Phase transition between two anhydrous modifications of NaHSO4 mediated by heat and water

The phase transition between the two anhydrous modifications of NaHSO₄ (α and β) was studied using Raman spectroscopy and differential scanning calorimetry. These measurements indicate that β-NaHSO₄ is a metastable phase and readily undergoes phase transition to thermodynamically stable α-NaHSO₄ with an exothermic enthalpy change of 3.5 kJ/mol. Both thermal (temperatures >434 K) and chemical (exposure to H₂O) pathways were identified for this transition. The transition is irreversible, and α-NaHSO₄ is an intermediate phase between β-NaHSO₄ and NaHSO₄·H₂O. The possible mechanism of the phase transition is discussed.     

抗癌药β-榄香烯分子内部运动的13C核自旋弛豫研究

首次应用变温实验方法和¹³C核自旋弛豫方法研究了抗癌药β-榄香烯小分子的内部运动状况。结果表明β-榄香烯分子的六元环在所研究的温度范围(298~318K)内几乎是刚性的。该分子的整体滚动自扩散活化能为14kJ/mol.其六元环外侧链基团CH₂=CCH₃-和CH₂=CH-的整体内旋转扩散活化能均为19kJ/mol.而与该六元环直接相连的甲基的内旋转扩散活化能为18kJ/mol.这个数值大大高于连在六元环上不同位置的两个侧链基团CH₂=CCH₃一中甲基的内旋转扩散活化能(其数值分别为了7kJ/mol和2.8KJ/mol).3个不同位置的甲基的内旋转扩散活化能有很大差别可能是由它们所处的分子空间环境不同而引起的。     

关于(α,β) -度量的S -曲率

给出(α,β) -度量F=α\phi(β/α)的S -曲率的计算公式. 证得对一般的(α,β) -度量,当β为关于α长度恒定的Killing1 -形式时,S=0.研究了Matsumoto -度量F=α²/(α-β)和(α,α) -度量F=α+εβ+kβ²/α)的S -曲率, 证得S=0当且仅当β为关于α长度恒定的Killing1 -形式.同时还得到这两类度量成为弱Berwald度量的充要条件.其中\phi(s)为光滑函数,α(y)=\sqrt{a_ij(x)yⁱy^j}为黎曼度量,β(y)=b_i(x)yⁱ为非零1 -形式且ε,k≠ 0为常数.     

Microwave-assisted immobilization of β-cyclodextrin on PEGylated Merrifield resins

β-Cyclodextrin was immobilized on PEGylated Merrifield resin through cross-linking with 1,6-hexamethylene diisocyanate (HMDI) reagent, using conventional and microwave-assisted methodologies. FT-IR analysis of the solid intermediates indicated the attachment of the linker arm to the resin due the appearance of characteristic bands centered at 1716 and 2270 cm⁻¹ and the attachment of cyclodextrin to the resin was accompanied with increased absorption at the OH stretching regions (3330-3400 cm⁻¹). β-Cyclodextrin linked PEGylated resins are water insoluble and can be used to trap volatile organic compounds (VOCs) from water and subsequently be analyzed by headspace HS/GC, after simple filtration and drying steps.     

Microreactors for the synthesis of fluorinated materials

The utility of microreactor for the synthesis of α-fluoro-α,β-unsaturated esters, trifluoromethylation and Michael addition reaction, is described.     

Regioselective ring-opening of aziridines with potassium thiocyanate in the presence of β-cyclodextrin in water

Aziridines are cleaved regioselectively with KSCN in the presence of β-cyclodextrin in water at room temperature with excellent yields.     

Candida Rugosa lipase-catalyzed kinetic resolution of β-hydroxy-β-arylpropionates and δ-hydroxy-δ-aryl-β-oxo-pentanoates

A simple and convenient method was reported for the preparation of optically active β-hydroxy-β-arylpropionates, δ-hydroxy-δ-aryl-β-oxo-pentanoates and their butyryl derivatives via CRL-catalyzed hydrolysis. The optically active products are potential precursors of some chiral pharmaceuticals and natural products.     

Radical-mediated hydroxyalkylation of α,β-unsaturated esters

The radical-mediated hydroxyalkylation of α,β-unsaturated esters with alkyl iodides, trialkylborane, water and KF in THF gave the corresponding α-hydroxy esters. The synthetic advantage of the method was demonstrated by a short-step total synthesis of (±)-tanikolide.     

The synthesis of ‘tyrosyl’ peptidomimetics by acid-catalyzed N(1)-C(4) ring opening of 4-(4′-hydroxyphenyl)-azetidine-2-ones

Under acidic conditions, the N(1)-C(4) bond of 4-(4′-hydroxyphenyl)-azetidine-2-ones are cleaved with the formation of a stabilized benzylic carbocation intermediates. The intermediates were reduced by silanes or participated in intramolecular or intermolecular Friedel-Crafts reactions to produce tyrosine mimetics.     

Silica gel-promoted synthesis of 3,4,5-triaryltetrahydro-1,4-thiazine derivatives from β,β′-dichloro sulfides and aromatic amines

A novel and efficient synthesis of 3,4,5-triaryltetrahydro-1,4-thiazine derivatives by treatment of β,β′-dichloro sulfides, 2:1 adducts of alkenes and sulfur dichloride, with aromatic amines in the presence of silica gel is described. The silica gel can be easily recovered and reused in up to four consecutive reactions without any significant decrease in product yield.