Molar Optical Rotation Research Articles

Study of optical rotation based on the molecular structure in fused oligomers of macrocycles.

We designed a unique oligomer form in which several helically twisted macrocycles (M- or P-helicity) are arranged through fusion. We investigated the optical rotation of a series of fused oligomers of macrocycles with a difference in the number and arrangement of elements associated with point-chiral auxiliary. Some oligomers cooperatively attained a situation where an identical sense of twisting was preferred throughout the entire molecule. On the basis of these results, we estimated diastereomeric excess induced in each oligomer. We revealed that the molar optical rotation per element was modulated with a rotational angle between elements: an increase via 0° rotational arrangement, a decrease via 180° rotational arrangement, or a decrease via cyclic arrangement. Alternatively, for other oligomers in which several diastereomeric conformers coexist, we uniquely attempted to consider the optical rotation based on the molecular structure through the assessment of a change ratio of the absorption dissymmetry factor before and after complexation with an achiral guest. We found that molar optical rotation could be different based on the arrangement, although actual measured values were similar.

Two-ring chirality generated by the alignment of two achiral phenylacetylene macrocycles.

When two achiral rings are bound mechanically, a chiral source is generated in the assembly. The chiroptical properties could be modulated according to the relative occupation of each ring in the assembly. In fact, we have found that two isomeric assemblies (1 and 2) show unique properties in each assembly with two achiral rings of phenylacetylene macrocycle (PAM). When considering the difference in the chiroptical properties of these two isomeric assemblies (6PAM × 2), no comparison was available based on no activity of the achiral component element itself (6PAM). In this work, we synthesized a two-ring chiral analog (4) by the ring-fusion of two 6PAMs to an 11PAM, and examined the chiroptical properties of 4, since the single helix was imparted as a chiral source. By comparison of the chiroptical properties (molar circular dichroism and molar optical rotation) of 1 and 2 to those of 4, we demonstrated that the disparity was related to the alignment of the two achiral rings.

Investigating the Clough, Lutz, and Jirgensons Rule for the pH Dependence of Optical Rotation of Amino Acids

Students in an upper-level physical chemistry course used a polarimeter to measure the molar optical rotation of different optically active amino acids to confirm the Clough, Lutz, and Jirgensons (CLJ) rule. This rule states that an amino acid is in the l-configuration if the molar optical rotation becomes more positive upon the addition of acid or the acid is of the d-configuration if the optical rotation becomes more negative in an acidified solution. Students demonstrated this rule for known configurations of amino acids and then applied this rule to determine the configuration of an amino acid with an unknown configuration.

Optical Rotatory Dispersion Measurement of D-Glucose with Fixed Polarizer Analyzer Accessory in Conventional Spectrophotometer

In the sample compartment of a conventional spectrophotometer, mounting of a polarizer before sample and an analyzer behind sample allows the determination of the optical rotatory dispersion of optical active media by measurement of the transmission ratio of crossed and parallel arranged polarizer and analyzer. A formula for the determination of the angle of rotation is derived from the transmission ratio. The arrangement is applied to determine the molar optical rotation of D-glucose in water in the wavelength range from 220 nm to 820 nm.

Asymmetric anionic polymerizations of 7-cyano-7-alkoxycarbonyl-1,4-benzoquinone methides

Asymmetric anionic polymerizations of 7-cyano-7-alkoxycarbonyl-1,4-benzoquinone methides (1) with various alkoxy groups were performed using chiral initiators such as lithium isopropylphenoxide (iPrPhOLi)/(S)-(–)-2,2′-isopropylidene-bis(4-phenyl-2-oxazoline) ((–)-PhBox) and lithium isopropylphenoxide (iPrPhOLi)/(–)-sparteine ((–)-Sp) to investigate the effect of the alkoxy groups of alkoxycarbonyl substituent in the monomers 1 and chiral ligands of chiral initiators on the control of chiral center in the formation of polymers. Molar optical rotation values of the polymers were significantly dependent upon alkoxy groups, and the polymers with higher molar optical rotation were obtained in monomers with primary alkoxy groups. The asymmetric anionic oligomerizations of the quinone methides having methoxy(1a), ethoxy(1b), and n-propoxy(1c) groups with chiral initiators were carried out. Both 1-mers and 2-mers were isolated and their optical resolutions were performed to determine the extent of stereocontrol. High stereoselectivity was observed at the propagation reaction, but not at the initiation reaction. The effect of the counterion on the control of chiral center in the formation of the polymer was investigated in the asymmetric anionic polymerizations of 1b with iPrPhOM(M = Li, Na, K)/(–)-Sp and iPrPhOM(M = Li, Na, K)/(–)-PhBox initiators and discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

