Spectroscopic probing of location and dynamics of an environment-sensitive intramolecular charge transfer probe within liposome membranes

Steady State and Time-Resolved Fluorescence Spectroscopy of Cinchonine Dication in Sodium Dodecylsulphate Micellar System

This paper reports the influence of surface charge of the micelles on to the photophysical properties of a cinchonine dication (C2+) fluorophore in anionic, sodium dodecylsulphate (SDS), surfactant at premicellar, micellar and post-micellar concentrations in aqueous phase at room temperature. The magnitude of edge excitation red shift (EERS) in the fluorescence maximum of C2+ in bulk water solution is 1897 cm- 1 whereas, in the case of SDS it is observed to be 1984 cm- 1. The fluorescence decay curve of C2+ fits with multi exponential functions in the micellar system. The increase in lifetime of C2+ in SDS has been attributed to the increase in radiative rate due to the incorporation of C2+ at the micelle -water interface. The value of dynamic quenching constant determined is 16.9 M- 1. The location of the probe molecule in micellar systems has been justified by a variety of spectral parameters such as dielectric constant, ET (30), viscosity, EERS, average fluorescence decay time, radiative and non-radiative rate constants. All experimental results suggest that the C2+ molecule binds strongly with the SDS micelles and resides at micellar-water interface. The binding constant (Kb) calculated (3.85 × 105 M- 1) for C2+ in SDS revealed that the electrostatic forces mediate charge probe-micelle association.

Understanding the intrinsic fluorescence of piperine in microheterogeneous media: partitioning and loading studies

Piperine, an ingredient of black pepper, is widely used in pharmaceutical applications.

How is the interaction of a chloride channel blocker with phospholipids influenced by divalent metal ions? Effect of unsaturation on the lipid side chain

The present study reveals the effect of various divalent ions (Ca²⁺, Mg²⁺and Zn²⁺) on the binding interaction of a prospective chloride channel blocker, 9-methylanthroate (9MA), with liposome membranes, namely, dimyristoylphosphatidylcholine (DMPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The liposome membranes DMPC and POPC differ in the unsaturation of the side-chain. The drug (9MA) is found to experience a greater degree of partitioning into the POPC lipid bilayer (containing unsaturated side-chain) in comparison to DMPC (containing saturated side-chain). The stronger 9MA-POPC binding interaction is found to be only nominally perturbed by the presence of metal salts. On the contrary, the 9MA-DMPC binding interaction is found to be significantly perturbed by the presence of metal salts and is manifested on the environment-responsive spectroscopic properties of the drug. The steady-state and picosecond-resolved fluorescence spectroscopic results reveal the effect of metal ions on DMPC bilayer to follow the trend Ca²⁺ < Mg²⁺ < Zn²⁺. This is also quantified by evaluating the partition coefficient of the drug into DMPC lipid in the presence of various divalent ions which is found to follow the same sequence. The degree of penetration of these cations has been rationalized on the basis of adsorption of cations on DMPC headgroup region resulting in dehydration of the headgroup along with shrinking of it.

A new and efficient carboxymethyl-hexanoyl chitosan/dodecyl sulfate nanocarrier for a pyrazoline with antileukemic activity

We describe herein a chitosan nanocarrier for drug delivery applications obtained through the self-assembly of carboxymethyl-hexanoyl chitosan and dodecyl sulfate (CHC-SDS). Nanocapsules with spherical morphology were obtained in phosphate buffer at pH 7.4. These CHC-SDS nanocapsules showed no toxicity toward Jurkat cells (acute lymphoblastic leukemia) and were used to encapsulate a new pyrazoline (H3TM04) with antileukemia activity. The samples were characterized by dynamic light scattering (DLS) and Laser Doppler Micro-Electrophoresis. The encapsulation efficiency was higher than 96% (293.6 μg mL^-1) and the H3TM04-loaded nanocapsules (CHC-SDS-H) had a negative surface charge (-29.8 ± 0.7 mV) and hydrodynamic radius of around 84 nm. For the first time, CHC-SDS-H were formed and the antitumoral cancer activity was proved. The in vitro assays showed the controlled release of H3TM04 from the CHC-SDS-H nanocapsules in phosphate buffer pH 7.4. The H3TM04 release data were described by the power law model, indicating that H3TM04 delivery occurred via an erosion mechanism. The cytotoxicity assays with Jurkat and K-562 cells (acute myeloid leukemia) demonstrated that the CHC-SDS-H nanocapsule decreases the half maximal inhibitory concentration (IC₅₀). The study showed that CHC-SDS nanocapsules represent a promising nanocarrier for pyrazoline derivates that could be applied in leukemia therapy.

