HPLC analysis of a syrup containing nimesulide and its hydrolytic degradation product

The present paper deals with the evaluation of nimesulide, 2-phenoxy-4-nitroaniline, the main hydrolytic degradation product of nimesulide, of methylparaben and propylparaben, and eventually of 4-hydroxybenzoic acid by HPLC with UV detection at 254 nm in syrup as a pharmaceutical formulation. HPLC analysis was employed on the reversed phase C18 with methanol and 0.01 M dibasic ammonium phosphate (ρ _r = 60: 40, pH 4.0). Validation was performed using standards and a pharmaceutical preparation containing the compounds described above.     

[Cu(X-salicylato)2(N,N-diethylnicotinamide)2(H2O)2] complexes: conformational polymorphism and its consequence in supramolecular hydrogen-bonding networks formation

Novel copper(II) X-salicylate complexes with N,N-diethylnicotinamide (dena) of the formula [Cu(RCOO)₂(dena)₂(H₂O)₂] (RCOO = 3-methylsalicylate anion (3-Mesal, 1), 4-methylsalicylate anion (4-Mesal, 2), 5-methylsalicylate anion (5-Mesal, 3), 5-methoxysalicylate anion (5-MeOsal, 4) or 4-methoxysalicylate anion (4-MeOsal, 5)), and complex [Cu(3-MeOsal)₂(dena)₂(H₂O)₂]∙2H₂O (3-MeOsal = 3-methoxysalicylate anion (6)) have been prepared in the crystalline forms and characterized by spectroscopic methods (IR, Vis–UV, EPR). All the compounds according to their composition (1–5) seem to possess octahedral copper(II) stereochemistry. The complex 1 has been prepared in two different forms. X-ray analyses of the complexes 1, 4, and 5 were carried out and they featured a tetragonal-bipyramidal geometry around the copper atoms. The tetragonal planes are created by X-salicylate anions bonded to the copper(II) atoms via unidentate carboxylate oxygen atoms and the pyridine ring nitrogen atoms of the neutral ligand N,N-diethylnicotinamide, while in axial positions are water molecules. The two forms of complex 1 present conformation polymorphs and supramolecular isomers.     

Gas phase and solution state stability of complexes L…M, where M = Cu, Ni, or Zn and L = R−C(O)NHOH (R = H, NH2, CH3, CF3, or Phenyl)

The structure and gas-phase metal affinities (M = Cu²⁺, Ni²⁺, and Zn²⁺) of formohydroxamic acid derivatives R–C(O)NHOH (R = H, NH₂, CH₃, CF₃ and Phenyl) were studied using the B3LYP/6-311+G(d,p) method of DFT theory. In order to evaluate the conformational behavior of these systems in water, we carried out CPCM-SCRF optimization calculations at the B3LYP/6-311+G(d,p) levels of theory. The obtained optimized geometries and interaction affinities of the gas and solution phase were compared. The following order of stability was found for ionic complexes of the transition metals: Cu²⁺ > Ni(t)²⁺ > Zn²⁺. The same stability order would be expected according to the Irving–Williams order of stability constants. The high-spin complexes of the Ni²⁺ were more stable than the low-spin complexes. The solvent effect reduced the observed relative stability of individual metallic complexes of substituted hydroxamic acids.     

Networking particles over distance using oligonucleotide-based devices

Microparticles covered with DNA-based computing elements that sense inputs and release oligonucleotides as outputs could be used to construct autonomous networks with increasingly complex functions. We demonstrate cascades of particles with up to three layers and a nonlinear network with an AND gate hub. In order to establish functional networks, particles do not have to be in direct physical contact.     

Method of fast trace microanalysis of the chiral pesticides epoxiconazole and novaluron in soil samples using off-line flow-through extraction and on-column direct large volume injection in reversed-phase high performance liquid chromatography

An analytical method combining off-line flow-through extraction of a soil micro-sample (mass around 100 mg, packed into a short HPLC glass column) and direct on-column large-volume injection (LVI up to 1.00 mL) of a methanol-water soil extract onto a conventional C18 RP HPLC column enabled fast (within 3.5 minutes) trace micro-analysis of the relatively new chiral pesticides epoxiconazole (E) and novaluron (N), respectively. Linear calibration curves were evaluated from UV detection (230 nm) data in the range from 0.1 to 5 mg/kg in three most abundant Slovak agricultural soils. LOD (confidence band) at the levels 0.08-0.11 mg/kg and LOQ 0.4-0.6 mg/kg and LOD (S/N = 3) at the levels 0.007-0.018 mg/kg and LOQ (S/N = 10) 0.024-0.060 mg/kg, respectively, of dry soil were achieved. Recovery of pesticides in the overall LVI method including flow-through 130-200 mg soil micro-sample extraction was: for epoxiconazole from 74 to 85% and from 56% to 90% for novaluron with reproducibility within +/- 6% RSD. This fast (30 min) and simple method consists of just three steps which are short column filling with a solid micro-sample; flow-through liquid extraction and direct large-volume injection RP HPLC DAD analysis. The method is prepared for automation and further analysis of enantiomers of both investigated pesticides by achiral-chiral column switching techniques.     

