The selective oxidation of ethanol to CO2 at Ptpc/Ir/Pt metallic multilayer nanostructured electrodes

In this work, Pt_pc/Ir/Pt metallic multilayer nanostructured electrodes were prepared. The composition and number of the constituent metal layers were varied and the number of Ir and Pt layers studied were: 1.5:1.5, 1.5:10, 10:1.5, 10:10 and 250:250 Ir and Pt monolayers. The ethanol electrooxidation reaction and its products was studied using electrochemical in situ FTIR technique and could be observed as a selective cleavage of the ethanol CC bond in acidic electrolyte. Neither acetaldehyde nor acetic acid IR band could be observed for ethanol electrooxidation at 1.5 V vs. RHE over Pt_pc/Ir₂₅₀/Pt₂₅₀ metallic multilayer electrodes. Also, the enhancement on CO₂ production over this electrode was more than six times the amount observed using the Pt_pc electrodes. Thus, the complete CC cleavage bond in ethanol molecule was observed, leading only CO₂ as reaction product.     

Homogeneous and supported copper(II) acetate as catalyst for CO coupling reactions

The reactivity of copper(II) acetate as catalyst in a standard CO coupling reaction has been systematically evaluated. Optimization of the reaction conditions resulted in a protocol involving stoichiometric amounts of reagents, a substoichiometric amount of base and 20 mol% catalyst, at 50 °C in 1,2-dichloroethane and under 1 atm O₂. Next, the reactivity of polymer-supported copper(II) acetate was evaluated. Although it is found that, in contrast to previous results obtained in related CN coupling reactions, the polymer-supported catalyst is in this case less efficient than the corresponding homogeneous one, the catalyst turns out to be conveniently recovered from the reaction mixture by simple filtration.     

A Raman spectroscopic study of the uranyl phosphate mineral bergenite

Raman spectroscopy at 298 and 77 K of bergenite has been used to characterise this uranyl phosphate mineral. Bands at 995, 971 and 961 cm-1 (298 K) and 1006, 996, 971, 960 and 948 cm-1 (77K) are assigned to the nu1(PO4)3- symmetric stretching vibration. Three bands at 1059, 1107 and 1152 cm-1 (298 K) and 1061, 1114 and 1164 cm-1 (77 K) are attributed to the nu3(PO4)3- antisymmetric stretching vibrations. Two bands at 810 and 798 cm-1 (298 K) and 812 and 800 cm-1 (77 K) are attributed to the nu1 symmetric stretching vibration of the (UO2)2+ units. Bands at 860 cm-1 (298 K) and 866 cm-1 (77 K) are assigned to the nu3 antisymmetric stretching vibrations of the (UO2)2+ units. UO bond lengths in uranyls, calculated using the wavenumbers of the nu1 and nu3(UO2)2+ vibrations with empirical relations by Bartlett and Cooney, are in agreement with the X-ray single crystal structure data. Bands at (444, 432, 408 cm-1) (298 K), and (446, 434, 410 and 393 cm-1) (77 K) are assigned to the split doubly degenerate nu2(PO4)3- in-plane bending vibrations. The band at 547 cm-1 (298 K) and 549 cm-1 (77 K) are attributed to the nu4(PO4)3- out-of-plane bending vibrations. Raman bands at 3607, 3459, 3295 and 2944 cm-1 are attributed to water stretching vibrations and enable the calculation of hydrogen bond distances of >3.2, 2.847, 2.740 and 2.637 A. These bands prove the presence of structurally nonequivalent hydrogen bonded water molecules in the structure of bergenite.     

Ion transfer across liquidliquid interfaces from transition-state theory and stochastic molecular dynamics simulations

We investigate the kinetics and dynamics of ion transfer across liquidliquid interfaces. We calculate the potential of mean force (pmf) of ion transfer from Monte Carlo simulations of a lattice–gas model, assuming independent chemical and electrostatic contributions. The shape of the pmf justifies considering the transfer as activated. The kinetics are obtained from transition-state theory and independently from stochastic molecular dynamics simulations. Both methods yield consistent results, with straight Tafel plots and friction effects in line with Kramers’ theory, but stronger than for a diffusing particle. A higher friction makes barrier recrossing more likely.     

