Synthesis of glycyrrhetinic acid monoglycoside by hydrolysis of glycyrrhizic acid in subcritical water

A method for the synthesis of glycyrrhetinic acid monoglycoside by hydrolysis of glycyrrhizic acid in subcritical water at temperatures ranging between 100 and 300°C is under development. The maximum yield of the target product is achieved at 160°C.     

Synthesis of Titania-supported Copper Nanoparticles via Refined Alkoxide Sol-gel Process

Nanoparticles of titania and copper-loaded titania were synthesized by a refined sol-gel method using titanium butoxide. Unlike the conventional sol-gel procedure of adding water directly, the esterification of anhydrous butanol and glacial acetic acid provided the hydrolyzing water. In addition, acetic acid also served as a chelating ligand to stabilize the hydrolysis-condensation process and minimize the agglomeration of titania. Following the hydrolysis, Cu/TiO₂ was prepared by adding copper chloride to titania sol. The sol was dried, then calcined at 500^°C to remove organics and transformed to anatase titania which was verified by XRD. Cu/TiO₂ was further hydrogen-reduced at 300^°C. The recovery of Ti was exceeded by an average of 95% from titanium butoxide. TEM micrographs show that the Cu/TiO₂ particles are near uniform. The average crystallite sizes are 17–20 nm estimated from the peak broadening of XRD spectra. The bandgaps of TiO₂ and reduced Cu/TiO₂ range from 2.70 to 3.15 eV estimated from the diffusive reflective UV-Vis spectra. XPS analysis shows that Cu 2p_3/2 is 933.4 eV indicating primary Cu₂O form on the TiO₂ supports. The binding energy of Ti does not exhibit chemical shift suggesting negligible interaction of Cu cluster and TiO₂ support.     

A study of oleic acid-based hydrothermal preparation of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Nearly monodisperse, well crystalline, superparamagnetic CoFe₂O₄ nanoparticles with diameter of 6 nm were synthesized in oleic acid–water–pentanol system at 180 °C. Hydrothermal procedure, as an efficient and environment friendly alternative to organic decomposition methods, was investigated by variation of reaction conditions, and the particle formation mechanism was finally proposed (i.e., hydrolysis of metal oleates in organic phase, with size of the particles (5–8 nm) controlled by polarity-driven precipitation into water phase). As-prepared particles were hydrophobic due to coating by oleic acid. Further modification with dimercaptosuccinic acid led to water-dispersible particles with hydrodynamic diameter of 20 nm. Prepared particles were investigated by TEM, XRD, ICP-AES, light scattering, SQUID magnetometry, and Mössbauer spectroscopy.     

Extraction of caftaric and cichoric acids from Echinacea purpurea L. in subcritical water

A procedure for extracting caftaric and cichoric acids from Echinacea purpurea L. in subcritical water was developed. The procedure is ecologically clean and more effective than the traditional extraction methods based on the use of expensive and toxic organic solvents.     

Environmental behavior of actinides

Since the plutonium concentration in ocean waters is quite low, most of the plutonium deposited in marine waters has been sorbed onto plants and sediments. Actinides in natural waters usually are not in a state of thermodynamic equilibrium for long time periods as their solubility and migration behavior is strongly related to the form in which the nuclides are introduced initially into the aquatic system for long time periods. Their solubility depends on pH (hydrolysis), E _H (oxidation state), reaction with complexants (e.g., carbonate, phosphate, humic acid, etc.), sorption to surfaces of minerals and/or colloids, etc. The primary variable is the oxidation state of the actinide cation. Actinides can be present in more than one oxidation state which complicates modeling actinide environmental behavior.Np(V)O₂ ⁺ and Pu(V)O₂ ⁺ are weakly complexing and resistant to hydrolysis and subsequent precipitation, but both can undergo reduction to the IV oxidation state. The solubility of NpO₂ ⁺ can be as high as 10^?4M, while that of PuO₂ ⁺ is more limited as the very low solubility of Pu(OH)₄ promotes reduction to Pu(IV). The solubility of hexavalent UO₂ ²⁺ in sea water is limited by hydrolysis, but has a relatively high concentration due to carbonate complexation. Americium(III) hydroxocarbonate, Am(CO₃)(OH), is the limiting species for the solubility of Am(III) in sea water. Thorium has a very low solubility due to the formation of Th(OH)₄.     

