Residual Reactant Research Articles

Competitive Specific Anchorage of Molecules onto Surfaces: Quantitative Control of Grafting Densities and Contamination by Free Anchors.

The formation of surfaces decorated with biomacromolecules such as proteins, glycans, or nucleic acids with well-controlled orientations and densities is of critical importance for the design of in vitro models, e.g., synthetic cell membranes and interaction assays. To this effect, ligand molecules are often functionalized with an anchor that specifically binds to a surface with a high density of binding sites, providing control over the presentation of the molecules. Here, we present a method to robustly and quantitatively control the surface density of one or several types of anchor-bearing molecules by tuning the relative concentrations of target molecules and free anchors in the incubation solution. We provide a theoretical background that relates incubation concentrations to the final surface density of the molecules of interest and present effective guidelines toward optimizing incubation conditions for the quantitative control of surface densities. Focusing on the biotin anchor, a commonly used anchor for interaction studies, as a salient example, we experimentally demonstrate surface density control over a wide range of densities and target molecule sizes. Conversely, we show how the method can be adapted to quality control the purity of end-grafted biopolymers such as biotinylated glycosaminoglycans by quantifying the amount of residual free biotin reactant in the sample solution.

Rational immobilization of l-threonine aldolase from Bacillus nealsonii for efficiently synthesis of l-syn-3-[4-(methylsulfonyl)] phenylserine

l-syn-3-[4-(methylsulfonyl)] phenylserine is a key industrial intermediate for the synthesis of florfenicol, thiamphenicol, and other products. l-Threonine aldolase can synthesize l-syn-3-[4-(methylsulfonyl)] phenylserine from glycine and 4-methylsulphonyl benzaldehyde directly. However, the selectivity of free l-threonine aldolase was difficult to meet the requirement of industrialization. Here, we selected the suitable site to insert His tag as immobilized site to improve the selectivity of l-threonine aldolase based on the molecular dynamics simulation and prior protein engineering. The phenanthroline was coupled to the surface of magnetic nanoparticles coated with silicon and thus enabled the selective and oriented immobilization of His-tagged l-threonine aldolase. Due to magnetic nanoparticles coated with silicon as supports, it was easy to separate the residual reactant and impurities from the immobilized enzyme by magnetic attraction. Moreover, the immobilization was combined with the purification of free enzymes through directional immobilization, which avoided heterozyme linking supports and improved the utilization efficiency of supports. Our study demonstrates an effective approach: how to analyze and select enzyme-targeted ligation sites in conjunction with previous modifications of engineered bacteria, and the immobilized enzyme obtained also provided a good candidate for the industrial production of l-syn-3-[4-(methylsulfonyl)] phenylserine.

Reactive sintering of yttrium-doped barium zirconate (BaZr0.8Y0.2O3-δ) without sintering aids

The effects of Yttrium-doped Barium Zirconate (BZY) synthesis steps by solid-state reaction and the number of starting reactants (2 or 3) on the characteristics of the synthesized ceramic powders were investigated. The slow diffusion rate associated with this synthesis route and the calcination steps used in this work lead to an incomplete synthesis reaction. This condition proved to be useful to improve densification during sintering for undoped samples by emulating the reactive sintering technique with transient reactions originating from the residual BaCO3 reactant. The effects of a low concentration (1 mol%) of ZnO as sintering aid on microstructure and electrical conductivity were also investigated and used for comparison to undoped samples. Electrical properties were analyzed and correlated with microstructural and compositional characteristics. Dense undoped BZY samples (99% of relative density) with high proton conductivity (2.4×10−2S/cm at 600 °C) were obtained by sintering at 1500 °C, while ZnO-doped samples achieved high relative density (97%) at only 1300 °C, but with lower electrical conductivity (7.8×10−3 S/cm at 600 °C).

