Electron chirality in amino acid molecules

We evaluated the total electron chirality in alanine, serine, and valine, which are molecules that have chiral structures. Previously, computations of the total electron chirality of molecules composed of only light elements are impossible within usual computational conditions of relativistic four-component wave functions. In this work, it is shown that the total electron chirality can be calculated if some diffuse functions are added to Gaussian basis sets. This is demonstrated for the H₂O₂ molecule. By adding diffuse Gaussian functions to basis sets, the total electron chirality of L-alanine, L-serine, and L-valine are evaluated. It is also shown that the total electron chirality is derived by the cancellation between large contributions from each orbital, and the total electron chirality in excited and ionized states is expected to be much larger than that of the ground state.     

具有三核Cd(Ⅱ)簇单元和螺旋链的脯氨酸类单一手性金属-有机框架材料的合成、 结构和性质

在溶剂热反应条件下, 使用含氮辅助配体1,4-二(4-吡啶基)苯(1,4-DPB)和半刚性脯氨酸衍生物配体(R)-5-(2-羧基吡咯烷-1-羰基)间苯二甲酸[(R)-H₃PIA]或(S)-5-(2-羧基吡咯烷-1-羰基)间苯二甲酸[(S)-H₃PIA]与Cd²⁺构筑了单一手性金属-有机框架材料[Cd_1.5((R)-PIA)(1,4-DPB)_1.5]·0.75H₂O·xGuest(1-D)和[Cd_1.5((S)-PIA)(1,4-DPB)_1.5]·0.75 H₂O·xGuest(1-L). 配合物1-D和1-L呈具有开放孔道的三维柱层式框架结构, 含有三核镉簇单元 Cd₃(CO₂)₆与两种螺旋链构建的波浪形Cd-PIA层. 分别对上述化合物进行了粉末X射线衍射、 热重分析、 圆二色谱和荧光光谱等测试. 测试结果显示配合物1-D和1-L都是以纯晶体的形式存在, 2种配合物的热失重曲线接近, 圆二色谱有明显的正负吸收峰, 符合其对映体的结构特征.     

The first contribution of capillary electrophoresis to the study of abiotic origins of homochirality: investigation of the enantioselective adsorption of 3-carboxy adipic acid on minerals

CE with UV detection was used for the first time to determine the enantioselective adsorption of the short-chain tricarboxylic acid, 3-carboxy adipic acid, on minerals as a mean of investigating plausible mechanisms for the origin of biochemical homochirality on Earth. The use of vancomycine as chiral selector in the separation buffer using the partial filling technique enabled the separation of the two enantiomers of this organic acid in about 12 min. Taking into account that this compound has a low absorption of the UV light, and in order to achieve the sensitivity needed to determine the enantiomeric excess of samples of 3-carboxy adipic acid adsorbed on minerals, we applied a strategy consisting of a field-amplified sample stacking together with the use of a bubble capillary and detection at low wavelength (192 nm). This combination enabled an LOD of about 10(-7) M and the determination of the enantiomeric excess of 3-carboxy adipic acid adsorbed on calcite and feldspar mineral samples at subnanomol levels of this acid. Results showed that an enantioselective adsorption of the enantiomers of 3-carboxy adipic acid on minerals took place.     

Hydrogen-Atom Tunneling in a Homochiral Environment

The role-exchanging concerted torsional motion of two hydrogen atoms in the homochiral dimer of trans-1,2-cyclohexanediol was characterized through a combination of broadband rotational spectroscopy and theoretical modeling. The results reveal that the concerted tunneling motion of the hydrogen atoms leads to the inversion of the sign of the dipole moment components along the a and b principal axes, due to the interchange motion that cooperatively breaks and reforms one intermolecular hydrogen bond. This motion is also coupled with two acceptor switching motions. The energy difference between the two ground vibrational states arising from this tunneling motion was determined to be 29.003(2) MHz. The corresponding wavefunctions suggest that the two hydrogen atoms are evenly delocalized on two equivalent potential wells, which differs from the heterochiral case where the hydrogen atoms are confined in separate wells, as the permutation-inversion symmetry breaks down. This intriguing contrast in hydrogen-atom behavior between homochiral and heterochiral environments could further illuminate our understanding of the role of chirality in intermolecular interactions and dynamics.     

