Properties of lipophilic nucleoside monolayers at the air-water interface

The capability of self-assembly and molecular recognition of biomolecules is essential for many nanotechnological applications, as in the use of alkyl-modified nucleosides and oligonucleotides to increase the cellular uptake of DNA and RNA. In this study, we show that a lipophilic nucleoside, which is an isomer mixture of 2`-palmitoyluridin und 3`-palmitoyluridin, forms Langmuir monolayers and Langmuir-Blodgett films as a typical amphiphile, though with a smaller elasticity. The nucleoside may be incorporated into dipalmitoyl phosphatidyl choline (DPPC) monolayers that serve as a simplified cell membrane model. The molecular-level interactions between the nucleoside and DPPC led to a remarkable condensation of the mixed monolayer, which affected both surface pressure and surface potential isotherms. The morphology of the mixed monolayers was dominated by the small domains of the nucleoside. The mixed monolayers could be deposited onto solid substrates as a one-layer Langmuir Blodgett film that displayed UV-vis absorption spectra typical of aggregated nucleosides owing to the interaction between the nucleoside and DPPC. The formation of solid films with DNA building blocks in the polar heads may open the way for devices and sensors be produced to exploit their molecular recognition properties. (C) 2010 Elsevier B.V. All rights reserved.

Surface Activity of the Triflate Ion at the Air/Water Interface and Properties of N,N,N-Trimethyl-N-Dodecylammonium Triflate Aqueous Solutions

The surface activity of salts added to water is Air orders of magnitude lower than that of surfactants. Sodium trifluoromethanesulfonate (NaTf) produced a change in surface tension. with concentration, Delta gamma/Delta c, of -13.2 mN.L/m.mol. This value is ca. 4-fold larger than those of simple salts and that of methanesulfonate. This unexpected surface effect suggested that positively charged micelles containing Tf could exhibit interesting properties. Dodecyltrimethylammonium triflate (DTATf) had a higher Kraft temperature (37 degrees C) and a lower cmc (5 x 10(-3)M) and degree of dissociation (0.11) than the chloride and bromide salts of DTA. Above the Kraft temperature, at a characteristic temperature t(1), the addition of NaTf above 0.05 M. to a DTATf solution induced phase separation. By increasing the temperature of the two-phase system to above t(1), a homogeneous, transparent solution was obtained at a characteristic temperature t(2). These results, together with well-known triflate properties, led us to suggest that the Tf ion pairs With DTA and that the -CF(3) group may be dehydrated in the interfacial region, resulting in new and interesting self-aggregated structures.

Impedance of carrier injection at the metal-organic interface mediated by surface states in electron-only tris(8-hydroxyquinoline) aluminium (Alq(3)) thin layers

Capacitance spectra of thin (< 200 nm) Alq(3) electron-only devices have been measured as a function of bias voltage. Capacitance spectra exhibit a flat response at high frequencies (> 10(3) Hz) and no feature related to the carrier transit time is observed. Toward low frequencies the spectra reach a maximum and develop a negative excess capacitance. Capacitance response along with current-voltage (J-V) characteristics are interpreted in terms of the injection of electrons mediated by surface states at the metal organic interface. A detailed model for the impedance of the injection process is provided that highlights the role of the filling/releasing kinetics of energetically distributed interface states. This approach connects the whole capacitance spectra to the occupancy of interface states, with no additional information about bulk trap levels. Simulations based on the model allow to derive the density of interface states effectively intervening in the carrier injection (similar to 1.5 x 10(12) cm (2)). (C) 2008 Elsevier B.V. All rights reserved.

Efficacy of Air-abrasion Technique and Additional Surface Treatment at Titanium/Resin Cement Interface

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of bur type and conditioning on the surface and interface of dentine

The purpose of this in vitro study was to evaluate the surface and resin-dentine interface characteristics of permanent tooth dentine cut with diamond or carbide burs and treated with phosphoric acid (PA) or an acidic conditioner. Labial surfaces of permanent incisors were prepared into dentine with high-speed carbide or diamond burs and divided into two halves. Phosphoric acid 36% was applied on one half and non-rinse conditioner (NRC) was applied on the other half. Ten randomly selected scanning electron microscopy (SEM) fields from each specimen (n = 15) were evaluated. Occlusal surfaces of third molars were divided in two halves for evaluation of the resin-dentine interface. The halves were randomly assigned to one of each conditioner and restored with Prime & Bond NT/Spectrum. Ten specimens were analysed by SEM to evaluate hybrid layer formation and interfacial seal. We observed that surfaces prepared with carbide bur presented less residual smear plugs (P < 0.05) than surfaces prepared with diamond burs. Surfaces conditioned with NRC, which is a smear layer modifier, presented more residual smear plugs than surfaces conditioned with PA (P < 0.05). Treatment with PA resulted in more sealed interfaces than specimens treated with NRC. Within the limitations of this study the results showed that carbide burs leave a surface that is more conducive to bonding than diamond burs.

