Nucleotides. Part XXVIII. Chemical syntheses of the 2′-5′-cordycepin-trimer core

The chemical synthesis of 3′-deoxyadenyly-(2′-5′)-3′-deoxyadenylyl-(2′-5′)-3′-deoxyadenosine ( 30 ; trimeric cordycepin) is described by three different routes using various protecting groups and applying the phosphotriester approach. The intermediates have been isolated and characterized by elemental analyses and spectroscopic means. High yields of 30 have been obtained on deprotection making this biologically very active compound available in preparative scale.     

Effects of phase separation on crystallization behavior

The effects of phase separation on the kinetics of crystal growth have been investigated for three compositions in the Na₂OSiO₂ system, containing about 1.5, 10 and 15 mol% Na₂O. In the two cases for which reliable data could be obtained over the full range of temperature (10 and 15% Na₂O), the measured growth rates are independent of time, for crystallization temperatures within as well as outside the miscibility gap. In both cases, the growth rate versus temperature relations are continuous through the region of the immiscible boundary. These results are related to previous data on the effects of phase separation on viscosity in the Na₂OSiO₂ system and on nucleation and crystallization in the Li₂OSiO₂ system. It is suggested that transport at the crystal-liquid interface in a phase-separating system involves different types of atomic rearrangements than those involved in viscous flow.     

Combined QCM-D/GE as a tool to characterize stimuli-responsive swelling of and protein adsorption on polymer brushes grafted onto 3D-nanostructures

A combined setup of quartz crystal microbalance and generalized ellipsometry can be used to comprehensively investigate complex functional coatings comprising stimuli-responsive polymer brushes and 3D nanostructures in a dynamic, noninvasive in situ measurement. While the quartz crystal microbalance detects the overall change in areal mass, for instance, during a swelling or adsorption process, the generalized ellipsometry data can be evaluated in terms of a layered model to distinguish between processes occurring within the intercolumnar space or on top of the anisotropic nanocolumns. Silicon films with anisotropic nanocolumnar morphology were prepared by the glancing angle deposition technique and further functionalized by grafting of poly-(acrylic acid) or poly-(N- isopropylacrylamide) chains. Investigations of the thermoresponsive swelling of the poly-(N-isopropylacrylamide) brush on the Si nanocolumns proved the successful preparation of a stimuli-responsive coating. Furthermore, the potential of these novel coatings in the field of biotechnology was explored by investigation of the adsorption of the model protein bovine serum albumin. Adsorption, retention, and desorption triggered by a change in the pH value is observed using poly-(acrylic acid) functionalized nanostructures, although generalized ellipsometry data revealed that this process occurs only on top of the nanostructures. Poly-(N-isopropylacrylamide) is found to render the nanostructures non-fouling properties.     

UV assisted photo reactive polyether-polyesteramide resin for future applications in 3D printing

Among additive manufacturing, photocuring 3D printing technologies are very relevant because of its high printing speed and high precision. However, the limited performance of photosensitive thermoset polymers is the bottleneck for the application of photocuring 3D printing in some fields, particularly in the biomedical sector. Thus, the development of biodegradable and biocompatible materials is highly desirable and of utmost importance. In this work, a biodegradable and non-cytotoxic thermoset polymer for photocuring 3D printing is reported. It consists of an unsaturated polyesteramide bearing phenylalanine, 2-butene-1,4-diol and fumarate building blocks, which is photocured under UV irradiation using a low molecular weight poly(ethylene glycol) diacrylate as crosslinker. The main characteristics of the new thermoset are: (1) very high volumetric and mechanical integrity stabilities, comparable to that of photocured epoxides; (2) very high degradation temperature; (3) very low water absorption capacity; (4) relatively fast enzymatic degradation, reaching 16.5% after 3 months; and (5) non-cytotoxic response in presence of epithelial cells, even when soluble molecular fragments coming from biodegradation are considered. These properties favor the future utilization of the new polyether-polyesteramide resin in the manufacturing of more sustainable products via 3D printing methods, such as stereolithography, that uses UV sources.     

Electromagnetic wormholes and virtual magnetic monopoles from metamaterials

We describe new configurations of electromagnetic (EM) material parameters, the electric permittivity epsilon and magnetic permeability micro, which allow one to construct devices that function as invisible tunnels. These allow EM wave propagation between the regions at the two ends of a tunnel, but the tunnels themselves and the regions they enclose are not detectable to lateral EM observations. Such devices act as wormholes with respect to Maxwell's equations and effectively change the topology of space vis-à-vis EM wave propagation. We suggest several applications, including devices behaving as virtual magnetic monopoles, invisible cables, and scopes for MRI-assisted surgery.     

A polarographic study of propene-maleic anhydride copolymers

The polarographic behaviour of hydrolyzed propene-maleic anhydride copolymers in the interval pH 2.0–11.0 has been investigated by differential pulse polarography in aqueous lithium chloride solution at 25°C. In dependence on the pH-value, one, two or three signals, belonging to the acid groups in the copolymer, appear in the polarograms. Three apparent polarographic acid constants have been determined graphically from the changes in the half-wave potential of the separate peaks in correlation with pH.     

SIMS-AES investigations on water vapour adsorption on nickel (100) at room temperature

By means of the methods SIMS and AES the adsorption of water vapour on the (100) surface of nickel was studied. We conclude from the results obtained that the adsorption has three stages: chemisorption of OH groups, formation of a surface hydroxide and finally, formation of an oxide layer containing O and OH. The quantity of oxygen detected corresponded maximally to about a monolayer coverage.     

SIMS-AES investigations of the oxygen adsorption on the (110) surface of Fe71Ni29

Oxygen adsorption was investigated on the (110) surface of Fe₇₁Ni₂₉ at room temperature by means of the methods AES and SIMS. Three stages of interaction of oxygen with the surface could be determined. A dissociative chemisorption occurs in the dose range up to 5 L, surface oxides are nucleated between 5 L and about 40 L, and in the case of longer oxygen exposures a thicker oxide layer grows. At first, iron and nickel contribute to the surface reaction in like manner.     

An example of a non-linear evolution equation showing ‘chaos-enhancement’

It is shown that for a non-linear evolution equation—a caricature of Boltzmann's equation—a family of H-theorems exists.