Kinetic Plots Research Articles

Reversible addition–fragmentation chain transfer (RAFT) polymerization of 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA)

This investigation reports reversible addition–fragmentation chain transfer (RAFT) polymerization of 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) in dioxane. In this case 4-cyanopentanoic acid dithiobenzoate (CPDTB) was used as the chain transfer agent (CTA) and 4,4′-azobis(4-cyanovaleric acid) (ABCVA) was used as the thermal initiator. The linear kinetic plot i.e. ln([M]0/[M]) vs polymerization time indicated that polymerization was first order with reference to monomer concentration. The resultant polymers had controlled molecular weight and had well-defined RAFT end group, as evidenced by 1H NMR and MALDI-TOF-MS analyses. These polymers were also characterized by GPC, 19F NMR, DSC and TGA analyses.

High‐resolution peptide separations using nano‐LC at ultra‐high pressure

We report on the optimization of nano-LC gradient separations of proteomic samples that vary in complexity. The gradient performance limits were visualized by kinetic plots depicting the gradient time needed to achieve a certain peak capacity, while using the maximum system pressure of 80 MPa. The selection of the optimal particle size/column length combination and corresponding gradient steepness was based on scouting the performance of 75 μm id capillary columns packed with 2, 3, and 5 μm fully porous silica C18 particles. At optimal gradient conditions, peak capacities up to 500 can be obtained within a 120 min gradient using 2 μm particle-packed capillary columns. Separations of proteomic samples including a cytochrome c tryptic digest, a bovine serum albumin tryptic digest, a six protein mix digest, and an Escherichia coli digest are demonstrated while operating at the kinetic-performance limit, i.e. using 2-μm packed columns, adjusting the column length and scaling the gradient steepness according to sample complexity. Finally, good run-to-run retention time stability (RSD values below 0.18%) was demonstrated applying ultra-high pressure conditions.

The Ozawa’s generalized time concept and YZ-master plots as a convenient tool for kinetic analysis of complex processes

The concept of generalized time $$ \theta = \int {{ \exp }\left( { - E_{\text{a}} /RT} \right){\text{d}}t} $$ in non-isothermal kinetics was introduced by Ozawa in 1965, together with the well-known isoconversional plot, i.e., Ozawa plot. The generalized time is the key concept to tie the kinetic data under varying temperature to the kinetic relationship at a constant temperature. It is well known that many processes studied by thermal analysis and calorimetry reveal a complex nature. Therefore, the generalized time concept seems to be very useful for the description of the change in the rate behavior depending on the fractional conversion. Using the concept of θ, three kinds of experimental master plots can be formalized in differential, integral, and multiplied forms. Among others, combination of the differential and multiplied master plots, y(α) = (dα/dθ) and z(α) = (dα/dθ)θ, show a high performance to discriminate the kinetic model based on the maxima condition of y(α y*) and z(α z*). The α y* − α y* kinetic plot is a useful tool to visualize the complexity of the kinetic process and to determine the most suitable kinetic model. The usefulness of α y* − α y* kinetic plot and the YZ-master plots is illustrated as exemplified by the kinetic analyses of complex crystallization processes of the as-prepared, thermally and mechanically treated amorphous zirconia.

Controlled cationic polymerization of furfuryl alcohol

CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyst system was used successfully in the controlled cationic polymerization of furfuryl alcohol initiated with benzyl bromide in acetonitrile. Polymerizations were carried out at 110°C open to air. The effect of reaction time, amount of initiator and solvent on the rate of polymerization was studied. The linear kinetic plot of ln([M]o/[M]) versus polymerization time, linear dependence of the molecular weight on the monomer conversion and low polydispersity of the polymers (1.07–1.50) showed the characteristics of the controlled polymerization. Soluble polymers with Mn up to 6.6kg/mol were obtained. The structural analysis of the polymer was carried out by 1H NMR, 13C NMR, FTIR and UV–VIS spectroscopies. Formation of carbonyl groups and CH2OCH2 bridges on poly(furfuryl alcohol) chains were observed. Thermal properties of the polymer were studied by DSC and TGA analyses.

