Near-monodisperse,n-alkyl,end-functionalized poly(methyl vinyl ether)s: Synthesis by living cationic polymerization and solution characterization

Water-soluble amphiphilic diblock copolymers were synthesized by the living cationic polymerization of methyl vinyl ether (hydrophilic block) and its subsequent termination with n-alcohols of chain lengths varying from one to eight, and three n-alkyl carboxylic acids with 10, 12, and 18 carbon atoms. Additionally, water and ethylene glycol were tested as terminating agents. The extent of the functionalization was determined using ¹H NMR spectroscopy. The cloud points of 1% w/w aqueous solutions of the polymers as determined by turbidimetry decreased from 32 to 21°C as the number of carbon atoms of the terminating agent increased. Aqueous GPC revealed micellization of the stearic acid-terminated block copolymer, while the other block copolymers existed mainly as unimers. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2547–2554, 1998     

Simulating brain tumor heterogeneity with a multiscale agent-based model: Linking molecular signatures,phenotypes and expansion rate

We have extended our previously developed 3D multi-scale agent-based brain tumor model to simulate cancer heterogeneity and to analyze its impact across the scales of interest. While our algorithm continues to employ an epidermal growth factor receptor (EGFR) gene–protein interaction network to determine the cells’ phenotype, it now adds an implicit treatment of tumor cell adhesion related to the model’s biochemical microenvironment. We simulate a simplified tumor progression pathway that leads to the emergence of five distinct glioma cell clones with different EGFR density and cell ‘search precisions’. The in silico results show that microscopic tumor heterogeneity can impact the tumor system’s multicellular growth patterns. Our findings further confirm that EGFR density results in the more aggressive clonal populations switching earlier from proliferation-dominated to a more migratory phenotype. Moreover, analyzing the dynamic molecular profile that triggers the phenotypic switch between proliferation and migration, our in silico oncogenomics data display spatial and temporal diversity in documenting the regional impact of tumorigenesis, and thus support the added value of multi-site and repeated assessments in vitro and in vivo. Potential implications from this in silico work for experimental and computational studies are discussed.     

Experimental observation of true left-handed transmission peaks in metamaterials

We report true left-handed (LH) behavior in a composite metamaterial consisting of a periodically arranged split ring resonator (SRR) and wire structures. We demonstrate the magnetic resonance of the SRR structure by comparing the transmission spectra of SRRs with those of closed SRRs. We have confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined LH transmission band with a peak value of -1.2 dB (-0.3 dB/cm) was obtained. The experimental results agree extremely well with the theoretical calculations.     

Transillumination spatially modulated illumination microscopy

The diagnostic utility of a conventional transillumination microscope, the most common imaging modality in clinical use today, is limited by the microscope's resolution. It is, however, possible to achieve lateral resolution well beyond the classical limit by using laterally structured illumination in a wide-field, nonconfocal microscope. In this method, the spatially modulated illumination (SMI) makes high-resolution information that is normally inaccessible visible in the observed image. Previously presented SMI microscopy systems operated in epifluorescence mode. We describe the design, construction, and testing of a novel transillumination SMI microscope. As transillumination is necessary for most medical applications, such as histopathologic evaluation of biopsy tissue and chromosomal analysis, such a system should have a significant diagnostic effect.     

Liquid chromatographic profiles of individual compounds of technical toxaphene

The elution orders of 20 hexa- to nonachlorobornanes and five hexa- to octachlorocamphenes were studied with normal-phase silica and amino phase HPLC, reversed-phase HPLC, as well as gel-permeation chromatography (GPC). Twenty-one compounds of technical toxaphene (CTTs) are commercially available and four were isolated from environmental samples. Structure-activity relationships and chromatographic properties were deduced from the data sets derived on these LC systems. The retention on silica (low-resolution LC and HPLC) increased with the polarity of the CTTs. The elution order of CTTs on amino normal-phase HPLC was, for the most part, the same as on silica normal-phase HPLC. The degree of chlorination determined the elution order of CTTs on C18 RP-HPLC. CTTs eluted from medium-pressure GPC with decreasing molecular size. Chlorobornanes with dichloro substituents on the six-membered ring eluted after the chloroboranes without geminal chlorine atoms on secondary carbons, indicating that these congeners are larger. Altogether, the results increase the knowledge of complex substance class and may serve as a tool in order to gain further standard components.     

