Glyceraldehyde (glyceral) is a

triose A triose is a monosaccharide, or simple sugar, containing three carbon atoms. There are only three possible trioses: the two enantiomers of glyceraldehyde, which are aldoses; and dihydroxyacetone, a ketose which is symmetrical and therefore ha ...

monosaccharide Monosaccharides (from Greek '' monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built. Chemically, monosaccharides are polyhy ...

with

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

C₃ H₆ O₃. It is the simplest of all common

aldose An aldose is a monosaccharide (a simple sugar) with a carbon backbone chain with a carbonyl group on the endmost carbon atom, making it an aldehyde, and hydroxyl groups connected to all the other carbon atoms. Aldoses can be distinguished from ket ...

s. It is a

sweet Sweetness is a basic taste most commonly perceived when eating foods rich in sugars. Sweet tastes are generally regarded as pleasurable. In addition to sugars like sucrose, many other chemical compounds are sweet, including aldehydes, ketones, ...

, colorless,

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

line

solid Solid is a state of matter where molecules are closely packed and can not slide past each other. Solids resist compression, expansion, or external forces that would alter its shape, with the degree to which they are resisted dependent upon the ...

that is an intermediate compound in

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

. The word comes from combining

glycerol Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...

and

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

, as glyceraldehyde is glycerol with one alcohol group oxidized to an aldehyde.

Structure

Glyceraldehyde has one

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

center and therefore exists as two different

enantiomer In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

s with opposite optical rotation: * In the nomenclature, either from Latin ''Dexter'' meaning "right", or from Latin ''Laevo'' meaning "left" * In the R/S nomenclature, either R from Latin ''Rectus'' meaning "right", or S from Latin ''Sinister'' meaning "left" While the

optical rotation Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...

of glyceraldehyde is (+) for ''R'' and (−) for ''S'', this is not true for all monosaccharides. The stereochemical configuration can only be determined from the chemical structure, whereas the optical rotation can only be determined

empirically In philosophy, empiricism is an Epistemology, epistemological view which holds that true knowledge or justification comes only or primarily from Sense, sensory experience and empirical evidence. It is one of several competing views within ...

(by experiment). It was by a lucky guess that the molecular geometry was assigned to (+)-glyceraldehyde in the late 19th century, as confirmed by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

in 1951.

Aqueous and concentrated solutions of glyceraldehyde

The description above focuses on classification of isomers, but the glyceraldehyde is subject to a further complications: the tendency of hydroxy-aldehydes to exist as hydrates. NMR measurements indicate that in aqueous solution, glyceraldehyde exists in a hydrate owing to this reaction: : The same study indicates that concentrated ("syrupy") forms of glyceraldehyde exist as dimers, indicating

hemiacetal In organic chemistry, a hemiacetal is a functional group the general formula , where is a hydrogen atom or an organic substituent. They generally result from the nucleophilic Addition reaction, addition of an Alcohol (chemistry), alcohol (a compo ...

formation.

Nomenclature

In the system, glyceraldehyde is used as the configurational standard for carbohydrates. Monosaccharides with an absolute configuration identical to (''R'')-glyceraldehyde at the ''last'' stereocentre, for example C5 in

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

, are assigned the stereo-descriptor . Those similar to (''S'')-glyceraldehyde are assigned an .

Synthesis and reactions

Glyceraldehyde can be prepared from acetals of acrolein (CH₂=CHCHO) in two steps, oxidation followed by hydrolysis of the acetal. Its cyclohexylidene acetal can also be produced by oxidative cleavage of the bis(acetal) of

mannitol Mannitol is a type of sugar alcohol used as a sweetener and medication. It is used as a low calorie sweetener as it is poorly absorbed by the intestines. As a medication, it is used to decrease pressure in the eyes, as in glaucoma, and to l ...

. Glyceraldehyde can also be synthesized through the partial oxidation of Glycerol, for example with a fenton type reagent. Glyceraldehyde is a precursor to four-carbon sugars ( tetroses) via cyanation followed by hydrolysis of the cyanohydrin: : :

Biochemistry

The enzyme glycerol dehydrogenase (NADP⁺) has two substrates,

and NADP⁺, and 3 products, D-glyceraldehyde,

NADPH Nicotinamide adenine dinucleotide phosphate, abbreviated NADP or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require N ...

and H+. The interconversion of the phosphates of glyceraldehyde (

glyceraldehyde 3-phosphate Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is a metabolite that occurs as an intermediate in several central pathways of all organisms.Nelson, D ...

) and dihydroxyacetone ( dihydroxyacetone phosphate), catalyzed by the

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

triosephosphate isomerase, is an intermediate step in

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...

References