Lateral self-sorting on surfaces: a practical approach to double-channel photosystems

We report that self-sorting during self-organizing surface-initiated copolymerization (co-SOSIP) provides facile access to oriented multicomponent architectures. Alternate lateral and uniform axial self-sorting into formal supramolecular n/p-heterojunction photosystems is found to generate up to 40 times more photocurrent. More or less topological matching gives rise to alternate axial self-sorting into inactive charge-transfer complexes or uniform lateral sorting into the less active macrodomains, respectively. Experimental support for self-repair during co-SOSIP is reported. Initiators on the surface are shown to serve as templates for the self-sorting into multichannel architectures of freely variable composition.     

HPLC-SEC: a new approach to characterise complex wastewater effluents

This work investigates the use of HPLC-SEC to characterise dissolved organic matter (DOM) of complex wastewater effluents. A silica-based column, sodium acetate eluent and multiple detections were employed: UV-254 absorbance for humictype, and tryptophan-like (Ex/Em = 270/355) and tyrosine-like (Ex/Em = 270/310) fluorescence for protein type compounds. Effects of eluent pH, eluent ionic strength and injection volume on separation efficiency were tested. Humic-type and protein-type fractions were clearly differentiated and eluted within and out of calibration range. Eluent ionic strength had the greatest influence on global resolution; the lowest eluent concentration of 0.01 M produced the best separation for all wastewater effluents tested at any detection. UV-254 absorbance was higher at neutral and basic eluent pH while tryptophan-like fluorescence depended on the sample composition rather than on the eluent pH or ionic strength. Tyrosine-like fluorescence decreased significantly with the increase of eluent ionic strength. Accurate molecular weight measurements could not be done, the separation being influenced by secondary interactions, but could be approximated using separate calibrations with sodium salts of polystyrene-sulfonates and protein standards. The results show that this method is suitable for determining DOM in wastewater at low eluent concentrations (up to 0.03 M), at neutral or slightly basic pH.     

Scandium fluorophosphate glasses: a structural approach

A systematic investigation on glass formation in the ternary system InF₃–BaF₂–Sc(PO₃)_3n has been carried out. Scandium polyphosphate Sc(PO₃)_3n has been used as a third component in order to investigate the possibilities of obtaining new stable glasses. The above long-chain polyphosphate has been prepared using a specially elaborated cryo-technique, which allowed the preparation of high-purity product. Stable ternary compositions have been obtained within the compositions range (in mol%): 5–75 InF₃, 0–80% BaF₂, 0–50% Sc(PO₃)_3n. Glasses were characterized by Differential Scanning Calorimetry, vibrational spectroscopy (Raman) and ³¹P NMR. Structural features for the glass were put forward. Isolated P(O,F)4 groups or fluoroindated metaphosphate units could be identified depending on glass compositions.     

Electrophile-induced ether transfer: a new approach to polyketide structural units

[Structure: see text] A strategically novel approach to the formation of syn-1,3-diol mono- and diethers through electrophilic activation of homoallylic alkoxymethyl ethers has been developed. The resulting polyketide-like synthetic fragments are generated in good yield and with excellent stereocontrol. A chairlike transition state is proposed to account for the high stereoselectivity. Varying the conditions of the reaction workup results in the efficient generation of mono- and diether containing structural units common to polyketide natural products.     

Online coupling of high-resolution chromatography with extreme UV photon activation tandem mass spectrometry: Application to the structural investigation of complex glycans by dissociative photoionization

The activation of ions by extreme-energy photons (XUV) produced by a synchrotron radiation beamline is a powerful method for characterizing complex glycans using tandem mass spectrometry (MS). As previously described, this activation method leads to rich fragmentation spectra with many structurally valuable cross-ring cleavages while maintaining labile modifications on the glycan structures. However, until now, the tandem MS event was too long to be compatible with liquid chromatography elution times. In this work, the duty cycle of the activation and detection of fragments was shortened, and the background signal on the spectra was drastically reduced. Both improvements allowed, for the first time, the successful coupling of a UHPLC system to XUV-activated tandem MS. The approach was used to characterize a complex mixture of oligo-porphyrans, which are a class of highly sulfated oligosaccharides, in a fully automated way. Due to an enhanced dynamic range and an increased sensitivity, some hypothetical structures of low abundance have been unequivocally confirmed in this study and others have been revised. Some previously undescribed species of oligo-porphyrans that exhibit lateral branching have been fully resolved. This work contributes to the scarce knowledge of the structure of porphyrans in red algae and pushes the current capacities of XUV-activation tandem MS by demonstrating the possibility of a direct coupling with UHPLC. This study will considerably broaden the applicability and practicality of this method in many fields of analytical biology.     

