Conditions for chiral asymmetry generation in the preparation of the chiral octahedral cobalt complex

We have reported that the random chiral asymmetry generation, which is a spontaneous preferential generation of one enantiomer, was observed in the synthesis of a chiral octahedral cobalt complex, cis-[CoBr(NH(3))(en)(2)]Br(2). In this article, we review our studies to explain in this system the autocatalytic growth of small enantiomeric excess that arises due to statistical fluctuations. One important experimental finding was that the rate of chiral autocatalysis increased with increasing the degree of supersaturation. Furthermore, our numerical simulation indicates that even small inhomogeneities in the reaction system may play a significant role because their effect is amplified by the autocatalytic reaction under appropriate conditions. In a small volume, fluctuations in concentration can grow if the autocatalytic growth overcomes the diffusional loss of the excess concentration from this volume. This may makes the enantiomeric excess of the chiral complex randomly fluctuate from run to run.     

Generation of molecular chiral asymmetry through stirred crystallization

In our earlier work we established that stirred crystallization of achiral compounds that crystallize in enantiomeric forms result in spontaneous chiral symmetry breaking. The asymmetry thus spontaneously generated is confined to the solid state. In this article, we present a case in which the crystal enantiomeric excess (CEE) can be converted to molecular enantiomeric excess (EE) through a solid state reaction which relates the enantiomeric form of the crystal to the enantiomeric form of the product. Such a process not only provides a means of detecting the CEE generated in stirred crystallization but it is also a means through which chiral asymmetry generated spontaneously is "propagated" to generate chiral compounds with enantiomeric excess.     

Studies in chiral symmetry breaking crystallization I: The effects of stirring and evaporation rates

Chiral symmetry breaking can be realized in stirred crystallization of Na-ClO₃. We present experimental and theoretical studies of the random distribution of crystal enantiomeric excess (cee) for various stirring and solvent evaporation rates. For a fixed solvent evaporation rate, as the stirring RPM is increased, the probability distribution of cee initially broadens and subsequently develops a sharp peak close to cee = 1. On further increase of stirring rate, the probability distribution once again broadens. This broad probability distribution becomes narrow, with a sharp peak near cee = 1, if the solvent evaporation rate is decreased. Thus we show some ways in which the probability distribution of cee can be controlled in stirred crystallization. In particular, our study shows that the stirring rate and the solvent evaporation rate can be adjusted to maximize crystal enantiomeric excess. © 1995 Wiley-Liss, Inc.     

Kinetics of chiral resolution in stirred crystallization of D/L‐glutamic acid

Stirred crystallization of racemic (D/L)‐glutamic acid (Glu) in the presence of small amounts of L‐ or D‐lysine (Lys) was studied for the effect of transient chiral resolution by monitoring the time evolution of optical rotation and the concentration of the solution. The presence of a small amount of L‐ or D‐Lys retards the crystallization rate of the corresponding enantiomer of Glu in a chirally selective manner, giving rise to transient optical resolution of racemic Glu during crystallization. The optical rotation of the Glu solution was found to increase from zero to a value corresponding to an enantiomeric excess (ee) of 22–35% and subsequently decreases to zero over a period of many hours. During this process, the ee of the crystallized Gu is nearly 100% during the first 35 min and then it decreases slowly to zero. Our results indicate that the time at which the ee of the solution reaches its maximum and the maximum value of the ee show a nonlinear dependence on the initial mole fraction of the chiral impurity. The effect of the impurity is highly chirally selective, indicating “molecular recognition.” Chirality 11:343–348, 1999. © 1999 Wiley‐Liss, Inc.     

Probability distributions of enantiomeric excess in unstirred and stirred crystallization of 1,1'-binaphthyl melt.

Crystallization of 1, l'-binaphthyl from its melt can generate optical activity spontaneously. Since crystallization is a stochastic process, the enantiomeric excess (ee) generated in each crystallization varies randomly. We investigated the qualitative features of probability distribution of the ee for crystallization at two temperatures, 150 degrees C and 152 degrees C, at which conglomerate crystallization occurs. No clear transparent crystals were produced at either temperature, indicating that the solid states formed in the melt were polycrystalline. The ee randomly fluctuated from run to run, with an average of 26.9% and 2.7% when the crystallization was carried out at 152 degrees C, and 150 degrees C, respectively. The spread of the probability distribution is also substantially different. We also studied the probability distribution of ee in stirred crystallization at different stirring RPM. The results show probability distribution's broadening and evolution to a bimodality with increasing stirring RPM--a typical behavior in symmetry-breaking transitions. These results shed light on the nature of enantioselectivity in secondary nucleation and crystal growth.     

