Hydrology of winter–spring “red tides” in Bahía de Mazatlán, Sinaloa, México

“Red tide” events are frequent and periodical in Bahía de Mazatlán, Sinaloa, México. Yet, the ones observed from 4 February to 4 June 2000, showed some distinctive features: First, the dinoflagellates Prorocentrum balticum (85%), P. mexicanum (5%), and Ceratium furca (5%), dominated the composition of the blooms; Second, the average cell abundance by date was 1.3×10⁶ cells l⁻¹, with a range of 3.5×10³ to 24,500 × 10³ cells l⁻¹, well above previous records; Third, the temperature registered at 10–20 m deep was unusually cold (19 °C), below the normal average of 21.5 °C observed over the last 10 years. Salinity was high (35.9 psu) and showed very little influence on the water density gradient. A mean thermal stratification index (TSI), of 3.4, with a maximum of 7 °C, was observed throughout the period, in spite of a weak upwelling activity and intermittent strong NW winds which were unable to break up water column stratification. Temperature fluctuations at the surface and at the bottom layers showed a 30-day periodicity, suggesting some association with the lunar cycle. To explain the characteristics of the “red tides” registered in Bahía de Mazatlán during the winter–spring period of year 2000, it is proposed that the temperature and density stratification, stabilized further by internal waves that compensated for the weak upwelling activity and provided the necessary nutrients to the surface layer, favored the persistence and intensity of the harmful algal bloom events then observed.     

Clonal selection by fluorescence redistribution after photobleaching (FRAP)--a "fast" lateral mobility fibroblast mutant (E7G1)

Fluorescence redistribution after photobleaching (FRAP) was utilized to select a "fast" lateral mobility clone from Kirsten murine sarcoma virus-transformed 3T3 (KMSV-3T3) fibroblasts. The clone, E7G1, demonstrated a lateral mobility for membrane wheat germ agglutinin (WGA) and succinylated concanavalin A (sCon A) receptors of (2.1 +/- 1.6) X 10(-9) cm2/s and (2.7 +/- 2.3) X 10(-9) cm2/s, respectively. These mobilities were approximately equivalent to phospholipid mobility (2.8 +/- 1.9 X 10(-9) cm2/s). The fast mobility phenotype is observed when the cells are unattached and spherical. Upon attachment, the mobility decreases to (0.19 +/- 0.19) X 10(-9) cm2/s. In addition, the ability of Con A to initiate global modulation was completely lost in spread as well as spherical cells in the E7G1 fast mobility clone. A comparison of F-actin patterns between untransformed Balb/c fibroblasts and the E7G1-transformed line suggests a correlation between well-developed stress fiber assemblies and the ability to induce global modulation. The fast mobility clone was stable for at least 23 passages.     

α-Factor inhibition of the rate of cell passage through the “start” step of cell division in Saccharomyces cerevisiae yeast: Estimation of the division delay per α-factor·receptor complex

A highly sensitive, kinetically unambiguous assay for α-factor-induced delay of cell passage through the “start” step of cell division in yeast is presented. The assay employs perfusion with periodic microscopy to monitor the bud emergence kinetics on the 20% of cells within an exponentially growing population which exist prior to the α-factor execution point of start. The t_1/2 for cell passage through start by this population of cells is 31 min in the absence of α-factor. The inhibition constant, K_I, represents the α-factor concentration which produces a 50% inhibition of this rate and is equal to 2×10⁻¹⁰M. A second assay for maximal cell division arrest by α-factor on whole populations of cells is presented. This assay shows a maximum cell division arrest time of 125±5 h at saturating α-factor, and a K₅₀ (that is, an α-factor concentration which produces a half-maximal response) of 2.5×10⁻⁸M. Both assays were performed in the effective absence of α-factor inactivation. Values of the dissociation constant K_D and total number of receptors per cell which specifically mediate cell division arrest or delay were estimated to be 2.5×10⁻⁸M and 10⁴, respectively. These estimates, along with the quantitative dose-response data for division arrest which are presented here, are consistent with each receptor·α-factor complex which is present on the cell at equilibrium producing a 43±10 s delay of cell passage through start. Surprisingly, this number is constant within twofold over the entire range of cellular division arrest responses to α-factor, that is, from a 1.9-fold inhibition of the rate of cell passage through start at 0.17 nM α-factor to a 125±5 h maximum arrest at saturating α-factor concentrations of >170 nM. The possible significance of this observation toward the mechanism of α-factor-induced cell division arrest is discussed.     

