bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal variability of the phytoplankton community structure in the North Water Polynya, investigated using pigment biomarkers
Authors: Vidussi Francesca , Roy Suzanne , Lovejoy Connie , Gammelgaard Marie , Thomsen Helge Abildhauge , Booth Beatrice , Tremblay Jean-Eric , Mostajir Behzad
Published: February 2005

Phytoplankton taxonomic pigments were measured by high-performance liquid chromatography (HPLC) during a 3-month survey (AprilJune 1998) in the North Water (NOW) Polynya (Canadian Arctic) to investigate changes in phytoplankton biomass and composition and the physicalchemical factors that influence these changes. A phytoplankton bloom with high chlorophyll a (Chl a) concentrations (up to 17.45 mg·m3at 15 m) occurred in mid-May along the Greenland coast in the southeastern part of the NOW Polynya. The initiation of the phytoplankton bloom was linked to shallow mixed-layer depths. The contribution of the different phytoplankton groups to Chl a inferred using a factorization program (CHEMTAX) indicated that the bloom was diatom-dominated (maximum 94% diatoms). The phytoplankton community structure was influenced by the water mass characteristics and the surface circulation pattern. Autotrophic flagellates dominated in April and May along the Canadian coast, where cold Arctic waters with relatively deep mixed layers were found. In contrast, diatoms dominated in May along the Greenland coast in warmer water masses of Atlantic origin and during June in the whole polynya, except in the southernmost part.
Inverse modelling of trophic flows through an entire ecosystem: the northern Gulf of St. Lawrence in the mid-1980s
Authors: Savenkoff Claude , Castonguay Martin , Vézina Alain F , Despatie Simon-Pierre , Chabot Denis , Morissette Lyne , Hammill Mike O
Published: February 2005

Mass-balance models using inverse methodology have been constructed for the northern Gulf of St. Lawrence ecosystem in the mid-1980s, before the groundfish collapse. The results highlight the effects of the major mortality sources (fishing, predation, and other sources of mortality) on the fish and invertebrate communities. Main predators of fish were large cod (Gadus morhua) followed by redfish (Sebastes spp.), capelin (Mallotus villosus), and fisheries. Large cod were the most important predator of small cod, with cannibalism accounting for at least 44% of the mortality of small cod. The main predators of large cod were harp (Phoca groenlandica) and grey (Halichoerus grypus) seals. However, predation represented only 2% of total mortality on large cod. Mortality other than predation dominated the mortality processes at 52% of the total, while the fishery represented 46%. Tests were performed to identify possible sources of this unexplained mortality. The only way to significantly reduce unexplained mortality on large cod in the model was to increase landings of large cod above those reported. This suggests that fishing mortality was substantially underestimated in the mid-1980s, just before the demise of a cod stock that historically was the second largest in the northwest Atlantic.
Use of length-based models to estimate biological parameters and conduct yield analyses for male Dungeness crab (Cancer magister)
Authors: Zhang Z , Hajas W , Phillips A , Boutillier J A
Published: February 2005

Length-based models were developed for the male Dungeness crab (Cancer magister) population on the Fraser delta near Vancouver, British Columbia. The models incorporate the probability of moulting, moult increments, natural mortality during moulting and non-moulting periods, direct fishing mortality, and handling mortality that occurs when sublegal-sized crabs are caught and released. The models were used to investigate how long-term yield might be affected by the combination of handling mortality and an intensive fishery. The models were calibrated to survey data, and key biological parameters were estimated. The probability of moulting is near one for male crabs in the 130- to 150-mm carapace width range and decreases as crabs get larger. There is a 70.1% probability a crab will survive the 1-month period beginning with a moult. The non-moulting natural mortality rate is 0.97 year1. When handling mortality is incorporated into the model, yield per recruit increases with the exploitation rate until it reaches approximately 94%. F0.1 is equivalent to 70%. An approach was developed to calculate the threshold ratio of discarded to retained crabs beyond which fishing would reduce the long-term yield.
Experimental evaluation of ontogenetic diet transitions in summer flounder (Paralichthys dentatus), using stable isotopes as diet tracers
Authors: Witting David A , Chambers R Christopher , Bosley Keith L , Wainright Sam C
Published: February 2005

We examined the rate of isotopic change of nitrogen (N) and carbon (C) and isotopic fractionation at two temperatures during several ontogenetic diet transitions in summer flounder (Paralichthys dentatus). We examined prefeeding larvae as they metabolize the maternal source of nutrition and evaluated three diet transitions in the early life stages of this species: (i) yolk dependency to first feeding on zooplankton, (ii) one zooplankton (rotifers) to another (Artemia), and (iii) zooplanktivory to piscivory. We used experimental results and simulations to contrast time- versus growth-based models for estimating parameters of isotopic change and fractionation. All rates of isotopic change were lowest for the transition between zooplanktivory and piscivory, most rapid for the transition from yolk dependency to first feeding, and generally lower at cooler temperatures. Estimates of fractionation were greater for N (2.83.8) than for C (0.230.91) but appeared to be unaffected by water temperature or fish life stage. Simulation results suggested that parameter estimates of isotopic change and fractionation may be compromised when growth rates are low unless sampling design is modified to address slow growth rates. We conclude that sampling strategy and the model used can influence the accuracy and precision of estimates of isotopic change and fractionation.
Bimodal population size distributions and biased gillnet sampling
Authors: Finstad Anders Gravbrøt , Berg Ole Kristian
Published: February 2005

