小球藻对镉离子的吸附速率方程

研究了小球藻对Cd^2 的吸附动力学。研究表明,小球藻对Cd^2 有一定的吸附作用,在吸附的起始阶段,吸附速率较快,且随温度的升高吸附速率增大,吸附过程在20min内达到平衡。结果还表明,该吸附是简单的一级反应,并由此建立了吸附反应的速率方程,推算出吸附反应的活化能Ea=31．42kl／mol。     

Solid model compounds and the thermodynamics of protein unfolding.

Analysis of thermodynamic data on the dissolution of solid cyclic dipeptides into water in terms of group additivity provides a rationale for the enthalpy and entropy convergence temperatures observed for small globular protein denaturation and the dissolution of model compounds into water. Convergence temperatures are temperatures at which the extrapolated enthalpy or entropy changes for a series of related compounds take on a common value. At these temperatures (TH* and TS*) the apolar contributions to the corresponding thermodynamic values (delta H degrees and delta S degrees) are shown to be zero. Other contributions such as hydrogen bonding and configurational effects can then be evaluated and their quantitative effects on the stability of globular proteins assessed. It is shown that the denaturational heat capacity is composed of a large positive contribution from the exposure of apolar groups and a significant negative contribution from the exposure of polar groups in agreement with previous results. The large apolar contribution suggests that a liquid hydrocarbon model of the hydrophobic effect does not accurately represent the apolar contribution to delta H degrees of denaturation. Rather, significant enthalpic stabilizing contributions are found to arise from peptide groups (hydrogen bonding). Combining the average structural features of globular proteins (i.e. number of residues, fraction of buried apolar groups and fraction of hydrogen bonds) with their specific group contributions permits a first-order prediction of the thermodynamic properties of proteins. The predicted values compare well with literature values for cytochrome c, myoglobin, ribonuclease A and lysozyme. The major thermodynamic features are described by the number of peptide and apolar groups in a given protein.     

Physiological characteristics underpinning successful cryopreservation of endemic and endangered species of Bromeliaceae from the Brazilian Atlantic Forest

The germination requirements and the basis of the optimal water content before and after cryopreservation were studied for ten endangered Brazilian species of Bromeliaceae. Constant and alternating temperature regimes were used to determine the best conditions for seed germination. The relationship between seed water content and relative humidity was evaluated using water sorption isotherms at 15 °C. Seeds were cryostored at four water contents (3, 5, 7 and 9%) and three storage periods (0, 180 and 365 days), and loss in viability and vigour were estimated. Fresh seeds of all species showed maximum germination in < 30 days at temperatures between 20 and 30 °C, indicating the absence of a physical/morphological dormancy. A sigmoidal relationship between seed water content and relative humidity was observed with no apparent differences in sorption characteristics among the species. The optimum water content for cryopreservation of most of these species was c. 7%. Ultra‐drying (3% seed water content) had a detrimental effect on seed viability and vigour. Our experiments suggested orthodox storage behaviour for all species of Bromeliaceae examined as they are able to survive desiccation and freezing. This study has shown the feasibility of ex situ conservation in seed cryobanks of endangered bromeliads from the Brazilian Atlantic Forest to support future reintroduction of these species in nature. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 567–576.     

Structure and stability of columnar cyclomaltohexaose (alpha-cyclodextrin) hydrate

Rapid recrystallization of cyclomaltohexaose (alpha-cyclodextrin, alpha-CD) from aqueous solution resulted in formation of the columnar crystal structure of alpha-CD containing only water as the guest molecule. Complementary water vapor sorption and wide-angle X-ray diffractometry (WAXD) experiments were performed on the alpha-CD columnar structure to elucidate the crystal structure present at varying sorption levels. Equilibrium isothermal water vapor sorption experiments at 40 degrees C revealed that the alpha-CD columnar structure is unstable above a water activity of approximately 0.67. This was confirmed by WAXD diffractograms collected over time, which further revealed that alpha-CD columnar structure undergoes a phase transformation to the cage structure after approximately 0.25 h at 40 degrees C and a water activity of 1.0.     

