Simultaneous determination of urocanic acid isomers and histidine in human stratum corneum by high-performance liquid chromatography

Positional Isomeric Symmetric Dipodal Receptors Dangled with Rotatable Binding Scaffolds: Fluorescent Sensing of Silver Ions and Sequential Detection of l-Histidine and Their Multifarious Applications

Three simple dipodal artificial acyclic symmetric receptors, SDO, SDM, and SDP, driven by positional isomerism based on xylelene scaffolds were designed, synthesized, and characterized by ¹H NMR, ¹³C NMR, and mass spectroscopy techniques. Probes SDO, SDM, and SDP demonstrated selective detection of Ag⁺ metal ions and amino acid l-histidine in a DMSO-H₂O solution (1:1 v/v, HEPES 50 mM, pH = 7.4). The detection of Ag⁺ metal ions occurred in three ways: (i) inhibition of the photoinduced electron-transfer (PET) process, (ii) blueshifted fluorescence enhancement via the intramolecular charge-transfer (ICT) process, and (iii) restricted rotation of the dangling benzylic scaffold following coordination with a Ag⁺ metal ion. Job's plot analysis and quantum yields confirm the binding of probes to Ag⁺ in 1:1, 1:2, and 1:2 ratios with LODs and LOQs found to be 1.3 μM and 3.19 × 10^-7 M, 6.40 × 10^-7 and 2.44 × 10 ^-6 M, and 9.76 × 10^-7 and 21.01 × 10^-7 M, respectively. ¹H NMR titration, HRMS, ESI-TOF, IR analysis, and theoretical DFT investigations were also used to establish the binding stoichiometry. Furthermore, the probes were utilized for the detection of Ag⁺ ions in water samples, food samples, soil analysis, and bacterial imaging in Escherichia coli cells and a molecular logic gate was constructed.

Analytical tools for urocanic acid determination in human samples: A review

Urocanic acid is a chromophore found in the skin that has been identified as an important immunosuppressant and carcinogenesis mediator through its photoisomerization from trans to cis form induced by ultraviolet radiation. Research on analytical methods that explore urocanic acid isomerization is indispensable to fully understand the deleterious effects mediated by this biomarker. In this context, the current relevant analytical methods for determination of these isomers in human samples are summarized in this review. The methods presented here are applicable to human samples collected by noninvasive methods (or minimally invasive), encompassing an array of analytical techniques, including high-performance capillary electrophoresis, confocal Raman spectroscopy, gas chromatography, high-performance liquid chromatography, and mass spectrometry, among others. Developed high-performance liquid chromatography methods have proven to be advantageous, allowing noninvasive collections for in vivo analysis and the confocal Raman, specially, for real-time analysis. Among all these methods, high-performance liquid chromatography is the most investigated one with mass spectrometry or ultraviolet detector, and the mass spectrometry detector being the most studied in the last years, demonstrating high sensitivity, very low detection limits, and accurate identification, especially for clinical investigations.

[2+2] Photodimerization of Stilbazoles Promoted by Oxalic Acid in Suspension

In this study, a very simple technique to perform efficiently photodimerization of some vinylpyridines is reported. By irradiating a stirred mixture of several stilbazoles with solid oxalic acid dihydrate dispersed in a nonpolar (i.e., cyclohexane) or moderately polar (benzene, dichloromethane, dioxane) solvent, the corresponding dimeric cyclobutane adducts were obtained in high yields and excellent regio- and stereoselectivities. The strategy could also be applied successfully to oily, waxy, or even insoluble stilbazoles. Moreover, the oxalic acid loading could be lowered to substoichiometric amounts. When further optimizations were needed, our strategy was found to be highly flexible to identify other oligocarboxylic acids as alternative additives to improve, or even overturn, the regioselectivity. Oxalic acid and other oligocarboxylic acids were found to be capable of orienting more than 50 stilbazoles toward photodimerization under these conditions.

A sensitive and selective electroanalysis strategy for histidine using the wettable well electrodes modified with graphene quantum dot-scaffolded melamine and copper nanocomposites

A wettable well was fabricated on an electrode, which was further modified with carbon quantum dot-scaffolded nanocomposites of melamine and copper for probing histidine through a unique displacement reaction route. The developed electrode with wettable well enables the condensing enrichment of analytes from the sample droplets, improving the electroanalytical sensitivity.

Highly selective and reproducible electroanalysis for histidine in blood with turn-on responses at a potential approaching zero using tetrahedral copper metal organic frameworks

Tetrahedral copper metal organic frameworks were fabricated for the electroanalysis of histidine with turn-on responses at a potential approaching zero.