Environmental behavior of actinides

Since the plutonium concentration in ocean waters is quite low, most of the plutonium deposited in marine waters has been sorbed onto plants and sediments. Actinides in natural waters usually are not in a state of thermodynamic equilibrium for long time periods as their solubility and migration behavior is strongly related to the form in which the nuclides are introduced initially into the aquatic system for long time periods. Their solubility depends on pH (hydrolysis), E _H (oxidation state), reaction with complexants (e.g., carbonate, phosphate, humic acid, etc.), sorption to surfaces of minerals and/or colloids, etc. The primary variable is the oxidation state of the actinide cation. Actinides can be present in more than one oxidation state which complicates modeling actinide environmental behavior. Np(V)O ₂ ⁺ and Pu(V)O ₂ ⁺ are weakly complexing and resistant to hydrolysis and subsequent precipitation, but both can undergo reduction to the IV oxidation state. The solubility of NpO ₂ ⁺ can be as high as 10⁻⁴M, while that of PuO ₂ ⁺ is more limited as the very low solubility of Pu(OH)₄ promotes reduction to Pu(IV). The solubility of hexavalent UO ₂ ²⁺ in sea water is limited by hydrolysis, but has a relatively high concentration due to carbonate complexation. Americium(III) hydroxocarbonate, Am(CO₃)(OH), is the limiting species for the solubility of Am(III) in sea water. Thorium has a very low solubility due to the formation of Th(OH)₄.     

Kinetic Carbon Isotope Effects in the Decarbonylation of Lactic Acid of Natural Isotopic Composition and of [1-14C] Lactic Acid

Studies of carbon-13 and carbon-14 kinetic isotope effects (K. I. E.) in the decarbonylation of lactic acid (L. A.) in sulphuric acid and in phosphoric acids media have been summarized and compared with earlier studies of ¹⁴C and ¹³C K. I. E. in the decarbonylation of formic and oxalic acids in concentrated sulphuric acid. Supplementary data concerning the decarbonylation of L. A. in sulphuric acid diluted with water and in pyrophosphoric acid are presented and discussed. The observed temperature dependences of ¹³C and ¹⁴C K. I. E. in concentrated H₂SO₄ and in concentrated phosphoric acids media have been rationalized by invoking a change of the mechanism of decarbonylation of L. A. in concentrated sulphuric and phosphoric acids with temperature. Preliminary calculational results concerning ¹³C and ^1??C K. I. E. in decarbonylation processes are also presented. In H₂SO₄ diluted with water and in H₃PO₄ diluted with water the temperature dependence of ¹³C and ¹⁴C K. I. E. is normal and well reproduced by one frequency approximation. In concentrated sulphuric acid and in concentrated phosphoric acids besides the C—OH bond rupture the rupture of a C—C bond had to be considered also to reproduce the observed ¹³C K. I. E. in selected temperature regions.     

Structural and electrical features induced by the leaching procedures on the LiNbO3 crystalline powder samples

ABSTRACT

The crystalline powders of the LiNbO₃ were studied. Measurements were carried out on the reference modified by the leaching procedure samples. Leaching reactions were conducted in the redistilled water and in the concentrated nitric acid. The Li⁺/H⁺ substitution was confirmed, for the crystal sample leached in nitric acid, by using time of flight-secondary ion mass spectroscopy (SIMS). The concentration of the lithium and niobium in liquid solutions was determined by using an inductively coupled plasma-optical emission spectrometry (ICP-OES). The X-ray diffraction (XRD) test was performed to verify the stability of the crystallographic structure of the powders, affected by the leaching procedure. For sample leached in the concentrated nitric acid, XRD pattern showed a structural distortion. The influence of the leaching reaction on the electric permittivity, conductivity and the coefficient loss was checked. The spectra were obtained for the frequency range 20–10⁶ Hz, in the temperature range 300–650 K.     

Hydrolysis of aralosides from Manchurian aralia to oleanolic acid and its derivatives in subcritical water

A method for preparing oleanolic acid (OA) and its derivatives by the hydrolysis of aralosides from Manchurian aralia in subcritical water has been developed. It has been used for the treatment of the Saparal pharmaceutical preparation at 120–240°C in a static regime. The maximal yield of OA has been obtained at 210°C.     

The proton inventory technique in a dual mechanistic system: the spontaneous hydrolysis of ethyl formate †

Ethyl formate undergoes spontaneous hydrolysis through two parallel mechanistic pathways: water catalysis and specific hydrogen-ion catalysis. The proton inventory of the water reaction at 37.0 ^°C was determined from the overall conversion curves, in H₂O/D₂O mixtures of deuterium atom fraction n, resulting in k ₁(n)=(2.1±0.1)×10^?5 s^?1 (1?n+0.42 n) (1?n+0.83 n)², in agreement with the results of six other cases of carboxylic acid derivatives. This result contributes to the validation of the accuracy of the proton inventory technique.     

