Microwave-assisted acid hydrolysis

M.P. Colombini, R. Fuoco, A. Giacomelli, B. Muscatello, Characterization of Proteinaceous Binders in Wall Painting Samples by Microwave Assisted Acid Hydrolysis and GC MS Determination of Amino Acids, Studies in Conservation, 43, 33 41 (1998). 

Zhong, H., Marcus, S.L. and Li, L. (2005) Microwave-assisted acid hydrolysis of proteins combined with liquid chromatography MALDI MS/MS for protein identification. J. Am. Soc. Mass Spectrom. 16, 471-481. 

Acetylsalicylic acid Tablets Microwave-assisted analyte hydrolysis UV-Vis 4.0 pg mL-1 Flow injection system merging zones in-line microwave-assisted alkaline hydrolysis of acetylsalicylic acid to salicylic acid that reacts with Fe(III) to form a coloured complex [414]... 

A.V. Pereira, C. Aniceto, O. Fatibello-Filho, Flow injection spectrophotometric determination of acetylsalicylic acid in tablets after on-line microwave-assisted alkaline hydrolysis, Analyst 123 (1998) 1011. 

L. Kunlan, X. Lixin, L. Jun, P. Jun, C. Guoying, and X. Zuwei, Salt-assisted acid hydrolysis of starch to D-glucose under microwave irradiation, Carbohydr. Res., 331 (2001) 9-12. 

Independently, Antane reported that arylisonipecotic acids were obtained from aryl bromides in a two-step process involving microwave-assisted palladium-catalyzed amination with ethyl isonipecotate followed by ester hydrolysis with KOH (Scheme 91) [96]. Interestingly, toluene, which is the standard solvent for Buchwald-Hartwig aminations under conventional heating, was used as the sole reaction medium, although it is a very weak... 

In addition to organic reactions, acid catalysed hydrolysis of cellulose has been performed in a rapid and controlled manner using a microwave reactor. Given this reaction, it is likely that aqueous phase microwave assisted reactions will play an important role in the rapid development of biorefinery based materials and chemicals. 

J0rgensen, N. O. G., andjensen, R. E. (1997). Determination of dissolved combined amino acids using microwave-assisted hydrolysis and HPCL precolumn derivatization for labeling of primary and secondary amines. Mar. Chem. 57, 287-297. 

The choice of solvent in a microwave-assisted sample treatment is a direct function of the type of treatment used. Thus, digestion and hydrolysis are best done with aqueous solutions of pure or mixed acids, whereas selective extraction of organic compounds from a sample matrix usually requires an organic solvent. 

The determination of metal purity and the elemental composition of alloys is of utmost importance to the metallurgical industry. Microwave-assisted digestion is often well-suited to metals and metallurgical samples that pose no difficulty and dissolve readily and safely with the aid of microwaves [148,186-196]. For example, hydrofluoric acid can be used in closed vessels to digest silicate matrices and stop the hydrolysis of refractory elements without loss of volatile fluorides or passivation. After cooling, boric acid can be added to complex unreacted hydrofluoric acid [14]. The solid sample itself may absorb microwave radiation, thus creating a heated surface on which the acid or acids can react. Microwave muffle furnaces are commercially available [197] based on oven linings made... 

Early studies in microwave-assisted hydrolysis of proteins showed the recoveries of amino acids after microwave hydrolysis to be quite consistent with the results provided by conventional hydrolysis [293,294]. Engelhardt et al. used on-line microwave hydrolysis in an HPLC system followed by derivatization with OPA to improve the detection sensitivity for proteins [295]. 

The initial work on microwave-assisted hydrolysis of proteins was conducted using commercial domestic microwave devices. Different laboratory microwave ovens featuring various methods of operation are now commercially available as well. The microwave-assisted hydrolysis of proteins or peptides is usually performed in sealed containers [296] where the sample is in direct contact with the concentrated acid used for hydrolysis. In vapour-gas microwave hydrolysis [297], the acid is evaporated and only the vapour contacts the sample, which prevents contamination of the samples by small amounts of amino acids potentially present in the acid used for analysis. 

Microwave-assisted hydrolysis systems equipped with temperature regulators suitable for quality control of protein products are now available. In fact, microwave hydrolysis is the sole technique in which the acid temperature and vapour pressure are measured directly, in situ. Other devices measure the temperature of a heating unit such as metal heating block or oven surrounding a hydrolysis chamber. 

One major concern in the hydrolysis process is the potential racemization of amino acids. Peter et al. [298] used both microwave and conventional hydrolysis to determine the amino acid composition of three synthetic peptides and found microwave-assisted hydrolysis to result in reduced racemization and in higher recovery of sensitive amino acids than hydrolysis by conventional heating with hydrochloric acid [299]. 

One of the most interesting fields of application of MAE in food analysis is the extraction of lipids. This step, traditionally performed with conventional Soxhlet extraction, has been performed with the focused microwave-assisted Soxhlet extractor prototype of Figure 2B. Extraction of oil from olives, srm-flower seeds, and soyabeans extraction of the lipid fraction of dairy products (milk and cheese) and extraction of fatty acids from precooked and sausage foods have significant advantages over conventional methods, including dramatically reduced extraction times, lower degradation of thermolabile analytes, and acceleration of other analytical steps such as hydrolysis in milk samples, in addition to completeness of analyte extraction, which is not always achieved with conventional methods. 

In this way, the desired metallated phthalocyanines remained on the solid support, while the unwanted by-products such as the symmetrically substituted B4-type moieties were formed in solution and could easily be discarded. After an acid-mediated cleavage from the resin using a TFA/TIPS/DCM mixture at ambient temperature, the e-amine of the lysine moiety of the metallated phthalocyanine was used for the attachment of suitable oligonucleotides connected with aryl aldehydes or acids (Scheme 8.9). Interestingly, both the reductive amination and the amidation reaction could be dramatically sped up using microwave irradiation, carrying out the reactions at 70-75°C for a mere 30 min. The reductive amination protocol was found to provide a far superior yield, owing to the competitive ester formation and hydrolysis observed in the microwave-assisted amidation protocol. 

While free amino acids can be directly extracted from food matrices, a preliminary hydrolysis step (normally microwave-assisted to speed up the hydrolysis reaction) is necessary to liberate protein-bound amino acids. After that, a sample cleanup using a precipitation agent, ultrafiltration, or SPE on Cis cartridges is carried out to remove interferences and concentrate these compoimds. 

Lee, B.-S. KRisHNANCHEmAR, S. Lateef, S. S. Gupta, S. Characterization of oligosaccharide moieties of glycopeptides by microwave-assisted partial acid hydrolysis and mass spectrometry. Rapid Commun. Mass Spectrom. 2005, 19, 1545-1550. 

Zhang Z, Zhao ZK. Solid acid and microwave-assisted hydrolysis of cellulose in ionic liquid. Carbohydr Res 2009 344 2069-72. 

An efficient and highly versatile microwave-assisted Paal-Knorr condensation of various 1,4-diketones gave furans, pyrroles and thiophenes in good yields. In addition, transformations of the methoxycarbonyl moiety, such as Curtius rearrangement, hydrolysis to carboxylic acid, or the conversion into amine by reaction with a primary amine in the presence of Me3Al, are described by Minetto et al. (2005). 

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