Initial Fast Step Research Articles

Reversible covalent inhibition of eEF-2K by carbonitriles.

eEF-2K is a potential target for treating cancer. However, potent specific inhibitors for this enzyme are lacking. Previously, we identified 2,6-diamino-4-(2-fluorophenyl)-4H-thiopyran-3,5-dicarbonitrile (DFTD) as an inhibitor of eEF-2K. Here we describe its mechanism of action against eEF-2K, on the basis of kinetic, mutational, and docking studies, and use chemoinformatic approaches to identify a similar class of carbonitrile-containing compounds that exhibit the same mechanism of action. We show that DFTD behaves as a reversible covalent inhibitor of eEF-2K with a two-step mechanism of inhibition: a fast initial binding step, followed by a slower reversible inactivation step. Molecular docking suggests that a nitrile group of DFTD binds within 4.5 Å of the active site Cys146 to form a reversible thioimidate adduct. Because Cys146 is not conserved amongst other related kinases, targeting this residue holds promise for the development of selective covalent inhibitors of eEF-2K.

Direct analytical sample quality assessment for biomarker investigation: qualifying cerebrospinal fluid samples.

Measurement of biochemical markers represents an important aid to clinicians in the early diagnosis and prognosis of neurological diseases. Many factors can contribute to increase the chances that a biomarker study becomes successful. In a cerebrospinal fluid analysis (CSF), more than 84% of laboratory errors can be attributed to several preanalytical variables that include CSF collection, storage, and freeze thawing cycles. In this concept paper, we focus on some critical issues arising from basic proteomics investigation in order to highlight some key elements of CSF quality control. Furthermore, we propose a direct assessment of sample quality (DASQ) by applying a fast MALDI-TOF-MS methodology to evaluate molecular features of sample degradation and oxidation. We propose DASQ as a fast and simple initial step to be included in large-scale projects for neurological biomarker studies. In fact, such a procedure will improved the development of standardized protocols in order to have well-characterized CSF biobanks.

Physisorption and chemisorption of a self-assembled monolayer by the quartz crystal microbalance.

A new adsorption model was developed to investigate the adsorption process of SAMs in the gaseous scenario, and the results were verified by using a prototype quartz crystal microbalance (QCM) sensor. In the experimental study, the observed properties in the gaseous scenario did not conform to the conventional theories well but matched the proposed adsorption model better. Hence, an optimal methodology for the theoretical study of adsorption process of SAMs was developed. The conventional adsorption model of Langmuir is suitable only for the fast initial adsorption step (i.e., physisorption) in the process of forming SAMs in the liquid scenario. Here, the rates of adsorption and desorption (ka, kd) at different temperatures were investigated. The activation barrier Ea= 59.738 kJ/mol was obtained by the Arrhenius equation. The result agreed well with that obtained experimentally. More importantly, this study has established a new avenue of QCM chip applications.

Exploiting the ion-exchange ability of titanate nanotubes in a model water softening process

Titanate nanotubes were utilized in Ca2+ and Mg2+ removal in a continuous ion-exchange unit. Three consecutive water softening–regeneration cycles were performed. The highest measured value of the total ion-exchange capacity was 1.2mmolg−1 which decreased to 0.66mmolg−1 in the third cycle. The capacity loss was due to the irreversible binding of Ca2+ ions to very strong adsorption sites, while the Mg2+/Na+ exchange was reversible. A relatively fast initial adsorption step and a subsequent slower concentration decrease were the two processes that governed the kinetics of the ion exchange reaction.

