Vikramjeet Singh

Conjugated polymer nanocomposites: Synthesis, dielectric, and microwave absorption studies

Nanocomposites of polyaniline with barium ferrite and titanium dioxide (TiO2) are synthesized via in situ emulsion polymerization. The transmission electron microscopy (TEM) and high resolution TEM result shows the formation of array of nanoparticles encapsulated within the polymer chains during the synthesis process. The high value of microwave absorption, 58dB (>99.999% attenuation) results from the combined effect of the nanoparticles and the polymer matrix. The amount of barium ferrite has the profound effect on permittivity (e), permeability (μ), and microwave absorption of the nanocomposite. The contribution to the absorption value comes mainly due the magnetic losses (μ″) in barium ferrite and dielectric losses (e″) in TiO2 and polyaniline.

Optimized synthesis and crystalline stability of γ-cyclodextrin metal-organic frameworks for drug adsorption.

The biocompatible and renewable cyclodextrin metal-organic frameworks (CD-MOFs) have addressed a range of opportunities in molecular storage and separation sciences. The reported protocols for their synthesis, however, were carried out at room temperature over long time periods of time (24h), producing crystals of relatively poor uniformity. In this investigation, micron sized γ-CD-MOFs were synthesized by an optimized vapor diffusion method at elevated temperature (50°C) within 6h, after which the size control, crystalline stability and drug adsorption behavior were investigated in detail. In this manner, uniform cubic γ-CD-MOF crystals were obtained when the reaction temperature was raised to 50°C with pre-addition of the reaction solvent. The size of γ-CD-MOFs was adjusted efficiently by changing the reactant concentrations, temperatures, time, γ-CD ratios to KOH and surfactant concentrations, without influencing the porosity and crystallinity of the material markedly. Varing degrees of reduction in crystallinity and change in morphology were observed when the γ-CD-MOF crystals are treated under conditions of high temperature (100°C), high humidity (92.5%) and polar solvents (e.g., MeOH and DMF). In relation to drug adsorption by γ-CD-MOFs, most of the drug molecules containing carboxyl groups showed relatively high adsorption (>5%), while low adsorption (<5%) was found for drugs with nitrogen-containing heterocyclic rings. In addition, the adsorption kinetics of captopril to standard γ-CD-MOFs matched a pseudo-second-order model rather well, whilst captopril adsorption to the damaged γ-CD-MOFs only partially matched the pseudo-second-order model. In summary, based upon the optimized synthesis and size control of γ-CD-MOFs, the crystalline stability and drug adsorption characteristics of γ-CD-MOF crystals have been evaluated as a fundamental requirement of a potential vehicle for drug delivery.The biocompatible and renewable cyclodextrin metal-organic frameworks (CD-MOFs) have addressed a range of opportunities in molecular storage and separation sciences. The reported protocols for their synthesis, however, were carried out at room temperature over long time periods of time (24h), producing crystals of relatively poor uniformity. In this investigation, micron sized γ-CD-MOFs were synthesized by an optimized vapor diffusion method at elevated temperature (50°C) within 6h, after which the size control, crystalline stability and drug adsorption behavior were investigated in detail. In this manner, uniform cubic γ-CD-MOF crystals were obtained when the reaction temperature was raised to 50°C with pre-addition of the reaction solvent. The size of γ-CD-MOFs was adjusted efficiently by changing the reactant concentrations, temperatures, time, γ-CD ratios to KOH and surfactant concentrations, without influencing the porosity and crystallinity of the material markedly. Varing degrees of reduction in crystallinity and change in morphology were observed when the γ-CD-MOF crystals are treated under conditions of high temperature (100°C), high humidity (92.5%) and polar solvents (e.g., MeOH and DMF). In relation to drug adsorption by γ-CD-MOFs, most of the drug molecules containing carboxyl groups showed relatively high adsorption (>5%), while low adsorption (<5%) was found for drugs with nitrogen-containing heterocyclic rings. In addition, the adsorption kinetics of captopril to standard γ-CD-MOFs matched a pseudo-second-order model rather well, whilst captopril adsorption to the damaged γ-CD-MOFs only partially matched the pseudo-second-order model. In summary, based upon the optimized synthesis and size control of γ-CD-MOFs, the crystalline stability and drug adsorption characteristics of γ-CD-MOF crystals have been evaluated as a fundamental requirement of a potential vehicle for drug delivery.

Glycoprotein profiling of stem cells using lectin microarray based on surface plasmon resonance imaging.

Lectin microarrays have emerged as a novel platform for glycan analysis during recent years. Here, we have combined surface plasmon resonance imaging (SPRi) with the lectin microarray for rapid and label-free profiling of stem cells. In this direction, 40 lectins from seven different glyco-binding motifs and three different cell lines-mouse embryonic stem cells (mESCs), mouse-induced pluripotent stem cells (miPSCs), and mouse embryonic fibroblast stem cells (MEFs)-were used. Pluripotent mouse stem cells were clearly distinguished from non-pluripotent stem cells. Eight lectins-DBA, MAL, PHA_E, PHA_L, EEL, AAL, PNA, and SNA-generated maximal value to define pluripotency of mouse stem cells in our experiments. The discriminant function based on lectin reactivities was highly accurate for the determination of stem cell pluripotency. These results suggested that glycomic analysis of stem cells leads to a novel comprehensive approach for quality control in cell-based therapy and regenerative medicine.

