One-step Processes Research Articles

Real-Space Approach to the Reaction Force: Understanding the Origin of Synchronicity/Nonsynchronicity in Multibond Chemical Reactions

In this article, we present a complementary analysis based on the reaction force F(ξ)/reaction force constant κ(ξ) and noncovalent interactions (NCI) index to characterize the energetics (kinetic and thermodynamics) and mechanistic pathways of two sets of multibond chemical reactions, namely, two double-proton transfer and two Diels-Alder cycloaddition reactions. This approach offers a very straightforward and useful way to delve into a deeper understanding of this type of process. While F(ξ) allows the partition of the whole pathway into three regions or phases, κ(ξ) describes how orchestrated are the bond-breaking and bond-formation events. In turn, NCI indicates how the inter- and intramolecular bonds evolve. The most innovative aspect is the inclusion of the formation of the reactant complex along the pathway, which, by means of NCI, unveils the early molecular recognition and the comprehension of its role in determining the degree of the synchronicity/nonsynchronicity of one-step processes. This approach should be a useful and alternative tool to characterize the energetics and the mechanism of general chemical reactions.

Experimental Study for the Stripping of PTFE Coatings on Al-Mg Substrates Using Dry Abrasive Materials.

Polytetrafluoroethylene (PTFE) coatings are used in many applications and processing industries. With their use, they wear out and lose properties and must be replaced by new ones if the cost of the element so advises. There are different stripping techniques, but almost all of them are very difficult and require strict environmental controls. It is a challenge to approach the process through efficient and more sustainable techniques. In the present work, we have studied the stripping of PTFE coatings by projection with abrasives (1 step) as an alternative to carbonization + sandblasting procedures (2 steps). For this purpose, different types of abrasives have been selected: brown corundum, white corundum, glass microspheres, plastic particles, and a walnut shell. The tests were performed at pressures from 0.4 to 0.6 MPa on PTFE-coated aluminium substrates of EN AW-5182 H111 alloy. Stripping rates, surface roughness, and substrate hardness have been studied. Scanning electron microscopy (SEM) images of sandblasted specimens have also been obtained. All abrasives improved mechanical and surface properties in one-step vs. two-step processes. The abrasives of plastic and glass microspheres are the most appropriate for the one-step process, which increases the hardness and roughness level Ra in the substrate. Corundum abrasives enable the highest stripping rates.

First passage time in multistep stochastic processes with applications to dust charging.

An approach was developed to describe the first passage time (FPT) in multistep stochastic processes with discrete states governed by a master equation (ME). The approach is an extension of the totally absorbing boundary approach given for calculation of FPT in one-step processes [N. G. Van Kampen, Stochastic Processes in Physics and Chemistry (Elsevier Science Publishers, North Holland, Amsterdam, 2007)] to include multistep processes where jumps are not restricted to adjacent sites. In addition, a Fokker-Planck equation (FPE) was derived from the multistep ME, assuming the continuity of the state variable. The developed approach and an FPE based approach [C. W. Gardiner, Handbook of Stochastic Methods, 3rd ed. (Springer-Verlag, New York, 2004)] were used to find the mean first passage time (MFPT) of the transition between the negative and positive stable macrostates of dust grain charge when the charging process was bistable. The dust was in a plasma and charged by collecting ions and electrons, and emitting secondary electrons. The MFPTs for the transitioning of grain charge from one macrostate to the other were calculated by the two approaches for a range of grain sizes. Both approaches produced very similar results for the same grain except for when it was very small. The difference between MFPTs of two approaches for very small grains was attributed to the failure of the charge continuity assumption in the FPE description. For a given grain, the MFPT for a transition from the negative macrostate to the positive one was substantially larger than that for a transition in a reverse order. The normalized MFPT for a transition from the positive to the negative macrostate showed little sensitivity to the grain radius. For a reverse transition, with the increase of the grain radius, it dropped first and then increased. The probability density function of FPT was substantially wider for a transition from the positive to the negative macrostate, as compared to a reverse transition.

