Heterogeneous diazo-transfer reaction: a facile unmasking of azide groups on amine-functionalized insoluble supports for solid-phase synthesis

Solid-supported azides are commonly generated through direct nucleophilic displacement of appropriately activated supports by the azide ion. This reaction usually proceeds rather sluggishly under harsh conditions. Here, we report that triflyl azide rapidly reacts with a series of amine-functionalized solid supports to generate azide-coated supports under mild conditions. Further, we demonstrate that the "azide coat" allows facile loading of alkyne-functionalized leader nucleoside monomers by click chemistry. Finally, we show that the nucleoside-functionalized supports are suitable for solid-phase oligonucleotide synthetic applications. The approach herein described extends the scope of the amine-azide conversion reaction and may be adaptable for the introduction of azide to diverse amine-terminated solid supports that are not easily accessible by the conventional nucleophilic displacement method.     

The application of atomic absorption spectrometry in the analysis of metallic sodium: Part 1. Volatilization Characteristics of Sodium Salts During Electrothermal Atomization

The volatilization characteristics of six common sodium salts from the graphite rod of an electrothermal atomizer are described. Most of the salts have a relatively simple volatilization behaviour and can be completely removed from the graphite rod during a 20 s heating stage at temperatures 200–300°C above their melting points. This predictable and controllable vaporization behaviour shows the potentiality of the graphite rod atomizer for selectively volatilizing a sodium salt matrix and leaving behind less volatile trace metals for subsequent high temperature volatilization and measurement by atomic absorption spectrometry.     

Synthesis and Characterization of Solid Supports Containing silicon

Combinatorial chemistry has been a new field of chemistry since 1990's.^[1][2] More than 90% of researchers play their emphases on the studies of the solid supports such as P-(CH₂)_n-N and P-(CH₂)_n-O(n=1,2,3), but only a couple researchers play their emphases on the studies of the P-(CH₂)_n-Si(n=1,2,3). Because of the characteristic of the Si-Ar bond, we devise a series of the solid supports containing Si-Ar bond.These solid supports containing silicon were synthesized in two methods. At the same time,we also synthesized the monomer of the solid supports containing silicon or tin. The structures of these compounds were characterized by IR, elemental analysis.The synthetic routes of the solid supports containing silicon are shown in scheme 1 and the synthetic routes of the monomer of the solid supports containing silicon or tin are shown in scheme 2.     

Electrochemical oxidation of a synthetic dye using a BDD anode with a solid polymer electrolyte

In this study the performance of an electrochemical cell with a solid polymer electrolyte (SPE) has been investigated using Safranin T, a synthetic dye, as a model compound. The cell consists of a Nafion membrane sandwiched between a BDD mesh anode and a Ti/RuO₂ mesh cathode operating at constant current. The effects of operating conditions such as applied current, stirring rate and electrolyte conductivity were studied. The experimental results showed that Safranin T was completely removed by reaction with OH radicals generated by water electrolysis and that the oxidation was under charge-transfer control. Furthermore, it was observed that addition of Na₂SO₄ to the solution decreased the removal rate but also decreased the specific energy required for the process.     

Direct determination of traces of molybdenum in synthetic sea water by atomic absorption spectrometry with electrothermal atomization and selective volatilization of the salt matrix

A simple and rapid method is described for the direct determination by graphite-furnace atomic absorption spectrometry (HGA-2100) of traces of molybdenum (O.1–4 ng) in synthetic sea water. It is shown that the salt matrix can be removed completely by selective volatilization at 1700–1850°C, but the original presence of NaCl, Na₂SO₄, and KCl causes a considerable decrease in molybdenum absorbance, and MgCl₂ and CaCl₂ a pronounced enhancement. The presence of MgCl₂ prevents the depressive effects. Samples of less than 50 μl can be analyzed directly without using a background corrector, with a precision of<10%.     

Completely "green" synthesis and stabilization of metal nanoparticles

In the present Communication, a completely "green" synthetic method for producing silver nanoparticles is introduced. The process is simple, environmentally benign, and quite efficient. By gentle heating of an aqueous starch solution containing silver nitrate and glucose, we produce relatively monodisperse, starched silver nanoparticles. beta-d-Glucose serves as the green reducing agent, while starch serves as the stabilization agent.     

