Experimental study of the radiation mechanism of the chiral action

The first results of the RAMBAS (Radiation Mechanism of Biomolecular Asymmetry) experiment on the study of the radiation mechanism of the effect on chiral molecules as a factor leading to chiral asymmetry formation are presented. It was found that irradiation with an electron flux from a radioactive source of a mixture of simple achiral materials initiates synthesis of the simplest amino acids; in a racemic mixture of complexes of amino acids and metals irradiation leads to asymmetric decomposition and chrial asymmetry formation. The results obtained can be essential for solving the problem of the origin of life and the formation of chiral asymmetry of the biosphere.     

Optical activity in mixed-ligand terbium complexes containing 1,2-Benzenedicarboxylic acid and chiral carboxylic acids

The optical activity of Tb(PHT)(L) complexes has been studied by means of circularly polarized luminescence (CPL) spectroscopy, where PHT=1,2-benzenedicarboxylic acid (phthalic acid) and L=L-mandelic, L-aspartic, and L-malic acids. The CPL spectra were characteristic of multidentate bonding, and close examination of the spectra revealed the nature of the metal-ligand bonding. The results obtained have demonstrated that the optical activity experienced by the Tb(III) ion is primarily determined by the nature of the chiral ligand, and that this chirality can be affected by the achiral ligands also bound in the metal coordination sphere.     

Results of the second stage of the study of radiation mechanism of chiral action (RAMBAS-2 experiment)

The results of the second stage of the RAMBAS (Radiation Mechanism of Biomolecular Asymmetry) experiment on the study of the radiation mechanism of the effect on chiral molecules are presented. The optical activity of samples containing racemic mixtures of amino acid complexes with heavy metals before and after their irradiation with an electron flux from a radioactive source was compared. It was shown that irradiation leads to asymmetric decomposition of amino acid complexes and amino acids themselves and chiral asymmetry formation. These results confirm the conclusions made in the first stage of the RAMBAS experiment and can be essential for solving the problem of the origin of life and the formation of chiral asymmetry of the biosphere.     

Photochirogenesis: photochemical models on the absolute asymmetric formation of amino acids in interstellar space

Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical L-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which interstellar ultraviolet (UV) circularly polarized light (CPL) induces an enantiomeric excess in chiral organic molecules in the interstellar/circumstellar media. This scenario is supported by a) the detection of amino acids in the organic residues of UV-photo-processed interstellar ice analogues, b) the occurrence of L-enantiomer-enriched amino acids in carbonaceous meteorites, and c) the observation of CPL of the same helicity over large distance scales in the massive star-forming region of Orion. These topics are of high importance in topical biophysical research and will be discussed in this review. Further evidence that amino acids and other molecules of prebiotic interest are asymmetrically formed in space comes from studies on the enantioselective photolysis of amino acids by UV-CPL. Also, experiments have been performed on the absolute asymmetric photochemical synthesis of enantiomer-enriched amino acids from mixtures of astrophysically relevant achiral precursor molecules using UV-circularly polarized photons. Both approaches are based on circular dichroic transitions of amino acids that will be highlighted here as well. These results have strong implications on our current understanding of how life's precursor molecules were possibly built and how life selected the left-handed form of proteinogenic amino acids.     

Effect of the medium and the formation of nanostructures on deexcitation of electronic excitation of Eu(III) and Tb(III) chelates

The intensity I _lum and lifetime τ_lum of the luminescence of complexes of Eu(III) and Tb(III) ions with β-diketones and o-phenanthroline in water-ethanol solutions of these ligands have been analyzed as functions of the concentrations of ligand, luminescing lanthanide ions, and added ions causing columinescence and of the solvent deuteration. It is shown that the formation of nanostructures from Ln complexes and their coarsening leads to an increase in τ_lum of Eu(III) and Tb(III) and that this increase is due to the suppression of both photochemical deexcitation of these ions and transfer of their electronic excitation energy to OH vibrations of water molecules. The disappearance of the dependence of I _lum of Eu(III) on deuteration of water-ethanol solutions of n-methoxybenzoyltrifluoracetone + o-phenanthroline caused by adding Gd(III) ions is explained by the shift of the equilibrium of formation of complexes of Ln chelates to neutral hydrophoblic forms corresponding to the formation of nanostructures of these chelates in the solution. The differences in effect of La(III) and Gd(III) ions on I _lum and τ_lum of Eu(III) and Tb(III) complexes are explained. It is shown that the widely discussed effect of columinescence not only results from the energy migration in mixed structures of Eu or Tb complexes and Gd complexes but is also due to a large extent to the decrease in τ_lum of Eu(III) or Tb(III) caused by their incorporation into nanostructures.     

