Abstract

Rutin (C₂₇H₃₀O₁₆), systematically named 3′,4′,5,7-tetrahydroxy-3-[α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranosyloxy]flavone, represents a flavonol glycoside compound of significant chemical interest. This polyphenolic compound exhibits a molecular weight of 610.52 g·mol⁻¹ and manifests as a yellow crystalline solid with a characteristic melting point of 242 °C. Rutin demonstrates limited aqueous solubility of approximately 12.5 mg per 100 mL at standard temperature and pressure. The compound's molecular architecture features a quercetin aglycone moiety linked through a glycosidic bond to the disaccharide rutinose, comprising glucose and rhamnose subunits. Rutin serves as a model compound for studying flavonoid glycoside chemistry, particularly in investigations of glycosidic bond stability, antioxidant mechanisms, and molecular recognition phenomena. Its extensive hydrogen bonding capacity and chiral centers contribute to complex solid-state packing arrangements and distinctive solution-phase behavior.

Introduction

Rutin constitutes an important member of the flavonoid glycoside family, first isolated from Ruta graveolens in the mid-19th century. This organic compound belongs to the flavonol subclass of flavonoids, characterized by the presence of a 3-hydroxyflavone backbone glycosylated at the 3-position. The compound's systematic name reflects its complex stereochemistry and functional group arrangement. Rutin represents one of the most extensively studied flavonoid glycosides due to its widespread natural occurrence and distinctive chemical properties. The compound's molecular architecture combines hydrophobic aromatic systems with hydrophilic carbohydrate moieties, creating an amphiphilic character that influences its physicochemical behavior. Rutin serves as a reference compound in analytical chemistry for flavonoid quantification and as a substrate for enzymatic studies involving glycosidases and transferases.

Molecular Structure and Bonding

Molecular Geometry and Electronic Structure

The molecular structure of rutin comprises a quercetin aglycone (3,3′,4′,5,7-pentahydroxyflavone) linked via a β-glycosidic bond at the 3-position to the disaccharide rutinose (α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranose). The flavone backbone exhibits near-planar geometry with dihedral angles between rings typically less than 10°. The glycosidic linkage introduces conformational flexibility, with the sugar moiety adopting various orientations relative to the planar aglycone. The electronic structure features extensive conjugation throughout the flavone system, with highest occupied molecular orbitals localized on the phenolic oxygen atoms and lowest unoccupied molecular orbitals delocalized across the chromone ring system. The compound contains fifteen hydrogen bond donors and sixteen hydrogen bond acceptors, creating extensive potential for intermolecular interactions.

Chemical Bonding and Intermolecular Forces

Covalent bonding in rutin follows typical patterns for flavonoid glycosides, with carbon-carbon bond lengths in the aromatic systems ranging from 1.38 to 1.44 Å and carbon-oxygen bonds varying from 1.36 to 1.43 Å depending on hybridization. The glycosidic C-O bond length measures approximately 1.43 Å, characteristic of β-glycosidic linkages. Intermolecular forces dominate rutin's solid-state behavior, with extensive hydrogen bonding networks involving all hydroxyl groups. The crystal structure exhibits O-H···O hydrogen bonds with distances between 2.70 and 2.90 Å. π-π stacking interactions occur between flavone systems with interplanar distances of approximately 3.4 Å. The molecule possesses a calculated dipole moment of approximately 5.2 D, primarily oriented along the long axis of the flavone system.

Physical Properties

Phase Behavior and Thermodynamic Properties

Rutin typically crystallizes as a trihydrate, forming yellow needles or plates with characteristic birefringence. The compound undergoes dehydration between 110 and 125 °C, followed by melting with decomposition at 242 °C. The density of crystalline rutin trihydrate measures 1.62 g·cm⁻³. Rutin exhibits limited solubility in water (12.5 mg·mL⁻¹ at 25 °C) but demonstrates improved solubility in polar organic solvents including methanol (15.2 mg·mL⁻¹), ethanol (8.7 mg·mL⁻¹), and dimethyl sulfoxide (43.6 mg·mL⁻¹). The octanol-water partition coefficient (log P) measures approximately -1.5, indicating hydrophilic character. The specific rotation [α]D²⁰ measures +13.5° (c = 2, pyridine), reflecting the compound's chiral centers. The refractive index of rutin crystals measures 1.78 at 589 nm.

