Encapsulation of cationic iridium(III) tetrazole complexes into a silica matrix: synthesis, characterization and optical properties

Encapsulation of cationic iridium(III) tetrazole complexes into a silica matrix: synthesis, characterization and optical properties

Ilaria Zanoni, Valentina Fiorini, Marcos Rosado, Belén Ballesteros, Maria Androulidaki, Magda Blosi, Simona Ortelli, Stefano Stagni, Michele Dondia and Anna Luisa Costa

Abstract

Herein we report the easy incorporation of brightly phosphorescent cationic iridium(III) tetrazole complexes into a silica based matrix via an easily scalable colloidal process. For this purpose, two cationic Ir(III) emitters bearing 5-aryl tetrazole ligands (R-CN4) were selected: blue [F2IrPTZ-Me]+ (C^N = F2ppy; N^N = PTZ-Me – 2-(2-methyl-2H-tetrazol-5-yl)pyridine) and red [IrQTZ-Me]+ (C^N = ppy; N^N = QTZ-Me – 2-(2-methyl-2H-tetrazol-5-yl)quinoline). The cationic complexes were readily adsorbed to negatively charged silica nanoparticles and trapped in the sol–gel matrix. The sol-to-solid phase transfer was performed by using an innovative spray-freeze-drying technique, leading to the formation of phosphorescent solid micro-granules. The structural and optical characterisation of the Ir(III) complexes together with SiO2 nanoparticles, nanosols (Ir@SiO2) and powders (Ir@SiO2 powders), revealed how the presence of the Ir(III)-based complexes did not alter the morphology of the colloidal silica or granulated phases. Moreover, the silica matrix did not interfere with the optical properties of the embedded complexes. The distribution of [F2IrPTZ-Me]+ and [IrQTZ-Me]+ in the spray-freeze-dried powders was qualitatively evaluated by fluorescence microscopy, revealing how the luminescent particles were homogeneously dispersed all over the silica matrix. Interestingly, in aqueous solution the release of complex [F2IrPTZ-Me]+ from the corresponding Ir@SiO2 powder is almost negligible, therefore suggesting that a strong interaction occurs between the host–silica matrix and the Ir(III) guest complex.

Spray freeze-dried monolithic silica aerogel based on water-glass with thermal superinsulating properties

Spray freeze-dried monolithic silica aerogel based on water-glass with thermal superinsulating properties

Yuelei Pan, Xudong Cheng, Ting zhou, Lunlun Gong, Heping Zhang

Abstract

In this study, silica aerogels were prepared using water-glass precursor based on two drying strategies, namely conventional freeze drying (C-FD) and spray freeze drying (S-FD). It was known that the pore structure of silica aerogel can be optimized uniformly based on S-FD method when tert-butyl alcohol is directly utilized as a solvent. As a result, silica aerogels obtained by the S-FD method are monolithic with high thermal stability and low thermal conductivity, showing a great potential of thermal insulation materials for high-temperature environment.

Keywords

Silica aerogels, Spray, Freeze drying, Thermal insulation, Thermal stability

Porous Microparticles Containing Raloxifene Hydrochloride Tailored by Spray Freeze Drying for Solubility Enhancement

Porous Microparticles Containing Raloxifene Hydrochloride Tailored by Spray Freeze Drying for Solubility Enhancement

Seyyed Pouya Hadipour Moghaddam, Sajjad Farhat, Alireza Vatanara

Abstract

Purpose: The goal of this study was to improve the solubility and dissolution behavior of Raloxifene Hydrochloride (RH) using Spray Freeze Drying (SFD) technique. Methods: For achieving this goal, series of samples containing RH with polyvinylpyrrolidone (PVP) or hydroxypropyl beta cyclodextrin (HPβCD) used as solubility enhancers were prepared and microparticles were formed via SFD. The resultant microparticles were physicochemically characterized. Morphology of the microparticles were observed using Scanning Electron Microscopy (SEM). High Performance Liquid Chromatography (HPLC) was used for analyzing the solubility and dissolution profile of the samples. Results: Fourier Transmission Infrared (FTIR) spectra showed that SFD processed compositions did not affect chemical structure of RH. SEM and Thermal Gravimetric Analysis (TGA) revealed that the fabricated spherical and highly porous microparticles were in amorphous state. SFD processed powders showed superior solubility and dissolution behavior; where, 80% of the drug was dissolved within 5 minutes. Conclusion: SFD method can be a promising alternative for enhancing the solubility of poorly water soluble compounds.

