La3+-catalyzed methanolysis of N-aryl-beta-lactams and nitrocefin

The kinetics of the La(3+)-catalyzed methanolysis of N-phenyl-beta-lactam (2) and N-p-nitrophenyl-beta-lactam (3) as well as that of nitrocefin (1) were studied at 25 degrees C under buffered conditions. In the case of 2 and 3, the observed second-order rate constants (k(2)(obs)) for catalysis plateau at pH 7.5-7.8, reaching values of 1 x 10(-)(2) and 35 x 10(-)(2) M(-)(1) s(-)(1) respectively. Potentiometric titrations of solutions of 2 x 10(-)(3) M La(OTf)(3) were analyzed in terms of a dimer model (La(3+)(2)((-)OCH(3))(n)()), where the number of methoxides varies from 1 to 5. The species responsible for catalysis in the pH range investigated contain 1-3 methoxides, the one having the highest catalytic activity being La(3+)(2)((-)OCH(3))(2), which comprises 80% of the total La(3+) forms present at its pH maximum of 8.9. The catalysis afforded by the La(3+) dimers at a neutral pH is impressive relative to the methoxide reactions: at pH 8.4 a 1 mM solution of catalyst (generated from 2 mM La(OTf)(3)) accelerated the methanolysis of 2 by approximately 2 x 10(7)-fold and 3 by approximately 5 x 10(5)-fold. As a function of metal ion concentration, the La(3+)-catalyzed methanolysis of 1 proceeds by pathways involving first one bound metal ion and then a second La(3+) leading to a plateau in the k(obs) vs [La(3+)](total) plots at all pH values. The k(max)(obs) pseudo-first-order rate constants at the plateaus, representing the spontaneous methanolysis of La(3+)(2)(1(-)) forms, has a linear dependence on [(-)OCH(3)] (slope = 0.84 +/- 0.05 if all pH values are used and 1.02 +/- 0.03 if all but the two highest pH values are used). The speciation of bound 1 at a La(3+) concentrations corresponding to that of the onset of the kinetic plateau region was approximated through potentiometric titration of the nonreactive 3,5-dinitrobenzoic acid in the presence of 2 equiv of La(OTf)(3). A total speciation diagram for all bound forms of La(3+)(2)(1(-))((-)OCH(3))(n)(), where n = 0-5, was constructed and used to determine their kinetic contributions to the overall pH vs k(max)(obs) plot under kinetic conditions. Two kinetically equivalent mechanisms were analyzed: methoxide attack on La(3+)(2)(1(-))((-)OCH(3))(n)(), n = 0-2; unimolecular decomposition of the forms La(3+)(2)(1(-))((-)OCH(3))(n)(), n = 1-3.     

Mechanistic studies of La3+ and Zn2+-catalyzed methanolysis of O-ethyl O-aryl methylphosphonate esters. An effective solvolytic method for the catalytic destruction of phosphonate CW simulants

The kinetics of methanolysis of six O-ethyl O-aryl methylphosphonates (6a-f) promoted by methoxide, La3+ and 1,5,9-triazacyclododecane complex of Zn2+(-OCH3) (5:Zn2+(-OCH3)) were studied as simulants for chemical warfare (CW) agents, and analyzed through the use of Br?nsted plots. The beta(lg) values are, respectively, -0.76, -1.26 and -1.06, pointing to significant weakening of the P-OAr bond in the transition state. For the metal-catalyzed reactions the data are consistent with a concerted process where the P-OAr bond rupture has progressed to the extent of 84% in the La3+ reaction and ca. 70% in the Zn2+ catalyzed reaction. The catalysis afforded by the metal ions is remarkable, being about 10(6)-fold and 10(8)-fold for poor and good leaving groups, respectively, relative to the background reactions at pH 9.1. Solvent deuterium kinetic isotope studies for two of the substrates promoted by 5:Zn2+(-OCH3) give kH/kD = 1.0 +/- 0.1, consistent with a nucleophilic mechanism. A unified mechanism for the metal-catalyzed reactions is presented which involves pre-equilibrium coordination of the substrate to the metal ion followed by intramolecular delivery of a coordinated methoxide.     

Mechanistic studies of La3+- and Zn2+-catalyzed methanolysis of aryl phosphate and phosphorothioate triesters. Development of artificial phosphotriesterase systems

The methanolyses of a series of O,O-diethyl O-aryl phosphates (2,5) and O,O-diethyl S-aryl phosphorothioates (6) promoted by methoxide and two metal ion systems, (La3+)2(-OCH3)2 and 4:Zn2+:-OCH3 (4 = 1,5,9-triazacyclododecane) has been studied in methanol at 25 degrees C. Br?nsted plots of the logk2 values vs. pKa for the phenol leaving groups give beta(lg) values of -0.70, -1.43 and -1.12 for the methanolysis of the phosphates and -0.63, -0.87 and -0.74 for the methanolysis of the phosphorothioates promoted by the methoxide, La3+ and Zn2+ systems respectively. The kinetic data for the metal-catalyzed reactions are analyzed in terms of a common mechanism where there is extensive cleavage of the P-XAr bond in the rate-limiting transition state. The relevance of these findings to the mechanism of action of the phosphotriesterase enzyme is discussed.     