Carbon Isotope Exchange During Calcite Interaction With Brine: Implications for 14C Dating of Hypersaline Groundwater

Due to its possible role in solid/water carbon isotope exchange, the effect of salinity on radiocarbon dating of groundwater was examined by batch interaction of alluvial sediment and calcite powder with freshwater (Cl– = 100 mg L–1) and Dead Sea (DS) brine (Cl– = 225 g L–1). These 2 water types were spiked with H13CO3– tracer and kept under constant agitation for about 1 yr. Several bottles were respiked twice with the tracer. The uptake of the 13C by calcite was monitored through repeated isotopic measurements of the aqueous solutions, and the effect on 14C groundwater dating was evaluated using a simple transport reaction model. The results indicate that the kinetics of water/calcite isotope exchange start with a very fast initial step followed by a slower one, which was used here to simulate the long-term water/solid exchange in “real” aquifers. The exchange model that best fits the data was homogeneous recrystallization that formed just a very thin layer of newly formed calcite. The estimated recrystallization rates for calcite powder/solution interaction were much smaller for the DS brine than for freshwater: 3 × 10–5 to 7 × 10–6 and 9 × 10–4 to 7 × 10–5 mol m2 yr–1, respectively. The 13C experimental data imply a very small effect of the brine/calcite isotope exchange on the 14C age estimate for the brines within the DS coastal aquifer. However, when calcite recrystallization reaches ∼1% of the solid, the 14C groundwater dating estimates will show aging by ∼10%.

Carbon Isotope Exchange During Calcite Interaction With Brine: Implications for 14C Dating of Hypersaline Groundwater

Due to its possible role in solid/water carbon isotope exchange, the effect of salinity on radiocarbon dating of groundwater was examined by batch interaction of alluvial sediment and calcite powder with freshwater (Cl–= 100 mg L–1) and Dead Sea (DS) brine (Cl–= 225 g L–1). These 2 water types were spiked with H13CO3–tracer and kept under constant agitation for about 1 yr. Several bottles were respiked twice with the tracer. The uptake of the13C by calcite was monitored through repeated isotopic measurements of the aqueous solutions, and the effect on14C groundwater dating was evaluated using a simple transport reaction model. The results indicate that the kinetics of water/calcite isotope exchange start with a very fast initial step followed by a slower one, which was used here to simulate the long-term water/solid exchange in “real” aquifers. The exchange model that best fits the data was homogeneous recrystallization that formed just a very thin layer of newly formed calcite. The estimated recrystallization rates for calcite powder/solution interaction were much smaller for the DS brine than for freshwater: 3 x 10–5to 7 x 10–6and 9 x 10–4to 7 x 10–5mol m2yr–1, respectively. The13C experimental data imply a very small effect of the brine/calcite isotope exchange on the14C age estimate for the brines within the DS coastal aquifer. However, when calcite recrystallization reaches ∼1% of the solid, the14C groundwater dating estimates will show aging by ∼10%.

Nano-sulphonated poly (glycidyl methacrylate) cations exchanger for cadmium ions removal: Effects of operating parameters

Nano-poly (glycidyl methacrylate) cation exchange resin with sulphonate functionality content ranging from 1.77 to 4.00 (mmol/g) was prepared and examined in removal of cadmium ions from synthetic cadmium solution. Initial fast adsorption step was recognized at 15 min where 90% of cadmium ions were adsorbed while equilibrium was reached within two hours. The equilibrium adsorption capacities ranged from 9.947 to 480 mg/g of polymer as initial cadmium concentration increased from 100 to 5000 ppm. The adsorption experiments for Cd 2+ were conducted at various operating conditions. It was concluded that the sorption was considerably affected by initial cadmium concentration, solution pH and resin dose. Nevertheless, there was slight dependence of sorption on agitation speed, solution temperature and the sulphonation degree. The order of kinetic reaction was found to follow closely the second-order kinetic model and ion exchange mechanism played a significant role in all studied cadmium sorption systems. Moreover, the obtained results indicate that film diffusion governs the rate limiting process.