MgI2-catalyzed halo aldol reaction: a practical approach to (E)-beta-iodovinyl-beta'-hydroxyketones

A novel generation of 1-iodo-3-siloxy-1,3-butadienes has been developed by reacting trimethylsilyl iodide (TMS-I) with alpha, beta-unsaturated ketones in dichloromethane at 0 degrees C without the use of any catalyst. The halo aldol reaction of these butadiene intermediates with aldehydes was efficiently carried out by using magnesium iodide as the catalyst. Twelve beta-iodo-alpha,beta-unsaturated-beta'-hydroxyketones (halo aldols) have been synthesized under the new condition with excellent geometric selectivity and good chemical yields (>80% chemical yields for 11 examples).     

Development of a practical solid-phase synthesis approach to 1,3,5-triazepan-2,6-diones

1,3,5-Triazepan-2,6-diones are a class of conformationally restricted heterocycles derived from dipeptides. With the aim to develop a general and practical method useful for library production, three polymer-assisted syntheses, all based on a catch and release approach, have been evaluated and compared. The method involving a Hofmann rearrangement of N-Boc dipeptide carboxamides and subsequent trapping of the isocyanate on polymer-supported N-hydroxysuccinimide (PS-HOSu) was found to be the most reliable and versatile, allowing rapid access to the 1,3,5-triazepan-2,6-dione skeleton.     

A practical approach to the implementation of autoverify

Autoverification is a process in which computer software will automatically evaluate laboratory test results, verify result integrity, and then release the results to the hospital interface without any technologist intervention. Autoverify release criteria are user defined and can be customized. The process of developing, implementing, and monitoring autoverify is achievable for most test results in laboratory medicine. The use of autoverification will improve result quality, increase revenue, and create faster turn-around times. All of this put together will ultimately lead to improved customer satisfaction. Computers and autoverification are survival tools in the competitive market of laboratory diagnostics services.Presented at the 8th Conference on Quality in the Spotlight, 17–18 March 2003, Antwerp, Belgium     

A practical approach to assessment of sampling uncertainty

The paper reports the approach followed in the SOILSAMP project, funded by the National Environmental Protection Agency (ANPA)of Italy. SOILSAMP is aimed at assessing uncertainties associated with soil sampling in agricultural, semi-natural, urban, and industrial environments. The uncertainty assessment is based on a bottom-up approach, according to the Guide to the Expression of Uncertainty in Measurement published by the International Organization for Standardization (ISO). A designated agricultural area, which has been characterized in terms of elemental spatial distribution, will be used in future as a reference site for soil sampling intercomparison exercises. Received: 19 November 2001 Accepted: 6 January 2002     

A practical approach to transferring linear gradient elution methods

Attempts to theoretically address the problems involved in transferring linear gradient elution methods have been somewhat ad hoc due to the simplifying assumptions usually made in conventional gradient elution theory. Until now, all equations based on the k* parameter of linear gradient elution theory used as the basis for predicting the separation selectivity have not explicitly included the effect of the dwell volume (VD). Using an exact equation for predicting k*, that is, one which fully accounts in an a priori fashion for VD, we find a set of simple yet exact equations which unequivocally must be satisfied to transfer an optimized linear gradient elution method from one system (column or instrument or both) to another. These relationships absolutely mandate that a change in the instrument dwell volume requires a proportional change in the column volume; in turn, a change in the column volume requires a proportional change in the flow rate and/or gradient time to maintain a constant gradient steepness. Although we are not the first to suggest these guidelines, this work provides a complete theoretical foundation for these exact guidelines for the maintenance of gradient selectivity for the case of transferring a linear gradient elution method between different columns packed with the same particles and/or between different instruments.     

