The Ugi reaction with CF3-carbonyl compounds: effective synthesis of α-trifluoromethyl amino acid derivatives

The Ugi reaction with CF₃-carbonyl compounds is described in detail. The method is efficient for the multicomponent preparation of α-trifluoromethyl (Tfm) amino acids, α-Tfm containing dipeptides, and iminodicarboxylic acids. In addition, the first protected CF₃-opine derivative was prepared. The scope, limitations, and stereochemistry of the approach are discussed.     

Amine oxidase amperometric biosensor coupled to liquid chromatography for biogenic amines determination

A selective and sensitive method is presented for biogenic amines (BA) determination. The novelty consists in coupling a highly selective electrochemical biosensor to a weak acid cation-exchange column for online detection of amines. A bienzyme design, based on a recently isolated amine oxidase from grass pea and commercial horseradish peroxidase, was used for the biosensor construction. The enzymes were co-immobilized on the surface of a graphite electrode together with the electrochemical mediator (Os-redox polymer). The electrochemical detection was performed at a low applied potential (?50 mV vs. Ag/AgCl, KCl_0.1 M), where biases from interferences are minimal. The separation and determination of six BA, with relevance in food analysis (tyramine, putrescine, cadaverine, histamine, agmatine and spermidine), were investigated. Irrespective of the BA nature, the amine oxidase-based biosensor showed a linear response up to 5 mM, and its sensitivity decreases in the following order: cadaverine, putrescine, spermidine, agmatine, histamine and tyramine. The approach was used to estimate the BA content in fish samples, after their extraction with methanesulfonic acid.     

Critical evaluation of buffering solutions for pKa determination by capillary electrophoresis

The performance of the most common and also some other less common CE buffers has been tested for the pKa determination of several types of compounds (pyridine, amines, and phenols). The selected buffers cover a pH ranging from 3.7 to 11.8. Whereas some buffers, like acetic acid/acetate, BisTrisH+/BisTris, TrisH+/Tris, CHES/CHES-, and CAPS/CAPS- can be used with all type of analytes, others like ammonium/ammonia, butylammonium/butylammonia, ethylammonium/ethylammonia, diethylammonium/diethylammonia, and hydrogenphosphate/phosphate are not recommended because they interact with a wide range of compounds. The rest of the tested buffers (dihydrogenphosphate/hydrogenphosphate, MES/MES-, HEPES/HEPES-, and boric acid/borate) can show specific interactions depending on the nature of the analytes, and their use in some applications should be restricted.     

Light-Responsive Elastin-Like Peptide-Based Targeted Nanoparticles for Enhanced Spheroid Penetration

We describe here a near infrared light-responsive elastin-like peptide (ELP)-based targeted nanoparticle (NP) that can rapidly switch its size from 120 to 25 nm upon photo-irradiation. Interestingly, the targeting function, which is crucial for effective cargo delivery, is preserved after transformation. The NPs are assembled from (targeted) diblock ELP micelles encapsulating photosensitizer TT1-monoblock ELP conjugates. Methionine residues in this monoblock are photo-oxidized by singlet oxygen generated from TT1, turning the ELPs hydrophilic and thus trigger NP dissociation. Phenylalanine residues from the diblocks then interact with TT1 via π-π stacking, inducing the re-formation of smaller NPs. Due to their small size and targeting function, the NPs penetrate deeper in spheroids and kill cancer cells more efficiently compared to the larger ones. This work could contribute to the design of “smart” nanomedicines with deeper penetration capacity for effective anticancer therapies.     

An electrochemical study into the interaction between complement-derived peptides and DOPC mono- and bilayers

Electrochemical methods employing the hanging mercury drop electrode were used to study the interaction between variants of the complement-derived antimicrobial peptide CNY21 (CNYITELRRQH ARASHLGLAR) and dioleoyl phosphatidylcholine (DOPC) monolayers. Capacitance potential and impedance measurements showed that the CNY21 analogues investigated interact with DOPC monolayers coating the mercury drop. Increasing the peptide hydrophobicity by substituting the two histidine residues with leucine resulted in a deeper peptide penetration into the hydrophobic region of the DOPC monolayer, indicated by an increase in the dielectric constant of the lipid monolayer (Deltaepsilon = 2.0 after 15 min interaction). Increasing the peptide net charge from +3 to +5 by replacing the histidines by lysines, on the other hand, arrests the peptide in the lipid head group region. Reduction of electroactive ions (Tl+, Pb2+, Cd2+, and Eu3+) at the monolayer-coated electrode was employed to further characterize the types of defects induced by the peptides. All peptides studied permeabilize the monolayer to Tl+ to an appreciable extent, but this effect is more pronounced for the more hydrophobic peptide (CNY21L), which also allows penetration of larger ions and ions of higher valency. The results for the various ions indicate that charge repulsion rather than ion size is the determining factor for cation penetration through peptide-induced defects in the DOPC monolayer. The effects obtained for monolayers were compared to results obtained with bilayers from liposome leakage and circular dichroism studies for unilamellar DOPC vesicles, and in situ ellipsometry for supported DOPC bilayers. Trends in peptide-induced liposome leakage were similar to peptide effects on electrochemical impedance and permeability of electroactive ions for the monolayer system, demonstrating that formation of transmembrane pores alone does not constitute the mechanism of action for the peptides investigated. Instead, our results point to the importance of local packing defects in the lipid membrane in close proximity to the adsorbed peptide molecules.     