Absolute enantioselective separation: optical activity ex machina

The paper describes methodology of using three independent macroscopic factors affecting molecular orientation to accomplish separation of a racemic mixture without the presence of any other chiral compounds, i. e., absolute enantioselective separation (AES) which is an extension of a concept of applying these factors to absolute asymmetric synthesis. The three factors may be applied simultaneously or, if their effects can be retained, consecutively. The resulting three mutually orthogonal or near orthogonal directors constitute a true chiral influence and their scalar triple product is the measure of the chirality of the system. AES can be executed in a chromatography-like microfluidic process in the presence of an electric field. It may be carried out on a chemically modified flat surface, a monolithic polymer column made of a mesoporous material, each having imparted directional properties. Separation parameters were estimated for these media and possible implications for the natural homochirality are discussed.     

On chiral pathways inE n : A dimensional analysis

Summary A dimensional analysis shows that all chiral labeled and unlabeled simplexes inE ² and all maximally labeled simplexes in higher dimensions, are unique in that they can be partitioned into disjoint heterochiral sets. Such partition is impossible for all other labeled and unlabeledm-point sets (m ⩾n + 2) inE ⁿ , since they and their enantiomorphs are chirally connected.     

Homochiral imidazole-based dicarboxylate metal complexes with SrSi2 topology: synthesis,crystal structures,and properties

Two new complexes with homochiral frameworks, {Co₃(EIDC)₂(H₂O)₅}_n (1) and {Zn₃(EIDC)₂(H₂O)₄}_n (2) (H₃EIDC?=?2-ethyl-1H-imidazole-4,5-dicarboxylic acid), have been synthesized from achiral starting precursors via spontaneous resolution and fully characterized by elemental analyses, IR, circular dichroism, photoluminescence (PL) spectroscopy, single-crystal X-ray diffraction, and thermogravimetric analysis. X-ray diffraction data revealed that 1 and 2 have SrSi₂ topologies and that both are homochiral metal–organic frameworks. Compound 1 is constructed by left-handed chiral chains; however, right-handed chains constitute the homochiral framework of 2. Variable temperature magnetic susceptibility measurements of 1 indicate strong antiferromagnetic interactions between the magnetic Co centers. Compound 2 exhibited weak blue PL in the solid state at room temperature.     

Concept of Absolute Enantioselective Separation

A novel approach to separations of racemates is described. It is a chromatography-like process in which molecules to be separated are oriented in two directions perpendicular to each other and parallel to the surface. If this requirement is met the opposite enantiomers differ in the energy of interaction with the surface. We call the process Absolute Enantioselective Separation (AES). Surface requirements for resolving a racemate to enantiomers are discussed. AES can be accomplished either by interaction of racemate components with a repeating pattern on the not necessarily chiral surface and interaction with a static electric field or by interaction with two repeating patterns defining the chirality of the surface. Additionally, a multiple use of electric fields to enable a separation in bulk is described. The ease of separation of selected natural compounds (amino acids and monosaccharides) in the AES process is also discussed.     

The role of nickel(II) on the homochirality of amino acids in living systems

<正>The origin of homochirality in living organisms is controversial,stands out of being particularly important and a question which is still not satisfactorily answered.A mental picture of sequence of events that is thought to have preceded the existence of chirality in molecules is described.A chemical model to mimic the original abiotic conditions in an attempt to explain the preference of homochirality in living systems was tried.The effect which might have influenced this preference is presented.The surprising and unexpected results are indeed interesting,significant,repeatable and indicate that complexing alanine with nickel(Ⅱ) ion alters the racemization rates of D and L isomers of the amino acid.However,why this difference happens is unclear and is difficult to explain.     

On the investigation of pseudoscalar molecular properties and polynomial approximations according to Ruch and Schönhofer

Analytic chirality functions in one or more ligand parameters representing pseudoscalar molecular properties are shown to decompose as linear combinations in the elementary chirality functions of a suitable module basis. The implications of this decomposition for an approximation ansatz are considered.