Glucose

• D-glucose D-glucose
• D-( ) -glucose
• Dextrose
• IUPAC: (2R, 3S, 4R, 5R) -2,3,4,5,6 - Pentahydroxyhexanal (as aldehyde)
• IUPAC: (3R, 4S, 5S, 6R ) -6 - (hydroxymethyl) oxan -2 ,3,4,5- tetrol (as pyranose )
• Glucose
• Starch sugar (deprecated)
• Hydratdextrose ( D-( )- glucose monohydrate )

• L-( -)- glucose
• IUPAC: (2S, 3R, 4S, 5S) -2,3,4,5,6 - Pentahydroxyhexanal (as aldehyde)

• 50-99-7 (D -glucose )
• 921-60-8 (L- glucose)
• 58367-01-4 (DL- glucose)

• B05CX01 (D -glucose )
• V04CA02 (D -glucose )
• V06DC01 (D -glucose )

D- Glucose: colorless and odorless solid relative sweetening power = 0.6-0.75

Fixed

1.562 g · cm -3

Well in water (470 g · l-1 at 20 ° C)

(D -glucose )

25.8 g · kg -1 ( LD50, Rat, oral, D- glucose)

Template: Infobox chemical / molecular formula search available

Glucose ( Glc short, well written glucose, γλυκύς of Greek, sweet ') is a monosaccharide ( simple sugar ) and thus belongs to the carbohydrates. There are two enantiomers: D -glucose and L-glucose ( for an explanation of the terms " D" and " L" see Fischer projection ). In nature only comes before D -glucose. This is also known as dextrose or in older literature as dextrose. Glucose is present in solid form, usually present as monohydrate Hydratdextrose. L-glucose is only accessible synthetically and has little practical significance.

• 4.1 glucose concentration in the blood

• 6.1 behavior in aqueous solution 6.1.1 mutarotation
• 6.1.2 isomerization

• 7.1 Classical qualitative detection reactions 7.1.1 Fehling's reaction
• 7.1.2 Tollens reaction

• 7.2.1 Optical methods for determining the concentration of glucose
• 7.2.2 Amperometric glucose sensor
• 7.2.3 Other sensory methods

Discovery history

The grape was discovered in 1792 by Johann Tobias Lowitz in grapes and recognized as cane sugar (sucrose ) is different. Glucose is the Jean Baptiste Dumas in 1838 coined term that has prevailed in the chemical literature. By Friedrich August Kekulé 's proposal comes dextrose (from Latin dexter = right ), since glucose has the physical ability to rotate the plane of plane-polarized light to the right. In contrast, D -fructose rotate ( a ketohexose ) and L- glucose polarized light to the left. The structure of the glucose and the structure of relations with the other monosaccharides were described in 1891 by Emil Fischer and represented a milestone in the chemistry of natural products represents the name initially refers to the natural products. Your enantiomers received with introducing systematic nomenclatures same name with consideration of the absolute stereochemistry (eg Fischer nomenclature, D / L nomenclature).

Occurrence and technical recovery

Dextrose is included as a component in double sugars such as lactose (milk sugar) or sucrose ( cane or beet sugar), in multiple sugars such as raffinose and multiple sugars such as starch, glycogen or cellulose. It is produced by enzymatic cleavage of the full thickness (for example from corn or potato). This results in the previously common term " starch sugar ".

Biochemistry

Glucose is mainly produced by plants using photosynthesis from sunlight, water and carbon dioxide and can be used by all living organisms as an energy and carbon source. Normally, glucose is not free, but in the form of polymers, ie, milk sugar, beet sugar, starch, cellulose and others from that are both reserve materials, as well as part of the cell structure in plants. These polymers are degraded in food intake by animals, fungi and bacteria using enzymes to glucose only. In humans, this is partly already during chewing by amylase is contained in saliva. All living beings are also able to produce glucose from certain source products themselves if the need arises. The glucose content of the blood is about 0.1 % and is controlled by the hormones insulin and glucagon.

Glucose is converted into living beings more other chemical compounds, that are the starting material of different metabolic pathways. In addition to the phosphorylation to glucose 6-phosphate, which is part of the glycolysis, glucose can first be oxidized to glucono -1 ,5 -lactone in its degradation. Glucose is used as a component in the biosynthesis of trehalose and glycogen in bacteria. Glucose can also be converted by the bacterial xylose isomerase to fructose.

Last but not least glucose to get into cells and cell compartments or out, are transported across membranes, for which there are several dozen specific transport proteins are the people who belong mainly to the major facilitator superfamily.

Biosynthesis

Biosynthesis of smaller molecules

The pathway, which starts with molecules that contain two to four carbon atoms (C) and terminating in glucose molecule contains six carbon atoms, is called gluconeogenesis and is found in all living beings. The smaller starting materials are the result of other metabolic pathways in plants and derived ultimately from the assimilation of carbon dioxide.

