Establishing the Coordination Chemistry of Antimony(V) Cations: Systematic Assessment of Ph4Sb(OTf) and Ph3Sb(OTf)2 as Lewis Acceptors

The coordination chemistry of the stiboranes Ph₄Sb(OTf) ( 1 a , OTf = OSO₂CF₃) and Ph₃Sb(OTf)₂ ( 3 ) with Lewis bases has been investigated. The significant steric encumbrance of the Sb center in 1 a precludes interaction with most ligands, but the relatively low steric demands of 4‐methylpyridine‐N‐oxide (OPyrMe) and OPMe₃ enabled the characterization of [Ph₄Sb(OPyrMe)][OTf] ( 2 a ) and [Ph₄Sb(OPMe₃)][OTf] ( 2 b ), rare examples of structurally characterized complexes of stibonium acceptors. In contrast, 3 was found to engage a variety of Lewis bases, forming stable isolable complexes of the form [Ph₃Sb(donor)₂][OTf]₂ [donor=OPMe₃ ( 6 a ), OPCy₃ ( 6 b , Cy=cyclohexyl), OPPh₃ ( 6 c ), OPyrMe ( 6 d )], [Ph₃Sb(dmap)₂(OTf)][OTf] ( 6 e , dmap=4‐(dimethylamino)pyridine) and [Ph₃Sb(donor)(OTf)][OTf] [donor=1,10‐phenanthroline ( 7 a ) or 2,2′‐bipy ( 7 b , bipy=bipyridine)]. These compounds exhibit significant structural diversity in the solid‐state, and undergo ligand exchange reactions in line with their assignment as coordination complexes. Compound 3 did not form stable complexes with phosphine donors, with reactions instead leading to redox processes yielding SbPh₃ and products of phosphine oxidation.     

Novel structural motifs consisting of chiral thiazolines: synthesis, molecular recognition, and anticancer activity

The facile synthesis of linear and cyclic chiral oligo(4-alpha/beta-methyl)thiazolines is described. Linear oligothiazolines have been efficiently synthesized by the iterative formation of thiazoline rings and two-directional block condensation. The construction of 24- to 36-membered cyclic oligothiazolines was achieved through the head-to-tail cyclo-oligomerization of doubly deprotected linear fragments. Studies of the interactions of both the linear and cyclic oligomers with chiral compounds revealed that cyclic oligomers displayed a strong binding affinity towards mandelic acid, whereas linear oligomers showed a poor affinity. Linear oligomers have been proven to inhibit the cell growth of the cancer cell lines HPAC, PC-3, and HCT-116. Studies of the structure-activity relationships showed that the IC50 values are clearly dependent on both the length and the terminal functionalities of the linear oligomers. Longer derivatives showed more potent activity (e.g., hexi- and octithiazolines exhibit IC50<1 microM) against all three cancer cell lines. In sharp contrast, cyclic oligomers were inactive to all three cell lines.     

Enantiocontrolled synthesis of the epoxycyclohexenone moieties of scyphostatin, a potent and specific inhibitor of neutral sphingomyelinase

The epoxycyclohexenone moieties 2 and 3b of scyphostatin (1), a potent and specific inhibitor of neutral sphingomyelinase, were synthesized in enantiomerically pure forms starting from (−)-quinic acid (11). The synthetic method features (i) the preparation of the olefin masked enones 25 and 29, the precursors for the key aldol-type coupling reaction, (ii) the efficient and stereocontrolled aldol-type coupling reactions between 25 (or 29) and benzaldehyde (8) and Garner's aldehyde analogue 9 to deliver alcohols 23 and 24, respectively, both of which possess the requisite asymmetric quaternary carbon center at the C6 position, and (iii) the stereospecific S_N2-type epoxide ring formation of the mesylates 35 and 47 under mild basic conditions to produce the targeted compounds 2 and 3b, respectively.     

A new strategy for the design of water-soluble synthetic receptors: specific recognition of DNA intercalators and diamines

Water-soluble zinc bisporphyrin receptors 1 and 2 having two Lewis acidic sites (zinc) in the hydrophobic environment consisting of alkyl chains and a bisporphyrin framework, and covered with hydrophilic exterior (twelve or eighteen carboxyl groups) were prepared. The receptors show high affinity for diamines and DNA intercalators in water where the binding constants K(a) are of the order of 10(7) and 10(8) M(-1), respectively. Diamines and DNA intercalators are bound to the receptor through different mechanisms. Diamines are bound through hydrophobic interactions and zinc-nitrogen interactions, while DNA intercalators are bound through hydrophobic interactions and charge-transfer interactions. Flexible alkyl chains can make van der Waals contact with guests and create a hydrophobic environment around the bound guest by an induced-fit-type mechanism. For the binding of DNA intercalators, the following features are noteworthy: 1). Binding constants are similar between the zinc porphyrins and zinc-free porphyrins; 2). the binding constant is larger for the guest having the lower LUMO; this indicates the important contribution of charge-transfer interactions to binding; 3). the hydrophobic and cationic nature of DNA intercalators is substantially important, and 4). higher ionic strength reduced the binding affinities; this shows a moderate contribution of electrostatic interactions. The conformational instability of the receptors also contributes to the tight binding: hydrophobic and electrostatic interactions cannot both be favorable at the same time in the guest-free receptor. Enthalpy-entropy compensation observed for the binding of diamines and DNA intercalators is characterized by a relatively small slope (alpha=0.74) and a large intercept (beta=7.75 kcal mol(-1)) in the DeltaH degrees versus TDeltaS degrees plot; this shows that a conformational change of receptors and a significant desolvation occur upon binding. The receptor can competitively bind to propidium iodide to deprive DNA of the intercalated propidium iodide. These features of water-soluble receptors consisting of a rigid framework and flexible side chains with a large solvent-accessible area are in contrast to highly preorganized rigid receptors, and they can provide useful guidelines for rational design of induced-fit artificial receptors in water.     

