No abstract

Raman spectroscopy of network solids such as zeolites is critical for shedding light on collective vibrations of medium-range structures such as rings that exist in crystals and that form during crystallization processes. Despite this importance, assignments of Raman spectra are not completely understood, though it is often assumed that Raman bands can be assigned to individual rings. We report a systematic zeolite synthesis, spectroscopy, and periodic DFT study of several all-silica zeolites to test this assumption and to determine the fundamental structural motifs that explain Raman spectral features. We have discovered from normal-mode analysis that Raman bands can be assigned to tricyclic bridgesthree zeolite rings that share a common Si–O–Si bridge. Furthermore, we have found that the vibrational frequency of a given Raman band can be correlated to the smallest ring of its tricyclic bridge and not to the ring that is actually vibrating. Finally, we have discovered a precise anticorrelation between Raman frequency and Si–O–Si angle. These discoveries open new ways to investigate structures of network materials made of corner-sharing tetrahedra and to study crystallization from amorphous gels where structural information is limited.

Brucella melitensis is a facultative intracellular bacterium that replicates within macrophages. The ability of brucellae to survive and multiply in the hostile environment of host macrophages is essential to its virulence. The RNA-binding protein Hfq is a global regulator that is involved in stress resistance and pathogenicity. Here we demonstrate that Hfq is essential for stress adaptation and intracellular survival in B. melitensis. A B. melitensis hfq deletion mutant exhibits reduced survival under environmental stresses and is attenuated in cultured macrophages and mice. Microarray-based transcriptome analyses revealed that 359 genes involved in numerous cellular processes were dysregulated in the hfq mutant. From these same samples the proteins were also prepared for proteomic analysis to directly identify Hfq-regulated proteins. Fifty-five proteins with significantly affected expression were identified in the hfq mutant. Our results demonstrate that Hfq regulates many genes and/or proteins involved in metabolism, virulence, and stress responses, including those potentially involved in the adaptation of Brucella to the oxidative, acid, heat stress, and antibacterial peptides encountered within the host. The dysregulation of such genes and/or proteins could contribute to the attenuated hfq mutant phenotype. These findings highlight the involvement of Hfq as a key regulator of Brucella gene expression and facilitate our understanding of the role of Hfq in environmental stress adaptation and intracellular survival of B. melitensis.