cardiac repair with a right lateral thoracotomy and cardiopulmonary bypass. Intraoperative device closure involved a minimal intercostal incision that was performed after full evaluation of the atrial septal defect by transthoracic echocardiography and the insertion of the device through the delivery sheath to occlude the atrial septal defect.ResultsThe procedure was successful in all patients. In group I, the diameter of the atrial septal defect ranged from 30 to 44 mm (mean, 35.3 ± 3.9 mm), and the size of the implanted occluder ranged from 34 to 48 mm (mean, 40 ± 2.1 mm). The total occlusion rate was 82.9% immediately after the operation, 97.1% at 3 months, and 100% at 12 and 24 months of follow-up. In group II, all patients had successful closure. A follow-up period of 12 to 24 months was obtained in both groups. During the follow-up, there was no recurrence, thrombosis, or device failure. In our comparative studies, group II had significantly longer operative time, intensive care unit stay, and hospital stay than group I (P < .001). The cost of group I was less than that of group II (20,450.9 ± 840.8 RMB vs 25,884.9 ± 701.8; P < .001).ConclusionsIntraoperative device closure of atrial septal defects with inferior vena cava rim deficiency is a safe and feasible technique. It has the advantages of cost savings, cosmetic results, and less trauma than surgical closure. Early and midterm results are encouraging

Nematic Films and Radially Anisotropic Delaunay Surfaces

We develop a theory of axisymmetric surfaces minimizing a combination of surface tension and nematic elastic energies which may be suitable for describing simple film and bubble shapes. As a function of the elastic constant and the applied tension on the bubbles, we find the analogues of the unduloid, sphere, and nodoid in addition to other new surfaces.Comment: 15 pages, 18 figure