Paeonol: Physicochemical Features, Uses, and Key Points for Research Applications

Paeonol (also known as paeonolum; 2-hydroxy-4-methoxyacetophenone) is a representative phenolic aromatic ketone with the molecular formula C9H10O3, molecular weight ~166.17, and CAS No. 552-41-0. It is typically a white to pale yellow crystalline powder with a characteristic odor. Paeonol shows a relatively low melting point (commonly reported around 48–50°C), moderate lipophilicity (reported logP ~2.16), low water solubility, and good solubility in organic solvents such as methanol and ethanol. Its phenolic hydroxyl group and aromatic ring confer weak acidity, metal-complexation color reactions (e.g., ferric chloride coloration), and chemical reactivity consistent with electrophilic aromatic substitution (halogenation, nitration, sulfonation) and condensation-type derivatization. Paeonol can be obtained from multiple botanical materials, classically including tree peony root bark, peony roots, and Cynanchum paniculatum. In application contexts, it is widely discussed for anti-inflammatory, analgesic, anti-allergic, antimicrobial, and antioxidant pharmacological leads, and it has attracted strong interest in skin care and personal-care formulations for soothing and pigmentation-related claims. In research, paeonol is frequently used as a “natural small-molecule anti-inflammatory/antioxidant candidate” in inflammation signaling, oxidative stress, allergy models, and delivery/formulation studies, and its content and exposure can be monitored with robust quantitative methods such as HPLC.

Keywords: paeonol; 2-hydroxy-4-methoxyacetophenone; phenolic aromatic ketone; anti-inflammatory; analgesic; anti-allergic; antioxidant; HPLC; skin barrier; formulation and delivery

I. Chemistry and Physicochemical Properties

1.1 Basic information

(1) Name:

Paeonol.

(2) Synonyms:

Paeony alcohol, moutan phenol, 2′-hydroxy-4′-methoxyacetophenone.

(3) Formula and molecular weight:

C9H10O3; ~166.17.

(4) CAS No.:

552-41-0.

1.2 Appearance and key physicochemical parameters

(1) Appearance:

White to pale yellow crystalline powder.

(2) Melting point:

Commonly reported around 48–50°C.

(3) Solubility:

Readily soluble in methanol and ethanol; soluble in many organic solvents; low solubility in cold water.

(4) Lipophilicity:

Reported logP ~2.16, implying appreciable membrane affinity with methodological relevance for cellular uptake and transdermal delivery.

1.3 Chemical reactivity and analytical characteristics

(1) Weak acidity driven by the phenolic hydroxyl:

Can form phenolate salts with sodium hydroxide; this supports salt-formation or solubility-tuning studies.

(2) Color reaction:

Aqueous solutions may show light brown coloration with ferric chloride reagents, providing a rapid qualitative cue.

(3) Aromatic substitution and derivatization:

The aromatic core supports halogenation, nitration, sulfonation, and condensation reactions, enabling structure modification, lead optimization, and structure–activity work.

(4) Redox-related sensitivity:

Oxidation/reduction transformations are possible; storage and preparation should consider light exposure and oxidative stability.

II. Natural Sources and Preparation

2.1 Representative botanical sources

(1) Ranunculaceae:

Tree peony (Paeonia suffruticosa) root bark; peony roots.

(2) Apocynaceae/Asclepiadoideae:

Cynanchum paniculatum whole plant.

(3) Betulaceae:

Birch bark (e.g., Betula spp.).

(4) Primulaceae:

Certain Primula species reported as sources.

(5) Moraceae:

Mulberry leaves and related materials reported in some contexts.

2.2 Extraction and purification logic

(1) Steam distillation followed by organic extraction:

Exemplified by Cynanchum paniculatum workflows, where water distillation is followed by ether extraction of the distillate; solvent removal yields crude product and ethanol recrystallization yields purified paeonol. This reflects volatility/transfer in steam distillation and high partitioning into organic phases.

(2) Recrystallization:

Leverages temperature- and solvent-dependent solubility differences; suitable for laboratory preparation and reference-standard work.

