Optical chemical sensor of Gd(iii) based on 5-(2'-bromophenyl- azo)-6-hydroxypyrimidine-2,4-dione immobilized on poly(methyl methacrylate) and 2-nitrophenyloctylether matrix.

A novel optical chemical sensor (optode) was fabricated for the determination of Gadolinium ions. The optical sensor was prepared by incorporating a recently synthesized ionophore, 5-(2'-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione (BPAHPD), and 2-nitrophenyloctylether (NPOE) as a plasticizer in poly(methyl methacrylate) (PMMA) membrane. The color of the sensing membrane in contact with Gd(iii) ions changed from yellow to red-orange due to the adsorption of Gd(iii) with the maximum absorbance (λ max) at 563 nm. The chemical sensor responds optimally towards Gd(iii) ions at the optimum conditions of pH 7.5, contact time 10 min, 150 ng mL-1 Gd(iii), and 5.0 mL solution. The linear regression equation achieved was A = 4.36C (µg mL-1) - 0.15 (r = 0.9976). A linear Gd(iii) calibration curve can be established in the concentration range of 5.0-250 ng mL-1 with R 2 = 0.9976. Detection and quantification limits are 1.47 and 4.75 ng mL-1, respectively. The molar absorptivity and Sandell sensitivity are found to be 6.86 × 107 L mol-1 cm-1 and 0.023 ng cm-2, respectively. In addition to its stability and reproducibility, the optode revealed a great selectivity toward Gd(iii) ions as compared to other coexisting ions in real samples. The recovery of Gd(iii) ions from the sensor material was achieved using 0.4 M HNO3 . The offered optode sensor membrane has been employed to monitor Gd(iii) in soil, sediments, river water, and urine with an internal standard addition method and compared statistically with the ICP-OES method. The results revealed calculated t-values between 1.11-1.85, whereas F values were in the range of 2.46-3.77 which did not exceed the theoretical values, indicating no significant difference at 95% confidence level. The observed percent recovery is in the range of 97.24-102.52%.

A highly selective bulk optode based on 6-{4-(2,4-dihydroxy-phenyl)diazenyl)phenyl}-2-oxo-4-phenyl-1,2-dihydro-pyridine-3-carbonitrile incorporating chromoionophore V for determination of nano levels of cadmium.

A novel optical sensor has been fabricated for highly accurate, simple and selective determination of nanomolar levels of cadmium ions. The sensor depends on the interaction of 6-{4-(2,4-dihydroxyphenyl)diazenyl)phenyl}-2-oxo-4-phenyl-1,2-dihydropyri-dine-3-carbonitrile (DDPODC) with Cd(II) in plasticized (2-nitrophenyloctyl ether) (o-NPOE) polyvinylchloride (PVC) membrane incorporating chromoionophore V as a lipophilic H+-selective indicator. It would seem that the higher Cd(II) concentration, the lower absorbance of chromoionophore V in the membrane at 668 nm, whereas the absorbance at 586 nm increased. The developed sensor at pH 4.7 has a linear range of 5.0 × 10-12 - 2.5 × 10-5 M with limits of detection and quantification of 1.62 × 10-12 and 4.95 × 10-12 M, respectively. The relative standard deviation (RSD) for eight determination of 1.0 × 10-7 M Cd(II) was 1.67%. Finally, the proposed sensor gives good results for applications in the direct determination of cadmium ions in water, food, and biological samples. Additionally, we compared the obtained results with the data obtained from the flame atomic absorption spectrometry (FAAS).

Utilization of a plasticized PVC optical sensor for the selective and efficient detection of cobalt(ii) in environmental samples.

A novel sensitive, selective, and reversible cobalt(ii) ion optical sensor was prepared by the incorporation of 5-[o-carboxyphenylazo]2,4-dihydroxybenzoic acid [CPDB] and sodium tetraphenylborate (NaTPB) in a plasticized polyvinyl chloride (PVC) membrane containing dioctyl adipate (DOA) as a plasticizer. The influence of several parameters such as pH, base matrix, solvent mediator and reagent concentration was optimized. A comparison of the obtained results with those of previously reported sensors revealed that the proposed method, in addition to being fast and simple, provided a good linear range (0.05-45.20 µM) and low detection limit (0.015 µM). Low detection and quantification limits and excellent selectivity in the presence of interfering ions such as Fe3+, Cu2+, Ni2+, Ag+, Au3+, Cr3+, Cd2+, Zn2+, Hg2+, and SO4 2- make it feasible to monitor Co2+ ion content accurately and repeatedly in environmental samples with complicated matrices. The optode was regenerated successfully using 0.3 M nitric acid (HNO3) solution while its response was reversible with a relative standard deviation (RSD) lower than 1.9% for seven replicate determinations of 20 µM Co2+ in various membranes. The optode was stable and was stored for at least 15 days without observing any change in its sensitivity.

