孔雀绿分子的共振态研究

用"分子空穴"的共振理论,解释了孔雀绿分子的¹H NMR谱图中质子数分配问题。     

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.     

Syntheses and Characterization of Molybdenum Complexes with the (1,3-Dithioliumyl)diphenylphosphine Containing Ligands

Treatment of [Et₄N][Mo(CO)₅(PPh₂CS₂)], 1 with unsaturated organic halides afforded the neutral complexes Mo(CO)₅(PPh₂CS₂R) (R = CH₂CN, 2 ; R = CH₂C≡CH, 3 ). Alkylation reactions take place at the sulfur atom. Protonation of complex 2 and 3 with HBF₄ produced the intramolecular cyclization products [Mo(CO)₅(PPh₂CS₂C₂H₃N)][BF₄], 4 and [Mo(CO)₅(PPh₂CS₂C₃H₄)][BF₄], 5 , respectively. In complex 4 and 5 , two five-membered 1,3-dithiolium rings formed. Protonation of 3 to 5 is not reversible, but deprotonation of 4 by n-BuLi or PPh₃ gave 2 quantitatively. Treatment of 4 with n-Bu₄NF yielded complex Mo(CO)₅PPh₂F, 6 and 2 with 1:1 ratio, but in the reaction of 5 and n-Bu₄NF only compound 6 was formed. All of these complexes are identified by spectroscopic methods.     

Zur Reaktivität des Ferriophosphaalkens (Z)‐[Cp*(CO)2FeP=C(tBu)NMe2] gegenüber Propiolsäureestern HC≡C‐CO2R (R=Me,Et) und Acetylendicarbonsäureestern RO2C‐C≡C‐CO2R (R=Me,Et, tBu)

On the Reactivity of the Ferriophosphaalkene (Z)‐[Cp*(CO)₂Fe‐P=C(tBu)NMe₂] towards Propiolates HC≡C‐CO₂R (R=Me, Et) and Acetylene Dicarboxylates RO ₂C‐C≡C‐CO₂R (R=Me, Et, tBu) The reaction of equimolar amounts of (Z)‐[Cp*(CO)₂Fe‐P=C(tBu)NMe₂] 3 and methyl‐ and ethyl‐propiolate ( 2a, b ) or of 3 and dialkyl acetylene dicarboxylates 1a (R=Me), 1b (Et), 1c (tBu) afforded the five‐membered metallaheterocycles [Cp*(CO) =C(tBu)NMe₂] ( 4a, b ) and [Cp*(CO) =C(tBu)NMe₂] ( 5a—c ). The molecular structures of 4b and 5a were elucidated by single crystal X‐ray analyses. Moreover, the reactivity of 4b towards ethereal HBF₄ was investigated.     

Mixing effects on the protonation of some polycarboxylates in NaClaq + KClaq at different ionic strengths

Protonation constants of succinic, 1,2,3-propanetricarboxylic and 1,2,3,4-butanetetracarboxylic anions were determined in NaCl_aq + KCl_aq mixtures, at three ionic strengths, I = 1.2, 3 and 4.5 mol L⁻¹. Experimental evidences showed that the function log K^H = f(y) (y = [Na⁺]/([Na⁺] + [K⁺])) is not linear, indicating mixing effects on the protonation constants. The Guggenheim zeroth approximation holds that the above function can be written as:

     

An ab initio study of electrophilic aromatic substitution

Proton affinities are calculated at all reactive positions for the normal benzenoid hydrocarbons, benzene, naphthalene, phenanthrene and anthracene, a strained benzenoid hydrocarbon, biphenylene, and a nonalternant hydrocarbon, fluoranthene, and the results are compared to experimental protodetritiation rates. Methods used include PM3 and Hartree-Fock calculations at the STO-3G, 3-21G*, 6-31G* and MP2//6-31G* levels. Generally good agreement is found between theory and experiment with 6-31G* giving the best correlations. Received: 11 June 1998 / Accepted: 3 September 1998 / Published online: 23 February 1999     

13C-NMR and Molecular Orbital Studies of Protonation to Formanilides

The effect of protonation to formanilides was studied by measurements of ¹³C-NMR chemical shifts in CDCl₃ and methanesulfonic acid. It was found that the ¹³C shift of the ring carbon, to which the amide group is attached, exhibits an upfield shift by the protonation, whereas the peaks of the rest of ring carbons and carbonyl carbon shift downfield. The protonation-induced shifts of the ring carbons were found to be roughly correlated with the differences of the total electron densities between formanilides and their monocations. From the comparison between the protonation-induced shifts and the differences of the total electron densities at the carbons, especially at the carbonyl carbon, it is suggested that N-protonation is partly involved, although O-protonation seems to be dominant.     

氧氟沙星的荧光光谱与质子化作用研究

研究了氧氟沙星(Ofloxacin,OFL)在不同pH条件下的荧光光谱、紫外光谱和质子化作用。在强酸性溶液中,OFL分子可以结合两个质子而以三元酸H₃L2+的形式存在,最大荧光发射波长(λ_max)为505 nm。随着pH值升高,OFL的荧光光谱发生变化,在激发光谱中352 nm 形成一等荧光点,同时在紫外吸收光谱中出现等色点,这一光谱特征表明H₃L2+逐渐失去4位C羰基氧结合的质子。在pH 2.5～4范围内,OFL以H₂L+形式存在,λ_max为499 nm。当pH＞4时,随pH值升高,位于499 nm 的荧光发射峰逐渐蓝移至455 nm,在484 nm形成一等荧光发射点,表明C-3位羧基质子的离解。在pH 7左右,OFL以双极离子HL形式存在,λ_max为455 nm,是最强的荧光型体。当pH＞8时,随pH值升高,λ_max由455 nm红移至约475 nm,同时荧光强度下降,表明HL失去哌嗪环N-4上结合的质子。当pH＞10时,OFL以阴离子L-形式存在, 荧光强度随pH值升高而降低,但λmax基本不变,表明介质环境对OFL的荧光性质有一定影响。     

金属硫蛋白加质子常数及与Cd(II)络合常数测定

用pH计和Cd离子选择电极测定了金属硫蛋白的加质子常数及其与Cd(Ⅱ)的络合常数, 用改进的简化络合模型处理实验结果, 得到了去金属硫蛋白(apo MT)中6类不同的加质子基团的数目及其加质子常数。对Cd(Ⅱ)滴定数据的计算表明, MT中两个结构域——α和β对Cd(Ⅱ)的络合常数相差约1000倍。从热力学定量描述了MT中两个结构域结合金属离子选择优先顺序。