Screening of functional solvent system for automatic aldehyde and ketone separation in aldol reaction: A combined COSMO-RS and experimental approach

An integrated reaction-separation process based on only solvents is presented, and thus without the need for related technical equipment (reactor-separator). Both product purification and reactant recovery are achieved automatically for an asymmetric aldol reaction employing a biphasic solvent system as compartmentalizing soft matter. Firstly, COSMO-RS based simulation is introduced as a theoretical guidance in the solvent selection for the reactant 3-chlorobenzaldehyde and non-solvent selection for the R-aldol product, (R)-4-(3-chlorophenyl)-4-hydroxybutan-2-one. This encompasses solubility as core critical parameter, as well as chemo-physical properties and environmental profiling. Such criteria-cascaded screening could effectively reduce a 7665 solvents-database into 1 candidate solvent, which is dodecane, before experimental process assessment. Secondly, this screening’s top candidate was validated as the best reaction solvent by first a solubility test and then by a batch reaction, in which a conversion of 69% was achieved. As desired, the mono-phase reaction yielded spontaneously the product layer and the separate dodecane phase as the second layer, which indeed allowed facile separation of the product from the residual reactant. In a third step, a segmented flow process was developed giving a highest product yield of 63% and a total conversion 92% respectively after a 2 h residence time.

Chemically-oscillating reactions during the diagenetic oxidation of organic matter and in the formation of granules in late Palaeoproterozoic chert from Lake Superior

Filamentous and coccoidal microfossils have been reported since the 1950's from a range of granular cherts from the late Palaeoproterozoic southwestern Superior Craton, Canada-United States. However, the chemical and mineral compositions of granules, the presence of microfossils in granules, and the common presence of granules in intercolumnar space of stromatolitic chert are poorly documented and explained. Furthermore, the depositional model for the origin of granules in wave-agitated waters does not entirely explain their mineral diversity nor their characteristic morphologies and patterns. We report on the crystallinity of organic matter, mineral diversity, and compositions of microfossils in granules from three different kinds of late Palaeoproterozoic cherts, namely phosphatic, organic, and haematitic. Stromatolitic organic-rich chert from the Gunflint Fm contains granules with euhedral carbonate and equidistant concentric laminations of organic matter, akin to fractal patterns from the Belousov-Zhabotinsky (B-Z) chemically-oscillating reaction. These granules also contain authigenic anatase, ferric-ferrous silicates, and Fe-oxides. Filamentous and coccoidal microfossils similar to those of the Gunflint occur in chert from the Biwabik Formation and share morphology, and co-occur with Mn-siderite and apatite. Granules in phosphatic chert in the Michigamme Formation often contain filamentous and coccoidal microfossils composed of organic matter, sericite, and apatite. Bulk carbonate associated with these Michigamme granular phosphatic chert beds has systematically negative δ13Ccarb values around −3.1±0.9‰ (1σ) and δ18Ocarb-SMOW between +20.8 and +30.7‰, which suggest some contribution from the diagenetic oxidation of organic matter. Notably, residual carboxylic acid is detectable in C-XANES spectra of organic matter from granular phosphatic chert, which is a residual reactant of B-Z type reactions. Along with previously reported observations of pyritised microfossils from the Gunflint Formation, these distinct mineralogies indicate variable modes of preservation for the products of chemically-oscillating reactions that likely relate to the availability of different oxidants in the diagenetic environment. We conclude that the late Palaeoproterozoic shallow-marine environments of the Lake Superior area were populated by morphologically similar micro-organisms, and that the diagenetic oxidation of organic matter through chemically-oscillating reactions contributed to the formation of spheroidal rosettes, granules, and concretions during a late Palaeoproterozoic Great Putrefaction Event. Granules in chert that contain organic matter or microfossils thus provide a reliable petrographic context to search for a record of putrefaction of microbial life on the early Earth and on other ancient planetary surfaces.

Dual-functional aniline-assisted wet-chemical synthesis of bismuth telluride nanoplatelets and their thermoelectric performance

