Optical rotatory properties of synthetic polymers. I. Optical inversion of poly(propylene oxide)

(+)-1,2-Diethoxypropane, a model diether for the repeating unit of poly(propylene oxide), was prepared, and its behavior in solutions regarding optical rotatory dispersion and proton magnetic resonance was compared with those of the polymer. It was found that the model compound and the poly(propylene oxide) show essentially the same optical properties in solutions. By using the Brewster model of optical activity, it was concluded that the solvation of the polymer may well modify the polarizability of the optically active species to cause changes in the order of the polarizabilities of four atoms directly attached to the asymmetric carbon atom. The explanation is shown to be applicable also to some of related polymers.     

Optical Rotatory Dispersion of Poly(propylene oxide) in Benzene Solution Determined from Channeled Spectra

The proposed method of channeled spectrum employs the recorded channeled spectrum of an optical active polymer solution placed between two crossed polarizers. The approach allows the evaluation of the optical rotatory dispersion of poly(propylene oxide) in benzene. The specific rotation, circular birefringence, and dispersion parameter depend on the wavelengths of the maxima and minima from the channeled spectrum.     

Asymmetric selective copolymerization of propylene oxide with d-camphoric acid anhydride

The ring-opening copolymerization of propylene oxide with d-camphoric acid anhydride [α]_D ?3.4° was carried out with diethylzinc and triethylamine as catalysts. It was found that the products were alternating copolymers which were optically active. The optical rotatory dispersion curves were found to fit a simple Drude equation having a λ_c value of 201 mμ. The specific rotation increased with increasing intrinsic viscosity of the product. The propylene oxide recovered from the polymerization system was optically active. Its specific rotation increased with increasing polymerization time. It is thought that the asymmetric selective copolymerization of propylene oxide is caused by the influence of the optically active camphoryl group of the polymer end.     

Optical rotatory dispersion and vacuum ultraviolet circular dichroism of poly[(R)-oxypropylene]

The circular dichroism (CD) spectrum of poly[(R)-oxypropylene] in a number of solvents has been measured in the vacuum ultraviolet region. Two CD bands were measured for cyclohexane, acetonitrile, and trifluoroethanol solutions. The CD spectrum was extended to 140 nm and three bands were measured in a 1,1,1,3,3,3-hexafluoro-2-propanol solution. The similarity of these four CD spectra in sign, shape, and intensity confirm that poly[(R)-oxypropylene] has similar conformations in all solvents studied, even though the optical rotatory dispersion (ORD) in the visible region is positive for the cyclohexane solution but negative for the alcohol solutions. A Kronig–Kramers transform of the two CD bands observed for the cyclohexane solution accounts for the observed positive ORD spectrum. In contrast, a third large and negative CD band centered below 160 nm is necessary to account for the negative ORD spectra observed for the alcohol solutions. Apparently the anomalous sign variation of the ORD curves observed in the visible region is due to subtle changes in the interplay of a large number of CD bands. Solvent interaction, observed as a blue shift of the first two CD bands for the alcohol solutions, could produce the subtle changes necessary to change the sign of the ORD curve in the visible region. The first two CD bands of poly[(R)-oxypropylene] are tentatively assigned as n? σ^* and the third as an n? 3s.     

Asymmetric Induction Copolymerization of Optically Active N-(1-Menthyl Carboxylatomethyl) Citraconimide with Methyl Methacrylate

Copolymerization of an optically active N-(1-menthyl carboxylatomethyl)citraconimide (MCMCI) was carried out with methyl methacrylate (MMA) with azobisisobutyronitrile as the initiator in benzene at 50°C. All the copolymers obtained were optically active. After the removal of the optically active menthyl group, the hydrolyzed poly(MCMCI-co-MMA)'s still showed optical activity. The asymmetric induction to the copolymer main chain and the mechanism are discussed based on the measurements of optical rotatory dispersion and circular dichroism of the original and hydrolyzed copolymers.     

Optical rotatory dispersion (ORD) of glycogen

The ORD spectra of three types of glycogen in salt solutions at different concentrations, pH and ionic strength values were determined to investigate the influence of these variables on the rotatory power.The ORD curves obtained with the samples recently prepared correspond to positive monotone dispersion curves, similar to available data for the other polysaccharides.Once the mutarotation equilibrium is attained a maximum is observed at 210±10 nm. The rotatory power decreases with the elapsed time and in some cases, it is possible to find a change in the sign of these curves. Such a phenomenon may be attributed to conformational changes in the monomer units constituting the macromolecule.A considerable increase in the rotatory power is found at pH extreme values.The dispersion constant, _c , was calculated by means of a modified Drude equation and results indicate that the _c value is higher for muscle glycogen in the mussel species, suggesting a higher degree of asymmetry in this macromolecule.     