In situ protein microarrays capable of real-time kinetics analysis based on surface plasmon resonance imaging.

In recent years, in situ protein synthesis microarray technologies have enabled protein microarrays to be created on demand just before they are needed. In this paper, we utilized the TUS-TER immobilization technology to allow label-free detection with real-time kinetics of protein-protein interactions using surface plasmon resonance imaging (SPRi). We constructed an expression-ready plasmid DNA with a C-terminal TUS fusion tag to directionally immobilize the in situ synthesized recombinant proteins onto the surface of the biosensor. The expression plasmid was immobilized on the polyethylene imine-modified gold surface, which was then coupled with a cell-free expression system on the flow cell of the SPRi instrument. The expressed TUS fusion proteins bind on the surface via the immobilized TER DNA sequence with high affinity (∼3-7×10(-13)M). The expression and immobilization of the recombinant in situ expressed proteins were confirmed by probing with specific antibodies. The present study shows a new low cost method for in situ protein expression microarrays that has the potential to study the kinetics of protein-protein interactions. These protein microarrays can be created on demand without the problems of stability associated with protein arrays used in the drug discovery and biomarker discovery fields.

Host-guest kinetic interactions between HP-β-cyclodextrin and drugs for prediction of bitter taste masking

&NA; Cyclodextrins (CD) are widely used bitter taste masking agents, for which the binding equilibrium constant (K) for the drug‐CD complex is a conventional parameter for quantitating the taste masking effects. However, some exceptions have been reported to the expected relationship between K and bitterness reduction and the relationship between kinetic parameters of a drug‐CD interaction, including association rate constant (Ka) and disassociation rate constant (Kd), and taste masking remains unexplored. In this study, based upon a database of kinetic parameters of drugs‐HP‐&bgr;‐CD generated by Surface Plasmon Resonance Imaging for 485 drugs, the host‐guest kinetic interactions between drugs and HP‐&bgr;‐CD for prediction of taste masking effects have been investigated. The taste masking effects of HP‐&bgr;‐CD for 13 bitter drugs were quantitatively determined using an electronic gustatory system (&agr;‐Astree e‐Tongue). Statistical software was used to establish a model based on Euclidean distance measurements, Ka and Kd of the bitter drugs/HP‐&bgr;‐CD‐complexes (R2 = 0.96 and P < 0.05). Optimized parameters, Ka3, Kd, KaKd, Kd3, Ka2 and Ka/Kd with notable influence, were obtained by stepwise regression from 12 parameters derived from Ka, Kd and K (Ka/Kd). 10‐fold cross‐validation was used to verify the reliability of the model (correlation coefficient of 0.84, P < 0.05). The established model indicated a relationship between Ka, Kd, K and taste masking by HP‐&bgr;‐CD and was successful in predicting the extent of taste masking by HP‐&bgr;‐CD of 44 bitter drugs, which was in accordance with the literature reported. In conclusion, the relationship between kinetics of drug‐CD interactions and taste masking was established and providing a new strategy for predicting the cyclodextrin mediated bitter taste masking. Graphical abstract Figure. No caption available. HighlightsThe relationship between kinetic parameter (Ka and Kd) of drug‐cyclodextrin inclusion and taste masking is revealed.A 3D model is successfully established to predict taste masking effect of drug‐cyclodextrin inclusion.A novel and high‐throughput method based on SPRi is developed to investigate taste masking.It offers a rapid way to surrogate conventional methods for taste evaluation of new drug candidates at early stage.

Template-directed synthesis of a cubic cyclodextrin polymer with aligned channels and enhanced drug payload

Despite its 3D porous structure, the pharmaceutical applications of cyclodextrin based cross-linked polymers are limited due to their structural irregularities. To address this issue, a template-directed strategy is used to obtain cubic micro and nano cyclodextrin cross-linked polymer (CD-cubes) from cyclodextrin metal organic frameworks in this study. The well-organized γ-CDs in MOFs were crosslinked by diphenyl carbonate by a facile single step chemical reaction. Scanning electron microscopy and X-ray diffraction analysis revealed the almost perfect cubic shapes of the particles with a disordered internal structure. Contrarily to the non-crosslinked materials which immediately dissolved in water, the CD-cubes were remarkably stable after extensive washing with water. The CD-cubes possessed a mesoporous structure with pore size in the range of 2–4 nm and showed much higher BET surface and 8 times higher adsorption capacity for doxorubicin as compared to conventional cyclodextrin-sponges.

