The rate of oxygen utilization by cells

The discovery of oxygen is considered by some to be the most important scientific discovery of all time—from both physical-chemical/astrophysics and biology/evolution viewpoints. One of the major developments during evolution is the ability to capture dioxygen in the environment and deliver it to each cell in the multicellular, complex mammalian body—on demand, i.e., just in time. Humans use oxygen to extract approximately 2550 calories (10.4 MJ) from food to meet daily energy requirements. This combustion requires about 22 mol of dioxygen per day, or 2.5 × 10^− 4 mol s^− 1. This is an average rate of oxygen utilization of 2.5 × 10^− 18 mol cell^− 1 s^− 1, i.e., 2.5 amol cell^− 1 s^− 1. Cells have a wide range of oxygen utilization, depending on cell type, function, and biological status. Measured rates of oxygen utilization by mammalian cells in culture range from < 1 to > 350 amol cell^− 1 s^− 1. There is a loose positive linear correlation of the rate of oxygen consumption by mammalian cells in culture with cell volume and cell protein. The use of oxygen by cells and tissues is an essential aspect of the basic redox biology of cells and tissues. This type of quantitative information is fundamental to investigations in quantitative redox biology, especially redox systems biology.     

Diurnal courses of net photosynthesis and photosystem II quantum efficiency of submerged Lagarosiphon major under natural light conditions

An optode device for net-photosynthesis measurements, based on oxygen-depending quenching of fluorescence from O₂-specific sensors, and PAM fluorometry have been used to study diurnal courses of net-photosynthesis and the F_v/F_m ratio of the submerged plant Lagarosiphon major. Plants were pre-cultivated and studied in large mesocosm flow-through outdoor tanks under 50% and 80% shade cloth, respectively. Growth under the different shade cloths resulted in similar light compensation points (∼20 μmol photons m⁻² s⁻¹), but strongly different light saturation levels, with about 150 μmol m⁻² s⁻¹ for plants grown under 80% shade cloth and about 350 μmol m⁻² s⁻¹ for plants grown under 50% shade cloth. Plants under both growth conditions showed a transient reduction of the maximum F_v/F_m value in the afternoon (down to 70% of the morning control values under 80% shade cloth and down to 85% under 50% shade cloth), which was not accompanied by a reduction of the net photosynthetic rate. This indicated that the fluorescence parameter F_v/F_m must not be a reliable indicator of the rate of photosynthesis under all conditions. The new photo-optical device became evidenced as a valuable tool not only for laboratory experiments, but also for field studies of gas exchange of submerged plants.     

Morphological and physiological adaptive traits of Mediterranean narrow endemic plants: The case of Centaurea gymnocarpa (Capraia Island,Italy)

A case study on Centaurea gymnocarpa Moris & De Not., a narrow endemic species, was carried out by analyzing its morphological, anatomical, and physiological traits in response to natural habitat stress factors under Mediterranean climate conditions. The results underline that the species is particularly adapted to the environment where it naturally grows. At the plant level, the above-ground/below-ground dry mass (1.73 ± 0.60) shows its investment predominately in the above-ground structure with a resulting total leaf area per plant of 1399 ± 94 cm². The senescent attached leaves at the base of the plant contribute to limit leaf transpiration by shading soil around the plant. Moreover, the dense C. gymnocarpa leaf pubescence, leaf rolling, the relatively high leaf mass area (LMA = 12.3 ± 1.3 mg cm⁻²) and leaf tissue density (LTD = 427 ± 44 mg cm⁻³) contribute to limit leaf transpiration, also postponing leaf death under dry conditions. At the physiological level, a relatively low respiration/photosynthesis ratio (R/P_N) in spring results from high R [2.26 ± 0.59 μmol (CO₂) m⁻² s⁻¹] and P_N [12.3 ± 1.5 μmol (CO₂) m⁻² s⁻¹]. The high photosynthetic nitrogen use efficiency [PNUE = 15.5 ± 0.4 μmol (CO₂) g⁻¹ (N) s⁻¹] shows the large amount of nitrogen (N) invested in the photosynthetic machinery of new leaves, associated to a high chlorophyll content (Chl = 35 ± 5 SPAD units). On the contrary, the highest R/P_N ratio (1.75 ± 0.19) in summer is due to a significant P_N decrease and increase of R in response to drought. The low PNUE [1.5 ± 0.2 μmol (CO₂) g⁻¹ (N) s⁻¹] in this season is indicative of a greater N investment in leaf cell walls which may contribute to limit transpiration. On the contrary, the low R/P_N ratio (0.05 ± 0.02) in winter is resulting from the limited enzyme activity of the respiratory apparatus [R = 0.23 ± 0.08 μmol (CO₂) m⁻² s⁻¹] while the low PNUE [3.5 ± 0.2 μmol (CO₂) g⁻¹ (N) s⁻¹] suggests that low temperatures additionally limit plant production. The experiment of the imposed water stress confirms that the C. gymnocarpa growth capability is in conformity with the severe conditions of its natural habitat, likewise as it may be the case with others narrow endemic species that have occupied niches with similar extreme conditions.     

