Chlorophyll Breakdown in Maize: On the Structure of Two Nonfluorescent Chlorophyll Catabolites

In extracts of senescent leaves of the maize plant Zea mays, two colorless compounds with UV/Vis-characteristics of nonfluorescent chlorophyll catabolites (NCCs) were detected and tentatively named Zm-NCCs. The constitution of the two polar Zm-NCCs was determined by spectroscopic means, which confirmed both of these tetrapyrroles to have the basic ligand structure typical of the NCCs from (other) senescent higher plants. In the less polar catabolite, named Zm-NCC-2, the core structure was conjugated at the 8²-position with a glucopyranose unit. Zm-NCC-2 had the same constitution as Nr-NCC-2, an NCC from tobacco (Nicotiana rustica). Indeed, the two NCCs were identified (further) based on their HPL-chromatographic and NMR-spectroscopic properties. The more polar NCC from maize, Zm-NCC-1, differed from Zm-NCC-2 by carrying a dihydroxyethyl side chain instead of a vinyl group at the 3-position. In earlier work on polar NCCs, only separate glucopyranosyl- and dihydroxyethyl-functionalities were detected. Zm-NCC-1 thus is a new constitutional variant of the structures of NCCs from senescent higher plants.     

分光光度法快速测定玉米叶片中的叶绿素

以玉米叶片为材料,利用双波长双光束紫外可见分光光度计,用最大决定系数增量回归算法,研究了叶片叶绿素a、b及SPAD值同时、快速测量方法.结果表明,用3个波长点建立的模型可以达到良好的预测效果,预测叶绿素a、b及SPAD值的相关系数分别为0.9919、0.9816和0.9757;标准差分别为1.52、0.43和1.96;预测相对标准差分别为4.64%、5.50%和4.88%.同时研究了仪器波长误差和带宽变化对测定结果的影响, 发现波长偏移超过0.2 nm,误差快速增大,且波长向长波方向偏移时对测量的影响要大于向短波方向偏移的影响;仪器带宽变大,预测误差也就越大.     

Detection of Fragment Genesis in the Mass Spectrometer: DADI Mass Spectrometry as an Aid in the Structure Analysis of Organic Compounds

“Direct Analysis of Daughter Ions” (DADI) can be carried out with commercial mass spectrometers embodying the Nier-Johnson inverse geometry. DADI measurements permit experimental detection of the consecutive formation of molecule fragments (fragment genesis). Knowledge of fragment genesis enables the chemist to clarify the fragmentation processes of molecule-ions and provides information on the structure of fragments formed in the mass spectrometer. In combination with classical mass spectrometry such information makes it easier to determine the structure of compounds, to analyze mixtures, to determine the sequence in periodically constructed molecules, for example oligopeptides, and to study rearrangement reactions occurring in the mass spectrometer.     

Collisional Activation Mass Spectrometry—A New Probe for Determining the Structure of Ions in the Gas Phase

Organic ions with high translational energy colliding inelastically with neutral atoms or molecules become excited electronically at the expense of their translational energy. The excitation energy enables a wide range of dissociation reactions to occur and the intensity relationships yield information about the structure of the ions concerned and also permit conclusions to be drawn about the mechanism of their formation.     

叶绿素a分子在乙醇溶剂中的瞬态吸收研究

The excited state of Chlorophyll a is investigated by femtosecond transient absorption. The transient absorption spectra of Q band and By band of Chlorophyll a in ethanol have been observed. The fast kinetics of Chlorophyll a which exhibit two ultrafast components were also measured. The one is assigned to transient absorption of the inhomogeneously broadened ground state absorption spectrum, while the other is the response of the solvent to the change of the electron configuration in the excited state due to salvation dynamics of the polar solvent molecules. To understand the anisotropy of Chlorophyll a in ethanol, the anisotropy profile was also performed by 405 nm excitation and found that the anisotropy profile is 0.143. The possible combination of θda, θdb and η at excitation of By band has been simulated.     

On the Exciton Coupling between Two Chlorophyll Pigments in the Absence of a Protein Environment: Intrinsic Effects Revealed by Theory and Experiment

Exciton coupling between two or more chlorophyll (Chl) pigments is a key mechanism associated with the color tuning of photosynthetic proteins but it is difficult to disentangle this effect from shifts that are due to the protein microenvironment. Herein, we report the formation of the simplest coupled system, the Chl a dimer, tagged with a quaternary ammonium ion by electrospray ionization. Based on action spectroscopic studies in vacuo, the dimer complexes were found to absorb 50–70 meV to the red of the monomers under the same conditions. First‐principles calculations predict shifts that somewhat depend on the relative orientation of the two Chl units, namely 50 and 30 meV for structures where the Chl rings are stacked and unstacked, respectively. Our work demonstrates that Chl association alone can produce a large portion of the color shift observed in photosynthetic macromolecular assemblies.     

