Insights into sulfinate formation from tosyl hydrazides

Benzylation of 1,2-ditosylhydrazine in DMF under various basic conditions results in a benzyl sulfone via intermediary sulfinate formation, providing new insights and allowing practical conclusions to be drawn. The half-lives of 1,2-ditosylhydrazine and several monotosylated hydrazides with 1,1,3,3-tetramethylguanidine in DMSO have been determined by ¹H NMR spectroscopy and are found to vary from a few minutes to several months. In the course of this work a benzylated, partly detosylated compound has been identified and a 1,1,3,3-tetramethyl guanidine-containing side-product characterized. A contradictory report is also commented on.     

Insights into electrocatalysis from ambient pressure photoelectron spectroscopy

Near ambient pressure X-ray photoelectron spectroscopy has recently emerged as a powerful tool for studies of electrocatalytic materials. This article provides a brief overview of the opportunities, which near ambient pressure X-ray photoelectron spectroscopy offers for furthering the understanding of electrocatalysis, and challenges, which have to be met in order to avoid certain pitfalls.     

Insights into uranyl chemistry from molecular dynamics simulations

First-principles and purely classical molecular dynamics (MD) simulations for complexes of the uranyl ion (UO(2)(2+)) are reviewed. Validation of Car-Parrinello MD simulations for small uranyl complexes in aqueous solution is discussed. Special attention is called to the mechanism of ligand-exchange reactions at the uranyl centre and to effects of solvation and hydration on coordination and structural properties. Large-scale classical MD simulations are surveyed in the context of liquid-liquid extraction, with uranyl complexes ranging from simple hydrates to calixarenes, and nonaqueous phases from simple organic solvents and supercritical CO(2) to ionic liquids.     

Insights into Ligand-Protein Binding from Local Mechanical Response

Computational studies of ligand-protein binding are crucial for properly designing novel compounds of potential pharmacological interest. In this respect, researchers are increasingly interested in steered molecular dynamics for ligand-protein binding and unbinding studies. In particular, it has been suggested that analyzing the work profiles along the ligand-protein undocking paths could be fruitful. Here, we propose that small portions of work profiles, termed "local mechanical responses" of the system to a steering force, could serve as a universal measure for capturing relevant information about the system under investigation. Specifically, we first collected a high number of steering trajectories using two biological systems of increasing complexity (i.e., alanine dipeptide and (R)-roscovitine/CDK5 complex). Then, we devised a novel postprocessing tool to be applied to the local mechanical responses, to extract structural information related to the biological processes under investigation. Despite the out-of-equilibrium character of the trajectories, the analysis carried out on the work profiles provided pivotal information about the investigated biological processes. This could eventually be applied to drug design.     

Effects of photodegradation on the physical and antioxidant properties of melanosomes isolated from retinal pigment epithelium

Melanosomes of the retinal pigment epithelium (RPE) are relatively long-lived organelles that are theoretically susceptible to changes induced by exposure to visible light. Here melanosomes were isolated from porcine RPE cells and subjected to high intensity visible light to determine the effects of illumination on melanosome structure and on the content and antioxidant properties of melanin. As compared to untreated melanosomes, illuminated granules showed morphologic changes consistent with photodegradation, which included variable reductions in electron density demonstrated by transmission electron microscopy (TEM), and particle fragmentation and surface disruption revealed by scanning electron microscopy (SEM) and atomic force microscopy. Illuminated melanosomes had lower melanin content, indicated by measures of absorbance and electron spin resonance (ESR) signal intensity, and reduced ability to bind iron, shown by chemical and ESR analyses. Compared to untreated melanosomes, ESR-spin trapping analyses further indicated that illuminated melanosomes show increased photogeneration of superoxide anion and reduced ability to inhibit the iron ion-catalyzed free radical decomposition of hydrogen peroxide. It appears therefore that visible light irradiation can disrupt the structure of RPE melanosomes and reduce the amount and antioxidant properties of melanin. Some of these changes occur in human RPE melanosomes with aging and the results obtained here suggest that visible light irradiation is at least partly responsible. The consequence of light-induced changes in RPE melanosomes may be a diminished capacity of melanin to help protect aged cells from oxidative damage, perhaps increasing the risk of diseases with an oxidative stress component such as age-related macular degeneration.     

