Molecular Chirality in Meteorites and Interstellar Ices,and the Chirality Experiment on Board the ESA Cometary Rosetta Mission

Life, as it is known to us, uses exclusively L ‐amino acid and D ‐sugar enantiomers for the molecular architecture of proteins and nucleic acids. This Minireview explores current models of the original symmetry‐breaking influence that led to the exogenic delivery to Earth of prebiotic molecules with a slight enantiomeric excess. We provide a short overview of enantiomeric enhancements detected in bodies of extraterrestrial origin, such as meteorites, and interstellar ices simulated in the laboratory. Data are interpreted from different points of view, namely, photochirogenesis, parity violation in the weak nuclear interaction, and enantioenrichment through phase transitions. Photochemically induced enantiomeric imbalances are discussed more specifically in the topical context of the “chirality module” on board the cometary Rosetta spacecraft of the ESA. This device will perform the first enantioselective in situ analyses of samples taken from a cometary nucleus.     

Molecular scaffold for the construction of three-armed and cage-like receptors

An efficient procedure was developed for the synthesis of the C3-symmetric molecular scaffold 2. The latter can easily be converted by a single step into either the three-armed receptors 11-16 or the cage-like receptor 17. X-ray structures were obtained for 2, 11, and 16, which are discussed in regard to their aptitude as receptor platforms. The interaction of the three-armed receptors 12-16 and the cage-like receptor 17 with phloroglucinol was investigated. In accordance with the conclusions obtained from molecular modeling and X-ray crystallographic studies on the host-guest complexes, the three-armed bipyridine receptor 16 exhibits, due to its induced fit, a larger association constant toward phloroglucinol than the cage 17. This new receptor system shows all of the positive features characteristic of 2,4,6-trialkylbenzene receptor systems, such as conformational control by steric gearing, ready availability, and versatility in derivatization. These attributes, combined with the advantageous size of the components, allows this system to be readily tailored to provide receptors for larger, biologically important molecules.     

Strong Positive Allosterism which Appears in Molecular Recognition with Cerium(IV) Double Decker Porphyrins: Correlation between the Number of Binding Sites and Hill Coefficients

Abstract

Cerium(IV) double decker porphyrins bearing one-to-four pairs of 4-pyridyl groups (3a, 3a′, 3bp, 3bd, 3c, and 3d) were synthesized from tetraarylporphyrins bearing mono-, bis-, tris-, and tetrakis(4-pyridyl) groups. In 3b bearing two pairs of 4-pyridyl groups, there exist two isomers in which the 4-pyridyl groups are either proximal or distal (3bp and 3bd, respectively). In a mixed solvent of dichloromethane: ethyl acetate (30:1 v/v), 3a′ bearing one pair of 4-pyridyl groups and three pairs of phenyl groups did not interact with any dicarboxylic acids whereas 3d bearing four pairs of 4-pyridyl groups interacted only with dicarboxylic acid guests with a dimethylene spacer [e.g., BOC-L-aspartic acid (L-4) and (1R,2R)-cyclohexane-1,2-dicarboxylic acid ((1R,2R)-5)]. Interestingly, the complexation process monitored by CD spectroscopy showed a positive homotropic allosterism which satisfied the Hill equation giving constants K = 2.63 × 1011M-4 and n = 3.9 for L-4 and K = 2.75 × 109 M-4 and n = 4.0 for (1R,2R)-5. The continuous variation plots (Job plots) also supported the formation of the 1:4 3d/dicarboxylic acid guest complexes. The results consistently indicate that four pairs of 4-pyridyl groups in 3d allosterically bind these guests. In 3d, the two porphyrin rings can still rotate, but once the rotation is suppressed by the first guest binding, the subsequent binding of the second, third and fourth guests can occur cooperatively. This is the origin of the present positive homotoropic allosterism. A similar positive homotropic allosterism was also observed for 3bp and 3bd with n = 1.5 and 1.7, respectively and 3c with n = 3.0. The X-ray crystallographic study of the 3d·[(1R,2R)-5]4 complex showed that the two porphyrin planes are warped outward to relax the electrostatic repulsion and chirally twisted. The two carboxylic acid groups form intermolecular hydrogen bonds (but not intramolecular bridge-type hydrogen bonds) with the pyridyl groups because of the close packing effect of rigid host 3d and rigid guest (1R,2R)-5. In conclusion, this is a rare example of positive homotropic allosterism in an artificial system which is frequently seen in nature where the biological events must be efficiently regulated in response to signals.     

