Tartaric acid unit

A large number of chiral crowns have been prepared by numerous groups. The reader is directed to the tables at the end of this chapter to obtain an overview of these structures. It would not be useful to try to recount the synthetic approaches used in the preparation of all of these compounds we have chosen rather to subdivide this mass of compounds into three principal groups. The groups are (1) Cram s chiral binaphthyl systems (2) chiral crowns based on the tartaric acid unit and (3) crowns incorporating sugar subunits. These are discussed in turn, below. 

Probably the best known early crown ether example is the chundle reported by Jullien and Lehn (Jullien and Lehn, 1988). Their strategy used a central crown ether unit with sidearms radiating from it. The stereochemistry of the sidearms was fixed by incorporation of tartaric acid units within the macrocycle. The name was given because the compound was a channel formed from a bundle of fibers. In this first report, no information about insertion or transport appeared, and the assertion that the compound was a channel apparently rested on the intent of the design. Later work from this group showed that related compounds, called bouquet molecules, did conduct cations, albeit rather slowly (Canceill etal., 1992). 

The specific rotation [ ]d of the Oth and first generation dendrimers (65 and 67) was recorded at — 59.60 and — 69.70, respectively molar rotation was reported as - 5690 (65) and - 17690 (67), and the molar rotation per tartaric acid unit was determined to be — 1900 (65) and - 1970 (67), respectively. The use of bis(aryl ether) 64 allowed construction of tetrakis(aryl ether) 68, which, when treated with the bistosylate 66, afforded the corresponding dendron to be used for the preparation of the second generation dendrimers subsequent reaction with trisphenol 61 failed to give the desired material presumably due to steric and solubility problems. 

The total synthesis of zaragozic acid C (1) by Evans [7] is shown in Schemes 11 and 12. Evans identified a tartaric acid unit in the C3-C4 partial structure of zaragozic acid. Accordingly, his synthesis commences from a tartaric acid derivative (Scheme 11). The... 

In modifying the successful mother host 34, Koga et al. have synthesized the first synthetic water soluble host 42 with a chiral cavity by using L-tartaric acid units The complexation of chiral aromatic carboxylic acids like 43 and 44 by the enantiomeric pure host has been proved by H-NMR spectroscopy in acidic water solution yielding strong upfield shifts of guest protons. 

Indeed, monomers in which two such groups are grafted onto tartaric acid units (e.g., replacing P and U units in TP2 and TU2 see Fig. 6) generate very high molecular weight aggregates that are characterized by various physical methods [29]. 

Tartaric acid [526-83-0] (2,3-dihydroxybutanedioic acid, 2,3-dihydroxysuccinic acid), C H O, is a dihydroxy dicarboxyhc acid with two chiral centers. It exists as the dextro- and levorotatory acid the meso form (which is inactive owing to internal compensation), and the racemic mixture (which is commonly known as racemic acid). The commercial product in the United States is the natural, dextrorotatory form, (R-R, R )-tartaric acid (L(+)-tartaric acid) [87-69-4]. This enantiomer occurs in grapes as its acid potassium salt (cream of tartar). In the fermentation of wine (qv), this salt forms deposits in the vats free crystallized tartaric acid was first obtained from such fermentation residues by Scheele in 1769. 

In the United States, prices for tartaric acid have ranged from 1.10 to 6.61/kg since the early 1970s with Httie consistency. The 1993 Hst price of tartaric acid in the United States was 6.50/kg fob plant packaged in 100-lb (45.5-kg) bags (39). Much of the fluctuation is a result of the availabihty of raw materials for production. 

Specifications and Analysis. (R-R, R )-Tartaric acid sold in the United States meets the specifications of the Food Chemicals Codex (40) and the tdationalFormulary (41) (Table 12). 

The united filtrate is evaporated on the steam bath until the volume amounts to 200 cc., at which point crystals should have already begun to separate from the hot solution. After standing at room temperature for twenty-four hours or longer, the crystals are filtered by suction as free from mother liquor as possible and recrystallized from an equal weight of distilled water (Note 5). The filtrate from this recrystallization is evaporated on the steam bath and the second crop of /-tartaric acid filtered and recrystallized as before. The -yield is 65-75 (32-5-35-5 per cent of the theoretical amount). 

Figure 14.8 Adsorption models of the bisuccinate and bitartrate phases on Cu(1 1 0). (a) Structural models for the two coexisting chiral domains for bisuccinate on Cu(1 1 0). The (2 2, -9 0) and (9 0, -2 2) unit cells of the overall structure are shown as are the (2 2, -2 0) and (2 0, -2 2) unit cells representing the packing within each chain, (b) Structural models of the bitartrate phases of the two tartaric acid enantiomers on Cu(1 1 0) (S,S)-bitartrate (9 0, -1 2) and (/ ,R)-bitartrate (1 2, -9 0). The (3 1, -2 1) unit cell is also shown for the (/ ,/ )-bitartrate phase showing the packing within the chain [203],...

