Orientation fields of nonlinear biological fibrils by second harmonic generation microscopy.

The orientation of fibrils within biological tissues is of primary importance. In this study, we propose a simple method based on second harmonic generation (SHG) microscopy to map, pixel by pixel, the orientation of the symmetry axis of the second-order nonlinear susceptibility tensor of fibrils that produce SHG. The method uses only four images acquired at specific polarizations of the input laser beam, and can be easily and cheaply implemented on a confocal microscope. In addition to orientation informations, the method also provides polarization independent images and estimations of the ratio of the nonlinear susceptibility components. We demonstrate the relevance of our concept by studying the orientation fields of the collagen meshwork in a healthy rat liver that provides well separated fibrils. By correlating the mean orientation of the nonlinear susceptibility to the fibril orientation itself for many fibril segments, and using circular statistics, it is shown that both orientations are truly parallel at the fibril scale. Our polarimetric method allows to map fibril orientation fields, independently of individual fibril contrast in the SHG image.

Orientational deconvolution of two-dimensional static disorder by a Tikhonov regularized method for 2H solid state NMR of nano-tubular-oriented structures.

A general trend of supramolecular chemistry is the building of mesoscopic-oriented nanotubes. When the typical radius of the channel almost fits the mean supramolecular cross-sectional radius, the guest supramolecule is ultraconfined in the channel. In that case, only rotational disorder around the channel axis is allowed. For sufficiently low temperatures, we expect this 2D disorder to be static on the NMR timescale, and it should reflect the local symmetry of the channels. In this article, we show that experiments performed with deuterium single crystal solid-state NMR as a function of rotation around the channel axis may lead to important information concerning the static orientational disorder of the confined supramolecules. Using an inversion method with Tikhonov regularization and a positivity constraint, that also takes into account of the nonideal pulse sequence response, the orientational probability density can be obtained from 1D experiments performed at different angles, even for significant disorder. As a first step, the method is validated on four different theoretical distributions. It is then applied to 2H NMR single crystal experiments performed on an archetype of parallel channels intergrowth compounds: selectively deuterated 1,10-decanedicarboxylic diacids in hydrogenated urea channels. The diacids form one-dimensional infinite hydrogen-bonded chains ultraconfined in urea linear channels.

Organization and orientation of amphiphilic push-pull chromophores deposited in Langmuir-Blodgett monolayers studied by second harmonic generation and atomic force microscopy.

Orientation and organization of two amphiphilic push-pull chromophores mixed with two phospholipids (dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine) in Langmuir-Blodgett (LB) monolayers are investigated by second harmonic generation. The LB monolayers have also been characterized by atomic force microscopy and UV-vis spectroscopy. The effective molecular orientations and hyperpolarizabilities of the chromophores are studied as a function of the phospholipid concentrations. The experimental results are discussed within the frame of a model of orientational distribution of the chromophores which gives the orientational mean angle and bounds on the orientational disorder. The mean orientation of the chromophores is found to be within 45-55 degrees whereas their hyperpolarizability coefficients, measured with respect to quartz, are estimated to be in the range (0.3-0.7) x 10(-27) esu taking account of the maximal orientational disorder.

Single-crystal 2H NMR of deuterated 1,10-decanedicarboxylic acid included in hydrogenated urea channels.

The intergrowth of 1,10-decanedicarboxylic acid and urea give infinite hydrogen-bonded chains of the guest included in the hexagonal urea host. A deuterium high-resolution solid-state NMR study of the selectively deuterated intergrowth compound 1,10-decanedicarboxylic acid/hydrogenated urea at variable temperature in the range 90 < or = T < or = 300 K was performed on a single crystal. The analysis of the second moment as a function of temperature is shown to be compatible with the known phase transition occurring near T(c) = 203 K. Moreover, the spectra indicate that the orientational disorder is strong, and is compared to an axial uniform disorder. For this purpose, the general equation for the second moment of a system with uniform two-dimensional axial orientational disorder is given, and a method to take into account the non-uniform excitation of the pulse sequence is proposed.

