Contribution Of Diatoms Research Articles

The effect of protonation site on bond strengths in simple peptides: Application of ab initio and modified neglect of differential overlap bond orders and modified neglect of differential overlap energy partitioning

A comparative study of ab initio 6-31G * and semiempirical modified neglect of differential overlap (MNDO) bond orders and MNDO diatomic energy contributions for the description of bond strenghts in neutral and protonated glycine, diglycine, triglycine, and dialanine is presented. Good correlations were found between 6-31G * and MNDO bond orders and between MNDO bond orders and diatomic energy contributions. Although bond orders and diatomic energy contributions are inherently different quantities, both predict the changes in bond strengths due to protonation to be qualitatively the same. The theoretically predicted differences in bond strengths for different protonated forms clearly indicate that in peptide fragmentation schemes one should consider even those protonated forms whose formation is not preferred energetically.

Distribution of sterols in the suspended particles of the Chang Jiang Estuary and adjacent East China Sea

The distribution of steroidal alcohols has been investigated in the suspended matter of the Chang Jiang Estuary and interpreted together with other parameters (chlorophyll a, POC, total suspended particles, and epifluorescence counts) to characterize the repartition of the biological communities of the river and adjacent East China Sea in response to rapid changes in turbidity, salinity and nutrient availability. This approach allowed us to distinguish a zonation of the phytoplanktonic population. In the dilution zone, for salinities ranging from 25 to 30%, where primary production was stronger, the sterol fingerprint indicated a major contribution of diatoms. At salinities lower than 10%, the sterol, organic carbon and chlorophyll a concentrations dropped significantly due to reduced light penetration of highly turbid waters. Above 30% salinity, subsequent to nutrient consumption in nearshore waters, concentrations reached similar values to those encountered in oligotrophic waters. Sterol distributions, after being processed using a multivariate model (Correspondence Factorial Analysis; CFA), were compared to epifluorescence counts and pigment fingerprints, allowing us to discuss the distribution of phytoplanktonic communities throughout the estuary. Factorial analysis indicated 24-ethyl-cholesta-5,22-dien-3β-ol (19) as a tracer of terrigenous inputs whereas the remaining sterols appeared as being essentially produced by autochthonous sources. The sterol fingerprint at stations 7 and 17, close to the mouth of the North and South channels, exhibited similar features to those observed in the riverine samples. The more productive waters of the dilution zone were characterized by higher amounts of autochthonous sterols such as 24-methyl-cholesta-5,22-dien-3β-ol (12) and 24-ethylcholesterol (26). Station 20 was distinguished from other stations by its high concentration of 24-methyl-cholesta-5,24(28)-dien-3β-ol (14) and peridinin suggesting a major contribution of dinoflagellates. Samples collected at different stages of the tide, at two mooring stations of the North and South channels, pointed out changes in the chemical and biological properties of the suspended particles upon tidal currents. Changes at C1 reflected the migration of the turbid river waters, whereas at C4 the terrigenous signal was less perceptible due to the landward motion of the more productive marine waters at high tide.

The role of plankton in particle flux: two case studies from the northeast Atlantic

Abstract The relationship between the vertical flux of microplankton and its standing stock in the upper ocean was determined in the subtropical (33°N, 21°W) and tropical (18°N, 30°W) northeast Atlantic in spring 1989 as part of the North Atlantic Bloom Experiment. In the subtropical area specific sedimentation rates at all depths were low (0.1% of standing stock) and 10–20% of settled particulate organic carbon (POC) was viable diatoms. The high contribution of viable diatoms, their empty frustules and tintinnid loricae to settled material characterized a system in transition between a diatom bloom sedimentation event and an oligotrophic summer situation. In the tropical area specific sedimentation rates were similar, but absolute rates (3 mg C m−2 day−1) were only about a third of those in the subtropical area. Microplankton carbon contributed only 2–6% to POC. Hard parts of heterotrophs found embedded in amorphous detrital matter suggest that particles had passed through a complex food web prior to sedimentation. Coccolithophorids, not diatoms dominated the autotrophic fraction in traps, and a shift in the composition of autotrophs may indicate a perturbation of the oligotrophic system.

A 220,000‐Year Climatic Record for the East Equatorial Atlantic Ocean and Equatorial Africa: Evidence from Diatoms and Opal Phytoliths in the Zaire (Congo) Deep‐Sea Fan

Accumulation rates of microfossil associations are independent of each other and, in addition to percentages, give indispensable information about the significance of micropaleontological data. Marine diatoms reveal that coastal upwelling in the Zaire fan region was strong during glacial stages and weaker during interglacial stages. Oceanic upwelling was intense in stages 6 and 2 and at the stage 5d–5c transition but not in stage 4. The Benguela Current did not penetrate into the Gulf of Guinea during the last 220,000 years. The PhFD index, based on the contribution of freshwater diatoms and phytoliths, is a measure of aridity in equatorial Africa. The production in the low‐salinity river plume was high in the most humid periods on land and low when the continent was arid. On the long term, nutrient supply of the Zaire River to the ocean was probably larger in humid than in arid periods. Periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals, except in the very humid interval with strong seasonal contrasts 35,000–20,000 years B.P.

