Hydrophilic Polyhedral Oligomeric Silsesquioxane Research Articles

Phase Behaviors of Multi‐tailed B2AB2‐Type Regio‐isomeric Giant Surfactants at the Columnar‐Spherical Boundary†

Main observation and conclusionWe report herein the precision synthesis and phase behaviors of multi‐tailed B2AB2‐type regio‐isomeric giant surfactants consisting of a hydrophilic polyhedral oligomeric silsesquioxane (POSS) head tethered with four hydrophobic polystyrene (PS) tails. The synthesis was accomplished through two sequential “click” reactions to give a series of regio‐isomeric giant surfactants S2DS2 (where S is short for PS tails and D for hydroxyl‐functionalized POSS) in para‐, meta‐, and ortho‐configurations. Their phase structures and phase behaviors at the columnar‐spherical boundary were investigated with a single PS tail molecular weight of 1.4 kDa. Specifically, the para‐ and meta‐isomers show hexagonally packed cylinders phases with slightly different order‐disorder transition temperatures (~120 °C and ~130 °C) and the ortho‐isomer exhibits an order‐order transition from a kinetically favored, metastable dodecagonal quasi‐crystal phase to a thermodynamically stable sigma phase at ~120 °C, as well as a further transition into the disordered state at ~140 °C. The phase diagram was constructed and their differences were rationalized based on the calculated interfacial area per molecule. This work demonstrates that tiny structural disparity could not only lead to unconventional phase formation in single‐component macromolecules, but also render dynamic and rich phase behaviors in these macromolecular assemblies.

Hydrophilic Polyhedral Oligomeric Silsesquioxane, POSS(OH)32, as a Complexing Nanocarrier for Doxorubicin and Daunorubicin.

A novel strategy, recently developed by us, to use polyhedral oligomeric silsesquioxanes (POSS) as an anti-cancer drug carrier is presented. Anthracycline:POSS complexes were prepared by simple co-addition of doxorubicin (DOX) or daunorubicin (DAU) with hydrophilic POSS(OH)32. Co-delivery of POSS and anthracyclines led to higher anti-cancer activity towards HeLa (cervical cancer endothelial) and MCF-7 (human breast adenocarcinoma) cell lines. The obtained supramolecular hybrid complexes were characterised by nuclear magnetic resonance (NMR) spectroscopy (nuclear Overhauser effect spectroscopy [NOESY] and homonuclear correlation spectroscopy [COSY]), Fourier transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS). The two-dimensional (2D) NOESY spectra of the complexes showed the cross-correlation peaks for hydroxyl groups of POSS (~4.3–4.8 ppm) with OH groups of DOX and DAU. FTIR showed that hydroxyl group of POSS can interact with amine and hydroxyl groups of DOX and DAU. The viability of HeLa and MCF-7 was analysed with the MTT assay to evaluate the cytotoxicity of free DOX and DAU and the relevant complexes with POSS at different molar ratios. At a low DOX concentration (2.5 µM), for molar ratios 1:1, 1:4, and 1:8 (POSS:DOX), the complexes showed two and three times higher cytotoxicity towards HeLa and MCF-7 cells, respectively, than DOX itself after both 24- and 48-h incubation. The 1 µM concentration for a 1:4 POSS:DOX molecular ratio and the 2.5 µM concentration for all complexes were more toxic towards MCF-7 cells than free DOX after 48-h incubation. In the case of POSS:DAU complexes, there was higher toxicity than that of free drug after 48-h incubation. It can be concluded that the formation of non-covalent complexes increases toxicity of anthracycline drugs towards Hela and MCF-7 cells. The novel complexes are inexpensive to prepare and more effective than free drugs at low systemic toxicity.

