The Structure of Cellulose by Conformational Analysis. Part 4. Crystalline Cellulose II

The Kolpack, Weih, and Blackwell antiparallel central chain model was found to be the most energetically stable for the crystalline structure of cellulose II. Computational results indicated that the two most probable Sarko models are considerably less stable and less probable. The conformations of the monomers terminating the crystalline zone have been described. The predominance of van der Waals and H-bond interactions in the crystalline zone have been confirmed, and the H-bond values, locations, and distribution in the crystalline zone have been accurately mapped. The cellulose II crystallite has been confirmed to be considerably more stable than the cellulose I crystallite. Positions of atomic groups from the ab initio conformational analysis are consistent with the x-ray data for the Kolpack, Weih, and Blackwell model.     

Chalcogen Bonds in Selenocysteine Seleninic Acid,a Functional GPx Constituent,and in Other Seleninic or Sulfinic Acid Derivatives

The controlled oxidation reaction of L-selenocystine under neutral pH conditions affords selenocysteine seleninic acid (3-selenino-L-alanine) which is characterized also by means of single-crystal X-ray diffraction. This technique shows that selenium forms three chalcogen bonds (ChBs), one of them being outstandingly short. A survey of seleninic acid derivatives in the Cambridge Structural Database (CSD) confirms that the C−Se(=O)O− functionality tends to act as a ChB donor robust enough to systematically influence the interactional landscape in the solid. Quantum Theory of Atom in Molecules (QTAIM) analysis proves the attractive nature of the short contacts observed in crystals containing the seleninic functionality and calculation of surface molecular electrostatic potential (MEP) reveals that remarkably positive σ-holes can frequently be found opposite to the covalent bonds at selenium. Both CSD searches and QTAIM and MEP approaches show that also the sulfinic acid moiety can function as a ChB donor, albeit less frequently than the seleninic acid one. These findings may contribute to a better understanding, at the atomic level, of the mechanism of action of the enzymes that control oxidative stress and ROS deactivation and that contain selenocysteine seleninic acid and cysteine sulfinic acid in the active site.     

Partially sulfonated ethylene–vinyl alcohol copolymer as new substrate for 3,4‐ethylenedioxythiophene vapor phase polymerization

A new conducting composite polymer film is obtained by vapor phase polymerization of 3,4‐ethylenedioxythiophene (EDOT) on a biocompatible polyanion derived from the partial sulfonation (32%) of statistical ethylene vinyl alcohol copolymer (EVAL32). EVALS32 and the oxidant (iron(III) p‐toluenesulfonate, [PTS]) are contemporaneously spin coated from a methanol/water solution on glass slide. EVALS32–PTS‐coated glass slides are exposed to EDOT vapors, and the polymerization is followed by Vis–NIR spectroscopy. We observed that PEDOT slowly grows into the bulk of EVALS32 matrix. Thanks to the sulfonic groups of the polyanion acting as doping agents, a highly conjugate p‐doped EVALS32‐PEDOT composite film with a good conductivity (1.6 × 10² S cm^?1), transparency, and stability in water is obtained. The EVALS32–PEDOT film seems an ideal candidate for the preparation of organic devices to be applied in electronics, biosensor, or actuation technology. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1203–1210     

Stereoselective Preparation of Allylic Alcohol Intermediates in the Synthesis of Deoxysugars

ABSTRACT

4S-cis-2, 2, 5-Trimethyl-l, 3-dioxolane-4-carboxaldehyde (1) undergoes stereoselective nucleophilic addition with different vinyl metals. Allylic alcohols thus obtained are possible intermediates in the synthesis of deoxysugars. By ? reiterative 1 C extension cycle, 6-deoxyhexoses can be obtained.     

Copper hexacyanoferrate modified electrodes for hydrogen peroxide detection as studied by X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) has been used to monitor the local geometry of Fe and Cu sites of copper hexacyanoferrates (CuHCF)-modified electrodes which find application in the electrochemical detection of hydrogen peroxide. The XAS approach has permitted to check the nature of the Cu and Fe sites and to investigate their local structure around about 500 pm from the metal centres. The measurements have been done on electrodes prior and after the addition of known quantities of hydrogen peroxide at two different concentration ranges, following a protocol consisting of H₂O₂ addition, applied potential, and rest period. For the CuHCF-modified electrode, this protocol leads to the increasing conversion to an already present “inactive” component, which limits the usability of the sensor; whereas the electrode modified with the Cu²⁺-loaded CuHCF displays a better resistance to this unavoidable process. In particular, the formation of the “inactive” component takes place more slowly, confirming the capability, at molecular scale, of such Cu-enriched CuHCF used as electrode modifier to detect more efficiently hydrogen peroxide, as recently demonstrated in our previous paper.     

