Although there have been many reports on the synthesis of NaLnF 4 nanoparticles (NPs), in particular ones that show upconversion luminescence, there is still an insufficient understanding of the mechanism to design the set of reaction conditions that will result in NPs of a particular diameter with a narrow size distribution. Here, we describe experiments that lead to the synthesis of uniform NaLnF 4 (Ln = Sm, Eu, Tb, Ho) nanoparticles (NPs) with diameters between 4 and 30 nm. NPs, in this size range, are particularly important as potential reagents for mass cytometry. The effects of varying the amount of ligand (oleic acid), precursor ratios, heating time, and temperature are discussed. In general, we found that identical reaction conditions cannot be used to synthesize NPs of identical sizes for different lanthanide elements. We found that to obtain larger uniform NaLnF 4 NPs, conditions should be found such that the NPs initially nucleate in the cubic phase and undergo a subsequent phase change to the hexagonal phase. The nucleating phase was found to be affected by the Na/Ln and F/Ln precursor ratios, where larger ratios led to initial nucleation in the hexagonal phase and smaller ratios led to initial nucleation in the cubic phase and progressively larger NPs. The nucleating phase was also affected by the amount of the ligand; however, the trends we observed were not consistent between different lanthanides.

Waterborne two-component polyurethanes (WB 2K-PUs) represent an environmentally friendly alternative to solvent-borne coatings, with reduced use of volatile organic compounds (VOCs). These coatings still cannot achieve the outstanding performance of solvent-borne 2K-PU formulations. In many WB 2K-PU formulations, a key step involves coalescence between polyol latex particles and nanoparticles formed from a water-dispersible polyisocyanate (PIC). Interactions between the PIC and the polyol take place both in the aqueous medium and after application of the coating to a substrate. A deeper understanding of this mechanism should guide improvements in formulations to improve WB 2K-PU coating performance. Our long-term goal is to investigate the film formation mechanism of a series of different polyol nanoparticles with aqueous dispersions of PICs based on a hexamethylene diisocyanate (HDI) trimer; as a first step in this direction, we examined the nature of the nanoparticles formed by dispersing an oligo-ethylene glycol (OEG)-modified HDI trimer in water. Typical techniques for nanoparticle size characterization (dynamic light scattering (DLS) and capillary hydrodynamic fractionation chromatography, (CHDF)) led to misleading information. These techniques indicated the presence of uniform nanoparticles with a diameter of ca. 100 nm that persisted for days. In contrast, DOSY 1 H NMR gave a diameter of 20 nm. Nanoparticle tracking analysis (NTA) confirmed the presence of the larger particles, but showed that they represented only 18 wt % of the dispersion. Over time, the isocyanate groups in the particles reacted with water, and the nanoparticles evolved from liquid droplets to mechanically robust polyurea particles. At this stage, imaging by electron microscopy showed a predominance of 20 nm particles. The kinetics of this chemical transformation was monitored by Fourier transform infrared (FT-IR) spectroscopy. The reaction of the isocyanate groups followed pseudo-first-order kinetics with a half-life of 11 to 14 h.

We are interested in developing lanthanide nanoparticles (LnNPs) of the general formula NaLnF 4 as high-sensitivity reagents for mass cytometry. These LnNPs must be coated to provide colloidal stability in aqueous buffer and functionality for detecting cellular biomarkers. Lipid bilayer coatings are a promising approach, but one requires an analytical technique to enable characterization of the NP coating composition as opposed to the composition of the lipid formulation used in the coating process. However, quantification of the lipid composition of lipid coatings on polymer and inorganic NPs is not common practice in the field.Here we describe a method based on high-performance liquid chromatography (LC) for separations and triple quadrupole tandem mass spectrometry (MS/MS) instrumentation for detection and show that it can quantify complex lipid mixtures using small (<1 μg) amounts of sample. Our lipid formulation consisted of a mixture of egg sphingomyelin, 1,2-dioleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-3-trimethylammonium-propane, cholesterol-PEG600, and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)-2000]. We were able to extract the coating from lipid-coated 35 nm diameter LnNPs, quantify the lipid/NP ratio, and show that the coating composition differed from the composition of the lipid formulation for several of the species. Knowledge of the actual composition of the lipid coating for lipidcoated NPs is critical for designing and optimizing application of these materials. Our results establish the value of LC-MS/MS characterization of lipid-coated NPs, thus providing an important new addition to the toolbox available for characterizing these types of nanomaterials.

