Luminescent probing of the simplest chiral α-amino acid-alanine in an enantiopure and racemic state.

Luminescent spectroscopy combined with the technique of luminescent probing with rare earth ions (europium, gadolinium, terbium) and an actinide ion (uranyl) was used to differentiate enantiopure and racemic alanine, the simplest chiral proteinogenic amino acid. Using the achiral luminescent probes, small differences between pure L and DL alanine in the solid state were strongly amplified. Based on the observed electronic transitions of the probes, the position of the triplet level of the coordinated alanine was estimated. Formation of homo- and heterochiral complexes between enantiomers of alanine and the metal ions is discussed as a possible mechanism of chiral self-discrimination.

Transfer of Asymmetry between Proteinogenic Amino Acids under Harsh Conditions.

The heating above 400 °C of serine, cysteine, selenocysteine and threonine leads to a complete decomposition of the amino acids and to the formation in low yields of alanine for the three formers and of 2-aminobutyric acid for the latter. At higher temperature, this amino acid is observed only when sublimable α-alkyl-α-amino acids are present, and with an enantiomeric excess dependent on several parameters. Enantiopure or enantioenriched Ser, Cys, Sel or Thr is not able to transmit its enantiomeric excess to the amino acid formed during its decomposition. The presence during the sublimation-decomposition of enantioenriched valine or isoleucine leads to the enantioenrichment of all sublimable amino acids independently of the presence of many decomposition products coming from the unstable derivative. All these studies give information on a potentially prebiotic key-reaction of abiotic transformations between α-amino acids and their evolution to homochirality.

High temperature sublimation of α-amino acids: a realistic prebiotic process leading to large enantiomeric excess.

The reiterative high temperature co-sublimation of an enantiopure or an enantioenriched α-amino acid mixed with racemic α-amino acids leads to deracemization of the latter. A synergistic effect is observed for complex mixtures, and the sense of the handedness is, for all compounds, identical to that of the enantioenriched starting material.

Recent advances in surface chemistry strategies for the fabrication of functional iron oxide based magnetic nanoparticles.

The synthesis of superparamagnetic nanostructures, especially iron-oxide based nanoparticles (IONPs), with appropriate surface functional groups has been intensively researched for many high-technological applications, including high density data storage, biosensing and biomedicine. In medicine, IONPs are nowadays widely used as contrast agents for magnetic resonance imaging (MRI), in hyperthermia therapy, but are also exploited for drug and gene delivery, detoxification of biological fluids or immunoassays, as they are relatively non-toxic. The use of magnetic particles in vivo requires IONPs to have high magnetization values, diameters below 100 nm with overall narrow size distribution and long time stability in biological fluids. Due to the high surface energies of IONPs agglomeration over time is often encountered. It is thus of prime importance to modify their surface to prevent aggregation and to limit non-specific adsorption of biomolecules onto their surface. Such chemical modifications result in IONPs being well-dispersed and biocompatible, and allow for targeted delivery and specific interactions. The chemical nature of IONPs thus determines not only the overall size of the colloid, but also plays a significant role for in vivo and in vitro applications. This review discusses the different concepts currently used for the surface functionalization and coating of iron oxide nanoparticles. The diverse strategies for the covalent linking of drugs, proteins, enzymes, antibodies, and nucleotides will be discussed and the chemically relevant steps will be explained in detail.

Partial sublimation of enantioenriched amino acids at low temperature. Is it coming from the formation of a euatmotic composition of the gaseous phase?

The partial sublimation of enantioenriched amino acids was performed slowly at low temperature with the aim to determine the rules of sublimation of these compounds. Although the formation of a euatmotic composition of the gaseous phase starting from DL + L mixtures of Leu, Pro, and Phe can be deduced from the enantiomeric excess of sublimates, the behavior of the kinetic conglomerate explains the results for D + L mixtures of Ala, Leu, Val, and Pro. Consequently, the enantiomeric excess of the partial sublimate is dependent not only on the studied compound but also on the composition of the starting mixture.

Deracemization of amino acids by partial sublimation and via homochiral self-organization.

Deracemization of a 50/50 mixture of enantiomers of aliphatic amino acids (Ala, Leu, Pro, Val) can be achieved by a simple sublimation of a pre-solubilized solid mixture of the racemates with a huge amount of a less-volatile optically active amino acid (Asn, Asp, Glu, Ser, Thr). The choice of chirality correlates with the handedness of the enantiopure amino acids--Asn, Asp, Glu, Ser, and Thr. The deracemization, enantioenrichment and enantiodepletion observed in these experiments clearly demonstrate the preferential homochiral interactions and a tendency of natural amino acids to homochiral self-organization. These data may contribute toward an ultimate understanding of the pathways by which prebiological homochirality might have emerged.