Search

Abstract: In this work we report on the simultaneous measurement of the hydrodynamic coefficient and the electric charge of single Bacillus subtilis spores. The latter has great importance in protein binding to spores and in the adhesion of spores onto surfaces. The charge and the hydrodynamic coefficient were measured by an accurate procedure based on the analysis of the motion of single spores confined by an optical trap. The technique has been validated using charged spherical polystyrene beads. The excellent agreement of our results with the expected values demonstrates the quality of our procedure. We measured the charge of spores of B. subtilis purified from a wild type strain and from two isogenic mutants characterized by an altered spore surface. Our technique is able to discriminate the three spore types used, by their charge and by their hydrodynamic coefficient which is related to the hydrophobic properties of the spore surface. [Copyright &y& Elsevier]

We describe a general way how to calculate optical forces acting on Rayleigh particles or colloids placed into general interference field. In this paper, we focus on a configuration with three interfering beams laying in one plane and we present a comprehensive analysis of trap properties and particle behaviour. We found that this arrangement can be used for simultaneous 2D/3D confinement or sorting of particles having refractive index higher or lower comparing to the surrounding immersion medium. [Copyright &y& Elsevier]

Micrometer-sized rod-like non-birefringent transparent particles trapped by an astigmatic laser beam having elliptical intensity profile spontaneously rotate until they become aligned with the major axis of the beam cross-section. The observed rotation confirms a simple picture based on orbital angular momentum transfer from the light beam to the trapped particle. A model which regards the particle as a thin cylindrical lens with effective focal lengths f1 and f2 has allowed to calculate the applied optical torque and, hence, the time law governing the particle alignment. The time evolution of the particle alignment is studied for different rod-like particles by analysing the sequence of frames recorded by a CCD camera. The time evolution of the angle α formed between the main axes of the body and the laser shape results in good agreement with the theory for bodies fully immersed in the spot size of the laser. Discrepancies observed for rod-like particles longer than the minor elliptical axis of the beam cross-section, were removed by developing a more general model taking into account the partial overlapping between the body and the laser profile. [Copyright &y& Elsevier]

Benzodiazepines, psychotropic drugs, are among the most frequently found pharmaceuticals in aquatic matrices. An increasing number of studies are reporting their harmful effects on adults' behaviour and physiology, while little information is available regarding developing organisms exposed since early stages. Improper activation of GABA receptors during embryonic development is likely to induce relevant consequences on the morphogenesis and, at later stages, on behaviour. This study investigated the negative effects of three increasing concentrations of delorazepam on Xenopus laevis retinal and skeletal muscle morphogenesis. Morphological and ultrastructural investigations were correlated with gene expression, while Raman spectroscopy highlighted the main biochemical components affected. Conventional phototactic response and orientation in the magnetic field were assessed as indicators of proper interaction between sensory organs and the nervous system. Results confirm the profound impact of delorazepam on development and return an alarming picture of the amphibians' survival potentialities in a benzodiazepine-contaminated environment. [Display omitted] • Delorazepam belongs to benzodiazepines, emerging water pollutant class. • Its impact was evaluated on Xenopus laevis embryos. • Delorazepam induced retinal dysmorphogenesis, with visual performance impairment. • Skeletal muscle was damaged, displaying disorganization of fibers and sarcomeres. • Raman spectroscopy revealed significant changes in biochemical components. [ABSTRACT FROM AUTHOR]

A popular picture of the intermittent dynamics of glassy materials depicts each particle as localized in a temporary cage formed by its neighbors, and seldom jumping to another cage. Drawing on experiments on hard sphere colloidal glasses and molecular dynamic simulations of supercooled liquids, here we show how this simplified scenario leads to quantitative relations between single particle motion and macroscopic properties, within a Continuous Time Random Walk (CTRW) framework. For example, the diffusivity and the relaxation time at different length scales can be directly predicted from the jump properties. In the accessible range of temperatures and volume fractions, these predictions work well, although the CTRW formalism neglects the spatially heterogeneous dynamics of glassy systems. In this respect, we show how these dynamic heterogeneities can be highlighted from a study of the correlations between jumps. Finally, the intermittent motion is exploited to infer correlations between local structure and dynamics. [ABSTRACT FROM AUTHOR]