On the error of Fokker-Planck approximations of some one-step density dependent processes

Using operator semigroup methods, we show that Fokker-Planck type second-order PDEs can be used to approximate the evolution of the distribution of a one-step process on $N$ particles governed by a large system of ODEs. The error bound is shown to be of order $O(1/N)$, surpassing earlier results that yielded this order for the error only for the expected value of the process through mean-field approximations. We also present some conjectures showing that the methods used have the potential to yield even stronger bounds, up to $O(1/N^3)$.

One-step Stochastization Methods for Open Systems

In this paper, two approaches (combinatorial and operatorial) to the stochastization of the one-step processes are discussed for the closed and open version of the Lotka–Volterra model, respectively.

Tomatoes’ skins as a rich source of natural pigments

Rhizome of Curcuma longa L. is rich in curcumin which is also an important natural pigment and has important biological activity. In order to obtain curcumin concentrated extracts, one-step and two-step processes were employed. The one step process involves supercritical carbon dioxide (scCO2) at 60 °C and 400 bar, ethanol at 25 °C and water at 60 °C, both at atmospheric pressure. Ethanol and/or water were used as solvents. In the two-step process, sequential extraction, using scCO2, was performed followed by ethanol or water extraction. All the extracts obtained were analyzed and results were reported for global extraction yield, the total phenolic content, total flavonoids, curcumin, antimalarial activity and antioxidant activity. The two-step process showed the highest global yield (23.4%) when water is used as solvent in the second step. However, high concentrations of curcumin and high antioxidant activity were obtained when ethanol is used as solvent. The supercritical extract presents low concentration of curcumin and high antimalarial activity; which shows that extracts of different compositions and functionality can be obtained from a sequential extraction.

Hepatitis C virus core antigen is cost-effective in community-based screening of active hepatitis C infection in Taiwan

Hepatitis C virus (HCV) core antigen is highly sensitive and specific in viremic HCV diagnosis. This study evaluated the cost-effectiveness of HCV core antigen (HCVcAg) in community-based screening for active HCV infection. Between 2017/07 and 2018/07, community-based screenings for active HCV infection with two-step (anti-HCV for screening and HCVRNA for diagnosis) and one-step processes (HCVcAg for screening and diagnosis) were conducted in two districts in Kaohsiung City. While HCVcAg test was positive at ≥3fmol/L, the lowest level of HCV-RNA detection was 12IU/mL. We analyzed the cost-effectiveness of two algorithms in identifying active HCV infection. There were two large-scale screenings using the two-step process with a total of 2452 residents enrolled; while six hundred and forty-four residents participated in continuous small-scale screening with the one-step process. The prevalence of anti-HCV and positive HCVcAg was 3.4% and 2.8%. The viremic rate was 1.4% and 2.8% for two- and one-step processes (p<0.001). While all positive HCVcAg were viremic, 42.4% of positive anti-HCV patients had viremia. The positive predictive value was 42.2% and 100% for two- and one-step processes in detecting active HCV infection (p<0.001). In identifying one active HCV infection, the cost was $755.3 and $711.1 dollars for two- and one-step processes respectively. Compared to the two-step process in community-based screening, continuous screening with the HCVcAg test as a one-step tool for active HCV infection was cost-effective in areas with low seroprevalence of HCV in Taiwan.

A Novel Regulated Hybrid Promoter That Permits Autoinduction of Heterologous Protein Expression in Kluyveromyces lactis.

