Coordinated pair chain folding model for solution-grown polyethylene single crystal

A new regular chain folding model, namely the “coordinated pair chain folding model” (CPCFM) is proposed to revive the consideration that a polymer chain should fold regularly rather than randomly in solution-grown polyethylene single crystals.     

Prediction of polymer miscibility from molecular mechanics calculations

A new computational method is presented for the rapid estimation of polymer miscibility. The algorithm (coined FLEXIBLEND) uses molecular mechanics calculations on a pair of polymer segments and takes into account the effects of local chain flexibility to estimate heats of mixing. This paper shows miscibility predictions in agreement with experiment for blends of poly(ethyleneoxide) (PEO) with isotactic poly(propylene) (PP) as an immiscible system and of PEO with poly(acrylic acid) (PAA) as a miscible system.     

Synthetic Diphenylacetylene-Based Retinoids Induce DNA Damage in Chinese Hamster Ovary Cells without Altering Viability

All-trans-retinoic acid (ATRA), the active metabolite of vitamin A, plays a pivotal role in cell differentiation, proliferation and embryonic development. It is an effective therapy for dermatological disorders and malignancies. ATRA is prone to isomerization and oxidation, which can affect its activity and selectivity. Novel diphenylacetylene-based ATRA analogues with increased stability can help to overcome these problems and may offer significant potential as therapeutics for a variety of cancers and neurodegenerative diseases, including amyotrophic lateral sclerosis. Here, we investigated the effects of these retinoids on cell viability and genotoxicity in the widely used model system of the rapidly proliferating Chinese hamster ovary cell line. DC360 is a fluorescent ATRA analogue and DC324 is a non-active derivative of DC360. EC23, DC525, DC540, DC645, and DC712 are promising analogues with increased bioactivity. The cytotoxic activity of the compounds was evaluated by ATP assay and DNA damage was tested by comet assay. No cytotoxicity was observed in the 10⁻⁶–10⁻⁵ M concentration range. All compounds induced DNA migration similar to ATRA, but DC324, DC360 and EC23 did so to a greater extent, particularly at higher concentrations. We believe that retinoid receptor-independent genotoxicity is a general characteristic of these compounds; however, further studies are needed to identify the molecular mechanisms and understand their complex biological functions.     

Hindered organoboron groups in organic synthesis. 17 [1]. Synthesis of 2,4,6-triisopropylphenylborane (TripBH2)2, a useful alternative to thexylborane

2,4,6-Triisopropylphenylborane (tripylborane, TripBH₂) resembles thexylborane in having a single, bulky organic group attached to boron, but the group is aromatic rather than aliphatic. The compound has been synthesized by two alternative routes, one involving direct reduction of dimethoxytripylborane and the other involving redistribution between ditripylborane and borane. It is a solid which is considerably more stable than thexylborane.     

2D Ising Model for Enantiomer Adsorption on Achiral Surfaces: L- and D-Aspartic Acid on Cu(111)

The 2D Ising model is well-formulated to address problems in adsorption thermodynamics. It is particularly well-suited to describing the adsorption isotherms predicting the surface enantiomeric excess, ees, observed during competitive co-adsorption of enantiomers onto achiral surfaces. Herein, we make the direct one-to-one correspondence between the 2D Ising model Hamiltonian and the Hamiltonian used to describe competitive enantiomer adsorption on achiral surfaces. We then demonstrate that adsorption from racemic mixtures of enantiomers and adsorption of prochiral molecules are directly analogous to the Ising model with no applied magnetic field, i.e., the enantiomeric excess on chiral surfaces can be predicted using Onsager’s solution to the 2D Ising model. The implication is that enantiomeric purity on the surface can be achieved during equilibrium exposure of prochiral compounds or racemic mixtures of enantiomers to achiral surfaces.     

Quantum Coherences and Classical Inhomogeneities as Equivalent Thermodynamics Resources

Quantum energy coherences represent a thermodynamic resource, which can be exploited to extract energy from a thermal reservoir and deliver that energy as work. We argue that there exists a closely analogous classical thermodynamic resource, namely, energy-shell inhomogeneities in the phase space distribution of a system’s initial state. We compare the amount of work that can be obtained from quantum coherences with the amount that can be obtained from classical inhomogeneities, and find them to be equal in the semiclassical limit. We thus conclude that coherences do not provide a unique thermodynamic advantage of quantum systems over classical systems, in situations where a well-defined semiclassical correspondence exists.     