Association and sequestered dissociation of an anticancer drug from liposome membrane: Role of hydrophobic hydration

Herein, the interaction of a potent anticancer drug (Sanguinarine, SG) with dimyristoyl-l-α-phosphatidylglycerol (DMPG) liposome membrane has been investigated at physiological pH. The spectroscopic fluorescence decay results demonstrate a modification of the photophysics of SG within DMPG-encapsulated state leading to preferential stabilization of the iminium ion over the alkanolamine form. This suggests a key role of electrostatic force underlying the interaction. The complex dependence of the thermodynamic parameters on temperature yields a unique finding of a positive heat capacity change (ΔC_p) indicating the signature of hydrophobic hydration. The study also demonstrates the application of β-cyclodextrin (βCD) as a prospective host system resulting in release of the DMPG-bound drug. A calorimetric exploration of the DMPG-βCD interaction reveals an intrinsically complex thermodynamics of the process leading to ΔC_p > 0 and thus marking the instrumental role of hydrophobic hydration which follows that the DMPG-βCD interaction is accompanied with burial of polar molecular surfaces. A systematic investigation of the diffusion of the drug within various microheterogeneous environments by Fluorescence Correlation Spectroscopy (FCS) categorically reinforces our arguments.

A red-emitting indolium fluorescence probe for membranes - flavonoids interactions

The red-emitting indolium derivative compound (E)-2-(4-(diphenylamino)styryl)-1,3,3-trimethyl-3H-indol-1-ium iodide (H3) was demonstrated as a sensitive membrane fluorescence probe. The probe located at the interface of liposomes when mixed showed much fluorescence enhancement by inhibiting the twisted intramolecular charge transfer state. After ultrasonic treatment, it penetrated into lipid bilayers with the emissions leveling off and a rather large encapsulation efficiency (71.4%) in liposomes. The ζ-potential and particle size measurement confirmed that the charged indolium group was embedded deeply into lipid bilayers. The probe was then used to monitor the affinities of antioxidant flavonoids for membranes. It was verified that quercetin easily interacted with liposomes and dissociated the probe from the internal lipid within 60 s under the condition of simply mixing. The assessment of binding affinities of six flavonoids and the coincident results with their antioxidation activities indicated that it was a promising membrane probe for the study of drug bio-affinities.

Theoretical rationalisation of the photophysics of a TICT excited state of cinnamoyl–coumarin derivatives in homogeneous and biological membrane models

Analysis of the potential energy barriers and structural dynamics of a new TICT-probe for monitoring biological environments.

Modulated photophysics and rotational-relaxation dynamics of coumarin 153 in nonionic micelles: the role of headgroup size and tail length of the surfactants

Effect of the variation of the headgroup size and tail length on the photophysics and rotational dynamics of embedded dye C153.

Location and freedom of single and double guest in dye-doped polymer nanoparticles

We report on time-resolved fluorescence anisotropy studies of poly(9-vinylcarbazole) (PVK) nanoparticles (NPs) encapsulating Coumarin 153 (C153) and Nile Red (NR).