Relationship of rapid light curves of variable fluorescence to photoacclimation and non-photochemical quenching in a benthic diatom

The response of rapid light–response curves (RLCs) of variable fluorescence to changes in short- and long-term photoacclimation status was studied in an estuarine benthic diatom. The diatom Nitzschia palea was grown under low- (LL, 20 μmol m⁻² s⁻¹) and high-light (HL, 400 μmol m⁻² s⁻¹) conditions, with the purpose of characterising the effects of long-term photoacclimation on (i) steady-state light–response curves (LC) of relative electron transport rate, rETR, (ii) the response of RLCs to changes in ambient irradiance (E, the irradiance to which the sample is acclimated to immediately before the RLCs), (iii) the relationship of RLCs to LC parameters and non-photochemical quenching (NPQ). Photoacclimation to LL and HL conditions induced distinct light–response patterns of rETR and NPQ. Higher growth light resulted in rETR vs. E curves with lower initial slopes (α, 0.591 μmol⁻¹ m² s vs. 0.661 μmol⁻¹ m² s, for HL and LL, respectively) and markedly higher maximum rates (rETR_m, 95.9 vs. 29.3), reached under higher E levels (higher light-saturation coefficient, E_k: 162.4 μmol m⁻² s⁻¹ vs. 44.3 μmol m⁻² s⁻¹). Acclimation to HL induced bi-phasic NPQ vs. E curves, with minimum values reached under low E levels (15–25 μmol m⁻² s⁻¹) and not on dark-acclimated samples. The response of RLCs to changes in ambient irradiance varied with the long-term photoacclimation status of the samples. The initial slope, α_RLC, decreased monotonically with E in LL cultures, from 0.68 to 0.25 μmol⁻¹ m² s, while varied bi-phasically in HL-acclimated samples. Typically, α_RLC of HL cultures increased under low E, reaching a maximum of 0.61 μmol⁻¹ m² s under 25–55 μmol m⁻² s⁻¹, and decreased gradually under higher E levels to 0.25 μmol⁻¹ m² s. RLC maximum rETR, rETR_m,RLC, and saturation coefficient E_k,RLC, increased with E following a saturation-like pattern, with the HL cultures presenting markedly higher values for all the E range (maximum rETR_m,RLC values were 108.6 and 33.4 for HL and LL cultures, respectively). An inverse relationship was consistently found between α_RLC and NPQ, both on LL and HL cultures, causing strong correlations (P < 0.001 in all cases) between NPQ and the high light-induced decrease of α_RLC, Δα_RLC. RLCs were confirmed to also provide information on the long-term photoacclimation status, as significant correlations (P < 0.001 both for HL and LL cultures) were verified between E_k and an index based on RLC parameters, Ê_k, both for LL and HL cultures. These results reinforce the usefulness of RLCs as a tool for inferring on the short- and long-term photoacclimation status of samples with different long-term light histories, through the estimation of LC parameters and the monitoring of NPQ levels.     