A Highly Efficient Chiral-Bridged Diphosphine Ligand Modified Cationic Palladium(II) Catalyst System for Asymmetric Alternating Copolymerization of Propene and Carbon Monoxide

A highly efficient chiral-bridged biphenyl diphosphine ligand [(R ax)-BuP] modified cationic palladium(II) catalyst system for the synthesis of optically active polyketone by stereoselective alternating copolymerization of propene and carbon monoxide is reported for the first time. The results show that [Pd(MeCN)4][OTf]2 is an excellent catalyst precursor in a mixed solvent of MeNO2-MeOH. The highest catalytic activity was found to be 221 g polymer/(g Pd˙h). A chiral polyketone with molecular weight Mn = 2.9 × 104, polydispersity = 1.4, and molar optical rotation = +37˚ was afforded under optimized reaction conditions.

Pd-catalyzed asymmetric alternating co-polymerization of propene with carbon monoxide using ionic liquids

A protocol for Pd-catalyzed stereoselective co-polymerization of propene and carbon monoxide using chiral ligands, such as (2S,3S)-DIOP and (R)-P-Phos in [C4mim][PF6]/[C6mim][PF6] as an ionic liquid medium was developed. With (2S,3S)-DIOP as chiral ligand and [C4mim][PF6] as medium, the Pd-catalyzed co-polymerization of propene and CO gave almost completely regioregular polyketones, and the product polymer showed moderate stereoregularity (61% of ℓ-diads). The highest molar optical rotation=+15.9 and polydispersity=1.2 were attained when (R)-P-Phos was used as the ligand and [C6mim]PF6 as the solvent. The co-polymer exhibited regioregularity of H–H/H–T/T–T (%)=17:66:17.

Synthesis of axially chiral dendrimers containing meta-terphenyl peripheral groups and a chiral binol core

Fréchet-type poly(arylether) dendritic bromides carrying m-terphenyl peripheral groups were synthesised up to second generation by convergent methodology. Simple O-alkylation of chiral (S)-BINOL with the dendritic bromides afforded the corresponding axially chiral dendrimers. The molar optical rotation values of the dendrimers become increasingly negative as the dendrimer generation increases.

Screw-sense-selective polymerization of aryl isocyanides initiated by a Pd-Pt mu-ethynediyl dinuclear complex: a novel method for the synthesis of single-handed helical poly(isocyanide)s with the block copolymerization technique

Living polymerization of chiral aryl isocyanides, such as m- and p-menthoxycarbonylphenyl isocyanides 2 and 5, initiated by the Pd-Pt mu-ethynediyl dinuclear complex 1, proceeds with a high screw-sense selectivity to give the poly(isocyanide)s 3 and 6, which exhibit a large specific rotation and an intense CD band at lambda = 364 nm as a consequence of a helical chirality. The molar optical rotation and molar circular dichroism of the resulting polymers 3 and 6 reach a constant value at a degree of polymerization (Pn) of more than 30. Screw-sense-selective polymerization of achiral aryl isocyanides that bear very bulky substituents, such as 3,5-di(propoxycarbonyl)phenyl isocyanide (11), 3,5-di(butoxycarbonyl)phenyl isocyanide (13), and 3,5-di(cyclohexyloxycarbonyl)phenyl isocyanide (15), is achieved by the use of chiral oligomer complexes 3(30) and 6(30), prepared from the reaction of 1 with 30 equivalents of 2 or 5, as an initiator to give predominantly single-handed helical polymers. In contrast, smaller aryl isocyanides are also polymerized by 3(30) and 6(30) with screw-sense selectivity in the initial stage of the reaction, but the single-handed helix is not preserved up to high molecular weight. Kinetic studies of the polymerization of (L)- and (D)-2, or (L)- and (D)-5 with chiral oligomer complexes (L)-3(50) or (L)-6(100) suggests that the screw sense of the polymer backbone is not controlled kinetically, but rather that the thermodynamically stable screw sense is produced.

