Route For Preparation Research Articles

Infertility treatment for Chinese women with P450 oxidoreductase deficiency: Prospect on clinical management from IVF to FET.

Cytochrome P450 oxidoreductase deficiency (PORD) is a rare recessive disease with multiple clinical manifestations, which is usually diagnosed in neonates and children because of ambiguous genitalia or skeletal malformations. Moreover, the paucity of studies does not allow us to establish whether adult-onset PORD is associated with infertility. Here, we report clinical and laboratory findings in two phenotypically normal women diagnosed with PORD who underwent in vitro fertilization (IVF) and frozen embryo transfer (FET). We modified the gonadotropin stimulation protocol during controlled ovarian hyperstimulation (COH) and suggest the use of the vaginal 17β-estradiol route for endometrium preparation in hormone replacement therapy (HRT) cycles. We presume that PORD may be associated with infertility in several aspects, including disordered steroidogenesis, endometrium impairment, attenuation of drug metabolism, and the high risk of miscarriage. Our observations will help the early diagnosis and make a tailored approach to infertility management in adult-onset PORD.

Hierarchical Porous SiO2 Cryogel via Sol-Gel Process.

The aim of this research work was to develop a new, low-cost and low-energy-consuming preparation route for highly porous silica systems. The precursor gel systems were synthesized by sol-gel chemistry. The starting materials were TEOS and water glass in the sol-gel syntheses. The effect of the chemical composition, the catalysis, the pH, and the additives were investigated on the structure and porosity of the cryogels. The gel systems were treated by freeze-drying process to obtain porous cryogel silica products. The cryogel systems possess hierarchical structures. The conditions of the freeze-drying process were also studied to increase the porosity. Small angle X-ray measurements, scanning electron microscope technique, and infrared spectroscopy were applied for the investigation of gel and cryogel systems.

Electronic control of catalytic activity of ZnO for higher alcohols synthesis via tailoring Fermi level

Metal doping are essential for electronic modulation of semiconductors, leading to different Fermi level, which determined the surface chemisorption and catalytic properties. Here, ZnO doping with 4 mol% Cu were synthesized by four preparation routes, which tuned Cu existing states and Fermi level appearing remarkable impacts on the catalytic performance of catalysts. It shows a negative correlation between synthesis of higher alcohols and Fermi level over electronically modified ZnO catalysts, and the lower Fermi level exerted better facilitation for the carbon chain growth. Copper was incorporated into ZnO lattice and existed in the form of isolated Cu2+, which regulated the electronic structure of ZnO with lower Fermi level and boosted the process of catalysts obtaining electrons. Thus, the lower Fermi level promoted the dissociation CO bond and p-type reaction of forming surface alkyl species, and a higher proportion of straight chain higher alcohols can be achieved via CO or CHxO* inserting into alkyl species. Especially the catalyst prepared by urea hydrolysis with the lowest Fermi level significantly increased the higher alcohols fraction in total alcohol products to 69.9%. For comparison, the higher Fermi level are unfavorable for p-type reaction, leading to high methanol selectivity. This work provides a new viewpoint for promoting catalytic performance from the perspective of electronic modification of ZnO.

Effects of A‐site replacement (Sm, Y, and Pr) on catalytic performances of mullite catalysts for NO oxidation

Mullite was one of the most promising catalysts that used in the selective catalytic oxidation of NO (NO-SCO), and deciphering its intrinsic properties that affect the catalytic performance was a great challenge but critical to the development of mullite catalysts. Herein, a series of Mn-based mullite nanofibers with different A-site cations were synthesized by electrospinning method and used for catalytic NO oxidation. Activity tests showed that SmMn2O5 exhibited a better NO conversion rate (77.8 %) than those of PrMn2O5 (63.3 %) and YMn2O5 (57.5 %) under typical experimental conditions (GHSV = 120 000 h−1, T = 325 °C). To investigate the factors influencing the catalytic activity, various techniques including XRD, N2 adsorption, SEM, TEM, EDX, XPS, H2-TPR, and O2-TPD were employed, and the results showed that abundant surface adsorbed oxygen species and good reducibility contributed greatly to the catalytic performance of SmMn2O5. DFT calculations revealed that A-site cation played the decisive role in the Fermi level relative to the Mn 3d-band centre, thus affecting the adsorption and dissociation of O2 molecule. The present synthetic strategy offered a new viable route for the large-scale preparation of metal oxide catalysts with remarkable NO oxidation performance for practical application.

