Biosynthesis of psilotin from [2′,3′-13C2,1′-14C,4-3H]phenylalanine studied with 13C-NMR

The 6-phenyl-dihydro-α-pyrone moiety of psilotin is formed from [2′,3′-¹³C₂,1′-¹⁴C,-4-³H]phenylalanine in the plant $\text{Psilotum}$$\text{nudum}$ with retention of all the isotopes.     

Laser spectroscopy ofD3

The D₃ was formed in a hollow cathode discharge in D₂. Transitions between the states 3p²E′, 3p²A″₂ and 2S²A′₁ were stimulated by dye-laser radiation. The resonances were monitored by observng the laser-induced change of the emission from selected levels of D₃. Many new lines were observed and assigned.     

31P-15N spin-spin coupling as a probe for the assignment of absolute configuration in RP- and SP-thymidine cyclic 3′,5′-phosphordimethylamidates

The synthesis of both diastereomeric ¹⁵N-labelled on the dimethylamino function thymidine 3′,5′ cyclic N,N-dimethylphosphoramidates is described. The applicability of ¹J_31P-¹⁵N to the configurational assignments at P-atom is demonstrated.     

DETERMINATION OF THE BINDING CONSTANT OF H14 CO−3 TO THE PHOTOSYSTEM II COMPLEX IN MAIZE CHLOROPLASTS: EFFECTS OF INHIBITORS AND LIGHT

The binding (dissociation) constant for HCO^?₃ to the photosystem II complex in maize chloroplasts is approximately 80 μM. One HCO^?₃ binds per 500–600 chlorophyll molecules. In the dark, formate is a competitive inhibitor of HCO^?₃ binding, while 3-(3′,4′-dichlorophenyl)-1, 1-dimethylurea (DCMU) inhibits HCO^?₃ binding non-competitively. Light decreases HCO^?₃ binding in the presence of formate. Light increases the binding of HCO^?₃ in the presence of DCMU. The high binding constant for HCO, discriminates strongly among the various hypotheses attempting to explain the “bicarbonate-effect” on photosystem II. The proposal by Stemler and Jursinic (Arch. Biochem. Biophys. 221, 227–237 1983), that HCO^?₃ is one of a class of monovalent anionic inhibitors of photosystem II, is favored. These anions compete for a specific binding site on the photosystem II complex.     

Vacuum UV emission by electronically-excited N2: The radicative lifetime of the N2(a′1Σ−u state

A measurement of the electronic transition moment variation for the N₂(a'¹Σ^?_uX¹Σ^+g) band system has allowed a reassessment of the radiative lifetime of N₂(a′). Relaxation to N₂(a′,υ=0) is established as the major channel for quenching of N₂(a¹Π_g, υ = 0) molecules by Ar.     

Permanganate oxidation of N6,N6,8-trisubstituted-2′,3′,5′- tri-o-acetyladenosines

Oxidation of 2′,5′ ,5′-tri-O-aaetyl derivatives of N⁶,N⁶-dialkyl- adenosines(3a-g) uifh KMnO₄ in 50% AcOH gave both the mono(5a-g) and didealkyl derivatives(6a-c); it uas conclusively proved that one and two methylene groups of the title nucleosides(2a-g) in the α position to the exocyclic nitrogen atom were simultaneously oxidized.     

The structure of C2H5InBr2 · tmen,C2H5InI2 · tmen (tmen = N,N,N,′,N′-tetramethylethanediamine) and [(C6H5)4P][C2H5InI3] in solution and in the solid state

The ¹H NMR spectra of C₂H₅InBr₂ · tmen (1) C₂H₅InI₂ · tmen (2) (tmen = N,N,N′,N′-tetramethylethanediamme) and [(C₆H₅)₄P][C₂H₅InI₃] (3) show only a broad singlet for the ethyl protons at 60 MHz. Spectra run at 400 MHz resolve these into a triplet + quartet for 1 and 3. The structure of each compound has been determined by X-ray crystallography; 1 and 2 are five-coordinate species, with InC₂N₂X (X = Br, I) nuclei, while 3 consists of [(C₆H₅)₄P]⁺ cations and anions whose InCI₃ nucleus has C_3v, symmetry.     

Preparation of diastereomeric thymidine 3′,5′-cyclic methylphosphonates. Assignment of RP and SP configurations by 13C NMR

The diastereomers of thymidine 3′,5′-cyclic methylphosphonate have been prepared and separated. A use of ¹³C NMR for the assignment of their phosphorus configurations is demonstrated which should be generally applicable to P-derivatized cyclic nucleotides.     

O-alkylation de la Quercetine et synthese de la tetra o-ethyl-3,7,3′,4′ O-ethyl [3H]-5 quercetine

An efficient procedure is described for alkylation of quercetin with alkylhalides by use of tetraethylammonium fluoride in DMF or HMPT. The method is applied successfully to the preparation of 3,7,3′,4′,tetra-O-ethyl 5 [³H] O-ethylquercetin with a specific radioactivity of 45 Ci/mmol.     