Keywords

Dissolution profile, Porous microparticles, Raloxifene, Solubility, Spray freeze drying

Spray-Freeze Drying: a Suitable Method for Aerosol Delivery of Antibodies in the Presence of Trehalose and Cyclodextrins.

Spray-Freeze Drying: a Suitable Method for Aerosol Delivery of Antibodies in the Presence of Trehalose and Cyclodextrins.

Pouya MA, Daneshmand B, Aghababaie S, Faghihi H, Vatanara A

Abstract

We aimed to prepare spray-freeze-dried powder of IgG considering physicochemical stability and aerodynamic aspects. Spray-freeze drying (SFD) exposes proteins to various stresses which should be compensated by suitable stabilizers. The competence of cyclodextrins (CDs), namely beta-cyclodextrin (βCD) and hydroxypropyl βCD (HPβCD), at very low concentrations, was investigated in the presence of separate mannitol- and trehalose-based formulations. Spray-freeze-dried preparations were quantified in terms of monomer recovery and conformation by size exclusion chromatography (SEC-HPLC) and Fourier transform infrared (FTIR) spectroscopy, respectively. Differential scanning calorimetry (DSC) and X-ray diffractometry (XRD) were employed to identify the thermal characteristics of powders. Particle morphology was visualized by scanning electron microscopy (SEM). Aerodynamic behavior of powders was checked through an Anderson cascade impactor (ACI). Although all formulations protected antibody from aggregation during the SFD process (aggregation < 1%), mannitol-containing ones failed upon the storage (19.54% in the worst case). Trehalose-HPβCD incomparably preserved the formulation with fine particle fraction (FPF) of 51.29%. Crystallization of mannitol resulted in IgG destabilization upon storage. Although employed concentration of CDs is too low (less than 50:1 molar ratio to protein), they successfully served as stabilizing agents in SFD with perfect improvement in aerosol functionality. Graphical Abstract ᅟ.

Keywords

IgG; aerodynamic property; cyclodextrins; spray-freeze drying; stability; trehalose

Effect of amino acids on the stability of spray freeze-dried immunoglobulin G in sugar-based matrices

Effect of amino acids on the stability of spray freeze-dried immunoglobulin G in sugar-based matrices

Fakhrossadat Emami, Alireza Vatanara, Abdolhosein Rouholamini Najafabadi, Yejin Kim, Eun Ji Park, Soroush Sardari, Dong Hee Na

Abstract

The purpose of this study was to prepare spray freeze-dried particles of immunoglobulin G (IgG) using various combinations of trehalose and different amino acids (leucine, phenylalanine, arginine, cysteine, and glycine), and investigate the effect of the amino acids on the stability of IgG during the spray freeze-drying (SFD) process and storage. The morphology and structural integrity of the processed particles were evaluated by physical and spectroscopic techniques. SFD-processed IgG without any excipient resulted in the formation of aggregates corresponding to approximately 14% of IgG. In contrast, IgG formulations stabilized using an optimal level of leucine, phenylalanine, or glycine in the presence of trehalose displayed aggregates <2.2%. In particular, phenylalanine combined with trehalose was most effective in stabilizing IgG against shear, freezing, and dehydration stresses during SFD. Arginine and cysteine were destabilizers displaying aggregation and fragmentation of IgG, respectively. Aggregation and fragmentation were evaluated by dynamic light scattering, ultraviolet spectrophotometry, size-exclusion chromatography, and microchip capillary gel electrophoresis. The IgG formulations prepared with leucine, phenylalanine, or glycine in the presence of trehalose showed good stability after storage at 40 °C and 75% relative humidity for 2 months. Thus, a combination of the excipients trehalose and uncharged, nonpolar amino acids appears effective for production of stable SFD IgG formulations.