Specific crystal structure of poly(3-hydroxybutyrate) thin films studied by infrared reflection–absorption spectroscopy

Infrared reflection–absorption (IR-RAS) and transmission spectra were measured for poly(3-hydroxybutyrate) (PHB) thin films to explore its specific crystal structure in the surface region. As IR-RAS is sensitive to the vibration mode of perpendicular orientation of the surface, differences between IR-RAS and transmission spectra indicate an orientation of the lamella structure in the surface of PHB thin films. The relative intensity of the crystalline CO stretching band in the IR-RAS spectrum is significantly weaker than that in the transmission spectrum. It may be concluded that the transient dipole moment of the CO stretching mode of the crystalline state is not oriented perpendicular but nearly parallel to the substrate surface. On the other hand, the relative intensity of the band at 3009 cm⁻¹ due to the C–H stretching mode of the C–HOC hydrogen bonding is similar between the IR-RAS and transmission spectra, suggesting that the C–H bond is oriented neither perpendicular nor parallel to the substrate surface but in an intermediate direction. Since the CO group of the C–HOC hydrogen bonding is oriented nearly parallel to the surface and its C–H group is in the intermediate direction, it is very likely that the C–HOC hydrogen bonding has a somewhat bent structure. These results are in good agreement with our previous conclusion that the C–HOC hydrogen bonding of PHB exists along the a-axis (not the b-axis) between the CH₃ group of one helix and the CO group of another helix.     

Monomer insertion mechanism of ring-opening polymerization of -caprolactone with yttrium alkoxide intermediate: A DFT study

The mechanism of -caprolactone (CL) insertion into a Y–OCH₃ bond was investigated using density functional theory (DFT) calculations. The optimized geometries and corresponding Gibbs-free energies of the intermediates were obtained, which confirmed a four-step coordination-insertion mechanism. The coordination of CL onto yttrium center led to a nucleophilic addition of the carbonyl group of CL, followed by an intramolecular alkoxide ligand exchange. A monomer insertion was completed by the CL ring opening via acyl–oxygen bond cleavage. The formation of the five-coordinated yttrium intermediate, 3, was found to be the rate-determining step. This study could be applicable to ring-opening polymerisation (ROP) of CL initiated by lanthanide metal complexes.     

Novel BrФnsted Acidic Ionic Liquid Based on a Cyclic Guanidinium Cation： a Green, Efficient, and Recyclable Dual Slovent-catalyst System for Fisher Esterification

A novel Brфnsted acidic ionic liquid(IL)based on the cyclic guanidinium cation has been synthesized.This IL,as a strong Brфnsted acid catalyst or solvent,shows high catalytic activity and biphsaic behavor in the esterifications of carboxylic acids and alcohols.The produced esters as a separate phase can be conveniently decanted out from the IL and the IL is recyclable without any loss of catalytic activity.     

BF3·OEt2-catalyzed synthesis of 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran and trans-fused hexahydropyrano[3,2-c]chromene derivatives

A novel intramolecular Prins cyclization of (E)-5-(2-(hydroxymethyl)phenyl)pent-4-en-1-ol with aldehydes has been achieved using 10 mol % BF₃·Et₂O to produce 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran derivatives in good to excellent yields with high selectivity. Similar type of coupling with salicylaldehydes provides the trans-fused hexahydropyrano[3,2-c]chromene derivatives in excellent yields.     

InBr3-catalyzed stereoselective synthesis of 3,4-disubstituted hexahydro-1H-furo[3,4-c]pyran derivatives

An ?,δ-unsaturated alcohol tethered with a hydroxyl group, that is, (E)-2-styrylbutane-1,4-diol (1) undergoes a smooth bicyclization with various aldehydes in the presence of 10 mol % InBr₃ and at 0 °C to afford a novel series of hexahydro-1H-furo[3,4-c]pyran derivatives in good yields with high diastereoselectivity.     

Patterning of biomolecules on a poly(-caprolactone) film surface functionalized by ion implantation

Biomolecule patterning is important due to its potential applications in biodevices, tissue engineering, and drug delivery. In this study, we developed a new method for a biomolecular patterning on poly(-caprolactone) (PCL) films based on ion implantation. Ion implantation on a PCL film surface resulted in the formation of carboxylic acid groups. The generated carboxylic acid groups were used for the covalent immobilization of amine-functionalized p-DNA, followed by hybridization with fluorescently tagged c-DNA. Biotin-amine was also covalently immobilized on the carboxylic acid generated PCL surfaces. Successful biotin-specific binding of streptavidin further confirmed the potential of this strategy for patterning of various biomolecules.     