(3) Quality control:

For extracts used in pharmacology or formulation work, a control framework should include “main-component content + impurity profile + residual solvents” to ensure cross-batch comparability.

III. Use Overview: Pharmacology, Skin Care, and Personal Care Contexts

3.1 Pharmacology-oriented use framework

(1) Pain-related:

Paeonol is frequently discussed for analgesic leads and used in pain-model studies and formulation discussions.

(2) Inflammation and allergy-related:

Suppressive signals are reported in multiple inflammation-induction and hypersensitivity models; application narratives often involve rheumatic pain, gastric pain, pruritus, allergic dermatitis, and eczema-related contexts.

(3) Antimicrobial leads:

Inhibitory activity against certain microorganisms is discussed in the literature, supporting exploration in topical microenvironment management and preservative-synergy concepts.

3.2 Skin care and personal-care framework

(1) Soothing and anti-inflammatory:

Positioned as a candidate active for irritation and inflammation-related skin phenotypes.

(2) Pigmentation-related:

Research narratives link paeonol to oxidative-stress suppression and pigmentation pathways, motivating “brightening” or “spot-fading” evaluation contexts.

(3) Oral-care concepts:

Some sources discuss potential inclusion in toothpaste or mouthwash concepts, typically coupled to anti-inflammatory, antimicrobial, and soothing claims.

IV. Mechanistic Leads and Research Models

4.1 Anti-inflammatory activity: stimuli and signaling axes

(1) Model context:

Paeonol is reported to show inhibitory signals in multiple inflammation models, including responses induced by carrageenan, egg albumin, formaldehyde, histamine, 5-hydroxytryptamine, bradykinin, xylene, and endotoxin-related triggers.

(2) Mechanistic hypothesis framework:

Commonly organized around inflammatory mediator production, immune-cell infiltration, and coupling to oxidative stress. At the molecular level, NF-κB and MAPK modules are frequent priority targets, with downstream cytokine panels and enzyme readouts used to build an evidence chain.

4.2 Analgesic, sedative, and CNS-depression leads

(1) Analgesic models:

Analgesic signals are discussed in tail-pressure and acetic-acid-related pain paradigms, supporting behavioral pain research and inflammatory pain mechanism studies.

(2) Sedation/sleep-related confounding:

If CNS-depression signals are present, designs should include locomotor/exploration controls to distinguish true analgesia from general behavioral suppression.

4.3 Anti-allergic and immune-related responses

(1) Hypersensitivity:

Reports discuss inhibitory signals across type II/III/IV hypersensitivity contexts. Experimental designs can integrate mast-cell degranulation, histamine release, IgE-related responses, and skin allergy models with multi-level endpoints.

(2) Skin inflammation models:

Eczema and pruritus models often involve barrier function and neuroinflammation coupling. Suggested linked readouts include TEWL (transepidermal water loss), stratum corneum lipid profiles, inflammatory infiltration, and neuropeptide-related indicators.

4.4 Antioxidant activity and oxidative-stress modulation

(1) ROS control:

Paeonol is discussed for suppressing intracellular ROS (e.g., O2−) in oxidative-stress models. To build mechanistic closure, it is recommended to jointly measure GSH/GSSG, lipid peroxidation markers (e.g., MDA or 4-HNE), mitochondrial membrane potential, and antioxidant enzyme expression.

(2) Coupling with inflammation:

Because oxidative stress and inflammatory pathways amplify each other, inflammation and oxidation endpoints should be monitored together to avoid overinterpretation from single-indicator shifts.

V. Analytical Measurement and Quality Control

5.1 HPLC quantitation and method considerations

(1) Typical UV wavelength:

274 nm is commonly used for UV detection in paeonol assays across materials and preparations.

(2) QC strategy:

Establish external standard curves and validate spike recovery, repeatability, and stability. For complex matrices, assess matrix effects and optimize sample pretreatment.

5.2 Sample handling and stability management

(1) Light protection and temperature control:

Given photo- and oxidation-sensitivity signals, preparation and storage should be protected from light and controlled for temperature and air exposure.

