On-Surface Driven Formal Michael Addition Produces m-Polyaniline Oligomers on Pt(111).

On-surface synthesis is emerging as a highly rational bottom-up methodology for the synthesis of molecular structures that are unattainable or complex to obtain by wet chemistry. Here, oligomers of meta-polyaniline, a known ferromagnetic polymer, were synthesized from para-aminophenol building-blocks via an unexpected and highly specific on-surface formal 1,4 Michael-type addition at the meta position, driven by the reduction of the aminophenol molecule. We rationalize this dehydrogenation and coupling reaction mechanism with a combination of in situ scanning tunneling and non-contact atomic force microscopies, high-resolution synchrotron-based X-ray photoemission spectroscopy and first-principles calculations. This study demonstrates the capability of surfaces to selectively modify local molecular conditions to redirect well-established synthetic routes, such as Michael coupling, towards the rational synthesis of new covalent nanostructures.

On-Surface Hydrogen-Induced Covalent Coupling of Polycyclic Aromatic Hydrocarbons via a Superhydrogenated Intermediate.

The activation, hydrogenation, and covalent coupling of polycyclic aromatic hydrocarbons (PAHs) are processes of great importance in fields like chemistry, energy, biology, or health, among others. So far, they are based on the use of catalysts which drive and increase the efficiency of the thermally- or light-induced reaction. Here, we report on the catalyst-free covalent coupling of nonfunctionalized PAHs adsorbed on a relatively inert surface in the presence of atomic hydrogen. The underlying mechanism has been characterized by high-resolution scanning tunnelling microscopy and rationalized by density functional theory calculations. It is based on the formation of intermediate radical-like species upon hydrogen-induced molecular superhydrogenation which favors the covalent binding of PAHs in a thermally activated process, resulting in large coupled molecular nanostructures. The mechanism proposed in this work opens a door toward the direct formation of covalent, PAH-based, bottom-up synthesized nanoarchitectures on technologically relevant inert surfaces.

On-Surface Bottom-Up Synthesis of Azine Derivatives Displaying Strong Acceptor Behavior.

On-surface synthesis is an emerging approach to obtain, in a single step, precisely defined chemical species that cannot be obtained by other synthetic routes. The control of the electronic structure of organic/metal interfaces is crucial for defining the performance of many optoelectronic devices. A facile on-surface chemistry route has now been used to synthesize the strong electron-acceptor organic molecule quinoneazine directly on a Cu(110) surface, via thermally activated covalent coupling of para-aminophenol precursors. The mechanism is described using a combination of in situ surface characterization techniques and theoretical methods. Owing to a strong surface-molecule interaction, the quinoneazine molecule accommodates 1.2 electrons at its carbonyl ends, inducing an intramolecular charge redistribution and leading to partial conjugation of the rings, conferring azo-character at the nitrogen sites.

Real-time acquisition of complex optical fields by binary amplitude modulation.

We describe, through simulations and experiments, a real-time wavefront acquisition technique using random binary amplitude masks and an iterative phase retrieval algorithm based on the Fresnel propagator. By using a digital micromirror device, it is possible to recover an unknown complex object by illuminating with this set of masks and simultaneously recording the resulting intensity patterns with a high-speed camera, making this technique suitable for dynamic applications.

ß-Carotene Concentration and Its Association with Inflammatory Biomarkers in Spanish Schoolchildren.

AIM: To examine the correlation between inflammatory biomarkers and plasma ß-carotene levels in children. METHODS: A total of 564 Spanish schoolchildren aged 9-12 were observed and studied. Plasma ß-carotene levels were assessed by HPLC. A ß-carotene level <4.83 µg/dL (0.09 µmol/L) was considered deficient. Plasma tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were measured by immunoenzyme assays. Serum high-sensitivity C-reactive protein (hs-CRP) was tested by immunonephelometry. RESULTS: Subjects who were ß-carotene-deficient (23.1% of the studied children) had higher IL-6 levels than subjects with normal ß-carotene concentrations. The log-IL-6 and log-hs-CRP concentrations, but not the log-TNF-α level, were strongly and inversely related to the plasma log-ß-carotene level (taking into account log-age, energy intake, log-triglycerides, gender, log-body mass index, log-ß-carotene intake, energy from lipids and cholesterol as covariables). When the 3 inflammatory biomarkers were introduced into the regression model along with the corresponding covariables, only the log-IL-6 level was related to the plasma log-ß-carotene level (ß = -0.505 ± 0.078; p < 0.001). CONCLUSIONS: Inflammatory status, in particular IL-6 levels, appears to be negatively associated with plasma ß-carotene levels in schoolchildren.