Spectroscopic,Electrochemical and Computational Characterisation of Ru Species Involved in Catalytic Water Oxidation: Evidence for a [RuV(O)(Py2Metacn)] Intermediate

A new family of ruthenium complexes based on the N‐pentadentate ligand Py₂^Metacn (N‐methyl‐N′,N′′‐bis(2‐picolyl)‐1,4,7‐triazacyclononane) has been synthesised and its catalytic activity has been studied in the water‐oxidation (WO) reaction. We have used chemical oxidants (ceric ammonium nitrate and NaIO₄) to generate the WO intermediates [Ru^II(OH₂)(Py₂^Metacn)]²⁺, [Ru^III(OH₂)(Py₂^Metacn)]³⁺, [Ru^III(OH)(Py₂^Metacn)]²⁺ and [Ru^IV(O)(Py₂^Metacn)]²⁺, which have been characterised spectroscopically. Their relative redox and pH stability in water has been studied by using UV/Vis and NMR spectroscopies, HRMS and spectroelectrochemistry. [Ru^IV(O)(Py₂^Metacn)]²⁺ has a long half‐life (>48 h) in water. The catalytic cycle of WO has been elucidated by using kinetic, spectroscopic, ¹⁸O‐labelling and theoretical studies, and the conclusion is that the rate‐determining step is a single‐site water nucleophilic attack on a metal‐oxo species. Moreover, [Ru^IV(O)(Py₂^Metacn)]²⁺ is proposed to be the resting state under catalytic conditions. By monitoring Ce^IV consumption, we found that the O₂ evolution rate is redox‐controlled and independent of the initial concentration of Ce^IV. Based on these facts, we propose herein that [Ru^IV(O)(Py₂^Metacn)]²⁺ is oxidised to [Ru^V(O)(Py₂^Metacn)]²⁺ prior to attack by a water molecule to give [Ru^III(OOH)(Py₂^Metacn)]²⁺. Finally, it is shown that the difference in WO reactivity between the homologous iron and ruthenium [M(OH₂)(Py₂^Metacn)]²⁺ (M=Ru, Fe) complexes is due to the difference in the redox stability of the key M^V(O) intermediate. These results contribute to a better understanding of the WO mechanism and the differences between iron and ruthenium complexes in WO reactions.     

Oligo(ethylene imine)-grafted glycidyl methacrylate linear and star homopolymers: Odd–even correlated transfection efficiency

The present study aims to investigate an odd–even effect of the number of ethylene imine units in the side-groups of totally abiotic synthetic polymers on their efficiency in DNA transfection. A library of fifteen polymers was fabricated. Two star homopolymers and one linear homopolymer based on glycidyl methacrylate were synthesized and used as precursors to which five linear oligo(ethylene imine)s (OEI) were grafted. The number of ethylene imine groups of the OEIs was varied. Specifically, ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine were used. Each of these fifteen OEI-grafted polymers was evaluated in terms of their efficiency to transfer plasmid DNA encoding firefly luciferase in C2C12 mouse myoblast cells. The transfection efficiency displayed an odd-even pattern, with all OEI-grafted polymers with an odd number of ethylene imine repeating units exhibiting higher transfection efficiency compared with those possessing an even number of ethylene imine repeating units. The odd–even effect was more pronounced for the star polymers with longer arms (degree of polymerization, DP = 100), while in case of the linear polymers, the odd–even effect was only observed for the lowest polymer loading. The cytotoxicity of the OEI-grafted polymers also followed an odd–even pattern, with the OEI-grafted star polymers with an arm DP of 100 and the linear polymers clearly presenting an odd-even effect, while the cytotoxicity of the OEI-grafted star polymers with an arm DP of 20 slightly increased with the number of ethylene imine repeating units.