Selective chemical reactions in supercritical carbon dioxide,water, and ionic liquids

Abstract

Alternative solvents such as supercritical carbon dioxide, water, and ionic liquids are receiving an increase of interest as better replacements for conventional solvents in chemical reactions. They have been called sustainable green solvents because they are highly promising reaction mediums for organic synthesis. This review presents an overview of some selected chemical reactions that have been developed in these green solvents with a particular emphasis on metal-catalyzed reactions.     

Inclusion of nitriles inside and outside the molecular bowls of tetrabromo calix[4]arene hosts

New tetrabromo calix[4]arene derivatives 2 and 5a/5b have been synthesised and found to function as inclusion hosts for nitrile guests. The X-ray structures of (2)₂ · (pivalonitrile)₃ and (5a) · (acetonitrile)₃ · (water) show that, in each compound, molecular inclusion occurs by a combination of complexation within the calixarene bowl and lattice inclusion outside the bowl. Racemic 5a/5b crystallises as a conglomerate, with chiral discrimination between these enantiomers being assisted by the propeller-shaped molecular conformation they adopt in the solid state.     

Crookes and Radioactivity: from Inorganic Evolution to Atomic Transmutation

Abstract

“On ions”—Such was the subject of Sir W. CROOKES' most recent lecture. Were they Spanish? Pickled? Boiled or fried …? They were made ‘visible’. This was hardly necessary, as in such a case the evidence to the eyes would be less convincing than that to the nose. (Punch, 1903)     

Sulfonamides as Ionophores for Ise. III. Guanidinium Ion-Selective Electrodes Based on Lipophilic Bis-Sulfonamide Podands

Abstract

PVC membrane ion-selective electrodes based on bis-sulfonamide podands and DOS (Bis(2-ethylhexyl)-sebacate) as plasticizer are described. They were found to behave as guanidinium ion sensors, exhibiting high selectivity for guanidinium ions over potassium ions.     

Phenanthroline-based fluorescence sensors for Eu3+ ion and subsequent enantioselective discriminating of malate

A pair of novel chiral fluorescent and colorimetric sensors L1 and D1 had been designed and synthesized, which were based on phenanthroline as the fluorophore and mandelohydrazide as the binding site. They showed selective recognition toward Eu³⁺ ion as ‘turn-off’ mode in DMSO-H₂O solution (v/v = 1:5, 10 mM HEPES, pH = 7.4). The fluorescence discrimination towards chiral carboxylate anions had been studied for L1-Eu³⁺ and D1-Eu³⁺ complex and they showed good enantioselective recognition ability towards malate as ‘turn-on’ mode. The interaction of sensor L1, D1 with Eu³⁺ and L1-Eu³⁺, D1-Eu³⁺ towards malate caused different color changes in the naked eye.     

CARBOHYDRATES CONTAINING SULFUR

Abstract

Thioglycosides with sulfur as the glycosidic bridge are naturally occurring. They have been examined chemically and also biochemically wherein they aid in establishment of enzyme activity. Sugars and sugar nucleoside derivatives with sulfur—and sometimes selenium and nitrogen—replacing the ring oxygen show interesting chemistry and are of great potential usefulness in medicine as indicated by initial biochemical investigations. Their value in biochemistry as analogs of natural structures is proving of useful interest. Carbohydrates with sulfur at positions other than at the anomeric carbon or with ring involvement have interesting chemical properties. This review presents a general survey of carbohydrates containing sulfur, of their special methods of synthesis, their special chemical properties and reactions and a very brief review of their biochemistry and potential clinical value.     

HUMIC MACROMOLECULES IN NATURAL WATERS

Abstract

Humic substances are the major organic constituents of soils and sediments. They also occur in small concentrations in natural surface waters and groundwaters. They form through the breakdown of plant and animal tissues by chemical and biological processes that tend to produce complex chemical structures that are more stable than the original material from which they were derived. One of the more important characteristics of humic substances is their ability to form water-soluble and water-insoluble complexes with metal ions and hydrous oxides and to interact with clay minerals and various organic compounds such as alkanes, fatty acids, and toxic organic substances such as pesticides.     