Bimodal size distributions have been commonly observed in Arctic char (Salvelinus alpinus). We document an example of such bimodality caused solely by biased gillnet sampling. The observed bimodality was a direct artefact of the sampling method resulting from an abrupt increase in gillnet catchability of fish larger in total length than between 25 and 30 cm. Mean gillnet selectivity (catchability) of char in the upper mode of the observed bimodal size distribution was about 40 times higher than the corresponding value for char in the observed lower mode. Fish of intermediate size, lacking in the gillnet samples, were present in the population and readily obtainable by electrofishing. The observed size difference in gillnet vulnerability is likely to result from behavioural changes following ontogenetic niche shifts.
Effects of a native crayfish (Orconectes virilis) on the reproductive success and nesting behavior of sunfish (Lepomis spp.)
Authors: Dorn Nathan J , Mittelbach Gary G
Published: February 2005

While crayfish are traditionally considered fish prey, they are capable of feeding on substrate-bound fish eggs and their introductions have been blamed for the decline in fish populations in Europe and North America. To investigate their potential effects on fish reproductive success we measured the effects of a native crayfish (Orconectes virilis) on the reproductive success of two substrate-nesting sunfish, pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus), in replicated pond experiments. Crayfish were observed feeding on eggs in both experiments. Crayfish presence delayed successful reproduction by pumpkinseeds in densely vegetated ponds, resulting in lower young-of-the-year biomass in ponds with crayfish. In the second experiment, with bluegills in less-vegetated ponds, crayfish prevented successful reproduction entirely. However, when we added crayfish-proof exclosures to the crayfish ponds late in the summer, bluegills located the crayfish-free habitat and successfully reproduced inside the exclosures (1 month after first successful reproduction in control ponds). The results of these experiments demonstrate the potential strong negative effects of crayfish on sunfish reproduction and suggest that the spatial distribution of crayfish and other egg predators may influence fish nesting behaviors and habitat choices. Further studies are needed to determine the magnitude of crayfish effects in natural lakes and ponds where sunfish and crayfish co-occur.
Widespread consumption-dependent systematic error in fish bioenergetics models and its implications
Authors: Bajer Przemyslaw G , Whitledge Gregory W , Hayward Robert S
Published: February 2005

Data from laboratory evaluations of seven fish bioenergetics models (BEMs) were used to investigate possible associations between BEM prediction error in relative growth rate (RGRerror) and levels of model input variables: mean daily food-consumption rate and fish body weight. Correlation between RGRerror and fish body weight was found in three BEMs applied under submaintenance feeding conditions. A strong correlation between RGRerror and mean daily consumption level was observed in all models over full consumption ranges; consumption level explained 70%96% of variation in RGRerror. All BEMs underestimated (by 2- to 5-fold) growth at lower consumption levels and overestimated (by 2- to 3-fold) growth at higher consumption levels. RGRerror values associated with higher consumption levels were greater (up to 22 cal·g1·day1) than those at lower consumption levels (up to 10 cal·g1·day1). Correlation between consumption rate and RGRerror in all seven models indicates widespread systematic error among BEMs that likely arises from deficiencies in consumption-dependent model parameters. Results indicate that many BEMs are substantially inaccurate when predicting fish growth from higher feeding rates or estimating consumption from higher growth rates, even when higher consumption levels or growth episodes are of short duration. Findings obtained under submaintenance feeding conditions indicate that additional body-weight- and consumption-dependent terms should be added to BEM subequations for routine metabolism to account for metabolic reduction.
Simultaneous identification and correction of systematic error in bioenergetics models: demonstration with a white crappie (Pomoxis annularis) model
Authors: Bajer Przemyslaw G , Hayward Robert S , Whitledge Gregory W , Zweifel Richard D
Published: February 2005

Recent evidence indicates that important systematic error exists in many fish bioenergetics models (BEMs). An approach for identifying and correcting this error is demonstrated with a white crappie (Pomoxis annularis) BEM. Model-predicted trajectories of growth and cumulative consumption for 39 individual white crappie obtained from six 60-day laboratory experiments diverged from observed values by up to 42.5% and 227%, respectively, indicating systematic error in the BEM. To evaluate correlates of the systematic error, model prediction errors were regressed against three major input/output variables of BEMs that were covered by the laboratory experiments: fish body weight (80341 g), temperature (2330 °C), and consumption level (0.5%6.2% daily). Consumption level explained >80% of the prediction error for growth and consumption. Two multiple regression equations containing body weight, temperature, and consumption variables were developed to estimate growth prediction error (R2 = 0.96) and consumption prediction error (R2 = 0.86), and incorporated into the white crappie BEM to correct its predictions. Cross-validation indicated that growth and consumption prediction error was reduced 2- to 4-fold by correction. Given recent evidence of widespread systematic error and increasing application rates of BEMs, the efficient error-identification and -correction approach described appears broadly applicable and timely.
Diurnal variation in acoustic densities: why do we see less in the dark?
Authors: Hjellvik Vidar , Godø Olav Rune , Tjøstheim Dag
Published: February 2005