Spectroscopic Characteristics

Infrared spectroscopy of rutin displays characteristic absorption bands at 3400–3200 cm⁻¹ (O-H stretch), 1655 cm⁻¹ (conjugated C=O stretch), 1605 cm⁻¹ and 1505 cm⁻¹ (aromatic C=C stretch), and 1070 cm⁻¹ (C-O-C glycosidic stretch). Proton NMR spectroscopy (DMSO-d₆) exhibits signals at δ 12.60 (s, 5-OH), 10.85 (s, 7-OH), 9.65 (s, 4′-OH), 9.15 (s, 3′-OH), 7.55 (d, J = 8.5 Hz, H-6′), 6.85 (d, J = 8.5 Hz, H-5′), 6.40 (d, J = 2.0 Hz, H-8), 6.20 (d, J = 2.0 Hz, H-6), 5.35 (d, J = 7.5 Hz, H-1″), 4.40 (s, H-1‴), and numerous sugar proton signals between δ 3.0–4.0. Carbon-13 NMR shows characteristic signals at δ 177.5 (C-4), 164.5 (C-7), 161.8 (C-5), 156.9 (C-2), 156.5 (C-9), 148.8 (C-4′), 145.5 (C-3′), 134.2 (C-3), 122.0 (C-1′), 121.5 (C-6′), 116.7 (C-5′), 116.0 (C-2′), 104.5 (C-10), 102.0 (C-1″), 101.5 (C-1‴), 98.5 (C-6), 94.0 (C-8), and sugar carbons between δ 60–80. UV-Vis spectroscopy reveals absorption maxima at 258 nm and 359 nm in methanol solution.

Chemical Properties and Reactivity

Reaction Mechanisms and Kinetics

Rutin demonstrates characteristic reactivity patterns of flavonol glycosides. Acid-catalyzed hydrolysis cleaves the glycosidic bond with rate constants of k = 2.3 × 10⁻³ s⁻¹ in 1 M HCl at 80 °C, producing quercetin and rutinose. Alkaline conditions induce decomposition of the flavone nucleus, particularly at elevated temperatures. Rutin undergoes oxidation at the catechol moiety (3′,4′-dihydroxyphenyl group) with a standard reduction potential of +0.53 V versus standard hydrogen electrode. The compound chelates metal ions including Fe³⁺, Al³⁺, and Cu²⁺ with formation constants ranging from 10⁴ to 10⁶ M⁻¹. Photochemical degradation follows first-order kinetics with a half-life of 48 hours under UV irradiation (254 nm) in aqueous solution. Thermal decomposition above 242 °C produces carbon monoxide, carbon dioxide, and various phenolic compounds.

Acid-Base and Redox Properties

Rutin exhibits multiple acid dissociation constants corresponding to its phenolic hydroxyl groups: pKₐ₁ = 7.5 (7-OH), pKₐ₂ = 8.5 (4′-OH), pKₐ₃ = 9.5 (3′-OH), pKₐ₄ = 11.5 (3-OH), and pKₐ₅ = 12.5 (5-OH). The compound demonstrates antioxidant activity through hydrogen atom transfer and single electron transfer mechanisms, with bond dissociation energies of approximately 82 kcal·mol⁻¹ for the 4′-OH group. Rutin undergoes reversible electrochemical oxidation at +0.45 V versus Ag/AgCl in aqueous buffer (pH 7.4), corresponding to two-electron oxidation of the catechol moiety. The compound exhibits stability in the pH range 3–6, with degradation occurring more rapidly under strongly acidic or basic conditions.

Synthesis and Preparation Methods

Laboratory Synthesis Routes

Laboratory synthesis of rutin typically employs quercetin as starting material. Protection of the 3′- and 4′-hydroxyl groups as benzyl ethers followed by selective glycosylation at the 3-position using peracetylated rutinose donors represents the most efficient synthetic route. Glycosylation employs silver triflate or boron trifluoride etherate as Lewis acid catalysts, providing the protected glycoside in 65–75% yield. Subsequent deprotection using sodium in liquid ammonia or catalytic hydrogenation affords rutin with overall yields of 45–55%. Alternative approaches utilize enzymatic glycosylation with glycosyltransferases, particularly UDP-glucose-dependent glycosyltransferases followed by rhamnosyltransferases. These biocatalytic methods provide superior stereoselectivity but lower overall yields of 30–40%.

Industrial Production Methods

Industrial production of rutin primarily utilizes extraction from natural sources rather than synthetic routes. Buckwheat (Fagopyrum esculentum) represents the most significant commercial source, particularly Tartary buckwheat varieties containing 0.8–1.7% rutin by dry weight. Extraction employs hydroalcoholic solvents (70% ethanol-water) at elevated temperatures (60–80 °C) followed by concentration and crystallization. Typical industrial processes achieve rutin yields of 1.2–1.5% from dried plant material. Purification involves recrystallization from aqueous methanol or ethanol, producing pharmaceutical-grade rutin with purity exceeding 98%. Annual global production estimates approach 500 metric tons, with China representing the primary producer. Production costs range from $120–180 per kilogram depending on purity specifications.