Membrane Permeability Characteristics of Metaphase II Mouse Oocytes at Various Temperatures in the Presence of Me2SO

In this study, the hydraulic conductivity (L_p), Me₂SO permeability ( _Me2SO), and the reflection coefficients (ς) and their activation energies were determined for Metaphase II (MII) mouse oocytes by exposing them to 1.5 M Me₂SO at temperatures of 30, 20, 10, 3, 0, and −3°C. These data were then used to calculate the intracellular concentration of Me₂SO at given temperatures. Individual oocytes were immobilized using a holding pipette in 5 μl of an isosmotic PBS solution and perfused with precooled or prewarmed 1.5 M Me₂SO solutions. Oocyte images were video recorded. The cell volume changes were calculated from the measurement of the diameter of the oocytes, assuming a spherical shape. The initial volume of the oocytes in the isoosmotic solution was considered 100%, and relative changes in the volume of the oocytes after exposure to the Me₂SO were plotted against time. Mean (means ± SEM) L_pvalues in the presence of Me₂SO ( ^Me₂SO_p) at 30, 20, 10, 3, 0, and −3°C were determined to be 1.07 ± 0.03, 0.40 ± 0.02, 0.18 ± 0.01, 7.60 × 10⁻²± 0.60 × 10⁻², 5.29 × 10⁻²± 0.40 × 10⁻², and 3.69 × 10⁻²± 0.30 × 10⁻²μm/min/atm, respectively. The _Me2SOvalues were 3.69 × 10⁻³± 0.3 × 10⁻³, 1.07 × 10⁻³± 0.1 × 10⁻³, 2.75 × 10⁻⁴± 0.15 × 10⁻⁴, 7.83 × 10⁻⁵± 0.50 × 10⁻⁵, 5.24 × 10⁻⁵± 0.50 × 10⁻⁵, and 3.69 × 10⁻⁵± 0.40 × 10⁻⁵cm/min, respectively. The ς values were 0.70 ± 0.03, 0.77 ± 0.04, 0.81 ± 0.06, 0.91 ± 0.05, 0.97 ± 0.03, and 1 ± 0.04, respectively. The estimated activation energies (E_a) for ^Me₂SO_p, _Me2SO, and ς were 16.39, 23.24, and −1.75 Kcal/mol, respectively. These data may provide the fundamental basis for the development of more optimal cryopreservation protocols for MII mouse oocytes.     

Production and recovery of recombinant protease inhibitor α1-antitrypsin

Human α₁-antitrypsin (AAT) was produced in the recombinant yeast Saccharomyces cerevisiae ATCC 20699 grown in batch and fed-batch culture. The final biomass concentration and antitrypsin concentration attained were 55 g·L⁻¹ and 1.23 g·L⁻¹, respectively, in the fed-batch. The maximum productivities of biomass and antitrypsin were 1.6 and > 0.04 g L⁻¹h⁻¹, respectively, or substantially greater than the highest productivity values reported in the past. For recovering the antitrypsin, the cell slurry was concentrated 4-fold (231 g·L⁻¹ biomass, 122 min of processing) by cross-flow microfiltration and the cells were disrupted by bead milling (3 passes of 3 min total retention time). The cell homogenate was treated with aluminum chloride or PBS (pH 7) to aid separation of the cell debris by flocculation and sedimentation. The clarified cell homogenate was subjected to ammonium sulfate fractionation to precipitate the recombinant antitrypsin. The AAT precipitated at 45–75% saturation of ammonium sulfate, depending on the age of the homogenate. The crude AAT in the homogenate degraded at room temperature (25°C), with a zero order deactivation rate of 1.815 × 10⁻³ ± 3.43 × 10⁻⁴ g AAT L⁻¹h⁻¹.     

