Theoretical evaluation of the order of reactivity of transfer agents utilized in RAFT polymerization: group Z

In the present study we report theoretical calculations, by means of density functional theory (DFT), for 28 transfer agents used in reversible addition-fragmentation chain transfer (RAFT) polymerization. Functional PBE1PBE and 3–21G* theory levels with Gaussian 03 software were used to determine the order of reactivity of RAFT agents through the evaluation of reactivity parameters such as global softness, global hardness and global philicity. It was found that the global softness of the agent was more favored when it contained benzyl or phenyl groups as the Z group, than in RAFT agents with Z groups based on oxygen, nitrogen, or sulfur. On the one hand, when the Z group is based on oxygen or nitrogen, the tendency to form zwitterionic bonds with the adjacent radical center is very high, causing reactivity reduction in these kinds of compounds (e.g., dithiocarbamates) in comparison with compounds that do not experience this type of event; on the other hand, with Z groups based on sulfur, two fragmentation paths are possible, which reduces the fragmentation rate since both Z and R can function as leaving groups. With this investigation we contribute to the understanding of RAFT-mediated polymerization mechanisms by proposing an order of reactivity based on evaluating the importance of the Z group.     

Contributions of C3 and C4 plants to higher trophic levels in an Amazonian savanna

We studied the energy flow from C₃ and C₄ plants to higher trophic levels in a central Amazonian savanna by comparing the carbon stable-isotope ratios of potential food plants to the isotope ratios of species of different consumer groups. All C₄ plants encountered in our study area were grasses and all C₃ plants were bushes, shrubs or vines. Differences in δ¹³C ratios among bushes (xˉ = −30.8, SD = 1.2), vines (xˉ = −30.7, SD = 0.46) and trees (xˉ = −29.7, SD = 1.5) were small. However the mean δ¹³C ratio of dicotyledonous plants (xˉ = −30.4, SD = 1.3) was much more negative than that of the most common grasses (xˉ = −13.4, SD = 0.27). The insect primary consumers had δ¹³C ratios which ranged from a mean of −29.5 (SD = 0.47) for the grasshopper Tropidacris collaris to a mean of −14.7 (SD = 0.56) for a termite (Nasutitermes sp.), a range similar to that of the vegetation. However, the common insectivorous and omnivorous vertebrates had intermediate values for δ¹³C, indicating that carbon from different autotrophic sources mixes rapidly as it moves up the food chain. Despite this mixing, the frogs and lizards generally had higher values of δ¹³C (xˉ = −21.7, SD = 1.6; xˉ = −21.9, SD = 1.8, respectively) than the birds (xˉ = −24.8, SD = 1.8) and the only species of mammal resident in the savanna (xˉ = −25.4), indicating that they are generally more dependent on, or more able to utilise, food chains based on C₄ grasses. Received: 7 May 1998 / Accepted: 30 November 1998     

Spectroscopic Behavior and Biological Activity of K<Subscript>2</Subscript>[VO(O<Subscript>2</Subscript>)NTA]·2H<Subscript>2</Subscript>O

The dihydrated potassium salt of the complex anion [VO(O₂)NTA]²⁻ (NTA = nitrilotriacetate anion, [N(CH₂-COO)₃]³⁻) was thoroughly characterized by electronic and vibrational (infrared and Raman) spectroscopies. The bioactivity of the complex on the cell proliferation was tested on three cell lines in culture (UMR106 rat osteosarcoma-derived cells, Caco-2 derived from a human colon adenocarcinoma, and RAW 264.7, a macrophage murine cell line).     

Respiratory and metabolic responses of the Australian Yabby Cherax destructor to progressive and sustained environmental hypoxia

