Intercalator-DNA interactions revealed by NIR surface-enhanced Raman spectroscopy

Using 1064 nm excited surface-enhanced Raman spectroscopy (SERS) a well known intercalator, ethidium bromide (EB), and a structurally related compound, 4-methyl-2,7-diamino-5,10-diphenyl-4,9-diazapyrenium hydrogensulfate (ADAP), have been studied. Concentration dependent SERS spectra of both aromatic species (1 × 10⁻⁷-5 × 10⁻⁵ M) indicated existence of dimeric associates at high concentration and an equilibrium shift towards monomers with a concentration decrease. Interactions of the intercalating molecules with DNA have been studied for various intercalator/DNA (base pair) molar ratios ranging from 10/1 to 1/10. In colloidal samples containing an intercalator in excess relative to DNA binding sites (from 10/1 to 2/1) enhancement of the Raman scattering gradually weakened, indicating a decrease in a number of free molecules adsorbed on the metal surface due to binding with DNA. At the drug/DNA ratios of 1/2 and 1/5 weaker but observable SERS bands indicated insertion of the drug molecules between the base pairs (intercalation strongly diminished interaction of the drug molecules with metal surface) as well as non-intercalative binding of the drug molecules able to stay in closer contact with a metal surface. A total intercalation of EB and ADAP molecules (intercalator/DNA of 1/7 and 1/10) resulted in almost complete loss of the SERS signal. Intensity of the SERS spectra of the intercalator/DNA complexes relative to the SERS intensity of the free intercalating molecules diminished to a lesser degree for ADAP/DNA than for EB/DNA. The obtained difference was attributed to a larger aromatic surface of the ADAP molecules which, although intercalated, could be positioned near the enhancing nanoparticles, unlike the smaller EB molecules which were deeply inserted within the DNA helix.     

Kinetics of the substitution reactions of some Pt(II) complexes with 5′‐GMP and L‐histidine

The reactions of platinum(II) complexes, [PtCl₂(dach)] (dach = (1R,2R)‐1,2‐diaminocyclohexane) and [PtCl₂(en)] (en = ethylenediamine) with biologically relevant ligands such as 5′‐GMP (guanosine‐5′‐monophosphate) and l ‐His (l ‐histidine) were studied by UV–vis spectrophotometry, ¹H NMR spectroscopy, and high‐performance liquid chromatography (HPLC). Spectrophotometrically, these reactions were investigated under pseudo‐first‐order conditions at 310 K in 25 mM Hepes buffer (pH 7.2) and 10 mM NaCl to prevent the hydrolysis of the complexes. The [PtCl₂(en)] complex reacts faster than [PtCl₂(dach)] in the reaction with studied nucleophiles. This confirms the fact that the reactivity of studied Pt(II) complexes depends on the structure of the inert bidentate ligand. Also, the substitution reactions with l ‐His are always faster than the reactions with nucleotide 5′‐GMP. The reactions of [PtCl₂(dach)] and [PtCl₂(en)] complexes with l ‐histidine are studied by ¹H NMR spectroscopy. The obtained rate constants are in agreement with those obtained by UV–vis. The same reactions were studied by HPLC comparing the obtained chromatograms during the reaction. The changes in intensity of signals of the free and coordinated ligand show that after a few days there is only one dominant product in the system. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 99–106, 2011     

Metalization of polymer beads via polymer‐supported hydrazines as reducing agents

A new method for depositing metal onto a polymer surface has been developed in which the metal coating of polymer beads is performed with hydrazine functions as reducing agents on the surface of the polymer itself. In this study, glycidyl methacrylate–methyl methacrylate–divinyl benzene terpolymer was prepared as spherical beads with a suspension polymerization methodology. Beads of the polymer sample (210–420‐μm fraction) containing 3.4 mmol g^?1 epoxy were treated with an excess of hydrazinium hydroxide to yield a polymer with 2.3 mmol g^?1 hydrazine functions. The hydrazine functions on the polymer surfaces were efficient in metal reductions. Therefore, the modified bead polymer samples, when soaked in aqueous ammonia solutions of Ni(II), Ag(I), and Cu(II) ions (0.1 M), were covered rapidly by the corresponding zero‐valent metal ions. Metal deposition took place almost quantitatively (ca. 4.5 mmol/g of the polymer) within 60 min of the contact times. The accumulations of metal were followed visually and occurred only on the polymer beads. There was no evidence that the reaction occurred within the solution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 748–754, 2002; DOI 10.1002/pola.10158     

Influence of substitution at the benzylic position on the behavior of stereoisomeric phosphorus compounds as precursors of stabilized carbon-centered radicals

Efficient benzylic radical formation from benzo[d]-1,2-oxaphospholes has demonstrated their suitability as precursors of stabilized C-centered radicals, a property associated with antioxidant potential. A remarkable stereodifferentiation is observed for alkyl- and aryl-substituted derivatives. [reaction: see text]     

1H‐Pyrrolo[2,3‐b]pyridine‐3‐acetic acid as a molecular probe for use in auxin physiology

The structural characterization of 1H‐pyrrolo­[2,3‐b]­pyridine‐3‐acetic acid (alternative name: 7‐aza­indole‐3‐acetic acid), C₉H₈N₂O₂, reveals similar molecular geometry, i.e. with the side chain perpendicular to the 7‐aza­indole ring, to that of the natural plant growth hormone indole‐3‐acetic acid (auxin) and its alkyl­ated and halogenated derivatives.     