Diurnal fluctuations in total integrated echo abundance and in vertical density profiles were examined using data from the Norwegian combined acoustic and bottom-trawl survey for demersal fish during winter in the Barents Sea. The total echo abundance was about 40%50% higher at day than at night. An unknown amount of fish was lost close to the seabed in the acoustic dead zone, but the systematic changes in the near-bottom vertical density profiles did not indicate that migration in and out of the dead zone was the major reason for the large diurnal differences in echo abundance. A more plausible explanation could be that diurnal changes in fish behaviour affect the mean acoustic target strength. Based on the present study, we recommend that the time series of acoustic surveys should be re analysed, taking the diurnal bias into account. Any comparison of the fish densities indicated by trawl and acoustic surveys will suffer if this bias is not corrected. We believe that model development utilizing this type of information is crucial for future ecosystem-based monitoring.
Predator-recognition training of hatchery-reared walleye (Stizostedion vitreum) and a field test of a training method using yellow perch (Perca flavescens)
Authors: Wisenden Brian D , Klitzke Josh , Nelson Ryan , Friedl David , Jacobson Peter C
Published: February 2005

Fishes reared in captivity are predator-naïve and suffer large predation mortality when stocked into lakes with a full complement of predators. We tested the potential of predator training to enhance post-stocking survival of hatchery-reared walleye (Stizostedion vitreum). In the first part of the study, we found that walleye (i) use chemical cues for assessing predation risk, (ii) do not have innate recognition of the odor of northern pike (Esox lucius) as an indicator of predation, and (iii) associate predation risk with pike odor after a single simultaneous encounter with pike odor and chemical alarm cues from walleye skin. In the second part of the study, we attempted to mass-train yellow perch, Perca flavescens (as a surrogate for walleye), to fear pike odor. Perch response to pike odor was not changed by placing sponge blocks containing pike odor and perch alarm cues around the perimeter of a pond. On pre- and post-training assays, perch avoided traps scented with perch alarm cues, but did not avoid traps labeled with pike odor or water. We conclude that recognition training offers potential as a management tool for walleye, but significant logistic challenges must be solved before it can be implemented.
Simulation and experimental measurement of side-aspect target strength of Atlantic salmon (Salmo salar) at high frequency
Authors: Lilja Juha , Marjomäki Timo J , Jurvelius Juha , Rossi Tuomo , Heikkola Erkki
Published: February 2005

Numerical simulations and empirical measurements of swimming Atlantic salmon (Salmo salar) were used to describe the effects of fish behavior on side-aspect target strength (TS). Simulation results were based on the numerical solution of the Helmholtz equation with the finite element method (FEM). A three-dimensional geometric model approximated the shape of the swimbladder of an Atlantic salmon. Numerical simulations were used to study the dependence of TS on the fish length, orientation, and swimming behavior. The results showed strong variation in TS, both when the side-aspect angle was changed and when the swimbladder was bent to the direction of the sonar beam. A total of 11 swimming adult Atlantic salmon 62107 cm long were measured with a horizontally aimed echosounder (200 kHz) and video camera, and the experimental results were compared with the corresponding simulation results. The linear regression between mean TS and the logarithm of fish length (L, cm) was TS = 24.4log10(L)  72.9 dB. The strong variability of TS owing to the orientation and bending of the fish and large L/λ ratios reduces the usefulness of TS alone for fish size estimation or species discrimination.
A long-term rusty crayfish (Orconectes rusticus) invasion: dispersal patterns and community change in a north temperate lake
Authors: Wilson Karen A , Magnuson John J , Lodge David M , Hill Anna M , Kratz Timothy K , Perry William L , Willis Theodore V
Published: February 2005

Rusty crayfish (Orconectes rusticus) were first observed in Trout Lake, Wisconsin, in 1979 and took 19 years to completely disperse around the littoral zone, advancing at an average rate of 0.68 km·year1. With the invasion of rusty crayfish, we found that fishes that share prey taxa with crayfish declined in numbers over time, but piscivorous fish species did not change in abundance. Snails declined from >10 000 to <5 snails·m2 in one of the first invaded areas. Mean abundance of Odonata, Amphipoda, and Trichoptera decreased significantly lake-wide. Resident crayfish species nearly disappeared, although total crayfish abundance, driven by high abundances of rusty crayfish, continued to rise. Submerged macrophyte species richness declined by as much as 80% at some locations. Together these responses demonstrate dramatic long-term changes in the littoral zone biota of Trout Lake. Continued invasions of similar lakes in the region suggest that these impacts are occurring on a region-wide basis with potentially irreversible effects on communities and ecosystems. Only through long-term natural experiments such as this study can researchers ascertain the full extent of invasions and their impacts on community and ecosystem process that respond at spatial and temporal scales not captured in mesocosm studies.
Efficient photodecarboxylation of 3- and 4-acetylphenylacetic acids in aqueous solution
Authors: Huck Lawrence A , Xu Musheng , Forest Kaya , Wan Peter
Published: February 2005

The photochemistry of 3- and 4-acetylphenylacetic acids (6 and 7) has been studied in aqueous solution. This work is a continuation of research efforts aimed at understanding the structural effects on the efficacy for benzyl carbanion photogeneration via photodecarboxylation. The nitro group (at the 3- and 4-positions) is known to be an exceptionally good activating group on the benzene ring  because of its enhanced electron-withdrawing effect in the excited triplet state  for photodecarboxylation and the related photo-retro-aldol type process. It is shown in this work that the acetyl group is an equally good activating group for the photodecarboxylation. Thus, the photochemistry of 6 and 7 parallels much of what was observed for the corresponding nitrophenylacetic acids 1 and 2. Both 6 and 7 photodecarboxylate efficiently (Φd = 0.60 and 0.22, respectively, at pH 7) via the carboxylate form, to give observable (by laser flash photolysis) benzyl carbanion or related intermediates. The meta isomer 6 displays an acid-catalyzed pathway for photodecarboxylation at pH < 3 and along with its enhanced overall reactivity, is consistent with a meta effect of the acetyl group. Triplet state reactivity is inferred from sensitization and laser flash photolysis experiments. Based on the results of this work, the acetyl group may now be viewed as an "enhanced" electron-withdrawing group (in the excited state) when attached to a benzene ring (i.e., in acetophenone derivatives) that is capable of inducing ionic reactions, which is not the traditional photochemistry that is expected from such compounds.Key words: photodecarboxylation, acid catalysis, acetophenone, photogenerated carbanion, enol, enolate.
Effect of cyclodextrins on iron-mediated dechlorination of trichloroethylene  A proposed new mechanism
Authors: Shirin Salma , Buncel Erwin , vanLoon Gary W
Published: February 2005

