Novel co-crystals of the nutraceutical sinapic acid

Sinapic acid (SA) is a nutraceutical with known anti-oxidant, anti-microbial, anti-inflammatory, anti-cancer, and anti-anxiety properties. Novel co-crystals of SA were prepared with co-formers belonging to the category of GRAS [isonicotinic acid (INC), nicotinamide (NIA)], non-GRAS [4-pyridinecarbonitrile (PYC)], and active pharmaceutical ingredients (APIs) [6-propyl-2-thiouracil (PTU)] list of compounds. Structural study based on the X-ray crystal structures revealed the intermolecular hydrogen-bonded interactions and molecular packing. The crystal structure of sinapic acid shows the anticipated acid-acid homodimer along with discrete hydrogen bonds between the acid carbonyl and the phenolic moiety. The robust acid-acid homodimer appears to be very stable and is retained in the structures of two co-crystals (SA[middle dot]NIA and SA[middle dot]PYC). In these cases, co-crystallization occurs via intermolecular phenol O-H[three dots, centered]Naromatic hydrogen bonds between the co-formers. In the SA[middle dot]PTU[middle dot]2MeCN co-crystal the acid-acid homodimer gives way to the anticipated acid-amide heterodimer, with the phenolic moiety of SA hydrogen-bonded to acetonitrile. Attempts at obtaining the desolvated co-crystal led to lattice breakdown, thus highlighting the importance of acetonitrile in the formation of the co-crystal. Among the co-crystals examined, SA[middle dot]INC (5 weeks), SA[middle dot]NIA (8 weeks) and SA[middle dot]PYC (5 weeks) were found to be stable under accelerated humidity conditions (40 [degree]C, 75% RH), whereas SA[middle dot]PTU[middle dot]2MeCN decomposed after one week into individual components due to solvent loss.

Intrastereomic proteins from the asteroid Asterias rubens. separation, partial characterization ,and interactions with growing calcite crystals

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Supercontinuum Generation by Stimulated Raman Scattering and Parametric Four-Wave Mixing in Photonic Crystal Fibers

Supercontinuum generation is investigated experimentally and numerically in a highly nonlinear indexguiding photonic crystal optical fiber in a regime in which self-phase modulation of the pump wave makes a negligible contribution to spectral broadening. An ultrabroadband octave-spanning white-light continuum is generated with 60-ps pump pulses of subkilowatt peak power. The primary mechanism of spectral broadening is identified as the combined action of stimulated Raman scattering and parametric four-wave mixing. The observation of a strong anti-Stokes Raman component reveals the importance of the coupling between stimulated Raman scattering and parametric four-wave mixing in highly nonlinear photonic crystal fibers and also indicates that non-phase-matched processes contribute to the continuum. Additionally, the pump input polarization affects the generated continuum through the influence of polarization modulational instability. The experimental results are in good agreement with detailed numerical simulations. These findings demonstrate the importance of index-guiding photonic crystal fibers for the design of picosecond and nanosecond supercontinuum light sources. © 2002 Optical Society of America.

White-Light Supercontinuum Generation with 60-ps Pump Pulses in a Photonic Crystal Fiber

The generation of a spatially single-mode white-light supercontinuum has been observed in a photonic crystal fiber pumped with 60-ps pulses of subkilowatt peak power. The spectral broadening is identified as being due to the combined action of stimulated Raman scattering and parametric four-wave-mixing generation, with a negligible contribution from the self-phase modulation of the pump pulses. The experimental results are in good agreement with detailed numerical simulations. These findings demonstrate that ultrafast femtosecond pulses are not needed for efficient supercontinuum generation in photonic crystal fibers. © 2001 Optical Society of America.

Fundamental limits to few-cycle pulse generation from compression of broadband supercontinua generated in photonic crystal fiber

The compression properties of octave-spanning supercontinuum spectra generated in photonic crystal fibers are studied using stochastic nonlinear Schrödinger equation simulations. The conditions under which sub-5 fs pulses can be obtained after compression are identified. © 2004 Optical Society of America.

Coherence Properties of Supercontinuum Spectra Generated in Photonic Crystal and Tapered Optical Fibers

Numerical simulations have been used in studies of the temporal and spectral features of supercontinuum generation in photonic crystal and tapered optical fibers. In particular, an ensemble average over multiple simulations performed with random quantum noise on the input pulse allows the coherence of the supercontinuum to be quantified in terms of the dependence of the degree of first-order coherence on the wavelength. The coherence is shown to depend strongly on the input pulse's duration and wavelength, and optimal conditions for the generation of coherent supercontinua are discussed. © 2002 Optical Society of America.

Numerical Simulations and Coherence Properties of Supercontinuum Generation in Photonic Crystal and Tapered Optical Fibers

Numerical simulations have been used to study broad-band supercontinuum generation in optical fibers with dispersion and nonlinearity characteristics typical and photonic crystal or tapered fibers structures. The simulations include optical shock and Raman nonlinearity terms, with quantum noise taken into account phenomenologically by including in the input field a noise seed of one photon per mode with random phase. For input pulses of 150-fs duration injected in the anomalous dispersion regime, the effect of modulational instability is shown to lead to severe temporal jitter in the output, and associated fluctuations in the spectral amplitude and phase across the generated supercontinuum. The spectral phase fluctuations are quantified by performing multiple simulations and calculating both the standard deviation of the phase and, more rigorously, the degree of first-order coherence as a function of wavelength across the spectrum. By performing simulations over a range of input pulse durations and wavelengths, we can identify the conditions under which coherent supercontinua with a well-defined spectral phase are generated.