Dose-related effect of the oxytocin fragment (prolyl-leucyl-glycinamide) on α-MPT-induced catecholamine disappearance and serotonin level in rat brain

Graded doses of Pro-Leu-Gly-NH₂ (3.5 × 10⁻¹², 3.5 × 10⁻¹¹, 3.5 × 10⁻¹⁰ or 3.5 × 10⁻⁹ mol) were administered into the lateral cerebral ventricle of rats. The noradrenaline level of the dorsal hippocampus was increased 30 min after a dose of 3.5 × 10⁻¹⁰ mol Pro-Leu-Gly-NH₂. The dopamine level was increased in the dorsal hippocampus and in the striatum. The serotonin level was increased in the hypothalamus, in the striatum and decreased in the dorsal hippocampus.The catecholamine disappearance following 350 mg/kg of α-methyl-p-tyrosine indicated an accelerated dopamine disappearance in the striatum for each dose studied, while the hypothalamic noradrenaline disappearance was inhibited by a dose of 3.5 × 10⁻¹¹ mol of Pro-Leu-Gly-NH₂.The data indicate that Pro-Leu-Gly-NH₂ induces dose and region-dependent changes in the cerebral monoamine metabolism. The striatal dopamine and hypothalamic serotonin metabolism appeared to be the most sensitive for intraventricular Pro-Leu-Gly-NH₂.     

Inhibition of prostaglandin E2-induced cyclic AMP accumulation in the rat anterior pituitary by 11-deoxyprostaglandin E analogs (9-ketoprostynoic acids)

The effects of various 11-deoxyprostaglandin E analogs on the basal and prostaglandin E₂ (PGE₂)-induced cyclic AMP accumulation in the rat anterior pitutiary were studied . 13-Hydroxy-9-oxoprost-14-ynoic acid at 5 × 10⁻⁴M, but not 5 × 10⁻⁵M, decreased (45%) the induced accumulation and did not alter the basal accumulation; 15-hydroxy-9-oxoprost-13-ynoic acid at 5 × 10⁻⁴M caused less of a decrease (29%) in the induced and also did not alter the basal accumulation. (14Z)-13-Hydroxy-9-oxoprost-14-enoic acid at 5 × 10⁻⁴M did not alter the induced and caused a slight increase (5 fold) in the basal accumulation. 7-Oxa-13-prostynoic acid increased slightly the basal accumulation at 5 × 10⁻⁵M (2 fold) and 2.33 × 10⁻⁴M (6 fold) and did not antagonize the induced accumulation. Thus, the 9-ketoprostynoic acids are effective PGE₂ antagonists in this system.     

Inhibition of prostagland in E2-induced cyclic AMP accumulation in the rat anterior pituitary by II-deoxyprostaglandin E analogs (9-ketoprostynoic acids)

The effects of various II-deoxyprostaglandin E analogs on the basal and prostaglandin E₂ (PGE₂)-induced cyclic AMP accumulation in the rat anterior pituitary were studied in vitro. 13-Hydroxy-9-oxoprost-14-ynoic acid at 5 × 10⁻⁴M, but not 5 × 10⁻⁵M, decreased (45%) the induced accumulation and did not alter the basal accumulation; 15-hydroxy-9-oxoprost-13-ynoic acid at 5 × 10⁻⁴M caused less of a decrease (29%) in the induced and also did not alter the basal accumulation. (14Z)-13-Hydroxy-9-oxoprost-14-enoic acid at 5 × 10⁻⁴M did not alter the induced and caused a slight increase (5 fold) in the basal accumulation. 7-Oxa-13-prostynoic acid increased slightly the basal accumulation at 5 × 10⁻⁵M (2 fold) and 2.33 × 10⁻⁴M (6 fold) and did not antagonize the induced accumulation. Thus, the 9-ketoprostynoic acids are effective PGE₂ antagonists in this system.     

