Measuring 0.1-nm motion in 1 ms in an optical microscope with differential back-focal-plane detection

Back-focal-plane detection of micrometer-sized beads offers subnanometer resolution for single-molecule, optical trapping experiments. However, laser beam-pointing instability and mechanical drift of the microscope limit the resolution of optical-trapping experiments. By combining two infrared lasers with improved differential beam-pointing stability (< or = 0.05 microrad), we simultaneously measure and subtract the motion of the microscope stage, leading to a resolution of <0.1 nm in 1 ms and stability of 0.5 nm over 60 s. Repeated steps of 0.4 nm at 1 Hz are resolved with a signal-to-noise ratio of 25.     

Adsorption and immobilization of cytochrome c on nanodiamonds

Methods have been developed to immobilize proteins onto the surfaces ofnanodiamonds with an average size of 5 +/- 1 nm. The immobilization started with carboxylation/oxidization of diamonds with strong acids, followed by coating the surfaces with poly-L-lysine (PL) for covalent attachment of proteins using heterobifunctional cross-linkers. The feasibility of this approach is proven with fluorescent labeling of the PL-coated diamonds by Alexa Fluor 488 and subsequent detection of the emission using a confocal fluorescence microscope. Immobilization of proteins onto the surfaces is also demonstrated with yeast cytochrome c, which possesses a free SH group for linkage and a characteristic Soret absorption band for observation.     

Protein driven patterning of self-assembled cubosomic nanostructures: long oriented nanoridges

Self-assembly lipid/protein cubosomic nanostructures are generated at high hydration level (dispersion of 5% lipid only) and examined by freeze-fracture electron microscopy (FF-EM) and synchrotron X-ray diffraction (XRD). The fracture surface of the three-dimensional (3D) soft-matter membranous assembly reveals starlike nanopatterns of oriented 100-nm-long cubosomic nanoridges with lateral periodicity defined by their 21-nm diameters. The average water channel radius in these liquid crystalline cubosomic nanoarchitectures, determined by high-resolution FF-EM and XRD, is 18.0 Angstrom. The protein-directed fragmentation of a diamond-type lipid cubic phase at high hydration can induce 3D patterns of oriented nanoporous building blocks, which are a unique example of tertiary organization of functionalized fluid lipid/water interfaces.     

Coordination complexes of 1-(4-[N-tert-butyl-N-aminoxyl]phenyl)-1H-1,2,4-triazole with paramagnetic transition metal dications

1-(4-(N-tert-Butyl-N-aminoxylphenyl))-1H-1,2,4-triazole (NIT-Ph-Triaz) forms isostructural cyclic 2:2 dimeric complexes with M(hfac)(2), M = Mn, Ni, Co, hfac = hexafluoroacetylacetonate. For M = Cu, only a sufficient sample for crystallographic analysis was isolated. For M = Mn, Ni, and Co, the M-NIT exchange is strongly antiferromagnetic. The intradimer exchange coupling between M-NIT units is J/k = +0.53 K for M = Mn, J/k = (-)3.5 K for M = Ni. For M = Co, J/k < 0 K, with the magnetic susceptibility tending toward zero at low temperatures. The exchange behavior is consistent with an intradimer spin polarization mechanism linking M-NIT units through the conjugated pi-system of the radical. Computational modeling of NIT-Ph-Triaz gives Mulliken spin populations in good accord with experimental electron spin resonance hyperfine coupling constants, and is consistent with the presumed radical spin density distribution in the complexes. The results provide useful guidelines to anticipate spin polarization effects in organic pi-radical building blocks in magnetic materials, particularly when qualitative connectivity-based analyses are clouded by nonalternant molecular connectivities.     

DNA damage induced by 4,6,8,9-tetramethyl-2H-furo[2,3-h]quinolin-2-one, a new furocoumarin analog: biological consequences

4,6,8,9-Tetramethyl-2H-furo[2,3-h]quinolin-2-one (HFQ) and its isomer FQ (1,4,6,8-tetramethyl-2H-furo[2,3-h]quinolin-2-one) showed very strong antiproliferative activity in mammalian cells, about two times greater than 8-methoxypsoralen (8-MOP). Both compounds induced DNA-protein cross-links (DPC) but not interstrand cross-links. The FQ generated DPC in a biphotonic process, yielding a new kind of diadduct, whereas HFQ induced DPC by a monophotonic one, probably without its physical participation in the covalent bridge. These lesions gave different toxic responses. Sensitization of FQ led to extensive DNA fragmentation and to a number of chromosomal aberrations. Conversely, HFQ seemed to be completely inactive and 8-MOP gave intermediate results. A strict relationship between DPC formation and induction of chromosomal aberrations was observed. The HFQ did not induce light skin erythemas, whereas FQ was more phototoxic than 8-MOP, thus suggesting that FQ lesions, DPC in particular, may be implicated in skin phototoxicity. Ehrlich ascites cells, a transplantable mouse tumor, inactivated by furoquinolinone sensitization and injected into healthy mice, protected them from a successive challenge by viable tumor cells. This response appeared to be based on an immune mechanism. Comparable amounts of base substitution revertants were scored when testing furoquinolinones and 8-MOP in bacteria but no DPC were detected. This suggests that classic mutagenesis tests on bacteria are insufficient to give adequate information on furocoumarin genotoxicity. Given its features, HFQ can be regarded as an interesting new agent for psoralen plus UVA photochemotherapy and photopheresis.     

