Using an effective surface charge to explain surface potentials of Langmuir monolayers from dialkyldimethylammonium halides with the Gouy-Chapman theory

The use of an effective surface charge density has allowed the Gouy-Chapman (CC) theory to explain surface potential isotherms of Langmuir monolayers of dioctadecyldimethylammonium bromide (DODAB). The effective surface charge density of DODAB monolayer increases with the electronegativity of the counterions in the subphase. The pressure-area isotherms indicate a very condensed monolayer for DODAB spread on an I--containing subphase, which exhibits the lowest surface charge density, whereas the monolayer on a F-containing subphase is extremely expanded owing to the high surface charge density or electrostatic repulsion between headgroups. (C) 2001 Published by Elsevier B.V. B.V.

Capacitance Spectroscopy: A Versatile Approach To Resolving the Redox Density of States and Kinetics in Redox-Active Self-Assembled Monolayers

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

Nanostructured screen-printed electrodes modified with self-assembled monolayers for determination of metronidazole in different matrices

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

The negligible effects of the antifungal natamycin on cholesterol-dipalmitoyl phosphatidylcholine monolayers may explain its low oral and topical toxicity for mammals

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

Hybridization effects on the out-of-plane electron tunneling properties of monolayers: is h-BN more conductive than graphene?

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Compressed Air, Wooden Clappers, and Other Non-Traditional Methods for Dispersing European Starlings from an Urban Roost

During autumn 2003, several thousand European starlings (Sturnus vulgaris) began roosting on exposed I-beams in a newly constructed, decorative glass canopy that covered the passenger pick-up area at the terminal building for Cleveland Hopkins International Airport, Ohio. The use of lethal control or conventional dispersal techniques, such as pyrotechnics and fire hoses, were not feasible in the airport terminal area. The design and aesthetics of the structure precluded the use of netting and other exclusion materials. In January 2004, an attempt was made to disperse the birds using recorded predator and distress calls broadcast from speakers installed in the structure. This technique failed to disperse the birds. In February 2004, we developed a technique using compressed air to physically and audibly harass the birds. We used a trailer-mounted commercial air compressor producing 185 cubic feet per minute of air at 100 pounds per square inch pressure and a 20-foot long, 1-inch diameter PVC pipe attached to the outlet hose. One person slowly (< 5 mph) drove a pick-up truck through the airport terminal at dusk while the second person sat on a bench in the truck bed and directed the compressed air from the pipe into the canopy to harass starlings attempting to enter the roost site. After 5 consecutive nights of compressed-air harassment, virtually no starlings attempted to roost in the canopy. Once familiar with the physical effects of the compressed air, the birds dispersed at the sound of the air. Only occasional harassment at dusk was needed through the remainder of the winter to keep the canopy free of starlings. Similar harassment with the compressor was conducted successfully in autumn 2004 with the addition of a modified leaf blower, wooden clappers, and laser. In conclusion, we found compressed air to be a safe, unobtrusive, and effective method for dispersing starlings from an urban roost site. This technique would likely be applicable for other urban-roosting species such as crows, house sparrows, and blackbirds.

Headgroup specificity for the interaction of the antimicrobial peptide tritrpticin with phospholipid Langmuir monolayers

We examined the interaction of the cationic antimicrobial peptide (AMP) tritrpticin (VRRFPWWWPFLRR, TRP3) with Langmuir monolayers of zwitterionic (dipalmitoyl phosphatidylcholine, DPPC, and dipalmitoyl phosphatidylethanolamine, DPPE) and negatively charged phospholipids (dipalmitoyl phosphatidic acid, DPPA, and dipalmitoyl phosphatidylglycerol, DPPG). Both surface pressure and surface potential isotherms became more expanded upon addition of TRP3 (DPPE similar to DPPC << DPPA < DPPG). The stronger interaction with negatively charged phospholipids agrees with data for vesicles and planar lipid bilayers, and with AMPs greater activity against bacterial membranes versus mammalian cell membranes. Considerable expansion of negatively charged monolayers occurred at 10 and 30 mol% TRP3, especially at low surface pressure. Moreover, a difference was observed between PA and PG, demonstrating that the interaction, besides being modulated by electrostatic interactions, displays specificity with regard to headgroup, being more pronounced in the case of PG, present in large quantities in bacterial membranes. In previous studies, it was proposed that the peptide acts by a toroidal pore-like mechanism [1,2]. Considering the evidence from the literature that PG shows a propensity to form a positive curvature as do toroidal pores, the observation of TRP3's preference for the PG headgroup and the dramatic increase in area promoted by this interaction represent further support for the toroidal pore mechanism of action proposed for TRP3. (C) 2012 Elsevier B.V. All rights reserved.

