CHARACTERIZATION, CONTROL AND MODELING OF PHASE SEPARATION IN MIXED PHOSPHOLIPID-PERFLUORINATED FATTY ACID MONOLAYERS

The overall objective of this PhD thesis research is to understand and control phase separation in mixed perfluorinated fatty acid-phospholipid surfactant systems that have applications as pulmonary surfactant (PS) mixtures, with an ultimate view of controlling film composition, morphology and mechanical properties. In this context the interaction between perfluorooctadecanoic acid (C18F), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), the major component of native PS extract, and 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) has been explored in Langmuir monolayers and Langmuir–Blodgett (LB) films using a combination of atomic force microscopy (AFM), fluorescence microscopy (FM) and Brewster angle microscopy (BAM) measurements. Thermodynamic and morphological studies of binary and ternary mixed films made of C18F, DPPC and DPPG indicated that both the phospholipids and C18F were miscible over a wide range of compositions. The mixed phospholipid-C18F films contained multimolecular aggregates that were highly enriched in the phospholipids. Furthermore, it was found that the magnitude of the DPPC-C18F interaction could be modulated by altering the concentration of sodium ions in the underlying subphase. Using a highly simplified lung mimic fluid (pH 7.4, 150mM NaCl), DPPC and C18F became fully immiscible. Moreover, the performance characteristics of the mixed films demonstrated the usefulness of C18F as an additive for PS formulations. The effectiveness of a PS protein mimicking peptide was evaluated against DPPC to allow comparison with previous measurements of DPPC-C18F mixed system. The mixing thermodynamics of the peptide and DPPC in Langmuir monolayer implied a repulsive interaction between the film components. The hysteresis response of the mixed monolayer films indicated that the lipid-protein mixture improved the re-spreading of DPPC films. Moreover, molecular-level organization of the mixed films explored by both FM and BAM confirmed the formation of liquid-expanded DPPC domains in the presence of minute amount of the peptide. In order to obtain a thorough understanding of the effect of the deposition process and surfactant tail polarities on the interfacial behavior of perfluorocarbon-hydrocarbon mixed monolayer films, both BAM and AFM measurements of arachidic acid (C20) with perfluorotetradecanoic acid (C14F) and palmitic acid (C16) with C18F mixed monolayer were performed. These measurements revealed that film morphology was minimally perturbed upon its deposition onto solid substrates. Coarse grained molecular dynamics (MD) simulations of films comprised of DPPC molecules with tails of various polarities suggested that the phase separation between the monolayer components could be controlled by varying surfactant tail polarities

Synthesis and applications of silver nanoparticles

AbstractOver the past few decades, nanoparticles of noble metals such as silver exhibited significantly distinct physical, chemical and biological properties from their bulk counterparts. Nano-size particles of less than 100nm in diameter are currently attracting increasing attention for the wide range of new applications in various fields of industry. Such powders can exhibit properties that differ substantially from those of bulk materials, as a result of small particle dimension, high surface area, quantum confinement and other effects. Most of the unique properties of nanoparticles require not only the particles to be of nano-sized, but also the particles be dispersed without agglomeration. Discoveries in the past decade have clearly demonstrated that the electromagnetic, optical and catalytic properties of silver nanoparticles are strongly influenced by shape, size and size distribution, which are often varied by varying the synthetic methods, reducing agents and stabilizers. Accordingly, this review presents different methods of preparation silver nanoparticles and application of these nanoparticles in different fields

Bioadhesive Controlled Metronidazole Release Matrix Based on Chitosan and Xanthan Gum

Metronidazole, a common antibacterial drug, was incorporated into a hydrophilic polymer matrix composed of chitosan xanthan gum mixture. Hydrogel formation of this binary chitosan-xanthan gum combination was tested for its ability to control the release of metronidazole as a drug model. This preparation (MZ-CR) was characterized by in vitro, ex vivo bioadhesion and in vivo bioavailability study. For comparison purposes a commercial extended release formulation of metronidazole (CMZ) was used as a reference. The in vitro drug-release profiles of metronidazole preparation and CMZ were similar in 0.1 M HCl and phosphate buffer pH 6.8. Moreover, metronidazole preparation and CMZ showed a similar detachment force to sheep stomach mucosa, while the bioadhesion of the metronidazole preparation was higher three times than CMZ to sheep duodenum. The results of in vivo study indicated that the absorption of metronidazole from the preparation was faster than that of CMZ. Also, MZ-CR leads to higher metronidazole Cmax and AUC relative to that of the CMZ. This increase in bioavailability might be explained by the bioadhesion of the preparation at the upper part of the small intestine that could result in an increase in the overall intestinal transit time. As a conclusion, formulating chitosan-xanthan gum mixture as a hydrophilic polymer matrix resulted in a superior pharmacokinetic parameters translated by better rate and extent of absorption of metronidazole

The role of the axial substituent in subphthalocyanine acceptors for bulk-heterojunction solar cells