Analytical Methods and Characterization

Identification and Quantification

High-performance liquid chromatography with ultraviolet detection (HPLC-UV) represents the standard analytical method for rutin quantification, typically using reversed-phase C18 columns with mobile phases consisting of water-acetonitrile or water-methanol mixtures acidified with formic or acetic acid. Detection occurs at 258 nm or 359 nm with quantification limits of 0.1 μg·mL⁻¹. Liquid chromatography-mass spectrometry (LC-MS) provides confirmatory identification through molecular ion detection at m/z 611 [M+H]⁺ and characteristic fragment ions at m/z 465 [M-rhamnose+H]⁺ and 303 [M-rutinose+H]⁺. Capillary electrophoresis with UV detection offers an alternative separation method with comparable sensitivity. Spectrophotometric methods based on complexation with aluminum ions allow rapid quantification with detection limits of 0.5 μg·mL⁻¹.

Purity Assessment and Quality Control

Pharmaceutical-grade rutin must comply with purity specifications established in various pharmacopeias. The United States Pharmacopeia requires identification by infrared spectroscopy, HPLC purity exceeding 95%, and limits for related substances including quercetin (<0.5%), isoquercitrin (<1.0%), and other flavonol glycosides (<2.0%). Residual solvent content must not exceed 5000 ppm for ethanol and 3000 ppm for methanol. Heavy metal limits follow standard pharmaceutical requirements (<20 ppm). Water content by Karl Fischer titration must not exceed 12.0% for the trihydrate form. Microbiological testing includes total aerobic microbial count (<1000 CFU·g⁻¹) and absence of specified pathogens. Stability testing demonstrates that rutin maintains specification compliance for at least 36 months when stored in sealed containers protected from light at room temperature.

Applications and Uses

Industrial and Commercial Applications

Rutin serves as a standard reference compound in analytical chemistry laboratories for flavonoid quantification and method validation. The compound finds application as a UV absorber in cosmetic formulations at concentrations up to 1.0%. Food industries utilize rutin as a natural antioxidant in lipid-containing products, with typical usage levels of 0.01–0.05%. The compound functions as a metal chelator in various industrial processes, particularly in preventing metal-catalyzed oxidation reactions. Rutin derivatives, particularly rutin esters with fatty acids, find application as emulsifiers and stabilizers in food and cosmetic products due to their amphiphilic character. Annual commercial consumption exceeds 300 metric tons globally, with market values estimated at $50–70 million.

Research Applications and Emerging Uses

Rutin serves as a model compound in studies of glycoside hydrolysis kinetics and mechanisms. The compound finds extensive use as a substrate for enzyme characterization, particularly for glycosidases, transferases, and oxidative enzymes. Materials science research investigates rutin as a building block for molecular assemblies and as a component in supramolecular chemistry. Rutin complexes with metals provide models for studying biological metal-flavonoid interactions. Emerging applications include use as a chiral selector in chromatographic separations and as a component in sensor technologies. Research continues into rutin derivatives with modified solubility properties and enhanced stability characteristics. Patent activity focuses on synthetic derivatives, formulation technologies, and extraction process improvements.

Historical Development and Discovery

Rutin was first isolated in 1842 from the herb Ruta graveolens by the French chemist Augustin-Pierre Dubrunfaut, who named the compound "rutin" based on its botanical source. Structural elucidation progressed throughout the early 20th century, with the glycosidic nature established by 1928 through acid hydrolysis studies. The complete structure, including the positions of glycosylation and the identity of the sugar components, was determined by 1936 through the work of multiple research groups. The absolute configuration of the sugar moieties was established in the 1950s using emerging techniques in stereochemistry. Synthetic approaches were developed beginning in the 1960s, with the first total synthesis achieved in 1972. Analytical methods for rutin quantification advanced significantly during the 1980s with the adoption of HPLC techniques. Industrial production methods were optimized throughout the late 20th century, particularly extraction processes from buckwheat sources.

Conclusion

Rutin represents a chemically significant flavonoid glycoside with distinctive structural features and physicochemical properties. The compound's molecular architecture combines a planar flavone aglycone with flexible carbohydrate substituents, creating unique conformational behavior and intermolecular interaction patterns. Rutin's acid-base properties, redox behavior, and metal complexation characteristics provide valuable insights into flavonoid chemistry. The compound serves important roles as an analytical standard, research tool, and industrial material. Ongoing research continues to explore rutin derivatives with modified properties and potential applications in materials science and technology. Further investigation of rutin's solid-state chemistry, solution behavior, and reactivity patterns will contribute to advanced understanding of flavonoid glycoside systems and their potential utilization in various chemical contexts.