Determination of Enantiomeric Compositions of Analytes Using Novel Fluorescent Chiral Molecular Micelles and Steady State Fluorescence Measurements

Novel fluorescent chiral molecular micelles (FCMMs) were synthesized, characterized, and employed as chiral selectors for enantiomeric recognition of non-fluorescent chiral molecules using steady state fluorescence spectroscopy. The sensitivity of the fluorescence technique allowed for investigation of low concentrations of chiral selector (3.0 x 10(-5) M) and analyte (5.0 x 10(-6) M) to be used in these studies. The chiral interactions of glucose, tartaric acid, and serine in the presence of FCMMs poly(sodium N-undecanoyl-L-tryptophanate) [poly-L-SUW], poly(sodium N-undecanoyl-L-tyrosinate) [poly-L-SUY], and poly(sodium N-undecanoyl-L-phenylalininate) [poly-SUF] were based on diastereomeric complex formation. Poly-L-SUW had a significant fluorescence emission spectral difference as compared to poly-L-SUY and poly-L-SUF for the enantiomeric recognition of glucose, tartaric acid, and serine. Studies with the hydrophobic molecule alpha-pinene suggested that poly-L-SUY and poly-L-SUF had better chiral discrimination ability for hydrophobic analytes as compared to hydrophilic analytes. Partial-least-squares regression modeling (PLS-1) was used to correlate changes in the fluorescence emission spectra of poly-L-SUW due to varying enantiomeric compositions of glucose, tartaric acid, and serine for a set of calibration samples. Validation of the calibration regression models was determined by use of a set of independently prepared samples of the same concentration of chiral selector and analyte with varying enantiomeric composition. Prediction ability was evaluated by use of the root-mean-square percent relative error (RMS%RE) and was found to range from 2.04 to 4.06%

Chiral Recognition of Amino Acids by Use of a Fluorescent Resorcinarene

The spectroscopic properties of a chiral boronic acid based resorcinarene macrocycle employed for chiral analysis were investigated. Specifically, the emission and excitation characteristics of tetraarylboronate resorcinarene macrocycle (TBRM) and its quantum yield were evaluated. The chiral selector TBRM was investigated as a chiral reagent for the enantiomeric discrimination of amino acids using steady-state fluorescence spectroscopy. Chiral recognition of amino acids in the presence of the macrocycle was based on diastereomeric complexes. Results demonstrated that TBRM had better chiral discrimination ability for lysine as compared to the other amino acids. Partial least squares regression modeling (PLS-1) of spectral data for macrocycle-lysine guest-host complexes was used to correlate the changes in the fluorescence emission for a set of calibration samples consisting of TBRM in the presence of varying enantiomeric compositions of lysine. In addition, validation studies were performed using an independently prepared set of samples with different enantiomeric compositions of lysine. The results of multivariate regression modeling indicated good prediction ability of lysine, which was confirmed by a root mean square percent relative error (RMS%RE) of 5.8%

Detection, Purity Analysis, and Quality Assurance of Adulterated Peanut (Arachis hypogaea) Oils

The intake of adulterated and unhealthy oils and trans-fats in the human diet has had negative health repercussions, including cardiovascular disease, causing millions of deaths annually. Sadly, a significant percentage of all consumable products including edible oils are neither screened nor monitored for quality control for various reasons. The prospective intake of adulterated oils and the associated health impacts on consumers is a significant public health safety concern, necessitating the need for quality assurance checks of edible oils. This study reports a simple, fast, sensitive, accurate, and low-cost chemometric approach to the purity analysis of highly refined peanut oils (HRPO) that were adulterated either with vegetable oil (VO), canola oil (CO), or almond oil (AO) for food quality assurance purposes. The Fourier transform infrared spectra of the pure oils and adulterated HRPO samples were measured and subjected to a partial-least-square (PLS) regression analysis. The obtained PLS regression figures-of-merit were incredible, with remarkable linearity (R2 = 0.994191 or better). The results of the score plots of the PLS regressions illustrate pattern recognition of the adulterated HRPO samples. Importantly, the PLS regressions accurately determined percent compositions of adulterated HRPOs, with an overall root-mean-square-relative-percent-error of 5.53% and a limit-of-detection as low as 0.02% (wt/wt). The developed PLS regressions continued to predict the compositions of newly prepared adulterated HRPOs over a period of two months, with incredible accuracy without the need for re-calibration. The accuracy, sensitivity, and robustness of the protocol make it desirable and potentially adoptable by health departments and local enforcement agencies for fast screening and quality assurance of consumable products

Chiral ionic liquids in chromatographic separation and spectroscopic discrimination

