Hydration scheme of uracil and cytosine

The comparison of a pure electrostatic approximation and complete supermolecule SCF ab initio computations on the hydration scheme of uracil and cytosine shows that the electrostatic procedure is capable to reproduce the general aspects of the results of the supermolecule treatment provided that different distances of shortest approach be adopted for the distances between the oxygen of water and the nitrogen of NH₂ or NH groups or the oxygen of C-O groups on the one hand and the oxygen of water and pyridine-type nitrogens on the other hand.     

Synthesis of 3′-fluoro-4′-amino-hexitol nucleosides with a pyrimidine nucleobase as building blocks for oligonucleotides

The synthesis of 3′-fluoro-4′-amino-hexitol nucleosides with a uracil and cytosine nucleobase was performed. The synthesis started from 1,5:2,3-dianhydro-4,6-benzylidene-allitol and afforded the target compounds in 15 steps. These protected hexitol nucleosides are valuable building blocks for the preparation of a new class of oligonucleotides.     

Iodine/persulfate-promoted site-selective direct thiolation of quinolones and uracils

A simple and general method for direct thiolation of 4-quinolones with disulfides or thiols under I₂/K₂S₂O₈ system has been developed. Under the optimal conditions, the C–S bond coupling can take place effectively with good to decent yields and excellent regioselectivity of the S-linked products. The established metal-free site-selective approach was also applicable to transform a range of uracil substrates to the thio-substituted products under mild conditions. Further transformation to the sulfone derivatives can be conveniently performed in one-pot. These easy-to-handle protocols represent a useful and interesting synthetic alternative with good substrate scope and functional group compatibility.     

Molecular Dynamics Simulation and Density Functional Theory Study of Chemisorption of Propranolol Optical Isomers on a Uracil‐modified Carbon Paste Electrode

To reveal the nature of the interaction of the optical isomers of propranolol with the surface of carbon paste electrodes modified by uracil, we performed a combined computational and experimental study. Our study comprised the different modes of complexation between propranolol and uracil molecules covering the carbon paste electrode within two approaches: molecular dynamics simulation (MD ) and quantum mechanics (QM) modeling. A graphene layer was used as a model of the carbon paste electrode. The computations showed that uracil modification of the carbon paste electrode surface enhanced the selectivity toward the D‐isomer of propranolol as compared to the unmodified case. These theoretical results agree with our voltammetric measurements.     

紫外光照下尿嘧啶在磷酸盐水溶液中的新型光化学反应研究

在中压汞灯光照下,无机磷酸盐能促进尿嘧啶水溶液(pH=8)的光解作用(磷酸盐效应),发生嘧啶碱基的光解取代反应,主要光解产物为6-磷酸基尿嘧啶(C₄H₅N₂O₆P).通过元素分析,UV,IR,EIMS,¹HNMR,¹³CNMR,³¹PNMR等测试手段和方法,确定了光解产物的组成和结构.实验表明,在中压汞灯的发射光谱(连续光谱)中,对磷酸盐效应起作用的波长为190～220nm.     

四氯苯醌与嘧啶类核酸碱基的光化学氢抽取和电子转移反应

采用纳秒时间分辨的激光闪光光解实验技术,研究了四氯苯醌(TCBQ)分子与两种嘧啶核酸碱基(胸腺嘧啶和尿嘧啶)分子在355nm激发下的光化学反应动力学. 355 nm将TCBQ分子布居到激发三重态³TCBQ^*,高反应活性的³TCBQ^*与碱基分子发生两个平行的反应,氢抽取反应和电子转移反应,分别对应生成瞬态光谱上观测到的两个光反应产物TCBQH·和TCBQ·^-. 这两个反应同时生成的碱基自由基和碱基阳     

Copper(II) complexes with the N,N,O-tridentate ligand 6-amino-5-formyl-1,3-dimethyluracilato-(N6)-benzoylhydrazone: synthesis, spectral and XRD studies

