A molecular propeller effect for chiral separation and analysis.

Enantiomers share nearly identical physical properties but have different chiral geometries, making their identification and separation difficult. Here we show that when exposed to a rotating electric field, the left- and right-handed chiral molecules rotate with the field and act as microscopic propellers; moreover, owing to their opposite handedness, they propel along the axis of field rotation in opposite directions. We introduce a new molecular parameter called hydrodynamic chirality to characterize the coupling of rotational motion of a chiral molecule into its translational motion and quantify the direction and velocity of such motion.

Multiporphyrin arrays with π-π interchromophore interactions.

A recently reported synthetic method has been employed to prepare several arrays of free base and zinc porphyrins. In the arrays, the porphyrins are arranged around a central benzene ring. The lack of aryl rings in the linkages to the central benzene ring, coupled with the presence of only one meso-aryl substituent on each porphyrin, allows strong electronic interactions between the porphyrin macrocycles.

Activity of Bradykinin B2 Receptor Is Regulated by Long-Chain Polyunsaturated Fatty Acids.

The molecular and cellular mechanisms by which long-chain polyunsaturated fatty acids (LCPUFA) exert their beneficial effects on cardiovascular health remain obscure. While both LCPUFA and bradykinin (BK) signaling pathway play a role in the cardiovascular system, any direct link between the two is yet to be established. Using picosecond time-resolved fluorescence microscopy and a genetically engineered bradykinin B2 receptor (B2R) sensor (B2K-CC), we detected LCPUFA-induced conformational responses in the B2R similar to those caused by its cognate ligand, BK.

Real-time detection of G protein activation using monomolecular Gγ FRET sensors.

G protein-coupled receptors (GPCRs) are involved in many diseases, and are the target of a large percentage of modern drugs. While only a few fluorescence resonance energy transfer (FRET) sensors have been made for real-time detection of GPCR activation, the human genome encodes roughly 950 GPCRs and a need for a broad real-time detection system is needed. In this study, we developed and characterized a new type of G protein sensor based on the Gγ subunit containing an intra-molecular FRET pair to allow detection of real-time G protein activation in multiple cell lines using time-resolved fluorescence spectroscopy.

PTH1 receptor is involved in mediating cellular response to long-chain polyunsaturated fatty acids.

The molecular pathways by which long chain polyunsaturated fatty acids (LCPUFA) influence skeletal health remain elusive. Both LCPUFA and parathyroid hormone type 1 receptor (PTH1R) are known to be involved in bone metabolism while any direct link between the two is yet to be established. Here we report that LCPUFA are capable of direct, PTH1R dependent activation of extracellular ligand-regulated kinases (ERK).

Effect of membrane tension on the physical properties of DOPC lipid bilayer membrane.

Molecular dynamics simulations of a dioleoylphosphocholine (DOPC) lipid bilayer were performed to explore its mechanosensitivity. Variations in the bilayer properties, such as area per lipid, volume, thickness, hydration depth (HD), hydration thickness (HT), lateral diffusion coefficient, and changes in lipid structural order were computed in the membrane tension range 0 to 15dyn/cm. We determined that an increase in membrane tension results in a decrease in the bilayer thickness and HD of ~5% and ~5.

Effect of membrane tension on the electric field and dipole potential of lipid bilayer membrane.

The dipole potential of lipid bilayer membrane controls the difference in permeability of the membrane to oppositely charged ions. We have combined molecular dynamics (MD) simulations and experimental studies to determine changes in electric field and electrostatic potential of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid bilayer in response to applied membrane tension. MD simulations based on CHARMM36 force field showed that electrostatic potential of DOPC bilayer decreases by ~45mV in the physiologically relevant range of membrane tension values (0 to 15dyn/cm).

Conformationally constrained macrocyclic diporphyrin-fullerene artificial photosynthetic reaction center.

Photosynthetic reaction centers convert excitation energy from absorbed sunlight into chemical potential energy in the form of a charge-separated state. The rates of the electron transfer reactions necessary to achieve long-lived, high-energy charge-separated states with high quantum yields are determined in part by precise control of the electronic coupling among the chromophores, donors, and acceptors and of the reaction energetics. Successful artificial photosynthetic reaction centers for solar energy conversion have similar requirements.

Apparent PKA activity responds to intermittent hypoxia in bone cells: a redox pathway?

We studied hypoxia-induced dynamic changes in the balance between PKA and PKA-counteracting phosphatases in the microfluidic environment in single cells using picosecond fluorescence spectroscopy and intramolecular fluorescence resonance energy transfer (FRET)-based sensors of PKA activity. First, we found that the apparent PKA activity in bone cells (MC3T3-E1 cells) and endothelial cells (bovine aortic endothelial cells) is rapidly and sensitively modulated by the level of O(2) in the media. When the O(2) concentration in the glucose-containing media was lowered due to O(2) consumption by the cells in the microfluidic chamber, the apparent PKA activity increases; the reoxygenation of cells under hypoxia leads to a rapid ( approximately 2 min) decrease of the apparent PKA activity.

