An Access Route to Polyferrocenes via Modular Conjugation

The application of copper‐catalyzed azide/alkyne cycloaddition to monomers containing a ferrocene unit leads to polyferrocenes with ferrocene in the backbone. Catalyst performance and kinetic studies of a model system comprising 1,1'‐bis(azidoethyl)ferrocene and propargyl ether revealed the usage of CuI and DBU as the catalyst in DMF at 50 °C as efficient reaction conditions for the synthesis. The resulting polymers display molecular weight‐averages up to $\overline {M} _{{\rm n}} $ = 10 000 and $\overline {M} _{{\rm w}} $ = 33 000. The polyaddition of monomers both containing ferrocene units led to polyferrocenes with $\overline {M} _{{\rm n}} $ between 4 000 and 11 000 ($\overline {M} _{{\rm w}} $ up to 78 000). The present study thus provides a pathway to polyferrocenes based on modular ligation chemistry.

     

Characterization of the timing and prevalence of receptor tyrosine kinase expression changes in oesophageal carcinogenesis

Despite being common in epithelial malignancies, the timing of receptor tyrosine kinase (RTK) up‐regulation is poorly understood and therefore hampers the identification of the receptor to target for effective treatment. We aimed to determine if RTK expression changes were early events in carcinogenesis. Oesophageal adenocarcinoma and its pre‐invasive lesion, Barrett's oesophagus, were used for immunohistochemical analysis of the RTK panel, EGFR, ErbB2, ErbB3, Met, and FGFR2, by utilizing a cohort of patients with invasive disease ($n = 367$ ) and two cohorts with pre‐invasive disease, one cross‐sectional ($n = 110$ ) and one longitudinal in time ($n = 91$ ). The results demonstrated that 51% of oesophageal adenocarcinomas overexpressed at least one of the RTK panel, with 21% of these overexpressing multiple receptors. Up‐regulation of RTK expression was an early event corresponding with low‐grade dysplasia development (25% in areas without dysplasia versus 63% in low‐grade dysplasia, $p < 0.001$ ). There was a trend for an increase in the prevalence of concomitant overexpression of multiple receptors as intestinal metaplasia progressed to low‐grade dysplasia, 7% versus 10%; and from low‐grade dysplasia to high‐grade dysplasia, 10% versus 19% ($p = 0.06$ and 0.24, respectively). The timing of receptor up‐regulation varied; FGFR, ErbB2, and Met overexpression occurred as dysplasia first developed, whilst EGFR overexpression was predominately seen in invasive disease and ErbB3 overexpression was uniformly rare. We provide evidence for a frequent and early role for multiple different RTKs in oesophageal carcinogenesis. Given the early timing of receptor deregulation, inhibiting RTKs in pre‐invasive disease may also represent a novel and effective chemopreventive strategy. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Enhancing the Activity and Thermal Stability of Iron Precatalysts Using 2‐(1‐{2,6‐bis[bis(4‐fluorophenyl)methyl]‐4‐methylphenylimino}ethyl)‐6‐[1‐(arylimino)ethyl]pyridines

A series of 2‐(1‐{2,6‐bis[bis(4‐fluorophenyl)methyl]‐4‐methylphenylimino}ethyl)‐6‐ [1‐(arylimino)ethyl]pyridine ligands is synthesized and fully characterized. The corresponding iron complexes are prepared and characterized by single‐crystal X‐ray diffraction for representative iron complexes, among other methods, revealing a pseudo square‐pyramidal geometry at the iron center. Upon activation with MMAO, all iron precatalysts exhibit high activity in ethylene polymerization, producing linear polyethylene. The observed activity is the highest reported for iron‐based precatalysts of this type. The polymerization parameters are shown to strongly affect the catalytic behavior, and both the activity and the polymer properties (i.e. $ \overline{M}_{\rm w}$ or $ \overline{M}_{\rm w}$ /$ \overline{M}_{\rm n}$ ) can be controlled.     