Secondary emission of chiral (mirror symmetric) phases of amino acids

The photoluminescence (PL) spectra of (1) chiral-pure phases and racemate of aromatic amino acid and (2) albumen protein in the solid state are presented. The PL spectra were excited by pulse-periodic ultraviolet radiation with a wavelength of 266 nm at an average power of 10 mW. A significant difference between the PL spectra of mirror symmetric phases of tryptophan and the racemic phase of this amino acid was detected. The developed technique can be used for diagnostics of the chiral state of aromatic amino acids and albumens, which is important for the vital functions of organisms.     

五种氨基酸钆络合物的ESR波谱

迄今未见任何稀土氨基酸络合物的ESR波谱报道,本文在合成Gd³⁺分别与甘氨酸、β-丙氨酸、谷氨酸、天冬氨酸和天冬酰胺五种氨基酸络合物的基础上,测定了不同温度下,水溶液、粉末及分子筛吸附样品的ESR谱,讨论了络合物中晶体场强,对称性及成键特性。     

NMR Studies of Agricultural Compounds. Applications of Achiral and Chiral Lanthanide Shift Reagents to the Herbicide,Fenoxaprop-Ethyl

The 200 MHz H NMR spectra of the herbicide, fenoxaprop-ethyl, 1, have been studied in CDCl₃ solution at ambient temperatures as the racemic ester free base with the added chiral lanthanide shift reagent (LSR), tris [3 - (heptafluoropropylhydroxymethylene) - (+) - camphorato]europium(III), Eu(HFC)₃, 2, with some additional runs using the achiral LSR, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium(III), Eu(FOD)₃, 3, for supplemental spectral simplification. With 2, definite enantiomeric shift differences (ΔΔδ) were observed only for the CH₃CH₂O resonance. Although increased spectral complexity for the CH₂O signal was seen with added 2, this could have resulted from anisochrony of the diastereotopic protons, H_a and H_b, of this methylene group rather than true ΔΔδ, since the achiral 3 led to near-baseline separation between the CH_aH_bO signals. Lanthanide-induced shift (LIS) magnitudes were interpreted as consistent with predominant LSR binding at the ester carbonyl.     

Asymmetric hydrogenation of (<Emphasis Type="Italic">E</Emphasis>)-dimethyl-2-acetamido-2-phenylvinylphosphonate in supercritical carbon dioxide in the presence of metal complex catalysts with phosphite-type ligands

Asymmetric hydrogenation of (E)-dimethyl-2-acetamido-2-phenylvinylphosphonate was performed in CH₂Cl₂ and supercritical carbon dioxide with the participation of Rh and Ir complexes with chiral phosphite-type ligands. Iridium catalysts dissolved in supercritical CO₂ allow high enantioselectivity (up to 98.5% ee) and conversion to be obtained. Rhodium catalysts yield exclusively racemic reaction products.     

Luminescence and circularly polarized luminescence of macrocyclic Eu(III) and Tb(III) complexes embedded in xerogel and sol–gel SiO2 glasses

Luminescence, time-resolved luminescence, circularly polarized luminescence (CPL) and decay profiles of Ln(III)(15-crownether-5) (Ln=Ce, Sm, Eu, Tb) and Tb(III)-(R),(S)-cyclen derivative complexes doped in xerogel and sol–gel silica glasses are measured at temperatures down to 10 K to characterize luminescence properties and the electronic structure in the excited states. Luminescence spectral profiles and calculation of crystal field parameters (B₀⁽²⁾,B₂⁽²⁾) in the ⁵D₀→⁷F_J(J=1,2) transition give evidence of the fact that the pentagonal and planar structure of Eu(III) (15-crownether-5) does hold in xerogel and sol–gel glasses prepared at temperatures below 100°C. As annealing temperatures are increased from 80°C to 750°C, Eu(III) complexes in sol–gel glasses are found to decompose gradually to SiO₂:Eu³⁺. Tb(III)-(R) and (S)-cyclen derivative complexes in xerogel reveal at room temperature and 10 K sharp CPL spectra with luminescence dissymmetry factors g_lum=−0.1 and 0.1, respectively. These complexes doped in sol–gel glasses represent luminescence characteristics of rare earth ions encapsulated in the nano-porous host.     