Sb2S3 with various nanostructures: controllable synthesis, formation mechanism, and electrochemical performance toward lithium storage

The size- and shape-controlled synthesis of Sb(2)S(3) nanostructures has been successfully realized by a facile hydrothermal route. A range of dimensional nanostructures, such as one-dimensional nanorods, two-dimensional nanowire bundles, three dimensional sheaf-like superstructures, dumbbell-shaped superstructures, and urchin-like microspheres, could be obtained through introducing different organic complex reagents or ionic liquids to the reaction system. The formation mechanisms of various Sb(2)S(3) nanostructures have been rationally proposed based on the crystal structure and the nature of the complex reagents and the ionic liquid. The effects of experimental parameters on the final product are also discussed in detail. In addition, electrochemical measurements demonstrate that the as-synthesized Sb(2)S(3) nanostructures have higher initial Li intercalation capacity and excellent cyclic performances, which indicates that the as-synthesized Sb(2)S(3) nanostructures could have potential applications in commercial batteries.     

Biodegradable and biomimetic poly(epsilon-caprolactone)/poly(lactobionamidoethyl methacrylate) biohybrids: synthesis, lactose-installed nanoparticles and recognition properties

Biodegradable and biomimetic SPCL-PLAMA biohybrids were synthesized via ATRP and characterized by FT-IR, (1)H NMR, GPC and DSC. Biohybrids with small PDI were obtained, and the block length of the PLAMA glycopolymer could be varied linearly by the varying the molar ratio of glycomonomer to macroinitiator. The outer PLAMA glycopolymer restrained the crystallization of inner PCL segments. The self-assembly properties of amphiphilic biohybrids were studied. Lactose-installed aggregates were fabricated in aqueous solution; they changed from spherical micelles to vesicles with increasing weight fraction of hydrophobic PCL. The SPCL-PLAMA biohybrids showed specific recognition for RCA(120) lectin.     

Mechanochemical synthesis of rutile-type CrMO4 (M=V, Sb) and their solid solutions

Grinding a mixture of hydrous amorphous chromium oxide (Cr₂O₃·nH₂O), vanadium oxide (V₂O₅) and antimony oxide (Sb₂O₅) was conducted by using a planetary ball mill, to investigate their mechanochemical reactions to form chromium vanadium oxide (CrVO₄) and chromium antimony oxide (CrSbO₄). The synthesis reactions proceed with an increase in grinding periods of time. The ground samples consist of agglomerates with particle size of about ten nanometers. The synthesized CrVO₄ sample exhibits a rutile-type tetragonal crystal structure, which is a high pressure phase. Additionally, solid solutions, CrV_1−xSb_xO₄ (x=0∼1, Δx=0.25), have been synthesized mechanochemically from the mixtures of Cr₂O₃·nH₂O, V₂O₅ and Sb₂O₅.     

Palladium(II)-mediated assembly of biotinylated ion channels

Simple synthetic methodology has been used to create biotinylated pyridyl cholate lipids that can undergo multiple self-assembly events when inserted into phospholipid vesicles; Pd(II) links cholates into transmembrane lipids, while avidin laterally clusters these complexes together and concomitantly assembles the vesicles into aggregates. The transmembrane assembly of cholates by Pd(II) "opened" the ion channels, whereas avidin addition produced vesicle aggregates, giving a system that mimicked both transmembrane transport and cellular adhesion. Complexation of these Pd(II)-linked cholates by avidin gave a measurable decrease in ion flow, suggesting some channels became blocked or were prevented from adopting the optimum geometry for ion conduction. This reflects the importance of spatially appropriate preorganisation when generating active supramolecular assemblies.     

Specific recognition of syndiotactic poly(methacrylic acid) in porous isotactic poly(methyl methacrylate) thin films based on the effects of stereoregularity,temperature, and solvent

The effects of stereoregularity, temperature, and solvent on the specific recognition of syndiotactic (st)‐poly(methacrylic acid) (PMAA) in macromolecularly porous isotactic (it)‐poly(methyl methacrylate) films were investigated to give important insights into the regularity and stability of nanospaces in the it‐PMMA films as well as template polymerization. The porous it‐PMMA films were fabricated on quartz crystal microbalance (QCM) substrates via the layer‐by‐layer (LbL) assembly of it‐PMMA/st‐PMAA, plus the st‐PMAA extraction from the assembly. QCM analysis and infrared spectroscopy revealed the first case of stereocomplex formation using st‐PMAA with lower stereoregularity (rr = 73%) in the LbL films, while st‐PMAA obtained with conventional free radical polymerization (rr = 62%) was barely incorporated into the porous it‐PMMA films. The maximum st‐PMAA incorporation increased from 25 to 40 °C, but there were almost no difference between 40 and 55 °C, indicating that the it‐PMMA crystallization would also be accelerated with increasing temperature. The studies on st‐PMAA incorporation with various complexing solvents revealed that the host it‐PMMA in the porous films could only form the original stereocomplex with 2/1 unit‐molar stoichiometry (st‐PMAA/it‐PMMA) in acetonitrile/water or ethanol/water. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3651–3657, 2010