Automation of solid-phase microextraction on a 96-well plate format

Studies have been performed assessing the feasibility and characterizing the automation of solid-phase microextraction (SPME) on a multi-well plate format. Four polycyclic aromatic hydrocarbons (PAHs), naphthalene, fluorene, anthracene and fluoranthene, were chosen as test analytes to demonstrate the technique due to their favorable partition coefficients, K(fw), between polydimethylsiloxane (PDMS) extraction phases and water. Four different PDMS configurations were investigated regarding their suitability. These included (i) a PDMS membrane; (ii) a multi-fiber device containing lengths of PDMS-coated flexible wire; (iii) a stainless steel pin covered with silicone hollow fiber membrane and (iv) commercial PDMS-coated flexible metal fiber assemblies. Of these configurations, the stainless steel pin covered with silicone tubing was chosen as a robust alternative. An array of 96 SPME devices that can be placed simultaneously into a 96-well plate was constructed to demonstrate the high-throughput potential when performing multiple microextractions in parallel. Different agitation methods were assessed including magnetic stirring, sonication, and orbital shaking at different speeds. Orbital shaking whilst holding the SPME device in a stationary position provided the optimum agitation conditions for liquid SPME. Once the analytes had been extracted, desorption of the analytes into an appropriate solvent was investigated. Liquid-phase SPME and solvent desorption on the multi-well plate format is shown to be a viable alternative for automated high-throughput SPME analysis compatible with both gas- and liquid-chromatography platforms.     

Semisynthetic Derivatives of Selected Amaryllidaceae Alkaloids as a New Class of Antimycobacterial Agents

The search for novel antimycobacterial drugs is a matter of urgency, since tuberculosis is still one of the top ten causes of death from a single infectious agent, killing more than 1.4 million people worldwide each year. Nine Amaryllidaceae alkaloids (AAs) of various structural types have been screened for their antimycobacterial activity. Unfortunately, all were considered inactive, and thus a pilot series of aromatic esters of galanthamine, 3-O-methylpancracine, vittatine and maritidine were synthesized to increase biological activity. The semisynthetic derivatives of AAs were screened for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Ra and two other mycobacterial strains (M. aurum, M. smegmatis) using a modified Microplate Alamar Blue Assay. The most active compounds were also studied for their in vitro hepatotoxicity on the hepatocellular carcinoma cell line HepG2. In general, the derivatization of the original AAs was associated with a significant increase in antimycobacterial activity. Several pilot derivatives were identified as compounds with micromolar MICs against M. tuberculosis H37Ra. Two derivatives of galanthamine, 1i and 1r, were selected for further structure optimalization to increase the selectivity index.     

Highly Enantioselective Synthesis of 1,2,3‐Substituted Cyclopropanes by Using α‐Iodo‐ and α‐Chloromethylzinc Carbenoids

Herein, we report the enantio‐ and diastereoselective formation of trans‐iodo‐ and trans‐chlorocyclopropanes from α‐iodo‐ and α‐chlorozinc carbenoids by using a dioxaborolane‐derived chiral ligand. The synthetically useful iodocyclopropane building blocks were derivatized by an electrophilic trapping of the corresponding cyclopropyl lithium species or a Negishi coupling to give access to a variety of enantioenriched 1,2,3‐substituted cyclopropanes. The synthetic utility of this method was demonstrated by the formal synthesis of an HIV‐1 protease inhibitor. In addition, the related stereoselective bromocyclopropanation was also investigated. New insights about the relative electrophilicity of haloiodomethylzinc carbenoids are also presented.     

Development of palladium-carbene catalysts for telomerization and dimerization of 1,3-dienes: from basic research to industrial applications

The following account summarises recent developments in the area of palladium-catalysed telomerisation and dimerisation reactions of 1,3-dienes. The most active types of catalyst, palladium-carbene complexes, were tested in pilot plant and proved to be industrially viable.     