Degradation of copolymers obtained by ring-opening polymerization of glycolide and -caprolactone: A high resolution NMR and ESI-MS study

Electrospray ionization-mass spectrometry (ESI-MS) and proton nuclear magnetic resonance (¹H NMR) have been used to investigate the hydrolytic degradation of copolymers obtained by bulk ring-opening copolymerization of glycolide and -caprolactone with monomer ratios ranging from 70/30 to 30/70. NMR allows changes of the average sequence distribution and composition of the components to be followed. In contrast, ESI-MS is able to reveal the detailed chemical structures of various sequences despite the molecular weight limit of 2000 Da. Combination of ESI-MS with NMR can thus provide information to describe microstructure changes during degradation. The distribution of various oligomers shown in the form of planar projections is of great interest for the design of biodegradable system aimed at medical applications.     

Reaction of diacetylmonoxime with morpholine N-thiohydrazide in the absence and in presence of a metal ion: Facile synthesis of a thiadiazole derivative with non-bonded SS interaction

The condensation of diacetylmonoxime (damnx) with morpholine N-thiohydrazide (mth) in 1:1 molar ratio in ethanol (16 h) afforded a nitrogen–sulfur zwitterionic heterocyclic compound, N-(3,4-dimethyl-1,2,5-thiadiazole-2-ium-2-yl)morpholine-4-carbothioate (dtmc). However, the same reaction in presence of [Zn(OAc)₂]·2H₂O in ethanol under gentle reflux on (3 h) yielded the zinc complex, [Zn(Hdammthiol)(OAc)(H₂O)]·H₂O, where H₂dammthiol (H₂L²) is the thiol form of tridentate NNS donor thiohydrazone ligand, diacetylmonoxime morpholine N-thiohydrazone (Hdammth). Both the nitrogen–sulfur heterocyclic compound and the zinc complex have been characterized by elemental analyses, spectroscopy (IR, UV–Vis, ¹H NMR and ¹³C NMR) and single crystal X-ray crystallography. It is noteworthy that the heterocyclic compound shows SS interaction with distance 2.738 Å in its planar conformation. The heterocyclic compound forms two dimensional supramolecular sheets through C–HO and ππ interactions while the zinc complex, with distorted square pyramidal geometry, forms 1D supramolecular chain. A mechanism has been proposed for the formation of nitrogen–sulfur heterocyclic compound.     

Boron trifluoride-catalyzed degradation of poly--caprolactone at ambient temperature

Poly--caprolactone (PCL) can be accelerated to degrade in the presence of boron trifluoride at ambient temperature. The degradation behaviors were studied by using the inherent viscosity measurement, gel permeation chromatography (GPC), infrared analysis (FTIR), nuclear magnetic resonance analysis (NMR), and thermal analysis (DSC). With increasing the addition amount of boron trifluoride, the molecular weight of PCL decreases; the molecular weight distribution is broadened; and the degree of crystallinity of PCL increases at first at low BF₃ level, then decreases when BF₃ content exceeds to 2.64 wt%. The results of IR, ¹HNMR and GPC reveal that -caprolactone monomer does not occur and the main degradation products are the oligomers of PCL with low molecular weight. The mechanism for boron trifluoride-catalyzed degradation of PCL is discussed.     

Particle size and concentration of poly(-caprolactone) and adipate modified starch blend on mineralization in soils with differing textures

The objective of this study was to evaluate the effect of particle size and concentration of poly(-caprolactone) and adipate modified starch blend on mineralization in soils with differing textures, comparing it with polyethylene under the same experimental conditions. Two soil types were used: a Kandiudalfic Eutrudox with a clayey texture and an Arenic Hapludult with a sandy texture. The two different plastic specimens were incorporated in the form of plastic films with three increasing particle sizes and six doses, from 0 to 2.5 mg C g⁻¹ soil. Each plastic dose was incorporated into 200 g of soil placed in a hermetically closed jar at 28 °C, and incubated for a 120-day period to determine CO₂ evolution. Once again it was confirmed that polyethylene is almost non-biodegradable, in contrast to PCL/S, which can be defined as a biodegradable material. Soil texture affected the mineralization kinetics of the plastic specimens, with higher values for the clayey soil. No changes in soil microbial biomass-C or -N were observed by adding polyethylene and PCL/S to the soil. Also, no significant differences were observed on seed emergence and development of rice seedlings (Oryza sativa L.) in plastic modified soil.     

