Fluorescence Probes Exhibit Photoinduced Structural Planarization: Sensing In Vitro and In Vivo Microscopic Dynamics of Viscosity Free from Polarity Interference.

We demonstrate the construction of wavelength λ-ratiometric images that allow visualizing the distribution of microscopic dynamics within living cells and tissues by using the newly developed principle of fluorescence response. The bent-to-planar motion in the excited state of incorporated fluorescence probes leads to elongation of the π-delocalization, resulting in microviscosity-dependent but polarity-insensitive interplay between well-separated blue and red bands in emission spectra. This allows constructing the exceptionally contrasted images of cellular dynamics. Moreover, the application of probes with increased affinity toward biological membranes allowed detecting the differences in dynamics between the plasma membrane and intracellular membrane structures. Such λ-ratiometric microviscosity imaging was extended for mapping the living tissues and observing their inflammation-dependent changes.

Cyclopentane rings in hydrophobic chains of a phospholipid enhance the bilayer stability to electric breakdown.

Archaeal lipids ensure unprecedented stability of archaea membranes in extreme environments. Here, we incorporate a characteristic structural feature of an archaeal lipid, the cyclopentane ring, into hydrocarbon chains of a short-chain (C12) phosphatidylcholine to explore whether the insertion would allow such a lipid (1,2-di-(3-(3-hexylcyclopentyl)-propanoate)-sn-glycero-3-phosphatidylcholine, diC12cp-PC) to form stable bilayers at room temperature. According to fluorescence-based assays, in water diC12cp-PC formed liquid-crystalline bilayers at room temperature. Liposomes produced from diC12cp-PC retained calcein for over a week when stored at +4 °C. diC12cp-PC could also form model bilayer lipid membranes that were by an order of magnitude more stable to electrical breakdown than egg PC membranes. Molecular dynamics simulation showed that the cyclopentane fragment fixes five carbon atoms (or four C-C bonds), which is compensated by the higher mobility of the rest of the chain. This was found to be the reason for the remarkable stability of the diC12cp-PC bilayer: restricted conformational mobility of a chain segment increases the membrane bending modulus (compared to a normal hydrocarbon chain of the same length). Here, higher stiffness practically does not affect the line tension of a membrane pore edge. Rather it makes it more difficult for diC12cp-PC to rearrange in order to line the edge of a hydrophilic pore; therefore, fewer pores are formed.

UV-promoted radical formation, and near-IR-induced and spontaneous conformational isomerization in monomeric 9-methylguanine isolated in low-temperature Ar matrices.

Three low-energy isomers of 9-methylguanine, the amino-oxo (AO) form and two amino-hydroxy (AH1 and AH2) conformers, were trapped from the gas phase into low-temperature argon matrices. The AH1 and AH2 isomers, differing in the orientation of the OH group, were found to transform into each other upon excitation with near-IR light. The population of the AO form of the compound was not changed upon any near-IR irradiation of the matrix samples. Using monochromatic near-IR light, generated by a frequency-tunable laser source, it was possible to selectively induce the AH1 → AH2 or AH2 → AH1 conversion. Photoreversibility of this conformational transformation was then demonstrated. Exposure of matrix-isolated monomers of 9-methylguanine to broadband near-IR light also led to conformational conversions within the amino-hydroxy tautomeric form; the final stage of this process was always the same photostationary state independent of the initial ratio of AH1 and AH2 populations. Spontaneous conformational conversion, transforming the higher-energy AH2 form into the lower-energy AH1 isomer, was observed for matrix-isolated monomers of 9-methylguanine kept in the dark. The mechanism of this process must rely on quantum tunneling of the light hydrogen atom. Irradiation of matrix-isolated 9-methylguanine with UV laser light at λ = 288 or 285 nm led to a substantial consumption of the two AH forms, while the amount of AO isomer remained unchanged. On the other hand, a decrease in the population of the AO isomer occurred upon excitations at shorter wavelengths, λ = 280 or 275 nm. The spectral changes observed after UV-irradiation suggest the generation (and stabilization in the matrix) of a radical species, resulting from the photocleavage of the O-H or N1-H bonds, in the AH or AO isomer, respectively.