Poly(methyl methacrylate‐co‐pentaerythritol tetraacrylate‐co‐butyl methacrylate)‐g‐polystyrene: Synthesis and high oil‐absorption property

AbstractWell‐defined high oil‐absorption resin was successfully prepared via living radical polymerization on surface of polystyrene resin‐supported N‐chlorosulfonamide group utilizing methyl methacrylate and butyl methacrylate as monomers, ferric trichloride/iminodiacetic acid (FeCl3/IDA) as catalyst system, pentaerythritol tetraacrylate as crosslinker, and L‐ascorbic acid as reducing agent. The polymerization proceeded in a “living” polymerization manner as indicated by linearity kinetic plot of the polymerization. Effects of crosslinker, catalyst, macroinitiator, reducing agent on polymerization and absorption property were discussed in detail. The chemical structure of sorbent was determined by FTIR spectrometry. The oil‐absorption resin shows a toluene absorption capacity of 21 g g−1. The adsorption of oil behaves as pseudo‐first‐order kinetic model rather than pseudo‐second‐order kinetic model. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Quasi-equilibrium crystal shapes and kinetic Wulff plots for gallium nitride grown by hydride vapor phase epitaxy

In this paper we demonstrate work on developing the kinetic Wulff plots and quasi-equilibrium crystal shapes of GaN by hydride vapor phase epitaxy to understand the stable polar, semipolar, and nonpolar planes that emerge naturally from the GaN crystal. High quality bulk m-plane GaN substrates were masked with circular openings to perform selective area growth studies. Growths were performed by hydride vapor phase epitaxy over a range of temperatures, pressures and carrier gases. The quasi-equilibrium crystal shapes were shown to have clear m-plane {11¯00} facets and a sharp and flat (0001¯) N-face or c− face. The (0001) Ga-face or c+ face became faceted with {101¯1} planes emerging with reduced pressures and temperatures. Based on the stable facets, kinetic Wulff plots were constructed.

A kinetic study of atom transfer radical polymerization of styrene with bis(2-pyridyl)ethylenedimethanimine derivative ligands

Atom transfer radical polymerization (ATRP) of styrene was carried out with multidentate nitrogen-based ligands, namely N,N'-bis[phenyl(pyrid-2-yl)methylene] ethane-1,2-diamine (BPDA) and N,N'-bis[methyl(pyrid-2-yl)methylene] ethane-1,2-diamine (BMDA), and catalyst systems at catalyst/ligand molar ratios of 1/0.33, 1/0.5, 1/1, and 1/1.5 by using 2 different initiators, (1-bromoethyl)benzene (BEB) and ethyl-2-bromopropionate (EBP). Linear first-order kinetic plots were observed for ATRP of styrene upon using BPDA as a ligand with both initiators. Even though the linear slopes indicate that radical concentration remains constant during reactions, high molecular weights were obtained at low conversion and showed a linear relation thereafter. To investigate the molecular weight effect, reactions were also performed in the presence of (1-bromoethyl)benzene initiator in dimethylformamide (DMF) for BPDA and in toluene for BMDA using a catalyst/ligand ratio of 1/1.

Living Radical Polymerizations of Methyl Methacrylate Mediated by Tris-(4-Carboxyphenyl) Methane

Pseudo-living radical polymerization and reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) were reported, utilizing tris-(4-carboxyphenyl)methane (TCOPM) as the thermal iniferter and initiator, respectively. The polymerization of MMA using TCOPM as thermal iniferter possesses pseudo-living characteristics: Mn increases with conversion in a certain range, and the resulted polymer can be used as the macro-initiator for chain extension. The RATRP using TCOPM as the initiator shows linear kinetic plot, linear increase of Mn with conversion and narrow polydispersity indice (PDI) of the resultant polymers. Effects of temperature on both polymerizations were investigated.

Adsorption of amphoteric aromatic compounds by hyper-cross-linked resins with amino groups and sulfonic groups

For efficient enrichment of amphoteric aromatic compounds p-aminophenol (PAP), p-aminobenzoic acid (PABA) and sulfanilic acid (SA) from water, two types of hyper-cross-linked resins NJ-6 with sulfonic groups and NJ-99 with tertiary amino groups were compared in this study. The kinetics plots show that the adsorption of PAP on NJ-6 and NJ-99 are both favorable processes with over 80% and 67% of the equilibrium capacity reached within 30min and all of the kinetics data follows the pseudo-second-order rate equation well. Intra-particle diffusion is not the only rate-limiting step except in the first 6min. In FT-IR spectra, the peaks concerned with the functional groups of the resins were weakened or shifted after adsorption. The ratio of the equilibrium adsorption capacities (Qe) between NJ-99 and NJ-6 increase with the decreasing pKa1 values of adsorbates and the character of adsorption on NJ-99 will be changed from reversible to irreversible with the decreasing pKa1 values of adsorbates, too. Therefore, we may deduce that the interaction between acidic groups of the adsorbates and amino groups of NJ-99 would play a more dominant role with the decreasing pKa values of the adsorbates. The Koble–Corrigan model, a combination of the Langmuir and Freundlich isotherm models give the best fit to the equilibrium adsorption isotherms of the adsorbates on NJ-99 at different temperatures. Molecular form of the adsorbate is favorable for the adsorption.