NMR Studies of Drugs. Applications of Achiral and Chiral Lanthanide Shift Reagents to a 5-Substituted-4-thiazolidinone

The 60 MHz ¹H NMR spectra of racemic 5-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-4-thiazolidinone, 1, have been studied in CDCl₃ solution at 28° with the achiral lanthanide shift reagent (LSR), tris (6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium (III), 2, and the chiral LSRs, tris[3-(heptafluoropropylhydroxymethylene)- (+)-camphoratojeuropium(III), 3, and tris[3-(trifluoromethylhydroxymethylene-(+) -camphorato]europium (III), 4, Significant enantiomeric shift differences were observed in the presence of added 3, for the aryl protons of 1 that should permit direct determination of enantiomeric excess. Relative magnitudes of lanthanide-induced shift for the different nuclei of 1 with the three LSRs are compared and discussed in terms of preferred LSR binding sites. A favored conformation of 1 with respect to rotation about the C(5)-CH₂ bond is suggested.     

NMR Studies of Drugs. Applications of Achiral and Chiral Wthanide Shift Reagents to Bupropion

Abstract

The ¹H NMR spectra of racemic samples of the antidepressant drug, bupropion, 1, have been studied in CDCl₃ solution at 60 and 200 MHz with the achiral lanthanide shift reagent (LSR), tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium (III), 2, and the chiral reagent, tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato]europium(III), 3. Both LSR produced substantial lanthanide induced shifts consistent with ¹H assignments, but the bound complexes of 1 with 2 versus 3 may not be isostructural. With 3, substantial enantiomeric shift differences were observed for the t-butyl, CH ₃CH, NCH, and the aryl H-2 and H-6 signals, which should permit potential direct determination of enantiomeric excess.     

Rise transient dynamics of supercooled sec-butyl chloride — a computer simulation

The role of chiral discrimination in the R enantiomer and racemic mixture of sec butyl chloride is investigated by computer simulation in the glassy condition at 50K. The effect of left or right handedness on the molecular dynamics is clearly measurable at equilibrium in the appropriate frame of reference. The physical (lab. frame) effects of chiral discrimination are emphasized by the application of a strong, external electric field. This produces deeply oscillatory rise transients whose time dependence is clearly different for enantiomer and racemic mixture at the same nominal temperature (50K).     

Photoactive thin films of polycaprolactam doped with europium (III) complex using phenylalanine as ligand

A photoactive complex based on europium(III) using the amino acid phenylalanine as ligand was prepared and characterized. The obtained europium(III)/phenylalanine complex presents an effective energy transfer from ligands to the rare earth center. The observed photoluminescent behavior for europium(III)/phenylalanine complex was similar to the well known europium(III)/ acetyl-β-acetonate hydrate. New photoactive polyamide thin films were prepared using polycaprolactam as host of these complexes. The structural characterizations of the films were studied through Rutherford backscattering (RBS), Fourier transform infrared (FTIR) and Raman spectroscopies. The polyamide films doped with the amino acid and acetyl-β-acetonate rare earth complexes maintain the original photoluminescent behavior, narrow emission bands corresponding to transitions ⁵D₀ → ⁷F_0-4, which indicates that this polymer is an excellent host to these complexes.     