Microbial treatment of high-strength perchlorate wastewater

To treat wastewater containing high concentrations of perchlorate, a perchlorate reducing-bacterial consortium was obtained by enrichment culture grown on high-strength perchlorate (1200 mg L⁻¹) feed medium, and was characterized in a sequence batch reactor (SBR) over a long-time operation. The consortium removed perchlorate in the SBR with high reduction rates (35-90 mg L⁻¹ h⁻¹) and stable removal efficiency over 200-day operations. The maximum specific perchlorate reduction rate (q_max), half saturation constant (K_s), and optimal pH range were 0.67 mg-perchlorate mg-dry cell weight⁻¹ h⁻¹, 193.8 mg-perchlorate L⁻¹, and pH 7-9, respectively. The perchlorate reduction yield was 0.48 mol-perchlorate mol-acetate⁻¹. A clone library prepared using the amplicons of cld gene encoding chlorate dismutase showed that the dominant (per)chlorate reducing bacteria in the consortium were Dechlorosoma sp. (53%), Ideonella sp. (28%), and Dechloromonas sp. (19%).     

Luminostat operation: a tool to maximize microalgae photosynthetic efficiency in photobioreactors during the daily light cycle?

The luminostat regime has been proposed as a way to maximize light absorption and thus to increase the microalgae photosynthetic efficiency within photobioreactors. In this study, simulated outdoor light conditions were applied to a lab-scale photobioreactor in order to evaluate the luminostat control under varying light conditions. The photon flux density leaving the reactor (PFD_out) was varied from 4 to 20 μmol photons m⁻² s⁻¹and the productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed.Maximal volumetric productivity (1.22 g kg⁻¹ d⁻¹) and biomass yield on PAR photons (400-700 nm) absorbed (1.27 g mol⁻¹) were found when PFD_out was maintained between 4 and 6 μmol photons m⁻² s⁻¹. The resultant photosynthetic efficiency was comparable to that already reported in a chemostat-controlled reactor. A strict luminostat regime could not be maintained under varying light conditions. Further modifications to the luminostat control are required before application under outdoor conditions.     

Influence of ammonium sulphate feeding time on fed-batch Arthrospira (Spirulina) platensis cultivation and biomass composition with and without pH control

Previous work demonstrated that a mixture of NH₄Cl and KNO₃ as nitrogen source was beneficial to fed-batch Arthrospira (Spirulina) platensis cultivation, in terms of either lower costs or higher cell concentration. On the basis of those results, this study focused on the use of a cheaper nitrogen source mixture, namely (NH₄)₂SO₄ plus NaNO₃, varying the ammonium feeding time (T = 7-15 days), either controlling the pH by CO₂ addition or not. A. platensis was cultivated in mini-tanks at 30 °C, 156 μmol photons m⁻² s⁻¹, and starting cell concentration of 400 mg L⁻¹, on a modified Schlösser medium. T = 13 days under pH control were selected as optimum conditions, ensuring the best results in terms of biomass production (maximum cell concentration of 2911 mg L⁻¹, cell productivity of 179 mg L⁻¹ d⁻¹ and specific growth rate of 0.77 d⁻¹) and satisfactory protein and lipid contents (around 30% each).     

Increased lipid production of the marine oleaginous microalgae Isochrysis zhangjiangensis (Chrysophyta) by nitrogen supplement

Effects of nitrate feeding on the cell growth and lipid accumulation of marine microalgae Isochrysis zhangjiangensis were investigated. When nitrate was supplied at interval of 24 h, instead of 72 h, a high lipid content of 40.9% and a biomass density of 3.1 g L⁻¹ were obtained. To confirm whether I. zhangjiangensis accumulates lipid during nitrogen-repletion, a two-stage cultivation method was applied. This algal strain had a high lipid content during sustained nitrate addition and showed a high carbohydrate content under nitrate-depletion conditions. These results revealed that this algal strain can accumulate lipids under nitrogen-repletion conditions and accumulate carbohydrate under nitrogen-depletion conditions. When cultured in an extremely high nitrate concentration, 9 g L⁻¹ at 24 h intervals, the growth of algal cells was suppressed, but the highest lipid content of 53% was attained. This special characteristic of lipid accumulation makes I. zhangjiangensis an ideal candidate for producing biodiesel using N-rich wastewater.     