Analysis of gases emitted during carbonization degradation of polyflavonoid tannin/furanic rigid foams

The gases emitted during thermal degradation of tannin based rigid foams have been monitored during the process of carbonization under nitrogen flow. The gases have been trapped on multi-bed solid-phase adsorbent (SPA) tubes and analyzed by gas chromatography/mass spectrometry (GC/MS). Toluene and dihydroxybenzenes have been identified throughout as the most common degradation compounds obtained. Phenols and xylenes, formed from the degradation of the polyflavonoid tannin structure, are also well represented in the emitted gases. A few furanic compounds are also present.     

Electrodeposited glucose oxidase/anionic clay for glucose biosensors design

An amperometric glucose biosensor was developed using an anionic clay matrix (layered double hydroxide (LDH), Ni/Al-NO₃) for the immobilization of glucose oxidase (GOx). The biofilm was prepared by electrodeposition of the clay and GOx and subsequent cross-linking with glutaraldeyde. The Pt surface modified with the Ni/Al-NO₃ shows a much reduced noise, giving rise to a better signal to noise ratio for the currents relative to H₂O₂ oxidation, and a linear range for H₂O₂ determination wider than the one observed for bare Pt electrodes. Under the optimised operative conditions, the performances of the biosensor have been evaluated by measuring the steady-state currents (at +0.45 V versus SCE) to increasing concentrations of glucose in “air saturated” 0.1 M phosphate buffer (pH 7.0). Both batch and flow injection modes were explored. The response to glucose was linear up to 8.0 and 12.0 mM, and the sensitivities were 7.7 ± 0.1 and 19.1 ± 0.2 mA M⁻¹ cm⁻², respectively. The current response of the biosensors does not significantly change for 15 consecutive days in batch and for 10 days in flow, at least, if stored at 4 °C in phosphate buffer, when not in use. The effects of interferants and applicability to fruit juices and soft drinks analysis of the biosensor were also investigated.     

Intercalation of iron(III) hexacyano complex in a Ni,Al hydrotalcite-like compound

The product obtained by the intercalation of hexacyanoferrate(III) inside a Ni, Al hydrotalcite-like compound (Htlc) has been characterized using XRD, FT-IR, Raman, and XAS spectroscopy. The intercalation was carried out by anionic exchange of the originally existing chloride ions. The combined use of those techniques gave more insight on the insertion chemistry of Htlcs. Extended X-ray absorption fine structure spectra of the intercalated Htlc demonstrated that the native structure was stable during the iron complex insertion, whereas the exchange process occurred with a partial reduction of hexacyanoferrate(III). Both Raman and FT-IR spectroscopy pointed out the concomitant formation of K(2)NiFe(II)(CN)(6) and KNiFe(III)(CN)(6). The effect of aging on the intercalated product is also addressed.     

Granular species segregation under vertical tapping: effects of size, density, friction, and shaking amplitude

We present extensive molecular dynamics simulations on species segregation in a granular mixture subject to vertical taps. We discuss how grain properties, e.g., size, density, friction, as well as shaking properties, e.g., amplitude and frequency, affect such a phenomenon. Both the Brazil nut effect (larger particles on the top, BN) and the reverse Brazil nut effect (larger particles on the bottom, RBN) are found and we derive the system comprehensive "segregation diagram" and the BN to RBN crossover line. We also discuss the role of friction and show that particles which differ only for their frictional properties segregate in states depending on the tapping acceleration and frequency.     

Mass 2 and 3 cluster structure study with quasi-free reactions induced by 58 MeV protons on 9Be, 12C and 14N

Cross sections for (p, pd) and (p,p³He) reactions at 58 MeV have been measured for ⁹Be, ¹²C and ¹⁴N targets. An energy resolution of about 400 keV permitted identification of several excited states in the different residual nuclei. The experimental results are presented and analysed in the framework of the distorted-wave impulse approximation. Spectroscopic and mechanism information is discussed. Some additional quasi-free reactions involving t, ³He and α structure of ⁹Be have been observed and are also reported.