Glass‐transition temperatures of nanostructured amorphous bulk polymers and their blends

Nanostructured amorphous bulk polymer samples were produced by processing them with small molecule hosts. Urea (U) and gamma‐cyclodextrin (γ‐CD) were utilized to form crystalline inclusion compounds (ICs) with low and high molecular weight as‐received (asr‐) poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), and their blends as included guests. Upon careful removal of the host crystalline U and γ‐CD lattices, nanostructured coalesced (c‐) bulk PVAc, PMMA, and PVAc/PMMA blend samples were obtained, and their glass‐transition temperatures, T_gs, measured. In addition, non‐stoichiometric (n‐s)‐IC samples of each were formed with γ‐CD as the host. The T_gs of the un‐threaded, un‐included portions of their chains were observed as a function of their degree of inclusion. In all the cases, these nanostructured PVAc and PMMA samples exhibited T_gs elevated above those of their as‐received and solution‐cast samples. Based on their comparison, several conclusions were reached concerning how their molecular weights, the organization of chains in their coalesced samples, and the degree of constraint experienced by un‐included portions of their chains in (n‐s)‐γ‐CD‐IC samples with different stoichiometries affect their chain mobilities and resultant T_gs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1041–1050     

Planarization-Induced Activation Wavelength Red-Shift and Thermal Half-Life Acceleration in Hydrazone Photoswitches

The optimization and modulation of the properties of photochromic compounds, such as their activation wavelengths and thermal relaxation half-lives (τ_1/2), are essential for their adaptation in various applications. In this work, we studied the effect of co-planarization of the rotary fragment of two photochromic hydrazones with the core of the molecule on their switching properties. The Z and E isomers of both compounds exhibit red-shifted absorption bands relative to their twisted versions, allowing for their photoswitching using longer wavelengths of light. Additionally, the thermal half-lives of both hydrazones are drastically shortened from hundreds of years to days.     

Synthesis and Tautomeric Structure of Tris(arylazo) Derivatives of Novel 1H‐Bis‐imidazo[1,2‐b:2′,1′‐e]pyrazole Ring System

An efficient and convenient synthesis of tris(arylazo) derivatives of novel heterocyclic ring system, namely, 1H‐bis‐imidazo[1,2‐b:2′,1′‐e]pyrazole, is described. The structures of the compounds prepared and their tautomeric structure were elucidated on the basis of their elemental analyses and spectral data in addition to correlation of their acidity constants by Hammett equation. The mechanism of the studied reactions and their site selectivity are discussed.     

金属纳米颗粒制备中的还原剂与修饰剂*

金属纳米颗粒由于其独特的光学、电学、化学性质以及各种潜在的应用价值,受到不少研究人员的广泛关注。实现金属纳米粒子尺寸、形貌可控,改善粒子分散性和稳定性,提高产率及纯度已成为具有挑战性的研究课题,不断发展和完善金属纳米粒子的合成方法则显得尤为重要。本文总结了目前制备金属纳米材料的几种化学方法：化学试剂还原法、电化学还原法、辐射还原法等,分类介绍了化学试剂还原法中常用的无机、有机还原剂,以及含氮、磷、羧基、巯基小分子有机化合物以及高分子聚合物等修饰剂并重点总结了其还原和修饰机理。     

Benzoyl Group Migrations in Methyl 2,3,6-Trio-O-Benzoyl-4-deoxy-4-(N-Hydroxyamino)-α-D-Gluco and α-D-Galacto-Pyranosides

Abstract

Deoxy-N-hydroxyaminosugars constitute a novel family of sugars. The interest in them is mainly due to their close structural similarity to natural sugars, coupled, with their easy oxidation to nitroxide free radicals, enabling their study by ESR spectroscopy.¹ From the point of view of their chemical reactivity, the hydroxyamino group is an ambident nucleophile possessing complex orbital and topographical factors, which direct its reactivity to either of its heteroatoms.     

Tuning CH Hydrogen Bond-Based Receptors toward Picomolar Anion Affinity via the Inductive Effect of Distant Substituents

Inspired by nature, artificial hydrogen bond-based anion receptors have been developed to achieve high anion selectivity; however, their binding affinity is usually low. The potency of these receptors is usually increased by the introduction of aryl substituents, which withdraw electrons from their binding site through the resonance effect. Here, we show that the polarization of the C(sp³)-H binding site of bambusuril receptors, and thus their potency to bind anions, can be modulated by the inductive effect. The presence of electron-withdrawing groups on benzyl substituents of bambusurils significantly increases their binding affinities to halides, resulting in the strongest iodide receptor reported to date with an association constant greater than 10¹³ M⁻¹ in acetonitrile. A Hammett plot showed that while the bambusuril affinity toward halides linearly increases with the electron-withdrawing power of their substituents, their binding selectivity remains essentially unchanged.     