The Australian Yabby, Cherax destructor, inhabits occasionally hypoxic water. The respiratory gas, acid-base, metabolite and energetic status of this crayfish was assessed during progressive hypoxia and during 3 h at a water PO₂ of 1.33 kPa. The O₂ affinity of haemocyanin from C. destructor was increased by lactate (Δlog P ₅₀/Δlog[lactate] = −0.111) and by Ca (Δlog P ₅₀/Δlog[Ca] = −0.62) but not by urate. While the non-bicarbonate buffering capacity was low (Δ[HCO₃ ⁻]/ ΔpH=−4.89) the haemocyanin had a low sensitivity to pH changes (ϕ = −0.33). The crayfish showed a compensatory hyperventilation, which induced a respiratory alkalosis, until the water O₂ partial pressure declined below 2.67 kPa, after which the O₂ uptake rate was approximately 10% of normoxic rates. The high haemocyanin-O₂ affinity maintained haemolymph O₂ content during progressive hypoxia despite the normally low arterial O₂ partial pressure of C. destructor. During severe hypoxia, pH decreased but increased lactate aided in maintaining haemocyanin-O₂ saturation. The importance of regulated haemocyanin-O₂ affinity in hypoxic C. destructor was reduced by lowered metabolism, including reduced cardiac output, and the consequent reduction in O₂ requirement. Anaerobiosis became important only at very low PO₂ but thereafter proceeded rapidly, supported by a marked hyperglycaemia. There was no depletion of adenylates, even after 3 h of severe hypoxia. The tail muscle of C. destructor held small amounts of glycogen which would sustain anaerobiosis for a only a few hours. Hypometabolism seems an important hypoxic response but severe hypoxia may encourage the crayfish to breathe air. Accepted: 26 February 1998     

Effects of <Emphasis Type="SmallCaps">l</Emphasis>-Canavanine and ozone on vascular reactivity in septicemic rats

Septicemia leads to oxidative stress with overproduction of reactive-oxygen species (ROS) and consumption of endogenous antioxidant enzymes. We tested a twofold hypothesis: (1) does oxidative stress (OxS) induced by sepsis acting alone or in concert with augmented inflammatory processes contributes to sepsis-related vascular dysfunction, and, (2) whether ozone (O₃) and l-canavanine (CAV) mitigate the negative impact of the aforementioned phenomena. We investigated the relative impact of treatment with CAV and/or O₃ on vascular OxS associated vascular functional changes in septicemic rats. For this study, 60 male Sprague–Dawley rats were used and divided into six experimental groups (n = 10): control group (C), sham-operated (Sham), septicemic rats (S), S rats treated with CAV (100 mg/kg. i.p; S + CAV), S rats treated with O₃ (1.2 mg/kg, i.p.; S + O₃) and S rats treated with both O₃ and CAV (S + O₃ + CAV). After 22 h, the mean arterial blood pressure (MAP), the aortic ring vascular reactivity to phenylephrine, abdominal aortic blood flow (AABF), serum tumor necrosis factor-α (TNF-α) and plasma nitrite/nitrate (NOx) concentration were measured. In addition, hepatic antioxidant enzyme activities sodium dismutase (SOD) and glutathione peroxidase (GSH-Px) were estimated. Septicemia caused significant elevation of serum TNF-α (p < 0.001) and plasma NOx (p < 0.001) and significant (p < 0.001) reduction of AABF (p < 0.001), aortic vascular response to phenylephrine (p < 0.001), MAP (p < 0.001) and hepatic SOD and GSH-Px activity (p < 0.001) compared with the C group, while treatment with O₃ and/or CAV induced significant amelioration of all those increases. Abnormalities were attenuated to a similar extent with treatment with both O₃ and CAV. These results suggested that concomitant administration of O₃ and CAV alleviated the compromised vascular reactivity in septicemic conditions and prevent its progression into septic shock compared with each alone.     

Length-based growth,maturity and natural mortality of the cockfish <Emphasis Type="Italic">Callorhinchus callorhynchus</Emphasis> (Linnaeus, 1758) off Coquimbo,Chile

The growth rate, reproductive aspects, and natural mortality of chimaeras and ratfish are poorly known. In this study, life-history parameters for cockfish Callorhinchus callorhynchus (Holocephali—Callorhinchidae) are estimated, which is an important fish resource exploited in Chile. Specimens were sampled from the artisanal fishery captures, from November 2006 to November 2007. The standard length (SL) of males fluctuated between 20 and 62 cm, and between 21 and 70 cm for females. Von Bertalanffy growth parameters were estimated through length-frequency data analysis using MULTIFAN. The length-weight relationship and von Bertalanffy growth parameters were significantly different for males and females, as well as the length at 50% maturity. For males a model with 5 age-classes was the best, with asymptotic length L _∞ = 52 cm SL, growth coefficient K = 0.473 yr⁻¹, and age at length zero t ₀ = −0.690 yrs. For females the best model was represented by 10 age-classes (L _∞ = 70.3 cm SL, K = 0.193 yr⁻¹, t ₀ = −1.158 yrs) in the length-frequency data sets. Length at 50% maturity of males was estimated in 43.7 cm SL, and in 50.2 cm SL for females. The natural mortality rate fluctuated between 0.42 and 0.82 yr⁻¹ for males and between 0.12 and 0.37 yr⁻¹ for females, depending upon the method used. It is concluded that C. callorhynchus is a species with life-history parameters significantly different between males and females, and such differences should be taken into account in future population dynamics analysis.     