Biointeraction analysis by high-performance affinity chromatography: Kinetic studies of immobilized antibodies

A system based on high-performance affinity chromatography was developed for characterizing the binding, elution and regeneration kinetics of immobilized antibodies and immunoaffinity supports. This information was provided by using a combination of frontal analysis, split-peak analysis and peak decay analysis to determine the rate constants for antibody–antigen interactions under typical sample application and elution conditions. This technique was tested using immunoaffinity supports that contained monoclonal antibodies for 2,4-dichlorophenoxyacetic acid (2,4-D). Association equilibrium constants measured by frontal analysis for 2,4-D and related compounds with the immobilized antibodies were 1.7–12 × 10⁶ M⁻¹ at pH 7.0 and 25 °C. Split-peak analysis gave association rate constants of 1.4–12 × 10⁵ M⁻¹ s⁻¹ and calculated dissociation rate constants of 0.01–0.4 s⁻¹ under the application conditions. Elution at pH 2.5 for the analytes from the antibodies was examined by peak decay analysis and gave dissociation rate constants of 0.056–0.17 s⁻¹. A comparison of frontal analysis results after various periods of column regeneration allowed the rate of antibody regeneration to be examined, with the results giving a first-order regeneration rate constant of 2.4 × 10⁻⁴ s⁻¹. This combined approach and the information it provides should be useful in the design and optimization of immunoaffinity chromatography and other analytical methods that employ immobilized antibodies. The methods described are not limited to the particular analytes and antibodies employed in this study but should be useful in characterizing other targets, ligands and supports.     

Effect of pre-incubation irradiance on survival of cryopreserved gametophytes of Undaria pinnatifida (Phaeophyta) and morphology of sporophytes formed from the gametophytes

Gametophyte strains originating from indigenous sporophytes of Undaria pinnatifida (Harvey) Suringar in Iwate Prefecture, Northeast Japan, were maintained for 9–10 months at 45 μmol photons m⁻² s⁻¹. Before cryopreservation in liquid nitrogen for more than 12 h (1–14 days) using a two-step cooling method with a mixture of cryoprotectants (10% l-proline and 10% glycerol), these were pre-incubated for 2, 4 and 8 months at 15 μmol photons m⁻² s⁻¹. After 1 week of thawing, no surviving gametophytes were detected in the strains without pre-incubation, but both the female and male gametophytes, pre-incubated for more than 4 months, showed high survival rates (43–60% for females and 64–100% for males). This revealed the induction of freezing tolerance by incubation at low irradiance. Thereafter, sporophytes derived from cryopreserved gametophytes and subcultured gametophytes, stored under pre-incubation conditions, were formed from the strain, and a morphological comparison was conducted with 10 characters (stipe length, stipe wet weight, blade length, blade wet weight, blade width, incision depth, blade thickness, sporophyll length, sporophyll wet weight, and sporophyll width). The morphology of the sporophytes formed from the cryopreserved gametophytes corresponded well with that of the subcultured gametophytes from the same strain. The results suggest that the cryopreservation method is applicable for preserving culture stocks of U. pinnatifida to be used in mariculture.     

Investigation on supraphysiological thermal injury in two well-differentiated human hepatoma cell lines,HepG2 and Hep3B

Hyperthermia is a promising treatment for carcinoma cells. The thermal injuries of two hepatoma carcinoma cell lines with the identical cytological grade, HepG2 and Hep3B cell lines, were investigated systematically in the present study. The homemade heating stage was used to provide a constant temperature between 40 and 70 °C for thermal treatment. When the cells were exposed to temperatures ranging from 40 to 45 °C, Hep3B cells had a lower thermotolerance than the HepG2 cells; however, the survival rate of these two cell lines was still high. The differences in thermotolerance between HepG2 and Hep3B cells were more significant at the range of 50–55 °C than those at lower-level temperatures of 40–45 °C. Furthermore, the viability of the cells was less than 10% when they were exposed to a supraphysiological temperature of 60 °C for 5 min; these cell lines suffered from injury saturation under that thermal treatment. The statistical analysis also concluded that Hep3B cells are more susceptible to heat stress than are the HepG2 cells when subjected to the thermal treatment applied in this work, the exception being when thermal injury saturation occurred. The kinematic parameters of the activation energy and frequency factor for HepG2 and Hep3B cells were also quantitatively determined herein. The activation energies (ΔE) for HepG2 and Hep3B cells were 170.17 and 152.44 kJ/mol, respectively. Furthermore, the frequency factors (A) for HepG2 and Hep3B cells were 4.11×10²⁴ and 1.07×10²² s⁻¹, respectively.     