Modulation in prototropism of the photosensitizer Harmane by host:guest interactions between β-cyclodextrin and surfactants

The present contribution demonstrates the photophysics of a prospective cancer cell photosensitizer Harmane (HM) belonging to the family of β-carboline in mixed microheterogeneous environments of β-cyclodextrin (β-CD) and surfactants having varying surface charges using steady-state and time-resolved fluorescence spectroscopic techniques. The remarkable modulations in prototropic activities of the micelle-bound drug in the presence of β-CD evinces for disruption of the micellar structural integrity by β-CD. The results are meticulously discussed in relevance to the effect of a potential drug delivery vehicle (CD) on the membrane-mimetic micellar system. Further, application of an extrinsic fluorescence probe for monitoring such interactions is fraught by the possibilities of no less than three equilibria that can operate simultaneously viz., (i) surfactant-cyclodextrin, (ii) surfactant-fluorophore and (iii) cyclodextrin-fluorophore. This aspect highlights the enormous importance of the issue of suitability of the fluorescence probe to study such complicated systems and interaction phenomena. Also the varying interaction scenario of β-CD with the nature of the surfactant highlights the importance of precise knowledge of the strength and locus of drug binding in delineating such complex interactions. The results of the present investigation advocate for the potential applicability of the drug (HM) itself as a fluorescence reporter in study of such complex microheterogeneous interactions.

A spectroscopic investigation on the interaction of a magnetic ferrofluid with a model plasma protein: effect on the conformation and activity of the protein

The understanding of the interaction of nanomaterials with relevant biological targets e.g., proteins is of paramount importance in biological and pharmaceutical fields of research. In a biological fluid, proteins can associate with nanomaterials which can subsequently exert a significant impact on the conformation and functionality of the protein. Here we report the binding interaction of a model plasma protein Bovine Serum Albumin (BSA) with a magnetic nanoparticle of mixed spinel origin (Ni(0.5)Zn(0.5)Fe(2)O(4), abbreviated as NZFO from now and onwards). The thermodynamic parameters (ΔH, ΔS and ΔG) for the protein-nanoparticle binding interaction have been evaluated from the van't Hoff equation to unveil that the binding interaction is enthalpically as well as entropically driven (ΔH < 0 and ΔS > 0), with an overall favorable Gibbs free energy change (ΔG < 0). Also the thermodynamic parameters delineate the predominant role of electrostatic interaction in the BSA-NZFO binding process. The results of temperature dependent fluorescence quenching and time-resolved fluorescence decay measurements indicate a static quenching mechanism in the present case. Steady-state absorption, synchronous fluorescence, three-dimensional (3D) fluorescence and circular dichroism (CD) spectroscopic techniques have been employed to unveil the conformational changes in BSA induced by the binding of NZFO. Disruption of the native conformation of the protein upon binding with NZFO is reflected through a reduced functionality (in terms of esterase activity) of the protein-NZFO conjugate system in comparison to the native protein. Based on the experimental findings the probable binding location of NZFO is argued to be the hydrophilic domain IB. This seems physically realizable since domain I of BSA is characterized by a net negative charge and hence can serve as a favorable binding site for NZFO carrying a positive surface charge. The key role of electrostatic forces in the BSA-NZFO interaction process is further substantiated from chemical denaturation study and measurement of the effect of ionic strength on the interaction process.

Response of an environment-sensitive intramolecular charge transfer probe towards solubilization of liposome membranes by a non-ionic detergent: association and dissociation kinetics

The present report describes an endeavor to follow the solubilization of DMPC and DMPG liposome membranes by a non-ionic detergent Triton X-100 on the lexicon of environment-sensitive intramolecular charge transfer (ICT) photophysics of an extrinsic molecular probe 5-(4-dimethylamino-phenyl)-penta-2, 4-dienoic acid methyl ester (DPDAME). The prospective applicability of the probe to function as a reporter for detergent-sequestered solubilization of liposome membranes is argued on the basis of comparison of the spectral properties of the probe in various environments. Fluorescence anisotropy study delineates the degree of motional restriction imposed on the probe in different microheterogeneous assemblies. The kinetics of association of the probe with the liposome membranes and the dissociation kinetics of TX-100-sequestered solubilization process of the liposomes have been monitored by the stopped-flow fluorescence technique and the results are rationalized in relevance to fluorescence anisotropy study.