Mimicking Tyrosine Phosphorylation in Human Cytochrome c by the Evolved tRNA Synthetase Technique

Phosphorylation of tyrosine 48 of cytochrome c is related to a wide range of human diseases due to the pleiotropic role of the heme‐protein in cell life and death. However, the structural conformation and physicochemical properties of phosphorylated cytochrome c are difficult to study as its yield from cell extracts is very low and its kinase remains unknown. Herein, we report a high‐yielding synthesis of a close mimic of phosphorylated cytochrome c, developed by optimization of the synthesis of the non‐canonical amino acid p‐carboxymethyl‐L ‐phenylalanine (pCMF) and its efficient site‐specific incorporation at position 48. It is noteworthy that the Y48pCMF mutation significantly destabilizes the Fe?Met bond in the ferric form of cytochrome c, thereby lowering the pK_a value for the alkaline transition of the heme‐protein. This finding reveals the differential ability of the phosphomimic protein to drive certain events. This modified cytochrome c might be an important tool to investigate the role of the natural protein following phosphorylation.     

Integration of Temperature and Blue‐Light Sensing in Acinetobacter baumannii Through the BlsA Sensor

BlsA is a BLUF photoreceptor present in Acinetobacter baumannii, responsible for modulation of motility, biofilm formation and virulence by light. In this work, we have combined physiological and biophysical evidences to begin to understand the basis of the differential photoregulation observed as a function of temperature. Indeed, we show that blsA expression is reduced at 37°C, which correlates with negligible photoreceptor levels in the cells, likely accounting for absence of photoregulation at this temperature. Another point of control occurs on the functionality of the BlsA photocycle itself at different temperatures, which occurs with an average quantum yield of photoactivation of the signaling state of 0.20 ± 0.03 at 15°C < T < 25°C, but is practically inoperative at T > 30°C, as a result of conformational changes produced in the nanocavity of FAD. This effect would be important when the photoreceptor is already present in the cell to avoid almost instantaneously further signaling process when it is no longer necessary, for example under circumstances of temperature changes possibly faced by the bacteria. This complex interplay between light and temperature would provide the bacteria clues of environmental location and dictate/modulate light photosensing in A. baumannii.     

ZnO–Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Au Hybrid Composites for Thioanisole Oxidation Under Visible Light: Experimental and Theoretical Studies

Organic sulfides are present in many materials such as coal, organic polymers, and xenobiotics and cause severe pollution problems during disposal, and their oxidation is essential from the environmental point of view. ZnO and ZnO–Fe₃O₄–Au NPs were prepared, and characterized by analytical methods (XRD, TEM, HRTEM, XPS and Confocal Microscope Analysis) for employment as photo-catalysts for the oxidation of thioanisole under visible light. A considerable visible light photo-oxidation of sulfur compound was observed in the presence of ZnO–Fe₃O₄–Au NPs, where the content Fe₃O₄ facilitates its isolation and recovery from the reaction medium by an external magnet for reuse in the oxidation. The oxidation of thioanisole was monitored spectroscopically, and was found to follow first order kinetics in the substrate, for which a possible mechanism is proposed. Density functional theory was used to analyze the oxidation pathway in order to predict the rate limiting step in the reaction since the sulfoxidation through sulfide radical cation >S^+· → >S=O is important biotechnologically and environmentally.     

A study of the effects of thiols on the frontal polymerization and pot life of multifunctional acrylate systems with cumene hydroperoxide

In an effort to create frontal polymerization systems with a “fail‐safe” curing mechanism, we studied the effects of thiols on the thermal frontal polymerization velocity and pot life of a mixture of a multifunctional acrylate, kaolin clay (filler), and cumene hydroperoxide with either trimethylolpropane tris(3‐mercaptopropionate) or 1‐dodecanethiol (DDT). The acrylates were trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, 1,6‐hexanediol diacrylate, and di(ethylene glycol) diacrylate. Without a thiol, frontal polymerization did not occur. The front velocity increased with the concentration of either thiol, which has not been observed with peroxide initiators. The use of DDT yielded longer pot lives than the trithiol. The front velocities were inversely related to the pot lives. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3850–3855     

Two new zinniol-related phytotoxins from Alternaria solani

Bioassay-guided purification of the organic crude extract of Alternaria solani resulted in the isolation of three metabolites responsible for causing necrosis on potato leaves. These phytotoxins were identified as 2-(2",3"-dimethyl-but-1-enyl)-zinniol (1), 8-zinniol methyl ether (2). and 8-zinniol methyl ether based on their spectroscopic data (IR, MS, 1H and 13CNMR). Metabolites 1 and 2 have been identified as new phytotoxins structurally related to zinniol (4). Additionally, 5-(3',3'-dimethylallyloxy)-7-methoxy-6-methyl-phthalide and 8-zinniol-2-(phenyl)-ethyl ether (3) were also isolated during the purification process.     