Resonance in the rotational dependence of the isotope-selective reaction between IiCl(A 3Π1) and acetylene

The rotational dependence of the isotope selective reaction between IⁱCl(A ³Π_l, υ′, J′) and acetylene (C₂H₂, C₂D₂) forming the photoaddition product 1,2-iodo-chloro-ethyene was studied for ν′ = 19 and ν′ = 20. The enrichment factor in the photoproduct shows resonances for J′ = 32, ν′ = 19 and J′ = 6, υ′ = 20.     

Diatomics-in-molecules potential energy surfaces for the collision-induced dissociation of excited Li2(1Πu) by helium atoms

The 1 ¹A″, 2 ¹A″, 3 ¹A′, 4 ¹A′, and 5 ¹A′ potential energy surfaces (PES) relevant to the collision-induced dissociation (CID) process $\text{Li}{}_2\text{(}{}^1\text{Π}{}_{\mathrm{u}}\text{) +}\text{He}\text{(}{}^1\text{S}{}_{\mathrm{g}}\text{) →}\text{Li}\text{(}{}^2\text{S}{}_{\mathrm{g}}\text{) +}\text{Li}\text{(}{}^2\text{P}{}_{\mathrm{u}}\text{) +}\text{He}\text{(}{}^1\text{S}{}_{\mathrm{g}}\text{)}$ are approximated by three diatomics-in-molecules models differing from each other in the source of diatomic input. The semi-empirical model, the most realistic of the three, shows the CID to depend critically on the position of avoided crossings on the PES and on the magnitude of the non-adiabatic coupling, which is estimated numerically. The ¹A″ calculations support a qualitative two-step mechanism recently proposed by Poppe and Whitton. The ¹A′ surfaces exhibit a degree of complexity which precludes a simple picture of the CID process. The results suggest that only a quantum scattering treatment or perhaps a very detailed surface-hopping trajectory calculation will be adequate for the interpretation of the experimental observations on this reaction, and the estimation of the cross sections.     

A general synthesis of side chain derivatives of Δ9-thc

The synthesis of (6aR, 10aR)-trans-3-[1′,3′-dithian-2′-yl]-6a,7,8,10a-tetrahydro-6,6,9- trimethyl-6H-dibenzo[b,d]pyran-l-ol t-butyldimethylsilyl ether ($\text{4b}$) is reported. The use of this compound as a source of side chain derivatives of cannabinoids is illustrated by syntheses of 1′-,2′-,3′- and 4′-hydroxy-Δ⁹-THC, and 3-carboxy-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-o1 ($\text{6}$).     

1H NMR studies of U(IV)-1,2-cyclohexane(dinitrilo)-N,N,N′,N′-tetraacetic acid complexes

¹H NMR spectrum of a U(IV)-trans-1,2-cyclohexane(dinitrilo)-N,N,N′,N′-tetraacetic acid (CyDTA) complex (prepared by dissolving U(IV)(Cy     

Synthèse et structure cristalline d'un nouvel oxyde mixte FeV2O6H0.5 relation avec la structure type diaspore

Single crystals of a new compound, FeV₂O₆H_0.5, have been obtained by hydrothermal synthesis at 650°C and 2 kbar. An electron microprobe analysis indicated that the chemical formula is FeV₂O₆. This compound has an orthorhombic symmetry, space group P2₁2₁2₁ with Z = 4. The unit cell dimensions are

$\text{a = 4.891}\text{A}\text{?}\text{, b = 9.553}\text{A}\text{?}\text{, c = 8.786}\text{A}\text{?}$

These parameters are related to a′, b′, c′ of the diaspore-type VO₂ by the relations: $\text{a ? a′, b ? b′, c ? 3c′}$. The structure, based on single crystal data, has been determined from Patterson and Fourier syntheses. A structural refinement gave a final R-factor of 2.4%. The new structure can be deduced from that of the diaspore-type VO₂, by displacement of one third of the cations from an octahedral site to an adjacent unoccupied tetrahedral site, which is located in a channel parallel to the c axis. The calculation of the cation and oxygen valences indicated that some O^2? were in fact OH^?. This conjecture was supported by thermogravimetric analysis. The chemical formula was indeed Fe³⁺₂V³⁺V⁴⁺V⁵⁺₂O₁₁(OH). Some intensities of the powder diffraction lines changed strongly when the preparation temperature was reduced from 650°C to 300°C. This was explained by an increase of the hydrogen ratio in the formula FeV₂O₆H_x, which implies a structural change. The different phases FeV₂O₆H_x can be considered as solid solutions between two extreme phases with different structure: one with the present one and the other with a diaspore-type structure.     

四种天然槲皮素-3-糖苷的合成

以芦丁为原料, 经苄基化、酸水解得到关键中间体3′,4′,7-O-三苄基槲皮素(3), 3与相应的1-溴代乙酰糖在四丁基溴化铵催化下在氯仿-0.25 mol•L^－1 K₂CO₃溶液中缩合成相应的糖苷, 脱去保护基得天然槲皮素3-糖苷类化合物 1a～1d. 其结构经IR, ¹H NMR, MS及元素分析确证.     