Dynamic Adsorption and Structure of Interfacial Bilayers Adsorbed from Lipopeptide Surfactants at the Hydrophilic Silicon/Water Interface: Effect of the Headgroup Length

Lipopeptides are an important group of biosurfactants expressed by microorganisms. Because they are well-known for being biocompatible, biodegradable, and highly surface active, they are attractive for a wide range of applications. Natural lipopeptide surfactants are however impure; it is hence difficult to use them for exploring the structure-function relation. In this work, a series of cationic lipopeptide surfactants, C(14)K(n) (n = 1-4), where C denotes the myristic acyl chain and K denotes lysine (Lys), have been synthesized, and their interfacial behavior has been characterized by studying their adsorption at the silicon/water interface (bearing a thin native oxide layer) using spectroscopic ellipsometry and neutron reflection (NR). The dynamic adsorption was marked by an initial fast step within the first 2-3 min followed by a slow molecular relaxation process over the subsequent 20-30 min. The initial rate of time-dependent adsorption and the equilibrated adsorbed amount showed a steady decrease with increasing n, indicating the impact of the molecular size, structure, and charge. NR revealed the formation of sandwiched bilayers from C(14)K(n), similar to conventional surfactants such as nonionic C(12)E(6) and cationic C(16)TAB. However, the electrostatic attraction between K and the silica surface caused confinement of the K groups, forcing the head segments into a predominantly flat-on conformation. This characteristic structural feature was confirmed by the almost constant thickness of the headgroup regions ranging from 8 to 11 Å as determined from NR combined with partial deuterium labeling to the acyl tail. An increase in area per molecular pair with n resulted directly from increasing the footprint. As a result, the hydrophobic back-to-back tail mixing and acyl chain tilting rose with n. The extent of chain-head intermixing became so intensified that the C(14)K(4) bilayer could be approximated to a uniform layer distribution.

Pharmaceuticals sorption behaviour in granulated cork for the selection of a support matrix for a constructed wetlands system

Biosorbents have been recently gaining importance, with an increasing number of publications on their environmental applications, especially for removal of organic pollutants from aqueous media. The aim of this work was to evaluate the sorption capacity of a biosorbent, namely granulated cork, to remove mixtures of ibuprofen (IB), carbamazepine (CB) and clofibric acid (CA) from water and wastewater. High removal efficiencies were attained for IB and CB while a less satisfactory performance was observed for CA. Simultaneous removal of the three compounds mixed in the same aqueous solution showed no significant differences in comparison to the removal of the isolated compounds in separate solutions, which indicates that no competitive sorption effects occurred at the highest concentrations tested. On the other hand, in wastewater medium the mixture of pharmaceuticals underwent a decrease in the sorbed amounts of all the three substances, probably due to the presence of dissolved organic matter which increases their solubilities. These compounds were removed in the following order of efficiencies in all the tested conditions: IB > CB > CA. The sorption kinetics were characterised by an initial fast step within the first 6 h, during which most of the removed pharmaceuticals amounts were sorbed. After the first 6 h, CA attained equilibrium concentrations whereas the sorption kinetics for IB and CB were characterised by two pseudo-second order stages, the first one up to 48 h and a slower one beyond 48 h. Shorter equilibration times and larger removed amounts of pharmaceuticals per unit weight of sorbent were observed in this study for granulated cork in comparison with a previously studied clay material (LECA). The results of this study showed the sorptive qualities of granulated cork but are only a first step in the evaluation of this material for use as support matrix in constructed wetlands designed for removal of pharmaceuticals from wastewaters.

Interfacial adsorption of lipopeptidesurfactants at the silica/water interface studied by neutron reflection

Lipopeptide surfactants are composed of amino acids and fatty acids and carry the inherent benefits of biocompatibility, degradability, functionality and easiness for structural design. In this work, the interfacial adsorption of a novel lipopeptide surfactant C14K1 has been examined by combining the measurements of spectroscopic ellipsometry (SE) and neutron reflection (NR). As for other model surfactants, the silicon oxide/water interface has been adopted to undertake the interfacial screening due to its readiness to facilitate the parallel measurements. SE revealed that the dynamic interfacial adsorption was characterized by an initial fast step within the first 2–3 min, followed by a slow relaxation step over the subsequent 30 min or so. Majority of the lipopeptide was found to adsorb with the fast initial step but the subsequent structural relaxation and adjustment led to the adsorption plateau. Interestingly, this pattern of dynamic adsorption is very different from amphiphilic peptides such as V6K1 and V6K2, but is similar to diblock copolymers bearing a hydrophilic MPC block and a pH responsive DEA block comprised of tertiary amine groups. Subsequent NR, in conjunction with deuterium labeling, revealed the formation of bilayer structure over a wide concentration and pH range, with the hydrophobic tails sandwiched in the middle and hydrophilic charged head groups projected outwards. The fully packed bilayer is some 40 Å thick and changes in pH did not affect layer thickness much but did alter the packing density due to the different electrostatic repulsion associated with the charge dissociation of the head groups. Whilst surface adsorption of C14K1 behaved in many aspects like nonionic C12E6 (surface tension, salt effect and bilayer packing), detailed structural determination revealed little intermixing between the heads and tails, an observation different from C12E6.

