Laser-Induced Thermal Desorption Facilitates Postsource Decay of Peptide Ions

We investigated the thermal mechanism involved in laser desorption/ionization (LDI) of thermally labile molecules from the flat surfaces of amorphous Si (a-Si) and crystalline Si (c-Si). a-Si was selected for this study because of its thermal property, such as low thermal conductivity; thus, it was predicted to be highly susceptible to laser-induced surface heating. By virtue of lack of surface nanostructures, the flat surfaces offer a simple model system to focus on the thermal mechanism, avoiding other effects, including possible non-thermal contributions that can arise from the physical existence of surface nanostructures. For the energetics study, the internal energies of substituted benzylpyridinium ions produced by LDI on the bare and coated surfaces of a-Si and c-Si were obtained using the survival yield method. The results, including LDI thresholds, ion yields, and internal energies all suggested that the LDI mechanism would be indeed thermal, which is most likely promoted by thermal desorption caused by laser-induced surface heating. In addition, the LDI process driven by laser-induced thermal desorption (LITD) was also found to be capable of depositing an excessive internal energy in resulting LDI ions, which underwent a dissociation. It exhibited the essentially same features as in postsource decay (PSD) in MALDI-TOF/TOF mass spectrometry. We report that the LDI process by LITD offers not only a way of intact ionization but also a facile means for PSD of peptide ions, which this work demonstrates is well suited to peptide sequencing using TOF/TOF mass spectrometry.     

Laser Induced Fluorescence Spectroscopy of IrN

High resolution laser induced fluorescence, spectra of IrN in the spectral region between 394 and 520 nm were recorded using laser vaporization/reaction free jet expansion and laser induced fluorescence spectroscopy. Seven new vibronic transition bands were observed and analyzed. Two Ω=1 and five Ω=0 new states were identified. Least squares fit of rotationally resolved transition lines yielded accurate molecular constants for the upper states. Spectra of isotopic molecules were observed, which provided confirmation for the vibrational assignment. Comparison of the observed electronic states of IrB, IrC, and IrN provides a good understanding of the chemical bonding of this group of molecules.     

Determination of Chlorpyrifos by a Multicommutated Photochemically Induced Fluorescence Optosensor

Abstract

We propose a multicommutated flow-through optosensor for the quantitation of the organophosphate pesticide chlorpyrifos in dried chili peppers. We used photochemically induced fluorescence detection to overcome the negligible native fluorescence of the target pesticide. Firstly, the photodegradation of chlorpyrifos was performed online with an ultraviolet lamp. Then, the fluorescent photoproduct was retained on a solid support (Sephadex QAE A-25) inside the flow-cell in order to record the analytical signal. The online photodegradation and preconcentration of the photoproduct on the solid support were critical for the automation, speed, and high sensitivity obtained. A QuEChERS procedure was selected for sample treatment, obtaining recovery yields close to 100%. The method proposed presents a quantitation limit of 18?mg?kg^?1 in real samples, hence fulfilling the maximum residue limit of Codex Alimentarius, 20?mg?kg^?1. Therefore, this approach offers a novel method for screening purposes in the agricultural and food industries.     

Double Naphthalene‐Tagged Cyclodextrin‐Peptide Capable of Exhibiting Guest‐Induced Naphthalene Excimer Fluorescence

A cyclodextrin‐peptide hybrid (17NNβ) bearing two naphthalene units in the peptide side chain has been designed and synthesized as a novel chemosensor molecule. Circular dichroism study of the compound revealed that the peptide has α‐helix structure with a helix content of 41%. The peptide revealed both monomer and excimer emission and the intensity of the excimer emission increased while that of the monomer emission decreased upon addition of the guest compound. This behavior was observed for various guest molecules, suggesting that the system can be used for detecting molecules in aqueous solution.     

超声射流CCl2自由基激光诱导荧光激发谱

对CCl4/Ar混合气体脉冲直流高压放电产生CCl2自由基,在超声射流冷却下获得了CCl2 1B1－ 1A1420～600 nm 波长范围的激光诱导荧光激发谱,系统标识了9个带系,81个振动带,其中56个振动带是我们新标识的.通过CCl2自由基的超声射流LIF谱与常温下压力为150 Pa 左右的LIF谱相结合分析,初步证实CCl2自由基电子态带源为17 255.04 cm－1.     