Mechanical stimulus alters conformation of type 1 parathyroid hormone receptor in bone cells.

The molecular mechanisms by which bone cells transduce mechanical stimuli into intracellular biochemical responses have yet to be established. There is evidence that mechanical stimulation acts synergistically with parathyroid hormone PTH(1-34) in mediating bone growth. Using picosecond time-resolved fluorescence microscopy and G protein-coupled receptor conformation-sensitive fluorescence resonance energy transfer (FRET), we investigated conformational transitions in parathyroid hormone type 1 receptor (PTH1R).

Angular resolved light scattering for discriminating among marine picoplankton: modeling and experimental measurements.

In order to assess the capability to optically identify small marine microbes, both simulations and experiments of angular resolved light scattering (ARLS) were performed. After calibration with 30-nm vesicles characterized by a nearly constant scattering distribution for vertically polarized light (azimuthal angle=90 degrees ), ARLS from suspensions of three types of marine picoplankton (two prokaryotes and one eukaryote) in seawater was measured with a scattering device that consisted of an elliptical mirror, a rotating aperture, and a PMT. Scattered light was recorded with adequate signal-to-noise in the 40-140 degrees .

G protein-coupled receptors sense fluid shear stress in endothelial cells.

Hemodynamic shear stress stimulates a number of intracellular events that both regulate vessel structure and influence development of vascular pathologies. The precise molecular mechanisms by which endothelial cells transduce this mechanical stimulus into intracellular biochemical response have not been established. Here, we show that mechanical perturbation of the plasma membrane leads to ligand-independent conformational transitions in a G protein-coupled receptor (GPCR).

Laurdan fluorescence senses mechanical strain in the lipid bilayer membrane.

The precise molecular mechanisms by which cells transduce a mechanical stimulus into an intracellular biochemical response have not yet been established. Here, we show for the first time that the fluorescence emission of an environment-sensitive membrane probe Laurdan is modulated by mechanical strain of the lipid bilayer membrane. We have measured fluorescence emission of Laurdan in phospholipid vesicles of 30, 50, and 100 nm diameter to show that osmotically induced membrane tension leads to an increase in polarity (hydration depth) of the phospholipid bilayer interior.

Counter-propagating optical trapping system for size and refractive index measurement of microparticles.

We propose and demonstrate a novel approach to measure the size and refractive index of microparticles based on two beam optical trapping, where forward scattered light is detected to give information about the particle. The counter-propagating optical trap measurement (COTM) system exploits the capability of optical traps to measure pico-Newton forces for microparticles' refractive index and size characterization. Different from the current best technique for microparticles' refractive index measurement, refractometry, a bulk technique requiring changing the fluid composition of the sample, our optical trap technique works with any transparent fluid and enables single particle analysis without the use of biological markers.

Two-beam optical traps: refractive index and size measurements of microscale objects.

A counter-propagating optical trap measurement (COTM) system is proposed and analyzed based on the ray-optics model. In this system, refractive index and size of trapped objects can be estimated by using forward scattered light from the two-beam laser trap with resolution Delta n = 0.013 for the refractive index measurements and 3.

Elastic light scattering from single cells: orientational dynamics in optical trap.

Light-scattering diagrams (phase functions) from single living cells and beads suspended in an optical trap were recorded with 30-ms time resolution. The intensity of the scattered light was recorded over an angular range of 0.5-179.

Use of moving optical gradient fields for analysis of apoptotic cellular responses in a chronic myeloid leukemia cell model.

To facilitate quantitation of cellular apoptotic responses to various antineoplastic agents, a laser-based technology, Optophoresis, has been developed to provide analysis of cells without any need for labeling or cell processing. Optophoresis is defined as the analysis of the motion of cells, where the motion is either induced or modified by a moving optical gradient field, which produces radiation pressure forces on the cells in an aqueous suspension. Quantitation of the induced motion provides a basis for distinguishing one population of cells from another.

Optical forces for noninvasive cellular analysis.

A novel, noninvasive measurement technique for quantitative cellular analysis is presented that utilizes the forces generated by an optical beam to evaluate the physical properties of live cells in suspension. In this analysis, a focused, near-infrared laser line with a high cross-sectional intensity gradient is rapidly scanned across a field of cells, and the interaction of those cells with the beam is monitored. The response of each cell to the laser depends on its size, structure, morphology, composition, and surface membrane properties; therefore, with this technique, cell populations of different type, treatment, or biological state can be compared.