Chirality and the origin of atmospheric humic-like substances

Aerosol water extracts and atmospheric humic-like substances (HULIS) obtained from PM2.5-fraction aerosol samples collected in a rural/continental background environment and in an urban environment in spring and summer, and at a tropical site that was heavily impacted by biomass burning were studied. HULIS was obtained as the water-soluble, methanol-elutable material isolated from a solid-phase extraction procedure. The mean organic matter-to-organic carbon mass conversion factor and the standard deviation of 2.04 +/- 0.06 were derived for HULIS from biomass burning. Mean atmospheric concentrations of HULIS for the rural and urban environments and for the biomass burning during daylight periods and nights, were 1.65, 2.2, 43, and 60 mu gm(-3), respectively. This and other abundances indicate that intense emission sources and/or formation mechanisms of HULIS operate in biomass burning. Mean contributions of C in HULIS (HULIS-C) to water-soluble organic carbon (WSOC) were 35, 48, 63, and 76%, respectively, for the sample set listed. HULIS-C is the major component of the WSOC in tropical biomass burning. The data also suggest that HULIS most likely do not share common origin in the three environments studied. Differentiation among the possible formation processes was attempted by investigating the optical activity of HULIS through their (electronic and vibrational) circular dichroism properties. The urban HULIS did not show optical activity, which is in line with the concept of their major airborne formation from anthropogenic aromatics. The rural HULIS revealed weak optical activity, which may be associated with one of their important formation pathways by photo-oxidation and oligomerisation, i.e., with the formation from chiral biogenic precursors with one of the enantiomers slightly enriched. The The biomass burning of HULIS exhibited a strong effect in the vibrational circular dichroism as a clear distinction from the other two types. This was related to the contribution of the thermal degradation products of lignins and cellulose. The biomass burning of HULIS resemble Suwannee River Fulvic Acid standard more closely in some aspects than the urban and rural types of HULIS, which may be related to their common origin from plant material

A multi-parametric screening platform for photosynthetic trait characterization of microalgae and cyanobacteria under inorganic carbon limitation.

Microalgae and cyanobacteria are considered as important model organisms to investigate the biology of photosynthesis; moreover, they are valuable sources of biomolecules for several biotechnological applications. Understanding the species-specific traits of photosynthetic electron transport is extremely important, because it contributes to the regulation of ATP/NADPH ratio, which has direct/indirect links to carbon fixation and other metabolic pathways and thus overall growth and biomass production. In the present work, a cuvette-based setup is developed, in which a combination of measurements of dissolved oxygen, pH, chlorophyll fluorescence and NADPH kinetics can be performed without disturbing the physiological status of the sample. The suitability of the system is demonstrated using a model cyanobacterium Synechocystis sp. PCC6803, as well as biofuel-candidate microalgae species, such as Chlorella sorokiniana, Dunaliella salina and Nannochloropsis limnetica undergoing inorganic carbon (Ci) limitation. Inorganic carbon limitation, induced by photosynthetic Ci uptake under continuous illumination, caused a decrease in the effective quantum yield of PSII (Y(II)) and loss of oxygen-evolving capacity in all species investigated here; these effects were largely recovered by the addition of NaHCO3. Detailed analysis of the dark-light and light-dark transitions of NADPH production/uptake and changes in chlorophyll fluorescence kinetics revealed species- and condition-specific responses. These responses indicate that the impact of decreased Calvin-Benson cycle activity on photosynthetic electron transport pathways involving several sections of the electron transport chain (such as electron transfer via the QA-QB-plastoquinone pool, the redox state of the plastoquinone pool) can be analyzed with high sensitivity in a comparative manner. Therefore, the integrated system presented here can be applied for screening for specific traits in several significant species at different stages of inorganic carbon limitation, a condition that strongly impacts primary productivity