Insights into hydrogen atom adsorption on and the electrochemical properties of nitrogen-substituted carbon materials

The nitrogen substitution in carbon materials is investigated theoretically using the density functional theory method. Our calculations show that nitrogen substitution decreases the hydrogen adsorption energy if hydrogen atoms are adsorbed on both nitrogen atoms and the neighboring carbon atoms. On the contrary, the hydrogen adsorption energy can be increased if hydrogen atoms are adsorbed only on the neighboring carbon atoms. The reason can be explained by the electronic structures analysis of N-substituted graphene sheets. Nitrogen substitution reduces the pi electron conjugation and increases the HOMO energy of a graphene sheet, and the nitrogen atom is not stable due to its 3-valent character. This raises an interesting research topic on the optimization of the N-substitution degree, and is important to many applications such as hydrogen storage and the tokamaks device. The electronic structure studies also explain well why nitrogen substitution increases the capacitance but decreases the electron conductivity of carbon electrodes as was experimentally observed in our experiments on the supercapacitor.     

Compartmentalisation in miniemulsions: exploration of compartmentalisation and some interesting end-uses

Infrared spectroscopy and differential scanning calorimetry were used to demonstrate that miniemulsions of relatively hydrophobic monomers are compartmentalised during the reaction. Experiments with blends of miniemulsions of different composition revealed that no mass transfer takes place between droplets of different composition in the same reactor. In addition, it was shown that it is possible to make high solids content, low viscosity latexes with bimodal particle size and molecular weight distributions because of this property.     

Comparison of structural and chemical properties of black and red human hair melanosomes

Melanosomes in black and red human hair are isolated and characterized by various chemical and physical techniques. Different yields of 4-amino-hydroxyphenolanaline by HI hydrolysis (a marker for pheomelanin) and pyrrole-2,3,5-tricarboxylic acid by KMnO(4)/H(+) oxidation (a marker for eumelanin) indicate that the melanosomes in black hair are eumelanosomes, whereas those in red hair are mainly pheomelanosomes. Atomic force microscopy reveals that eumelanosomes and pheomelanosomes have ellipsoidal and spherical shapes, respectively. Eumelanosomes maintain structural integrity upon extraction from the keratin matrix, whereas pheomelanosomes tend to fall apart. The black-hair eumelanosomes have an average of 14.6 +/- 0.5% amino acids content, which is attributed to the internal proteins entrapped in the melanosomes granules. The red-hair melanosomes contain more than 44% of amino acid content even after extensive proteolytic digestion. This high content of amino acids and the poorly reserved integrity of red-hair melanosomes suggest that some proteins are possibly covalently bonded with the melanin constituents in addition to those that are entrapped inside the melanin species. Soluene solubilization assay indicates the absorbance of melanin per gram of sample, adjusted for the amino acid content, is a factor of 2.9 greater for the black-hair melanosomes than the red-hair melanosomes. Metal analysis reveals significant amounts of diverse heavy metal ions bound to the two types of melanosomes. The amount of Cu(II) and Zn(II) are similar but Fe(III) content is four times higher in the red-hair melanosomes. (13)C solid-state nuclear magnetic resonance spectra and infrared spectra are presented and are shown to be powerful techniques for discerning differences in the amino acid contents, the 5,6-dihydroxyindole-2-carboxylic acid:5,6-dihydroxyindole ratio, and the degree of cross-linking in the pigment. Excellent agreement is observed between these spectral results and the chemical degradation data.     

Experiments on temporal and spatial chemical patterns

Two examples of bifurcation sequences observed in experiments on nonequilibrium reactions in continuous flow stirred reactors are discussed: one experiment demonstrates that bifurcation diagrams can serve as a tool for elucidating chemical mechanisms, and another experiment illustrates that even very complex bifurcation sequences need not include chaotic states. A discussion of chemical spatial patterns emphasizes the need for the development of spatially extended reactors in which patterns can be maintained indefinitely. Three such recently developed reactors are described.     