The yeast Kluyveromyces lactis has been a successful host for the production of heterologous proteins for over 30 years. Currently, the galactose-/lactose-inducible and glucose-repressible LAC4 promoter (P LAC4 ) is the most widely used promoter to drive recombinant protein expression in K. lactis However, P LAC4 is not fully repressed in the presence of glucose and significant protein expression still occurs. Thus, P LAC4 is not suitable in processes where tight regulation of heterologous gene expression is required. In this study, we devised a novel K. lactis promoter system that is both strong and tightly controllable. We first tested several different endogenous K. lactis promoters for their ability to express recombinant proteins. A novel hybrid promoter (termed P350) was created by combining segments of two K. lactis promoters, namely, the strong constitutive P GAP1 promoter and the carbon source-sensitive P ICL1 promoter. We demonstrate that P350 is tightly repressed in the presence of glucose or glycerol and becomes derepressed upon depletion of these compounds by the growing cells. We further illustrate the utility of P350-controlled protein expression in shake flask and high-cell-density bioreactor cultivation strategies. The P350 hybrid promoter is a strong derepressible promoter for use in autoinduction of one-step fermentation processes for the production of heterologous proteins in K. lactisIMPORTANCE The yeast Kluyveromyces lactis is an important host for the expression of recombinant proteins at both laboratory and industrial scales. However, the system lacks a tightly regulated promoter that permits controlled expression of heterologous proteins. In this study, we report the engineering of a highly regulated strong hybrid promoter (termed P350) for use in K. lactis P350 is tightly repressed by glucose or glycerol in the medium but strongly promotes gene expression once the carbon source has been consumed by the cells. This feature permits heterologous protein expression to be "autoinduced" at any scale without the addition of a gratuitous inducer molecule or changing feed solutions.

Laser-induced nitrogen-doped hierarchically porous graphene for advanced electrochemical energy storage

Development of one-step processes combining hierarchical porous architecture with heteroatom doping control has remained a challenge. This is especially important for structure-engineered graphene materials as high performance active electrodes for energy and advanced applications. Herein, we present a facile and general approach for synthesizing patternable, nitrogen-doped and hierarchical porous graphene from graphene oxide/urea mixture using high-repetition picosecond laser in ambient air. Impressively, the highest areal capacitance of laser-induced nitrogen-doped graphene (LING) is 60.7 mF/cm2, which is about 3 times that of undoped porous graphene. After 25,000 consecutive cycles of galvanostatic charge-discharge at a current density of 10 mA/cm2, the optimized LING electrode maintained 98.7% of its original capacitance. Most importantly, the as-prepared LING electrode material has high energy and power density due to the synergistic effect of hierarchical porous structure, nitrogen-doping and engineering defects. The proposed laser one-step synthesis of LING may also be applied to other heteroatom-doped hierarchical porous graphene-based electrodes for high-performance electrochemical energy storage.

Low-temperature electrochemical codeposition of aluminum-neodymium alloy in a highly stable solvate ionic liquid

A highly stable solvate ionic liquid comprising a 2:1 (mol/mol) mixture of ethylene carbonate (EC) and AlCl3 was used for near room-temperature electrochemical codeposition of an Al-Nd alloy using chlorides as precursors. This liquid is low-cost, easy to prepare, and has high electrochemical stability. The ionic structure was analyzed by 27Al nuclear magnetic resonance; Raman spectroscopy and the dissolution phenomenon was studied by ultraviolet-visible spectroscopy. The dissolution mechanism of NdCl3 in this solvate ionic liquid was derived as 3[AlCl2(EC)n]+ + 2NdCl3 ⇆ 2Nd(III) + 3[AlCl4]− + 3nEC. Cyclic voltammetry was used to explore the electrochemical behavior of Nd- and Al-containing species, revealing that the reduction of Al and Nd are both one-step electron-gaining processes. X-ray diffraction confirmed that an Al-Nd alloy can be obtained in the form of thermally stable Al2Nd by potentiostatic electrolysis at high cathode overpotential (− 3.5 V vs. Al). Although the deposited alloy layer is not dense, Al-containing solvate ILs have immense potential in green electrometallurgy because of their higher tunability and similar properties to ILs.