A review article: Drug delivery systems, preparation techniques, and biological applications using nanoemulsion as a novel platform

Nanotechnology, particularly nanoemulsions (NEs), is an essential topic that has piqued the interest of researchers over the years. These significant molecules feature a spherical solid structure, a lipophilic amorphous negative charge surface, with small droplet size, and a large surface area, all of which contribute to the promising future of nanomedicine and the importance of NEs in a variety of sectors. The advantages and disadvantages of the components, preparation, characterization, assessment, and applications as a delivery medication system are summarized in this review paper. There are two different methods for NEs preparation: the high and low energy methods. In high energy methods, high-pressure homogenization, ultrasonication micro fluidization, and Spontaneous emulsification are described thoroughly. Low energy approaches emphasize phase inversion temperature, solvent evaporation technology, and hydrogel technologies. Low-energy procedures should be preferred over high-energy methods since they utilize less energy and do not necessitate the use of specific instruments. The transdermal application, aerosolized, ingestible NEs, and parenteral techniques are the four primary lines of biomedical uses of NEs as a delivery strategy. To summarize, these novel strategies are very promising, but additional research is needed to fully understand the relationship between NE formulation and physiological and pathological problems associated with diverse preparation, characterization, and administration routes.

Optimized Route for the Fabrication of MnAlC Permanent Magnets by Arc Melting

The rare-earth-free MnAlC alloy is currently considered a very promising candidate for permanent magnet applications due to its high anisotropy field and relatively high saturation magnetization and Curie temperature, besides being a low-cost material. In this work, we presented a simple fabrication route that allows for obtaining a magnetically enhanced bulk τ-MnAlC magnet. In the fabrication process, an electric arc-melting method was carried out to melt ingots of MnAlC alloys. A two-step solution treatment at 1200 °C and 1100 °C allowed us to synthesize a pure room-temperature ε-MnAlC ingot that completely transformed into τ-MnAlC alloy, free of secondary phases, after an annealing treatment at 550 °C for 30 min. The Rietveld refinements and magnetization measurements demonstrated that the quenched process produces a phase-segregated ε-MnAlC alloy that is formed by two types of ε-phases due to local fluctuation of the Mn. Room-temperature hysteresis loops showed that our improved τ-MnAlC alloy exhibited a remanent magnetization of 42 Am2/kg, a coercive field of 0.2 T and a maximum energy product, (BH)max, of 6.07 kJ/m3, which is higher than those reported in previous works using a similar preparation route. Experimental evidence demonstrated that the synthesis of a pure room-temperature ε-MnAlC played an important role in the suppression of undesirable phases that deteriorate the permanent magnet properties of the τ-MnAlC. Finally, magnetic images recorded by Lorentz microscopy allowed us to observe the microstructure and magnetic domain walls of the optimized τ-MnAlC. The presence of magnetic contrasts in all the observed grains allowed us to confirm the high-quality ferromagnetic behavior of the system.

"PREPARATION AND CHARACTERIZATION OF CHITIN HYDROGEL COMPOSITED WITH HALLOYSITE CLAY SOLUTION VIA PHASE INVERSION "

In this study, halloysite clay (HC), a reinforcing nanofiller, was mixed with 1 and 1.5% chitin solutions to prepare chitin–halloysite clay composite hydrogel by phase inversion under water vapor atmosphere at 25 °C. Chitin, extracted chemically from crab shell, was dissolved in N,N-dimethyl acetamide in the presence of 5% lithium chloride (DMAc/5% LiCl), and then different amounts of HC solution (0, 3, 5 and 7%) were added to evaluate the effect of HC on the fundamental properties of the obtained composite hydrogels. After the green route of preparation, the diameter and thickness of the hydrogel samples seemed to remain the same, while varying the concentrations of chitin and inorganic filler solution. As a result, in the case of the 1% chitin hydrogel, the tensile strength of the composite films increased from 335.9 to 489.8 kPa, while the elongation was around 61.3 and 86.0% with the addition of 0 and 7% HC solution. With the increase in the chitin content to 1.5%, the mechanical strength of the resultant composite hydrogels was enhanced. Moreover, the reduction in the equilibrium water content confirmed the formation of a composite hydrogel incorporating a well dispersed nanofiller, with good interfacial interaction between the nanofiller and the biopolymer matrix.

