Derivatization of substances,separated on thin-layer plates,by means of an automatic spraying device

Summary An accurate and reproducible derivatization of substances, separated on TLC- and HPTLC-plates, can be achieved by mechanized spraying. The plate is moved horizontally to and fro, whilst the spraying vessel is driven up and down. The extent of movement and distance of the vessel from the plate are both adjustable.     

A fast microwave-assisted,acid-vapor,steam-cleaning procedure for autosampler cups

A new and fast procedure is proposed for cleaning autosampler cups using acid-vapor steam-cleaning with a miniaturized assembly in a microwave-heated sealed Teflon vessel. A glass cactus-shaped holder was made to support six polyethylene autosampler cups (volume, 2.0 mL) inside a 100 mL microwave vessel. Regent-grade nitric acid was added to the vessels, and the system was heated in a microwave oven for 5 min at 300 W. Chromium was determined by graphite-furnace atomic-absorption spectrophotometry. The blank values were lower with cleaned cups compared to untreated cups (i.e., as received from supplier). The quantification limits, estimated from detection limits established with Milli-Q water, were 0.66 and 0.95 μg Cr L⁻¹ for cleaned and untreated auto-sampler cups, respectively.     

Glutaraldehyde treatment of bacterial cellulose/fibrin composites: impact on morphology, tensile and viscoelastic properties

Bacterial cellulose/fibrin composites were treated with glutaraldehyde in order to crosslink the polymers and allow better match of the mechanical properties with those of native small-diameter blood vessels. Tensile and viscoelastic properties of the glutaraldehyde treated composites were determined from tensile static tests and cyclic creep tests, respectively. Glutaraldehyde-treated (bacterial cellulose) BC/fibrin composites exhibited tensile strength and modulus comparable to a reference small-diameter blood vessel; namely a bovine coronary artery. However, the breaking strain of the glutaraldehyde-treated composites was still well below that of the native blood vessel. Yet a long strain hardening plateau was induced by glutaraldehyde treatment which resembled the stress–strain response of the native blood vessel. Tensile cyclic creep test indicated that the time-dependent viscoelastic behavior of glutaraldehyde-treated BC/fibrin composites was comparable to that of the native blood vessel. Covalent bonding between BC and fibrin occurred via glutaraldehyde, affording mechanical properties comparable to that of the native small blood vessel.     

Direct ICP-MS determination of trace and ultratrace elements in geological materials after decomposition in a microwave oven. Part II. Quantitation of Ba, Cs, Ga, Hf, In, Mo, Nb, Pb, Rb, Sn, Sr, Ta and Tl

A new method has been developed for the rapid determination of traces of Ba, Cs, Ga, Hf, In, Mo, Nb, Pb, Rb, Sn, Sr, Ta and Tl in silicate rocks and lake, stream and river sediments. The method involved dissolution of samples in a microwave oven by heating in a pressure decomposition Teflon vessel with a mixture of HF + HNO₃ + HCl + H₃BO₃ + EDTA followed by direct multielement determination using inductively coupled plasma-mass spectrometry (ICP/MS). The method is faster than conventional dissolution of samples by open vessel acid digestion and fusion and determination by instrumental methods. The accuracy and precision of the developed method were tested by replicate analyses of a number of international geochemical reference samples of established trace element contents. Satisfactory correlation with the “recommended” or “consensus” values was found and recoveries were in most cases 95–100%. New values for Ga, In, Nb and Tl in several international geochemical reference materials are first reported in this paper.     

Vessel effects in organic chemical reactions; a century-old,overlooked phenomenon

One of the most intriguing aspects of synthetic chemistry is the interplay of numerous dependent and independent variables en route to achieve a successful, high-yielding chemical transformation. The experienced synthetic chemist will probe many of these variables during reaction development and optimization, which will routinely involve investigation of reaction temperature, solvent, stoichiometry, concentration, time, choice of catalyst, addition sequence or quenching conditions just to name some commonly addressed variables. Remarkably, little attention is typically given to the choice of reaction vessel material as the surface of common laboratory borosilicate glassware is, incorrectly, assumed to be chemically inert. When reviewing the scientific literature, careful consideration of the vessel material is typically only given during the use of well-known glass-etching reagents such as HF, which is typically only handled in HF-resistant, polyfluorinated polymer vessels. However, there are examples of chemical transformations that do not involve such reagents but are still clearly influenced by the choice of reaction vessel material. In the following review, we wish to condense the most significant examples of vessel effects during chemical transformations as well as observations of container-dependent stability of certain molecules. While the primary focus is on synthetic organic chemistry, relevant examples from inorganic chemistry, polymerization reactions, atmospheric chemistry and prebiotic chemistry are also covered.

