Ninhydrin, aOrganic compound, the molecular formula is CnineHsixOfour, molecular weight 178.141, white to yellowish crystalline powder, which can be used as a color development analysis probe foramino acidandproteinQuantitative analysis.[1]
Ninhydrin can be used to monitor the deprotection in solid phase peptide synthesis (Kaiser test).Peptide chainadoptC-endConnecting with solid matrix, usingN-endExtended peptide chain, when N is deprotected, ninhydrin test shows blue.Amino acid residueIt is connected to the peptide chain when the N-terminal is protected. Therefore, if the next amino acid residue is successfully connected to the peptide chain, ninhydrin test will give colorless or yellow results.
Fingerprint identification
Ninhydrin can also be usedproteinOfamino acidanalysis.exceptprolineMost other amino acids can react with ninhydrin after hydrolysis.Of certain amino acids in hydrolysisSide chainIt will also be degraded.Therefore, amino acids that do not react with ninhydrin or have other reactions need to be analyzed separately.The rest of amino acids pass throughchromatographic separationThen it can be quantified by colorimetry.Analyzingchemical reactionOfThin layer chromatographyIn TLC, it can be used to detect all amines and carbamates, which can be detected after full heat treatmentamideClass substances.CO can be released when ninhydrin reacts with amino acidtwo。carbon dioxideThe carbon atom in is derived from thecarboxylCarbon.In archaeological research, this reaction is used to release carboxyl carbon from ancient bonesstable isotope Analysis to help reproduce the food structure of ancient creatures.The soil treated with a labeled substrate, and then the reaction of ninhydrin with amino acid to release carboxylamine, can prove whether this substrate is absorbed into microbial protein.This method has successfully found some ammonia oxidizing bacteria (also callednitrifying bacteria）UtilizeureaAscarbon source[2]。Forensic doctors often use ninhydrin solution to analyze latent fingerprints on porous surfaces such as paper.Fine secreted by fingerssweatGather on the surface of unique finger lines, that is, fingerprints containing amino acids. After ninhydrin treatment, amino acid fingertip lines can become visible purple.
Properties: This reagent is approximately white crystal or light yellow crystalline powder, slightly soluble inEtherandTrichloromethaneIt turns red above 100 ℃.
chemical property
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Characteristic reaction
Ninhydrin is a reagent used to detect ammonia or primary and secondary amines.When it comes to theseFree amineReaction timeThe substance that can produce dark blue or purple is called Ruhemann purple.Ninhydrin is often used to detect fingerprints, which is due to the slough off of the fingerprint surfaceproteinAnd peptidesLysineResidueThe primary amine on it was detected by ninhydrin.At room temperature, it is a white solid substance, soluble inethanolandacetone。Ninhydrin can be regarded as dihydroindene-1,2,3-trionehydrate。[4]The color development mechanism is shown in Figure 2.
Reactivity
Fig. 2 Reaction equation[2]
carbonylOfcarbon atomWith partpositive charge, if it is connected to theAdjacencyThe group has the ability to absorb electrons (such as the carbonyl basic body), thenCarbonyl carbonThe positive charge of will be further strengthened.Therefore, 1,2,3-threeCarbonyl compoundThe central carbon atom ofElectrophilicity。Therefore, indan-1,2,3-trione is easy to followNucleophileReactions occur, such as water.However, for most carbonyl compounds, the form of carbonyl is more stable than that of water binding products. The reason why ninhydrin can form stable hydrates with central carbon atoms is due to the destabilization of its adjacent carbonyl groups.Note: In order to produce ninhydrinChromophore, amine needs to be condensed with one molecule of ninhydrin to produce Schiff base.Only ammonia and primary amine can go through this step.In this step, there must be an alpha proton for Schiff base transfer, so if the carbon adjacent to the amine is a third-order carbon atom, it cannot be detected by ninhydrin.The reaction of ninhydrin with secondary amine will produceImineSalt ([RoneRtwoC=NRthreeRfour]+）Imine salt also has color, generally orange.[4]
