Ultrafast spectroscopy of linear carbon chains: the case of dinaphthylpolyynes.

The dynamics of excited states in α,ω-dinaphthylpolyyne, a class of linear sp-carbon chains, has been investigated by ultrafast transient absorption spectroscopy and DFT//TDDFT calculations. We show that the role of molecular conformers, in which end-capped naphthalene rings are planar or perpendicular to the polyyne plane, is fundamental for understanding both the steady state properties, such as UV-Vis absorption spectra and vibronic transitions, and the ultrafast transient absorption features. In particular, we observed in one of the conformers the ultrafast formation of a narrow photo-induced absorption band rising within 30 ps. This band can be assigned to an inter-system crossing event leading to the formation of triplet excited states.

Modeling of Coulomb coupling and acoustic wave propagation in LiNbO3.

The angular spectrum propagation technique is applied to modeling of wave propagation through piezoelectric media. The calculations of the angular spectrum propagator are based on the relevant equation for the slowness surface resulting from the solution of the Christoffel equation with piezoelectrically stiffened elastic constants. A two-dimensional FFT algorithm is applied in the final field superposition. We concentrate on the case of Coulomb coupling through local electrical point contacts on both the excitation and detection side. To model that case we superpose solutions for acoustic Green's functions of different propagation modes convoluted with equivalent distributed effective sources. Calculated results are in good agreement with the measured ones.

Phase-sensitive acoustic microscopy of polymer thin films.

The three-dimensional images obtained by scanning acoustic microscopy with vector contrast (PSAM), contain significant qualitative and quantitative information that is not easily obtainable by other methods. We employ this technique to examine homopolymer and polymer blend thin films. The complex V(z) functions derived from the images, and the results obtained by image processing and meticulous analysis are employed to render the morphology, composition and micro-mechanical properties of the polymer films. In addition, ways by which the information inherent in the phase images can be extracted are examined. This is highly desirable, as the phase images contain very useful additional information.

Apertureless near-field optical microscopy of metallic nanoparticles.

Image formation in apertureless near-field optical microscopes employing evanescent-wave excitation is studied quantitatively as a function of the polarisation and the wavelength of the excitation. Aggregate Mie theory is used to describe the probe-sample interactions self-consistently, including retardation. Only p-polarised excitation yields images, which closely reproduce the sample, and the contrast is much higher in this case than for s-polarised waves. Particular attention is paid to the case of imaging of metallic nanoparticles, for which local and nonlocal versions of aggregate Mie theory are compared. Nonlocality arises from the excitation of longitudinal bulk plasmons at the particle surface. It is shown that this effect is essential in the imaging of such particles and implies comparatively rapid convergence, in contrast to the local theory. The converged images calculated within the nonlocal theory resemble the results of the local theory, when, arbitrarily, within the latter only dipole-dipole interactions are taken into account. Significant qualitative and quantitative differences, however, are shown to exist. Signal and contrast enhancements due to resonant excitation of surface plasmon polaritons are studied quantitatively using the results of the converged nonlocal theory.

Propagation of femtosecond light pulses through near-field optical aperture probes.

The propagation of femtosecond light pulses through near-field optical fiber tips has been modelled numerically in three spatial dimensions by means of the finite integration technique. Ideally conducting as well as real metallic coatings of the tip have been considered, and the influence of surface plasmon polaritons (SPP) on shape, spectrum, and amplitude of the light pulse in the near and far fields of the tip have been investigated in this way. Special attention has been devoted to the superluminal tunneling of light through the fiber tip. The variation of phase and group velocities along the fiber axis has been characterized for a number of real metals and for different tip angles. A maximum of both velocities in the near field of the tip is characteristic for coatings of finite conductivity. For some tip angles negative values of the phase and/or group velocities are observed, which are caused by the propagation of SPP on the outer surface of the coating and their conversion into photons. It is shown, that the excitation of SPP on the metallic coating leads to strongly altered spatial emission characteristics of the tip.

Laser microstructuring and scanning microscopy of plasmapolymer-silver composite layers.