A practical approach to metrology in chemistry and biology

 The inherent difficulties of measurement in chemistry and biology have made it necessary to open discussion forums solely devoted to bench level work. This contribution summarises the conclusions of the Standards, Measurements and Testing Project (SMT4-CT96-6505) of the European Commission, devoted to the application of metrology in chemistry and biology. The objective of this project was to provide orientations and some recommendations which could partially satisfy end-users needs in the near future. Received: 29 September 1998 · Accepted: 21 December 1998     

A practical synthesis of D-erythro-sphingosine using a cross-metathesis approach

Starting from a vinylepoxide, a short and practical synthesis of D-erythro-sphingosine is described. The key transformations are a regioselective opening of the vinylepoxide and an E-selective cross-metathesis, affording the target molecule 5 in steps and 51% overall yield.     

Backbone thioester exchange: a new approach to evaluating higher order structural stability in polypeptides

An amide bond has been replaced by a thioester in bovine pancreatic polypeptide (bPP) to allow rapid and reversible (dynamic) exchange of the alpha-helical segment with other thiols in solution. We have begun to study the higher order structural stability of bPP by measuring the equilibrium constant of the "backbone thioester exchange" (BTE) reaction. The extent to which the equilibrium (KBTE) favors one set of peptides over the other, which can be easily measured, can be directly correlated to the energy gained from favorable noncovalent interactions that occur between peptide segments on either side of the thioester bond (Kfold).     

Copper-schiff base complex forming a mesophase: Magnetic and structural parameters

Kazan Technical Physics Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 28, No. 5, pp. 157–158, September–October, 1987     

Enantioselective organo-SOMO cycloadditions: a catalytic approach to complex pyrrolidines from olefins and aldehydes

A new method to rapidly generate pyrrolidines via a SOMO-activated enantioselective (3 + 2) coupling of aldehydes and conjugated olefins has been accomplished. A radical-polar crossover mechanism is proposed wherein olefin addition to a transient enamine radical cation and oxidation of the resulting radical furnish a cationic intermediate which is vulnerable to nucleophilic addition of a tethered amine group. A range of olefins, including styrenes and dienes, are shown to provide stereochemically complex pyrrolidine products with high chemical efficiency and enantiocontrol.     

A simple and practical phase-separation approach to the recycling of a homogeneous metathesis catalyst

The air stable asarone-derived Ru carbene 16, a robust olefin metathesis catalyst, can be easily separated after reaction by deposition on silica gel and reused up to nine times. This procedure provides products of excellent purity with low Ru content.     

Stereoselective convergent synthesis of 24,25-dihydroxyvitamin D3 metabolites: a practical approach

Vitamin D3 active metabolites 24R,25-(OH)2-D3, 24S,25-(OH)2-D3, and 1 alpha, 24R,25-(OH)3-D3 were synthesized by a convergent and stereoselective approach. In the synthetic route, the stereogenic center at C-24 was generated through ultrasonically induced aqueous conjugate addition of iodide 6 to Seebach's dioxolanone 5, and the vitamin D triene system was constructed using the Lythgoe approach. The synthesis, which is both short (seven steps from iodide 6) and efficient (32-40% overall yield), allows the preparation of large quantities of the metabolites and provides a novel example of a highly stereoselective reaction promoted by the zinc-copper couple in aqueous media.     

Peak capacity optimization in comprehensive two dimensional liquid chromatography: a practical approach

In this work we develop a practical approach to optimization in comprehensive two dimensional liquid chromatography (LC x LC) which incorporates the important under-sampling correction and is based on the previously developed gradient implementation of the Poppe approach to optimizing peak capacity. The Poppe method allows the determination of the column length, flow rate as well as initial and final eluent compositions that maximize the peak capacity at a given gradient time. It was assumed that gradient elution is applied in both dimensions and that various practical constraints are imposed on both the initial and final mobile phase composition in the first dimension separation. It was convenient to consider four different classes of solute sets differing in their retention properties. The major finding of this study is that the under-sampling effect is very important and causes some unexpected results including the important counter-intuitive observation that under certain conditions the optimum effective LC x LC peak capacity is obtained when the first dimension is deliberately run under sub-optimal conditions. In addition, we found that the optimum sampling rate in this study is rather slower than reported in previous studies and that it increases with longer first dimension gradient times.