Biosynthesis of storage compounds and polymers

Glucose is a building block of many carbohydrates and can be split off from these by using specific enzymes. So-called glycosidases catalyze the hydrolysis of long-chain polysaccharides initially, terminal glucose or disaccharides are removed. Disaccharides in turn are usually degraded by specific glycosidases to glucose. The names of the degrading enzymes are often derived from the respective poly - and disaccharide; so there are among others for the degradation of polysaccharide chains amylases (of amylose component of starch), cellulases ( cellulose ), chitinase ( chitin ) and more; further for the cleavage of the disaccharides lactase, sucrase, trehalase and others.

In humans, about 70 genes are known that encode glycosidases. You have functions in digestion and the breakdown of glycogen, the sphingolipids, mucopolysaccharides and poly (ADP- ribose).

Condensing and recycling

Physiological caloric value of glucose is 15.7 kJ / g (3.74 kcal / g). The high availability of carbohydrates through the plant biomass has led during evolution, especially the micro-organisms to a variety of methods to exploit the energy and carbon storage of glucose. Differences are leading to what is no longer usable for energy end product of the way. This decides the presence of individual genes and their gene products, enzymes which reactions are possible (see figure). Here, the metabolic pathway of glycolysis by almost all living organisms used. Only adapted to extreme conditions bacteria and archaea have developed further degradation reactions, which are summarized in the Entner- Doudoroff pathway. A major difference of this pathway consists in the extraction of NADP as a reducing agent for anabolism, which would otherwise be generated indirectly.

Last place of glucose as a component in the glycosylation of proteins and other substances ( catalyzed by glycosyltransferases ) use and may be cleaved off from the resulting glycoproteins, peptidoglycans and glycosides again.

Medicine

Glucose can be metabolized via glycolysis, oxidative decarboxylation, the citric acid cycle and the respiratory chain completely water and carbon dioxide. Is it not enough oxygen available, the glucose degradation occurs anaerobically to lactate by lactic acid fermentation and uses less energy. With a high supply of glucose metabolite acetyl -CoA can also be used for fatty acid synthesis. Also is replenished by glucose of glycogen storage of the body again, which is found mainly in the liver and skeletal muscle. These processes are hormonally regulated. By gluconeogenesis can build up under energy consumption of the organism glucose from other metabolites, including from lactate or certain amino acids. The formation of up to 250 g of glucose per day will take place mainly in the liver. The tubular cells of the kidneys can form glucose. A permanent increase in the glucose content in the blood is referred to as diabetes (diabetes mellitus).

Glucose concentration in the blood

The glucose in the blood is called blood sugar. The blood sugar level of a healthy person is in the fasting state, that is, after overnight fasting, about 70 to 100 mg / dl blood ( 4 to 5.5 mM). In the blood plasma, the measured values ​​are about 10-15% higher. In addition, the values ​​in the arterial blood through the venous blood concentrations are as glucose is added during the passage of the capillary bed in the tissue. Also in capillary blood, which is often used for blood sugar determination, the values ​​are partly higher than in venous blood. By feeding the glucose concentration increases. Values ​​above 180 mg / dl in venous whole blood is definitely abnormal, referred to as hyperglycemia. A repeated or permanently elevated blood sugar value indicates usually on diabetes mellitus. Glucose concentrations below 40 mg / dl in venous whole blood is referred to as hypoglycaemia.

Nomenclature of glucose

As a carbohydrate with six carbon atoms of glucose is one of the hexoses. As aldose glucose has an aldehyde function at the first carbon atom ( in contrast, carbohydrates with a keto group as ketoses called ). By intramolecular hemiacetal form a ring is formed: in the pyranose form of the first to the fifth, the rare furanose form the first to the fourth carbon atom via an oxygen bridge is bonded. The carbonyl oxygen of the aldehyde group is doing to the hydroxyl group.

The pictured above representation of pyranoid form - in the example the β -D -glucopyranose - is called the Haworth projection. The ring is shown as a flat, which does not correspond to reality, but is sufficient for many purposes. Through the ring closure is the first C- atom to form a new, more chiral center, so that the formation of diastereomers is possible. The structure in which the hydroxy of the hemiacetal function to the Haworth projection facing downwards is referred to as α -D - glucose. With the hydroxy function upward as β -D-glucose In general, in the α - form formed in the ring-closing - hydroxy function on the opposite side of the ring plane of the Haworth projection as it is, the hydroxymethylene group ( carbon atom 6 ), wherein the β - form thereof. In this form, the definition applies to both the D-and L-sugars, as well as aldoses and ketoses. α - and β -D-glucose are described as examples of anomers structures. Anomers are stereoisomeric sugars that differ only in the configuration at the chiral structures during ring closure. Anomeric are thus a special case of epimers.

The Fischer projection is in the cyclic hemiacetal forms, see 1, confusing. To illustrate the angled arrangement of the carbon chain, the chair - representation 3 is selected. The representation 4 is common and stereochemically unambiguous.

