Can we trust the experiment? Anisotropic displacement parameters in 1‐(halomethyl)‐3‐nitrobenzene (halogen = Cl or Br)

1‐(Chloromethyl)‐3‐nitrobenzene, C₇H₆NClO₂, and 1‐(bromomethyl)‐3‐nitrobenzene, C₇H₆NBrO₂, were chosen as test compounds for benchmarking anisotropic displacement parameters (ADPs) calculated from first principles in the harmonic approximation. Crystals of these compounds are isomorphous, and theory predicted similar ADPs for both. In‐house diffraction experiments with Mo Kα radiation were in apparent contradiction to this theoretical result, with experimentally observed ADPs significantly larger for the bromo derivative. In contrast, the experimental and theoretical ADPs for the lighter congener matched reasonably well. As all usual quality indicators for both sets of experimental data were satisfactory, complementary diffraction experiments were performed at a synchrotron beamline with shorter wavelength. Refinements based on these intensity data gave very similar ADPs for both compounds and were thus in agreement with the earlier in‐house results for the chloro derivative and the predictions of theory. We speculate that strong absorption by the heavy halogen may be the reason for the observed discrepancy.     

Acid dissociation constants of uridine-5′-diphosphate compounds determined by phosphorus nuclear magnetic resonance spectroscopy and internal pH referencing

The acid dissociation constant (pK_a) of small, biological molecules is an important physical property used for investigating enzyme mechanisms and inhibitor design. For phosphorus-containing molecules, the ³¹P nuclear magnetic resonance (NMR) chemical shift is sensitive to the local chemical environment, particularly to changes in the electronic state of the molecule. Taking advantage of this property, we present a ³¹P NMR approach that uses inorganic phosphate buffer as an internal pH reference to determine the pK_a values of the imide and second diphosphate of uridine-5′-diphosphate compounds, including the first reported values for UDP-GlcNAc and UDP-S-GlcNAc. New methods for using inorganic phosphate buffer as an internal pH reference, involving mathematical correction factors and careful control of the chemical shift reference sample, are illustrated. A comparison of the newly determined imide and diphosphate pK_a values of UDP, UDP-GlcNAc, and UDP-S-GlcNAc with other nucleotide phosphate and thio-analogs reveals the significance of the monosaccharide and sulfur position on the pK_a values.     

Thermodynamics of protonation of AMP,ADP, and ATP from 50 to 125°C

The interaction of adenosine 5-monophosphate (AMP), adenosine 5-diphosphate (ADP), and adenosine 5-triphosphate (ATP) ions with protons in aqueous solution has been studied calorimetrically from 50 to 125°C and 1.52 MPa. At each temperature, the reaction of acidic AMP with tetramethylammonium hydroxide was combined with the heat of ionization for water to obtain the enthalpy of protonation of AMP, while the reactions of HCl with deprotonated tetramethylammonium salts of ADP and ATP were used to obtain the enthalpies of protonation of ADP and ATP. Equilibrium constant K, enthalpy change H^o, entropy change S^o, and heat capacity change C _p ^o values were calculated for the stepwise protonation reactions as a function of temperature. The reactions involving the first protonation of AMP, ADP, and ATP and the third protonation of ADP and ATP were endothermic over the temperature range studied, while that involving the second protonation is exothermic for AMP and ADP, but is exothermic below 100°C and endothermic at 125°C in the case of ATP. Consequently, log K values for the first and third protonation reactions (phosphate groups) increase while those for the second protonation reaction (N₁-adenine) decrease in the cases of AMP and ADP and go through a minimum in the case of ATP as temperature increases. The H^o values for all protonation reactions increase with temperature. The magnitude and the trend for the H^o, S^o, and C _p ^o values with temperature are discussed in terms of solvent-solute interactions. The magnitude of the C _p ^o values for the second protonation is consistent with little interaction between the phosphate ion and the protonated N₁ site of the adenine moiety in AMP, but indicates moderate interaction between these groups in ADP, and strong interaction in ATP.     

Amperometric determination of serum lactate dehydrogenase activity using an ADP-modified graphite electrode

Graphite electrodes modified with a drop-coated layer of polyethyleneimine (PEI) and adenosine diphosphate (ADP) displayed an electrocatalytic response to NADH after the adenine moiety of ADP was electrochemically oxidised. NADH can be detected amperometrically in alkaline solution (pH 9.0) at low applied potentials (+50 mV (Ag/AgCl)). Using a stationary electrode arrangement, linear response for NADH concentrations between 1.0×10⁻⁸ and 1.0×10⁻⁴ M was found, with a response time of 12 s and a detection limit of 8×10⁻⁹ M. The electrode was applied to the amperometric monitoring of the reaction between lactate and NAD⁺ catalysed by lactate dehydrogenase (LDH). A flow injection-amperometric method for the determination of LDH activity in human serum was developed. The method allows a fast and accurate discrimination between pathological and normal LDH activity levels, with a sampling rate of 40 h⁻¹. Quantitative results for a random set of human serum samples were found to be in good agreement with the standard spectrophotometric method.     