From reactions between different Cu(II) salts and the Schiff base 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone (H₂BEZDO) in alcohol, six new copper complexes with simplified formulas [Cu(HBEZDO)(H₂O)(MeOH)]NO₃ (1), [CuCl(HBEZDO)(DMF)] (2), [CuBr(HBEZDO)]·2H₂O (3), CuBr(HBEZDO) (4), Cu(ClO₄)(HBEZDO)·H₂O (5), and Cu(SO₄)_1/2(HBEZDO)·1 H₂O (6) were isolated. The structures of compounds 1, 2 and 3 have been established by means of XRD diffraction methods. In the three compounds, the Schiff base acts as a tridentate monodeprotonated ligand through the N(6), N(51) and O(52) atoms, making two five- and six-membered chelate rings. In the structure of 1 and 2, the solvent molecules are coordinated giving square-based pyramidal environments, with the basal plane completed by a MeOH (1) or Cl (2) and the apical positions occupied by the oxygen atom of a water (1) or a DMF molecule (2). The molecular unit of the complex [CuBr(HBEZDO)]·2H₂O (3) is defined by a square-plane containing the three donor atoms of the organic ligand and a bromide ligand (Cu–Br 2.384 Å), but there is a stronger tetragonally elongated pyramidal geometry around the metal, the apical position of the polyhedron being occupied by a weakly bound-to-copper bromine atom (3.086 Å) of a neighbouring molecule. This fact gives the appearance of an apparent dimer with very asymmetric bromine bridges, in which there are no exchange interactions between metal centres. Also, infrared, magnetic and EPR data of the isolated complexes are reported.     

Design,Synthesis, and Herbicidal Evaluation of Novel Uracil Derivatives Containing 1,3,4‐Thiadiazolyl Moiety

Uracil derivatives, such as commercial herbicides butafenacil and benzfendizone, have been identified as inhibitors of protoporphyrinogen oxidase (Protox, EC 1.3.3.4), one of the most important action targets of herbicides. In order to search for novel Protox inhibitors with high efficacy, broad‐spectrum activity, and safety to crops, commercially herbicide butafenacil was used as lead compound for further optimization; a series of title compounds 8a , 8b , 8c , 8d , 8e , 8f , 8g , 8h , 8i , 8j , 8k , 8l , 8m , 8n were designed and synthesized by introducing 1,3,4‐thiadiazole moiety into the uracil skeleton. The preliminary bioassays (in vitro) indicated that most of the target compounds displayed better inhibition against Echinochloa crus‐galli than Brassica campestris. The greenhouse bioassay results indicated that most of the compounds tested exhibited good‐to‐excellent herbicidal activities against B. campestris, A. retroflexus, E. crusgalli, and D. sanguinalis in pre‐emergence treatment at a dose of 1500 g/ha, for example, compound 8d showed 100% inhibition against the four plants tested in pre‐emergence treatment at a dose of 1500 g/ha. So, these types of skeletons can be used as valuable lead compounds for the development of a pre‐emergent herbicide.     

Accurate measurements of peak variances: importance of this accuracy in the determination of the true corrected plate heights of chromatographic columns

The true efficiency of a column is derived from the differences between the variances of the peak profiles of the same compound recorded in the presence and the absence of the chromatographic column. These variances are usually derived using one of three methods: (1) the retention time of the peak apex and its half-height width; (2) the moments of the best fit between the experimental data and a hybrid response function, e.g., an exponentially convoluted Gaussian; or (3) the exact moments of the experimental band profiles. Comparisons of the results of these methods show that the first method is always inaccurate because all the band profiles recorded are strongly tailing. The peak fit method is accurate only for 4.6mm I.D. columns operated with instruments having low extra-column volume but fails for short narrow-bore columns due to the severe tailing of peaks passing through the complex channels of the extra-column volumes and to the inaccuracies in the fit of experimental data to the selected function. Although far better, the moment method may be inaccurate when the zero dead volume union used to measure the extra-column peak variances has a higher permeability than the column, causing the upstream part of the instrument to operate under comparatively low pressures.     

Structure and dynamics of pyrimidine-based macrocycles in solution

The conformational structure of macrocycles obtained from two thiopyrimidine and uracil nucleic acids linked by polymethylene spacers is determined by the length of the spacers, intramolecular NH bonding, pH and solvent. In CDCl₃, NH-OC hydrogen bonding can impact the overall stabilization of the folded conformation, however spatial preorganization to such hydrogen bonding is a prerequisite. Protonation leads to disruption of intramolecular hydrogen bonds, destabilization of the folded conformation and to strong counterion assisted self-aggregation of macrocyles which can be destroyed in polar solvents.