Assessing the Accuracy of SAPT(DFT) Interaction Energies by Comparison with Experimentally Derived Noble Gas Potentials and Molecular Crystal Lattice Energies

The density functional version of symmetry‐adapted perturbation theory, SAPT(DFT), is a computationally efficient method for calculating intermolecular interaction energies. We evaluate its accuracy by comparison with experimentally determined noble gas interaction potentials and sublimation enthalpies, most of which have not been previously calculated using this method. In order to compare the results with wavefunction methods, we also calculate these quantities using MP2 and, for noble gas dimers, using CCSD(T). For the crystal lattice energy calculations, we include corrections to the dispersion, electrostatic, and induction energies that account for the finite interaction distance cutoff and higher‐order induction contributions. Overall, the energy values extrapolated to the complete basis set limit show that SAPT(DFT) achieves significantly better agreement with experiment than MP2.     

C_（60）分子间相互作用势及其晶体压缩系数的计算

根据Ｃ（６０）晶体升华焓的实验值求得了Ｃ（６０）分子间相互作用势的解析表达式。用该表达式计算了Ｃ（６０）分别为面心立方和六方晶格时晶体的结合能，讨论了不同晶格的稳定性问题，解释了Ｃ（６０）晶体一般是面心立方的原因。本文还根据Ｃ（６０）分子间相互作用势计算了Ｃ（６０）晶体的压缩系数，并与文献的实验值进行了比较，所得结果与实验值相符合。     

Chirality,twist and structures of micellar lyotropic cholesteric liquid crystals in comparison to the properties of chiralic thermotropic phases

Phase chirality in disk-like lyotropic cholesteric phases (Ch(D)) was investigated, which was induced by addition of center and axial chiral dopants to achiral lyotropic nematic host phases (N(D)). In a lyotropic nematic matrix of the disk-like N(D) phase in the ternary system hexadecyldimethylethyl ammonium bromide (C16Me2EABr)/water/n-decanol, a disk-like lyotropic cholesteric phase Ch(D) was induced by addition of the axial optically active compound R(-)-1,1'-binaphthalene-2,2'-diyl-hydrogen-phosphate (BDP). The helical twisting power (HTP) of the BDP is generally lower than the HTP value of inducing substances with center chirality as cholesterol, prednisolone and taurocholic acid. At constant composition of the N(D) phase, the helix lengths were determined in dependence on the BDP and steroid concentration by means of evaluation of the 'spaghetti-like' texture using polarizing microscopy. The reciprocal helix lengths are changing linearly with rising BDP concentration. The properties of the Ch(D) phase (textures, helix lengths, structural parameters of the micelles) induced by the chiral compounds and changed by the composition of host phases can give information to the mechanism of chirality transfer from the molecular level to that of the micellar aggregates and finally, to the liquid crystalline superstructure. Furthermore, the matrix influence of the N(D) phase on the helix formation was examined at constant BDP and steroid concentration. The structure in the Ch(D) phase was described in terms of micelle parameters. Finally, the inducing properties of a center chiral optically active compound such as cholesterol, prednisolone and taurocholic acid were compared with those of the axial chiral compound BDP. Last but not least, the situation of the theoretical and structural background for helix formation in liquid crystals, e.g. the explanation of chiralic transfer between micelles is analyzed and discussed. Two main conditions are necessary to build up the helix in the Ch(D) phase: the formation of H-bridges; and the existence of a specific chiralic interaction energy between neighboring micelles in the cholesteric superstructure.     

原子量基准的设定及其教育价值

从以氢为基准到以氧为基准,再到以碳为基准,原子量基准的设定与化学学科的发展紧密相关.运用原子量基准的设定史实,可以帮助学生解决相关的困惑,学习其中蕴含的思想方法和科学态度,认识科学的本质,充分发挥史实的教育价值.     

Molecular Mechanics Modeling of the Interactions between the Active Domain of CAP18106–137 and Lipid A

In this work, a computer search with molecular mechanics calculations is applied to determine the possible low-energy configurations of two adjacent molecules, CAP18_106–137 and lipid A. This computer search is performed by systematically searching the five degrees of freedom that define the relative orientations of the two adjacent molecules. Hydrophilic and hydrophobic units are separated into several small domains along the CAP18_106–137 molecule so that it can interact with the lipid A either through the Coulombic interactions with the diphosphoryl head group or through the hydrophobic interactions with the fatty acyl chains. The intermolecular interactions are calculated through the van der Waals and Coulombic interactions. The Coulombic interactions are calculated by using a dielectric constant either with a value of unity ϵ = 1 or with a distance-dependent dielectric function ϵ(r) = r_ij. Based on the 400 lowest searched configurations, the intermolecular interactions calculated with ϵ = 1 are found to be about sevenfold lower than those calculated with ϵ(r) = r_ij. Based on the inspection of the sixteen snapshots of molecular associations, the hydrophobic interactions calculated with ϵ(r) = r_ij are more favorable than those calculated with ϵ = 1. The high population of the lipid A binding to the CAP 18_106–137 molecule is located within the first 19 residues near the N-terminus of the peptide, as calculated either with e = 1 or with ϵ(r) = r_ij, by observing the diphosphoryl groups of the lipid A. The orientations of the lipid A with respect to the CAP18_106–137 molecule complete an angle of 260°, which appose to the positively charged residues in the N-terminal half by using the helical wheel projection of the peptide.     