Preparation of single or double-network chitosan/poly(vinyl alcohol) gel films through selectively cross-linking method

A selectively cross-linking method, which is based on the “di–diol” interaction between poly(vinyl alcohol) and borate and the strong electrostatic interaction between chitosan and tripolyphosphate, was developed. Chitosan/poly(vinyl alcohol) films cross-linked separately with borate, tripolyphosphate and borate/tripolyphosphate were then prepared in terms of this method. Water vapor permeation, mechanical strength, surface morphology and molecular interactions of the films were studied by water permeation test, texture test, atomic force microscopy and ATR-FTIR spectroscopy. With the introduction of cross-linking structure, there is a large improvement in elastic modulus from 271 ± 14.2 to 551 ± 14.7 MPa and a large decrease in water vapor permeability from (5.41 ± 0.21) × 10⁻⁷ g/m h Pa to (3.12 ± 0.24) × 10⁻⁷ g/m h Pa of chitosan/poly(vinyl alcohol) films. The surface morphology of the cross-linked films exhibits a nanoparticle aggregation structure. The size and aggregation behavior of these nanoparticles are strongly related to the type of cross-linker. Furthermore, ATR-FTIR results indicate that strong interaction between polymer matrix and cross-linker exists in our system. This work provides a simple and efficient way to prepare chitosan/poly(vinyl alcohol) films with controllable network structure.     

Acid dissociation constants and pH values for standard “bes” and “tricine” buffer solutions in 30, 40, and 50 mass% dimethyl sulfoxide/water between 25 and −25 °C

Information is given concerning two standard buffer solutions suitable as pH references in 30, 40, and 50 mass% dimethyl sulfoxide (DMSO)/H₂O mixed solvents at subzero temperatures from −20 to 0 °C, with the intention of establishing a pH (designated pH^*) scale. The two buffers selected were the ampholytes N,N-bis(2-hydroxyethyl)-2-aminoethane sulfonic acid (“bes”) and N-tris(hydroxymethyl)methylglycine (“tricine”), and the reference standard consisted of equal molal quantities of the buffer and its respective sodium salt. The assignment of pH^* values was based on measurements of the emf of cells without liquid junction of the type: Pt;H₂(g,1 atm) ¦Bes, Na Besate, NaCl ¦ AgCl;Ag and Pt;H₂(g,1 atm) ¦Tricine, Na Tricinate, NaCl ¦AgCl;Ag and the pH^* was derived from a determination of K₂, the equilibrium constant for the dissociation process (Buffer)^±/ai (Buffer)⁻ + H⁺.     

Effect of prostaglandin F2α on propulsive activity of the isolated segmental colon of the guinea-pig

The effects of prostaglandin F_2α (PGF_2α) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated.Using experimental conditions under which spontaneous propulsive activity was negligible, PGF_2α (5×10⁻⁸×1×10⁻⁶M), added to the bathing medium, increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1×10⁻⁷g/ml).The contractions produced by PGF_2α(5×10⁻⁷ − 1×10⁻⁵M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1×10⁻⁷ g/ml).From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF_2α may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.     

The acetylcholine receptor: Isolation of a brain nicotinic receptor and its preliminary characterization in lipid bilayer membranes

The technique of affinity chromatography with the curarizing neurotoxins of Naja naja venom has been employed to extract nicotinic acetylcholine receptors from the brain tissues of mouse and hog. Both carbochol and hexamethonium were used as linear or step gradients to elute the receptor and its properties were investigated in lipid bilayer membranes. Of particular interest is the observation that discrete quanta of conductance could be observed across an NaCl gradient of 1.0:0.1 M. By switching the voltage-clamp across the bilayer between a positive and negative 80 mV, the separate Na⁺ and Cl⁻ conductances of these quanta could be estimated and the following conductances of the smallest discrete quanta were observed: 3.7 · 10⁻¹¹ Ω⁻¹ (Na⁺) and 5.9 · 10⁻¹¹ Ω⁻¹ (Cl⁻) for mouse brain receptors; 3.8 · 10⁻¹¹ Ω⁻¹ (Na⁺) and 4.7 · 10⁻¹¹ Ω⁻¹ (Cl⁻) for hog brain receptors. Large aggregates of receptors appeared to activate and deactivate as multiples of a basic conductance size, although there is evidence that they may not represent the actual gating of ion channels. A “background noise” that is not within the temporal capability of the recording system is also present at an intensity that seems to parallel the number of activated receptors, and in view of recent electrophysiological evidence that the relaxation lifetime of the open channel state is of a millisecond duration, it may be that this “noise” actually represent the channel gating.     