Broadband echo sequence using a pi composite pulse for the pure NQR of a spin I = 32 powder sample

This work presents a numerical approach to optimizing sequences with composite pulses for the pure NQR of a spin I = 32 powder sample. The calculations are based on a formalism developed in a previous paper, which allows a fast powder-averaging procedure to be implemented. The framework of the Cayley-Klein matrices to describe space rotations by 2 x 2 unitary and unimodular complex matrices is used to calculate the pulse propagators. The object of such a study is to design a high-performance echo sequence composed of a single preparation pulse and a three-pulse composite transfer pulse. We mean a sequence leading to a large excitation bandwidth with a good signal-to-noise ratio, a flat excitation profile near the irradiation frequency, and a good linearity of the phase as a function of frequency offset. Such a composite echo sequence is intended to give a better excitation profile than the classical Hahn (θ)-tau-(2θ) echo sequence. It is argued that in pure NQR of a powder sample, the sequence must be optimized as a whole since both the excitation and the reception of the signal depend on the relative orientation of the crystallites with respect to the coil axis. To our knowledge, this is the first time such a global approach is presented. An extensive numerical study of the composite echo sequence described above is performed in this article. The key of the discrimination between the sequences lies in using the first five reduced moments of the excitation profile as well as an estimator of the phase linearity. Based on such information, we suggest that the echo sequence that best fulfills our criterion is (1)(0)-tau-(0.35)(0)(2.1)(pi)(0.35)(0), the pulse angles omega(RF)t(p) being in radians. The subscripts are the relative pulse phases. We outlined the way to implement the spin echo mapping method to reconstruct large spectra with this sequence, and it is shown that it reduces the acquisition time by a factor of 1.7 if compared to the classical Hahn echo. Some other broadband echo sequences are also briefly discussed. We also study the effect of a small delay between the pulses of the composite pulse to take into account the experimental constraint imposed by the spectrometer. To be complete, we give an estimation of the performances of the Hahn echo, the stimulated echo, and the composite echo sequence optimized for a powder sample when applied to a monocrystal. Experiments performed on chloranil at ambient temperature confirm the predicted excitation profiles. Copyright 2000 Academic Press.

Calculations of multipulse sequence in NQR of spins 32.

The general formalism of the interaction representation with respect to an operator which is its own inverse is developed and applied to pure NQR of spins I = 32. Under the assumption of no relaxation and no dipolar coupling, it is shown that the calculation of the response to pure NQR multipulse sequences can be performed with the same concepts used in high field NMR, such as coherence pathways. All the tools and mathematical expressions to predict the time evolution of the signal created by a pure NQR multipulse sequence are presented explicitly. It takes into account the off-resonance irradiation as well as the angular dependence of the excitation and detection for every value of the electric field gradient asymmetry parameter. Particular attention is devoted to the powder average, which is performed via a probability function derived analytically for the first time, leading to a drastic reduction of simulation times. The theory is illustrated by the study of the optimization and excitation bandwidths of one- to three-pulse sequences and compared to experimental results on Chloranil. We show that the three-pulse "stimulated echo" sequence gives a more uniform excitation profile than the traditional two-pulse echo sequence for powder samples. Thus, the "stimulated echo" sequence could be useful to cover a large spectrum when the experiment duration, or the signal to noise ratio, are not critical parameters. Analytical expressions for the nutation spectra obtained by one or two-pulse sequences are also derived for the first time.

[Atypical locations of tuberculosis of the colon]. / Localizaciones atípicas de la tuberculosis en el colon.

We present four cases of tuberculosis of the colon in the form of multiple segmental lesions located in the ascendant, transverse and descendant colon. We comment on the rarity of these locations and how they are easily confused with other diseases, like adenocarcinoma or Crohn's disease. For a correct diagnosis, affectation of the cecum and terminal ileum is useful. In cases in which these zones are not involved, differentiation is very difficult and can only achieved by bacteriological and histological studies after colonoscopy and biopsy.