Design of oxide nanoparticles by aqueous chemistry

The elaboration of nanoparticles designed for technological applications in various fields such as catalysis, optics, magnetism, electronics… needs the strict control of their characteristics, especially chemical composition, crystalline structure, size, and shape. These characteristics bring the physical properties (color, magnetism, band gap…) of the material, and also the surface to volume ratio of particles which is of high importance when they are used as a chemically active or reactive support, in catalysis for instance. The nanoparticles may have also to be surface functionalized by various species, and/or dispersed in aqueous or non aqueous media. We will show that the aqueous chemistry of metal cations is a very versatile and attractive way for the design of oxide nanomaterials, allowing the control of size, shape, and crystalline structure for polymorphic materials. Aqueous surface chemistry, including adsorption of various species, may be used to modify the morphology of nanoparticles. In some cases, redox processes can be involved to control the morphology of nanoparticles. Technologically important nanomaterials such as titania, alumina, and iron oxides are studied.     

Mono- and diprotonation of the superbasic bisguanidine 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) and Pt II and Pt IV complexes of chelating bisguanidines and guanidinates

New Pt complexes of chelating bisguanidines and guanidinate ligands were synthesized and characterized. 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) was used as a neutral chelating bisguanidine ligand, and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate (hpp(-)) as a guanidinate ligand. The salts [btmgbH](+)[HOB(C(6)F(5))(3)](-) and [btmgbH(2)]Cl(2) and the complexes [(btmgb)PtCl(2)], [(btmgb)PtCl(dmso)](+)[PtCl(3)(dmso)](-), and [(btmgb)PtCl(dmso)](+)[Cl(-)] were synthesized and characterized. In the [btmgbH](+) cation the proton is bound to only one N atom. In the other complexes, both imine N atoms are coordinated to the Pt(II), thus adopting a eta(2)-coordinational mode. The hpp(-) anion, which usually prefers a bridging binding mode in dinuclear complexes, is eta(2)-coordinated in the Pt(IV) complex [(eta(2)-hpp)(hppH)PtCl(2){N(H)C(O)CH(3)}], which is formed (in low yield) by reaction between cis-[(hppH)(2)PtCl(2)] and H(2)O(2) in CH(3)CN.     

A novel Ni(4) complex exhibiting microsecond quantum tunneling of the magnetization

A highly asymmetric Ni(II) cluster [Ni(4)(OH)(OMe)(3)(Hphpz)(4)(MeOH)(3)](MeOH) (1) (H(2)phpz=3-methyl-5-(2-hydroxyphenyl)pyrazole) has been prepared and its structure determined by means of single-crystal X-ray diffraction by using synchrotron radiation. Variable-temperature bulk-magnetization measurements show that the complex exhibits intramolecular-ferromagnetic interactions leading to a spin ground state S=4 with close-lying excited states. Magnetization and high-frequency EPR measurements suggest the presence of sizable Ising-type magnetic anisotropy, with zero-field splitting parameters D=-0.263 cm(-1) and E=0.04 cm(-1) for the spin ground state, and an isotropic g value of 2.25. The presence of both axial and transverse anisotropy was confirmed through low-temperature specific heat determinations down to 300 mK, but no slow relaxation of the magnetization was observed by AC measurements down to 1.8 K. Interestingly, AC susceptibility measurements down to temperatures as low as 23 mK showed no indication of slow relaxation of the magnetization in 1. Thus, despite the presence of an anisotropy barrier (U approximately 4.21 cm(-1) for the purely axial limit), the magnetization relaxation remains extremely fast down to the lowest temperatures. The estimated quantum tunneling rate, Gamma>0.667 MHz, makes this complex a prime candidate for observation of coherent tunneling of the magnetization.     

Biological Pretreatment of Chicken Feather and Biogas Production from Total Broth

Chicken feathers are available in large quantities around the world causing environmental challenges. The feathers are composed of keratin that is a recalcitrant protein and is hard to degrade. In this work, chicken feathers were aerobically pretreated for 2–8 days at total solid concentrations of 5, 10, and 20 % by Bacillus sp. C₄, a bacterium that produces both α- and β-keratinases. Then, the liquid fraction (feather hydrolysate) as well as the total broth (liquid and solid fraction of pretreated feathers) was used as substrates for biogas production using anaerobic sludge or bacteria granules as inoculum. The biological pretreatment of feather waste was productive; about 75 % of feather was converted to soluble crude protein after 8 days of degradation at initial feather concentration of 5 %. Bacteria granules performed better during anaerobic digestion of untreated feathers, resulting in approximately two times more methane yield (i.e., 199 mlCH₄/gVS compared to 105 mlCH₄/gVS when sludge was used). Pretreatment improved methane yield by 292 and 105 % when sludge and granules were used on the hydrolysate. Bacteria granules worked effectively on the total broth, yielded 445 mlCH₄/gVS methane, which is 124 % more than that obtained with the same type of inoculum from untreated feather.