Molecular inclusion in functionalized macrocycles part 10*: Crystal and molecular structure of ap-tert-butylcalix[6]arene hexapodand

Colourless prismatic crystals of (3) were obtained from ethanol/CH₂Cl₂ (1:1) solution, space groupP2₁/c,a=14.581(5),b=22.517(8),c=11.799(5) , =92.13(4)°. Refinement led to a final conventionalR value of 0.074 for 4247 reflections. The conformation of the molecule, which lies on a center of symmetry, is 1,2,3-alternate with one oligoethereal chain pointing inside the molecular cavity. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. 82011 (30 pages).For part 9, see [1]. Results presented in part at the Second International Symposium of Clathrate Compounds and Molecular Inclusion Phenomena, Parma, Italy, 1982.     

Synthesis and Characterization of Mixed-Ligand Nickel(II) Chelates of β-Diones and α-Diimines. Crystal and Molecular Structure of [Ni(ncup)2Etacet]ClO4

A series of new nickel(II) perchlorate complexes containing an α-diimine(enR) and the anion of a β-dione (1,3-ketoenol or 1,3-ketoester, βH) was prepared and characterized. The composition and the overall structure of the new chelates depend on ligand concentration, on steric and electronic effects induced by substituents within the ligands and the ability of the perchlorate group to coordinate. The IR and electronic excitation spectra of [Ni(enR)₂β]ClO₄ and [Ni(enR)β(O₂ClO₂)] indicate, in conjunction with other physicochemical measurements, bidentate coordination of the ligands and replacement of the (O,O′) perchlorato group by basic solvents. The structure of the new chelates was further supported by an X-ray structure analysis of [Ni(ncup)₂Etacet]ClO₄, where ncup denotes neocuproine and Etacet the anion of the ethyl acetoacetate (orthorhombic, space group Pc2₁n, a = 14.087(5), b = 14.713(5) and c = 15.952(5) Å, Z = 4). The coordination sphere of nickel is a distorted octahedron, arised from the chromophore NiN₄O₂, in which the base is favored by three neocuproine nitrogens and one Etacet oxygen. The apical sites are occupied by the remaining oxygen and nitrogen atoms, one from Etacet and one from neocuproine respectively.     

真空条件下β-环糊精和对-甲基苯酚包结物动态结构的分子动力学模拟

本文报道了真空状态下主体β-环糊精和客体对-甲基苯酚形成的包结物在一定时间间隔内动态微观结构的分子动力学模拟结果。研究表明，对-甲基苯酚在环糊精腔内的运动具较大的自由度，但由于存在范德华作用，其运动受到一定的限制，同时通过计算观察到包结前后主客体的某些微观结构和性质发生了较为明显的变化。本文还给出了计算得到的主客体包结物的时间平均构象。     

乙酰丙酮和1-萘甲酸甲酯加成物C17H18O4的晶体结构和分子力学计算

The structure of the product from the [2+2] photocycloaddition of acetylacetone to methyl 1-naphthoate was determined by X-ray crystallography. Crystal data. C_(17)H_(18)O_4, triclinic, P_1~-, a=0.7401(1), b=0.7656(1), c=1.3882(1) nm, α=84.75(1), β=86.49(1), γ=65.08(1)°, V=0.7102 nm, Z=2, D_c=1.339 g·cm~(-3), μ(MoK_a)=1.0 cm~(-1), F(000)=304. The structure was solved by direct methods and refined to final R=0.049 for 2442 MoKa reflections. The particular bridged structure of the product molecule indicates a [2+2+2] intramolecular cycloaddition in succession to the primary [2+2] photocycloaddition. Molecular mechanics calculations confirmed further that the molecular structure of the ultimate product takes a configuration of comparatively favourable steric energy even though the bridged structure itself is rather strained.     