Immobilization of -glucose oxidase onto a hydrogen peroxide permselective membrane and application for an enzyme electrode

A hydrogen peroxide permselective membrane with asymmetric structure was prepared and -glucose oxidase (EC 1.1.3.4) was immobilized onto the porous layer. The activity of the immobilized -glucose oxidase membrane was 0.34 units cm⁻² and the activity yield was 6.8% of that of the native enzyme. Optimum pH, optimum temperature, pH stability and temperature stability were found to be pH 5.0, 30–40°C, pH 4.0–7.0 and below 55°C, respectively. The apparent Michaelis constant of the immobilized -glucose oxidase membrane was 1.6 × 10⁻³ mol l⁻¹ and that of free enzyme was 4.8 × 10⁻² mol l⁻¹. An enzyme electrode was constructed by combination of a hydrogen peroxide electrode with the immobilized -glucose oxidase membrane. The enzyme electrode responded linearly to -glucose over the concentration 0–1000 mg dl⁻¹ within 10 s. When the enzyme electrode was applied to the determination of -glucose in human serum, within day precision (CV) was 1.29% for -glucose concentration with a mean value of 106.8 mg dl⁻¹. The correlation coefficient between the enzyme electrode method and the conventional colorimetric method using a free enzyme was 0.984. The immobilized -glucose oxidase membrane was sufficiently stable to perform 1000 assays (2 to 4 weeks operation) for the determination of -glucose in human whole blood. The dried membrane retained 77% of its initial activity after storage at 4°C for 16 months.     

Peroxidase catalyzed phenolic compounds oxidation in presence of surfactant Dynol 604: A kinetic investigation

The kinetics of fungal peroxidase-catalyzed phenolic compounds (PCs) oxidation was investigated in presence of acetylenic-based surfactant Dynol 604 at pH 5.5 and 25 °C. It was shown that the presence of ppm concentrations of surfactant did not influence initial rate of PCs oxidation. The calculated apparent bimolecular rate constants were (1.8 ± 0.2) × 10⁵ M⁻¹ s⁻¹, (1.4 ± 0.4) × 10⁷ M⁻¹ s⁻¹, (1.30 ± 0.06) × 10⁷ M⁻¹ s⁻¹ and 1.1 × 10⁸ M⁻¹ s⁻¹ for phenol, 1-naphthol, 2-naphthol and 1-hydroxypyrene, respectively.During an extensive substrates conversion Dynol 604 showed diverse action for different PCs. The oxidation of phenol practically did not change, whereas the surfactant enhanced the conversion of 1- and 2-naphthol and 1-hydroxypyrene in dose response manner. The results accounted by a scheme, which contains a stadium of enzyme inhibition by oligomeric PC oxidation products. The action of the surfactant was explained by avoidance the enzyme active center clothing with the oligomers. The results acquired demonstrate a remarkable increase of substrates conversion in the presence of Dynol 604.     

The effects of prostaglandins E2 and F2α on synaptosomal accumulation and release of H-norepinephrine

Prostaglandins (PG) of both the E and F series may serve as modulators of norepinephrine (NE) release from peripheral sympathetic neurons. We have studied the effects of PGE₂ and PGF_2α on the accumulation and release of ³H-NE in the CNS using synaptosomes isolated from rat hypothalami.The release of ³H-NE from synaptosomes superfused with Krebs-Ringer bicarbonate buffer was multiphasic with an initial fast release phase followed by a slower release. Raising KC1 concentration of the superfusion medium to 56mM during the slow release phase is known to stimulate ³H-NE release. PGE₂ (1 × 10⁻⁶M) attenuated ³H-NE release during the fast phase and reduced the amount of ³H-NE released due to KC1 stimulation. At lower concentrations of PGE₂ there was no change in the release profile. PGF_2α was without effect on ³H-NE release at all concentrations tested.The accumulation of ³H-NE was significantly diminished by PGE₂ at a concentration of 1 × 10⁻⁶M, while a lower concentration (1 × 10⁻⁷M) was ineffective. PGF_2α had no effect on ³H-NE accumulation at all concentrations investigated.     

