8-Hydroxy-5-nitroquinoline: Properties, Uses & Lab Guidelines

8-Hydroxy-5-nitroquinoline is a nitro-substituted derivative of 8-hydroxyquinoline that serves as a bidentate metal chelator and biologically active scaffold widely employed in analytical chemistry, antimicrobial research, and medicinal chemistry investigations.

CAS Number

4790-29-8

Molecular Formula

C₉H₆N₂O₃

Molecular Weight

190.16 g/mol

Chelation Mode

Bidentate via N-1 and O-8 donor atoms

Key Functional Groups

Hydroxyl (–OH) at C-8, nitro (–NO₂) at C-5, quinoline ring nitrogen

Aladdin SKU

H107536

Typical Applications

Metal ion detection, antimicrobial assays, medicinal chemistry synthesis

Chemical Identity and Physicochemical Properties

8-Hydroxy-5-nitroquinoline (CAS 4790-29-8) is a planar, aromatic heterocyclic compound belonging to the 8-hydroxyquinoline (oxine) family. The introduction of a nitro group at the 5-position profoundly modulates its electronic character relative to the unsubstituted parent compound. The electron-withdrawing nitro substituent lowers the pKa of the phenolic hydroxyl group and shifts the compound's UV-visible absorption to longer wavelengths, enabling chromogenic applications in analytical chemistry.

The compound typically appears as a yellow to orange crystalline solid. It is sparingly soluble in water but dissolves readily in polar organic solvents such as ethanol, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF). Stock solutions in DMSO (typically 10–50 mM) are commonly prepared for biological assays; aqueous dilutions should be made fresh to avoid precipitation. Stability is best maintained by storing the solid under cool, dry, dark conditions, as prolonged exposure to light and moisture may cause gradual decomposition.

Note: Specific melting point, exact solubility values, and spectroscopic data should be verified against the Aladdin Scientific Certificate of Analysis (CoA) for lot H107536 before use.

Metal Chelation Chemistry and Mechanism

Like all 8-hydroxyquinolines, 8-hydroxy-5-nitroquinoline acts as a bidentate ligand, coordinating metal ions through its ring nitrogen (N-1) and the deprotonated phenolate oxygen (O-8). This N,O-chelation forms stable five-membered metallocycles with a wide range of transition and post-transition metal ions, including Cu²⁺, Zn²⁺, Fe³⁺, Al³⁺, Ni²⁺, and Co²⁺.

The nitro group at C-5 exerts an electron-withdrawing inductive effect that modifies the stability constants of the resulting metal complexes compared with unsubstituted 8-hydroxyquinoline. This electronic perturbation is exploited in analytical applications where selectivity or colorimetric sensitivity toward specific metal ions is required. Metal complexes of 8-hydroxy-5-nitroquinoline are often highly colored, facilitating spectrophotometric quantification of metal ions at low concentrations.

In biological contexts, disruption of essential metal ion homeostasis—particularly copper and zinc—is proposed as one mechanism underlying the antimicrobial and antitumor activities observed for hydroxyquinoline chelators. However, researchers should note that the precise mechanism varies by cell type and metal ion, and definitive structure-activity data for 8-hydroxy-5-nitroquinoline specifically should be sourced from peer-reviewed literature.

Laboratory Applications and Protocols

Analytical Chemistry: 8-Hydroxy-5-nitroquinoline can be used as a chromogenic chelating agent for the spectrophotometric determination of metal ions in solution. To prepare a working reagent, dissolve the compound in a minimum volume of ethanol or DMSO, then dilute into the appropriate aqueous buffer at the desired pH. Chelation and color development are typically pH-dependent; consult the relevant literature for optimal pH windows for each target metal ion. Measure absorbance at the complex's characteristic wavelength using a UV-Vis spectrophotometer.

Biological and Antimicrobial Assays: For minimum inhibitory concentration (MIC) or cell-based assays, prepare a stock solution in sterile DMSO (e.g., 10–50 mM), aliquot, and store at –20 °C protected from light. Ensure the final DMSO concentration in assay media does not exceed 0.1–0.5% (v/v) to avoid solvent cytotoxicity artifacts. Include appropriate vehicle controls in all experiments.

Medicinal Chemistry and Synthesis: The compound serves as a versatile building block or ligand precursor for synthesizing novel metal complexes with potential pharmacological properties. Standard metal-complex synthesis involves combining stoichiometric quantities of the ligand and metal salt in a suitable solvent under controlled conditions. Characterize resulting complexes by elemental analysis, IR, NMR, and mass spectrometry.

Stock Solution Guidance: Prepare fresh aqueous dilutions before each experiment. For long-term storage of DMSO stocks, use amber vials, seal under inert gas if possible, and avoid repeated freeze-thaw cycles.

