Исследование реакционной способности производных коричной кислоты – предшественников лигнина

Objectives. Cinnamic acid derivatives belong to a large class of phenolic compounds, which are widely distributed in plants and have high potential for use in the medical and industrial fields. They have various useful practical properties, e.g., antioxidant, anti-inflammatory, antiplatelet, and anti-melanogenic properties. Hydroxycinnamic acids are of particular interest as phenylpropanoids, which are the starting compounds of lignin. The aim of this work was to study the electronic structure and analyze the reactivity of the simplest representatives of phenylpropanoids formed during the biosynthesis of the coumaric (p-hydroxycinnamic), caffeic (3,4-dihydroxycinnamic), ferulic (3-methoxy-4-hydroxycinnamic), sinapic (3,5-dimethoxy-4- hydroxycinnamic), and 3,4-dimethoxycinnamic acids. These acids are the biogenetic precursors of most other phenolic compounds (coumarins, melanins, lignins, and flavonoids) and are found in almost all higher plants.Methods. Calculations with full optimization of the geometric parameters were performed using the original Hartree–Fock theory and hybrid density functional method. All calculations were performed using the Firefly program. Results. A comparative quantum chemical calculation of the geometric parameters of hydroxycinnamic acid molecules was conducted via two methods, and the values of the charges on atoms according to Mulliken were determined. It was found that with the addition of hydroxyl and methoxy substituents at the meta and para positions relative to the carboxyl fragment, the electron density shifts toward the benzene ring, and the symmetry of the molecule decreases. Additionally, in these structures, there is π,π-conjugation of the carboxyl fragment of the –СН=СНСООН molecule with the aromatic ring, which significantly affects the geometric configuration of the molecule. The maximum positive charge is concentrated on the C9 atom, while the maximum negative charge is on the oxygen atoms belonging to the methoxy substituents and the hydroxyl group, which confirms the role of oxygen atoms in the chemical transformations of acids. Conclusions. Two different methods were used to calculate the geometric, electronic, and energy parameters and electrophilicity indices of the studied hydroxycinnamic acids in the gas phase. The obtained values were consistent (within the limits of error) with the experimental data as well as the results described in earlier works’ calculations by other methods.Цели. Производные коричной кислоты относятся к большому классу фенольных соединений, которые широко распространены в растительности и обладают высоким потенциалом для применения в медицине и промышленности. Они обладают различными практически полезными свойствами, например, антиоксидантными, противовоспалительными, антиагрегантными и антимеланогенными свойствами. Отдельный интерес представляют оксикоричные кислоты как фенилпропаноиды, являющиеся исходными соединениями лигнина. Целью данной работы является исследование электронной структуры и анализ реакционной способности простейших представителей фенилпропаноидов, образующихся в процессе биосинтеза: кумаровой (п-оксикоричной), кофейной (3,4-дигидроксикоричной), феруловой (3-метокси-4-гидроксикоричной), синаповой (3,5-диметокси-4-гидроксикоричной) и 3,4-диметоксикоричной кислот. Эти кислоты являются биогенетическими предшественниками большинства других фенольных соединений (кумаринов, меланинов, лигнина и флавоноидов) и встречаются практически во всех высших растениях. Методы. В рамках ограниченного метода Хартри Фока и метода гибридного функционала плотности оптимизированы исследуемые молекулы. Все расчеты проводились с использованием программы Firefly. Результаты. Проведен сравнительный квантово-химический расчет геометрических параметров молекул оксикоричных кислот двумя методами, приведены значения зарядов на атомах по Малликену. При введении гидроксильных и метоксильных заместителей в м- и п-положения относительно карбоксильного фрагмента происходит смещение электронной плотности в сторону бензольного кольца и, как следствие, понижение симметрии молекулы. Также в исследуемых структурах имеется π,π-сопряжение карбоксильного фрагмента молекулы –СН=СНСООН с ароматическим кольцом, что существенно сказывается на геометрической конфигурации молекул. Максимальный положительный заряд сосредоточен на атоме С9, а максимальный отрицательный – на атомах кислорода, относящихся к метоксильным заместителям и гидроксильной группе, что подтверждает роль кислородных атомов в химических превращениях кислот. Выводы. В работе двумя различными методами были рассчитаны геометрические, электронные и энергетические параметры, а также индексы электрофильности исследуемых оксикоричных кислот в газовой фазе. Полученные величины согласуются в пределах погрешностей с экспериментальными данными, а также описываемыми в ранних работах при расчетах другими методами

The reactivity of cinnamic acid derivatives as lignin precursors

Objectives. Cinnamic acid derivatives belong to a large class of phenolic compounds, which are widely distributed in plants and have high potential for use in the medical and industrial fields. They have various useful practical properties, e.g., antioxidant, anti-inflammatory, antiplatelet, and anti-melanogenic properties. Hydroxycinnamic acids are of particular interest as phenylpropanoids, which are the starting compounds of lignin. The aim of this work was to study the electronic structure and analyze the reactivity of the simplest representatives of phenylpropanoids formed during the biosynthesis of the coumaric (p-hydroxycinnamic), caffeic (3,4-dihydroxycinnamic), ferulic (3-methoxy-4-hydroxycinnamic), sinapic (3,5-dimethoxy-4- hydroxycinnamic), and 3,4-dimethoxycinnamic acids. These acids are the biogenetic precursors of most other phenolic compounds (coumarins, melanins, lignins, and flavonoids) and are found in almost all higher plants.Methods. Calculations with full optimization of the geometric parameters were performed using the original Hartree–Fock theory and hybrid density functional method. All calculations were performed using the Firefly program. Results. A comparative quantum chemical calculation of the geometric parameters of hydroxycinnamic acid molecules was conducted via two methods, and the values of the charges on atoms according to Mulliken were determined. It was found that with the addition of hydroxyl and methoxy substituents at the meta and para positions relative to the carboxyl fragment, the electron density shifts toward the benzene ring, and the symmetry of the molecule decreases. Additionally, in these structures, there is π,π-conjugation of the carboxyl fragment of the –СН=СНСООН molecule with the aromatic ring, which significantly affects the geometric configuration of the molecule. The maximum positive charge is concentrated on the C9 atom, while the maximum negative charge is on the oxygen atoms belonging to the methoxy substituents and the hydroxyl group, which confirms the role of oxygen atoms in the chemical transformations of acids. Conclusions. Two different methods were used to calculate the geometric, electronic, and energy parameters and electrophilicity indices of the studied hydroxycinnamic acids in the gas phase. The obtained values were consistent (within the limits of error) with the experimental data as well as the results described in earlier works’ calculations by other methods