Continuous one-step synthesis of N-doped titania under supercritical and subcritical water conditions for photocatalytic reaction under visible light

N-doped titania was prepared continuously by one-step synthetic method under supercritical and subcritical water conditions using titanium(IV)tetraisopropoxide (TTIP) and nitric acid as a titania precursor and nitrogen source, respectively. The synthesized N-doped titania particles were characterized by XRD, N₂-adsorption, TEM, XPS, UV-vis diffuse reflectance spectroscopy. N-doped titania was successfully synthesized and its crystalline structure was homogenous anatase phase with high surface area. The absorption edge of synthesized N-doped titania shifted into the visible light region compared with commercial titania P25. All synthesized N-doped titania have higher photocatalytic activity than P25 under visible light irradiation. The photocatalytic activity of N-doped titania synthesized under supercritical water condition was the highest for the degradation of methyl orange under visible light due to the larger crystallite size compared with the N-doped titania synthesized under subcritical water condition.     

Cleavage of esters under nearly neutral conditions at high pressure

Abstract

Hydrolysis of esters proceeded at room temperature under high pressure in the presence of iPr₂, NEt or N-methylmorpholine using CH₃CN—H₂O (60:1) as the solvent. This very mild procedure enables the smooth hydrolysis of biologically important compounds such as amino esters, aliphatic unsaturated fatty esters, and β-hydroxy ester; no racemization, no isomerization, and no side reactions take place. Selective hydrolysis of two ester groups is also accomplished with alcohol exchange reactions. This new synthetic technique can be utilized for the mild and selective hydrolysis of sophisticated molecules.

Hydrolysis of esters is one of the most essential transformations in organic synthesis. Normally, a basic or acidic aqueous solution is used for ester hydrolysis. However, the hydrolysis of biologically related molecules such as amino esters, peptides, …, or unstaturated fatty esters, under such conditions is accompanied by side reactions, loss of chirality, or isomerization.¹ We report an entirely new approach to this problem via high pressure induced hydrolysis. Hydrolysis is carried out at room temperature under > 8 Kbar in CH₃CN—H₂, O.²     

酸碱分步催化对溶胶-凝胶ZrO2膜光学性能的影响

 以丙醇锆作为前驱体,利用酸碱分步催化法制备了ZrO₂溶胶,用粒度仪检测胶体粒度;用N₂吸脱附表征凝胶的结构;采用旋转镀膜法在K9基片上镀制单层ZrO₂薄膜;用分光光度计和椭偏仪检测膜层的透过率、折射率及膜层厚度;用红外光谱仪检测胶体内部粒子间化学键状态。实验结果发现,在脉宽1 nm,波长1 064 nm时,采用此种胶体镀制的单层ZrO2膜层折射率达到1.74,单层膜损伤阈值为9.0 J/cm²,表明该方法集中了酸与碱两种催化方式的优点,一定程度上提高了膜层的光学性能。     

An asymmetric approach to the radiosynthesis of both enantiomers of α-[11C]methyldopa and α-[11C]methyltyrosine for positron emission tomography

In PET, α-methyl amino acids can play a dual role: a) precursors of neurotransmitters analogues for the study of neurodegenerative diseases; b) non-metabolised analogues of proteinogenic amino acids for the study of amino acids uptake into normal and cancer cells. The difference in the uptake rates during a PET scan could visualise cancer cells in a human body. Clinical applications of such amino acids are strongly limited due to their poor availability. For the synthesis of α-[¹¹C]methyl-tryptohan, an industrial procedure was adopted. All attempts to prepare enantiomerically pure α-[¹¹C]methylated tyrosine failed. We carried out [¹¹C]methylation of metalocomplex synthons derived from protected DOPA or tyrosine. Individual diastereomers were successfully separated by preparative HPLC, diluted with excess of water and extracted on C₁₈ cartridges. Optimisation of the procedure followed by hydrolysis of the complexes and purification of the enantiomers of α-[¹¹C]methylDOPA and α-[¹¹C]methyltyrosine is underway.     

Preparation of PS/TiO2 as a white pigment for electrophoretic displays

PS (polystyrene)/TiO₂, TiO₂ coated onto PS by a hydrolysis reaction, was prepared as a white pigment for electronic paper (e-paper). Two key parameters, density and zetapotential, were precisely controlled for use as a white pigment. The density was manipulated by changing the mixture ratio of EtOH to H₂O, and the concentration of titanium tetrabutoxide (TBO) in the hydrolysis reaction. The modification of PS/TiO₂ with (3-aminopropyl)triethoxy silane (APTES) and acetic acid showed positive zetapotential originated from the mutual effects between an amino functional group in APTES, and a proton from acetic acid. The mutual effect was studied, and PS/TiO₂ with density of 1.6 g/cm² and zetapotential of 75 mV was prepared using the results.     

