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In order to investigate in detail the influence of chemical treatments (reduction, hydrolyzed eggwhite protein (HEWP) treatment, and oxidation) on damaged hair keratin fibers, the structure of cross-sections at various depths of excessively bleached (damaged) black human hair resulting from a permanent waving process was directly analyzed using Raman spectroscopy. It was found that l -cysteine (CYS) largely reacted with the gauche-gauche-gauche (GGG) conformation of disulfide (–SS–) groups (while CYS did not react with the trans-gauche-trans (TGT) conformation). In particular, not only the GGG content, but also the cysteic acid content existing throughout the cortex region of the excessively bleached human hair remarkably decreased by performing the oxidation process after reduction. On the other hand, the GGG content of the excessively bleached black human hair increased, while the TGT content decreased by performing the oxidation process after reduction and then HEWP treatment processes. From these experiments, the authors concluded that some of the keratin associated protein (KAP), which has a rich –SS– content and cysteic acid content was eluted from the cortex region along with the disconnection of –SS– groups, thereby leading to the remarkable reduction in the reconnection of –SS– groups of the excessively bleached black human hair after the permanent waving process (the reduction and oxidation processes). Also, the authors concluded that the HEWP treatment process in the permanent waving process caused the reconstruction of the KAP, thereby contributing to the acceleration of the reconnection of –SS– groups during the oxidation process.

The assessment of quantification results of the alcohol abuse marker ethyl glucuronide (EtG) in hair in comparison to the cut-off values for the drinking behavior may be complicated by cosmetic hair bleaching. Thus, the impact of increasing exposure to hydrogen peroxide on the EtG content of hair was investigated. Simultaneously, the change of absorbance in the range of 1000-1100 cm(-1) indicative for the oxidation of cystine was investigated non-destructively by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) using pulverized portions of the respective hair samples. Hair samples treated with hydrogen peroxide consistently displayed a significantly increased absorbance at 1040 cm(-1) associated with the formation of cysteic acid. The EtG content decreased significantly if the hair was treated with alkaline hydrogen peroxide as during cosmetic bleaching. It could be shown that ATR-FTIR is capable of detecting an exposure to hydrogen peroxide when still no brightening was visible and already before the EtG content deteriorated significantly. Thus, hair samples suspected of having been exposed to oxidative treatment may be checked non-destructively by a readily available technique. This assay is also possible retrospectively after EtG extraction and using archived samples.

A chemical mapping with high lateral resolution using an atomic force microscope in the pulsed force mode with chemically modified tips, introduced as "dynamic chemical force microscopy" (dCFM), was carried out to investigate the chemical properties of the cuticle of human hair and its changes following an oxidative treatment. Chemically modified atomic force microscopy (AFM) tips, CH3- and NH2-terminated, were applied to achieve a defined chemical contrast (hydrophobic and ionic) in aqueous medium. A comparative Fourier transform infrared spectroscopy-attenuated total reflection identified the dominant chemical groups of the surface vicinity of the hair fiber resulting from the bleaching process. The combined experimental results lead to the conclusion that the hydrophobic top layer is partially removed after bleaching, resulting mostly in hydrophilic SO3(-) end groups at the top of the surface of the hair, with a mean surface density "δ(mean)" of negatively charged groups of approximately 2.2 molecules/nm(2), corresponding to ∼600 μg/m(2) cysteic acid. This indicates that thioester bonds are disrupted and fatty acids are removed as a result of cysteine oxidation. At the molecular level, our results indicate a clustered "self-assembled monolayer" alignment of cysteic acid with a crystal-like structuring, reminiscent of the "fluid mosaic model of cell membranes", with a surface energy of approximately 0.04 N/m. Despite previous extensive works of AFM on human hair, this is, to our knowledge, the first time that the hydrophobic and ionic sites at the top surface of hair have been imaged at the nanoscale with dCFM.

The aim of this manuscript is to develop a combined method for the detection and elimination of oxalic acid (OA) in aqueous environment. For that, the surface of glassy carbon (GC) electrode has been modified by oxidation of L-cysteine using cyclic voltammetric (CV) technique. After modification, the formation of a compact and uniform cysteic acid layer film was achieved and it was confirmed by surface analysis (scanning electron microscopy (SEM) and atomic force microscopy (AFM)). Estimation of the linear range, calibration function and limit of detection for OA were performed by differential pulse voltammetry using Cysteine-modified electrode (Cysteine-MGC). Due to its stability and sensitive response to OA, it was used for monitoring OA during its electrochemical oxidation at Ti/Pt anode. DPV analyses have been compared with classic titration method and HPLC achieving a good fit, confidence intervals and limits. The results are described and discussed in the light of the existing literature.

