Circular Dichroism of Amino Acids: Following the Structural Formation of Phenylalanine

Circular dichroism (CD) is frequently used to assess the secondary structure of peptides and proteins, whereas less attention has been given to their building blocks, that is, single amino acids, as they do not possess a secondary structure. Here, we follow the CD signal of amino acids and reveal that several acids exhibit a unique CD pattern as a function of their concentration. Accordingly, we propose an eight‐level classification of the CD signal of the various amino acids. Special focus is given to the CD pattern of phenylalanine (Phe), for which we observe the formation of an ultra‐narrow CD peak (full width at high maximum of only 5 nm). This CD peak can be attributed to the formation of Phe‐based chiral structural features. Further support for the formation of an ordered structure is given by using NMR, and the additional self‐assembly process of Phe to tubular structures.     

Hydrothermal synthesis,crystal structure and photoluminescence of two homochiral zinc(II) coordination polymers

Metal–organic frameworks (MOFs) have potentially useful applications and an intriguing variety of architectures and topologies. Two homochiral coordination polymers have been synthesized by the hydrothermal method, namely poly[(μ‐N‐benzyl‐L‐phenylalaninato‐κ⁴O,O′:O,N)(μ‐formato‐κ²O:O′)zinc(II)], [Zn(C₁₆H₁₆NO₂)(HCOO)]_n, (1), and poly[(μ‐N‐benzyl‐L‐leucinato‐κ⁴O,O′:O,N)(μ‐formato‐κ²O:O′)zinc(II)], [Zn(C₁₃H₁₈NO₂)(HCOO)]_n, (2), and studied by single‐crystal X‐ray diffraction, elemental analyses, IR spectroscopy and fluorescence spectroscopy. Compounds (1) and (2) each have a two‐dimensional layer structure, with the benzyl or isobutyl groups of the ligands directed towards the interlayer interface. Photoluminescence investigations show that both (1) and (2) display a strong emission in the blue region.     

以苯丙氨酸为例刍议芳香族氨基酸的生物合成机理

从磷酸烯醇式丙酮酸和4-磷酸赤藓糖为始探讨了3种芳香族氨基酸合成代谢共享的分支酸合成途径, 并以苯丙氨酸为例从多学科角度讨论分析其合成代谢的独特性。通过多学科角度展示了生物体内不同代谢路径之间的关联及相似性, 旨在展示一种教学新模式,帮助学生建立起跨学科内容的学习及归纳方法。     

Laminarin Induces Defense Responses and Efficiently Controls Olive Leaf Spot Disease in Olive

Olive leaf spot (OLS) caused by Fusicladium oleagineum is mainly controlled using copper fungicides. However, the replacement of copper-based products with eco-friendly alternatives is a priority. The use of plant resistance-inducers (PRIs) or biological control agents (BCAs) could contribute in this direction. In this study we investigated the potential use of three PRIs (laminarin, acibenzolar-S-methyl, harpin) and a BCA (Bacillus amyloliquefaciens FZB24) for the management of OLS. The tested products provided control efficacy higher than 68%. In most cases, dual applications provided higher (p < 0.05) control efficacies compared to that achieved by single applications. The highest control efficacy of 100% was achieved by laminarin. Expression analysis of the selected genes by RT-qPCR revealed different kinetics of induction. In laminarin-treated plants, for most of the tested genes a higher induction rate (p < 0.05) was observed at 3 days post application. Pal, Lox, Cuao and Mpol were the genes with the higher inductions in laminarin-treated and artificially inoculated plants. The results of this study are expected to contribute towards a better understanding of PRIs in olive culture and the optimization of OLS control, while they provide evidence for potential contributions in the reduction of copper accumulation in the environment.     

Centerband-Only Detection of Exchange NMR with Natural-Abundance Correction Reveals an Expanded Unit Cell in Phenylalanine Crystals

The NMR pulse sequence CODEX (centerband-only detection of exchange) is a widely used method to report on the number of magnetically inequivalent spins that exchange magnetization via spin diffusion. For crystals, this rules out certain symmetries, and the rate of equilibration is sensitive to distances. Here we show that for ¹³C CODEX, consideration of natural abundance spins is necessary for crystals of high complexity, demonstrated here with the amino acid phenylalanine. The NMR data rule out the C₂ space group that was originally reported for phenylalanine, and are only consistent with a larger unit cell containing eight magnetically inequivalent molecules. Such an expanded cell was recently described based on single crystal data. The large unit cell dictates the use of long spin diffusion times of more than 200 seconds, in order to equilibrate over the entire unit cell volume of 1622 ų.     