Effect of sucrose and maltodextrin on the physical properties and survival of air-dried Lactobacillus bulgaricus: an in situ fourier transform infrared spectroscopy study

The effect of sucrose, maltodextrin and skim milk on survival of L. bulgaricus after drying was studied. Survival could be improved from 0.01% for cells that were dried in the absence of protectants to 7.8% for cells dried in a mixture of sucrose and maltodextrin. Fourier transform infrared spectroscopy (FTIR) was used to study the effect of the protectants on the overall protein secondary structure and thermophysical properties of the dried cells. Sucrose, maltodextrin and skim milk were found to have minor effects on the membrane phase behavior and the overall protein secondary structure of the dried cells. FTIR was also used to show that the air-dried cell/protectant solutions formed a glassy state at ambient temperature. 1-Palmitoyl 2-oleoyl phosphatidyl choline (POPC) was used in order to determine if sucrose and maltodextrin have the ability to interact with phospholipids during drying. In addition, the glass transition temperature and strength of hydrogen bonds in the glassy state were studied using this model system. Studies using poly-L-lysine were done in order to determine if sucrose and maltodextrin are able to stabilize protein structure during drying. As expected, sucrose depressed the membrane phase transition temperature (Tm) of POPC in the dried state and prevented conformational changes of poly-L-lysine during drying. Maltodextrin, however, did not depress the Tm of dried POPC and was less effective in preventing conformational changes of poly-L-lysine during drying. We suggest that when cells are dried in the presence of sucrose and maltodextrin, sucrose functions by directly interacting with biomolecules, whereas maltodextrin functions as an osmotically inactive bulking compound causing spacing of the cells and strengthening of the glassy matrix.     

Superior Performance of Microporous Aluminophosphate with LTA Topology in Solar‐Energy Storage and Heat Reallocation

Hydrophilic porous materials are recognized as very promising materials for water‐sorption‐based energy storage and transformation. In this study, a porous, zeolite‐like aluminophosphate with LTA (Linde Type A) topology is inspected as an energy‐storage material. The study is motivated by the material's high predicted pore volume. According to sorption and calorimetric tests, the aluminophosphate outperforms all other zeolite‐like and metal‐organic porous materials tested so far. It adsorbs water in an extremely narrow relative‐pressure interval (0.10 < p /p ₀ < 0.15) and exhibits superior water uptake (0.42 g g^?1) and energy‐storage capacity (527 kW h m^?3). It also shows remarkable cycling stability; after 40 cycles of adsorption/desorption its capacity drops by less than 2%. Desorption temperature for this material, which is one of crucial parameters in applications, is lower from desorption temperatures of other tested materials by 10–15 °C. Furthermore, its heat‐pump performance is very high, allowing efficient cooling in demanding conditions (with cooling power up to 350 kW h m^?3 even at 30 °C temperature difference between evaporator and environment). On the microscopic scale, sorption mechanism in AlPO₄‐LTA is elucidated by X‐ray diffraction, nuclear magnetic resonance measurements, and first‐principles calculations. In this aluminophosphate, energy is stored predominately in hydrogen‐bonded network of water molecules within the pores.     

表面活性剂对链霉素在内蒙古牧区土壤中吸附解吸的影响

通过静态吸附实验,研究了3种不同类型的表面活性剂(阳离子:十六烷基三甲基溴化铵,CTAB;阴离子:十二烷基苯磺酸钠,SDBS;非离子,曲拉通100,TX-100)对链霉素(Streptomycin,STR)在内蒙古牧区土壤中吸附解吸的影响。结果表明,3种表面活性剂的存在均会增加STR在土壤中吸附的线性程度。CTAB的存在抑制了STR在土壤表面的吸附同时抑制了STR的解吸,然而SDBS的存在降低了STR在土壤中的吸附量并增加了吸附过程的可逆性。与CTAB和SDBS不同,TX-100对STR在土壤中的吸附的影响取决于其添加浓度。低浓度的TX-100对STR的吸附促进作用大于高浓度。随着TX-100浓度的增加,TX-100对STR的增溶作用加剧。促使吸附在土壤表面的STR迁移到水相中,从而抑制了STR的吸附,进而促进了STR的解吸。     

Characterization of cellulosic fibers and fabrics by sorption/desorption

Three cellulosic substrates: lyocell (CLY), viscose (CV), and modal (CMD) in the form of fibers and fabrics were subjected to wet/dry or wash/dry treatments. The accessibility of untreated and treated substrates to water and iodine was investigated using dynamic water-vapor sorption, moisture retention, and iodine sorption methods, to study the influence of treatments on sorption-desorption hysteresis, fraction of moisture sorbed as a monomolecular layer, water retention, and iodine sorption. It was found that the sorption properties of untreated and treated substrates differed with sorbate type as well as substrate type and form.     