This paper evaluates the possibility of using cyclodextrins (CDs) as solubility-enhancing agents that could be employed to increase the rate of the mass delivery of trichloroethylene (TCE) to an iron wall where dechlorination will occur. Dechlorination of TCE by zero-valent iron was performed in the absence and in the presence of CDs in batch (static) and column (dynamic) systems. The presence of CDs slowed the overall degradation of TCE. The effect of various concentrations of different CDs on the rate of TCE degradation was evaluated, and it was found that as the CD concentration increased, reaction rate decreased. However, the overall decrease in reaction rate could not be explained solely on the basis of TCE:CD host-guest complexation. A novel mechanism involving CD binding to the iron surface, in addition to TCE:CD complexation, was proposed, and this enabled satisfactory interpretation of the kinetic data. A central feature of the proposal is that Fe:CD binding impedes electron transfer from the underlying iron metal to the TCE molecule. The overall rate of TCE degradation by zero-valent Fe in the presence of CDs is governed by several factors: the extent of binding of CD with the iron surface, the binding constant between CD and TCE, and the degradation of complexed TCE (TCE:CD), where CD is, in turn, associated with the iron surface. It appeared that CD binding to the iron surface depends largely on the type of substituent groups present in the β-CD derivatives as well as their degree of substitution. Association constants for the Fe:CD interaction were determined. The new hypothesis explained well both batch and column data, and the magnitude of Fe:CD binding constants was found to be similar in the two systems. Key words: cyclodextrin, trichloroethylene, zero-valent iron, reductive dechlorination.
Crystal structure, spectroscopic studies, and nonlinear optical (NLO) properties of Schiff base metal complexes containing an N, S donor ligand
Authors: Xue Zhao-Ming , Tang Ying-Wen , Wu Jie-Ying , Tian Yu-Peng , Jiang Min-Hua , Fun H -K , Usman A
Published: February 2005

A new ligand, 4-dipropylaminobenzaldehyde thiosemicarbazone (abbreviated as HL), and its complexes ML2 (M = Ni, Pd, and Cu) have been synthesized and fully characterized by elemental analyses, EI-MS, IR and UVvis spectroscopy, and photoluminescence measurements. All of the compounds exhibit a bluegreen color with dual fluorescence in DMF solution. The quantum yield ratio (Φ′(CT)/Φ(LE)) decreases in the order NiL2 > HL > PdL2 > CuL2. The ligand HL crystallizes in the monoclinic system, space group P21/n, with a = 15.1680, b = 8.5573, and c = 25.3920 Å, β = 100.3457°, and V = 3242.2 Å3. The nickel complex (NiL2) crystallizes in the triclinic system, space group Pī, with a = 8.3093, b = 9.7540, and c = 10.2802 Å, α = 101.383°, β = 107.693°, γ = 96.703°, and V = 764.12 Å3. In these complexes, HL has lost a proton from its tautometric thiol form and acts as a single negatively charged bidentate ligand coordinating to the nickel ion via the mercapto sulfur and β-nitrogen atoms. The geometry around Ni(II) is almost square-planar with two equivalent NiN and two equivalent NiS bonds. The monomeric structure of HL or NiL2 is extended into an infinite two-dimensional network via hydrogen bonds. The two-photon absorption of HL and ML2 solutions (in DMF) was measured at 532 nm by the open-aperture Z-scan technique. Key words: crystal structure, metal complex, dual fluorescence, NLO.
The complex photochemistry of 2,3-dibenzylidenesuccinates
Authors: Assoumatine Tokouré , Yvon Brigitte L , Charlton James L
Published: February 2005

The photochemistry of diethyl E,E-2,3-(3,4,5-trimethoxybenzylidene)succinate (8) is solvent dependent. In both protic and aprotic solvents, there is a photoequilibrium established between 8 and its E,Z-isomer (9). In chloroform at high light intensity, very little 9 is formed and the main product is 1,4-dihydronaphthalene (10), formed via photoinduced intramolecular [1,3]-sigmatropic hydrogen shift within an intermediate 1,8a-dihydronaphthalene (11). In protic solvents, irradiation of either 8 or 9 ultimately gives primarily the cis-1,2-dihydronaphthalene product (13), along with smaller amounts of the trans isomer (14). By using deuterated solvents, it was shown that 13 and 14 are formed by solvent protonation (or deuteration) of the 1,8a-dihydronaphthalene intermediate (11 or 12). Key words: 2,3-dibenzylidenesuccinate, photocyclization, dihydronaphthalene, lignan.
A novel crown ether generation containing the pyrilium heteroaromatic cation  Synthesis, characterization, and solid-phase 13C NMR
Authors: Moghimi Abolghasem , Rastegar Majid Faal , Ghandi Mehdi
Published: February 2005

