Two-dimensional Arrays of Amphiphilic Zn2+ -cyclens for Guided Molecular Recognition at Interfaces

The sterically guided molecular recognition of nucleobases, phosphates, adenosine, and uridine nucleotides on Langmuir monolayers and Langmuir-Blodgett monolayers of amphiphilic mono- or bis(Zn2+-cyclen)s assembled on thiolated surfaces was investigated. The stepwise selective binding of metal ions, uracil, or phosphate by dicetyl cyclen monolayers with variously tuned structures at the air/water interface was corroborated by the measurements of the corresponding LB films deposited onto quartz crystals. Two types of recognition surfaces were fabricated from Zn2+-dicetyl cyclen. The surface covered with a complex preformed in the Langmuir monolayer was capable both of imide and of phosphate binding. The similar complex formed directly in an LB film on thiolated gold was inactive with respect to imide. The surface plasmon resonance measurements evidenced the stepwise assembly of complementary nucleotides on SAM/LB templates through consecutive phosphate-Zn2+-cyclen coordination. Base pairing between nucleotides resulted in a formation of A-U bilayers comprising two complementary monolayers. Finally, we report on SAM/LB patterns designed for divalent molecular recognition of uridine phosphate by amphiphilic bis(Zn2+-cyclen)

Analytical Modeling of Runway Stone Lofting

This investigation aims to develop a closed-form analytical model to understand and predict runway stone lofting processes by considering the rigid-body interaction of a tire partially rolling over a stone. Any leading-edge aircraft structures impinging into the path of such stones could experience impacts at speeds up to the aircraft takeoff velocity, despite being some distance from the sides of the wheels. The results of the analytical model provide upperbound envelopes of the vertical loft speeds obtained in previous numerical simulations and modified drop-weight experiments. Parametric studies conclude that the vertical loft speeds rise with increasing stone-tire overlap, stone size, and aircraft speed and with deceasing tire diameter. The outcomes of this model form a basis for vehicle designers to assess the runway stone impact threat by better understanding the physics of lofting. © 2010 by S. N. Nguyen, E. S. Greenhalgh, and R. Olsson. Published by the American Institute of Aeronautics and Astronautics, Inc.</p

Redox-controlled multistability of double-decker cerium tetra-(15-crown-5)-phthalocyaninate ultrathin films

The optical and electrochemical properties of novel double-decker cerium bis-tetra-15-crown-5-phthalocyaninate [ Ce ( R 4 Pc 2−)2]0 (R4Pc2− = [4,5,4',5',4",5",4'",5'"-tetrakis-(1,4,7,10,13-pentaoxapentadecamethylene)-phthalocyaninate-anion]) Langmuir-Blodgett and cast films were investigated. The particular feature of cerium ion in complex with tetra-15-crown-5-phthalocyanine is the stability of oxidation state +4 unlike other lanthanide metal centers. Cyclic voltammetry curves exhibited three stable redox states in the Langmuir-Blodgett and cast films. Redox processes in Langmuir-Blodgett films are reversible and reproducible at multiple scan procedures. The mechanisms of redox transformations in Langmuir-Blodgett films are suggested. We demonstrated that the well-defined structure of Langmuir-Blodgett film is essential for fast electron transfer within the planar system, in which the charge is delocalized along the conjugated assembly of uniformly ordered stacks of discotic crown-phthalocyaninate. Fast charge relaxation was observed in highly ordered Langmuir-Blodgett film whereas the electrochemically written redox states remained unchanged in unordered cast film. The combination of electrochemistry with surface plasmon resonance spectroscopy allowed us to demonstrate that stepwise change of potential in the range 200-850 mV induced the respective optical response, which can be observed as the change in resonance angle value. High-speed response and reversibility of the switching process between stable states may be utilized as the basis for switchable optoelectronic devices. Electrochemical multistability of cerium crown-phthalocyaninate provided a basis for developing a simple strategy to fabricate nanoelectromechanical systems with high efficiency and fast response. Our approach relies on the modulation of the distance between decks in a complex stack via redox-controlled change of metal center size that results in change of linear dimensions of the stacks. The reported results are valuable, not only because of their potential applications, for instance, in OFET and MEMS fabrication, but also from a fundamental point of view since they illustrate the interplay between the orientation of stacks bearing discotic aromatic molecules and charge transfer within such a planar assembly. </jats:p

Two-Dimensional Arrays of Amphiphilic Zn²⁺-Cyclens for Guided Molecular Recognition at Interfaces

The sterically guided molecular recognition of nucleobases, phosphates, adenosine, and uridine nucleotides on Langmuir monolayers and Langmuir−Blodgett monolayers of amphiphilic mono- or bis(Zn2+-cyclen)s assembled on thiolated surfaces was investigated. The stepwise selective binding of metal ions, uracil, or phosphate by dicetyl cyclen monolayers with variously tuned structures at the air/water interface was corroborated by the measurements of the corresponding LB films deposited onto quartz crystals. Two types of recognition surfaces were fabricated from Zn2+-dicetyl cyclen. The surface covered with a complex preformed in the Langmuir monolayer was capable both of imide and of phosphate binding. The similar complex formed directly in an LB film on thiolated gold was inactive with respect to imide. The surface plasmon resonance measurements evidenced the stepwise assembly of complementary nucleotides on SAM/LB templates through consecutive phosphate-Zn2+-cyclen coordination. Base pairing between nucleotides resulted in a formation of A-U bilayers comprising two complementary monolayers. Finally, we report on SAM/LB patterns designed for divalent molecular recognition of uridine phosphate by amphiphilic bis(Zn2+-cyclen)

Two-Dimensional Arrays of Amphiphilic Zn²⁺-Cyclens for Guided Molecular Recognition at Interfaces

The sterically guided molecular recognition of nucleobases, phosphates, adenosine, and uridine nucleotides on Langmuir monolayers and Langmuir−Blodgett monolayers of amphiphilic mono- or bis(Zn2+-cyclen)s assembled on thiolated surfaces was investigated. The stepwise selective binding of metal ions, uracil, or phosphate by dicetyl cyclen monolayers with variously tuned structures at the air/water interface was corroborated by the measurements of the corresponding LB films deposited onto quartz crystals. Two types of recognition surfaces were fabricated from Zn2+-dicetyl cyclen. The surface covered with a complex preformed in the Langmuir monolayer was capable both of imide and of phosphate binding. The similar complex formed directly in an LB film on thiolated gold was inactive with respect to imide. The surface plasmon resonance measurements evidenced the stepwise assembly of complementary nucleotides on SAM/LB templates through consecutive phosphate-Zn2+-cyclen coordination. Base pairing between nucleotides resulted in a formation of A-U bilayers comprising two complementary monolayers. Finally, we report on SAM/LB patterns designed for divalent molecular recognition of uridine phosphate by amphiphilic bis(Zn2+-cyclen)