An investigation on eutectic binary phase diagram of volatilizable energetic materials by high pressure DSC

The eutectic binary phase diagrams of volatilizable energetic material 1,3,3-trinitroazetidine (TNAZ) with 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1-methyl-2,4-dinitroimidazole (MDNI) have been investigated by high pressure differential scanning calorimeter (PDSC), respectively. The liquefying and melting processes of TNAZ/RDX and TNAZ/MDNI volatilizable systems have been studied. On the basis of the data of apparent fusion heat and liquefying temperature, the phase diagrams of apparent fusion heat (H) with composition (X) and liquefying temperature (T) with composition (X) were constructed, respectively. The results showed that the gasification or volatilization of easy volatile energetic materials could be efficiently restrained by high pressure atmosphere, and the perfect and ideal phase diagrams can be constructed. The eutectic temperatures for TNAZ/RDX and TNAZ/MDNI are measured to be 95.5 and 82.3 °C, respectively. The eutectic compositions of mole ratios for the two systems are obtained to be 93.55/6.45 (T–X method), 93.79/6.21 (H–X method) and 62.25/37.75 (T–X method), 63.29/33.71 (H–X method), respectively.     

Pyrolysis-capillary gas chromatography-mass spectrometry for the determination of polyvinyl chloride traces in solid environmental samples

A novel method based on pyrolysis-capillary gas chromatography-mass spectrometry (CGC-MS) was developed for the quantitative analysis of polyvinylchloride (PVC) in solid environmental samples like sludge and dust. The samples are extracted and the extract is fractionated by solid-phase extraction (SPE). Possibly interfering biological and frequently occuring synthetic polymers are removed by this clean-up. The final extract is analyzed by pyrolysis-CGC-MS. Selective detection of PVC is performed by using specific markers in the pyrogram. Quantitation is done on naphthalene. Good linearity was obtained in a range from 0.5 to 100 microg applied to the pyrolyser. The limit of quantitation (LOQ) in sludge and dust samples is 10 mg/kg dry mass. A correlation between PVC and phthalates was made for sewage sludge samples.     

Towards the Chemical Synthesis of Proteins

The chemical total synthesis of proteins using solid supports has made great progress. It is therefore becoming a reality what E. Fischer already predicted in 1902 1 1 Cited from Nobel Lectures—Chemistry 1901-1921, Elsevier, Amsterdam 1966, p. 34.
: “I foresee the time when physiological chemistry… is able to prepare synthetic enzymes.” The synthesis of peptides of up to 20 amino acids by the well-established solid-phase procedure on polymeric supports (SPPS) has made great progress through the development of newer supports. At the same time, methods have emerged which facilitate the separation and characterization of peptides, thus allowing optimization of the synthesis of pure materials. The new supports which enable one to synthesize peptides by a rapid continuous flow procedure are characterized by hydrophilicity, beads of approximately equal size, similar swelling properties in the solvents used for peptide synthesis, and stability at high pressure. With graft copolymers of weakly cross-linked polystyrene and linear polyethylene glycol (PEG), the synthetic cycle for coupling of one amino acid can routinely be reduced to 10–20 min with a concomitant higher yield. With beads of monodispersed graft copolymer of 10 μm diameter, a synthetic cycle can, in principle, be shortened to 1–5 min. By utilizing this high-speed solid-phase procedure, larger peptides up to the size of proteins could also be prepared in a few hours. With newer mass spectroscopic methods such as ion-spray mass spectrometry, peptides of up to a molecular mass of 100 kDa can be characterized, and with the advent of capillary electrophoresis, another very efficient separation tool, besides HPLC, is at our disposal.     

Sand als Rohstoff

Pure sand and gravel qualities are becoming to be rare resources and technical goods of increasing strategic importance for various industrial branches worldwide. Quartz sand as a crystalline raw material is chemically transformed into intermediates for the final production of synthetic amorphous silicon dioxides (SAS). Precipitated SAS are produced by chemical reaction of sodium silicates. Chlorosilanes are produced by reaction of silicon and ferrosilicon with HCl. They are used to produce pyrogenic SAS. High‐resolution transmission electron microscopy is needed to reveal the fine structure of these amorphous materials. Pyrogenic and precipitated SAS show a similar nanostructure as silica‐gels and ‐aerogels. Differences in amorphicity and short range order in finely divided, alkaline‐free, amorphous SAS on the one hand and in alkaline‐containing amorphous SiO₂‐networks such as solid sodium silicates on the other still are not completely clarified.     

