The impact of polystyrene resins in solid-phase organic synthesis

Summary A major objective of the DIVERSOMER^® technology is to provide pure and characterized compounds for biological testing in order to prevent false negatives in our libraries. On several occasions, analysis of the final products by¹H-NMR and MS, has revealed by-products from the polystyrene solid support. Subsequently, three alternative methods were studied to remove polystyrene by-products; (i) prewashing of the resin prior to execution of the synthesis; (ii) pretreatment of the resin with the cleavage conditions consistent with the solid-phase synthesis reaction scheme; and (iii) parallel purification.     

The structure of poly(ethylene oxide)8: NaBPh4 from a single crystal oligomer and polycrystalline polymer

We show that the structure of a polymer electrolyte may be solved by growing single crystals of an oligomeric (short chain) complex which provided an adequate starting model for refinement of the equivalent polymeric structure using powder diffraction: the efficacy of this method has been demonstrated by determining for the first time the structure of an 8 : 1 complex, poly(ethylene oxide)(8) : NaBPh(4).     

Self-assembled low-molecular-weight gelator injectable microgel beads for delivery of bioactive agents

We report the preparation of hybrid self-assembled microgel beads by combining the low molecular weight gelator (LMWG) DBS-CONHNH₂ and the natural polysaccharide calcium alginate polymer gelator (PG). Microgel formulations based on LMWGs are extremely rare due to the fragility of the self-assembled networks and the difficulty of retaining any imposed shape. Our hybrid beads contain interpenetrated LMWG and PG networks, and are obtained by an emulsion method, allowing the preparation of spherical gel particles of controllable sizes with diameters in the mm or μm range. Microgels based on LMWG/alginate can be easily prepared with reproducible diameters <1 μm (ca. 800 nm). They are stable in water at room temperature for many months, and survive injection through a syringe. The rapid assembly of the LMWG on cooling plays an active role in helping control the diameter of the microgel beads. These LMWG microbeads retained the ability of the parent gel to deliver the bioactive molecule heparin, and in cell culture medium this enhanced the growth of human mesenchymal stem cells. Such microgels may therefore have future applications in tissue repair. This approach to fabricating LMWG microgels is a platform technology, which could potentially be applied to a variety of different functional LMWGs, and hence has wide-ranging potential.

We report microgel beads with diameters of ca. 800 nm based on interpenetrating networks of a low-molecular-weight gelator and a polymer gelator, and demonstrate their use as heparin delivery vehicles to enhance stem cell growth.     

Tuning the [L2Rh···H3B·NR3]+ interaction using phosphine bite angle. Demonstration by the catalytic formation of polyaminoboranes

Efficient catalysts for the dehydrocoupling or dehydropolymerisation of H(3)B·NMe(x)H((3-x)) (x = 1, 2) have been developed by variation of the P-Rh-P angle in {Rh(Ph(2)P(CH(2))(n)PPh(2))}(+) fragments (n = 2-5).     

Using the Hill cipher to teach cryptographic principles

The Hill cipher is the simplest example of a block cipher, which takes a block of plaintext as input, and returns a block of ciphertext as output. Although it is insecure by modern standards, its simplicity means that it is well suited for the teaching of such concepts as encryption modes, and properties of cryptographic hash functions. Although these topics are central to modern cryptography, it is hard to find good simple examples of their use. The conceptual and computational simplicity of the Hill cipher means that students can experiment with these topics, see them in action, and obtain a better understanding that would be possible from a theoretical discussion alone. In this article, we define the Hill cipher and demonstrate its use with different modes of encryption, and also show how cryptographic hash functions can be both designed and broken. Finally, we look at some pedagogical considerations.     

Synthesis of Highly Fluorinated Arene Complexes of [Rh(Chelating Phosphine)]+ Cations,and their use in Synthesis and Catalysis

The synthesis of rhodium complexes with weakly binding highly fluorinated benzene ligands is described: 1,2,3-F₃C₆H₃, 1,2,3,4-F₄C₆H₂ and 1,2,3,4,5-F₅C₆H are shown to bind with cationic [Rh(Cy₂P(CH₂)_xPCy₂)]⁺ fragments (x=1, 2). Their structures and reactivity with alkenes, and use in catalysis for promoting the Tishchenko reaction of a simple aldehyde, are demonstrated. Key to the synthesis of these complexes is the highly concentrated reaction conditions and use of the [Al{OC(CF₃)₃}₄]⁻ anion.