Metabolic rate, maximum metabolism, and advantages of torpor in the fat mouse Steatomys pratensis natalensis Roberts, 1921 (Dendeomurinae)

1. The fat mouse Steatomys pratensis natalensis (mean body mass 37.4±0.43 (se)) has a low euthermic body temperature T_b=30.1–33.8 °C and a low basal metabolic rate (BMR)=0.50 ml O₂ g⁻¹ h⁻¹.

2. Below an ambient temperature (T_a)=15 °C, the mice were hypothermic.

3. The lowest survivable T_a=10 °C.

4. Torpor is efficient in conserving energy between T_a=15–30 °C, below T_a=15 °C, the mice arouse.

5. Euthermic and torpid mice were hyperthermic at T_a=35 °C.

6. Thermal conductance was 0.159 ml O₂ g⁻¹ h⁻¹ °C⁻¹, 98.8% of the expected value.

7. Non-shivering thermogenesis (NST) was 2.196 ml O² g⁻¹ h⁻¹ (3.69×BMR).

8. Maximal oxygen consumption, however, was 3.83 ml O₂ g⁻¹ h⁻¹ (6.44×BMR), indicating that other methods of heat production are additive.

9. Because fat mice conserve energy by torpor only between T_a=15–30 °C, we suggest that torpor may be a more important mechanism for surviving food shortages than for surviving cold weather.

Progesterone receptor associated with the “melanosome” fraction of Pleurodeles waltlii oocytes (urodela amphibian)

A proteinaceous receptor associated with the melanosome fraction of Pleurodeles waltlii oocytes binds progesterone with high affinity and limited capacity (K_D ≈ 5 · 10⁻⁸ M).     

Interactions between Prorocentrum donghaiense Lu and Scrippsiella trochoidea (Stein) Loeblich III under laboratory culture

Interactions between Prorocentrum donghaiense Lu and Scrippsiella trochoidea (Stein) Loeblich III, two species of causative bloom dinoflagellates in China, were investigated using bi-algal cultures under controlled laboratory conditions. The growth of P. donghaiense and S. trochoidea were significantly suppressed when the initial cell densities were set at 1.9 × 10⁴ cells mL⁻¹ or 1.9 × 10⁵ cells mL⁻¹ for P. donghaiense and 1.0 × 10⁴ cells mL⁻¹ for S. trochoidea when the initial size/density ratio was 1:1 or 10:1, respectively, but no out-competement was observed in either bi-algal culture by the end. The simultaneous assay on the culture filtrate showed that P. donghaiense filtrate prepared at a lower initial density (1.9 × 10⁴ cells mL⁻¹) stimulated the co-cultured S. trochoidea at a density of 1.0 × 10⁴ cells mL⁻¹, but filtrate at a higher density (1.9 × 10⁵ cells mL⁻¹) depressed its growth. Differently, the filtrate of S. trochoidea at a density of 1.0 × 10⁴ cells mL⁻¹ significantly suppressed the growth of P. donghaiense at a density of 1.9 × 10⁴ cells mL⁻¹, but had little stimulatory effect on P. donghaiense at a density of 1.9 × 10⁵ cells mL⁻¹compared to the control (P > 0.05). It is likely that these two species of microalgae interact with each other mainly by releasing allelochemical substance(s) into the culture medium, and a direct cell-to-cell contact was not necessary for their mutual interaction. We then quantify their interactions in the bi-algal culture by using a mathematical model. The estimated parameters from the model showed that the inhibition exerted by S. trochoidea on P. donghaiense was about 43 and 24 times stronger than the inhibitory effect that P. donghaiense exerted on S. trochoidea when the initial size/density were 1:1 and 10:1, respectively. S. trochoidea seemed to have a survival strategy that was superior to P. donghaiense in the bi-algal culture under controlled laboratory conditions. We also observed a closely positive relationship between the initial cell density and its effect on the co-cultured microalga by measuring the fluorenscence: filtrate prepared from higher initial cell density had stronger interference on the co-cultured microalga. Moreover, pre-treated under different temperature conditions (30 °C, 60 °C and 100 °C) would significantly changed the effect of culture filtrate on the co-cultured microalga. Result inferred that P. donghaiense or S. trochoidea would release allelochemicals into the bi-algal culture medium and the allelochemicals might be a mixture with temperature-sensitive components in it.     

