DL-proline
Enable an agent to recognise DL-proline, assess the identity and condition of a material sample, and determine whether its stereochemical composition and quality permit an intended use.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an agent to recognise DL-proline, assess the identity and condition of a material sample, and determine whether its stereochemical composition and quality permit an intended use.
DL-proline is the racemic mixture of the cyclic α-amino acid pyrrolidine-2-carboxylic acid, i.e. equimolar D- and L-proline, typically isolated or supplied as the zwitterionic solid rather than as a resolved enantiomer.
It can be Identify and qualify a sample as DL-proline using structural and stereochemical evidence.; Calculate usable proline amount or prepare a solution using the measured assay and water basis.; Select a lot against application-specific impurity and D:L composition limits.; Aliquot, store and retest material under conditions supported by its product documentation and observations.; Route material to a specified synthesis, analysis or enantiomer-separation workflow when its requirements are met.; Hold or reclassify material whose composition no longer supports the DL-proline designation..
Distinguishing features
Confirm the pyrrolidine-2-carboxylic acid connectivity; formula or nominal mass alone cannot establish this structure. Reference identity: [PubChem DL-proline](https://pubchem.ncbi.nlm.nih.gov/compound/%28%2B%2F-%29-Proline).
Use an enantiomer-resolving measurement to distinguish racemic DL-proline from D-proline, L-proline or an unequally mixed sample; record the permitted departure from an equimolar mixture.
Require free proline identity rather than a peptide-bound residue, protected amine or esterified carboxyl group.
Determine water and counterion content before treating a sample as the anhydrous parent material; a separate DL-proline monohydrate record exists in [PubChem](https://pubchem.ncbi.nlm.nih.gov/compound/18474102).
Treat a near-zero optical rotation as supporting evidence only, with solvent, concentration, temperature and wavelength recorded; require sufficient identity and composition evidence to exclude misleading cancellation or inadequate sensitivity.
Scope
+ Recognition of free DL-proline and separation of verified identity from supplier naming
+ D-proline and L-proline proportions and evidence supporting a racemic designation
+ Solid or dissolved presentation, water content and material-form qualification
+ Proline assay, relevant impurities and changes during storage or preparation
+ Suitability of a particular sample for an explicitly specified laboratory use
- Independent models of enantiopure D-proline and L-proline
- Proline residues incorporated into peptides, proteins or polyproline
- Hydroxyproline, protected prolines, proline esters and other covalent derivatives
- Complete formulations, reaction systems and separation equipment
- Organism-level proline metabolism, nutritional requirements and therapeutic effects
Characteristics
- Chemical identity assignment
- Confirmed free proline; derivative; unresolved identity Prevents a matching label or nominal mass from substituting for structural identification.
- D-proline mole fraction
- mol% of total D-proline plus L-proline, with uncertainty Tests the racemic designation independently of total chemical purity.
- Racemic designation status
- Declared; analytically supported within stated tolerance; nonconforming; unresolved Separates a supplier claim from demonstrated stereochemical composition.
- Total free-proline assay
- Mass%, explicitly as received or corrected to a stated dry basis Supports dose and concentration calculations without confusing chromatographic area with material content.
- Water content
- Mass%, with method and sampling date Affects weighed proline content and helps investigate hydration or moisture uptake.
- Material presentation
- Solid with qualified hydration state; solution with specified solvent; unresolved Determines which preparation, identity and concentration assumptions are valid.
- Solution concentration
- mol/L of total free proline, with solvent and preparation basis Makes solution use traceable to assay, water correction and dilution.
- Impurity profile
- Identified impurity concentrations in mass%, mg/kg or method-specific units, with detection limits Determines whether apparently acceptable proline content conceals application-relevant contaminants.
- Lot evidence linkage
- Sample linked to supplier lot, certificate, analytical results and applicable safety data sheet Prevents properties from another proline grade or enantiomer being assigned to this sample.
- Intended-use disposition
- Eligible; conditionally eligible; hold for testing; unsuitable for specified use Expresses a decision against explicit chemical and stereochemical requirements.
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Proline identity Establish that the material contains free proline with the intended chemical connectivity.
The DL prefix specifies stereochemical composition but cannot establish chemical identity or exclude a derivative.
Molecular recognition
Connect the sample designation to evidence for the proline parent structure.
Parent structure confirmation
Record the evidence distinguishing free proline from similar compounds and identity based only on a label.
- Which structural measurements or authenticated reference comparisons establish pyrrolidine-2-carboxylic acid in this sample? measurement
- Which lot-specific documents support the DL-proline identity, and do their identifiers agree? provenance
Chemical boundaries
Separate the parent material from derivatives and proline incorporated into larger molecules.
Free proline boundary
Make explicit whether the named material is free proline, a salt or a covalently modified substance.
- Is proline present as the free amino acid, an externally counterion-containing salt, a protected derivative or a peptide residue? boundary
- If another chemical entity is present, which neighbouring model owns it and what relation connects it to DL-proline? boundary
Racemic composition Establish and maintain the evidence for the DL designation.
A chemically pure proline sample can still have the wrong enantiomeric composition for DL-proline use.