Formation and some properties of barium titanate embedded into porous matrices

Embedding of barium titanate into porous oxide matrices via sol–gel synthesis and introduction in structured slurry based on fumed oxides has been carried out. Prepared compositions have been studied using XRD, DTA-TG, FTIR, TEM, and adsorption of nitrogen. It has been established that simultaneous formation both barium titanate crystal structure and porous structure of matrices occurs. Crystallites of barium titanate, which arise in pores, possess lesser size in comparison with that for bulk BaTiO₃.     

Insights into the structure and function of redox-active tyrosines from model compounds

Redox-active tyrosine residues play important roles in long distance electron-transfer reactions in enzymes, including prostaglandin H synthase, ribonucleotide reductase, and photosystem II. In cytochrome c oxidase, a cross-linked tyrosine-histidine cofactor has been proposed to play a role in proton and electron transfer reactions. Studies of tyrosyl radicals in model compounds, generated by UV photolysis, have recently provided new information about the structure and function of these redox-active species. The results of these studies, which combine magnetic resonance and optical spectroscopies, are described in this review.     

Insights into photodissociation dynamics of benzamide and formanilide from ab initio calculations

In the present study, the five lowest electronic states that control the UV photodissociation of formanilide and benzamide have been characterized using the complete active space self-consistent field theory. The mechanisms for the initial relaxation and subsequent dissociation processes have been determined on the basis of the calculated potential energy surfaces and their intersections. It was found that the S(1)/T(1)/T(2) three-surface intersection plays an important role in the photodissociation processes of benzamide. However, the dissociation behavior of formanilide and benzamide was found to be quite different from that for aliphatic amides. The present study provides several insights into the photodissociation dynamics of formanilide and benzamide.     

Insights into the luminescent properties of anionic cyclometalated iridium(III) complexes with ligands derived from natural products

In the search of remarkable anionic electroluminescent semiconductors to be applied in energy conversion devices such as Light Emitting Electrochemical Cells, we report the electronic, photophysical, and charge injection/transfer properties of a series of cyclometalated iridium(III) complexes through a DFT/TD‐DFT procedure. The proposed semiconductors involve bidentated ligands based on natural products (salicylic acid and boldine), and phenylpyridine and phenylpyrazole as the cyclometalating units. The proposed compounds emit in the range of 446 to 571 nm, where the boldine based compounds have red‐shifted emissions compared to their analogs with salicylic acid. Blue phosphors were obtained by the use of phenylpyrazole units; however, the ligand field is weak in these cases compared to the ligand field exerted by the phenylpyridine ligands. The latter allows the accessibility to the radiationless states for emitters below 495 nm as a result of the increased stability of the metal centered excited states; consequently, the luminescent quantum yield could be decreased. Conversely, the semiconductors with phenylpyridine units show a restricted accessibility to radiationless processes, which could result in emitters with a high luminescent quantum yield and low non‐radiative constants. Finally, the proposed anionic semiconductors show a better balance between hole/electron transfer rate compared to related cationic Ir(III) complexes; while, the easier hole‐electron injection is favored for semiconductors with salicylic acid and phenylpyridine units.     

Pyrimidine-core extended pi-systems: general synthesis and interesting fluorescent properties

We have developed a simple but powerful synthetic strategy that permits the assembly of pi-systems onto a pyrimidine core in a programmable and diversity-oriented format. The nucleophilic addition of ArLi to 2-methylthiopyrimidine, followed by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidation, resulted in the production of 4-aryl-2-methylthiopyrimidines. The iterative reaction sequence then gave 4,6-diaryl-2-methylthiopyrimidines. The resulting adduct was further allowed to react with ArMgBr under the catalytic influence of NiCl2(dppe) to afford 2,4,6-triarylpyrimidines. By following this synthetic scheme, interesting pyrimidine-core pi-systems were rapidly constructed in a programmable fashion. The successful discovery of a number of interesting fluorescent materials and properties (e.g., solvatofluorochromism) speaks well for the potential of our platform strategy in the development of functional organic materials.     