The dependence of slow crack growth in a polyethylene copolymer on test temperature and morphology

The slow crack growth resistance was measured in an ethylene-octene copolymer as a function of the morphological changes produced by varying the thermal history. Morphology was varied by annealing the quenched state at temperatures between 86°C and the melting point. The slow crack growth behavior was measured by the lifetime of a notched tensile specimen under a constant load. In general, the lifetime exhibited a maximum at a critical value of the annealing temperature. This critical annealing temperature decreased with a decrease in the temperature at which the lifetime was measured. The former result is understandable in terms of the increase in crystal strength as the annealing temperature is increased and the decrease in the number of tie molecules when more material is melted as the annealing temperature increases. The latter result depends on the relationship between crystal size and the effect of testing temperature. Differential scanning calorimetry data played a key part in analyzing the results. © 1992 John Wiley & Sons, Inc.     

Investigation of Protonation of the Tetraazamacrocyclic Complex of Gold(III) [Au(C14H22N4)]+ in Water. Synthesis and Crystal and Molecular Structures of [Au(C14H23N4)](ClO4)2

The equilibrium of protonation of tetraazamacrocyclic complex of gold(III) [AuL]⁺ (L = 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,6,11,13-tetraenato(2-)) in a water solution has been investigated. A monoprotonated tetraazamacrocyclic metallocomplex with two inequivalent (iminate and imine) six-membered chelate cycles and charge 1- was obtained and isolated for the first time. The compound [AuHL](ClO₄)₂ was characterized by chemical analysis, IR and UV-VIS spectroscopy, powder and single crystal X-ray diffraction. The proton was shown to be attached to the β-carbon of one of the two six-membered chelate rings of the macrocycle. Crystal data for [AuHL](ClO₄)₂ are: a = 7.693(1) Å, b = 17.366(2) Å, c =15.172(2) Å; β = 96.82(1)°, V = 2012.6(4) ų, Z = 4, d _calc = 2.123 g/cm³, space group P2₁/c. The structure is built from practically planar [Au(C₁₄H₂₃N₄)]²⁺ cations and perchlorate anions [ClO₄]⁻.Original Russian Text Copyright © 2004 by V. A. Afanasieva, I. V. Mironov, L. A. Glinskaya, R. F. Klevtsova, and L. A. Sheludyakova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1059–1066, November–December, 2004.     

Hydrogen bonding between aromatic H and F groups leading to a stripe structure with R‐ and S‐columns: the crystal structure of (2,7‐dimethoxynaphthalen‐1‐yl)(3‐fluorophenyl)methanone and comparison with its 1‐aroylnaphthalene analogues

In the molecule of (2,7‐dimethoxynaphthalen‐1‐yl)(3‐fluorophenyl)methanone, C₁₉H₁₅FO₃, (I), the dihedral angle between the plane of the naphthalene ring system and that of the benzene ring is 85.90 (5)°. The molecules exhibit axial chirality, with either an R‐ or an S‐stereogenic axis. In the crystal structure, each enantiomer is stacked into a columnar structure and the columns are arranged alternately to form a stripe structure. A pair of (methoxy)C—H...F hydrogen bonds and π–π interactions between the benzene rings of the aroyl groups link an R‐ and an S‐isomer to form a dimeric pair. These dimeric pairs are piled up in a columnar fashion through (benzene)C—H...O=C and (benzene)C—H...OCH₃ hydrogen bonds. The analogous 1‐benzoylated compound, namely (2,7‐dimethoxynaphthalen‐1‐yl)(phenyl)methanone [Kato et al. (2010). Acta Cryst. E 66 , o2659], (II), affords three independent molecules having slightly different dihedral angles between the benzene and naphthalene rings. The three independent molecules form separate columns and the three types of column are connected to each other via two C—H...OCH₃ hydrogen bonds and one C—H...O=C hydrogen bond. Two of the three columns are formed by the same enantiomeric isomer, whereas the remaining column consists of the counterpart isomer. In the case of the fluorinated 1‐benzoylated naphthalene analogue, namely (2,7‐dimethoxynaphthalen‐1‐yl)(4‐fluorophenyl)methanone [Watanabe et al. (2011). Acta Cryst. E 67 , o1466], (III), the molecular packing is similar to that of (I), i.e. it consists of stripes of R‐ and S‐enantiomeric columns. A pair of C—H...F hydrogen bonds between R‐ and S‐isomers, and C—H...O=C hydrogen bonds between R(or S)‐isomers, are also observed. Consequently, the stripe structure is apparently induced by the formation of R...S dimeric pairs stacked in a columnar fashion. The pair of C—H...F hydrogen bonds effectively stabilizes the dimeric pair of R‐ and S‐enantiomers. In addition, the co‐existence of C—H...F and C—H...O=C hydrogen bonds makes possible the formation of a structure with just one independent molecule.