Semi-quantitative "spot-test" of cyanide.

A selective, sensitive, rapid and simple-handling analytical method for the determination of cyanide at low detection limits in surface and underground water, soil and industrial waste samples was developed. The method is based on a reaction, proposed by Guilbault and Kramer, where free cyanide reacts with p-nitrobenzaldehyde to form an intermediate cyanohydrin, which reacts with o-dinitrobenzene to give a highly colored purple compound. The original procedure was modified for application in a small device containing a gas-permeable membrane. The cyanide is converted in the volatile hydrogen cyanide, which permeates through a PTFE membrane, reaching colorimetric reagents. In order to obtain semi-quantitative results, printed color scales were built. The method allows rapid, accurate, selective, low-cost and simple-handling determinations of free cyanide, even in complex samples. About 150 real samples were analyzed. Less than 10 ng of free cyanide per ml (10 microg l(-1)) can be easily detected. For more concentrated solutions, the results had been compared to those obtained using differential pulse polarography. The standard addition method was used for more diluted solutions.     

The Immobiline family: from "vacuum" to "plenum" chemistry.

We list here a total of 17 acrylamido acids and bases as potential buffers and titrants for isoelectric focusing separations in immobilized pH gradients. The chemistry of these compounds is reviewed and general guidelines are given for their proper use. In particular, it is shown that the most delicate compounds are the basic species, since they can undergo several degradation pathways, including: (i) spontaneous hydrolysis to acrylic acid and a diamine; (ii) spontaneous autopolymerization to oligomers and n-mers; (iii) oxidation to N-oxides during the persulfate polymerization step. A hydrophobicity scale has been constructed, by partitioning the deprotonated species in water/1-octanol phases. A scale of resistance to alkaline hydrolysis for the basic acrylamido buffers is also given, followed by general consideration on the structure/stability relationship of these chemicals.     

"Proteomineering" serum biomarkers. A study in scarlet

The performance of sera pre-treatment for biomarker searching via combinatorial peptide ligand libraries (CPLL) has recently been challenged (Proteomics 2010, 10, 1416-1425) and stated to allow discovery of only medium to high-abundance proteins. We have thus investigated four elution protocols, as published in recent reports: (i) in 4?M urea+1% CHAPS; (ii) in 4?M urea+1% CHAPS+5% acetic acid; (iii) in 8?M urea+2% CHAPS+5% acetic acid; (iv) in boiling 4% SDS+25?mM DTT. One milliliter of serum, in all cases, was captured with 50?μL of CPLL beads, which were then eluted with the four eluants described above. In the first three cases, after the first elution, the beads were re-eluted with cocktail (iv), known to offer maximal release of proteins adsorbed by the CPLL ligands. Eluant (i) released only ca. 20% of the species adsorbed, eluant (ii) ca. 60%, eluant (iii) ca. 80%. Thus, the poor performance of the CPLL methodology, as reported in (i) is not due to any fault of the capture technique, but simply to the adoption of a very poor elution protocol. Even those using eluants (ii) and (iii) should know that a substantial fraction of the captured species still remains bound to the beads and is thus not available to biomarker discovery. Once more, eluant (iv) is recognized as the only one able to offer optimal recovery from the CPLL baits.     

Carbon networks based on dehydrobenzoannulenes. 4. Synthesis of "star" and "trefoil" graphdiyne substructures via sixfold cross-coupling of hexaiodobenzene

The synthesis and characterization of star- and trefoil-shaped polyethynyl aromatic structures, which represent model substructures of the all-carbon network graphdiyne, are described. Assembly of these macrocycles is accomplished via 6-fold Sonogashira cross-coupling of hexaiodobenzene using Pd[P(o-Tol)(3)](2) and CuI as the catalytic system. The development of these modified Sonogashira conditions is detailed. This work has led to the synthesis of a new family of hexakis(phenylbutadiynyl)benzene derivatives (4a-c), the largest of which is the D(3)(h)()-symmetric "trefoil" 2 and is composed of three [18]annulenes fused at a common benzene ring. Attempts at the synthesis of "wheel" 3 are also described. Compound 2 represents the largest fragment of the graphdiyne network to date. UV-vis spectroscopic studies indicate enhanced electron delocalization throughout the extended pi-system.     

评G.L.Patrick著Instant Notes in Organic Chemistry

G．L．Patrick著“Instant Notesin Organic Chemistry”一书是2000年由英国BIOS Scientific Publishers出版的Instant Notes系列参考书的一种。该书同年由科学出版社影印出版,中文译名为《精要速览系列有机化学(影印版)》。全书共315页,分十五章(Section),每章又分若干分章。每     

"Demonstration" vs. "designation" of measurement competence: the need to link accreditation to metrology

Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. "traceable" to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be "external" to the measurement laboratories which are being evaluated. This is realized in IRMM's International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using "metrology", the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be "demonstrated" rather than just "designated" and this can be shown to both customers and regulators. It inspires more confidence.     

"Flexiball" toolkit: a modular approach to self-assembling capsules.

We report the synthesis and characterization of new, self-assembling molecular capsules. The modular strategy makes use of glycoluril building blocks available in multigram amounts combined with aromatic spacer elements. The lengthy syntheses encountered with earlier generations of capsules are avoided, and several capsules of nanometer dimensions are now accessible. Single bond attachments between spacers and glycoluril modules result in monomers as dimeric capsules that are less rigid than their earlier counterparts. The host-guest properties of the homo- and heterodimeric capsules were studied using a combination of NMR and ESI-mass spectrometry. They show a less pronounced selectivity for guests of different sizes, and their increased flexibility prevents self-assembly when no rigidifying elements are present on the central spacer unit. Some of the new capsules bear inwardly directed, secondary amide N-H protons. These can be further functionalized, as shown by their methylation to give tertiary analogues. The structures hold broader implications for the placement of functional groups on concave molecular surfaces.     

Stille couplings catalytic in tin: the "Sn-O" approach.

A one-pot tandem Pd-catalyzed hydrostannylation/Stille coupling protocol for the stereoselective generation of vinyltins and their subsequent union, employing only catalytic amounts of tin, is described. By recycling the organotin halide Stille byproduct back to organotin hydride, a hydrostannylation/cross-coupling sequence can be carried out with catalytic amounts of tin. Such a process is most effective with Me(3)SnCl serving as the tin source. This protocol allows a 94% reduction of the tin requirement, while maintaining good yields (up to 90%) for a variety of Stille products. Furthermore, since one cycle requires the tin to undergo at least four transformations, each moiety of trialkyltin is experiencing a minimum of 60 reactions over the course of the hydrostannylation/Stille sequence.