X-ray structure of tricyclohexylmethyl chloride

The X-ray crystallographic structure of tricyclohexylmethyl chloride, a precursor of the tricyclohexylmethyl radical, has been determined. Colourless tablets of C₁₉H₃₃Cl crystallized from hexane/chloroform in the orthorhombic space group Pnma, with cell dimensions a=10.725(3),b=15.670(3),c=10.168(3) Å;V=1708.8(1.3) ų;Z=4. 1586 reflections withI>3 (I), and 302 with zero intensity, on refinement gaveR=0.046,R _w=0.076. The three cyclohexyl rings are arranged to give the molecule a plane of symmetry containing the central C–H axis. The large volume per nonhydrogen atom, of about 21.3 ų, is close to values found in the crystal structures of analogous tricyclohexyl compounds.     

Colloid probe AFM investigation of the influence of cross-linking on the interaction behavior and nano-rheology of colloidal droplets

The repulsive forces between a glass sphere and immobilized colloidal droplets of poly(dimethylsiloxane) (PDMS) (with various levels of internal cross-linking) have been determined in aqueous solution using colloid probe atomic force microscopy. On initial surface approach, droplet deformation is negligible and interaction forces resemble those expected for electrical double layer interaction of rigid spheres. Upon further approach, droplet flattening results in forces that deviate below rigid body electrical double layer interaction. The extent of droplet deformation has been determined in terms of the deviation from hard-sphere interaction. Droplet deformability is strongly dependent on the droplet cross-linking level and hence controlled by some combination of the bulk rheological and interfacial properties of the droplets. Droplet nano-rheology has been determined from the extent of force curve hysteresis. For liquidlike droplets, with low levels of cross-linking, no force curve hysteresis is observed and the elastic deformation may be described by a single spring constant, which is controlled by the interfacial properties. For highly cross-linked droplets, the extent of deformation is controlled by the droplet's bulk rheology rather than the interfacial properties. Upon retraction of the surfaces, force curve hysteresis is observed and is due to the viscoelastic response of the PDMS. The extent of hysteresis is dependent on the rate of approach/retraction and the loading force and has been theoretically analyzed to determine nano-rheological parameters that describe droplet relaxation processes. Elastic moduli and relaxation times of the PDMS droplets vary over several orders of magnitude as a function of cross-linking.     

A vibrational probe for local nucleic acid environments: 5-cyano-2'-deoxyuridine

Nitriles have been shown to be effective vibrational probes of local environments in proteins but have yet to be fully utilized for the study of nucleic acids. The potential utility of 5-cyano-2'-deoxyuridine ( 1) as a probe of local nucleic acid environment was investigated by measuring the dependence of the IR nitrile stretching frequency (nu CN), line shape, and absorbance on solvent and temperature. The nu CN was found to be sensitive to solvent with an observed blue shift of 9.2 cm (-1) in going from THF to water. The dependence of the nitrile IR absorbance band was further investigated in water-THF mixtures. Global line shape analysis, difference FTIR spectroscopy, and singular value decomposition (SVD) were used to show the presence of three distinct local environments around the nitrile group of 1 in these mixtures. A modest blue shift in nu CN was observed upon a hydrogen-bond-mediated heterodimer formation between 2 (a silyl ether analogue of 1) and 2,6-diheptanamido-pyridine ( 3a) in chloroform. The intrinsic temperature dependence of the nu CN was found to be minimal and linear over the temperature range studied. The experimental studies were complemented by density functional theory (DFT) calculations on the dependence of the nitrile stretching frequency on solute-solvent interactions and upon heterodimer formation with model systems.     

Slow relaxation of longitudinal multispin orders in weakly and strongly coupled two‐spin systems

Longitudinal multispin order (LOMO) corresponds to a nonequilibrium population distribution in spin systems that exhibit scalar (J), dipolar, or quadrupolar coupling. We investigated the relaxation of longitudinal two‐spin order (2‐LOMO) in systems that had either weakly or strongly J‐coupled spins. Our results indicated longer relaxation times for the 2‐LOMO state compared with the corresponding longitudinal single‐spin state (1‐LOMO). Accessing nuclear spin states that have relaxation times longer than T₁, without the use of external contrast agents, is potentially useful for in vivo imaging and also for studying systems using dynamically hyperpolarized nuclear spins where longer life times are sought to increase the time available to study (bio)chemical events. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman enhancement of azobenzene monolayers on substrates prepared by Langmuir-Blodgett deposition and electron-beam lithography techniques

Nanostructured metallic platforms for Raman enhancement were fabricated using Langmuir-Blodgett and electron beam (e-beam) lithography techniques. The gold platforms were inscribed on thin glass slides with the purpose of using them in a transmission geometry experimental setup under a confocal microscope. The plasmon frequency of the gold nanostructures was determined in the visible-near-infrared range for various pattern sizes prepared by Langmuir-Blodgett transfer and e-beam lithography. The surface Raman enhancement factors were determined for a monolayer of azobenzene molecules adsorbed on gold through thiol bonding and compared for both LB transfer and e-beam samples for nanostructures of comparable geometries.     