A multiscale approach to thermoplastic deformation

The paper applies a multiscale formulation to thermoplasticity problems. The plasticity model is based on the variationally consistent formulation at the micro level. It is suitable for problems involving large strains. The temperature field is calculated at the macro level and is assumed to be homogeneous at the micro level. The proposed formulation is implemented in the Abaqus software by means of user subroutines. User subroutines are introduced both at the macro and at the micro level. The consistent tangent operator is calculated by the numerical differentiation procedure. Implementation details are briefly addressed. Finally, the methodology is verified on a representative example and relevant results are presented and discussed. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Development and validation of an HPLC method for the determination of verapamil residues in supports of cleaning procedure

Analytical method validation, determining the recovery rate from the equipment surface, and stability of a potential contaminant are important steps of a cleaning validation process. An HPLC method for the determination of the verapamil residues on stainless steel surfaces of the equipment employed in drug manufacture is described. The cleaning validation sample impurities as well as excipients of the commercial sample did not interfere in the analysis which proved the selectivity of the method. The validation of the method demonstrated acceptable levels of the linearity, precision and accuracy. Cotton swabs, moistened with methanol were used to remove any residues of drugs from stainless steel surfaces, and give recoveries of above 78.59% for three diferent concentration levels. The precision of the results, reported as the relative standard deviation (RSD, %), were below 1.58%. Low quantities of the drug residues were determined by HPLC using a Hypersil ODS column (125 × 4.0 mm, 5 μm) at 25°C with the mobile phase metanol-water-triethylamine (70: 30: 0.2, v/v/v) at a flow rate of 0.6 mL/min, injection volume of 50 μL and detection at 278 nm.     

Physical and Bioengineering Properties of Polyvinyl Alcohol Lens-Shaped Particles Versus Spherical Polyelectrolyte Complex Microcapsules as Immobilisation Matrices for a Whole-Cell Baeyer–Villiger Monooxygenase

Direct comparison of key physical and chemical-engineering properties of two representative matrices for multipurpose immobilisations was performed for the first time. Polyvinyl alcohol lens-shaped particles LentiKats® and polyelectrolyte complex microcapsules were characterised by advanced techniques with respect to the size distribution of the particles, their inner morphology as revealed by fluorescent probe staining, mechanical resistance, size-exclusion properties, determination of effective diffusion coefficient and environmental scanning electron microscope imaging. While spherical polyelectrolyte complex microcapsules composed of a rigid semipermeable membrane and a liquid core are almost uniform in shape and size (diameter of 0.82 mm; RSD?=?5.6 %), lens-shaped LentiKats® are characterised by wider size distribution (diameter of 3.65 mm; RSD?=?10.3 % and height of 0.341 mm; RSD?=?32.3 %) and showed the same porous structure throughout their whole volume at the mesoscopic (micrometre) level. Despite differences in their inner structure and surface properties, the pore diameter of?～?2.75 nm for regular polyelectrolyte complex microcapsules and?～?1.89 nm for LentiKats® were similar. These results were used for mathematical modelling, which provided the estimates of the effective diffusion coefficient of sucrose. This value was 1.67?×?10^?10 m² s^?1 for polyelectrolyte complex microcapsules and 0.36?×?10^?10 m² s^?1 for LentiKats®. Recombinant cells Escherichia coli-overexpressing enzyme cyclopentanone monooxygenase were immobilised in polyelectrolyte complex microcapsules and LentiKats® for comparison of their operational stability using model Baeyer–Villiger oxidation of (±)-cis-bicyclo [3.2.0] hept-2-en-6-one to regioisomeric lactones as important chiral synthons for potential pharmaceuticals. Both immobilisation matrices rendered high operational stability for whole-cell biocatalyst with no reduction in the biooxidation rate over 18 repeated reaction cycles.     

Supercritical CO2 Extract from Microalga Tetradesmus obliquus: The Effect of High-Pressure Pre-Treatment

High-pressure pre-treatment followed by supercritical carbon dioxide (ScCO₂) extraction (300 bar, 40 °C) was applied for the attainment of the lipophilic fraction of microalga Tetradesmus obliquus. The chemical profile of supercritical extracts of T. obliquus was analyzed by ultra-high-performance liquid chromatography–high-resolution mass spectrometry with electrospray ionization (UHPLC-ESI-HRMS). Moreover, the impact of ScCO₂ on the microbiological and metal profile of the biomass was monitored. The application of the pre-treatment increased the extraction yield approximately three-fold compared to the control. In the obtained extracts (control and pre-treated extracts), the identified components belonged to triacylglyceroles, fatty acid derivatives, diacylglycerophosphocholines and diacylglycerophosphoserines, pigments, terpenes, and steroids. Triacylglycerols (65%) were the most dominant group of compounds in the control extract. The pre-treatment decreased the percentage of triacylglycerols to 2%, while the abundance of fatty acid derivatives was significantly increased (82%). In addition, the pre-treatment led to an increase in the percentages of carotenoids, terpenoids, and steroids. Furthermore, it was determined that ScCO₂ extraction reduced the number of microorganisms in the biomass. Considering its microbiological and metal profiles, the biomass after ScCO₂ can potentially be used as a safe and important source of organic compounds.