(2) Solvent selection:

Due to low water solubility, in vitro studies often require co-solvents; solvent controls and tight control of final solvent fraction are necessary to avoid solvent-driven cytotoxicity or permeability artifacts.

VI. Formulation and Delivery: Common Research Strategies

6.1 Solubility and bioavailability constraints

(1) Solubility limitations:

Insufficient aqueous solubility may limit effective exposure in vitro and in vivo; high in vitro concentrations should not be directly extrapolated to in vivo effective dose ranges.

(2) Lipophilicity and distribution:

LogP ~2.16 supports membrane partitioning and transdermal feasibility but may increase protein binding or shift tissue distribution; exposure monitoring should be used to correct interpretation.

6.2 Common delivery and optimization directions

(1) Nanocarriers and emulsions:

Used to improve dispersion, stability, and local/systemic exposure consistency.

(2) Cyclodextrin inclusion or salt formation:

Improves solubility and formulation operability.

(3) Topical formulations:

Transdermal performance, irritation potential, and barrier compatibility should be evaluated via in vitro skin permeation and irritation-relevant assays.

VII. Safety and Experimental Design Considerations

7.1 Toxicity leads and general boundaries

(1) Low-toxicity signals in some models:

Some reports describe relatively low toxicity in rodents with metabolites largely excreted via urine; certain pregnancy-related models and hypertensive dog models are also discussed as not showing overt hepatic/renal abnormalities under specific conditions.

(2) Boundary setting:

Safety conclusions should be restricted to the specific model, dose, and exposure window, supported by biochemical markers, pathology, and behavioral endpoints.

7.2 Confounder controls commonly required in research

(1) Behavioral confounding:

Sedation/hypnosis can interfere with pain and pruritus behavioral readouts; include locomotion and arousal controls.

(2) Solvent and pH confounding:

Co-solvents or salt forms may change membrane permeability and inflammatory readouts; use matched vehicle, osmolality, and pH controls.

(3) Batch and purity:

Coexisting components in botanical extracts may contribute substantially; for mechanistic attribution, compare to high-purity paeonol and use fingerprint profiling for extract standardization.

VIII. Aladdin-Related Products

8.1 Paeonol-Related Products

Catalog No.	Product Name	CAS No.	Grade and Purity	Use Stage	Functional Role in the Workflow
H111082	Paeonol	552-41-0	Analytical standard	Quantitation / QC reference	External calibrant for HPLC/UPLC quantitation, method validation (linearity, recovery, stability), and batch-to-batch comparability control
P1423390	Paeonol-d	55712-78-2	≥99%	LC–MS quantitation internal standard	Stable isotope-labeled internal standard to correct matrix effects, sample-prep recovery, and instrument drift, improving reliability of in vitro/in vivo exposure quantitation

8.2 Key Reagents Commonly Used for Paeonol Identification, Quantitation, Anti-inflammatory/Anti-allergic Models, Antioxidant Assays, and Skin Delivery Studies

