Local environments of coumarin dyes within mesostructured silica-surfactant nanocomposites

The local environments surrounding dye molecules were studied with use of coumarin dyes in a mesostructured silica-surfactant nanocomposite, which was formed in a porous alumina membrane by a surfactant-templated method and has an average pore diameter of 3.4 nm. Coumarin dyes, such as coumarin 480 (C480), coumarin 343 (C343), and propylamide coumarin 343 (PAC343), were extracted into the silica-surfactant nanocomposite and time-resolved fluorescence spectra of these dyes were examined. C480 and C343 show slow dynamic Stokes shifts and the decay curve can be fitted by a biexponential function. The decay-time constants obtained from the fitting are almost identical for C480 and C343: 0.87 and 7.5 ns for C480, and 0.86 and 7.6 ns for C343. In contrast to these two coumarin dyes, short decay-time constants (0.50 and 4.8 ns) were obtained for PAC343 in the silica-surfactant nanocomposite. These results indicate that the local environments of C480 and C343 are almost identical but different from that of PAC343. By considering the origin of the dynamic Stokes shift and the mesostructure of the silica-surfactant nanocomposite, the location and microenvironment of coumarin dyes within the silica-surfactant nanocomposite are discussed.     

A microfluidic device for parallel 3-D cell cultures in asymmetric environments

We demonstrate a concept for how a miniaturized 3-D cell culture in biological extracellular matrix (ECM) or synthetic gels bridges the gap between organ-tissue culture and traditional 2-D cultures. A microfluidic device for 3-D cell culture including microgradient environments has been designed, fabricated, and successfully evaluated. In the presented system stable diffusion gradients can be generated by application of two parallel fluid flows with different composition against opposite sides of a gel plug with embedded cells. Culture for up to two weeks was performed showing cells still viable and proliferating. The cell tracer dye calcein was used to verify gradient formation as the fluorescence intensity in exposed cells was proportional to the position in the chamber. Cellular response to an applied stimulus was demonstrated by use of an adenosine triphosphate gradient where the onset of a stimulated intracellular calcium release also depended on cell position.     

Charge displacement by adhesion and spreading of a cell

The potentiostatic control of surface charge density and interfacial tension of an electrode immersed in an aqueous electrolyte solution offers a possibility for direct studies of non-specific interactions in cell adhesion. Unicellular marine alga, Dunaliella tertiolecta (Chlorophyceae) of micrometer size and flexible cell envelope was used as a model cell and 0.1 M NaCl as supporting electrolyte. The dropping mercury electrode acted as in situ adhesion sensor and the electrochemical technique of chronoamperometry allowed measurement of the spread cell-electrode interface area and the distance of the closest approach of a cell. The adhesion and spreading of a single cell at the mercury electrode causes a displacement of counter-ions from the electrical double layer over a broad range of the positive and negative surface charge densities (from +16.0 to -8.2 microC/cm2). The flow of compensating current reflects the dynamics of adhesive contact formation and subsequent spreading of a cell. The adhesion and spreading rates are enhanced by the hydrodynamic regime of electrode's growing fluid interface. The distance of the closest approach of an adherent cell is smaller or equal to the distance of the outer Helmholz plane within the electrical double layer, i.e. 0.3-0.5 nm. There is a clear evidence of cell rupture for the potentials of maximum attraction as the area of the contact interface exceeded up to 100 times the cross-section area of a free cell.     

Semiempirical Pm3 Quantum Mechanics Calculations of Carbohydrate Crystals

ABSTRACT

Miniature crystal models of six small carbohydrates were examined using the PM3 semiempirical quantum mechanics method. The minicrystal structures, consisting of 27 sugar residues, were optimized by the combined procedure of partial optimization and reconstruction of the model, while maintaining the original crystal symmetries. All of the minicrystals were successfully optimized without exhibiting a great increase in an energy at any reconstruction step. Some minicrystals showed a prolonged behavior of optimization cycles. A major source of structure change appeared to arise from hydroxyl group rotations wherein the largest movements mostly occurred in an early optimization stage. No significant deformations in geometry of either residues or hydrogen bonds were observed in the final minicrystal structures. The thermodynamic values calculated for the optimized minicrystals were in reasonably good agreement with the literature data. The present study indicated that the PM3 semiempirical method successfully predicted the basic features of intermolecular hydrogen bonding involved in a condensed system.     

