Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time.

Electrocyclic reactions are characterized by the concerted formation and cleavage of both σ and π bonds through a cyclic structure. This structure is known as a pericyclic transition state for thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule α-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated π bonds. The σ bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.

Conformer-specific photochemistry imaged in real space and time.

Conformational isomers (conformers) of molecules play a decisive role in biology and organic chemistry. However, experimental methods for investigating chemical reaction dynamics are typically not conformer-sensitive. We report on a gas-phase megaelectronvolt ultrafast electron diffraction investigation of α-phellandrene undergoing an electrocyclic ring-opening reaction. We directly imaged the evolution of a specific set of α-phellandrene conformers into the product isomer predicted by the Woodward-Hoffmann rules in real space and time. Our experimental results are in quantitative agreement with nonadiabatic quantum molecular dynamics simulations, which provide considerable detail of how conformation influences the time scale and quantum efficiency of photoinduced ring-opening reactions.

Multiple Perianal Ulcers Related to Use of a Hemorrhoidal Ointment With the Active Ingredients Triamcinolone Acetonide, Lidocaine, and Pentosan Polysulfate Sodium: A Series of 11 Spanish Patients. / Múltiples úlceras perianales en relación con el uso de una pomada antihemorroidal con acetónido de triamcinolona, lidocaína y pentosano polisulfato sódico como principios activos: una serie de 11 pacientes españoles.

The development of perianal ulcers related to the use of a hemorrhoidal ointment has not been reported in the literature. We describe a series of 11 patients who were treated for perianal ulcers in 10 Spanish hospitals after they used the same ointment containing the active ingredients triamcinolone acetonide, lidocaine, and pentosan polysulfate sodium. No prior or concomitant conditions suggesting an alternative cause for the condition could be identified, and after the patients stopped using the ointment, their ulcers cleared completely in 8 weeks on average. This case series shows the damage that can be caused by an over-the-counter pharmaceutical product used without medical follow-up. It also illustrates the need to ask patients with perianal ulcers about any topical agents used before the lesions appeared.

Putting Photomechanical Switches to Work: An Ab Initio Multiple Spawning Study of Donor-Acceptor Stenhouse Adducts.

Photomechanical switches are light sensitive molecules capable of transducing the energy of a photon into mechanical work via photodynamics. In this Letter, we present the first atomistic investigation of the photodynamics of a novel class of photochromes called donor-acceptor Stenhouse adducts (DASA) using state-of-the-art ab initio multiple spawning interfaced with state-averaged complete active-space self-consistent field theory. Understanding the Z/E photoisomerization mechanism in DASAs at the molecular level is crucial in designing new derivatives with improved photoswitching capabilities. Our dynamics simulations show that the actinic step consists of competing nonradiative relaxation pathways that collectively contribute to DASAs' low (21% in toluene) photoisomerization quantum yield. Furthermore, we highlight the important role the intramolecular hydrogen bond plays in the selectivity of photoisomerization in DASAs, identifying it as a possible structural element to tune DASA properties. Our fully ab initio simulations reveal the key degrees of freedom involved in the actinic step, paving the way for the rational design of new generations of DASAs with improved quantum yield and efficiency.

The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction.

The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D synthesis. Although the relaxation from the photoexcited electronic state during the ring-opening has been investigated in numerous studies, the accompanying changes in atomic distance have not been resolved. Here we present a direct and unambiguous observation of the ring-opening reaction path on the femtosecond timescale and subångström length scale using megaelectronvolt ultrafast electron diffraction. We followed the carbon-carbon bond dissociation and the structural opening of the 1,3-cyclohexadiene ring by the direct measurement of time-dependent changes in the distribution of interatomic distances. We observed a substantial acceleration of the ring-opening motion after internal conversion to the ground state due to a steepening of the electronic potential gradient towards the product minima. The ring-opening motion transforms into rotation of the terminal ethylene groups in the photoproduct 1,3,5-hexatriene on the subpicosecond timescale.