Keywords

Spray freeze drying, Stability, Immunoglobulin G, Antibody, Amino acids, Trehalose

Effect of the microstructure on the stability of red onion microcapsules

Effect of the microstructure on the stability of red onion microcapsules

E. Flores-Andrade, E. Bonilla, G. Luna-Solano, U. R. Marin, M. T. González-Arnao, M. P. Rascón

Abstract

The effect of microstructure on the stability of red onion encapsulated by two processes: (a) spray drying and (b) spray freezing into liquid cryogenic, was evaluated in this work. Water sorption isotherms and glass transition temperature of microcapsules conditioned at various water activities were determined and coupled to evaluate conditions of storage stability. The stability of red onion microcapsules was influenced not only by water activity increase but also by microstructural differences between the two types of microcapsules. Critical water content was a useful tool to establish adequate storage conditions for red onion microcapsules.

Keywords

Critical water content, glass transition, microencapsulation, microstructure, spray drying, spray freezing into liquid cryogenic

Microstructure of high battery-performance Li2FeSiO4/C composite powder synthesized by combining different carbon sources in spray-freezing/freeze-drying process

Microstructure of high battery-performance Li2FeSiO4/C composite powder synthesized by combining different carbon sources in spray-freezing/freeze-drying process

Yukiko Fujita, Tomoaki Hira, Kenji Shida, Masayuki Tsushida, Jinsun Liao, Motohide Matsuda

Abstract

Spray-freezing/freeze-drying technique was applied to the synthesis of Li2FeSiO4/C composite powders using solutions containing various carbon sources, water-soluble and colloidal carbon, followed by heat treatment. The effects of the carbon sources on the microstructure and battery performance of the synthesized composite powders were investigated. The microstructures of the composite powders were clearly different when different carbon sources were used, ascribed from the thermal behavior of the carbon sources during the heat treatment. It was possible to control the microstructures of Li2FeSiO4/C composite powders by combining different carbon sources, and the synthesized composite powders exhibited high discharge capacities by mixing with only a binder for cathode. The composite powders using glucose and Ketjenblack dispersion as carbon sources delivered 165 mAh/g at first discharge capacity at 0.1 C. The developed chain structure suitable for conducting paths in the electrodes and a higher-specific BET surface area, attributed from Ketjenblack, were likely responsible for the higher performance.

Keywords

B. Microstructure-final, D. Silicate, E. Batteries, Spray-freezing/freeze-drying

Fabrication of uniform enzyme-immobilized carbohydrate microparticles with high enzymatic activity and stability via spray drying and spray freeze drying

Fabrication of uniform enzyme-immobilized carbohydrate microparticles with high enzymatic activity and stability via spray drying and spray freeze drying

Shengyu Zhang, Hong Lei, Xingmin Gao, Xingxing Xiong, Winston Duo Wu, Zhangxiong Wu, Xiao Dong Chen

Abstract

Enzyme-immobilized particles with high enzymatic activities are fundamentally and practically important for many areas, such as pharmaceuticals, medicine, and biocatalysis. In this study, by selecting trypsin and trehalose as the representative enzyme and excipient, two techniques, spray drying (SD) and spray freeze drying (SFD), have been utilized to generate enzyme-immobilized particles and comparatively studied. In both methods, uniform enzyme-immobilized microparticles are successfully obtained by using a micro-fluidic aerosol nozzle (MFAN) as the monodisperse droplet generator. The particle morphology, size and inner structure are distinctly different between the SD- and SFD-derived trypsin/trehalose composite microparticles. The former shows crumpled morphology, smaller sizes and dense inner structure while the latter shows spherical and open porous morphology with larger particle sizes. The particle formation processes in both methods are discussed. The more surface-active and large-sized trypsin molecules tend to be accumulated at the air-liquid interface of drying droplets, leading to particle buckling in SD and the formation of thin surface trypsin-enriched layer in SFD. The trypsin enzymatic activity is highly related to the presence of trehalose and the processing method. For the pure trypsin microparticles, SFD leads to a better activity preservation than SD does due to the much higher temperature adopted in SD. The presence of trehalose can significantly protect the enzymatic activity of trypsin, reaching 97.7 ± 2.6% and 97.3 ± 1.6% activity preservation with the optimal trypsin/trehalose mass ratio of 1:1 for both the SD- and SFD-derived microparticles, respectively. The protection of the enzymatic activity originates from the hydrogen bonding formation between trypsin and trehalose and the formation of highly amorphous glass matrices, which decrease enzyme unfolding and aggregation. In terms of process operability, SD offers a rather simple and economic means to produce enzymatic microparticles of high activity with the appropriate dosage of trehalose.

