Compact Interrogation System of Fiber Bragg Grating Sensors Based on Multiheterodyne Dispersion Interferometry for Dynamic Strain Measurements.

Dual-comb multiheterodyne spectroscopy is a well-established technology for the highly sensitive real-time detection and measurement of the optical spectra of samples, including gases and fiber sensors. However, a common drawback of dual-comb spectroscopy is the need for a broadband amplitude-resolved absorption or reflection measurement, which increases the complexity of the dual comb and requires the precise calibration of the optical detection. In the present study, we present an alternative dispersion-based approach applied to fiber Bragg grating sensors in which the dual comb is compacted by a single dual-drive-unit optical modulator, and the fiber sensor is part of a dispersion interferometer. The incident dual comb samples a few points in the spectrum that are sensitive to Bragg wavelength changes through the optical phase. The spectra reading is improved due to the external interferometer and is desensitized to changes in the amplitude of the comb tones. The narrow-band detection of the fiber sensor dispersion changes that we demonstrate enables the compact, cost-effective, high-resolution multiheterodyne interrogation of high-throughput interferometric fiber sensors. These characteristics open its application both to the detection of fast phenomena, such as ultrasound, and to the precise measurement at high speed of chemical-/biological-sensing samples. The results with a low-reflectivity fiber Bragg grating show the detection of dynamic strain in the range of 215 nε with a 30 dB signal to noise ratio and up to 130 kHz (ultrasonic range).

Acousto-Optic Comb Interrogation System for Random Fiber Grating Sensors with Sub-nm Resolution.

The broad-frequency response and nanometer-range displacements of ultrasound detection are essential for the characterization of small cracks, structural health monitoring and non-destructive evaluation. Those perturbations are generated at sub-nano-strain to nano-strain levels. This corresponds to the sub-nm level and, therefore, to about 0.1% of wavelength change at 1550 nm, making it difficult to detect them by conventional interferometric techniques. In this paper, we propose a demodulation system to read the random fiber grating spectrum using a self-heterodyne acousto-optic frequency comb. The system uses a self-heterodyne approach to extract phase and amplitude modulated signals to detect surface acoustic waves with sub-nanometer amplitudes in the frequency domain. The method can detect acoustic frequencies of 1 MHz and the associated displacement. The system is calibrated via phase detection with a heterodyne interferometer, which has a limited frequency response of up to 200 kHz. The goal is to achieve sub-nanometer strain detection at MHz frequency with random fiber gratings.

Sub-ppm-Level Ammonia Detection Using Photoacoustic Spectroscopy with an Optical Microphone Based on a Phase Interferometer.

A sensitive optical microphone for photoacoustic spectroscopy based on the common path topology of a fibre laser Doppler vibrometer (FLDV) using phase-generated carrier demodulation and a slim diaphragm as an acoustic wave transducer was demonstrated. A resonant gas cell was adapted to enhance gas-detection performance and simultaneously provide efficient cancellation of the window background acoustic signal. Ammonia (NH3) was selected as the target gas. The absorption line was experimentally identified using a distributed feedback laser diode emitting at 1530 nm. The linearity and sensitivity of the gas sensor were measured using wavelength modulation spectroscopy with second harmonic detection. A Teflon diaphragm was used to implement the optical microphone, along with the FLDV, showing a minimum detectable pressure of 79.5 µPa/Hz1/2. The noise-equivalent absorption sensitivity for NH3 detection at the absorption line at 1531.7 nm was 1.85 × 10-8 W cm-1 Hz-1/2, and the limit of detection was 785 ppbv.

DFT Rationalization of the Diverse Outcomes of the Iodine(III)-Mediated Oxidative Amination of Alkenes.

A computational study of the mechanism for the iodine(III)-mediated oxidative amination of alkenes explains the experimentally observed substrate dependence on product distribution. Calculations with the M06 functional have been carried out on the reaction between PhI(N(SO2 Me)2 )2 and three different representative substrates: styrene, α-methylstyrene, and (E)-methylstilbene. All reactions start with electrophilic attack by a cationic PhI(N(SO2 Me)2 )(+) unit on the double bond, and formation of an intermediate with a single C-I bond and a planar sp(2) carbocationic center. The major path, leading to 1,2-diamination, proceeds through a mechanism in which the bissulfonimide initially adds to the alkene through an oxygen atom of one sulfonyl group. This behavior is now corroborated by experimental evidence. An alternative path, leading to an allylic amination product, takes place through deprotonation at an allylic C-H position in the common intermediate. The regioselectivity of this amination depends on the availability of the resonant structures of an alternate carbocationic intermediate. Only in cases where a high electronic delocalization is possible, as in (E)-methylstilbene, does the allylic amination occur without migration of the double bond.

Substitution Effects of Hypervalent Iodine(III) Reagents in the Diamination of Styrene.