Laser-induced coalescence of silver nanoparticles embedded in thin plasma polymer films has been used to generate permanent submicrometer structures in the films, which exhibit unusual optical properties. Scanning-electron-microscope images and spatially resolved optical transmission spectra reveal the changes in the nanostructure of the films that are due to the irradiation. The structural modifications result from thermally induced coalescence of the irradiated nanoparticles and are accompanied by significant changes in the optical transmission spectra. A planar micro-optical element has been generated in this way, and its optical properties have been characterized by means of the depth resolution of a confocal microscope.

Efficacy of the topical skin protectant in advanced development.

A topical skin protectant (TSP) (ICD 2289) is being developed to protect service members from exposure to chemical warfare agents (CWA). The TSP is designed for use on the skin at the overgarment closures and other vulnerable areas to enhance protection. The TSP, which is in phase II clinical studies, is a cream containing two chemically inert substances: perfluoroalkylpolyether and polytetrafluoroethylene. Animal data showed that the TSP was effective against percutaneous penetration of a blister agent, sulfur mustard (HD), by reducing the size of skin lesions and against T-2 mycotoxin by preventing the development of erythema and edema. The insect repellent N,N-diethyl-m-toluamide (DEET) reduced the TSP protection against HD regardless of the order of application on rabbit skin prior to dosing of HD. The protection was sustained when DEET was removed with a dry gauze prior to TSP application. The TSP was also effective against percutaneous exposure of nerve agents-thickened (with 5% methyl methacrylamide) soman (TGD) and VX (O-ethyl-S-[2-(diisopropylamino)ethyl]methylphosphonothioate )-by reducing the mortality rate and protecting the red blood cell acetylcholinesterase activity. The TSP was effective against VX when DEET was applied prior to TSP application. Because human efficacy studies using CWA cannot be conducted, the efficacy will be demonstrated by the level of protection against poison ivy (urushiol) contact dermatitis in humans.

Evanescent-wave scattering in near-field optical microscopy.

Extended Mie theory is used to investigate the scattering and extinction of evanescent waves by small spherical particles and aggregates of such particles. Metallic, dielectric and metal-coated dielectric particles are taken into consideration. In contrast to plane-wave excitation, p- and s-polarized spectra differ in the case of evanescent waves due to the inherent asymmetry of both polarizations. Furthermore, contributions from higher multipoles are strongly enhanced, compared with plane-wave excitation, and the enhancement factors are polarization dependent. The corresponding changes in the scattering and extinction spectra are most pronounced in cases where higher multipoles exhibit resonances in the spectral range considered. This applies, for example, to morphological resonances of dielectric particles with size parameters > 1. The effect of the surface, where the evanescent wave is generated by total internal reflection, on the scattering and extinction spectra is investigated via numerical field calculations employing the multiple multipole method. In an application to apertureless near-field optical microscopy, the variation of the scattered power is calculated when a silicon particle is scanned across a silver particle in the evanescent field.

Protection by the heavy metal chelator N,N,N',N'-tetrakis (2-pyridylmethyl)ethylenediamine (TPEN) against the lethal action of botulinum neurotoxin A and B.

The ability of N,N,N',N'-tetrakis (2-pyridylmethyl)-ethyenediamine (TPEN) to protect against botulinum neurotoxin (BoNT) A and B was examined in vivo in mice. To determine the protective efficacy of TPEN, mice were injected i.p. with TPEN as a single bolus or as multiple injections 30 min before and 0, 2, 4 and 6 hr following i.v. challenges with BoNT-A or -B. TPEN treatment did not alter the 24 hr lethality of BoNT but did produce a significant delay in the time to death. For a moderate dose of serotype A (20 LD50), five divided doses of TPEN prolonged the time to death from 7.8 +/- 0.4 hr to 9.9 +/- 0.5 hr. For serotype B, examined under comparable conditions, the prolongation of the time to death was from 6.1 +/- 0.2 hr to 9.4 +/- 0.6 hr. The range of TPEN doses that could be examined in vivo was limited by its acute toxicity. Although low doses of TPEN (< or = 10 mg/kg) were well tolerated, higher doses (> or = 30 mg/kg) led to ataxia, loss of coordination, convulsions and death in 20.3 min or less. In clonal NG108-15 cells, TPEN was found to produce cytotoxicity as revealed by increases in the secretion of the marker enzyme lactate dehydrogenase (LDH), and enhanced reactivity with the vital dye trypan blue. From LDH concentration-response data determined 24 hr after addition of TPEN, the threshold concentration for observing cytotoxicity was 10 microM and the IC50 was 19.8 microM. At the highest TPEN concentration tested (100 microM), cytotoxicity was detected 8 hr after TPEN addition and increased in severity over a 3 day period. The cytotoxicity in NG108-15 cells appears to be distinct from the rapid-onset toxicity observed in whole animals. These results suggest that TPEN may be of potential benefit in delaying the lethal actions of BoNT-A and -B, but its use is limited by its initial and delayed toxicity. Since the therapeutic and toxic actions of TPEN are both related to zinc chelation, the use of TPEN would need to be restricted to low doses as part of a combination therapy.

