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Layer-by-layer films have been constructed from a cationic diazoresin and poly(sodium 4-styrenesulfonate)-functionalized single-wall carbon nanotubes (SWNT). Raman and near-IR absorption spectra indicate that some diazonium ions reacted with SWNT during film construction. The ionic bonds in the film between diazonium ions and sulfonate ions converted to covalent bonds upon UV irradiation as shown by the disappearance of diazonium ion peaks in the UV and IR spectra and appearance of an arenesulfonate peak in the IR spectra. The resistance of the film toward etching by polar solvents increased significantly after irradiation.

Atomic force microscopy (AFM) was employed to characterize the surface chemistry distribution on individual polystyrene latex particles. The particles were obtained by surfactant-free emulsion polymerization and contained hydrophilic quaternary ammonium chloride, sodium sulfonate, or hydroxyethyl groups. The phase shift in dynamic force mode AFM is sensitive to charge/chemical interactions between an oscillating atomic force microscope tip and a sample surface. In this work, the phase imaging technique distinguished phase domains of 50−100 nm on the surfaces of dried latex particles in ambient air. The domains are attributed to the separation of ion-rich and ion-poor components of the polymer on the particle surface.

Poly(4-vinylpyridine) grafts to single-walled carbon nanotubes (SWNT) during in situ free radical polymerization of 4-vinylpyridine. After removal of catalyst particles and unattached polymer by centrifugation and ultrafiltration, the SWNT−PVP contains about 63 wt % SWNT by TGA. SWNT−PVP solutions in DMF, methanol, and 2-propanol are stable for at least 8 months. Atomic force microscopy images show individual tubes. Raman spectra are consistent with debundled SWNT having PVP covalently attached. Near-infrared (NIR) spectra show band gap electronic transitions of SWNT. Layer by layer deposition of alternating thin films of SWNT−PVP and poly(acrylic acid) (PAA) adds a constant amount of SWNT−PVP in each bilayer. FTIR spectra of the films show hydrogen bonding between the PVP and the PAA.

The stages of transformation of a colloidal crystalline film of latex spheres to a new periodic structure were imaged by atomic force microscopy. Colloidal crystalline films were prepared with 320 nm diameter poly(styrene-co-2-hydroxyethyl methacrylate) (PSt/HEMA) spheres. The hexagonally ordered surfaces of the colloidal crystalline films were transformed with styrene vapor at room temperature to a new morphology having holes in the surface and the same periodicity as the original films. The surfaces of colloidal crystals and the transformed films have a raspberry-like texture superposed on the 320 nm hexagonal periodicity. Both height images and phase images reveal that the latex spheres shrink and the transformation proceeds by an order−disorder−order sequence. The final structure is an interconnected colloidal array with smaller polystyrene particles dispersed in a continuous PSt/HEMA matrix.

Single-walled carbon nanotubes (SWNT) were functionalized with polystyrene (PSt) by grafting to and grafting from methods. PSt-N3 with designed molecular weight and narrow molecular weight distribution was synthesized by atom transfer radical polymerization (ATRP) of styrene (St) followed by end group transformation and then added to SWNT. The grafting from functionalization was achieved by ATRP of St using 2-bromopropionate groups immobilized SWNT as initiator. Methyl 2-bromopropionate (MBP) was added as free initiator to control the chain propagation on SWNT during the polymerization. Raman and near-IR spectra show that PSt was covalently attached to the sidewalls of SWNT by the grafting to approach, and the degree of functionalization was about 1 in 48 SWNT carbon atoms as determined by thermogravimetric analyses (TGA). In the grafting from approach, size exclusion chromatography (SEC) results show that the molecular weight of free St increased linearly with St conversion, and the PSt cleaved from the SWNT after high conversion had the same molecular weight as the PSt produced in solution. TGA show that the amount of PSt grafted from the SWNT increased linearly with the molecular weight of the free PSt. By both methods, the final functionalized SWNT dissolved well in organic solvents, and the original SWNT bundles were broken into very small ropes or even individual tubes as revealed by AFM.

Self-association behavior and conformation variation of long chain branched (LCB) poly(2-ethyloxazoline) (PEOx) with a CH3-(CH2)17 (C18) modified surface are investigated using light scattering techniques in various solvents. It is found that this LCB-PEOx self-associates in less polar solvents to form metastable nanoaggregates instead of undergoing precipitation. The critical aggregation concentration (cac) of this LCB polymer was obtained from the sharp increase of both hydrodynamic radius (Rh) and scattering light intensity measured in dynamic light scattering. The cac strongly depends on solvent polarity, decreasing as the solvent becomes more hydrophobic. As the polarity of the solvent increases, C18 chains move from the outside surface to the interior. Inward movement of C18 chains can cause coupled LCB-polymer chains to move with them, resulting in shrinkage of the particle size. The self-association process in the LCB-PEOx involves intrachain (C18 chains) collapse and interchain association. By a combination of dynamic and static light scattering, the average density of individual LCB-PEOx molecules in ethanol was estimated below the cac. The hydrodynamic radius of the LCB-PEOx in ethanol was found to shrink upon increasing temperature, indicating that the solvent becomes poorer. During the heating process, self-association did not occur.