Conformational structure of some trimeric and pentameric structural units of heparin

The molecular structure of trimeric units (D-E-F and F-G-H) and the pentamer D-E-F-G-H of heparin (sodium salts and their anionic forms) was studied using the B3LYP/6-31G(d) method. The equilibrium structure of the sodium salts of the trimers and pentamer investigated in the isolated state was determined by multidentate coordination of the sodium cations with oxygen atoms of the sulfate, carboxyl, and hydroxyl (hydroxymethyl) groups, respectively. The displacement of Na+ ions from the binding sites in the sodium salt of oligosaccharides studied resulted in the appreciable change of the overall conformation of the corresponding anion. Upon dissociation, a large change in both the position of the sulfate groups and the conformation across the glycosidic bonds was observed. The stable energy conformations around the glysosidic bonds found for the pentamer investigated are compared and discussed with the available experimental X-ray structural data for the structurally related heparin-derived pentasaccharides in cocrystals with proteins.     

The thermodynamic dissociation constants of the anticancer drugs camptothecine, 7-ethyl-10-hydroxycamptothecine, 10-hydroxycamptothecine and 7-ethylcamptothecine by the least-squares nonlinear regression of multiwavelength spectrophotometric pH-titration data

The mixed dissociation constants of four anticancer drugs - camptothecine, 7-ethyl-10-hydroxycamptothecine, 10-hydroxycamptothecine and 7-ethylcamptothecine, including diprotic and triprotic molecules at various ionic strengths I of range 0.01 and 0.4, and at temperatures of 25 and 37 °C - were determined with the use of two different multiwavelength and multivariate treatments of spectral data, SPECFIT32 and SQUAD(84) nonlinear regression analyses and INDICES factor analysis. A proposed strategy for dissociation constants determination is presented on the acid-base equilibria of camptothecine. Indices of precise modifications of the factor analysis in the program INDICES predict the correct number of components, and even the presence of minor ones, when the data quality is high and the instrumental error is known. The thermodynamic dissociation constant was estimated by nonlinear regression of {pK_a, I} data at 25 and 37 °C: for camptothecine and 3.02(8), and 10.23(8); for 7-ethyl-10-hydroxycamptothecine, and 2.46(6), and 8.74(3), and 9.47(8); for 10-hydroxycamptothecine and 2.84(5), and 8.92(2), and 9.98(4); and for 7-ethylcamptothecine and 3.30(16), and 10.98(18). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates found to be proven. Pallas and Marvin predict pK_a being based on the structural formulae of drug compounds in agreement with the experimental value.     

High Sensitivity Analysis of Nanoliter Volumes of Volatile and Nonvolatile Compounds using Matrix Assisted Ionization (MAI) Mass Spectrometry

First results are reported using a simple, fast, and reproducible matrix-assisted ionization (MAI) sample introduction method that provides substantial improvements relative to previously published MAI methods. The sensitivity of the new MAI methods, which requires no laser, high voltage, or nebulizing gas, is comparable to those reported for MALDI-TOF and n-ESI. High resolution full acquisition mass spectra having low chemical background are acquired from low nanoliters of solution using only a few femtomoles of analyte. The limit-of-detection for angiotensin II is less than 50 amol on an Orbitrap Exactive mass spectrometer. Analysis of peptides, including a bovine serum albumin digest, and drugs, including drugs in urine without a purification step, are reported using a 1 μL zero dead volume syringe in which only the analyte solution wetting the walls of the syringe needle is used in the analysis.

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Molecular distortion effect on ff-emission in a Pr(III) complex with 4,7-diphenyl-1,10-phenanthroline.

The electronic and structural behaviour of a Pr(III) complex with 4,7-diphenyl-1,10-phenanthroline, [Pr(bathophen)(2)(NO(3))(3)], is investigated with respect to the effect of configuration changes on the Pr(III) centre. [Pr(bathophen)(2)(NO(3))(3)] luminesces from the excited states of the ligand and the metal ion. The fluorescence, ff-emission ((1)D(2)-->(3)H(4)), and phosphorescence bands appear at 394, 608.2 and 482 nm, respectively, in the solid state. In acetonitrile, the complex also shows multiple emissions. From the time-resolved emission and the lifetime measurements, the excitation energy-transfer in [Pr(bathophen)(2)(NO(3))(3)] is clarified, that is, the upper excited triplet level of the ligand acts as an energy donor, while the (1)D(2) levels of Pr(III) is the acceptor. Additionally, the emission phenomena of the complex can be modified by molecular distortion, particularly by rotation of the phenyl groups in the ligand.