A Synthetic Strategy for Cofacial Porphyrin-Based Homo- and Heterobimetallic Complexes

We present a straightforward and generally applicable synthesis route for cofacially linked homo- and heterobimetallic porphyrin complexes. The protocol allows the synthesis of unsymmetrical aryl-based meso-meso as well as β-meso-linked porphyrins. Our method significantly increases the overall yield for the published compound known as o-phenylene-bisporphyrin (OBBP) by a factor of 6.8. Besides the synthesis of 16 novel homobimetallic complexes containing Mn^III, Fe^III, Ni^II, Cu^II, Zn^II, and Pd^II, we achieved the first single-crystal X-ray structure of an unsymmetrical cofacial benzene-linked porphyrin dimer containing both planar-chiral enantiomers of a Ni^II₂ complex. Additionally, this new methodology allows access to heterobimetallic complexes such as the Fe^III-Ni^II containing carbon monoxide dehydrogenase active site analogue. The isolated species were investigated by various techniques, including ion mobility spectrometry, DFT calculations, and UV/Vis spectroscopy. This allowed us to probe the influence of interplane distance on Soret band splitting.     

HCl-H2O和DCl-H2O二聚体的分子内和分子间振转态的全维和完全耦合量子计算

本文报道了氯化氢-水二聚体的两种同位素,HCl-H₂O和DCl-H₂O(DH)的J=1分子内和分子间振转态的全维和完全耦合量子束缚态计算. 本研究补充了我们最近对于这两类体系J=0九维(9D)振动水平结构的理论研究,并采用相同的精确9D置换不变多项式-神经网络势能面. 该计算得到了所有这些分子间和分子内低能的振转态的基本量,将结果与相同二聚体的9D J=0计算的结果进行了比较. K=1和K=0本征态之间的能量差异表现出与分子间振转态的明显变化,为此本文提供了定性的解释.     

Distinctive dielectric properties of nematic liquid crystal dimers

ABSTRACT

We provide an overview of the effect of the molecular structure on the dielectric properties of dimers exhibiting nematic and twist-bend nematic phases with special focus on how the conformational distribution changes are reflected by the dielectric behaviour. Nematic dimers show distinctive dielectric properties which differ from those of archetypical nematic liquid crystals, as for example, unusual temperature dependence of the static permittivity or dielectric spectra characterised by two low-frequency relaxation processes with correlated strengths. The interpretation of such characteristic behaviour requires that account is taken of the effect of molecular flexibility on the energetically favoured molecular shapes. The anisotropic nematic interactions greatly influence the conformational distribution. Dielectric behaviour can be used to track those conformational changes due to dependence of the averaged molecular dipole moment on the averaged molecular shape. Results for a number of dimers are compared and analysed on the basis of the influence of details of the molecular structure, using a recently developed theory for the dielectric properties of dimers.     

The twist-bend nematic phase: molecular insights from a generalised Maier–Saupe theory

ABSTRACT

Bent-shaped liquid crystal dimers exhibit a non-conventional nematic phase, which in the last few years has been actively investigated. A structural model of this phase has been proposed, which is characterised by a helical modulation with a periodicity of the order of few molecular lengths. Such a model, which is generally denoted as twist-bend nematic (N_TB), is consistent with various experimental evidences and is supported by theories and simulations. Here, we will examine in more detail the features and the implications of a generalised Maier–Saupe theory, which was recently proposed to explain the origin and structure of the N_TB phase. In particular we will analyse the relevant molecular order parameters, with special attention to the polar and biaxial ones, and we will discuss the concept of ‘tilted director’, which may give rise to some ambiguity. The phase behaviour will be described as a function of the bend angle between the mesogenic moieties of a dimer, which in the generalised Maier–Saupe theory is the key molecular feature. Extension of the theory to include fluctuations of the bend angle will allow us to examine the effect of the molecular flexibility on the phase diagram.     

A New Way to Silicone‐Based Peptide Polymers

We describe a new class of silicone‐containing peptide polymers obtained by a straightforward polymerization in water using tailored chlorodimethylsilyl peptide blocks as monomeric units. This general strategy is applicable to any type of peptide sequences, yielding linear or branched polymer chains composed of well‐defined peptide sequences.     

