Entropy effects in conformational distribution and conformationally dependent UV-induced photolysis of serine monomer isolated in solid argon

Abstract

Monomeric serine can be trapped in low temperature argon matrices in different conformers, which can be classified in three groups (A, B, C) accordingly to the main intramolecular interaction they exhibit: A (OH A /N hydrogen bond), B (OH C /N) and C (OH A /Oa) (subscripts A and C stand for alcohol and carboxylic group, respectively). The OH C /N intramolecular interaction found in B-type conformers is considerably stronger than both the OH A /N and OH A /Oa hydrogen bonds, and leads to reduce the abundance of B-type form relatively to A and C forms at high temperatures due to entropy effects. When submitted to UV irradiation (lO200 nm), the main observed photoprocess is decarboxylation, leading to production of CO 2 and ethanolamine. A less important photochemical process is also observed, where the compound undergoes decarbonylation, with formation of CO, H 2 O and acetamide. The two observed photoprocesses were found to be dependent on the conformation assumed by the reactant molecule, with Aand C-type conformers of serine undergoing decarboxylation and B-type conformers decarbonylation.

Thermal and Photoinduced Control of Relative Populations of 4-Methoxybenzaldehyde (p-Anisaldehyde) Conformers

“…This possibility opens the gate for exciting conformational studies on p-anisaldehyde. The optical control of conformational compositions is of fundamental importance, for example, to the study of conformation-dependent photochemical reactions [12][13][14][15] and may receive potential application in the building up of molecular devices (e.g., in the design of light-controlled molecular switches).…”

Low-temperature infrared spectra and hydrogen bonding in polycrystalline dl-serine and deuterated derivatives

“…Indeed, taking in this case the n 0 1 and n 0 4 reference values as 3640 and 300 cm À1 (the calculated scaled frequencies for nOH and tOH of isolated serine conformers that do not have the OH group involved in any intramolecular H-bond [14,15], which also closely match the observed frequencies for these two modes in the spectrum of t-butanol in CCl 4 diluted solutions [40]) and the observed n 4 frequency in the spectrum of Ser10 (average value: 743 cm À1 ) the n 1 frequency value estimated from the empirical relationship for the nOH uncoupled mode is 2905 cm À1 . Hence, in the spectrum of Ser10, the nOH stretching band is, with all probability buried below the intense bands due to nCH 2 symmetric and nCH modes (see Fig.…”

“…In the present study, the above mentioned experimental approach is applied to the amino acid serine, which, in its nonwww.elsevier.com/locate/vibspec Vibrational Spectroscopy 41 (2006) [73][74][75][76][77][78][79][80][81][82] ionic neutral form, was recently characterized structurally and spectroscopically in our laboratories [14,15]. In the gaseous phase, the compound was found to exist in several different conformers, which can be classified in three groups (A, B, C) accordingly to the main intramolecular interaction they exhibit: A (OH Alcohol Á Á ÁN hydrogen bond), B (OH Carboxylic Á Á ÁN) and C (OH Alcohol Á Á ÁO ).…”

“…In the gaseous phase, the compound was found to exist in several different conformers, which can be classified in three groups (A, B, C) accordingly to the main intramolecular interaction they exhibit: A (OH Alcohol Á Á ÁN hydrogen bond), B (OH Carboxylic Á Á ÁN) and C (OH Alcohol Á Á ÁO ). Representatives of each of these groups were trapped in low temperature argon matrices and characterized structurally and spectroscopically by matrix isolation infrared spectroscopy and DFT/B3LYP/6-311++G(d,p) theoretical calculations [14,15]. On the other hand, in the crystalline state, the conformations assumed by individual molecules are not directly comparable with those found in the gaseous phase (or for the matrix-isolated molecule), since the molecules exist as zwitterions and the most important interactions result from intermolecular hydrogen-bonding and packing.…”

The Raman spectra of serine and 3,3-dideutero-serine in aqueous solution

“…This species was recently studied in detail in our laboratories by a concerted matrixisolation infrared spectroscopic and quantum chemical calculations approach [4,5]. In those studies, relevant serine conformers could be characterized both structurally and vibrationally [4] and their photochemistry investigated [5].…”