Investigation of degradation mechanisms by portable Raman spectroscopy and thermodynamic speciation: the wall painting of Santa María de Lemoniz (Basque Country, North of Spain)

To characterise the polymeric properties of processed lignins, a new method has been developed using hydrophobic interaction chromatography (HIC). This method separates the lignin polymers into fractions based on differences in hydrophobicity using low pressure liquid chromatography (LPLC). The hydrophobic column material consists of monodisperse polystyrene/divinylbenzene beads. An elution gradient was prepared monitoring the electrolyte concentration and pH. Citric acid buffer, containing ammonium sulphate that promotes adsorption to the column material, was used as mobile phase in a step-wise gradient together with ethanol (20/80% (v/v) ethanol/water, pH 12) and isopropanol (40/60% (v/v) isopropanol/water, pH 12). Depending on eluent composition, the degree of elution was 94% or higher. With the HIC method developed, lignosulphonates and kraft lignins were separated into seven distinctive peaks according to hydrophobicity.     

Encuentros Latinoamericanos de Fotoquímica y Fotobiología (ELAFOT): the Latin-American Photochemical and Photobiological Community

The photochemical and photobiological researchers in Latin American meet biannually at a regional meeting known as Encuentros Latinoamericanos de Fotoquímica y Fotobiología (ELAFOT). The goals of this series of meetings are to discuss leading scientific work, to become acquainted with the latest research findings in the discipline, to exchange ideas, to initiate collaborations between groups and to strengthen the scientific interactions between young researchers and senior experts from the region and from developed countries. During 8-12 November 2004, the eighth such meeting took place in La Plata, Argentina. In this introduction we present a brief history of the ELAFOT meetings and a summary of the most recent gathering and the papers presented in this Symposium-in-Print.     

Structure,dynamics, and solvation in a disordered metal–organic coordination polymer: a multiscale study

Metal–organic coordination polymers are a growing class of technologically-important materials in which transition metal ions are connected by multitopic organic chelators to form a 3-D network structure. While the structures of many highly-ordered metal–organic frameworks have been determined, far less structural information is available about the more common disordered materials. Our study combines pair distribution function analysis from total X-ray scattering, ab initio quantum mechanical calculations, and all-atom molecular dynamics to explore the structure and dynamics of a poorly-ordered branched coordination polymer. The polymer structure is highly flexible and dynamic, and is dramatically affected by its solvation state, a finding with far-reaching implications for the incorporation of coordination polymers into nanocomposite materials.     

Lev V. Vilkov (1931–2010): scientist,friend, editorial board member

Torvard C. Laurent (1930–2009) was one of the pioneers of hyaluronan science and in particular of its structural aspects. He was the first who ever established the metrical characteristics of hyaluronan. He determined many of its physicochemical properties and their relationship to the versatile biological functions of this noted molecule. He also contributed to its medical applications. He was a leading personality in science administration and science policy in Sweden and internationally.     

TUD-1: synthesis and application of a versatile catalyst, carrier, material…

The three-dimensional sponge-like mesoporous material TUD-1 is straightforward to prepare. Its synthesis can readily be modified to introduce metals into the framework of TUD-1, imparting many different catalytic activities. M-TUD-1 catalysts have proven to be very active, unlimited by diffusion and very stable. By combining two metals into one TUD-1 catalyst, synergy between Lewis and Br?nsted acid sites could be induced; incorporation of zeolites similarly gave rise to synergy. In addition to successful applications in redox-, acid- and photo-catalysis TUD-1 proved to be an excellent carrier material for catalysts, enabling new applications. TUD-1 was used as a contrast agent and drug delivery system, indicating that this material is but at the beginning of its potential applications.     

Development of Functionalized Cyclotriveratrylene Analogues: Introduction of Withdrawing and π-Conjugated Groups

Cyclotriveratrylene analogues (CTVs) are supramolecular bowl-shaped molecules known for their ability to complex organic and organometallic guests, to form liquid crystals, polymers, or nanostructures. In this Article, we report the synthesis of new cyclotriveratrylene analogues with fluorescence properties in which various electron-withdrawing or π-extended conjugated groups are appended to the wide rim ortho to the methoxy-donating groups. Synthetically, these functionalized CTVs cannot be obtained as CTVs with electron-rich functions by the typical method (i.e., the trimerization of the corresponding benzyl alcohol) but are prepared from a common key intermediate, the C(3)-triiodocyclotriveratrylene (CTV-I(3)), in good yields. Despite the synthetic difficulties encountered due to the presence of three reactive centers, we have demonstrated the possibility of performing Sonogashira coupling and Huisgen cycloaddition reactions directly to the CTV core for the first time. CTVs with π-extended conjugated groups reveal interesting fluorescence profiles. More broadly, this study utilizes CTV-I(3) to introduce novel functionalities into CTVs to keep exploring their potential applications.     