Intramolecular interactions of L‐phenylalanine: Valence ionization spectra and orbital momentum distributions of its fragment molecules

Intramolecular interactions between fragments of L ‐phenylalanine, i.e., phenyl and alaninyl, have been investigated using dual space analysis (DSA) quantum mechanically. Valence space photoelectron spectra (PES), orbital energy topology and correlation diagram, as well as orbital momentum distributions (MDs) of L ‐phenylalanine, benzene and L ‐alanine are studied using density functional theory methods. While fully resolved experimental PES of L ‐phenylalanine is not yet available, our simulated PES reproduces major features of the experimental measurement. For benzene, the simulated orbital MDs for 1e_1g and 1a_2u orbitals also agree well with those measured using electron momentum spectra. Our theoretical models are then applied to reveal intramolecular interactions of the species on an orbital base, using DSA. Valence orbitals of L ‐phenylalanine can be essentially deduced into contributions from its fragments such as phenyl and alaninyl as well as their interactions. The fragment orbitals inherit properties of their parent species in energy and shape (ie., MDs). Phenylalanine orbitals show strong bonding in the energy range of 14‐20 eV, rather than outside of this region. This study presents a competent orbital based fragments‐in‐molecules picture in the valence space, which supports the fragment molecular orbital picture and building block principle in valence space. The optimized structures of the molecules are represented using the recently developed interactive 3D‐PDF technique. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Supramolecular heterogeneity in β-turn forming synthetic tripeptides nucleated by isomers of fluorinated phenylalanine and aib as corner residues

The influences of fluorines in chemistry have emerged as a breakthrough in various arenas of bio-organic and medicinal chemistry. But its incorporation in β-turn design and its implications for supramolecular chemistry remains in a rudimentary stage. Inspired by the diversity displayed by the isomers of mono-fluorinated phenylalanine in biological sciences, here our effort is to modulate the solid state conformational analysis of three terminally protected synthetic tripeptides Boc-(Y)-F-Phe-Aib-Xaa-OMe, where (Y is (2)-F-Phe, Xaa; Leu in peptide I, (3)-F-Phe, Xaa; Leu in peptide II and (4)-F-Phe, Xaa; Ile in peptide III). Interestingly, all the three peptides display a conformational preference for β-turns, stabilized by 4→1 intramolecular hydrogen bonding. Our investigation further demonstrates that mere interchange of positions of fluorines in mono-fluorinated phenylalanine in peptides I–III introduces significant diversity in supramolecular chemistry. X-ray crystallography sheds some light at atomic resolution. Furthermore, this supramolecular heterogeneous behavior is evident from the morphologies obtained from the materials of all the three peptides grown from acetone to petroleum ether solution, studied by field emission scanning electron microscopy. Thus, these monofluorinated peptides I–III may serve as prominent candidates in understanding the structure and function of misfolded disease causing peptides like prion and Alzheimer's amyloid.     

D-脯氨酸催化的(3S,4S)-4-氨基-3-羟基-5-苯基戊酸衍生物的合成

报道了一条合成(3S,4S)-4-氨基-3-羟基-5-苯基戊酸(Ahppa)衍生物的新路线。以氨基保护的L-苯丙氨酸为起始原料,依次经Weinreb胺缩合、还原、aldol缩合及溴仿4步反应合成了3个Ahppa衍生物,总收率5.8%~6.7%,其结构经¹H NMR, ¹³C NMR和ESI-MS确证。对反应条件进行了探讨,结果表明：催化剂D-脯氨酸用量对反应收率影响不大,对立体选择性影响较大;氨基上保护基体积较大有利于提高反应立体选择性。     

水液相环境下羟自由基诱导的苯丙氨酸分子损伤机理

在MP2/ SMD/6-311++g(3df, 2pd)//WB97X-D/SMD/6-311++G(d, p)理论水平上,研究了水液相环境下羟自由基诱导的苯丙氨酸分子的损伤机理。研究发现,羟自由基（水分子簇）抽取α-氢、β-氢、苯环-氢以及羟自由基与苯环加成均可致苯丙氨酸分子损伤。势能面计算表明,羟自由基（水分子簇）抽取α-氢和β-氢的最低能垒分别为68.4和89.3 kJ·mol^-1,羟自由基抽取苯环-氢的最低能垒为111.6 kJ·mol^-1,羟自由基加成到苯环不同位点碳的能垒大约在106.5~110.2 kJ·mol^-1,羟自由基（水分子簇）抽α-氢和β-氢是显著的放热反应。结果表明,羟自由基（水分子簇）抽取α-氢是苯丙氨酸分子损伤的主要途径。