surfactants and inorganic precursors, it has been possible to create mesoporous materials with different symmetries and pore sizes, and diverse compositions. [5,8] For example, using chiral surfactants as a liquid crystal template has created chiral mesoporous materials with twisted helical structures. [13] In 1999, three research groups independently reported on the incorporation of organic groups into mesoporous silica by using (R′O) 3 SiRSi(OR′) 3 precursors in the place of Si(OR) 4 precursors for the sol-gel condensation. [7,9,14] It proved possible to construct periodic mesoporous silica with organic groups directly integrated into the walls of the mesoporous structure. [11,[15][16][17][18][19][20][21][22][23] Sol-gel processing of silicate materials is highly versatile-it can incorporate various types of precursors and can be carried out under a variety of reaction conditions (e.g., variable pH, temperature, concentration, and solvent mixtures). [24] Therefore, mesoporous organosilica materials have attracted increasing interest for applications including catalysis, [1,25] metal scavenging, [26] chromatography, [27] and biomedical applications. [2] Cellulose nanocrystals (CNCs) obtained from sulfuric-acidcatalyzed hydrolysis of biomass are remarkable materials. [28,29] In 1951, Rånby isolated the crystalline regions within plant cellulose microfibers to form colloidal CNCs with nanoscale dimensions. [28] CNCs have impressive mechanical properties that arise from their high crystallinity and large aspect ratios. [30] Remarkably, CNCs also form a chiral nematic liquid crystal in water. [31] This order can be retained upon drying the aqueous suspension to give a colored, iridescent film. [32] The CNCs arrange into a Bouligand structure, where the crystallites themselves are aligned in layers, but twist with a characteristic helical pitch, P. It is the repeating helicoidal structure that leads to diffraction of circularly polarized light from the CNC films. [33] Many researchers are making new materials that take advantage of the unique properties of CNCs. [30,[34][35][36][37][38][39][40][41][42][43][44][45][46][47] In 2010, we discovered that films of mesoporous silica with chiral nematic structure could be prepared using CNCs as a template. [20] When Si(OR) 4 is condensed with CNCs in water, the resulting composite film contains silica and a chiral nematic assembly of CNCs. CNCs can be removed from the composite materials using pyrolysis, leaving behind thin films of iridescent mesoporous silica with a chiral nematic arrangement of pores inside the glass. These materials are of interest Mesoporous organosilica films with chiral nematic structures are prepared with a bridging urea group and with alkylene bridges, where the length of the alkylene bridge varies from C 1 -C 6 . To synthesize these materials, cellulose nanocrystals (CNCs) are used as liquid crystal templates, which coassemble with the organosilica precursor to give composite materials with a chiral nematic structure of CNCs embedded within. Remova...

While there have been many advances in techniques to synthesize uniform lanthanide-doped upconversion nanoparticles (UCNPs), it is still a challenge to synthesize small (ca. 5 nm) hexagonal phase UCNPs that are also bright. The most common method to obtain strongly emissive UCNPs is to synthesize core–shell structures with a passivating shell coating the luminescent core. This approach normally results in larger NPs (>20 nm) and requires two-step procedures. Here, we report a one-pot synthesis of 4 nm NaLuF4:Gd­(37%),Yb­(16%),Er­(2%) UCNPs, whose colloidal solutions show upconversion luminescence (UCL) visible to the eye. We initially hypothesized that the origin of UCL from such small UCNPs was due to a Gd-rich hexagonal upconverting core containing Yb and Er with a Lu-rich passivating shell. This idea is based on the different nucleation rates of the NaLnF4 NPs. Interestingly, the 4 nm NaLuF4-based UCNPs are in the cubic phase, and subsequently undergo a phase transformation with prolonged heating to form larger (12–14 nm) uniform hexagonal phase UCNPs. We also found that if the molar ratio of Lu:Gd in the reaction mixture was decreased from 45:37 to 20:62, the resulting UCNPs still initially nucleated in the cubic phase. Additional studies in which we varied other reaction parameters (temperature, ratios of Na+/Ln3+ and F–/Ln3+, and solvent composition) also resulted in initial nucleation in the cubic phase. In contrast, both the NaGdF4:Yb,Er and NaYF4:Gd,Yb,Er UCNPs nucleated in the hexagonal phase. Our results suggest that the presence of Lu in the reaction mixture influences the nucleation of NaLnF4 NPs. Lanthanide compositions that would normally nucleate in the hexagonal phase appear to nucleate in the cubic phase when Lu is present.