Liquid-phase synthesis method

Figure 1.11 summarizes the general procedure of the liquid-phase synthesis method used in the preparation of perovskite oxides with a large surface... 

Fig. 1.11 General procedure of the liquid-phase synthesis method...

Table 1.4 Proposed liquid phase synthesis method for perovskite oxides...

Among various methods to synthesize nanometer-sized particles [1-3], the liquid-phase reduction method as the novel synthesis method of metallic nanoparticles is one of the easiest procedures, since nanoparticles can be directly obtained from various precursor compounds soluble in a solvent [4], It has been reported that the synthesis of Ni nanoparticles with a diameter from 5 to lOnm and an amorphous-like structure by using this method and the promotion effect of Zn addition to Ni nanoparticles on the catalytic activity for 1-octene hydrogenation [4]. However, unsupported particles were found rather unstable because of its high surface activity to cause tremendous aggregation [5]. In order to solve this problem, their selective deposition onto support particles, such as metal oxides, has been investigated, and also their catalytic activities have been studied. 

In a closely related study, Tung and Sun discussed the microwave-assisted liquid-phase synthesis of chiral quinoxalines [80], Various L-a-amino acid methyl ester hydrochlorides were coupled to MeOPEG-bound ortho-fluoronitrobenzene by the aforementioned ipso-fluoro displacement method. Reduction under microwave irradiation resulted in spontaneous synchronous intramolecular cyclization to the corresponding l,2,3,4-tetrahydroquinoxalin-2-ones (Scheme 7.71). Retention of the chiral moiety could not be monitored during the reaction, but after release of the desired products it was found that about 10% of the product had undergone racemization. 

Initially, the term Hquid-phase synthesis was used to contrast the differences between soHd-phase peptide synthesis and a method of synthesis on soluble polyethylene glycol (PEG) [5, 6]. Although soluble polymer-supported synthesis is less ambiguous than Hquid-phase synthesis, the latter term is more prevalent in the Hterature. In-keeping with previous reviews [7-12], the phrases classical or solution synthesis will be used to describe homogeneous reaction schemes that do not employ polymer supports while liquid-phase synthesis will be reserved... 

Traditionally, soluble polymers have received less attention as polymeric supports than their insoluble counterparts. A perceived problem with the use of soluble polymers rested in the ability to isolate the polymer from all other reaction components. Yet, in practice this separation is not difficult and several methods have capitalized on the macromolecular properties of the soluble support to achieve product separation in liquid-phase synthesis. Most frequently the homogeneous... 

A frequent complication in the use of an insoluble polymeric support lies in the on-bead characterization of intermediates. Although techniques such as MAS NMR, gel-phase NMR, and single bead IR have had a tremendous effect on the rapid characterization of solid-phase intermediates [27-30], the inherent heterogeneity of solid-phase systems precludes the use of many traditional analytical methods. Liquid-phase synthesis does not suffer from this drawback and permits product characterization on soluble polymer supports by routine analytical methods including UV/visible, IR, and NMR spectroscopies as well as high resolution mass spectrometry. Even traditional synthetic methods such as TLC may be used to monitor reactions without requiring preliminary cleavage from the polymer support [10, 18, 19]. Moreover, aliquots taken for characterization may be returned to the reaction flask upon recovery from these nondestructive... 

As the intermediate products resulting from individual synthetic steps cannot be purified, a virtually 100% selectivity is essential for the synthesis of larger-peptide molecules. Even at a selectivity of 99% per reaction step, the purity will drop to less than 75% for a dekapeptide (30 steps) It is practically infeasible to go beyond 10-15 amino acid peptides by using the solid-phase method. In order to prepare larger peptides, individual fragments are first produced, purified, and then combined with the final molecule by liquid phase synthesis. This combination of methods is listed under chemical hybrid in Table 4.2. 

The use of supported reagents offers an attractive option for improving the quality of products prepared using solution-phase chemistry. Additionally, liquid-phase synthesis, for example using PEG, provides opportunities to combine some of the benefits of solid-phase approaches with the versatility of solution-phase synthesis. Smart methods such as resin capture for isolating specific compounds from mixtures of products will also help to increase the utility of solution-based approaches. This chapter encompasses developments in each of these areas. 

As already mentioned, components of libraries produced by the original split-mix method are discrete compounds. If the libraries are cleaved from the solid support, however, mixtures are formed. The products of the liquid phase synthesis are always mixtures. At the beginnings, finding an active component in a mixture of thousands, or millions of structurally related compounds seemed to be a task like finding a needle in a haystack. Later on, however, reliable methods have been developed to solve this problem. All these methods are based on preparation and screening of properly designed partial libraries. 

