1-Methylpyridinium-3-carboxylate
[CAS 535-83-1]

Identification

• Classification: Biochemical >> Plant extracts
• Name: 1-Methylpyridinium-3-carboxylate
• Synonyms: Trigonelline
• Molecular Formula: C₇H₇NO₂
• Molecular Weight: 137.14
• CAS Registry Number: 535-83-1
• EC Number: 208-620-5
• SMILES: C[N+]1=CC=CC(=C1)C(=O)[O-]

Properties

• Melting point: 260 °C (Decomposes) (Expl.)

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319
• Safety Statements: P264-P264+P265-P280-P302+P352-P305+P351+P338-P321-P332+P317-P337+P317-P362+P364

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315

Discovery and Applications

1-Methylpyridinium-3-carboxylate is a zwitterionic heteroaromatic compound derived from pyridine, containing a permanently quaternized nitrogen atom and a deprotonated carboxylate group on the aromatic ring. Structurally, it can be described as a pyridinium system in which the nitrogen is methylated to form a positively charged N-methylpyridinium center, while a carboxylate substituent is present at the 3-position of the ring.

The core structure is based on pyridine, a six-membered aromatic heterocycle containing one nitrogen atom. In 1-methylpyridinium-3-carboxylate, the nitrogen atom is alkylated by a methyl group, converting the neutral pyridine nitrogen into a quaternary ammonium center. This modification results in a permanent positive charge localized on the nitrogen, forming a pyridinium cationic center.

At the 3-position of the ring, a carboxylate group (–COO⁻) is present. This functional group arises from deprotonation of a carboxylic acid precursor and carries a negative charge distributed over two oxygen atoms through resonance. The combination of a positively charged pyridinium nitrogen and a negatively charged carboxylate group within the same molecule makes this compound a zwitterion.

The aromatic pyridinium ring retains delocalized π-electron character, but the positive charge on nitrogen significantly alters its electron distribution. Pyridinium systems are more electron-deficient than neutral pyridine due to the quaternization of the nitrogen atom, which withdraws electron density from the aromatic ring through inductive effects.

The carboxylate group is strongly electron-withdrawing overall but stabilizes negative charge through resonance between its two oxygen atoms. Its presence also introduces strong hydrogen-bond-accepting capability, although the absence of acidic protons in the deprotonated form means it does not act as a hydrogen-bond donor.

Because the molecule contains both ionic centers, its physicochemical behavior is strongly influenced by electrostatic interactions. Zwitterionic compounds often exhibit high polarity, strong solvation in polar media, and limited solubility in nonpolar solvents. The internal charge separation also contributes to high lattice energy in solid-state forms, often leading to crystalline structures stabilized by ionic interactions.

The molecule can be considered a modified amino acid-like aromatic system in terms of charge distribution, although it is not a peptide or biological amino acid. The spatial separation of positive and negative charges influences dipole moment and intermolecular interactions.

From a chemical stability perspective, the pyridinium N-methyl bond is generally stable under normal conditions but can be susceptible to nucleophilic attack under strongly basic conditions. The carboxylate group is stable under neutral and basic conditions but may become protonated under acidic environments, converting the molecule into a cationic carboxylic acid form.

Overall, 1-methylpyridinium-3-carboxylate is a highly polar zwitterionic aromatic compound featuring a quaternized pyridinium nitrogen and a carboxylate substituent. Its key structural characteristic is internal charge separation within a conjugated heteroaromatic framework, which strongly influences its electronic properties, solvation behavior, and solid-state interactions.

References

2026. Characterizing Human Oxidative, Anabolic and Glycolytic Metabolism in Athletes with Extreme Physiologies. Sports Medicine - Open.
DOI: 10.1186/s40798-026-00989-z

2026. Effects of grind size and brewing time on properties of cold brewed Robusta Ijen coffee. Journal of Food Science and Technology.
DOI: 10.1007/s13197-026-06628-5

2026. Sensory analysis and biochemical composition of Arabica coffee leaves. Journal of Food Science and Technology.
DOI: 10.1007/s13197-026-06588-w