Structure formation of amphiphilic molecules at the air,water interface and after film transfer

One of the basic concepts of molecular self-assembly is that the morphology of the aggregate is directly related to the structure and interaction of the aggregating molecules. This is not only true for the aggregation in bulk solution, but also for the formation of Langmuir films at the air/water interface. Thus, molecules at the interface do not necessarily form flat monomolecular films but can also aggregate into multilayers or surface micelles. In this context, various novel synthetic molecules were investigated in terms of their morphology at the air/water interface and in transferred films. rnFirst, the self-assembly of semifluorinated alkanes and their molecular orientation at the air/water interface and in transferred films was studied employing scanning force microscopy (SFM) and Kelvin potential force microscopy. Here it was found, that the investigated semifluorinated alkanes aggregate to form circular surface micelles with a diameter of 30 nm, which are constituted of smaller muffin-shaped subunits with a diameter of 10 nm. A further result is that the introduction of an aromatic core into the molecular structure leads to the formation of elongated surface micelles and thus implements a directionality to the self-assembly. rnSecond, the self-assembly of two different amphiphilic hybrid materials containing a short single stranded desoxyribonucleic acid (DNA) sequence was investigated at the air/water interface. The first molecule was a single stranded DNA (11mer) molecule with two hydrophobically modified 5-(dodec-1-ynyl)uracil nucleobases at the terminal 5'-end of the oligonucleotide sequence. Isotherm measurements revealed the formation of semi-stable films at the air/water interface. SFM imaging of films transferred via Langmuir-Blodgett technique supported this finding and indicated mono-, bi- and multilayer formation, according to the surface pressure applied upon transfer. Within these films, the hydrophilic DNA sequence was oriented towards air covering 95% of the substrate.rnSimilar results were obtained with a second type of amphiphile, a DNA block copolymer. Furthermore, the potential to perform molecular recognition experiments at the air/water interface with these DNA hybrid materials was evaluated.rnThird, polyglycerol ester molecules (PGE), which are known to form very stable foams, were studies. Aim was to elucidate the molecular structure of PGE molecules at the air/water interface in order to comprehend the foam stabilization mechanism. Several model systems mimicking the air/water interface of a PGE foam and methods for a noninvasive transfer were tested and characterized by SFM. It could be shown, that PGE stabilizes the air/water interface of a foam bubble by formation of multiple surfactant layers. Additionally, a new transfer technique, the bubble film transfer was established and characterized by high speed camera imaging.The results demonstrate the diversity of structures, which can be formed by amphiphilic molecules at the air/water interface and after film transfer, as well as the impact of the chemical structure on the aggregate morphology.

Kontrolle der Grenzflächeneigenschaften anorganischer Nanopartikel mittels amphiphiler Polymere

Im Rahmen dieser Arbeit wurden amphiphile Co- und Terpolymere verwendet, um die Grenzflächeneigenschaften anorganischer Nanopartikel zu kontrollieren. Es wurde eine effiziente und vielseitige Methode entwickelt, mit der in-situ hydrophobierte, formanisotrope ZnO-, CdS- und Au-Nanopartikel sowie poröse TiO2-Nanopartikel hergestellt werden konnten. Diese Technik basierte auf der Fällung anorganischer Nanopartikel in einer inversen Emulsion mittels kombinierten Einsatzes zweier maßgeschneiderter amphiphiler Polymere. Ein Copolymer ermöglichte sowohl die Stabilisierung der Emulsion als auch die Hydrophobierung der Partikel, und ein weiteres Struktur-dirigierendes Agens (SDA) kontrollierte den Kristallisationsprozess. Infolge ihrer Form zeigten die Nanopartikel von sphärischen Teilchen abweichende Lagen der Oberflächenplasmonenresonanz und der Bandlücke. Aufgrund der hervorragenden Hydrophobierung dieser Kolloide mittels amphiphiler Copolymere konnten diese homogen in polymere Materialien eingearbeitet werden. Dies erlaubte es die speziellen Eigenschaften von nicht-sphärischen Kolloiden auf Nanokompositmaterialien zu übertragen. Darüber hinaus wurden amphipolare Copolymere genutzt, um superhydrophobe Oberflächen zu generieren. Hierzu wurden Filme bestehend aus rauen SiO2-Nanopartikeln mit fluorierten Emulgatoren beschichtet. In einem dritten Schwerpunkt dieser Arbeit wurden amphiphile Co- und Terpolymere verwendet, um anorganische Nanopartikel zu hydrophilieren. Durch Variation der Emulgatorzusammensetzung konnten die Ladung und Ladungsdichte auf der Partikeloberfläche gezielt gesteuert werden. Darüber hinaus konnte die Partikelhülle zusätzlich mit Farbstoffmolekülen funktionalisiert werden, was den erfolgreichen Einsatz der Kolloide in Zellaufnahmeexperimenten ermöglichte.