Online high-efficient specific detection of zearalenone in rice by using high-loading aptamer affinity hydrophilic monolithic column coupled with HPLC

Via the facile photopolymerization and thiol-ene click chemistry, a hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing affinity monolithic column with a high load of aptamers and fast preparation was presented, and successfully applied to the efficient specific recognition and sensitive detection of zearalenone (ZEN) by coupling with HPLC. Optimization of polymerization reaction and polymer recipe were studied, and characteristics such as structural morphology, affinity performance and specificity to ZEN were evaluated. A highly hydrophilic POSS-based aptamer affinity monolith was rapidly prepared in 1.1 h, and a high capacity of aptamer reached 2772.61 pmol/μL that was much higher than that of the current POSS-based aptamer affinity monoliths. By this way, the hydrophilic nature and aptamer coverage indensity in POSS monoliths were well improved. The mixed-mode mechanism including aptamer affinity recognition and hydrophilic interaction were employed for the specific analysis of ZEN. Applied to the monitoring of ZEN, a good selective recognition and sensitive detection were obtained with the detection limit (LOD) of 0.02 ng/mL. The stability and reproducibility were acceptable and the intra-day, inter-day and column-to-column relative standard deviations (RSDs) of the ZEN recovery were gained in the range from 2.28% to 5.32%, respectively. Satisfactory recoveries of ZEN in rice samples were realized ad 98.6 ± 2.8%–100.8 ± 2.0%. It might provide a preferable access to online specific analysis of ZEN via the hydrophilic POSS-based affinity monolith with a large capacity of aptamers and a high preparation efficiency.

Transition Kinetics of Self-Assembled Supramolecular Dodecagonal Quasicrystal and Frank-Kasper σ Phases in ABn Dendron-Like Giant Molecules.

A series of noncrystalline ABn dendron-like giant molecules DPOSS-MPOSSn (n = 2-6, DPOSS: hydrophilic polyhedral oligomeric silsesquioxane (POSS) cage; MPOSS: hydrophobic POSS cage) were synthesized. These samples present a thermodynamically stable phase formation sequence from the hexagonal cylinder phase (plane group of P6mm), to the Frank-Kasper (F-K) A15 phase (space group of Pm3̅n), and further to the F-K σ phase (space group of P42/mnm), with increasing the number of MPOSS in a single molecule (n, from 2 to 6). Moreover, for DPOSS-MPOSS5 and DPOSS-MPOSS6, an intriguing dodecagonal quasicrystal (DQC) structure has been identified and revealed as a kinetic favorable metastable phase at lower temperatures, while the thermodynamically stable phase is the σ phase. The detailed investigation of the transition kinetics between the DQC and σ phase in these samples makes it possible to identify how the self-assembly directs the phase transition in terms of molecular and supramolecular aspects.

Preparation and evaluation of highly hydrophilic aptamer-based hybrid affinity monolith for on-column specific discrimination of ochratoxin A

Nonspecific adsorption is a challenge of specific recognition on aptamer-based affinity monoliths. Here, a novel highly hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-based hybrid-silica affinity monolith with a good recognition nature was prepared and used for specific discrimination of ochratoxin A (OTA). A homogeneous polymerization mixture consisted of POSS chemicals, hydrophilic monomers and aptamer solution was directly polymerized via the “one-pot” method. Preparation and characterization of the resultant affinity monolith were studied in detail. A highly hydrophilic nature was obtained and the typical hydrophilic interaction liquid chromatography (HILIC) was observed when acetonitrile (ACN) content in mobile phase was 25%, which reached the highest hydrophilicity of POSS-based hybrid monoliths. By using OTA as model analyte, the nonspecific adsorption was effectively suppressed. The recovery of the analogue ochratoxin B (OTB) was only about 0.1% even if the content of OTB was 50 times more than OTA, which was much better than other POSS-containing monoliths and polar siloxane-based hybrid monoliths. Applied to beer samples, the adsorption of background materials was drastically resisted, and efficient recognition of OTA was obtained with the recoveries of 94.9–99.8%. Much less disturbance was observed than that occurred in hydrophobic POSS-based affinity monolith. It lights an attractive implement with high hydrophilicity and specificity for online selective recognition of OTA.

