Models of defect-mediated melting

A survey is given of recent Monte Carlo studies of lattice defect models for melting in three and two dimensions. In two dimensions special emphasis is laid upon a recently proposed model which exhibits a crossover from a single first-order transition to two successive transitions of the Kosterlitz-Thouless type.     

Hydrogen bond formation to cyclic and acyclic polyethers

Equilibrium constants and enthalpies of hydrogen-bond formation of mcresol to various cyclic (crown) and acyclic polyethers have been determined in benzene solvent. Equilibrium constants indicated no evidence for an operative macrocyclic effect; the relationship between the increasing size of the equilibrium constant and the number of ether oxygens was rationalized with a simple statistical thermodynamic model. Enthalpies of interactions ranged between –19 and –23 kJ-mol^–1. In agreement with PCILO calculations, enthalpies of interaction were essentially independent of the number of oxygen atoms in the ether; no significant difference in enthalpies of interaction between cyclic and acyclic ethers was found.     

Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution

Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo‐dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high‐generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1–G4) pseudo‐dendrimers strongly resembles the behavior of dendrimers in higher generations (G5–G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano‐sphere with a smooth surface even in the first generation.     

Solution-phase counterion effects in supramolecular and mechanostereochemical systems

The self-assembly of molecular components into complex superstructures involves the subtle interplay of various noncovalent forces. Charged species are often utilised in self-assembly processes as a result of the favorable π-π, cation-π, electrostatic, and hydrogen bonding interactions that form between these species. Although the counterions associated with these charged species can exert significant effects on the synthesis, stability, and operation of superstructures in solution, rarely are the counterions considered, leading to misinterpretations and misunderstandings of the studied systems. In this tutorial review, we discuss a variety of solution-phase counterion effects, from the fundamental origins to innovative ways in which these effects are exploited for useful functions.     

A scaleable formal total synthesis of dehydrogliotoxin

A formal total synthesis of the epidithiodiketopiperazine natural product, dehydrogliotoxin (2), utilizing an intramolecular ring closure to form key intermediate 5 is described.     

In vitro evolution of ligands to the membrane protein caveolin

Membrane proteins comprise a third of the human genome, yet present challenging targets for reverse chemical genetics. For example, although implicated in numerous diseases including multiple myeloma, the membrane protein caveolin-1 appears to offer a poor target for the discovery of synthetic ligands due to its largely unknown structure and insolubility. To break this impasse and identify new classes of caveolae controlling lead compounds, we applied phage-based, reverse chemical genetics for the discovery of caveolin-1 ligands derived from the anti-HIV therapeutic T20. Substitution of homologous residues into the T20 sequence used a process analogous to medicinal chemistry for the affinity maturation to bind caveolin. The resultant caveolin-1 ligands bound with >1000-fold higher affinity than wild-type T20. Two types of ELISAs and isothermal titration calorimetry (ITC) measurements demonstrated high affinity binding to caveolin by the T20 variants with K(d) values in the 150 nM range. Microscopy experiments with the highest affinity caveolin ligands confirmed colocalization of the ligands with endogenous caveolin in NIH 3T3 cells. The results establish the foundation for targeting caveolin and caveolae formation in living cells.     

Catalytic oxidative cleavage of olefins promoted by osmium tetroxide and hydrogen peroxide

Hydrogen peroxide was employed as the terminal oxidant in the osmium tetroxide mediated oxidative cleavage of olefins, producing the corresponding aldehyde and ketone products. Aryl olefins are cleaved in good to excellent yield regardless of arene electronics. Alkyl olefins cleave in moderate to good yield for di- and tri-substituted alkenes.     

Hydroxyl-directed cyclizations of 1,6-enynes

The palladium-catalyzed, hydroxyl-directed cyclization reactions of 1,6-enynes provide a highly diastereoselective process for the syntheses of stereochemically defined cyclopentanes. Consistently high levels of cis-selectivity are possible using homopropargyl alcohols in contrast to the corresponding propargyl alcohols. Hydroborylative enyne cyclizations coupled with this directing group effect provide a useful method for the syntheses of multifaceted compounds bearing all carbon quaternary centers.     

A cubic, 12-connected, microporous metal-organometallic phosphate framework sustained by truncated tetrahedral nodes

A rare example of a microporous metal-organic phosphate, [Co(12)(L)(6)(μ(3)-PO(4))(4)(μ(3)-F)(4)(μ-H(2)O)(6)][NO(3)](2) (1), is synthesized by the reaction of a [(η(5)-C(5)H(5))Fe(II)](+)-functionalized terephthalate ligand with Co(NO(3))(2)·6H(2)O and phosphate and fluoride ions generated from the in situ hydrolysis of hexafluorophosphate. 1 is a cubic, 12-connected, face-centered cubic framework sustained by the linear connection of unprecedented, dodecanuclear truncated tetrahedral coordination clusters.