Knowledge of human papillomavirus and anal cancer among men who have sex with men attending a New York City sexually transmitted diseases clinic.

Men who have sex with men (MSM) are at risk for human papillomavirus (HPV) infection and anal cancer (AC) yet little is known regarding MSM knowledge and risk perception for these outcomes. We surveyed 116 MSM attending a sexually transmitted disease clinic and found that over a quarter (27%) did not know HPV is transmitted via anal sex and most (77%) were unaware of the link with AC. Many MSM (60%) perceived risk for HPV; far fewer (35%) perceived risk for AC. In adjusted logistic regression analyses, having friends or acquaintances with HPV or genital warts was associated with knowledge of anal HPV transmission (odds ratio [OR] = 4.3; 95% confidence interval [CI] = 1.4, 13.4) and AC risk-perception (OR = 6.2; 95% CI = 2.3, 16.7); reporting a regular source of care was associated with awareness of a link between HPV and AC (OR = 3.1; 95% CI = 1.1, 9.1); and MSM and women versus MSM, had less perceived risk for HPV (OR = 0.05; CI = 0.01, 0.29). Nearly all expressed hypothetical acceptance of HPV vaccine. In our sample, many MSM were unaware of a link between MSM sexual practices and HPV-related outcomes.

[Clinical-pathological features of cutaneous melanomas diagnosed in a Mediterranean tertiary hospital between 1990 and 2004: a comparison between sexes and age groups and analysis of longterm outcomes]. / Características clínicopatológicas de los melanomas cutáneos diagnosticados en un hospital terciario mediterráneo entre 1990 y 2004: comparación entre sexos, por grupos de edad y evolución a lo largo del tiempo.

BACKGROUND: The incidence of malignant melanoma has increased over recent decades. Early diagnosis continues to be essential for effective treatment. Our objective was to analyze cutaneous malignant melanomas diagnosed over a 15-year period in a tertiary hospital for trends towards earlier diagnosis and to identify subgroups with poorer prognosis. MATERIAL AND METHODS: Retrospective analysis of primary cutaneous melanomas analyzed in the pathology department of Hospital La Paz, Madrid, Spain, between 1990 and 2004. RESULTS: In total, 526 melanomas were diagnosed. The mean (SD) Breslow thickness was 2.63 (4.84) mm and the median thickness was 0.98 mm (range, 0-65 mm). The mean size (widest point) was 16.59 (12.11) mm. The most common histological type was surface-spreading melanoma and the most common site was the trunk. Melanomas detected in men were generally larger and thicker than in women (P=0.05). Individuals aged over 60 years consulted for significantly thicker and larger tumors than younger individuals. The incidence of malignant melanomas has increased steadily over the years whereas the mean Breslow thickness and size have decreased. CONCLUSIONS: Diagnosis of melanoma in Spain is made increasingly earlier, although locally advanced tumors are still sometimes seen in men and in individuals aged over 60 years.

Mercury content in vegetation and soils of the Almadén mining area (Spain).

The Almadén area is an exceptional case of mercury concentration in the world, where cinnabar is the predominant mineralised form. Mining activities have been carried out over the past two thousand years and once this activity is concluded, a restoration of the environment is necessary for the affected areas. That implies the selection, optimisation and application of the most appropriate techniques focused on the recovery of contaminated areas. Phytotechnology is one of the proposed techniques, which considers the use of plants due to the low environmental impact and their proved efficiency. In this framework, it is necessary to study the behaviour of mercury in the soil-plant system and to determine the mercury absorption capacity of the different Almadén plant species. Therefore, field and laboratory studies have been carried out to determine the easily available forms of mercury in ten test plots in the Almadén area and the resulting data is related to the mercury accumulation in different plant species of the studied territory. Special attention is given to the easily available forms of mercury in the analysed soils and used as the transfer factor for the Hg-availability index that relates the amount of mercury in a plant with the total amount of mercury in a soil and with the easily available forms. The result of this experimental work is selecting the plant species suitable to be used in a future implementation of phytotechnologies in this area.

