Fourier transform Raman spectroscopy and chemometric tools have been used for exploratory analysis of pure corn and cassava starch samples and mixtures of both starches, as well as for the quantification of amylose content in corn and cassava starch samples. The exploratory analysis using principal component analysis shows that two natural groups of similar samples can be obtained, according to the amylose content, and consequently the botanical origins. The Raman band at 480 cm(-1), assigned to the ring vibration of starches, has the major contribution to the separation of the corn and cassava starch samples. This region was used as a marker to identify the presence of starch in different samples, as well as to characterize amylose and amylopectin. Two calibration models were developed based on partial least squares regression involving pure corn and cassava, and a third model with both starch samples was also built; the results were compared with the results of the standard colorimetric method. The samples were separated into two groups of calibration and validation by employing the Kennard-Stone algorithm and the optimum number of latent variables was chosen by the root mean square error of cross-validation obtained from the calibration set by internal validation (leave one out). The performance of each model was evaluated by the root mean square errors of calibration and prediction, and the results obtained indicate that Fourier transform Raman spectroscopy can be used for rapid determination of apparent amylose in starch samples with prediction errors similar to those of the standard method.

Determination of amylose content in starch using Raman spectroscopy and multivariate calibration analysis

Publisher Summary This chapter discusses the synthesis and transformation of glycosyl azides. Owing to their functional group, glycosyl azides constitute important and versatile derivatives for carbohydrate chemistry. Because of the dipole character of organic azides, they can function both as nucleophiles and electrophiles and readily undergo dipolar cycloadditions. In addition, as configurationally stable groups, azides are well suited as starting materials for the formation of other nitrogen-containing functionalities such as amines, amides, ureas, carbodiimides, and others. The only method known up to 1974 for preparing glycosyl azides was from acylated glycosyl halides by the treatment with sodium or silver azide. However, because of the reactivity of glycosyl halides with water, the very low solubility of sodium azide in organic solvents, and the thermal ability of silver azide, there were considerable difficulties in preparing the corresponding glycosyl azides. This chapter discusses the synthesis of 1,2- trans glycosyl azides from glycosyl halides. It also explains the synthesis of 1,2- trans -glycopyranosyl azides by intramolecular rearrangement and elaborates the reduction and oxidation of glycosyl azides.

Synthesis and transformation of glycosyl azides.

Conventional methods for quantitation of starch content in cells generally involve starch extraction steps and are usually labor intensive, thus a rapid and non-invasive method will be valuable. Using the starch-producing unicellular microalga Chlamydomonas reinhardtii as a model, we employed a customized Raman spectrometer to capture the Raman spectra of individual single cells under distinct culture conditions and along various growth stages. The results revealed a nearly linear correlation (R(2) = 0.9893) between the signal intensity at 478 cm(-1) and the starch content of the cells. We validated the specific correlation by showing that the starch-associated Raman peaks were eliminated in a mutant strain where the AGPase (ADP-glucose pyrophosphorylase) gene was disrupted and consequentially the biosynthesis of starch blocked. Furthermore, the method was validated in an industrial algal strain of Chlorella pyrenoidosa. This is the first demonstration of starch quantitation in individual live cells. Compared to existing cellular starch quantitation methods, this single-cell Raman spectra-based approach is rapid, label-free, non-invasive, culture-independent, low-cost, and potentially able to simultaneously track multiple metabolites in individual live cells, therefore should enable many new applications.

Raman spectroscopy provides a rapid, non‐invasive method for quantitation of starch in live, unicellular microalgae

A fast and efficient protocol for the synthesis of N,N'-disubstituted urea derivatives from alkyl halides and primary or secondary amines has been developed. The synthetic pathway combines nucleophilic substitutions and a Staudinger–aza-Wittig reaction in the presence of polymer-bound diphenylphosphine under 14 bar of CO2 pressure and has been performed in a one-pot two-step process. The protocol has been optimized under microwave irradiation and the scale-up experiment has been conducted under conventional conditions in a Parr reactor. The final compounds were isolated after simple filtration in almost quantitative overall yields which makes this procedure facile and rapid to execute.

https://www.beilstein-journals.org/bjoc/content/pdf/1860-5397-9-274.pdf

One-pot sequential synthesis of isocyanates and urea derivatives via a microwave-assisted Staudinger–aza-Wittig reaction

This work presents the use of Raman spectroscopy and chemometrics for on-line control of the fermentation process of glucose by Saccharomyces cerevisiae. In a first approach, an on-line determination of glucose, ethanol, glycerol, and cells was accomplished using multivariate calibration based on partial least squares (PLS). The PLS models presented values of root mean square error of prediction (RMSEP) of 0.53, 0.25, and 0.02% for glucose, ethanol and glycerol, respectively, and RMSEP of 1.02 g L(-1) for cells. In a second approach, multivariate control charts based on multiway principal component analysis (MPCA) were developed for detection of fermentation fault-batch. Two multivariate control charts were developed, based on the squared prediction error (Q) and Hotelling's T(2) . The use of the Q control chart in on-line monitoring was efficient for detection of the faults caused by temperature, type of substrate and contamination, but the T(2) control chart was not able to monitor these faults. On-line monitoring by Raman spectroscopy in conjunction with chemometric procedures allows control of the fermentative process with advantages in relation to reference methods, which require pretreatment, manipulation of samples and are time consuming. Also, the use of multivariate control charts made possible the detection of faults in a simple way, based only on the spectra of the system.

