Monodisperse Macromolecules by Self-Interrupted Living Polymerization.

Biological macromolecules such as proteins and nucleic acids are monodisperse just as low-molar-mass organic compounds are. However, synthetic macromolecules contain mixtures of different chain lengths, the most uniform being generated by living polymerizations, which exhibit a maximum of 1-3% of chains with the desired length. Monodisperse natural and synthetic oligomers can be obtained in low quantities by tedious, multistep iterative methods. Here we report a methodology to synthesize monodisperse synthetic macromolecules by self-interrupted living polymerization. This methodology relies on a concept that combines supramolecular and macromolecular chemistry and differs from the conventional reactivity principles employed in the synthesis of polymers for over 100 years.

Dendronized Poly(2-oxazoline) Displays within only Five Monomer Repeat Units Liquid Quasicrystal, A15 and σ Frank-Kasper Phases.

Liquid quasicrystals (LQC) have been discovered in self-assembling benzyl ether, biphenylmethyl ether, phenylpropyl ether, biphenylpropyl ether and some of their hybrid dendrons and subsequently in block copolymers, surfactants and other assemblies. These quasiperiodic arrays, which lack long-range translational periodicity, are approximated by two Frank-Kasper periodic arrays, Pm3̅ n cubic (Frank-Kasper A15) and P42/ mnm tetragonal (Frank-Kasper σ), which have been discovered in complex soft matter in the same order and compounds. Poly(2-oxazoline)s dendronized with (3,4) nG1 minidendrons (where n denotes an alkyl chain, C nH2 n+1) self-organize into the Pm3̅ n cubic phase ( n = 14 and 15) and, as reported recently, the P42/ mnm tetragonal phase ( n = 16). However, no LQC of a poly(2-oxazoline) is yet known. Here we report the synthesis, structural and retrostructural analysis of a dendronized poly(2-oxazoline) with n = 17 which self-organizes not only into the LQC but also in the above two Frank-Kasper approximants. All three phases are observed from the same polymer within a very narrow range of degree of polymerization that corresponds to only five monomer repeat units (5 ≤ DP ≤ 10). The formation of the Pm3̅ n cubic, P42/ mnm tetragonal and LQC phases from a single polymer chain within such a narrow range of DP raises the questions of how and why each of these phases is self-organized. This system may provide a model for theoretical investigations into the self-organization of soft matter into Frank-Kasper and related periodic and quasiperiodic arrays.

Noninvasive measurement of reepithelialization and microvascularity of suction-blister wounds with benchmarking to histology.

We explored use of the suction-blister wound model in the assessment of not only epidermal regeneration but also pain, the microvascular response and bacteriology. The effects of topical zinc sulfate were studied to articulate the methodologies in this double-blind trial. One epidermal suction blister (10 mm) was induced on each buttock in 30 healthy volunteers (15 females:15 males) and deroofed on day 0. The wounds were randomized to daily treatment with 1.4% zinc sulfate shower gel (n = 20), placebo (n = 20) or control (n = 20). Digital photography coupled with planimetry, transepidermal water loss (TEWL) measurement and optical coherence tomography (OCT) was benchmarked to the gold standard of histology of 60 full-thickness wound biopsies on day 4. Pain increased after application of the shower gels. Microvessel density, determined from OCT images, increased from day 0 to day 2 in the three groups but increased more with the placebo than with the zinc shower gel (p = 0.003) or the control treatment (p = 0.002) and correlated (rS = 0.313, p = 0.015) with the inflammatory response on day 4, as determined by histology. Coagulase-negative staphylococci were more common in wounds compared with skin (p = 0.002) and was reduced (p = 0.030) with zinc sulfate treatment. Planimetric analysis of digital wound images was not biased (p = 0.234) compared with histology, and TEWL measurements showed no correlation (rS = 0.052, p = 0.691) with epithelialization. Neoepidermal formation, determined by histology, did not differ (p = 0.290) among the groups. Zinc sulfate reduced (p = 0.031) the release of lactate dehydrogenase from cultured gel-treated keratinocytes isolated from the blister roofs. Therefore, combination of the standardized suction-blister wound model with noninvasive planimetry and OCT is a useful tool for assessing wound therapies. Zinc sulfate transiently dampened inflammation and reduced bacterial growth.

Computational Study of the Small Zr(IV) Polynuclear Species.

