A semi-quantitative method for the determination of microgram amounts of manganese on millipore filters

A method is described in which the intensity of coloration of brown manganese dioxide on white Millipore filters is taken as the measure of the manganese content. A solution of manganese(II) is made strongly basic, whereupon manganese dioxide precipitates via its auto-oxidation. Optimum conditions for the precipitation are studied. Less than 0.5 μg of manganese can be determined.     

First lipase catalysed resolution of epoxy enol esters

We report the first enzyme-catalysed kinetic resolution of epoxy enol esters. The lipase-promoted hydrolysis of these compounds provided α-hydroxyketones or α-hydroxyaldehydes (arising from the spontaneous rearrangement of the epoxy enols) and the residual esters with moderate to good enantioselectivity (E up to 100).     

Structures, stabilities, and electronic and optical properties of c(58) fullerene isomers, ions, and metallofullerenes.

The 1205 classical isomers of fullerene C58, as well as one quasi-fullerene C58 isomer with a heptagonal ring (labeled as Cs:hept) have been investigated by the quantum chemical methods PM3, HCTH/3-21G, and B3LYP/6-31G(d). Isomer C3v:0001, which has the lowest number of adjacent pentagons, is predicted to be the most stable isomer, but the quasi-fullerene isomer Cs:hept is only 2.50 kcal mol-1 higher in energy. Systematic investigations of the electronic properties of C3v:0001 and Cs:hept find that the C3v:0001 isomer has high vertical electron affinity (3.19 eV). The nucleus-independent chemical shifts (NICS) value at the center of Cs:hept (-5.1 ppm) is more negative than that of C60 (-2.8 ppm). The NICS value at the center of the heptagonal ring in Cs:hept (-2.5 ppm) indicates weakly aromatic character. In contrast, the C58(6-) and C58(8-) ions of the C3v:0001 and Cs:hept geometries possess large aromatic character, with NICS values between -14.0 and -26.2 ppm. To clarify the thermodynamic stabilities of C58 isomers at different temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP/6-31G(d) level. The C3v:0001 isomer prevails in a wide range of temperatures, and the Cs:hept isomer is also an important component around 2800 K. The IR spectra of C58 isomers are simulated to facilitate experimental identification of different isomers. In addition, the electronic spectra and the second-order hyperpolarizabilities are predicted by ZINDO and the sum-over-states model. The static second-order hyperpolarizability of the C3v:0001 isomer is 96.5 % larger than that of C60, and its second-order hyperpolarizabilities at external field frequencies are at least nine times larger than those of C60.     

离子交换树脂纯化酪蛋白磷酸肽研究

通过单因素实验和正交试验确定了使用D-201型大孔强碱性阴离子交换树脂纯化酪蛋白磷酸肽(CPPs)的操作条件为：洗脱温度40℃、洗脱酸(HCI)浓度0．2mol／L、洗脱速度2．3ml／min、进样浓度2％(w／v)，进一步应用HPSEC技术分析考察了离子交换树脂纯化后含磷洗脱峰分子量分布情况，并计算了产品氮磷比与纯化收率．     

Novel heterocycles. 6. The condensation of ethyl o-fluorobenzoyl acetate with cyclic imino ethers

The reaction between ethyl o-fluorobenzoylacetate and cyclic imino ethers is described. The products, the corresponding 1,2-fused quinolines ( 13a-17a ), were isolated in good yields. In one instance the uncyclized condensation intermediate 18 was isolated and characterized.     

Total Synthesis of Crenulatan Diterpenes: Strategy and stereocontrolled construction of a bicyclic keto-lactone building block

The bicyclic keto lactone 26 was synthesized for the purpose of developing a viable route to marine diterpenes of the crenulatan type. Following the efficient conversion of (S)-citronellol ( 5 ) to the allylated alcohol 9a (Scheme 2), the αβ-unsaturated lactone 12 was efficiently accessed in preparation for stereocontrolled conjugate addition. The hydroxymethyl equivalent most suited to this task was (i-PrO)Me₂SiCH₂MgCl, which gave 13 predominantly in the presence of CuI and Me₃SiCl. Once the OH group was deprotected (→ 14 ), it proved an easy matter to implement acid-catalyzed isomerization to lactone 15 , oxidation of which gave the pivotal aldehyde 16 . Condensation of 16 with PhSeCH₂Li led via 21 to 22 (Scheme 3). Once the OH group was protected (→ 22b ), it proved possible to effect aldolization with crotonaldehyde (→ 23 ). Exposure of 23 to acid gave the sub-target compound 25 . Its subsequent oxidation and thermal activation resulted in sequential selenoxide elimination with Claisen rearrangement (→ 26 ). The structural features of 26 require that a chair-like transition state be adopted during the [3.3]sigmatropic event. With the clarification of these issues, a highly serviceable and more advanced assault on the crenulatans should prove capable of being mounted.     

Reaction of triphenylphosphine with phenylethanethiolate-protected Au38 nanoparticles

The replacement of phenylethanethiolate (SC2Ph) ligands on 1.1 nm (core diameter) Au38(SC2Ph)24 monolayer-protected clusters (MPCs) with varied amounts of triphenylphosphine (PPh3) is investigated in methylene chloride. UV-vis spectra suggest that changes in the MPC Au core size occur when large amounts (> 10 equiv moles per cluster) of PPh3 are reacted with Au38(SC2Ph)24. 1H and 31P NMR spectra following the addition of smaller amounts (< 5 equiv moles) of PPh3 indicate that the reaction liberates a AuISC2Ph complex, as opposed to a SC2Ph thiol, disulfide, or anion. A 1H NMR kinetic study shows that the exchange is surprisingly rapid, even faster than exchanges of thiolates with other thiolates, at room temperature and in air. The reaction is slowed when cooled or conducted under Ar. The difference in potentials of the initial one-electron voltammetric reduction and oxidation of Au38(SC2Ph)24 decreases slightly upon reaction with small amounts of PPh3.     

The phenolic oxidation of a β-methylchalcone

The phenolic oxidation of 2',4-dihydroxy-4'-methoxy-β-methylchalcone using alkaline potassium ferricyanide gives an aurone rather than an isoflavone. This result is discussed in the context of current theories regarding the biosynthesis of flavonoid and isoflavonoid compounds.     

Mixed valence—Rydberg states

A survey of recent calculations involving the mixing of Rydberg and valence states in the spectra of molecular systems is undertaken. It is pointed out that when such states undergo curve crossings with one another, minimal energy splittings of 1.0–2.0 eV can occur at the respective 50-50 composition points. The significance of such large interactions between valence and low-lying Rydberg states is considered in terms of the properties of the resulting mixed CI states, particularly with reference to the oscillator strengths for the pertinent ground state transitions and also the spatial extension of the corresponding upper orbitals. It is thereupon argued that such mixings have important consequences in the spectra of a wide variety of systems, including those of O₂, ethylene and ethane.     

Synthesis of angiotensins,bradykinins and substance P octapeptides in which the residues Phe and Tyr have been replaced with car and of [Car1, Leu5]-enkephalin

Thirteen peptides, analogues of bradykinin (BK), enkephalin, Substance P (SP) and [Sar¹]-angiotensin II ([Sar¹]-AT_II) have been synthesized by the solid-phase method. In all these peptides the residue Phe and Tyr were substituted with the boron-containing amino-acid L -o-carboranylalanine (Car). The purity and identity of the peptides were established by TLC., cellulose-electrophoresis and amino acid analysis.