Porcelain monolayers and porcelain/alumina bilayers reinforced by Al2O3/GdAlO3 fibers

Aim. This work tested the effect of the addition of Al2O3/GdAlO3 longitudinal fibers in different contents to veneering porcelain of two dental all ceramic systems. Methods: Fibers (0.5 mm diameter) obtained by the Laser Heated Pedestal Growth (LHPG) method were added to bar-shaped specimens made by veneer porcelain (monolayers) or both the veneer and the core ceramic (bilayers) of two all-ceramic systems: In-Ceram Alumina - glass infiltrated alumina composite (GIA) and In-Ceram 2000 AL Cubes - alumina polycrystal (AP) (VITA Zahnfabrik). The longitudinal fibers were added to veneering porcelain (VM7) in two different proportions: 10 or 17 vol%. The bars were divided into nine experimental conditions (n = 10) according to material used: VM7 porcelain monolayers, VM7/GIA, VM7/AP; and according to the amount of fibers within the porcelain layer: no fibers, 10 vol% or 17 vol%. After grinding and polishing the specimens were submitted to a three point bending test (crosshead speed = 0.5 mm/min) with porcelain positioned at tensile side. Data were analyzed by means of one-way ANOVA and a Tukey's test (alpha = 5%). Scanning electronic microscopy (SEM) was conducted for fractographic analysis. Results. Regarding the groups without fiber addition, VM7/AP showed the highest flexural strength (MPa), followed by VM7/GIA and VM7 monolayers. The addition of fibers led to a numerical increase in flexural strength for all groups. For VM7/GIA bilayers the addition of 17 vol% of fibers resulted in a significant 48% increase in the flexural strength compared to the control group. Fractographic analysis revealed that the crack initiation site was in porcelain at the tensile surface. Cracks also propagated between fibers before heading for the alumina core. Conclusions. The addition of 17 vol% of Al2O3/GdAlO3 longitudinal fibers to porcelain/glass infiltrated alumina bilayers significantly improved its flexural strength. 10 vol% or 17 vol% of fibers inclusion increased the flexural strength for all groups. (C) 2011 Elsevier Ltd. All rights reserved.

Microelectrode array in mixed alkanethiol self-assembled monolayers: Electrochemical studies

We report an efficient alternative to obtain recessed microelectrodes device on gold electrode surface, in which mixed self-assembled monolayer of long and short carbon alkanethiol chains was used for this purpose. Development of the modified electrodes included the chemical adsorption of 11-mercaptoundecanoic acid and 2-mercaptoethanol solution, as well as their mixtures, on gold surface, resulting in the final mixed self-assembled monolayer configuration. For comparison, the electrochemical performance of self-assembled monolayer of 11-mercaptoundecanoic acid. 3-mercaptopropionic acid, 4-mercapto-1-butanol and 6-mercapto-1-hexanol modified electrodes was also investigated. It was verified that, in the mixed self-assembled monolayer, the 11-mercaptoundecanoic acid acts as a barrier for electron transfer while the short alkanethiol chair is deposited in an island-like shape through which electrons can be freely transferred to ions in solution, allowing electrochemical reactions to occur. The performance of the modified electrodes toward microelectrode behavior was investigated via cyclic voltammetry and electrochemical impedance spectroscopy measurements using [Fe(CN)(6)](3-/4-) redox couple as a probe. In this case, sigmoidal voltammetric responses were obtained, very similar to those observed for microelectrodes. Such behavior reinforces the proposition of electron transfer through the short alkanethiol chain layer and surface blockage by the long chain one. Electrochemical impedance results allowed calculated the mean radius value of each microelectrode disks of 3.8 mu m with about 22 mu m interval between them. The microelectrode environment provided by the mixed self-assembled monolayer can be conveniently used to provide an efficient catalytic conversion in biosensing applications. (C) 2012 Elsevier Ltd. All rights reserved.

Formation of thin luminescent Eu3+-LB films by in situ coordination with 2,3,5,6-tetra(2 '-pyridyl)pyrazine and 1-octadecanol in pure and mixed Langmuir monolayers

The in situ complexation between 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) molecules and europium ions at the air-liquid interface by means of mixed 1-octadecanol Langmuir films is reported. These films were transferred to solid supports by means of the Langmuir-Blodgett (LB) technique. The EDS maps attested the homogeneity of the LB films as well as the presence of the europium ions. The mixed alcohol/tppz LB film contained a larger amount of europium ions as compared to the pure octadecanol LB film. This work reports the production of a thin luminescent Eu3+ film containing europium ions using only alcohol molecules as ligands an unexpected result, since it is well known that there is an occurrence of non-radiative deactivation of excited europium by hydroxyl groups. Europium ion multiple binding sites were detected from lifetime decay measurements of these films in the presence of tppz molecules. (C) 2012 Elsevier B.V. All rights reserved.

