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The search for alternative ways to give a second life to materials paved the way for detailed investigation into three silica-polyethylenimine (Si-PEI) materials for the purpose of CO2 adsorption in carbon capture and storage. A solvent extraction procedure was investigated to recover degraded PEIs and silica, and concomitantly, pyrolysis was evaluated to obtain valuable chemicals such as alkylated pyrazines. An array of thermal (TGA, Py-GC-MS), mechanical (rheology), and spectroscopical (ATR-FTIR, 1H-13C-NMR) methods were applied to PEIs extracted with methanol to determine the relevant physico-chemical features of these polymers when subjected to degradation after use in CO2 capture. Proxies of degradation associated with the plausible formation of urea/carbamate moieties were revealed by Py-GC-MS, NMR, and ATR-FTIR. The yield of alkylpyrazines estimated by Py-GC-MS highlighted the potential of exhausted PEIs as possibly valuable materials in other applications. [ABSTRACT FROM AUTHOR]

Three sets of oligomers containing the 4-carboxy-5-methyloxazolidin-2-one (Oxd) moiety were synthesized in a study with the aim of checking whether these molecules are able to fold in ordered structures. A deeper insight into the CD spectra reveals that the secondary structure adopted by one set of oligomers is a beta-bend ribbon spiral, which is a subtype of the 3(sub 10)-helix.

The asymmetric aldol condensation of acetone with isatin, its N-alkylated derivatives, and 5-` is described. A new quaternary stereocenter is obtained with good enantioselectivity, which can easily be enriched by silica flash chromatography and the effect proved to be general for the class of compounds.

Research describes a synthetic methodology for preparing enantiomerically pure oligomer foldamers containing three and four residues without involving ring hydrolysis. Proton nuclear paramagnetic analysis shows that these heterocycle trimers and tetramers, belonging to the family of pseudoprolines, fold into ordered structures.

The reactivity of lithium enolates of both cis and trans chiral aziridine-2-amides with p-toluenesulfonyl chloride and benzenesulfonyl bromide and iodine as electrophiles was examined. (1'S,6R)6-methylperhydropyrimidin-4-one was treated with LiHMDS in dry THF at 0 degrees C for 1 h. After the enolate was cooled at -30 degrees C, the halogenating agent was added by drops. The reaction was then quenched with water. Results indicate that trans- or cis-2-carboxyaziridines can be derived in good yield by acid hydrolysis.

A study was conducted to characterize the synthesis of aziridine-2-imides by cyclization of chiral 3'-benzyloxyamino imide enolates. Semiempirical computations were carried out to determine information about the preferential structure of the transition state. Results suggested that the delocalization of electrons will influence the geometry of centers toward a preferential semi-W transition mode that results in a trans relationship between the substituents in the final aziridines.

The use of immobilized penicillin G acylase in the kinetic resolution of alpha-substituted beta-amino acids provides an alternative synthetic route to highly stereocontrolled (S,S)- or (R,R)-alpha-alkyl beta-amino acids in high yields. This was proven in experiments involving the enzymatic hydrolysis of racemic N-phenylacetyl alpha-alkyl beta-amide acids. The results showed the dependence of the product mixture's yield and enantiomeric purity on the pH, solvent, temperature and reaction time.

Experimental studies of various 6-substituted perhydropyrimidin-4-ones demonstrate the influence of the electrophile and the bulkiness of the substituent at C6 on the alkylation reactions. A dialkylation reaction at C5 leads to a preferential formation of 5,6-cis-trisubstituted product. The 5,6-trans-disubstituted perhydropyrimidin-4-ones undergo hydrolysis, producing the corresponding beta-amino acids, which form 5, 6-trans-disubstituted azetidin-2-ones by cyclization.

The occurrence of several Lewis acids is necessary for imides to accept the 1,4-incorporation of O-benzylhydroxylamine. Two different products are generated when the interaction takes place in CH2Cl2 at -78 degrees centigrade. Substantial chemical quantities of the products are observed in various diastereomeric proportions, which are influenced by the type of Lewis acid involved in the interaction. Opposite diastereoselectivities are obtained from TiCl4 and Me2AlCl. One of the products yields a substantial amount of enantiomerically pure beta-amino acid.

Chiral imidazolidin-4-ones and perihydropyrimidin-4-ones can undergo hydrolysis in acidic conditions to form D or L alpha- and beta-amino acids, respectively. The two heterocycles are produced from the electrophilic Hg(TFA)2 cyclization of the amidals formed in the reaction between 1,3,5-tris-( S -1-phenylethyl)hexahydrotriazine and 2, 3-unsaturated acyl chlorides. Moreover, the H NMR analysis of the stereogenic center allows further examination of the compound's absolute configuration.

A method in the synthesis of syn beta-amino alpha-hydroxy acids is described. The method is used in the preparation of (2R,3S)-N-benzoylphenylisoserine methyl ester moiety. Antihalogenation through the iodination reaction of methyl (3R)-N-benzoyl-3-amino-3-phenylpropanoate. The iodination reaction directly yields trans oxazoline in significant yields, diastereoselectivity. Enzymatic kinetic resolution of the N-(phenylacetyl)amide derivative of the racemate yields beta-amino acid.