Influence of current speed on clearance rate, algal cell depletion in the water column and resuspension of biodeposits of cockles (Cerastoderma edule)

The main objectives of this study were: 1) to determine the influence of water currents on the suspension feeding rate of cockles (Cerastoderma edule); 2) to quantify the interaction between cockle feeding and flow on algal cell depletion in the overlying water column, and 3) to measure the effect of flow on resuspension of their pseudofaeces and faeces. Flume experiments demonstrated that suspension feeding rate (i.e. clearance rate) of C. edule was not significantly affected by increasing current speed, at least between 5 and 35 cm s^− 1. Measurement of vertical profiles in algal cell concentrations within the water column showed a marked depletion above the bed, and the size of this was inversely related to currents' speeds below 5 cm s^− 1. At 2 cm s^− 1 the algal cell depletion was maximum immediately above the bed. However, below currents of 1 cm s^− 1 the maximum depletion was at 10 cm above the bed. This was a result of the exhalent jet of the cockle pumping filtered water (i.e. algal free) vertically into the water column and above the intake level of the inhalant siphon. Such stratification of the water column would appear to be beneficial to the cockle because it reduces the degree of re-filtration of algal cell depleted water at times of low flow, when there is poor mixing and thus poor replenishment of phytoplankton to the boundary layer. Critical erosion thresholds for cockle biodeposits, produced from a diet of silt and unicellular algae, were recorded at current velocities of 15 and 25 cm s^− 1, or shear velocities of 0.6 and 1.0 cm s^− 1, for pseudofaeces and faeces respectively.     

Kinetic and thermodynamic properties of the folding and assembly of formate dehydrogenase

The folding mechanism and stability of dimeric formate dehydrogenase from Candida methylica was analysed by exposure to denaturing agents and to heat. Equilibrium denaturation data yielded a dissociation constant of about 10⁻¹³ M for assembly of the protein from unfolded chains and the kinetics of refolding and unfolding revealed that the overall process comprises two steps. In the first step a marginally stable folded monomeric state is formed at a rate (k₁) of about 2 × 10⁻³ s⁻¹ (by deduction k₋₁ is about10⁻⁴ s⁻¹) and assembles into the active dimeric state with a bimolecular rate constant (k₂) of about 2 × 10⁴ M⁻¹ s⁻¹. The rate of dissociation of the dimeric state in physiological conditions is extremely slow (k₋₂ ∼ 3 × 10⁻⁷ s⁻¹).     

Rheology and dynamic light scattering of octa-ethyleneglycol-monododecylether/chitosan solutions

In this work we used rheometry and DLS to probe relaxation phenomena in solutions of chitosan and octa-ethyleneglycol-monododecylether. The dispersions had a marked pseudoplastic behavior, which became less evident, as surfactant concentration was increased. Arrhenius plots showed that systems with surfactant presented a characteristic temperature at which apparent enthalpy of activation (varying from 3 to 40 kJ mol⁻¹) changed: this change was correlated to a possible transition of colloidal aggregates to a wormlike configuration. DLS intensity correlation functions were described by KWW equation: pure chitosan solutions had relaxation rate distributions centered at a characteristic relaxation rate around 4.6 × 10⁻⁶ μS⁻¹; as surfactant was added, a new component, with a faster characteristic relaxation rate with a magnitude order of 10⁻³ μs⁻¹, appeared. It was shown that the dependence between these relaxation rates and surfactant concentration could be used to describe DLS-related relaxation phenomena as an Arrhenius-activated process, agreeing with results obtained using rheometry.     