Synthesis and characterization of MgO nanostructures: A comparative study on the effect of preparation route

In this study, MgO nanostructures were synthesized by five facile and diverse chemical synthesis routes, viz. precipitation (PT), sonication-precipitation (SPT), microwave combustion (MWC), conventional combustion (CC), and solvothermal (ST) processes. The influence of aforementioned synthesis routes on crystallinity, crystallite size, morphology, optical, and surface traits of MgO nanostructures was evaluated by XRD, BET, FESEM, FETEM, optical absorption, steady-state and time-resolved photoluminescence analyses. Furthermore, antioxidant and antibacterial properties of MgO nanostructures were examined. XRD analysis revealed that crystallite size and relative crystallinity (%) of MgO varied from 9 to 42 nm and 90.70–99.06%, respectively, depending on the synthesis route followed. The application of microwave irradiation (MWC) and sonication (ST) reduced particle size and increased specific surface area of MgO nanostructures compared to nanostructures obtained via CC and PT methods. This could be due to faster reaction kinetics in MWC and small-scale turbulence generated during sonication that restricts growth and agglomeration of nuclei during nanostructure synthesis. FESEM analysis revealed flake, sphere, natural rose, and marigold flower-like morphologies of MgO due to different methods followed, that can be attributed to the differences in nanostructure formation mechanism involved. The highest photoluminescence intensity observed with MgO synthesized via MWC is likely to produce a maximum number of reactive oxygen species. Consequently, MgO synthesized through MWC process showed highest bactericidal and antioxidant activities compared to MgO synthesized via other routes. Thus, present study demonstrated that properties of nanostructures required for a particular application could be customized by proper choice of the synthesis route.

A route for large-scale preparation of multifunctional superhydrophobic coating with electrochemically-modified kaolin for efficient corrosion protection of magnesium alloys

Superhydrophobic coating has been widely studied for its great applicational potential, such as for corrosion protection of magnesium alloys while it has been restrained by expensive materials, sophisticated preparation process and infirm rough structures. In this study, the electrochemical method was adopted by using a two-electrode system for rapid hydrophobic modification to obtain superhydrophobic kaolin. By mixing the modified superhydrophobic kaolin with commercial epoxy resin and polydimethylsiloxane glue, a paint can be formed and easily used on various substrates for preparation of superhydrophobic coating via spraying method. The influence factors on wettability of the modified kaolin and the mixing ratio of each component of the coating were explored. Also, the wettability, durability and anticorrosion of the prepared coating were evaluated comprehensively. The coating was able to maintain superhydrophobic after immersed in HCl solution at pH 1, the NaOH solution at pH 14, and 3.5 wt.% NaCl solution for 16, 21, 30 days, respectively. In addition, the coating exhibited 4A grade adhesion, high hydrophobicity after abraded for 200 cycles on a 600-mesh sandpaper with 100 g weight, and 99.86% anticorrosion efficiency after soaked in 3.5 wt.% NaCl solution for 20 days, demonstrating a good robustness and anti-corrosion property. Furthermore, the coating showed good transparency, flexibility and was easy to make in a large scale by the spraying method, which is of great significance to promote the practical application of superhydrophobic coatings and the anticorrosion Mg alloys.

Green preparation of nano-zero-valent iron-copper bimetals for nitrate removal: Characterization, reduction reaction pathway, and mechanisms

