Formation of β-distonic oxonium ions: Study of ROCH2CH2OR′ radical cations

Radical cations derived from the ethers ROCH₂CH₂OR′ (R, R′ = H, CH₃, C₂₅) were studied, since β-distonic oxonium ions are often prepared from ionized ethers of glycol. The first step in the fragmentation is a 1,5-transfer of an α-hydrogen to oxygen of a terminal alkoxy group leading to a δ-distonic oxonium ion. This step is thermo-neutral and reversible in the ROCH₂CH₂OH radical cations and exothermic and irreversible in the dialkyl ether radical cations. Depending on R and R,′ these δ-distonic oxonium ions fragment by three reactions: the loss of an alcohol or a water molecule, the formation of a β-distonic oxonium ion ˙CH₂CH₂O(H)⁺R and a 1,4-H migration between carbon atoms. Competition between these processes is discussed.     

IsoméRisation avant la perte d'eau des ions aldéhydes et cétones protonés en spectrométrie de masse

Isomerization of Protonated Aldehyde and Ketone Ions in the Mass-Spectrography Before the Loss of Water In mass spectrometry, protonated aldehyde and ketone ions isomerize before the loss of a molecule of water. In order to specify this process, the spectra of deuterium labelled protonated aldehydes and ketones have been compared to the spectra of the corresponding isomer ions.     

Mechanism of CO loss for protonated 1-indanone and isomeric [C9H9O]+ ions

In order to establish the mechanism of CO loss occurring during metastable decomposition of protonated 1-indanone, fragmentations of monocyclic [C₉H₉O]⁺ isomers have been studied. These ions of known structure were prepared by CI protonation and fragmentation of the corresponding acids chlorides. It is demonstrated that the wide component of the [MH? CO]⁺ metastable peak induced by protonated 1-indanone fragmentation is the result of fragmentation of the [C₆H₅CH₂CH₂CO]⁺ isomer ion.     

Stable γ-distonic oxonium ions: R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCHR′ĊH2CHR″ and their characteristic reaction

The γ-distonic radical ions R$ \mathop {\rm O}\limits^ + $CHR′CH₂?HR″ and their molecular ion counterparts R$ \mathop {\rm O}\limits^{{\rm + } \cdot } $CHR′CH₂CH₂R″ have been studied by isotopic labelling and collision-induced dissociation, applying a potential to the collision cell in order to separate activated from spontaneous decompositions. The stability of CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, C₂H₅$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?H₂, CH₃$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃ and C₂H₅$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃, has been demonstrated and their characteristic decomposition, alcohol loss, identified. For all these γ-distonic ions, the 1,4-H abstraction leading to their molecular ion counterpart exhibits a primary isotope effect.     

α-Distonic ions as transient species in the reactions of metastable alkyl benzoate radical cations

The key intermediates to the fragmentation of metastable methyl and ethyl benzoate radical cations are α- and β-distonic isomers of the molecular ions. The α-distocic isomers are also formed by fragmentation of longer chain alkyl benzoates, but may not be long-lived, stable species. Rearrangement of the α-distonic ions prior to fragmentation can take place, but (re)formation of the benzoate molecular ions does not occur.     

Universal cycles of classes of restricted words

It is well known that Universal cycles (U-cycles) of k-letter words on an n-letter alphabet exist for all k and n. In this paper, we prove that Universal cycles exist for several restricted classes of words, including non-bijections, “equitable” words (under suitable restrictions), ranked permutations, and “passwords”. In each case, proving the connectedness of the underlying de Bruijn digraph is a non-trivial step.     

An atomic force microscopy investigation of cyanophage structure

Marine viruses have only relatively recently come to the attention of molecular biologists, and the extraordinary diversity of potential host organisms suggests a new wealth of genetic and structural forms. A promising technology for characterizing and describing the viruses structurally is atomic force microscopy (AFM). We provide examples here of some of the different architectures and novel structural features that emerge from even a very limited investigation, one focused on cyanophages, viruses that infect cyanobacteria (blue-green algae). These were isolated by phage selection of viruses collected from California coastal waters. We present AFM images of tailed, spherical, filamentous, rod shaped viruses, and others of eccentric form. Among the tailed phages numerous myoviruses were observed, some having long tail fibers, some other none, and some having no visible baseplate. Syphoviruses and a podovirus were also seen. We also describe a unique structural features found on some tailed marine phages that appear to have no terrestrial homolog. These are long, 450 nm, complex helical tail fibers terminating in a unique pattern of 3+1 globular units made up of about 20 small proteins.     

Fabrication of organic phase biosensors based on multilayered polyphenol oxidase protected by an alginate coating

We describe herein, the creation of an organic phase enzyme electrode (OPEE) via avidin–biotin interactions built over an electrogenerated polymer. Multilayered polyphenol oxidase (PPO) assemblies were transferred into an organic solvent (chloroform) for the catechol detection at −0.2 V. In conjunction with an alginate gel, as a hydrophilic additive, the biosensor performance was widely enhanced. The effects of biotinylated polypyrrole film and alginate gel on the diffusion process through the biosensor coating are studied by rotating disk electrode experiments carried out in chloroform with hydroquinone as electroactive permeant.     

A Convenient One-Pot Synthesis of Phosphino-Dipeptide Analogs

A general "one-pot" synthetic method is described for the preparation of phosphinodipeptides of type 1 , in 60-80% overall yield, allowing the variation of the substituents in f and/or g position to the phosphorus atom and also in f position to the nitrogen atom.