Synthesis of High Performance Thiophene–Aromatic Polyesters from Bio-Sourced Organic Acids and Polysaccharide-Derived Diol: Characterization and Degradability Studies

In this work, the feasibility of replacing petroleum-based poly(ethylene terephthalate) (PET) with fully bio-based copolyesters derived from dimethyl 2,5-thiophenedicarboxylate (DMTD), dimethyl 2,5-dimethoxyterephthalate (DMDMT), and polysaccharide-derived 1,6-hexanediol (HDO) was investigated. A systematic study of structure-property relationship revealed that the properties of these poly(thiophene–aromatic) copolyesters (PHS(20–90)) can be tailored by varying the ratio of diester monomers in the reaction, whereby an increase in DMTD content noticeably shortened the reaction time in the transesterification step due to its higher reactivity as compared with DMDMT. The copolyesters had weight-average molar masses (Mw) between 27,500 and 38,800 g/mol, and dispersity Đ of 2.0–2.5. The different polarity and stability of heterocyclic DMTD provided an efficient mean to tailor the crystallization ability of the copolyesters, which in turn affected the thermal and mechanical performance. The glass transition temperature (T_g) could be tuned from 70–100 °C, while the tensile strength was in a range of 23–80 MPa. The obtained results confirmed that the co-monomers were successfully inserted into the copolyester chains. As compared with commercial poly(ethylene terephthalate), the copolyesters displayed not only enhanced susceptibility to hydrolysis, but also appreciable biodegradability by lipases, with weight losses of up to 16% by weight after 28 weeks of incubation.     

Synthesis and Applications of Silyl 2‐Methylprop‐2‐ene‐1‐sulfinates in Preparative Silylation and GC‐Derivatization Reactions of Polyols and Carbohydrates

Trimethylsilyl, triethylsilyl, tert‐butyldimethylsilyl, and triisopropylsilyl 2‐methylprop‐2‐ene‐1‐sulfinates were prepared through (CuOTf)₂?C₆H₆‐catalyzed sila‐ene reactions of the corresponding methallylsilanes with SO₂ at 50 °C. Sterically hindered, epimerizable, and base‐sensitive alcohols gave the corresponding silyl ethers in high yields and purities at room temperature and under neutral conditions. As the byproducts of the silylation reaction (SO₂+isobutylene) are volatile, the workup was simplified to solvent evaporation. The developed method can be employed for the chemo‐ and regioselective semiprotection of polyols and glycosides and for the silylation of unstable aldols. The high reactivity of the developed reagents is shown by the synthesis of sterically hindered per‐O‐tert‐butyldimethylsilyl‐α‐d ‐glucopyranose, the X‐ray crystallographic analysis of which is the first for a per‐O‐silylated hexopyranose. The per‐O‐silylation of polyols, hydroxy carboxylic acids, and carbohydrates with trimethylsilyl 2‐methylprop‐2‐ene‐1‐sulfinate was coupled with the GC analysis of nonvolatile polyhydroxy compounds both qualitatively and quantitatively.     

A new acylated triterpene with antimicrobial activity from the leaves of <Emphasis Type="Italic">Rauvolfia vomitoria</Emphasis>

A new acylated tritrepene, 3β-hexadecanoyloxy-lup-20(29)-en-21-ol (1), along with seven known compounds, lupeol (2), betulinic acid (3), ursonic acid (4), -sitosterol (5), β-stigmasterol (6), 3-O-β-D-glucopyranosyl-β-stigmasterol (7), and palmitic acid (8), were isolated from the leaves of Rauvolfia vomitoria (Apocynaceae). Their structures were established on the basis of spectroscopic analysis and chemical evidence. The new acylated triterpene exhibited interesting antimicrobial activity against Candida albicans (a yeast) with the MIC value 64 μg/mL.     