Establishing a new conductance stopped-flow apparatus to investigate the initial fast step of reaction between 1,1,1-trichloro-3-methyl-3-phospholene and methanol under a dry inert atmosphere

In the present work, for the first time, investigation of the initial fast step of reaction between 1,1,1-trichloro-3-methyl-3-phospholene (TCMP) and methanol was studied under a dry inert atmosphere by a newly constructed CSF apparatus by means of a further development in the configuration of the previous stopped-flow spectrophotometer (SFS). Hence, it was necessary to make many changes to the stopped-flow apparatus: replacement of the spectrophotometer amplifier with a conductance amplifier and the use of a conductivity cell to replace the optical one. The conductivity cell was made of polyethylene capillary tube (1 mm internal diameter; i.d.) and its inside dimensions were 1 mm i.d. × 3 mm long. Two tube electrodes which are made of stainless steel (0.8 mm i.d. × 14 mm long) were fixed at opposite ends of the observation cell and their outer surfaces were connected to the conductivity bridge amplifier by the two lead wires. The mixer was a 3-way Teflon valve and the distance between the mixer and the end of the observation cell was 30 mm. For each run, at least 24 µL of solution was required for a typical trace with a dead time of about 5 ms. Because of the extreme sensitivity of TCMP to moisture, the stopped-flow (CSF) apparatus was used inside a glove bag under a dry nitrogen atmosphere. Kinetic parameters for pseudo first-order reaction involving k(obs) = 30 s(-1) at 22 °C and activation energy E(a) = 13.55 KJ mol(-1) were successfully calculated for the initial fast step of the reaction between TCMP and methanol at 22 °C.

A tiered procedure for assessing the formation of biotransformation products of pharmaceuticals and biocides during activated sludge treatment

Upon partial degradation of polar organic micropollutants during activated sludge treatment, transformation products (TPs) may be formed that enter the aquatic environment in the treated effluent. However, TPs are rarely considered in prospective environmental risk assessments of wastewater-relevant compound classes such as pharmaceuticals and biocides. Here, we suggest and evaluate a tiered procedure, which includes a fast initial screening step based on high resolution tandem mass spectrometry (HR-MS/MS) and a subsequent confirmatory quantitative analysis, that should facilitate consideration of TPs formed during activated sludge treatment in the exposure assessment of micropollutants. At the first tier, potential biotransformation product structures of seven pharmaceuticals (atenolol, bezafibrate, ketoprofen, metoprolol, ranitidine, valsartan, and venlafaxine) and one biocide (carbendazim) were assembled using computer-based biotransformation pathway prediction and known human metabolites. These target structures were screened for in sludge-seeded batch reactors using HR-MS/MS. The 12 TPs found to form in the batch experiments were then searched for in the effluents of two full-scale, municipal wastewater treatment plants (WWTPs) to confirm the environmental representativeness of this first tier. At the second tier, experiments with the same sludge-seeded batch reactors were carried out to acquire kinetic data for major TPs that were then used as input parameters into a cascaded steady-state completely-stirred tank reactor (CSTR) model for predicting TP effluent concentrations. Predicted effluent concentrations of four parent compounds and their three major TPs were corroborated by comparison to 3-day average influent and secondary effluent mass flows from one municipal WWTP. CSTR model-predicted secondary effluent mass flows agreed within a factor of two with measured mass flows and confidence intervals of predicted and measured mass flows overlapped in all cases. The observed agreement suggests that the combination of batch-determined transformation kinetics with a simple WWTP model may be suitable for estimating aquatic exposure to TPs formed during activated sludge treatment. Overall, we recommend the tiered procedure as a realistic and cost-effective approach to include consideration of TPs of wastewater-relevant compounds into exposure assessment in the context of prospective chemical risk assessment.