Optical rotatory dispersion studies—CXII thiosteroids (20) An octant rule for the thiocyanate chromophore and its application to rotameric equilibrium studies in the steroid series

Optical rotatory dispersion and circular dichroism measurements of a number of steroidal thiocyanates have demonstrated that a low intensity absorption near 250 nm is optically active. On the assumption that this transition of thiocyanates is qualitatively similar to the n → π^* transition of azides, an octant rule is proposed for thiocyanates, which leads to the prediction of the sign of the Cotton effect. Its potential utility is demonstrated by analyzing rotameric contributions of various steroidal thiocyanates.     

Resolution enhancement for infrared rotatory dispersion spectra of induced cholesteric phases

For a solution of optically active compounds in liquid crystals, the infrared rotatory dispersion can be measured by Fourier transform spectroscopy. The results of a resolution enhancement by Fourier deconvolution and second derivative approach for the spectral features of the so-called A-Cotton effects are discussed. The experimental spectrum shown was recorded from a solution of cholesteryl oleyl carbonate in liquid crystal MBBA.     

Asymmetric induction radical copolymerization of optically active l-menthyl vinyl ether with vinylene carbonate and indene

The copolymerizations of l-menthyl vinyl ether (l-MVE) with the monomers vinylene carbonate (VCA) and indene (IN) were carried out in benzene with azobisisobutyronitrile (AIBN) as an initiator to obtain optically active copolymers. The optically active l-menthyl residue from the copolymer main chain was removed using dry hydrogen bromide gas. After the ether cleavage reaction, the copolymers prepared (VA–VCA and VA–IN) were still optically active, and hence it was found that asymmetric induction had taken place in the copolymer main chain. The optical rotatory dispersion (ORD) and circular dichroism (CD) data of the original and ether-cloven copolymers were also determined.     

Optical rotatory dispersion of indole alkaloids from the yohimban, corynanthean, and quebrachamine groups

It has been shown that optical rotatory dispersion curves can be used to determin- the absolute stereochemistry at C(3) of indole alkaloids of the yohimban and corynane thean types. This is dependent on the absence of strong chromophores other than that of the aromatic system.     

Optical rotatory dispersion of indoline alkaloids with keto groups

The optical rotatory dispersion curves of a series of indolines, N(a)-acetyl-indolines and N(a)-methoxycarbonyl-indolines containing keto groups have been measured. It has been shown that the absolute stereochemistry of N(a)-acetyl-indolines containing keto groups can still be determined from the character of the Cotton Effect due to the aromatic chromophore, the ketone Cotton Effect however being more difficult to interpret. The use of N(a)-methoxycarbonyl-indoline and indoline chromophores is dangerous due to the complex nature of the Cotton Effect of the former and the overlapping of that of the latter with the ketone Cotton Effect.     

Optical rotatory dispersion of water-soluble cellulose derivatives

Dilute solutions of water-soluble cellulose esters and also solutions of model compounds — glucose and cellobiose — have been investigated. It has been shown that a definite influence on optical rotatory dispersion is exerted by the conformational difference of the pyranose rings of cellulose arising when the hydroxy groups in the macromolecule are partially replaced by functional groups of different natures.     

Asymmetric induction copolymerization of optically active l-menthyl vinyl ether with styrene and N-phenylmaleimide

The copolymerizations of l-menthyl vinyl ether (l-MVE) with styrene (St) and N-phenylmaleimide (N-PMI) as comonomers were carried out in benzene with azobisisobutyronitrile (AIBN) as an initiator to give optically active copolymers. After the removal of the optically active menthyl group by use of hydrogen bromide gas, the ether-cloven l-MVE-N-PMI copolymer (VA-N-PMI) was still optically active. On the other hand, the optical activity of l-MVE-St copolymer disappeared after ether cleavage. It is thought that asymmetric induction took place in the polymer main chains. The optical rotatory dispersion and circular dichroism of the original and ether-cloven copolymers were measured in order to confirm the asymmetric induction.     

An optical rotatory detector for high-performance liquid chromatography using polarization modulation.

A sensitive and variable-wavelength optical rotatory (OR) detector for high-performance liquid chromatography is presented. This design is entirely different from that of conventional OR detectors consisting of a crossed polarizer pair. By placing a polarizing prism and a retardation plate into a commercial circular dichroism (CD) detector, the OR signal was obtained. The Mueller matrix approach was used to prove the principle of the OR signal appearance. Sugars and 4-androstene-3,17-dione were chosen as test compounds. The limit of detection was below 0.5 microg of injected sucrose at 260 nm, which was superior to that obtained with a conventional OR detector. For 4-androstene-3,17-dione, which is CD active, and shows a large anomalous OR dispersion curve, our detector gave a large OR signal with approximately half the intensity of the CD signal at 340 nm.     

Structure and conformation of DAB dendrimers in solution via multidimensional NMR techniques.