Antioxidant status in a group of institutionalised elderly people with chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is one of the most important and prevalent diseases suffered by the elderly. Evidence exists that its onset and severity might be conditioned by antioxidant status. The aim of the present study was to investigate the relationship between antioxidant status and COPD in institutionalised elderly people. In all, 183 elderly people aged >65 years (twenty-one had COPD and 160 healthy controls) were studied. The subjects' diets were investigated via the use of precise individual weighing for 7 d. Body weight, height, and biceps and triceps skinfold thickness were measured, and body fat (kg) and BMI (kg/m2) were calculated. Serum retinol, α-tocopherol, ß-carotene and vitamin C levels were determined. Subjects with COPD ate less fruits than healthy controls (117 (sd 52) v. 192 (sd 161) g/d), their coverage of the recommended intake of vitamin C was smaller (150 (sd 45) v. 191 (sd 88) %; note that both exceeded 100 %) and their diets had a lower antioxidant capacity (6558 (sd 2381) v. 9328 (sd 5367) mmol trolox equivalent/d). Those with COPD had lower serum vitamin C and α-tocopherol concentrations than healthy controls (32·4 (sd 15·3) v. 41·5 (sd 14·8) µmol/l and 12·1 (sd 3·2) v. 13·9 (sd 2·8) µmol/l, respectively). In addition, subjects with α-tocopherol <14·1µmol/l (50th percentile) were at 6·43 times greater risk of having COPD than those subjects with ≥14·1µmol/l (OR 6·43; 95 % CI 1·17, 35·24; P<0·05), taking sex, age, use of tobacco, body fat and vitamin E intake as covariables. Subjects with COPD had diets of poorer antioxidant quality, especially with respect to vitamins C and E, compared with healthy controls.

Image transmission through dynamic scattering media by single-pixel photodetection.

Smart control of light propagation through highly scattering media is a much desired goal with major technological implications. Since interaction of light with highly scattering media results in partial or complete depletion of ballistic photons, it is in principle impossible to transmit images through distances longer than the extinction length. Nevertheless, different methods for image transmission, focusing, and imaging through scattering media by means of wavefront control have been published over the past few years. In this paper we show that single-pixel optical systems, based on compressive detection, can also overcome the fundamental limitation imposed by multiple scattering to successfully transmit information. But, in contrast with the recently introduced schemes that use the transmission matrix technique, our approach does not require any a-priori calibration process that ultimately makes the present method suitable to use with dynamic scattering media. This represents an advantage over previous methods that rely on optical feedback wavefront control, especially for short speckle decorrelation times.

Moderate vitamin D deficiency and inflammation related markers in overweight/obese schoolchildren.

OBJECTIVE: Obesity has been associated with vitamin D deficiency and increased oxidative stress, which can lead to the dysregulation of adipokines and inflammation. The aim of the present work was to examine the association of vitamin D status [25(OH)D] on inflammatory related markers in overweight/obese children. SUBJECTS/METHODS: A total of 137 Spanish schoolchildren between 9 and 12 years of age (31.4% with overweight/obesity) were studied. Being overweight was defined as BMI≥85th percentile and obesity as BMI≥97th percentile using the reference tables of Hernández. Serum 25(OH)D concentrations were measured by chemiluminescent assay. Plasma tumor necrosis factor (TNF-α) and interleukin-6 (IL-6) were measured by immunoenzyme assay. Serum adiponectin was determined using an ELISA kit. Serum high-sensitivity C-reactive protein (hs-PCR) was tested by immunonephelometry. RESULTS: IL-6 concentrations were higher in the overweight/obese children with deficient serum 25(OH)D (<20 ng/mL) than in those in this group but whose serum 25(OH)D concentrations were adequate (≥20 ng/mL). Serum 25(OH)D was inversely associated with IL-6 concentrations in the overweight/obese subjects taking into account different covariates; thus, for every 1 ng/mL rise in the former, the latter fell by 0.160 pg/mL (ß=-0.160±0.068; R2=0.131; p=0.023). The obese subjects with concentrations of ≥25 ng/mL had lower hs-CRP values compared to those with concentrations of <25 ng/mL (0.053±0.035 vs. 0.356±0.613 mg/dL; p=0.035). CONCLUSION: Low serum 25(OH)D was significantly associated high serum IL-6 in overweight/obese children, and with increased hs-CRP in obese children.