EVALUATION OF DIATOM CONTENT BY COUNTING AND INFRARED ANALYSIS IN QUATERNARY FLUVIO-LACUSTRINE DEPOSITS FROM BOLIVIA

The abundance of diatom remains in quaternary lacustrine sediments was estimated by counting under the inverted microscope. Infrared analysis was performed on the same sediment samples in order to quantify the biogenic silica content. Agreement between the numbers of frustules and amount of biogenic silica shows (1) that the counting method is a useful tool for determining the diatom content in sediments, (2) that direct physical measurements are necessary for a precise evaluation of the diatom contribution to the sediments.

The response of Asterionella formosa to germanium: implications for the germanium inhibition technique for estimating diatom contribution to community productivity

SUMMARY. 1. The effect of added germanium on the assimilation of carbon by Asterionella formosa Hass. in mixed phytoplankton assemblages was measured weekly from July to December 1981 by auto‐radiography.2. Contrary lo a major assumption of the germanium‐inhibition method of partitioning primary productivity, the germanium‐induced inhibition varied considerably and with no apparent pattern.3. Inhibition values determined for laboratory cultures are probably not indicative of the responses of in situ populations, and serious errors can occur in estimating diatom contribution to total community photosynthesis. This places severe limitations on the use of the method.

Seasonal variation in diet of Chironomus plumosus (L.) and C. anthracinus Zett. (Diptera: Chironomidae) in mesotrophic Lake Erken

SUMMARY. 1. Microscopic gut content analysis of Chironomus plumosus (L.) and C. anthracinus Zett. collected from 18m depth in mesotrophic Lake Erken. revealed significant seasonal differences between the two species.2. C. plumosus dietary constituents showed greater seasonal variation than those of C. anthracinus, with diatom contribution to the gut contents reflecting temporal changes in the phytoplankton.3. Overall the percentage of gut content constituted by detritus, algae, animal remains, and inorganic matter averaged 96%, 4%, 0.4% and 0.03% for C. plurnosus and 97%, 3%, 0.6% and 0.03% for C. anthracinus.4. Coefficients ot dietary overlap for non‐detrital foods decreased markedly from August to September. During this period the proportion of centric diatoms in the guts of C. plumosus increased by 94% while no marked changes were noted in C. anthracinus.5. C. ptttmosus ingested more diatoms than C. anthracinus, especially during diatom blooms in spring and autumn. These results are consistent with the known differences in feeding behaviour between these two speeies.

Partitioning of MNDO energy and description of bonding

The MNDO energy is partitioned into monatomic and diatomic contributions. A term E R, the resonance integral contribution, is separated out from the diatomic contribution E AB. A nonclassical term, E NC, as the sum of E R and the exchange integral contribution E K, as also separated out. Fairly good correlations of E AB, E R, and E NC with bond length show that they can serve as a measure of bonding. E R gives the best correlation, and E AB the worst, showing that E R is the best measure of covalent bonding, and E NC the second. E AB seems to be an overall measure of bond strength, but this is not true. The reason is that the monatomic contributions to energy also take a share in bond strength. Bond energies are also correlated with these energy contributions. The correlations are not very good, because bond energy is defined by some arbitrary postulates and does not serve as a rational measure of bond strength.

Sources of neutral lipids in a temperate intertidal sediment

The compositions of sterol, alcohol and ketone fractions from an oxic intertidal surface sediment from Corner Inlet. Victoria, Australia, have been examined by capillary gas chromatographymass spectrometry and related to the lipids of diatoms cultured from the sediment and to lipids of the sea-grass Zostera muelleri. Of the more than thirty sterols in the sediment most appear to derive from diatoms, including the major sterol 24-methylcholesta-5.22E-dien-3β-ol. Small amounts of 24-ethylcholesterol probably derive from Zostera, with a minor diatom contribution. 5α-stanols, both fully saturated and with a side-chain double bond, represented ca. 14% of the total sterols: a significant proportion of these are probably derived from marine invertebrates. These organisms also contribute C 26 sterols. most of the cholesterol and possibly small amounts of Δ-sterols. The data suggest that in situ biohydrogenation of stenols was not a major process in sterol transformation in the surface oxic sediment. Alcohols ranged from C 12 to C 30 and showed an unusual abundance of unsaturated components with Δ 9-16:1 being the major constituent. The long-chain alcohols probably originate largely from Zostera but the shorter-chain. C 12-C 20. alcohols are at least partly derived from wax esters of unknown origin. Diatoms do not contribute significant amounts of alcohols. Ketones were not major constituents of the sediment and consisted mainly of 6.10.14-trimethylpentadecan-2-one and a series of n-alkan-2-ones ranging from C 16 to C 33. The latter showed a similar distribution to that of the n-alkanes but the correspondence was not sufficient to substantiate a product-precursor relationship. Very long-chain C 3- C 39 unsaturated methyl and ethyl ketones, which may originate from the marine unicellular alga Emiliania huxleyi. were present in low concentration.