Versatile Construction of Single-Tailed Giant Surfactants with Hydrophobic Poly(ε-caprolactone) Tail and Hydrophilic POSS Head.

Giant surfactants refer to a new kind of amphiphile by incorporating functional molecular nanoparticles with polymer tails. As a size-amplified counterpart of small-molecule surfactants, they serve to bridge the gap between small-molecule surfactants and amphiphilic block copolymers. This work reports the design and synthesis of single-tailed giant surfactants carrying a hydrophobic poly(ε-caprolactone) (PCL) as the tail and a hydrophilic cage-like polyhedral oligomeric silsesquioxane (POSS) nanoparticle as the head. The modular synthetic strategy features an efficient “growing-from” and “click-modification” approach. Starting from a monohydroxyl and heptavinyl substituted POSS (VPOSS-OH), a PCL chain with controlled molecular weight and narrow polydispersity was first grown by the ring-opening polymerization (ROP) of ε-CL under the catalysis of stannous octoate, leading to a PCL chain end-capped with heptavinyl substituted POSS (VPOSS-PCL). To endow the POSS head with adjustable polarity and functionality, three kinds of hydrophilic groups, including hydroxyl groups, carboxylic acids, and amine groups, were installed to the periphery of POSS molecule by a high-efficiency thiol-ene “click” reaction. The compounds were fully characterized by NMR, gel permeation chromatography (GPC), MALDI-TOF mass spectrometry, and TGA analysis. In addition, the preliminary self-assembly study of these giant surfactants was also investigated by TEM and dynamic laser light scattering (DLS), which indicated that they can form spherical nanoparticles with different diameters in aqueous solution. This work affords a straightforward and versatile way for synthesizing single-tailed giant surfactants with diverse head surface functionalities.

Highly hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-modified affinity hybrid monolith for efficient on-column discrimination with low nonspecific adsorption.

A novel polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-modified hybrid affinity monolith with excellent hydrophilicity and unique architecture without Si-OH groups is presented herein, and the nonspecific adsorption caused by the hydrophobic nature of the monolithic column or polar interaction with silanol groups is minimized. Via a simple "one-pot" procedure, hydrophilic monomers were facilely polymerized with the POSS-methacryl substituted (POSS-MA) and aptamer; a highly hydrophilic nature was obtained and the lowest contact angle of 11° was achieved. By using ochratoxin A (OTA) as the model analyte, highly selective recognition of OTA in the mixture was achieved and the control of nonspecific interactions and the cross-reactivity of OTB and AFB1 were significantly improved. The recovery yield of OTB caused by nonspecific adsorption in the resultant monolith was only about 0.1% and remained steady even with the coexistence of a high OTB content (OTA : OTB = 1 : 50), which reached the best level to date and was obviously less than the 6.1% occurring in the hydrophobic POSS-containing control monolith, 8.3% in the POSS-PEI@AuNPs@aptamer affinity monolith and 18.7% in the silica-hybrid affinity monolith. When applied to wine and wheat samples, the nonspecific adsorption was significantly reduced and efficient discrimination of OTA was obtained with better results than that of the hydrophobic POSS-containing affinity column. This provides an attractive tool for minimizing the nonspecific adsorption for highly selective on-column recognition.

Influence of Regio-Configuration on the Phase Diagrams of Double-Chain Giant Surfactants

It has been established that a minute difference of the primary chemical and topological structures influences the self-assembly behaviors of giant surfactants; however, the regio-configuration effect has been rarely reported. Herein, we report a systematic study on the self-assembly behaviors of a series of double-chain giant surfactant regio-isomers, which consist of a hydrophilic polyhedral oligomeric silsesquioxane (POSS) head and two identical hydrophobic polystyrene (PS) tails with various molecular weights tethered in para-, meta-, and ortho-configurations, respectively. Small-angle X-ray scattering and transmission electron microscopy characterizations have been combined to investigate the phase behaviors of each sample and construct the phase diagrams for the three isomers with respect to the molecular weights of PS tails. It is observed that the regio-configuration significantly impacts the self-assembly behaviors of the giant surfactant isomers, including order-to-disorder (ODT) and order-to-or...