How microwave treatment of gluten affects its toxicity for celiac patients? A study on the effect of microwaves on the structure, conformation, functionality and immunogenicity of gluten.

The microwave heating of wheat kernels, flour, and gluten, has attracted attention lately because it has been claimed to abolish gluten toxicity for celiac patients. Nevertheless, contradictory results have been reported regarding the effect on gluten celiac-immunotoxicity. In order to better understand the effect of the microwave treatment on gluten structure, conformation, functionality and celiac-immunotoxicity, a central composite design with two factors, power level, and treatment time, was used to investigate a possible quadratic and interaction effects between both factors. Extractable gliadins content was affected by the power and time in a linear and quadratic fashion; extractable glutenins were not affected. Gluten secondary structure was affected by the microwave treatment and related to the polymer's disaggregation phenomenon observed. In fact, the microwave treatment increased the amount of potentially toxic epitopes released after peptic and tryptic digestion, showing inefficiency as a treatment to detoxify the gluten for celiac disease patients.

NMR studies of excluded volume interactions in peptide dendrimers.

Peptide dendrimers are good candidates for diverse biomedical applications due to their biocompatibility and low toxicity. The local orientational mobility of groups with different radial localization inside dendrimers is important characteristic for drug and gene delivery, synthesis of nanoparticles, and other specific purposes. In this paper we focus on the validation of two theoretical assumptions for dendrimers: (i) independence of NMR relaxations on excluded volume effects and (ii) similarity of mobilities of side and terminal segments of dendrimers. For this purpose we study 1H NMR spin-lattice relaxation time, T1H, of two similar peptide dendrimers of the second generation, with and without side fragments in their inner segments. Temperature dependences of 1/T1H in the temperature range from 283 to 343 K were measured for inner and terminal groups of the dendrimers dissolved in deuterated water. We have shown that the 1/T1H temperature dependences of inner groups for both dendrimers (with and without side fragments) practically coincide despite different densities of atoms inside these dendrimers. This result confirms the first theoretical assumption. The second assumption is confirmed by the 1/T1H temperature dependences of terminal groups which are similar for both dendrimers.

Crystal Structure and Photocatalytic Activity of Al-Doped TiO2 Nanofibers for Methylene Blue Dye Degradation.

Al-TiO2 nanofibers were prepared using a sol-gel derived electrospinning by varying the Al/Ti molar ratio from 0 to 0.73 to investigate the effect of Al doping on the crystal structure and the photocatalytic activity of Al-TiO2 for methylene blue (MB) degradation. XRD results indicated that as the Al/Ti molar ratio rose, crystal structure of Al-TiO2 was changed from anatase/rutile (undoped), anatase (0.07-0.18), to amorphous phase (0.38-0.73), which was confirmed by XPS and Raman analysis. The degradation kinetic constant increased from 7.3 x 10(-4) min(-1) to 4.5 x 10(-3) min(-1) with the increase of Al/Ti molar ratios from 0 to 0.38, but decreased to 3.4 x 10(-3) min(-1) when the Al/Ti molar ratio reached 0.73. The Al-TiO2 catalyst doped with 0.38 Al/Ti molar ratio demonstrated the best MB degradation. Experimental results indicated that the Al doping in Al-TiO2 was mainly attributed to the crystal structure of TiO2 and the photocatalytic degradation of MB.

Crystal structure of the nucleosome containing ultraviolet light-induced cyclobutane pyrimidine dimer.

The cyclobutane pyrimidine dimer (CPD) is induced in genomic DNA by ultraviolet (UV) light. In mammals, this photolesion is primarily induced within nucleosomal DNA, and repaired exclusively by the nucleotide excision repair (NER) pathway. However, the mechanism by which the CPD is accommodated within the nucleosome has remained unknown. We now report the crystal structure of a nucleosome containing CPDs. In the nucleosome, the CPD induces only limited local backbone distortion, and the affected bases are accommodated within the duplex. Interestingly, one of the affected thymine bases is located within 3.0 Å from the undamaged complementary adenine base, suggesting the formation of complementary hydrogen bonds in the nucleosome. We also found that UV-DDB, which binds the CPD at the initial stage of the NER pathway, also efficiently binds to the nucleosomal CPD. These results provide important structural and biochemical information for understanding how the CPD is accommodated and recognized in chromatin.