Quantum-chemical study of reaction routes and centers in the interaction of propylene with an oxide catalyst surface

The MINDO/3 method was employed to study the interaction of propylene with the surface of gallium oxide for various orientations of the molecule with respect to the cluster. The heterolytic dissociation of the CH bond accompanied by the formation of an allyl complex was shown to proceed with the methylhydrogen oriented on the oxygen ion and with the methylene group turned aside from the cluster surface. The heat of the process (≈10 kcal/mol) was close to that observed for adsorption forms which lead to partial oxidation products. If the hydrogen is oriented on the gallium ion, stable bonds form between the hydrocarbon and the cluster oxygen. In this case, the heat of the process is relatively high (≈30 kcal/mol). This is close to the heat of formation of surface oxidized structures which are precursors of complete oxidation products. The diatomic energy contributions from the interaction of the molecule with each of the reaction centers (oxygen and gallium ions) have been analyzed. The energy barriers arise from the Coulomb repulsion of the molecule by the cation at large distances, which is displaced by a strong stabilizing covalent binding at small distances. Interaction between the molecule and the anion, in all cases, provides a stabilizing function. The requirements of the optimal catalyst for allyl activation of olefins have been formulated.

Calculation of the H4 Potental Energy Surface by a Semi-empirical Method

Abstract A semi-empirical method recently proposed for the calculation of the potential energy surface of the H3 system is extended to a larger polyatomic H4 system. The energy formula is based on the valence-bond formulation and is expressed as functions of many multiple exchange integrals. These integrals can be decomposed into “diatomic” contributions by using the Mulliken approximation. The diatomic contributions are estimated from accurate values of the H2 molecule. Calculations of the H4 potential energy for the symmetric linear, linear equidistant, and square planar configurations are presented. The present method is of use for dynamical studies of the H2+D2 exchange reaction.

Application of intermolecular SCF-perturbation theory to the regioselectivity in the Diels-Alder reaction

Intermolecular perturbation theory in the density matrix formalism is applied to investigate the directional behaviour of an electron-donating (-CH3) or an electron-accepting (-CN) group in 1- or 2-substituted butadienes in the Diels-Alder reaction with acrylonitrile. The calculated CNDO/2 perturbation energies are analysed in three different ways by considering: a) the different perturbation energies, b) the diatomic parts of the interaction energy and c) the HOMO-LUMO contribution to the second-order energy. The regioselectivity is due to a subtle balance of charge-transfer interactions and steric effects of the substituents on the diene and the dienophile. The changes of intra- and intermolecular diatomic energy contributions are correlated with the process of bond formation and bond weakening. The intermolecular perturbation energies are dominated by pairwise interactions between the terminal C-atoms and by the secondary Woodward-Hoffmann interaction. These three localized interactions determine the endo addition and reflect the orienting power of the substituents.

Light, nitrogen, and phosphorus limitation of edaphic algae in a delaware salt marsh

The effects on edaphic algae associated with a pure stand of the cord grass, Spartina alterniflora Loisel of manipulating light intensity and additions of inorganic nitrogen and phosphorus as fertilizers to the marsh surface have been investigated for one year. The standing crop of edaphic algae as measured by chlorophyll a production was limited only by phosphorus supplies during fall and winter, by both phosphorus and nitrogen in spring, and only by nitrogen during the summer. Since the responses were in phase with the seasonal fluctuations in the concentration of nitrogen and phosphorus, it is concluded that the flood tide is the major source of nitrogen and phosphorus compounds for edaphic algal growth. Reduction in the quantity of light reaching the edaphic algae by Spartina cover is always a limiting factor for the standing crop. A gradient in the composition of the algal flora is directly related to light intensity, and indicates that this factor determines the relative contribution of diatoms and filamentous algae to the community. The interaction of light intensity and nutrients in regulating the production of edaphic algae and cord grass on the marsh under study over a yearly cycle has also been investigated.

The contribution of diatoms to the sediments of Crystal Lake, Vilas County, Wisconsin

The contribution of diatoms to the sediments of Crystal Lake, Vilas County, Wisconsin