Metabolic rates in an anadromous clupeid, the American shad (Alosa sapidissima)

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s⁻¹, 13–24 °C). Metabolic rate (M_O2) was logarithmically related to swimming speed (Bl s⁻¹; r ² = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min⁻¹; r ² = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r ² = 0.41) with a Q₁₀ of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide, ranged from 2.2–6.2 mmolO₂ kg⁻¹ h⁻¹ and scaled with mass (W) such that SMR = 4.0 (±0.03)W^{0.695(±0.15)}. Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates (M_O2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among anadromous fishes that may be important to understanding the relative success of different migratory species under varying environmental conditions. Accepted: 3 March 1999     

The Impact of heat exposure and repeated exercise on circulating stress hormones

To determine if heat exposure alters the hormonal responses to moderate, repeated exercise, 11 healthy male subjects [age = 27.1 (3.0) years; maximal oxygen consumption, V˙O_2max = 47.6 (6.2) ml · kg · min⁻¹; mean (SD)] were assigned to four different experimental conditions according to a randomized-block design. While in a thermoneutral (23°C) or heated (40°C, 30% relative humidity) climatic chamber, subjects performed either cycle ergometer exercise (two 30-min bouts at ≈50% V˙O_2max, separated by a 45-min recovery interval, CEx and HEx conditions), or remained seated for 3 h (CS and HS conditions). Blood samples were analyzed for various exercise stress hormones [epinephrine (E), norepinephrine (NE), dopamine, cortisol and human growth hormone (hGH)]. Passive heating did not alter the concentrations of any of these hormones significantly. During both environmental conditions, exercise induced significant (P < 0.001) elevations in plasma E, NE and hGH levels. At 23°C during bout 1: E = 393 (199) pmol · l⁻¹ (CEx) vs 174 (85) pmol · l⁻¹ (CS), NE = 4593 (2640) pmol · l⁻¹ (CEx) vs 1548 (505) pmol · l⁻¹ (CS), and hGH = 274 (340) pmol · l⁻¹ (CEx)vs 64 (112) pmol · l⁻¹ (CS). At 40°C, bout 1: E = 596 (346) pmol · l⁻¹ (HEx) vs 323 (181) pmol · l⁻¹ (HS), NE = 7789 (5129) pmol · l⁻¹ (HEx) vs 1527 (605) pmol · l⁻¹ (HS), and hGH = 453 (494) pmol · l⁻¹ (HEx) vs 172 (355) pmol · l⁻¹ (HS). However, concentrations of plasma cortisol were increased only in response to exercise in the heat [HEx = 364 (168) nmol · l⁻¹ vs HS = 295 (114) nmol · l⁻¹). Compared to exercise at room temperature, plasma levels of E, NE and cortisol were all higher during exercise in the heat (P < 0.001 in all cases). The repetition of exercise did not significantly alter the pattern of change in cortisol or hGH levels in either environmental condition. However, repetition of exercise in the heat increased circulatory and psychological stress, with significantly (P < 0.001) higher plasma concentrations of E and NE. These results indicate a differential response of the various stress hormones to heat exposure and repeated moderate exercise. Accepted: 16 April 1997     

Assessing the influence of the carbon oxidation-reduction state on organic pollutant biodegradation in algal-bacterial photobioreactors