Removal of pharmaceuticals in microcosm constructed wetlands using Typha spp. and LECA

Microcosm constructed wetlands systems established with a matrix of light expanded clay aggregates (LECA) and planted with Typha spp. were used to evaluate their ability to remove pharmaceuticals ibuprofen, carbamazepine and clofibric acid from wastewaters. Seasonal variability of these systems’ performances was also evaluated. Overall, removal efficiencies of 96%, 97% and 75% for ibuprofen, carbamazepine and clofibric acid, respectively, were achieved under summer conditions after a retention time of 7 days. In winter, a maximum loss of 26% in removal efficiency was observed for clofibric acid. Removal kinetics was characterized by a fast initial step (>50% removal within 6 h) mainly due to adsorption on LECA but, on a larger timescale, plants also contributed significantly to the system’s performance. Despite the fact that further tests using larger-scale systems are required, this study points to the possible application of these low-cost wastewater treatment systems for dealing with pharmaceuticals contaminated wastewater.

Impact of Structural Perturbation of Aluminum Hydroxides by Tannate on Arsenate Adsorption

The impacts of the biomolecule‐induced structural perturbation of Al hydroxides and the resultant alteration of their surface reactivity toward the adsorption of nutrients and contaminants have received, to date, scant attention, in spite of their significance in determining the mineralogy and surface chemistry of these mineral colloids. This study investigated the equilibria and kinetics of As(V) adsorption on a crystalline Al hydroxide, a pure amorphous Al hydroxide and a short‐range ordered Al–tannate coprecipitate. Isotherms and kinetics of As(V) adsorption were conducted at pH 6.5; the kinetic experiments (0.083–24 h) were performed at 288, 298, 308, and 318 K. The adsorption data followed multiple second‐order kinetics, with an initial fast reaction step, followed by a slow reaction. While As(V) adsorption on the crystalline Al hydroxide was a rapid process, the poorly ordered minerals required longer contact intervals and greater activation energies. Compared with the pure amorphous Al hydroxide, the incorporation of tannate into the structural network of Al hydroxide decreased the adsorption rate, capacity, and affinity for As(V). These effects were attributable to the blocking of part of the adsorption sites by tannate, to the electrostatic repulsion induced by the net negative charge caused by the deprotonated organic molecules exposed on the surface of the Al–tannate coprecipitate, and to the steric hindrance of tannate, hampering access of the adsorbate to the micropores. These findings are of fundamental significance in understanding the sorption behavior and mobility of As as influenced by biomolecule‐induced structural perturbation of Al hydroxides in the environment.

Atenolol removal in microcosm constructed wetlands

Microcosm constructed wetland systems established with a matrix of light expanded clay aggregates (LECA) and Typha spp. or Phragmites australis were used to evaluate their ability to remove atenolol from wastewater. Combined with an efficient SPE concentration step, the use of HPLC-DAD yielded an analytical method for atenolol quantification with very low LOQ (9 ng mL−1) and high reproducibility (RSD < 4%). Overall removal efficiencies of 92.5% and 94.5% were achieved after a retention time of only 4 days with the microcosm systems planted with Phragmites australis and Typha spp., respectively. The removal kinetics was characterised by an initial fast step (removal of about 75% after just 24 h) which is mainly attributable to adsorption on the LECA matrix. Atenolol removal in LECA beds continues to increase in a steady pace up to the end of the assay (8 days) being nevertheless about 5–10% lower than those observed in the planted beds after the first 4 days. For the retention time of 4 days most of the atenolol is removed by the LECA matrix but an additional 12–14% of the overall removal efficiency can be attributed to the Typha and Phragmites plants, which is in agreement with other published reports. Despite the fact that further tests using larger-scale flowing systems are required to evaluate fully the atenolol behaviour in constructed wetlands, this study points to the possible application of these low-cost wastewater treatment systems to treat atenolol contaminated wastewater.