Chiral ionic liquids (CILs) are a subclass of ionic liquids (ILs) in which the cation, anion, or both may be chiral. The chirality can be central, axial, or planar. CILs possess a number of unique advantageous properties which are inherited from ionic liquids including negligible vapor pressure, wide liquidus temperature range, high thermal stability, and high tunability. Due to their dual functionalities as chiral selectors and chiral solvents simultaneously, CILs recently have been widely used both in enantiomeric chromatographic separation and in chiral spectroscopic discrimination. In this chapter, the various applications of CILs in chiral chromatographic separations such as GC, HPLC, CE, and MEKC are reviewed. The applications of CILs in enantiomeric spectroscopic discrimination using techniques such as NMR, fluorescence, and NIR are described. In addition, chiral recognition and separation mechanism using the CILs as chiral selectors or chiral solvents is also discussed. © 2010 Springer-Verlag Berlin Heidelberg

Electrochemical and Colorimetric Nanosensors for Detection of Heavy Metal Ions: A Review

Human exposure to acute and chronic levels of heavy metal ions are linked with various health issues, including reduced children’s intelligence quotients, developmental challenges, cancers, hypertension, immune system compromises, cytotoxicity, oxidative cellular damage, and neurological disorders, among other health challenges. The potential environmental HMI contaminations, the biomagnification of heavy metal ions along food chains, and the associated risk factors of heavy metal ions on public health safety are a global concern of top priority. Hence, developing low-cost analytical protocols capable of rapid, selective, sensitive, and accurate detection of heavy metal ions in environmental samples and consumable products is of global public health interest. Conventional flame atomic absorption spectroscopy, graphite furnace atomic absorption spectroscopy, atomic emission spectroscopy, inductively coupled plasma–optical emission spectroscopy, inductively coupled plasma–mass spectroscopy, X-ray diffractometry, and X-ray fluorescence have been well-developed for HMIs and trace element analysis with excellent but varying degrees of sensitivity, selectivity, and accuracy. In addition to high instrumental running and maintenance costs and specialized personnel training, these instruments are not portable, limiting their practicality for on-demand, in situ, field study, or point-of-need HMI detection. Increases in the use of electrochemical and colorimetric techniques for heavy metal ion detections arise because of portable instrumentation, high sensitivity and selectivity, cost-effectiveness, small size requirements, rapidity, and visual detection of colorimetric nanosensors that facilitate on-demand, in situ, and field heavy metal ion detections. This review highlights the new approach to low-cost, rapid, selective, sensitive, and accurate detection of heavy metal ions in ecosystems (soil, water, air) and consumable products. Specifically, the review highlights low-cost, portable, and recent advances in smartphone-operated screen-printed electrodes (SPEs), plastic chip SPES, and carbon fiber paper-based nanosensors for environmental heavy metal ion detection. In addition, the review highlights recent advances in colorimetric nanosensors for heavy metal ion detection requirements. The review provides the advantages of electrochemical and optical nanosensors over the conventional methods of HMI analyses. The review further provides in-depth coverage of the detection of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) ions in the ecosystem, with emphasis on environmental and biological samples. In addition, the review discusses the advantages and challenges of the current electrochemical and colorimetric nanosensors protocol for heavy metal ion detection. It provides insight into the future directions in the use of the electrochemical and colorimetric nanosensors protocol for heavy metal ion detection

Protein separations using polyelectrolyte multilayer coatings with molecular micelles in open tubular capillary electrochromatography

Novel polyelectrolyte multilayer (PEM) coatings for enchanced protein separations in open tubular CEC (OT-CEC) are reported. Use of four cationic polymers (poly-L-lysine, poly-L-ornithine, poly-L-lysine-serine, and poly-L-glutamic acid-lysine), and three anionic molecular micelles, sodium poly(N-undecanoyl-L-leucyl-alaninate) (poly-L-SULA), sodium poly(N-undecanoyl-L-leucyl-valinate) (poly-L-SULV), and sodium poly(undecylenic sulfate) (poly-SUS) were investigated in PEM coatings for protein separations. The simultaneous effects of cationic polymer concentration, number of bilayers, temperature, applied voltage, and pH of the BGE on the separation of four bask proteins (α-chymotrypsinogen A, lysozyme, ribonuclease A, and cytochrome c) were analyzed using a Box Behnken experimental design. The influence of NaCl on the run-to-run reproducibility was investigated for PEM coatings containing each cationic polymer. All coatings exhibited excellent reproducibilities with a %RSD of the EOF less than 1% in the presence of NaCl. Optimal conditions were dependent on both the cationic and anionic polymers used in the PEM coatings. Poly-L-glutamic acid-lysine produced the highest resolution and longest migration time. The use of molecular micelles to form PEM coatings resulted in better separations than single cationic coatings. Chiral poly-L-SULA and poly-L-SULV resulted in higher protein resolutions as compared to the achiral, poly-SUS. Furthermore, the use of poly-L-SULV reversed the elution order of lysozyme and cytochrome c when compared to poly-L-SUIA and poly-SUS. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Use of multivariate analysis for optimization of separation parameters and prediction of migration time, resolution, and resolution per unit time in micellar electrokinetic chromatography