In order to investigate in detail the internal structure changes in virgin black human hair keratin fibers resulting from bleaching treatments, the structure of cross-sections at various depths of black human hair, which had been impossible due to high melanin grande content, was directly analyzed using Raman spectroscopy. The gauche – gauche – gauche (GGG) content of the SS groups existing from the cuticle region to the center of cortex region of the virgin black human hair remarkably decreased, while the gauche – gauche – trans and trans – gauche – trans contents were not changed by performing the excessive bleaching treatment. In particular, it was found that not only the β-sheet and/or random coil content, but also the α-helix content existing throughout the cortex region of virgin black human hair decreased. In addition, the transmission electron microscope observation shows that the proteins in the cell membrane complex, the cuticle and cortex of the virgin black human hair were remarkably eluted by performing the excessive bleaching treatment. From these experiments, the author concluded that the SS groups, which have a GGG conformation were decomposed and finally converted to cysteic acid, and the α-helix structure of some of the proteins existing in the keratin was changed to the random coil structure, or eluted from the cortex region, thereby leading to the reduction in the protein density of the virgin human hair after the excessive bleaching treatment.

The CyDye family of fluorescent dyes is currently the overwhelming choice for applications in proteomic analysis, using two-dimensional difference gel electrophoresis (2D-DIGE). Protein labeling with CyDyes is hampered by protein precipitation and gel smearing when used above minimal labeling. The solubility of labeled protein may be improved by introducing water solubilizing groups on the dye such as cysteic acids. However, addition of a negatively charged functionality will have the undesired effect of shifting the pI in relation to the unlabeled protein. These limitations have been addressed through the synthesis of highly water-soluble and pI balancing zwitterionic CyDye fluorophores (Z-CyDyes). The new dyes feature a cysteic acid motif, a titratable amine functionality and a NHS activated ester group. In side by side 2D-DIGE comparisons of Z-CyDyes and CyDyes, the new dyes significantly enhanced protein spot volume and the number of spots that were detected. Z-CyDyes have the potential to enhance the depth of proteome coverage and provide a general strategy for improving the performance of protein tagging reagents.

Cordyceps militaris (CM) occurring from a fruiting body by a host insect is a kind of mushroom, which is composed of animal host and plant fruit body. CM contains large amounts of useful ingredients including polysaccharides, vitamins, amino acids, minerals, etc. The essential amino acids from CM including cystine, lysine, and methionine can be expected to improve damaged hair treatment as effective ingredients. In this study, the improvement effect of the CM extracts on chemical and physical properties for damaged-hair treatment was investigated. The cysteic acid and cystine monooxide produced by oxidation of cystine were analyzed their chemical structure by FT-IR spectroscopy. It was confirmed that the vibration absorption peak (1,041 cm-1) of cysteic acid was reduced and increased sulfur content considerably which means meaningful improvement effect on damaged-hair treatment. Apparently, the cuticle morphology of the damaged-hair was improved significantly by treatment with CM extracts. Especially, confocal laser scanning microscope images of the damaged-hair treated with the extract showed highly increased fluorescence intensity which means promising effect in hair treatment. The tensile strength of the damaged hair treated also increased by 168% compared with the damaged hair.

A novel cysteic acid modified carbon paste electrode (cysteic acid/CPE) based on electrochemical oxidation of l -cysteine was developed to simultaneously determine ofloxacin and gatifloxacin in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectra (FTIR) indicated that l -cysteine was oxidated to cysteic acid. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) indicated that cysteic acid was successfully modified on electrode. The large peak separation (116 mV) between ofloxacin and gatifloxacin was obtained on cysteic acid/CPE while only one oxidation peak was found on bare electrode. And the peak currents increased 5 times compared to bare electrode. Moreover, the current could be further enhanced in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate. The differential pulse voltammograms (DPV) exhibited that the oxidation peak currents were linearly proportional to their concentrations in the range of 0.06–10 μM for ofloxacin and 0.02–200 μM for gatifloxacin, and the detection limits of ofloxacin and gatifloxacin were 0.02 μM and 0.01 μM (S/N = 3), respectively. This proposed method was successfully applied to determine ofloxacin and gatifloxacin in pharmaceutical formulations and human serum samples.

A chiral electrochemical sensor has been prepared via cysteic acid modified glassy carbon (CyA-GC) electrode to discriminate tyrosine (Tyr) enantiomers. Sweep cycles of CyA-GC in modification process and pH of solution were investigated to obtain optimum experimental conditions. Electrochemical impedance spectroscopy was employed to characterize the electrical conductivity of the modified electrode. For the first time, different oxidation peak potentials (Ep) of l- and d-Tyr were observed in the differential pulse voltammograms obtained in the solution containing l- or d-Tyr. Further study showed that only one peak appeared in mixture solution containing l- and d-Tyr and Ep of that peak shifted positively and linearly with an increasing percentage of l-isomer of Tyr racemic mixture. Keywords: Chiral electrochemical recognition, Tyrosine, Cysteic acid, Modified electrode