NOESY-HSQC 3D-NMR and NOESY 2D-NMR techniques have been used on a 750 MHz spectrometer to study the chain conformations of different generation DAB dendrimers (poly[propylene imine] dendrimers) in chloroform and benzene solutions. The high-field multidimensional NMR techniques provided the chemical shift dispersion needed to resolve all of the unique resonances in the dendrimers. By studying the NOE interactions among dendritic chain protons, information about through space interactions between protons on different parts of the dendrimer chain is obtained, which is directly related to the conformation of the dendrimer. These experiments also give further proof of the chemical shift assignments obtained from the HMQC-TOCSY 2D and 3D NMR experiments. The concentration effects on chemical shifts have also been observed, revealing information about the interactions between solvent and different parts of dendrimer molecules. These studies clearly show for DAB dendrimers, that folded chain conformations can occur in nonpolar solvents such as benzene and extended chain conformations are predominant in polar solvents such as chloroform.     

Poly(γ-alkyl L-glutamates). II. Optical rotatory dispersion studies in organic solvents

Conformations of a series of poly(γ-alkyl L -glutamates) (ethyl, n-propyl, n-butyl, isobutyl, and isoamyl) were studied by ORD and infrared absorption methods. All except the n-propyl ester were found to be in helical form in nonpolar non-aromatic solvents such as ethyl acetate, chloroform, ethylene dichloride, methylene chloride, carbon tetrachloride, 2-chloroethanol, dimethylformamide, and dioxane. In such cases, the Cotton effects due to the n–π* transition of peptide bonds occurred near 234 mμ and were of a magnitude similar to those found for poly(γ-benzyl L -glutamate) and poly-L -methionine in nonpolar non-aromatic organic solvents. These four polypeptides in aromatic nonpolar solvents, such as benzene, benzyl alcohol, pyridine, and m-cresol, were also found to be in helical form, although the ORD parameters differed considerably from the values in non-aromatic solvents. An essential cause seems to be the interaction of π electrons on peptide bonds with π electrons in the solvents. Helix-coil transitions of these esters in chloroform-dichloroacetic acid mixtures (dichloroacetic acid seems to be a random coil-forming solvent) were expressed by the Shechter-Blout formulation. This was not true, however, for helix–coil transitions in benzyl alcohol–dichloroacetic acid mixtures. The dependence of the helical stability of these polypeptides in chloroform solution upon the side-chain length and upon temperature is discussed.     

Optical properties of inherently dissymmetric polyamides

A study of the optical rotatory dispersion (ORD), circular dichroism (CD), and ultraviolet spectra (UV) of polyamides derived from optically active biphenyl acid chlorides, and aromatic, and aliphatic diamines, was made. The optically active monomers were (–)-(S)-2,2′-dinitro-6,6′-dimethylbiphenyl-4,4′-dicarbonyl chloride and (–)-(S)-2,2′-dichloro-6,6′-dimethylbiphenyl-4,4′-dicarbonyl chloride. The diamines were o-, m-, and p-phenylenediamine, piperazine, trans-2,5-dimethylpiperazine, and 1,2-pyrazolidine. The ORD spectra of the o-phenylenediaminepolyamide taken in different solvents indicated the existence of some ordered structure in the least polar solvent. All other polyamides existed in a random coil conformation in the solvents employed.     

Time dependent density functional theory modeling of specific rotation and optical rotatory dispersion of the aromatic amino acids in solution

Time Dependent Density Functional Theory (TDDFT) along with the COnductor-like Screening MOdel (COSMO) has been applied to model the specific rotation at 589.3 nm and the optical rotatory dispersion (ORD) of the aromatic amino acids phenylalanine, tyrosine, histidine, and tryptophan. Solution structures at low, neutral, and high pH were determined. Both the anomalous dispersion absorbing (resonance) region and the lower energy (transparent) region of the ORD of the compounds were modeled. Linear response calculation of the specific rotation and ORD as well as Kramers-Kronig transformations of calculated circular dichroism spectra to model resonant ORD were compared with experimental data from the literature.     

Asymmetric radiation-induced inclusion polymerization of 3-methyl-1,4-pentadiene in deoxycholic acid

The radiation-induced polymerization of 3-methyl-1,3-pentadiene (3MPD) as an inclusion complex in deoxycholic acid (DOCA) has produced in good yield the optically active polymer poly(3-methyl-1,4-pentadiene) (P3MPD) whose structure and properties were studied by FT-IR spectroscopy and thermal analysis (TGA, DTG and DTA). The data show that the polymer is essentially trans-1,4-P3MPD as expected for the polymerization in constrained media. Trans-1,4-P3MPD is optically active with [α]_D values comprised between +4.3 and +5.6. The optical rotatory dispersion curve of the P3MPD is completely different from that of DOCA as expected.     

Optical rotatory power of biodegradable polylactic acid films

Polylactic acid (PLA) is a polymer material on which biodegradability research has been the most advanced. PLA is a chiral polymer in which molecules containing asymmetric carbon atoms have a helical structure. Two optical isomers of PLA exist, PLLA (poly(L-lactic acid)) and PDLA (poly(D-lactic acid)). In this study, using various physical processes, we fabricated various samples such as oriented PLLA film, PLLA fiber, rolled PLLA film and forged PLLA plate. We observed a large optical rotatory power ρ in the cylindrical plate fabricated using a forging process. ρ of forged PLLA plates is 7200°/mm which is approximately 300 times larger than that of α-quartz.