三磷酸腺苷、二磷酸腺苷和一磷酸腺苷的毛细管电泳分析研究

研究了三磷酸腺苷(ATP)、二磷酸腺苷(ADP)和一磷酸腺苷(AMP)的毛细管电泳行为，考察了运行缓冲液的pH值、磷酸盐浓度、分离电压、分离温度等因素对这三种化合物的迁移时间和分离效果的影响。结果发现，这些因素对上述三种化合物的分离有显著的影响，在优化的分离条件下，三种物质在10min内可得到分离。方法的检出限为0．125mg／mL，线性范围为0．125～2．00mg／mL。相关系数为0．991～0．997。     

Synthesis of silylene–propenylene oligomers via catalytic polycondensation of diallyldiorganosilanes

Acyclic diene polycondensation (ADP) of diallyldiorganosilanes (CH₂CHCH₂)₂SiR₂ (where R = Me, Ph), in the presence of various ruthenium and rhodium complexes, led predominantly to linear silylene–propenylene oligomers. Ruthenium catalysts (e.g. RuCl₂(PPh₃)₃, RuHCl(CO)(PPh₃)₃, and RuCl(SiMe₃)(CO)(PPh₃)₂) were found to be more efficient than the rhodium ones. The reaction proceeds via preliminary catalytic isomerization of allylsilane to silyl-1-propenes followed by their oligococondensation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3299–3304, 1997     

Growth and electrical characterization of L‐arginine added KDP and ADP single crystals

Potassium dihydrogen orthophosphate (KDP) and ammonium dihydrogen orthophosphate (ADP) single crystals added with L‐arginine have been grown by the solution methods. DC and AC electrical measurements were carried out at various temperatures along both a‐ and c‐ directions. Results indicate an increase of the electrical parameters with the increase of temperature which can be attributed mainly to the increase of thermally generated hydrogen bond vacancies (L. defects). Also, the present study indicates that L‐arginine addition leads to reduction of electrical parameters of KDP and ADP single crystals which can be attributed mainly to the decrease of L‐defects due to creation of additional hydrogen bonds by the impurity in random directions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于化学衍生和CID碎裂模式鉴定蛋白精氨酸-ADP-核糖基化的新方法

建立了一种新的基于碰撞诱导解离（CID）碎裂模式鉴定精氨酸-腺苷二磷酸（ADP）-核糖基化多肽的新方法. 首先,在碱性条件下将精氨酸-ADP-核糖基化血管紧张素-Ⅰ转变为鸟氨酸化血管紧张素-Ⅰ,或在磷酸二酯酶和碱性磷酸酶处理下水解为精氨酸核糖基化血管紧张素-Ⅰ,然后对上述2种衍生物进行基于CID碎裂模式的串联质谱分析. 结果表明,与未衍生的精氨酸-ADP-核糖基化血管紧张素-Ⅰ相比,在鸟氨酸化血管紧张素-Ⅰ和精氨酸核糖基化血管紧张素-Ⅰ的质谱图上发现大部分来自于肽骨架碎裂的离子峰,可提供足够的序列信息以确定精氨酸-ADP-核糖基化位点.     

Cascaded third-harmonic-generation converter based on a single ADP crystal

Based on a specially designed optical structure, an efficient cascaded third-harmonic-generation(THG) output of a 1064-nm, pico-seconds pulse laser is successively realized by using an NH_4H_2PO_4(ADP) crystal that acts as the secondharmonic-generation component and sum-frequency-generation component. The maximum THG output is 1.61 mJ, and the highest conversion efficiency from 1064 nm to 355 nm reaches 35%, which are obviously superior to the results obtained using a KDP crystal under the same circumstance. The further phase-matching analysis indicates that this THG configuration of ADP crystal can be applied to various fundamental wavelengths in a range of 1 μm–1.1 μm. Compared with the previously reported KDP THG converter, which is based on a similar principle, the present ADP THG converter is favorable for large-energy, high-efficiency operation because of the larger effective nonlinear optical coefficient deffand higher laser damage threshold.