Demonstrating Basic Properties and Application of Polarimetry Using a Self-Constructed Polarimeter

Kinetic Method Coupled with Thermal-Assisted Paper Spray Ionization Mass Spectrometry for Direct Determination of Enantiomeric Excess of Multiple d/l-Amino Acids in Functional Foods

Amino acids are commonly used as nutritional fortification substances in functional foods, and their chiral configuration is an important determinant of food function. Rapid chiral screening methods are urgently needed in food analysis but are limited by the long-time chiral separation and matrix interference. In this study, we show a kinetic method coupled to thermal-assisted paper spray ionization mass spectrometry for direct determination of enantiomeric excess (ee) of multiple d/l-amino acids in complex food matrixes without sample pretreatment. 3-(2-Naphthyl)-l-alanine was selected as a new chiral reference ligand for the kinetic method to achieve efficient chiral differentiation (discrimination degree is 8.7 for d/l-phenylalanine and 10.2 for d/l-tyrosine). An additional thermal-auxiliary device was developed for paper spray ionization mass spectrometry to facilitate the enantiomeric purity determination. The developed method allowed a rapid simultaneous enantiomeric purity determination of multiple chiral amino acids (d/l-phenylalanine and d/l-tyrosine) within 30 s. Good linearities were achieved for the quantitation of ee (R2 = 0.9996 for phenylalanine and 0.9995 for tyrosine) with unknown amino acid concentrations ranging from 10 μM to 600 μM. The developed method was successfully applied for the enantiomeric purity determination of multiple chiral amino acids in functional capsules and beverages and showed great potential for efficient enantiomer-related food safety screening and nutrition analysis.

A "hand-held" polarimeter for on-site chiral drug measurement and chemical reaction monitoring

A polarimeter is a common but critical instrument for measuring the optical rotation of chiral compounds, ranging from the pharmaceutical to chemical industry, or even employed in monitoring chemical reactions for research purposes. Developing a portable polarimeter helps to transfer the measurements from the laboratory to on-site detection. Herein, we design a new portable polarimeter with a "hand-held" scale. Technically, we innovatively adopted a rotary potentiometer coupled with a high-precision voltmeter to signify the angle changes after polarized light travels through the chiral compound solution. Compared with the commercial disc polarimeter that uses a dial to measure the optical rotation, such a design shows superiority in being easy to read. This "hand-held" polarimeter meets the high demand for on-site detection on the premise of low cost. Bland-Altman analysis results showed consistency between our device's optical rotation detection method and the commercial disc polarimeter. The "hand-held" polarimeter can measure the optical rotation of a chiral drug and be applicable to monitor the progress of a chemical reaction. As such, this "hand-held" polarimeter shows great potential to assist scientists in scientific research, or for on-site measurement with high portability.

Chemical Composition, Enantiomeric Distribution and Antimicrobial, Antioxidant and Antienzymatic Activities of Essential Oil from Leaves of Citrus x limonia

Citrus x limonia is an aromatic species belonging to the Rutaceae family. In the present study, the chemical composition, enantiomeric distribution, and biological activity of the essential oil isolated from leaves of Citrus x limonia were determined. The essential oil was extracted through hydrodistillation. The chemical composition of the essential oil was determined by gas chromatography (GC) coupled to a flame ionization detector (GC-FID), and a mass spectrometer detector (GC-MS) using a nonpolar column. The enantiomeric distribution was performed using two enantioselective chromatographic columns. Antimicrobial activity was determined using the broth microdilution method. The antimicrobial activity was tested against eight bacteria and two fungi. The antioxidant activity was determined through ABTS and DPPH methods. The spectrophotometric method was used to determine anticholinesterase activity. In the essential oil, forty-three compounds were identified. These compounds represent 99.13% of the total composition. Monoterpene hydrocarbons were the most representative group in number of compounds (fourteen) and in terms of relative abundance (65.67%). The main constituent is found to be limonene (25.37 ± 0.80%), β-pinene (23.29 ± 0.15%) and sabinene (8.35 ± 0.10%). Six pairs of enantiomers were identified in the essential oil from fruits of Citrus x limonia. The essential oil showed moderate antibacterial activity against Gram-positive cocci Enterococcus faecalis, and Gram-positive bacillus Lysteria monocytogenes with a MIC of 1000 μg/mL. The oil exhibited strong antifungal activity against fungi Aspergillus niger, and yeasts Candida albicans with a MIC of 250 and 500 μg/mL, respectively. The antioxidant activity of essential oil was weak in ABTS method with a SC50 of 9.12 mg/mL. Additionally, the essential oil presented moderate anticholinesterase activity with an IC50 of 71.02 ± 1.02 µg/mL.

