Cyclization of the methyl ester of α-propionyllevulinic acid

Summary Cyclization of methyl -propionyllevulinate to 2,3-dimethylcyclopenten-2-one and methyl 3,4-dimethylcyclopenten-3-one-2-carboxylate was accomplished.     

What is the future of electrophoresis in large-scale genomic sequencing?

Although a finished human genome reference sequence is now available, the ability to sequence large, complex genomes remains critically important for researchers in the biological sciences, and in particular, continued human genomic sequence determination will ultimately help to realize the promise of medical care tailored to an individual's unique genetic identity. Many new technologies are being developed to decrease the costs and to dramatically increase the data acquisition rate of such sequencing projects. These new sequencing approaches include Sanger reaction-based technologies that have electrophoresis as the final separation step as well as those that use completely novel, nonelectrophoretic methods to generate sequence data. In this review, we discuss the various advances in sequencing technologies and evaluate the current limitations of novel methods that currently preclude their complete acceptance in large-scale sequencing projects. Our primary goal is to analyze and predict the continuing role of electrophoresis in large-scale DNA sequencing, both in the near and longer term.     

What is the structure of the RecA-DNA filament?

The bacterial RecA protein has been a model system for understanding how a protein can catalyze homologous genetic recombination. RecA-like proteins have now been characterized from many organisms, from bacteriophage to humans. Some of the RecA-like proteins, including human RAD51, appear to function as helical filaments formed on DNA. However, we currently have high resolution structures of inactive forms of the protein, and low resolution structures of the active complexes formed by RecA-like proteins on DNA in the presence of ATP or ATP analogs. Within a crystal of the E. coli RecA protein, a helical polymer exists, and it has been widely assumed that this polymer is quite similar to the active helical filament formed on DNA. Recent developments have suggested that this may not be the case.     

What is the enthalpy of formation of acrylonitrile?

Acrylonitrile is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious. There is a 12 kJ mol⁻¹ range of values reported for the gas phase quantity: 173–185 kJ mol⁻¹. Quantum chemical calculations, using current methodologies and defining reactions, suggest values between 185 and 191 kJ mol⁻¹: the recommended value, an average, is 188 ± 7 kJ mol⁻¹.     

What is the mole?

The mole is a difficult concept. Surveys have shown that even many teachers do not have a proper understanding of it. To help to meet this problem, the SI/IUPAC formulation of the mole is carefully presented and explained. New SI proposals are also briefly discussed.     

To What Extent is FAIMS Beneficial in the Analysis of Proteins?

High field asymmetric waveform ion mobility spectrometry (FAIMS), also known as differential ion mobility spectrometry, is emerging as a tool for biomolecular analysis. In this article, the benefits and limitations of FAIMS for protein analysis are discussed. The principles and mechanisms of FAIMS separation of ions are described, and the differences between FAIMS and conventional ion mobility spectrometry are detailed. Protein analysis is considered from both the top-down (intact proteins) and the bottom-up (proteolytic peptides) perspective. The roles of FAIMS in the analysis of complex mixtures of multiple intact proteins and in the analysis of multiple conformers of a single protein are assessed. Similarly, the application of FAIMS in proteomics and targeted analysis of peptides are considered.

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What is the unperturbed state in polymer solutions?

We report theoretical results about amphiphilic random copolymers in a quasi‐ideal conformation with an overall size very close to that of the analogue homopolymers. We found that a few states may coexist with about the same free energy and a similar radius of gyration, but with different intramolecular conformations. We also argue that, in most cases, amphiphilic copolymers may never achieve the unperturbed Θ state, defined thermodynamically by a vanishing second virial coefficient. Thus, we suggest that such copolymers usually show neither an unperturbed conformation nor an unperturbed state from the thermodynamic viewpoint. We also briefly discuss star homopolymers, which show a depression of the Θ temperature with respect to linear chains and a significant, though finite, Θ swelling, as well as linear chains in the Θ state and in the melt. The main general conclusion is that interactions between chain segments do not cancel each other and are non‐negligible. Accordingly, we suggest that the word "unperturbed" be used only with reference to solution thermodynamics and not for the chain size or conformation.     

What is the mechanism of soap film entrainment?

Classical Frankel's law describes the formation of soap films and their evolution upon pulling, a model situation of film dynamics in foams (formation, rheology, and destabilization). With the purpose of relating film pulling to foam dynamics, we have built a new setup able to give an instantaneous measurement of film thickness, thus allowing us to determine film thickness profile during pulling. We found that only the lower part of the film is of uniform thickness and follows Frankel's law, provided the entrainment velocity is small. We show that this is due to confinement effects: there is not enough surfactant in the bulk to fully cover the newly created surfaces which results in immobile film surfaces. At large velocities, surfaces become mobile and then Frankel's law breaks down, leading to a faster drainage and thus to a nonstationary thickness at the bottom of the film. These findings should help in understanding the large dispersion of previous experimental data reported during the last 40 years and clarifying the pulling phenomenon of thin liquid films.     

What is the acidity of a plutonium solution?

The determination of the pH of a plutonium solution has traditionally depended on an electrode or a titration in the presence of a complexing agent. A new approach uses the equilibrium distribution of the Pu oxidation states to estimate the hydrogen ion concentration. The method is used to estimate the equilibrium constant of the first hydrolysis reaction of tetravalent plutonium.     

