Synthesis of high molecular weight comb block copolymers and their assembly into ordered morphologies in the solid state

This Article describes a simple two-step synthesis of comb block copolymers with molecular weights exceeding 1,000,000 g mol(-1) and their assembly into ordered morphologies in the solid state. This work is exciting because these polymers assembled into morphologies with domain sizes exceeding 100 nm and, in some examples, 200 nm without the use of additives. These materials reflected selected wavelengths of visible light, and these wavelengths could be affected by swelling with methylene chloride vapor. A comparison between the structures of comb block copolymers and linear block copolymers is presented with a discussion of important parameters affecting their assembly in the solid state. This Article will first describe the synthesis of comb block copolymers using ring opening metathesis polymerization and atom transfer radical polymerization and their subsequent characterization. The comb block copolymers, backbone polymers, and polystyrene arms were all characterized independent of each other and had low polydispersities. The comb block copolymers were assembled by dissolving in methylene chloride and allowing the solvent to evaporate. After thermal annealing, the polymers were characterized by scanning electron and optical microscopy. These polymers assembled into spherical, lamellar, and cylindrical arrays with domain sizes from 132 to 258 nm. This work extends the molecular architectures of polymers that can be assembled in the solid state, the molecular weights of block copolymers that were assembled, and the domain sizes that can be realized without the use of additives.     

A low temperature study of antiferromagnetic YbVO4 by NMR thermally detected by nuclear orientation

NMR-TDNO results using an external ⁶⁰CoCo (hcp) nuclear orientation thermometer for non-irradiated, single crystal, antiferromagnetic YbVO₄ are compared with those obtained earlier with neutron activated samples using both internal and external γ-ray thermometers. Detailed comparisons are made for the ¹⁷¹Yb (I=1/2, 14.31% abundant) stable nucleus. This strongly asymmetric, largely homogeneous, resonance lineshape was retained and is readily power broadened. Extremely broad, field-dependent homogeneous thermometric responses are observed in the expected frequency range for the quadrupolar stable nucleus ¹⁷³Yb (I=5/2, 16.13% abundant) for both irradiated and non-irradiated samples. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of the tumor promoter TPA on the induction of DNA synthesis in normal and RSV-transformed rat fibroblasts.

Induction of DNA synthesis by the tumor promoter tetradecanoyl phorbol acetate (TPA) was studied in a line of cultured rat fibroblasts (Rat-1) and their Rous sarcoma virus-transformed derivative (Rat-1 (RSV)). Following serum deprivation for 54 h to achieve quiescence, semiconservative DNA replication was measured by incubation of cells in BrdUrd and FdUrd after serum stimulation in the presence or absence of TPA. Optimal concentrations of TPA (0.1--0.5 microgram/ml) in serum-free medium induced a small increase (10--15%) in the amount of DNA made over a 30-h period in both Rat-1 and Rat-1 (RSV) cells. When Rat-1 cells were stimulated by a 4-h serum pulse, 30% of the DNA was replicated by 30 h. If the serum pulse was followed by TPA addition, 70% DNA replication was observed. If the serum pulse was preceded by TPA addition, the onset of DNA synthesis was delayed by several houses, but stimulation of DNA synthesis occurred. In contrast, the Rat-1 (RSV) cells did not show an increased in DNA synthesis induced by TPA in similar protocols, but the serum-induced onset of DNA synthesis was delayed by several hours in the presence of TPA. Therefore, TPA acts as a co-inducer of DNA synthesis in the Rat-1 but not in the Rat-1 (RSV) cells. The parent alcohol, phorbol, was inactive in Rat-1 cells, but delayed the onset of DNA synthesis in the Rat-1 (RSV) cells. We conclude that the co-inducing and delaying activities of TPA on DNA synthesis appear to be distinct and to act a different points in the G1 phase of the cell cycle.     

Suppression of matrix ions in ultraviolet laser desorption: Scanning electron microscopy and raman spectroscopy of the solid samples

Suppression of low-mass ion peaks in matrix-assisted ultraviolet laser desorption has been found to occur at low matrix-to-analyte molar ratios when using nicotinic acid as matrix, independent of the angle of illumination. Microscopic Raman scattering spectroscopy has been employed to investigate the matrix–analyte solid-state composition. The matrix-to-analyte molar ratios employed in preparing the solutions are reliable guides to the relative amounts of matrix and analyte molecules in the solid crystals, given the method of sample preparation employed involving drying under a stream of nitrogen. A qualitative model based on the proton supply-and-demand argument is tentatively proposed to explain the suppression phenomenon.     

Natural polyene α-pyrones. Synthesis of (±)-citreoviral

The total synthesis of (±)-citreoviral(2) and also of $\text{iso}$-citreoviral(21), using two conceptually distinct approaches starting from methyl tiglate, are described.     

Studies of Australian Ascidians. 5. Virenamides A-C, New Cytotoxic Linear Peptides from the Colonial Didemnid Ascidian Diplosoma virens

Three new linear cytotoxic tripeptides, virenamides A-C have been isolated from extracts of the Didemnid ascidian Diplosoma virens collected on the Great Barrier Reef, Australia. Their structures were deduced from 1D and 2D NMR spectral data and confirmed by HPLC analysis of the constituent amino acids after hydrolysis of the peptides and derivatization with 1-fluoro-2,4-dinitrophen-5-yl-L-alanine amide using Marfey's procedure.     

Some analytical results forABC,ABCD, andXBCD coupled spin 1/2 systems. II

In the preceding paper, it was shown that the calculation of the density matrix(t) for multiply connectedABC, etc., spin 1/2 spin systems can be greatly simplified by subdividing the Hamiltonian into , where is a suitable linear combination of the constants of the motion. In this paper, a framework for the determination of the time evolution of high-order multipolar quantum states is presented and discussed. It is shown that the necessary mathematical labour is reduced to a minimum by (i) exploiting the fact that is a good quantum number, and (ii) using the theory of partitioned matrices. For example, it is shown that for a generaln-coupled spin 1/2 system, the spin dynamics of the multipolar states, whereK _max is the maximum tensorial rank, can be determined without the need to diagonalize the full 2 ⁿ × 2 ⁿ Hamiltonian matrix, wheren is the number of spins. In fact, to describe the time evolution of the multipolar states it is only necessary to diagonalize twon ×n matrices at most. Finally, some cautionary remarks are made concerning the use of the weak-coupling approximation.     

Phosphoryl choline introduces dual activity in biomimetic ionomers

Dual activity of phosphoryl choline (PC) functional poly(trimethylene carbonate) (PTMC) was found which induces the zwitterionic biomimetic PC group to form physical cross-links with ionomers in the bulk, and at the same time enrich at the surface of cast films. The formation of zwitterionic domains from a bifunctional PC-PTMC-PC (ionomer) provided firm films with a low elastic modulus in contrast to the tacky PTMC starting material (Mn approximately 3900 g/mol) with poor mechanical performance. In addition, the ionomer possessed improved hemocompatible properties that was explained by the enrichment of PC at the surface, suggesting a way to tailor the mechanical performance of biodegradable PTMC-based ionomers while providing its bioactivity. Tailored elasticity while maintaining hemocompatibility of a biodegradable ionomer should be of particular interest for a variety of in vivo applications.