Inhibition of mugineic acid-ferric complex uptake in barley by copper, zinc and cobalt

The interfering effects of copper, zinc, and cobalt on the uptake of mugineic acid-ferric complex were studied in barley ( Hordeum vulgare , cv. Minorimugi) grown in nutrient solution. Short-term uptake experiments of 3 h were performed utilizing both ionic and mugineic acid-complex forms of each metal at two different concentrations. Copper was most effective in decreasing iron uptake when added in an ionic form at either concentration. The inhibition order at higher concentrations followed Cu(II) > Zn(II) ≥ Co(II), Co(III), which is consistent with the stability constants of these metal complexes with mugineic acid. The displacement of iron from its mugineic acid complex by these metals is suggested as a probable explanation for the decreased iron uptake. The inhibitory effect of metal complexes with mugineic acid on iron uptake was only found in cases with higher concentrations of Cu(II) and Zn(II) complexes. Deformation of the specific iron transport system in the plasma membrane due to their adsorption may be responsible for this effect.     

手性源、手性池和手性农药中间体的开发研究

介绍手性源、手性池和手性分子化合物的基本概念;由手性池化合物制备手性衍生物;比较了手性化合物生物加工与化学加工过程的优、缺点,寻求高效、经济和最合理的综合工艺流程。     

Advances in asymmetric oxidative kinetic resolution of racemic secondary alcohols catalyzed by chiral Mn(III) salen complexes

Enantiomerically pure secondary alcohols are essential compounds in organic synthesis and are used as chiral auxiliaries and synthetic intermediates in the pharmaceutical, agrochemical, and fine chemical industries. One of the attractive and practical approaches to achieving optically pure secondary alcohols is oxidative kinetic resolution of racemic secondary alcohols using chiral Mn(III) salen complexes. In the last decade, several chiral Mn(III) salen complexes have been reported with excellent enantioselectivity and activity in the homogeneous and heterogeneous catalysis of the oxidative kinetic resolution of racemic secondary alcohols. This review article is an overview of the literature on the recent development of chiral Mn(III) salen complexes for oxidative kinetic resolution of racemic secondary alcohols. The catalytic activity of monomeric, dimeric, macrocyclic, polymeric, and silica/resin supported chiral Mn(III) salen complexes is discussed in detail.     

Role of latent heat in chiral symmetry breaking transition in the crystallization of 1,1'-binaphthyl

The influence of latent heat dissipated by the crystallization of 1,1'-binaphthyl in its supercooled molten state on the chiral symmetry breaking transition was investigated. Temperature change in the crystallization system was monitored by infrared thermocamera. Temperature rise due to the dissipation of latent heat in the growing front of polycrystalline aggregate was about 2 degrees C in an unstirred crystallization system. The melting point of racemic mixture and racemic compound of 1,1'-binaphthyl is 145 degrees C and 158 degrees C, respectively. The latent heat generated by the crystallization could thus change the crystallization behavior when the initial temperature of the melt was slightly lower than 145 degrees C. The temperature change in both unstirred and stirred crystallization systems was monitored. In the stirred crystallization system, even in the case when the initial temperature of the melt was about 2 degrees C lower than 145 degrees C, the temperature rose by about 4 degrees C immediately after the onset of crystallization. This indicates that the role of stirring as the critical parameter for the chiral symmetry breaking transition is not only to clone the chiral crystals but also to enhance the dissipation of latent heat due to secondary nucleation.     

Mechanism of chiral recognition in the enantioseparation of 2-aryloxypropionic acids on new brush-type chiral stationary phases

New brush-type chiral stationary phases (CSP I-IV) comprising N-3,5,6-trichloro-2,4-dicyanophenyl-L-alpha-amino acids (1-4) were prepared by binding of chiral selectors 1-4 to gamma-aminopropyl silica gel. To check the role of excess free aminopropyl groups, CSP V was prepared by binding N-3,5,6-trichloro-2,4-dicyanophenyl-L-alanyl-(3-triethoxysilyl)propylamide to unmodified silica gel. The best separation of racemic 2-aryloxypropionic acids (TR-1-13) was obtained with CSP I; the -(-)-S enantiomer were regularly eluted first, as determined by a CD detector. The mechanism of chiral recognition implies a synergistic interaction of carboxylic acid analyte with the chiral selector and achiral free gamma-aminopropyl units on silica. In fact, CSP V, which is lacking an achiral aminopropyl spacer, shows a lower separation ability for 2-aryloxypropionic acids, but a similar enantioselective discrimination of esters TR-19-20, in comparison with CSP I. CSP I-IV retain unaltered separation ability after a few months of continuous work using a large number of various mobile phases.     