What are the relative steric demands of carboxyl and methyl groups?

The relative steric demands of carboxyl and methyl groups are compared by contrasting the difference quantity H _f ^o (g, ArCOOH) — H _f ^o (g, ArCH₃) for a collection of alkylated benzoic acids and toluenes with the value for Ar=C₆H₅, the archetypical (i.e., unsubstituted) benzoic acid and toluene. We conclude that carboxyl and methyl groups are nearly the same size.     

Native Mass Spectrometry: What is in the Name?

Electrospray ionization mass spectrometry (ESI-MS) is nowadays one of the cornerstones of biomolecular mass spectrometry and proteomics. Advances in sample preparation and mass analyzers have enabled researchers to extract much more information from biological samples than just the molecular weight. In particular, relevant for structural biology, noncovalent protein–protein and protein–ligand complexes can now also be analyzed by MS. For these types of analyses, assemblies need to be retained in their native quaternary state in the gas phase. This initial small niche of biomolecular mass spectrometry, nowadays often referred to as “native MS,” has come to maturation over the last two decades, with dozens of laboratories using it to study mostly protein assemblies, but also DNA and RNA-protein assemblies, with the goal to define structure–function relationships. In this perspective, we describe the origins of and (re)define the term native MS, portraying in detail what we meant by “native MS,” when the term was coined and also describing what it does (according to us) not entail. Additionally, we describe a few examples highlighting what native MS is, showing its successes to date while illustrating the wide scope this technology has in solving complex biological questions.

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Liquid crystals 100 years later. What are the new concepts used in the design of molecular,macromolecular and supramolecular liquid crystals?

A brief discussion of selected synthetic strategies pursued in the field of molecular, macromolecular and supramolecular liquid crystals is made by reviewing some tandem historical events of the past 100 years of activity in this field. This survey will try to suggest the rational for the discovery, evolution and investigation of some of these new concepts. Also a brief and speculative forecast of the future of this field will be presented.     

What is the effective charge of TGA-stabilized CdTe nanocolloids?

The surface charge of semiconductor nanoparticles, Q, is an important parameter which determines their electrokinetic behavior, stability in water and polar solvents, functions of optical and electronic devices, self-assembly properties, and interactions with cell membranes. We have developed a simple method for quantitative determination of Q in their native aqueous environment. The method does not require the knowledge of exact atomic structure or make assumptions about effects of drying on charge distribution. The method is based on titration of nanoparticle dispersion with a solution of oppositely charged polyelectrolyte. The point of complete neutralization is recognized as an inflection point on the dependence of fluorescence intensity on the amount of polyelectrolyte added. Thioglycolic acid-stabilized CdTe nanoparticles 2 nm in diameter were found to carry an average Q from -2.6 to -5.5 for pH 7.5 to 10, respectively. This charge is found to be smaller than that calculated theoretically for an analogous structure (i.e., Q = -8), presumably due to adsorption of Cd(2+) ions on the stabilizer shell and on Te atoms with unsaturated valence located on the side planes of CdTe tetrahedrons.     

What is the first hydrolysis constant of tetravalent Plutonium?

A new method for estimating the numerical value of the first hydrolysis constant of tetravalent plutonium is illustrated by examples. It uses the pH and the equilibrium fractions of two of the Pu oxidation states. They are substituted into one or more of a choice of formulas that render explicit estimates of the hydrolysis constant.     

What is the initiation step of the Grubbs-Hoveyda olefin metathesis catalyst?

Density function theory calculations reveal that the Grubbs-Hoveyda olefin metathesis pre-catalyst is activated by the formation of a complex in which the incoming alkene substrate and outgoing alkoxy ligand are both clearly associated with the ruthenium centre. The computed energies for reaction are in good agreement with the experimental values, reported here.     

A facile electrochemical synthesis of caffeic acid derivatives in the presence of acetylacetone or methyl acetoacetate in aqueous medium

The anodic oxidation of caffeic acid in the presence of acetylacetone or methyl acetoacetate in aqueous solution has been studied by cyclic voltammetry and controlled-potential electrolysis techniques. The result showed that caffeic acid was oxidized to the corresponding o-benzoquinone, which underwent further Michael-addition with acetylacetone or methyl acetoacetate to produce caffeic acid derivative 3,4-dihydroxy-6-(1-acetylacetone)-yl cinnamic acid 4a or 3,4-dihydroxy-6-(1-acetyl-methylacetate)-yl cinnamic acid 4b.     

Retention behaviour of carboxylic acid methyl esters in supercritical fluid chromatography

The study on retention behavior in supercritical fluid chromatography (SFC) is necessary to understand the mechanism of the various interactions in SFC. The retention of SFC in carboxylic acid methyl ester/polymethylsiloxane/CO2 system was studied systematically and the retention behavior of this kind of compounds under various typical operation conditions was described using the method of an alternative unified theory of chromatographic retention. The results illustrated that expression: Ink.= a + b/T + cp + dp/T + ep2/T can be used to describe quantitatively the retention behavior of carboxylic acid methyl ester/polymethylsiloxane/CO2 system in the ranges of reduced density from 0.549 to 1.411. It was also found that the entropy of solute in stationary phase is dependent on the density of supercritical fluid (SF) under typical operating conditions of SFC.