Retention characteristics of Cu2+, Pb2+, and Zn2+ from aqueous solutions by two types of low lime fly ashes

The technical feasibility of utilization of fly ash as a low-cost adsorbent for the removal of metals from water has been studied. For two types of fly ashes, the retention capacities of copper, lead, and zinc metal ions have been studied. Contact time, initial concentration, and pH have been varied and their effect on retention mechanism has been studied. The dominant mechanisms responsible for retention are found to be precipitation due to the presence of calcium hydroxide, and adsorption due to the presence of silica and alumina oxide surfaces in the fly ash. First-order kinetic plots have revealed that the rate constant increases with increase in the initial concentration and pH. Langmuir adsorption isotherms have been plotted to study the maximum adsorption capacities for metal ions considered under different conditions. X-ray diffraction studies revealed the formation of new peaks corresponding to respective metal ions precipitates under alkaline conditions.

Effect of storage conditions on MMA polymerization via Fe(III)-mediated ATRP without any reducing agent

In a variety of storage conditions, Fe(III)-mediated polymerization of methyl methacrylate (MMA) uses FeX3 (X=Cl & Br), diphenyl-2-pyridylphosphine (DPPP) ligand and ethyl-2-bromoisobutyrate (EBriB) as an initiator at 80 °C in toluene without using any external reducing agents. The FeCl3 and FeBr3 containing 980 and 1,890 ppm of water during outside storage for 2 and 4 days, respectively, were successfully used for MMA polymerization through atom transfer radical polymerization (ATRP) without using any reducing agent. Moisture content of the polymerization system increases as the period of outside storage increases. It turned out that most of the polymerizations were under control even after keeping metal salts and their complexes outdoors for 4 days exhibiting a polydispersity less than 1.5. The kinetic plot between ln [M]0/[M] and time demonstrated linearity during the polymerization. A chain extension study clearly reveals that the moisture contaminated FeX3 due to outdoor storage, is able to catalyze the ATRP of MMA in the absence of any additive by a living radical mechanism. Open image in new window

Investigating of Synthesis Parameters, Kinetics and Pilot Plant of Sodium Sarcosinate

Abstract Sodium sarcosinate, an anionic surfactant, is known as a methylated glycine derivative, that is synthesized in a one-step amidation reaction. In this work, to find out the best conditions, several experiments carried out. So, the highest yield was obtained at (303)°C, by gradual addition of sodium monochloro acetate to methylamine solution. The total reaction time is 6 hours. Based on data, and the plots of kinetics of the reaction, a second-order reaction equation was suggested for this synthesis reaction. The rate constant (κ), and the regression coefficient (R2) were found as 0.0085 and 0.0934, respectively, which were in the best agreement with second-order reactions. According to the results, these data were applied for scale up laboratory to pilot phase. In addition, an industrial plant was suggested and designed.

Kinetic Studies of Colour and Phenol Removal from Wastewater using Mango Seed Shell Activated Carbon

Kinetic studies by batch technique were carried out using activated carbon prepared from mango seed shell for the adsorption of colour and phenol from wastewater. The data generated from the studies were used for kinetic modelling in order to determine the rate and mechanism of adsorption. The results revealed that adsorption was best fitted by the pseudo-second order model for both methylene blue (MB) and phenol adsorptions. Intra-particle diffusion kinetic plots did not pass through the origin, indicating that intra-particle diffusion was not the only rate controlling mechanism. The results showed that mango seed shell activated carbon (MSSAC) is more effective for adsorption of colour than phenol in wastewater.