On noninvertible mappings of the plane: Eruptions

In this paper we are concerned with the dynamics of noninvertible transformations of the plane. Three examples are explored and possibly a new bifurcation, or "eruption," is described. A fundamental role is played by the interactions of fixed points and singular curves. Other critical elements in the phase space include periodic points and an invariant line. The dynamics along the invariant line, in two of the examples, reduces to the one-dimensional Newton's method which is conjugate to a degree two rational map. We also determine, computationally, the characteristic exponents for all of the systems. An unexpected coincidence is that the parameter range where the invariant line becomes neutrally stable, as measured by a zero Lyapunov exponent, coincides with the merging of a periodic point with a point on a singular curve. (c) 1996 American Institute of Physics.     

Physico-chemical investigation of asymmetrical peptidolipidyl-cyclodextrins

A new class of amphiphilic peptidolipidyl-cyclodextrins is reported. The derivatives are chiral due to the presence of an L-leucine in the spacer arm that links a saccharide moiety and a grafted, saturated hydrocarbon chain. Self-assembly properties of the peptidolipidyl-cyclodextrins are characterized by quasi-elastic light scattering, turbidity and UV-visible absorption measurements. NMR experiments give insight into the intermolecular dipolar interactions as a function of temperature and concentration. N-dodecyl-N alpha-(6 I-amidosuccinyl-6 1-deoxy-cyclomaltoheptaose)-L-leucine (1) is poorly soluble in aqueous media. N-dodecyl-N(alpha)-(6 I-amidosuccinyl-6 I-deoxy-2 I,3 I-di-O-methyl-hexakis-(2 II-VII,3 II-VII,6 II-VII-tri-O-methyl)-cyclomaltoheptaose)-L-leucine (2) is found to be more soluble and self-assembles into stable supramolecular colloidal aggregates with nanometric dimensions above a critical aggregation concentration (CAC). It has a propensity for solubilization of hydrophobic species revealing a micellar-like behavior, which is compared to that of the non-ionic detergent octyl glucoside. On the contrary, compound 1 precipitates in a crystalline phase beyond its water solubility limit, and it does not display any solubilizing capacity. The observed behavior corroborates at the molecular level with the NMR results.     

An effort toward molecular biology of food deprivation induced food hoarding in gonadectomized NMRI mouse model: focus on neural oxidative status

Background

Environmental uncertainty, such as food deprivation, may alter internal milieu of nervous system through various mechanisms. In combination with circumstances of stress or aging, high consumption of unsaturated fatty acids and oxygen can make neural tissues sensitive to oxidative stress (OS). For adult rats, diminished level of gonadal steroid hormones accelerates OS and may result in special behavioral manifestations. This study was aimed to partially answer the question whether OS mediates trade-off between food hoarding and food intake (fat hoarding) in environmental uncertainty (e.g., fluctuations in food resource) within gonadectomized mouse model in the presence of food deprivation-induced food hoarding behavior.

Results

Hoarding behavior was not uniformly expressed in all male mice that exposed to food deprivation. Extended phenotypes including hoarder and non-hoarder mice stored higher and lower amounts of food respectively as compared to that of low-hoarder mice (normal phenotype) after food deprivation. Results showed that neural oxidative status was not changed in the presence of hoarding behavior in gonadectomized mice regardless of tissue type, however, glutathione levels of brain tissues were increased in the presence of hoarding behavior. Decreased superoxide dismutase activity in brain and spinal cord tissues and increased malondialdehyde in brain tissues of gonadectomized mice were also seen.

Conclusions

Although, food deprivation-induced hoarding behavior is a strategic response to food shortage in mice, it did not induce the same amount of hoarding across all colony mates. Hoarding behavior, in this case, is a response to the environmental uncertainty of food shortage, therefore is not an abnormal behavior. Hoarding behavior induced neural OS with regard to an increase in brain glutathione levels but failed to show other markers of neural OS. Decreased superoxide dismutase activity in brain and spinal cord tissues and increased malondialdehyde levels in brain tissues of gonadectomized mice could be a hallmark of debilitated antioxidative defense and more lipid peroxidation due to reduced amount of gonadal steroid hormones during aging.