Quinone-based molecular electrochemistry and their contributions to medicinal chemistry: A look at the present and future

Molecular electrochemistry is closely linked to life sciences. Electron transfers play important roles in the bioactivation of redox-active drugs, in their metabolism/catabolism, and in their targeted release at precise destinations and frequently promote their ligand–target interactions. Altogether, this rich chemistry and the complexity of cellular environments and biocompartmentation often impede full investigation in situ of the whole chain of processes that sustain their therapeutic applications. Conversely, electrochemical ex situ investigations of drug properties and interactions performed in aqueous/aprotic/micellar/membrane/cell-mimetic media, combined with in vitro and in vivo data, are expected to provide extremely useful information on these processes. Therein, considering the ubiquitous case of quinones, we exemplified how such strategies allow controlling their beneficial or negative impact on cellular environments.     

The effect of temperature on the photoacidity of merocyanine photoacids in water

Merocyanine photoacids are molecular photoswitches that can be used to regulate acid-base reactions reversibly. Despite their growing impact across multiple research areas including materials science and nanotechnology, the effect of temperature on their functioning in aqueous environments has not yet been explored. Here we employ variable-temperature pH and UV-Vis analyses to rationalize their temperature-dependent (photo)chemical behaviors in water, showing that their photoacidity is inversely proportional to the temperature (by ca. ?0.01 pK/°C).     

New thioglycoside derivatives for use in odourless synthesis of MUXFN-glycan fragments related to food allergens

Thioglycosides are valuable tools for complex oligosaccharides' constructions. They present precious advantages due to their stability and crystalline nature. However, their major drawbacks are the repulsive smell of thiols utilised as precursors and, often, their toxicity such as in case of the commonly employed thiophenol and thioethanol. The use of commercially available methyl tert-butyl phenyl thiol (MbpSH) avoids these problems and is compatible with gram scale synthesis of thioglycoside donors. In this paper, we describe that Mbp thioglycosides are useful and convenient precursors for odourless oligosaccharide synthesis and we further demonstrate, as a proof of their versatility, their use in the construction of most of the glycosidic linkages found in N-glycans.     

Synthesis,Structural and Biological Properties of the Ring-A Sulfonamido Substituted Chalcones: A Review

Sulfonamidochalcones continue to assert themselves as versatile synthetic intermedi-ates and several articles continue to appear in literature describing their synthesis, chemical transformation and biological properties. These compounds are not only of interest from the medicinal chemistry context, their conformations and crystalline structures also continue to attract attention to explore non-covalent (intramolecular and intermolecular) interactions, control molecular conformations, and improve their physicochemical and optical properties. Despite an exhaustive list of examples of the ring-A sulfonamide-appended chalcones described in the literature, there is no com-prehensive review dedicated to their synthesis, structural and biological properties. This review focuses attention on the synthesis, structure and biological properties of the ring-A sulfonamide-appended chalcones (o/m/p-sulfonamidochalcones) as well as their potential as non-linear optical materials.     

In vitro antioxidant/prooxidant effects of combined use of flavonoids

The present study was undertaken to investigate the individual and combined antioxidant or prooxidant effects of genistein, daidzein and quercetin in human erythrocytes and rat microsomes in vitro. Their reducing potential against oxidation of a redox sensitive fluorescent probe, their protective effect against H₂O₂-induced membrane lipid peroxidation and their inhibitory effect on AAPH-induced hemolysis were evaluated. Genistein and daidzein were prooxidant in erythrocytes but antioxidant in microsomes where their metabolites might have been formed which suggests the importance of metabolic capacity in in vitro models to predict the physiological situation. Quercetin showed antioxidant effects in all models and conditions. Prooxidant effect of ‘genistein–daidzein mixture’, at their concentrations reflecting the real life, was suppressed by addition of quercetin to the mixture. Our study shows that flavonoids can exert prooxidant effects depending on the conditions, but the mixture effect should be considered while assessing their effects and safety in humans.     