A scanning drift tube apparatus for spatio-temporal mapping of electron swarms

A "scanning" drift tube apparatus, capable of mapping of the spatio-temporal evolution of electron swarms, developing between two plane electrodes under the effect of a homogeneous electric field, is presented. The electron swarms are initiated by photoelectron pulses and the temporal distributions of the electron flux are recorded while the electrode gap length (at a fixed electric field strength) is varied. Operation of the system is tested and verified with argon gas, the measured data are used for the evaluation of the electron bulk drift velocity. The experimental results for the space-time maps of the electron swarms - presented here for the first time - also allow clear observation of deviations from hydrodynamic transport. The swarm maps are also reproduced by particle simulations

Structure analysis of proteins, peptides and metal complexes by vibrational circular dichroism

There are two principal forms of vibrational optical activity (VOA), an IR form referred to as vibrational circular dichroism (VCD) and Raman form known as Raman optical activity (ROA). This paper reports examples of the application of VCD spectroscopy for the determination of the absolute configuration and conformation of chiral molecules, e. g. cyclic beta-lactams. VCD spectroscopy can be applied for the characterization of the conformation of proteins and peptides in solution. VCD based conformational analysis of cyclic peptides is discussed. Examples are the cyclic hexapeptide cyclo(Pro(2)-Gly-Pro(2)-Gly) and cyclic peptides comprising beta-homoamino acids (trans-2-aminocyclopentane or trans-2-aminocyclohexane carboxylic acid). Structure analysis by VCD of opiate peptides, glycopeptides, peptidomimetics and chiral transition metal complexes are also discussed

Coregulated Genes Link Sulfide:Quinone Oxidoreductase and Arsenic Metabolism in Synechocystis sp. Strain PCC6803

Although the biogeochemistry of the two environmentally hazardous compounds arsenic and sulfide has been extensively investigated, the biological interference of these two toxic but potentially energy-rich compounds has only been hypothesized and indirectly proven. Here we provide direct evidence for the first time that in the photosynthetic model organism Synechocystis sp. strain PCC6803 the two metabolic pathways are linked by coregulated genes that are involved in arsenic transport, sulfide oxidation, and probably in sulfide-based alternative photosynthesis. Although Synechocystis sp. strain PCC6803 is an obligate photoautotrophic cyanobacterium that grows via oxygenic photosynthesis, we discovered that specific genes are activated in the presence of sulfide or arsenite to exploit the energy potentials of these chemicals. These genes form an operon that we termed suoRSCT, located on a transposable element of type IS4 on the plasmid pSYSM of the cyanobacterium. suoS (sll5036) encodes a light-dependent, type I sulfide:quinone oxidoreductase. The suoR (sll5035) gene downstream of suoS encodes a regulatory protein that belongs to the ArsR-type repressors that are normally involved in arsenic resistance. We found that this repressor has dual specificity, resulting in 200-fold induction of the operon upon either arsenite or sulfide exposure. The suoT gene encodes a transmembrane protein similar to chromate transporters but in fact functioning as an arsenite importer at permissive concentrations. We propose that the proteins encoded by the suoRSCT operon might have played an important role under anaerobic, reducing conditions on primordial Earth and that the operon was acquired by the cyanobacterium via horizontal gene transfer

Time sequence of the damage to the acceptor and donor sides of photosystem II by UV-B radiation as evaluated by chlorophyll a fluorescence

The effects of ultraviolet-B (UV-B) radiation on photosystem II (PS II) were studied in leaves of Chenopodium album. After the treatment with UV-B the damage was estimated using chlorophyll a fluorescence techniques. Measurements of modulated fluorescence using a pulse amplitude modulated fluorometer revealed that the efficiency of photosystem II decreased both with increasing time of UV-B radiation and with increasing intensity of the UV-B. Fluorescence induction rise curves were analyzed using a mechanistic model of energy trapping. It appears that the damage by UV-B radiation occurs first at the acceptor side of photosystem II, and only later at the donor side