Isolation and structure elucidation of two new alkaloids,pandamarilactonine-C and -D,from Pandanus amaryllifolius and revision of relative stereochemistry of pandamarilactonine-A and -B by total synthesis

Two new pyrrolidine alkaloids, pandamarilactonine-C and -D, were isolated from Pandanus amaryllifolius. Based on the total synthesis of pandamarilactonine-C and its related alkaloid, pandamarilactonine-A, the relative stereochemistry of pandamarilactonine-A and -B, which was previously proposed by spectroscopic analysis, was revised.     

Novel stereoselective synthesis of enantiopure (+)-N-Boc-norpandamarilactonine-A, the intermediate for pandamarilactonines

A novel synthesis of enantiopure N-Boc-norpandamarilactonine-A was established by employing a double ring-closing metathesis of a tetraene derivative, as a key step, where two five-membered rings were constructed in one step. N-Boc-Norpandamarilactonine-A was also converted to ent-norpandamarilactonine-A, and subsequently to pandamarilactonine-A and B.     

Optimization of parameters for semiempirical methods. III Extension of PM3 to Be,Mg, Zn,Ga, Ge,As, Se,Cd, In,Sn, Sb,Te, Hg,Tl, Pb,and Bi

Using a recently developed procedure for optimizing parameters for semiempirical methods,¹ PM3 has been extended to a total of 28 elements. Average ΔH_f errors for the newly parameterized elements are Be: 8.6, Mg: 8.4, Zn: 5.8, Ga: 14.9, Ge: 11.4, As: 8.5, Se: 11.1, Cd: 2.6, In: 11.3, Sn: 9.0, Sb: 13.7, Te: 11.3, Hg: 6.8, Tl: 6.5, Pb: 7.4, and Bi: 10.9 kcal/mol. For some elements the paucity of data has resulted in a method, which, while highly accurate, is likely to be only poorly predictive.     

Certification of the mass fractions of Ca,Cu, Cl,I, Fe,K, Mg,P, Pb,N, Na and Zn in skim milk powder

Analyses of milk and milk products are routinely performed by a number of dairy laboratories to control the quality of these products with regard to e.g. nutritional components and potential exposure to toxic elements. In order to improve and control the quality of such analyses the Community Bureau of Reference (BCR) has organized series of certification campaigns to produce reference material of milk certified for a variety of elements and compounds. The increasing demand is such that the stock of some of these materials is now exhausted. Consequently, the BCR decided to produce a new batch of CRM of skim milk powder certified for its contents of Ca, Cu, Cl, I, Fe, K, Mg, P, Pb, N, Na and Zn (CRM 063R). This material was carefully prepared (spray-drying) and its homogeneity and long term stability was verified. This paper presents the certification work performed.     

Enthalpies of dilution of aqueous solutions of formamide,acetamide, propionamide,andN,N-dimethylformamide

The enthalpies of dilution of aqueous solutions of formamide, acetamide, propionamide,N,N-dimethylformamide, and sucrose have been measured from about 0.15 to 2.0 moles-kg ^–1 at 25.0°C. The results of the enthalpy measurements were used to calculate the pairwise enthalpies of interaction for each compound with itself. The equation of Savage and Wood together with their interaction parameters are used to predict the experimental results. All of the predictions are within the standard deviation of the original correlation of Savage and Wood (±220 J-kg-mole ^–2 ). Detailed examination of the results shows that specific effects are present but they are less than 220 J-kg-mole ^–2 . Results on urea and substituted ureas are used to determine interaction coefficients for a urea group with itself and with another CH ₂ group. The result,H _U,U =–280 andH _{U,CH 2} =29 J-kg-mole ^–2 , is an improvement on the previous arbitrary assignment of parameters for urea interactions.     

Thin-layer chromatographic separation of aldrin,dieldrin, γ-hexachlorocyclohexane,malathion, ethyl-parathion,pentachlorophenol, and of chlordane,dieldrin, γ-hexachlorocyclohexane,malathion, ethyl-parathion,and pentachlorophenol from each other

A thin-layer chromatographic method is reported for the separation of aldrin (or chlordane), dieldrin, γ-hexachlorocyclohexane, malathion, ethyl-parathion, and pentachlorophenol from each other. The procedure, however, does not separate aldrin and chlordane from each other although it does separate either pesticide from the other components. The method employs alumina plates with n-hexane:xylene:benzene:toluene:cyclohexane:methyl cyclohexane (50:50:50:50:50:50:) as developing solvent.     