The synthesis and structural characterization of two members, 5 and 6, of a novel generation of crown ethers containing the pyrilium cation are reported. These two compounds contain two and three benzo-9-crown-3 (B9C3) units, respectively, connected to the 2 and 6 or 2, 4, and 6 positions of a central pyrilium cation. The crown ethers 5 and 6 were obtained from the condensation reaction of appropriate aldehydes and methyl ketones in the presence of POCl3. A variety of physicochemical methods including electrospray mass spectroscopy, solution 1H and 13C NMR, and solid-phase 13C NMR were applied for structural characterization. The 1H and 13C NMR studies indicate rapid rotation of the B9C3 unit about the CC bond that connects the two units to each other. The solid-phase 13C NMR spectra of these two crown ethers reveal that there are deviations from planarity for the two phenyl rings attached at the 2 and 6 positions of the central pyrilium cation.Key words: crown ether, pyrilium, solid-phase NMR, crownpyrilium, heteroaromatic.
Asymmetric formal synthesis of ()-cryptosporiopsin, a metabolite of Phialophora asterris, and its 3-deschloro congener
Authors: MaGee David I , Mallais Tammy , Strunz George M
Published: February 2005

An asymmetric formal synthesis of the fungal metabolites ()-cryptosporiopsin and ()-3-deschloro crypto sporiopsin has been accomplished. The asymmetry was introduced via a diastereoselective [2+2]-cycloaddition between an enoxy-ester, bearing a bulky chiral auxiliary, and dichloroketene. Diastereomeric ratios of 10:1 were obtained from the reaction mixture, but this could be increased by simple crystallization. Completion of the synthesis was only accomplished after the serendipitous discovery of a base-catalyzed rearrangement to furnish the requisite 3-chloroenone moiety.Key words: diastereoselective [2+2]-cycloaddition, rearrangement, chiral auxiliary.
Scavenging of photogenerated singlet molecular oxygen and superoxide radical anion by sulpha drugs - Kinetics and mechanism
Authors: Díaz Marta , Luiz Marta , Bertolotti Sonia , Miskoski Sandra , García Norman A
Published: February 2005

The ability of the sulfanilic antibiotics (SDs), dapsone (DAP), sulfisoxazole (SFX), sulfadiazine (SFD), and sulfanilic acid (SFNA) to act as scavengers of the visible-light-photogenerated species superoxide radical anion (O2·) and singlet molecular oxygen (O2(1Δg)) was studied employing the natural pigment riboflavin (Rf) and the artificial dye Rose Bengal as photosensitisers. A complex mechanism, common to all the SDs studied, was elucidated through stationary photolysis, polarographic detection of oxygen uptake, fluorescence spectroscopy, time-resolved phosphorescence detection of O2(1Δg), and laser flash photolysis. Visible-light irradiation of aqueous and aqueous methanolic solutions of Rf (ca. 0.02 mmol/L) plus SD (ca. 0.5 mmol/L) photogenerated excited singlet and triplet Rf (1Rf* and 3Rf*). Under these experimental conditions, only 3Rf* is quenched either by oxygen, giving rise to O2(1Δg) by electronic energy transfer to dissolved ground-state oxygen, or by SD, yielding semireduced Rf through an electron-transfer process. Complementary experiments performed in pure water employing superoxide dismutase and sodium azide inhibition of oxygen uptake, in parallel with laser flash photolysis data, showed that O2· is also formed, probably due to the reaction of the anion radical from Rf with dissolved oxygen, yielding also neutral, ground-state Rf. Both active oxygen species, namely, O2· and O2(1Δg), are quenched by the SDs and, as a result, photodegradation of the SDs  each to a different extent  and photodegradation of the sensitiser itself were observed. The SDs that kinetically behave as the better physical quenchers of O2(1Δg), which are in principle good candidates as photoprotectors, namely, DAP and SFD, suffer photooxidation, exhibiting high to moderate oxygen consumption rates due to the O2· oxidative pathway, whereas for SFNA and SFX, oxidation predominantly occurs through an O2(1Δg)-mediated mechanism. Microbiological results for SFX, taken as a representative SD, indicate that the photodegradation of the drug, upon visible-light Rf-sensitised irradiation, is accompanied by a net loss in bacteriostatic activity.Key words: photooxidation, singlet oxygen, superoxide radical anion, sulpha drugs.
Platinum pyridinecarboxaldimine complexes containing boronate esters
Authors: Darwish Hanni A , Scales Stephen J , Horton Jennifer L , Nikolcheva Liliya G , Zhang Haiwen , Vogels Christopher M , Saleh Mazen T , Ireland Robert J , Decken Andreas , Westcott Stephen A
Published: February 2005

Condensation of 2-pyridinecarboxaldehydes with 2-, 3-, and 4-H2NC6H4Bpin (pin = 1,2-O2C2Me4) gave the corresponding boron-containing pyridinecarboxaldimines (NNBpin). Addition of these ligands to [PtCl2(coe)]2 (coe = cis-cyclooctene) gave complexes of the type cis-PtCl2(NNBpin) in moderate yields. The platinum complexes have been examined for their potential cytotoxicities against OV2008 (human ovarian carcinoma) and the analogous cisplatin-resistant cell line C13. Key words: boronate esters, pyridinecarboxaldimines, cytotoxicity, platinum, boron.
A novel unexpected two-dimensional layer-like luminescent dysprosium coordination polymer [Dy2(phth)3H2O]nby hydrothermal synthesis
Authors: Song Yi-Shan , Yan Bing , Chen Zhen-Xia
Published: February 2005