The influence of the carbon oxidation–reduction state (CORS) of organic pollutants on their biodegradation in enclosed algal–bacterial photobioreactors was evaluated using a consortium of enriched wild-type methanotrophic bacteria and microalgae. Methane, methanol and glucose (with CORS −4, −2 and 0, respectively) were chosen as model organic pollutants. In the absence of external oxygen supply, microalgal photosynthesis was not capable of supporting a significant methane and methanol biodegradation due to their high oxygen demands per carbon unit, while glucose was fully oxidized by photosynthetic oxygenation. When bicarbonate was added, removal efficiencies of 37 ± 4% (20 days), 65 ± 4% (11 days) and 100% (2 days) were recorded for CH_4, CH₃OH and C₆H₁₂O₆, respectively due to the additional oxygen generated from photosynthetic bicarbonate assimilation. The use of NO₃⁻ instead of NH₄⁺ as nitrogen source (N oxidation–reduction state of +5 vs. −3) resulted in an increase in CH₄ degradation from 0 to 33 ± 3% in the absence of bicarbonate and from 37 ± 4% to 100% in the presence of bicarbonate, likely due to a decrease in the stoichiometric oxygen requirements and the higher photosynthetic oxygen production. Hypothetically, the CORS of the substrates might affect the CORS of the microalgal biomass composition (higher lipid content). However, the total lipid content of the algal–bacterial biomass was 19 ± 7% in the absence and 16 ± 2% in the presence of bicarbonate.     

The influence of either no fluid or carbohydrate-electrolyte fluid ingestion and the environment (thermoneutral versus hot and humid) on running economy after prolonged, high-intensity exercise

This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O_2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment (Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O_2max = 55.5 (4.4 SD) ml kg⁻¹ min⁻¹]. The RE was measured at 3 m s⁻¹ [65 (6)% V˙O_2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined from prior tests, to maintain body mass (group mean = 17.4 ml min⁻¹). The V˙O₂ during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase in V˙O₂ from RE1 to RE2 ranged from 3.4 to 4.7 ml kg⁻¹ min⁻¹ across treatments. In conclusion, the deterioration in RE at 3 m s⁻¹ (65% V˙O_2max) after 60 min of running at 80% V˙O_2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or electrolytes, in both a thermoneutral and in a hot, humid environment. Accepted: 30 October 1997     

Effects of hypercapnia on blood-gas and acid-base status in the white sturgeon, Acipenser transmontanus

The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO₂, PO₂, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia (water PCO₂ < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute (≤ 2h) hypercapnia significantly increased arterial PCO₂ (8-fold increase), ventilation frequency (2-fold increase), plasma HCO₃ ⁻ (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO₂ (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min⁻¹) stabilized, HCO₃ ⁻ reached its apparent maximum (23.6 ± 0.0 mmol⁻¹), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored arterial PCO₂ (2.5 ± 0.14 Torr), HCO₃ ⁻ (7.4 ± 0.59 mmol · l⁻¹), ventilation frequency (71 ± 7 breaths · min⁻¹), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine “spike”, and increased plasma catecholamines, cortisol, and arterial PO₂. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted in a significantly decreased blood-O₂ affinity (Bohr effect), as determined by construction of in vitro blood O₂ equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively affect growth of white sturgeon. Accepted: 17 August 1997     

The effect of growth conditions on the biodegradation of tributyl phosphate and potential for the remediation of acid mine drainage waters by a naturally-occurring mixed microbial culture

The biodegradation of tributyl phosphate (Bu₃-P, TBP), releasing phosphate at a high enough concentration locally to precipitate uranium from solution, was demonstrated by a mixed culture consisting primarily of pseudomonads. The effect of various parameters on Bu₃-P biodegradation by growing cells is described. Growth at the expense of Bu₃-P as the carbon and phosphorus source occurred over a pH range from 6.5 to 8, and optimally at pH 7. Bu₃-P biodegradation was optimal at 30 °C, reduced at 20 °C and negligible at 4 °C and 37 °C. Incorporation of Cu or Cd inhibited, and Ni, Co and Mn reduced its degradation. Inorganic phosphate (above 10 mM) and kerosene (up to 1 g/l) reduced Bu₃-P biodegradation significantly, but nitrate had no effect. Sulphate (10–100 mM) was inhibitory. When pregrown biomass was used the fastest rates of tributyl and dibutyl phosphate biodegradation were 25 μmol h⁻¹ mg protein⁻¹ and 37 μmol h⁻¹ mg protein⁻¹ respectively. Microcarrier-immobilised biomass decontaminated uranium-bearing acid mine waste water by uranium phosphate precipitation at the expense of Bu₃-P hydrolysis in the presence of 35 mM SO₄ ²⁻. At pH 4.5, 79% of the UO₂ ²⁺ was removed at a flow rate of 1.4 ml/h on a 7-ml test column. Received: 2 June 1997 / Received revision: 15 September 1997 / Accepted: 19 September 1997     