Raman spectroscopy and chemometrics for on-line control of glucose fermentation by Saccharomyces cerevisiae.

The reaction of azido sugars with triphenylphosphine and carbon dioxide leading to cyclic carbamates has been studied by means of PM3 semiempirical quantum chemical computations to elucidate the detailed mechanisms of chemical processes involved in this transformation. Our results clearly indicate that the mechanism involving an isocyanate intermediate is preferred for both α- and β-anomers. In addition, we find that, in the case of the α-anomer, steric hindrance prevents the occurrence of direct cyclization and requires the opening of the pyranose ring, in contrast to the case of the β-anomer. This result explains the poor yield and the occurrence of three isomeric cyclic carbamates when the reaction is performed on the α- anomer.

PM3 study of cyclization of α- and β-d-glucosyl azides into 1,2-cyclic carbamates

In this paper, we investigate the possibility of scaling, on a reference molecule, the force field computed by means of a semiempirical quantum chemical method, here PM3, and transferring the scaling factors to other parent molecules. The scaling, performed on α- d -glucose, allows good prediction of the vibrational spectra of β- d -glucose, α- d -galactose, α- d -mannose, methyl-α- d -glucopyranoside, methyl-α- d -mannopyranoside, cellobiose and gentiobiose within 20 cm −1 in the high and medium frequency range. Low frequency bands are less well reproduced, but they are also less widely used to characterize these molecules. The influence of the crystal field and intermolecular hydrogen bonds is discussed. The method can be extended to other chemical families.

Scaled semiempirical method for the calculation of vibrational spectra Molecular vibrational frequencies of monosaccharides and disaccharides by PM3 method

Total energies of various conformations of trans- and cis-isomers of 2-amino-cyclohexanol (5) and those of 2-amino-3-hydroxy-tetrahydropyrane (6) as well as those of 2,3-cyclic carbamates of 2-amino-3-hydroxy-tetrahydropyrane (7) were computed at HF/6-31G and HF/6-31G∗∗ level of theory for modelling the energy differences between trans- and cis-1,2-cyclic carbamates of gluco- and xylopyranosyl amine (1,2 and 3,4, respectively). In the case of the chair forms of both 5 and 6, the trans isomers were found to be more stable than the cis ones. The stability of the different structures was also governed by the internal hydrogen bonds involving NH2 and OH groups, as well as the ring oxygen atom. In the case of 7, the formation of the oxazolinone ring results in decreasing the total energy of the cis isomer with respect to the trans compound. Using appropriate isodesmic reaction equations, stabilization energies were calculated for all of the model structures of 5–7, as well as for the transition from cyclohexane to tetrahydropyrane. The energy values indicated that the introduction of the ring oxygen causes stabilization in all cases.

An ab initio study on selected models of 1,2-cis-and 1,2-trans-cyclic carbamates of glucopyranosyl amine

Different pathways have been considered to describe heterocyclization between monosubstituted or unsubstituted amidines and 2-bromo-2-alkenoic carbonyl compounds, giving N-substituted 2-dihydroimidazole heterocycles. Semiempirical calculations (PM3) have been carried out on the reactants and intermediates. The transition states have been analysed. From both thermodynamic and kinetic arguments, it appears that mechanisms involving a 6-exo-trig ring closure leading to pyrimidin-4-(3 H )-one, or a 5-endo-trig ring closure process in the case of N-substituted amidines, are more probable than the one expected in which the intermediate is an aziridine.

Reaction of 2-bromo-2-alkenoic carbonyl compounds with amidines: Part 2. Theoretical (PM3) studies of the mechanism of heterocyclization into dihydroimidazole and pyrimidin-4-(3H)-one

P. Friant-Michel

Papers

PM3 study of cyclization of α- and β-d-glucosyl azides into 1,2-cyclic carbamates

Scaled semiempirical method for the calculation of vibrational spectra Molecular vibrational frequencies of monosaccharides and disaccharides by PM3 method

An ab initio study on selected models of 1,2-cis-and 1,2-trans-cyclic carbamates of glucopyranosyl amine

Reaction of 2-bromo-2-alkenoic carbonyl compounds with amidines: Part 2. Theoretical (PM3) studies of the mechanism of heterocyclization into dihydroimidazole and pyrimidin-4-(3H)-one