One of the most intriguing aspects of synthetic chemistry is the interplay of numerous dependent and independent variables en route to achieve a successful, high-yielding chemical transformation.     

Towards a continuous dynamic kinetic resolution of 1-phenylethylamine using a membrane assisted, two vessel process

A continuous process with two separated reaction vessels provides a solution to the problems surrounding the combination of two catalysts in dynamic kinetic resolution reactions by retaining the biocatalyst in a lower temperature vessel with a microfiltration membrane and allowing the racemisation to occur efficiently in a higher temperature vessel.     

A novel approach to decomposition of foodstuffs for stripping voltammetric determination of lead,cadmium and copper

Samples (ca. 0.3 g) are digested in 10-ml quartz vessels and the same vessel is used for anodic stripping voltammetry. Thus possible contamination during handling and dilution of the decomposed sample solution are avoided. A special design of column placed over the vessel provides digestion under reflux conditions without leakage and a glass cap fitted to another condenser enables the residual mineral acids (especially sulfuric acid) to be boiled out under low pressure conditions. The usual PTFE holder for electrodes and gas tubes is modified to facilitated insertion of the 10-ml vessel underneath. The system was checked on NBS standard reference materials (wheat flour and rice flour) and tested for the determinaton of Cd, Pb and Cu in baby foods. The limits of detection obtained for 3-min decomposition times were 0.3 ng g^?1, 4 ng g^?1 and 8 ng g^?1 for cadmium, lead and copper, respectively. The levels of these elements in various commercial baby foods are given.     

Calorimetric sensing in bioanalytical chemistry: Principles, applications and trends

Calorimetry has shown great potential in bioanalytical chemistry as most biochemical processes involve a change in enthalpy. Two types of approach have been developed: (1) adiabatic calorimetry, which relies on the absence of heat exchange between the reaction vessel and the external environment, and (2) heat conduction calorimetry, involving measurement of the heat transferred from the vessel to a surrounding heat sink. Both principles, with their respective advantages and drawbacks, have been applied to microcalorimetry for the analysis of (bio)chemical compounds. Immobilization of the biomaterial in the vicinity of, or directly onto a small temperature or heat sensitive transducer has led to the concept of a calorimetric biosensor. In comparison to the traditional calorimeter, the calorimetric biosensor is better suited to continuous monitoring and size reduction. This simplified but sensitive device is expected to solve numerous problems in various fields of analytical chemistry.     

One-pot, multicomponent route to pyrazoloquinolizinones

[reaction: see text] An efficient synthesis of 5a-hydroxy-4,5,5a,6,7,8-hexahydropyrazolo[4,3-c]quinolizin-9-ones based on the three-component condensation of 5-aminopyrazoles, aromatic aldehydes, and cyclic 1,3-diketones is described. The multicomponent reaction is performed under strongly basic conditions applying controlled microwave heating in a sealed vessel and involves an unusual base-mediated ring-opening/recyclization of the cyclic 1,3-diketone moiety.     

Photochemical mineralization of europium, titanium, and iron oxyhydroxide nanoparticles in the ferritin protein cage

The Fe storage protein ferritin was used as a size-constrained reaction vessel for the photoreduction and reoxidation of complexed Eu, Fe, and Ti precursors for the formation of oxyhydroxide nanoparticles. The resultant materials were characterized by dynamic light scattering, gel electrophoresis, UV-vis spectroscopy, and transmission electron microscopy. The photoreduction and reoxidation process is inspired by biological sequestration mechanisms observed in some marine siderophore systems.     

Combinatorial Chemistry Online - Volume 4, Issue 12, December 2002

Current literature highlights: Thrombin is a trypsin-like serine protease which plays a crucial role in blood coagulation by cleaving soluble fibrinogen into fibrin. Subsequent polymerisation of fibrin stabilises the initially formed thrombozyte clots at the site of blood vessel damage. Undesired activation of the blood coagulation cascade can result in cardiovascular disorders such as deep vein thrombosis, myocardial infarction, unstable angina, pulmonary embolism and ischaemic stroke. Thrombin has therefore become an important target for the treatment of thromboembolic diseases.     