Bias and learning in temporal binding: intervals between actions and outcomes are compressed by prior bias

It has consistently been shown that agents judge the intervals between their actions and outcomes as compressed in time, an effect named intentional binding. In the present work, we investigated whether this effect is result of prior bias volunteers have about the timing of the consequences of their actions, or if it is due to learning that occurs during the experimental session. Volunteers made temporal estimates of the interval between their action and target onset (Action conditions), or between two events (No-Action conditions). Our results show that temporal estimates become shorter throughout each experimental block in both conditions. Moreover, we found that observers judged intervals between action and outcomes as shorter even in very early trials of each block. To quantify the decrease of temporal judgments in experimental blocks, exponential functions were fitted to participants’ temporal judgments. The fitted parameters suggest that observers had different prior biases as to intervals between events in which action was involved. These findings suggest that prior bias might play a more important role in this effect than calibration-type learning processes.

Self assembled monolayers for engineering of structured inorganic materials in the micrometer and submicrometer range

Deutsch:In der vorliegenden Arbeit konnten neue Methoden zur Synthese anorganischer Materialien mit neuartiger Architektur im Mikrometer und Nanometer Maßstab beschrieben werden. Die zentrale Rolle der Formgebung basiert dabei auf der templatinduzierten Abscheidung der anorganischen Materialien auf selbstorganisierten Monoschichten. Als Substrate eignen sich goldbedampfte Glasträger und Goldkolloide, die eine Mittelstellung in der Welt der Atome bzw. Moleküle und der makroskopischen Welt der ausgedehnten Festkörper einnehmen. Auf diesen Substraten lassen sich Thiole zu einer monomolekularen Schicht adsorbieren und damit die Oberflächeneigenschaften des Substrates ändern. Ein besonderer Schwerpunkt bei dieser Arbeit stellt die Synthese speziell auf die Bedürfnisse der jeweiligen Anwendung ausgerichteten Thiole dar.Im ersten Teil der Arbeit wurden goldbedampfte Glasoberflächen als Template verwendet. Die Abscheidung von Calciumcarbonat wurde in Abhängigkeit der Schichtdicke der adsorbierten Monolage untersucht. Aragonit, eine der drei Hauptphasen des Calciumcarbonat Systems, wurde auf polyaromatischen Amid - Oberflächen mit Schichtdicken von 5 - 400 nm Dicke unter milden Bedingung abgeschieden. Die einstellbaren Parameter waren dabei die Kettenlänge des Polymers, der w-Substituent, die Bindung an die Goldoberfläche über Verwendung verschiedener Aminothiole und die Kristallisationstemperatur. Die Schichtdickeneinstellung der Polymerfilme erfolgte hierbei über einen automatisierten Synthesezyklus.Titanoxid Filme konnten auf Oberflächen strukturiert werden. Dabei kam ein speziell synthetisiertes Thiol zum Einsatz, das die Funktionalität einer Styroleinheit an der Oberflächen Grenze als auch eine Möglichkeit zur späteren Entfernung von der Oberfläche in sich vereinte. Die PDMS Stempeltechnik erzeugte dabei Mikrostrukturen auf der Goldoberfläche im Bereich von 5 bis 10 µm, die ihrerseits über die Polymerisation und Abscheidung des Polymers in den Titanoxid Film überführt werden konnten. Drei dimensionale Strukturen wurden über Goldkolloid Template erhalten. Tetraethylenglykol konnte mit einer Thiolgruppe im Austausch zu einer Hydroxylgruppe monofunktionalisiert werden. Das erhaltene Molekül wurde auf kolloidalem Gold selbstorganisiert; es entstand dabei ein wasserlösliches Goldkolloid. Die Darstellung erfolgte dabei in einer Einphasenreaktion. Die so erhaltenen Goldkolloide wurden als Krstallisationstemplate für die drei dimensionale Abscheidung von Calciumcarbonat verwendet. Es zeigte sich, dass Glykol die Kristallisation bzw. den Habitus des krsitalls bei niedrigem pH Wert modifiziert. Bei erhöhtem pH Wert (pH = 12) jedoch agieren die Glykol belegten Goldkolloide als Template und führen zu sphärisch Aggregaten. Werden Goldkolloide langkettigen Dithiolen ausgesetzt, so führt dies zu einer Aggregation und Ausfällung der Kolloide aufgrund der Vernetzung mehrer Goldkolloide mit den Thiolgruppen der Alkyldithiole. Zur Vermeidung konnte in dieser Arbeit ein halbseitig geschütztes Dithiol synthetisiert werden, mit dessen Hilfe die Aggregation unterbunden werden konnte. Das nachfolgende Entschützten der Thiolfunktion führte zu Goldkolloiden, deren Oberfläche Thiol funktionalisiert werden konnte. Die thiolaktiven Goldkolloide fungierten als template für die Abscheidung von Bleisulfid aus organisch/wässriger Lösung. Die Funktionsweise der Schutzgruppe und die Entschützung konnte mittels Plasmonenresonanz Spektroskopie verdeutlicht werden. Titanoxid / Gold / Polystyrol Komposite in Röhrenform konnten synthetisiert werden. Dazu wurde ein menschliches Haar als biologisches Templat für die Formgebung gewählt.. Durch Bedampfung des Haares mit Gold, Assemblierung eines Stryrolmonomers, welches zusätzlich eine Thiolfunktionalität trug, Polymerisation auf der Oberfläche, Abscheidung des Titanoxid Films und anschließendem Auflösen des biologischen Templates konnte eine Röhrenstruktur im Mikrometer Bereich dargestellt werden. Goldkolloide fungierten in dieser Arbeit nicht nur als Kristallisationstemplate und Formgeber, auch sie selbst wurden dahingehend modifiziert, dass sie drahtförmige Agglormerate im Nanometerbereich ausbilden. Dazu wurden Template aus Siliziumdioxid benutzt. Zum einen konnten Nanoröhren aus amorphen SiO2 in einer Sol Gel Methode dargestellt werden, zum anderen bediente sich diese Arbeit biologischer Siliziumoxid Hohlnadeln aus marinen Schwämmen isoliert. Goldkolloide wurden in die Hohlstrukturen eingebettet und die Struktur durch Ausbildung von Kolloid - Thiol Netzwerken mittels Dithiol Zugabe gefestigt. Die Gold-Nanodrähte im Bereich von 100 bis 500 nm wurden durch Auflösen des SiO2 - Templates freigelegt.