Chlorophyll Catabolites in Fall Leaves of the Wych Elm Tree Present a Novel Glycosylation Motif

Fall leaves of the common wych elm tree (Ulmus glabra) were studied with respect to chlorophyll catabolites. Over a dozen colorless, non‐fluorescent chlorophyll catabolites (NCCs) and several yellow chlorophyll catabolites (YCCs) were identified tentatively. Three NCC fractions were isolated and their structures were characterized by spectroscopic means. Two of these, Ug‐NCC‐27 and Ug‐NCC‐43, carried a glucopyranosyl appendage. Ug‐NCC‐53, the least polar of these NCCs, was identified as the formal product of an intramolecular esterification of the propionate and primary glucopyranosyl hydroxyl groups of Ug‐NCC‐43. Thus, the glucopyranose moiety and three of the pyrrole units of Ug‐NCC‐53 span a 20‐membered ring, installing a bicyclo[17.3.1]glycoside moiety. This structural motif is unprecedented in heterocyclic natural products, according to a thorough literature search. The remarkable, three‐dimensional bicyclo[17.3.1]glycoside architecture reduces the flexibility of the linear tetrapyrrole. This feature of Ug‐NCC‐53 is intriguing, considering the diverse biological effects of known bicyclo[n.3.1]glycosidic natural products.     

质谱技术在神经多肽酶结构与功能研究中的应用

分子神经科学是本世纪生命科学中最有挑战性和前瞻性学科之一。信号传导与催化多肽的神经多肽酶有着密切的联系。本文以海兔等软体动物为素材,综述近年来采用质谱和高效液相色谱技术研究中枢神经系统多肽酶结构与功能的进展。     

Theoretical Study of the Dimerization of Chlorophyll (a) and Its Hydrates: Implication for Chlorophyll (a) Aggregation

Dimeric structures chlorophyll (a) (Chla) and their mono‐ and dihydrated have been suggested to play an important role in the mechanism of photoreaction center chlorophyll special pairs PSI and PSII. Despite their functional importance, the molecular basis structures for interacting two Chla molecules and the structural stabilization role of H₂O in the formation of hydrated Chla dimer complexes is poorly understood. In this article, the different coordination modes between two interacting Chla molecules and the configurational (orientation and distance) features between the dimer and bound H₂O molecules are characterized by means of super molecule approach the density functional theory DFT. An estimation of the thermodynamic quantities is made for Chla dimerization and hydration processes. The results indicate that structure including ester linkages via H₂O hydrogen bonding is the most favorable conformation for the dihydrated chlorophyll (a) dimer at B3LYP/6‐31G*‐DCP level of calculation. The dispersion interaction is shown to be of great significance for the Chla dimer stabilization. In aqueous nonpolar solvent, the thermodynamics show that Chla has a slightly stronger driving force for full hydration than for dimerization and that hydration of the dimers is rather weakly exergonic. The tetrahydrated dimers having a similar arrangement to that in crystals of ethyl chlorophyllide (a) dihydrate are found to be more stable than the Chla dihydrated dimer. The data underscore the key role of H‐bonding in the stability of Chla‐H₂O adducts and, in particular, the great importance of the Chla monomeric dihydrated species in the hydration and dimerization of Chla in aqueous media. Clearly, the Chla dihydrates (Chla‐2 H₂O) are found more stable than the monohydrates (Chla‐H₂O) and the Chla dimers (Chla₂), owing to a particular structure in which cooperative interactions occur between the H₂O molecules and Chla. Calculations also indicate that the most thermodynamically preferred pathway for the formation of Chla dimer hydrates can be represented by two steps: the first corresponds to the formation of Chla monomeric dihydrates and the second is the dimerization of the dihydrates on to tetrahydrated Chla dimers. These results allow to obtain a new possible pathway for Chla dimer formation processes and could provide new insights to the aggregation of chlorophyll (a) in solution.     

Application of Laser Induced Breakdown Spectroscopy as a Novel Approach for Monitoring of the Activity of Nano Palladium Catalyst as Compared to Two Well-known Methods

Catalyst deactivation is an unavoidable process that occurs in catalytic chemical reactions. Laser Induced Breakdown Spectroscopy (LIBS) is used here as a novel approach to investigate the activity of palladium supported with carbon catalyst (Pd/C) over the hydrogenation of cinnamic acid with tetralin. Their outputs for four catalyst samples are reported for different time intervals of 0, 5, 10, 15 min during the reaction. The results of LIBS analysis are compared to Inductively Coupled Plasma Mass Spectrometry (ICP-MS), which shows a good agreement. Experimental data specify that line intensities of palladium (Pd) are decreased significantly with an increment of the reaction time. Moreover, the Field Emission Scanning Electron Microscope with energy dispersive spectroscopy (FESEM-EDS) of catalysts samples show aggregation of palladium particles for some places in the catalyst surface. The changes of Pd content and sintering of Pd particles in the catalyst during the reaction play substantial roles in catalyst deactivation.     