Tubular Flame Combustion for Nanoparticle Production

Requirements for nanoparticle processing based on energy and cost-effective technologies have increased in recent years. Flame synthesis is widely used on an industrial scale and is superior to gas phase one-step processes for producing nanoparticles; however, further improvements are required from the viewpoint of energy efficiency. In this work, we present a new aerodynamically stable nanoparticle processing method with extremely low energy losses, based on the use of a tubular flame. The developed tubular flame apparatus is inexpensive and simple to set up, allowing for a uniform and high temperature field with a high energy efficiency. Consequently, highly crystalline and uniform WO3 nanoparticles were successfully synthesized with a high production rate. The simple and energy-effective process proposed in this work has potential for application to various types of functional nanoparticle production.

Electrochemical Conversion of CO2 to 2-Bromoethanol in a Membraneless Cell

Tremendous research efforts have been made to electrochemically convert CO2 into useful chemicals, with the main products being limited to hydrocarbons and oxygenates. One-step processes that integ...

Bidentate Ru(ii)-NC complexes as catalysts for the dehydrogenative reaction from primary alcohols to carboxylic acids.

Four Ru(ii)-NC complexes were synthesized by one-step processes from the corresponding NC ligands with RuHCl(CO)(PPh3)3. These complexes were tested as catalysts for alcohol dehydrogenative reactions, and complex {(C5H4N)-(C6H4)}RuCl(CO)(PPh3)2 (1) showed the highest activity. With KOH as the nucleophile and 0.5 mol% catalyst loading, a series of carboxylic acids were synthesized in toluene without any oxidant. Catalyst 1 could be transformed to complex {(C5H4N)-(C6H4)}RuH(CO)(PPh3)2 (6) when treated with KOH and benzyl alcohol. Complex 6 further reacted with PhCHO and H2O to generate product {(C5H4N)-(C6H4)}Ru(OCOPh)(CO)(PPh3)2 (7). Complexes 6 and 7 exhibited similar efficiency to complex 1, suggesting that they can be regarded as the catalytic intermediates of 1.

Metal nanoparticles fabricated by green chemistry using natural extracts: biosynthesis, mechanisms, and applications.

Nanoparticles (NPs) are new inspiring clinical targets that have emerged from persistent efforts with unique properties and diverse applications. However, the main methods currently utilized in their production are not environmentally friendly. With the aim of promoting a green approach for the synthesis of NPs, this review describes eco-friendly methods for the preparation of biogenic NPs and the known mechanisms for their biosynthesis. Natural plant extracts contain many different secondary metabolites and biomolecules, including flavonoids, alkaloids, terpenoids, phenolic compounds and enzymes. Secondary metabolites can enable the reduction of metal ions to NPs in eco-friendly one-step synthetic processes. Moreover, the green synthesis of NPs using plant extracts often obviates the need for stabilizing and capping agents and yields biologically active shape- and size-dependent products. Herein, we review the formation of metallic NPs induced by natural extracts and list the plant extracts used in the synthesis of NPs. In addition, the use of bacterial and fungal extracts in the synthesis of NPs is highlighted, and the parameters that influence the rate of particle production, size, and morphology are discussed. Finally, the importance and uniqueness of NP-based products are illustrated, and their commercial applications in various fields are briefly featured.

Biocatalytic synthesis of polylactate and its copolymers by engineered microorganisms.