Synthesis and characterization of copolymer grafted magnetic nanoparticles via surface‐initiated nitroxide‐mediated radical polymerization

Abstract“Grafting from” surface‐initiated nitroxide‐mediated radical polymerization (SI‐NMRP) techniques were used to synthesize poly[styrene‐co‐(maleic anhydride)] copolymer brushes from the Fe3O4 surfaces. Well‐defined polymer chains were grown from the Fe3O4 surfaces to yield particles with a Fe3O4 core and a polymer outer layer. The observed narrow molecular weight distributions (Mw/Mn), linear kinetic plots and linear plots of molecular weight (Mn) versus conversion for the free polymer indicated that the chain growth from the Fe3O4 surface was a controlled process by adding an excess of 2,2,6,6‐tetramethylpiperidinyloxy (TEMPO). The modified nanoparticles were subjected to detailed characterization using XRD, TEM, FT‐IR, and TGA. The analyses of vibration sample magnetometer (VSM) verified that the nanoparticles owned good magnetic property. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Tris(2,4,6-trimethoxyphenyl)phosphine (TTMPP) as Potent Organocatalyst for Group Transfer Polymerization of Alkyl (Meth)acrylates

Several commercial trialkyl phosphines were tested as organic catalysts for the group transfer polymerization (GTP) of methyl methacrylate (MMA) and tert-butyl acrylate (tBA). Among them, only tris(2,4,6-trimethoxyphenyl)phosphine (TTMPP) was able to bring about the “controlled/living” GTP of both monomers at room temperature, in bulk and/or in THF solution, using 1-methoxy-2-methyl-1-[(trimethylsilyl)oxy]prop-1-ene (MTS) as initiator. However, control of the polymerization appeared to be more difficult in the case of tBA compared to MMA. Poly[alkyl(meth)acrylate]s exhibiting dispersities <1.37 in bulk and <1.45 in THF, and molar masses in good accordance with the initial [monomer]0/[MTS]0 molar ratio could thus be obtained in quantitative yields. Poly(methyl methacrylate)-b-poly(tert-butyl acrylate) block copolymers, with final dispersity <1.2 and controlled molar masses, were also synthesized by sequential TTMPP-catalyzed GTP. First order kinetics plot of the GTP of MMA revealed an induction period of a few hours, which strongly depended on the initial polymerization conditions. The tacticity of the final PMMA’s (mm/mr/rr = 0.06/0.42/0.52) were very similar to that of an anionically derived PMMA. These data are in favor of the occurrence of a dissociative mechanism, forming minute amounts of true enolate-type propagating species, during the TTMPP-catalyzed GTP of MMA in THF. Analyses by 13C and 29Si NMR spectroscopy at room temperature of 1/1 molar MTS/TTMPP mixtures did not show the formation of enolate-type species.

Biphasic Kinetic Behavior of E. coli WrbA, an FMN-Dependent NAD(P)H:Quinone Oxidoreductase

The E. coli protein WrbA is an FMN-dependent NAD(P)H:quinone oxidoreductase that has been implicated in oxidative defense. Three subunits of the tetrameric enzyme contribute to each of four identical, cavernous active sites that appear to accommodate NAD(P)H or various quinones, but not simultaneously, suggesting an obligate tetramer with a ping-pong mechanism in which NAD departs before oxidized quinone binds. The present work was undertaken to evaluate these suggestions and to characterize the kinetic behavior of WrbA. Steady-state kinetics results reveal that WrbA conforms to a ping-pong mechanism with respect to the constancy of the apparent Vmax to Km ratio with substrate concentration. However, the competitive/non-competitive patterns of product inhibition, though consistent with the general class of bi-substrate reactions, do not exclude a minor contribution from additional forms of the enzyme. NMR results support the presence of additional enzyme forms. Docking and energy calculations find that electron-transfer-competent binding sites for NADH and benzoquinone present severe steric overlap, consistent with the ping-pong mechanism. Unexpectedly, plots of initial velocity as a function of either NADH or benzoquinone concentration present one or two Michaelis-Menten phases depending on the temperature at which the enzyme is held prior to assay. The effect of temperature is reversible, suggesting an intramolecular conformational process. WrbA shares these and other details of its kinetic behavior with mammalian DT-diaphorase, an FAD-dependent NAD(P)H:quinone oxidoreductase. An extensive literature review reveals several other enzymes with two-plateau kinetic plots, but in no case has a molecular explanation been elucidated. Preliminary sedimentation velocity analysis of WrbA indicates a large shift in size of the multimer with temperature, suggesting that subunit assembly coupled to substrate binding may underlie the two-plateau behavior. An additional aim of this report is to bring under wider attention the apparently widespread phenomenon of two-plateau Michaelis-Menten plots.