Porpholactams and chlorolactams: replacement of a β,β'-double bond in meso-tetraphenyl-porphyrin and -chlorin by a lactam moiety

Reaction of meso-tetraphenylporpholactone with hydrazine converts the lactone moiety to an N-aminolactam. It also reduces the opposite pyrrolic moiety of both the starting material and the N-aminolactam, generating chlorin-like chlorolactone and N-aminochlorolactam, respectively. Reductive N-N cleavage of the N-aminoporpholactam generates the parent porpholactam.     

Heme-Cu bound aβ peptides: spectroscopic characterization, reactivity, and relevance to Alzheimer's disease

Recently, it has been shown that heme binds to Aβ peptides which may play a major role in Alzheimer's disease (AD). This study illustrates that Aβ peptides can bind both Cu and heme cofactors at the same time. Both cofactors have unique spectroscopic and electrochemical features which are unaffected in the presence of the other, implying that they are electronically, chemically, and electrochemically uncoupled. These data clearly indicate that Cu cannot bind to three histidine residues simultaneously in Cu-Aβ complexes as previously proposed, since one of the histidines is involved in binding heme. The heme-Aβ and the heme-Cu-Aβ peptide complexes function as peroxidases. Interestingly, the Cu-Aβ complex also exhibits peroxidase activity, which may have significant implications in AD. Both Cu(+)-Aβ and heme (Fe(2+))-Aβ complexes reduce O(2) to H(2)O(2) quantitatively. Only one of the two electrons that are required for the reduction of O(2) to H(2)O(2) is derived from the reduced metal site, while the Tyr(10) residue of the native Aβ peptide donates the second electron. This Tyr(10) residue, the source of electron for the generation of partially reduced oxygen species (PROS, e.g., H(2)O(2)) is absent in rodents, which do not get affected by AD. When both heme and Cu are bound to the Aβ peptides, which is likely to happen physiologically, the amount of toxic PROS generated is maximum, implying that heme-Cu-Aβ complexes could potentially be most toxic for AD.     

Benzylation of β-dicarbonyl compounds and 4-hydroxycoumarin using TMSOTf catalyst: a simple, mild, and efficient method

The direct benzylation of 1,3-dicarbonyl compounds and 4-hydroxycoumarin with a wide variety of benzylic alcohols was achieved using trimethylsilyl trifluoromethanesulfonate as an efficient catalyst. The reaction proceeded under very mild conditions at room temperature providing the desired products in good to excellent yields.     

The effect of natural UV-B radiation on a perennial Salicornia salt-marsh in Bahía San Sebastián,Tierra del Fuego,Argentina: a 3-year field study

The Antarctic ozone hole and a general depletion of the stratospheric ozone layer cause increased levels of ultraviolet-B solar radiation (UV-B) over Tierra del Fuego, the southernmost tip of South America. For three consecutive growing seasons (1997–2000), we studied the biological impacts (morphology, physiology, demography and phenology) of natural UV-B radiation on a perennial Salicornia ambigua Michx. community in San Sebastian Bay (53° S and 68° W), Tierra del Fuego, Argentina. This is the first UV-B screening experiment on a subantarctic halophytic community. The shortwave UV-B spectrum (280 to 320 nm) was excluded by covering plots with UV-B blocking film (Mylar). These plots were compared to controls covered with UV-B transparent (Aclar) plastic screens, and unscreened plots. Shoot length in Salicornia was not affected by UV-B. Exposure to natural UV-B reduced biomass and density (by 17% and 38%, respectively). Concentration of UV-shielding pigments and cuticle thickness were both significantly higher (25–48% and 21–40%, respectively) in plants receiving ambient UV-B. The increase in cuticle thickness persisted throughout the growing season, whereas pigment concentration was higher at the beginning of the growing season. Also, the number of dead shoots was higher in plants exposed to UV-B. At the end of the growing season (March) shoot mortality was higher in plants exposed to ambient UV-B, and post-flowering senescence was 30 days earlier. Slight changes in the relative composition of Salicornia to Puccinellia were seen. The reduction observed in Salicornia shoot density under ambient UV-B was cumulative over time; 23% in the first growing-season, rising to 38% by the third growing-season. A similar incremental increase in pigment absorption at 305 nm was seen; 25% in the first and 48% in the third growing season.     

J. J. Thomson and The Electron: 1897–1899 An Introduction

Three Seminal Papers of J. J. Thomson This being the 100th anniversary of J. J. Thomsons discovery of the electron, the October 1897 paper in which he presented his case that cathode rays are streams of subatomic corpuscles is attracting a great deal of attention. Viewed from 100 years later, this paper stands out as the starting point for the research into the structure of the atom that has dominated 20th-century science. Viewed in its original historical context, however, this paper was but one of a group by Thomson and his Cavendish Laboratory research students and is matched in importance by his two ensuing papers: On the Charge of Electricity carried by the Ions produced by Röntgen Rays published in December 1898 and On the Masses of the Ions in Gases at Low Pressures published in December 1899. All three of these seminal papers, which appeared in the prestigious Philosophical Magazine, are included here, along with the published text of Thomsons talk of April 30, 1897, in which he first put the subatomic proposal forward and George Fitzgeralds commentary on this talk.