Dendrimers with inherently axially chiral units

We have designed and successfully synthesised dendrimers with axially chiral units in the interior structure. Starting from chiral 2,2′-dimethoxy-1,1′-binaphthalene building blocks 2 and 4 and from the four-directional initiator cores 7 and 8 the dendritic homochiral and heterochiral oligomers 9–16 were prepared. Using the [ϕ]D and Δε values of monomers 2 and 4, we calculated [ϕ]D and Δε values for dendrons 11, 13, and dendrimers 9, 10, 15 and 16. Although the observed molar optical rotation [ϕ]D of the dendrimers agrees relatively well with the calculated values, the CD measurements of all the dendrimers in THF and CH2Cl2, except that of heterochiral dendrimer 16 in THF, were significantly different from the calculated values. The intensive hypochromism of the dendrimers (between 37–59% in THF) and the agreement between the calculated and observed Δε values of the dendrons (between 14 and 6% in THF) led to the assumption that the hypochromic effect is caused by intramolecular interactions. From the NMR measurements it was proved that in the homochiral dendrimer 15, the N–H groups of the amides can form intramolecular hydrogen bonds that in CHCl3, with the help of the axially chiral moieties, cause a different conformation of the molecule than in the diastereomeric dendrimer 16.

Cyclocopolymerization of α,ω-Dienes with Carbon Monoxide Catalyzed by (R,S)-BINAPHOS–Pd(II)

Abstract Cyclocopolymerization of 1,4-pentadiene with carbon monoxide gave polyketone 3 in the presence of a Pd(II) catalyst bearing an unsymmetrical bidentate ligand, (R,S)-BINAPHOS {=(R)-2-(diphenylphosphino)-1,1′-binaphthalen-2′yl (S)-1,1′-binaphthalene-2,2′-diyl phsophite}. In the repeating unit of 3, exclusive formation of a cyclopentanone framework rather than cyclohexanone has been revealed by 13C NMR and IR spectroscopies. A single-unit analog 2 was prepared to identify the structure of 3. In the cyclopentanone unit of 3, the two substituents are cis and trans to each other in almost 1 : 1 ratio. The polymer 3 showed different behavior in thermal analysis from that of propene–CO alternating copolymer. 1,5-Hexadiene also afforded the corresponding cyclocopolymer 5. The molar optical rotation of polymer 3 was much lower than that of 5.

Chirality induction in cyclopolymerization. VI. Enantioselective cationic cyclopolymerization of divinyl ethers with chiral 10-camphorsulfonic acid/zinc chloride initiating system

Cyclopolymerization of benzaldehyde divinyl acetal (1) and 1,2-divinyloxybenzene (4) was carried out using (+)- or (−)-camphorsulfonic acid [(+)- or (−)-2]/ZnCl2 initiating system. Polymer 3 obtained from monomer 1 consisted essentially of cyclic repeating units, whereas polymer 5 from 4 possessed a small amount of residual vinyloxy groups. Both polymers 3 and 5 using (+)-2/ZnCl2 showed optical activity with a negative sign of optical rotation. The molar optical rotation values of polymer 3 using ZnCl2 · OEt2 were larger than those using ZnCl2. The CD spectra of the polymer with [Φ] = −30.1° ((−)-3) and (4S,6S)-4,6-dimethyl-2-phenyl-1,3-dioxane showed a negative Cotton effect at 210 nm, whereas the polymer with [Φ] = +24.1° ((+)-3) and (4R,6R)-4,6-dimethyl-2-phenyl-1,3-dioxane had mirror image CD curves with a positive Cotton effect at 210 nm. The absolute configurations of the major chiral cyclic units in (−)- and (+)-3 were the SS- and RR-forms, respectively. © 1997 John Wiley & Sons, Inc.