Synthesis and Hybridization Properties of Oligodeoxynucleotides with Long‐Chain Linkers

New oligonucleotides with a long‐chain linker (6,9‐dioxa‐3,12‐diazatetradecane‐1,14‐diyl) in their backbone were synthesized, and their hybridization properties were studied by measurement of their T_m curves and fluorescence spectra. The T_m analyses revealed that these oligonucleotides could bind to their complementary strands despite the presence of the long‐chain linker. We also demonstrated interesting fluorescence properties of oligodeoxynucleotides with an anthracen‐9‐ylmethyl group on one of the two N‐atoms in the long‐chain linker. The fluorescence intensity of these oligonucleotides increased upon their hybridization to the complementary strands and was sensitive to the presence of the mismatch base pairs at a specific position.     

Chemical behavior of antimony and tellurium fission products in aqueous solutions

The oxidation states of antimony and tellurium fission products formed in the aqueous solutions of²³³U and²³⁵U irradiated in a reactor were studied by means of anion exchange method. Results were corrected for the thermal reactions such as radiation induced reactions using double tracers for each element. In hot reactions, the isotopes formed independently by fission take their reduced states almost completely, whereas the isotopes formed by β-decay of their precursors favor their oxidized states. The fractions of the tellurium isotopes in the oxidized state depend on the β-decay energy of their precursors, whereas those of the antimony isotopes are nearly constant irrespective of the β-decay energy. The different behaviors between those two elements would reflect the chemical properties of their precursors.     

Chitosan Bio‐Based Organic–Inorganic Hybrid Aerogel Microspheres

Recently, organic–inorganic hybrid materials have attracted tremendous attention thanks to their outstanding properties, their efficiency, versatility and their promising applications in a broad range of areas at the interface of chemistry and biology. This article deals with a new family of surface‐reactive organic–inorganic hybrid materials built from chitosan microspheres. The gelation of chitosan (a renewable amino carbohydrate obtained by deacetylation of chitin) by pH inversion affords highly dispersed fibrillar networks shaped as self‐standing microspheres. Nanocasting of sol–gel processable monomeric alkoxides inside these natural hydrocolloids and their subsequent CO₂ supercritical drying provide high‐surface‐area organic–inorganic hybrid materials. Examples including chitosan–SiO₂, chitosan–TiO₂, chitosan–redox‐clusters and chitosan–clay‐aerogel microspheres are described and discussed on the basis of their textural and structural properties, thermal and chemical stability and their performance in catalysis and adsorption.     

Phased cycles

We define a phased graph G to yield an adjacency matrix A(G) having general magnitude-1 values in the same locations as the usual unphased case, but subject to the restriction that A be Hermitian. Some characteristics of phased cycles, their eigenspectra, their symmetry, and their net energy are contemplated and described.     

Characterizing polymer macrostructures by identifying and locating microstructures along their chains with the kerr effect

In this brief report, we demonstrate that Kerr effect measurements, which determine the excess birefringence contributed by polymer solutes in dilute solutions observed under a strong electric field, are highly sensitive to and capable of determining their microstructures, as well as their locations along the macromolecular backbone. Specifically, using atactic triblock copolymers with the same overall composition of styrene (S) and p-bromostyrene (pBrS) units, but with two different block arrangements, that is, pBrS₉₀-b-S₁₂₀-b-pBrS₉₀ (I) and S₆₀-b-pBrS₁₈₀-b-S₆₀ (II), which are indistinguishable by NMR, we detected a dramatic difference in their molar Kerr constants (_mK), in agreement with those previously estimated. Although similar in magnitude, their Kerr constants differ in sign, with _mK(II) positive and _mK(I) negative. In addition, S/pBrS random and gradient copolymers synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization exhibit a heretofore unexpected enhanced enchainment of racemic (r) pBrS-pBrS diads. Comparison of their observed and calculated _mKs suggests that the gradient S/pBrS copolymers possess an unanticipated additional gradient in stereosequence that parallels their comonomer gradient, that is, as the concentration of pBrs units decreases from one end of the copolymer chain to the other, so does the content of r diads. This conclusion could only be reached by comparison of observed and calculated Kerr effects, which access the global properties of macromolecules, and not NMR, which is only sensitive to local polymer structural environments, but not to their locations on the copolymer chains. Molar Kerr constants are characteristic of entire polymer chains and are highly sensitive to their constituent microstructures and their distribution along the chain. They may be used to both identify constituent microstructures and locate them along the polymer chain, thereby enabling, for the first time, characterization of their complete macrostructures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

LC–HRMS methods for the quantification of two artemisinin drugs and their metabolites in rat blood and plasma

