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.     

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.     

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.     

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.     

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.     

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.     

Phase controllable synthesis of unusual -Ga2O3 single crystals with promising luminescence property

A new synthetic approach to unusual -Ga₂O₃ with improved luminescence properties was developed by taking advantage of a microwave-assisted synthesis followed by calcinations at appropriate temperatures. Upon control of crystallinities of GaOOH precursors and the followed calcination temperature, the single crystalline -Ga₂O₃ nanorods can be synthesized in a large scale. The resulting products were characterized by transmission electron microscopy, powder X-ray diffraction, and cathodoluminescence. The luminescence property of this unusual Ga₂O₃ phase was investigated for the first time.     

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.     

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.     

Conformational influences of the polymorphic forms on the CO and C–H stretching modes of five saturated monoacid triglycerides studied by Raman spectroscopy at various temperatures

A study of the vibrational behavior of five saturated monoacid triacylglycerides is performed by Raman spectroscopy at various temperatures in two separate spectral ranges: 1780–1700 and 3100–2650 cm⁻¹. The samples are studied in polycrystalline phase at room temperature, in isotropic liquid phase, and in polycrystalline phase after cooling from the isotropic liquid phase. The CO stretching mode of these triglycerides changes significantly according to the temperature: we observe three components, or an unresolved doublet, or a resolved doublet. The I(2845)/I(2880) ratios (in the C–H stretching spectral region) of the different saturated monoacid triglycerides vary also according to the temperature. The study of these two indicators (the CO stretching mode and the I(2845)/I(2880) ratio) has permitted us to determine the polymorphic forms of the studied triglycerides.     

Distribution of Sorbitan Monooleate in poly(l-lactide-co--caprolactone) nanofibers from emulsion electrospinning

The aim of this study was to investigate the distribution of Sorbitan Monooleate (Span80) in poly(l-lactide-co--caprolactone) (PLLACL) nanofibers from emulsion electrospinning. The hypothesis was that PLLACL/Span80 nanofibrous mats would have some Span80 on the surface of the composite nanofibers. To test the hypothesis, the electrospinning of emulsions made of PLLACL, chloroform, Span80, and distilled water to prepare PLLACL/Span80 nanofibers was systematically investigated. The morphology of PLLACL/Span80 nanofibers was investigated by atomic force microscopy. The surface hydrophilicity of the nanofibrous mats were examined by water contact angle test. The distribution of Span80 on the surface of nanofibrous mats was also confirmed by the performance of pig iliac endothelium cells on the nanofibrous mats.     

Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.     

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.     

H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about CC bond

The rotational barriers between the configurational isomers of two structurally related push–pull 4-oxothiazolidines, differing in the number of exocyclic CC bonds, have been determined by dynamic ¹H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl₃ at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG^# 98.5 kJ/mol (at 298 K). The variable-temperature ¹H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d₆, possessing the two exocyclic CC bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG^# separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the SCCCO entity. The ¹³C NMR Δδ_C(2)C(2′) values, ranging from 58 to 69 ppm in 1a–d and 49-58 ppm in 2a–d, correlate with the degree of the push-pull character of the exocyclic C(2)C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh COEt > CONHPh > CONHCH₂CH₂Ph. The decrease of the Δδ_C(2)C(2′) values in 2a–d has been discussed for the first time in terms of an estimation of the electron donor capacity of the S fragment on the polarization of the CC bonds.     

Infrared diode laser spectroscopy of the ν = 2 band of AlF

A vibrational–rotational spectrum of the ν = 2 transitions of a high-temperature molecule AlF was observed between 1490 and 1586 cm⁻¹ with a diode laser spectrometer. Measurements were made on the ν = 3–1, 4–2, 5–3 and 8–6 bands at a temperature of 900 °C. Measured spectral lines were fitted to effective band constants ν₀, B_ν and D_ν for each band. Present measurements were made with only one Pb-salt laser diode. Physical significance of the effective band constants is discussed.     

