This paper addresses the use of graft polymer layers as spacers to control interparticle distance in 2-dimensional monolayers. Gold nanoparticles grafted with thermosensitive PNIPAM-based polymers with a large range of molecular mass and different degrees of hydrophobicity have been studied. The hydrophobicity of the polymer is adjusted by incorporation of a comonomer n-propylamine. The resulting copolymer, PNIPAM-co-NPAM, exhibits lower collapse transition temperature and increased cooperativity in the collapse process with n ≈ 150 compared to n ≈ 100 for PNIPAM, n being the number of monomers per collapse domain. Langmuir isotherms of these polymers under moderate compression follow closely a π ≈ c3 behavior with corresponding critical exponent ν = 3/4 as predicted for 2-dimensional polymer conformation in good solvent. Nanoparticles grafted with these polymers form stable Langmuir monolayers where the graft polymer chains adopt a 2-D stretched conformation that tethers the nanoparticles to the interface. The nanoparticle cores are thus isolated by the polymer shells resulting in nanoparticle areas that increase with polymer chain length. Correspondingly, the interparticle distance is found to vary with chain length as Dp ≈ N0.8. For the Au-PNIPAM-NPAM, a moderate increase in temperature to near-θ conditions decreases the nanoparticle area by about 30% through lateral collapse of the polymer layer. This thermally induced molecular collapse in a 2-D monolayer is an unusual and novel observation that may be attributed to cooperative effects of the collapse transition of the new copolymer PNIPAM-co-NPAM.
A novel process for identifying reusable program clones is described in this work. The process is applied to a very demanding context, a large-scale closed source healthcare software system. As results, the applicability and maturity of the clone detection system are discussed but also the results of the study are summarized. In this, especial care has been taken in order to retain result comparability with other hallmark studies on clone detection.
Calix[4]arene and calix[4]arene/alkanethiol protected gold nanoparticles with narrow size distributions were synthesised and characterized with NMR, thermogravimetric analysis (TGA) and a transmission electron microscope (TEM). NMR and light scattering (LS) were used to study the complexation of the nanoparticles with a pyridinium modified polyethylene oxide (Pyr-PEO2k-Pyr) complexant and a small 16 carbon pyridinium compound (Pyr-C16). Results give clear evidence of complexation induced aggregation of the nanoparticles as pyridinium proton signals shift upon changing the host : guest ratio and LS shows a change from a narrow size distribution into a broad one. The addition of alkanethiols with longer dimensions than that of the calixarene derivative and the type of the complexant can be used to tune the complexation. The studies also provide evidence of induced fit complexation into calix[4]arene cavities and solution phase interdigitation (secondary monolayer formation) when the nanoparticles are complexed with Pyr-C16.
This paper describes a detailed study on the complexation of pyridinium derivatives with calixarenes bound to gold nanoparticles (AuNPs). The studied calixarene derivatives are mixed with alkanethiols to form mixed monolayers on AuNP surfaces. The key findings are: (i) even a small amount (less than 11 mol%) of calixarenes can retain their complexation abilities among a majority of alkanethiols in a mixed monolayer, showing that it is possible to dilute the active calixarene (and possibly other receptors) in gold surfaces, (ii) the chain length of the alkanethiol compared with the calixarene spacer length can be used to fine tune the complexation ability of the calixarene, and there exist calixarene–alkanethiol mixed monolayer compositions in which the particles become unstable due to mismatching ligand spacer lengths, (iii) calixarenes with very short spacers bound to the gold surface can experience an enhancement in the delocalized π-electron density available for cation complexation, likely due to the proximity of the gold-bound sulphur to the calixarene cavity.
Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]arenes to the Au25 cluster surface with two or four thiolates per moiety.
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