The wet-chemical approach is of great significance for the synthesis of two-dimensional (2D) bismuth telluride nanoplatelets as a potential thermoelectric (TE) material. Herein, we proposed a simple and effective solution method with the assistance of aniline for the fabrication of bismuth telluride nanoplatelets at a low temperature of 100 °C. The choice of aniline with its dual function avoided the simultaneous use of a capping regent and a toxic reductant. The as-synthesized nanoplatelets have a large size of more than 900 × 500 nm2 and a small thickness of 15.4 nm. The growth of bismuth telluride nanoplatelets are related to the Bi/Te ratio of precursors indicating that a larger content of the Bi precursor is more conducive to the formation of 2D nanoplatelets. The bismuth telluride nanoplatelets pressed into a pellet show a smaller electrical resistivity (∼6.5 × 10−3 Ω · m) and a larger Seebeck coefficient (−135 μV K−1), as well as a lower thermal conductivity (0.27 W m−1 K−1) than those of nanoparticles. The next goal is to further reduce the electrical resistivity and optimize the TE performance by disposing of the residual reactant of aniline adsorbed on the surface of the nanoplatelets.

Fractionation of sulfur and hydrogen isotopes in Desulfovibrio vulgaris with perturbed DsrC expression.

Dissimilatory sulfate reduction is the central microbial metabolism in global sulfur cycling. Understanding the importance of sulfate reduction to Earth's biogeochemical S cycle requires aggregating single-cell processes with geochemical signals. For sulfate reduction, these signals include the ratio of stable sulfur isotopes preserved in minerals, as well as the hydrogen isotope ratios and structures of microbial membrane lipids preserved in organic matter. In this study, we cultivated the model sulfate reducer, Desulfovibrio vulgaris DSM 644T, to investigate how these parameters were perturbed by changes in expression of the protein DsrC. DsrC is critical to the final metabolic step in sulfate reduction to sulfide. S and H isotopic fractionation imposed by the wild type was compared to three mutants. Discrimination against 34S in sulfate, as calculated from the residual reactant, did not discernibly differ among all strains. However, a closed-system sulfur isotope distillation model, based on accumulated sulfide, produced inconsistent results in one mutant strain IPFG09. Lipids produced by IPFG09 were also slightly enriched in 2H. These results suggest that DsrC alone does not have a major impact on sulfate-S, though may influence sulfide-S and lipid-H isotopic compositions. While intriguing, a mechanistic explanation requires further study under continuous culture conditions.

Extractive bioconversion of poly-ϵ-caprolactone by Burkholderia cepacia lipase in an aqueous two-phase system

In this study, the optimum condition for extractive bioconversion of poly-ϵ-caprolactone using Burkholderia cepacia lipase in an aqueous two-phase system (ATPS) was established. The optimum condition was found using a combined approach of full factorial design and conventional one-factor-at-a-time studies. Optimum extractive bioconversion was achieved at pH 7.0, 40°C and composed of 19% (w/w) PEG 3000, 8.1% (w/w) potassium phosphate, with TLL of 28% (w/w) and VR of 80:20. Under this condition, 79.8% products and 42.0% lipase was recovered from the upper and lower phases, respectively. The products consisted of both the monomeric and dimeric forms of ϵ-caprolactone. An inverse relationship was observed between the temperature of bioconversion and the melting, crystallization as well as initial decomposition temperatures of the residual reactant. The molecular weight of the residual reactant decreased with increasing bioconversion temperature whereas the opposite trend was observed for its polydispersity index.

Simplified multiple equations' inverse problem of vented vessels subjected to internal gas explosions

This paper analyses the experimental data reported by Höchst and Leuckel (1998) for combustion in partially confined vessels and uses the data from these experiments to establish the burning rate based on a simplified model for the combustion process in such vessels. The model establishes three fundamental parameters which are necessary in characterizing the combustion process. These are: i) the burning rate, ii) the fraction of vent area occupied by burnt gas (or discharge sub-model), and iii) the vent area model (if cover mechanisms with variable vent areas are utilized). A set of independent equations is derived to determine the burning rate according to conservation of mass and volume for each gas fraction separately along with a general equation based on general volume conservation. Using this method we are able to describe the combustion process and examine the effect of various discharge models. The advantages of the model presented here include rapid applicability and a valuable analysis to derive mass burn rate and other useful parameters using experimental data from vented explosions with reasonable residual reactant values. Based on these results, the correct interpretation of the obtained burning rate can be used in order to explain the correct prediction of flame velocity and position according to a reasonable discharge model. The paper also evaluates the suitability of several discharge models for phenomenological models of vented explosions. The most appropriate is a Heaviside step function which considers that only unburnt gas is initially expelled, with that component decreasing and the burnt gas component increasing until finally only burnt gas is expelled. The obtained results in this study can be used to predict the burning rate behavior and the combustion process of similar problems.