Heat‐Free Biomimetic Metal Molding on Soft Substrates

Fabrication of bio‐templated metallic structures is limited by differences in properties, processing conditions, packing, and material state(s). Herein, by using undercooled metal particles, differences in modulus and processing temperatures can be overcome. Adoption of autonomous processes such as self‐filtration, capillary pressure, and evaporative concentration leads to enhanced packing, stabilization (jamming) and point sintering with phase change to create solid metal replicas of complex bio‐based features. Differentiation of subtle differences between cultivars of the rose flower with reproduction over large areas shows that this biomimetic metal patterning (BIOMAP) is a versatile method to replicate biological features either as positive or negative reliefs irrespective of the substrate. Using rose petal patterns, we illustrate the versatility of bio‐templated mapping with undercooled metal particles at ambient conditions, and with unprecedented efficiency for metal structures.     

Advances in ultra-high load polymer-supported peptide synthesis with phenolic supports: 2. Use of ‘hydrazinolysis-hplc’ to check for racemization on c-terminal amino acid loading and to determine peptide homogeneity during synthesis with selectively labile c-terminal anchoring linkages

2, 4-Dinitrophenyl-L-phenylalanine has been coupled to L-, D-, and DL-amino acid phenyl esters pendant upon a polymer matrix. The esters had been prepared by di-isopropylcarbodiimide-mediated condensation, catalyzed by 4-dimethylaminopyridine. Reverse phase high pressure liquid chromatography (HPLC), using elution solvents consisting of 10 vol.-% trifluoroacetic acid in water/acetonitrile mixtures, has been used to investigate the 2,4-dinitrophenyl L-L and L-D dipeptide mixtures obtained on hydrazinolysis of each of the dipeptide-matrix assemblies. ‘Hydrazinolysis-HPLC’ has been used also to determine intermediate peptide homogeneity in ultra-high load solid (gel) phase synthesis with Boc amino acids. Cross-linked poly(N-[2-(4-hydroxyphenyl)ethyl]acrylamide) and two derived polymers incorporating spacer groups have been used as supports. The spacer groups made possible peptide C-terminal attachment by either HF-labile benzyl ester or HF-labile cyclohexyl ester bonds, while still incorporating the phenolic ester linkage susceptible to rapid hydrazinolytic scission.     

High-field MRS studies in brain slices

We are applying multi-nuclear high-field (500 MHz) MR spectroscopy of metabolising whole tissue preparations of the mammalian brain to studies on individual components of convulsions, which include prolonged depolarization, metabolic deprivation, and the effects of excitotoxins. The responses of glial cells and neurones can be partially distinguished by following labelling patterns of metabolic intermediates from ¹³C-labelled glucose or acetate (which enters only glial cells). This approach clearly confirmed our earlier indications that the metabolic response to depolarization (40 mM extracellular K⁺) occurs essentially in glial cells. Some evidence for metabolic shuttling between glia and neurones was obtained from the changes in C3/C4 ratios of glutamate and glutamine, and the C2/C3 of GABA. Mechanisms for metabolic support of neurones by glia may be of importance in neuronal protection under such metabolic stress as occurs in epilepsy. Changes in free intracellular divalent cations ([Ca²⁺]_i and [Zn²⁺]_i) were monitored using the ¹⁹F-MRS indicator, 5FBAPTA. Large increases in [Ca²⁺]_i and decreases in PCr were produced by excitotoxins (glutamate and NMDA), depolarization or ischaemia, but intracellular Zn²⁺ appeared only after exposure to the excitotoxins. The NMDA receptor blocker, MK801, removed all of the responses to NMDA, but only prevented the appearance of Zn²⁺ observed with glutamate. These results indicate that the damage caused to neurones by such insults as convulsions is not due simply to the presence of excessive excitotoxic glutamate.