Solid-phase synthesis of asymmetrically substituted "AB3-type" phthalocyanines

Synthesis of phthalocyanines with asymmetrical substitution on the periphery is often difficult due the problems in purification of the phthalocyanine mixtures obtained. Using a poly(ethylene glycol) (PEG)-based support with a Wang-type linker, we have developed the synthesis of monohydroxylated, oligoethylene glycol substituted phthalocyanines utilizing an amidine-base-promoted phthalonitrile tetramerization reaction. The use of a hydrophilic support allows symmetrical phthalocyanine product formed in solution to be readily and completely removed by washing while leaving the "AB3" product on the support. Acid cleavage with 10% trifluoroacetic acid provides the pure unsymmetrically substituted Pc. This method was applied to several metallo Pcs. Additionally, methods to avoid premature reactions on-resin that give A2B2 products are provided.     

Biomimetic Processing of Gel Glasses and Organic-Inorganic Hybrids

Biological hard tissues like bone and shell show combinations of strength and toughness that are hard to duplicate with synthetic materials. These properties are attained by a composite of organic and inorganic phases with very organized microstructures. The structures are hierarchical in that several different scales of organization contribute to the final properties.Biological systems form by chemical precipitation at room temperature in contrast to synthetic processing, which usually depends on thermal solidification. In principle, chemical solidification can give much more control over composition and structure but is limited by the time taken for diffusion processes in any solid component.A family of solid freeform fabrication methods have recently been developed which allow parts to be built under the direct control of a 3-dimensional CAD drawing without the need for a mold. These methods also offer a way of building composite structures, with full control of structure and composition at the scale of 100 m and up. Since this is a layerwise process, like biological growth, diffusion paths are short and so chemical processing of large parts is feasible.We have been developing an SFF system based on extrusion of a reactive slurry through a 300 m needle. The needle is moved on three axes so as to build up a part. The application of this method to the formation of components from sol-gel glasses and organic-inorganic hybrids is described.     

Removal of graphite by oxidation with perchloric acid plus periodic acid: Inapplicability to the spectrophotometric determination of manganese in steel

An attempt has been made to improve the Willard and Greathouse periodate method for the determination of manganese in high-carbon steel and cast iron by oxidizing the graphite with periodic acid in the presence of perchloric acid and phosphoric acid. Graphite is rapidly oxidized at 150° by this mixture but manganese is lost by volatilization as the heptoxide and decomposition of the latter on hot surfaces to manganese dioxide. No way was found for either the quantitative removal and recovery of manganese by volatilization or for quantitative return to the main solution. The spectrophotometric determination of manganese in the supernatant liquid after allowing graphite to settle yields imprecise but not wholly unacceptable results; for the highest accuracy, graphite should be removed along with silica following dehydration of the latter with perchloric acid.     

Synthesis of fluorescein-labelled O-mannosylated peptides as components for synthetic vaccines: comparison of two synthetic strategies

Mannose-binding proteins on the surface of antigen-presenting cells (APCs) are capable of recognizing and internalizing foreign agents in the early stages of immune response. These receptors offer a potential target for synthetic vaccines, especially vaccines designed to stimulate T cells. We set out to synthesize a series of fluorescein-labelled O-mannosylated peptides using manual solid phase peptide synthesis (SPPS) on pre-loaded Wang resin, in order to test their ability to bind mannose receptors on human APCs in vitro. A flexible and reliable method for the synthesis of fluorescein-labelled O-mannosylated glycopeptides was desired in order to study their lectin-binding properties using flow cell cytometry. Two synthetic strategies were investigated: incorporation of a fluorescein label into the peptide chain via a lysine side chain epsilon-amino group at the final stage of standard Fmoc solid phase peptide synthesis or attachment of the fluorescein label to the N(alpha)-amino group of a lysine with further incorporation of a mannosylated peptide unit through the side chain N(epsilon)-amino group. The latter strategy proved more effective in that it facilitated SPPS by positioning the growing mannosylated peptide chain further removed from the fluorescein label.     

Electrochemical oxidation of p-hydroxybenzoic and protocathecuic acids at a dimensional stable anode (DSA) in the presence of NaCl

This work is part of a wider research programme on innovative technologies for industrial wastewater treatment. Results from electrolyses at DSA commercial anodes of synthetic solutions with composition analogous to that of agro-industrial wastes are presented. The results obtained indicate that the rate of degradation of phenolic compounds is high, provided that chloride ions are present in solution. Oxidation of phenolic compounds is faster than that of biodegradable substances, such as sugars or amminoacids. Moreover, investigation on the trend of toxicity during the treatment, seems to exclude that toxic intermediates persist in solution when phenolic compounds are removed. Experiments on olive oil mill wastewater (OMW) samples show that the results obtained from synthetic solutions are extensible to real wastewater. When phenolic compounds are completely removed, the toxicity of the solution is very low; the initial dark colour of the solution, due to the brown pigment which characterises OMW, is nearly completely disappeared.     