Dispersion-to-spectrum mapping in nonlinear fibers based on optical wave-breaking.

In this work we recognize new strategies involving optical wave-breaking for controlling the output pulse spectrum in nonlinear fibers. To this end, first we obtain a constant of motion for nonlinear pulse propagation in waveguides derived from the generalized nonlinear Schrödinger equation. In a second phase, using the above conservation law we theoretically analyze how to transfer in a simple manner the group-velocity-dispersion curve of the waveguide to the output spectral profile of pulsed light. Finally, the computation of several output spectra corroborates our proposition.

Compressive holography with a single-pixel detector.

This Letter develops a framework for digital holography at optical wavelengths by merging phase-shifting interferometry with single-pixel optical imaging based on compressive sensing. The field diffracted by an input object is sampled by Hadamard patterns with a liquid crystal spatial light modulator. The concept of a single-pixel camera is then adapted to perform interferometric imaging of the sampled diffraction pattern by using a Mach-Zehnder interferometer. Phase-shifting techniques together with the application of a backward light propagation algorithm allow the complex amplitude of the object under scrutiny to be resolved. A proof-of-concept experiment evaluating the phase distribution of an ophthalmic lens with compressive phase-shifting holography is provided.

Dispersion management in two-photon microscopy by using diffractive optical elements.

We demonstrate efficient generation of wide-field fluorescence signals in two-photon microscopy exploiting diffractive optical elements and short pulses by using a dispersion-compensated beam delivery optics module. Computer-generated holograms are codified onto a phase-only spatial light modulator, which allows for arbitrary single-shot patterning of the sample. Spatiotemporal shaping of the pulse is mandatory to overcome spatial chirp and pulse-front tilt effects that spread both in space and time the irradiance patterns, thus limiting not only the spatial resolution but also the signal-to-noise ratio in two-photon microscopy. By using a multipass amplifier delivering 30 fs, 0.8 mJ pulses at 1 kHz repetition rate, we experimentally demonstrated arbitrary single-shot fluorescence irradiance patterns in Rhodamine B.

Femtosecond digital lensless holographic microscopy to image biological samples.

The use of femtosecond laser radiation in digital lensless holographic microscopy (DLHM) to image biological samples is presented. A mode-locked Ti:Sa laser that emits ultrashort pulses of 12 fs intensity FWHM, with 800 nm mean wavelength, at 75 MHz repetition rate is used as a light source. For comparison purposes, the light from a light-emitting diode is also used. A section of the head of a drosophila melanogaster fly is studied with both light sources. The experimental results show very different effects of the pinhole size on the spatial resolution with DLHM. Unaware phenomena on the field of the DLHM are analyzed.

Shift-variant digital holographic microscopy: inaccuracies in quantitative phase imaging.

Inaccuracies introduced in quantitative phase digital holographic microscopy by the use of nontelecentric imaging systems are analyzed. Computer modeling of the experimental result shows that even negligible errors in the radius and center of curvature of the numerical compensation needed to get rid of the remaining quadratic phase factor introduce errors in the phase measurements; these errors depend on the position of the object in the field-of-view. However, when a telecentric imaging system is utilized for the recording of the holograms, the numerical modeling and experimental results show the shift-invariant behavior of the quantitative-phase digital holographic microscope.

In situ observation of the on-surface thermal dehydrogenation of n-octane on Pt(111).

The catalytic dehydrogenation of alkanes constitutes a key step for the industrial conversion of these inert sp3-bonded carbon chains into other valuable unsaturated chemicals. To this end, platinum-based materials are among the most widely used catalysts. In this work, we characterize the thermal dehydrogenation of n-octane (n-C8H18) on Pt(111) under ultra-high vacuum using synchrotron-radiation X-ray photoelectron spectroscopy, temperature-programmed desorption and scanning tunneling microscopy, combined with ab initio calculations. At low activation temperatures, two different dehydrogenation stages are observed. At 330 K, n-C8H18 effectively undergoes a 100% regioselective single C-H bond cleavage at one methyl end. At 600 K, the chemisorbed molecules undergo a double dehydrogenation, yielding double bonds in their carbon skeletons. Diffusion of the dehydrogenated species leads to the formation of carbon molecular clusters, which represents the first step towards poisoning of the catalyst. Our results reveal the chemical mechanisms behind the first stages of alkane dehydrogenation on a platinum model surface at the atomic scale, paving the way for designing more efficient dehydrogenation catalysts.

