Effects of structure variation on solution properties of hydrotropes: phenyl versus cyclohexyl chain tips

The physicochemical behavior of the phenyl-n-alkanoate (PhenCx) and cyclohexyl-n-alkanoate (CyclohexCx) series has been investigated, supporting previous work on the understanding of hydrotropes (Hopkins Hatzopoulos, M.; Eastoe, J.; Dowding, P.J.; Rogers, S. E.; Heenan, R.; Dyer, R. Langmuir2011, 27, 12346-12353). Electrical conductivity, surface tension, (1)H NMR, and small-angle neutron scattering (SANS) were used to study adsorption and aggregation in terms of critical aggregation concentration (cac). The PhenCx series exhibited very similar d log(cac)/dn to n-alkylbenzoates (CnBenz), exhibiting two branches of behavior, with a common inflection point at four linear carbons, whereas the CyclohexCx series showed no break point. Electrical conductivity and (1)H NMR concentration scans indicate a difference in physicochemical behavior between higher and lower homologues in both the PhenCx and CyclohexCx series. Surface tension measurements with compounds belonging to either group gave typical Gibbs adsorption profiles, having d log(cac)/dn curves consistent with limiting headgroup areas in the region of (35-55 ?(2)) indicating monolayer formation. SANS profiles showed no evidence for aggregates below the electrical conductivity determined cac values, inferring an "on-off" mode of aggregation. Analyses of SANS profiles was consistent with charged ellipsoidal aggregates, persisting from lower through to higher homologues in both the PhenCx and CyclohexCx series.     

A high-throughput, high-resolution strategy for the study of site-selective DNA binding agents: analysis of a "highly twisted" benzimidazole-diamidine

A general strategy for the rapid structural analysis of DNA binding ligands is described as it was applied to the study of RT29, a benzimidazole-diamidine compound containing a highly twisted diphenyl ether linkage. By combining the existing high-throughput fluorescent intercalator displacement (HT-FID) assay developed by Boger et al. and a high-resolution (HR) host-guest crystallographic technique, a system was produced that was capable of determining detailed structural information pertaining to RT29-DNA interactions within approximately 3 days. Our application of the HT/HR strategy immediately revealed that RT29 has a preference for 4-base pair (bp), A.T-rich sites (AATT) and a similar tolerance and affinity for three A-T-bp sites (such as ATTC) containing a G.C bp. On the basis of these selectivities, oligonucleotides were designed and the host-guest crystallographic method was used to generate diffraction quality crystals. Analysis of the resulting crystal structures revealed that the diphenyl ether moiety of RT29 undergoes conformational changes that allow it to adopt a crescent shape that now complements the minor groove structure. The presence of a G.C bp in the RT29 binding site of ATTC did not overly perturb its interaction with DNA-the compound adjusted to the nucleobases that were available through water-mediated interactions. Our analyses suggest that the HT/HR strategy may be used to expedite the screening of novel minor groove binding compounds leading to a direct, HR structural determination.     

On the Scaling Behavior of the Force/Extension Relation of a Chain

Applying an extending force F along the end‐to‐end vector r of a chain enlarges the initial size ρ_i ∼ | r _i| leading to a final state with ρ_f larger than ρ_i. Assuming a power law dependence of the size ρ ∼ N^ν of the chain on its length N, at the two different states with different exponents ν_i and ν_f, a scaling relationship is derived between the measure of the extending force F and the extension ρ of the chain. The exponent γ of the force/extension relation, ρ ∼ F^γ, depends on both exponents ν_i and ν_f of the initial and the final states. A relation between γ and the exponents ν_i and ν_f is derived which permits the explanation of previous results and predicts some more. The scaling behavior is checked with the exactly soluble model of a random walk under a force.

     

Synthesis, structure, magnetic properties and aqueous solution characterization of p-hydroquinone and phenol iminodiacetate copper(II) complexes

The reaction of Cu2+ acetate monohydrate with 2-[N,N'-bis(carboxymethyl)aminomethyl]-4-carboxyphenol (H4cacp), 2-[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H4cah) and the dinucleating 2,5-bis[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (H6bicah) in water results in the formation of several Cu2+ species, which are in dynamic equilibrium in aqueous solution and their stability is pH dependent. A systematic crystallographic study of these species was pursued, resulting in the characterization of most of the species. Additional techniques were employed to characterize the molecules in the solid state (infrared spectroscopy) and in solution (UV-vis spectroscopy and electrochemistry). These measurements show that the Cu2+ ions are ligated mainly to the iminodiacetate at pH < 6, exhibiting only weak interactions with the phenol oxygen. At pH > 6, the phenol oxygen was deprotonated and dinuclear-bridged species, from the phenolate oxygen complexes exhibiting a Cu2+ 2O2 core, were isolated. The coordination environment around the copper ions varies between trigonal bipyramidal, tetragonal pyramidal and distorted octahedral geometries. The two unpaired electrons of the Cu2+ ions are found to be antiferromagnetically coupled. A survey of the magnetic and structural properties of the dinuclear phenoxide bridged Cu2+ complexes shows that the strength of the antiferromagnetic coupling is linearly dependent on the Cu-Ophenolate bond lengths, at bond distances below 1.98 angstroms. The effect of the Cu-O-Cu angles on the magnetic properties of the complexes is also discussed.     

