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crystals are called enantiomorphic crystals. This method is known to as spontaneous resolution by crystallization. Fig. 1-9. Enantiomorphic crystals. Abstract model [16]. Preferential crystallization by inoculation The selective crystallization of a single enantiomer is possible to perform in the presence of traces of the same enantiomer that is to be separated. In this case an oversaturated racemic solution is "seeded" in small amount of pure enantiomer and the resulting precipitate will have domination of the enantiomer in the seed. However, with the exception of the separation of glutamic acid and of a copper complex of DLaspartic acid, this method has been found to be impractical or resulted in portion resolution only. Biochemical processes The chiral compounds that react at different rates with the two enantiomers may be present in a living organism. For example, in 1858 Pasteur discovered that aqueous solution of racemic tartaric acid after contact with the mould fungus (Penicillium glaucum) slowly became enantioenriched. The mould was preferentially metabolizing the right rotatory enantiomer. This method is limited, since it is necessary to find the proper organism and since one of the enantiomer is destroyed in the process. However, when the proper organism is found, the method leads to a high extent of resolution since biological processes are usually very stereoselective. Another disadvantage of this method is that only dilute solutions can be used. Conversion in diastereomers If the racemic mixture to be resolved contains a carboxyl group (and no strongly basic group), it is possible to form a salt with an optically active base. Fig. 1-10 illustrates reaction of S-brucine with racemic hydroxypropanoic acid produced a mixture of two salts having the configuration SS and RS. Although the acids are enantiomers, the salts are diastereomers and have different properties e.g. solubility. The mixture of diastereometric salts is allowed to crystallize from a suitable solvent. 5
R H COOH C OH CH 3 H COO - Bricine-H + C OH CH 3 S-brucine R S S COO - Bricine-H + COOH HO C H HO C H CH 3 CH 3 S S Fig. 1-10 formation of diastereometric salts [3]. Since the solubilities are different, the initial crystals formed will be richer in one diastereomer. Once the two diastereomers have been separated, it is easy to convert the salt back to the free acids and the recovered base can be used again. Advantages of this approach are that naturally occurring optically active bases (mostly alkaloids: brucine, ephedrine, morphine, etc.) are readily available. However, unfortunately, the difference in solubilities is rarely if ever great enough to effect total separation with one crystallization. Differential absorption When a racemic mixture is placed on a chromatographic column consisting of chiral phase, then, in principal the enantiomers should move along the column at different rates and should be separated. This technique is widely in use in different chromatography applications: GC, HPLS. Chiral recognition In order to separate enantiomers from racemic mixture the use of chiral host to form diastereometric inclusion is possible. Some hosts can form an inclusion with one enantiomer only or this formation is faster then with another enantiomer. For example, chiral host (Fig. 1-11-A) can partially resolve the racemic amine salt [17] (Fig. 1-11-B). O O O O O O Ph CH 3 C + NH 3 - PF 6 H A B Fig. 1-11. Chiral host-A and guest molecule –B [3]. Kinetic resolution Since enantiomers react with chiral compounds at different rates, it is sometimes possible to effect a partial separation by stopping the reaction before completion. An example is the resolution of allylic alcohol [18] (Fig. 1-12-A) with one enantiomer of a chiral epoxidizing agent, in this case the discrimination was extreme. One enantiomer was converted to the epoxide and the other was not, the ratio being more than 100. Reactions catalyzed by enzymes can be utilized for this kind of resolution. 6
Page 1 and 2: Preparation and Characterization of
Page 3 and 4: 5.4 Summary 66 Chapter 6 Cinchonidi
Page 5 and 6: Abstract Studies of the interaction
Page 7 and 8: many compounds are biologically act
Page 9: Fig. 1-7. Hexahelicene [3]. 7. Chir
Page 13 and 14: Catalyst activity, expressed in the
Page 15 and 16: In fact, there are only two heterog
Page 17 and 18: similar way as relative abundance o
Page 19 and 20: surface concentration of cinchonidi
Page 21 and 22: site on Pt surface formed by a adso
Page 23 and 24: Chapter 2 Introduction to the nanos
Page 25 and 26: Triangular prism 5 4 Comments: A -
Page 27 and 28: precursors and building-up. This me
Page 29 and 30: 2.3 Preparation of nanoclusters on
Page 31 and 32: Paris Marseille Ljubljana Synphos Q
Page 33 and 34: Chapter 4 Cinchonidine modified Pt
Page 35 and 36: dihydrocinchonidine (355 mg or 1.2
Page 37 and 38: Table 4-1. Comparison between 5 % P
Page 39 and 40: widening can be used in estimation
Page 41 and 42: 1 Absorbance 0.1 2 1600 1400 1200 1
Page 43 and 44: the focus of these prior experiment
Page 45 and 46: Fig. 4-11. Tilted adsorbed cinchoni
Page 47 and 48: sci., QL. comp. 768 (str) 756 (str)
Page 49 and 50: Conversion, % 100 80 60 40 ITP time
Page 51 and 52: 6A c 10 19.5 B, 20 61 0 3 0.18 0.51
Page 53 and 54: pressure, exposing time, cinchonidi
Page 55 and 56: Fig. 4-16. Linear relationship betw
Page 57 and 58: 1 , 1209 cm -1 and 1382 cm -1 remai
Page 59 and 60: Our results are in line with previo
Page 61 and 62:
eaction. The stability of the catal
Page 63 and 64:
Table 5-1. Ee and reaction rate ind
Page 65 and 66:
Enantiomeric excess, % 85 80 75 A2
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35 30 Before After Percent of parti
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catalyst activation seems to indica
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Table 5-3. Assignment of some vibra
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6.2 Experimental Materials Cinchoni
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Fig. 6-3. TEM image of cinchonidine
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From the results of EP and EB hydro
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enhancement. However the exact fact
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Further, this family of man-made li
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Fig. 7-2. TEM of quiphos modified P
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of quiphos adsorbed on Pt and Pd an
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Fig. 7-8 Flat adsorbed quiphos via
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comp., H 11,12,13,14 2 C b., 2 P 11
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Chapter 8 “Quiphos-spider” modi
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flat crystal surface due to the hig
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Chapter 9 Diphos and diop modified
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Table 9-1. Average crystal size of
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Fig. 9-4. Conformation of diphos mo
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ings. Due to these reasons we can n
Page 103 and 104:
Fig. 9-9. Proposed orientation of a
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The model of adsorption of diop on
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The calculation of energy of formin
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For the preparation of synphos modi
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1 2 20 40 60 80 2Θ Fig. 10-3. XRD
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The DRIFT spectra of synphos (Fig.
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peaks which can be used for analysi
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References [1] G.E. Tranter, J. Che
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[64] A. Szabo, N. Kunzle, T. Mallat
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[128] J.D. Aiken III, R.G. Finke, J
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[189] K. Umezawa, T. Ito, M. Asada,
Page 125:
I declare that the current Ph.D. th
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