Directional asymmetry in the forelimb of Macaca mulatta

Asymmetry was investigated in the forelimbs of 150 rhesus monkey (Macaca mulatta) skeletons using measurements of right and left humerii, radii, ulnae, second metacarpals, and femora. Seven of the ten forelimb dimensions were larger on the right than on the left side. Paired t-tests revealed that the mean of the right side was significantly larger than that for the left for two measurements of the ulna and two of the humerus. No measurement was significantly larger on the left than on the right side. These results indicate a small but significant asymmetry in the forelimb bones of rhesus monkeys and, as is the case for humans, the direction of asymmetry favors the right side. Our findings are consistent with an interpretation of hypertrophy of certain muscles and opens the question of whether rhesus monkeys preferentially use their right forelimbs for manipulative tasks that require manual dexterity, as is the case for humans. These forelimb skeletal asymmetries are discussed in light of the recent literature on cortical asymmetry and handedness in nonhuman primates.     

Discrimination of chiral guests by chiral channels: variable temperature studies by SXRD and solid state 13C NMR of the deoxycholic acid complexes of camphorquinone and endo-3-bromocamphor

3alpha,12alpha-dihydroxy-5beta-cholan-24-oic acid (deoxycholic acid DCA) is able to discriminate between the R- and S-enantiomers of camphorquinone and endo-(+)-3-bromocamphor and select only the S-enantiomers from a racemic mixture. DCA forms novel well ordered 1:1 adducts with (1S)-(+)-camphorquinone and (1S)-endo-(-)-3-bromocamphor, both of which have been characterized by single crystal X-ray diffraction (SXRD). When DCA is cocrystallized with (RS)-camphorquinone and (RS)-endo-3-bromocamphor, 1:1 adducts of the S-enantiomers are produced together with crystals of the free racemic guest. In contrast, in the absence of (1S)-(+)-camphorquinone, DCA forms a 2:1 adduct with (1R)-(-)-camphorquinone. In this 2:1 adduct the guest is disordered at ambient temperature and undergoes a phase change in the region 160-130 K similar to that observed for the ferrocene adduct, but with only partial ordering of the guest. The SXRD structure of the low temperature form and the variable temperature (13)C CP/MAS NMR are reported. Cocrystallizing DCA with (1R)-endo-(+)-3-bromocamphor gives the free guest and a glassy solid.     

Demonstration of different complexation modes between cobalt and 5' AMP, by direct NMR observation of the low-temperature complex

We report the first direct NMR observation of transition metal-nucleotide complexes. The phosphorus and proton spectra of a cobalt-5' AMP complex were observed in water, pH 7, -- 10 degrees C. This complex is different from the high temperature species : for instance its 31P chemical shift is -- 50 ppm, whereas the published value obtained indirectly for the high temperature form corresponds to ca. -- 1200 ppm. The -- 50 ppm complex is present in significant proportion at 20 degrees C and possibly at higher temperatures. Multiple complexation modes are also observed for Co-ATP.     

Synthesis, characterization, cytotoxic activity and DNA binding properties of the novel dinuclear cobalt(III) complex with the condensation product of 2-acetylpyridine and malonic acid dihydrazide

A novel dinuclear cobalt(III) complex with the condensation product of 2-acetylpyridine and malonic acid dihydrazide, N′,N′²-bis[(1E)-1-(2-pyridyl)ethylidene]propanedihydrazide was synthesized and characterized by elemental analysis, spectroscopy (NMR and infrared), and X-ray crystal analysis. The complex showed a moderate activity towards Artemia salina. The highest cytotoxic potential of the complex was observed on the epithelial breast cancer (MDA-361) cell line. The investigated complex induced apoptosis, the early apoptotic cells comprising 28.18%, compared to 5.64% of control cells in the same phase. The interaction of the complex with calf thymus DNA (CT-DNA) was monitored by blue shift and hyperchromism in the UV-vis spectra. The observed intrinsic binding constant (K_b = 4.2 × 10⁵ M^− 1) together with structural analysis of the complex indicate the groove binding.     

