Cristobal Viedma

Evolution of Solid Phase Homochirality for a Proteinogenic Amino Acid

The inexorable evolution of solid-phase single chirality is demonstrated for the first time for a proteinogenic amino acid. Enantioenrichment is observed both under attrition-enhanced conditions and without the aid of particle grinding. Differences in the form of the conversion profiles for the process under the two sets of conditions provide suggestions concerning the mechanism of the transformation.

Salt crystallization in porous construction materials I Estimation of crystallization pressure

Abstract The crystallization process of soluble salts inside the natural and artificial porous materials partially immersed in different saline solutions has been studied. This procedure is used to simulate the conditions of exposure to salt weathering in which foundations and lower walls of building structures are within the zone of capillary rise of saline ground water. Crystallization pressures that can develop in the samples, which are a function of the pore size and salt-solution interfacial tension, have been calculated and are compared with experimental values of the materials tensile strength, since both these parameters allow the prediction of porous materials behaviour against salt weathering.

Pasteur's tweezers revisited: on the mechanism of attrition-enhanced deracemization and resolution of chiral conglomerate solids.

Insights into the mechanism of attrition-enhanced deracemization and resolution of solid enantiomorphic chiral compounds are obtained by crystal size and solubility measurements and by isotopic labeling experiments. Together these results help to deconvolute the various chemical and physical rate processes contributing to the phenomenon. Crystal size measurements highlight a distinct correlation between the stochastic, transient growth of crystals and the emergence of a single solid enantiomorph under attrition conditions. The rapid mass transfer of molecules between the solution and solid phases under attrition is demonstrated, and the concept of a crystal-size-induced solubility driving force is exploited to overcome the stochastic nature of the crystal growth and dissolution processes. Extension to non-racemizing conditions provides a novel methodology for chiral resolution. Implications both for practical chiral separations and for the origin of biological homochirality are discussed.

Homochirality beyond grinding: deracemizing chiral crystals by temperature gradient under boiling

A single-chirality solid phase can be obtained in boiling solutions containing a racemic mixture of left- and right-handed enantiomorphous crystals due to dissolution-crystallization cycles induced by a temperature gradient. This phenomenon provides further insights into asymmetric amplification mechanisms under presumably prebiotic conditions.

Enantiomer-Specific Oriented Attachment: Formation of Macroscopic Homochiral Crystal Aggregates from a Racemic System†

Lets get together: Racemic samples of d- and l-enantiomorphous NaBrO3 (or NaClO3) crystals aggregate with nearly complete enantioselection. Centimeter-sized enantiopure megacrystals are often produced, and these can be sorted easily.

Salt crystallization in porous construction materials. II. Mass transport and crystallization processes

In order to study the processes of salt weathering of monumental stones, several samples were partially immersed in sodium, potassium and magnesium sulphate solutions which ascended through their capillary network and, eventually, crystallized. This procedure pretends to simulate the conditions in which foundations and lower walls of building structures are, within the zone of capillary rise of saline groundwater. Mass transport and the rhythmic nature of crystallization fronts inside samples reminds the Liesegang phenomenon, so they have been considered as a form of dissipative structures. The saline deposits developed on the surface of the samples were efflorescences (mirabilite and epsomite), subefflorescences (picromerite, aphthitalite and arcanite) and crusts (aphthitalite and arcanite). The most devastating effects resulted from massive crystallization inside the samples or from surface peeling due to the development of subefflorescences or crusts.

Crystal quality of lysozyme single crystals grown by the gel acupuncture method

Abstract Lysozyme single crystals up to 2.0 mm in size have been grown from solution into capillaries which are previously punctuated into a gel layer through which the precipitant agent diffuse. These large single crystals show an excellent optical quality and it is demonstrated by in situ X-ray diffraction that they diffract up to 1.8–1.9 A.

On the Physical Basis of Asymmetry and Homochirality

Mirror symmetry breaking is ubiquitous in our visible universe taking place in elementary particles, atoms, and molecules. Molecular chirality is not biogenic in itself, although its detection is often considered a biosignature, a conjecture inferred from the fact that we do not know life devoid of homochirality. The question of whether there is a connection between the cosmic preference for one enantiomer, as imposed by the weak force, and the single chirality displayed on Earth is vividly debated. This article gives a glimpse on the origin of asymmetry from a cosmological perspective and on physical transformations that lead to an enantiomeric imbalance, leaving chemical reactions essentially aside. These processes are more plausible as sources of prebiotic chirality than asymmetric amplifications requiring unnatural substrates and conditions and fighting against racemization. The latter may actually be a friend, not foe, and a driving force for enantioselection.

Mass-transfer and supersaturation in crystal growth in gels: Application to CaSO4·2H2O

Abstract Supersaturation evaluation is an essential requirement to describe, confront and explain crystal growth experiences. However, in the particular case of crystal growth in gels, experiences are often described by attending to the initial concentration of reagent. This fact is connected with deficiencies in the theoretical quantification of mass-transfer, and therefore in both time and location prediction for the first precipitate. In this paper laboratory experiences have been specifically designed to test supersaturation evolution through an actual (finite) diffusion system. The problem is carried out by keeping into account several complexity factors: free ions as well as complexes and silica gel Na + and Cl − “unloading” are considered to evaluate the supersaturation.

Formation of peptide bonds from metastable versus crystalline phase: implications for the origin of life.

Formation of peptide bonds was attempted bythermal activation of dry amino acids from aqueous solutionthat simulated prebiotic evaporative environments. Theevaporation trend of amino acids solutions shows abifurcation and can lead to either a crystalline phase(near equilibrium) or a metastable non-crystalline phase(far from equilibrium). Only amino acids in this metastablephase are able to form peptide bonds by thermal activationat temperatures that are generated by solar radiationtoday. We suggest that this metastable phase is the idealinitial material to trigger amino acid assemblage withprotein-like structure because provide the driving force(supersaturation) for an intense interaction betweenmonomers of different amino acids and allows activation ofthese monomers in plausible prebiotic conditions.