Challenging the absence of observable hydrogens in the assignment of absolute configurations by NMR: application to chiral primary alcohols

The absolute configuration of beta-chiral primary alcohols devoid of observable hydrogens on one of the beta-substituents at the asymmetric carbon (L(1)/L(2)) can be determined by comparison of the (1)H NMR of their (R)- and (S)-9-AMA ester derivatives and analysis of the Deltadelta(RS) for the L substituent and the Cbeta-H.     

Major and Trace Element Accumulation in Coastal Sediments along Southeastern Baja California Studied by Instrumental Neutron Activation Analysis and 210Pb Age-Dating

The vertical distribution of K, Rb, Cs, Ca, Sr, Ba, Fe, Cr, Co, Ni, Zn, Sc, Zr, Sb, Se and As was studied by means of instrumental neutron activation analysis in four sediment cores collected from the eastern shelf of tectonically active Baja California peninsula accompanied by ²¹⁰Pb age-dating. ²¹⁰Pb analysis was performed by extraction chromatography with measuring the ingrowing daughter 210Bi radioactivity by liquid-scintillation spectrometry. It was found that concentration variations of Se, As, Sb, Zr and Zn are probably controlled by the intensity and composition of the material supplied from the drainage basin constituted by volcanic and sedimentary rocks.     

Role of barium(II) in the determination of the absolute configuration of chiral amines by 1H NMR spectroscopy

The assignment of the absolute configuration of alpha-chiral primary amines by complexation of their MPA derivatives with Ba2+ and NMR analysis of the changes generated is presented. All that is required is (a) the derivatization of the amine of unknown configuration with one enantiomer of the auxiliary reagent (MPA), either (R) or (S)-alpha-methoxyphenylacetic acid, (b) the recording of the 1H NMR spectrum of the resulting amide in MeCN-d3, (c) the addition of Ba(ClO4)2 to the NMR tube, and (d) the recording of a second spectrum after a few minutes of shaking. The above steps take a few minutes and are followed by an analysis of the shifts (measured as Deltadelta(Ba)) produced on the L1 and L2 substituents of the amine by the addition of Ba2+ and their comparison with those expected from the conformational changes produced by the complexation. The conformational changes initiated by complexation have been subjected to NMR and CD studies, which showed that the formation of the complex shifts the equilibrium from an antiperiplanar (AP) to a synperiplanar (SP) form, leading to an increase of the shielding by the phenyl group of MPA of the substituent of the amine located on the same side. In addition, theoretical calculations [density functional theory (DFT)] provide further support for the formation, structure, and stability of the complexes. The general applicability of this method and the trustworthiness of the resulting configurational assignment were guaranteed with a series of amines of known absolute configuration and varied structures, used as test compounds. The method proposed is simple, fast, and inexpensive, and it requires a very small amount of sample, only one derivatization, and the recording of just two 1H NMR spectra at room temperature. A graphical guide to simplify the application of this method is included.     

Lab-in-a-tube: ultracompact components for on-chip capture and detection of individual micro-/nanoorganisms

A review of present and future on-chip rolled-up devices, which can be used to develop lab-in-a-tube total analysis systems, is presented. Lab-in-a-tube is the integration of numerous rolled-up components into a single device constituting a microsystem of hundreds/thousands of independent units on a chip, each individually capable of sorting, detecting and analyzing singular organisms. Such a system allows for a scale-down of biosensing systems, while at the same time increasing the data collection through a large, smart array of individual biosensors. A close look at these ultracompact components which have been developed over the past decade is given. Methods for the capture of biomaterial are laid out and progress of cell culturing in three-dimensional scaffolding is detailed. Rolled-up optical sensors based on photoluminescence, optomechanics, optofluidics and metamaterials are presented. Magnetic sensors are introduced as well as electrical components including heating, energy storage and resistor devices.     

Collective motion of microspheres in suspensions observed by phase-mode dynamic ultrasound scattering technique

Compared with a nano-sized particle, dynamics of a micron-sized particle in a liquid is often associated with sedimentation (or floating) due to its relatively large mass. The motion of more than two particles is dominated by the hydrodynamic interactions, which are known to persist over a fairly long range, e.g., several millimeters, in suspensions. The particle size may be obtained from the dynamic ultrasound scattering (DSS) technique by the analysis of velocity fluctuations, whose origin is believed to take root in the particle-number fluctuations among temporally formed domains involving collective motion of particles with a certain cut-off length. In this study, such collective particle motion in highly turbid solutions was visualized by means of the phase-mode DSS technique with a single element transducer. Quantitative agreement between the velocity fluctuations obtained by the phase- and conventional amplitude-mode analyses was confirmed, followed by examination of the concentration and the particle size dependences on the dynamic structures induced by the long-ranged interactions. It was found that the phase mode-DSS was a promising method to evaluate the time-dependent structures of the micro-particles in highly turbid suspensions.