Correction: In situ observation of the on-surface thermal dehydrogenation of n-octane on Pt(111).

Correction for 'In situ observation of the on-surface thermal dehydrogenation of n-octane on Pt(111)' by Daniel Arribas et al., Nanoscale, 2023, https://doi.org/10.1039/d3nr02564k.

Broadband dispersion compensation using inner cladding modes in photonic crystal fibers.

A photonic crystal fiber is optimized for chromatic dispersion compensation by using inner cladding modes. To this end, a photonic-oriented version of the downhill-simplex algorithm is employed. The numerical results show a dispersion profile that accurately compensates the targeted dispersion curve, as well as its dispersion slope. The presented fiber has a simple structure, while radiation losses can be reduced simply by adding a few more air-hole rings. Fabrication tolerances are also considered showing how fabrication inaccuracies effects can be overridden by just adjusting the compensation length.

Spectral broadening enhancement in silicon waveguides through pulse shaping.

Spectral broadening in silicon waveguides is usually inhibited at telecom wavelengths due to some adverse effects related to semiconductor dynamics, namely, two-photon and free-carrier absorption (FCA). In this Letter, our numerical simulations show that it is possible to achieve a significant enhancement in spectral broadening when we properly preshape the input pulse to reduce the impact of FCA on spectral broadening. Our analysis suggests that the use of input pulses with the correct skewness and power level is crucial for this achievement.

Weakly interacting molecular layer of spinning C60 molecules on TiO2 (110) surfaces.

The adsorption of C(60), a typical acceptor organic molecule, on a TiO(2) (110) surface has been investigated by a multitechnique combination, including van der Waals density functional calculations. It is shown that the adsorbed molecules form a weakly interacting molecular layer, which sits on the fivefold-coordinated Ti that is confined between the prominent bridging oxygen rows (see figure).

Estimation of salt intake by 24 h urinary sodium excretion in a representative sample of Spanish adults.

The present study reports the Na intake of a representative sample of Spanish young and middle-aged adults aged 18-60 years (n 418, 53·1 % women, selected from the capitals of fifteen provinces and the surrounding semi-urban/rural area), measured with a 24 h urinary Na excretion method. To validate the paper collection of 24 h urine, the correlation between fat-free mass determined by electrical bioimpedance (50·8 (sd 11·3) kg) and that determined via urinary creatinine excretion (51·5 (sd 18·8) kg) was calculated (r 0·633, P < 0·001). Urinary Na excretion correlated with systolic and dyastolic blood pressure data (r 0·243 and 0·153, respectively). Assuming that all urinary Na (168·0 (sd 78·6) mmol/d) comes from the diet, Na excretion would correspond with a dietary salt intake of 9·8 (sd 4·6) g/d, and it would mean that 88·2 % of the subjects had salt intakes above the recommended 5 g/d. Logistic regression analysis, adjusted for sex, age and BMI, showed male sex (OR 3·678, 95 % CI 2·336, 5·791) and increasing BMI (OR 1·069, 95 % CI 1·009, 1·132) (P < 0·001) to be associated with excreting >200 mmol/d urinary Na--a consequence of the higher salt intake in men and in participants with higher BMI. The present results help us to know the baseline salt intake in the Spanish young and middle-aged adult population, and can be used as the baseline to design policies to reduce salt consumption.

Single-shot color digital holography based on the fractional Talbot effect.

We present a method for recording on-axis color digital holograms in a single shot. Our system performs parallel phase-shifting interferometry by using the fractional Talbot effect for every chromatic channel simultaneously. A two-dimensional binary amplitude grating is used to generate Talbot periodic phase distributions in the reference beam. The interference patterns corresponding to the three chromatic channels are captured at once at different axial distances. In this scheme, one-shot recording and digital reconstruction allow for real-time measurement. Computer simulations and experimental results confirm the validity of our method.