Optical activity, overview

Poly(hydroxyalkanoates) (PHAs), of which poly(hydroxybutyrate) (PHB) is the most common, can be accumulated by a large number of bacteria as energy and carbon reserve. Due to their bio degradability and bio compatibility these optically active biopolyesters may find industrial applications. A general overview of the physical and material properties of PHAs, alongside with accomplished applications and new developments in this field is presented in this chapter. 

In the following sections we will first in Section 2 briefly discuss the necessary background to understand optical activity effects in linear and nonlinear optics and to illustrate the similarities and differences between both types. In Section 3 we present a more thorough analysis of nonlinear optical effects in second-harmonic generation, both from a theoretical and an experimental point of view. Section 4 deals with experimental examples that illustrate the usefulness of nonlinear optical activity in the study of chiral thin films and surfaces. Finally, in Section 5 we give an overview of the role of chirality in the field of second-order nonlinear optics and show that chiral molecules can be useful for applications in this field. 

As mentioned above, several syntheses of optically active y8-benzyl-y-bu-tyrolactones have been reported in the literature [1, 2]. A comprehensive overview of the methods available for the synthesis of / -benzyl-y-butyrolac-tones is displayed in Scheme 6. Asymmetry was introduced involving either... 

A general overview for the formation of optically active sulfinylated compounds from menthyl (S)-4-methylbenzenesulfinate can be gained from the literature13-14-18-26. 

In order to place later chapters in proper context, the first chapter offers a comprehensive overview of industrially important catalysts for oxidation and reduction reactions. Chapters 2 and 3 describe the preparation of chiral materials by way of the asymmetric reduction of alkenes and ketones respectively. These two areas have enjoyed a significant amount of attention in recent years. Optically active amines can be prepared by imine reduction using chiral catalysts, as featured in Chapter 4, which also discloses a novel reductive amination protocol. 

Asymmetric Mannich reactions provide useful routes for the synthesis of optically active p-amino ketones or esters, which are versatile chiral building blocks for the preparation of many nitrogen-containing biologically important compounds [1-6]. While several diastereoselective Mannich reactions with chiral auxiliaries have been reported, very little is known about enantioselective versions. In 1991, Corey et al. reported the first example of the enantioselective synthesis of p-amino acid esters using chiral boron enolates [7]. Yamamoto et al. disclosed enantioselective reactions of imines with ketene silyl acetals using a Bronsted acid-assisted chiral Lewis acid [8]. In all cases, however, stoichiometric amounts of chiral sources were needed. Asymmetric Mannich reactions using small amounts of chiral sources were not reported before 1997. This chapter presents an overview of catalytic asymmetric Mannich reactions. 

A variety of other excellent texts are available for in-depth review of the fundamentals of Raman spectroscopy, including core technologies and applications [2, 3]. This is intended as a very brief, non-rigorous overview for non-spectroscopists who may be unfamiliar with the principles of Raman, its strengths, and practical limitations. For discussion of the experimental details of variant techniques such as ROA (Raman optical activity) or SERS, the reader is directed to the appropriate chapters in this text. 

Numerous modes of signalling of fluorescence for the distinction of optically active compounds are known. For an excellent overview of all methods... 

Enantioselective catalytic alkylation is a versatile method for construction of stereo-genic carbon centers. Typically, phase-transfer catalysts are used and form a chiral ion pair of type 4 as an key intermediate. In a first step, an anion, 2, is formed via deprotonation with an achiral base this is followed by extraction in the organic phase via formation of a salt complex of type 4 with the phase-transfer organocata-lyst, 3. Subsequently, a nucleophilic substitution reaction furnishes the optically active alkylated products of type 6, with recovery of the catalyst 3. An overview of this reaction concept is given in Scheme 3.1 [1],... 

The design of host compounds for optical resolution has received much attention. Toda [23,24] has reviewed the subject, and has used a number of novel techniques to effect efficient optical separation. He has demonstrated the possibility of resolving a racemic oil by stirring in a water suspension of a chiral host [25], and has applied fractional distillation techniques at different temperatures to separate a variety of racemic guests in the presence of chiral hosts [26]. An overview of the industrial applications and production of optically active materials is given in the book Chirality in Industry [27],... 

A broader overview on the industrial methods used for the production of optically active intermediates is recently reviewed by Breuer et al.100... 

The second chapter ends with two overviews by Stephens Devlin and by Hug on the theoretical and the physical aspects of two vibrational optical activity spectroscopies (VCD and VROA, respectively). In both overviews the emphasis is more on their basic formalism and the gas-phase quantum chemical calculations than on the analysis of solvent effects. For these spectroscopies, in fact, both the formulation of continuum solvation models and their applications to realistic solvated systems are still in their infancy. 

In particular, reduction of unsymmetric ketones to alcohols has become one of the more useful reactions. To achieve the selective preparation of one enantiomer of the alcohol, chemists first modified the classical reagents with optically active ligands this led to modified hydrides. The second method consisted of reaction of the ketone with a classical reducing agent in the presence of a chiral catalyst. The aim of this chapter is to highlight one of the best practical methods that could be used on an industrial scale the oxazaborolidine catalyzed reduction.1 1 This chapter gives an introductory overview of oxazaborolidine reductions and covers those of proline derivatives in-depth. For the oxazaborolidine derivatives of l-amino-2-indanol for ketone reductions see Chapter 17. 

