Single-molecule pump-probe detection resolves ultrafast pathways in individual and coupled quantum systems

We report the first experimental study of individual molecules with femtosecond time resolution using a novel ultrafast single-molecule pump-probe method. A wide range of relaxation times from below 100 up to 400 fs is found, revealing energy redistribution over different vibrational modes and phonon coupling to the nanoenvironment. Addressing quantum-coupled molecules we find longer decay times, pointing towards inhibited intramolecular decay due to delocalized excitation. Interestingly, each individual system shows discrete jumps in femtosecond response, reflecting sudden breakup of the coupled superradiant state.     

An efficient, stereoselective approach to syn-1,2-diols protected as cyclic carbonates

Enantioenriched 4-hydroxyalk-2-ynyl carbonates (or benzoates) have been prepared by stereoselective zinc-mediated addition of alkyl 2-propynyl carbonates (or their benzoate analogues) to aldehydes. Their partial reduction to Z-olefins followed by cyclization under mild Pd-catalyzed conditions allowed a straightforward access to enantioenriched syn-1,2-diols protected as cyclic carbonates.     

A simple approach to sensor discovery and fabrication on self-assembled monolayers on glass

Self-assembled monolayers (SAMs) on glass were used as a platform to sequentially deposit fluorophores and small molecules for ion sensing. The preorganization provided by the surface avoids the need for complex receptor design, allowing for a combinatorial approach to sensing systems based on small molecules. The resulting libraries are easily measured and show varied responses to a series of both cations and anions. This technology is transferable from the macro- to the microscale both via microcontact printing (microCP), where the fluorophore is printed onto a glass surface, and via direct attachment of the fluorophore to microchannel walls. The ease of miniaturization of this technology may make the generation of a wide variety of simple yet efficient microarrays possible.     

Design and synthesis of two pyrazole libraries based on o-hydroxyacetophenones

Two new solid-phase syntheses of substituted pyrazoles are described. The first includes supporting an o-hydroxyacetophenone on Merrifield resin, Vilsmeier-Haack formylation on the methyl group and cyclization with a substituted hydrazine to afford a pyrazole ring with two diversity centers. The second starts from o-hydroxyacetophenone supported on Wang resin, which undergoes a Claisen condensation with a carboxylic acid ester to yield a 1,3-dicarbonyl compound that cyclizes to a pyrazole using a hydrazine. Both methods have been used to synthesize two small pyrazole libraries.     

Ultrasonic inspection of batters for on-line process monitoring

A new method for on-line batter monitoring using ultrasound techniques is presented. Air or gas incorporation is done during the beating process which produces bubbles in the mixture. The density and the compressibility of the batter vary as a function of mixing time and are quality index of batter. Traditionally, a batter sample of a fixed volume is removed and weighted in order to determine its density. This is a time consuming process. Batters are air filled mixtures of high viscosity which do not support significant transmission of ultrasound. For this reason conventional ultrasonic density sensors for liquids are not suitable for this application. Therefore, a special transducer has been developed. The sensor was constructed using a piezoelectric ceramic at the fundamental frequency of 1 MHz. Instead of measuring density, in this work, changes in compressibility in batters are monitored by measuring the acoustic impedance of the batter. Main advantage of this novel approach is that changes in acoustic impedance are easier to detect than changes in density especially when air incorporation is in small quantities. Experimental results on different liquids and batters with different gas contents are presented and discussed.     

Effect of non-significant proportional bias in the final measurement uncertainty

The trueness of an analytical method can be assessed by calculating the proportional bias of the method in terms of apparent recovery. If the apparent recovery does not differ significantly from one, the analytical method has not a significant bias. If this is the case, the bias is neglected and the uncertainty associated with this bias is included in the uncertainty budget of results. However, when assessing trueness there is always a probability of incorrectly concluding that the proportional bias is not significant. Therefore, the uncertainty of results may be underestimated. In this paper, we study how non-significant bias affects the uncertainty of analytical results. Moreover, we study how to avoid the underestimation of uncertainty by including the non-significant bias calculated in the uncertainty budget. To answer these questions, we have used the Monte-Carlo method to simulate the process of estimating the apparent recovery of a biased analytical method and, subsequently, the future results this method provides. The results of the simulation show that non-significant bias may underestimate the uncertainty of analytical results when bias contributes in more than 20% to the overall uncertainty. Uncertainty is specially underestimated when bias contributes in more than 50% to the overall uncertainty.     

Classification of Dansgaard–Oeschger climatic cycles by the application of similitude signal processing

In this work we have performed a detailed analysis, using signal processing tools, to study time series of data (temperature proxy) extracted from the GRIP ice-core records and we relate it with the evolution of atmospheric CO₂ within the last glacial period. Our method is based in considering the warm periods known as Dansgaard–Oeschger (D/O) events and posterior returns to the cold stage as a climatic cycle. After the warming phase, D/O events relax to the initial cold state in three different ways, what gives rise to three classes of cycles. Also, the Younger/Dryas–Bolling/Allerod (Y/D–B/A) cycle corresponds to one of the classes obtained. We have found that all cycles start with identical warming phases which seem completely unrelated to variations in CO₂ concentration. We discuss on the consequences for global climatology of such steady pattern of cycles.     

Linear and non-linear conduction regimes in broken down gate oxides

We have investigated conduction properties of gate oxides in metal-oxide–semiconductor structures in which dielectric breakdown has occurred. The measurements were performed on p- and n-type substrate samples with oxide thickness ranging from 2.0 to 13.5 nm. It is shown that the post-breakdown differential conductance has two typical modes, which, in terms of the physics of mesoscopic conducting systems, are referred to as linear and non-linear conduction regimes. In this work, we propose an analytic model for the conductance based on the electron transmission properties of quantum point contacts, which captures the essential features and consistently explains both breakdown modes.     

Crystalline structure of sequential poly(ester amide)s derived from glycolic acid, 1,6‐hexanediamine,and even aliphatic dicarboxylic acids

Basic structural data of two sequential poly(ester amide)s derived from glycolic acid, 1,6‐hexanediamine, and adipic acid or dodecanodioic acid have been determined by means of X‐ray and electron diffraction patterns from fibers and single crystals. Chain‐folded lamellar crystals were obtained by isothermal crystallization from diol or glycerine solutions, and the crystalline habit was investigated by real space electron microscopy. Polyethylene decoration techniques were applied to evaluate the regularity of the folding surfaces. Spherulites prepared from evaporation of formic acid solutions were also studied. The two sequential poly(ester amide)s crystallized according to triclinic and monoclinic unit cells, in which the a crystallographic parameter was close to the typical distance between hydrogen‐bonded chains. Projections viewed down the chain axis revealed differences in the packing mode since oblique and rectangular cells were found for the adipic acid and dodecanodioic acid derivatives, respectively. Both structures can be envisaged as a stacking of hydrogen‐bonded sheets although clear differences concerning the shift between consecutive sheets and the number of layers comprising the unit cell were found. The large unit cells that have been deduced seem to be a consequence of the different packing preferences of the diester and diamide moieties. Both polymers have a molecular conformation that deviates from the all‐trans conformation typical of aliphatic polyamides and polyesters with a large number of methylene groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 194–206, 2009