Hydroxymethylated Phyllobilins: A Puzzling New Feature of the Dioxobilin Branch of Chlorophyll Breakdown

Colorless nonfluorescent chlorophyll (Chl) catabolites (NCCs) are formyloxobilin‐type phyllobilins, which are considered the typical products of Chl breakdown in senescent leaves. However, in degreened leaves of some plants, dioxobilin‐type Chl catabolites (DCCs) predominate, which lack the formyl group of the NCCs, and which arise from Chl catabolites by oxidative removal of the formyl group by a P450 enzyme. Here a structural investigation of the DCCs in the methylesterase16 mutant of Arabidopsis thaliana is reported. Eight new DCCs were identified and characterized structurally. Strikingly, three of these DCCs carry stereospecifically added hydroxymethyl groups, and represent bilin‐type linear tetrapyrroles with an unprecedented modification. Indeed, DCCs show a remarkable structural parallel, otherwise, to the bilins from heme breakdown.     

Activity of Arsenic in Liquid Cu–Fe Base Alloys

Summary. The activity of arsenic in liquid Cu–Fe base alloys was determined by isopiestic and Knudsen cell-mass spectrometer methods. Based on the activity data, the volatilization of arsenic in the extraction and recycling of copper was thermodynamically evaluated.     

On the intersection of electrochemistry and mass spectrometry

The application of nanopipettes, developed first as a tool for electrochemistry and electrophysiology, as tools for mass spectrometry is considered. Recent examples of advances in electrospray ionization and sampling for mass spectrometry with nanopipettes is discussed. These examples show a scientific intersection that is ripe for further development.     

Structure of Protonated Heterodimer of Proline and Phenylalanine: Revealed by Infrared Multiphoton Dissociation Spectroscopy and Theoretical Calculations

The infrared multiphoton dissociation (IRMPD) spectrum of the protonated heterodimer of ProPheHbegin{document}$ ^+ $end{document}, in the range of 2700-3700 cmbegin{document}$ ^{-1} $end{document}, has been obtained with a Fourier-transform ion cyclotron mass spectrometer combined with an IR OPO laser. The experimental spectrum shows one peak at 3565 cmbegin{document}$ ^{-1} $end{document} corresponding to the free carboxyl O-H stretching vibration, and two broad peaks centered at 2935 and 3195 cmbegin{document}$ ^{-1} $end{document}. Theoretical calculations were performed on the level of M062X/6-311++G(d, p). Results show that the most stable isomer is characterized by a charge-solvated structure in which the proton is bound to the unit of proline. Its predicted spectrum is in good agreement with the experimental one, although the coexistence of salt-bridged structures cannot be entirely excluded.     

兴奋剂检测中的化学衍生化方法

本文评述了兴奋剂检测中的各种化学衍生化方法,对蛋白同化激素、麻醉镇痛剂、β-阻断剂和利尿剂分别进行了讨论。这四类药物结构各不相同,但绝大多数属于高沸点、难挥发的极性化合物,不适于直接进行GC或GC/MS分析。通过化学衍生化.不仅可增大试样的挥发性和稳定性,减小样品的极性,使原来难以进行GC分析的试样转变成适合于色谱分析的试样,而且通过衍生化还可达到改善分离效果、提高检测灵敏度的目的。     

FluClass: A novel algorithm and approach to score and visualize the phylogeny of the influenza virus using mass spectrometry

A novel computer algorithm FluClass has been developed to facilitate the phylogenetic classification of influenza virus using mass spectral data. FluClass accepts a DNA or protein-based phylogenetic tree as input and generates theoretical peptide mass lists for each node. An experimental mass spectrum from an influenza virus protein digest is then placed onto the phylogenetic tree using a novel random resampling function (Z-score) that allows the scoring of spectrum against both internal and leaf nodes. Testing of the algorithm using hemagglutinin protein sequences from human-host influenza viruses showed that the Z-score performs comparably to the Profound scoring method for the scoring of leaf nodes and is substantially better at scoring internal nodes. Scoring of internal nodes allows colorizations of nodes of the phylogenetic tree enabling the classification of the query spectrum to be rapidly visualized. Finally we demonstrate the utility of FluClass on experimental spectra from six strains. Given that mass spectrometry data can be generated rapidly for influenza virus proteins, FluClass provides a fast and direct method for phylogenetic analysis of influenza proteins.