SP1 mediates the link between methylation of the tumour suppressor miR‐149 and outcome in colorectal cancer

Although recent studies indicate that DNA methylation contributes to the down‐regulation of microRNAs (miRNAs) in colorectal cancer (CRC), this field remains largely unexplored. To identify methylation‐silenced miRNAs and clarify their role in CRC, we performed a microarray analysis and screened for miRNAs that were induced in CRC cells by 5‐aza‐2′‐deoxycytidine treatment or by the knockdown of DNA methyltransferases. The DNA methylation status of the candidate miRNA was analysed by bisulphite sequencing PCR and methylation‐specific PCR. We found that miRNA‐149 (miR‐149) was epigenetically silenced in CRC and down‐regulation of miR‐149 was associated with hypermethylation of the neighbouring CpG island (CGI). Quantitative RT‐PCR analysis demonstrated that the miR‐149 level was markedly reduced in 51.6% of the CRC tissues compared with matched non‐cancerous tissues. In addition, low expression of miR‐149 was associated with a greater depth of invasion ($\it{p} = 0.012$ ), lower 5‐year survival rate ($\it{p} = 0.025$ ), and was found to be an independent prognostic factor for overall survival ($\it{p} = 0.016$ ) in a multivariate analysis. Moreover, transfection of miR‐149 inhibited cell growth and invasion of CRC cells in vitro. We also identified mRNA for Specificity Protein 1 (SP1, Sp1), a potential oncogenic protein, as a target of miR‐149. Our data suggest that, as a methylation‐sensitive miRNA, miR‐149 may play an important role as a tumour suppressor in CRC, which has prognostic and therapeutic implications. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Thermally Curable Polyoxanorbornene by Ring Opening Metathesis Polymerization

A novel norbornene monomer bearing a thermally curable benzoxazine group is synthesized and polymerized by ROMP using the Grubbs first‐generation ruthenium catalyst. The $\overline {M} _{{\rm w}} $ of the side‐chain benzoxazine functionalized polyoxanorbornene can be up to 87 000 Da with unimodal molecular‐weight distribution and narrow polydispersity between 1.18 and 1.65. Thermally activated ring‐opening polymerization of benzoxazine moieties leads to the formation of highly cross‐linked structures. The effects of molecular weight on the thermal ROP of polybenzoxazine precursors are examined.

     

Molar Mass and Microstructure Analysis of PI‐b‐PMMA Copolymers by SEC‐NMR

The online coupling of size‐exclusion chromatography and NMR is used to characterize block copolymers consisting of polyisoprene (PI) and poly(methyl methacrylate) (PMMA) regarding their distributions of molar mass (MMD) and chemical composition (CCD). Using the CCD, $\overline{M}_{\rm n}$ and $\overline{M}_{\rm w}$ are calculated on the basis of PI and PMMA homopolymer calibrations. The microstructure distribution of PMMA and the distribution of isomeric units of PI in dependence of molar mass is also demonstrated. Furthermore, a simulation analysis is presented for a bimodal eluting sample. It allows for full separation, quantification and molar mass determination of the coeluting co‐ and homopolymer fractions. The quantification of the fractions is verified by liquid chromatography at critical conditions.     

Bismuth‐Triflate‐Catalyzed Polymerizations of ε‐Caprolactone

εCL was polymerized using the triflates of lanthanum, samarium, magnesium, aluminum, scandium, and bismuth as catalysts. Bismuth triflate proved to be extraordinarily reactive, and catalyzed polymerizations of εCL even at 20 °C. Adding DTBMP reduced the polymerization rate only slightly. Furthermore, no evidence of a cationic mechanism was found by end‐group analyses. Polymerization at 20 °C either in bulk or in solution only yielded polyesters of low or medium molecular weights ($\overline {M} _{{\rm n}} $ up to 30 000 Da). Yet addition of alcohols allowed for a proper control of molecular weight and end‐groups. Additionally, low catalyst concentrations and low temperature resulted in narrow molecular weight distributions and polylactones almost free of cyclic compounds.