Catabolism of 2-keto-3-deoxy-galactonate and the production of its enantiomers

2-Keto-3-deoxy-galactonate (KDGal) serves as a pivotal metabolic intermediate within both the fungal D-galacturonate pathway, which is integral to pectin catabolism, and the bacterial DeLey-Doudoroff pathway for D-galactose catabolism. The presence of KDGal enantiomers, L-KDGal and D-KDGal, varies across these pathways. Fungal pathways generate L-KDGal through the reduction and dehydration of D-galacturonate, whereas bacterial pathways produce D-KDGal through the oxidation and dehydration of D-galactose. Two distinct catabolic routes further metabolize KDGal: a nonphosphorolytic pathway that employs aldolase and a phosphorolytic pathway involving kinase and aldolase. Recent findings have revealed that L-KDGal, identified in the bacterial catabolism of 3,6-anhydro-L-galactose, a major component of red seaweeds, is also catabolized by Escherichia coli, which is traditionally known to be catabolized by specific fungal species, such as Trichoderma reesei. Furthermore, the potential industrial applications of KDGal and its derivatives, such as pyruvate and D- and L-glyceraldehyde, are underscored by their significant biological functions. This review comprehensively outlines the catabolism of L-KDGal and D-KDGal across different biological systems, highlights stereospecific methods for discriminating between enantiomers, and explores industrial application prospects for producing KDGal enantiomers. KEY POINTS: • KDGal is a metabolic intermediate in fungal and bacterial pathways • Stereospecific enzymes can be used to identify the enantiomeric nature of KDGal • KDGal can be used to induce pectin catabolism or produce functional materials.

Polarimeters for the Detection of Anisotropy from Reflectance

Polarimetry is used to determine the Stokes parameters of a laser beam. Once all four S0,1,2,3 parameters are determined, the state of polarisation is established. Upon reflection of a laser beam with the defined S polarisation state, the directly measured S parameters can be used to determine the optical properties of the surface, which modify the S-state upon reflection. Here, we use polarimetry for the determination of surface anisotropies related to the birefringence and dichroism of different materials, which have a common feature of linear patterns with different alignments and scales. It is shown that polarimetry in the back-reflected light is complementary to ellipsometry and four-polarisation camera imaging; experiments were carried out using a microscope.

Identification of the enantiomeric nature of 2-keto-3-deoxy-galactonate in the catabolic pathway of 3,6-anhydro-L-galactose

A novel metabolic pathway of 3,6-anhydro-L-galactose (L-AHG), the main sugar component in red macroalgae, was first discovered in the marine bacterium Vibrio sp. EJY3. L-AHG is converted to 2-keto-3-deoxy-galactonate (KDGal) in two metabolic steps. Here, we identified the enantiomeric nature of KDGal in the L-AHG catabolic pathway via stereospecific enzymatic reactions accompanying the biosynthesis of enantiopure L-KDGal and D-KDGal. Enantiopure L-KDGal and D-KDGal were synthesized by enzymatic reactions derived from the fungal galacturonate and bacterial oxidative galactose pathways, respectively. KDGal, which is involved in the L-AHG pathway, was also prepared. The results obtained from the reactions with an L-KDGal aldolase, specifically acting on L-KDGal, showed that KDGal in the L-AHG pathway exists in an L-enantiomeric form. Notably, we demonstrated the utilization of L-KDGal by Escherichia coli for the first time. E. coli cannot utilize L-KDGal as the sole carbon source. However, when a mixture of L-KDGal and D-galacturonate was used, E. coli utilized both. Our study suggests a stereoselective method to determine the absolute configuration of a compound. In addition, our results can be used to explore the novel L-KDGal catabolic pathway in E. coli and to construct an engineered microbial platform that assimilates L-AHG or L-KDGal as substrates. KEY POINTS: • Stereospecific enzyme reactions were used to identify enantiomeric nature of KDGal • KDGal in the L-AHG catabolic pathway exists in an L-enantiomeric form • E. coli can utilize L-KDGal as a carbon source when supplied with D-galacturonate.