Hydrophilic interaction liquid chromatography – charged aerosol detection as a straightforward solution for simultaneous analysis of ascorbic acid and dehydroascorbic acid

Ascorbic acid (AA) and dehydroascorbic acid (DHA) are small polar molecules difficult to be retained in conventional chromatographic RP systems. Hydrophilic interaction liquid chromatography (HILIC) using Obelisk R (100 × 3.2 mm, 5 μm, Sielc) analytical column and isocratic elution by ammonium acetate buffer pH 4.2 was found to be successful at this task, while other tested HILIC columns – Obelisk N (100 × 3.2 mm, 5 μm, Sielc) and Luna HILIC (100 × 3.0 mm, 3 μm, Phenomenex) were unsuccessful for the purposes of analysis. Charged aerosol detection (CAD) has recently become a new alternative universal detection system in HPLC, and was extremely convenient for the simultaneous analysis of AA and DHA without the need of subtraction approach and oxidation/reduction step. CAD response was found linear in defined range in spite of the fact that CAD is designated as non-linear detection method. A simple and fast HILIC-CAD method was applied for the analysis of pharmaceutical preparations containing AA. Method validation was performed including parameters of precision, accuracy, linearity, limit of detection and limit of quantitation (LOQ). The method was fast, accurate and precise for both detectors with LOQ_AA 5 μg/ml for UV detection and 10 μg/ml for CAD, respectively. DHA was detected only by CAD within tested concentration range with LOQ_DHA 1 μg/ml.     

Study of the retention behavior of small polar molecules on different types of stationary phases used in hydrophilic interaction liquid chromatography

The retention behavior of a large group of analytes (35) with varied properties (pK_a and logP) was studied on eight hydrophilic interaction LC columns with different surfaces, stationary phase chemistries, and types of particles. The acetonitrile content (5–95%), buffer concentration (0.5–200 mM), and pH of the mobile phase (3.8 and 6.8) were evaluated for their effects on the retention behavior. The type of stationary phase had a significant impact on the selectivity and retention time of the tested analytes. Completely different selectivity was observed on the aminopropyl stationary phase. In this study, the influence of the buffer concentration was similar for all tested columns, except for the aminopropyl stationary phase. Increasing the buffer concentration led to decreased retention times for the basic compounds and increased retention times for the acidic compounds, while the inverse behavior was observed on the aminopropyl stationary phase. The selectivity of the individual stationary phases was evaluated at pH 3.8 and 6.8. Much lower selectivity differences between the stationary phases were observed at pH 6.8 than pH 3.8. Bare silica stationary phases were used in the comparison of the particles (fused‐core and fully porous particles of 3 and 1.7 μm) and the columns provided by different manufacturers.     

Hydrophilic interaction liquid chromatography method for the determination of ascorbic acid

Hydrophilic interaction liquid chromatography (HILIC) method using internal standard for the determination and stability study of ascorbic acid was developed. HILIC method was very fast and simple using the following analytical conditions: ZIC HILIC (150 x 2.1 mm, 3.5 microm) chromatographic column and mobile phase composed of ACN and 50 mM ammonium acetate buffer pH 6.8 (78:22 v/v). Diode array detection was performed and chromatograms were processed at 268 nm, the maximum wavelength of absorbance of ascorbic acid. An extensive stability study of ascorbic acid as a function of various factors including temperature, stabilizing agents, oxygen presence and its concentration in solution was performed in order to gain information about the quantitative influence of individual stability factors. Low temperature and stabilizing agents (o-phosphoric acid and oxalic acid) were found to be key factors enabling substantial enhancement of the stability of ascorbic acid.     

Aligned rank tests in measurement error model

Aligned rank tests are introduced in the linear regression model with possible measurement errors. Unknown nuisance parameters are estimated first and then classical rank tests are applied on the residuals. Two situations are discussed: testing about an intercept in the linear regression model considering the slope parameter as nuisance and testing of parallelism of several regression lines, i.e. whether the slope parameters of all lines are equal. Theoretical results are derived and the simulation study is also made to illustrate good performance of introduced tests.     

Influence of UV irradiation and subsequent chemical grafting on the surface properties of cellulose

Cellulose - This work is devoted to the study of surface properties of cellulose before and after a surface modification. Surface modification of polymeric materials was carried out in two steps:...     

Influence of oxygen concentration on optical properties of semi-insulating polycrystalline silicon films

Optical properties of semi-insulating polycrystalline silicon (SIPOS) films were investigated over the wide region of wavelengths. The vibrational modes of Si-O-Si and Si-Si bonds were studied by IR and Raman spectroscopy. A pronounced effect of oxygen content on the measured spectra was observed. Optical constants of SIPOS films have been compared with those of amorphous silicon and glassy silicon dioxide and their values have been successfully interpreted in terms of the theory of effective medium. The results have shown that the amorphous character prevails in the as-deposited SIPOS films.