Deciphering the evolution of supramolecular nanofibers in solution and solid-state: a combined microscopic and spectroscopic approach.

Supramolecular self-assembly of small organic molecules has emerged as a powerful tool to construct well-defined micro- and nanoarchitecture through fine-tuning a range of intermolecular interactions. The size, shape, and optical properties of these nanostructures largely depend on the specific assembly of the molecular building units, temperature and polarity of the medium, and external stimuli. The engineering of supramolecular self-assembled nanostructures with morphology-dependent tunable emission is in high demand due to the promising scope in nanodevices and molecular machines.

Time-dependent enhancement of fluorescence from Rhodobacter capsulatus SB1003 and its critical dependence on concentration temperature and static magnetic field.

Continuous exposure of 395 nm light increases the fluorescence emission intensity of photosynthetic purple non-sulphur bacteria, Rhodobacter capsulatus (SB1003). We show that such an increase in fluorescence emission of extracellular pigment complexes (PC) from these photosynthetic bacteria depends on the concentration of the pigment and temperature and can also be modulated by the static magnetic field. The time-dependent enhanced emission disappears either at or below 300 K or below a threshold sample concentration (0.

Probing Viscosity of Co-Polymer Hydrogel and HeLa Cell Using Fluorescent Gold Nanoclusters: Fluorescence Correlation Spectroscopy and Anisotropy Decay.

Fluorescence dynamics of gold nanoclusters (Au and Au ) are studied in the complex and crowded environment of a triblock co-polymer (F127) hydrogel and inside cervical cancer cell, HeLa. In the hydrogel, spherical micelles of F127 remain immobilized with a hydrophobic core (PPO) and a hydrophilic corona (PEO) region. The fluorescence anisotropy decay suggests that the timescale of rotational relaxation in the hydrogel is similar to that in bulk water (viscosity ∼1 cP).

Time Evolution of Local pH Around a Photo-Acid in Water and a Polymer Hydrogel: Time Resolved Fluorescence Spectroscopy of Pyranine.

In this work, we propose a new analysis of the time resolved emission spectra of a photo-acid, HA, pyranine (8-hydroxypyrene-1,3,6-trisulphonic acid, HPTS) based on time resolved area normalized emission spectra (TRANES). Presence of an isoemissive point in TRANES confirms the presence of two emissive species (HA and A ) inside the system in bulk water and inside a co-polymer hydrogel [F127, (PEO) -(PPO) -(PEO) ]. We show that following electronic excitation, the local pH around HPTS, is much lower than the bulk pH presumably because of ejection of proton from the photo-acid in the excited state.

Probing Deviation of Adhered Membrane Dynamics between Reconstituted Liposome and Cellular System.

The dynamics of cell-cell adhesion are complicated due to complexities in cellular interactions and intra-membrane interactions. In the present work, we have reconstituted a liposome-based model system to mimic the cell-cell adhesion process. Our model liposome system consists of one fluorescein-tagged and one TRITC (tetramethyl-rhodamine isothiocyanate)-tagged liposome, adhered through biotin-neutravidin interaction.

Structure, Activity, and Dynamics of Human Serum Albumin in a Crowded Pluronic F127 Hydrogel.

Structure, activity, and dynamics of a plasma protein, human serum albumin (HSA), inside a crowded environment of F127 gel are studied by circular dichroism (CD), fluorescence correlation spectroscopy (FCS), and picosecond time-resolved fluorescence spectroscopy. For this purpose, the protein is covalently labeled by a maleimide dye, 7-(diethylamino)-3-(4-maleimidylphenyl)-4-methyl-coumarin (CPM). The circular dichroism (CD) spectra suggest that the protein is more structured in the gel reflecting about the biological activities of the protein.

Local environment of organic dyes in an ionic liquid-water mixture: FCS and MD simulation.

The composition dependent local environment of three organic dyes in binary mixtures of a room temperature ionic liquid (1-methyl-3-pentylimidazolium bromide, [pmim][Br]) and water is studied by fluorescence correlation spectroscopy (FCS) and molecular dynamics (MD) simulations. We used three dyes-neutral coumarin 480 (C480), anionic coumarin 343 (C343), and highly hydrophobic 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM)-to probe different environments in the binary mixtures. The heterogeneity of the [pmim][Br]-water mixture leads to multiple values (i.

Live Cell Microscopy: A Physical Chemistry Approach.

Probing dynamics of intracellular components using physical chemistry techniques is a remarkable bottom-up approach for understanding the structures and functions of a biological cell. In this "Feature Article", we give an overview on local polarity, solvation, viscosity, acid-base property, red-ox processes (thiol-disulfide exchange), and gene silencing at selected intracellular components inside a live cell. Significant differences have been observed between cancer cells and their noncancer counterparts.

Probing the conformational dynamics of photosystem I in unconfined and confined spaces.

The fluorescence dynamics of Photosystem I (PSI) in bulk water and inside a confined environment like a liposome have been investigated using time resolved confocal microscopy. In bulk water, PSI exhibits a major emission peak at ∼680 nm, while in the liposome it exhibits a markedly blue shifted emission maximum at ∼485 nm. This is indicative of conformational changes due to entrapment and emergence of a stressed conformation of PSI inside the liposome.

Preferential targeting of i-motifs and G-quadruplexes by small molecules.

i-Motifs and G-quadruplexes are dynamic nucleic acid secondary structures, which are believed to play key roles in gene expression. We herein report two peptidomimetic ligands ( and ) that selectively target i-motifs and G-quadruplexes over double-stranded DNA. These peptidomimetics, regioisomeric with respect to the position of triazole/prolinamide motifs, have been synthesized using a modular method involving Cu(i)-catalyzed azide and alkyne cycloaddition.

