Intensity clamping and re-focusing of intense femtosecond laser pulses in nitrogen molecular gas

We present results of measurements of fluorescence spectra due to the interaction of a Ti:sapphire laser pulse with N₂ molecules at different gas pressures and pulse energies. The analysis of the data together with the results of numerical simulations, using a propagation model, reveal signatures of the phenomena of intensity clamping and of re-focusing of the laser pulse at high gas pressure. The laser pulse energy for intensity clamping as a function of the gas pressure is determined. Received: 21 May 2001 / Revised version: 10 July 2001 / Published online: 19 September 2001     

Piperidinium 3‐[(4‐hydroxy‐5,7‐di­methyl‐2‐oxo‐2H‐chromen‐3‐yl)­phenyl­methyl]‐5,7‐di­methyl‐2‐oxo‐2H‐chromen‐4‐olate

In the title salt, C₅H₁₂N⁺·C₂₉H₂₃O₆^?, both benzo­pyran systems are planar. Intermolecular N—H?O hydrogen bonds and a short O—H?O intramolecular hydrogen bond are observed in the structure.     

A simple uric acid assay by using 3-hydroxytyramine as a chromogenic colorimetric sensor in human serum samples: Density functional theory supported mechanistic approach

A simple, fast, sensitive, convenient, and economical accurate enzymatic colorimetric sensor is developed for the quantification of the clinically important biomarker uric acid (UA) in human serum samples. The method is based on the quantification of UA using 3-hydroxytyramine (3-HT) as a chromogenic substrate by using peroxidase (POD) and uricase (UOx). UOx catalyzes the oxidation of UA where H₂O₂ is generated in-situ to produce allantoin and CO₂. The POD in oxidative coupling of peroxide in presence of 3-HT, forms an intense orange-colored product with λ_max = 500 nm. The reaction was carried out in a citric acid-tripotassium-citrate buffer (12.5 mM) of pH = 6.8 at room temperature. Computational calculations were done by Gaussian-16 employing the B3LYP functional basis set. The standard curve for UA was found to be linear between 12.3–297.3 and 3.07–396.5 μM by rate and fixed time method, respectively. The LOD and LOQ for UA were 1.5 and 2.9 μM, respectively. Within-day and day-to-day precision was 1.50–3.07 and 3.10–4.16% (n = 7), respectively. The accuracy ranges for UA concentrations of 24.7, 198 and 297.3 μM were 87%–101.50%, 90%–105%, and 89%–107%, respectively. The UA recovery range by the proposed method was 98.00%–100.47% with a mean recovery of 99.5% and has A good correlation coefficient of 0.981 with the standard method.