A novel green synthesis of α/β-amino acid functionalized pyrimidinone peptidomimetics using triazole ligation through click-multi-component reactions

An innovative synthetic pathway for the preparation of a new series of triazole-decorated dihydropyrimidinone peptidomimetics with skeletal α or β-amino acid residue is reported. The protocol involves two synthetic steps with an initial solvent-free and catalyst-free synthesis of propargylated dihydropyrimidinone precursors using Biginelli condensations. The subsequent cycloaddition reactions of pyrimidinone alkynes with small peptide like azides prepared from Ugi or alternate Mannich type multi-component reactions afforded the triazole decorated pyrimidinone peptide conjugates in excellent yield with high regio and stereospecificities. In total, a scaffold diversity contains 11 new pyrimidinone alkynes and 18 new pyrimidinone peptidomimetics were introduced into the chemical space.     

Protein stabilization through supramolecular host–guest interactions with cyclodextrin-modified nanoparticles

This study demonstrates the protein stabilization of gelatin through supramolecular interactions of silica nanoparticles and the influence on the point of denaturation. The phenomenon was studied in diluted solutions by dynamic light scattering, viscosity measurements, and differential scanning calorimetry. Native gelatin is stabilized by cyclodextrin functionalized SiO₂ nanoparticles. After heating, increased supramolecular interactions of the nanoparticles with the denaturated gelatin coils are observed by progressive agglomeration. The described observation also resulted in a melting temperature shift from 30 °C, for native gelatin, to about 47 °C for the gelatin/CD-SiO₂, which indicates the supramolecular stabilization of the gelatin chain structure. It was found that the gelatin is supramolecularly immobilized on the nanoparticle up to a certain temperature through complexation by cyclodextrin. The described results, also confirmed by DSC and viscosity measurements, show the prospect of using cyclodextrin-modified surfaces for the immobilization of the proteins.     

Selective stabilization of self-assembled hydrogen-bonded molecular capsules through π-π interactions

Subtle noncovalent forces such as π-π interactions play an import role in the folding of biological macromolecules such as DNA and proteins. We describe here a system where such interactions on the outside of a molecular capsule trigger a selective change of its structure as a self-assembled receptor.     

Methyl-RNA: an evolutionary bridge between RNA and DNA?

Given the apparent limitation of double-stranded RNA (dsRNA) genomes to about 30 kb, together with the complexity of DNA synthesis, it appears difficult for a dsRNA genome to encode all the information required before the transition from an RNA to a DNA genome. Ribonucleotide reductase itself, which synthesizes deoxyribonucleotides from ribonucleotides, requires complex protein radical chemistry, and RNA world genomes may have reached their limits of coding capacity well before such complex enzymes had evolved. The transition from RNA to DNA thus appears to require intermediate steps, and we suggest that the naturally occurring 2'-O-methylated RNA, with chemical properties intermediate between RNA and DNA, is a suitable candidate.     

Is latex surface charge an important parameter for foam stabilization?

We describe the facile production of highly stable foams stabilized solely by cationic polystyrene latex particles. Three model polystyrene latexes were synthesized using either a cationic 2,2'-azobis(2-diisobutyramidine) dihydrochloride (AIBA) or an anionic ammonium persulfate (APS) radical initiator: a 724 +/- 81 nm charge-stabilized cationic polystyrene latex [AIBA-PS], an 800 +/- 138 nm sterically stabilized cationic latex prepared using a poly(ethylene glycol) monomethacrylate macromonomer [PEGMA-AIBA-PS], and a 904 +/- 131 nm charge-stabilized anionic polystyrene latex [APS-PS], respectively. The effect of particle surface charge, latex concentration, and solution pH on foam stability was studied in detail. The PEGMA-AIBA-PS latex proved to be the best foam stabilizer even at relatively low latex concentrations (3.0 wt %), with long-term foam stabilities being obtained after drying. The AIBA-PS latex also produced stable foams, albeit only at higher latex concentrations. However, the APS-PS latex proved to be an ineffective foam stabilizer. This is believed to be primarily due to the anionic surface character of this latter latex, which prevents its adsorption at the anionic air-water interface. This hypothesis is supported by the observation that the AIBA-PS latex no longer acts as an effective foam stabilizer above its isoelectric point (pH 7.04). Scanning electron microscopy studies revealed the formation of well-defined latex bilayers within dried foams, which indicates that the wet air bubbles are stabilized by latex monolayers prior to drying. However, little or no long-range ordering of the latex particles was observed on the surface of the bubbles, which is presumably related to the latex polydispersity.     

