Synthesis and cation binding properties of fluorescent calix[4]arene derivatives bearing tryptophan units at the lower rim

The fluorescent peptidocalixarenes, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,27-di(O-methyl)-26,28-bis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (2), were prepared by introducing tryptophan subunits at a lower calixarene rim. Coordination abilities of 1 and 2 towards Eu(III) and alkali metal cations were studied by spectrophotometric, spectrofluorimetric, conductometric and potentiometric titrations in acetonitrile at 25°C. Rather strong complexation was observed for smaller alkali metal cations Li⁺ and Na⁺ (log K _Li1 >6, log K _Li2 >6, log K _Na1  = 8.25, log K _Na2  = 6.94), and moderate for K⁺ (log K _K1  = 5.09, log K _K2  = 4.09). Larger Rb⁺ and Cs⁺ cations did not fit in the ion binding site of 1 so no complexation was detected, whereas the more flexible ligand 2 accommodated Rb⁺ cation (log K _Rb2  = 3.44). The fluorescence of 1 (λ_ex = 280 nm, λ_em = 340 nm) was remarkably quenched by Eu(III). Stability constant of 1:1 (Eu³⁺:1) complex determined spectrofluorimetrically amounted to log K _Eu1  = 6.16.     

Electronic and Steric Effects of Lewis Acidic Organoaluminum Reagents in the Diels-Alder Reaction

The influence of electronic and steric effects of modified organoaluminum reagents to the stereoselectivity in the Diels-Alder and hetero-Diels-Alder reactions has been examined.     

Generation of 3-Carbanion Species from 3-Phenylsulfinyl- and 3-Phenylsulfonyl Propionic Acids

During the course of studies on butenolide synthesis¹ we have investigated the utilities of 3-sulfur-functionalized propionic acid derivatives. We report the results with 3-carbanion species obtained from 3-phenylsulfiny1- and 3-phenylsulfonylpropionic acids (1) and (2). These compounds were easily prepared from 3-phenylthiopropionic acid.     

A Pd(II)-hydroxyporphycene: synthesis, characterization, and photoinduced proton-coupled electron transfer

A Pd(II) complex, Pd(TPrPc-OH) (1, TPrPc-OH = 9-hydroxy-2,7,12,17-tetrapropylporphycenato dianion), has been synthesized and characterized. ¹H NMR spectroscopy revealed that compound 1 exists as its enol form in solution. The H atom of the hydroxy group in 1 was exchanged with deuterium on addition of ethanol-d ₆. UV–visible spectra showed a red shift of the Q band of 1 in THF compared with that of the acetoxy derivative Pd(TPrPc-OAc) (2, TPrPc-OAc = 9-acetoxy-2,7,12,17-tetrapropylporphycenato dianion). The pK _a value of the hydroxy group in 1 was determined, by means of a UV–visible titration experiment, to be 10.56. A cyclic voltammogram of 1 in a mixture of THF and Britton–Robinson buffered aqueous solution revealed one-electron and one-proton coupled transfer in the oxidation process in the pH range from 2.7 to 10.5, which was identified by pH-varying experiments and the Pourbaix diagram. Transient absorption spectroscopy revealed that an electron-transfer reaction occurred from the triplet excited-state of 1 to 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone, DQ) upon pulse laser irradiation at 532 nm. Such an intermolecular photoinduced electron-transfer reaction was not observed between the Ni analog, Ni(TPrPc-OH), and DQ. The reaction rate constant, k _q, was indicative of a kinetic isotope effect with k _q(H)/k _q(D) = 1.7, supporting the belief that the exited-state electron transfer from 1 to DQ is accompanied by proton transfer.     

Synthesis of phospholipids on a glyceric acid scaffold: design and preparation of phospholipase A2 specific substrates

Synthesis of a new series of phospholipid analogues to serve as activity-based probes of secretory phospholipase A₂ enzymes is reported. The synthesis is based upon (1) preparation of long-chain esters and amides of glyceric acid, followed by (2) regioselective derivatization of the diol function of the molecule to achieve phosphorylation at the primary hydroxyl group, and to introduce the incipient sn-2-ester group of the target compounds. The sequence has been shown to allow incorporation of fluorescent, paramagnetic, and redox-active reporter groups, leading to phospholipid analogues applicable to detect and measure enzyme activity, to develop highly specific, real-time spectroscopic assay of phospholipase A₂ enzymes, as well as to track the metabolic fate of the hydrolysis products. The synthetic method has a great deal of flexibility to open the way to the design and synthesis of activity-probes for other phospholipid metabolizing enzymes as well.     