[Risks of black henna tattoos]. / Riesgos de los tatuajes de henna negra.

Temporary henna tattoos have become increasingly popular in the last few years, because of their apparent harmlessness and disappearance in few weeks. Black henna contains paraphenylenediamine (PPD), a synthetic colorant which is used in hair dyes and can cause sensitization. Many cases of allergic contact dermatitis occurring after tattooing have been reported, especially in children and teenagers during the summer time, since there are many tattoo-painters at holiday places and the parents are unaware of the risks of these tattoos. Clinicians, particularly pediatricians, primary care physicians and dermatologists should seek to remedy this misinformation. We can be the first person to be consulted before the tattoo painting and we will treat patients with lesions. We present our experience of eight cases of allergic contact dermatitis after tattooing and briefly review the literature on the risks of black henna tattoos.

Mercury and trace element fractionation in Almaden soils by application of different sequential extraction procedures.

A comparative evaluation of the mercury distribution in a soil sample from Almaden (Spain) has been performed by applying three different sequential extraction procedures, namely, modified BCR (three steps in sequence), Di Giulio-Ryan (four steps in sequence), and a specific SEP developed at CIEMAT (six steps in sequence). There were important differences in the mercury extraction results obtained by the three procedures according to the reagents applied and the sequence of their application. These findings highlight the difficulty of setting a universal SEP to obtain information on metal fractions of different mobility for any soil sample, as well as the requirement for knowledge about the mineralogical and chemical characteristics of the samples. The specific six-step CIEMAT sequential extraction procedure was applied to a soil profile (Ap, Ah, Bt1, and Bt2 horizons). The distribution of mercury and major, minor, and trace elements in the different fractions were determined. The results indicate that mercury is mainly released with 6 M HCl. The strong association of mercury with crystalline iron oxyhydroxides, present in all the horizons of the profile, and/or the solubility of some mercury compounds in such acid can explain this fact. Minor mercury is found in the fraction assigned to oxidizable matter and in the final insoluble residue (cinnabar).

Preconcentration speciation method for mercury compounds in water samples using solid phase extraction followed by reversed phase high performance liquid chromatography.

A simple and rapid method for in situ preconcentration of inorganic and organic mercury compounds in water samples, based on solid phase extraction using dithizone immobilised on a reversed-phase C18 cartridge, has been developed. The adsorbed complexes were stable on the cartridge for at least 2 weeks. The speciation analysis of methylmercury (MeHg), phenylmercury (PhHg) and inorganic mercury (Hg (II)) were done by reversed-phase high performance liquid chromatography. The calibration graphs of MeHg, PhHg and Hg (II) were linear (r>0.999) from the detection limits (0.58, 0.66 and 0.54 ng) to 38, 25 and 26 ng of Hg, respectively. The average recoveries of MeHg, PhHg and Hg (II) from spiked samples (0.3-48.0 mug l(-1) Hg) were 98+/-3, 99+/-1 and 100+/-7%, respectively. By applying SPE procedure a 200-fold concentration of the sample was obtained.

Sequential extraction of U, Th, Ce, La and some heavy metals in sediments from Ortigas river, Spain.

The extractable contents of U, Th, Ce, La, Cu, Cr, Ni and Zn in two sediment samples collected from the Ortigas river have been analysed using the three step sequential extraction procedure (SEP) described by BCR, Community Bureau of Reference (now Standards Measurements and Testing Programme) of the European Union. In order to perform a mass balance, a fourth step has been included, i.e. digestion of the residue from the third extraction step. ICP-AES was used for the determination of Cu, Cr, Ni, Zn, Th, Ce and La. Because of the inadequate sensitivity of ICP-AES for the analysis of uranium, ICP-MS was used for the determination of this element. Standard addition method was required, because of the matrix effects. Finally, SEP was applied to the Ortigas river sediments, showing that most of the elements were found mainly associated with the residual sediment fraction, except for uranium, which was found as an exchangeable species in approximately 60% of its total content. Recoveries of 86-108% have been obtained.