Enzymatic Resolution of α-Amino Phosphonous Acids -A Kinetic Comparison with Other α-Amino Acids Using 19F and 31P NMR Analysis

Abstract

We have previously reported (1,) the synthesis of a range of α-aminophosphonous acids and found them to be mimics of the naturally occurring amino acids. They inhibit the protein synthesis of E.Coli B (2) and other synthetases (3). We have now found that such compounds can be conveniently resolved via their N-acyl derivatives by enzymatic methods. Using penicillin-G-amidase from E.Coli (EC 3.5.1.11) the R-enantiomer is cleanly hydrolysed leaving the S-enantiomer intact.     

Ferroelectric properties of a series of core-fluorinated dopants containing the 2,3-difluoroalkoxy tail

Abstract

Previous reports from these laboratories [1] have discussed the synthesis and properties of core-fluorinated phenylpyridines with an attached difluoroalkoxy tail. This paper discusses core-fluorinated phenylpyridine difluoroalkoxides and compares their properties to those of the corresponding phenylpyrimidines. The pyridine and pyrimidine series are found to be remarkably similar in properties. They have similar high polarizations and fast rise times, attractive in surfacestabilized ferroelectric liquid crystal (SSFLC) applications, and in high concentration have pitch properties compatible with deformable helix FLC applications.     

Studies on the synthesis and properties of open-chain and macrocyclic crown compounds

Eight new open-chain crown compounds (1–8) and two new macrocyclic crown ethers (9 and10) were synthesized from 1,5-bis(2-aminophenoxy)-3-oxapentane (15) and 1,8-bis(2-aminophenoxy)-3,6-dioxaoctane (16) which were prepared by the catalytic hydrogenation of the corresponding bis(2-nitrophenoxy) derivatives13 and14. The fluorescent property investigation of two open-chain crown ethers (7 and8) indicated that they exhibit complexing effects on Ag⁺ and Mn²⁺ cations and can be used as fluorescent reagents for the microanalysis of the metal cations. The pyrolysis kinetics measurement for compounds5 and6 in nitrogen and air was carried out, and their reaction orders and activation energy were obtained. They are one-step and two-step pyrolysis reactions in nitrogen and air, respectively.     

Proline-catalysed asymmetric ketol cyclizations: The template mechanism revisited

A modified template mechanism based on modelling studies of energy minimised complexes is presented for the asymmetric proline-catalysed cyclization of triketones1,2 and3 to the 2S,3S-ketols1a,2a and3a respectively. The template model involves a three-point contact as favoured in enzyme-substrate interactions. Our minimisation studies are in agreement with the divergent behaviour of the 6,5-, 6,6-and 6,7-bicyclic systems. They support the high 93.4%ee observed with the 6,5-bicyclic ketol and the lower 73%ee found with the 6,6-bicyclic ketol. The calculations also explain the lack of asymmetric induction with the 6,7-bicyclic system     

A new antibacterial benzophenone glycoside from Psidium guajava (Linn.) leaves

Bioactivity-guided fractionation of methanol extract from the leaves of Psidium guajava L. (Myrtaceae) yielded a new benzophenone glycoside, Guajaphenone A (2) together with two known compounds, Garcimangosone D (1) and Guaijaverin (3). Their structures were elucidated by analysis of spectroscopic data including 1D and 2D NMR and electrospray ionisation mass spectrometry (ESI-MS). The isolated compounds were screened against standard strains of Gram-positive and Gram-negative bacteria using broth dilution assay method, and the MIC values determined and compared with reference antibiotic ceftriaxone. They were found to have significant antibacterial activities against Escherichia coli and Staphylococcus aureus with all of them showing better activities against S. aureus, but displaying weaker activities, in comparison to ceftriaxone. However, despite reduced effect of these compounds against the organisms, this work opens the perspective to use these molecules as ‘leads’ for the design of novel and selective drug candidates for some tropical infectious diseases.     