Molecular shuttles have been built from motor proteins capable of moving cargo along engineered paths. We illustrate alternative methods of controlling the direction of motion of microtubules on engineered kinesin tracks, how to load cargo covalently to microtubules, and how to exploit UV-induced release of caged ATP combined with enzymatic ATP degradation by hexokinase to turn the shuttles on and off sequentially. These are the first steps in the development of a tool kit to utilize molecular motors for the construction of nanoscale assembly lines.

This paper describes a simple and convenient method that uses patterned monolayers as templates to fabricate highly ordered 2D arrays of magnetic particles (Co, Ni, or α-Fe, and ferrites such as MgFe2O4 or NiFe2O4) with lateral dimensions in the range of 70−460 nm. In this method, the hydrophilic, hydroxyl-terminated surface of a Si/SiO2 wafer was patterned with a hydrophobic monolayer of octadecyltrichlorosilane using microcontact printing with an elastomeric stamp and subsequently used as template to define and deposit a regular 2D array of 2-propanol droplets that contained inorganic salts such as Co(NO3)2, Ni(NO3)2, and Fe(NO3)3, or a combination of these compounds. Evaporation of the solvent led to the formation of a 2D array of nitrate nanoparticles on the hydrophilic, bare regions of Si/SiO2. Each nanoparticle could be well-positioned within the hydrophilic region by withdrawing the substrate from the nitrate solution and by letting the solvent evaporate with the wafer being held at a specified orientation relative to the gravitational field. The nitrate was subsequently converted into metal oxide (Co3O4, NiO, and α-Fe2O3) by thermal decomposition in air at 600 °C, and finally into a magnetic substance (that is, Co, Ni, and α-Fe) through the reduction by hydrogen gas at 400 °C. The dimensions of these particles could be controlled by changing the concentration of the nitrate solution and/or the area of the hydrophilic region. We have also shown that coprecipitation of two (or more) different nitrates within the liquid droplets could lead to the formation of highly ordered 2D arrays of magnetic ferrites such as MgFe2O4 or NiFe2O4. The magnetic properties of these 2D arrays of nanoparticles supported on silicon substrates were studied using magnetic force microscopy.

Time-resolved Fourier transform IR emission spectroscopy has been used to monitor the population distribution of both the energy giving molecules and the energy receiving molecules during collisional quenching of highly vibrationally excited SO2 by bath-gas SF6. The change in population of the SF6 v3 = 1 level measured as a function of time is compared with that calculated based on the transition dipole coupling model with the transition dipole of highly excited SO2 extracted from its IR emission spectra. The excellent agreement indicates that long-range interaction through transition dipole coupling is responsible for the vibration to vibration energy transfer from the highly excited molecules.

“Living”/controlled radical polymerization of methyl methacrylate (MMA) was successfully carried out using the diethyl 2,3-dicyano-2,3-di(p-tolyl)succinate (DCDTS)/CuCl2/bipy initiation system, in which DCDTS is a hexasubstituted ethane thermal iniferter. The polymerization mechanism belongs to a new reverse atom transfer radical polymerization (ATRP) process with the initiator DCDTS reversibly decomposed to primary radicals in the initiation step. The molecular weights of the resulting PMMA increased with conversion, the molecular weight distributions of PMMA were quite narrow (Mw/Mn < 1.30), and the first-order plots of ln([M]0/[M]) versus time were linear. ¹H NMR analysis of PMMA revealed the presence of an α-(carbethoxy−cyano−tolyl)methyl end group from DCDTS fragments and an ω-chlorine group from catalyst. Since polymer is end-functionalized with a chlorine atom, it can then proceed the chain extension reaction with fresh MMA or the block copolymerization with the second monomer styrene (St) in the presence of CuCl/bipy catalyst.

Analogues of a bipartite compound, dequalinium (DECA) (quinolinium, 1,1‘-(1,10-decanediyl)bis(4-amino-2-methyl diiodide)), were tested for inhibition of protein kinase Cα (PKCα). In vitro assays of monomeric and dimeric analogues support a model in which DECA inhibits PKCα by an obligatory two-point contact, a unique mechanism among PKC inhibitors. The presence of unsaturation in the center of the C10-alkyl linker produced geometric isomers with different inhibitory potencies:  cis IC50 = 52 ± 12 μM and trans IC50 = 12 ± 3 μM, where the trans isomer was equipotent to that of the saturated C10-DECA. DECA analogues with longer, saturated linkers (C12, C14, or C16) exhibited enhanced inhibitory potencies which reached a plateau with the C14-linker (IC50 = 2.6 ± 0.2 μM). Metastatic melanoma cells treated with 250 nM C12-, C14-, or C16-DECA and irradiated with long-wave UV light (which causes irreversible inhibition of PKCα by DECA) confirmed the linker-dependent inhibition of intracellular PKCα activity.