Valeraldehyde is a colorless, transparent liquid at room temperature with a pungent, acrid odor. The molecule contains an aldehyde functional group and is chemically reactive, readily undergoing oxidation, addition, and condensation reactions; it slowly oxidizes and deteriorates upon exposure to air. This substance is flammable and volatile; its vapors can form explosive mixtures with air. It is primarily used as an organic synthesis intermediate for the preparation of fragrances, resins, pharmaceuticals, and rubber additives, and can also serve as an industrial solvent.

TiO2-Catalyzed n-Valeraldehyde Self-Condensation Reaction

The mechanism of a TiO2-catalyzed n-valeraldehyde self-condensation reaction was first investigated using in situ Fourier transform–infrared spectroscopy (FT-IR) analysis. The result shows that the n-valeraldehyde molecule is adsorbed in two ways separately to Ti4+ and Ti–OH active sites: one involving a strong interaction between the surface Ti4+ and the carbonyl oxygen of n-valeraldehyde molecule, causing a red shift of ν(C═O) and the other involving an interaction between the TiO2 surface hydroxyl group Ti–OH and the carbonyl oxygen of n-valeraldehyde molecule via a hydrogen bond, causing a significant shift of Ti–OH peaks to a lower wavenumber. On the basis of the in situ FT-IR analysis, a TiO2-catalyzed n-valeraldehyde self-condensation reaction mechanism was proposed.[1]

In the process of n-valeraldehyde adsorption, the infrared characteristic peaks of 2-propyl-3-hydroxyheptanal were not observed, indicating that the dehydration of 2-propyl-3-hydroxyheptanal to 2-propyl-2-heptenal proceeded very quickly. In the process of desorption of products, the infrared characteristic peaks of carboxylates were detected on the surface of TiO2, suggesting that n-pentanoic acid is generated in the reaction system. In addition, we speculate that n-pentanoic acid has a strong interaction with the surface of TiO2 and the generated carboxylates are hardly desorbed, leading to the deactivation of TiO2 catalyst. In order to get a better understanding of the process of TiO2-catalyzed n-valeraldehyde self-condensation, the liquid-phase reaction was monitored in real time by an in situ IR (React-IR). In the whole course of the reaction, 2-propyl-3-hydroxyheptanal was not detected, confirming that this intermediate cannot exist stably, not only on the TiO2 surface but also in the reaction liquid. In order to further verify the reaction mechanism and to confirm the rate-determining step, several possible Langmuir–Hinshelwood models were assumed. By the model identification, the Langmuir–Hinshelwood model with the surface reaction as the rate-determining step is found to be the most probable one.

Interaction of Valeraldehyde with Collagen

The present study explains the molecular level interaction of valeraldehyde with collagen. Valeraldehyde (VLD) is a monoaldehyde, which involves crosslinking with protein through covalent linkages. The role of VLD as a crosslinking agent for collagen stabilization was studied. Molecular modeling approaches was used to understand the interaction of collagen like peptide with VLD, which mimic the aldehyde tanning processes involved in protein stabilization. Crosslinking efficiency of valeraldehyde was found to increase with an increase in concentration due to the higher availability of aldehydic groups involved in crosslinking with collagen. Valeraldehyde interacted collagen membrane showed an increase in thermal stability by 25°C at pH 8. In the presence of VLD, collagen fibrils nucleation center was shifted from a lower to a higher range.[2]

Shift in the nucleation center was observed in the reduction of gelling time. Water accessibility in valeraldehyde interacted collagen membrane was reduced due to a higher crosslinking rate in the collagen. Modified collagen membrane by valeraldehyde at incubation of about 96 h showed higher resistance to collagenolytic activity of 81%. The amino groups reacting appear to be involved in crosslinking with VLD. Several interaction sites were identified and the docking energy obtained was ?5.539 kcal/mol. The participation of the aldehyde group with amino groups in collagen was observed, which plays a dominant role in the stabilization of peptide by valeraldehyde. It was found that complexes exhibit covalent bonding, hydrogen bonding and electrostatic interaction in the process of stabilization.

References

[1]Lili Zhao. (2017). TiO2-Catalyzed n-Valeraldehyde Self-Condensation Reaction Mechanism and Kinetics. ACS Catalysis , 7 7, 4451–4461. https://doi.org/10.1021/acscatal.7b00432

[2]Usharani, N., Jayakumar, G., Kanth, S., Rao, J., & Chandrasekaran, B. (2012). Molecular Understanding of Collagen Stabilization: Interaction of Valeraldehyde with Collagen. Journal of Macromolecular Science, Part A, 92 1, 666–673. https://doi.org/10.1080/10601325.2012.697038