A Novel pH-Sensitive MRI Contrast Agent

A tetrasubstituted derivative of 1,4,7,10-tetraazacyclododecane with amide coordinating groups and extended noncoordinating phosphonate groups forms a complex with gadolinium(III) (shown in the picture) which contains one slowly exchanging inner-sphere water molecule (tau(M)=21 μs). The 20-MHz water proton relaxivity of the complex was found to be highly pH dependent. Protonation of the noncoordinating phosphonate groups appears to catalyze prototropic exchange of the bound water protons, thereby providing a mechanism for enhanced water contrast below pH 7.     

Sterically demanding diporphyrin ligands and rhodium(II) porphyrin bimetalloradical complexes

A series of sterically demanding diporphyrins H2(por)-X-(por)H2 ligands that contain spacers (X) with different degrees of flexibility were synthesized from the trimesitylporphyrin derivatives 5-(4-hydroxyphenyl)-10,15,20-trimesitylporphyrin (TMP-OH)H2 (1a) and 5-(2,6-dimethyl-4-hydroxyphenyl)-10,15,20-trimesityl-porphyrin, (DMTMP-OH)H2 (1b). The monomeric porphyrins 1a,b, which have steric demands similar to that of tetramesitylporphyrin, (TMP)H2, and carry a hydroxyl functional group at the para position of one of the mesophenyl substituents, were constructed from reaction of pyrrole with two aromatic aldehydes by a mixed aldehyde condensation approach. The diporphyrins with alkyl diether tethers were obtained stepwise from reactions of the hydroxy functionalized porphyrins 1a,b with dibromides Br(CH2)nBr. The diporphyrin which contains a more rigid m-xylylene spacer, was made directly from reaction of 1b with alpha,alpha'-dibromo-m-xylene. Rhodium was inserted into the porphyrins using Rh2(CO)2Cl2 and converted to dimethyl complexes Me-Rh(Por)-X-(Por)Rh-Me. The dirhodium(II) derivatives .Rh(por)-X-(por)Rh.) were generated by photolysis of the dimethyl complexes and observed to occur as stable bimetalloradicals because the ligand steric demands prohibit Rh(II)-Rh(II) bonding. EPR spectra of the dirhodium(II) derivatives, triphenyl phospine adducts, and dioxygen complexes are reported. The kinetic advantage of bimetalloradical complexes for substrate reactions that have two metal-centered radicals in the transition state is demonstrated by reactions of dihydrogen with dirhodium(II) bimetalloradical complexes.     

Triorganosilyl Ethers of Benzaldehyde,m-Methoxybenzaldehyde and Anisoles

Synthesis of six new triorganosiloxybenzaldehydes, two m-methoxy-(triorganosiloxy)benzaldehydes, and seven methoxy(triorganosiloxy)benzenes are reported. From comparison of the stability of these compounds in the atmosphere, it is concluded that formyl group shows unfavorable influence and methoxy group shows favorable influence on the stability of these compounds. The oposite influences of these two groups on phenoxysilane linkage seems to connect with the oposite directiones of inductive effect of formyl group and resonance effect of methoxy group on the benzene ring.     

Development of a modified beta-cyclodextrin based fluorosensor for dipyridamole

2,6-O-diethyl-β-cyclodextrins were prepared and immobilized onto silica gel to develop a fluorosensor for dipyridamole. The analytical performance characteristics of the proposed sensor for analysis of dipyridamole were as follows: the detection limit was 0.8 nmol/L with a relative standard deviation of 1.4% for 10 determinations of 50 nmol/L of dipyridamole. The modification of β-CD improved the sensitivity and selectivity for measuring dipyridamole. The recommended method has been successfully tested for the determination of dipyridamole in clinical samples (urine and pharmaceutical preparations). Received: 23 January 1997 / Revised: 14 April 1997 / Accepted: 21 April 1997     

Synthesis of fused polycyclic aromatics by palladium-catalyzed annulation of arynes using 2-halobiaryls

The Pd-catalyzed annulation of arynes by 2-halobiaryls and related vinylic halides provides a very efficient, high yielding synthesis of polycyclic aromatic and heteroaromatic hydrocarbons. This process appears to involve the catalytic, stepwise coupling of two very reactive substrates, an aryne and an organopalladium species, to generate excellent yields of cross-coupled products.     

The Substituent Effects of tert-Butyl Radical Addition to 2-Substituted Allyl Chlorides

The relative rates for the addition reactions of tert-butyl radical to 2-substituted ally chlorides I have een determined. The correlation of log k/k₀, vs. σ_m gives a ρ mvalue of 3.59 with correlation coefficient of 0.930. When the substituent CH₂Cl is excluded, correlation coefficient raises to 0.990 and ρ value becomes 3.39. The large p value and the deviation of relative rate of substituent CH₂C1 are discussed.     

Cu(I) catalyst in DMF: an efficient catalytic system for the synthesis of furans from 2-(1-alkynyl)-2-alken-1-ones

The cyclization of 2-(1-alkynyl)-2-alken-1-ones 1 proceeded very smoothly in the presence of alcohols 2 with a catalytic amount of Cu(I)Br in DMF at 80 degrees C, leading to the formation of highly substituted furans 3. The catalytic system reported herein is easy to handle, compared to the previously known system wherein the reaction between 1 and 2 needed to use moisture sensitive gold(III) chloride.     

深圳市1408例儿童发中钙,铁,镁含量调查与分析

用火焰原子吸收法检测了深圳市１４０８例１３岁以下儿童发中钙，铁，镁的元素含量，并探讨了元素含量与年龄，性别的关系，结果显示，性别差异有显著意义，钙，镁含量随年龄增长有相似变化。     

Studies on the determination of diacetyl guanfubase A concentration in rabbit plasma and pharmacokinetics

A gas chromatographic method for monitoring diacetyl guanfubase A in plasma is described. The procedure involved a single solvent extraction of drug from rabbit plasma into ethyl acetate with guanfubase A as an internal standard. The extract was analyzed subsequently on a gas chromatograph equipped with a hydrogen flame ionization detector. The recovery was 86.43% +/- 6.90% (+/- SD); the RSD of within-day and between-day was 2.81%-5.26% and 5.22%-8.24%, respectively; the regression line was linear over the concentration range of 25-200 micrograms/mL, the limit of detection was 10 micrograms/mL. No endogeneous interference was found in chromatograms of the biological samples. This method was applied to the pharmacokinetic study of diacetyl guanfubase A in rabbits.