As first-line antimalarials used in the artemisinin combination therapy, artemisinin drugs exert their action inside red blood cells. However, the blood pharmacokinetic characteristics of artemisinin drugs have not been fully revealed owing to their built-in chemical instability initiated by Fe²⁺ released from hemoglobin, with limited information on their metabolites. In this study, liquid chromatography tandem high-resolution mass spectrometric (LC–HRMS) methods were developed for the quantification of two representative artemisinin drugs (artemisinin, ART; dihydroartemisinin, DHA) and their respective metabolite (deoxyartemisinin, D-ART; dihydroartemisinin glucuronide, DHA-Glu) in rat blood/plasma. The blood samples were pretreated with the stabilizer (0.4 m potassium dichromate and 3% EDTA-2Na). The methods displayed excellent specificity, linearity, accuracy and precision for ART (17.7–709.2 nm ) and its metabolite D-ART (18.8–751.9 nm ), and the linear range was 40.0–4,000.0 nm for both DHA and DHA-Glu. The methods were successfully applied to the pharmacokinetic studies of ART and DHA in rats. The blood-to-plasma ratio was 0.8–1.5 for ART, 1.0–1.5 for D-ART, 1.2–2.2 for DHA and 0.9–1.3 for DHA-Glu, which was time dependent. The results indicated that artemisinin drugs and their metabolites showed a high but different blood-to-plasma ratio, which should be considered when optimizating their dosing regimens or evaluating their clinical outcomes.     

Structural-functional characteristics of toxins from spiders of the araneidae family

With the aid of a series of chromatographic operations we have isolated 14 individual tow-molecular-mass compounds (M_T — 624-744 Da) blocking postsynaptic glutamate and acetylcholine receptors from the venoms of species of spiders of the family Araneidae. It has been shown that from their structural characteristics and the nature of their action they can be divided into two families differing by their chromophoric groups and the degree of reversibility of their interaction with various receptors.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 916–920, November–December, 1996. Original article submitted March 18, 1996.     

Synthese von Diterpenen als mögliche biogenetische Vorläufer des C20-Carotinoides Crocetin

Synthesis of Diterpenes as Possible Biogenetic Precursors of the C₂₀-Carotenoid Crocetin With regard to the investigation of the biosynthesis of the C₂₀-carotenoids in saffron the four diterpenes 6–9 were synthesized, who differ only in their degree of saturation. A detailed analysis of their ¹H- and ¹³C-NMR spectra has been achieved by their mutual comparison.     

Organizational stabilities of bulk neat and well‐mixed,blended polymer samples coalesced from their crystalline inclusion compounds formed with cyclodextrins

Cyclodextrins (CDs) are cyclic starches containing α‐1,4‐linked glucose units. Commonly available α‐, β‐, and γ‐CDs have six, seven, and eight glucose units, respectively. They are well known for forming noncovalent inclusion complexes (ICs) with a variety of guest molecules, including many polymers, by threading and inclusion into their relatively hydrophobic interior cavities, which are roughly cylindrical, with diameters of ～0.5–1.0 nm. Warm water washing of crystalline CD‐ICs containing polymer guests insoluble in water or treatment with amylase enzymes serve to remove the host CDs and result in the coalescence of the guest polymers into solid bulk samples. When guest polymers are coalesced from their CD‐ICs by carefully removing the host CD lattices, they are observed to solidify with structures, morphologies, and even conformations that are distinct from bulk samples made from their solutions and melts. In addition, molecularly mixed, intimate blends can be obtained upon coalescence of two or more normally immiscible polymer guests from their common CD‐ICs. Not only are the organizations and behaviors of bulk polymer samples significantly modified on coalescence from their CD‐ICs, but both are also maintained for significant periods of time even when heated above their T_gs and T_ms, where their chains are mobile. Here, we discuss the long‐time, high temperature stabilities of the organizations and properties of bulk polymers coalesced from their crystalline CD‐ICs. While random‐coiling of their initially coalesced, largely extended, separated, and unentangled chains may be relatively rapid, we conclude that the subsequent slow establishment of homogeneous melts or phase‐segregated blends results from the extremely sluggish center‐of‐mass diffusion that must accompany full entanglement of their chains. Apparently, the process of entangling the largely separated and not fully interpenetrating randomly coiled chains initially coalesced from their CD‐ICs is particularly slow, much slower in fact than the center‐of mass diffusion of polymer chains in their fully entangled melts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1543–1553, 2009