Highly Efficient Far Red/Near-Infrared Solid Fluorophores: Aggregation-Induced Emission, Intramolecular Charge Transfer, Twisted Molecular Conformation, and Bioimaging Applications.

The development of organic fluorophores with efficient solid-state emissions or aggregated-state emissions in the red to near-infrared region is still challenging. Reported herein are fluorophores having aggregation-induced emission ranging from the orange to far red/near-infrared (FR/NIR) region. The bioimaging performance of the designed fluorophore is shown to have potential as FR/NIR fluorescent probes for biological applications.

New Evidence for Hydroxyalkyl Radicals and Light- and Thermally Induced Trapped Electron Reactions in Rhamnose.

Radical formation and trapping of radicals in X-irradiated crystals of rhamnose at 6 K were investigated using electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques, complemented with periodic density functional theory (DFT) calculations. The two major radical species at 6 K were the O4-centered alkoxy radical and the intermolecularly trapped electron (IMTE), previously also detected by other authors. The current experimental results provided hyperfine coupling constants for these two species in good agreement with the previous data, thus providing a consistency check that improves their credibility. In addition to the O4-centered alkoxy radical and the IMTE, the C3-centered and C5-centered hydroxyalkyl radicals are the most prominent primary species at 6 K. The C3-centered radical appears in two slightly different conformations at 6 K, designated C and D. The C5-centered radical exhibits a coupling to a methyl group with tunneling rotation at 6 K, and analysis of one of the rotational substates (A) of the spin system yielded an understanding of the structure of this radical. Visible light bleaching of the IMTE at 6 K led to the C3-centered radical C, and thermal annealing above 6 K resulted in a conversion of the C to the D conformation. In addition, thermal annealing releases the IMTE, apparently resulting in the formation of the C2-centered radical. It is possible that the thermal decay of the IMTE also contributes to a small part of the C3-centered radical (D) population at 85 K. There are several other products trapped in rhamnose crystals directly after irradiation at 6 K, among which are resonance lines due to the C2 H-abstraction product. However, these other products are minority species and were not fully characterized in the current work.

Gas-phase study on uridine: Conformation and X-ray photofragmentation.

Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. The measurements by combined electron and ion spectroscopy have been performed in gas phase utilizing synchrotron radiation. As uridine is a combination of d-ribose and uracil, which have been studied earlier with the same method, this study also considers the effect of chemical environment and the relevant functional groups. Furthermore, since in core ionization the initial core hole is always highly localized, charge migration prior to fragmentation has been studied here. This study also demonstrates the destructive nature of core ionization as in most cases the C 1s ionization of uridine leads to concerted explosions producing only small fragments with masses ≤43 amu. In addition to fragmentation patterns, we found out that upon evaporation the sugar part of the uridine molecule attains hexagonal form.

Instability-induced pattern formation of photoactivated functional polymers.

Since the pioneering work of Turing on the formation principles of animal coat patterns [Turing AM (1952) Phil Trans R Soc Lond B 237(641):37-72], such as the stripes of a tiger, great effort has been made to understand and explain various phenomena of self-assembly and pattern formation. Prominent examples are the spontaneous demixing in emulsions, such as mixtures of water and oil [Herzig EM, et al. (2007) Nat Mater 6:966-971]; the distribution of matter in the universe [Kibble TWB (1976) J Phys A: Math Gen 9(8):1387]; surface reconstruction in ionic crystals [Clark KW, et al. (2012) Nanotechnol 23(18):185306]; and the pattern formation caused by phase transitions in metal alloys, polymer mixtures and binary Bose-Einstein condensates [Sabbatini J, et al. (2011) Phys Rev Lett 107:230402]. Photoactivated pattern formation in functional polymers has attracted major interest due to its potential applications in molecular electronics and photoresponsive systems. Here we demonstrate that photoactivated pattern formation on azobenzene-containing polymer films can be entirely explained by the physical concept of phase separation. Using experiments and simulations, we show that phase separation is caused by an instability created by the photoactivated transitions between two immiscible states of the polymer. In addition, we have shown in accordance with theory, that polarized light has a striking effect on pattern formation indicated by enhanced phase separation.