Design and operation of a filter reactor for continuous production of a selected pharmaceutical intermediate

A novel filter reactor system for continuous production of selected pharmaceutical intermediates is presented and experimentally verified. The filter reactor system consists of a mixed flow reactor equipped with a bottom filter, to retain solid reactant particles, followed by a conventional plug flow reactor, where residual reactant is converted by titration. A chemical case study, production of the pharmaceutical intermediate allylcarbinol by a reaction between allylmagnesium chloride and 2-chloro-thioxanthone, in the presence of a side reaction is considered. The synthesis is conducted in tetrahydrofuran solvent. The use of the filter reactor design was explored by examining the transferability of a synthesis step in a present full-scale semi-batch pharmaceutical production into continuous processing. The main advantages of the new continuous minireactor system, compared to the conventional semi-batch operation, are reduced impurity formation and the use of much lower reactor volumes (factor of 1000 based on the laboratory reactor) and less solvent consumption (from 5.8 to 2.3L/kg reactant). Added challenges include handling of continuous solid powder feeding, stable pumping of reactive slurries, and a possibility of continuous control.

Powder synthesis and aerosol deposition of the BaCe 0.9Y 0.1O 2.95 and SrCe 0.9Y 0.1O 2.95 phases for gas separation membrane application

Mixed-conducting oxide powders, BaCe 0.9Y 0.1O 2.95 (BCY) and SrCe 0.9Y 0.1O 2.95 (SCY), were prepared using a solid-state reaction method. X-ray diffraction patterns of the prepared powders showed the sharp peaks of the BaCe 0.9Y 0.1O 2.95 and SrCe 0.9Y 0.1O 2.95 phases. XRD patterns and FE-SEM morphologies of the oxide powders, fabricated by attrition milling and ball milling, were compared. The oxide powders that were prepared by attrition milling showed rather large particles and severe necking between particles in FE-SEM images as well as residual reactant (BaCO 3) and secondary phases (SrCeO 3 and CeO 2) in XRD patterns. The oxide powders prepared using ball milling showed particles under approximately 500 nm and typical XRD patterns of the BaCe 0.9Y 0.1O 2.95 and SrCe 0.9Y 0.1O 2.95 phases. Ceramic membranes of the BaCe 0.9Y 0.1O 2.95 and SrCe 0.9Y 0.1O 2.95 phases were fabricated by the aerosol deposition method using the oxide powders synthesized. Two fabricated ceramic membranes demonstrated somewhat dense morphologies and relatively fine grains in the FE-SEM surface images.

ROTATIONAL BARRIERS AND VIBRATIONAL SPECTRA OF PHENYL KETENE, AZIDE, AND ISOCYANATE

Our interest in conjugation effects in substituted phenyl compounds has turned our attention to the highly reactive compounds phenyl ketene, azide, and isocyanate, which due to their reactivity are of utmost importance in organic synthesis. We performed local density functional theory (DFT) calculations using a 6-311G** basis set to calculate the structures and potential functions of the internal rotation. Further for the minimum structures we computed the vibrational infrared and Raman spectra of the three molecules. In order to confirm that DFT works rather well in these systems we performed the geometry optimizations also using ab initio Moeller–Plesset perturbation theory of second order (MP2) in the same basis set. As expected there exist just two minimum structures for each of the molecules which both correspond to planar structures and are identical due to the symmetry of the phenyl ring. The transitions states (TS) of the internal rotations are the perpendicular ones. We expect conjugation to play no major role in these molecules since extensive conjugation effects would imply a large reduction of the aromatic character of the phenyl ring which in turn would greatly destabilize the systems. However, although the rotational barriers appear to be rather small in these systems conjugation must play at least some role in stabilizing the planar ground state. As detailed later, the relative heights of the rotational barriers can all be explained naturally. Experimental vibrational spectra could be obtained only for phenyl isocyanate and azide, but not for the ketene because of the high reactivity of this molecule. Since in the former cases the calculated spectra agree fairly well with the measured ones, we present those of the other molecule as theoretical prediction, which could be useful to detect spectroscopically in a reaction mixture residual reactant. On the basis of potential energy distribution (PED) calculations we present a complete assignment of the vibrational lines to symmetry coordinates, where, for example, ring breathing must show up with rather large intensities in the Raman spectra of the molecules.