Highly sensitive fluorescent detection of glutathione and histidine based on the Cu(ii)-thiamine system

A novel fluorescence method for the simultaneous detection of glutathione and histidine based on their inhibitory effects on the oxidation of thiamine by Cu(ii) is proposed.

Exploring (bio)catalytic activities of structurally characterised Cu(ii) and Mn(iii) complexes: histidine recognition and photocatalytic application of Cu(ii) complex and derived CuO nano-cubes

The multifunctional properties of two polymeric complexes of Cu(ii) and Mn(iii) have been evaluated.

A highly selective phosphorescence probe for histidine in living bodies

A heterobimetallic ruthenium(ii)–nickel(ii) complex has been developed for phosphorescence imaging of histidine in live cells and bodies.

Rapid, simultaneous and nanomolar determination of pyroglutamic acid and cis-/trans-urocanic acid in human stratum corneum by hydrophilic interaction liquid chromatography (HILIC)-electrospray ionization tandem mass spectrometry

A rapid, sensitive and specific hydrophilic interaction liquid chromatography coupled to tandem mass spectrometric (HILIC-MS/MS) method for the simultaneous determination of pyroglutamic acid, cis- and trans-urocanic acid in human skin stratum corneum (SC) were developed and validated. This method was carried out without derivatization or addition of ion-pair additives in mobile phase. The analytes were extracted by PBS buffer solution and analyzed using an electrospray positive ionization mass spectrometry in the multiple reaction monitoring (MRM) mode. Chromatographic separation was performed on an AQUITY UPLC amide column using gradient elution with the mobile phase of water and acetonitrile. The standard curves were linear over the concentration range of 1.0-250 ng/mL with a correlation coefficient higher than 0.999 with an LLOQ of 0.5 ng/mL. The lower limits of detection (LLOD) of these analytes were lower than 0.2 ng/mL. The intra- and inter-day precisions were measured to be below 7.7% and accuracies were within the range of 94.3-102.6%. The validated method was successfully applied to determine the level of pyroglutamic acid and cis-/trans-urocanic acid in the SC samples from forearm and forehead region of 19 human volunteers.

Natural moisturizing factor components in the stratum corneum as biomarkers of filaggrin genotype: evaluation of minimally invasive methods

BACKGROUND

The carriers of loss-of-function mutations in the filaggrin gene (FLG) have reduced levels of natural moisturizing factor (NMF) in the stratum corneum. The concentration of NMF components which are formed by filaggrin protein breakdown in the stratum corneum might therefore be useful as a biomarker of the FLG genotype. OBJECTIVES To investigate the feasibility of different sampling methods for the determination of two NMF components, 2-pyrrolidone-5-carboxylic acid (PCA) and urocanic acid (UCA), in the stratum corneum as biomarkers for the FLG genotype.

METHODS

PCA and UCA from the stratum corneum were sampled by using a tape stripping technique and an extraction technique using skin patches containing potassium hydroxide (KOH). The concentrations of PCA and UCA were measured by high-performance liquid chromatography. Eleven carriers of an FLG mutation and 10 individuals wild type for the two most common FLG mutations (R501X and R2447X) [corrected] were included in the study.

RESULTS

The most significant difference between the FLG genotypes was found for PCA sampled by the tape stripping technique. The mean values of PCA obtained by the tape stripping technique were, respectively, 0.18, 0.50 and 1.64 mmol g(-1) protein in homozygous (or compound heterozygous), heterozygous and wild-type genotypes (P < 0.005 homozygous vs. heterozygous; P < 0.0001 heterozygous vs. wild type). The tape stripping technique showed less intrasubject variation compared with the KOH patches, in particular when the concentrations of UCA and PCA on the tape strips were normalized for protein amount.

CONCLUSIONS

The concentration of PCA in the stratum corneum collected by tape stripping showed it to be a feasible biomarker of the FLG genotype.

Recent advances in urocanic acid photochemistry, photobiology and photoimmunology

Urocanic acid (UCA), produced in the upper layers of mammalian skin, is a major absorber of ultraviolet radiation (UVR). Originally thought to be a 'natural sunscreen', studies conducted a quarter of a century ago proposed that UCA may be a chromophore for the immunosuppression that follows exposure to UVR. With its intriguing photochemistry, its role in immunosuppression and skin cancer development, and skin barrier function, UCA continues to be the subject of intense research effort. This review summarises the photochemical, photobiological and photoimmunological findings regarding UCA, published since 1998.