Mechanically versatile isosorbide-based thermoplastic copolyether-esters with a poly(ethylene glycol) soft segment

Segmented thermoplastic copolyether esters (TPEE's) with a partially renewable hard block containing isosorbide (ISB) and poly(ethylene glycol) (PEG) soft blocks were prepared by melt polycondensation. A range of compositions was accessible despite the relatively low reactivity of the sterically and electronically hindered ISB monomer. The small-scale reactions performed in the melt were limited in terms of achievable molar mass. This is attributed to the challenge of attaining stoichiometric balance in the feed and maintaining this balance throughout the high temperature (>200°C) reactions. Nevertheless, products were isolated that could be manipulated and melt-pressed into specimen for tensile testing. Varying the feed compositions gave rise to copolymers exhibiting a broad range of mechanical properties (elastic modulus from 1–66 MPa). These characteristics are consistent with a segmented polymer architecture with morphological features similar to commercially available TPEE counterparts. These results pave the way for more responsibly sourced building blocks being incorporated into materials with high market value potential.     

Weak long-range correlated motions in a surface patch of ubiquitin involved in molecular recognition

Long-range correlated motions in proteins are candidate mechanisms for processes that require information transfer across protein structures, such as allostery and signal transduction. However, the observation of backbone correlations between distant residues has remained elusive, and only local correlations have been revealed using residual dipolar couplings measured by NMR spectroscopy. In this work, we experimentally identified and characterized collective motions spanning four β-strands separated by up to 15 ? in ubiquitin. The observed correlations link molecular recognition sites and result from concerted conformational changes that are in part mediated by the hydrogen-bonding network.     

Where there's a web,there's a way: commercial genetic testing and the Internet

The Internet has become a "global marketplace", enabling consumers to purchase health care products and services, including genetic testing, through a variety of national and international sources. A web search for commercial (for-profit) genetic testing companies found 12 with a web presence that were offering adult genetic susceptibility testing, of which 3 offered direct-to-consumer access. In this paper, Canada--with its educated population and universal health care system--will serve as a case study for illustrating the social, ethical and policy issues (e.g., information privacy, just access to health care, product safety, and access to unbiased health information) arising with Internet-based access to commercial genetic testing. Health professionals, policy makers and consumers in all developed nations will be faced with complex technical, social and ethical issues, but without further discussion it will not be possible to determine how best to manage and maximise the benefits of this increased accessibility and choice, while minimising the associated personal and social costs.     

Kinetics of the Antibody Recognition Site in the Third IgG‐Binding Domain of Protein G

Protein dynamics occurring on a wide range of timescales play a crucial role in governing protein function. Particularly, motions between the globular rotational correlation time ( ) and 40 μs (supra‐ window), strongly influence molecular recognition. This supra‐ window was previously hidden, owing to a lack of experimental methods. Recently, we have developed a high‐power relaxation dispersion (RD) experiment for measuring kinetics as fast as 4 μs. For the first time, this method, performed under super‐cooled conditions, enabled us to detect a global motion in the first β‐turn of the third IgG‐binding domain of protein G (GB3), which was extrapolated to 371±115 ns at 310 K. Furthermore, the same residues show the plasticity in the model‐free residual dipolar coupling (RDC) order parameters and in an ensemble encoding the supra‐ dynamics. This β‐turn is involved in antibody binding, exhibiting the potential link of the observed supra‐ motion with molecular recognition.     