Impregnated carbon for degradation of diethyl sulphide

Activated carbon of surface area 1100 m 2/g was impregnated with 5 wt.% ruthenium chloride by using its aqueous solution. Obtained carbon was exposed to the vapors of diethyl sulphide at room temperature (30 ± 1 °C). Thereafter, the reaction products were extracted in dichloromethane and analyzed using gas chromatography and mass spectrometry. The data revealed that, the impregnated carbon reacted with diethyl sulphide producing the diethyl sulphone. In addition to the above reaction product, residual reactant was also observed. Reaction mechanisms have also been proposed for these interesting surface reactions.

Bimolecular ion-molecule collisions in real time: co +( 3f 4) + n-butane and isobutane reactions

A pulsed beam of Co +( 3F 4) is crossed with a pulsed beam of n-butane or isobutane gas under single collision conditions at collision energies of 0.01 eV and 0.22 or 0.23 eV, respectively. After a variable time delay t ext = 1–8 μs, a fast high voltage pulse extracts product ions and residual reactant ions into a field-free flight tube for mass analysis. Consistent with earlier work, we observe four product channels in the Co + + n-butane reaction: long-lived CoC 4H 10 + complexes and three elimination products, CoC 2H 4 + + C 2H 6, CoC 3H 6 + + CH 4, and CoC 4H 8 + + H 2. In the Co + + isobutane reaction, we detect long-lived CoC 4H 10 + complexes and two elimination products, CoC 3H 6 + + CH 4 and CoC 4H 8 + + H 2. We discuss plausible mechanisms for these reactions, based on insights from our recent statistical modeling based on density functional theory (B3LYP) calculations for the related systems, Ni + + propane, Co + + propane, and Ni + + n-butane. The postulated reaction pathways for Co + + n-butane and Co + + isobutane neatly explain the data from our experiment and a variety of others. From a combination of theory and experiments, a satisfyingly consistent picture of the reactions of late 3d-series metal cations with alkanes has emerged.

Gas-Phase Ni+(2D5/2) + n-C4H10 Reaction Dynamics in Real Time: Experiment and Statistical Modeling Based on Density Functional Theory

A beam of Ni+(2D5/2) is formed at a sharp zero of time by resonant two-photon ionization with a nanosecond dye laser pulse and crossed with a beam of n-butane-h10 or n-butane-d10 gas. The ion−molecule reaction occurs under single-collision conditions in field-free space in the extraction region of a time-of-flight mass spectrometer. After a variable time delay text = 0.5−8 μs, a fast high-voltage pulse extracts product ions and residual reactant ions into a field-free flight tube for mass analysis. Analysis of the metastable decay of NiC4H10+ complexes from tailing of fragment ion peaks and from retarding field separation reveals detailed information about the formation of elimination products (primarily ethane and H2) and the decay back to Ni+ reactants in different time windows from 0.2 to 25 μs after initiation of the collision. To understand the data, we have used density functional theory in its B3LYP variant to locate and characterize the geometries, potential energies, and vibrational frequencies o...

Bimolecular reaction dynamics of Co +( 3F 4) + acetone reaction in real time

A beam of Co +( 3F 4) is formed at a sharp zero of time by resonant two-photon ionization with a ns dye laser pulse and crossed with a beam of acetone gas under single collision conditions at collision energies E t = 0.01 eV and 0.23 eV. The ion-molecule reaction occurs in field-free space in the extraction region of a time-of-flight mass spectrometer. After a variable time delay t ext = 0.8 − 8 μs, a fast high voltage pulse extracts product ions and residual reactant ions into a field-free flight tube for mass analysis. Consistent with earlier work, we observe three product channels, formation of long-lived CoC 3H 6O + complexes and the two elimination products, CoCO + (+ C 2H 6) and CoC 2H 6 + (+ CO). The long-lived complexes decay to elimination products and back to Co + + acetone reactants on a wide range of time scales, as revealed by retarding field analysis of the metastable decay. Some complexes eliminate C 2H 6 on a 500 ns timescale, as revealed by tailing of the CoCO + peak. Other complexes still have not decayed on a 25 μs time scale. Deuteration of the acetone substantially decreases the elimination rates. We discuss how angular momentum conservation can lead to nonexponential complex decay and time-dependent product branching.