Hierarchical Self-Organization of AB n Dendron-like Molecules into a Supramolecular Lattice Sequence.

To understand the hierarchical self-organization behaviors of soft materials as well as their dependence on molecular geometry, a series of ABn dendron-like molecules based on polyhedral oligomeric silsesquioxane (POSS) nanoparticles were designed and synthesized. The apex of these molecules is a hydrophilic POSS cage with 14 hydroxyl groups (denoted DPOSS). At its periphery, there are different numbers (n = 1–8) of hydrophobic POSS cages with seven isobutyl groups (denoted BPOSS), connected to the apical DPOSS via flexible dendron type linker(s). By varying the BPOSS number from one to seven, a supramolecular lattice formation sequence ranging from lamella (DPOSS-BPOSS), double gyroid (space group of Ia3̅d, DPOSS-BPOSS2), hexagonal cylinder (plane group of P6mm, DPOSS-BPOSS3), Frank–Kasper A15 (space group of Pm3̅n, DPOSS-BPOSS4, DPOSS-BPOSS5, and DPOSS-BPOSS6), to Frank–Kasper sigma (space group of P42/mnm, DPOSS-BPOSS7) phases can be observed. The nanostructure formations in this series of ABn dendron-like molecules are mainly directed by the molecular geometric shapes. Furthermore, within each spherical motif, the spherical core consists hydrophilic DPOSS cages with flexible linkages, while the hydrophobic BPOSS cages form the relative rigid shell, and contact with neighbors to provide decreased interfaces among the spherical motifs for constructing final polyhedral motifs in these Frank–Kasper lattices. This study provides the design principle of molecules with specific geometric shapes and functional groups to achieve anticipated structures and macroscopic properties.

Sequential “Click” Synthesis of “Nano-Diamond-Ring-like” Giant Surfactants Based on Functionalized Hydrophilic POSS/C60Tethered with Cyclic Polystyrenes

This paper reports the design and facile synthesis of a novel series of “nano-diamond-ring-like” giant surfactants composed of a functionalized hydrophilic polyhedral oligomeric silsesquioxane (such as dihydroxyl-functionalized DPOSS) or fullerene (such as carboxylic acid-functionalized AC60) head as the “diamond” and a hydrophobic, cyclic polystyrene (CPS) tail as the “ring”. The synthetic route combines several steps of “click-type” reactions, demonstrating highly efficient and modular features. Starting from a specifically designed initiator, trifunctional linear polystyrene (LPS) precursors bearing vinyl, bromo, and alkyne groups were prepared by atom transfer radical polymerization (ATRP). Upon the subsequent azidation of LPS, copper-catalyzed Huisgen [3 + 2] cycloaddition reaction was employed to afford vinyl-functionalized CPS ring in high yield and purity. The vinyl group was then subjected to the thiol–ene reaction to introduce an azide group onto the CPS, providing an azide-functionalized CPS (C...

Soft-graphoepitaxy using nanoimprinted polyhedral oligomeric silsesquioxane substrates for the directed self-assembly of PS-b-PDMS

We report here the fabrication of periodic sub-25nm diameter size cylinder structures using block copolymer (BCP) directed self-assembly on nanoimprinted topographically patterned substrates. Tailored polyhedral oligomeric silsesquioxanes (POSSs) films were spin coated onto silicon substrates and were patterned by nanoimprint lithography to produce topographies commensurable with the BCP domain spacing. The chemistry of the POSS was tuned to control the alignment and orientation of the BCP films. The substrates were used to direct the microphase separation (following toluene solvent annealing) of a hexagonal structure forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) having a domain spacing of 42.6nm and PDMS cylinder widths of 23.7nm. On more hydrophilic POSS substrates the cylinders were obtained parallel to the substrate plane and aligned with the topography. In contrast, in more hydrophobic POSS patterns, the cylinders align perpendicular to the substrate plane. The use of these methods for the nanofabrication of vias, nanofluidic devices or interconnect structures of sub-25nm feature size is discussed.