荧光成像及手性特异性生物识别

癌症是威胁人类健康的重大疾病之一,实现早查早治是降低癌症死亡率的重要手段。目前在癌症的众多识别方式中,荧光检测凭借无创伤、检测快和可视化等优点受到了持续关注。文章对荧光探针靶向识别肿瘤的研究新进展进行了综述;对赋予荧光探针靶向性的叶酸(FA)和叶酸受体(FR)介导研究进展进行了介绍和深入分析。叶酸受体是癌细胞表面过量表达的特有物质,利用叶酸和叶酸受体特异性结合的特点,叶酸对荧光探针分子进行修饰可赋予荧光探针识别癌细胞的靶向性。叶酸受体有4种亚型（FRα,FRβ,FRγ和FRδ）,前两者FRα和FRβ因分别在癌细胞和炎症巨噬细胞表面过量表达而备受关注,FRα和FRβ约有70%的同源性,两者均具有能与叶酸结合的特性,造成了荧光探针分子在生物识别过程中难以区分癌细胞和炎症巨噬细胞的弱势;针对叶酸修饰荧光探针难以区分叶酸受体亚型造成癌细胞和炎症巨噬细胞混淆问题的结构性缺陷,分析了两种叶酸受体亚型结构具有的手性区别特征：FRα和FRβ主要区别位于三个末端未翻译区,有三种不同手性特征的氨基酸形成一个用来包结叶酸分子的三角空腔,分别固定在氨基酸堆积体节点上的三种氨基酸形成了不同手性特性的区域性“手性空间”。FRα和FRβ本身的结构对不同的配体表现出立体差异性。讨论了基于叶酸受体亚型存在的“手性空间”差异性,构建叶酸受体亚型荧光及手性识别探针的可能性;有望借助光谱成像,通过手性荧光探针分子对氨基酸的识别区分叶酸受体两种亚型,实现可视化区分肿瘤细胞和炎症巨噬细胞的识别难题,进而提高癌细胞识别的准确性;文章介绍了手性荧光探针识别氨基酸原理及结构优化设计进展;近年来手性量子点对氨基酸不同对映体的研究备受关注。对无机手性量子点手性产生的本质特征和氨基酸对映体的识别特性进行了总结分析。最后对荧光探针及手性识别领域进行了展望。     

Chemical Sensors and Microinstrumentation

The ¹H NMR spectra of racemic (erythro) methoxamine free base, 1, 1-(1-aminoethyl)-2,5-dimethoxybenzenemethanol, have been studied at or near ambient temperatures in CDCl₃ or CD₃CN with the added chiral lanthanide shift reagent (LSR), tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato] europium (III), 2. Spectrometers operating at 60, 200 and 300 MHz were employed; some COSY spectra were acquired to support assignments. Enantiomeric shift differences (Δ Δ Δ) were observed for several nuclei of 1 with added 2 in either CDCl₃ or CD₃CN and an “anomalous” (upfield) shift was seen for the NCH signal. A high degree of signal broadening was seen for runs with either solvent, and surprising similarity was found for the slopes in plots of chemical shift versus [2]/[1] molar ratios for the different nuclei of 1 whether the hydrogen bond donor solvent (CDCl₃) or the hydrogen bond acceptor solvent (CD₃CN) was used. Together with the anomalous shift noted above, these results are interpreted as consistent with strong bidentate chelation of 2 by 1.     

A mechanism of energy transfer in binuclear fluoride lanthanide complexes in aqueous electrolyte solutions

The energy transfer between different pairs of lanthanide ions bonded by fluoride bridges into labile binuclear complexes is studied in aqueous solution at different ratios between the concentrations of lanthanide ions and fluoride anions ([Ln]: [F]). It is shown that, if the concentrations [Ln] and [F] are of the same order of magnitude, the energy transfer rate constant k _t does not depend on the choice of the pairs of interacting ions and is determined by the association rate constant of Ln(III) ions into binuclear complexes. If the concentration of the lanthanide ions is much greater than that of the fluoride ions, k _t varies proportionally to the monomolecular energy transfer rate constants in the binuclear complexes. It is assumed that, in the first case, Ln(III) ions are bonded through two fluoride anions, whereas, in the second case, they are bonded through one anion. The analysis of the variations in k _t in the latter systems shows that the exchange-resonance mechanism should be taken into account for the explanation of the experimental data. The effects that the introduction into the solution of different contents of salts of strong acids—AlCl₃, MgCl₂, Ca(NO₃)₂, CsCl, RbBr, and NaCl—have on k _t and on the regularities of the energy transfer between Ln(III) ions bonded into binuclear fluoride complexes are studied. The effects of these electrolytes on the luminescence intensity and spectrum of Eu(III) ions and on the values of k _t for the energy transfer between Ln(III) ions bonded into binuclear complexes are analyzed. It is shown that, at some concentration ratio [Ln]: [F], for all electrolytes studied except AlCl₃, the value of k _t increases despite the fact that the concentration of mononuclear complexes of Ln(III) ions with fluorine decreases in the presence of these electrolytes. It is ascertained that the anions of strong acids in the outer sphere of lanthanide ions increase the association constant of Ln(III) ions in binuclear fluoride complexes.     