Cross-correlation frequency resolved optical gating analysis of broadband continuum generation in photonic crystal fiber: Simulations and experiments

Numerical simulations are used to study the temporal and spectral characteristics of broadband supercontinua generated in photonic crystal fiber. In particular, the simulations are used to follow the evolution with propagation distance of the temporal intensity, the spectrum, and the cross-correlation frequency resolved optical gating (XFROG) trace. The simulations allow several important physical processes responsible for supercontinuum generation to be identified and, moreover, illustrate how the XFROG trace provides an intuitive means of interpreting correlated temporal and spectral features of the supercontinuum. Good qualitative agreement with preliminary XFROG measurements is observed. © 2002 Optical Society of America.

Single-mode white-light supercontinuum with 60 ps pump pulses in a photonic crystal fiber

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Application of modelling for predicting the behaviour of polymers and adhesives in microelectronic and photonic devices

With the growth in computing power, and advances in numerical methods for the solution of partial differential equations, modeling technologies based around computational fluid dynamics, finite element analysis and optimisation are now being widely used by researchers and industry. Polymer and adhesive materials are now being widely used in electronic and photonic devices. This paper will illustrate the use of modeling tools to predict the behaviour of these materials from product assembly to its performance and reliability.

Optical bistability in nonlinear surface-plasmon polaritonic crystals

Nonlinear optical transmission through periodically nanostructured metal films (surface-plasmon polaritonic crystals) has been studied. The surface polaritonic crystals have been coated with a nonlinear polymer. The optical transmission of such nanostructures has been shown to depend on the control-light illumination conditions. The resonant transmission exhibits bistable behavior with the control-light intensity. The bistability is different at different resonant signal wavelengths and for different wavelengths of the control light. The effect is explained by the strong sensitivity of the surface-plasmon mode resonances at the signal wavelength to the surrounding dielectric environment and the electromagnetic field enhancement due to plasmonic excitations at the controlled light wavelengths.

Ferroelectricity and isotope effects in hydrogen-bonded KDP crystals

Based on an accurate first principles description of the energetics in H-bonded potassium-dihydrogen-phosphate crystals, we conduct a first study of nuclear quantum effects and of the changes brought about by deuteration. Tunneling is allowed only for clusters involving correlated protons and heavy ion displacements, the main effect of deuteration being a depletion of the proton probability density at the O-H-O bridge center, which in turn weakens its proton-mediated covalent bonding. The ensuing lattice expansion couples self-consistently with the proton off-centering, thus explaining both the giant isotope effect and its close connection with geometrical effects.

Interplay between proton ordering and ferroelectric polarization in H-bonded KDP-type crystals

The origin of ferroelectricity in KH2PO4 (KDP) is studied by first-principles electronic structure calculations. In the low-temperature phase, the collective off-centre ordering of the protons is accompanied by an electronic charge delocalization from the near and localization at the far oxygen within the O-H...O bonds. Electrostatic forces. then, push the K+ ions towards off-centre positions, and induce a macroscopic polarization. The analysis of the correlation between different geometrical and electronic quantities, in connection with experimental data. supports the idea that the role of tunnelling in isotopic effects is irrelevant. Instead, geometrical quantum effects appear to play a central role. (C) 2001 Elsevier Science B.V. All rights reserved.

First-principles study of ferroelectricity and isotope effects in H-bonded KH2PO4 crystals

By means of extensive first-principles calculations we studied the ferroelectric phase transition and the associated isotope effect in KH2PO4 (KDP). Our calculations revealed that the spontaneous polarization of the ferroelectric phase is due to electronic charge redistributions and ionic displacements which are a consequence of proton ordering, and not vice versa. The experimentally observed double-peaked proton distribution in the paraelectric phase cannot be explained by a dynamics of only protons. This requires, instead, collective displacements within clusters that include also the heavier ions. These tunneling clusters can explain the recent evidence of tunneling obtained from Compton scattering measurements. The sole effect of mass change upon deuteration is not sufficient to explain the huge isotope effect. Instead, we find that structural modifications deeply connected with the chemistry of the H bonds produce a feedback effect on tunneling that strongly enhances the phenomenon. The resulting influence of the geometric changes on the isotope effect agrees with experimental data from neutron scattering. Calculations under pressure allowed us to analyze the issue of universality in the disappearance of ferroelectricity upon compression. Compressing DKDP so that the distance between the two peaks in the deuteron distribution is the same as for protons in KDP, corresponds to a modification of the underlying double-well potential, which becomes 23 meV shallower. This energy difference is what is required to modify the O-O distance in such a way as to have the same distribution for protons and deuterons. At the high pressures required experimentally, the above feedback mechanism is crucial to explain the magnitude of the geometrical effect.