Showing papers by "Virgil Percec published in 2014"

Single electron transfer in radical ion and radical-mediated organic, materials and polymer synthesis.

Abstract: The article discusses the mechanisms and the applications in organic synthesis, materials, supramolecular, and polymer synthesis of most organic reactions mediated by single electron transfer. Each reaction or class of reactions will be discussed by starting with the original discovery publication, followed by a summary of all or most review articles published in the field, and a discussion of the mechanism(s) and of the most important methodologic and synthetic developments since the most recent review was published. The mechanisms of most organic reactions are considered to proceed by two-electron transfer pathways, even though both biology and radical chemistry rely extensively on one-electron transfer processes. Radicals generated by homolytic cleavage at high temperature were traditionally employed in the industrial production of polymers and to a lesser extent in the synthesis of organic molecules.

Copper(II)/Tertiary Amine Synergy in Photoinduced Living Radical Polymerization: Accelerated Synthesis of ω-Functional and α,ω-Heterofunctional Poly(acrylates)

Abstract: Photoinduced living radical polymerization of acrylates, in the absence of conventional photoinitiators or dye sensitizers, has been realized in “daylight’”and is enhanced upon irradiation with UV radiation (λmax ≈ 360 nm). In the presence of low concentrations of copper(II) bromide and an aliphatic tertiary amine ligand (Me6-Tren; Tren = tris(2-aminoethyl)amine), near-quantitative monomer conversion (>95%) is obtained within 80 min, yielding poly(acrylates) with dispersities as low as 1.05 and excellent end group fidelity (>99%). The versatility of the technique is demonstrated by polymerization of methyl acrylate to a range of chain lengths (DPn = 25–800) and a number of (meth)acrylate monomers, including macromonomer poly(ethylene glycol) methyl ether acrylate (PEGA480), tert-butyl acrylate, and methyl methacrylate, as well as styrene. Moreover, hydroxyl- and vic-diol-functional initiators are compatible with the polymerization conditions, forming α,ω-heterofunctional poly(acrylates) with unparalleled ...

Self-assembly of amphiphilic Janus dendrimers into uniform onion-like dendrimersomes with predictable size and number of bilayers.

Abstract: A constitutional isomeric library synthesized by a modular approach has been used to discover six amphiphilic Janus dendrimer primary structures, which self-assemble into uniform onion-like vesicles with predictable dimensions and number of internal bilayers. These vesicles, denoted onion-like dendrimersomes, are assembled by simple injection of a solution of Janus dendrimer in a water-miscible solvent into water or buffer. These dendrimersomes provide mimics of double-bilayer and multibilayer biological membranes with dimensions and number of bilayers predicted by the Janus compound concentration in water. The simple injection method of preparation is accessible without any special equipment, generating uniform vesicles, and thus provides a promising tool for fundamental studies as well as technological applications in nanomedicine and other fields.

Homochiral Columns Constructed by Chiral Self-Sorting During Supramolecular Helical Organization of Hat-Shaped Molecules

Abstract: A library of dendronized cyclotriveratrylene (CTV) crowns substituted with chiral, racemic, or achiral peripheral alkyl chains, including enantiopure R and S branched alkyls, “racemic by mixture”, “racemic by synthesis”, n-octyl, and n-dodecyl groups was synthesized. In solvophobic solvents and in bulk they self-assemble in helical columns. Their solution and bulk shape-persistent supramolecular structures were determined by a complementary combination of circular dichroism (CD) and UV in solution and thin film, microspot CD in thin film, differential scanning calorimetry combined with fiber X-ray diffraction, computer simulation, and molecular models. In solution, self-assembly via a cooperative mechanism generates single-handed columns from enantiopure CTVs and mixtures of right- and left-handed columns from racemic by mixture, racemic by synthesis, other combinations of R and S, and even from achiral compounds. In bulk state all supramolecular columns form a 3D hexagonal crystalline phase, Φhk (P63 sym...

Mimicking biological membranes with programmable glycan ligands self-assembled from amphiphilic Janus glycodendrimers.

Abstract: An accelerated modular synthesis produced 18 amphiphilic Janus glycodendrimers with three different topologies formed from either two or one carbohydrate head groups or a mixed constellation with a noncarbohydrate hydrophilic arm. By simple injection of their THF solutions into water or buffer, all of the Janus compounds self-assembled into uniform, stable, and soft unilamellar vesicles, denoted glycodendrimersomes. The mixed constellation topology glycodendrimersomes were demonstrated to be most efficient in binding plant, bacterial, and human lectins. This evidence with biomedically relevant receptors offers a promising perspective for the application of such glycodendrimersomes in targeted drug delivery, vaccines, and other areas of nanomedicine.