The fundamental requirement for the existence of molecular dissymmetry is that the molecule cannot possess any improper axes of rofation, the minimal interpretation of which implies additional interaction with light whose electric vectors are circularly polarized. This property manifests itself in an apparent rotation of the plane of linearly polarized light (polarimetry and optical rotatory dispersion) [1-5], or in a preferential absorption of either left- or right-circularly polarized light (circular dichroism) that can be observed in spectroscopy associated with either transitions among electronic [3-7] or vibrational states [6-8]. Optical activity has also been studied in the excited state of chiral compounds [9,10]. An overview of the instrumentation associated with these various chiroptical techniques is available [11]. 

A NIR-laced article by Heise et al. discusses the technologies used in noninvasive glucose monitoring [167]. In this article, he describes his own work with a FT-NIR instrument, but also provides a nice overview of other NIR applications plus luminescence, optical activity, and Raman spectroscopy. He gives 38 references on these topics. 

A classic example of a typical enzymatic resolution on an industrial scale is the acylase-mediated production of L-methionine. This method has also been applied for the production of L-phenylalanine and L-valine. In addition to acylases, amidases, hydantoinases, and /i-lactam hydrolases represent versatile biocatalysts for the production of optically active L-amino acids. A schematic overview of the different type of enzymatic resolutions for the synthesis of L-amino acids is given in Fig. 2. 

This chapter presents an overview of existing strategies for asymmetric catalytic epoxidation of unfunctionalized olefins with synthetic catalysts. The significant progress in metal-catalyzed oxo transfer and dioxirane epoxidation has increased the accessibility of several classes of optically active epoxides and concurrently highlighted important problems yet to be solved. 

Before reviewing the different routes to optically active silanes and discussing some relevant points, namely, the determination of enantiomeric purity and configuration, we shall give a brief overview of the stereochemical stability of chiral silicon species. 

Several groups of investigators have reported on the production of optically active acids from racemic mixtures of nitriles. A comprehensive overview has recently been presented [41f... 

Much work has also been conducted on the hydrosilylation of ketones and imines (Equation 16.16). The products from these reactions are silyl ethers and sdylamines. These additions of silanes across C-X ir-bonds have been conducted predominantly for the purpose of generating optically active alcohols and amines after hydrolysis. Because the mechanism of these reactions is less defined than the mechanism of alkene hydrosilylation, and this chemistry lies outside the theme of this chapter, the hydrosilylation of ketones and imines is presented only briefly. Instead, this chapter provides an overview of the scope and motivation for the hydrosilylation of alkenes and alkynes and provides details on the mechanisms of these reactions catalyzed by complexes of various metals. Several comprehensive reviews of the scope of these reactions have been published. ... 

This section gives a brief overview of PLA matrix (for further reading, readers should refer to Chapters 1,4 and 5). As with other commodity polymers, PLA actually refers to a large family of compounds that includes copolymers with other monomers. The monomer, that is, lactic acid (2-hydroxy propanoic acid) is the simplest hydroxy acid with an asymmetric carbon atom and exists in two optically active configurations (d and l). Generally, two major routes are followed for the synthesis of PLA, such as polycondensation... 

The same nucleophilic substitution at the asymmetric Si atom takes place by an inversion mechanism called Sii 2-Si, similar to the organic S, 2 reaction and a retention mechanism called S -Si, rare in organic chemistry (Scheme 7, bottom) [1]. Thus, C and Si already behave differently. With the help of the new optically active transition metal compounds the stereochemical course of reactions of organometallic compounds can be studied. In Scheme 8 an overview shows that retention reactions, inversion reactions and racemization reactions of various types have been observed [12]. 

Diheterolevulosans, 209-211, 240 Dihexulose dianhydrides, 207 -266, see also Caramels Di-D-fructose dianhydrides 13C NMR spectra, 245-246 conformation, electronic control, 224-228 conformational rigidity, energetic outcomes, 228 hexulopyranose rings, 226 historical overview, 210-213 H NMR spectra, 248 -249 intramolecular hydrogen-bonds, 227 isomerization, 231 -232 1,2-linked, ero-anomeric effect, 224-225 listing, 240-241 nomenclature, 208-210 optical rotations and melting points, 242-243 protonic activation... 

We have overviewed some strategies for the surface-mediated fabrication of metal and alloy nanoscale wires and particles in mesoporous space, and their structural characterization and catalytic performances. Extension of the present approaches for metal/alloy nanowires may lead to the realization of the prospechve tailored design of super active, selective and stable catalysts applicable in industrial processes. The organometallic clusters and nanowires offer exciting and prospechve opportunities for the creahon of new catalysts for industry. Various metal/ alloy nanowires and nanoparhcles in the anisotropic arrangement in porous supports would help in understanding the unexpected electronic and optic properties due to the quantum effect, which are relevant to the rational design of advanced electronic and optic devices. 

In this chapter, we provide an overview of our recent efforts to develop a fundamental science base for the design and preparation of optimal lipid-based carriers of DNA and siRNA for gene therapy and gene silencing. We employ synthesis of custom multivalent lipids, synchrotron X-ray diffraction (XRD) techniques, optical and cryo-electron microscopy, as well as biological assays in order to correlate the structures, chemical, and biophysical properties of cationic liposome (CL)-NA complexes to their biological activity and to clarify the interactions between CL-NA complexes and cellular components. Earlier work has been reviewed elsewhere [1-7] and will not be covered exhaustively here. 

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