Enantiomer quantification
Record separate D and L measurements and their analytical limitations.
D:L ratio
Represent measured enantiomer proportions rather than inferring them from total proline assay.
- What D:L molar ratio was measured, with what uncertainty and enantiomer-resolving method? measurement
- How were D and L peak identities, separation adequacy and quantitative response established? provenance
Racemate acceptance
Translate stereochemical evidence into a defensible material designation.
Racemic qualification
Apply an explicit tolerance and distinguish direct composition measurements from supporting optical observations.
- What departure from an equimolar D:L mixture is acceptable for the stated DL-proline specification? definition
- Does the available evidence justify the designation, or must the sample remain unresolved or be reclassified? action
Material form and preparation Describe the physical material being weighed, sampled or dissolved.
Water, solid form and solution conditions affect how much proline is delivered and which observations are comparable.
Solid and water state
Qualify hydration and physical presentation without treating appearance as chemical proof.
Water basis
Distinguish measured water content from a demonstrated hydrate assignment.
- What water content is measured, and is there evidence distinguishing a hydrate from adsorbed or residual water? measurement
- Which material-form assignment and assay basis must be used when converting a weighed portion into moles of proline? action
Dissolved proline
Make solution composition and preparation conditions explicit.
Solution qualification
Record whether preparation delivers the intended dissolved proline concentration under the actual conditions.
- What solvent, temperature, pH where applicable, and assay-corrected total proline concentration describe the solution? measurement
- Is dissolution complete, and what evidence supports using or resampling a preparation containing precipitate? action
Lot quality and change Assess chemical quality and whether handling has invalidated earlier qualification.
The DL designation does not establish assay, impurity limits or continued fitness after storage.
Assay and contaminants
Separate proline content from impurities relevant to the intended application.
Chemical quality evidence
Record meaningful assay and impurity results with their methods and reporting bases.
- What total free-proline assay is supported, and is it an absolute content measurement or a chromatographic area percentage? measurement
- Which related compounds, residual solvents, inorganic residues or other contaminants require limits for this use? boundary
Qualification over time
Connect exposure and observed changes to retesting requirements.
Sample requalification
Determine whether previous assay, water and D:L measurements still represent the available material.
- What storage, opening, drying, heating or solution-treatment history occurred after the last qualifying measurements? provenance
- Which documented excursion or observed change requires renewed identity, water, impurity or enantiomer-ratio testing? action
Use eligibility Translate the qualified material record into permitted next actions for a specified application.
Racemic proline cannot be assumed interchangeable with an enantiopure reagent or a differently qualified grade.
Stereochemical fit
Check whether the application accepts both proline enantiomers in the measured proportions.
Application composition match
Evaluate substitution and use against explicit stereochemical requirements.
- Does the intended reaction, assay or biological experiment require DL-proline, a particular enantiomer or a specified D:L ratio? boundary
- What evidence permits this lot to be used or substituted without invalidating the application's stereochemical requirements? action
Handling and disposition
Link sample-specific documentation and qualification to preparation, storage and release decisions.
Documented next action
Make the next action depend on the actual DL-proline product, material form and intended use.
- Which current supplier instructions and safety data sheet apply to this DL-proline grade and its solid or solution presentation? provenance
- Given the assay, D:L ratio, water content and impurity results, should this material be released, retested, reclassified or rejected for the specified use? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- DL-proline racemate (unresolved, typically CAS 609-36-9)
- L-proline (proteinogenic S-enantiomer)
- D-proline (R-enantiomer)
- DL-proline hydrochloride and other salts
- N-protected DL-proline (Boc, Fmoc, Cbz) used in peptide chemistry
- cis/trans ring conformers of the pyrrolidine (not separately sold, but distinguished in spectroscopy)
- Which of these kinds and varieties hold for the sense of DL-proline this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- CAS Registry Number - 609-36-9 - Racemic / unspecified-stereochemistry proline (DL-proline). Distinct from L-proline 147-85-3 and D-proline 344-25-2.
- PubChem CID - 614 - Parent compound record for proline without specified configuration.
- EC number - 210-189-3 - EINECS/EC inventory number corresponding to CAS 609-36-9.
- InChIKey - ONIBWKKTOPOVIA-UHFFFAOYSA-N - Non-isomeric key (racemate or unspecified stereo). Enantiomers use ONIBWKKTOPOVIA-BYPYZUCNSA-N (L) and ONIBWKKTOPOVIA-STGXRNPVSA-N (D).
- Molecular formula - C5H9NO2 - Neutral (zwitterionic) molecular formula; MW 115.13 g/mol.
- UNII - DCA150089W - FDA Unique Ingredient Identifier commonly cited for unspecified/DL-proline; confirm against the current UNII file before treating as authoritative.