Hydrogen‐bonded networks in trans‐3‐(3‐pyridyl)acrylic acid and rctt‐3,3′‐(3,4‐dicarboxycyclobutane‐1,2‐diyl)dipyridinium dichloride

The structure of trans‐3‐(3‐pyridyl)acrylic acid, C₈H₇NO₂, (I), possesses a two‐dimensional hydrogen‐bonded array of supramolecular ribbons assembled via heterodimeric synthons between the pyridine and carboxyl groups. This compound is photoreactive in the solid state as a result of close contacts between the double bonds of neighbouring molecules [3.821 (1) Å] along the a axis. The crystal structure of the photoproduct, rctt‐3,3′‐(3,4‐dicarboxycyclobutane‐1,2‐diyl)dipyridinium dichloride, C₁₆H₁₆N₂O₄²⁺·2Cl⁻, (II), consists of a three‐dimensional hydrogen‐bonded network built from crosslinking of helical chains integrated by self‐assembly of dipyridinium cations and Cl⁻ anions via different O—H...Cl, C—H...Cl and N⁺—H...Cl hydrogen‐bond interactions.     

Reduction of substituted 1H-4,5-dihydroimidazolium salts

Reactions of several substituted 1H-4,5-dihydroimidazolium salts 1 with nucleophilic and electrophilic reducing agents acting via hydride transfer were explored. Reaction of compounds 1 with lithium aluminum hydride in THF afforded the corresponding imidazolidines 2 . When alkaline borohydrides (sodium borohydride, potassium borohydride, sodium cyanoborohydride) in ethanol at room temperature were used, partial or total over-reduction of compounds 2 leading to N,N,N'-trisubstituted ethylenediamines took place on occasion. Results may be explained taking into account that reductive cleavage of 2 proceeds via a stabilized iminium ion present in protic solvents. Treatment of compounds 1 with an excess of borane in THF afforded the corresponding imidazolidines 2 or their borane complexes, according to the substituent type.     

Molecular Encapsulation of Half-Sandwich Complexes of Iron with Cyclodextrins: New Laminar Materials

The treatment of - and -cyclodextrins with the half-sandwich complexes of iron afford the inclusion compounds CpFe(L₂)XCD ( and ) (X = Cl, I; L = CO; L₂ = dppe, dppe = (Ph)₂P(CH₂)₂P(Ph)₂), [CpFe(L₂)L-]PF₆CD ( and ) L- neutral donor ligands and[(Cp(dppe)Fe)₂-µ-CN]PF₆2CD ( and ). The inclusion compounds [Cp(dppe)Fe-NCCH₃]PF₆-CD and [Cp(dppe)Fe-(¹-dppm)]PF₆-CD have a laminar structure. The - and -cyclodextrin encapsulation effect on the electro-oxidation of the binuclear complex was studied using cyclic voltammetry.The electron-transfer reactions associated with the oxidation of the two different N-bonded and C-bonded organometallic fragments are substantially affected by and encapsulation.     

Thermal curing behavior of MWCNT modified vinyl ester‐polyester resin suspensions prepared with 3‐roll milling technique

This study aims to investigate the curing behavior of a vinyl ester‐polyester resin suspensions containing 0.3 wt % of multiwalled carbon nanotubes with and without amine functional groups (MWCNTs and MWCNT‐NH₂). For this purpose, various analytical techniques, including Differential Scanning Calorimetry (DSC), Fourier infrared spectroscopy (FTIR), Raman Spectroscopy, and Thermo Gravimetric Analyzer (TGA) were conducted. The resin suspensions with carbon nanotubes (CNTs) were prepared via 3‐roll milling technique. DSC measurements showed that resin suspensions containing CNTs exhibited higher heat of cure (Q), besides lower activation energy (E_a) when compared with neat resin. For the sake of simplicity of interpretation, FTIR investigations were performed on neat vinyl ester resin suspensions containing the same amount of CNTs as resin. As a result, the individual fractional conversion rates of styrene and vinyl ester were interestingly found to be altered dependent on MWCNTs and MWCNT‐NH₂. The findings obtained from RS measurements of the cured samples are highly proportional to those obtained from FTIR measurements. TGA measurements revealed that CNT modified nanocomposites have higher activation energy of degradation (E_d) compared with the cured polymer. The findings obtained revealed that CNTs with and without amine functional groups alter overall thermal curing response of the surrounding matrix resin, which may probably impart distinctive characteristics to mechanical behavior of the corresponding nanocomposites achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1511–1522, 2009     

Deterministic chaos and natural phenomena

The natural time seriesf ₀ F ₂, F10.7, and AE are analyzed and low-dimensional attractors are found, characterized by the correlation dimension and the lower bound of the Kolmogorov entropy. Sources of noise in natural time series are discussed and the concept of extended systems is introduced and used to explain why the number of data required to calculate the correlation dimension of natural time series is higher than that reported by other authors.