Poly(lactate), also called poly(lactic acid) or poly(lactide) [PLA], has been one of the most attractive bio-based polymers since it possesses desirable material properties for its use in general performance plastics in addition to biodegradability and biocompatibility. PLA has been produced by biological and chemical hybrid process comprising microbial fermentation for lactate (LA) production followed by purification and chemical polymerization process of LA. Recently, the direct one-step fermentative processes for production of PLA and several LA-containing polyesters have been developed by employing metabolically engineered microorganisms. Since natural microorganisms cannot produce the LA-containing polymers, several engineering strategies have been employed together based on the polyhydroxyalkanoate (PHA) biosynthesis system. In this chapter, we summarize strategies and procedures on developing the engineered microorganisms producing PLA and its copolymers, cultivating the cells, and extracting the polymers from the cells. Focuses were given on construction of enzymatic polymerization process of LA: design of metabolic pathway for PLA by mimicking PHA biosynthetic pathway, examination of possible enzymes, and engineering of the enzymes for better performances. This synthetic pathway has been established in a microorganism producing LA that enabled one-step fermentative production of LA-containing polyesters from carbohydrates derived from renewable biomass. Polymer production has been further enhanced by implementing strain engineering to concentrate the metabolic fluxes toward PLA formation. In addition, various monomers such as glycolate, 2-hydroxybutyrate, and phenyllactate have been copolymerized with LA by the microbial system. These fermentative production systems developed by using the engineered microorganisms can be versatile and sustainable platforms for the production of LA-containing polyesters and other non-natural polymers.

Phosphate glass matrix composites incorporating trisilanol phenyl polyhedral oligomeric silsesquioxane prepared by viscous flow sintering method with enhanced benefits

The effect of mixing and sintering processes to prepare tin fluorophosphate glass (Pglass) matrix composites incorporating trisilanol phenyl polyhedral oligomeric silsesquioxane (TSP-POSS) was investigated by comparing manual and suspension mixing, one-step and stepwise sintering processes to explore the structure dynamics and physical properties in the composites as a function of the different process conditions used. Energy Dispersive X-ray analysis confirmed optimal homogeneous dispersion of the TSP-POSS molecules in the composites prepared by the suspension method. The observed increase of glass transition temperature and the reduction of non-bridging bonds in the composites are believed to be the reason for the effective dispersion of TSP-POSS molecules in the composites. The chemical reaction between the TSP-POSS and Pglass was strongly influenced by the mixing/dispersion and sintering processes investigated. 13C cross polarized magic angle spinning (CP MAS) solid state nuclear magnetic resonance (NMR) spectroscopy confirmed the chemical stability of the TSP-POSS during the sintering process at elevated temperatures. In addition, a chemical reaction between the TSP-POSS and Pglass was evidenced by 29Si CP MAS NMR analysis. This study will provide a better fundamental understanding of the effective dispersion mechanism of the TSP-POSS molecules in the Pglass matrix that will facilitate tailoring the physicochemical properties of the composites with addition of various small concentrations of TSP-POSS for a number of applications where the pure Pglass is not applicable due to the intrinsic properties of the Pglass.

Effect of (H2O)n (n = 1–3) clusters on H2O2 + HO → HO2 + H2O reaction in tropospheric conditions: competition between one-step and stepwise routes

ABSTRACTEffects of (H2O)n (n = 1–3) on the H2O2 + HO → HO2 + H2O reaction have been investigated by the reactions of H2O2L(H2O)n (n = 1–3) + HO and H2O2 + HOL(H2O)n (n = 1–3) at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level of theory, coupled with rate constant calculations by using canonical variational transition state theory. Interestingly, for the former reactions, one-step process and stepwise mechanism are involved, where one-step processes occurring though cage-like hydrogen bonding network complexes and the transition states are favourable. Due to larger effective rate constants, these favourable processes are also favourable than the corresponding latter reactions. Meanwhile, the catalytic effect of (H2O)n (n = 1–3) is mainly taken from water monomer, because the effective rate constant (k'(R_WM2)) of H2O2···H2O + HO reaction is, respectively, larger by 3, 6–10 orders of magnitude than that of H2O2···(H2O)2 + HO (k'(R_WD1)) and H2O2···(H2O)3 + HO (k'(R_WT1)) reactions. Furthermore, the enhancement factor of water molecular (k'(R_WM2)/ktot) is only 0.28% at 240 K, while at high temperature (such as at 425 K), the positive water vapour effect enhances up to 27.13%. This shows that at high temperatures the positive water effect is obvious under atmospheric conditions.