Giant gemini surfactants based on polystyrene–hydrophilic polyhedral oligomeric silsesquioxane shape amphiphiles: sequential “click” chemistry and solution self-assembly

This paper reports our recent investigations in the synthesis, characterization, and solution self-assembly of giant gemini surfactants consisting of two hydrophilic carboxylic acid-functionalized polyhedral oligomeric silsesquioxane (APOSS) heads and two hydrophobic polystyrene (PS) tails covalently linked via a rigid spacer (p-phenylene or biphenylene) (PS–(APOSS)2–PS). The sequential “click” approach was employed in the synthesis, which involved thiol–ene mono-functionalization of vinyl-functionalized POSS, Cu(I)-catalyzed Huisgen [3 + 2] azide–alkyne cycloadditions for “grafting” polymer tails onto the POSS cages, and subsequent thiol–ene “click” surface functionalization. The study of their self-assembly in solution revealed a morphological transition from vesicles to wormlike cylinders and further to spheres as the degree of ionization of the carboxylic acid groups on POSS heads increases. It was found that the PS tails are generally less stretched in the micellar cores of these giant gemini surfactants than those of the corresponding single-tailed (APOSS–PS) giant surfactant. It was further observed that the PS tail conformations in the micelles were also affected by the length of the rigid spacers where the one with longer spacer exhibits even more stretched PS tail conformation. Both findings could be explained by the topological constraint imposed by the short rigid spacer in PS–(APOSS)2–PS gemini surfactants. This constraint effectively increases the local charge density and leads to an anisotropic head shape that requires a proper re-distribution of the APOSS heads on the micellar surface to minimize the total electrostatic repulsive free energy. The study expands the scope of giant molecular shape amphiphiles and has general implications in the basic physical principles underlying their solution self-assembly behaviors.

CELL MIGRATION AND PROLIFERATION IN BIONANOHYBRIDS COMPOSED OF TYPE II COLLAGEN AND POSS AMPHIPHILES

Polyhedral oligomeric silsesquioxane (POSS) based nanocompounds have recently emerged as viable compounds to make totally synthetic biocompatible tissue substitutes for use in the clinical arena. Here, we report on the use of three POSS based compounds to develop bionanohybrid scaffolds composed primarily of purified Type II collagen. The bionanohybrid scaffolds were prepared by blending purified Type II collagen with octa maleamic acid POSS, octa ammonium POSS, or polyethylene glycol POSS. We were able to differentially detect the presence of the different POSS compounds in the bionanohybrid scaffolds using attenuated total reflectance Fourier transformed infrared (ATR-FTIR) spectroscopy. The differential scanning calorimetry (DSC) characterized the effect of the hydrophilic POSS additives on the thermal behavior of the bionanohybrid scaffolds. Next, scanning electron microscopy revealed that different POSS compounds enhanced, refined, or altered the three-dimensional scaffold microstructure. Finally, by using these scaffolds to create three-dimensional tissue constructs, we measured the ability of human foreskin fibroblasts to migrate out and proliferate into the biomaterials. Our data suggest that POSS can be incorporated with native polymeric structural proteins to influence biomaterial architecture where cells can migrate and proliferate.