Assembling potassium acid phthalate (KHphth) and dysprosium nitrate, a novel luminescent two-dimensional layer-like dysprosium coordination polymer with the formula [Dy2(phth)3H2O]nhas been synthesized by a hydrothermal process. It is unexpected that the complex exhibits a new coordination mode with phthalate and an asymmetrical structure for the two dysprosium fragments in the molecular unit. The title coordination polymer crystallizes in the mono clinic system, space group P21/c, with lattice parameters a = 7.913(2) Å, b = 26.360(7) Å, c = 11.563(3) Å, β = 106.864(3)°, V = 2308.3(11) Å3, Dc = 2.404 Mg/m3, Z = 4, F(000) = 1576, GOF = 1.079, R1 = 0.0282. The luminescence spectrum shows that the blue emission intensity of the4F9/2→6H15/2transition is stronger than the yellow emission intensity of the4F9/2→6H13/2transition. Key words: dysprosium (III), two-dimensional layer-like coordination polymer, molecular structure, luminescence, hydrothermal synthesis.
Chemical-shift link to the KamletTaft β parameter
Authors: Brown Keith C , El-Bermani Muhsin , Weil John A
Published: February 2005

In investigating liquid-phase proton NMR spectra of 2,2-dimethyl-1-(2,4,6-trinitrophenyl)hydrazine in various solvents, we have found an interesting correlation, at sufficiently low temperatures T, between the chemical-shift difference (splitting) of the picryl proton peaks, measured as f(T), and the KamletTaft hydrogen-bonding basicity parameter β. The observed solvolytic effect offers a convenient way of determining and checking the value of the empirical parameter β. The phenomenon discloses that the molecular geometric configuration is affected vividly by hydrogen bonding with the surrounding solvent molecules. It follows that the internal conformation interchange taking place (in a higher T range) is not in fact solely a unimolecular property.Key words: picryl proton NMR, chemical shift, solvent effects, hydrogen bonding, KamletTaft β.
Chemical oxidation of fluoroanilines to fluoroazobenzenes and fluorophenazines with potassium ferricyanide and potassium hydroxide
Authors: Leyva Elisa , Medina Concepción , Moctezuma Edgar , Leyva Socorro
Published: February 2005

The oxidation of several fluoroanilines with potassium ferricyanide and potassium hydroxide is described. In this oxidation, the major products are fluoroazobenzenes. In the case of 2-fluoro-substituted anilines, heterocyclic fluorophenazines were obtained in low to moderate yields. The optimal conditions for the reaction and the mechanism are presented.Key words: oxidation, fluoroanilines, fluoroazobenzenes, fluorophenazines.
Comparison of the free radical scavenger activities of quercetin and rutin  An experimental and theoretical study
Authors: Aliaga Carolina , Lissi Eduardo A
Published: February 2005

Natural radical scavengers have recently received considerable interest owing to the role of free radicals in causing oxidative stress in living organisms. Flavonoids constitute one of the most important families of molecules with antioxidant activities, a characteristic associated with the presence in their structure of hydroxyl groups bound to aromatic rings. Quercetin is a potent antioxidant whose high reactivity could be associated with the presence of the OH group in the C ring. To address the role of this group in quercetin's free radical scavenging capacity, we have carried out experimental determinations and theoretical calculations regarding the reactivity of quercetin and rutin. The reactivity of both compounds towards free radicals was assessed employing the radical anion 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) and peroxyl radicals. These measurements indicate that quercetin is more reactive and has more reactive centers than rutin, suggesting that the extra OH group located in the C ring could directly contribute to reactivity of quercetin. This conclusion is in agreement with the evaluation of local reactivity indexes, such as the Fukui function.Key words: quercetin, rutin, antioxidant activity, ABTS, peroxyl radicals, Fukui function, local reactivity index.
The 2-oxo-3,3,5,5-tetramethylcyclopentanecarboxylic acid ketoenol system in aqueous solution  Generation of the enol by flash photolytic Wolff rearrangement of 2-diazo-4,4,6,6-tetramethylcyclohexane-1,3-dione followed by hydration of the acylketene thus formed
Authors: Chiang Y , Kresge A J , Nikolaev V A , Onyido I , Zeng X
Published: February 2005

Flash photolysis of 2-diazo-4,4,6,6-tetramethylcyclohexane-1,3-dione in aqueous solution produced 2-oxo-3,3,5,5-tetramethylcyclopentylideneketene, which underwent hydration to the enol of 2-oxo-3,3,5,5-tetramethylcyclo pentanecarboxylic acid; the enol then isomerized to the keto form of the acid. Rates of hydration of the ketene and rates of ketonization of the enol were measured in perchloric acid, sodium hydroxide, and buffer solutions, and rate profiles were constructed. Rates of enolization of 2-oxo-3,3,5,5-tetramethylcyclopentanecarboyxlic acid were also measured, using bromine to scavenge the enol as it formed, and rates of enolization and ketonization were then combined to give the ketoenol equilibrium constant pKE = 1.65. This and other results are discussed in comparison with the behavior of the unmethylated 2-oxocyclopentanecarboxylic acid system.Key words: flash photolysis, photo-Wolff reaction, ketene hydration, enolization, ketonization, ketoenol equilibria, β-oxocarboxylic acids.
Synthesis and characterization of a series of 4-methyl-1-[2-aryl-1-diazenyl]-1,4-diazepanes and 1,4-di-[2-aryl-1-diazenyl]-1,4-diazepanes
Authors: Moser Shasta Lee , Vaughan Keith
Published: February 2005