The influence of electronic parameters on the reaction performance of hypervalent iodine(III) reagents in the vicinal diamination of styrene has been investigated. It demonstrates the influence of the relative electron density on the aryl substituent of the hypervalent iodine reagent. In these cases, compounds with donor substituents outperform the corresponding acceptor-substituted systems. In line with this observation, a rapid enantioselective diamination was observed for a preformed chiral bisimidoiodine(III) reagent. For the first time, X-ray structural data could be obtained for an isolated chiral bisimidoiodine(III).

Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs.

Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal.

Sigmatropic Rearrangement of Vinyl Aziridines: Expedient Synthesis of Cyclic Sulfoximines from Chiral Sulfinimines.

A novel rearrangement of 2-vinyl aziridine 2-carboxylates to unusual chiral cyclic sulfoximines is described herein. The method allows the synthesis of substituted cyclic sulfoximines in high yields with complete stereocontrol, and tolerates a wide substrate scope. A one-pot process starting directly from sulfinimines provides access to complex chiral sulfoximines in only two steps from commercially available aldehydes. A mechanistic hypothesis and synthetic application in the formal synthesis of trachelanthamidine, by transformation of a cyclic sulfoximine into a pyrroline, is also disclosed.

Development of a flow method for the hydroboration/oxidation of olefins.

A method for the continuous preparation of alcohols by hydroboration/oxidation of olefins using flow techniques is described. The process allows the isolation of up to 120 mmol h(-1) of the desired alcohol in a very rapid manner with good functional group tolerance. The flow setup can be modified to perform a continuous extraction of the desired alcohol from the biphasic mixture produced by the reaction.

Indole synthesis based on a modified Koser reagent.

A new metal-free method for the rapid and productive preparation of indoles has been developed. This process is based on sterically congested hypervalent iodine compounds of the family of Koser reagents, and iodosobenzene in combination with 2,4,5-tris-isopropylbenzene sulfonic acid provides the highest yields and fastest reaction times. This reagent alone promotes the chemoselective oxidative cyclization of 2-amino styrenes to indoles in high yields under mild conditions.

Metal-free iodine(III)-promoted direct intermolecular C-H amination reactions of acetylenes.

A direct metal-free amination of arylalkynes has been developed, which proceeds by reaction of the terminal alkyne with the hypervalent iodine reagent PhI(OAc)NTs(2) within a single-step operation. This unprecedented intermolecular C-H to C-N bond conversion provides rapid access to the important class of ynamides. In addition to the title reaction, the related transformation between alkylated alkynes and the iodine(III) reagent is also discussed.

Iodine(III)-mediated intermolecular allylic amination under metal-free conditions.

A new approach to direct intermolecular allylic amination has been developed using metal-free conditions at room temperature. The reaction employs a hypervalent iodine(III) reagent as an oxidant and bistosylimide as a nitrogen source. A series of different allylic aminations are presented with up to a 99% yield. Mechanistic studies including isotope labeling and Hammett correlation suggest that depending on the substrate structure two different mechanisms can be operating.

Fiber optic sensor for acoustic detection of partial discharges in oil-paper insulated electrical systems.

A fiber optic interferometric sensor with an intrinsic transducer along a length of the fiber is presented for ultrasound measurements of the acoustic emission from partial discharges inside oil-filled power apparatus. The sensor is designed for high sensitivity measurements in a harsh electromagnetic field environment, with wide temperature changes and immersion in oil. It allows enough sensitivity for the application, for which the acoustic pressure is in the range of units of Pa at a frequency of 150 kHz. In addition, the accessibility to the sensing region is guaranteed by immune fiber-optic cables and the optical phase sensor output. The sensor design is a compact and rugged coil of fiber. In addition to a complete calibration, the in-situ results show that two types of partial discharges are measured through their acoustic emissions with the sensor immersed in oil.

Competing thermal electrocyclic ring-closure reactions of (2Z)-hexa-2,4,5-trienals and their Schiff bases. Structural, kinetic, and computational studies.

The electrocyclic ring closure reactions of (2Z)-hexa-2,4,5-trienals (vinylallenals) to alkylidene-2H-pyrans and of the corresponding Schiff base derivatives to alkylidenepyridines can be concurrent. Rates of vinylallenal cyclization and imine formation upon addition of n-butylamine determine the extent of the competition. The activation energies for the electrocyclization of a series of 6-substituted-(2Z)-4-tert-butyl-3-methylhexa-2,4,5-trienals 2 and trienimines 4 depend on the steric interactions between the substituents at C6 and the tert-butyl group at C4. Mixtures of alkylidene-2H-pyrans 3 and alkylidenepyridines 5 are obtained with bulky groups at C6, whereas only the latter is obtained with a C6-t-Bu and only the former with substituents of moderate size at C6. The reaction rates were indirectly derived from the empirical observations using a global optimization study based on differential evolution. The cyclizations are torquoselective, and the kinetically favored (E)-alkylidene heterocycles evolve by electrocyclic ring opening/ring closure toward the thermodynamic Z isomers upon extended reaction times. Density functional theory (DFT) calculations of the electrocyclizations helped in their characterization as monorotatory processes with pseudopericyclic features and made it possible to rationalize the reactivity trends and the torquoselectivity.

