ROP of vic-disubstituted lactones: A diastereoselective way to polymerize

For this work, at first we have studied the acid catalysed lactonization of several γ-hydroxyesters, bearing methyl substituents at different positions. A 1H-NMR kinetic study of this set of monomethyl and/or gem-dimethyl substituted esters in CDCl3 was carried out. We evaluated the effect of the leaving group (ethyl vs. i-propyl ester) and the catalyst efficiency. We found that i) a monomethyl substitution produces a lowering of the energy barrier similar to that of a gem-dimethyl substitution (Thorpe–Ingold effect), ii) the ring closure of i-propyl esters is slower than that of ethyl esters, iii) strong acids are more efficient than weak acids according to the Brønsted relationship, and iv) the Thorpe– Ingold effect is not just an intrinsic feature of the linear precursor but it depends on the catalyst as well.[1,2] FASTER Now, we would like to give an explanation and clarify three issues: i) how is the cyclization affected by the vicinal substitution? ii) is the effect stereospecific, that is to say, dependent on the diastereomeric relation (syn or anti) between the two vicinal substituents? iii) is it possible to observe a stereospecific effect in the Ring Opening Polymerization (ROP) of lactones as well? Preliminaries studies on model compounds indicate that the vic-disubstituent effect is not only stereospecific, since the anti linear precursors undergo to the cyclisation reaction much faster than the corresponding syn diastereoisomers, but it is more efficient than the above mentioned Thorpe-Ingold effect. Please click Additional Files below to see the full abstract

(2S)-[3-(Anthracen-9-yl)-4,5-dihydroisoxazol-5-yl]methyl 2-[(tert-butoxycarbonyl)amino]propanoate

The synthesis of the (2S)-[3-(anthracen-9-yl)-4,5-dihydroisoxazol-5-yl]methyl 2-[(tert-butoxycarbonyl)amino]propanoate is obtained through the 1,3-dipolar cycloaddition of the stable anthracenenitrile oxide and the N-Boc protected (S)-alanine allyl ester as dipolarophile. The structure and the fluorescence properties are described upon the relative analytical and spectroscopic data

Microplastic Identification via Holographic Imaging and Machine Learning

Microplastics (MPs) are a major environmental concern due to their possible impact on water pollution, wildlife, and the food chain. Reliable, rapid, and high‐throughput screening of MPs from other components of a water sample after sieving and/or digestion is still a highly desirable goal to avoid cumbersome visual analysis by expert users under the optical microscope. Here, a new approach is presented that combines 3D coherent imaging with machine learning (ML) to achieve accurate and automatic detection of MPs in filtered water samples in a wide range at microscale. The water pretreatment process eliminates sediments and aggregates that fall out of the analyzed range. However, it is still necessary to clearly distinguish MPs from marine microalgae. Here, it is shown that, by defining a novel set of distinctive "holographic features," it is possible to accurately identify MPs within the defined analysis range. The process is specifically tailored for characterizing the MPs' "holographic signatures," thus boosting the classification performance and reaching accuracy higher than 99% in classifying thousands of items. The ML approach in conjunction with holographic coherent imaging is able to identify MPs independently from their morphology, size, and different types of plastic materials

(2S)-[3-(Anthracen-9-yl)-4,5-dihydroisoxazol-5-yl]methyl 2-[(tert-butoxycarbonyl)amino]propanoate

The synthesis of the (2S)-[3-(anthracen-9-yl)-4,5-dihydroisoxazol-5-yl]methyl 2-[(tert-butoxycarbonyl)amino]propanoate is obtained through the 1,3-dipolar cycloaddition of the stable anthracenenitrile oxide and the N-Boc protected (S)-alanine allyl ester as dipolarophile. The structure and the fluorescence properties are described upon the relative analytical and spectroscopic data

A practical synthesis of (3-(phenanthren-9-yl)-4,5-dihydroisoxazol-5-yl)methyl (tert-butoxycarbonyl)-L-alaninate

Nitrile oxides are highly reactive, but often unstable, compounds that can be used to substitute for other 1,3-dipoles in [3+2] cycloaddition reactions. Bioorthogonal chemistry reactions that can occur within living systems without interfering with their native biochemical processes, is an area in which stable nitrile oxides can find useful and valuable applications. The rapid and selective synthesis of a phenanthrene-isoxazolyl derivative containing a protected amino acidic residue, through a facile 1,3-dipolar cycloaddition of a stable phenanthrenenitrile oxide to a N-Boc-protected (S)-alanine allyl ester as the dipolarophile is described. The synthetic strategy and the fluorescence properties of the single cycloadduct are presented along with the corresponding analytical and spectroscopic data