The acidity of organic ligands is enhanced by coordination with the oxide surface, i.e. the surface promotes deprotonation of the functional groups (COOH or OH). Such ligands, therefore, adsorb on the surface at a pH 2-3 units lower than that at which complexation with Fe in solution would occur (Kummert and Stumm, 1980). An example of this is the deprotonation of the alcoholic OH group of tartaric acid upon adsorption on the goethite surface (Cornell and Schindler, 1980). The appropriate reaction for the acid in water is. 

These chiral domains of tartaric acid are found to be formed by its bitartrate form. They follow a 2-dimensional ordered structure. In the case of the (R,K)-isomer the supramolecular assembly can be described by the following matrix notation, which defines the unit cell of the adlayer unambiguously in terms of the unit cell of the substrate ... 

According to this method, Fyles analyzed the transport rate of alkali metal cations for a series of 21 synthetic transporters (Figure 14). The whole molecules were designed to elucidate the structure-function relationship. They are composed of three parts core, wall, and head units. The core units were derived from tartaric acids so that the wall units may be fixed to provide structural control by incorporating both the polar and nonpolar functionality (Y and Z in Figure 14). The head groups (X) are attached to provide an overall amphiphilic nature. 

Fig. 33. Monoclinic system. (See also Fig. 26.) a. Unit aell type. 6. Left- and right-handed tartaric acid. ClasB 2. c. 2,4,6 Tribromobenzonitrile. Class m. d, p-Dinitro-benzene. Class 2/m. e. (CH3COO)8Pb.3HaO. Class 2/m.

Acidulants. The preferred acidulant for dilutable (and other) soft drinks is citric acid, which is readily available both as a crystalline solid (citric acid anhydrous) and as a 50% w/w solution in bulk. Other acidulants that are used in specific products include malic acid, lactic acid and tartaric acid. Phosphoric acid, until recently permitted only in cola drinks, is now available for use in the United Kingdom but has so far found little, if any, use in dilutable products. Acids other than citric are usually employed only where a slightly different taste profile is needed. Ascorbic acid is usually employed as an antioxidant rather than as a direct acidulant. 

Chow and Mak came to a similar conclusion on investigating the chiroptical properties of dendrimers containing enantiomerically pure threitol building blocks obtained from tartaric acid as spacers between the achiral phloroglucin branching units (see Fig. 4.73) [27]. They found that the chiral spacers in the dendrimer scaffold do not influence one another and contribute additively to the overall rotation. Moreover, they also observed that on introduction of both enantiomers one (R,R)-threitol unit precisely compensated the rotational contribution of one (S,S)-threitol unit, provided that the enantiomeric building blocks were located at equivalent positions within the dendrimer scaffold. However, CD-spectroscopic data revealed that the contribution of the exterior threitol units to the total rotation must be slightly different from that of the interior units. 

The Fyles family of channels is illustrated schematically in the accompanying figure. The tartaric-acid-based crown ether central unit defines the position of the sidearms and serves as a selectivity filter and central relay within the bilayer membrane. Four phospholipid molecules are also shown in cartoon form to illustrate the position in which the channel is thought to reside. The spacer chains or walls of the channel are based on substituted succinic acid groups, terminated at each membrane boundary by a polar residue, designated H for headgroup in the figure (Fyles et al., 1993). A typical... 

A number of other synthetic ion channels have been developed that incorporate crown ethers as critical elements. They cannot all be described and illustrated in this short chapter but it is important to note them. Voyer and coworkers developed channels that use an a-helical backbone to align a series of crowns into a channel that was both functional and biologically active (Voyer and Robataille, 1995 Voyer et al., 1997). Pechulis and coworkers developed a channel in which a central crown used tartaric acid subunits to anchor steroids, which formed the channel s walls (Pechulis et al., 1997). Mendoza and coworkers prepared an active channel based on a calixaiene central unit but that had crown ether headgroups (de Mendoza et al., 1998). Hall and coworkers modified the tris(macrocycle) design originating in our lab to form a redox-switchable crown that was active in bilayers (Hall et al., 1999, 2003). 

Chow and coworkers 40,41 reported the synthesis and characterization of homochiral dendrimers through the first generation by using (2R, 3i )-tartaric acid as the chiral building block. The mode of preparation is based on three parts the three-directional core, 1,3,5-trihydroxybenzene (61), the chiral connector, l-0-tosyl-4-terf-butyl-phenoxy-2,3-O-isopropylidene-L-threitol (62), and a branching unit, l-benzyloxy-3,5-dihydroxyben-zene (63). 

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