Nanostructuring by templated synthesis of nanowires and controlled crystallization of calcium phosphate on self-assembled monolayers

The idea was to obtain nanowires in a chemical laboratory under convenient and simple conditions by employing templates. Thus it was possible to produce nanochains by interlinking of gold colloids synthesized by the two-phase-method of M. Brust with by making use of vanadiumoxide nanotubes as template. The length of the resulting nanowires is varying between 1100 nm and 200 nm with a diameter of about 16 nm. Due to a flexible linker the obtained nanowires are not completely rigid. These unique structural features could make them interesting objects for structuring and assembling in the nanoscale range. Another way to produce gold nanowires was realized by a two-step surface metallization procedure, using type I collagen fibres as a template. Gold colloids were used to label the collagen fibres by direct electrostatic interaction, followed by growth steps to enhance the size of the adsorbed colloidal gold crystals, resulting in a complete metallization of the template surface. The length of the resulting gold nanowires reaches several micrometers, with a diameter ~ 100 to 120 nm. To gain a deeper insight into the process of biomineralization the cooperative effect of self-assembled monolayers as substrate and a soluble counterpart on the nucleation and crystal growth of calcium phosphate was studied by diffusion techniques with a pH switch as initiator. As soluble component Perlucin and Nacrein were used. Both are proteins originally extracted from marine organisms, the first one from the Abalone shell and the second one from oyster pearls. Both are supposed to facilitate the calcium carbonate formation in vivo. Studies with Perlucin revealed that this protein shows a clear cooperative effect at a very low concentration with a hydrophobic surface promoting the calcium phosphate precipitation resulting in a sponge like structure of hydroxyapatite. The Perlucin molecule is very flexible and is unfolded by adsorbing to the hydrophobic surface and uncovers its active side. Hydrophilic surfaces did not have a deeper impact. Studies with Nacrein as additive have shown that the protein stabilizes octacalcium phosphate at room temperature on carboxylic self-assembled monolayer and at 34 °C on all other employed surfaces by interaction with the mineral. On the hydroxyl-, alkyl-, and amin-terminated self-assembled monolayers at room temperature the octacalcium phosphate get transformed to hydroxyapatite. Main analytical techniques which are used in this work are transmission electron microscopy, high resolution scanning electron microscopy, surface plasmon resonance spectroscopy, atomic force microscopy, Raman micro-spectroscopy and quartz crystal microbalance.