Techno-economic implications of improved high gravity corn mash fermentation

The performance of Saccharomyces cerevisiae MBG3964, a strain able to tolerate >18% v/v ethanol, was compared to leading industrial ethanol strain, Fermentis Ethanol Red, under high gravity corn mash fermentation conditions. Compared to the industrial ethanol strain, MBG3964 gave increased alcohol yield (140 g L⁻¹ vs. 126 g L⁻¹), lower residual sugar (4 g L⁻¹ vs. 32 g L⁻¹), and lower glycerol (11 g L⁻¹ vs. 12 g L⁻¹). After 72 h fermentation, MBG3964 showed about 40% viability, whereas the control yeast was only about 3% viable. Based on modelling, the higher ethanol tolerant yeast could increase the profitability of a corn-ethanol plant and help it remain viable through higher production, lower unit heating requirements and extra throughput. A typical 50 M gal y⁻¹ dry mill ethanol plant that sells dried distiller’s grain could potentially increase its profit by nearly $US3.4 M y⁻¹ due solely to the extra yield, and potentially another $US4.1 M y⁻¹ if extra throughput is possible.     

Strong light-induced reorganization of pigment-protein complexes of thylakoid membranes in rye (spectroscopic study)

The supramolecular reorganization of LHCII complexes within the thylakoid membrane in Secale cereale leaves under low and high light condition was examined. Rye seedlings were germinated hydroponically in a climate chamber with a 16 h daylight photoperiod, photosynthetic photon flux density (PPFD) of 150 μmol m⁻² s⁻¹ and 24/16 °C day/night temperature. The influence of pre-illumination of the plants with high light intensity on the PSII antenna complexes was studied by comparison of the structure and function of the LHCII complexes and organization of thylakoid membranes isolated from 10-day-old plants illuminated with low (150 μmol m⁻² s⁻¹) or high (1200 μmol m⁻² s⁻¹) light intensity. Aggregated and trimeric with monomeric forms of LHCII complexes were separated from the whole thylakoid membranes using non-denaturing electrophoresis. Analyses of fluorescence emission spectra of these different LHCII forms showed that the monomer was the most effective aggregating antenna form. Moreover, photoprotection connected with LHCII aggregation was more effective upon LHCII monomers in comparison to trimer aggregation. Light stress induced specific organization of neighboring LHCII complexes, causing an increase in fluorescence yield of the long-wavelength bands (centered at 701 and 734 nm). The changes in the organization of the thylakoid membrane under light stress, observed by analysis of absorbance spectra obtained by Fourier transform infrared spectroscopy, also indicated light-induced LHCII aggregation.     

Mechanism and biological implications of the NO release of cis-[Ru(bpy)2L(NO)](n+) complexes: a key role of physiological thiols

Nitric oxide (NO) has a critical role in several physiological and pathophysiological processes. In this paper, the reactions of the nitrosyl complexes of [Ru(bpy)₂L(NO)]ⁿ⁺ type, where L = SO₃²⁻ and imidazole and bpy = 2,2′-bipiridine, with cysteine and glutathione were studied. The reactions with cysteine and glutathione occurred through the formation of two sequential intermediates, previously described elsewhere, [Ru(bpy)₂L(NOSR)]ⁿ⁺ and [Ru(bpy)₂L(NOSR)₂] (SR = thiol) leading to the final products [Ru(bpy)₂L(H₂O)]ⁿ⁺ and free NO. The second order rate constant for the second step of this reaction was calculated for cysteine k₂(SR⁻) = (2.20 ± 0.12) × 10⁹ M^− 1 s^− 1 and k_2(RSH) = (154 ± 2) M^− 1 s^− 1 for L = SO₃²⁻ and k₂(SR⁻) = (1.30 ± 0.23) × 10⁹ M^− 1 s^− 1 and k₂(RSH) = (0.84 ± 0.02) M^− 1 s^− 1 for L = imidazole; while for glutathione they were k₂(SR⁻) = (6.70 ± 0.32) × 10⁸ M^− 1 s^− 1 and k₂(RSH) = 11.8 ± 0.3 M^− 1 s^− 1 for L = SO₃²⁻ and k₂(SR⁻) = (2.50 ± 0.36) × 10⁸ M^− 1 s^− 1 and k₂(RSH) = 0.32 ± 0.01 M^− 1 s^− 1 for L = imidazole. In all reactions it was possible to detect the release of NO from the complexes, which it is remarkably distinct from other ruthenium metallocompounds described elsewhere with just N₂O production. These results shine light on the possible key role of NO release mediated by physiological thiols in reaction with these metallonitrosyl ruthenium complexes.     

