All-Optical Method to Assess Stromal Concentration of Riboflavin in Conventional and Accelerated UV-A Irradiation of the Human Cornea.

PURPOSE. We investigated the concentration of riboflavin in human donor corneas during corneal cross-linking using two-photon optical microscopy and spectrophotometry. METHODS. Eight corneal tissues were de-epithelialized and soaked with 20% dextran-enriched 0.1% riboflavin solution for 30 minutes. After stromal soaking, three tissues were irradiated using a 3 mW/cm(2) UV-A device for 30 minutes and three tissues irradiated using a 10 mW/cm2 device for 9 minutes. Two additional tissues were used as positive controls. A Ti:sapphire laser at 810 nm was used to perform two-photon emission fluorescence (TPEF) and second harmonic generation axial scanning measurements in all specimens before and after stromal soaking and after UV-A irradiation. In addition, spectrophotometry was used to collect the absorbance spectra of each tissue at the same time intervals. Analysis of the absorbance spectra and TPEF signals provided measures of the concentration depth profile of riboflavin in corneal stroma. RESULTS. After stromal soaking, the average peak concentration of riboflavin (0.020% +-0.001%) was found between a stromal depth of 100 and 250 lm; the concentration of riboflavin was almost constant up to 320 6 53 lm depth, then decreased toward the endothelium, though riboflavin was still enriched in the posterior stroma (0.016%% 6 0.001%). After conventional and accelerated UV-A irradiation, the concentration of riboflavin decreased uniformly 87% 6 2% and 67% 6 3% (P < 0.001), respectively. CONCLUSIONS. The combined use of two-photon optical microscopy and spectrophotometry provides relevant information for investigating the concentration of riboflavin in corneal stroma. The method can assist with the assessment of novel riboflavin formulations and different UV-A irradiation protocols

On the ergodicity of supercooled molecular glass-forming liquids at the dynamical arrest: the o-terphenyl case

The dynamics of supercooled ortho-terphenyl has been studied using photon-correlation spectroscopy (PCS) in the depolarized scattering geometry. The obtained relaxation curves are analyzed according to the mode-coupling theory (MCT) for supercooled liquids. The main results are: i) the observation of the secondary Johari-Goldstein relaxation (β) that has its onset just at the dynamical crossover temperature T[subscript B] (T[subscript M] > T[subscript B] > T[subscript g]); ii) the confirmation, of the suggestion of a recent statistical mechanical study, that such a molecular system remains ergodic also below the calorimetric glass-transition temperature T[subscript g]. Our experimental data give evidence that the time scales of the primary (α) and this secondary relaxations are correlated. Finally a comparison with recent PCS experiments in a colloidal system confirms the primary role of the dynamical crossover in the physics of the dynamical arrest.United States. Dept. of Energy. Office of Basic Energy Sciences (Contract DE-FG02-90ER45429

Design principles of chiral carbon nanodots help convey chirality from molecular to nanoscale level

The chirality of (nano)structures is paramount in many phenomena, including biological processes, self-assembly, enantioselective reactions, and light or electron spin polarization. In the quest for new chiral materials, metallo-organic hybrids have been attractive candidates for exploiting the aforementioned scientific fields. Here, we show that chiral carbon nanoparticles, called carbon nanodots, can be readily prepared using hydrothermal microwave-assisted synthesis and easily purified. These particles, with a mean particle size around 3 nm, are highly soluble in water and display mirror-image profile both in the UV–Vis and in the infrared regions, as detected by electronic and vibrational circular dichroism, respectively. Finally, the nanoparticles are used as templates for the formation of chiral supramolecular porphyrin assemblies, showing that it is possible to use and transfer the chiral information. This simple (and effective) methodology opens up exciting opportunities for developing a variety of chiral composite materials and applications

Fractal Structures and Their Effects on the Dynamics of Supramolecular Aggregates Studied by Light and Thermodynamic Measurements

We report a review on light scattering, viscosity, sound propagation and calorimetric data in aggregating disperse systems, i.e. colloidal suspensions of polystyrene latex spheres and water in oil microemulsions. By elastic (intensity) and quasielastic light scattering (dynamics) direct information is obtained on aggregated clusters being built with a fractal structure and on the corresponding different kinetic mechanisms. In particular, dynamic data, showing a well-defined sealing behaviour in the measured mean linewidth, confirm the picture proposed by intensity data and allow a rough estimate of the cluster dimension. All the thermodynamic data, discussed in terms of a two- fluid model (suspending fluid and disperse interacting system), give evidence of the main role played by the attractive interparticle interaction. In fact, the typical features observed in viscosity and specific heat data and in the viscoelastic behaviour shown by these disperse systems can be connected to the long range structural order built by fractal aggregation processes. All the experimental data are consistent with the Derjaguin-Landau-Ver- wey-Overbeek theory on colloidal stability