1-Methylhomopiperazine was coupled with a series of diazonium salts to afford the 4-methyl-1-[2-aryl-1-diazenyl]-1,4-diazepanes (6), a new series of triazenes. These compounds are, in the main, stable crystalline solids (some of the series are stable oils), and they have been characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and mass spectrometry. NMR assignments were determined by 2D NMR and variable-temperature NMR experiments and by comparison with model compounds. A second series of new compounds, namely, 1,4-di-[2-aryl-1-diazenyl]-1,4-diazepanes (5), were prepared by coupling unsubstituted homopiperazine (1,4-diazepane) with 2 molar equivalents of the diazonium salt and were similarly characterized. The crystal and molecular structure of the parent member of this bis-triazene series (5, X = H) has been determined by single-crystal X-ray diffraction analysis.Key words: triazene, bis-triazene, diazenyl, bis-diazenyl, diazonium salt, NMR, diazepane.
Using ellipsoids to model charge distributions in gas phase protein complex ion dissociation
Authors: Csiszar Susan , Thachuk Mark
Published: February 2005

Gas phase protein complex dissociation was modelled using ellipsoids on which discrete charges were placed in randomly chosen charge sites. A number of sizes, shapes, orientations, and types of ellipsoids were considered. For each case, charge transfer parameters and electrostatic energies were calculated as a function of the fractional surface area. It was found that to within 1015%, the charge on product ions after dissociation is distributed according to their fractional surface area. This can imply, for example, that in experiments measuring the dissociation of homodimers, charge asymmetries of greater than 1015% in the product ions signal that one of the ions has greatly increased its surface area, such as would occur with unfolding. This assumes that proton transfer occurs on a timescale fast enough that the dissociation products adopt the minimum electrostatic energy configuration. Calculation of this energy shows that it is minimized when one or more of the monomers is in an extended conformation.Key words: protein complex dissociation, ellipsoid charge model, charge asymmetry.
InCl3·4H2O-promoted green preparation of xanthenedione derivatives in ionic liquids
Authors: Fan Xuesen , Hu Xueyuan , Zhang Xinying , Wang Jianji
Published: February 2005

A green procedure for the synthesis of xanthenedione derivatives (3) through InCl3·4H2O-promoted condensation of aldehydes (1) and 5,5-dimethyl-1,3-cyclohexanedione (2) in ionic liquids is described in this paper. This novel method has such advantages as operational simplicity and environmental benignancy together with enhanced atom utilization. Moreover, the reaction media and the catalyst can be recovered conveniently and reused effectively for at least six times.Key words: ionic liquid, xanthenedione derivatives, indium trichloride, green synthesis.
Computational investigation of isomeric and conformeric structures of methyl iodoperoxide
Authors: Drougas Evangelos , Kosmas Agnie M
Published: February 2005

Quantum mechanical electronic structure methods are employed to investigate the isomeric and conformeric stuctures of methyl iodoperoxide. Optimized geometries and harmonic vibrational frequencies are calculated at the MP2 level of theory using two types of basis sets, the 6-311G(d,p) for all atoms and the 6-311G(d,p) combined with the LANL2DZ relativistic ECP procedure for iodine. Refinement of the energetics has been accomplished by performing single-point CCSD(T) calculations. Five isomers were determined in total among which iodomethyl hydroperoxide (ICH2OOH) is found to be the lowest energy structure. Conformational barriers and transition states that connect the isomeric forms have been characterized.Key words: methyl iodoperoxide, isomers, conformers.
Effects of di-, tri-, and tetraethylene glycols on the thermodynamic and micellar properties of Triton X-100 in water
Authors: MacIsaac Gwen , Al-Wardian Aiysha , Glenn Karen , Palepu Rama M
Published: February 2005

Micellar and surface thermodynamic properties of aggregation of Triton X-100 (TX-100) in mixed solvent systems containing di-, tri-, and tetraethylene glycol with water have been investigated by employing surface tension, density, and fluorescence methods. The differences in Gibbs energies of micellization between water and binary solvent mixtures were determined to evaluate the influence of the co-solvent on the micellization process. From the surface tension measurements, the effects of the co-solvent on parameters such as surface excess, minimum area per molecule, and surface pressure indicate that the surface activity of the surfactant decreases with increasing concentration of the glycol co-solvent. Partial specific volumes, obtained from density measurements, indicate that the fraction of solvent molecules interacting with the micelles by hydrogen bonding vary with the type of additive. Fluorescence studies reveal that quenching of the pyrene probe by cetyl pyridinum chloride in TX-100 micelles is accompanied by simultaneous static and dynamic processes.Key words: Triton X-100, glycols, thermodynamics, micelles, fluorescence quenching.
Synthesis and thermolysis of a spiro-fused oxadiazoline  Evidence for sequential formation of carbene and oxirane intermediates, and for oxirane dimerization
Authors: Klys Arkadiusz , Czardybon Wojciech , Warkentin John , Werstiuk Nick Henry
Published: February 2005