毛细管电色谱-激光诱导荧光联用技术进展

作为一种新兴的微分离技术,毛细管电色谱(CEC)结合了毛细管电泳的高效性和高效液相色谱高选择性的优点,近年来备受关注。本文简单介绍了CEC的基本原理、常用色谱柱和检测器。重点针对毛细管电色谱-激光诱导荧光检测联用技术进行了综述,包括该方法在生物、医药、环境等诸多领域的应用。     

超声射流CCl2 自由基激光诱导荧光激发谱

用CCl4/Ar混合气体脉冲直流高压放电产生CCl2自由基,在超声射流冷却下获得了CCl2 1B1- 1A1 440～580 nm 的K-结构分辨的激光诱导荧光激发谱.通过K-结构分辨谱的分析,对722条转动子谱带进行了归属,得到了激发态CCl2 1B1的两个全对称振动模式的振动频率、非谐性常数和转动常数差值,即激发态的振动频率ω1=631.20 cm-1, ω2=302.00 cm-1, A′-B′=3.476 cm-1.     

Stimuli Induced Uptake of Protein-Like Peptide Brush Polymers

Recently, we presented a strategy for packaging peptides as side-chains in high-density brush polymers. For this globular protein-like polymer (PLP) formulation, therapeutic peptides were shown to resist proteolytic degradation, enter cells efficiently and maintain biological function. In this paper, we establish the role charge plays in dictating the cellular uptake of these peptide formulations, finding that peptides with a net positive charge will enter cells when polymerized, while those formed from anionic or neutral peptides remain outside of cells. Given these findings, we explored whether cellular uptake could be selectively induced by a stimulus. In our design, a cationic peptide is appended to a sequence of charge-neutralizing anionic amino acids through stimuli-responsive cleavable linkers. As a proof-of-concept study, we tested this strategy with two different classes of stimuli, exogenous UV light and an enzyme (a matrix metalloproteinase) associated with the inflammatory response. The key finding is that these materials enter cells only when acted upon by the stimulus. This approach makes it possible to achieve delivery of the polymers, therapeutic peptides or an appended cargo into cells in response to an appropriate stimulus.     

Nonexponential relaxation and fragility in a model system and in supercooled liquids

Among the outstanding problems in the theory of supercooled liquids are the reasons for the rapid increase in their viscosity and relaxation times as the temperature is lowered towards the glass transition temperature Tg, the nonexponential time dependence of the relaxation, and the possible connection between these two properties. The ferromagnetic Potts model on a square latice is a simple system that is found to exhibit these properties. Our calculations show that in this system the connection between them is associated with the dependence on temperature and time of the average environment of the sites. Some of the consequences of this for understanding the behavior of supercooled liquids are discussed.     

Photo-Chemically Induced Fluorescence Determination of Tigecycline by a Stopped-Flow Multicommutated Flow-Analysis Assembly

In this paper, the conversion of tigecycline, a first-in-class glycylcycline antibiotic, into a fluorescent degradation product with quantitative purposes by UV irradiation and its fluorimetric determination are reported for the first time through the presentation of a spectroscopic method for the determination of this compound. A multicommutated flow-assembly employing three-way solenoid valves is used for the analysis, with the entire procedure being computer-controlled. The degradation product is measured at excitation and emission wavelengths of 333 and 453 nm, respectively, obtaining 33 µg L^?1 as the detection limit, a linear dynamic range between 0.1–2 µg mL^?1, and a R.S.D. of 2.8% (n = 10).     

Peptide Conjugated Dihydroazulene/Vinylheptafulvene Photoswitches in Aqueous Environment

Light-responsive molecules have seen a major advance in modulating biological functions in recent years. Especially photoswitches are highly attractive building blocks due to the reversible nature of their light-mediated reactivity. They are frequently used to affect both the properties of small bioactive compounds and biomacromolecules if incorporated suitably. Despite their success in a plethora of applications, only a limited set of photochromic core structures is routinely employed and a large number of photochromic couples are under-investigated in biological context. Broadening the toolbox of photoswitches available to modulate biological activity would open new avenues and unlock the full potential of photoswitchable molecules for biological studies. In this work, we explore the photochemical and thermal properties of the dihydroazulene/vinylheptafulvene photochromic couple as peptide conjugates in aqueous environment.     

