Systematic prediction of the products and intermediates of isotopic labeling in reaction pathway studies

Isotopic labeling experiments can be highly informative in reaction pathway studies, but inferring the implications of a mechanistic hypothesis can be difficult, especially in the case of complex reactions. We report systematic methods for predicting the distribution of labeled products and intermediates given: (1) a mechanistic hypothesis; and (2) a proposed labeling experiment. The methods have been implemented with MECHEM—a computer aid for elucidating reaction mechanisms. As an illustration, we predict the outcomes of ethylene and propylene hydrogenation and n-heptane dehydrocyclization, for a variety of mechanisms and labeling experiments. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 741–753, 1998     

Graph labeling and radio channel assignment

The vertex-labeling of graphs with nonnegative integers provides a natural setting in which to study problems of radio channel assignment. Vertices correspond to transmitter locations and their labels to radio channels. As a model for the way in which interference is avoided in real radio systems, each pair of vertices has, depending on their separation, a constraint on the difference between the labels that can be assigned. We consider the question of finding labelings of minimum span, given a graph and a set of constraints. The focus is on the infinite triangular lattice, infinite square lattice, and infinite line lattice, and optimal labelings for up to three levels of constraint are obtained. We highlight how accepted practice can lead to suboptimal channel assignments. © 1998 John Wiley & Sons, Inc. J Graph Theory 29: 263–283, 1998     

放射性核素标记单克隆抗体的化学研究进展

研究用放射性核素标记单克隆抗体作为肿瘤的导向药物,是核药物化学领域的研究热点.本文从化学角度介绍了单克隆抗体标记技术发展的概况,包括核素的选择,标记的方法,抗体的偶联修饰以及提高肿瘤/正常组织比的方法。     

加速器生产医用同位素211At及单抗标记

²¹¹At, 半衰期7.2 h, 发射的α粒子具有很高的线性传能密度, 是一种理想的靶向α治疗核素. 利用中国科学院近代物理研究所强流超导直线加速器提供的α束流辐照Bi靶生产²¹¹At, 系统考察了加速器生产²¹¹At的整个流程, 包括加速器辐照、干蒸馏分离、质量分析以及单抗标记. 研究结果表明, 干蒸馏分离²¹¹At的总收率最高达78.53%, 获得的固体²¹¹At产品具有极高的比活度、核纯度以及化学纯度, 其中杂质元素Bi、Cu、Zn、Al含量均低于100 ng/GBq, 且入射粒子能量低于28.2 MeV时, N(²¹⁰At)/N(²¹¹At)值低于10^–5, 研究也实现了²¹¹At在尼妥珠单抗上的标记, 标记率高达94.86%. 基于以上研究我们确立了一套简单、高效的分离方法, 为后续我国²¹¹At的生产和应用奠定了良好基础.     

99mTc放射性药物化学

^99mTc放射性药物在科学研究和临床上已经得到了广泛的应用,但如何发展药效更好的药物以适应临床诊断的需求,依然是亟待解决的问题。新药物配体和金属核的引入以及新的标记方法的发展是目前^99mTc的放射性药物的热点。本文介绍^99mTc放射性药物化学的几种新标记方法,包括羰基锝标记的新型配体和新方法、^99mTc高价配合物的制备和应用等,旨在对有关研究者提供参考。     

Quantitative display of the redox status of proteins with maleimide‐polyethylene glycol tagging

Cysteine oxidation, either biologically reversible or irreversible, is the main posttranslational modification associated with redox signaling and oxidative stress. Maleimide‐polyethylene glycol (m‐PEG) has been used to detect reversibly oxidized proteins by reacting to the reduced cysteine residues leading to mobility shift in immunoblots; a method called PEG‐switch. With PEG‐switch, both reduced and oxidized proteins can be observed on the same immunoblot simultaneously, providing a simple quantitative measurement for protein thiol modifications. In this report, we optimized the assay conditions and exploited the applications of PEG‐switch in quantitation of the extent of protein thiol oxidation in cells in response to H₂O₂ and insulin. In addition, we have proposed a redox scoring system for measuring the redox status of any given protein from the m‐PEG immunoblot. Our results provided quantitative data showing that two cysteine residues of protein tyrosine phosphatase 1B are prone to oxidation following insulin treatment in cultured HeLa cells.     

Efficient Building Blocks for Solid-Phase Peptide Synthesis of Spin Labeled Peptides for Electron Paramagnetic Resonance and Dynamic Nuclear Polarization Applications

Specific spin labeling allows the site-selective investigation of biomolecules by EPR and DNP enhanced NMR spectroscopy. A novel spin labeling strategy for commercially available Fmoc-amino acids is developed. In this approach, the PROXYL spin label is covalently attached to the hydroxyl side chain of three amino acids hydroxyproline (Hyp), serine (Ser) and tyrosine (Tyr) by a simple three-step synthesis route. The obtained PROXYL containing building-blocks are N-terminally protected by the Fmoc-protection group, which makes them applicable for the use in solid-phase peptide synthesis (SPPS). This approach allows the insertion of the spin label at any desired position during SPPS, which makes it more versatile than the widely used post synthetic spin labeling strategies. For the final building-blocks, the radical activity is proven by EPR. DNP enhanced solid-state NMR experiments employing these building-blocks in a TCE solution show enhancement factors of up to 26 for ¹H and ¹³C (¹H→¹³C cross-polarization). To proof the viability of the presented building-blocks for insertion of the spin label during SPPS the penta-peptide Acetyl-Gly-Ser(PROXYL)-Gly-Gly-Gly was synthesized employing the spin labeled Ser building-block. This peptide could successfully be isolated and the spin label activity proved by EPR and DNP NMR measurements, showing enhancement factors of 12.1±0.1 for ¹H and 13.9±0.5 for ¹³C (direct polarization).     

Tag‐Convertible Photocrosslinker with Click‐On/Off N‐Acylsulfonamide Linkage for Protein Identification

The N‐acylsulfonamide group, known as a safety‐catch linker, has been applied to photoaffinity labeling (PAL) using a cinnamate‐type photocrosslinker to improve the efficiency of PAL‐based target identification. A bioorthogonal sulfo‐click reaction was used to stably link a photocrosslinker unit with N‐acylsulfonamide linkage to produce a photoactivatable probe without any protection. In addition, the crosslinked protein was selectively isolated with a small cinnamate tag via linkage disruption upon N‐alkylation. Furthermore, the tag moiety was photochemically converted to a stable coumarin derivative by losing a water molecule, which is a useful property in MS‐based identification.     

Relaxation-based distance measurements between a nitroxide and a lanthanide spin label

Distance measurements by electron paramagnetic resonance techniques between labels attached to biomacromolecules provide structural information on systems that cannot be crystallized or are too large to be characterized by NMR methods. However, existing techniques are limited in their distance range and sensitivity. It is anticipated by theoretical considerations that these limits could be extended by measuring the enhancement of longitudinal relaxation of a nitroxide label due to a lanthanide complex label at cryogenic temperatures. The relaxivity of the dysprosium complex with the macrocyclic ligand DOTA can be determined without direct measurements of longitudinal relaxation rates of the lanthanide and without recourse to model compounds with well defined distance by analyzing the dependence of relaxation enhancement on either temperature or concentration in homogeneous glassy frozen solutions. Relaxivities determined by the two calibration techniques are in satisfying agreement with each other. Error sources for both techniques are examined. A distance of about 2.7 nm is measured in a model compound of the type nitroxide–spacer–lanthanide complex and is found in good agreement with the distance in a modeled structure. Theoretical considerations suggest that an increase of the upper distance limit requires measurements at lower fields and temperatures.