Experimental design applied to spin coating of 2D colloidal crystal masks: a relevant method?

Monolayers of colloidal spheres are used as masks in nanosphere lithography (NSL) for the selective deposition of nanostructured layers. Several methods exist for the formation of self-organized particle monolayers, among which spin coating appears to be very promising. However, a spin coating process is defined by several parameters like several ramps, rotation speeds, and durations. All parameters influence the spreading and drying of the droplet containing the particles. Moreover, scientists are confronted with the formation of numerous defects in spin coated layers, limiting well-ordered areas to a few micrometers squared. So far, empiricism has mainly ruled the world of nanoparticle self-organization by spin coating, and much of the literature is experimentally based. Therefore, the development of experimental protocols to control the ordering of particles is a major goal for further progress in NSL. We applied experimental design to spin coating, to evaluate the efficiency of this method to extract and model the relationships between the experimental parameters and the degree of ordering in the particles monolayers. A set of experiments was generated by the MODDE software and applied to the spin coating of latex suspension (diameter 490 nm). We calculated the ordering by a homemade image analysis tool. The results of partial least squares (PLS) modeling show that the proposed mathematical model only fits data from strictly monolayers but is not predictive for new sets of parameters. We submitted the data to principal component analysis (PCA) that was able to explain 91% of the results when based on strictly monolayered samples. PCA shows that the ordering was positively correlated to the ramp time and negatively correlated to the first rotation speed. We obtain large defect-free domains with the best set of parameters tested in this study. This protocol leads to areas of 200 μm(2), which has never been reported so far.     

Local structure and triplet energy migration in p-dichlorobenzene-p-dibromobenzene solid solutions

Studies of the first triplet absorption and emission spectra of p-dichlorobenzene-p-dibromobenzene (DCB-DBB) mixed crystals agree generally with the data, indicating that this system forms solid solutions. However, the spectral properties are found to be very different from that of isotopically mixed crystals of comparable concentrations. The singlet-triplet absorption spectra of the DCB-DBB mixtures are generally broad and not amenable to detailed analysis indicating significant site dependent perturbations of the DCB and DBB triplet energies. Energy migration enhances emission from the lower energy sites and in consequence a red shift in the position of the emission (0,0) is observed, which is a maximum at equimolar concentrations. The emission bands are generally much broader than found for isotopically mixed crystals, indicating that the many types of sites in the DCB-DBB system remained uncoupled. This is a direct consequence of exciton trapping by inhomogeneous energy broadening caused by the site energy disorder being greater than the triplet exciton band width. Long-range triplet energy migration is not observed at DCB concentrations less than 99 per cent. This high limit is only expected for near one-dimension energy migration topologies. New structure observed at low DCB concentrations is tentatively interpreted as being due to the formation of DCB n-mers. The observed splittings indicate that the gas-to-crystal shift of the DCB T ₁ state increases (becomes more negative) by 11 cm^-1 when a neighbouring DBB molecule is replaced by DCB.     

3-Hydroxy-1,4-diphenyl-7-oxabicyclo[4.1.0]hept-3-ene-2,5-dione. A microbial product from streptomyces species (AAA566)

The epoxyenedione 1a has been isolated from a strain $\text{Streptomyces}$ and its structure has been established by nmr spectroscopy and by its conversion to 2,5-diphenyl-3,4-dihydroxyphenol. Selective hetero J-resolved nmr spectroscopy played a pivotal role in the structure elucidation.     

Polybenzoylenebenzimidazoles

A polyamide amino acid was prepared by the solution condensation of 3,3′-diaminobenzidine and pyromellitic dianhydride. This polymer was cast as a film and converted to a polybenzoylenebenzimidazole. The gross conversion path was elucidated by spectroscopy and was substantiated by model compound studies. A novel ladder polymer was prepared from 1,2,4,5-tetraaminobenzene and pyromellitic dianhydride.     

Energy transfer in constant period free-electron lasers

A simple single particle model of a free-electron laser (FEL) amplifier has been used in a computer simulation to determine the maximum fractional conversion of electron kinetic energy to laser energy. The simulation results can be represented by a single universal curve. A simple scaling relationship for the length of the optimized constant period helix together with the universal curve permit one to predict maximum fractional energy conversion for any set of values of initial electron energy, initial laser intensity, magnetic field amplitude, and magnet period.     