A high-performance liquid chromatographic method for determining [3H]T-2 and its metabolites in biological fluids of the cynomolgus monkey.

High-performance liquid chromatography (HPLC) was used to separate, identify, and quantitate the trichothecin mycotoxin, T-2 (4 beta,15-diacetoxy-3 aopha-hydroxy-8 alpha [3-methyl-butyryloxy]-12,13-epoxy delta 9-trichothecin), and its metabolites in plasma and urine samples from cynomolgus monkeys treated with the toxin. A 15-min gradient elution system was developed to separate and measure radiolabeled T-2 mycotoxin and its metabolites. The HPLC technique for separating T-2 and its metabolites was compared with thin-layer chromatography. Samples from the in vitro metabolism of T-2 by plasma and urine were included as controls and as a measure of the toxin's stability in biological samples. Within 5 min, 22% of the plasma radiolabeled T-2 toxin was detected as metabolites after an intravenous administration of [3H] T-2 toxin to cynomolgus monkeys. By 24 h post-exposure, there was no parent T-2 toxin detected in plasma or urine. T-2 tetraol was the major metabolite detected in the plasma and urine of monkeys. Other metabolites observed in urine up to 5 days after exposure were 3'OH-T-2 and 3'OH-HT-2. We conclude that T-2 toxin was rapidly metabolized to more polar metabolites, which were eliminated in urine.

Immunohistochemical localization of the cytochrome P450 isozymes LMC2 and LM4B (P4501A1) in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated zebrafish (Brachydanio rerio).

Dibenzo-p-dioxins are persistent pollutants in our environment that exert a variety of biological and toxic effects in various species, in particular developmental toxicity in fish. Using zebrafish (Brachydanio rerio) as a model system, we analyzed the expression and inducibility of a constitutive isozyme (LMC2) and a dioxin-inducible isozyme (LM4B or P4501A1) of cytochrome (cyt.) P450 in different organs by immunohistochemical techniques. In untreated zebrafish, LMC2 was constitutively expressed at high levels in the liver, kidney, skin, and oral mucosa, while moderate expression was detected in gills, pseudobranch, intestine, and ovaries. LM4B was either not expressed in these organs or was found at comparatively low levels. After treatment of zebrafish with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; total dose of 15 ng per fish), LM4B expression was strongly induced in livers and kidneys and less pronounced in gills and pseudobranches, whereas no or only marginal induction was seen in skin, intestine, oral mucosa, and ovaries. In addition, cyt. P450 catalyzed 7-ethoxyresorufin-O-deethylation and phenol UDP-glucuronosyltransferase activity were also found to be inducible in liver and kidney. Our results demonstrate that zebrafish respond to inducing stimuli of TCDD in a fashion similar to that observed with related compounds in other fish species, suggesting that zebrafish may be a useful experimental model for studying biological and toxic effects of TCDD and other environmental pollutants in fish.

[3H]-saxitoxinol metabolism and elimination in the rat.