Polarimetric and fluorescence spectroscopic based classification of mono and disaccharide solutions

In this article, we demonstrate the potential application of polarimetry and fluorescence spectroscopy for classifying mono and disaccharides (sugar) both qualitatively and quantitatively. A phase lock-in rotating analyzer (PLRA) polarimeter has been designed and developed for real time quantification of sugar concentration in a solution. Polarization rotation in the form of phase shift in sinusoidal photovoltages of reference and sample beams occurred when incident on the two spatially distinct photodetectors. Monosaccharide (fructose and glucose) and disaccharide (sucrose) have been quantitatively determined with sensitivities of 122.06 deg ml g^-1, 272.84 deg ml g^-1 and 163.41 deg ml g^-1 respectively. Calibration equations have been obtained from the respective fitting functions to estimate the concentration of each individual dissolved in deionized (DI) water. In comparison to the predicted results, the absolute average errors of 1.47 %, 1.63 % and 1.71 % are calculated for the readings of sucrose, glucose and fructose, respectively. Furthermore, the performance of the PLRA polarimeter has been compared with fluorescence emission results acquired from the same set of samples. The Limit of detections (LODs) attained from both experimental setups are comparable for mono and disaccharides. A linear detection response is observed by both polarimeter and fluorescence spectrometer in a wide range 0-0.28 g/ml of sugar. These results depict that PLRA polarimeter is novel, remote, precise and cost-effective for quantitative determination of optically active ingredient in the host solution.

A portable elliptical dichroism spectrometer targeting secondary structural features of tumorous protein for pancreatic cancer detection

Stereochemical analysis is essential for understanding the complex function of biomolecules. Various direct and indirect approaches can be used to explore the allosteric configuration. However, the size, cost, and delicate nature of these systems limit their biomedical usage. Here, we constructed elliptical dichroism (ED) spectrometer for biomedical applications, whose performance is validated by experiment and theoretical simulation (Jones/Mueller calculus and time-dependent density-functional theory). Instead of complicated control of circular polarization, ED spectrometer adopted the absorbance of left- and right-oriented elliptically polarized light. With a simplified design, we demonstrated the potential of ED spectrometry as an alternative for secondary structural analysis of biomolecules, their conformation and chirality. It not only provides a portable, low-cost alternative to the sophisticated instruments currently used for structural analysis of biomolecules but also provides superior translational features: low sample consumption(200 μl), easy operation, and multiple working modes, for noninvasive cancer detection.

Sulfur-Doped Graphene-Based Electrochemical Sensors for Fast and Sensitive Determination of (R)-(+)-Limonene from Beverages

Two sensors based on sulfur-doped graphene, a gold nanoparticle paste modified with 5,10,15,20-tetraphenyl-21H,23H-porphine and 5,10,15,20-tetrakis (pentafluorophenyl chloride)-21H,23H-iron (III) porphyrin, were proposed for the determination of R-limonene in beverages (triple sec liqueur and limoncello). Differential pulse voltammetry was the method used to characterize and validate the proposed sensors. The response characteristics showed that the detection limits for both sensors were 3 × 10^-6 mol L^-1, while the quantification limits were 1 × 10^-5 mol L^-1. Both sensors can be used to determine R-limonene in a concentration range between 1 × 10^-5-6 × 10^-4 mol L^-1 for TPP/AuNPs-S-Gr and 1 × 10^-5-1 × 10^-3 mol L^-1 for Fe(TPFPP)Cl/AuNPs-S-Gr. The highest sensitivity (0.7068 µA/mol L^-1) was recorded when the TPP/AuNPs-S-Gr sensor was used, proving that the electrocatalytic effect of this electrocatalyst is higher compared to that of Fe(TPFPP)Cl/AuNPs-S-Gr. High recoveries (values greater than 99.00%) and low RSD values (%) (below 5.00%) were recorded for both sensors when used to determine R-limonene in triple sec liqueur and limoncello.