Control of the Structural Stability of α‑Crystallin under Thermal and Chemical Stress: The Role of Carnosine

The structural properties of α-crystallin, the major protein of the eye lens of mammals, in aqueous solution are investigated by means of small angle X-ray and dynamic light scattering. The research interest is devoted in particular to the effect of carnosine in protecting the protein under stress conditions, like temperature increase and presence of denaturant (guanidinium–HCl). The results suggest that carnosine interacts, through mechanisms involving hydrophobic interactions, with α-crystallin and avoids the structural changes in the quaternary structure induced by thermal and chemical stress. It is also shown that, if mediated by carnosine, the self-aggregation of α-crystallin induced by the denaturant at higher temperature can be controlled and even partially reversed. Therefore, carnosine is effective in preserving the structural integrity of the protein, suggesting the possibility of new strategies of intervention for preventing or treating pathologies related to protein aggregation, like cataracts

A novel potential nanophototherapeutic based on the assembly of an amphiphilic cationic ß-cyclodextrin and an anionic porphyrin

The development of cyclodextrin nanoassemblies as useful carriers for photosensitizer drugs (PS) delivery in biological environment is a topic of increasing interest. In this paper, we present a spectroscopic investigation on a nanosystem based on an amphiphilic cationic ß-cyclodextrin derivative (CD-N) and an anionic porphyrin (TPPS). Nanoassemblies were prepared by hydration of an organic film containing the two species. The system was characterized by complementary techniques such as UV-vis, stationary and time-resolved fluorescence, and Dynamic Light Scattering (DLS) at different TPPS/CD-N molar ratios. Time-resolved fluorescence data showed that, at all the investigated molar ratios, TPPS is present both as self-aggregated species and monomers forming supramolecular adducts with CD-N. Moreover, DLS measurements evidenced families of aggregates having hydrodynamic radii ranging between 50 and 350 nm and the size distribution profile depending on the TPPS/CD-N molar ratio. At the highest CD-N concentration, the hydrodynamic radii of the aggregates were nearly the same as those of neat CD-N in the absence of TPPS (50 nm). No aging phenomena were registered, pointing out the high stability of these nanoassemblies in aqueous solution for at least a month. Preliminary studies on the internalization in tumoral cells and subsequent irradiation for PDT application were carried out. The results support the feasibility of these nanoaggregates to promote PS internalization in HeLa cells, inducing cell death upon visible light irradiation. © 2017 World Scientific Publishing Company.Peer Reviewe

Brillouin scattering from cross-linked gels

In this letter we report Brillouin scattering measurements on methyl-methacrylate (MMA) gels crosslinked with varying amounts of ethylene-dimethacrylate (EDMA). We find that the $k$ dependence of the phase velocity changes on increasing the cross-link content. For higher concentrations of crosslink we observe maxima and minima in the $k$ dependence of the phase velocity. We associate these minima and maxima with spatial inhomogeneities in the gel, with the formation of regions of low and high cross-link density, respectively. This micro-phase separation is frozen in by the presence of the already existing spanning network

Hydrodynamic and Thermophoretic Effects on the Supramolecular Chirality of Pyrene-Derived Nanosheets

Chiroptical properties of two-dimensional (2D) supramolecular assemblies (nanosheets) of achiral, charged pyrene trimers (Py3) are rendered chiral by asymmetric physical perturbations. Chiral stimuli in a cuvette can originate either from controlled temperature gradients or by very gentle stirring. The chiroptical activity strongly depends on the degree of supramolecular order of the nanosheets, which is easily controlled by the method of preparation. The high degree of structural order ensures strong cooperative effects within the aggregates, rendering them more susceptible to external stimuli. The samples prepared by using slow thermal annealing protocols are both CD and LD active (in stagnant and stirred solutions), whereas for isothermally aged samples chiroptical activity was in all cases undetectable. In the case of temperature gradients, the optical activity of 2D assemblies could be recorded for a stagnant solution due to migration of the aggregates from the hottest to the coldest regions of the system. However, a considerably stronger exciton coupling, coinciding with the J-band of the interacting pyrenes, is developed upon subtle vortexing (0.5 Hz, 30 rpm) of the aqueous solution of the nanosheets. The sign of the exciton coupling is inverted upon switching between clockwise and counter-clockwise rotation. The supramolecular chirality is evidenced by the appearance of CD activity. To exclude artefacts from proper CD spectra, the contribution from LD to the observed CD was determined. The data suggest that the aggregates experience asymmetrical deformation and alignment effects because of the presence of chiral flows