Four hexachlorosubphthalocyanines SubPcCl6‐X bearing different axial substituents (X) have been synthesized for use as novel electron acceptors in solution‐processed bulk‐heterojunction organic solar cells. Subphthalocyanines are aromatic chromophoric molecules with cone‐shaped structure, good solution processability, intense optical absorption in the visible spectral region, appropriate electron mobilities, and tunable energy levels. Solar cells with subphthalocyanines as the electron acceptor and PTB7‐Th as the electron donor exhibit a power conversion efficiency up to 4 % and an external quantum efficiency approaching 60 % due to significant contributions from both the electron donor and the electron acceptor to the photocurrent, indicating a promising prospect of non‐fullerene acceptors based on subphthalocyanines and structurally related systems.The work was performed in the framework of the Mujulima (EU-FP7, No. 604148) and TripleSolar (ERC Adv Grant No. 339031) projects, and received funding from the Ministry of Education, Culture and Science, The Netherlands (Gravity program 024.001.035). We are also grateful to MINECO, Spain (CTQ2014-52869-P) and the Comunidad de Madrid, Spain (FOTOCARBON, S2013/MIT-2841)

Enantiopure versus Racemic Naphthalimide End-Capped Helicenic Non-fullerene Electron Acceptors: Impact on Organic Photovoltaics Performance

Impact of the enantiopurity on organic photovoltaics (OPV) performance was investigated through the synthesis of racemic and enantiomerically pure naphthalimide end-capped helicenes and their application as non-fullerene molecular electron acceptors in OPV devices. A very strong increase of the device performance was observed by simply switching from the racemic to the enantiopure forms of these π-helical non-fullerene acceptors with power conversion efficiencies jumping from 0.4 to about 2.0 % in air-processed poly(3-hexylthiophene)-based devices, thus highlighting the key role of enantiopurity in the photovoltaic properties

(Photo)physical properties of new molecular glasses end-capped with thiophene rings composed of diimide and imine units

New symmetrical arylene bisimide derivatives formed by using electron-donating-electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N′-bis(5- aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5- thiophenedicarboxaldehyde or 2,2′-bithiophene-5,5′-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (Eg) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and Eg were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm2 were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of Voc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69-0.90%

Comparative analysis of co-processed starches prepared by three different methods

Co-processing is currently of interest in the generation of high-functionality excipients for tablet formulation. In the present study, comparative analysis of the powder and tableting properties of three co-processed starches prepared by three different methods was carried out. The co-processed excipients consisting of maize starch (90%), acacia gum (7.5%) and colloidal silicon dioxide (2.5%) were prepared by co-dispersion (SAS-CD), co-fusion (SAS-CF) and co-granulation (SAS-CG). Powder properties of each co-processed excipient were characterized by measuring particle size, flow indices, particle density, dilution potential and lubricant sensitivity ratio. Heckel and Walker models were used to evaluate the compaction behaviour of the three co-processed starches. Tablets were produced with paracetamol as the model drug by direct compression on an eccentric Tablet Press fitted with 12 mm flat-faced punches and compressed at 216 MPa. The tablets were stored at room temperature for 24 h prior to evaluation. The results revealed that co-granulated co-processed excipient (SAS-CG) gave relatively better properties in terms of flow, compressibility, dilution potential, deformation, disintegration, crushing strength and friability. This study has shown that the method of co-processing influences the powder and tableting properties of the co-processed excipient

Comparative analysis of co-processed starches prepared by three different methods

Co-processing is currently of interest in the generation of high-functionality excipients for tablet formulation. In the present study, comparative analysis of the powder and tableting properties of three co-processed starches prepared by three different methods was carried out. The co-processed excipients consisting of maize starch (90%), acacia gum (7.5%) and colloidal silicon dioxide (2.5%) were prepared by co-dispersion (SAS-CD), co-fusion (SAS-CF) and co-granulation (SAS-CG). Powder properties of each co-processed excipient were characterized by measuring particle size, flow indices, particle density, dilution potential and lubricant sensitivity ratio. Heckel and Walker models were used to evaluate the compaction behaviour of the three co-processed starches. Tablets were produced with paracetamol as the model drug by direct compression on an eccentric Tablet Press fitted with 12 mm flat-faced punches and compressed at 216 MPa. The tablets were stored at room temperature for 24 h prior to evaluation. The results revealed that co-granulated co-processed excipient (SAS-CG) gave relatively better properties in terms of flow, compressibility, dilution potential, deformation, disintegration, crushing strength and friability. This study has shown that the method of co-processing influences the powder and tableting properties of the co-processed excipient

Bioadhesive Controlled Metronidazole Release Matrix Based on Chitosan and Xanthan Gum

Metronidazole, a common antibacterial drug, was incorporated into a hydrophilic polymer matrix composed of chitosan xanthan gum mixture. Hydrogel formation of this binary chitosan-xanthan gum combination was tested for its ability to control the release of metronidazole as a drug model. This preparation (MZ-CR) was characterized by in vitro, ex vivo bioadhesion and in vivo bioavailability study. For comparison purposes a commercial extended release formulation of metronidazole (CMZ) was used as a reference. The in vitro drug-release profiles of metronidazole preparation and CMZ were similar in 0.1 M HCl and phosphate buffer pH 6.8. Moreover, metronidazole preparation and CMZ showed a similar detachment force to sheep stomach mucosa, while the bioadhesion of the metronidazole preparation was higher three times than CMZ to sheep duodenum. The results of in vivo study indicated that the absorption of metronidazole from the preparation was faster than that of CMZ. Also, MZ-CR leads to higher metronidazole Cmax and AUC relative to that of the CMZ. This increase in bioavailability might be explained by the bioadhesion of the preparation at the upper part of the small intestine that could result in an increase in the overall intestinal transit time. As a conclusion, formulating chitosan-xanthan gum mixture as a hydrophilic polymer matrix resulted in a superior pharmacokinetic parameters translated by better rate and extent of absorption of metronidazole