Discontinuous anchoring transition and photothermal switching in composites of liquid crystals and conducting polymer nanofibers.

We prepared nanocomposites of a nematic liquid crystal and nanofibers of a conducting polymer (polyaniline). All the nanocomposites exhibit a discontinuous surface anchoring transition from planar to homeotropic in the nematic phase on a perfluoropolymer coated surface with a thermal hysteresis (≈ 5.3 °C). We observe a relatively large bistable conductivity and demonstrate a light driven switching of conductivity and dielectric constant in dye doped nanocomposites in the thermal hysteresis (bistable) region. The experimental results have been explained based on the reorientation of the nanofibers driven by the anchoring transition of the nematic liquid crystal. We show a significant enhancement of the bistable temperature range (≈ 13 °C) by an appropriate choice of compound in the binary system.

Red light as a 12-oxo-leukotriene B4 antagonist: an explanation for the efficacy of intensive red light in the therapy of peripheral inflammatory diseases.

To explain the successful treatment of various inflammatory diseases by using intensive red light, a non-linear theory is presented for the interaction of electric dipoles with light involving frequency doubling. It is applied to analyze the influence of light on organic molecules with permanent electric dipoles. The molecule 5-hydroxy-12-oxo-(5S,6Z,8E,10E,14Z)-6,8,10,14-eicosatetraenoic acid, 12-oxo-leukotriene B4 (12-Oxo-LTB4, an intermediate in the lipoxygenase-catalyzed path of arachidonic acid metabolism), is suspected to play a major role in the healing process, as, first, it plays a key role in the metabolism of leukotriene B4 (LTB4), which in many diseases acts as a source of inflammatory reactions; second, its dipole resonance is located at a wavelength of 316 nm, which can be excited by a 632 nm source through frequency doubling. From the structure of 12-Oxo-LTB4 and the knowledge of the partial charges of its 54 atoms, the equivalent values for dipole charges and dipole moment are derived. The power balance demonstrates that intensive red light with a power density of 0.4 W/cm2 transfers sufficient energy to 12-Oxo-LTB4 to render it biologically inactive. Hence, by generating a reactive high-energy leukotriene pathway intermediate, the law of mass action steers the chemical equilibrium to interrupt the inflammatory cascade.

Photoinduced symmetry-breaking intramolecular charge transfer in a quadrupolar pyridinium derivative.

We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridinium derivative of interest as a potential non-linear optical material. The spectral and photophysical behaviour of this symmetric system is greatly affected by the polarity of the medium. A very efficient photoinduced intramolecular charge transfer, surprisingly more efficient than in the dipolar asymmetric analogue, is found to occur by femtosecond resolved transient absorption spectroscopy. TD-DFT calculations are in excellent agreement with these experimental findings and predict large charge displacements in the molecular orbitals describing the ground state and the lowest excited singlet state. The theoretical study also revealed that in highly polar media the symmetry of the excited state is broken giving a possible explanation to the fluorescence and transient absorption spectra resembling those of the one-branched analogous compound in the same solvents. The present study may give an important insight into the excited state deactivation mechanism of cationic (donor-π-acceptor-π-donor)(+) quadrupolar compounds characterised by negative solvatochromism, which are expected to show significant two-photon absorption (TPA). Moreover, the water solubility of the investigated quadrupolar system may represent an added value in view of the most promising applications of TPA materials in biology and medicine.

Electron-induced hydrogen loss in uracil in a water cluster environment.

Low-energy electron-impact hydrogen loss due to dissociative electron attachment (DEA) to the uracil and thymine molecules in a water cluster environment is investigated theoretically. Only the A(')-resonance contribution, describing the near-threshold behavior of DEA, is incorporated. Calculations are based on the nonlocal complex potential theory and the multiple scattering theory, and are performed for a model target with basic properties of uracil and thymine, surrounded by five water molecules. The DEA cross section is strongly enhanced when the attaching molecule is embedded in a water cluster. This growth is due to two effects: the increase of the resonance lifetime and the negative shift in the resonance position due to interaction of the intermediate negative ion with the surrounding water molecules. A similar effect was earlier found in DEA to chlorofluorocarbons.

Ultrafast laser ablation in liquids for nanomaterials and applications.