Photodissociation spectrum of CH3I+ prepared by multiphoton ionization

Two-photon resonant multiphoton ionization has been used to prepare rotationally cooled and selected CH₃I⁺ ions with controlled vibrational and electronic distributions. These ions are photodissociated by a second laser. The highly simplified photodissociation spectrum displays a clear dissociation threshold as well as bands hidden in earlier spectra. The data suggests corrections to previously determined vibrational constants.     

Enhancement of the critical temperature of HgBa₂CuO(4+δ) by applying uniaxial and hydrostatic pressure: implications for a universal trend in cuprate superconductors

It is well known that the superconducting transition temperature (T(c)) of cuprate superconductors can be enhanced by varying certain structural and electronic parameters, such as the flatness of the CuO? planes or their doping level. We determine the uniaxial and hydrostatic pressure derivatives of T(c) in the structurally simple tetragonal compound HgBa?CuO(4+δ) near optimal doping. Our results provide experimental evidence for two further methods to enhance T(c): (i) reducing the area of the CuO? planes, and (ii) increasing the separation of the CuO? planar groups. T(c) is found to couple much more strongly to the ratio c/a of the lattice constants than to the unit cell volume. A comparison with prior results for structurally more complicated cuprates reveals a general trend of uniaxial pressure derivatives with T(c).     

Temperature dependence of the gap size near the brillouin-zone nodes of HgBa2CuO4+delta superconductors

Although more than 20 years have passed, the identification of the superconducting order parameter in cuprates is still under debate. Here, we show that the gap size near the nodes is a good candidate for the order parameter: it scales with the critical temperature Tc over a wide doping range and displays a significant temperature dependence below Tc in both the underdoped and the overdoped regimes. In contrast, the gap size at the antinodes does not scale with Tc in the underdoped regime and appears to be controlled by the pseudogap which persists below Tc.     

G-quadruplex DNA assemblies: loop length, cation identity, and multimer formation

G-rich DNA sequences are able to fold into structures called G-quadruplexes. To obtain general trends in the influence of loop length on the structure and stability of G-quadruplex structures, we studied oligodeoxynucleotides with random bases in the loops. Sequences studied are dGGGW(i)GGGW(j)GGGW(k)GGG, with W = thymine or adenine with equal probability, and i, j, and k comprised between 1 and 4. All were studied by circular dichroism, native gel electrophoresis, UV-monitored thermal denaturation, and electrospray mass spectrometry, in the presence of 150 mM potassium, sodium, or ammonium cations. Parallel conformations are favored by sequences with short loops, but we also found that sequences with short loops form very stable multimeric quadruplexes, even at low strand concentration. Mass spectrometry reveals the formation of dimers and trimers. When the loop length increases, preferred quadruplex conformations tend to be more intramolecular and antiparallel. The nature of the cation also has an influence on the adopted structures, with K(+) inducing more parallel multimers than NH4(+) and Na(+). Structural possibilities are discussed for the new quadruplex higher-order assemblies.     

Stretch‐Induced Drug Delivery from Superhydrophobic Polymer Composites: Use of Crack Propagation Failure Modes for Controlling Release Rates

The concept of using crack propagation in polymeric materials to control drug release and its first demonstration are reported. The composite drug delivery system consists of highly‐textured superhydrophobic electrosprayed microparticle coatings, composed of biodegradable and biocompatible polymers poly(caprolactone) and poly(glycerol monostearate carbonate‐co‐caprolactone), and a cellulose/polyester core. The release of entrapped agents is controlled by the magnitude of applied strain, resulting in a graded response from water infiltration through the propagating patterned cracks in the coating. Strain‐dependent delivery of the anticancer agents cisplatin and 7‐ethyl‐10‐hydroxycamptothecin to esophageal cancer cells (OE33) in vitro is observed. Finally the device is integrated with an esophageal stent to demonstrate delivery of fluorescein diacetate, using applied tension, to an ex vivo esophagus.