Theoretical characterization of SOME amides and esters DERIVATIVES of valproic acid

The equilibrium structures, the planarity of the C(=O)X linkage and the nature of the chemical bond in the Y−C(=O)−XR₁R₂ [where: Y= −CH−(CH₂−CH₂−CH₃)₂, X=N,O and R₁, R₂= H; alkyl and aryl groups and lone pair electrons (lp)] molecular fragment of derivates of Valproic acid (Vpa) with antiepileptic activity were studied systematically by means of B3LYP calculations and topological analysis of the electron localization function (ELF). The covariance parameter cov[Ω_i, Ω_j] reveals a dominating delocalization effect between the lone pair V(O₁), V(X) and the electron density of the H−C and H−X₁ bonds resulting from the existence of not only non-conventional intramolecular hydrogen bonding patterns as C−H...O/N but also a weak closed-shell stabilizing interaction type arising from a dihydrogen bonding as C−H...H−N, where H...H contacts at a significantly shorter distance than twice the hydrogen atom van der Waals radius. The analyzed data derived from ELF domains were found to be in agreement with the known features and properties of the hydrogen bonding interactions discussed in this work.     

Extrapolation of water and formaldehyde harmonic and anharmonic frequencies to the B3LYP/CBS limit using polarization consistent basis sets

The harmonic and anharmonic frequencies of fundamental vibrations in formaldehyde and water were successfully estimated using the B3LYP Kohn-Sham limit. The results obtained with polarization- and correlation-consistent basis sets were fitted with a two-parameter formula. Anharmonic corrections were obtained by a second order perturbation treatment (PT2). We compared the performance of the PT2 scheme on the two title molecules using SCF, MP2 and DFT (BLYP, B3LYP, PBE and B3PW91 functionals) methods combined with polarization consistent pc-n (n = 0, 1, 2, 3, 4) basis sets, Dunning’s basis sets (aug)-cc-pVXZ where X = D, T, Q, 5, 6 and Pople’s basis sets up to 6-311++G(3df,2pd). The influence of SCF convergence level and density grid size on the root mean square of harmonic and anharmonic frequency deviations from experimental values was tested. The wavenumber of formaldehyde CH₂ anharmonic asymmetric stretching mode is very sensitive to grid size for large basis sets; this effect is not observed for harmonic modes. BLYP-calculated anharmonic frequencies consistently underestimate observed wavenumbers. On the basis of formaldehyde anharmonic frequencies, we show that increasing the Pople basis set size does not always lead to improved agreement between anharmonic frequencies and experimental values.     

Temperature dependence of habituation of the initial responses to cold-water immersion

The initial responses to cold-water immersion, evoked by stimulation of peripheral cold receptors, include tachycardia, a reflex inspiratory gasp and uncontrollable hyperventilation. When immersed naked, the maximum responses are initiated in water at 10°C, with smaller responses being observed following immersion in water at 15°C. Habituation of the initial responses can be achieved following repeated immersions, but the specificity of this response with regard to water temperature is not known. Thirteen healthy male volunteers were divided into a control (C) group (n = 5) and a habituation (H) group (n = 8). Each subject undertook two 3-min head-out immersions in water at 10°C wearing swimming trunks. These immersions took place at a corresponding time of day with 4 days separating the two immersions. In the intervening period the C group were not exposed to cold water, while the H group undertook another six, 3-min, head-out immersions in water at 15°C. Respiratory rate (f _R), inspiratory minute volume (V˙ _I) and heart rate (f _H) were measured continuously throughout each immersion. Following repeated immersions in water at 15°C, the f _R, V˙ _I and f _H responses of the H group over the first 30 s of immersion were reduced (P < 0.01) from 33.3 breaths · min⁻¹, 50.5 l · min⁻¹ and 114 beats · min⁻¹ respectively, to 19.8 breaths · min⁻¹, 26.4 l · min⁻¹ and 98 beats · min⁻¹, respectively. In water at 10°C these responses were reduced (P < 0.01) from 47.3 breaths · min⁻¹, 67.6 l · min⁻¹ and 128 beats · min⁻¹ to 24.0 breaths · min⁻¹, 29.5 l · min⁻¹ and 109 beats · min⁻¹, respectively over a corresponding period of immersion. Similar reductions were observed during the last 2.5 min of immersions. The initial responses of the C group were unchanged. It is concluded that habituation of the cold shock response can be achieved by immersion in warmer water than that for which protection is required. This suggests that repeated submaximal stimulation of the cutaneous cold receptors is sufficient to attenuate the responses to more maximal stimulation. Accepted: 6 February 1998     