Synthesis,characterization, and pharmacological aspects of metal(II) complexes incorporating 4-[phenyl(phenylimino)methyl]benzene-1,3-diol

New metallointercalators (1a–1e) have been synthesized using the Schiff base, 4-[phenyl(phenylimino)methyl]benzene-1,3-diol and metal(II) ions, viz. Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). They are characterized by analytical and spectral methods. Elemental analyses and molar conductance values reveal that the Schiff base metal(II) complexes have 1?:?2 stoichiometry and are non-electrolytes. The Schiff base (HL) binds with M(II) ions through azomethine and deprotonated phenolic groups. Thermal studies reveal the presence of water in 1a–1c. Powder X-ray diffraction and SEM studies show that all the complexes are microcrystalline with homogenous morphology. In vitro biological activities of HL and 1a–1e have been screened against bacteria and fungi by well diffusion technique, revealing that these complexes are good antimicrobial agents against various pathogens. The complexes exhibit better biological activities than HL. Complex 1d binds with Calf thymus DNA through intercalation and weak covalent interactions. The oxidative cleavage of 1a–1e with pUC 19 DNA has also been explored. The results indicate that they bind to DNA through intercalation and are efficient metallointercalators and cleaving agents.     

FluMag-SELEX as an advantageous method for DNA aptamer selection

Aptamers are ssDNA or RNA oligonucleotides with very high affinity for their target. They bind to the target with high selectivity and specificity because of their specific three-dimensional shape. They are developed by the so-called Systematic Evolution of Ligands by Exponential Enrichment (SELEX) process. We have modified this method in two steps—use of fluorescent labels for DNA quantification and use of magnetic beads for target immobilization. Thus, radioactive labelling is avoided. Immobilization on magnetic beads enables easy handling, use of very small amounts of target for the aptamer selection, rapid and efficient separation of bound and unbound molecules, and stringent washing steps. We have called this modified SELEX technology FluMag-SELEX. With FluMag-SELEX we have provided a methodological background for our objective of being able to select DNA aptamers for targets with very different properties and size. These aptamers will be applied as new biosensor receptors. In this work selection of streptavidin-specific aptamers by FluMag-SELEX is described. The streptavidin-specific aptamers will be used to check the surface occupancy of streptavidin-coated magnetic beads with biotinylated molecules after immobilization procedures.     

Syntheses,crystal structures,and electrochemistry of novel Fe2SN and FeSN carbonyl complexes with pendant bases

Reactions of Fe₂(CO)₉ with thioacylhydrazones ArCH=NNHCSPh in THF afford Fe₂(CO)₆(μ-κ²S:κ²N-PhC(S)=NNCHArCHArN(CHAr)N=CSPh) (1, Ar?=?C₆H₅; 3, Ar?=?4-CH₃C₆H₄) and Fe(CO)₃(κ²S:N-PhC(=S)NHNCHArCHArN(CHAr)N=CSPh) (2, Ar?=?C₆H₅; 4, Ar?=?4-CH₃C₆H₄). They have been characterized by elemental analyses, IR, ¹H NMR, and ¹³C NMR and structurally determined by X-ray crystallography. Electrochemical studies reveal that when using HOAc as a proton source, they exhibit high catalytic H₂-production.     

SYNTHETIC POLYMERIC AMPHOLYTES IN SOLUTION

Abstract

Polyampholytes are classified as polyelectrolytes whose macromolecules contain functional groups of acidic and basic character [1, 2]. They possess unique physicochemical properties due to the contamination of oppositely charged units in the polymer chain. The interest in studying polyampholytes arises because they include such important natural polymers as proteins and nucleic acids [3]. Biopolymers possess specific structures, functions, and properties which are fully revealed only in living organisms [4]. Nevertheless, some properties of natural polymers can be simulated by using synthetic amphoteric macromolecules.     