• A successful preparation of green nano-zero-valent iron-copper bimetals by a simple method. • The removal rate of nitrate by GT-nZVI/Cu under optimal conditions can reach 99.00%. • The prepared GT-nZVI/Cu has good anti-oxidation and anti-agglomeration properties. • Most of the reaction products for the removal of nitrate by GT-nZVI/Cu are N 2 . • The mechanism of GT-nZVI/Cu denitrification is complexation, redox and adsorption co-precipitation. In this study, green tea was used as a reducing agent to prepare GT-nZVI/Cu nano-zero-valent iron-copper bimetallic materials for nitrate degradation. Through single factor experiments, the process conditions for nitrate removal by GT-nZVI/Cu were optimized. By measuring the contents of nitrate, nitrite, and ammonia nitrogen in the reaction products, the reduction pathway of nitrate-nitrogen in GT-nZVI/Cu was studied. In addition, the removal mechanism of nitrate by GT-nZVI/Cu was also analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and kinetic experiments. The results showed that the size of GT-nZVI/Cu particles is between 50 and 70 nm, and they are irregular spherical shapes. The polyphenol antioxidants in green tea make GT-nZVI/Cu have stronger antioxidant properties, and the denitration products are mostly nitrogen. The addition of copper ions accelerates the reaction time and reaction rate. The maximum removal rate of nitrate by GT-nZVI/Cu within 75 min can be up to 99 %. After three repeated experiments, the removal rate of GT-nZVI/Cu can still reach 70 %. The removal mechanism of GT-nZVI/Cu has enhanced nitrate removal through complexation, redox, and adsorption co-precipitation. This study provides a new route for the green preparation and efficient application of nZVI.

Molten salt synthesis of mullite whiskers entirely derived from fly ash for electronic packaging toughening ceramic applications

Preparation of mullite from high-alumina coal fly ash (CFA) has become one of the most important ways for high-value utilization. However, low Al2O3/SiO2 ratio, poor reaction activity and various impurities in fly ash led to poor quality of mullite products. Conventional sintering method requires addition of aluminum sources and sintering additives, and high synthesis temperature. This paper proposes a new technical route for preparation of mullite whiskers entirely from fly ash by molten salt method based on additive activation-acid leaching process. The growth process and synthesis mechanism of mullite whiskers in Na2SO4 molten salt from fly ash were systematically investigated, and the application of fly ash-derived mullite whiskers in electronic packaging toughening ceramic was also explored. The results show that leaching liquor containing Al3+, Na+, and SO42−, and amorphous silica slag can be separated and obtained after acid leaching of activated fly ash at 80 °C, and the fly ash-derived mullite whiskers with a length of about 1 μm can be synthesized from the mixture of crystalline products and silica slag by the proposed method under the optimal synthesis conditions. Using amorphous silica slag with higher dissolution activity as the silicon source, the nucleation of mullite whiskers with homogeneous nucleation process is promoted and highly monodispersed mullite whiskers derived from fly ash form. The fly ash-derived mullite whiskers can improve the mechanical strength, reduce the dielectric constant and dielectric loss of the composite ceramic substrates, and the dielectric constant and dielectric loss of the composite ceramic are the lowest 5.16 and 0.006, respectively, when the mullite addition content is 20 wt.%, indicating that they could be used as electronic packaging materials. This paper provides a novel pathway for synthesis of mullite whiskers and high-value utilization of fly ash.

Preparation and characterization of sodium polyacrylate grafted montmorillonite nanocomposite for the adsorption of cadmium ions form aqueous solution

High-efficiency adsorbents made from clay minerals have a wide application in remediation of soil and water pollution, especially in the treatment of refractory and highly toxic heavy metals. Montmorillonite itself has a good adsorption capacity and a large modification space for its layered structure. Therefore, carboxylate polymer grafted montmorillonite was developed to improve the adsorption capacity of heavy metals in this paper. Two kinds of modified preparation routes were compared, and a series of batch adsorption tests were conducted to evaluate the influence degree of parameters (contact time, pH, temperature, and cadmium concentration). The structural changes of montmorillonite samples before and after modification were characterized by a series of microscopic analyses and measurement techniques. The results show that the silicon hydroxyl produced by the hydrolysis of silane coupling agent can indeed be grafted by dehydration condensation with Si/Al-OH on clay surface. The grafting chain can be greatly increased by C=C double bond breaking polymerization. The polycarboxylate group can effectively improve the adsorption performance of modified montmorillonite for cadmium ions. The maximum adsorption capacity of modified montmorillonite increased by about 224.75%, reaching 63.49 mg/g. The adsorption model of montmorillonite conforms to Langmuir monolayer adsorption model, while modified montmorillonite samples exhibit Freundlich adsorption model and S-type isothermal adsorption curve characteristics of resin. The preparation method of neutralizing after polymerization of acrylic acid was proposed to be better, which provides technical guidance for scientific and efficient application.