Oberflächenstrukturierte amphiphile Polyphenylendendrimere zur Imitation natürlicher Transportproteine

In dieser Arbeit werden formstabile, amphiphile, oberflächenstrukturierte Polyphenylendendrimere (PPDs) mit verschiedenen Oberflächenpolaritäten beschrieben. Die physikalisch-chemischen Eigenschaften dieser Makromoleküle wurden studiert, welche ein gutes Verständnis der Nanoumgebung amphiphiler PPDs lieferten. Auch lichtinduzierte Polaritätsänderung wurde untersucht. Mit dem Konzept einer gleichmäßigen Verteilung polarer Bereiche auf der Peripherie hydrophober PPPs gelang es, Transportsysteme für Fettsäuren und Zytostatika zu erzeugen, welche charakteristische Merkmale natürlicher Transportproteine wie Albumin in sich vereinen. Hierzu zählen eine stabile dreidimensionale Form, die Ausbildung von Bindungstaschen sowie eine definierte strukturierte Oberfläche aus hydrophilen und hydrophoben Bereichen. Die Verfügbarkeit von lipophilen Bindungstaschen übertrifft sogar die des Albumins. Im Gegensatz zu Polymeren kann die Wirkstoffaufnahme bei PPDs exakt bestimmt werden. Die Anpassung der peripheren Gruppen beeinflusst den zellulären Aufnahmemechanismus. Es konnten effiziente Zellaufnahmen in A549-Zellen sowie der Transport und die intrazelluläre Freisetzung von Doxorubicin erreicht werden. Manche PPDs bieten eine Größe und Architektur, die es ermöglicht, Endothelzellen des Gehirns zu durchdringen. Es wurde auch der andere Extremfall untersucht, indem alle polaren Gruppen auf einer Hemisphäre akkumuliert wurden. Zur Darstellung solcher Janus-Dendrimere wurde ein neues Synthesekonzept herausgearbeitet und die erhaltenen Janus-Dendrimere mittels Lichtstreuung untersucht, wobei definierte perlenschnurartige Aggregate gefunden wurden. Weiterhin wurden semifluorierte Amphiphile vorgestellt, welche die Möglichkeit zur Selbstorganisation durch Nanophasenseparation bieten.

Liquid–Vapor Interface of Formic Acid Solutions in Salt Water: A Comparison of Macroscopic Surface Tension and Microscopic in Situ X-ray Photoelectron Spectroscopy Measurements

The liquid–vapor interface is difficult to access experimentally but is of interest from a theoretical and applied point of view and has particular importance in atmospheric aerosol chemistry. Here we examine the liquid–vapor interface for mixtures of water, sodium chloride, and formic acid, an abundant chemical in the atmosphere. We compare the results of surface tension and X-ray photoelectron spectroscopy (XPS) measurements over a wide range of formic acid concentrations. Surface tension measurements provide a macroscopic characterization of solutions ranging from 0 to 3 M sodium chloride and from 0 to over 0.5 mole fraction formic acid. Sodium chloride was found to be a weak salting out agent for formic acid with surface excess depending only slightly on salt concentration. In situ XPS provides a complementary molecular level description about the liquid–vapor interface. XPS measurements over an experimental probe depth of 51 Å gave the C 1s to O 1s ratio for both total oxygen and oxygen from water. XPS also provides detailed electronic structure information that is inaccessible by surface tension. Density functional theory calculations were performed to understand the observed shift in C 1s binding energies to lower values with increasing formic acid concentration. Part of the experimental −0.2 eV shift can be assigned to the solution composition changing from predominantly monomers of formic acid to a combination of monomers and dimers; however, the lack of an appropriate reference to calibrate the absolute BE scale at high formic acid mole fraction complicates the interpretation. Our data are consistent with surface tension measurements yielding a significantly more surface sensitive measurement than XPS due to the relatively weak propensity of formic acid for the interface. A simple model allowed us to replicate the XPS results under the assumption that the surface excess was contained in the top four angstroms of solution.