Safety, Handling, and Storage Guidelines

8-Hydroxy-5-nitroquinoline contains a nitro group and should be handled with appropriate caution. Although it is not classified as a primary explosive under standard laboratory conditions, nitroaromatic compounds warrant careful handling to minimize exposure. Always consult the current Safety Data Sheet (SDS) supplied by Aladdin Scientific before use.

Personal Protective Equipment (PPE): Wear nitrile gloves, a laboratory coat, and safety glasses when handling the solid or solutions. Work in a well-ventilated area or a chemical fume hood, particularly when preparing concentrated solutions or handling powders, to avoid inhalation of dust.

Storage: Store the compound in a tightly sealed container away from heat, ignition sources, moisture, and direct light. Recommended storage temperature is typically 2–8 °C or as specified on the product label. Keep away from strong oxidizers, reducing agents, and bases.

Waste Disposal: Dispose of all waste materials in accordance with local, institutional, and national regulations governing chemical and hazardous waste. Do not pour organic solvent solutions down the drain.

First Aid: In case of skin or eye contact, flush immediately with copious amounts of water and seek medical attention. If ingested or inhaled, seek immediate medical advice.

All safety information provided here is general guidance. The Aladdin Scientific SDS for H107536 is the authoritative safety reference and must be reviewed before handling.

Regulatory Considerations and Quality Specifications

When procuring 8-Hydroxy-5-nitroquinoline (SKU H107536) from Aladdin Scientific, researchers should request and review the Certificate of Analysis (CoA) for the specific lot to confirm identity (by NMR or HPLC), purity, and compliance with the stated specification grade. For analytical or biological applications requiring high precision, purity of ≥98% (by HPLC) is commonly required; verify the exact purity specification on the CoA for your lot.

Export and import of nitroaromatic compounds may be subject to regulatory controls in certain jurisdictions. Procurement managers should verify applicable regulations with their institution's chemical compliance officer before placing international orders.

For GMP or regulated research environments, confirm whether the grade and documentation supplied by Aladdin Scientific (research-grade reagent) are appropriate for the intended application. Research-grade reagents are intended for laboratory research use only and are not suitable for clinical diagnostic or therapeutic use without appropriate validation and regulatory authorization.

Frequently asked questions

What solvents are recommended for dissolving 8-Hydroxy-5-nitroquinoline?

8-Hydroxy-5-nitroquinoline is sparingly soluble in water but dissolves readily in polar organic solvents such as DMSO, ethanol, and DMF. For biological assays, prepare a concentrated stock in DMSO (10–50 mM) and dilute into aqueous media immediately before use, keeping the final DMSO concentration below 0.5% (v/v).

How does the nitro substituent affect the chelation properties compared with 8-hydroxyquinoline?

The electron-withdrawing nitro group at C-5 lowers the electron density on the chelating N and O donor atoms, which modifies the stability constants of the resulting metal complexes relative to unsubstituted 8-hydroxyquinoline. This change in electronic character can alter selectivity and affinity for different metal ions and shifts the UV-Vis absorption of metal complexes to different wavelengths, which can be advantageous for analytical applications.

What storage conditions are required for 8-Hydroxy-5-nitroquinoline (SKU H107536)?

Store the compound in a tightly sealed container at 2–8 °C (or as specified on the product label), away from light, moisture, heat, and incompatible materials such as strong oxidizers and bases. DMSO stock solutions should be stored at –20 °C in amber vials, sealed under inert gas where possible, and protected from repeated freeze-thaw cycles.

Is 8-Hydroxy-5-nitroquinoline suitable for use in cell-based antimicrobial assays?

Yes, 8-hydroxy-5-nitroquinoline has been investigated in antimicrobial research owing to its metal chelation capability and the known bioactivity of the hydroxyquinoline scaffold. For MIC or cell-based assays, use sterile DMSO stocks, ensure appropriate vehicle controls, and verify that solvent concentrations do not confound results. Researchers should consult primary literature for established assay conditions specific to their organism of interest.

Where can I find purity and specification data for lot H107536?

Purity, identity, and specification data for SKU H107536 are provided in the lot-specific Certificate of Analysis (CoA), available from Aladdin Scientific upon request or via the product page. Always verify lot-specific data before commencing experiments, particularly for analytical or quantitative applications.

References

1. Manske, R. H. F. (Ed.). The Chemistry of Heterocyclic Compounds: Quinolines. Academic Press. (General reference for quinoline chemistry.)
2. Cuin, A. et al. Metal complexes of 8-hydroxyquinoline derivatives: synthesis, characterization, and biological activity. (General review; specific title and authors require verification.)
3. Aladdin Scientific. Certificate of Analysis, 8-Hydroxy-5-nitroquinoline, SKU H107536. (Lot-specific; request from supplier.)
4. Aladdin Scientific. Safety Data Sheet, 8-Hydroxy-5-nitroquinoline, SKU H107536. (Request from supplier or product page.)

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.