Determination of homocitrulline in urine of patients with HHH syndrome by liquid chromatography tandem mass spectrometry

A liquid chromatography tandem mass spectrometric method is described for the analysis of homocitrulline in human urine, a key metabolite in the differential diagnosis of hyperammonemia, hyperornithinemia, homocitrullinuria (HHH) syndrome. Urine samples were prepared by mere five-fold dilution with a mixture of internal standards (²H₂-citrulline and ²H₃-creatinine) used for the simultaneous quantification of creatinine. Analytes were separated on a cyano column and eluted isocratically within seven min. Detection was achieved by monitoring transitions of 190 > 84 and 190 > 127 for homocitrulline, 178 > 115 for ²H₂-citrulline, 114 > 44 for creatinine and 117 > 47 for ²H₃-creatinine. Calibration curves were linear up to 100 micromol/L. Intraday (n = 7) and interday (n = 6) variations were less than 10%. In urine samples from three siblings confirmed to have HHH syndrome, homocitrulline levels were at 13.3 (74), 21.1 (50) and 108.2 (103) mmol/mol creatinine (micromol/L). Control values were 0–9 mmol/mol creatinine (n = 120). The current method solves specificity issues in homocitrulline determination often encountered with some ninhydrin-based systems (coelution with methionine) and some o-phthalaldehyde-based ones (coelution with taurine), and presents an attractive alternative with a relatively high throughput.     

Caging effects on the ground and excited states of 2,2'-bipyridine-3,3'-diol embedded in cyclodextrins

The 2,2'-bipyridine-3,3'-diol (BP(OH)(2)) molecule shows unique spectroscopic features in water that may position it as a new biological probe. In an attempt to mimic biological environments, we explore in this paper the caging effects of cyclodextrins on the steady state spectra of BP(OH)(2). The caging effects of gamma-, beta-, and 2,6-di-O-methyl-beta-cyclodextrins (CDs) on the ground and excited state properties of BP(OH)(2) in aqueous solutions are investigated by steady state absorption and fluorescence spectroscopy, and by ab initio calculations. The stoichiometry of the three complexes was found to be 1:1 and the binding constants were estimated from the absorption and fluorescence spectra. In the case of gamma-CD, the large cavity size supports only small binding, whereas such binding increases in the cases of the smaller cavity sizes of beta-CD and 2,6-di-O-methyl-beta-CD. Maximum binding was measured in the case of 2,6-di-O-methyl-beta-CD due to the increased hydrophobicity of the host cavity. The unique absorption features of BP(OH)(2) in water show a dramatic decrease in intensity due to caging effects. The decrease in intensity correlates very well with the extent of binding and hydrophobicity of the host molecules. Similar results were also obtained from the fluorescence spectra. The calculated structure of the BP(OH)(2):beta-CD complex predicts that the inclusion of BP(OH)(2) is nearly axial and centered inside the beta-CD cavity. The BP(OH)(2) molecule maintains its dienol moiety in the complex with no possible hydrogen bonding with the host interior H-atoms. The results are discussed in light of the possible use of BP(OH)(2) as a water sensor in biological systems.     

Designing of Zn (II)-based novel coordination polymer (CP): Synthesis,characterization, and heavy metal removal from water

A new coordination polymer, Zn-(OC-AMAM-CO) CP, has been synthesized from Zn (II) as ionic node and 2,2′-((1,2-phenylenebis [azanediyl])bis (carbonyl))dibenzoic acid, (OC-AMAM-CO), as a new linker, where (OC-AMAM-CO) has been synthesized as an amide product through condensation reaction of phthalic acid and o-phenylenediamine. The amide product (OC-AMAM-CO) and Zn-(OC-AMAM-CO) CP were characterized via FTIR and PXRD analyses, and Zn-(OC-AMAM-CO) CP was further characterized via SEM/EDX and XPS analyses. Moreover, DFT study was performed to shed light on the both structures of (OC-AMAM-CO) and Zn-(OC-AMAM-CO). PXRD analysis revealed the successful syntheses of the new linker (OC-AMAM-CO) and Zn-(OC-AMAM-CO) CP where the new CP is crystalline. DFT study revealed that the 3D topological structure assembled through coordination, π–π stacking, and hydrogen bonding. Zn-(OC-AMAM-CO) CP was applied as an adsorbent for the removal of Cu (II) from water as it has abundant chelating groups that serve as adsorptive coordinating sites. Isotherm study revealed the obedience of Cu (II)/Zn-(OC-AMAM-CO) CP adsorption system to Langmuir modeling with adsorption capacity of about 55 mg/g. A kinetic study showed that the rate of adsorption was a pseudo-first-order type. Further, adsorption process was found to be strongly diffusion dependent.