Synthesis of some O,O-diethyl S-(β-acylaminoethyl) dithiophosphates

The ethyleneimides of N-phthalyl-D,L-valine, N-phthalyl-D,L-glycine, N-phthalyl-D,L-alanine, N-carbobenzoxy-D,L-valine, N-benzoyl-D,L-leucine, and of the -methyl ester of N-carbobenzoxy-L-glutamic acid and monomethyl succinate were synthesized. A number of O,O-diethyl S-(-acrylaminoethyl) dithiophosphates were obtained by opening the ethyleneimine ring in the ethyleneimides of N-acylated amino acids with diethyl dithiophosphoric acid. The -chloroethylamides of phthalyl-D,L-valine, N-acetyl-D,L-valine, and monomethyl succinate were obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 479–482, April, 1972.     

Billion-fold acceleration of the methanolysis of paraoxon promoted by La(OTf)3 in methanol

The methanolysis of the insecticide paraoxon (2) was investigated in methanol solution containing varying [La(OTf)(3)] (OTf = (-)OS(O)(2)CF(3)) as a function of at 25 degrees C. Plots of the pseudo-first-order rate constants (k(obs)) for methanolysis as a function of [La(OTf)(3)](total) were obtained under buffered conditions from 5.15 to 10.97, and the slopes of the linear parts of these were used to determine the second-order rate constants (k(2)(obs)) for the La(3+)-catalyzed methanolysis of 2. Detailed analysis of the potentiometric titration data of La(OTf)(3) in methanol through fits to a multicomponent equilibrium mixture of dimers of general stoichiometry La(3+)(2)((-)OCH3)n, where n assumes values of 1-5, gives the equilibrium distribution of each as a function of. These data, when fit to a second expression describing k(2)(obs) in terms of a linear combination of individual rate constants k(2)(2:1), k(2)(2:2).k(2)(2:)n for the dimers, allow one to describe the overall catalytic profile in terms of the individual contributions. The most catalytically important species are the three dimers La(3+)(2)((-)OCH3)1, La(3+)(2)((-)OCH3)2, and La(3+)(2)((-)OCH3)3. The catalysis of the methanolysis of 2 is spectacular: a 2 x 10(-3) M solution of [La(3+)](total), at neutral, affords a 10(9)-fold acceleration relative to the base reaction (t(1/2) approximately 20 s at 8.2) with excellent turnover. A mechanism of the catalyzed reaction involving the La(3+)(2)((-)OCH3)2 species is proposed.     

Synthesis and some transformations of O,O-diethyl S-(o-carboran-9-yl) thiophosphite

A synthesis is reported for O,O-diethyl S-(o-carboran-9-yl) thiophosphite and its transformations were studied. A series of new carboranyl esters of seleno- and thioacids of pentavalent phosphorus acids were obtained.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2857–2859, December, 1990.     

3-氰基-2-羟基吡啶磷酸酯的合成

β-酮醛和氰乙酰胺在碱的作用下环化得到3-氰基-2-羟基吡啶,用亚磷酸二乙酯在Atherton-Todd条件下磷酰化可以高产率得到3-氰基-2-羟基吡啶磷酸二乙酯,这些化合物显示了一定的生物活性,并可用于磷酸酯酶抑制剂的活性结构的设计。     

Electrochemical reactions of La(Ni,Cr)O3 and La(Ni,Fe)O3 in acidic aqueous solutions

Voltammetry of immobilised microcrystalline perovskites La(Ni,Cr)O₃ and La(Ni,Fe)O₃ revealed that these oxides yield three types of reactions in acidic aqueous solutions (0.1 M HClO₄): irreversible oxidative dissolution of Cr-rich oxides, irreversible reductive dissolution of Fe-rich oxides, and a quasi-reversible reaction most likely related to alteration of the valencies of Cr, Fe and/or Ni in the solid state. The samples of La(Cr_{1− x} Ni _x )O₃ with x = 0.3 and 0.5 especially showed limited cycling stability that is particularly surprising in the very strongly acidic solution. Received: 4 January 1999 / Accepted: 16 February 1999     

1,4-二(o,o-二乙基硫代磷酰亚胺基)苯的合成及表征

阻燃剂;三氯硫磷;二(o;o-二乙基硫代磷酰亚胺基)苯;合成     

四元轻稀土硝酸盐水溶液体系{H2O+La(NO3)3+Pr(NO3)3+Nd(NO3)3}的热力学研究

在298.15 K条件下, 利用等压法研究了四元轻稀土硝酸盐水溶液{H2O La(NO3)3 Pr(NO3)3 Nd(NO3)3}及其3个二元亚系{H2O La(NO3)3}, {H2O Pr(NO3)3}和{H2O Nd(NO3)3}的热力学性质. 以NaCl或CaCl2水溶液为参考溶液, 测定了不同水活度条件下该四元溶液的渗透系数及各溶质组元的活度系数. 实验结果表明, 上述四元系与其3个二元亚系之间存在简单共性, 在实验误差允许范围之内(|Δ|≤0.0010), 该四元系符合偏理想溶液模型.     