Seasonal and spatial variability of coccolithophore export production at the South-Western margin of Crete (Eastern Mediterranean)

Six moorings were deployed at different locations in the deep submarine canyons along the south–west margin of Crete, providing a total of eight sediment-trap time series from June 2005 to May 2006. Within this dataset, we analyzed the record from intact coccospheres, which represent the signal of export production from the coccolithophore community. The most abundant species at all stations during the whole investigated period were E. huxleyi and A. robusta, followed by S. pulchra HET, G. flabellatus, H. carteri, F. profunda, S. pulchra HOL oblonga, while the rest of the species represented ≤ 1% of the assemblage. Overall the assemblage composition was comparable at all stations, with slight variations mostly related to the different preservation of coccosphere integrity at the different collection depths. The consistent pattern of seasonal variation in species distribution and total coccolithophore export allowed us to define the occurrence of three main periods: a) March to June, with high overall coccosphere flux (up to 4.3 × 10⁵–3.4 × 10⁶ coccospheres m^− 2 day^− 1), increased abundance of E. huxleyi and subordinate H. carteri s.s., Umbilicosphaera spp. and S. pulchra; b) June to November, with high but gradually decreasing total coccosphere flux (up to 7 × 10⁵–1.4 × 10⁶ coccospheres m^− 2 day^− 1) and high relative abundance of the deep photic zone species A. robusta, F. profunda, G. flabellatus as well as S. pulchra and Coronosphaera spp., R. clavigera, U. tenuis, D. tubifera and holococcolithophores; c) November to February, with low overall export fluxes (3.5–9 × 10⁴ coccospheres m^− 2 day^− 1) and high relative abundance of A. robusta, S. pulchra and Syracosphaera spp. These three periods correspond to the seasonal changes in sea surface temperature, surface mixed layer depth and rainfall and are associated with varying total surface primary production, as detected through remote sensing in the surface waters.     

Synthesis and magnetic properties of bis(μ-hydroxo)bis[(2,2 ′-bipyridyl)copper(II)] squarate. Crystal structure of bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] squarate tetrahydrate

The compound [Cu₂(bipy)₂(OH)₂](C₄O₄)·5.5H₂O, where bipy and C₄O₄²⁻ correspond to 2,2′-bipyridyl and squarate (dianion of 3,4-dihydroxy-3-cyclo- butene-1,3-dione) respectively, has been synthesized. Its magnetic properties have been investigated in the 2–300 K temperature range. The ground state is a spin-triplet state, with a singlet-triplet separation of 145 cm⁻¹. The EPR powder spectrum confirms the nature of the ground state.Well-formed single crystals of the tetrahydrate, [Cu₂(bipy)₂(OH)₂](C₄O₄)·4H₂O, were grown from aqueous solutions and characterized by X-ray diffraction. The system is triclinic, space group P , with a = 9.022(2), b = 9.040(2), c = 8.409(2) Å, α = 103.51(2), β = 103.42(3), γ = 103.37(2)°, V = 642.9(3) ų, Z = 1, D_x = 1.699 g cm⁻³, μ(Mo Kα) = 17.208 cm⁻¹, F(000) = 336 and T= 295 K. A total of 2251 data were collected over the range 1θ25°; of these, 1993 (independent and with I3σ(I)) were used in the structural analysis. The final R and R_w residuals were 0.034 and 0.038 respectively. The structure contains squarato-O¹, O³-bridged bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] units forming zigzag one-dimensional chains. Each copper atom is in a square-pyramidal environment with the two nitrogen atoms of 2,2′-bipyridyl and the two oxygen atoms of the hydroxo groups building the basal plane and another oxygen atom of the squarate lying in the apical position.The magnetic properties are discussed in the light of spectral and structural data and compared with the reported ones for other bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] complexes.