Monomer migration and degradation of polycarbonate via UV-C irradiation within aquatic and atmospheric environments

Polycarbonates (PC) are widely used in daily life as commodity plastics and it is a critical material regarding to the public health for the consequences that may arise especially for infants due to usage in baby bottles. Therefore, understanding the behavior of PC within the degradative environment is vital. In this study, degradation of polycarbonate via UV-C irradiation was studied within atmospheric and aquatic environments. Mechanical, morphological, thermal tests NMR, TGA, SEM, DSC, Extensometer, Yellowness Index, FTIR and HPLC tests of samples irradiated with different irradiation periods within these two environments were carried out. The analysis results have shown that for both of aquatic and atmospheric environments, the degradation and morphological changes were occurred. Structure tests results show that the main degradation occurred on the carbonate group of PC. In addition, significant amount of Bisphenol A was detected via HPLC analysis in the aquatic solution after irradiation in aquatic environment that could be hazardous for the public health.     

Spectroscopic analyses of chemical adaptation processes within microalgal biomass in response to changing environments

Via photosynthesis, marine phytoplankton transforms large quantities of inorganic compounds into biomass. This has considerable environmental impacts as microalgae contribute for instance to counter-balancing anthropogenic releases of the greenhouse gas CO₂. On the other hand, high concentrations of nitrogen compounds in an ecosystem can lead to harmful algae blooms. In previous investigations it was found that the chemical composition of microalgal biomass is strongly dependent on the nutrient availability. Therefore, it is expected that algae’s sequestration capabilities and productivity are also determined by the cells’ chemical environments. For investigating this hypothesis, novel analytical methodologies are required which are capable of monitoring live cells exposed to chemically shifting environments followed by chemometric modeling of their chemical adaptation dynamics.     

Fast determination of nicotine and 3-ethenylpyridine in indoor environments

Summary Different sampling and analysis techniques for the determination of gas-phase nicotine and 3-ethenylpyridine in environmental tobacco smoke are reported. Graphitized carbon traps, annular diffusion denuders, and nebulizer collectors have been used as sampling devices in combination with either thermal desorption or with water extraction. Capillary gas chromatography and ion-pair reversed-phase chromatography were applied to desorbed and liquid samples obtained in an intercomparison indoor study. The methods developed here show some advantages over existing methods in terms of analysis time, sensitivity and loading capacity.     

Expression of membrane-associated proteins within single emulsion cell facsimiles

MreB is a structural membrane-associated protein which is one of the key components of the bacterial cytoskeleton. Although it plays an important role in shape maintenance of rod-like bacteria, the understanding of its mechanism of action is still not fully understood. This study shows how segmented flow and microdroplet technology can be used as a new tool for biological in vitro investigation of this protein. In this paper, we demonstrate cell-free expression in a single emulsion system to express red fluorescence protein (RFP) and MreB linked RFP (MreB-RFP). We follow the aggregation and localisation of the fusion protein MreB-RFP in this artificial cell-like environment. The expression of MreB-RFP in single emulsion droplets leads to the formation of micrometer-scale protein patches distributed at the water/oil interface.     

Microsolvation of HCl within cold NH3 clusters

The solid state solvation of HCl molecules with small ammonia clusters at an average temperature of 100 K was investigated by on-the-fly molecular dynamics methodology. Structures close to the proton jump from HCl molecule to the ammonia have been further checked with the MP2/aug-cc-pvDZ calculations. Ionization of HCl and/or sharing of the proton were found. Two Zundel-type ions were observedone with proton being shared between ammonium ion and Cl (-) anion (Cl (-)...H (+)...NH 3) in all complexes, and the second, between hydrogen chloride and Cl (-) anion in the HCl...Cl (-)...NH 4 (+)...(NH 3) 2 complex. However, in contrast to methanol clusters, ammonia clusters are not good for the proton wires since once the proton moves to ammonia, it is localized on the ammonium ion units.     

First-principle study of hydrogen stability within TiCo3

Structural and electronic changes due to hydrogen uptake within TiCo₃ are examined ab initio within DFT using both pseudo-potential and all electron calculations. For the monohydride two starting hypotheses for H position, at cube center and cube-edge middle, were considered and analyzed: the system stabilizes with a cubic structure which undergoes a tetragonal distortion when H is at edge middle. Detailed analyses of the site projected density of states and of the electron count conclude to meaningful changes of the electronic structure when H is inserted, especially for the weakening of the chemical bonding in the tetragonally distorted lattice. The results could explain the brittleness characterizing the hydrided 1:3 alloy systems.     