Effects of elevated atmospheric CO2 and tropospheric O3 on nutrient dynamics: decomposition of leaf litter in trembling aspen and paper birch communities

Atmospheric changes could strongly influence how terrestrial ecosystems function by altering nutrient cycling. We examined how the dynamics of nutrient release from leaf litter responded to two important atmospheric changes: rising atmospheric CO₂ and tropospheric O₃. We evaluated the independent and combined effects of these gases on foliar litter nutrient dynamics in aspen (Populus tremuloides Michx) and birch (Betula papyrifera Marsh)/aspen communities at the Aspen FACE Project in Rhinelander, WI. Naturally senesced leaf litter was incubated in litter bags in the field for 735 days. Decomposing litter was sampled six times during incubation and was analyzed for carbon, and both macro (N, P, K, S, Ca, and Mg) and micro (Mn, B, Zn and Cu) nutrient concentrations. Elevated CO₂ significantly decreased the initial litter concentrations of N (−10.7%) and B (−14.4%), and increased the concentrations of K (+23.7%) and P (+19.7%), with no change in the other elements. Elevated O₃ significantly decreased the initial litter concentrations of P (−11.2%), S (−8.1%), Ca (−12.1%), and Zn (−19.5%), with no change in the other elements. Pairing concentration data with litterfall data, we estimated that elevated CO₂ significantly increased the fluxes to soil of all nutrients: N (+12.5%), P (+61.0%), K (+67.1%), S (+28.0%), and Mg (+40.7%), Ca (+44.0%), Cu (+38.9%), Mn (+62.8%), and Zn (+33.1%). Elevated O₃ had the opposite effect: N (−22.4%), P (−25.4%), K (−27.2%), S (−23.6%), Ca (−27.6%), Mg (−21.7%), B (−16.2%), Cu (−20.8%), and Zn (−31.6%). The relative release rates of the nine elements during the incubation was: K ≥ P ≥ mass ≥ Mg ≥ B ≥ Ca ≥ S ≥ N ≥ Mn ≥ Cu ≥ Zn. Atmospheric changes had little effect on nutrient release rates, except for decreasing Ca and B release under elevated CO₂ and decreasing N and Ca release under elevated O₃. We conclude that elevated CO₂ and elevated O₃ will alter nutrient cycling more through effects on litter production, rather than litter nutrient concentrations or release rates.     

Biodegradation of propanol and isopropanol by a mixed microbial consortium

The aerobic biodegradation of high concentrations of 1-propanol and 2-propanol (IPA) by a mixed microbial consortium was investigated. Solvent concentrations were one order of magnitude greater than any previously reported in the literature. The consortium utilized these solvents as their sole carbon source to a maximum cell density of 2.4 × 10⁹ cells ml⁻¹. Enrichment experiments with propanol or IPA as carbon sources were carried out in batch culture and maximum specific growth rates (μ_max) calculated. At 20 °C, μ _max values were calculated to be 0.0305 h⁻¹ and 0.1093 h⁻¹ on 1% (v/v) IPA and 1-propanol, respectively. Growth on propanol and IPA was carried out between temperatures of 10 °C and 45 °C. Temperature shock responses by the microbial consortium at temperatures above 45 °C were demonstrated by considerable cell flocculation. An increase in propanol substrate concentration from 1% (v/v) to 2% (v/v) decreased the μ _max from 0.1093 h⁻¹ to 0.0715 h⁻¹. Maximum achievable biodegradation rates of propanol and IPA were 6.11 × 10⁻³% (v/v) h⁻¹ and 2.72 × 10⁻³% (v/v) h⁻¹, respectively. Generation of acetone during IPA biodegradation commenced at 264 h and reached a maximum concentration of 0.4% (v/v). The results demonstrate the potential of mixed microbial consortia in the bioremediation of solvent-containing waste streams. Received: 14 December 1999 / Received revision: 3 April 2000 / Accepted: 7 April 2000     