Category	Reagent	CAS No.	Typical Applications	Functional Role in the Workflow	Practical Notes
Colorimetric ID	Ferric chloride (FeCl3)	7705-08-0	FeCl3 color test; rapid phenolic reactivity check	Forms characteristic complexes with phenolic –OH groups for qualitative indication	Strongly pH- and concentration-dependent; include blanks and a positive control
Solubilization / dosing	Dimethyl sulfoxide (DMSO)	67-68-5	Cell-based dosing; stock preparation for poorly soluble compounds	Improves preparation consistency and dosing reproducibility	Fix final (v/v) percentage; Always include vehicle controls.
Chromatography / sample prep	Methanol	67-56-1	HPLC sample preparation; protein precipitation	Improves recovery and repeatability	Volatile/toxic; standardize precipitation ratios
Chromatography / sample prep	Acetonitrile	75-05-8	HPLC/LC–MS protein precipitation; mobile phase	Enhances peak shape and repeatability	Salt co-presence can cause salting-out; verify compatibility
LC–MS additive	Formic acid	64-18-6	LC–MS mobile-phase additive	Improves peak shape and ionization efficiency	Fix acid strength; reduce inter-batch drift
LC–MS volatile buffer	Ammonium formate	540-69-2	LC–MS volatile buffering	Provides controlled ionic strength and pH background	Control concentration to prevent salt deposits; keep consistent across batches
LC–MS volatile buffer	Ammonium acetate	631-61-8	LC–MS volatile buffering	Same as above	Same as above
Pro-inflammatory stimulus	Lipopolysaccharide (LPS)	93572-42-0	Macrophage inflammation models (NO/cytokines)	Activates inflammatory signaling to define inhibition efficacy and dose window	Batch variability can be substantial; include endotoxin controls and cytotoxicity normalization
Inflammation readout	Sulfanilamide	63-74-1	Griess assay for NO/nitrite	Forms azo intermediate with nitrite	Light-sensitive; strict order-of-addition
Inflammation readout	N-(1-naphthyl)ethylenediamine dihydrochloride (NED·2HCl)	1465-25-4	Griess assay (coupling step)	Generates chromophore for quantitation	Control reaction time; run a standard curve each batch
Inflammation/allergy mediator	Histamine dihydrochloride	56-92-8	Mast cell/allergy stimulation; pruritus-related skin models	Provides histamine challenge to evaluate inhibition/degranulation-associated endpoints	Prepare fresh; monitor pH/ionic strength
Allergy model control	Compound 48/80	37366-09-9	Mast cell degranulation model	Triggers degranulation and mediator release for anti-allergic efficacy testing	Narrow toxicity window; optimize dose range
Antioxidant (chemical)	DPPH	1898-66-4	DPPH radical-scavenging assay	Stable radical readout for comparative antioxidant capacity	Protect from light; fix reaction time and solvent system
Antioxidant (chemical)	ABTS	30931-67-0	ABTS•+ scavenging assay	Radical cation system for antioxidant capacity	Standardize radical generation and starting absorbance
ABTS accessory	Potassium persulfate (K2S2O8)	7727-21-1	ABTS•+ generation	Oxidizes ABTS to ABTS•+	Control generation time; fresh preparation improves stability
Cellular ROS probe	DCFH-DA	4091-99-0	Cellular ROS detection (oxidative stress models)	Intracellular conversion to fluorescent probe reporting ROS changes	Light-sensitive; include probe auto-oxidation and vehicle controls
Oxidative stress inducer	Hydrogen peroxide (H2O2)	7722-84-1	Controlled oxidative injury window; protection validation	ROS challenge to define dose–response and protective effects	Prepare fresh; decomposition causes dose drift
Barrier/permeability	FITC-dextran	60842-46-8	Monolayer/skin permeability assays	Tracer for barrier integrity and permeability changes	Keep MW consistent; protect from light; include no-tissue/no-cell blanks
Buffer / pH control	Tris (Tris base)	77-86-1	pH-window studies; solubility/ionization control	Stabilizes pH to reduce kinetic drift	Strong temperature coefficient; fix temperature
Ionic strength	Sodium chloride (NaCl)	7647-14-5	Ionic-strength scans (complexation/solubility/aggregation)	Adjusts ionic strength to assess readout sensitivity	Fix total ionic strength together with buffer salts
NMR solvent	Deuterium oxide (D2O)	7789-20-0	NMR structural confirmation	Solvent for structural assignment and peak annotation	–OH exchange affects lineshape; consider solvent comparisons when needed

As a phenolic aromatic ketone, paeonol combines clear physicochemical characteristics, workable extraction/purification pathways, and rich pharmacological leads, supporting sustained research value in anti-inflammatory, analgesic, anti-allergic, antimicrobial, and antioxidant directions, and it is widely positioned in skin care and personal-care formulation contexts. For research studies, it is recommended to build a closed loop linking “target endpoints–mechanistic pathways–effective exposure”: define the causal structure of inflammation/allergy/pain/oxidative stress models, control solvent, behavioral, and batch confounders, and correct formulation and in vivo/in vitro exposure using quantitative methods such as HPLC or LC-MS, thereby achieving conclusions that are reproducible, comparable, and mechanistically interpretable.