The optimization of separation parameters in chromatography for better separation and resolution of analytes continues to be a labor intensive procedure usually performed by a trial and error method. A multivariate analysis in the form of multilinear regression (MLR) is used to optimize separation parameters and predict the migration behavior, resolution, and resolution per unit time of achiral (4-chlorophenol, penta-chlorophenol, clonazepam, and diazepam) and chiral (1,1′-binaphthyl 2,2′-dihydrogen phosphate (BNP), and 1,1′-bi-2-naphthol (BOH)) compounds in MEKC. Separations of achiral and chiral analytes were performed using an achiral (poly(sodium N-undecylenic sulfate)) molecular micelle and chiral (poly(sodium N-undecanoyl-L-leucylvalinate) or poly(sodium N-undecanoyl-L-isoleucylvalinate)) molecular micelle, respectively, at various operating temperatures, applied voltages, pH values, and molecular micelle concentrations in the BGE. The separation parameters were subsequently used as input variables for MLR models. The models were validated with independent samples. The root-mean-square percent relative error (RMS% RE) is used as a figure of merit for characterizing the performance of the migration time, resolution, and resolution per unit time models. The RMS%RE obtained for predicted migrated times, resolutions, and resolution per unit time of 4-chlorophenol, pentachlorophenol, clonazepam, diazepam, BNP, and BOH ranged between 8 and 19%. The same experimental procedure was used to optimize the separation parameters of six other chiral analytes of different compound class. The predicted migration times, resolutions, and resolution per unit time of the chiral as well as the achiral analytes compare favorably with the experimental migration times and resolutions, indicating versatility and wide applicability of the technique in MEKC. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Use of experimental design to model separation parameters in micellar electrokinetic chromatography

A chemometric experimental design using principal component analysis and multivariate regression modeling in the form of partial-least-square-regression (PLS-1) was developed to predict the retention behavior of toluene, 1,1′-binaphthyl 2,2′-dihydrogen phosphate (BNP), and 1,1′-bi-2-naphthol (BOH) in micellar electrokinetic chromatography (MEKC). Separations of analytes were performed at various operating temperatures, applied voltages, pH values, and polymeric surfactant concentration added to the buffered system. The polymeric surfactants used were poly (sodium N-undecanoyl-L-leucylvalinate), poly(sodium N-undecanoyl-L-isoleucylvalinate), and poly(sodium N-undecylenic sulfate). The performance of the model to correctly predict migration times of the analytes was evaluated using the root mean square percent relative error (RMS%RE). The RMS%RE obtained for toluene, R_BNP, S_BNP, S_BOH, and R_BOH were 9.92, 7.08, 6.99, 14.7, and 14.1%, respectively. The models were able to correctly predict the migration times of chiral as well as achiral analytes, indicating the versatility and wide applicability of the technique in MEKC. This is an abstract of a paper presented at the 230th ACS National Meeting (Washington, DC 8/28/2005-9/1/2005)

Experimental design and multivariate analysis for optimizing poly(D,L-lactide-co-glycolide) (PLGA) nanoparticle synthesis using molecular micelles

The utility of polymeric nanoparticles as drug delivery systems depends on effective control of synthetic parameters with a significant impact on their physico-chemical characteristics. In this study, a chemometric central composite experimental design (CCD) was used to optimize the synthesis of poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles by emulsification solvent evaporation using anionic molecular micelles, such as poly(sodium N-undecylenic sulfate) (poly-SUS), poly(sodium N-undecanoyl-glycinate) (poly-SUG) and poly(sodium N-undecanoyl-L-leucyl-valinate) (poly-L-SULV) as well as conventional emulsifiers, such as anionic sodium dodecyl sulfate (SDS) and non-ionic polyvinyl alcohol) (PVA). The individual and combined effects of PLGA concentration, emulsifier concentration, homogenization speed, and sonication time (design variables) on particle size and polydispersity index (responses) were investigated using multivariate analysis. The most significant design variables influencing the nanoparticle size and size distribution were PLGA concentration and emulsifier concentration (p \u3c 0.05) in comparison to the other design variables. The quadratic model demonstrated the highest predictive ability when the molecular micelles were used as emulsifiers. The PLGA nanoparticles optimally synthesized according to the CCD were further purified by dialysis and then freeze-dried. Dried nanoparticles synthesized with molecular micelles and PVA were readily re-suspended in water, as compared with SDS for which nanoparticle aggregation occurred. The size of PLGA nanoparticles synthesized using molecular micelles increased after freeze-drying, but remained smaller than 100 nm when poly-L-SULV was used as emulsifier. The PDI values indicated monodisperse nanoparticle suspensions after purification and freeze-drying for all investigated molecular micelles (PDI \u3c 0.100). The nanoparticle suspensions synthesized using molecular micelles were the most stable after dialysis and freeze-drying, having low negative zeta potential values ranging from -54 ± 1.6 mV for poly-L-SULV to -63.2 ± 0.4 mV for poly-SUS. Transmission electron microscopy (TEM) micrographs showed spherical shape and smooth surface for the PLGA nanoparticles synthesized using molecular micelles. Copyright © 2008 American Scientific Publishers All rights reserved