A Tetrahedral Bisacridine Donor Enables Fast Radiative Decay in Thermally Activated Delayed Fluorescence Emitter

Achieving high efficiency and low efficiency roll-off simultaneously is of great significance for further application of thermally activated delayed fluorescent (TADF) emitters. A balance between radiative decay and reversed intersystem crossing must be carefully established. Herein, we propose a qunolino-acridine (QAc) donor composing two acridine with both planar (pAc) and bended (bAc) geometries. Combining with triazine, a TADF emitter QAc-TRZ is assembled. The pAc provides a well interaction with triazine which ensures a decent TADF behavior, while the bAc offers a delocalization of highest occupied molecular orbital (HOMO) which guarantees an enhancement of radiative decay. Remarkably, QAc-TRZ enables a highly efficient organic light emitting diode (OLED) with maximum external quantum efficiency (EQE) of 37.3 %. More importantly, the efficiencies under 100/1000 cd m⁻² stay 36.3 % and 31.7 %, respectively, and remain 21.5 % even under 10 000 cd m⁻².     

Allosteric Modulation of Human Serum Albumin Induced by Peptide Ligand

Human serum albumin (HSA ) is an abundant protein in plasma that can bind and transport many small molecules, and the corresponding affinity‐controlled drug delivery shows great advantage in the biological system. Peptide SA06 is a reported ligand comprising 20 amino acids, and is known to non‐covalently bind with HSA to extend the lifetime and improve the pharmacokinetic performance. The structural information of the HSA ‐peptide complex is keen for obtaining molecular insight of the binding mechanism. We studied the secondary structural change and structure‐affinity relations of Peptide SA06 with HSA by using circular dichroism (CD ) spectroscopy in solution. Noticeable allosteric effect can be identified by compositional increase of α ‐helix structures when the peptide was co‐incubated with HSA . Furthermore, the equilibrium dissociation constant of Peptide SA06 with HSA can be determined by CD ‐based method. This work provides structural evidence on the allosteric interaction between peptide ligand and HSA , and sheds light on optimization of therapeutic properties in the affinity‐controlled delivery systems.     

Pathways of Peptide Ion Fragmentation Induced by Vacuum Ultraviolet Light

One Hundred Fifty-Seven nm photodissociation of singly protonated peptides generates unusual distributions of fragment ions. When the charge is localized at the C-terminus of the peptide, spectra are dominated by x-, v-, and w-type fragments. When it is sequestered at the N-terminus, a- and d-type ions are overwhelmingly abundant. Evidence is presented suggesting that the fragmentation occurs via photolytic radical cleavage of the peptide backbone at the bond between the alpha- and carbonyl-carbons followed by radical elimination to form the observed daughter ions.     

荧光标识的环糊精二聚体与小肽衍生物之间的包合行为研究

报道了利用荧光偏振方法研究导硫氰酸盐荧光素（FITC）标识,并由天冬氨酸 、谷氨酸、(1R, 3R)-1-氨基-1,3-二羟基环丁烷和（1R, 3R）-1-氨基-1,3-二 羟基环戊烷衍生物桥联的环糊精二聚体（1～4,作为主体）,在pH = 7.4的水溶液 中与几个低分子量的多肽衍生物:Adm-Lys(Adm)-Arg-Arg 5; Adm-Lys(Adm)-D-Arg- D-Arg 6; Adm-Cha-Arg-Arg 7; Adm-Cha-D-Arg-D-Arg 8（作为客体,其中Arg, Lys, Cha和Adm分别为精氨酸,赖氨酸,β-环已烷丙氨酸和1-羟基金刚烷）之间 的键合常数（K_b)和包合反应的热力学参数（△G°,△H°,△S°）。从主-客体 键合常数的比较、客体嵌入基团的结构与周边环境的考察发现,主、客体之间的键 合能力因客体非进入基团（Arg)空间构型上的变化而有所不同。通过比较主体包结 一对手性异构体的自由能变化增量（-△△G_(DL)°）以及一对手性异构体（L-与 D-）与同一主体的键合常数之比（K_L/K_D),讨论了环糊精二聚体对D-型或L-型多 肽衍生物的手性识别能力。根据各体系T△S°与△H°之间较好的线性关系,探讨 了环糊精二聚体与多肽衍生物之间相互作用的焓-熵补偿行为。     

一种微流控芯片激光诱导荧光检测器的研制及应用

研制了一台正交结构的微流控芯片激光诱导荧光检测器.将较宽的芯片架固定在1个三维操作平台上,可用于检测点的调节和激光光斑校准微调.不同发射波长的半导体激光器以及不同波长的窄带滤光片均可方便更换,以满足不同品种的分析要求.该检测器结构简单、体积小和操作灵活方便,对微流控芯片的尺寸及通道结构适应性强.能在一定程度上满足多种芯片的应用研究需要.