Insights into the Oxidation Chemistry of SiOC Ceramics Derived from Silsesquioxanes

We have undertaken a systematic study of the oxidation chemistry for a range of SiOC ceramics derived from silsesquioxane polymeric precursors. This study examines the oxidation for 500 hours at 600, 800, 1000 and 1200°C for four SiOC powders. The material changes upon oxidation were characterized qualitatively by color change and optical microscopy and quantitatively by weight and composition change. In this study we employ a very easy method that uses the weight change upon oxidation and a carbon analysis after oxidation to arrive at the composition of the oxidized SiOC. Combined these qualitative and quantitative techniques have shown that on oxidation at 800 and 600°C the SiOC composition is more rapidly changed to that of silica than oxidation over the same time frame at 1000 or 1200°C. The data indicates that this difference is due to the relative rates of oxidation of the excess carbon versus the Si—C bonds in the SiOC. At lower temperatures initially the carbon oxidation predominates which leads to higher porosity throughout the material and an increase in the surface area with eventually complete oxidation to silica. At higher temperatures the Si—C bond oxidation rate is comparable to the rate of oxidation of carbon. This allows a silica-like surface to build up on the SiOC, which slows all subsequent reactions due to the necessity to diffuse O2 in and COx out of the bulk. Under these oxidation conditions materials that originally contain high amounts of excess carbon are more quickly oxidized to silica than those that contain minimal amounts of excess carbon, as confirmed by elemental analysis and optical microscopy. Regardless of the time or temperature of the oxidation conditions no materials were found to be completely stable to oxidation. SiOC materials with low levels of excess carbon showed the best resistance to change upon oxidation.     

Entrapment of some compounds into biocompatible nano-sized particles and their releasing properties

Two types of biocompatible nanoparticles with an average diameter of around 200 nm were formed only by mixing hydrolysates of chitosan and carboxymethyl cellulose (CMC). Nanoparticle A was produced from chitosanase hydrolysate of chitosan and cellulase hydrolysate of carboxymethyl cellulose, and nanoparticle B was produced from lysozyme hydrolysate of chitosan and the carboxymethyl cellulose hydrolysate. Negatively charged or amphoteric compounds were first mixed with chitosan hydrolysate and then added to carboxymethyl cellulose hydrolysate to effectively entrap them in the particles. Positively charged compounds could also be effectively entrapped by mixing the hydrolysates and the compound in the reverse order. Negatively charged compounds with high molecular weights were maintained in the particles even at the higher pH levels than the pK(a) of the amino groups of chitosan. Entrapped compounds were gradually released from nanoparticle A by lysozyme treatment. In contrast, there was no release from nanoparticle B. These results indicate that nanoparticle A can be applied to controlled-release drug delivery systems, and that nanoparticle B is stably retained in the body without releasing the entrapped compounds.     

Insights into coal structure from degradation with ruthenium tetroxide and tandem mass spectrometry

The products of ruthenium tetroxid oxidation of coal (Illinois No. 2) at ambient temperature were examined by tandem mass spectrometry using positive and negative chemical ionization. The negative-ion mass spectrum of the coal sample displays seven homologous series of ions. Individual compounds were characterized by recording daughter spectra. In this way, the following types of compounds were identified: aliphatic dicarboxylic acids, aromatic dicarboxylic and tricarboxylic acids, anhydrides of the di- and tri-carboxylic acids, and dianhydrides corresponding to the tetracarboxylic aromatic acids. The positive-ion mass and daughter spectra provided additional confirmation. Two series of ions dominate the positive-ion mass spectrum, those from the aliphatic dicarboxylic acids, and the corresponding anhydrides. The fragmentation behavior of model compounds was examined to confirm these assignments. The carboxylic acids and anhydrides identified suggest the presence of particular structural features in the coal prior to oxidation. These include C₂–C₆ aliphatic bridges between aromatic units, fused ring aromatic structures, tetralin and indan structures.     