Background G-quadruplex DNA is involved in many physiological and pathological processes. Both clinical and experimental studies on DNA G-quadruplexes are slowed down by their enzymatic instability. In this frame, more stable chemically modified analogs are needed. Methods The bis-end-linked-(gggt) 2 PNA molecule (BEL-PNA) was synthesized using in solution and solid phase synthetic approaches. Quadruplex formation was assessed by circular dichroism (CD) and surface enhanced Raman scattering (SERS). Results An unprecedented bimolecular PNA homo quadruplex is here reported. To achieve this goal, we developed a bifunctional linker that once functionalized with gggt PNA strands and annealed in K + buffer allowed the obtainment of a PNA homo quadruplex. The identification of the strong SERS band at ~ 1481 cm − 1 , attributable to vibrations involving the quadruplex diagnostic Hoogsteen type hydrogen bonds, confirmed the formation of the PNA homo quadruplex. Conclusions By tethering two G-rich PNA strands to the two ends of a suitable bifunctional linker it is possible to obtain bimolecular PNA homo quadruplexes after annealing in K + -containing buffers. The formation of such CD-unfriendly complexes can be monitored, even at low concentrations, by using the SERS technique. General significance Given the importance of DNA G-quadruplexes in medicine and nanotechnology, the obtainment of G-quadruplex analogs provided with enhanced enzymatic stability, and their monitoring by highly sensitive label-free techniques are of the highest importance. This article is part of a Special Issue entitled "G-quadruplex" Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio. [ABSTRACT FROM AUTHOR]

Background About twenty variants of apolipoprotein A-I (ApoA-I) are associated to hereditary systemic amyloidoses. Although the molecular bases of this disease are still largely unknown, it has been hypothesized that ApoA-I proteolysis is a key event in pathogenesis, since it triggers the release of an N-terminal fragment (80–100 residue long) that misfolds to form amyloid deposits in peripheral organs and tissues. It is also known that cell membrane lipids play a key role in the fibrillogenic pathway. In the case of ApoA-I related amyloidosis caused by L174S mutation, the 93-residue N-terminal fragment of ApoA-I ([1-93]ApoA-I) was found to be the major constituent of ex vivo fibrils. Methods With the main goal to investigate the interaction of either [1-93]ApoA-I and ApoA-I with biomimetic membranes, we set-up an experimental system based on the Raman Tweezers methodology. We tested GUVs composed by two types of zwitterionic lipids with a different fluidity degree, i.e. dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC). Results We found that [1-93]ApoA-I induces conformational disorder in an ordered lipid bilayer. When interacting with fluid phases, instead, the fragment was found to be able to penetrate the membrane bilayer inducing an alignment of lipid chains. Conclusions The interaction features of [1-93]ApoA-I with biomimetic membranes strongly depend on the lipid phase. Full-length ApoA-I was found to have similar effects, even if significantly less pronounced. General significance Our observations shed light on still largely unknown molecular bases of ApoA-I fibrillogenic domain interaction with membranes. [ABSTRACT FROM AUTHOR]

Abstract: In this work we discuss on a compact spectrometer based on DFB diode lasers for detection of chloridric and fluoridric acids. HCl and HF concentrations are determined through optical absorption of the P(4) line (λ =1.7μm) and the R(3) line (λ =1.3μm), respectively. Both lines belong to first overtone vibrational bands and their linestrengths are 7.8×10−21 cm/molecule for HCl and 2.8×10−20 cm/molecule for HF. We chose these lines for their relative high intensities and because they are quite far from water vapour lines which represent the main interfering gas for trace-gases analysis. To detect these species we used two different high frequency modulation techniques: two-tone frequency modulation spectroscopy (f 1 =800MHz and f 2 =804MHz) was used for HCl while for HF we followed a simpler approach based on wavelength modulation spectroscopy (f =600kHz). We demonstrate that the two techniques provide comparable detection limit of about 80ppbV at atmospheric pressure. Positive testing of our spectrometer makes it suitable for in situ measurements of exhaust gases coming from waste incinerators. [Copyright &y& Elsevier]