Intramolecular Inclusion of L-tryptophan within 3-functionalized Cyclodextrins

Abstract

The synthesis of L-tryptophan attached to the C3 group of a β-cyclodextrin through amide linkages with ethylenediamine or propylenediamine is reported. Circular dichroism and fluorescence investigations were carried out showing great differences between the two derivatives. The derivative containing the propylenediamine chain shows clear self-inclusion and exhibits spectral variations upon guest inclusion detected both by circular dichroism or by fluorescence. The difference in conformation of the two derivatives could be explained on the basis of the chain length.     

Large scale synthesis of the Cdc42 inhibitor secramine A and its inhibition of cell spreading

We describe a large scale synthesis of secramine A. Consistent with its ability to inhibit activation of the small GTPase Cdc42, we find that secramine A inhibits cell spreading, a process previously shown to be Cdc42-dependent.     

Microcirculation within grooved substrates regulates cell positioning and cell docking inside microfluidic channels

Immobilization of cells inside microfluidic devices is a promising approach for enabling studies related to drug screening and cell biology. Despite extensive studies in using grooved substrates for immobilizing cells inside channels, a systematic study of the effects of various parameters that influence cell docking and retention within grooved substrates has not been performed. We demonstrate using computational simulations that the fluid dynamic environment within microgrooves significantly varies with groove width, generating microcirculation areas in smaller microgrooves. Wall shear stress simulation predicted that shear stresses were in the opposite direction in smaller grooves (25 and 50 microm wide) in comparison to those in wider grooves (75 and 100 microm wide). To validate the simulations, cells were seeded within microfluidic devices, where microgrooves of different widths were aligned perpendicularly to the direction of the flow. Experimental results showed that, as predicted, the inversion of the local direction of shear stress within the smaller grooves resulted in alignment of cells on two opposite sides of the grooves under the same flow conditions. Also, the amplitude of shear stress within microgrooved channels significantly influenced cell retainment in the channels. Therefore, our studies suggest that microscale shear stresses greatly influence cellular docking, immobilization, and retention in fluidic systems and should be considered for the design of cell-based microdevices.     

Solid-state spreading of oxides: Morphology and conductivity of In2O3-based films

Spontaneous solid-state spreading of In₂O₃ over the surface of ceramic and single crystal substrates of Al₂O₃, ZrO₂(0.08Y₂O₃), Y₃Al₅O₁₂ and YAlO₃ at 1380 and 1500 °C has been investigated. The films structure, element and phase composition were studied by means of XRD and SEM/EDS. The phase compositions of all films correspond to that of powder In₂O₃. The most films are dense with monolithic “film/substrate” interface. AC-conductivity in the range 25–250 °C is reported. Depending on the substrate material, the films demonstrate a whole set of conductivity types (semi-conductive, metallic) and wide range of magnitudes (more than 3 orders).Thermodynamic and kinetic aspects of oxide spreading and subsequent crystallization on the surface of primary border film are discussed. It is shown, in particular, that the solid-state spreading is facilitated in systems with high chemical affinity (mutual solubility, formation of intermediate interface compounds). In the case of eutectic-type systems, heteroepitaxy of diffusant at substrate surface results in formation of dense films.     

Three-dimensional microfiber devices that mimic physiological environments to probe cell mechanics and signaling

Many physiological systems are regulated by cells that alter their behavior in response to changes in their biochemical and mechanical environment. These cells experience this dynamic environment through an endogenous biomaterial matrix that transmits mechanical force and permits chemical exchange with the surrounding tissue. As a result, in vitro systems that mimic three-dimensional, in vivo cellular environments can enable experiments that reveal the nuanced interplay between biomechanics and physiology. Here we report the development of a minimal-profile, three-dimensional (MP3D) experimental microdevice that confines cells to a single focal plane, while allowing the precise application of mechanical displacement to cells and concomitant access to the cell membrane for perfusion with biochemical agonists. The MP3D device--an ordered microfiber scaffold erected on glass--provides a cellular environment that induces physiological cell morphologies. Small manipulations of the scaffold's microfibers allow attached cells to be mechanically probed. Due to the scaffold's minimal height profile, MP3D devices confine cells to a single focal plane, facilitating observation with conventional epifluorescent microscopy. When examining fibroblasts within MP3D devices, we observed robust cellular calcium responses to both a chemical stimulus as well as mechanical displacement of the cell membrane. The observed response differed significantly from previously reported, mechanically-induced calcium responses in the same cell type. Our findings demonstrate a key link between environment, cell morphology, mechanics, and intracellular signal transduction. We anticipate that this device will broadly impact research in fields including biomaterials, tissue engineering, and biophysics.     