How CO2 Interacts with Carboxylic Acids: A Rotational Study of Formic Acid–CO2

The rotational spectra of the 1:1 formic acid–carbon dioxide molecular complex and of its monodeuterated isotopologues are analysed in the 6.5–18.5 and 59.6–74.4 GHz frequency ranges using a pulsed jet Fourier transform microwave spectrometer and a free‐jet absorption millimetre wave spectrometer, respectively. Precise values of the rotational and quartic centrifugal distortion constants are obtained from the measured frequencies, and quadrupole coupling constants are determined from the deuterium hyperfine splittings. Structural parameters are estimated from the moments of inertia and their differences among isotopologues: the complex has a planar structure with the two subunits held together by a HC(O)OH???O=C ? O (2.075 Å) and a HC(OH)O???CO₂ (2.877 Å) interactions. The ab initio intermolecular binding energy, obtained at the counterpoise corrected MP2/aug‐cc‐pVTZ level of calculation, is D_e=17 kJ mol^?1.     

Two new macrosporin dimers from the fungus Alternaria sp. XZSBG-1

Two new macrosporin dimers (1–2) along with four known compounds (3–6) were isolated from the extracts of the fungal strain Alternaria sp. XZSBG-1 from the sediment of the salt lake in the Bange, Tibetan, China. Their structures were determined by spectroscopic methods, mainly by 2D NMR spectra. Compounds 1 and 2 are new macrosporin dimers with symmetric chemical structures. In the cytotoxicity assay and inhibited alpha-glucosidase activity assay, all these compounds showed no notable inhibitory activity.     

Rapid evaluation of the binding energies between peptide amide and DNA base

The binding energies and the equilibrium hydrogen bond distances as well as the potential energy curves of 20 hydrogen‐bonded amide–base dimers are evaluated from the analytic potential energy function established in our laboratory recently. The analytic potential energy function is used to calculate the N? H···N, N? H···O?C, C? H···N, and C? H···O?C dipole–dipole attractive interaction energies and C?O···O?C, N? H···H? N, and N? H···H? C dipole–dipole repulsive interaction energies in the 20 dimers composed of DNA bases adenine, guanine, cytosine, or thymine and peptide amide. The calculation results show that the potential energy curves obtained from the analytic potential energy function are in good agreement with those obtained from MP2/6‐311+G** calculations by including the basis set superposition error (BSSE) correction. For all the 20 dimers, the analytic potential energy function yields the binding energies of the MP2/6‐311+G** with BSSE correction within the error limits of 0.50 kcal/mol for 19 dimers, only one difference is larger than 0.50 kcal/mol and the difference is only 0.61 kcal/mol. The analytic potential energy function produces the equilibrium hydrogen bond distances of the MP2/6‐311+G** with BSSE correction within the error limits of 0.030 Å for all the 20 dimers. The analytic potential energy function is further applied to four more complicated DNA base‐peptide amide systems involving amino acid side chain and β‐sheet. The values of the binding energies and equilibrium hydrogen bond distances obtained from the analytic potential energy function are also in good agreement with those obtained from MP2 calculations with the BSSE correction. These results demonstrate that the analytic potential energy function can be used to evaluate the binding energies in hydrogen‐bonded peptide amide–DNA base dimers quickly and accurately. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

核酸碱基的非谐性振动:Ⅲ,DNA叠加二聚体的一维和二维红外光谱

用量子化学计算方法研究了DNA碱基单体及其15个B型和2个G-四链体的叠加二聚体的非谐性振动光谱特征.研究发现,从碱基单体到二聚体,C=O伸缩模式之间的相互作用很强,表现在其非谐性振动频率和非谐性常数都发生了明显的改变,特别是在含碱基G的叠加体中.这些变化能在一维和二维红外光谱中很好地表现出来.利用振动模式的势能分布和非谐性常数的组成分析,讨论了叠加二聚体中C=O模式的离域化程度.