A New Family of Jumonji C Domain-Containing KDM Inhibitors Inspired by Natural Product Purpurogallin.

Aberrant epigenetic modifications are involved in cancer development. Jumonji C domain-containing histone lysine demethylases (KDMs) are found mainly up-regulated in breast, prostate, and colon cancer. Currently, growing interest is focusing on the identification and development of new inhibitors able to block the activity of KDMs and thus reduce tumor progression. KDM4A is known to play a role in several cellular physiological processes, and was recently found overexpressed in a number of pathological states, including cancer. In this work, starting from the structure of purpurogallin 9aa, previously identified as a natural KDM4A inhibitor, we synthesized two main sets of compound derivatives in order to improve their inhibitory activity against KDM4A in vitro and in cells, as well as their antitumor action. Based on the hypothetical biogenesis of the 5-oxo-5H-benzo[7]annulene skeleton of the natural product purpurogallin (Salfeld, 1960; Horner et al., 1961; Dürckheimer and Paulus, 1985; Tanaka et al., 2002; Yanase et al., 2005) the pyrogallol and catechol units were first combined with structural modifications at different positions of the aryl ring using enzyme-mediated oxidative conditions, generating a series of benzotropolone analogs. Two of the synthetic analogs of purpurogallin, 9ac and 9bc, showed an efficient inhibition (50 and 80%) of KDM4A in enzymatic assays and in cells by increasing levels of its specific targets, H3K9me3/2 and H3K36me3. However, these two compounds/derivatives did not induce cell death. We then synthesized a further set of analogs of these two compounds with greater structural diversification. The most potent of these analogs, 9bf, displayed the highest KDM4A inhibitory enzymatic activity in vitro (IC50 of 10.1 and 24.37 µM) in colon cancer cells, and the strongest antitumor action in several solid and hematological human cancer cell lines with no toxic effect in normal cells. Our findings suggest that further development of this compound and its derivatives may lead to the identification of new therapeutic antitumor agents acting through inhibition of KDM4A.

Continuous flow synthesis of lipophilic cations derived from benzoic acid as new cytotoxic chemical entities in human head and neck carcinoma cell lines.

Continuous flow chemistry was used for the synthesis of a series of delocalized lipophilic triphenylphosphonium cations (DLCs) linked by means of an ester functional group to several hydroxylated benzoic acid derivatives and evaluated in terms of both reaction time and selectivity. The synthesized compounds showed cytotoxic activity and selectivity in head and neck tumor cell lines. The mechanism of action of the molecules involved a mitochondrial uncoupling effect and a decrease in both intracellular ATP production and apoptosis induction.

Ligand Design for Modulation of RXR Functions.

Retinoid X receptors (RXRs) are promiscuous partners of heterodimeric associations with other members of the Nuclear Receptor (NR) superfamily. RXR ligands ("rexinoids") either transcriptionally activate the "permissive" subclass of heterodimers or synergize with partner ligands in the "nonpermissive" subclass of heterodimers. The rationale for rexinoid design with a wide structural diversity going from the structures of existing complexes with RXR determined by X-Ray, to natural products and other ligands discovered by high-throughput screening (HTS), mere serendipity, and rationally designed based on Molecular Modeling, will be described. Included is the new generation of ligands that modulate the structure of specific receptor surfaces that serve to communicate with other regulators. The panel of the known RXR agonists, partial (ant)agonists, and/or heterodimer-selective rexinoids require the exploration of their therapeutic potential in order to overcome some of the current limitations of rexinoids in therapy.

High resolution (<1nm) interferometric fiber-optic sensor of vibrations in high-power transformers.

A novel fiber-optic interferometric sensor is presented for vibrations measurements and analysis. In this approach, it is shown applied to the vibrations of electrical structures within power transformers. A main feature of the sensor is that an unambiguous optical phase measurement is performed using the direct detection of the interferometer output, without external modulation, for a more compact and stable implementation. High resolution of the interferometric measurement is obtained with this technique (<1 nm). The optical-fiber transducer is also specifically designed for magnifying the localized vibrations in order to modulate deeply the interferometric signal. Other advantages of the implementation for measurements within transformers are also highlighted.

2-Alkylidenesulfol-3-enes by (regio- and) stereoselective cheletropic addition of SO2 to (di)vinylallenes.

[reaction: see text] The cheletropic addition of SO(2) to divinylallenes is regioselective, taking place at the most substituted vinylallene and at the E unit if vinyl groups of opposite geometry are competing. Diastereofacial differentiation results from the approach of the reagent from the less-substituted direction of the allene and from the concomitant disrotatory movement of the termini of the vinylallene to afford the sterically more congested 2-alkylidenesulfol-3-ene isomer. DFT computations confirm the regio- and the stereoselectivity of these cheletropic additions.