Computerized technique in organic microelemental analysis: Part IV: Automated determination of chlorine,bromine, and iodine in organic compounds

The automatic and computerized rapid microanalytical determination of chlorine, bromine, and iodine in organic and organometallic compounds is described. The method consists of combustion of the compound in a large diameter empty tube connected to a titration vessel. The combustion products are transferred from the end of the combustion tube to the titration vessel by means of an automatic reductive SO₂-containing wash. Automatic potentiometric titration with AgClO₄ to the preset endpoint potential, using a combination silver microelectrode, serves as the endpoint detection of the titration of halides. The entire analysis, including automatic preparation of the equipment for the next determination, is programmed in a 6-min cycle. The method is blank-free; the results are accurate. Standard deviations amount to: 0.05, 0.14, and 0.18% absolute for Cl, Br, and I, respectively.The analyzer is interfaced to a real-time, time-sharing computer along with electronic microbalances and other analyzers, as part of the microanalytical laboratory computer service. The results of the analyses are reported on CR-terminals and are stored on magnetic disk for further processing.     

Endothelial cell-pericyte interactions stimulate basement membrane matrix assembly: influence on vascular tube remodeling, maturation, and stabilization

Extracellular matrix synthesis and deposition surrounding the developing vasculature are critical for vessel remodeling and maturation events. Although the basement membrane is an integral structure underlying endothelial cells (ECs), few studies, until recently, have been performed to understand its formation in this context. In this review article, we highlight new data demonstrating a corequirement for ECs and pericytes to properly deposit and assemble vascular basement membranes during morphogenic events. In EC only cultures or under conditions whereby pericyte recruitment is blocked, there is a lack of basement membrane assembly, decreased vessel stability (with increased susceptibility to pro-regressive stimuli), and increased EC tube widths (a marker of dysfunctional EC-pericyte interactions). ECs and pericytes both contribute basement membrane components and, furthermore, both cells induce the expression of particular components as well as integrins that recognize them. The EC-derived factors--platelet derived growth factor-BB and heparin binding-epidermal growth factor--are both critical for pericyte recruitment to EC tubes and concomitant vascular basement membrane formation in vitro and in vivo. Thus, heterotypic EC-pericyte interactions play a fundamental role in vascular basement membrane matrix deposition, a critical tube maturation event that is altered in key disease states such as diabetes and cancer.     

Evaluation of a sensitive,reasonable, and fast detection method for 55Fe in steel

Journal of Radioanalytical and Nuclear Chemistry - A pilot study to quantify 55Fe in steel from a reactor vessel of a nuclear power plant by accelerator mass spectrometry (AMS) without any chemical...     

Minimising the risk of some systematic errors by the use of the single vessel principle for cold vapour atomic absorption spectrometric determination of mercury in biological solids

The suitability of the single vessel principle (performing all steps of an analytical procedure in one vessel) for cold vapour atomic absorption spectrometric determination of mercury in biological solids was evaluated. The single vessel method gave a lower mean blank level with better precision, hence lower detection limits, as compared to the conventional method. The determination of total mercury in biological standard reference materials by the single vessel method also produced significantly higher mercury values and better precision than the conventional method. However, the mercury concentrations obtained in certified reference materials by the use of both methods were close to the mean certified values. Moreover, the use of the single vessel method is cost effective, rapid and environment friendly. The use of the single vessel technique is therefore recommended for accurate and reliable determination of mercury in biological solids.     

THE EFFECTS OF PHOTODYNAMIC THERAPY USING DIFFERENTLY SUBSTITUTED ZINC PHTHALOCYANINES ON VESSEL CONSTRICTION, VESSEL LEAKAGE AND TUMOR RESPONSE

Abstract— The effects of four different zinc phthalocyanines were studied during and after photodynamic therapy (PDT). Measurements of vessel constriction, vessel leakage, tumor interstitial pressure, eicosanoid release, and tumor response of chondrosarcoma were made in Sprague-Dawley rats. Animals were injected intravenously with 1 μmol/ kg of mono-, di-, or tetrasulfonated zinc phthalocyanine, or 1 μmol/kg of a zinc phthalocyanine substituted with four tertiary butyl groups. Tissues were exposed to 400 J/cm² 670 nm light 24 h after photosensitizer injection. An additional group of animals was given indomethacin before treatment. The use of the monosulfonated and tertiary butyl substituted zinc phthalocyanines in PDT caused the release of specific eicosanoids, caused vessel constriction, and induced venule leakage and increases in tumor interstitial pressure. Tumor cures of 27% and 7% were observed. Photodynamic therapy using the disulfonated zinc phthalocyanine did not induce vessel constriction or the release ofeicosanoids, however; tumor cure was 43%. The use of thc tetrasulfonated zinc phthalocyanine caused intermediate effects between the mono- and disulfonated compounds. The administration of indornethacin to animals completely inhibited the effects of PDT using the monosulfonated compound but had minimal effects on treatment using the disulfonated compound. This suggests that the monosulfonated and disulfonated compounds act by different mechanisms of destruction.     