Tritiated saxitoxinol was used to obtain preliminary information on saxitoxin metabolism in the rat. Sublethal doses of tritiated saxitoxinol (18.9-microCi/kg; 3.8 micrograms/kg) were injected i.v. into each of six rats. Urine and fecal samples were collected up to 144 hr post-injection. Within 4 hr, 60% of injected radioactivity was excreted in urine. No radioactivity was found in feces. High performance liquid chromatography analyses of urine showed that saxitoxinol was not metabolized by the rats.

In vivo effects of T-2 mycotoxin on synthesis of proteins and DNA in rat tissues.

Rats were given an ip injection of T-2 mycotoxin (T-2), the T-2 metabolite, T-2 tetraol (tetraol), or cycloheximide. Serum, liver, heart, kidney, spleen, muscle, and intestine were collected at 3, 6, and 9 hr postinjection after a 2-hr pulse at each time with [14C]leucine and [3H]thymidine. Protein and DNA synthesis levels in rats were determined by dual-label counting of the acid-precipitable fraction of tissue homogenates. Rats given a lethal dose of T-2, tetraol, or cycloheximide died between 14 and 20 hr. Maximum inhibition of protein synthesis at the earliest time period was observed in additional rats given the same lethal dose of the three treatments and continued for the duration of the study (9 hr). With sublethal doses of T-2 or tetraol, the same early decrease in protein synthesis was observed but, in most of the tissues, recovery was seen with time. In the T-2-treated rats. DNA synthesis in the six tissues studied was also suppressed, although to a lesser degree. With sublethal doses, complete recovery of DNA synthesis took place in four of the six tissues by 9 hr after toxin exposure. The appearance of newly translated serum proteins did not occur in the animals treated with T-2 mycotoxin or cycloheximide, as evidenced by total and PCA-soluble serum levels of labeled leucine. An increase in tissue-pool levels of free leucine and thymidine in response to T-2 mycotoxin was also noted. T-2 mycotoxin, its metabolite, T-2 tetraol, and cycloheximide cause a rapid inhibition of protein and DNA synthesis in all tissue types studied. These results are compared with the responses seen in in vitro studies.

Acute inhalation toxicity of T-2 mycotoxin in the rat and guinea pig.

In this study, concentration-response parameters were determined for rats and guinea pigs systematically exposed to an aerosol of T-2 toxin. The LC50 for a 10-min exposure to T-2 toxin aerosol was 0.02 mg T-2/liter air for rats and 0.21 mg T-2/liter air for guinea pigs. Data from total T-2 deposition in rats and guinea pigs exposed to their respective LC50 aerosol concentration gave an LD50 of 0.05 mg T-2/kg body weight for the rat and 0.4 mg T-2/kg body weight for the guinea pig. These data show that inhaled T-2 toxin is approximately 20 times more toxic to the rat (0.05 mg T-2/kg body wt inhaled vs 1.0 mg T-2/kg body wt ip) and at least twice as toxic to the guinea pig (0.4 mg T-2/kg body wt inhaled vs 1-2 mg T-2/kg body wt ip) than ip administered T-2 toxin. Histopathologic examination of major organs in both the rat and guinea pig after respiratory exposure to T-2 toxin indicated that lesions were similar to those described after systemic administration of the toxin. Gross and microscopic alterations of respiratory tract tissue after T-2 aerosol exposure were minimal and could not account for the increase in toxicity.

Cutaneous absorption and decontamination of [3H]T-2 toxin in the rat model.

Cutaneous absorption and decontamination of [3H]T-2 mycotoxin using various treatment modalities incorporating water, detergent, sprays, and scrubbing of application sites were examined in the rat model at 5, 30, 60, and 1440 min (24 h) postexposure. Rats were killed immediately after treatment and radiolabeled T-2 remaining in full-thickness skin samples were determined. Absorption and decontamination were followed over time, and decontaminating treatment modalities were evaluated for efficacy. Less than 1% of the applied dose was absorbed in 5 min, and 50% was absorbed in 24 h. At 5 min, 99.5 +/- 0.05% of nonabsorbed (residual) [3H]T-2 was removed, and 58 +/- 5.2% of residual toxin was removed at 24 h with a 2.5% detergent/water spray. When treatment modalities were evaluated at 60 min, a 2.5% detergent/water scrub followed by a detergent/water spray produced optimal decontamination by removing 81 +/- 2.2% of residual toxin. All treatment modalities using detergent and/or water removed significant amounts of toxin (p less than or equal to .0001); a dry scrub was not efficacious. Treatment should be initiated as soon as possible after exposure for best results. However, the stratum corneum acts as a reservoir for the toxin, and decontamination should be carried out even if delayed several hours or days after exposure. Dermal absorption pharmacokinetics found in these studies are similar to those described for other low-molecular-weight compounds, and the decontamination results from T-2 toxin should be applicable to other, similar toxic substances.