DNA and polylysine adsorption and multilayer construction onto cationic lipid-coated microbubbles

We report on a novel application of the layer-by-layer (LbL) assembly technique to attach multiple layers of DNA and poly-l-lysine (PLL) onto preformed lipid-coated microbubbles to increase the DNA loading capacity. We first measured the effects of the cationic lipid fraction and salt concentration on the microbubble stability. Microbubble production and stability were robust up to a cationic lipid fraction of 40 mol % in 10 mM NaCl. DNA adsorption was heterogeneous over the microbubble shell and occurred primarily on the condensed phase domains. The amount of adsorbed DNA, and subsequently adsorbed PLL, increased linearly with the fraction of cationic lipid in the shell. DNA loading was further enhanced by the LbL assembly method to construct polyelectrolyte multilayers (PEMs) of DNA and PLL. PEM buildup was demonstrated by experimental results from zeta potential analysis, fluorescence microscopy, UV spectroscopy, and flow cytometry. The PEMs exhibited two growth stages and were heterogeneously distributed over the microbubble surface. The DNA loading capacity onto the microbubbles was enhanced by over 10-fold by using five paired layers. However, the PEM shell did not prevent oscillation or destruction during ultrasound insonification. These results suggest that the surface can be compartmentalized to make multifunctional, high-payload ultrasound contrast agents for targeted gene therapy.     

Artificial cilia for active micro-fluidic mixing

In lab-on-chip devices, on which complete (bio-)chemical analysis laboratories are miniaturized and integrated, it is essential to manipulate fluids in sub-millimetre channels and sub-microlitre chambers. A special challenge in these small micro-fluidic systems is to create good mixing flows, since it is almost impossible to generate turbulence. We propose an active micro-fluidic mixing concept inspired by nature, namely by micro-organisms that swim through a liquid by oscillating microscopic hairs, cilia, that cover their surface. We have fabricated artificial cilia consisting of electro-statically actuated polymer structures, and have integrated these in a micro-fluidic channel. Flow visualization experiments show that the cilia can generate substantial fluid velocities, up to 0.6 mm s(-1). In addition, very efficient mixing is obtained using specially designed geometrical cilia configurations in a micro-channel. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices.     

Aquantitative assessment of stochastic electrodynamics with spin (SEDS): Physical principles and novel applications

Stochastic electrodynamics (SED) without spin, denoted as pure SED, has been discussed and seriously considered in the literature for several decades because it accounts for important aspects of quantum mechanics (QM). SED is based on the introduction of the nonrenormalized, electromagnetic stochastic zero-point field (ZPF), but neglects the Lorentz force due to the radiation random magnetic field Br. In addition to that rather basic limitation, other drawbacks remain, as well: i) SED fails when there are nonlinear forces; ii) it is not possible to derive the Schrödinger equation in general; iii) it predicts broad spectra for rarefied gases instead of the observed narrow spectral lines; iv) it does not explain double-slit electron diffraction patterns. We show in this short review that all of those drawbacks, and mainly the first most basic one, can be overcome in principle by introducing spin into stochastic electrodynamics (SEDS). Moreover, this modification of the theory also explains four observed effects that are otherwise so far unexplainable by QED, i.e., 1) the physical origin of the ZPF, and its natural upper cutoff; 2) an anomaly in experimental studies of the neutrino rest mass; 3) the origin and quantitative treatment of 1/f noise; and 4) the high-energy tail (～ 10²¹ eV) of cosmic rays. We review the theoretical and experimental situation regarding these things and go on to propose a double-slit electron diffraction experiment that is aimed at discriminating between QM and SEDS. We show that, in the context of this experiment, for the case of an electron beam focused on just one of the slits, no interference pattern due to the other slit is predicted by QM, while this is not the case for SEDS. A second experiment that could discriminate between QED and SEDS regards a transversely large electron beam including both slits obtained in an insulating wall, where the ZPF is reduced but not vanished. The interference pattern according to SEDS should be somewhat modified with respect to QED’s.     

Heteronuclear double resonance on formamide-15N and ammonium-15N using weak perturbing radiofrequency fields

Weak radiofrequency fields have been used to perturb nitrogen transitions in the formamide-¹⁵N and ammonium-¹⁵N molecules. Observation of the proton spectra has completed the determination of the relative signs of the coupling constants in formamide-¹⁵N. Chemical shifts precisely related to tetramethylsilane are reported and a discussion of a method for presentation of shift results is included.