Production of FAME and FAEE via Alcoholysis of Sunflower Oil by Eversa Lipases Immobilized on Hydrophobic Supports

The performance of two new commercial low-cost lipases Eversa® Transform and Eversa® Transform 2.0 immobilized in different supports was investigated. The two lipases were adsorbed on four different hydrophobic supports. Interesting results were obtained for both lipases and for the four supports. However, the most active derivative was prepared by immobilization of Eversa® Transform 2.0 on Sepabeads C-18. Ninety-nine percent of fatty acid ethyl ester was obtained, in 3 h at 40 °C, by using hexane as solvent, a molar ratio of 4:1 (ethanol/oil), and 10 wt% of immobilized biocatalyst. The final reaction mixture contained traces of monoacylglycerols but was completely free of diacylglycerols. After four reaction cycles, the immobilized biocatalyst preserved 75% of activity. Both lipases immobilized in Sepabeads C-18 were very active with ethanol and methanol as acceptors, but they were much more stable in the presence of ethanol.     

Enantioselective synthesis of N1999A2

An enantioselective synthetic route to the enediyne antibiotic N1999A2 (1) is described, proceeding in 21 steps (0.4% yield, 77% average yield per step) from (R)-(+)-glycidol. The route involves the convergent assembly of three components: a (1-iodovinyl) stannane (2), a 1,5-hexadiyne-3,4-diol derivative (3), and a substituted naphthoic acid (4). Important transformations in the synthetic sequence include the palladium-catalyzed coupling of 2 and 3, an intramolecular oxidative cyclization of a terminal bisacetylene, and a transannular anionic (bi)cyclization of a cyclic bromoenetriyne. The careful selection and manipulation of protective groups throughout the sequence proved to be critical to the development of the synthetic route, where all late-stage intermediates were unstable and could not be concentrated. In the final step of the sequence, three protective groups were removed in a single operation, providing synthetic N1999A2 (1) in 76% yield. Conditions were found that, for the first time, led to the precipitation of 1 as a solid.     

MgI2‐Mediated Chemoselective Cleavage of Protecting Groups: An Alternative to Conventional Deprotection Methodologies

The scope of MgI₂ as a valuable tool for quantitative and mild chemoselective cleavage of protecting groups is described here. This novel synthetic approach expands the use of protecting groups, widens the concept of orthogonality in synthetic processes, and offers a facile opportunity to release compounds from solid supports.     

Synthesis of Oligonucleotides Carrying Anchoring Groups and Their Use in the Preparation of Oligonucleotide–Gold Conjugates

Oligodeoxynucleotide conjugates 1 – 15 carrying anchoring groups such as amino, thiol, pyrrole, and carboxy groups were prepared. A post‐synthetic modification protocol was developed. In this method 2′‐deoxy‐O⁴‐(p‐nitrophenyl)uridine‐3‐phosphoramidite was prepared and incorporated in oligonucleotides. After assembly, the modified nucleoside was made to react with different amines carrying the anchoring groups. At the same time, protecting groups were removed to yield the desired oligonucleotide conjugates. In a second approach, amino, thiol, and carboxylic groups were introduced into the 3′‐end of the oligonucleotides by preparing solid supports loaded with the appropriate amino acids. Oligonucleotide gold conjugates were prepared and their binding properties were examined.     

From polymer to small organic molecules: a tight relationship between radical chemistry and solid-phase organic synthesis

Since Gomberg's discovery of radicals as chemical entities, the interest around them has increased through the years. Nowadays, radical chemistry is used in the synthesis of 75% of all polymers, inevitably establishing a close relationship with Solid-Phase Organic Synthesis. More recently, the interest of organic chemists has shifted towards the application of usual "in-solution" radical chemistry to the solid-phase, ranging from the use of supported reagents for radical reactions, to the development of methodologies for the synthesis of small molecules or potential libraries. The aim of this review is to put in perspective radical chemistry, moving it away from its origin as a synthetic means for solid supports, to becoming a useful tool for the synthesis of small molecules.