The effect of clustering of VO2+ ions in sub- and supercritical water. An in situ EPR study

Temperature variations of the EPR spectra of VO²⁺ ions in sub- and supercritical water under isothermal and temperature gradient conditions are investigated using an in situ EPR. Broadening of the hyperfine structure at increasing temperature and the appearance of an unresolved broad low-intensity line (ΔH _pp ≈ 300 Oe) in the supercritical state are observed in the absence of temperature gradients, indicating an increase of exchange interaction between VO²⁺ ions in supercritical water. An exchange-narrowed anisotropic absorption line is observed under the temperature-gradient conditions in the subcritical water near the transition to a supercritical state. The shape of this line is close to that observed in the solid salt VOSO₄ · 3H₂O. It is shown that in situ EPR allows us to investigate the effects of changing the local environment of paramagnetic ions, which precedes the well-known process of clustering and formation of amorphous oxide particles in sub- and supercritical conditions.     

Dynamics of helical-wave emission in a fiber-coupled diode end-pumped solid-state laser

We have generated TEM_0,l ^* modes in an end-pumped microchip laser using a standard fiber-coupled diode. A rich set of dynamic behaviors, such as periodic and quasi-periodic self-modulation, chaotic pulsing and frequency locking was observed in the generated TEM_0,l ^* modes. Experimental results confirm the theoretical predictions that the locking occurs as a subcritical bifurcation and that a region of coexisting locked and unlocked states exists. Received: 14 November 2000 / Revised version: 22 January 2001 / Published online: 23 May 2001     

Influence of additional metal ions on the ratio of the rates of intermediate product transformations in the hydrolysis of adenizine-5′-triphosphoric acid catalyzed by divalent Cu ions

It was shown earlier that the hydrolysis of the (CuATP²⁻)₂ dimeric complex to CuADP⁻ and inorganic phosphate P _i was an irreversible reaction. The main intermediate hydrolysis product, the formation of which should be taken into account at comparatively early hydrolysis stages, was the IntK pentacovalent intermediate. It was formed in parallel with hydrolysis to CuADP⁻ and P _i through the common intermediate product (CuATP²⁻)₂OH⁻ — DOH⁻. We studied the influence of the addition of various concentrations of Mg²⁺ ions to the reaction mixture at pH 7.1–7.2, a range for which the kinetics of hydrolysis is sensitive to the rate constants of deactivation of DOH⁻ active centers (conjugated with CuADP⁻ formation and occurring via the formation of IntK). The conversion of ATP above which stationary hydrolysis regime was observed decreased as the concentration of Mg²⁺ grew. The DOH⁻ $ \underset{{OH^ - }}{\overset{{OH^ - }}{\longleftrightarrow}}$ \underset{{OH^ - }}{\overset{{OH^ - }}{\longleftrightarrow}} IntK equilibrium according to the conversion of ATP was established more rapidly, and it was to a greater extent shifted toward IntK. It was assumed that hydrated Mg²⁺ linked as a second metal ion with ATP β and γ phosphate groups hydrated IntK much stronger than DOH⁻. The Cu · OH₂ · AMP complex played the role of a common acid catalyst and hydrated DOH⁻ better than Mg²⁺ · OH₂. The selective hydration of DOH⁻ by the CuOH₂ · AMP complex at early hydrolysis stages directed the process toward the formation of IntK, which caused the appearance of an induction period in the formation of CuADP⁻.     

Understanding the role of Zn2+ in the hydrolysis of glycylserine: a mechanistic study by using density functional theory

The hydrolysis mechanism of glycylserine in the presence of Zn²⁺ was theoretically studied by means of density functional theory calculations. Two possible reaction mechanisms are proposed for the hydrolysis reaction: (1) the first one involves a stepwise reaction with an initial attack of the serine –OH to the amide carbonyl group through a general base catalysis of a water molecule, which undergoes to a proton transfer to the carboxylate group to give a cyclic intermediate. Its further rearrangement finally forms an ester that hydrolyses to yield products. (2) The second mechanism involves a general base catalysis by the carboxylate group for the water attack to the amide carbonyl group to generate a tetrahedral intermediate. Upon comparison of both mechanisms, it is observed that the former is favoured; furthermore, its first step is the rate-limiting step in a bicyclic asynchronous transition state with evolution of 86% in C₍₁₎–O₍₂₎ bond. The crucial role of Zn²⁺ in this hydrolysis process can be rationalised in terms of the inductive effect and the formation of a rigid structure that increases the electrophilicity of the amide carbonyl group. The calculations presented in this report are in good agreement with reported values for the activation barrier.