New triterpenoids from the stem barks of Drypetes tessmanniana

The MeOH extract of the stem barks of Drypetes tessmanniana (Euphorbiaceae) afforded two new triterpene derivatives characterized as 3beta-O-(E)-3,5-dihydroxycinnamoyl-11-oxo-olean-12-ene and 3beta,6alpha-dihydroxylup-20(29)-ene together with seven known compounds. Their structures were established on the basis of spectral analysis.     

New flavan and unusual chalcone glycosides from Drypetes parvifolia

Two new compounds 7-hydroxy-5-O-（β-D-glucopyranoside） flavan （1） and （Z）-4＇,6＇-dihydroxy-2＇-O-（β-D-glucopyranoside） chalcone （2）, along with eight known compounds, were isolated from the stem bark of Drypetes parvifolia （Euphorbiaceae）. Their structures were established on the basis of spectroscopic analysis and chemical evidence.     

Strain relaxation in epitaxial GaAs/Si (0 0 1) nanostructures

Abstract

Crystal defects, present in ~100 nm GaAs nanocrystals grown by metal organic vapour phase epitaxy on top of (0 0 1)-oriented Si nanotips (with a tip opening 50–90 nm), have been studied by means of high-resolution aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. The role of 60° perfect, 30° and 90° Shockley partial misfit dislocations (MDs) in the plastic strain relaxation of GaAs on Si is discussed. Formation conditions of stair-rod dislocations and coherent twin boundaries in the GaAs nanocrystals are explained. Also, although stacking faults are commonly observed, we show here that synthesis of GaAs nanocrystals with a minimum number of these defects is possible. On the other hand, from the number of MDs, we have to conclude that the GaAs nanoparticles are fully relaxed plastically, such that for the present tip sizes no substrate compliance can be observed.     

Direct determination of tagitinin C in Tithonia diversifolia leaves by on-line coupling of supercritical carbon dioxide extraction to FT-IR spectroscopy by means of optical fibres

Supercritical fluid extraction (SFE) with carbon dioxide as extraction medium was on-line coupled to a FT-IR spectrometer equipped with a Mercury Cadmium Telluride (MCT) detector using a tailor-made high-pressure fibre optic flow cell. This method was optimised and developed for the monitoring in real time and the quantification of dynamic extractions of tagitinin C from Tithonia diversifolia leaves.In order to demonstrate the method ability to allow the direct quantification of tagitinin C in the extract medium the standard addition method was used. The area integration of curves obtained by plotting the absorbance of the highly specific CO stretching vibration at 1668 cm⁻¹ versus time (i.e. extractograms) was used as instrumental response.The SFE/FT-IR process was successfully validated using the accuracy profile as decision tool. On this basis, a linear regression model was chosen for the calibration curve. The relative standard deviation for repeatability and intermediate precision were between 0.8 and 3.1 %, respectively. Moreover, the method was found to be accurate as the two-sided 95% beta-expectation tolerance interval did not exceed the acceptance limits of 85 and 115% on the analytical range investigated (500-2500 μg of added amount of tagitinin C).The proposed method allowed the non-destructive extraction of tagitinin C and its on-line quantitative determination in less than 25 min thus facilitating the subsequent experiments or the pharmacological studies performed on this compound.     

Photoinitiated Energy Transfer in Porous-Cage-Stabilised Silver Nanoparticles

We report a new composite material consisting of silver nanoparticles decorated with three-dimensional molecular organic cages based on light-absorbing porphyrins. The porphyrin cages serve to both stabilize the particles and allow diffusion and trapping of small molecules close to the metallic surface. Combining these two photoactive components results in a Fano-resonant interaction between the porphyrin Soret band and the nanoparticle-localised surface-plasmon resonance. Time-resolved spectroscopy revealed the silver nanoparticles transfer up to 37 % of their excited-state energy to the stabilising layer of porphyrin cages. These unusual photophysics cause a 2-fold current increase in photoelectrochemical water-splitting measurements. The composite structure provides a compelling proof of concept for advanced photosensitiser systems with intrinsic porosity for photocatalytic and sensing applications.