Protease footprinting reveals a surface on transcription factor TFIIB that serves as an interface for activators and coactivators.

Transcriptional stimulation by the model activator GAL4-VP16 (a chimeric protein consisting of the DNA-binding domain of the yeast activator GAL4 and the acidic activation domain of the herpes simplex virus protein VP16) involves a series of poorly understood protein-protein interactions between the VP16 activation domain and components of the RNA polymerase II general transcription machinery. One of these interactions is the VP16-mediated binding and recruitment of transcription factor TFIIB. However, TATA box-binding protein (TBP)-associated factors (TAFs), or coactivators, are required for this interaction to culminate in productive transcription complex assembly, and one such TAF, Drosophila TAF40, reportedly forms a ternary complex with VP16 and TFIIB. Due to TFIIB's central role in gene activation, we sought to directly visualize the surfaces of this protein that mediate formation of the ternary complex. We developed an approach called protease footprinting in which the broad-specificity proteases chymotrypsin and alkaline protease were used to probe binding of 32P-end-labeled TFIIB to GAL4-VP16 or TAF40. Analysis of the cleavage products revealed two regions of TFIIB protected by VP16 from protease attack, one of which overlapped with a region protected by TAF40. The close proximity of the VP16 and TAF40 binding sites on the surface of TFIIB suggests that this region could act as a regulatory interface mediating the effects of activators and coactivators on transcription complex assembly.

Oblique surface waves at an interface between a metal–dielectric superlattice and an isotropic dielectric

We investigate the existence and dispersion characteristics of surface waves that propagate at an interface between a metal–dielectric superlattice and an isotropic dielectric. Within the long-wavelength limit, when the effective-medium (EM) approximation is valid, the superlattice behaves like a uniaxial plasmonic crystal with the main optical axes perpendicular to the metal–dielectric interfaces. We demonstrate that if such a semi-infinite plasmonic crystal is cut normally to the layer interfaces and brought into contact with a semi-infinite dielectric, a new type of surface mode can appear. Such modes can propagate obliquely to the optical axes if favorable conditions regarding the thickness of the layers and the dielectric permittivities of the constituent materials are met. We show that losses within the metallic layers can be substantially reduced by making the layers sufficiently thin. At the same time, a dramatic enlargement of the range of angles for oblique propagation of the new surface modes is observed. This can lead, however, to field non-locality and consequently to failure of the EM approximation.

Microstructural analysis of surface and interface zones in concrete

Several of OPC paste and concrete specimens, with different mix proportions, were cast against CPF and impermeable formwork (IF) and the profiles of pore structure, microhardness and scratch hardness of the cover zone were established. The chloride ingress and the depth of carbonation of the surface zone of concrete cast against CPF and IF were investigated. The main mechanisms controlling the ECR processes and the factors affecting such treatment were critically reviewed. Subsequently, as a means of restoring passivation of steel embedded in carbonated concrete, such HCP specimens were subjected to ECR. The influence of ECR on the chemistry of the pore solution and the microstructure of the surface and the steel/cement past interface zones were also studied. The main findings of this investigation were as follows: (a) The thickness of the microstructure gradient of cover concrete is significantly decreased with increasing period of water curing but is relatively unaffected by curing temperature, w/e ratio and the use of cement replacement materials. (b) The scratch hardness technique was shown to be potentially useful for characterising the microstructure and microhardness gradients of the surface zone. (c) A relationship between the microstructure gradient and mass transport properties of the surface zone was established. (d) The use of CPF resulted in a significant reduction in porosity of both the cement paste matrix and the aggregate/cement paste transition zone, and a marked improvement in the resistance of the surface zone to carbonation and the ingress of chloride ions. (e) The ECR treatment resulted in a marked densification of the pore structure and in changes to the pore solution chemistry and the cement phases of near-surface and steel/cement paste transition zones. This effect was more pronounced with current density, period of treatment and particularly with the use of sodium phosphate as an electrolyte.