Electrospray ionization mass spectrometric study of mercury complexes of N-heterocyclic carbenes derived from 1,2,4-triazolium salt precursors

By mixing 1,2,4-triazolium salts (precursors of N-heterocyclic carbenes 1–6) with mercury acetate, a number of complexes have been obtained under electrospray ionization condition. Carbenes 1 and 2 contain one carbene center; therefore, they are able to bond only one mercury cation. Carbenes 3–5 contain two carbene centers; therefore, they can bond two mercury cations. Mercury complexes of 1–5 always contain an acetate anion attached to a mercury cation. Carbene 6 also contains two carbene centers; however, its structure allows formation of a complex containing mercury bonded simultaneously to both centers, therefore, the complex that does not contain an acetate anion. The MS/MS spectra taken for complexes of carbenes 1–5 have shown formation of a cation corresponding to N1 substituent (adamantyl or benzyl), and those of complexes of carbenes 3–5 (doubly charged ions) have also shown the respective complementary partner ions. Mercury complex of 2 has yielded some other interesting fragmentation pathways, e.g. a loss of the HHgOOCCH₃ molecule. The fragmentation pathway of the mercury complexes of 6 was found to be complicated.     

Synthesis and X-Ray Crystal Structure of New Oxathiacrown Ethers Containing Sulfoxide Group and Their Metal-Binding Properties: Highly Selective Receptors for Ag+ and Cu2+

Three new oxathiacrown ethers 1, 2 and 3 containing a sulfoxide group were synthesized in a simple way. Conductometric titration studies in pure acetonitrile were employed to invistigate their binding affinities towards Ag ⁺, Cu ²⁺, Pb ²⁺, Cd ²⁺, Zn ²⁺, Co ²⁺, Ni ²⁺, Cr ³⁺and Hg ²⁺. They were found to be selective for Ag ⁺ and Cu ²⁺ over the other metals investigated. Ligand 1 has the highest selectivity towards Ag ⁺. The structure of compound 3 was confirmed by X-ray crystallography.Supplementary Data relevant to this article have been deposited at the Cambridge Crystallographic Data Centre under the deposition number 232076.     

Two hydrogen-bond-cross-linked molybdenum (VI) network polymers: synthesis, crystal structures and cyclooctene epoxidation with H2O2

Two molybdenum (VI) hydrogen-bonded network polymers [MoO₂F₄]·(4,4′-H₂bpd)(H₂O)₂ (1) and [MoO₂Cl₃(H₂O)]·(4,4′-H₂bpd)Cl (2) (bpd = bipiperidine) have been synthesized and examined as catalysts for epoxidation of cyclooctene. Complexes of the Mo compounds containing the bpd ligand are prepared and characterized by infrared spectroscopy, thermogravimetric and elemental analyses. They have been structurally characterized by single crystal X-ray diffraction analysis. The structures of both the complexes are shown to be comprised of molybdenum and two protonated N-ligand cations that have resulted in a cross-linked hydrogen-bonded network structure. These complexes are applicable as catalysts for the cis-cyclooctene epoxidation reactions with hydrogen peroxide as a source of oxygen and NaHCO₃ as a cocatalyst. It has been observed that the formation of the oxidant peroxymonocarbonate ion, HCO₄ ⁻ by hydrogen peroxide and bicarbonate enhances the epoxidation reaction. Both the complexes have exhibited a good activity and a very high selectivity for the formation of cyclooctene oxide. An erratum to this article can be found at     

The Synthesis of Perfluorocyclohexano-15-crown-5 Ether

Perfluorocyclohexano-15-crown-5 ether, trans- (1) and cis-(2) isomers have been prepared by direct fluorination using the LaMar fluorination technique¹. They have several potential applications and are of special interest in a variety of fields².