Theoretical study of the gas-phase chemiionization reactions La + O and La + O2

The La + O and La + O 2 chemiionization reactions have been investigated with quantum chemical methods. For La + O 2(X (3)Sigma g) and La + O 2(a (1)Delta g), the chemiionization reaction La + O 2 --> LaO 2 (+) + e (-) has been shown to be endothermic and does not contribute to the experimental chemielectron spectra. For the La + O 2(X (3)Sigma g) reaction conditions, chemielectrons are produced by La + O 2 --> LaO + O, followed by La + O --> LaO (+) + e (-). This is supported by the same chemielectron band, arising from La + O --> LaO (+) + e (-), being observed from both the La + O( (3)P) and La + O 2(X (3)Sigma g) reaction conditions. For La + O 2(a (1)Delta g), a chemielectron band with higher electron kinetic energy than that obtained from La + O 2(X (3)Sigma g) is observed. This is attributed to production of O( (1)D) from the reaction La + O 2(a (1)Delta g) --> LaO + O( (1)D), followed by chemiionization via the reaction La + O( (1)D) --> LaO (+) + e (-). Potential energy curves are computed for a number of states of LaO, LaO* and LaO (+) to establish mechanisms for the observed La + O --> LaO (+) + e (-) chemiionization reactions.     

Electronic Band Structure and Madelung Potential Study of the Nickelates La(2)NiO(4), La(3)Ni(2)O(7), and La(4)Ni(3)O(10)

Tight-binding electronic band structures and Madelung potentials were calculated for La(2)NiO(4), La(3)Ni(2)O(7), and La(4)Ni(3)O(10) to examine why a metal-to-metal transition occurs in the nickelate Ln(4)Ni(3)O(10) (Ln = La, Nd, Pr). La(4)Ni(3)O(10) and La(3)Ni(2)O(7) are each found to have two hidden one-dimensional (1D) Fermi surfaces, which suggests that both compounds should possess a charge density wave instability. Factors leading to hidden 1D Fermi surfaces in the e(g) block bands of the nickelates were discussed.     

LnBaB9O16:Eu3+(Ln=La,Y)的结构与荧光性质

利用电子衍射、X射线衍射和荧光光谱等方法研究了LnBaB₉O₁₆(Ln=La,Y)的结构特性.LnBaB₉O₁₆为单斜晶系,其中LaBaB₉O₁₆的晶胞参数a=1.3660nm,b=0.7882nm,c=1.6253nm,β=106.15°;YBaB₉O₁₆的晶胞参数a=1.3476nm,b=0.7776nm,c=1.6040nm,β=106.38°.荧光光谱研究表明,这两种化合物结构不同,Y³⁺在YBaB₉O₁₆结构中处于中心对称格位,而LaBaB₉O₁₆中La³⁺的格位则无中心对称性.Gd³⁺部分取代LaBaB₉O₁₆:Eu³⁺中的La³⁺可改善Eu³⁺离子的发光性质.LaBaB₉O₁₆:Eu³⁺在真空紫外区的吸收比较弱,这可能与硼氧比较小有关.     

Magnetic studies on (U,La)O2+x solid solutions

Magnetic susceptibilities of La_yU_1−yO_2+x solid solutions with fluorite structure were measured from 4.2 K to room temperature. An antiferromagnetic transition was observed for the solid solutions with lanthanum concentration0 ≤ y ≤ 0.3 in both stoichiometric (x = 0) and hypostoichiometric oxygen range (x < 0). From comparison of the magnetic properties of solid solutions with different oxygen amounts (x < 0, x = 0, x > 0), both oxygen vacancies and interstitial oxygens were found to weaken the magnetic exchange interactions between uranium ions. The Ne´el temperature decreased with decreasing uranium concentration. The variation of the Ne´el temperature of (U, La)O₂ solid solutions with uranium concentration was different from that of (U, Th)O₂ solid solutions. The magnetic moment decreased with decreasing uranium concentration. Its rate was larger than that of (U, Th)O₂ solid solutions and was comparable with that of (U, Y)O₂ solid solutions. The oxidation state of uranium in the solid solutions was examined from the magnetic susceptibility data. The uranium ions were found to be in either the tetravalent or the pentavalent state. The effect of magnetic dilution was larger with La₂O₃ than with Y₂O₃ and/or Sc₂O₃.     

Gel synthesis by transesterification of glycol-modified poly(N-isopropylacrylamide) with O,O-diethyl dithiophosphate

Synthesis of poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate) gels containing pendant mercapto groups via transesterification of 2-hydroxyethyl methacrylate moieties with O,O-diethyl dithiophosphate is described and the gel structure elucidated by ¹H and ³¹P NMR and elemental analysis. The gels respond to changes in their liquid environment.