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We present here the thermodynamic investigation of in situ cascade polycondensation-coupling ring-opening polymerization (PROP) for three cyclic aromatic ester monomers, i.e., cyclic oligo(2-methyl-1,3-propylene terephthalate)s (COMPTs), cyclic oligo(neopentylene terephthalate)s (CONTs) and cyclic oligo(2-methyl-2-propyl-1,3-propylene terephthalate)s (COMPPTs). The equibrium monomer to polymer weight ratio in bulk at different polymerization temperatures for each monomer was estimated by the size exclusion chromatography (SEC), and the thermodynamic parameters were estimated by Dainton equation. Quite different from the thermodynamics of aliphatic lactones polymerization, which is an exothermic process with entropy reduction, our results showed the polymerization thermodynamics for three cyclic aromatic ester monomers was a weak exothermic process with slight entropy increment, i.e., a both enthalpy and entropy driving process. Among them, CONTs showed the largest value of enthalpy change, due to its symmetric dimethyl substitution on β-position of propandiol segments. [ABSTRACT FROM AUTHOR]

Abstract: We report the design, synthesis and biological evaluation of a novel 99mTc 4-(4-cyclohexylpiperazine-1-yl)-butan-1-one-1-cyclopentadienyltricarbonyl technetium ([99mTc]5) as a potential SPECT tracer for imaging of σ2 receptors in tumors. [99mTc]5 was prepared in 25±5% isolated radiochemical yield with radiochemical purity of >99% via double-ligand transfer (DLT) reaction from the ferrocene precursor 2b (4-(4-cyclohexylpiperazine-1-yl)-1-ferrocenylbutan-1-one). The corresponding Re-complex 4 and the ferrocenyl complex 2b showed relatively high affinity towards σ2 receptors in in vitro competition binding assay (K i values of 4 and 2b were 64.4±18.5nM and 43.6±21.3nM, respectively) and moderate to high selectivity versus σ1 receptors (K iσ1/K iσ2 ratios were 12.5 and 95.5, respectively). The log D value of [99mTc]5 was determined to be 2.52±0.33. Biodistribution studies in mice revealed comparably high initial brain uptake of [99mTc]5 and slow washout. Administration of haloperidol 5min prior to injection of [99mTc]5 significantly reduced the radiotracer uptake in brain, heart, lung, and spleen by 40–50% at 2h p.i.. Moreover, [99mTc]5 showed high uptake in C6 glioma cell lines (8.6%) after incubation for 1h. Blocking with haloperidol to compete with [99mTc]5 significantly reduced the cell uptake. Preliminary blocking study in C6-brain-tumor bearing rats showed that [99mTc]5 binds to σ receptors in the brain-tumor specifically. These results are encouraging for further exploration of 99mTc-labeled probes for σ2 receptor tumor imaging in vivo. [Copyright &y& Elsevier]