"Single-single" amphiphilic janus dendrimers self-assemble into uniform dendrimersomes with predictable size.

Abstract: An accelerated modular synthesis of six libraries containing 29 amphiphilic Janus dendrimers, employed to discover and predict functions via primary structures, is reported. These dendrimers were constructed from a single hydrophobic and a single hydrophilic dendron, interconnected with l-Ala to form two constitutional isomeric libraries, with Gly to produce one library, and with l-propanediol ester to generate two additional constitutional isomeric libraries. They are denoted "single-single" amphiphilic Janus dendrimers. Assemblies obtained by injection of their ethanol solution into water were analyzed by dynamic light scattering and cryogenic transmission electron microscopy. A diversity of complex structures including soft and hard dendrimersomes, cubosomes, solid lamellae, and rod-like micelles were obtained in water. It was discovered that the "single-single" amphiphilic Janus dendrimers containing three triethylene glycol groups in the hydrophilic dendron favored the formation of dendrimersomes. Assemblies in bulk analyzed by differential scanning calorimetry and powder X-ray diffraction revealed that the amphiphilic Janus dendrimers with melting point or glass transition below room temperature self-assemble into soft dendrimersomes in water, while those with higher temperature transitions produce hard assemblies. In the range of concentrations where their size distribution is narrow, the diameter of the dendrimersomes is predictable by the d-spacing of their assemblies in bulk. These results suggested the synthesis of Library 6 containing two simpler constitutional isomeric benzyl ester based amphiphilic Janus dendrimers that self-assemble in water into soft dendrimersomes and multidendrimersome dendrimersomes with predictable dimensions.

Single Electron Transfer in Radical Ion and Radical-Mediated Organic, Materials and Polymer Synthesis

Abstract: The article discusses the mechanisms and the applications in organic synthesis, materials, supramolecular, and polymer synthesis of most organic reactions mediated by single electron transfer. Each reaction or class of reactions will be discussed by starting with the original discovery publication, followed by a summary of all or most review articles published in the field, and a discussion of the mechanism(s) and of the most important methodologic and synthetic developments since the most recent review was published. The mechanisms of most organic reactions are considered to proceed by two-electron transfer pathways, even though both biology and radical chemistry rely extensively on one-electron transfer processes. Radicals generated by homolytic cleavage at high temperature were traditionally employed in the industrial production of polymers and to a lesser extent in the synthesis of organic molecules.

Modular synthesis of amphiphilic Janus glycodendrimers and their self-assembly into glycodendrimersomes

Abstract: The invention concerns compounds of the formula (I) wherein: Y 1 and Y 2 are independently a monosaccharide or disaccharide; X 1 and X 2 are independently —(R 9 —O) m —, —(R 10 ) p —, —O—(R 11 —O) q —, —R 16 —O—R 17 —O— or a covalent bond; Q 1 and Q 2 are independently a nitrogen-containing heterocycle moiety; Z 1 and Z 2 are independently —(O—R 7 )—, —(O—C(═O)—R 8 )a-, —O—C(═O)—R 12 —C(=0)-R 13 —, —O—C(═O)—R 14 —C(═O)—R 15 or a covalent bond; R 7 -R 17 are each independently C 1 -C 6 alkyl; R 1 -R 6 are each independently a linear or branched alkyl group; b, c, d, e, f, and g are 0 or 1, provided b+c+d equals at least 2 and e+f+g equals at least 2; and a, m, p, and q are each an integer from 1-6.

Self‐Assembly of Dendritic Dipeptides as a Model of Chiral Selection in Primitive Biological Systems

Abstract: Biological macromolecules are homochiral, composed of sequences of stereocenters possessing the same repeated absolute configuration. This chapter addresses the mechanism of homochiral selection in polypeptides. In particular, the relationship between the stereochemistry (l or d) of structurally distinct α-amino acids is explored. Through functionalization of Tyr–Xaa dipeptides with self-assembling dendrons, the effect of stereochemical sequence of the dipeptide on the thermodynamics of self-assembly and the resulting structural features can be quantified. The dendritic dipeptide approach effectively isolates the stereochemical information of the shortest sequence of stereochemical information possible in polypeptide, while simultaneously allowing for dendron driven tertiary and quaternary structure formation and subsequent transfer of chiral information from the dipeptide to the dendritic sheath. This approach elucidates a mechanism of selecting a homochiral relationship between dissimilar but neighboring α-amino acids through thermodynamic preference for homochirality in solution-phase and bulk supramolecular helical polymerization.