Bimolecular Ni+(2D5/2) + C3H8 Reaction Dynamics in Real Time

A beam of Ni+(2D5/2) is formed at a sharp zero of time by resonant two-photon ionization with a nanosecond dye laser pulse and crossed with a beam of propane gas under single-collision conditions at collision energies of 0.01 and 0.21 eV. The ion−molecule reaction occurs in field-free space in the extraction region of a time-of-flight mass spectrometer. After a variable time delay text = 1−8 μs, a fast high-voltage pulse extracts product ions and residual reactant ions into a field-free flight tube for mass analysis. In contrast with many earlier studies of this reaction under more energetic conditions, at 0.01 eV collision energy we find that Ni+(2D5/2) reacts with C3H8 to form long-lived NiC3H8+ complexes almost exclusively (≥96%) on the time scale 0−25 μs after initiation of the collision. Retarding field analysis of the decay of the long-lived NiC3H8+ complexes reveals that on a 6−24 μs time scale 28% revert to Ni+ + C3H8 and 6% form NiC2H4+ + CH4 elimination products; the remaining complexes have not yet decayed at t = 25 μs. At 0.21 eV collision energy, both CH4 and H2 elimination products are formed promptly (in less than 1 μs) and also over the entire range of time scales studied, 0.5−25 μs. Even at this higher collision energy, about 25% of the long-lived complexes survive beyond t = 25 μs. The apparent energetic threshold observed here for the first time provides new evidence of a potential energy barrier to elimination products comparable to the energy of ground-state reactants. In addition, direct measurement of the time scale of the reaction under carefully controlled conditions provides new dynamical information that serves as a benchmark for the theoretical treatment presented in the accompanying paper.

An Easy Preparation of Chemically Pure, High-Activity Tritium-LabelledN-Propionylampicillin for the Analysis of Penicillin-Binding Proteins

Abstract The laboratory preparation of chemically pure, 3H-labelled β-propionylampicillin suitable for studies of the mode of action of β-lactam antibiotics has been investigated. The chemical purity of the labelled antibiotic is a crucial factor for the quantitative determination of penicillin-binding proteins. Ampicillin (D-α-aminobenzylpenicillin) was N-[3H]propionylated by N-succinimidyl [3H]propionate, the labelled reaction products were analyzed by thin-layer chromatography followed by fluorography. The synthesis and the purification of the resulting N-[3H]propionylampicillin have been optimized, the best conditions for the acylation reaction were at pH 8.25 for 2 h, giving both a high yield of the labelled antibiotic and minimal amounts of unwanted by-products. The reaction mixture was fractionated by a two-step procedure, the purified radioactive antibiotic did not contain any residual reactant, especially free ampicillin, or degradation products such as D-α.-[3H]propionamidobenzylpenicilloic acid. This improved procedure allows an easy, fast and rather inexpensive preparation of a good quality radiolabeled antibiotic for studies of penicillin-interacting proteins.

Photochemical Dehalogenation of Polyhalobenzenes. I. Survey of the Reactivity in Hexane Solution

Abstract Photochemical dechlorinations and debrominations of C6HnX6−n (X=Cl, Br) isomers were carried out in hexane. The products and residual reactant were determined quantitatively by means of gas chromatography. From these experiments, the relative rates of dehalogenation were obtained. The different rates among unequivalent sites in a molecule were interpreted by the effect of steric acceleration by the neighboring halogen atom(s). The reactivity of the halogen atom in polyhalobenzene towards photochemical elimination reaction is dependent both on its position in the molecule when compared among isomers and on the number of halogen atoms in a molecule when compared among polyhalobenzenes of various degrees of substitution. The latter effect is more predominant in the series of polybromobenzenes.