Post functionalization of carboxymethylated starch and acrylonitrile based networks through amidoximation for use as ion sorbents

Carboxymethylation of starch provided carboxymethyl starch (CMS) and the modification was followed by grafting CMS with acrylonitrile (AN) using ammonium per sulphate-N,N,N,N-tetramethylethylene diamine as initiator–accelerator system. Crosslinked networks of CMS and AN were obtained using two crosslinkers, viz., N,N-methylenebisacrylamide and ethyleneglycoldimethacrylate. The networks were further reacted with hydroxylamine to generate metal ion active amidoxime groups. The synthesized hydrogels were characterized by FTIR, SEM, nitrogen analysis and swelling studies to evaluate water uptake and the candidate polymers were used as matrices for the sorption of Fe²⁺ ions, as a model metal ion, as a function of time, temperature, pH and ionic strength. An attempt was made to investigate the thermodynamics of its sorption behaviour.     

Structure and stability of columnar cyclomaltooctaose (gamma-cyclodextrin) hydrate

Rapid recrystallization of cyclomaltooctaose (gamma-cyclodextrin, gamma-CD) from aqueous solution resulted in formation of a columnar structure with only water as the guest molecule. Upon vacuum drying at 90 degrees C for 15 h, gamma-CD, which was initially in the columnar structure, became amorphous. Complementary water vapor sorption and wide-angle X-ray diffractometry experiments were performed on columnar gamma-CD in its vacuum dried and as-precipitated states to elucidate its stability in humid environments and the crystal structure present at varying sorption levels. These experiments show that both types of gamma-CD transform to the cage crystal structure upon exposure to water vapor at 40 degrees C and with an activity of 1.0. Sorption equilibrium is reached long before the crystal structure transformation is complete, indicating that a significant amount of molecular mobility exists in the various hydrated gamma-CD crystal structures.     

The use of dynamic vapour sorption methods for the characterisation of water uptake in amorphous trehalose

Water uptake by amorphous sugars is an issue of high importance for the food and pharmaceutical industries. However, while the processes associated with sorption-induced crystallisation have been widely studied, little is known regarding the uptake mechanisms associated with pre-crystallisation water levels. In the present investigation we use dynamic vapour sorption to study the water uptake mechanisms associated with amorphous trehalose. More specifically, we have prepared spray-dried amorphous trehalose with three initial water contents and studied water uptake as a function of time and relative humidity. We model the data obtained prior to crystallisation and suggest two mechanisms that are based on Type II diffusion (using the Peleg equation), which predominates under high humidity conditions (50% RH and above), while we use a Type I Fickian diffusion expression to model uptake under low relative humidity conditions (40% RH and below). The model allows prediction of equilibrium sorption values which correlate well with previously published data calculated from equilibrium vapour pressure data. We also note that the water content following recrystallisation is greater than that predicted by the stoichiometric ratio. A novel model is suggested whereby recrystallisation onset times may be estimated from the vapour sorption data. In conclusion the study has demonstrated that pre-crystallisation water sorption may be associated with two mechanisms depending on the humidity conditions and that such modelling allows insights into both the mechanisms of uptake and the storage behaviour of amorphous sugar samples.     

Geochemical behavior of lead in an alfisol and an ultisol at high leveis of contamination

The behavior of Pb in the A and B horizons of an Alfisol from Michigan and an Ultisol from Virginia was studied to determine the effects of “shock”; loading. Combined sequential extraction‐sorption isotherm analysis (CSSA), a relatively new and little tested method, was used in the study. After spiking to simulate severe contamination (～3000 to 60,000 mg/kg), CSSA revealed unexpectedly high levels of exchangeable Pb in the A horizon of the Alfisol and in both horizons of the Ultisol, and showed that the sorption capacities of the phases commonly responsible for fixation of Pb at low to moderate levels of contamination were exceeded. Carbonate sorbed the bulk of the Pb in the Alfisol B horizon and has a high sorption capacity in both soils, despite the presence of other phases with a strong affinity for Pb. Thus, when shock loading occurs (e.g., at a shooting range or dump sites), the highly contaminated A horizons of both soils are expected to pose a serious toxic hazard to humans, and groundwater contamination is possible in association with the Ultisol. CSSA proved useful for determining the sorption capacities of the individual phases while together in a natural soil system and therefore is a valuable method for predicting the attenuation capabilities of soils.     