Effect of synthesis routes for preparation of lead sulphide quantum dots based thin films by spin coating technique

Effect of synthesis routes for preparation of lead sulphide quantum dots based thin films by spin coating technique

Insights into memory effect mechanisms of layered double hydroxides with solid-state NMR spectroscopy

Layered double oxides (LDOs) can restore the parent layered double hydroxides (LDHs) structure under hydrous conditions, and this “memory effect” plays a critical role in the applications of LDHs, yet the detailed mechanism is still under debate. Here, we apply a strategy based on ex situ and in situ solid-state NMR spectroscopy to monitor the Mg/Al-LDO structure changes during recovery at the atomic scale. Despite the common belief that aqueous solution is required, we discover that the structure recovery can occur in a virtually solid-state process. Local structural information obtained with NMR spectroscopy shows that the recovery in aqueous solution follows dissolution-recrystallization mechanism, while the solid-state recovery is retro-topotactic, indicating a true “memory effect”. The amount of water is key in determining the interactions of water with oxides, thus the memory effect mechanism. The results also provide a more environmentally friendly and economically feasible LDHs preparation route.

Highly Active Ni-Ru Bimetallic Catalyst Integrated with MFI Zeolite-Loaded Cerium Zirconium Oxide for Dry Reforming of Methane.

The dry reforming of methane (DRM) is a new potential technology that converts two major greenhouse gases into useful chemical feedstocks. The main challenge faced by this process is maintaining the catalyst with high catalytic activity and long-term stability. Here, a simple and effective preparation route for the synthesis of functional nanomolecular sieve catalysts (NiRuxCZZ5) from kaolinite tailings was developed for dry reforming of methane with CO2. The silica monoliths with flower-like spherical and micropore structures (ZSM-5) were prepared by crystal growth method, and the metal components were loaded by ultrasonic-assisted impregnation method. The NiRu0.5CZZ5 catalyst exhibited excellent catalytic performance (maxmium CO2 and CH4 conversions up to 100 and 95.6%, respectively) and very good stability (up to 100h). The interfacial confinement and the strong support interaction are principally responsible for the excellent catalytic activity of the catalyst. The in situ DRIFTS was used to elucidate the possible carbon conversion steps, and stable surface intermediates were also identified.

On the influence of the preparation routes of NiMgAl-mixed oxides derived from hydrotalcite on their CO2 methanation catalytic activities

In this work, a series of NiMgAl oxides (NMA) derived from hydrotalcite catalysts were prepared via co-precipitation (NMA-CP), urea hydrolysis (NMA-UH), and impregnation (NMA-IMP) techniques, then subsequently tested for CO2 methanation. The well-defined synthesis of derived hydrotalcite mixed oxides was confirmed by physicochemical characterizations including XRD, SEM, BET, H2-TPR and CO2-TPD. The preparation methods showed a substantial influence on the structure and thermal activity of catalysts. Indeed, the NMA-UH catalyst demonstrated a high and stable catalytic activity in terms of CO2 conversion and CH4 selectivity, with ca. 82.3% and 99.8% (GHSV = 12,000 h−1, H2/CO2 = 4/1) respectively, at 300 °C. This is mainly due to its large specific surface area, small Ni-particle size, and higher basicity.

Reducing graphene oxide carbon skeleton supported P-N heterostructure of bimetallic sulfide CoS-MoS2 nanorods for high-performance lithium storage

Constructing bimetallic sulfide components are considered to be a promising and efficient lithium storage materials. Nonetheless, preparation routes of rational structures that have abundant hierarchical interfaces or phase boundaries bimetallic sulfide are still a problem to over come. In this work, a novel hierarchical nanostructure of bimetal sulfide CoS-MoS2 nanorods are synthesized successfully by in-situ self-growth means at the hydrothermal conditions. Subsequently, we loaded it to the carbon matrix (CoS-MoS2@rGO) forming a three-dimensional structures with the help of freeze drying technology. This well-designed hierarchical structure could created a stable heterogeneous contact surface, which guarantees rapid Li+ ions diffusion and facilitates charge transfer at the heterointerface. Which can maintain capacity of 776 mAh/g over 800 cycles at 1 A/g. On the other hand, it shows an excellent rate capability of 464 mAg h−1 at 5 A/g. From the perspective of electrochemical kinetics, we analyze and explore the reason about the improved lithium storage performance. Furthermore, to insight into the relationship between matter and phase conversion, the in-situ X-ray diffraction characterization is executed. The strategy of rationally designing hierarchical heterostructures will shed light on outstanding electrochemical performance in energy storage applications.