In parallel with the arc method in gaseous phase and the pyrolytic method for synthesis of carbon nanostructures, since 2000 year the present group of researchers has been investigating and developing the method for arc synthesis in liquid phase. This method has a number of advantages over those used at present. 

The solubilizing effect of PEG on the attached peptide and the absence of any direct influence of the polyoxyethylene chain on the physicochemical properties of the peptides provide a wider range of possibilities for analytical control during the liquid phase peptide synthesis than those in the solid phase method. The reactions employed in the stepwise liquid phase synthesis can thus be quantitatively monitored by several analytical methods. 

Automation of the liquid-phase synthesis, at its present stage, is advantageous only when the optimum reaction conditions for the synthesis of a specific peptide have been elucidated in advance, and the synthesis of small- to medium-sized peptides appears to be within the scope of this automated method. 

Linear polystyrene can be functionalized by various methods . The functional group capacity in these polymers diould not be too high otherwise, steric complications may arise. Poly(ethylene ycol) has been found to be most suitable for liquid-phase synthesis. This linear polyether and the block copolymers with functional groups at defined distances are chemically stable and soluble in a large number of solvents including water and can be precipitated selectively. Partially hydrolyzed poly(vinylpyrrolidone) and its copolymers with vinyl acetate were successfully applied in peptide synthesis. Poly(acrylic acid), poly(vinyl alcdiol), and poly-(ethylenimine) are less suitable for the sequential type synthesis because of the... 

As some of these techniques can also, and mainly, be applied to the purification of all libraries, and not only the ones built-up in solution, they will be addressed later. In this section only the methods developed to speed up and facilitate liquid-phase synthesis of libraries, i.e. capture-release methods, supported reagents and supported... 

The basic approach to classify powder production methods is based on whether a method is top-down or bottom-up. In a top-down method, micro- and nano-particles are produced due to the stracture and size refinement through the breakdown of the larger particles in a bottom-up method, the mechanism of particle formation is usually by means of nucleatimi, growth and aggregation of atoms and molecules. In a more practical approach, one may divide the powder synthesis methods as follows (1) wet chemistry, such as the chemical precipitation, sol-gel, microemulsion, sonochemistry, and hydrothermal synthesis methods (2) mechanical attrition, grinding and milling (3) gas phase methods, such as the chemical and physical vapor deposition (4) liquid phase spray methods, such as the molten metal spray atomization, spray pyrolysis, and spray drying, and (5) liquid/gas phase methods. 

Fig. 18. Time dependence of potential drop at 10 mA cm for air electrodes in KOH solution. 1,12 on carbon from melt synthesis 2,12 on carbon from liquid-phase synthesis 3,12 on carbon by gas-phase synthesis 4,12 on carbon by impregnation method...

One of the issues in the practical application of nanostructured materials is the ability to synthesize sufficient quantities with appropriate and controllable properties at low cost. Gas phase combustion processes provide one of the best methods for the bulk production of nanostructured materials due to the relative ease of scale-up and the relative simplicity of the process. The magnetic system chosen for study was y-Fc203/Si02 because a composite of this class has been demonstrated to yield superparamagnetic properties (3) via a liquid phase synthesis route. 

Transition-metal complex of n bowls have attracted much attention [12, 34, 35]. Controlled positioning of metal centers inside the bowls is expected to provide a direct route to the inclusion complexes of fiillerenes and nanotubes. On the other hand, the coordination of metal centers to the outside of the bowls should permit applications in the field of surface activation and functionalization of fiiUerenes and nanotubes. To date, some n bowl (mainly corannulene or its derivatives) complexes with several coordination modes have been synthesized [12, 34, 35]. In addition to the conventional liquid phase synthesis, a microscale gas-phase coordination method was introduced [36] to prepare and/or jj -binding complexes, which is based on co-deposition of volatile complementary building units such as Rh2(02CCF3)4, Ru2(02C(3,5-CF3)2C H3)2(C0)5, and Ru2(02CCF3)2(C0)4 under reduced pressure. 

Since their discovery by Ijima in the early nineties as a byproduct of fullerene synthesis [1], carbon nanotubes have received a growing interest. A huge number of synthesis routes have been proposed, ranging from laser ablation of carbon target, catalytic chemical vapour deposition (CCVD), liquid phase synthesis, plasma methods, and so forth [2]. Also, a large variety of application niches have been identified that render nanotubes a promising material [3]. 

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