Effect of chirality on domain wall dynamics in molecular ferrimagnet [Mn<Superscript>II</Superscript>(HL-pn)(H<Subscript>2</Subscript>O)][Mn<Superscript>III</Superscript>(CN)<Subscript>6</Subscript>]·2H<Subscript>2</Subscript>O

In this paper we distinguish the contributions of switching, slide, creep and Debye relaxation modes of the domain wall dynamics to the low-frequency magnetic properties of chiral and racemic [Mn^II(HL-pn)(H₂O)][Mn^III(CN)₆]·2H₂O molecular ferrimagnets. We demonstrate that crystal and spin chirality affects the characteristic transition temperatures between different modes. In chiral crystals, transitions to the creep and Debye relaxation modes were observed at T = 7 K and 5 K, whereas in racemic crystals the same transitions occurred at higher temperatures T = 13 K and 9 K, respectively. Difference of the Peierls relief in chiral and racemic crystals is a possible reason of the chirality effect on the domain walls dynamics.     

NMR Studies of Agricultural Products. Applications of Achiral and Chiral Lanthanide Shift Reagents to the Fungicide,Triadimefon.

Abstract

The 60 MHz ¹H NMR spectra of the systemic agricultural fungicide, triadimefon, 1, have been studied in CDCl₃ at 28±1° (as the racemic free base) with the added achiral lanthanide shift reagent (LSR), tris(6, 6, 7, 7, 8, 8, 8-heptafluoro-2, 2-dimethyl-3, 5-octanedionato) europium(III), Eu(FOD)₃, 2, for spectral simplification, and with the chiral LSR, tris [3-(heptafluoropropylhydroxymethylene)-(+) -camphorato)europium(III), Eu(HFC)₃, 3, to induce enantiomeric shift differences (ΔΔδ) for several nuclei. Significant ΔΔδ values were seen for the two protons of the heterocyclic ring, the OCH methine, and aryl H-2′, 6′ of the chlorophenoxy ring. For each of these nuclei exhibiting ΔΔδ with added 3, the ΔΔδ magnitudes reached maximum values with 3: 1 molar ratios ca. 0. 18–0. 29, and decreased with higher levels of 3. To confirm analytical utility of 3 for % e. e. determinations of 1, a nonracemic (“spiked”) sample of racemic 1, with added R-(?) triadimefon, was examined with 3. At low 3: 1 ratios, both triazole H-3 and H-5, as well as the OCH and aryl H-2′, 6′ protons of (?)-1 showed a downfield sense of magnetic nonequivalence with (+) -3. With 3: 1 ratios ca. 0. 8, triazole proton H-3 reversed its sense of magnetic noneguivalence. The H-3 and H-5 signals were useful for % e. e determinations at this higher 3: 1 ratio.     

Influence of chirality on the electron spin resonance in molecular magnets [MnII(H L )(H2O)][MnIII(CN)6] · 2H2O with chiral ligands L

Chiral and racemic molecular ferrimagnets [Mn^II(HL)(H₂O)][Mn^III(CN)₆] · 2H₂O, where L = S-or R-1,2-diaminopropane for chiral samples (S-pn, R-pn) and L = rac-pn for racemic samples, are investigated by the electron spin resonance technique. It is revealed that the electron spin resonance spectra of the chiral and racemic samples differ from each other at temperatures below the Curie temperature T _C = 21 K. The maximum in the temperature dependence of the integrated magnetic susceptibility χ(T) calculated by the double integration of the line centered at a negative field of −250 Oe for the racemic samples is broadened as compared to the maxima in the corresponding dependences for the enantiomers of the chiral samples with “right” (R) and “left” (S) symmetry. The new compounds under investigation differ from the previously synthesized crystals by the strong spin-orbit interaction between Mn³⁺ ions, which leads to a dependence of their magnetic properties on the chirality of the structure. Original Russian Text ? R.B. Morgunov, F.B. Mushenok, M.V. Kirman, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 7, pp. 1252–1256.