     

Polymer Loops vs. Brushes on Surfaces: Adsorption,Kinetics, and Viscoelastic Behavior of α,ω‐Thiol Telechelics on Gold

Telechelic thiopolymers were explored towards formation of doubly‐bound (polymer loops) vs. singly‐bound (polymer brushes) chains on gold substrates. The conformation, adsorption kinetics, and viscoelastic properties of the α,ω‐dithiol and monothiol PS telechelics were investigated by means of XPS and QCM‐D techniques. The oxidation behavior of the free thiol proved to be important for distinguishing doubly‐bound vs. singly‐bound chains. The results show a critical dependence of $\overline {M} _{{\rm n}} $ on the ability to obtain polymer loops. Comparison with unperturbed dimensions obtained by scaling theory show that the loop is less stretched and occupies more lateral space than the brush. The results are important in demonstrating the different and perhaps superior properties of polymer loops vs. singly‐bound polymer brushes.

     

Influence of Molecular Weight on Physical and Mechanical Properties of Linear Symmetric S‐(S/B)‐S Triblock Copolymers

Symmetric linear S‐(S/B)‐S triblock copolymers with 80 wt.‐% of PS having a block composition of 20‐60‐20 and a S/B ratio of 70:30 in the middle block are studied with varying molecular weights ( ). Increase in the leads to a change in the morphology from disordered to ordered microphase separated structure, as characterised by TEM and SAXS. Two distinct glass transitions for PS‐ and PB‐rich phases are observed from DMA measurements, which are due to phase separation at high . Rheological studies (master curves) reveal an extended rubbery plateau and a delay in the terminal response with an increase in , whereas a terminal flow behaviour is observed for materials having a disordered nature at low . A brittle‐to‐tough transition is observed from tensile tests with the increase in .

     

Parallel Synthesis of Polymer Libraries Using Atom Transfer Radical Polymerization (ATRP)

Parallel atom transfer radical polymerization (ATRP) of styrene and t‐butyl acrylate (t‐BA) was investigated. A series of ATRP polymerizations were carried out in parallel with varying targeted molecular weight ( ) and showed excellent reproducibility of , polydispersity, and conversion. In addition, polymerizations were done to determine the effect of inhibitor on styrene polymerization, yielding similar results. In synthesizing a library of polymers having varying using ATRP, polymers having lower reach their target values earlier and the others continue to react under heating, resulting in peak broadening for the low polymers. Reinitiation experiments indicated that termination reactions were taking place resulting in “dead” polymer chains which were unable to reinitiate polymerization.

     

Enzymatic Synthesis and Chemical Recycling of Polythiocaprolactone

High‐molecular‐weight polythiocaprolactone (PTCL) was prepared in a green process via lipase‐catalyzed ROP of a cyclic 6‐mercaptohexanoic acid (6MH) oligomer. PTCL was readily depolymerized by lipase to cyclic 6MH in dilute toluene solution, which was then readily repolymerized by the same lipase to produce PTCL with the same $\overline {M} _{{\rm w}} $ as the initial PTCL in a chemical recycling process. The T_m of PTCL was higher than that of the corresponding PCL. A P(TCL‐co‐CL) copolymer with 60 mol‐% TCL (6MH) units showed a higher T_m as the PCL homopolymer. Similar apparent K_m values were obtained for the cyclic 6MH oligomers and caprolactone oligomers, however, the V_max of cyclic 6MH oligomers was significantly lower than that of the corresponding caprolactone oligomers.