Pyrolysis of polyphenylenes with PCL or/and PSt side chains

Thermal degradation characteristic of polyphenylenes is an important issue for developing a rational technology of polymer processing and applications. In this study, we discussed thermal degradation of polyphenylenes (PP) with poly(-caprolactone) (PCL) and/or PCL/polystyrene copolymers (PSt) prepared by combined controlled polymerization and cross-coupling processes via direct pyrolysis mass spectrometry. When PP-graft-PCL/PSt copolymers were considered, thermally less stabile PCL side chains decomposed in the first step. In the second stage of pyrolysis, the decomposition of the polystyrene chains has taken place. A slight increase in thermal stability of PCL chains for PP-graft-PCL/PSt copolymers was noted compared to copolymer PP-graft-PCL due to the interaction between PSt and PCL chains. This interaction was stronger when PSt chains were linked to the 2-position of the 1,4-phenylene ring.     

Effect of soy protein isolate on the thermal, mechanical and morphological properties of poly (-caprolactone) and corn starch blends

The development of biodegradable polymers is considered to be a good alternative to decrease the volume of the plastic waste disposed into the environment every year. The use of natural polymers as raw materials to develop polymer blends and composites has increased the demand for renewable sources such as starch and soy protein.In this work, the authors prepared and characterized the thermal, mechanical and morphological properties of blends based on poly (-caprolactone) and modified corn starch, with added soy protein isolate (SPI) and sorbitol. All samples were processed by extrusion in a single-screw extruder and hot pressing. It was observed that the addition of modified corn starch and SPI were responsible for the reduction of thermal and mechanical properties of the materials, compared to pristine PCL. However, with increasing amounts of SPI and the reduction of starch incorporated into the samples, their properties tend to recover. The insertion of soy protein isolate in the formulations was done with the aim of balancing the C/N ratio of the blend, which plays a key role in the biodegradation process of these materials.     

Determination of hydroxyl radical in Fenton system

Under visible light illumination,2,3-diaminophenazine(DAPN) was generated from the oxidation of o-phenylenediamine (OPDA) in Fe~(3+)/H_2O_2 solution.Hydroxyl radical(~·OH) produced in this system was determined by directly measuring the concentration of DAPN.In comparison with the traditional methods,the determination is more accurate and simple.     

Theoretical studies on the imine germylenoid HNGeNaF and its insertion reaction with R-H (R = F, OH, NH2, CH3)

The geometries and isomerization of the imine germylenoid HNGeNaF as well as its insertion reactions with R-H (R = F, OH, NH₂, CH₃) have been systematically investigated at the B3LYP/6-311+G^∗ level of theory. The potential barriers of the four insertion reactions are 117.2, 172.6, 219.7, and 322.3 kJ/mol, respectively. Here, all the mechanisms of the four reactions are identical to each other, i.e., an intermediate has been formed first during the insertion reaction. Then, the intermediate could dissociate into the substituted germylene (HNGeHR) and NaF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies for the four reactions are 185.0, 208.1, 224.4, and 266.9 kJ/mol, respectively, which are linearly correlated with the calculated barrier heights. Compared with the insertion reaction of HNGe: and R-H, the introduction of NaF makes the insertion reaction occur easily though it is more difficult to proceed than that of insertion reaction between H₂GeNaF and R-H. Furthermore, the effects of halogen (F, Cl, Br) substitution and inorganic salts employed on the reaction activity have also been discussed. As a result, the relative reactivity among the four insertion reactions should be as follows: H-F > H-OH > H-NH₂ > H-CH₃.     

Pyrolysis of poly(phenylene vinylene)s with polycaprolactone side chains

The thermal degradation characteristics of a new macromonomer poly(-caprolactone) with central 4,4′-dicarbaldehyde terphenyl moieties and poly(phenylene vinylene)s with well defined (-caprolactone), (PPV/PCL) as lateral substituents were investigated via direct pyrolysis mass spectrometry. The unexpectedly high thermal stability of the macromonomer was attributed to intermolecular acetylation of benzaldehyde yielding a hemiacetal and causing a crosslinked structure during the pyrolysis. Increased thermal stability of the PCL chains was detected for all samples. The increase in stability of PCL chains was much more pronounced than was detected for poly(p-phenylene)-graft-poly(-caprolactone) copolymer (PPP/PCL); the upward temperature shift was about 100 °C for PPV/PCL and only 20 °C for PPP/CL. This pronounced effect may be due to higher thermal stability of PPV compared to PPP and the decrease in steric hindrance for PPV with PCL side chains.