RM1: a reparameterization of AM1 for H, C, N, O, P, S, F, Cl, Br, and I

Twenty years ago, the landmark AM1 was introduced, and has since had an increasingly wide following among chemists due to its consistently good results and time-tested reliability--being presently available in countless computational quantum chemistry programs. However, semiempirical molecular orbital models still are of limited accuracy and need to be improved if the full potential of new linear scaling techniques, such as MOZYME and LocalSCF, is to be realized. Accordingly, in this article we present RM1 (Recife Model 1): a reparameterization of AM1. As before, the properties used in the parameterization procedure were: heats of formation, dipole moments, ionization potentials and geometric variables (bond lengths and angles). Considering that the vast majority of molecules of importance to life can be assembled by using only six elements: C, H, N, O, P, and S, and that by adding the halogens we can now build most molecules of importance to pharmaceutical research, our training set consisted of 1736 molecules, representative of organic and biochemistry, containing C, H, N, O, P, S, F, Cl, Br, and I atoms. Unlike AM1, and similar to PM3, all RM1 parameters have been optimized. For enthalpies of formation, dipole moments, ionization potentials, and interatomic distances, the average errors in RM1, for the 1736 molecules, are less than those for AM1, PM3, and PM5. Indeed, the average errors in kcal x mol(-1) of the enthalpies of formation for AM1, PM3, and PM5 are 11.15, 7.98, and 6.03, whereas for RM1 this value is 5.77. The errors, in Debye, of the dipole moments for AM1, PM3, PM5, and RM1 are, respectively, 0.37, 0.38, 0.50, and 0.34. Likewise, the respective errors for the ionization potentials, in eV, are 0.60, 0.55, 0.48, and 0.45, and the respective errors, in angstroms, for the interatomic distances are 0.036, 0.029, 0.037, and 0.027. The RM1 average error in bond angles of 6.82 degrees is only slightly higher than the AM1 figure of 5.88 degrees, and both are much smaller than the PM3 and PM5 figures of 6.98 degrees and 9.83 degrees, respectively. Moreover, a known error in PM3 nitrogen charges is corrected in RM1. Therefore, RM1 represents an improvement over AM1 and its similar successor PM3, and is probably very competitive with PM5, which is a somewhat different model, and not fully disclosed. RM1 possesses the same analytical construct and the same number of parameters for each atom as AM1, and, therefore, can be easily implemented in any software that already has AM1, not requiring any change in any line of code, with the sole exception of the values of the parameters themselves.     

Stereochemistry of the oxidation of 1, 2, 3, 5, 6, 7, 8, 8a-octahydro-1-naphthoic acids

Summary It was shown that the oxidation of syn- and anti-1,2,3,5,6,7,8,8a-octahydro-1-naphthoic acids with peroxyacetic acid and with osmium tetraoxide proceed stereospecifically from the side opposite to that of the carboxy group. On the other hand, the oxidation of syn-cis-1,2,3,5,6,7,8,8a-octahydro-1, 2-naphthalenedicarboxylic acid goes in both of the possible sterically different directions with formation of isomeric- and-epoxides.     

电感耦合等离子体质谱法(ICP-MS)测定稀土矿中钇、镧、铈、镨、钕、钐、铕、钆、铽、镝、钬、铒、铥、镱、镥和钪量

通过用四酸与微波消解法溶解样品对比,建立了用硝酸、盐酸、氢氟酸、高氯酸分解样品,采用电感耦合等离子体质谱法(ICP-MS)测定稀土矿中16种元素含量。方法采用_¹⁰³Rh作为内标消除干扰,确定了最优测定条件,16种稀土元素检出限为0.0029-0.0099ng/mL,测定范围为0.0005-0.020%。精密度试验、加标回收试验及标准物质检测,结果验证了方法的可行性及准确性。该方法简单易操作,结果可靠,能满足实验分析要求。