     

Amphiphilic PEG‐b‐PMCL‐b‐PDMAEMA Triblock Copolymers: From Synthesis to Physico‐Chemistry of Self‐Assembled Structures

A synthetic route toward a new family of amphiphilic mPEG‐b‐PMCL‐b‐PDMAEMA triblock copolymers is reported. Chemical structures and compositions are confirmed by ¹H NMR and SEC. Polydispersity indices are typically <1.4, indicating good control of the reactions. The physicochemical parameters associated with mPEG‐b‐PMCL‐b‐PDMAEMA self‐assembled structures are investigated. Nanoparticles are prepared via a co‐solvent method, and parameters such as nanoparticle $\overline {M} _{{\rm w}} $ , N_agg, A₂, and R_h are calculated based on static and dynamic light scattering data. Critical aggregation concentrations for the polymers are determined by measuring surface tensions of polymer solutions. TEM is employed to visualize the morphology of the assemblies.

     

Syntheses of Polyesters from Succinic Anhydride and Various Diols Catalyzed by Metal Triflates

Succinic anhydride (SuAh) was polymerized with various α,ω‐alkanediols from 1,3‐propanediol up to 1,10‐decanediol. Most polycondensations were conducted in bulk at temperatures of 80 °C with bismuth triflate as catalyst and number average molecular weights ( , uncorrected SEC data) up to 35 000 Da were obtained. Polycondensations of SuAh with 1,6‐hexanediol were also catalyzed with aluminum, tin(II), scandium, lanthanium, samarium, and hafnium triflate. Whereas, poor results were achieved with La‐triflate, aluminum and tin(II) triflate yielded comparable to those obtained with Bi‐triflate. With exception of the basic lanthanum triflate, all other catalysts generated small amounts of ether groups. The MALDI‐TOF mass spectra proved that the molecular weights depended on the conversion and on the extent of cyclization. The polycondensations of 1,4‐butanediol at temperatures up to 120 °C were affected by the formation of tetrahydrofuran, and even with an excess of the diol <10 000 Da were not obtained. Yet, BiCl₃ and Bi‐triflate catalyzed polycondensations in refluxing decalin gave satisfactory results ( ≈ 30 000 Da, uncorrected SEC data).

     

Controlled/“Living” Radical Polymerization of Methyl Methacrylate Catalyzed by Cobalt Acetate

Using cobalt acetate as a catalyst, the controlled/“living” polymerization of MMA was carried out. PMMA with a predicted molecular weight and a low polydispersity was obtained. Using the obtained PMMA as a macroinitiator, a chain extension reaction was carried out. This increased the molecular weight of PMMA from 23 600 to 36 100, in good agreement with the predicted value, and the polydispersity index became lower . This indicated the “living” character of the polymerization. Bulk polymerization of styrene catalyzed by cobalt acetate using the obtained polystyrene as a macroinitiator yielded well‐defined PS‐b‐PMMA.

     

Spontaneous Deposition of FITC‐Labeled Dextran into Covalently Assembled (PGMA/PAH)4 Microcapsules

Spontaneous deposition of fluorescein isothiocyanate labeled dextran (FITC‐dextran) in covalently assembled poly(glycidyl methylacrylate) (PGMA)/poly(allylamine hydrochloride) (PAH) microcapsules was studied and its mechanism was proposed. Incubation of the microcapsules in the FITC‐dextran solution resulted in strong fluorescence emission from the capsule interiors. The deposition was found to be molecular weight ( ) dependent and the number of capsules filled with FITC‐dextran was increased along with the of FITC‐dextran. Furthermore, the correlation between the deposited substances and the charged species in the capsules was explored quantitatively through UV–Vis and fluorescence spectroscopy.

     

p53 mutation and loss have different effects on tumourigenesis in a novel mouse model of pleomorphic rhabdomyosarcoma