Despite widespread zirconium use ranging from nuclear technology to antiperspirants, important aspects of its solvation chemistry, such as the nature of small zirconium(IV) hydroxy cluster ions in aqueous solution, are not known due to the complexity of the zirconium aqueous chemistry. Using a combination of Car-Parrinello molecular dynamics simulations and conventional quantum mechanical calculations, we have determined the structural characteristics and analyzed the aqueous solution dynamics of the two smallest zirconium(IV) cluster species possible, i.e., the dimer and trimer. Our study points to and provides detailed geometrical information for a stable structural motif for building zirconium polymers, the Zr(OH)2Zr bridging unit with 7-8 coordinated Zr ions, which, however, cannot be used to construct a stable structure for the trimer. We find that a stacked trimer, not featuring this motif, is a possible structure, though not a very stable one, shedding new light on this species, and its possible importance in the aqueous chemistry of Zr(4+) ion.

Computational study of the Zr4+ tetranuclear polymer, [Zr4(OH)8(H2O)16]8+.

The Zr(4+) tetramer, [Zr(4)(OH)(8)(H(2)O)(16)](8+), is thought to be the major component of the Zr(4+) polymer system in aqueous solution, present as a dominant ionic cluster species compared to other Zr(4+) clusters under various experimental conditions. Despite widespread applications of zirconium, the structure and dynamics of the tetramer in aqueous solution are not well understood. We conducted a combination of ab initio molecular dynamics and quantum mechanical studies in the gas phase and aqueous solution and related our results to the available experimental data to provide atom-level information on the behavior of this species in aqueous solution. Our simulations indicate that the tetramer structure is stable on the picosecond time scale in an aqueous environment and that it is of a planar form, comprising eight-coordinated Zr(4+) ions with an antiprism/irregular dodecahedron ligand arrangement. In combination with our studies of Zr(4+) dimer and trimer clusters, our results provide detailed geometrical information on structural motifs for building zirconium polymers and suggest a possible polymerization path.

Exploring and expanding the structural diversity of self-assembling dendrons through combinations of AB, constitutional isomeric AB2, and AB3 biphenyl-4-methyl ether building blocks.

General, efficient and inexpensive methods for the synthesis of dendritic building blocks methyl 3',4'-dihydroxybiphenyl-4-carboxylate, 3',5'-dihydroxybiphenyl-4-carboxylate, and methyl 3',4',5'-trihydroxybiphenyl-4-carboxylate were elaborated. In all syntheses the major step involved an inexpensive Ni(II)-catalyzed Suzuki cross-coupling reaction. These three building blocks were employed together with methyl 4'-hydroxybiphenyl-4-carboxylate in a convergent iterative strategy to synthesize seven libraries containing up to three generations of 3',4'-, 3',5'-, and 3',4',5'-substituted biphenyl-4-methyl ether based amphiphilic dendrons. These dendrons self-assemble into supramolecular dendrimers that self-organize into periodic assemblies. Structural and retrostructural analysis of their assemblies demonstrated that these dendrons self-assemble into hollow and non-hollow supramolecular dendrimers exhibiting dimensions of up to twice those reported for architecturally related dendrons based on benzyl ether repeat units. These new dendrons expand the structural diversity and demonstrate the generality of the concept of self-assembling dendrons based on amphiphilic arylmethyl ethers.

Exploring and expanding the three-dimensional structural diversity of supramolecular dendrimers with the aid of libraries of alkali metals of their AB(3) minidendritic carboxylates.

The synthesis of the alkali metal salts of 3,4,5-tris(n-alkan-1-yloxy)benzoic acid [(3,4,5)nG1-CO(2)M, where n is the number of methylenic units in the alkane group for n=12, 14, 16, 18 and M=Li, Na, K, Rb, Cs] is described. The structural analysis of these AB(3) molecules by a combination of methods which includes X-ray diffraction experiments was performed. These experiments have demonstrated that (3,4,5)nG1-CO(2)M self-assemble at low temperatures into supramolecular cylinders and at high temperatures into spheres which subsequently self-organize into two-dimensional c2mm rectangular columnar, p6mm hexagonal columnar, three-dimensional Pm(-)3n and Im(-)3m cubic lattices. In addition a novel unidentified liquid crystalline lattice was also discovered. The dependence between the symmetry of the lattice and the molecular structure of (3,4,5)nG1-CO(2)M was established. (3,4,5)nG1-CO(2)M represents one of the AB(3) minidendrons (i.e., first-generation monodendron attached to the periphery of larger generation dendrons) that is responsible for the control of the three-dimensional structures created from libraries of larger generations of dendrimers. Therefore, the molecular structure-lattice dependence elaborated here will aid the rational design of the three-dimensional shapes from larger generations of supramolecular dendrimers and of their lattices. In addition, the temperature responsive shape change of these supramolecular objects may generate new supramolecular concepts and technological applications.