Comparison of processing windows and electronic properties between CH3NH3PbI3 perovskite fabricated by one-step and two-step solution processes

Abstract Despite the rapid progress in device efficiency of the perovskite solar cells (PVSCs), the origin of commonly observed large variability of device performance from one-step to two-step approaches is still elusive. Herein, the processing windows of perovskite films prepared by one-step and two-step processes have been investigated. We find that both perovskite films prepared by one-step and two-step methods in air are much rougher than that prepared in glovebox. For the one-step method, complete perovskite conversion can be readily achieved both in air and in glovebox, but totally different in surface morphology. For the two-step method, residual PbI2 are remained in perovskite film, particularly with larger amount for the film prepared in air. Both rough surface and incomplete conversion hinder the realization of high quality perovskite film in air. The photovoltaic performances of the PVSCs prepared by one-step and two-step methods in glovebox are systematically compared. The generally observed lower photovoltaic performance of two-step PVSCs is ascribed to the additional trap-assisted recombination process due to larger trap density in the two-step perovskite film. This is confirmed by carrier recombination study using steady state photoluminescence, transient photovoltage and photocurrent measurements. Finally, combining the high work function hole transporting material poly-TPD, and the high-quality one-step perovskite film, a 17.5% high-efficiency PVSCs can be achieved. The results reveal the major impacts on the morphological and electronic properties of perovskite films between one-step and two-step method, and it brings insight into the strategy for extending the processing windows to achieve highly reliable PVSCs.

Improving Interfacial Charge-Transfer Transitions in Nb-Doped TiO2 Electrodes with 7,7,8,8-Tetracyanoquinodimethane

Interfacial charge-transfer (ICT) transitions involved in charge-separation mechanisms are expected to enable efficient photovoltaic conversions through one-step charge-separation processes. With this in mind, the charge-transfer complex fabricated from TiO2 nanoparticles and 7,7,8,8-tetracyanoquinodimethane (TCNQ) has been applied to dye-sensitized solar cells. However, rapid carrier recombination from the conduction band of TiO2 to the highest occupied molecular orbital (HOMO) of TCNQ remains a major issue for this complex. In this study, to inhibit surface-complex recombinations, we prepared Nb-doped TiO2 nanoparticles with different atomic ratios for enhanced electron transport. To investigate the effects of doping on electron injection through ICT transitions, these materials were examined as photoelectrodes. When TiO2 was doped with 1.5 mol % Nb, the Fermi level of the TiO2 electrode shifted toward the conduction band minimum, which improved electron back-contact toward the HOMO of TCNQ. The enhancement in electron transport led to increases in both short circuit current and open circuit voltage, resulting in a slight (1.1% to 1.3%) improvement in photovoltaic conversion efficiency compared to undoped TiO2. Such control of electron transport within the photoelectrode is attributed to improvements in electron injection through ICT transitions.

Pre-deposition of CdS layers to improve the diode quality of CZTSSe solar cells

The CdS layers are vital for diode quality of cell devices, which have great influences on high-performance CZTSSe solar cells. Optimizing the deposition processes of CdS layers are necessary to improve the diode quality and device efficiency. In this work, CZTSSe solar cells were fabricated without and with pre-deposited CdS layers, which are referred to as one-step and two-step processes, respectively. Then the performances of the CZTSSe solar cells were comparatively studied. Comparing with one-step processes, the efficiency of the solar cell by two-step processes improves from 7.24% to 9.45%. The efficiency improvement is mainly due to the gain of fill factor (FF) from 60.3% to 73.1%. Although the cell devices by different CdS processes have similar levels of interface recombination deduced from the activation energy (Ea), the temperature-dependent ideality factor A and shunt resistance (Rsh) indicate that the device fabricated by two-step possess higher diode quality and lower leakage current, which results in the increase of FF and efficiency. The optimization of CdS layer preparation is an effective approach to improve the efficiencies of solar cells.