Strong interactions through the XAu–Y bridge: the Au bond?

The interaction between AuOH and the lone-pair donors (HF, H₂O) is shown to result in well-bound complexes whose structure resembles that of the corresponding H-bonded systems with the gold atom replacing hydrogen. The dissociation energies are estimated to be 10.7 and 27.4 kcal/mol for HFAu–OH and H₂OAu–OH, respectively. However, the interaction between AuOH and the lone pair donors is found to involve significant charge transfer. Furthermore, the Au–O stretching frequency increases upon the complex formation. It is concluded that, in spite of certain similarity to the H-bonded species, the Au-bonded complexes should be considered as Lewis acid–base pairs.     

Enhanced nonlinear optical properties of porphyrin with an extended π-conjugated bridge

In this work, a series of molecules with an extended π-conjugated bridge have been theoretically designed based on porphyrin, where -(CH=CH)_n- (n = 1–4, 8, 12) chain is served as an extended π-conjugated bridge. It is found that all molecules exhibit large energy gaps in the range of 3.484–4.151 eV for porphyrin-(CH=CH)_n-NH₂, and 3.624–4.250 for porphyrin-(CH=CH)_n-NO₂. The maximum absorption wavelengths of all molecules show a red shift trend with increasing -(CH=CH)_n- length, which leads to small transition energy. It is observed that long chain brings these molecules the large first hyperpolarizability, which are 1.04 × 10⁵ au for porphyrin-(CH=CH)₁₂-NH₂, 1.26×10⁵ au for porphyrin-(CH=CH)₁₂-NO₂. Moreover, compared with -(CH=CH)_n-NH₂ with the same chain length, -(CH=CH)_n-NO₂ chain can achieve larger nonlinear optical response. It is hoped that the research in this paper can provide a new strategy for the experimental design of nonlinear optical materials.

     

β-Lactones through Catalytic Asymmetric Heterodimerization of Ketenes

Simple, but effective: The asymmetric heterodimerization of two different ketenes has been developed 65?years after the first seminal studies on ketene dimerization. The key to sufficiently suppressing the competing homodimerization of the monosubstituted ketene donor (shown in blue) is its slow addition to the disubstituted acceptor (shown in red).     

Synthesis and characterization of an anion triazole framework containing μ 3-Cl and μ 2-Cl bridges

Using 3,5-dimethyl-4-amino-1,2,4-triazole (L) and corresponding Ag(I), K(I) salts under ammonia solution and hydrothermal conditions, a triazole–silver(I)–potassium(I) complex {K[Ag₂L₂(μ ₃-Cl)(μ ₂-Cl)₂]} _n (1) has been isolated. In 1, μ ₃-Cl, μ ₂-Cl and L bridge Ag^I ions forming a rare 1-D [Ag₂L₂(μ ₃-Cl)(μ ₂-Cl)₂]^? anion while K⁺ cations are located between neighboring anion chains. Strong solid-state fluorescence spectrum of 1 was also investigated showing that the excited peak is located at 320 nm while the maximum emission peak is located at 440 nm.     

Preparation of N3-thymidine–butylene–N3-thymidine interstrand cross-linked DNA via an orthogonal deprotection strategy

A DNA duplex containing an N3-thymidine–butylene–N3-thymidine interstrand cross-link (ICL) was prepared using an on-column orthogonal deprotection strategy to permit different nucleotide sequence composition around the cross-linked site. The conditions used to remove 5′-O-allyloxycarbonyl and 3′-O-tert-butyldimethylsilyl protective groups for various on-column oligonucleotide intermediates did not affect the cross-linked lesion. Efficient removal of these groups enabled successful coupling of 2′-deoxyphosphoramidites to produce the desired duplex with a 31% yield after deprotection and purification.     

