Distribution of acetyl groups alters the properties of acetylated starch.

The performance of two native lipases (lipase from Aspergillus niger and Rhizoupus oligosporus) in the resolution of (RS)-phenylethylamine (1), varying the temperature, acyl donor type (ethyl acetate, vinyl acetate, iso-propenyl acetate and acetic anhydride) and organic medium, was studied. The effect of the nature of the anion using native A. niger lipase in n-heptane with a series of imidazolium-based ILs [BMIm][X], where X = BF4, PF6, SCN and Cl, was also evaluated. Using the lipase from A. niger, the R-2b amide was obtained with conversions from 6 to > 99% and E-values from 2 to > 200, with n-heptane or n-hexane. This lipase showed better E-values in a two-phase system using n-heptane and [BMIm][PF6] or [BMIm][BF4] 9:1 (v/v), obtaining values of 9 and 7, respectively, when vinyl acetate was used as the acyl donor, compared to the use of pure n-heptane (E = 2). The series for the anions in terms of decreasing performance was as follows: PF6- >BF4- > SCN- > Cl-.

Pasting properties and (chemical) fine structure of acetylated yellow pea starch is affected by acetylation reagent type and granule size

Summary Sapwood of Scots pine (Pinus silvestris L.) was acetylated with 14C- and 3H-labelled acetic anhydride. The distribution of acetyl groups was investigated with microautoradiography and microautoradiographs were evaluated with ESEM, Environmental Scanning Electron Microscopy. The investigation showed that the impregnation of wood with radioisotope-labelled substances provides a good opportunity to investigate the location of substances covalently bonded to the wood material. Introduced 14C-labelled acetyl groups show an even distribution in the wood cell wall, with no discernible concentration gradients at acetylation levels of about 5, 15 and 20% weight gain. 3H-labelled acetyl groups show an even distribution in the wood cell wall at 15 and 20% weight gain, with no discernible concentration gradients. At the 5% weight gain level, however, an uneven distribution of 3H-labelled acetyl groups over the cell wall is observed. Nevertheless, the unevenness is random and no concentration gradient is discernible at this level. 3H with a relatively high resolution, 0.5–1 μm, compared to 14C with a resolution of 2–5 μm, gives more accurate information about where exactly the acetyl groups are situated in the wood cell wall. Acetic anhydride was evenly distributed when a full impregnation procedure was used. The chemical and physical properties of acetic anhydride allow a uniform penetration into the pine cell wall and a complete acetylation takes place when the specimens are heated.

In order to establish the relationships between structure and properties, the chemical composition, structural properties and functional properties of five Thai rice starches were determined. These starches were classified into 3 groups according to the true amylose content: low amylose content (1-3%, RD6 and a commercial waxy rice starch), medium amylose content (14-15%, Jasmine rice starch) and high amylose content (21-23%, Supanburi 1 and a commercial rice starch). The rice starches with low amylose and medium amylose content had an amylopectin chain ratio (ACR) of 0.25 (S-type amylopectin), while the rice starches with high amylose content had an ACR of 0.19 (L-type amylopectin). There were no significant differences in granule size (average size of 4-6 micrometre) and shape among these rice starches. For the medium and high amylose starch, the weight average molecular weights of amylose were in the range of 1.8 to 2.9 x 10[superscript 5]. The crystallinity (measured by x-ray diffraction) and ratio of short-range molecular order to amorphous (measured by infrared spectroscopy) decreased from 34.62% to 23.00% and from 0.91 to 0.72, respectively, with increasing amylose content from 1.70% to 22.70%. The functional properties, namely swelling power, water solubility index, pasting characteristics, intrinsic viscosity ([eta]), consistency index (k), and storage modulus (G') were related to the true amylose content. An increase in amylose content (from 1.70% to 22.70%) increased water solubility index (linearly from 6.01% to 26.60%), setback viscosity (exponentially from 300 to 2526 mPa.s), and G'(exponentially from 47 to 478 Pa, for 12%, w/w, measured at 1 Hz and 60 ํC). Furthermore, an increase in amylose content decreased the swelling power (linearly from 34.92 to 14.17 g swollen/g dry starch), [eta] (from 192 to 156 ml/g), and k (from 6.32 to 0.29 Pa.s[superscript n], for 5%, w/w, measured at 60 ํC and 50-1000 sec[superscript -1]). However, the breakdown viscosity, onset of pasting temperature and gelatinization temperature related to the ACR values. L-type amylopectin resulted in a lower breakdown viscosity but higher onset of pasting temperature and gelatinization temperature than S-type amylopectin. The onset concentrations (c[subscript 0]), when the granule-granule interactions occur, were 2.5%, 1.5% and 1.10% for the rice starch with high amylose, medium amylose and low amylose content, respectively. For the same amylose content, a higher loss in the short-range molecular order on gelatinisation decreased this onset concentration. In the concentration range from 6% to 15% (w/w), G' was higher than loss modulus (G") at 0.1-10 Hz, 25 ํC and 60 ํC for all rice starches, which indicates strong interactions between the components or phases. The rice starches with high amylose and medium amylose content had rubber-like gel property, while rice starch with a low amylose content was a weak gel. For the rice starches with high amylose content, G{7f2019}of the starch gel increased upon cooling, except for the RD6 starch at the lowest concentration measured (6%), which exhibited only the flow component, all others exhibited the combination of ideal elastic, retard elastic and flow components, which could be represented by the 4-element Burger model. Retrogradation was followed during storage for 100 hours at 25 ํC on gels (30%, w/w) and was found to occur for the high amylose starch only. For the initial stage of retrogradation, G' and the ratio of short-range molecular order to amorphous increased rapidly at a rate of 0.44-0.57 kPa/h and 0.001-0.002 h[superscript 1], respectively. It was suggested that the high propotion of amylopectin chains with DP is less than or equal 10 prevented retrogradation in the low and medium amylose starches.