Preliminary media screening for application in the removal of clofibric acid, carbamazepine and ibuprofen by SSF-constructed wetlands

The aim of the present work was to evaluate the sorption capacity of light expanded clay aggregates (LECA) to remove mixtures of ibuprofen, carbamazepine and clofibric acid in water and wastewater. High removal efficiencies were attained for carbamazepine and ibuprofen while a less satisfactory performance was observed for clofibric acid. In a mixture of the three compounds in water a slight decrease in the sorbed amounts is observed in comparison with solutions of the single compounds, indicating some competitive sorption. In wastewater, the pharmaceuticals mixture also undergoes a slight reduction in the sorbed amounts of carbamazepine and ibuprofen, probably due to the presence of dissolved organic matter which increases their solubility. These compounds were removed in the following order of efficiencies in all the tested conditions: carbamazepine > ibuprofen > clofibric acid. Two other clay materials – sepiolite and vermiculite – were tested for the removal of the more recalcitrant clofibric acid, and vermiculite exhibited higher removal efficiency than LECA. The sorption is characterized by an initial fast step, with most pharmaceuticals being removed within the first 24 h. The results of this study are a first step in the process of selecting an appropriate material or combination of materials to be used as media in SSF-CWs designed for the removal of pharmaceuticals from wastewaters.

Formation Mechanism of Amorphous TiO2 Spheres in Organic Solvents 2. Kinetics of Precipitation

This paper (Part 2) is a report on the kinetics of precipitation in a sol−gel system developed in Part 1 of this series for the formation of monodispersed amorphous TiO2 spheres through hydrolysis of titanium butoxide (TBO) in its homogeneous solution of a mixed solvent of butanol/acetonitrile (vol. ratio 1:1) with ammonia. The precipitation was performed by adding 5 cm3 of a composite solution of 1.0 M H2O and 0.20 M NH3 to 5 cm3 of 0.10 M TBO in 1 s and the following aging, under constant agitation at 25 °C. From Nielsenʼs chronomal analysis on the change of the electric conductivity of the system, 83% of the precipitation of the hydrolysis product was found to be completed by 2.5 s from the start of the admixing. The preceding hydrolysis of TBO was likely to have finished earlier than the start of the nucleation of the product particles, as revealed from the kinetic analysis on the hydrolysis and precipitation processes. The particle growth proceeded through a two-step process consisting of a very fast initial step finished at latest by 2.5 s and the following much slower one. The cause of the two-step process was explained in terms of the high initial reactivity of the particle surfaces prior to the adsorption of ammonia, as well as the possibility of precipitation of higher clusters under the extremely high supersaturation, and the following deactivation of the particle surfaces by retarded adsorption of ammonia. The second step was found to proceed in a third-order reaction-controlled kinetics supposedly by direct deposition of the trimer of hydrolysis product in equilibrium with the monomer and dimer. Finally, mechanisms of particle formation in relevant sol−gel systems of TiO2 and ZrO2 are discussed in the light of the present results.

Interfacial adsorption and denaturization of human milk and recombinant rice lactoferrin