Tetracycline prevents Aβ oligomer toxicity through an atypical supramolecular interaction

The antibiotic tetracycline was reported to possess an anti-amyloidogenic activity on a variety of amyloidogenic proteins both in in vitro and in vivo models. To unveil the mechanism of action of tetracycline on Aβ1-40 and Aβ1-42 at both molecular and supramolecular levels, we carried out a series of experiments using NMR spectroscopy, FTIR spectroscopy, dynamic laser light-scattering (DLS) and atomic force microscopy (AFM). Firstly we showed that the co-incubation of Aβ1-42 oligomers with tetracycline hinders the toxicity towards N2a cell lines in a dose-dependent manner. Therefore, the nature of the interaction between the drug and Aβ oligomers was investigated. To carry out NMR and FTIR studies we have prepared Aβ peptide solutions containing assemblies ranging from monomers to large oligomers. Saturation transfer difference (STD) NMR experiments have shown that tetracycline did not interact with monomers at variance with oligomers. Noteworthy, in this latter case we observed that this interaction was very peculiar since the transfer of magnetization from Aβ oligomers to tetracycline involved all drug protons. In addition, intermolecular cross-peaks between tetracycline and Aβ were not observed in NOESY spectra, indicating the absence of a specific binding site and suggesting the occurrence of a supramolecular interaction. DLS and AFM studies supported this hypothesis since the co-dissolution of Aβ peptides and tetracycline triggered the immediate formation of new aggregates that improved the solubility of Aβ peptides, preventing in this way the progression of the amyloid cascade. Moreover, competitive NMR binding experiments showed for the first time that tetracycline competes with thioflavin T (ThT) in the binding to Aβ peptides. Our data shed light on a novel mechanism of anti-amyloidogenic activity displayed by tetracycline, governed by hydrophobic and charge multiparticle interactions.     

Enantioselective synthesis of optically active cis-β-thio-α-amino acid derivatives through an organocatalytic cascade thio-Michael/ring opening process

Non-naturally enantioenriched cis-β-thio-α-amino acid derivatives were synthesized through one pot, cascade thio-Michael/ring opening reaction of aromatic thiols with (Z)-olefinic azlactones in good yields with high levels of diastereoselectivities and enantioselectivities, which was catalyzed by a chiral bifunctional thiourea-tertiary amine catalyst.     

A new sesquiterpene with a novel 1β, 8β-oxygen bridge from Heteropappus altaicus (willd.) Novopokr

A new guaiane-type sesquiterpene, 4α,7β-dihydroxy-10βH-guai-5-en-1β,8β-endoxide (1), was isolated from Heteropappus altaicus (Compositea). The structure of compound 1, which contains exhibited a rare 1,8-oxide bridge, was established on the basis of spectroscopic data.     

Thermische Analyse an Fluβsedimenten der Saale

Samples of sediments taken from the River Saale at different locations were investigated by thermogravimetry, differential thermal analysis, mass spectrometry and FTIR spectroscopy.The thermal behaviour of these sediments varied significantly depending on contents of organic and inorganic compounds. The variable organic loading resulted from the different degrees of treatment of communal or industrial waste water. Mass spectrometric investigations in the lower temperature ranges demonstrated humic substances as essential components.The mineral components in the river sections of the slate mountains differed significantly from those of the shell limestone. The results of FTIR analysis of these samples confirmed well with the findings of thermoanalytical investigations.This revised version was published online in November 2005 with corrections to the Cover Date.     

Enantioselective synthesis of β-pyrazole-substituted alcohols through an asymmetric ring-opening reaction of meso-epoxides

An efficient and practical synthesis of optically pure β-pyrazole-substituted alcohols was achieved by an asymmetric ring-opening reaction of meso-epoxides with pyrazole derivatives as the nucleophile. In the presence of 1?mol?% of an N,N'-dioxide-Sc(OTf)(3) complex, excellent enantioselectivity and yields were obtained from meso-epoxides. The process could also be used for a mixture of cis- and trans-stilbene oxides. A proposed transition-state model is provided.     

Production of biosurfactants through biodesulfurization of spent engine oil – an experimental study

Spent engine oil, a mixture of aliphatic and aromatic compounds, is one of the frequent environmental pollutants. In this paper, biodesulfurization of spent oil using Rhodococcus sp. was studied. Batch studies were conducted varying the oil to aqueous medium ratio of 10:90 to 90:10. The results demonstrated that maximum desulfurization of 80% was obtained at the oil to aqueous phase ratio of 70:30. Kinetic parameters of Monod type growth model, namely, µ_max, maximum specific growth rate and K_s, the half saturation constant were determined by varying the initial sulfur content of spent oil in the range of 0.16–1.05% (w/v). Gas chromatography–mass spectrometry was done to identify the compounds present in treated and untreated spent engine oil. The surface tension and emulsification indices of both oil and aqueous phases were also determined at different reaction times.