A comparative study on the acetylation of wood by reaction with vinyl acetate and acetic anhydride

Objective : Chemically modify by acetylation, Arracacia xanthorrhiza starch, and to physicochemically and pharmacotechnically characterize it, thereby evaluating its potential as a pharmaceutical excipient, in comparison with the native starch of Arracacia xanthorrhiza. Methods : The chemical modification was performed through acetylation with acetic anhydride (AA) on different levels, determining following starch’s characteristics: degree of substitution (DS), size and form of particles, its degree of crystallinity through X-ray powder diffraction (XRPD), gelatinization temperature (Tg) through differential scanning calorimetry (DSC), swelling power (SP) and sorption isotherms by means of Enslin method, and its application as excipient in tablet production, using diclofenac as model drug. Results : On the third level of substitution, the morphology of modified-starch particles presented changes on their surface and all modified starches increased their particle average sizes, in comparison to native starch. Starch crystallinity was not altered by acetylation, and the DS increased as more AA was added to the reaction. This modification caused a decrease of Tg by approx. 9.45 °C for A. xanthorrhiza starch modified to level III, in comparison to native starch. SP and water uptake capacity increased with starch modification, being greater to higher DS. Dissolution studies conducted on tablets showed that diclofenac delivery occurs practically immediately when using native starch, while those made of acetylated starch were close-fitting with Korsmeyer-Peppas model, with a release mechanism that suggests an anomalous, non-Fickian transport behaviour, related to a mechanism governed by swelling and diffusion. Conclusion : The results suggest A. xanthorrhiza acetylated starches, as promising materials for the development of controlled-delivery matrix systems.

Comparative determination of the grafting distribution and viscoelastic properties of wood blocks acetylated by vinyl acetate or acetic anhydride

Between 721.7 and 636.4 K, vinyl acetate undergoes thermal decomposition according to the rate equation log (k/s–1)= 10.43 – 182.4/2.303 RT(R= 8.312 J mol–1 K–1). Approximately 95% of reaction is decarbonylation to give acetone, with decomposition to ketene and acetaldehyde being the minor component. The latter reaction is an analogue of acetic anhydride pyrolysis which takes place at least 106 times faster per β-hydrogen at 600 K. This very large rate difference parallels that between β-keto-acids and βγ-alkenoic acids and contrasts markedly with pyrolysis of alkyl acetates and alkyl vinyl ethers, which occurs at closely similar rates. The contrasting behaviour most probably reflects differences in the principal bond-breaking step of the reaction, which for vinyl acetate and acetic anhydride (and also the acids) is breaking of the β–X–H bond so that the nucleophilicity of the attacking group assumes major importance; for esters and vinyl ethers this is not the most important step so their reaction rates are similar. The relative reactivities to the acids support an alternative view that both vinyl acetate and acetic anhydride pyrolyse via their enol forms. The greater understanding of the factors affecting gas-phase elimination rates permits prediction of the relative rates of compounds not yet studied. Pyrolysis of 1,2-diacetoxyethane gave non-first-order plots, with rate acceleration due to formation of the more reactive vinyl acetate. The β-acetoxy-group (OCOMe) increased the rate of elimination (per β-hydrogen at 600 K)ca. 7-fold, which compares with factors of 388 and 144 for COMe and CO2Me respectively, and a reduction of 3.6-fold by OMe.