Pleomorphic rhabdomyosarcoma is the most common variant of this tumour in adults and has a very poor outcome. Two genes which are known to play a role in rhabdomyosarcoma development are KRas and p53. In the majority of human tumours, p53 abnormalities are point mutations that result in the expression of a mutant form of the protein. It is now hypothesized that these mutant forms of p53 may be playing an oncogenic role, over and above simple loss of the wild‐type function. In this study, we use Cre‐LoxP technology to develop a novel mouse model of rhabdomyosarcoma, crossing mice expressing a common KRas mutation (G12V) with mice that either lose p53 expression or express a mutant form of p53. We use this model to explore the different effects of p53 loss and mutation in the setting of an activating KRas mutation. We found that either complete loss of p53 (p53 ) or the expression of one mutant p53 allele with concomitant loss of the second allele (p53 ) resulted in the rapid development of rhabdomyosarcoma in 15/16 and 19/19 mice, respectively. In contrast, there was a marked difference between mice which lose a single copy of p53 (p53 ) and mice expressing a single copy of mutant p53 (p53 ). Fourteen out of 16 p53 mice developed rhabdomyosarcoma, compared with two out of 31 p53 mice. As a consequence of this, p53 mice had a median lifespan nearly double that of the p53 mice. To underline the enhanced effect of p53 mutation in tumour progression, metastases were seen only in those mice which expressed the mutant form. These data demonstrate that mutant p53 can co‐operate with activated, mutant KRas to influence tumourigenesis and metastatic potential, over and above simple loss of normal protein function. Copyright © 2010 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Long‐Chain Branches in Syndiotactic Polypropene Induced by Vinyl Chloride

Syndiotactic polypropene was synthesized using a metallocene catalyst system and traces of VC. The use of VC was found to decrease the molar mass of the samples distinctly and linearly, while retaining the molar mass distribution, the crystallinity, and the syndiotacticity. The VC, however, initiates the formation of long‐chain branches, which were detected by GPC‐MALLS and rheology. Besides their effect on the viscosity and modulus functions, a thermorheologic complexity can be observed. Also the flow activation energy E_a was found to be increased. The modified samples did not obey the relation for linear sPP, indicating the presence of LCBs.

     

Acetyl Halide Initiator Screening for the Cationic Ring‐Opening Polymerization of 2‐Ethyl‐2‐Oxazoline

Kinetic investigations on the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline were conducted using acetyl chloride, acetyl bromide, and acetyl iodide as initiators. Various polymerization temperatures ranging from 80 to 220 °C were applied under microwave irradiation. The resulting polymerization mixtures were characterized with GC and GPC for the determination of monomer conversion and molecular weight distribution, respectively. Well defined polymers with narrow molecular weight distributions ( = 6 000 Dalton, PDI ≈ 1.10) were obtained with all three initiators.

     

Controlled RAFT Polymerization of N‐Vinylphthalimide and its Hydrazinolysis to Poly(vinyl amine)

Polymerization of NVPI was carried out by a RAFT process using five xanthate‐type, a dithiocarbamate‐type, and a dithioester‐type CTA. The xanthate‐type [O‐ethyl‐S‐(1‐ethoxy carbonyl) ethyl dithiocarbonate and O‐ethyl‐S‐(1‐ethoxycarbonyl‐1‐methyl)ethyl dithiocarbonate] and the dithiocarbamate‐type CTA (benzyl‐1‐pyrrolecarbodithioate) were the most efficient to obtain poly(NVPI) with controlled molecular weights ( = 4 100–13 000) and low polydispersities ( = 1.29–1.38). The effects of parameters such as solvent, temperature, and CTA‐to‐initiator molar ratio, were examined in order to determine the conditions leading to optimal control of the polymerization.

     

AB2 Functional Polyesters via Ring Opening Polymerization: Synthesis and Characterization

Aliphatic AB₂ functional polyesters were conveniently prepared by the ring opening polymerization of ε‐caprolactone and L ‐lactide in the presence of the AB₂ functional initiator 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) and Sn(Oct)₂ as the catalyst. In L ‐lactide polymerization, both bis‐MPA hydroxyl groups initiated the polymerization reaction, but for ε‐caprolactone polymerization this depended on the monomer to initiator to catalyst ratio. Initiation at two hydroxyl groups occurred at high monomer to initiator ([M]/[I]) ratio and at high Sn(Oct)₂ to monomer ratio. The melting temperatures of the AB₂‐functional PLLA and PCL polymers were comparable to linear polymers with a equal to the per arm in the polymer.