Implementation of the k 0-standardization method for analysis of geological samples at the Neutron Activation Analysis Laboratory, São Paulo, Brazil

The Neutron Activation Analysis Laboratory (LAN-IPEN) has been analysing geological samples for many years with the INAA comparative method, for geochemical and environmental research. This study presents the results obtained in the implementation of the k ₀-standardization method at LAN-IPEN, for geological samples analysis, by using the program k ₀-IAEA, provided by the International Atomic Energy Agency (IAEA). The thermal to epithermal flux ratio f and the shape factor α of the epithermal flux distribution of the IEA-R1 nuclear reactor of IPEN were determined for the pneumatic irradiation facility and one selected irradiation position, for short and long irradiations, respectively. To obtain these factors, the “bare triple-monitor” method with ¹⁹⁷Au–⁹⁶Zr–⁹⁴Zr was used. In order to validate the methodology, the geological reference materials basalts JB-1 (GSJ) and BE-N (IWG-GIT), andesite AGV-1 (USGS), granite GS-N (ANRT), SOIL-7 (IAEA) and sediment Buffalo River Sediment (NIST–BRS-8704), which represent different geological matrices, were analysed. The concentration results obtained agreed with assigned, with bias <10 % except for Zn in AGV-1. The U-score test showed that all results, except Mg in JB-1, are within 95 % confidence interval. These results indicate excellent possibilities of using this parametric method at the LAN-IPEN for geochemical and environmental studies.     

Immobilization of Eversa® Transform via CLEA Technology Converts It in a Suitable Biocatalyst for Biolubricant Production Using Waste Cooking Oil

The performance of the previously optimized magnetic cross-linked enzyme aggregate of Eversa (Eversa-mCLEA) in the enzymatic synthesis of biolubricants by transesterification of waste cooking oil (WCO) with different alcohols has been evaluated. Eversa-mCLEA showed good activities using these alcohols, reaching a transesterification activity with isoamyl alcohol around 10-fold higher than with methanol. Yields of isoamyl fatty acid ester synthesis were similar using WCO or refined oil, confirming that this biocatalyst could be utilized to transform this residue into a valuable product. The effects of WCO/isoamyl alcohol molar ratio and enzyme load on the synthesis of biolubricant were also investigated. A maximum yield of around 90 wt.% was reached after 72 h of reaction using an enzyme load of 12 esterification units/g oil and a WCO/alcohol molar ratio of 1:6 in a solvent-free system. At the same conditions, the liquid Eversa yielded a maximum ester yield of only 34%. This study demonstrated the great changes in the enzyme properties that can be derived from a proper immobilization system. Moreover, it also shows the potential of WCO as a feedstock for the production of isoamyl fatty acid esters, which are potential candidates as biolubricants.     

α-Trifluoromethyl Chalcones as Potent Anticancer Agents for Androgen Receptor-Independent Prostate Cancer

α-Trifluoromethyl chalcones were prepared and evaluated for their antiproliferative activities against androgen-independent prostate cancer cell lines as well as five additional types of human tumor cell lines. The most potent chalcone 5 showed superior antitumor activity in vivo with both oral and intraperitoneal administration at 3 mg/kg. Cell-based mechanism of action studies demonstrated that 5 induced cell accumulation at sub-G1 and G2/M phases without interfering with microtubule polymerization. Furthermore, several cancer cell growth-related proteins were identified by using chalcone 5 as a bait for the affinity purification of binding proteins.     

Tungsten‐Catalyzed Regio‐ and Enantioselective Aminolysis of trans‐2,3‐Epoxy Alcohols: An Entry to Virtually Enantiopure Amino Alcohols

The first catalytic enantioselective aminolysis of trans‐2,3‐epoxy alcohols has been accomplished. This stereospecific ring‐opening process was efficiently promoted by a tungsten/bis(hydroxamic acid) catalytic system, furnishing various anti‐3‐amino‐1,2‐diols with excellent regiocontrol and high enantioselectivities (up to 95 % ee). Moreover, virtually enantiopure 3‐amino‐1,2‐diols could be obtained by the sequential combination of two reactions that both involve the use of a chiral catalyst.