Sago contains carbohydrates that are stored in the starch form. Starch is generally formed from two molecules of glucose polymer, namely amylose and amylopectin, which its composition varies for each type of starch [1]. The weakness of starch can be overcome through a modification of the functional properties of starch to expand sago starch. Chemical modification of starches can enlarge the range of certain starch physical properties of the parent starch [2] and enhance their use in a number of applications found in industrial processes and food manufacture. Chemical modification of starch can be performed by various methods such as acetylation. Generally, native starch has a low Degree of Substitution (DS) because of their limited degree or reaction on the granule surface. Increasing DS can be obtained by modification of native starch through acetylation reaction using few catalysts such as pyridine and NaOH. Several researchers have reported the effects of acetylation on many sort of starch sources such potato, corn, pea and cassava [3-5]. There are few studies about the effects of acetylation of starches with a wide range of amylose contents. We have carried out some work on effects of acetic anhydride concentration toward DS value of native and modified sago starch from Papua.

Position of acetyl groups on anhydroglucose unit in acetylated starches with intermediate degrees of substitution

A novel type of malonate decarboxylase which is induced and located in periplasm of Acinetobacter calcoaceticus grown on malonate as sole carbon and energy source was purified to homogeneity. The purified 185-kDa decarboxylase was found to be an oligomer composed of three different polypeptides in a ratio of 2:1:1, designated alpha (65 kDa), beta (32 kDa), and gamma (25 kDa). Optimum pH was 6.8, while pI was 6.39. The enzyme was highly specific for malonate with Km 1.4 mM. This enzyme contained a biotin prosthetic group on alpha subunit which does not seem to be directly related to malonate decarboxylation. The purified enzyme showed almost no activity; activity was restored, however, by treatment with acetic anhydride or malonyl-CoA, which formed an acetyl-enzyme. The 14C-acylated enzyme was isolated by a gel filtration from the reaction mixtures containing [2-14C]malonyl-CoA and the enzyme or [2-14C]malonate, malonyl-CoA, and the enzyme. When treated by thiol-specific reagents, such as N-ethylmaleimide, 5,5'-dinitro-bis(2-nitrobenzoic acid), and 2-nitro-5-thiocyanobenzoic acid, the purified enzyme showed no increase in activity after the acetic anhydride treatment. The thiol-specific reagents failed to inhibit, however, the catalytically active acetyl-enzyme, suggesting that the site of acylation is the thiol group. Further evidence was provided when sodium borohydride inactivated the acetyl-enzyme. These results suggest that malonate decarboxylation by this enzyme may proceed by a catalytic cycle in which the acetyl group on the active enzyme is displaced by malonate, which binds covalently to a thiol group on the enzyme and is subsequently decarboxylated.

The purpose of this study was to compare two different acetylation mechanisms using acetic anhydride (AA) or vinyl acetate (VA) modification with using various catalysts. Acetylation of Scots pine wood flour with acetic anhydride could be significantly improved in the presence of potassium acetate, potassium carbonate, and sodium carbonate at 100°C. Sodium carbonate had low effect on VA acetylation, potassium acetate was found to be more effective, and potassium carbonate was better for vinyl acetate modification of wood flour. The two modification methods and the effect of different catalysts on AA or VA modification were characterized by infrared and NMR spectra and analyzed in detail. The acetylation of Scots pine flour with VA and AA showed almost the same WPG values for catalysts when based on long reaction times.

Acetyl substitution patterns of amylose and amylopectin populations in cowpea starch modified with acetic anhydride and vinyl acetate

In this study, the reactivity of wood components with acetic anhydride or vinyl acetate was studied. It was found that the reactivity of wood components was virgin wood flour > holocellulose >> a-cellulose. Acetylation of Turkish pine or cedar wood flour with acetic anhydride was significantly improved in the presence of potassium carbonate at 100°C. Maximum of about 20 and 18% weight percentage gain (WPG) values were obtained with Turkish pine ( Pinus brutia ) and cedar ( Cedrus libani ) wood flour after 3 h reaction at 100°C, respectively. The two modification methods and the effect of wood components on vinyl acetate (VA) or acetic anhydride (AA) modification, were characterised by infrared analysis in detail. As an apparent advantage of this new method, acetaldehyde was formed as by-product which is non-acidic was removed easily after the reaction due to low the boiling point of acetaldehyde [b.p. (760 mm Hg) = 21°C]. Key words : Acetic anhydride, vinyl acetate, holocellulose, α-cellulose, FTIR, chemical modification

Chemical modifications of Scots pine (Pinus sylvestris) wood flour were performed with vinyl acetate (VA) and acetic anhydride (AA) in the presence of potassium carbonate as a catalyst. Scots pine wood flour samples were successfully acetylated with VA (19 wt% gain) and AA (24 wt% gain). The effect of chemical modification of the Scots pine wood flour with AA and VA on the mechanical properties of wood high-density polyethylene composites (WPC) was determined. It was observed that acetylation of wood flour allowed a significant increase in both the mechanical properties and the thermal stability of the WPCs. It was concluded that acetylation of lignocellulosic fibers improves thermal stability, dispersion in the polymer matrix, and compatibility with the polymer matrix.