A neutral carrier-based liquid membrane microelectrode for divalent putrescine cations

A new ion-selective liquid membrane microelectrode, based on the neutral carrier 1,1′-bis(2,3-naphtho-18-crown-6), is described that shows the dependence of EMF on the activity of divalent putrescine cations a _Put, with the linear slope s _Put = 26 ± 3 mV/decade (mean ± SD, N = 18), in the range 10⁻⁴–10⁻¹ M at 25 ± 1 °C. Values of potentiometric putrescine cation selectivity coefficients of logK ^Pot _{Put j} (mean ± SD, N) are obtained by the separate solution method for the ions K⁺ (1.0 ± 0.4, 10), Na⁺ (−1.2 ± 0.4, 8), Ca²⁺ (−2.3 ± 0.5, 10) and Mg²⁺ (−2.5 ± 0.5, 7). The microelectrode can be applied for the direct analysis of the activities of free divalent putrescine cations in the range 5 × 10⁻⁴ to 10⁻¹ M in an extracellular ionic environment. Established analytical methods, e.g. high performance liquid chromatography, determine the total concentration of the derivatives of free and bound putrescine. Received: 20 December 1998 / Revised version: 7 May 1999 / Accepted: 27 May 1999     

Mode of depolymerisation of hemicellulose by various mannanases and xylanases in relation to their ability to bleach softwood pulp

Endo-mannanases and endo-xylanases cleave different heteromannans and xylans yielding mainly dimers and trimers of the corresponding sugars as end-products. However, in the early stages of hydrolysis, four purified mannanases and four xylanases from fungal and bacterial origin, examined in this study, showed a different pattern of released oligomers (determined up to the pentamers). Furthermore, some of these enzymes showed a preference for cleaving the polysaccharides in the middle of the chain while others acted more at the end. When the increase in the specific fluidity of mannan and xylan solutions per reducing sugar released (K _v) was measured against the bleaching effect of the enzymes on softwood kraft pulp, a correlation was found. A xylanase from Penicillium simplicissimum (K _v = 0.15 l mPa⁻¹s⁻¹g⁻¹) and a mannanase from Sclerotium rolfsii (K _v = 0.12 l mPa⁻¹s⁻¹g⁻¹) applied in a O(QX)P bleaching sequence (O = oxygen delignification, X = treatment with hemicellulolytic enzymes, Q = chelation of metals, P = treatment with hydrogen peroxide in alkaline solution) gave a high brightness increase of 3.0% and 1.9% ISO respectively. A less significant brightness increase was obtained with enzymes showing lower K _v values, such as a xylanase from Schizophyllum commune (K_v = 0.051  l mPa⁻¹s⁻¹g⁻¹, 0.2% ISO) and a bacterial mannanase (K _v = 0.061 l mPa⁻¹s⁻¹g⁻¹,0.5% ISO). Received: 19 December 1996 / Received revision: 20 February 1997 / Accepted: 22 February 1997     

Actual and potential rates of hydrogen photoproduction by continuous culture of the purple non-sulphur bacterium Rhodobacter capsulatus

The influence of (NH₄)₂SO₄ concentration and dilution rate (D) on actual and potential H₂ photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H₂ production in a photobioreactor was maximal (approx. 80 ml h⁻¹l⁻¹) at D = 0.06 h⁻¹ and 4 mM (NH₄)₂SO₄. However, it was lower than the potential H₂ evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h⁻¹ l⁻¹ at D = 0.03–0.08 h⁻¹. Taking into account the fact that H₂ production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting) factor should be sought. One possibility is an inhibition of H₂ production by the H₂ accumulated in the gas phase. This is apparent from the non-linear kinetics of H₂ evolution in the vials or from its inhibition by the addition of H₂; initial rates were restored in both cases after the vials had been refilled with argon. The actual H₂ production in the photobioreactor at D = 0.06 h⁻¹ was shown to increase from approximately 80 ml h⁻¹ l⁻¹ to approximately 100 ml h⁻¹ l⁻¹ under an argon flow at 100 ml min⁻¹. Under maximal H₂ production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H₂ production and 50% for biomass synthesis. Received: 22 April 1997 / Received revision: 14 July 1997 / Accepted: 27 July 1997