Mechanism of negative membrane curvature generation by I-BAR domains

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Measurement of circular birefringence and circular dichroism of the single crystals of lambda-(+)589- and delta-(-)589-tris(ethylenediamine)cobalt(III) triiodide monohydrate by the extended HAUP method

We have achieved measuring four optical parameters simultaneously, namely, linear birefringence (LB), circular birefringence (CB), linear dichroism (LD), and circular dichroism (CD), of single crystals of Lambda-(+)(589)- and Delta-(-)(589)-tris(ethylenediamine) cobalt(III) triiodide monohydrate (1) along the <001> plane at the fixed wavelength (514.5 nm). Such measurements are possible only when the High Accuracy Universal Polarimeter (HAUP) is employed; it is called the extended HAUP method. Our experimental results showed that both LB and LD of the Lambda-(+)(589)-(1) crystal have the same magnitude as those of the Delta-(-)(589)-(1) crystal. It was also revealed for the first time that the CB data of crystals of Lambda-(+)(589)-(1) and Delta-(-)(589)-(1) are almost of the same magnitude, but are of opposite sign, reflecting their opposite absolute configurations. On the other hand, although the CD data obtained for Lambda-(+)(589)-(1) is almost three times larger than that for Delta-(-)(589)-(1,) these CD data are also opposite in sign, as expected from the opposite chirality of crystals. .     

Characterization of dioxygenated cobalt(II)-carnosine complexes by Raman and IR spectroscopy

Raman and IR studies are carried out on carnosine (beta-alanyl-L-histidine, Carnos) and its complexes with cobalt(II) at different metal/ligand ratios and basic pH. Binuclear complexes that bind molecular oxygen are formed and information regarding the O-O bridge is obtained from the Raman spectra. When the Co(II)/Carnos ratio is 相似文献   

Absorption, fluorescence, and cd spectroscopic study of chiral recognition by a binaphthyl-derived chromogenic calixcrown host

The (R)- and (S)-enantiomers of a binaphthyl-appended calix[4]crown-6 ether with two 2,4-dinitrophenylazo chromophore units ((R)-1 and (S)-1) as chiral hosts were tested in their reactions with the enantiomers of alpha-methylbenzylamine ((R)-MBA, (S)-MBA)) and phenylglycinol ((R)-PGL, (S)-PGL) as chiral guests. The visible absorption spectra indicate a two-step process: the first is a nonenantioselective proton transfer from the host to the guest, which is followed by the enantioselective real complexation. In the visible range of the CD spectra a positive/negative band belongs to the absorption of pure (R)-1/(S)-1, and a negative/positive exciton couplet to the absorption of (R)-1-(S)-MBA/(S)-1-(R)-MBA complexes. The latter phenomenon suggests that the complexation of amines is accompanied by a chiral arrangement of the two chromophore units in the hosts. The UV fluorescence of (R)-1/(S)-1 arising from the binaphthyl moiety is quenched by K+ ions, but not by the amine guests, showing that the interaction between the binaphthyl group and the complexed amines is weak.     

Visualization of the retino-hypothalamic projection in the rat by cobalt precipitation

Summary The technique of cobalt sulfide precipitation combined with Timm's sulfide-silver method for intensification of heavy metals was used to delineate the retino-hypothalamic projection of the rat. Freshly isolated rat brains were dissected and a solution of cobaltous chloride was applied to one of the cut optic nerves. Sixteen hours later, after cobalt ions had passed into the brain along the entire length of the optic fibers, the preparation was treated with ammonium sulfide to precipitate the cobalt as cobalt sulfide. In thick light microscopic sections, cobalt-filled axons were visualized as black fibers against a light gold background. Such fibers were observed to leave the posterior medial portion of the optic chiasm and, after arching dorsally, to project into the posterior fifth of the suprachiasmatic nucleus (SCN), as well as into the rostral part of the arcuate nucleus. Neither bifurcation of these axons nor looping of the axons back to the chiasm was seen. Most fibers projected to the SCN contralateral to the filled nerve, but the projection represented less than 0.1 % of the total number of fibers in one optic nerve. These observations are considered to be graphic evidence of a retino-hypothalamic projection. The interpretation of the cobalt method is discussed, as are the functions of the connections that have been observed.This work was supported by the Nuffield FoundationWe are grateful to Mr. Clifford Jeal of the Department of Pathology for excellent advice on photomicrography     

Interpopulation variation in fluctuating asymmetry of the palmar A-B ridge-count

Fluctuating asymmetry was measured by the Pearson correlation coefficient between a-b ridge-counts of the right and left hands. Such data were available for 38 samples, which were grouped by major geographical regions. Significant heterogeneity exists within some of the geographical groups but the between geographical group component is highly significant in both sexes. Our results show that a sizable fraction of variation in fluctuating asymmetry is related to geographical race. There is no evidence that it follows environmental or ecological lines. The variation between geographical races suggests that there is a genetic component in the magnitude of fluctuating asymmetry.