Collision-induced dissociation products of the protonated dipeptide carnosine: structural elucidation, fragmentation pathways and potential energy surface analysis.

Collision-induced dissociation (CID) experiments on protonated carnosine, [carnosine + H](+), with several collision energies were shown to yield eleven different fragment ions with the generation of product ions [carnosine-H2O + H](+) and [carnosine-NH3 + H](+) being the lowest energy processes. Energy-resolved CID showed that at slightly higher collision energies the ions [histidine + H](+) and [histidine-H2O-CO + H](+) are formed. At even higher energies four other product ions were observed, however, attained relatively lower abundances. Quantum chemistry calculations, carried out at different levels of theory, were employed to probe fragmentation mechanisms that account for all the experimental data. All the adopted computational protocols give similar energetic trends, and the range of the calculated free energy barrier values for the generation of all the observed product ions is in agreement with the fragmentation mechanisms offered here.

Fragmentation pathways analysis for the gas phase dissociation of protonated carnosine-oxaliplatin complexes.

Collision-induced dissociation (CID) experiments on the protonated carnosine-oxaliplatin complex, [Carnosine + OxPt + H](+) using several collision energies were shown to yield nine different fragment ions. Energy-resolved CID experiments on [Carnosine + OxPt + H](+) showed that the generation of the product ion [Carnosine - H + Pt(dach)](+) (where dach is 1,2-diaminocyclohexane) is the lowest energy process. At slightly higher collision energies, the loss of neutral carnosine from [Carnosine + OxPt + H](+) to produce [OxPt + H](+) was observed, followed by the loss of oxaliplatin from the same precursor ion to produce [Carnosine + H](+). At significantly higher energies, the ion [OxPt - CO2 + H](+) was shown to be formed, while the last two investigated ions [Carnosine + OxPt - CO2 + H](+) and [Carnosine - NH3 - H + Pt(dach)](+) did not attain any significant relative abundance. Density functional calculations at the B3LYP/LANL2DZ level were employed to probe the fragmentation mechanisms that account for all experimental data. The lowest free energy barriers for the generation of each of the ions [Carnosine - H + Pt(dach)](+), [OxPt + H](+), [Carnosine + H](+), [Carnosine + OxPt - CO2 + H](+) and [Carnosine - NH3 - H + Pt(dach)](+) from [Carnosine + OxPt + H](+) according to the fragmentation mechanisms offered here were calculated to be 31.9, 38.8, 49.3, 75.2, and 85.6 kcal mol(-1), respectively.

Oxaliplatin complexes with carnosine and its derivatives: in vitro cytotoxicity, mass spectrometric and computational studies with a focus on complex fragmentation.

The complexation of the Pt-based anti-cancer drug oxaliplatin (OxPt) with biological ligands other than DNA is believed to be a major cellular sink for the drug reducing its therapeutic potential and acting as a potential cause of toxicity. In this paper, the very first hypothesis driven investigation of the role of the naturally abundant cytoplasmic dipeptide ligand ß-alanyl-l-histidine dipeptide (carnosine) in OxPt detoxification is presented. In vitro studies on hepatocellular carcinoma HepG2 cells suggest that carnosine may inhibit the cytotoxic action of OxPt most likely through the formation of complexes that are less cytotoxic than OxPt alone. Evidence is provided to suggest that pre-exposure of HepG2 cells to elevated levels of carnosine appears to have a lasting effect on reducing the cytotoxicity of OxPt even after the removal of the externally added carnosine. This effect, however, is likely under kinetic control as its magnitude was shown not to vary significantly with the level of carnosine exposure within the concentration range used in this study. Various mass spectrometry techniques employing electrospray ionization and chip nanospray were employed to study the interaction of oxaliplatin with carnosine as well as two of its derivatives ß-alanyl-N-methylhistidine (anserine) and N-acetylcarnosine (NAC). Evidence of complexation between OxPt and each of the three ligands examined is presented. Most species observed were unambiguously assigned and compared to their theoretical isotopic patterns. Common fragmentation products due to the collisionally-activated protonated complexes of each of the ligands examined with OxPt, [M + OxPt + H](+), where M = carnosine, anserine or NAC, were reported. Density functional calculations at the B3LYP/LANL2DZ level were used to obtain structural information and relative free energies of different isomers of the observed precursor [Carnosine + OxPt + H](+) both in the gas phase and in solution as well as to probe its fragmentation, highlighting plausible fragmentation mechanisms that account for all the experimental results. Data are presented to show several binding modes between electron rich sites such as N and O centers of carnosine and the Pt metal of OxPt. Calculations were also employed to obtain proton affinities and free energies of key reactions. The proton affinities of carnosine, anserine and NAC at 298 K were calculated to be 254.4, 255.9 and 250.2 kcal mol(-1) respectively. To the best of our knowledge the proton affinities of anserine and N-acetyl-carnosine are the first reported values in the literature.