Interaction of proteins with ionic liquid, alcohol and DMSO and in situ generation of gold nano-clusters in a cell.

In this review, we give a brief overview on how the interaction of proteins with ionic liquids, alcohols and dimethyl sulfoxide (DMSO) influences the stability, conformational dynamics and function of proteins/enzymes. We present experimental results obtained from fluorescence correlation spectroscopy on the effect of ionic liquid or alcohol or DMSO on the size (more precisely, the diffusion constant) and conformational dynamics of lysozyme, cytochrome c and human serum albumin in aqueous solution. The interaction of ionic liquid with biomolecules (e.

Physical chemistry in a single live cell: confocal microscopy.

A live cell is a complex, yet extremely important container. Understanding the dynamics in a selected intracellular component is a challenging task. We have recently made significant progress in this direction using a confocal microscope as a tool.

Differential role of nonmuscle myosin II isoforms during blebbing of MCF-7 cells.

Bleb formation has been correlated with nonmuscle myosin II (NM-II) activity. Whether three isoforms of NM-II (NM-IIA, -IIB and -IIC) have the same or differential roles in bleb formation is not well understood. Here we report that ectopically expressed, GFP-tagged NM-II isoforms exhibit different types of membrane protrusions, such as multiple blebs, lamellipodia, combinations of both, or absence of any such protrusions in MCF-7 cells.

Enzyme activity of α-chymotrypsin: Deactivation by gold nano-cluster and reactivation by glutathione.

Effect of gold nanoclusters (Au-NCs) on the circular dichroism (CD) spectra and enzymatic activity of α-chymotrypsin (ChT) (towards hydrolysis of a substrate, N-succinyl-l-phenylalanine p-nitroanilide) are studied. The CD spectra indicate that on binding to Au-NC, ChT is completely unfolded, resulting in nearly zero ellipticity. α-chymotrypsin (ChT) coated gold nano-clusters exhibit almost no enzymatic activity.

Effect of alcohol on the structure of cytochrome C: FCS and molecular dynamics simulations.

Effect of ethanol on the size and structure of a protein cytochrome C (Cyt C) is investigated using fluorescence correlation spectroscopy (FCS) and molecular dynamics (MD) simulations. For FCS studies, Cyt C is covalently labeled with a fluorescent probe, alexa 488. FCS studies indicate that on addition of ethanol, the size of the protein varies non-monotonically.

Amyloid beta peptides inside a reconstituted cell-like liposomal system: aggregation, FRET, fluorescence oscillations and solvation dynamics.

Aggregations of amyloid-beta (Aβ) peptides were studied inside a reconstituted cell like liposomal system using time-resolved confocal microscopy. Fluorescence correlation spectroscopy (FCS) and confocal images indicate that Aβ forms a very large aggregate in bulk and more efficiently, in the bilayer region of the liposome, respectively. The aggregates formed inside the liposome gradually migrate out to bulk water.

Split-ubiquitin yeast two-hybrid interaction reveals a novel interaction between a natural resistance associated macrophage protein and a membrane bound thioredoxin in Brassica juncea.

Natural resistance associated macrophage proteins (NRAMPs) are evolutionarily conserved metal transporters involved in the transport of essential and nonessential metals in plants. Fifty protein interactors of a Brassica juncea NRAMP protein was identified by a Split-Ubiquitin Yeast-Two-Hybrid screen. The interactors were predicted to function as components of stress response, signaling, development, RNA binding and processing.

Spectral mapping of 3D multi-cellular tumor spheroids: time-resolved confocal microscopy.

A tumor-like multi-cellular spheroid (3D) differs from a 2D cell in a number of ways. This is demonstrated using time resolved confocal microscopy. Two different tumor spheroids - HeLa (cervical cancer) and A549 (lung cancer) - are studied using 3 different fluorescent dyes - C153 (non-covalent), CPM (covalent) and doxorubicin (non-covalent, anti-cancer drug).

Fluorescence Dynamics in the Endoplasmic Reticulum of a Live Cell: Time-Resolved Confocal Microscopy.

Fluorescence dynamics in the endoplasmic reticulum (ER) of a live non-cancer lung cell (WI38) and a lung cancer cell (A549) are studied by using time-resolved confocal microscopy. To selectively study the organelle, ER, we have used an ER-Tracker dye. From the emission maximum (λmaxem) of the ER-Tracker dye, polarity (i.

Small molecule regulated dynamic structural changes of human G-quadruplexes.

The changes in structure and dynamics of oncogenic () and telomeric () G-rich DNA sequences due to the binding of a novel carbazole derivative () are elucidated using single-molecule Förster resonance energy transfer (sm-FRET), fluorescence correlation spectroscopy (FCS) and NMR spectroscopy. In contrast to the previous reports on the binding of ligands to pre-folded G-quadruplexes, this work illustrates how ligand binding changes the conformational equilibria of both unstructured G-rich DNA sequences and K-folded G-quadruplexes. The results demonstrate that K free and exist as unfolded and partially folded conformations.

Cytochrome c-Capped Fluorescent Gold Nanoclusters: Imaging of Live Cells and Delivery of Cytochrome c.

Cytochrome c-capped fluorescent gold nanoclusters (Au-NCs) are used for imaging of live lung and breast cells. Delivery of cytochrome c inside the cells is confirmed by covalently attaching a fluorophore (Alexa Fluor 594) to cytochrome c-capped Au-NCs and observing fluorescence from Alexa 594 inside the cell. Mass spectrometry studies suggest that in bulk water, addition of glutathione (GSH) to cytochrome c-capped Au-NCs results in the formation of glutathione-capped Au-NCs and free apo-cytochrome c.