Balance laws and energy release rates for cracks in dipolar gradient elasticity

It is the purpose of this work to derive the balance laws (in the Günther–Knowles–Sternberg sense) pertaining to dipolar gradient elasticity. The theory of dipolar gradient (or grade 2) elasticity derives from considerations of microstructure in elastic continua [Mindlin, R.D., 1964. Microstructure in linear elasticity. Arch. Rational Mech. Anal. 16, 51–78] and is appropriate to model materials with periodic structure. According to this theory, the strain–energy density assumes the form of a positive-definite function of the strain (as in classical elasticity) and the gradient of both strain and rotation (additional terms). The balance laws are derived here through a more straightforward procedure than the one usually employed in classical elasticity (i.e. Noether’s theorem). Indeed, the pertinent balance laws are obtained through the action of the standard operators of vector calculus (grad, curl and div) on appropriate forms of the Hamiltonian of the system under consideration. These laws are directly related to the energy release rates in the processes of crack translation, rotation and self-similar expansion. Under certain conditions, they are identified with conservation laws and path-independent integrals are obtained.     

Products from furans. VII. A General Route for the Synthesis of α-(1,2-cis) and β-(1,2-trans) Glycoconjugates via 1-O-Acyl and 1-O-Ethoxycarbonyl-2-azido-2,3-dideoxyglycopyranosides

A methodology for the synthesis of 2,3,6-trideoxy- and 2,3-dideoxy-2-aminoglycosides is presented. 2,3-Dideoxyhex-2-enopyranos-4-uloses (named also as 2H-pyran-3(6H)-ones) were used for the synthesis of 1-O-acetyl, 1-O-ethyloxycarbonyl and 1-S-phenyl-2,3,6-trideoxy-(or 2,3-dideoxy)-2-azidoglycopyranosyl donors. Glycosidation of the above thio-ethers with a variety of alcohols in the presence of N-bromosuccinimide as activator yielded predominantly α-glycosides, while acetates afforded β-glycosides when TMSOTf was used as a promoter. The coupling of carbonates using tin tetrachloride or TMSOTf proved to be the most successful procedure, yielding the β-glycoside as the predominant product. Thus, glycoconjugates of aminosugars, steroids and aminoacids have been synthesized.     

A combinatorial-probabilistic analysis of bitcoin attacks*

In 2008, Satoshi Nakamoto famously invented bitcoin, and in his (or her, or their, or its) white paper sketched an approximate formula for the probability of a successful double spending attack by a dishonest party. This was corrected by Meni Rosenfeld, who, under more realistic assumptions, gave the exact probability (missing a foundational proof); and another formula (along with foundational proof), in terms of the Incomplete Beta function, was given later by Cyril Grunspan and Ricardo Pérez-Marco, that enabled them to derive an asymptotic formula for that quantity. Using Wilf-Zeilberger algorithmic proof theory, we continue in this vein and present a recurrence equation for the above-mentioned probability of success, that enables a very fast compilation of these probabilities. We next use this recurrence to derive (in algorithmic fashion) higher-order asymptotic formulas, extending the formula of Grunspan and Pérez-Marco who did the leading term. We then study the statistical properties (expectation, variance, etc.) of the duration of a successful attack.     

Atomic and Molecular Decomposition of Homogeneous Spaces of Distributions Associated to Non-negative Self-Adjoint Operators

We deal with homogeneous Besov and Triebel–Lizorkin spaces in the setting of a doubling metric measure space in the presence of a non-negative self-adjoint operator whose heat kernel has Gaussian localization and the Markov property. The class of almost diagonal operators on the associated sequence spaces is developed and it is shown that this class is an algebra. The boundedness of almost diagonal operators is utilized for establishing smooth molecular and atomic decompositions for the above homogeneous Besov and Triebel–Lizorkin spaces. Spectral multipliers for these spaces are established as well.

     

Fluxes of physical quantities and ozone concentration within a fruit tree

Summary Implicit to an understanding of the eco-physiological behaviour and yield of cultivated plants is a knowledge of air-vegetation interaction. One of the basic factors controlling the quantity and quality of plant growth is the turbulent exchange of such physical quantities as temperature and humidity, a fact making the impact assessment of gaseous pollutant deposition also important. Oxidants such as ozone are potentially harmful to plants via metabolic responses and cell injury and, once the threshold of adaptation is exceeded, the death of the plant may even ensue. Experimental application of the micrometeorological gradient method to a peach tree so as to determine the in-canopy transfer coefficients and to derive the fluxes of physical quantities and ozone is reported.