Variation in Phosphorus Sorption with Soil Particle Size

Phosphorus (P) is considered a primary cause for surface water eutrophication that leads to anoxia. Understanding the relationships between soil particle size and P sorption helps devise effective best management practices (BMPs) to control P transport by erosion, leaching, and overland flow from agricultural land. Consequently, this study examined the effect of surface soil particle size on the sorption of P in five soil series (four Ultisols and one Entisol) from the Mid-Atlantic region. The sorption of P in each soil was assessed by equilibrating (after shaking for 24?h) 5?g soil containing varied amounts of KH₂PO₄ in 20?mL of 0.01?M KCl solution. Phosphorus in solution was determined by the molybdate blue method of Murphy and Riley. The P adsorption characteristics of these soils were described using the Langmuir isotherm. Results indicated that variability in P sorption was related to particle size and soil type. Soil organic matter content contributed a great deal to P sorption in the Entisol. However, soil clay had influence on the P sorption characteristics of each soil. The maximum P retentive capacities of soils (as determined by Sm from Langmuir equation) and P sorbed at 500?mg P kg^?1 addition showed a linear relationship (r2 = 0.94). Therefore, based on the results obtained, the single point method of Bache and Williams may be appropriate to describe the maximum P sorption capacity of non-sandy soils, as observed in this study.     

Water Content�CWater Activity�CGlass Transition Temperature Relationships of Spray-Dried Boroj�� as Related to Changes in Color and Mechanical Properties

The water content–water activity–glass transition temperature relationships of commercial spray-dried borojó powder, with and without maltodextrin, have been studied as related to changes in color and mechanical properties. The GAB and Gordon and Taylor models were well fitted to the sorption and glass transition data, respectively. The Boltzman equation adequately described the evolution of the mechanical parameter characterized in the samples with the difference between the experimental temperature and the glass transition temperature (T _g) of the sample. The color of the samples showed a sigmoid change with water activity. The changes in the mechanical properties of borojó powder related to collapse development started when the sample moved to the rubbery state and began to be significant at about 10 °C above T _g. The increase in the molecular mobility from this point on also favors browning reactions. Maltodextrin presence slows the caking kinetics but induces color changes to spray-dried borojó powder.     

Impacts of Soil Organic Matter and Temperature on Sorption of Acetazolamide on Four Soils

Batch sorptions of acetazolamide (AZ) were conducted using four soils from China. Sorption of AZ was found to be impacted by OC, clay content, and soil pH, with higher k_d values for soils with higher clay content. The k_d values of SOM-removed soils are much lower than those of bulk soils. Sorption data were well fitted with a Freundlich model (r² > 0.99). Chelating with the metal ions on the surfaces of soil particles was probably involved. With pH increase, the electrostatic attraction between anionic AZ and positively charged soil surface may increase. The sorption capacity decreased when the temperature increased from 20 to 40°C, and the calculated thermodynamics parameters of ΔG₀, ΔH₀, and ΔS₀ indicated that the sorption was a non-spontaneous, physisorption, and exothermic process. Sorption coefficients (k_d) for the compound in soil were low (ranging from 0.42 to 1.19 L·kg^?1) and indicated that low level sorption of AZ with appreciable risk of ground water contamination.     

Excipient selection can significantly affect solid-state phase transformation in formulation during wet granulation

Phase transformations in formulations can lead to instability in physicochemical, biopharmaceutical, and processing properties of products. The influences of formulation design on the optimal dosage forms should be specified. The aim here was to investigate whether excipients with different water sorption behavior affect hydrate formation of nitrofurantoin in wet masses. Nitrofurantoin anhydrate was used as a hydrate-forming model drug, and 4 excipients with different water-absorbing potential (amorphous low-substituted hydroxypropylcellulose, modified maize starch, partially amorphous silicified microcrystalline cellulose, and crystalline α-lactose monohydrate) were granulated with varying amounts of purified water. Off-line evaluation of wet masses containing nitrofurantoin anhydrate and excipient (1∶1) was performed using an X-ray powder diffractometer (XRPD) and near-infrared spectroscopy, and drying phase was evaluated by variable temperature XRPD. Only amorphous excipient in the formulation retarded hydrate formation of an active pharmaceutical ingredient (API) at high water contents. Hygroscopic partially crystalline excipient hindered hydrate formation of API at low water contents. Crystalline excipient was unable to control hydrate formation of API. The character of excipient affects the stability of formulation. Thus, correct selection of excipients for the formulation can control processing-induced phase transitions and improve the storage stability of the final dosage form. Published: October 6, 2005     