We present an inclusive overview of the ultrafast ablation technique performed in liquids. Being a comparatively new method, we bring out the recent progress achieved, present the challenges ahead, and outline the future prospects for this technique. The review is conveniently divided into five parts: (a) a succinct preamble to the technique of ultrafast ablation in liquids (ULAL) is provided. A brief introduction to the conventional ns ablation is also presented for the sake of completeness (b) fundamental physical processes involved in this technique are elaborated (c) specific advantages of the technique compared to other physical and chemical methodologies are enumerated (d) applications of this technique in photonics; biomedical and explosives detection [using surface-enhanced Raman scattering (SERS)] is updated (e) future prospects describing the potential of this technique for creating unique nanoparticles (NPs) and nanostructures (NSs) for niche applications. We also discuss some of the recently reported significant results achieved in a variety of materials, especially metals, using this technique. Furthermore, we present some of our own experimental data obtained from ULAL of Ag, Cu, and Zn in a variety of liquids such as acetone, water, acetonitrile etc. The generated NPs (colloidal solutions) and NSs (on substrates) have been successfully utilized for nonlinear optical, SERS, and biomedical applications.

Nanopatterning by laser interference lithography: applications to optical devices.

A systematic review, covering fabrication of nanoscale patterns by laser interference lithography (LIL) and their applications for optical devices is provided. LIL is a patterning method. It is a simple, quick process over a large area without using a mask. LIL is a powerful technique for the definition of large-area, nanometer-scale, periodically patterned structures. Patterns are recorded in a light-sensitive medium that responds nonlinearly to the intensity distribution associated with the interference of two or more coherent beams of light. The photoresist patterns produced with LIL are the platform for further fabrication of nanostructures and growth of functional materials used as the building blocks for devices. Demonstration of optical and photonic devices by LIL is reviewed such as directed nanophotonics and surface plasmon resonance (SPR) or large area membrane reflectors and anti-reflectors. Perspective on future directions for LIL and emerging applications in other fields are presented.

Electronic and structural response of nanomaterials to ultrafast and ultraintense laser pulses.

The interaction of materials with ultrafast and ultraintense laser pulses is a current frontier of science both experimentally and theoretically. In this review, we briefly discuss some recent theoretical studies by the present authors with our method of semiclassical electron-radiation-ion dynamics (SERID). In particular, Zhou et al. and Jiang et al. respectively, determined the optimal duration and optimal timing for a series of femtosecond scale laser pulses to excite a specific vibrational mode in a general chemical system. A set of such modes can be used as a "fingerprint" for characterizing a particular molecule or a complex in a solid. One can therefore envision many applications, ranging from fundamental studies to detection of chemical or biological agents. Allen et al. proved that dimers are preferentially emitted during photofragmentation of C60 under an ultrafast and ultraintense laser pulse. For interactions between laser pulses and semiconductors, e.g., GaAs, Si and InSb, besides experimentally accessible optical properties--epsilon(omega) and chi(2)-Allen et al. offered many other indicators to confirm the nonthermal nature of structural changes driven by electronic excitations and occurring during the first few hundred femtoseconds. Lin et al. found that, after the application of a femtosecond laser pulse, excited electrons in materials automatically equilibrate to a Fermi-Dirac distribution within roughly 100 fs, solely because of their coupling to the nuclear motion, even though the resulting electronic temperature is one to two orders of magnitude higher than the kinetic temperature defined by the nuclear motion.

Pulse laser deposited nanostructured ZnO thin films: a review.

This review summarizes the work principles of pulse laser deposition (PLD) apparatus, physical processes like ablation, and plasma plume formation accompanying the deposition of un-doped ZnO from target to substrate material. Various modes of deposition and factors influencing the properties of thin films such as substrate temperature, background gas pressure, laser energy density (laser fluence), target to substrate distance, repetition rate, oxygen partial pressure in deposition chamber, deposition time and post growth annealing which control deposition parameters such as adsorption, desorption, surface diffusion, nucleation, and crystallization/re-crystallization are also discussed in this review. Moreover, various film properties such as morphology, roughness of the film surface, film thickness, grain size, optical transmittance, sensitivity, electrical conductivity, uniformity and electrical resistivity of the deposited ZnO thin films have also been enumerated in the present review.