Role of interface in dispersion and surface energetics of polymer nanocomposites containing hydrophilic POSS and layered silicates

Three different hydrophilic nanofillers – natural and synthetic layered silicate as well as octaammonium polyhedral oligomeric silsesquioxane (POSS) – were incorporated into polyamide-6 by a solution-mixing method. The surfaces of the resulting polymer nanocomposites were characterized by X-ray diffraction, polarized optical microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements. All polymer nanocomposites displayed enhancement in surface hydrophilicity as well as increase in surface free energy due to surface enrichment of the nanofillers. The degree of enhancement was found to depend on both nanofiller type and dispersion state. Interfacial interactions in the form of hydrogen bonding played an important role in affecting the dispersion state of the layered silicates. Exfoliated layered silicates caused a larger increase in hydrophilicity than aggregated layered silicate. On the other hand, aggregated POSS molecules were able to induce a large increase in hydrophilicity. Significant spreading of water was also observed on surfaces containing POSS molecules. Surface models have been proposed to explain these phenomena.

Diffusion permeability of hybrid chitosan/polyhedral oligomeric silsesquioxanes (POSS™) membranes to amino acids

Hybrid membranes of chitosan (Chi), hydrophilic polyhedral oligomeric silsesquioxanes (POSS™, 2.5 mol%) and ethylene glycol diglycidyl ether (EGDGE, 75 mol%) as a crosslinker were prepared by casting the blends onto nonwoven microporous polymer support, drying at 70 °C and treating with 0.5% sodium hydroxide solution. The POSS differed by the tether used: {[3-(2,3-Dihydroxypropoxy)propyl]dimethylsilyloxy}in DL-POSS, 3-aminopropyl in OA-POSS and (tetramethylammonio)oxy in TMA-POSS. The diffusion permeability of the hybrid membranes both to hydrophobic (alanine, tryptophane) and hydrophilic (glutamic acid, lysine) amino acids was investigated to elucidate the effect of POSS on the membrane transport properties. The experiments were carried out at pH 3 and 11, i.e., with the chitosan amino groups fully protonated or deprotonated. Diffusion transport of amino acids was affected by their p I, hydrophilic indexes and molecular sizes. Membrane permeability was indirectly affected by the POSS tethers due to changes in the morphology of the hybrid membranes on nanoscale. The longer the tether used, the higher the packing density of chitosan chains in the membrane and the lower its diffusion permeability to amino acids. The TMA-POSS, undergoing hydrolytic-condensation in acidic chitosan solution during membrane preparation, formed large silica segments, which caused the largest morphological disorder in Chi/TMA-POSS membranes and, as result, their highest permeability to all amino acids studied. The contribution of incorporated POSS to transport of amino acids is discussed.

Effect of POSS™ functionality on morphology of thin hybrid chitosan films

—Organic-inorganic hybrid films based on chitosan (Chi) and hydrophilic polyhedral oligomeric silsesquioxanes (POSS™) were prepared by alkaline precipitation of the dried blends. The effect of the POSS type and concentration on morphology and permeability of Chi/POSS hybrid films were evaluated by IR spectroscopy, solid phase NMR, SEM and AFM and by diffusion transport of low-molecular-weight electrolytes. In mechanically stable hybrid films, contents of octakis{[3-(2,3- dihydroxypropoxy)propyl]dimethylsilyl}-POSS™ (DL-POSS), octakis(trimethylammonium)-POSS™ (TMA-POSS) and octaammonium-POSS™ (OA-POSS) range between 0.625 and 2.5 mol% (in relation to amount of the deacetylated chitosan amino groups). The large POSS molecules (approx. 2–3 nm) influenced the packing the chitosan chains on a nanoscale due to multiple intermolecular bonds and changed the heterogeneity of hybrid films. The electrolyte (HCl, NaCl and NaOH) transport through the films depended on the POSS type, its content, and the preparation method. With increasing POSS content, the permeabilities tended to increase across the hybrid films with the crosslinker (ethyleneglycol diglycidyl ether, 75 mol%), which was added into a precursor film before its drying and alkaline treatment. In contrast, the electrolyte penetration usually decreased through the films cross-linked after their drying and alkaline precipitation. The dependence of the diffusion permeability of Chi/POSS hybrid films on their morphology is discussed.