Dialdehyde starch (DAS) is a multifunctional biopolymer obtained from natural starch by selectively oxidizing the C2-C3 bonds of its glucose units, resulting in a high-density dialdehyde structure. This process imparts unique physicochemical properties to starch that allow it to be used in applications ranging from biomedical materials to industrial adsorbents.
What is the Oxidation Process of Dialdehyde Starch?
The oxidation and mechanism of DAS mainly consists of oxidizing specific hydroxyl units of the glucose unit in the starch molecule to aldehydes. Sodium periodate is the oxidizing agent here, which selectively oxidizes the hydroxyls in the glucose unit’s C2 and C3 hydroxyl groups, breaking the C2-C3 bond and resulting double aldehyde starch with double aldehyde groups.
Acidolytic oxidation is mainly one-step acidolytic oxidation in which the acidolytic catalyst is hydrochloric acid. Studies have shown that reaction conditions such as temperature, time, hydrochloric acid concentration and starch milk concentration have a significant effect on the aldehyde group content of DAS. The aldehyde content gradually increased with the increase of reaction temperature and time. The acidolytic oxidation reaction tends to stabilize when the reaction temperature reaches 55 ℃ and lasts for 4 hours.
Fig.1 The reaction equation of acid hydrolysis and oxidation of starch[1].
The oxidation mechanisms of different oxidizing agents are different. For example, potassium permanganate mainly acts on the amorphous region of starch by selectively oxidizing the primary hydroxyl group at C6 position to aldehyde group, without affecting the secondary hydroxyl group and without causing carbon chain breakage. On the other hand, periodate acts exclusively on the C2-C3 bond, causing it to break and form an aldehyde group to obtain double aldehyde starch.
The oxidation rate of double-aldehyde starch is in practice precisely controlled by varying the ratio of material amount of sodium periodate to starch. For instance, if the molar concentration of sodium periodate to starch is 1:1, pH is 3.5 (diluted sulfuric acid) and the reaction is conducted at 25 °C for 6 hours, double aldehyde starch with high aldehyde group composition can be obtained.
What are the Properties of Dialdehyde Starch?
DAS exhibits unique physicochemical properties due to the introduction of aldehyde groups. These properties include:
Enhanced Reactivity: the aldehyde group enables DAS to form Schiff base and acetal bonds, thus broadening its chemical modification.
Water Solubility and Swelling: Depending on the degree of oxidation, DAS can exhibit improved water solubility or enhanced swelling ability in aqueous environments.
Biodegradability: Like its precursor starch, DAS retains full biodegradability, making it a sustainable alternative to synthetic polymers.
Thermal Stability: DAS shows improved thermal properties, which are critical for its performance in high temperature applications.
Is Dialdehyde Starch Toxic?
DAS was shown to be biocompatible and biodegradable, and experimental toxicity testing in guinea pigs and rats showed no demonstrated toxicity at doses of 1 g/kg body weight[2]. However, acute LD50 toxicity was seen at oral doses of 6800 g/kg body weight or more. In addition, DAS was tested for cytotoxicity when used in biomedical applications to evaluate its effects on MG-63 cells. This suggests that glutaraldehyde starch may be used in the preparation of biomaterials under certain conditions, but the specific toxicity data are not detailed.
It is important to note that glutaraldehyde is a different chemical with high toxicity and potential carcinogenic risk that is primarily used for disinfection and sterilization and is not directly associated with DAS.
Taken together, DAS shows no significant toxicity in animal models at certain doses and is used in biomedical applications for the preparation of biocompatible materials. However, the toxic properties of glutaraldehyde cannot simply be attributed to DAS due to its chemical properties and uses. Therefore, when using glutaraldehyde starch, its specific application conditions and dosage still need to be carefully evaluated to ensure safety and efficacy.
What is Dialdehyde Starch Used for?
The presence of multiple aldehyde groups in DAS gives it unique properties such as reduced crystallinity, altered molecular interactions and increased reactivity. These properties make DAS a valuable material in various fields.