The spiro-fused oxadiazoline, 3,4-diaza-2,2-dimethyl-1,6,10-trioxaspiro[4.5]dec-3-ene, when thermolysed in a sealed tube in benzene-d6 at 110 °C, afforded acetone and an apparent oxirane intermediate (2,2-dimethyl-1,4,8-trioxaspiro[2.5]octane) that could not be isolated. Attempts to isolate the oxirane gave a dimer (8,8,11,11-tetramethyl-1,5,7,10,12,16-hexaoxadispiro[5.2.5.2]hexadecane) as the major product. The oxirane is thermally stable at 110 °C but it is very sensitive to water, as indicated by its gradual disappearance after the tube was opened. The dimer of the oxirane is believed to form from a cation arising from the ring-opening of the oxirane when it reacts with moisture. This cation then reacts with the oxirane itself to regenerate water, which is effectively a catalyst for conversion of the oxirane to the dimer.Key words: carbene, dioxacarbene, dialkoxyoxirane, oxadiazoline, 2,5-dihydrooxadiazole.
Synthesis of novel optically pure β-lactams
Authors: Yang Yan , Wang Fengyun , Rochon Fernande D , Kayser Margaret M
Published: February 2005

Several new β-lactams were synthesized as racemates via a Staudinger reaction. The corresponding optically pure compounds were obtained in subsequent biotransformation steps either through baker's yeast reduction or lipase resolution. Their absolute configurations were established. The X-ray crystal structures of three new substituted β-lactams are reported here. These compounds represent key building blocks for a variety of medicinally important molecules, including inhibitors of aspartyl proteases and Taxol® analogues.Key words: optically pure β-lactams, lipase resolutions, baker's yeast reductions, Staudinger reaction.
A quantitative structure-activity relationship study for α-substituted acetamido-N-benzylacetamide derivatives  A novel anticonvulsant drug class
Authors: Jin Albert Y , Kohn Harold , Béguin Cécile , Andurkar Shridhar V , Stables James P , Weaver Donald F
Published: February 2005

A library of 35 benzylacetamide derivatives was evaluated for anticonvulsant activity as reflected in the ED50(mg/kg) required to suppress seizure activity in the maximal electroshock seizure (MES) test. Using the method of partial least-squares regression in conjunction with cross-validation, the influence of 31 topological, electronic, physico chemical, and structural properties on anticonvulsant activity was investigated. A QSAR model of the logED50in the MES test was established (R2adj= 0.77) as a function of the following seven properties: the Wiener index on distance code (Wmean), the mean information index on atomic composition (rIac), the partial charge at the C-terminal carbonyl carbon (qCC), the sum of partial charges in the α substituent (qαtotal), the number of hydrogen bond donors and acceptors in the α substituent (Hdα and Haα), and the calculated value of the squared n-octanol/water partition coefficient. Based on this model, two new amido ketone compounds  (R,S)-2-acetamido-5-phenyl-3-pentanone and cis/trans-(R,S)-2-acetamido-5-phenyl-4-penten-3-one  were synthesized and shown to have significant anticonvulsant activity in the MES test.Key words: QSAR, anticonvulsant, benzylacetamide, functionalized amino acid, amido ketones.
N-Iodosuccinimide  An effective reagent for regioselective heterocyclization of o-cyclohex-2′-enylanilines for the synthesis of hexahydrocarbazoles
Authors: Majumdar K C , Kundu U K , Das U , Jana N K , Roy B
Published: February 2005

A number of carbazoles are synthesized in good yields by the N-iodosuccinimide mediated heterocyclization of o-cyclohex-2′-enylanilines in acetonitrile at 10 °C for 45 min followed by heating with palladiumcharcoal (10%) in benzene (80 °C) for 1820 h.Key words: N-iodosuccinimide, hexahydrocarbazole, heterocyclization, carbazole, Claisen rearrangement.
Glycosides from the sea cucumber Cucumaria frondosa. III. Structure of frondosides A2-1, A2-2, A2-3, and A2-6, four new minor monosulfated triterpene glycosides
Authors: Silchenko Alexandra S , Avilov Sergey A , Antonov Alexandr S , Kalinovsky Anatoly I , Dmitrenok Pavel S , Kalinin Vladimir I , Stonik Valentin A , Woodward Carl , Collin Peter D
Published: February 2005

Frondosides A2-1 (1), A2-2 (2), A2-3 (3), and A2-6 (4) are new monosulfated holostane pentaosides isolated from the sea cucumber Cucumaria frondosa. Their structures have been elucidated on the basis of spectral data (2D NMR and MS). Frondoside A2-2 (2) contains an α,β-unsaturated ketone fragment in the side chain of the aglycon, unique for triterpene glycosides of sea cucumbers.Key words: Cucumaria frondosa, sea cucumbers, frondosides, triterpene glycosides.
Chiral bidentate N-heterocyclic carbene complexes of Rh and Pd
Authors: Ren Li , Chen Austin C , Decken Andreas , Crudden Cathleen M
Published: February 2005

The synthesis of a new chiral, bidentate oxazoline/imidazolidene carbene precursor is described. This species is reacted with various metal salts in the presence of a base to generate rhodium and palladium complexes, which are characterized spectroscopically and crystallographically.Key words: chiral N-heterocyclic carbene, rhodium, palladium, oxazolidine, asymmetric catalysis.
Synthesis and X-ray crystal structure of Cr(NR2)3 (R = CH(Me)Ph)
Authors: Samuel Ryan S , Patrick Brian O , Smith Kevin M
Published: February 2005

The reaction of CrCl3 with three equivalents of the lithium salt of [R-(R*,R*)]-(+)-bis(α-methylbenzyl)amine produces the trigonal planar Cr(III) tris(amido) complex. The X-ray structure of Cr[N{CH(Me)Ph}2]3 is reported.Key words: chromium, X-ray crystal structure, amido ligands, chiral ligands.