- Which of these identifiers and schemes hold for the sense of DL-proline this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- IUPAC/IUBMB Recommendations on amino-acid nomenclature (proline = pyrrolidine-2-carboxylic acid; DL/RS for unresolved stereo) - International Union of Pure and Applied Chemistry / International Union of Biochemistry and Molecular Biology
- Ph. Eur. / USP proline monographs - apply to L-proline as a pharmaceutical substance; DL-proline is not the pharmacopoeial article and must not be substituted for it - EDQM and United States Pharmacopeia
- REACH registration / CLP classification for proline (EC 210-189-3) as an industrial chemical - European Chemicals Agency
- Food-additive and flavouring listings for L-proline (e.g. FEMA/JECFA amino-acid flavouring use) - do not automatically cover the racemate - JECFA / FEMA / relevant food-law bodies
- Which of these standards and regulation hold for the sense of DL-proline this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Sold as a bulk amino-acid chemical for organic synthesis, racemic building-block supply, and as a cheaper feedstock than resolved L-proline when chirality is not required.
- Starting material or reference racemate in chiral resolution, HPLC method development, and enantiomeric-excess assays for proline.
- Intermediate toward N-protected proline derivatives and proline-based organocatalysts; the racemate is used when a catalyst screen does not yet demand a single enantiomer.
- Component of some industrial fermentation or chemical amino-acid streams before optical resolution; L-proline for food, feed, and pharma is usually the resolved or biosynthesized enantiomer, not DL.
- Which of these real-world use hold for the sense of DL-proline this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- specific optical rotation [α]D - approximately 0 (racemate); L-proline is strongly levorotatory in water (order of −80 to −86 deg mL g−1 dm−1 depending on concentration and t) - deg mL g^-1 dm^-1
- melting / decomposition point - about 205-228 (decomposes; literature values scatter with purity and heating rate) - °C
- enantiomeric excess (ee) - 0 for true DL; specification limits for a racemic product are typically within a few percent of 50:50 - %
- aqueous solubility (20-25 °C) - high, on the order of 1-2×10^2 g per litre (freely soluble; exact figure is grade- and temperature-dependent) - g L^-1
- pKa (α-COOH / pyrrolidinium NH2+) - approximately 2.0 and 10.6 - pKa units
- Which of these typical measurements hold for the sense of DL-proline this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Optical contamination: residual L- or D-excess in a lot labelled DL, or conversely DL material substituted for pharmacopoeial L-proline, invalidates chiral synthesis, food, and drug use.
- Racemization on heating, strong acid/base, or prolonged processing of an enantiopure proline lot, producing unintended DL-proline.
- Hygroscopic caking and discoloration of the solid on storage; amine oxidation / Maillard-type browning if mixed with reducing sugars.
- Not a high-acute-toxicity industrial chemical, but dust irritation and incorrect GRAS/food use of the racemate (only L-proline has the established nutritional/flavouring status) are the practical hazards.
- Which of these failure modes and hazards hold for the sense of DL-proline this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Catalogues in Europe and North America usually list 'DL-Proline' with CAS 609-36-9 separately from 'L-Proline' 147-85-3; some Asian commodity listings still use 'proline' without stereo, which may mean L from fermentation or DL from chemical synthesis.
- Pharmacopoeial 'Proline' in USP/Ph. Eur./JP means L-proline; Japanese and Chinese pharmacopoeias follow the same enantiomer convention.
- Biochemical literature writes Pro/P for the L-residue in proteins and 'DL-Pro' only when the racemate is intended; chemical suppliers use DL-, (±)-, or (RS)- interchangeably.
- Which of these regional variation hold for the sense of DL-proline this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- L-proline - Non-zero specific rotation and a chiral HPLC/GC or enzymatic assay showing a single enantiomer; CAS 147-85-3 vs 609-36-9.
- D-proline - Opposite sign of [α]D relative to L; chiral chromatography vs a D-proline standard (CAS 344-25-2).
- 4-hydroxyproline (Hyp) - Extra ring OH (C5H9NO3 vs C5H9NO2); mass spectrometry (m/z +16) or ninhydrin/amino-acid analysis retention time.
- pipecolic acid (piperidine-2-carboxylic acid) - Six-membered ring (C6H11NO2); molecular mass 129 vs 115 and distinct NMR/MS.
- prolinamide / proline esters - Neutral amide or ester IR/NMR (no carboxylate zwitterion); not amphoteric at the same pKa pair.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of DL-proline this model covers, and on what evidence? provenance
Sources
- Proline (CID 614) compound summary - Identity of the racemic/unspecified-stereochemistry proline record, molecular formula C5H9NO2, InChIKey without stereo, and the associated CAS/synonym set.
- Nomenclature and symbolism for amino acids and peptides - IUPAC/IUBMB naming of proline as pyrrolidine-2-carboxylic acid and the DL-/RS- convention for unresolved stereochemistry.
- Proline substance information - EC inventory identity for racemic/unspecified proline (EC 210-189-3) used in REACH listings.
What the second pass must settle
- What authoritative specification, if any, defines the acceptable D:L tolerance for the grades represented by this registry entry?
- Should verified DL-proline hydrates be represented as material forms within this entry or linked to distinct existing registry entries?
- Which enantiomer-resolving methods are validated for the relevant grades and impurity matrices, and what uncertainty do they achieve?
- What experimentally supported storage and preparation conditions preserve assay and enantiomer composition for the actual products in scope?
- Which application-specific impurity limits and qualification requirements are supported by authoritative sources rather than supplier marketing?