Serine octamer cluster
Encyclopedia
The Serine octamer cluster in physical chemistry
is an unusually stable cluster consisting of eight serine
molecule
s (Ser) implicated in the origin of homochirality
. This cluster was first discovered in mass spectrometry
experiments. Electrospray ionization
of an aerosol
of serine in methanol
results in an mass spectrum with a prominent ion peak of 841 corresponding to the Ser8+H+ cation. The smaller and larger clusters are virtually absent in the spectrum and therefore the number 8 is called a magic number
. The same octamer ions are also produced by rapid evaporation
of a serine solution on a hot (200-250°C) metal surface or by sublimation
of solid serine. After production, detection again is by mass-spectroscopic means. For the discussion of homochirality, these laboratory production methods are designed to mimic prebiotic conditions.
The cluster is not only unusually stable but also unusual because the clusters have a strong homochiral preference. A racemic
serine solution produces a minimum amount of cluster and with solutions of both enantiomer
s a maximum amount is formed of both homochiral D-Ser8 and L-Ser8. In another experiment cluster formation of a racemic mixture with deuterium
enriched L-serine results in a product distribution with hardly any 50/50 D/L clusters but a preference for either D or L enantioenriched clusters.
A model for chiral amplification is proposed whereby enantioenriched clusters are formed from a non-racemic mixture already enriched by L-serine as a result of a mirror-symmetry breaking process. Cluster formation is followed by isolation and on subsequent dissociation of the cluster a serene solution forms with a higher concentration of L-serine than in the original mixture. A cycle can be maintained in which each turn results in an incremental enrichment in L-serine. Many such cycles eventually result in enantiopure L-serine. This model has been experimentally verified.
Chiral transmission is assumed to take place through so-called substitution reactions of serine clusters. In these reactions, a serine monomer in a cluster can be replaced by another small biologically relevant molecule. For instance Ser8 reacts with glucose
(Glc) to the Ser6 + Glc3 + Na+ cluster. Moreover the cluster of synthetic L-glucose with Ser8 is less abundant than that with the biological D-glucose.
Physical chemistry
Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of physical laws and concepts...
is an unusually stable cluster consisting of eight serine
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s (Ser) implicated in the origin of homochirality
Homochirality
Homochirality is a term used to refer to a group of molecules that possess the same sense of chirality. Molecules involved are not necessarily the same compound, but similar groups are arranged in the same way around a central atom. In biology homochirality is found in the chemical building blocks...
. This cluster was first discovered in mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
experiments. Electrospray ionization
Electrospray ionization
Electrospray ionization is a technique used in mass spectrometry to produce ions. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized...
of an aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
of serine in methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
results in an mass spectrum with a prominent ion peak of 841 corresponding to the Ser8+H+ cation. The smaller and larger clusters are virtually absent in the spectrum and therefore the number 8 is called a magic number
Magic number (chemistry)
In case a gas condenses into clusters of atoms, the number of atoms in these clusters varies between a few and hundreds. However, there are peaks at specific sizes, usually one at lower and one at larger numbers. Often, specific numbers dominate...
. The same octamer ions are also produced by rapid evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
of a serine solution on a hot (200-250°C) metal surface or by sublimation
Sublimation (physics)
Sublimation is the process of transition of a substance from the solid phase to the gas phase without passing through an intermediate liquid phase...
of solid serine. After production, detection again is by mass-spectroscopic means. For the discussion of homochirality, these laboratory production methods are designed to mimic prebiotic conditions.
The cluster is not only unusually stable but also unusual because the clusters have a strong homochiral preference. A racemic
Racemic
In chemistry, a racemic mixture, or racemate , is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was "racemic acid", which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid.- Nomenclature :A...
serine solution produces a minimum amount of cluster and with solutions of both enantiomer
Enantiomer
In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...
s a maximum amount is formed of both homochiral D-Ser8 and L-Ser8. In another experiment cluster formation of a racemic mixture with deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
enriched L-serine results in a product distribution with hardly any 50/50 D/L clusters but a preference for either D or L enantioenriched clusters.
A model for chiral amplification is proposed whereby enantioenriched clusters are formed from a non-racemic mixture already enriched by L-serine as a result of a mirror-symmetry breaking process. Cluster formation is followed by isolation and on subsequent dissociation of the cluster a serene solution forms with a higher concentration of L-serine than in the original mixture. A cycle can be maintained in which each turn results in an incremental enrichment in L-serine. Many such cycles eventually result in enantiopure L-serine. This model has been experimentally verified.
Chiral transmission is assumed to take place through so-called substitution reactions of serine clusters. In these reactions, a serine monomer in a cluster can be replaced by another small biologically relevant molecule. For instance Ser8 reacts with glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
(Glc) to the Ser6 + Glc3 + Na+ cluster. Moreover the cluster of synthetic L-glucose with Ser8 is less abundant than that with the biological D-glucose.
See also
- Other magic numbers in chemistry: methane clathrateMethane clathrateMethane clathrate, also called methane hydrate, hydromethane, methane ice, "fire ice", natural gas hydrate or just gas hydrate, is a solid clathrate compound in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice...
, Magic angle spinningMagic angle spinningIn nuclear magnetic resonance, magic angle spinning is a technique often used to perform experiments in solid-state NMR spectroscopy.By spinning the sample at the magic angle θm In nuclear magnetic resonance, magic angle spinning (MAS) is a technique often used to perform experiments in... - Other stable clusters in: aluminium superatomSuperatomSuperatoms are clusters of atoms that seem to exhibit some of the properties of elemental atoms.Sodium atoms, when cooled from vapor, naturally condense into clusters, preferentially containing a magic number of atoms . The first two of these can be recognized as the numbers of electrons needed to...
s