Interaction of ruthenium(III) chloride with bis(3,5-dimethylpyrazol-1-yl)methane oxyanions, potential κ-N,N,O scorpionates

When RuCl₃ was set to react with both bis(3,5-dimethylpyrazol-1-yl)acetate (bdmpza) and bis(3,5-dimethylpyrazol-1-yl)methane sulfonate (bdmpzsa) new ruthenium(II) complexes were obtained. The reduction of ruthenium(III) was studied by the NMR Evans method and spectrophotometrically, for 1:1 (Ru:L) molar ratios. Using the Evans method pseudo first-order constants of 2.5 × 10⁻³ s⁻¹ (bdmpzsa) and 3.9 × 10⁻³ s⁻¹ (bdmpza) were obtained in DMSO-d₆ (2% t-butanol) solutions. Spectrophotometrically the corresponding constants were also calculated: 1.1 × 10⁻³ s⁻¹ for bdmpzsa, and 1.6 × 10⁻³ s⁻¹, for bdmpza. Both ligands behave as κ³-N,N,O scorpionates but with a weak oxyanionic coordination to the metal, susceptible to be substituted with NEt₃ for a 1:1 molar ratio.     

Temperature-sensitive paramagnetic liposomes for image-guided drug delivery: Mn versus [Gd(HPDO3A)(H2O)]

Temperature-sensitive liposomes (TSLs) loaded with doxorubicin (Dox), and Magnetic Resonance Imaging contrast agents (CAs), either manganese (Mn^2 +) or [Gd(HPDO3A)(H₂O)], provide the advantage of drug delivery under MR image guidance. Encapsulated MRI CAs have low longitudinal relaxivity (r₁) due to limited transmembrane water exchange. Upon triggered release at hyperthermic temperature, the r₁ will increase and hence, provides a means to monitor drug distribution in situ. Here, the effects of encapsulated CAs on the phospholipid bilayer and the resulting change in r₁ were investigated using MR titration studies and ¹H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles. Our results show that Mn^2 + interacted with the phospholipid bilayer of TSLs and consequently, reduced doxorubicin retention capability at 37 °C within the interior of the liposomes over time. Despite that, Mn^2 +-phospholipid interaction resulted in higher r₁ increase, from 5.1 ± 1.3 mM^− 1 s^− 1 before heating to 32.2 ± 3 mM^− 1 s^− 1 after heating at 60 MHz and 37 °C as compared to TSL(Gd,Dox) where the longitudinal relaxivities before and after heating were 1.2 ± 0.3 mM^− 1 s^− 1 and 4.4 ± 0.3 mM^− 1 s^− 1, respectively. Upon heating, Dox was released from TSL(Mn,Dox) and complexation of Mn^2 + to Dox resulted in a similar Mn^2 + release profile. From 25 to 38 °C, r₁ of [Gd(HPDO3A)(H₂O)] gradually increased due to increase transmembrane water exchange, while no Dox release was observed. From 38 °C, the release of [Gd(HPDO3A)(H₂O)] and Dox was irreversible and the release profiles coincided. By understanding the non-covalent interactions between the MRI CAs and phospholipid bilayer, the properties of the paramagnetic TSLs can be tailored for MR guided drug delivery.     

Experimental evidence for a 9-binding subsite of Bacillus licheniformis thermostable α-amylase

The action pattern of Bacillus licheniformis thermostable α-amylase (BLA) was analyzed using a series of ¹⁴C-labeled and non-labeled maltooligosaccharides from maltose (G2) to maltododecaose (G12). Maltononaose (G9) was the preferred substrate, and yielded the smallest K_m = 0.36 mM, the highest k_cat = 12.86 s⁻¹, and a k_cat/K_m value of 35.72 s⁻¹ mM⁻¹, producing maltotriose (G3) and maltohexaose (G6) as the major product pair. Maltooctaose (G8) was hydrolyzed into two pairs of products: G3 and maltopentaose (G5), and G2 and G6 with cleavage frequencies of 0.45 and 0.30, respectively. Therefore, we propose a model with nine subsites: six in the terminal non-reducing end-binding site and three at the reducing end-binding site in the binding region of BLA.