Synthesis and EPR Studies of 2′‐Deoxyuridines with Alkynyl,Rodlike Linkages

Sonogashira coupling of diacetyl 5‐ethynyl‐2′‐deoxyuridine with diacetyl 5‐iodo‐2′‐deoxyuridine gave the acylated ethynediyl‐linked 2′‐deoxyuridine dimer ( 3 b ; 63 %), which was deprotected with ammonia/methanol to give ethynediyl‐linked 2′‐deoxyuridines ( 3 a ; 79 %). Treatment of 5‐ethynyl‐2′‐deoxyuridine ( 1 a ) with 5‐iodo‐2′‐deoxyuridine gave the furopyrimidine linked to 2′‐deoxyuridine (78 %). Catalytic oxidative coupling of 1 a (O₂, CuI, Pd/C, N,N‐dimethylformamide) gave butadiynediyl‐linked 2′‐deoxyuridines ( 4 ; 84 %). Double Sonogashira coupling of 5‐iodo‐2′‐deoxyuridine with 1,4‐diethynylbenzene gave 1,4‐phenylenediethynediyl‐bridged 2′‐deoxyuridines ( 5 ; 83 %). Cu‐catalyzed cycloisomerization of dimers 4 and 5 gave their furopyrimidine derivatives. One‐electron addition to 1 a , 3 a , and 4 gave the anion radical, the EPR spectra of which showed that the unpaired electron is largely localized at C6 of one uracil ring (17 G doublet) at 77 K. The EPR spectra of the one‐electron‐oxidized derivatives of ethynediyl‐ and butadiynediyl‐linked uridines 3 a and 4 at 77 K showed that the unpaired electron is delocalized over both rings. Therefore, structures 3 a and 4 provide an efficient electronic link for hole conduction between the uracil rings. However, for the excess electron, an activation barrier prevents coupling to both rings. These dimeric structures could provide a gate that would separate hole transfer from electron transport between strands in DNA systems. In the crystal structure of acylated dimer 3 b , the bases were found in the anti position relative to each other across the ethynyl link, and similar anti conformation was preserved in the derived furopyrimidine–deoxyuridine dinucleoside.     

Porphyrin‐Ryleneimide Hybrids: Low‐Bandgap Acceptors in Energy‐Transfer Cassettes

Energy‐transfer cassettes consisting of naphthaleneimide‐fused metalloporphyrin acceptors (M=Zn and Pd) and BODIPY donors have been designed and synthesized. These systems have rigid pseudo‐tetrahedral structures with a donor‐acceptor separation of ca. 17.5 Å. Spectroscopic investigations, including femtosecond transient absorption measurements, showed efficient excitation energy transfer (EET) occurring according to the Förster mechanism. Strong fluorescence of the donor units and significant spectral overlap of the donor and acceptor subunits are prerequisites for the efficient EET in these systems.     

Exact penalty functions method for mathematical programming problems involving invex functions

In this paper, some new results on the exact penalty function method are presented. Simple optimality characterizations are given for the differentiable nonconvex optimization problems with both inequality and equality constraints via exact penalty function method. The equivalence between sets of optimal solutions in the original mathematical programming problem and its associated exact penalized optimization problem is established under suitable invexity assumption. Furthermore, the equivalence between a saddle point in the invex mathematical programming problem and an optimal point in its exact penalized optimization problem is also proved.     

Optimality and duality for nonsmooth multiobjective programming problems with V-r-invexity

In the paper, we consider a class of nonsmooth multiobjective programming problems in which involved functions are locally Lipschitz. A new concept of invexity for locally Lipschitz vector-valued functions is introduced, called V-r-invexity. The generalized Karush–Kuhn–Tuker necessary and sufficient optimality conditions are established and duality theorems are derived for nonsmooth multiobjective programming problems involving V-r-invex functions (with respect to the same function η).     

柱塞泵油膜压力分析的高效有限单元法

利用有限单元法,数值分析轴向柱塞泵缝隙高度可变时阀门板上油膜的压力分布.缝隙中油压变化的确定,通常是应用Pasynkow 润滑理论中的Reynolds方程.使用基于有限单元法的自编程序,数值地求解该方程.为了提高结果的精度,基于解的残差估计,应用了加密的自适应网格.给出了依赖于泵的几何条件和工作参数的计算结果.     

DFT analysis of co-alkyl and co-adenosyl vibrational modes in B12-cofactors

Density functional theory (DFT)-based normal mode calculations have been carried out on models for B12-cofactors to assign reported isotope-edited resonance Raman spectra, which isolate vibrations of the organo-Co group. Interpretation is straightforward for alkyl-Co derivatives, which display prominent Co-C stretching vibrational bands. DFT correctly reproduces Co-C distances and frequencies for the methyl and ethyl derivatives. However, spectra are complex for adenosyl derivatives, due to mixing of Co-C stretching with a ribose deformation coordinate and to activation of modes involving Co-C-C bending and Co-adenosyl torsion. Despite this complexity, the computed spectra provide a satisfactory re-assignment of the experimental data. Reported trends in adenosyl-cobalamin spectra upon binding to the methylmalonyl CoA mutase enzyme, as well as on subsequent binding of substrates and inhibitors, provide support for an activation mechanism involving substrate-induced deformation of the adenosyl ligand.     

Progressive-convergent elucidation of stereochemistry in complex polyols. The absolute configuration of (-)-sagittamide A

The absolute stereostructure of sagittamide A (1), a O-hexacetyl long-chain hexahydroxy-alpha,omega-dicarboxylic acid, was assigned using a progressive-convergent approach that integrates three powerful regimens for stereochemical analysis of acyclic natural products: J-based analysis, 13C NMR universal database comparisons, and exciton coupling circular dichroism.     

Synthesis and cytostatic activity of 4,7-dihydroxythioaurone derivatives. Effect of B ring substitution on the activity

Biological activity of thioaurones was not tested so far and the group constitute completely unexplored source of new molecules of pharmacological interest. We report synthesis and evaluation of cytotoxic activity of thioaurone derivatives bearing p-hydroquinone system in ring A. Their activity was found to depend strongly on substitution pattern, so eventually both the activity and pharmacokinetic parameters of the molecules could be tailored by further structural modifications.     

Search of structure and ligands exchange for palladium(II) complexes with N-allylimidazole; X-ray and solid-state/solution NMR studies

Two coordination compounds of palladium(II) with N-allylimidazole (l) of the general formula [PdL₄]Cl₂ · 3H₂O (1) and trans-[PdL₂Cl₂] (2) have been synthesized. The crystal and molecular structure of complexes 1 and 2 was established by single-crystal X-ray diffraction analysis. The X-ray structural data were supplemented by solid-state ¹³C NMR measurements (CP MAS and PASS 2D). The 1D and 2D NMR studies in solution reveal that complex 1 is unstable at room temperature and undergoes reversible decomposition to 2. The method for how to preserve a complex with four allyl-imidazole ligands in solution is shown.