Chirality induction in cyclopolymerization. VI. Enantioselective cationic cyclopolymerization of divinyl ethers with chiral 10‐camphorsulfonic acid/zinc chloride initiating system

Cyclopolymerization of benzaldehyde divinyl acetal (1) and 1,2-divinyloxybenzene (4) was carried out using (+)- or (−)-camphorsulfonic acid [(+)- or (−)-2]/ZnCl2 initiating system. Polymer 3 obtained from monomer 1 consisted essentially of cyclic repeating units, whereas polymer 5 from 4 possessed a small amount of residual vinyloxy groups. Both polymers 3 and 5 using (+)-2/ZnCl2 showed optical activity with a negative sign of optical rotation. The molar optical rotation values of polymer 3 using ZnCl2 · OEt2 were larger than those using ZnCl2. The CD spectra of the polymer with [Φ] = −30.1° ((−)-3) and (4S,6S)-4,6-dimethyl-2-phenyl-1,3-dioxane showed a negative Cotton effect at 210 nm, whereas the polymer with [Φ] = +24.1° ((+)-3) and (4R,6R)-4,6-dimethyl-2-phenyl-1,3-dioxane had mirror image CD curves with a positive Cotton effect at 210 nm. The absolute configurations of the major chiral cyclic units in (−)- and (+)-3 were the SS- and RR-forms, respectively. © 1997 John Wiley & Sons, Inc.

Synthesis and chiroptical properties of layerblock dendrimers

Abstract

Palladium(II)-Catalyzed Isospecific Alternating Copolymerization of Aliphatic .alpha.-Olefins with Carbon Monoxide and Isospecific Alternating Isomerization Cooligomerization of a 1,2-Disubstituted Olefin with Carbon Monoxide. Synthesis of Novel, Optically Active, Isotactic 1,4- and 1,5-Polyketones

The compound [Pd(Me-DUPHOS)(MeCN){sub 2}](BF{sub 4}){sub 2}, 1 [Me-DUPHOS = 1,2-bis(2,5-dimethylphospholano)-benzene], has been found to be an effective catalyst for the highly enantioselective, alternating copolymerization of aliphatic {alpha}-olefins with carbon monoxide to form optically active, isotactic polymers. The {alpha}-olefin--carbon monoxide copolymers, as synthesized in CH{sub 3}NO{sub 2}/CH{sub 3}OH, had a mixture of 1,4-ketone and spiroketal repeating units in the backbone. The interchange between 1,4-keto and spiroketal units was observed even in the absence of any added metal catalyst. The temperature dependence of the molar optical rotation of the isotactic pure poly(1,4-ketone)s indicated that the chirality of the copolymers was due to the presence of stereogenic tertiary carbons in the polymer backbone rather than due to polymer conformation. The degree of enantioselectivity in the formation of chiral, isotactic propylene-carbon monoxide copolymer was found to be > 90{degree} (as determined by NMR spectroscopy using a chiral NMR shift reagent). The isotactic {alpha}-olefin-carbon monoxide copolymers serve as excellent starting materials for the synthesis of other classes of chiral polymers. 14 refs., 10 figs., 1 tab.

The First Report of Cyclopolymerization of Bis(oxazolines) To Give Optically Active Polymacrocycles

Optically active polymers with high molecular weights have been obtained in high yields by cyclopolymerization of bis(oxazolines). The polymers are soluble in organic solvents, have T g 's of 200 and 278°C, decomposition onset temperature of 400°C and a high mean residue molar optical rotation (Φ 27°C D -1157° (THF, c= 0.9))

Enantioselective cyclopolymerization of 1,5-hexadiene catalyzed by chiral zirconocenes: a novel strategy for the synthesis of optically active polymers with chirality in the main chain

Enantioselective cyclopolymerization represents a novel strategy for the synthesis of optically active main-chain chiral polymers. Cyclopolymerization of 1,5-hexadiene using the optically active catalyst precursor, (R,R)-(EBTHI)ZrBINOL ((R,R)-1) [EBTHI = ethylene-1,2-bis([eta][sup 5]-4,5,6,7-tetrahydro-1-indenyl); BINOL = 1,1[prime]-bi-2-naphtholate], yields optically active poly(methylene-1,3-cyclopentane) (PMCP) with a molar optical rotation of [[Phi]][sup 28][sub 405] +51.0[degrees] (c = 0.80, CHCl[sub 3]). The molar optical rotation for the polymer derived from (R,R)-1 is higher than that of the model compound trans-(1R,3R)-1,3-dimethylcyclopentane and is also temperature dependent, suggesting that the polymer adopts chiral conformations which contribute to the observed optical rotation. The microstructure of the polymer was interpreted by [sup 13]C NMR at tetrad resolution. A statistical model for the microstructure based on an enantiomorphic site control mechanism provided good agreement with the experimental data. On the basis of this model, the enantioface selectivity for the cyclopolymerization of 1,5-hexadiene in the presence of catalysts derived from (R,R)-1 is 91% at 20[degrees]C, indicative of a highly isotactic microstructure. The molar optical rotation of poly(methylene-1,3-cyclopentane) is independent of molecular weight, which provides experimental support for an enantiomorphic site control mechanism. The absolute configuration of PMCP was tentatively assigned on the basis of the sign of the optical rotation of the model compoundmore » trans-(1R,3R)-1,3-dimethylcyclopentane and the known enantioface selectivity of 1 with similar [alpha]-olefins. 46 refs., 12 figs., 5 tabs.« less