Reactions of glucose

Behavior in aqueous solution

In aqueous solution, the ring can be opened and closed so that an equilibrium between pyranose ( six-membered ring with endozyklischem oxygen atom, 99.75 %), furanose ( five-membered ring in traces ) and open-chain aldehyde form (0.25 % ) is present. The addition of acid or alkali accelerates this process. Since the ring closure can occur either the alpha or the beta form, a balance between alpha form is present ( 36.4 % ) and beta - form ( 63.6 %). The balance is located, as can be seen in the percentages on the side of the β -D-glucose. It is the more stable anomer, because all hydroxyl groups are located in equatorial positions in the chair conformation and thus have the greatest possible distance from each other. The fact that the α -anomer with at least 36.4 % is present in spite of the axial OH group, suggests that there must be other influences. The relative stability of the α - anomeric configuration is referred to as effect.

Mutarotation

The conversion between the two anomers can be observed in the polarimeter, because pure α -D-glucose has a specific angle of rotation of 112 °, pure β -D-glucose of 18.7 °. If after a certain time the balance set, there is an angle of rotation of 52.7 °. This change of the rotational angle is referred to as mutarotation. By addition of acid or base, this conversion can be greatly accelerated. Equilibration passes over the open chain aldehyde form.

Isomerization

In dilute sodium hydroxide solution, mannose, glucose and fructose are converted to each other ( Lobry -de Bruyn - Alberda -van- Ekenstein rearrangement), so that a balance between these isomers is formed. This reaction proceeds via an enediol: R- CH ( OH) -CH = O R -C ( OH) = CH -OH R -C ( = O)- CH2 -OH

Analysis

Classical qualitative detection reactions

These reactions have only historical significance:

Fehling's reaction

The Fehling's test is a classic proof of aldoses. Due to the mutarotation of glucose is always available for a small proportion as open-chain aldehyde. The addition of Fehling's reagents, the aldehyde group is oxidized to a carboxylic acid, while the Cu2 to Cu Tartratkomplex is reduced, and the red precipitate ( Cu2O ) fails.

Tollens reaction

After addition of ammoniacal AgNO3 to Ag sample solution of glucose is reduced to elemental silver, which deposits on the vessel wall as a silver mirror.

Instrumental quantitative determination

Optical methods for determining the concentration of glucose

Photometric - enzymatic processes in solution

The enzyme glucose oxidase ( GOx ) is to glucose, using oxygen to gluconic acid and hydrogen peroxide. Another enzyme, peroxidase, catalyzes a chromogenic reaction ( Trinder ) reaction of phenol with 4-aminoantipyrine to form a violet dye.

Photometric test strip method

The test strip method is using the above-mentioned enzymatic reaction of glucose to gluconic acid with the formation of hydrogen peroxide. The reagents are immobilized in a polymer matrix, the so-called test strips, which assumes a more or less pronounced color. This can be read using an LED-based hand photometer at 510 nm reflectometry. This allows the routine determination of blood sugar by laymen. In addition to the reaction of phenol with 4-aminoantipyrine new chromogenic reactions have been developed that allow the photometry at higher wavelengths (550 nm, 750 nm).

Amperometric glucose sensor

The electrochemical analysis of glucose is also based on the above-mentioned enzymatic reaction. The produced hydrogen peroxide can be quantified by amperometry at a potential of 600 mV by means of anodic oxidation. GOx is immobilized on the electrode surface or in front of the electrode a sealing membrane arranged. The electrodes come in addition to the classic precious metals such as platinum or gold in increasingly often carbon nanotube electrodes are used, which were doped with boron, for example. Also Cu - CuO nanowires are used as enzyme-free amperometric electrodes use. There was thus obtained a detection limit of 50 mol / L. A particularly promising method is the so-called "enzyme wiring". Here, the current flowing in the oxidation of electron is directly derived from the enzyme over a molecular wire to the electrode.

Other sensory methods

For glucose, there are a variety of other chemical sensors. Given the importance of the analysis of glucose in biological sciences, numerous optical probes have been developed for saccharides based on the use of boronic acids and especially for intracellular sensor applications come into question, where other (optical ) methods do not or only partially can be used. In addition to the organic boronic acid derivatives which bind specifically to the often high 1,2- diol groups of the sugar, there are further classified according to function mechanisms probe approaches that use selective glucose -binding proteins (e.g., concanavalin A) receptor. Furthermore, methods have been developed which detect the concentration of glucose indirectly the concentration of metabolised products, such as the consumption of oxygen by means of fluorescence- optical sensors. Finally, there are enzyme- based approaches that utilize the intrinsic absorbance and fluorescence of ( fluorescently labeled ) enzymes as an information carrier.

Biotechnological products from glucose

Glucose is a major biotechnological resource. The following chart provides a brief overview of important products (click on the name leads to the same products ). The industrially interesting products or their precursors are shown in bold:

Memory aids for the stereochemistry

To memorize the glucose configuration in Fischer projection, there are the following mnemonic: The positions of the hydroxyl groups on the right and left of the carbon chain can be described by "Ta - doors -Ta- Ta " (as the siren ) " represent ". The arrangement of the hydroxyl groups of the galactose one can contrast than blue light ( see Figure ) remember.