Hydrogels with Dynamically Controllable Mechanics and Biochemistry for 3D Cell Culture Platforms

Many cell-matrix interaction studies have proved that dynamic changes in the extracellular matrix(ECM)are crucial to maintain cellular properties and behaviors.Thus,developing materials that can recapitulate the dynamic attributes of the ECM is highly desired for threedimensional(3 D)cell culture platforms.To this end,we sought to develop a hydrogel system that would enable dynamic and reversible turning of its mechanical and biochemical properties,thus facilitating the control of cell culture to imitate the natural ECM.Herein,a hydrogel with dynamic mechanics and a biochemistry based on an addition-fragmentation chain transfer(AFCT)reaction was constructed.Thiol-modified hyaluronic acid(HA)and allyl sulfide-modifiedε-poly-L-lysine(EPL)were synthesized to form hydrogels,which were non-swellable and biocompatible.The reversible modulus of the hydrogel was first achieved through the AFCT reaction;the modulus can also be regulated stepwise by changing the dose of UVA irradiation.Dynamic patterning of fluorescent markers in the hydrogel was also realized.Therefore,this dynamically controllable hydrogel has great potential as a 3 D cell culture platform for tissue engineering applications.     

Spontaneous spreading of nematic liquid crystals

The spontaneous spreading of macroscopic drops of nematic liquid crystals on hydrophilic substrates has been investigated by interferometric techniques. There is a complex interplay between the elastic energy, due to antagonist anchoring at the interfaces, and the radial flow in the spreading drop. A relevant parameter appears to be the relative humidity of the atmosphere, because it controls the amount of water molecules adsorbed on the substrate and, therefore, the strength of anchoring defects. The spreading laws differ from the ones of simple wetting liquids, and contact line instabilities coupled to short- (anchoring) or large-scale (disclinations) defects of the nematic film are observed.     

Electron microscope study of alkoxide-derived compositions within the PbZrO3-PbTiO3 phase diagram

Pb(Zr_0.50Ti_0.50)O₃ solid solution was prepared using lead acetate and transition metal n-propoxides in n-propanol or n-butoxides in n-butanol. The complex solutions were hydrolysed with an excess of H₂O. The resultant powders were calcined up to 700°C for 30 minutes in a flowing oxygen atmosphere. Scanning electron microscope analysis showed different morphologies of the resultant powders. The n-propoxide derived powder consisted of gel fragments, while the n-butoxide derived one had agglomerated submicrometre particles. EDS analysis of the powders revealed no chemical heterogeneities in the examined samples upon calcining up to 600°C, notwithstanding the type of precursor used. Both samples, calcined at 700°C, exhibited a slight deficiency of lead in the pyrochlore type phase as compared to the perovskite phase.     

Evaluating cell migration in vitro by the method based on cell patterning within microfluidic channels

Cell migration is an early-stage and critical step for cancer metastasis. The most common approach to monitor this process is wound-healing assay. However, this traditional method has some unavoidable limitations. We observed that simply scratching the monolayer of cultured cells might cause local cell damage around the injury line. The cells along the scratched border seemed to be irritated and exhibited abnormal distribution of cytoskeleton reassembly with protruding "cell islands" and "pseudopodia" during wound healing, which might potentially affect the assessment of cell migration behavior. Herein, we applied a microfluidic device that mechanically constrained cells seeded in a designed pattern inside microchannels, and monitored cell movement in a way of mimicking the natural microenvironment of cancerous tissues. We illustrated the capacity of this simple method to probe cellular migration behaviors and to screen some biological active agents that reflected in their influence on cellular motility.     

Calculation ofL 3 subshell alignment within a coupled-state formalism

Theoretical results for the impact parameter dependence of theA ₂₀ alignment parameter are compared with experimental data. The calculations have been performed within a coupled channel formalism, using relativistic atomic wave functions as basis states.