Low-temperature phases of the solid electrolyte Ag26I18W4O16

Single crystal X-ray diffraction photographs taken with a Buerger precession camera, at temperatures 250, 214, and 122 K, corroborate the existence of three low-temperature phases of Ag₂₆I₁₈W₄O₁₆. These phases are labeled α′, β, and γ in order of decreasing temperature. The α′ phase is monoclinic, space group P2₁, Z = 2; the β phase is triclinic, space group $\text{P}\text{1}$ or P1, Z = 2; and the γ phase is triclinic, space group P1, Z = 1. Lattice constants at the aforementioned temperatures are given. Twins in the β and γ phases are related by the albite and pericline laws, as are twins in the feldspars. The highest symmetry known to be attained by the (W₄O₁₆)^8? entity is 2(C₂), which, strictly, it must lose at the transition to the α′ phase.     

Synthesis of some oxadiazole derivatives of d-mannose

The syntheses of 2-methyl-5-[1′,2′,3′,4′,5′-penta-O-benzoyl-D-manno-pentitol-1′-yl]-1,3,4-oxadiazole and 5-methyl-3-[1′,2′,3′,4′,5′-penta-O-benzoyl-D-manno-pentitol-1-′yl]-1,2,4-oxadiazole, as well as their intermediate products, are described. Their ¹H and ¹³C nmr and ms spectra are presented and their preferential conformation in solution are proposed.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Alkali Metal/Ammonia Reductions of Ketones Should Be Run in the Presence of Ammonium Ion

Reduction of (+)-[3,3?²H₂]camphor ([3,3?²H₂] 1 ) with lithium, sodium or potassium in ammonia and a co-solvent gave; 1) the enolate of [3,3?²H₂] 1 and the alcoholates of (?)-[2,3,3?²H₃]isoborneol ([2,3,3?²H₃] and (+)-[2,3,3?²H₃]borneol ([2,3,3?²H₃] 3 ); 2) the alcoholates of [3,3?²H₂] 2 and [3,3?²H₂] 3 ; 3) the dialcoholates of the pinacols [3,3,3′,3′?²H₄] 4 and [3,3,3′,3′?²H₄] 5 . It is proposed that these are formed from the ketyls [3,3?²H₂] 1 - M⁺, by: 1) disproportionation; 2) H-atom abstraction from the medium; 3) dimerization. Protonation upon work-up afforded [endo?3²H] 1 , [2,3,3?²H₃] 2 , [2,3,3?²H₃] 3 ,[3,3?²H₂] 2 , [3,3?²H₂] 3 , [3,3,3′,3′?²H₄] 4 and [3,3,3′,3′?²H₄] 5 . Pinacol [3,3,3′,3′?²H₄] 5 was the main and pinacol [3,3,3′,3′?²H₄] 4 a minor product in the reductions with lithium and both were minor products in the reductions with sodium; pinacols were not formed in the reductions with potassium. Parallel reductions of 1 , unlabeled, analogously led to 2 , 3 , 4 and 5 , and the ratios 2/3 differed from the ratios ([2,3,3?²H₃] 2 +[3,3?²H₂] 2 /([2,3,3?²H₃]+[3,3?²H₂] 3 ) under certain conditions. Different values for these ratios were found in the reductions with each metal, all of which corresponded to low overall diastereoselectivities. Reactions 1 and 3 persisted when the reductions were carried out in ammonia/water/co-solvent mixtures and the enolate formed via reaction 1 was protonated and the resulting [endo-3-²H] 1 recycled. Reaction 2 cannot be monitored under these conditions. Reactions 1 and 3, and by inference also reaction 2, were almost completely suppressed when analogous reductions were carried out in the presence of ammonium chloride, [3,3?²H₂] 2 and [3,3?²H₂] 3 being obtained almost exclusively, in a 6: 94 ratio. It is proposed that the mechanism outlined in House [1] was dominant when, and only when, ammonium ion was the proton source; it may have competed when water was the proton source.     

The luminescence of Pr3+ in BaY4Si5O17

The cell constants of four new monoclinic compounds BaR₄X₅O₁₇ (R = Y, Gd; X = Si, Ge) are given. The luminescence of various RE activators in the silicates is reported. Pr³⁺-activated BaY₄Si₅O₁₇ shows efficient ultraviolet 5d → 4f emission and weak 4f → 4f emission (mainly red luminescence from the ¹D₂ level). The 5d → 4f emission is ascribed to Pr³⁺ on Y sites, the 4f → 4f emission to Pr³⁺ on Ba sites. Energy transfer from Pr³⁺ to Gd³⁺ has been observed. Gd³⁺ plays an intermediate role in the energy transfer from Pr³⁺ to Sm³⁺ and to Dy³⁺ in BaGd₄Si₅O₁₇. Upon activation with Tb³⁺ the silicates show characteristic green Tb³⁺ luminescence with a quantum efficiency of 75% for ultraviolet excitation.