Phase separation and gel formation in kinetically trapped gelatin/maltodextrin gels

The kinetics of phase separation and gel formation of gelatin/maltodextrin mixtures have been studied using confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), stereological image analysis and rheology. The quantified microstructural parameters were the volume-weighted mean volume and the interfacial area. The temperature of phase separation was defined as the temperature where the first signs of phase separation were observed in CLSM. The gelatin concentration varied between 4 (wt.) and 5% and the maltodextrin concentration varied between 2 and 6%. Maltodextrin was labelled covalently with RITC to improve the contrast between the gelatin phase and the maltodextrin phase. The solutions were cooled from 60 to 10 degrees C, and the cooling rates used were 0.4, 1 and 3 degrees C/min. All systems were found to be gelatin continuous under the experimental conditions used. The results showed that the temperature of phase separation (TPS) increased both with the gelatin concentration and the maltodextrin concentration, but particularly with the former. The size of the maltodextrin inclusions increased with TPS, and the interfacial area decreased with increasing TPS. The diameter of the maltodextrin inclusions varied between 1.6 and 8.5 microm at 1 degrees C/min. The size of the maltodextrin inclusions was found to increase with decreasing cooling rate and was largest at 0.4 degrees C/min. The TPS was compared with the gelation temperature (Tgel) at three different concentrations of gelatin and maltodextrin (4/3, 4/5, 5/5%). CLSM micrographs and TEM micrographs showed that these three concentrations of gelatin and maltodextrin had different microstructures. At a TPS above Tgel (5/5%), the phase separation proceeded faster than the gel formation and the microstructure had few, large maltodextrin inclusions and a clean continuous gelatin phase. At a TPS comparable with Tgel (4/5%), phase separation occurred during gel formation, which led to a varying microstructure and competition between the phase separation and the gel formation. At a TPS below Tgel (4/3%), gel formation proceeded faster than the phase separation and the microstructure had many, small inclusions and a diffuse microstructure, and the phase separation was incomplete. It was established that the microstructure was determined by the relative rates of the phase separation and the gel formation. Three different zones of phase separation could be distinguished based on comparisons of TPS and Tgel, and results from CLSM, TEM and image analysis.     

Effect of glycerol on behaviour of amylose and amylopectin films

The effect of water and glycerol on sorption and calorimetric T_gs of amylose and amylopectin films were examined. The mechanical properties of the films were also analysed under varying glycerol content at constant RH and temperature. Based on changes observed in sorption and tensile failure behaviour glycerol was strongly interacted with both starch polymers. Even though water was observed to be more efficient plasticiser than glycerol, glycerol also affected the T_g. But in spite of the observed decrease in T_g under low glycerol contents brittleness of the films increased based on changes in elongation. The increase in brittleness of both polymers was also in agreement with their actual behaviour. At around 20% glycerol great change in the rheological properties occurred. Above 20% glycerol amylose film showed much larger elongation than the low glycerol content films and was still strong but the amylopectin produced a very week and non-flexible film.     

Cadmium(II) sorption from water samples by powdered marble wastes

Abstract

A series of batch adsorption experiments were carried out, with the aim of removing cadmium ions from aqueous solutions and water samples using powdered marble wastes (PMW) as an effective inorganic sorbent. PMW is inexpensive, widespread, and may be considered as environmental problem. The main parameters (i.e. solution pH, sorbent and cadmium concentrations, stirring time, and temperature) influencing the sorption process were investigated. The results obtained for sorption of cadmium ions onto PMW are well described by the Freundlich and Langmuir models. The Dubinin-Radushkevick (D–R) isotherm model was applied to describe the nature of the adsorption of the metal ion; it was found that the adsorption process was chemical in nature. The thermodynamic parameters were also calculated from the Gibbs free energy change (ΔG°), enthalpy (AH°) and entropy (ΔS°). These parameters indicated that the adsorption process of cadmium(II) ions on PMW was spontaneous and endothermic in nature. Under the optimum experimental conditions employed the removal of ca ~100% of Cd²⁺ ions was attained. The procedure was successfully applied to removal of the cadmium ions from aqueous and various natural water samples. The adsorption mechanism is discussed.