High-throughput measurement of drug–cyclodextrin kinetic rate constants by a small molecule microarray using surface plasmon resonance imaging

Applications of small molecule microarrays (SMMs) has been extensively studied but have been limited to the screening of small molecule inhibitors. Here for the first time, we conjugated SMMs with label free surface plasmon resonance imaging (SPRi) for measurement of kinetic parameters for drug–cyclodextrins interactions in high-throughput manner. A collection of insoluble drugs was immobilized onto biosensor surface using photo-cross-linked technique to form SMMs. A highly sensitive and recently reported surface chemistry based on surface initiated polymerization chemistry was used for SMMs fabrication. In total, 38 insoluble drugs were evaluated for their interaction profile and kinetic rate constants against 5 different types of cyclodextrins (CDs) including, α-CD, β-CD, γ-CD, 2-hydroxylpropyl β-CD (HP-β-CD) and sulphobutyl-ether-β-CD (SBE-β-CD). For the supramolecular drug–CD interaction kinetics, the response magnitude and detailed kinetic parameters were calculated and presented in the article. The presented method described a label free and high-throughput technique for real time measurement of kinetic constants for drug–CDs interactions which will assist the selection and use of different CDs in number of different applications.

Sodium dodecyl sulfate/β-cyclodextrin vesicles embedded in chitosan gel for insulin delivery with pH-selective release

In an answer to the challenge of enzymatic instability and low oral bioavailability of proteins/peptides, a new type of drug-delivery vesicle has been developed. The preparation, based on sodium dodecyl sulfate (SDS) and β-cyclodextrin (β-CD) embedded in chitosan gel, was used to successfully deliver the model drug-insulin. The self-assembled SDS/β-CD vesicles were prepared and characterized by particle size, zeta potential, appearance, microscopic morphology and entrapment efficiency. In addition, both the interaction of insulin with vesicles and the stability of insulin loaded in vesicles in the presence of pepsin were investigated. The vesicles were crosslinked into thermo-sensitive chitosan/β-glycerol phosphate solution for an in-situ gel to enhance the dilution stability. The in vitro release characteristics of insulin from gels in media at different pH values were investigated. The insulin loaded vesicles–chitosan hydrogel (IVG) improved the dilution stability of the vesicles and provided pH-selective sustained release compared with insulin solution–chitosan hydrogel (ISG). In vitro, IVG exhibited slow release in acidic solution and relatively quick release in neutral solutions to provide drug efficacy. In simulated digestive fluid, IVG showed better sustained release and insulin protection properties compared with ISG. Thus IVG might improve the stability of insulin during its transport in vivo and contribute to the bioavailability and therapeutic effect of insulin.

Universal screening platform using three-dimensional small molecule microarray based on surface plasmon resonance imaging

Although much progress has been made in the field of small molecule microarrays in the past decades, its potential has been limited by a lack of efficient methodology. Herein we report a potent methodology for drug screening on a three-dimensional (3D) surface using a carbene based photo-cross-linking reaction. The simultaneous display of a large number of small molecules on a single polymer chain in various orientations allows for the retention of their activity. The presented method was tested using high throughput surface plasmon resonance (SPRi) with the immunosuppressive drugs rapamycin and FK506. We showed that rapamycin and FK506 immobilized on the 3D surface, not the conventional 2D surface, bound to the FKBP with high affinity. Using FKBP-binding ligands and FKBP mutants with altered mutual binding affinities, we observed a strong correlation between the relative binding affinities determined by SPRi and those previously reported. In addition, other important parameters including blocking, washing, robustness and surface reproducibility were also validated. Some well known kinase inhibitors of p38α, JNK and EKR2 proteins were also used to extend the applications of the method. All together, these results suggested that the newly developed 3D small molecule microarray in conjunction with SPRi can be a powerful platform for high throughput drug screening.

Evaluation of drug loading capabilities of γ-cyclodextrin-metal organic frameworks by high performance liquid chromatography

Drug loading into γ-cyclodextrin-metal organic frameworks (γ-CD-MOFs) using the impregnation approach is a laborious process. In this study, a γ-CD-MOF construct (2-5μm particle diameter) was used as the stationary phase under HPLC conditions with the aim to correlate retention properties and drug loading capability of the CD-based structure. Ketoprofen, fenbufen and diazepam were chosen as model drugs with m-xylene as a control analyte to investigate the correlation of drug loading and their chromatographic behaviour in the γ-CD-MOF column. Furthermore, γ-CD itself was also prepared as the stationary phase by coupling with silica in the column to illustrate the enhanced interaction between drugs and γ-CD-MOF as a reference. The retention and loading efficiency of the drugs were determined with different ratios of hexane and ethanol (10:90, 20:80, 50:50, 80:20, 90:10, v/v) at temperatures of 20, 25, 30 and 37°C. With the increment in hexane content, the loading efficiency of ketoprofen and fenbufen increased from 2.39±0.06% to 4.38±0.04% and from 5.82±0.94% to 6.37±0.29%, respectively. The retention time and loading efficiency of ketoprofen and diazepam were the lowest at 30°C while those of fenbufen had the different tendency. The excellent relation between the retention and loading efficiency onto γ-CD-MOF could be clearly observed through mobile phase and temperature investigation. In conclusion, a highly efficient chromatographic method has been established to evaluate the drug loading capability of γ-CD-MOF.