Caged phosphite complexes of copper(I) halides

The coordination chemistry of the caged phosphites 4-2,6,7-trioxa-1-phosphabicyclo [2.2.2]octane (MeCage) and 4-nitro-t2,6,7-trioxa-1t-phosphabicyclo[2.2.2]octane (NO₂Caget) with copper(I) halides is reported. Reactions of CuX = CuCl, CuBr, and CuI with the phosphite ligands afford complexes of the type [CuX(MeCage)]₄, [CuX(NO₂Cage)]₄, [CuX(MeCage)₂]₂, [CuX(NO₂Cage)₂]₂, and [CuX(MeCage)₃]. Recrystallization of [CuBr(NO₂Cage)₂]₂ in MeCN produced [CuBr(NO₂Cage)(NCMe)]₂. Three X-ray crystal structures are reported: [CuCl(MeCage)]₄ (I – 4, a = 13.4292(5) Å, b = 13.4292(5) Å, c = 9.4641(5) Å, V = 1706.79(13) ų, Z = 2), [CuBr(MeCage)₂]₂ (I4₁/a, a = 19.5751(17) Å, b = 19.5751(17) Å, c = 16.4513(15) Å, V = 6303.9(10) ų, Z = 8), and [CuBr(NO₂Cage)(NCMe)]₂ (P2₁/c, a = 9.0506(4) Å, b = 15.2428(7) Å, c = 8.8673(4) Å, = 109.7640(10), V = 1151.24(9) ų, Z = 2).     

Isolation, characterization, and DNA binding kinetics of three dirhodium(II,II) carboxyamidate complexes: Rh2(μ-L)(HNOCCF3)3 where L= [OOCCH3]-, [OOCCF3]-, or [HNOCCF3]-

Several transition metal compounds are effective antitumor drugs whose biological activity can be attributed to their ability to bind deoxyribonucleic acid (DNA). In this study, DNA-binding experiments reveal that changing one bridging ligand on compounds with the general formula Rh(2)(μ-L)(HNOCCF(3))(3) alters the rate of DNA-binding by greater than 100-fold with μ-L = trifluoroacetate ? acetate > trifluoroacetamidate. These three dirhodium compounds are isolated as the major products of the reaction between Rh(2)(OOCCH(3))(4) and trifluoroacetamide in either refluxing chlorobenzene or molten trifluoroacetamide and have been characterized by NMR and LC/MS. By using (15)N-enriched trifluoroacetamide, NMR spectroscopy was used to assign the cis-(2,1) orientations of Rh(2)(μ-L)(HNOCCF(3))(3) compounds where μ-L = trifluoroacetate or acetate. This is the first report of Rh(2)(OOCCF(3))(HNOCCF(3))(3), a novel compound that may play a significant role in the biological and/or catalytic activity of compound mixtures commonly isolated as "Rh(2)(HNOCCF(3))(4)".     

The double-tree method: An O(n) unsteady aerodynamic lifting surface method

Two new methods for reducing the computational cost of the unsteady vortex lattice method are developed. These methods use agglomeration to construct time-saving tree structures by approximating the effect of either a group of vortex rings or query points. A case study shows that combining the two new O(n·log n) tree methods together results in an O(n) method, called the double-tree method. Other case studies show that the trade-off between accuracy and speed can be easily and reliably controlled by the agglomeration cutoff distance. For a flat plate with 5 × 200 panels analyzed over 20 time steps, the double-tree method is 7 times faster than the unsteady vortex lattice method with a <5% difference in the force distribution and total lift coefficient. The case studies suggest that the computational benefit will increase for the same level of accuracy if the size of the problem is increased, making the method beneficial for full-aircraft analysis within optimization or dynamic load analysis, where the computational cost of the unsteady vortex lattice method can be large.     

The secretary problem on an unknown poset

We consider generalizations of the classical secretary problem, also known as the problem of optimal choice, to posets where the only information we have is the size of the poset and the number of maximal elements. We show that, given this information, there is an algorithm that is successful with probability at least \begin{align*}\frac{1}{e}\end{align*}. We conjecture that if there are k maximal elements and k ≥ 2 then this can be improved to \begin{align*}\sqrt\lbrack k-1\rbrack {\frac{1}{k}}\end{align*}, and prove this conjecture for posets of width k. We also show that no better bound is possible. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 43, 429–451, 2013