Essential fatty acid deficiency and neutrophil function: studies of lipid-free total parenteral nutrition in monkeys.

Linoleic acid (18:2 omega 6), the obligate precursor of arachidonic acid (20:4 omega 6), is an essential nutrient for humans and other mammals. Because arachidonic acid release and metabolism are components of neutrophil activation by certain stimuli, we questioned whether neutrophils depleted of arachidonate as a result of essential fatty acid deficiency might be functionally impaired. We examined this possibility by producing essential fatty acid deficiency in monkeys with lipid-free total parenteral nutrition (TPN). Rhesus and African green monkeys were given calorically equal TPN for up to 23 days with and without a vegetable fat emulsion rich in linoleic acid. Fatty acids were analyzed in total lipid extracts of serum and isolated blood neutrophils by gas-liquid chromatography. Although fatty acids in the serum and neutrophils of monkeys given TPN with lipid did not change, linoleic acid levels decreased by at least 60% in serum and 50% in neutrophils from animals given TPN with no lipid. Moreover, arachidonate levels in neutrophil lipids decreased by at least 50% within 12 days of lipid-free TPN, and the abnormal fatty acid 20:3 omega 9 (characteristic of essential fatty acid deficiency) appeared and steadily increased with time. These biochemical signs of omega 6 fatty acid deficiency were associated with impaired neutrophil function in vitro. Both migration responses and superoxide generation stimulated by N-formyl-methionyl-leucyl-phenylalanine were significantly decreased by 12 days of lipid-free TPN, as was the capacity of activated cells to synthesize leukotriene B4. In contrast, functional responses of fatty acid-deficient neutrophils to leukotriene B4 and phorbol myristate acetate, which have little or no effect on arachidonate release or metabolism, were not significantly altered. These findings indicate that endogenous supplies of arachidonic acid and other essential omega 6 fatty acids influence the functional responsiveness of neutrophils. These studies also indicate that altered neutrophil function is a feature of essential fatty acid deficiency and that it may contribute to the increased risk of infection and decreased inflammatory responses observed in this condition.

Acute inhalation toxicity of T-2 mycotoxin in mice.

Experiments were conducted to study the acute inhalation toxicity of T-2 mycotoxin in both young adult and mature mice. For a 10-min aerosol exposure, the 24-hr LC50 of T-2 mycotoxin in young adult mice was 0.08 +/- 0.04 mg T-2/liter air and that for mature mice was 0.325 +/- 0.1 mg T-2/liter air. Deaths among mice exposed to the higher aerosol concentrations used in this study (i.e., 1.5 to 2.4 mg T-2/liter air) occurred in less than 5 hr. General clinical symptoms in these animals immediately postexposure were tremors, lethargy, stilted gait, and, in some animals, prostration. In experiments separate from the concentration-response studies, total deposition of T-2 aerosol and selective retention of T-2 in the respiratory tract and nasal turbinates were determined analytically from 3H-labeled T-2. When total deposition of T-2 was quantitated, there was excellent agreement between that amount of T-2 deposited and that amount of T-2 predicted from calculations based on aerosol size and animal minute volume. Based on the aerosol deposition data, the LD50 values of T-2 mycotoxins was 0.24 mg/kg for young adult mice and 0.94 mg/kg for mature mice. For mice, inhalation of T-2 mycotoxin is at least 10 times more toxic than systemic administration (LD50 approximately 4.5 mg/kg) and at least 20 times more toxic than dermal administration (LD50 greater than 10 mg/kg).