Lactoferrin (LF) produced from recombinant technologies can achieve almost identical amino acid sequences and three-dimensional structures to those extracted from mammals, but differences often arise in the carbohydrate chains attached through N-glycosylation, with altered sizes, structures, and chemical nature. We compare the differences in solvation and interfacial adsorption from two samples, human milk lactoferrin (hLF) and recombinant rice lactoferrin (rLF). Lactoferrin is a bilobal protein with a molecular weight of about 80 kD. It has three N-glycosylation sites. Each of the three attached glycan chains on rLF contains seven to eight sugar groups. In comparison, each of the three glycan chains attached to hLF contains 12-13 sugar groups and is twice as long. The rLF meting point in 1 mg/ml aqueous solution (pH 7 phosphate buffer, I=20 mM) was 43 degrees C from dynamic light scattering, compared to 53 degrees C for hLF, exhibiting the enhanced solvation and stability of hLF due to its longer carbohydrate side chains. Silicon oxide surfaces provided a model substrate for assessment of lactoferrin adsorption and comparison with other proteins. The time dependent interfacial adsorption studied by spectroscopic ellipsometry (SE) was characterized by a fast initial step followed by a slow relaxation process. In addition, the SE results revealed the persistently higher adsorption of rLF, again showing the effect of glycan side chains. In spite of the different adsorbed amounts, neutron reflection revealed similar interfacial structures of the adsorbed protein layers. At the low lactoferrin concentration around 10 mg/l, a flat-on molecular monolayer formed with both LF lobes attached to the SiO(2) surface through electrostatic attraction. As the protein concentration increased, a secondary molecular layer further adsorbed to the first one and the attachment was again driven by electrostatic attraction. The intermixing between the globular lobes resulted in the dense packing in the middle 60 A with some of the lobes projected toward the aqueous bulk solution.

Kinetic Model for the Antiradical Activity of the Isolated p-Catechol Group in Flavanone Type Structures Using the Free Stable Radical 2,2-Diphenyl-1-picrylhydrazyl as the Antiradical Probe

The time evolution of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH*) concentration in four solvents (methanol, ethanol, propanol, and acetonitrile) during its reduction by three flavanones containing an isolated p-catechol group (taxifolin, eriodyctiol, and fustin) as well as the time evolution of the mass spectra of the reaction mixture has been determined by spectrophotometry and liquid mass spectrometry, respectively. In alcoholic solvents the reduction curves consisted of an initial short but fast kinetics step followed by a longer slow kinetics step; in contrast, in acetonitrile the reduction curves completely lacked the slow kinetics step. From the results, a kinetic model for the reaction of reduction of the DPPH* by the isolated p-catechol group in flavanone type structures is proposed. According to this model, the p-catechol group rapidly transfers two hydrogen atoms to DPPH*, through a fast rate constant k1, yielding the corresponding o-quinone. Then, the intermediate o-quinone forms an adduct with the alcoholic solvent, through a slow rate constant k2, and regenerates the p-catechol group. The regenerated p-catechol group reduces additional DPPH* through a fast rate constant k3, yielding the corresponding o-quinone, which can form a new adduct with the solvent to regenerate the p-catechol group, and so on. From the kinetics model, two explicit kinetics equations have been derived that fit very well the experimental data points acquired from all assayed compounds in all of the experiments carried out, thus allowing an accurate determination of the corresponding rate and stoichiometric constants.

Spermidine and Spermine Catalyze the Formation of Nanostructured Titanium Oxide

Naturally occurring polyamines putrescine, cadaverine, spermidine, and spermine are analogues of the species-specific long-chain polyamines found in diatoms. Scanning electron microscopy and energy-dispersive spectroscopy show that the reactions of a soluble Ti(IV) precursor with spermidine and spermine, but not putrescine or cadaverine, produce nanostructured irregular polyhedra of titanium oxide. At 25 degrees C, the average size of the particles formed with spermidine is 400 +/- 150 nm, and with spermine, 140 +/- 50 nm. Although the particles are X-ray amorphous at room temperature, annealing studies reveal that the particles adopt crystallinity at higher temperatures characteristic of anatase (TiO2). The major portion of the biopolyamines is not coprecipitated with the solid but is left in solution. Kinetic measurements reveal an initial fast step followed by two slower phases of reaction. At 25 degrees C, k(1obs) and k(2obs) for the reaction with spermidine are 5 x 10(-3) s(-1) and 3.6 x 10(-4) s(-1), respectively, and for spermine, 4.8 x 10(-3) s(-1) and 4.2 x 10(-4) s(-1), respectively. Taken together, the data suggest spermidine and spermine are biocatalysts for the precipitation of nanostructured titanium oxide.