Chain length of bioinspired polyamines affects size and condensation of monodisperse silica particles.

Polyamines play a major role in biosilicification reactions in diatoms and sponges. While the effects of polyamines on silicic acid oligomerization and precipitation are well known, the impact of polyamines chain length on silica particle growth is unclear. We studied the effects of polyamine chain length on silica particle growth and condensation in a known, simple, and salt-free biphasic reaction system; with tetraethyl orthosilicate as organic phase and polyamine dissolved in the aqueous phase. The particles at various growth stages were characterized by Cryo- Transmission Electron Microscopy, Scanning Electron Microscopy, Thermogravimetric Analysis, Zeta Potential, and solid-state NMR analysis. Polyamines were found co-localized within silica particles and the particle diameter increased with an increase in polyamine chain length, whereas silica condensation showed the opposite trend. Particle growth is proposed to progress via a coacervate intermediate while the final particles have a core shell structure with an amine-rich core and silica-rich shell. The results presented in this paper would of interest for researchers working in the field of bioinspired materials.

Modifying the thickness, pore size, and composition of diatom frustule in Pinnularia sp. with Al3+ ions.

Diatoms are unicellular photosynthetic algae that produce a silica exoskeleton (frustule) which exposes a highly ordered nano to micro scale morphology. In recent years there has been a growing interest in modifying diatom frustules for technological applications. This is achieved by adding non-essential metals to the growth medium of diatoms which in turn modifies morphology, composition, and resulting properties of the frustule. Here, we investigate the frustule formation in diatom Pinnularia sp., including changes to overall morphology, silica thickness, and composition, in the presence of Al3+ ions at different concentrations. Our results show that in the presence of Al3+ the total silica uptake from the growth medium increases, although a decrease in the growth rate is observed. This leads to a higher inorganic content per diatom resulting in a decreased pore diameter and a thicker frustule as evidenced by electron microscopy. Furthermore, 27Al solid-state NMR, FIB-SEM, and EDS results confirm that Al3+ becomes incorporated into the frustule during the silicification process, thus, improving hydrolysis resistance. This approach may be extended to a broad range of elements and diatom species towards the scalable production of silica materials with tunable hierarchical morphology and chemical composition.

Flexibility of components alters the self-assembly pathway of Pd2L4 coordination cages.

The self-assembly process of a Pd2L4 cage consisting of flexible ditopic ligands and Pd(ii) ions was revealed by QASAP (quantitative analysis of self-assembly process), which enables one to obtain information about the intermediates transiently produced during the self-assembly as the average composition of all the intermediates. It was found that the dominant pathway to the cage is the formation of a submicrometre-sized sheet structure, which was characterized by dynamic light scattering (DLS) and scanning transmission electron microscopy (STEM), followed by the addition of free ditopic ligands to the Pd(ii) centres of the sheet structure to trigger the cage formation. This assembly process is completely different from that of a Pd2L4 cage composed of rigid ditopic ligands, indicating that the flexibility of the components strongly affects the self-assembly process.

Heterogeneous catalase-like activity of gold(i)-cobalt(iii) metallosupramolecular ionic crystals.

Unique heterogeneous catalase-like activity was observed for metallosupramolecular ionic crystals [AuI4CoIII2(dppe)2(d-pen)4]X n ([1]X n ; dppe = 1,2-bis(diphenylphosphino)ethane; d-pen = d-penicillaminate; X n = (Cl-)2, (ClO4-)2, (NO3-)2 or SO42-) consisting of AuI4CoIII2 complex cations, [1]2+, and inorganic anions, X- or X2-. Treatment of the ionic crystals with an aqueous H2O2 solution led to considerable O2 evolution with a high turnover frequency of 1.4 × 105 h-1 for the heterogeneous cobalt complexes, which was dependent on their size and shape as well as the arrangement of cationic and anionic species. These dependencies were rationalized by the presence of cobalt(ii) centers on the crystal surface and their efficient exposure on the (111) plane rather than the (100) plane based on morphological and theoretical studies.

Intracellular delivery of BSA by phosphonate@silica nanoparticles.

Intracellular protein (BSA) delivery by a phosphonate@mesoporous silica nanoparticle vehicle, PMSN, with high load capacity for the relatively large test protein BSA, is described. Wide pore (11.6 nm) PMSN nanoparticles were synthesised and loaded with a BSA cargo to give BSA#@PMSN*, where # and * signify Fluorescein and Rhodamine fluorescent labels respectively. Internalisation of BSA#@PMSN*s by HeLa cells was analysed from confocal microscopy and TEM images after dose and time dependent treatments. No evidence of cytotoxicity was observed after 24 h and in contrast to PMSN* no significant loss of BSA#@PMSN* was observed after 3 h incubation of the loaded cells in DMEM. Receptor blocking experiments showed caveolar uptake of PMSN* and folate receptor mediated uptake of BSA#@PMSN*s.

Large pore raspberry textured phosphonate@silica nanoparticles for protein immobilization.

This paper reports the synthesis of large pore (11 nm) monodisperse raspberry textured phosphonate@silica nanoparticles (70-90 nm) with high capacity for protein immobilization. The raspberry nanoparticles denoted RNP_PME(2.5) with phosphonate loading 2.5 mmol g-1, formed using an organosilanephosphonate (MeO)3SiCH2CH2PO(OMe)2, as silica surface modifier and structure directing agent. Specific reaction conditions including temperature and concentration of phosphonate, base, surfactant and co-solvent were required for RNP_PME(2.5) formation. Rhodamine B labelled RNP_PME(2.5) was readily internalised by HeLa cells with no deficit of cell viability. Aqueous dispersions of RNP_PME(2.5) were stable over several months. In protein immobilization studies using BSA, bovine serum albumin, with RNP_PME(2.5), smaller pore (∼3 nm) phosphonate@silica nanoparticles NP_PME(1.0) and NP_PME(0.2) and mesoporous silica nanoparticles, MSN, the large pore RNP_PME(2.5) gave highest BSA loading 266 mg g-1, formed the most stable aqueous dispersions (BSA@MSN was unstable and precipitated) and gave the best protection against BSA structural distortion at pH 7.4.