Structure and stability of p-cresol – xenon clathrate:Raman spectroscopy study

Abstract Interaction between p-cresol and xenon was studied by Raman spectroscopy. The main questions are crystal structure of resulting clathrate and its stability. The most informative regions of our spectra are those related to the O-H stretching vibrations, the aromatic ring vibrations between 900 and 800 cm⁻¹ and the lattice vibrations of the host. From obtained data and their analysis we confirmed formation of hexagonal rings of [···O-H⋯O-]₆ hydrogen bonds as the main structural motif of the clathrate cages and we estimated length of the O⋯O bridges of these bonds. We found evidence that the last factor is responsible for low stability of studied complex and for higher stability of similar clathrates formed by hydroquinone

Discrete Cuboidal 15- and 16-Membered Water Clusters in Brucine 3.86-Hydrate, Water Release and Its Consequences

Up to now, three brucine hydrates are known, brucine di-, tetra-, and 5.25-hydrate. All of them were obtained from solutions containing the additive diethanolamine, adenosine, and urea, respectively. Studying the role of the additives on crystallization of the brucine hydrates, we obtained a new, kinetically favored brucine 3.86-hydrate. In crystals of brucine 3.86-hydrate, large 15- and 16-membered water clusters of cuboidal topology are encapsulated in cages formed between honeycomb-like brucine layers. Dehydration of the brucine hydrate leads to formation of the known anhydrous brucine, giving insight into a mechanism of the dehydration process, in which a shift of brucine ribbons in the honeycomb-like layers leads to an openining of channels and water release. A collapse of brucine layers after the water release results in formation of the common anhydrous brucine. The anhydrous brucine undergoes a phase transition at 249 K in the cooling mode and at 277 K in the heating mode. The phase transition is attributable to a huge shift of brucine corrugated layers in relation to each other. The phase transition for anhydrous brucine obtained by dehydration is accompanied by thermal effects one order larger than anhydrous brucine, obtained by crystallization from acetone solution

Clathrate structure determination by combining crystal structure prediction with computational and experimental ¹²⁹Xe NMR spectroscopy

Abstract We present an approach for the structure determination of clathrates using NMR spectroscopy of enclathrated xenon to select froma set of predicted crystal structures. Crystal structure prediction methods have been used to generate an ensemble of putative structures of o- and m-fluorophenol, whose previously unknown clathrate structures have been studied by ¹²⁹Xe NMR spectroscopy. The high sensitivity of the ¹²⁹Xe chemical shift tensor to the chemical environment and shape of the crystalline cavity makes it ideal as a probe for porous materials. The experimental powder NMR spectra can be used to directly confirm or reject hypothetical crystal structures generated by computational prediction, whose chemical shift tensors have been simulated using density functional theory. For each fluorophenol isomer we find one predicted crystal structure whose measured and computed chemical shift tensors agree within experimental and computational error margins and these are thus proposed as the true fluorophenol xenon clathrate structures

Genome-wide analysis reveals two novel mosaic regions containing an ACME with an identical DNA sequence in the MRSA ST398-t011 and MSSA ST8-t008 isolates

OBJECTIVES: The presence of the arginine catabolic mobile element (ACME) in Staphylococcus aureus has been reported to enhance the colonization of the human host. The aim of this study was to determine the genetic organization of composite islands harbouring ACME. METHODS: Two ACME-positive S. aureus isolates obtained during two different surveys conducted in the Netherlands and Poland were characterized in this study. The isolates were analysed by spa typing, DNA microarrays and whole-genome sequencing. RESULTS: The two isolates harboured a truncated yet fully functional ACME type II with an identical nucleotide sequence, but differed in their adjacent mobile genetic elements. The first strain was a livestock-associated ST398-t011 MRSA, which had a staphylococcal cassette chromosome mec (SCCmec) composite island composed of SCCpls adjacent to orfX followed by ACME type II and SCCmec type IVa. The second ACME-positive isolate was an ST8-t008 MSSA. Its composite island showed an SCC-like element carrying the ccrC gene followed by ACME II. CONCLUSIONS: This is the first report of an ACME in a livestock-associated MRSA ST398. It is also the first presentation of an ACME composite island structure in an MSSA isolate. Our findings indicate an extensive mosaicism of composite islands in S. aureus, which has implications for the transmissibility among humans and thus for public health