Design and evaluation of various methods for the construction of kinetic performance limit plots for supercritical fluid chromatography

Supercritical fluid chromatography (SFC) is attributed many advantages over high performance liquid chromatography (HPLC). Next to the fact that SFC is greener than HPLC, which is especially important for preparative separations, SFC is claimed to be able to deliver faster separations at higher efficiencies (N) than HPLC. This is due to the higher diffusitivity of analytes in supercritical fluids compared to liquids (higher optimum mobile phase velocity) and to the lower viscosity of the mobile phases in SFC compared to HPLC, which results in smaller pressure drops allowing the use of longer columns and/or columns packed with smaller particles at higher velocities. In order to quantify this claimed kinetic performance advantage, it is essential to construct unbiased kinetic plots to make the comparison between HPLC and SFC. The high compressibility of the mobile phase in SFC however makes this problematic. A variable column length (L) kinetic plot method is therefore developed in this work. Because the pressure history in the column is kept constant for every data point in this method, this way of working definitely delivers exact values for the kinetic performance limits in SFC. It is shown that the traditional way of measuring the performance as a function of flow rate (fixed back pressure and column length) cannot deliver the same correct results as this variable L method. However, the isopycnic way of working on a fixed column length has also been proven to be a good alternative for the expensive and time consuming variable L method. Finally, isopycnic kinetic plots are used to compare SFC and HPLC performance in a quantitative way.

Kinetic performance comparison of a capillary monolithic and a fused-core column in micro-scale liquid chromatography

The kinetic performance of monolithic and fused-core capillary C18 columns was compared in isocratic-elution liquid chromatography. Heptanophenone was chosen as a test compound. The (u0, H) couple obtained in a column with permeability Kv0 was transferred into a plate number, dead time (N, t0) couple and the kinetic plots were achieved by using a Kinetic Method Plot Analyzer template. The u0,opt (0.98mm/s for the monolith and 1.05mm/s for the fused-core column) and Hmin (17.58μm for the monolith and 18.08μm for the fused-core column) values determined from the van Deemter curve were found to be almost identical, whereas the Nopt (the plate number for which the support achieves its best analysis time/pressure cost ratio) (150,000 for monolith and 41,000 for fused-core column), maximal plate number, Nmax (the maximum plate number that can ever be reached with a support) (550,000 for monolith and 120,000 for the fused-core column) and optimal analysis time, topt (the time needed to obtain Nopt plates) (18,583s for the monolith and 4,068s for the fused-core column) performance numbers determined from the kinetic plots were found to be significantly different.

Adsorption kinetics of Rhodamine-B on used black tea leaves

Rhodamine B (Rh-B) is one of the most common pollutants in the effluents of textile industries effluents in developing countries. This study was carried out to evaluate the applicability of used black tea leaves (UBTL) for the adsorptive removal of Rh-B from aqueous system by investigating the adsorption kinetics in batch process. The effects of concentration and temperature on adsorption kinetics were examined. First-, second- and pseudo-second order kinetic equations were used to investigate the adsorption mechanism. The adsorption of Rh-B on UBTL followed pseudo-second order kinetics. The equilibrium amount adsorbed and the equilibrium concentration were calculated from pseudo-second-order kinetic plots for different initial concentrations of Rh-B to construct the adsorption isotherm. The adsorption isotherm was well expressed by Langmuir equation. The maximum adsorption capacity of UBTL to Rh-B was found to be 53.2 mg/g at pH = 2.0. The equilibrium amount adsorbed, calculated from pseudo-second-order kinetic plots, increased with temperature increase. The positive value of enthalpy of adsorption, ΔHads = 31.22 kJ/mol, suggested that the adsorption of Rh-B on UBTL at pH = 2.0 is an endothermic process.

Maximizing the peak capacity using coupled columns packed with 2.6 μm core–shell particles operated at 1200 bar

We report on the peak capacity that can be produced by operating a state-of-the-art core–shell particle type (dp=2.6μm) at its kinetic optimum at ultra-high pressures of 600 and 1200bar. The column-length optimization needed to arrive at this kinetic optimum was realized using column coupling. Whereas the traditional operating mode (using a single 15cm column operated at its optimum flow rate of 0.4mL/min) offered a peak capacity of 162 in 10.8min, a fully optimized train of 60cm (4×15cm) columns offered a peak capacity of 325 in 61min when operated at 1200bar. Even though the particles have a reputed low flow resistance and a relatively large size (>2μm), it was found that the increase in performance that can be generated when switching from a fully optimized 600bar operation to a fully optimized 1200bar operation is significant (roughly 50% reduction of the analysis time for the same peak capacity and approximately a 20% increase in peak capacity if compared for the same analysis time). This has been quantified in a generic way using the kinetic plot method and is illustrated by showing the chromatograms corresponding to some of the data points of the kinetic plot curve.