Keywords

Particle processing, Drying technology, Uniform microparticles, Enzyme immobilization, Activity preservation

Spray freeze drying of small nucleic acids as inhaled powder for pulmonary delivery

Spray freeze drying of small nucleic acids as inhaled powder for pulmonary delivery

Wanling Liang, Alan Y.L. Chan, Michael Y.T. Chow, Fiona F.K.Lo, Yingshan Qiu, Philip C.L. Kwok, Jenny K.W. Lam

Abstract

The therapeutic potential of small nucleic acids such as small interfering RNA (siRNA) to treat lung diseases has been successfully demonstrated in many in vivo studies. A major barrier to their clinical application is the lack of a safe and efficient inhaled formulation. In this study, spray freeze drying was employed to prepare dry powder of small nucleic acids. Mannitol and herring sperm DNA were used as bulking agent and model of small nucleic acid therapeutics, respectively. Formulations containing different solute concentration and DNA concentration were produced. The scanning electron microscope (SEM) images showed that the porosity of the particles increased as the solute concentration decreased. Powders prepared with solute concentration of 5% w/v were found to maintain a balance between porosity and robustness. Increasing concentration of DNA improved the aerosol performance of the formulation. The dry powder formulation containing 2% w/w DNA had a median diameter of 12.5 µm, and the aerosol performance study using next generation impactor (NGI) showed an emitted fraction (EF) and fine particle fraction (FPF) of 91% and 28% respectively. This formulation (5% w/v solute concentration and 2% w/w nucleic acid) was adopted subsequently to produce siRNA powder. The gel retardation and liquid chromatography assays showed that the siRNA remained intact after spray freeze drying even in the absence of delivery vector. The siRNA powder formulation exhibited a high EF of 92.4% and a modest FPF of around 20%. Further exploration of this technology to optimise inhaled siRNA powder formulation is warranted.

Keywords

Inhalation, Pulmonary delivery, Small interfering RNA, Spray freeze drying

System-level analysis of a novel air-cooled condenser using spray freezing of phase change materials

System-level analysis of a novel air-cooled condenser using spray freezing of phase change materials

Ben Xu, Swanand Bhagwat, Hongxin Xu, Arif Rokoni, Matthew McCarthy, Ying Sun

Abstract

A comprehensive system-level analysis is performed for a novel air-cooled condenser based on spray freezing of phase change materials (PCMs). This novel air-cooled condenser uses PCMs to decouple the process of steam condensation and heat rejection to air in order to significantly improve air-side heat transfer and reduce steam condensation temperature as compared to conventional air-cooled condensers (ACCs). Melting of solid PCM particles in a two-phase PCM slurry flow anchors the steam condensation temperature close to the PCM melting point regardless of the change in ambient air temperature. Spray freezing of millimeter-sized liquid PCM droplets increases the air-side heat transfer coefficient by five times compared to the finned-tubed ACCs. A multiscale model, which directly captures the melting and settling of PCM particles at the microscopic level and accounts for phase change through energy source terms at the macroscopic level, has been developed to simulate the PCM slurry flow over heated tube bundles. Using this multiscale model, the effects of particle volume fraction, Reynolds number, and particle to steam tube diameter ratio on the averaged wall Nusselt number of the steam tubes are investigated. It is found that the averaged wall Nusselt number for a PCM slurry flow of 20% solid fraction achieves a 38% enhancement over the PCM single-phase flow of same Reynolds number. On the air side, the freezing/melting of PCM droplet/particle is approximated based on a 1-D transient heat conduction model and the air-side pressure drop across the PCM droplet array is determined using a 3-D k-ε turbulence model. The performance of this spray-freezing PCM ACC is compared against a baseline ACC of a 500 MWe power plant. It is found that, for comparable footprint area and ambient conditions, the spray-freezing PCM ACC reduces the initial temperature difference to as low as 16.8 °C and provides up to 10.8 MW net power production gain compared to the baseline ACC.

Keywords

Phase change material; Dry cooling; Slurry flow and heat transfer; Power plant cooling