Insights into the acid-base properties of Pt(IV)-diazidodiam(m)inedihyroxido complexes from multinuclear NMR spectroscopy

Platinum(IV) am(m)ine complexes are of interest as potential anticancer pro-drugs, but there are few reports of their acid-base properties. We have studied the acid-base properties of three photoactivatable anticancer platinum(IV)-diazidodiam(m)ine complexes (cis,trans,cis-[Pt(IV)(N(3))(2)(OH)(2)(NH(3))(2)], trans,trans,trans-[Pt(IV)(N(3))(2)(OH)(2)(NH(3))(2)], and cis,trans-[Pt(IV)(N(3))(2)(OH)(2)(en)]) using multinuclear NMR methods and potentiometry. In particular, the combination of both direct and indirect techniques for the detection of (15)N signals has allowed changes of the chemical shifts to be followed over the pH range 1-11; complementary (14)N NMR studies have been also carried out. A distinct pK(a) value of approximately 3.4 was determined for all the investigated complexes, involving protonation/deprotonation reactions of one of the axial hydroxido groups, whereas a second pH-dependent change for the three complexes at approximately pH 7.5 appears not to be associated with a loss of an am(m)ine or hydroxido proton from the complex. Our findings are discussed in comparison with the limited data available in the literature on related complexes.     

Cordierite-based refractory ceramics from natural halloysite and peridotite: Insights on technological properties

Cordierite-based ceramics were fabricated from Moroccan natural halloysite clay by using a simple and low-cost manufacturing method. To this end, peridotite and halloysite samples, collected from Beni Bousera and Melilla sites, Morocco, were used as raw materials for ceramics manufacturing. A starting mixture was prepared (76.08 wt% of clay and 23.92 wt% of peridotite), molded and heated to the desired temperature (1250, 1300 and 1350 °C) to fabricate cordierite ceramic specimens. Both raw materials (peridotite and halloysite) and final ceramics were analyzed using routine characterization techniques including chemical analysis by XRF, mineralogical analysis by XRD, thermogravimetric analysis, and morphological characteristics using scanning electron microscopy (SEM). The prepared ceramics were investigated regarding their mineralogical composition, thermal and technological properties, chemical resistance, and microstructural characteristics. Our results indicated that peridotite sample is mainly composed of silica (40.25 wt%) and magnesia (38.05 wt%) while halloysite is consisted essentially of silica (38.00 wt%) and alumina (34.13 wt%). This was confirmed by XRD, TG-DTA and FTIR analyses. The prepared ceramic specimens at different sintering temperatures (i.e., 1250, 1300 and 1350 °C) have regular cylindrical forms, displaying good ceramic properties. This is consolidated with the main technological tests including porosity (4.56–3.11%), bulk density (2.45–2.78 g/cm³), shrinkage (6.51–10.31%), indirect tensile strength (20.35–27.60 MPa), and low linear thermal expansion coefficient (3.05–2.18 × 10^?6/°C). Cordierite specimen prepared at 1350 °C provided the best ceramic sample with the highest technological properties, good chemical resistance and thermal properties. Thus, naturally abundant halloysite and peridotite deposits are potential candidates for cordierite-based ceramic manufacture. Therefore, the achieved results have provided cost-effective ceramic bricks with physical, thermal and mechanical properties that are favorable to be used as refractory bricks.     

Insights into the Biosynthesis of Cyclic Guanidine Alkaloids from Crambeidae Marine Sponges

Among the outstanding chemical diversity found in marine sponges, cyclic guanidine alkaloids, present in species of the family Crambeidae, are particularly attractive, not only because of their unique chemical features, but also due to a broad range of biological activities. Despite a growing interest in these natural products as therapeutic agents, their metabolic pathway has not been experimentally investigated. Ex situ feeding experiments using radiolabeled precursors performed on the Mediterranean sponge Crambe crambe suggest arginine and fatty acids as precursors in the metabolic pathway of crambescins. A subsequent bio‐inspired approach supported the change of paradigm in the metabolic pathway of cyclic guanidine alkaloids. A large part of the chemical diversity of this family would therefore originate from a tethered Biginelli‐like reaction between C‐2/C‐3 activated fatty acids and a central guanidinylated pyrrolinium.