A REVIEW ON ADVANCES IN PHARMACEUTICAL CO-CRYSTAL PREPARATION ROUTES, INTELLECTUAL PROPERTY PERSPECTIVE AND REGULATORY ASPECTS

As in recent years, due to the pervasiveness of poorly soluble APIs that demonstrates poor and erratic bioavailability, pharmaceutical cocrystal’s applicability to tailor the physicochemical properties has gained attention. Pharmaceutical cocrystal has been an exciting field of interest to researchers as this encouraged several regulatory bodies to create regulatory standards, which led to the approval of these crystals for marketing in various nations. With the upsurge in the growth of pharmaceutical cocrystals, the major concern is over the intellectual property perspective and regulatory status of cocrystals. With the new guidelines from the United States Food and Drug Administration (USFDA) and European Medicines Agency (EMA), the manufacturing and characterization of cocrystal have become less complicated. In this article, various preparation routes are mentioned along with this intellectual property perspective and regulatory perspective, including regulatory guidelines, which give an idea of whether cocrystals meet the criteria for patent eligibility and how they would change the current state of the pharmaceutical industry. Here, we also reviewed some recently approved patients on pharmaceutical crystals, which provided benefits over poor physicochemical property of drug substances and also enhanced the therapeutic effectiveness of that drugs.

Compressive Properties and Degradable Behavior of Biodegradable Porous Zinc Fabricated with the Protein Foaming Method.

A new protein foaming–consolidation method for preparing porous zinc was developed using three proteins (egg white protein (EWP), bovine bone collagen protein (BBCP), and fish bone collagen protein (FBCP)) as both consolidating and foaming agents. The preparation route utilized powder mixing and sintering processing, which could be divided into three steps: slurry preparation, low-temperature foaming, and high-temperature sintering. The morphological characteristics of the pore structures revealed that the porous zinc had an interconnected open-cell structure. Compared to the porous zinc prepared with EWP or BBCP, the porous zinc prepared with FBCP possessed the largest average pore size and the highest compressive properties. The porosity of the porous zinc increased with the stirring time, the content of protein and sucrose, and higher sintering temperatures. Moreover, a compression test and immersion test were performed to investigate the stress–strain behavior and corrosion properties of the resulting porous zinc. A fluctuated stress plateau could be found due to the brittle fracture of the porous cells. The porous zinc prepared with FBCP showed the highest compressive strength and elastic modulus. The corrosion rate of the porous zinc obtained through an immersion test in vitro using simulated bodily fluids on the thirty-second day was close to 0.02 mm/year. The corresponding corrosion mechanism of porous zinc was also discussed.

Chemoenzymatic Asymmetric Synthesis of Complex Heterocycles: Dihydrobenzoxazinones and Dihydroquinoxalinones

Chiral dihydrobenzoxazinones and dihydroquinoxalinones serve as essential building blocks for pharmaceuticals and agrochemicals. Here, we report short chemoenzymatic synthesis routes for the facile preparation of these complex heterocycles in an optically pure form. These synthetic routes involve a highly stereoselective hydroamination step catalyzed by ethylenediamine-N,N′-disuccinic acid lyase (EDDS lyase). This enzyme is capable of catalyzing the asymmetric addition of various substituted 2-aminophenols to fumarate to give a broad range of substituted N-(2-hydroxyphenyl)-l-aspartic acids with excellent enantiomeric excess (ee up to >99%). This biocatalytic hydroamination step was combined with an acid-catalyzed esterification–cyclization sequence to convert the enzymatically generated noncanonical amino acids into the desired dihydrobenzoxazinones in good overall yield (up to 63%) and high optical purity (ee up to >99%). By means of a similar one-pot, two-step chemoenzymatic approach, enantioenriched dihydroquinoxalinones (ee up to >99%) were prepared in good overall yield (up to 78%) using water as solvent for both steps. These chemoenzymatic methodologies offer attractive alternative routes to challenging dihydrobenzoxazinones and dihydroquinoxalinones, starting from simple and commercially available achiral building blocks.