The self-assembly of block copolymers in solution leads to micellar structures with various morphologies. One way to modify the morphology of these micelles is to blend the block copolymer with a homopolymer corresponding to the core-forming block. Although the self-assembly of blends of amorphous homopolymers and block polymers has been extensively studied, there are few examples of solution self-assembly of blends of a core-crystalline block copolymer with a semicrystalline homopolymer. Here we describe a systematic study of the assembly in decane of blends of a polyferrocenylsilane-block-polyisoprene sample (PFS 48 -b-PI 264 ) with two different PFS homopolymer samples (PFS 50 and PFS 20 ). We examine the structures formed as a function of blend composition and compare them to the structures formed from the individual components. PFS 48 -b-PI 264 itself forms long cylindrical micelles, while the two homopolymer samples form stacks of lamellar crystals. Self-assembly of block copolymer mixtures leads to structures with an elongated planar core and fiber-like protrusions from the ends. The details of the structure vary in an interesting and systematic way as the ratio of homopolymer/block copolymer is increased, with important differences seen for the PFS50 and PFS20 homopolymer samples. This study demonstrates that cocrystallization plays a crucial role in determining the structures formed from these mixtures.

The demand for practical and convenient enzyme assays for histone lysine methyltransferases (HKMTs) emerges along with the rapid development of this young class of enzymes. A supramolecular reporter pair composed of p-sulfonatocalix[4]arene (CX4) and the fluorescent dye lucigenin (LCG) has been used to monitor enzymatic trimethylation of lysine residues in peptide substrates. The assay affords a switch-ON fluorescence response and operates in a continuous, real-time, and label-free fashion. The underlying working principle relies on the higher affinity of the macrocycle towards the trimethylated product of the enzymatic reaction as compared to the substrate, which allows the assay to be carried out in the product-selective mode. The final product incorporates a trimethylammonium moiety, a known high-affinity binding motif for CX4. Two substrates corresponding to the H3 N-terminal tail, namely, S2 (RTKQTARKSTGGKAP) and S6 (QTARKSTGGS), were selected as model compounds for methylation with the Neurospora crassa Dim-5 enzyme and investigated by the newly developed supramolecular tandem HKMTs assay. Only the longer substrate S2 underwent methylation in solution. The potential of the assay for inhibitor screening was demonstrated by means of inhibition studies with 1,10-phenanthroline to afford an inhibition constant of (70±20) μM.

Steady-state and time-resolved fluorescence techniques were used to study the behavior of 2I,3I-O-(o-xylylene)-per-O-Me-alpha- and -beta-cyclodextrins in aqueous solution, based on the fluorescence of the bidentate xylylene moiety. Fluorescence decay profiles obtained upon excitation of the xylylene group were fitted to three-exponential decay functions. In addition to a fast component due to stray and/or scattered light, two other components ascribed to the monomer and dimer species, respectively, were identified. The dimer/monomer ratio increases with concentration and decreases with temperature, which is in agreement with an enthalpy-driven association process. The corresponding dimerization equilibrium constants (KD) were obtained from nonlinear regression analysis of the plots of tau against [CD] in the 5-45 degrees C range. A linear van't Hoff analysis for KD allows us to obtain the DeltaH and DeltaS associated to dimer formation. Molecular mechanics as well as molecular dynamics calculations in the presence of water were also employed to study the conformational behavior of such secondary-face-substituted cyclodextrins and rationalize the dimerization processes.