Quantification of trace levels of β‐cyclodextrin and substitution patterns in hydroxypropyl‐β‐cyclodextrin using high‐performance liquid chromatography with polarimetric detection

AbstractA high‐performance liquid chromatographic (HPLC) method has been developed for separation and determination of components in hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD). The method involves separation on an amino‐bonded HPLC column using water–acetonitrile as a mobile phase with a polarimetric HPLC detector for quantification. It provides good selectivity and sensitivity and can also be used to compare different sources of HP‐β‐CD and to measure batch to batch variation. The similarity of the values of molar optical rotation for β‐cyclodextrin (β‐CD) and HP‐β‐CD suggests that a polarimetric HPLC detector may be used with a straightforward area normalization method, to quantify the proportion of β‐CD in any HP‐β‐CD sample. Trace amounts of β‐CD in HP‐β‐CD have been measured to a precision of 0.01%. © 1993 Wiley‐Liss, Inc.

Chiral polymers via cyclopolymerization

Cyclopolymerization of nonconjugated dienes provides a route to a number of stereochemically complex poly(methylene-1,3-cycloalkanes). The stereochemistry of these polymers derives from both tacticity and cis/ trans stereochemistry of the carbocyclic rings. A unique feature of isotactic polymers with a predominance of trans rings is that they contain no mirror elements of symmetry and are thus chiral by virtue of their main-chain stereochemistry. The enantioselective cyclopolymerization of 1,5-hexadiene in the presence of optically active precursors such as (−)-( R)-ethylene-bis(tetrahydroindenyl) zirconium ( R)-binaphtholate ([α] 435 = −1431°) and a methylaluminoxane (MAO) co-catalyst yields optically active poly(methylene-1,3-cyclopentane) (PMCP) with a molar optical rotation [Φ] 28 405 of +50.1° ( c = 7.8, CHCl 3). Since the enantioface selectivity of the chiral zirconocene catalyst with propene is known, the absolute stereochemistry of the polymer can be tentatively assigned if an analogous enantioface selectivity with 1,5-hexadiene is assumed. The enantioselective cyclopolymerization of symmetrical dienes requires both a high enantioface selectivity for olefin insertion and a high diastereoselectivity for olefin cyclization in order to obtain a chiral macromolecular architecture.

Purification and Characterization of an Acetoin Dehydrogenase fromLactobacillus KefirSuitable for the Production of (+)-Acetoin

A dehydrogenase catalyzing the NADH-dependent reduction of diacetyl to (+)-acetoin was found in Lactobacillus kefir. The enzyme could be purified by heat treatment, ion exchange chroraatography and gel filtration (130 U/mg). Further purification resulted in two isoenzymes, E1 (1061 U/mg) with a molecular weight of 66 kD and E2 (366 U/mg) of 74 kD. Important biochemical data concerning the application of the enzyme are: pH-optimum at 4.3 (E1,) and 5.0 (E2), temperature optimum at 70d`C, stable at 57d`C for 10 min. Besides diacetyl several other diketones were reduced. For diacetyl, a KM-value of 310 mM for E1 and 67 mM for E2 was measured. The reverse reaction of acetoin oxidation in the presence of NAD could not be observed, whereas D(—)-lactate was oxidized by the enzyme. In exploratory experiments conversions of 200 mM diacetyl in batch reactions with coenzyme regeneration resulted in 170 mM product concentration. The formation of (+)-acetoin was confirmed by determination of its molar optical rotation ...