Weak hydrogen-, halogen- and stacking ππ bonding in crystalline 5-chloro-1-indanone. An analysis by using X-ray diffraction, vibrational spectroscopy and theoretical methods

Intermolecular forces of C–HO, C–Hπ, COCl and ππ types are present in the stable triclinic crystal structure of 5-chloro-1-indanone. They are analysed from a geometrical point of view supported in some extent by the analysis of the vibrational spectrum of the titled compound. Moreover, the molecular structure of the isolated species is calculated by using ab initio as well as density functional theory (DFT) methods together an assortment of basis sets. In order to obtain some information about the influence of intermolecular forces on the molecular structure, the calculated geometries of a free molecule were compared with the experimental solid phase geometry determined by X-ray crystallography.An analysis and assignment of the vibrational spectrum of the 5-chloro-1-indanone is accomplished by using IR and Raman experimental data along with Pulay et al.’s scaled quantum mechanical force field (SQM) methodology starting from the theoretical B3LYP/6-31G(d) and BLYP/6-31G(d) force fields under C_s symmetry.     

Nonadiabatic dissociation dynamics of ClHD van der Waals complex initiated by electron detachment of Cl–HD

Nuclear dynamics following the electron detachment of the Cl⁻–HD anion is investigated by a time-dependent wave packet propagation approach. Photodetachment of Cl⁻–HD promotes it to the van der Waals well region of the reactive ClHD potential energy surface. The latter is a manifold of three electronic states coupled by the electronic and (relativistic) spin-orbit coupling. Among the three surfaces, the electronic ground one is of ²Σ_1/2 type and yields products in their electronic ground state. The remaining two, ²Π_3/2 and ²Π_1/2, on the other hand, yield products in their excited electronic states. However, these two can yield products in their electronic ground state via nonadiabatic transitions to the ²Σ_1/2 state. The channel specific, HCl + D or DCl + H or Cl + HD, dissociation probabilities on this latter state are calculated both in the uncoupled and coupled surface situations. Separate initial transitions (via, photodetachment) to the ²Σ_1/2, ²Π_3/2 and ²Π_1/2 adiabatic electronic states of ClHD are considered in order to elucidate the nonadiabatic coupling effects on this important class of chemical reactions initiated by an electron detachment.     

Electronic structure and luminescence of [AuS2PPh(OCH2CHCH2)]2 complex

The complex [AuS₂PPh(OCH₂CHCH₂)]₂ (1) presents an Au(I)–Au(I) intramolecular and intermolecular bonding with luminescence properties. To understand the nature of these features, fully optimized geometries were obtained by three computational methods, DFT/B3LYP, MPW1B95 and MP2. An Au(I)–Au(I) intramolecular bond was found in the ground state, at the three levels of theory, exhibiting an aurophilic interaction between the two gold atoms. Two molecules of the complex were optimized using DFT/B3LYP, in order to analyze the intermolecular interaction between them. The resulting intermolecular bonding distance between the two adjacent gold atoms on each molecule is 3.16 Å, indicating a strong aurophilic attraction. Time dependent calculations indicate that the first excited state with nonzero oscillator strength is a singlet, with an excitation energy equal to 3.16 eV. This should correspond to the absorption band seen experimentally at 3.10 eV. The lowest energy emission of (1) was obtained at 2.73 eV, which corresponds to the emission peak resulting from phosphorescence and located at 2.53 eV. This transition comes from an excited electron on the p orbitals of the ligands that is transferred to the d orbitals of the gold atoms on the HOMO. This interaction may be attributed to Ligand to Ligand–Metal Charge Transfer (LL–MCT).     

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.     

Facile hydrosilylation of norbornadiene by silanes R3SiH and R2SiH2 with molybdenum catalysts

Photochemically activated [Mo(CO)₆] and [Mo(CO)₄(η⁴-nbd)] have been demonstrated to be very effective catalysts for hydrosilylation of norbornadiene (nbd) by tertiary (Et₃SiH, Cl₃SiH) and secondary (Et₂SiH₂ and Ph₂SiH₂) silanes to give 5-silyl-2-norbornene, which under the same reaction conditions transform in ring-opening metathesis polymerization (ROMP) to unsaturated polymers and to a double hydrosilylation product, 2,6-bis(silyl)norbornane. The yield of a particular reaction depends very strongly on the kind of silane involved. The reaction products were identified by means of chromatography (GC–MS) and ¹H and ¹³C NMR spectroscopy. In photochemical reaction of [Mo(CO)₄(η⁴-nbd)] and Ph₂SiH₂ in cyclohexane-d₁₂, η²-coordination of the SiH bond to the molybdenum atom is supported by ¹H NMR spectroscopy due to the detection of two equal-intensity doublets with ²J_HH = 5.4 Hz at δ 6.12 and −5.86 ppm.