Minimising the risk of some systematic errors by the use of the single vessel principle for cold vapour atomic absorption spectrometric determination of mercury in biological solids

The suitability of the single vessel principle (performing all steps of an analytical procedure in one vessel) for cold vapour atomic absorption spectrometric determination of mercury in biological solids was evaluated. The single vessel method gave a lower mean blank level with better precision, hence lower detection limits, as compared to the conventional method. The determination of total mercury in biological standard reference materials by the single vessel method also produced significantly higher mercury values and better precision than the conventional method. However, the mercury concentrations obtained in certified reference materials by the use of both methods were close to the mean certified values. Moreover, the use of the single vessel method is cost effective, rapid and environment friendly. The use of the single vessel technique is therefore recommended for accurate and reliable determination of mercury in biological solids. Received: 15 December 1997 / Revised: 9 April 1998 / Accepted: 18 April 1998     

Ag-catalyzed asymmetric mannich reactions of enol ethers with aryl, alkyl, alkenyl, and alkynyl imines

An efficient catalytic and enantioselective method (up to >98% ee) for Mannich reactions between trimethylsilyl enol ethers derived from acetone and acetophenone and aryl, alkenyl, alkynyl, and alkyl imines is disclosed. A large variety of beta-amino ketones can be synthesized in the presence of 1-5 mol % AgOAc and an inexpensive and readily available amino acid-derived phosphine. All Ag-catalyzed asymmetric Mannich reactions can be run in undistilled THF and air. The o-anisyl activating groups of product amines can be removed in >70% isolated yield through a single vessel operation. The synthetic utility of the catalytic asymmetric method is illustrated by a four-pot synthesis of optically pure alkaloid (-)-sedamine.     

Determination of 14C, 55Fe, 63Ni and gamma emitters in activated RPV steel samples: a comparison between calculations and experimental analysis

Journal of Radioanalytical and Nuclear Chemistry - Determination of 14C, 55Fe, 63Ni and gamma emitters in two different types of activated reactor pressure vessel (RPV) steel samples were carried...     

Automatic twin vessel recrystallizer. Effective purification of acetaminophen by successive automatic recrystallization and absolute determination of purity by DSC

I describe an interchangeable twin vessel (J, N) automatic glass recrystallizer that eliminates the time-consuming recovery and recycling of crystals for repeated recrystallization. The sample goes in the dissolution vessel J containing a magnetic stir-bar K; J is clamped to the upper joint H of recrystallizer body D. Empty crystallization vessel N is clamped to the lower joint M. Pure solvent is delivered to the dissolution vessel and the crystallization vessel via the head of the condenser A. Crystallization vessel is heated (P). The dissolution reservoir is stirred and heated by the solvent vapor (F). Continuous outflow of filtrate E out of J keeps N at a stable boiling temperature. This results in efficient dissolution, evaporation and separation of pure crystals Q. Pure solvent in the dissolution reservoir is recovered by suction. Empty dissolution and crystallization vessels are detached. Stirrer magnet is transferred to the crystallization vessel and the role of the vessels are then reversed. Evacuating mother liquor out of the upper twin vessel, the apparatus unit is ready for the next automatic recrystallization by refilling twin vessels with pure solvent. We show successive automatic recrystallization of acetaminophen from diethyl ether obtaining acetaminophen of higher melting temperatures than USP and JP reference standards by 8× automatic recrystallization, 96% yield at each stage. Also, I demonstrate a novel approach to the determination of absolute purity by combining the successive automatic recrystallization with differential scanning calorimetry (DSC) measurement requiring no reference standards. This involves the measurement of the criterial melting temperature T₀ corresponding to the 100% pure material and quantitative ΔT in DSC based on the van’t Hoff law of melting point depression. The purity of six commercial acetaminophen samples and reference standards and an eight times recrystallized product evaluated were 98.8 mol%, 97.9 mol%, 99.1 mol%, 98.3 mol%, 98.4 mol%, 98.5 mol% and 99.3 mol% respectively.