Silica nanoparticles containing a rhodamine dye and multiple gold nanorods

Silica shells are grown around colloidally synthesized gold nanorods (AuNRs) to form core–shell particles (AuNR@SiO₂) of variable occupancy, defined as the number of AuNRs per silica particle. Multiple AuNR occupancy within the silica shell, confirmed with high-resolution electron microscopy, is reflected in a redshift of the longitudinal plasmon mode of the nanorods due to multipolar coupling between AuNRs of a favored end–end orientation. In addition to the plasmon resonance that dominates their absorbance spectra, FL-AuNR@SiO₂, core–shell particles incorporating a lipid probe (rhodamine-DOPE), can be monitored by their fluorescence and Raman signals. Optical and scanning electron microscopy (SEM) images are compared directly, enabling the correlation of spectroscopic characteristics with particle morphology. Raman and SEM images show that the most intense Raman signals come from aggregates of AuNRs trapped within the silica matrix. Biexponential fits to fluorescence decays indicate that competing mechanisms of quenching and fluorescence enhancement contribute to a reduced fluorescence lifetime of rhodamine-DOPE located near the AuNRs.     

Influence of zirconium on the structure of pristine and leached soda-lime borosilicate glasses: Towards a quantitative approach by O MQMAS NMR

¹⁷O MQMAS NMR was used to characterize the influence of zirconium on the structural organization of soda-lime borosilicate glasses. A new method of quantitative analysis of the ¹⁷O MQMAS spectra is presented, by a direct fit of the two-dimensional MQMAS spectrum which provides the resolution of all the structural groups in glasses containing up to five oxides. Additional data were also obtained from the quantitative deconvolution of the ¹¹B MAS NMR spectra, with the help of the direct fit of MQMAS data as well. Excess of non-bridging oxygen is clearly identified in these glasses. Sixfolded zirconium is preferentially compensated rather than the tetrahedral boron and calcium only partially compensate the tetrahedral boron. Alteration gels arising from glass leaching were probed by oxygen-17 supplied by the alteration solution. Most of the zirconium is inserted in the silicate network forming Si-O-Zr bonds with the same configuration in the glass and in the gel. During leaching, calcium clearly remains in the alteration gel, either near non-bridging oxygen or as a zirconium charge compensator. This quantitative approach applied to ¹⁷O MQMAS spectra demonstrates its potential for investigating the structure of increasingly complex glass and gel compositions.     

Conception and Evaluation of a Library of Cleavable Mass Tags for Digital Polymers Sequencing

A library of phosphoramidite monomers containing a main-chain cleavable alkoxyamine and a side-chain substituent of variable molar mass (i.e. mass tag) was prepared in this work. These monomers can be used in automated solid-phase phosphoramidite chemistry and therefore incorporated periodically as spacers inside digitally-encoded poly(phosphodiester) chains. Consequently, the formed polymers contain tagged cleavable sites that guide their fragmentation in mass spectrometry sequencing and enhance their digital readability. The spacers were all prepared via a seven steps synthetic procedure. They were afterwards tested for the synthesis and sequencing of model digital polymers. Uniform digitally-encoded polymers were obtained as major species in all cases, even though some minor defects were sometimes detected. Furthermore, the polymers were decoded in pseudo-MS³ conditions, thus confirming the reliability and versatility of the spacers library.     

Pulsed‐Laser Polymerization in Compartmentalized Liquids, 2. Miniemulsions

The propagation rate coefficient (k_p) of methyl methacrylate has been measured in miniemulsions. The molecular weight distributions show many higher order peaks, which seems to be specific for pulsed initiation polymerization in compartmentalized liquids. The k_p values are very similar to bulk values although a frequency dependence is observed. This frequency dependence, which was overlooked in earlier research, is also present in pulsed laser experiments in bulk.     

Unprecedented Relaxivity Gap in pH-Responsive FeIII-Based MRI Probes

Two mononuclear ferric complexes are reported that respond to a pH change with a 27- and 71-fold jump, respectively, in their capacity to accelerate the longitudinal relaxation rate of water-hydrogen nuclei, and this starting from a negligible base value of only 0.06. This unprecedented performance bodes well for tackling the sensitivity issues hampering the development of Molecular MRI. The two chelates also excel in the fully reversible and fatigue-less nature of this phenomenon. The structural reasons for this performance reside in the macrocyclic nature of the hexa-dentate ligand, as well as the presence of a single pendant arm displaying a five-membered lactam or carbamate which show (perturbed) pK_a values of 3.5 in the context of this N6 N5O1 coordination motif.