Measurement of gastric pH during digestion of a solid meal in dogs

The behavior of gastric pH during digestion of a solid meal in beagle dogs was determined by use of an ion-selective field effect transistor pH sensor. The pH in the stomach was 3.9 +/- 0.4 (mean +/- S.D., n = 6) at 0.5 h after meals. It was maintained at a mildly acidic (about pH 3) level for long periods.     

Claisen-type addition of glycine to a pyridoxal iminium ion in water

The 5'-deoxypyridoxal stabilized glycine carbanion has been generated in water at neutral and mildly basic pH. At pH < 7, this carbanion reacts mainly with the carbonyl carbon of 1 to form a stable Claisen-type adduct. At pH > or = 8, this carbanion reacts with the iminium carbon of the pyridoxal-glycine iminium ion to form the second Claisen-type adduct 3 as the major reaction product.     

pH对两步法非离子模板合成MSU-X类硅基介孔结构的影响

采用两步法以非离子型表面活性剂Tween 20为模板剂合成硅基介孔材料, 研究了pH对介孔材料结构的影响. 结果表明, 没有氟离子存在且模板剂浓度较低(约为2%(w))的条件下, 在弱酸性环境中(pH=3.32-4.26)可以制备有序的MSU-X类硅基介孔材料, 本研究中的简单合成体系有助于查明MSU-X合成机理. 对所得介孔材料测试表明, 在同样的合成体系中, 随着体系pH的变化, 所得硅基介孔材料的形貌和孔壁结构都发生了变化.     

Addition of arenes to ethylene and propene catalyzed by ruthenium

TpRuII(CO)(Me)(NCMe) (Tp = hydridotris(pyrazolyl)borate) serves as a catalyst precursor for the conversion of benzene and ethylene or propene to alkylaromatic products. The reaction proceeds via the formation of the active catalyst TpRu(CO)(Ph)(NCMe) and is mildly selective for linear propylbenzene over isopropylbenzene.     

DISAL glycosyl donors for the synthesis of a linear hexasaccharide under mild conditions

[reaction: see text] The new class of glycosyl donors with a methyl 3,5-dinitrosalicylate (DISAL) anomeric leaving group has proved efficient for glycosylation under strictly neutral, mildly basic, or mildly acidic conditions. Here, we report the synthesis of novel DISAL disaccharide glycosyl donors prepared by easy nucleophilic aromatic substitution. These DISAL donors proved efficient in the synthesis of a starch-related hexasaccharide under very mild conditions. Glycosylations proceeded with alpha-selectivity and were compatible with Trt protecting groups.     

Unusual oxidation behaviour of a propargylic alcohol

Attempts to convert a propargylic alcohol bearing an imidazolone substituent to the corresponding aldehyde under Parikh-Doering conditions gave an α,β-unsaturated-β-methylsulfanyl aldehyde, which cyclised under mildly acidic conditions.     

酸诱导介观相转变硅基介孔材料的合成机理及其改性

采用两步法以三嵌段共聚物P104(PEO27-PPO61-PEO27)为模板剂合成介孔材料, 研究了介孔材料结构随体系pH 值的变化, 探讨了体系中介观相转变的机理. 研究表明,随着pH 的升高, 发现体系中无机物种和模板剂所组成的介观相发生了转变,由P6mm 的SBA-15(pH=1.51-2.67)2D六角孔道结构转变为3D 蠕虫状孔道的MSU-X(pH=3.93-4.56)结构. 对所得的两种不同种类的硅基材料以γ-胺丙基三乙氧基硅烷(APTES: NH2(CH2)3Si(C2H5O)3)进行表面烷基化改性结果表明, 在同样的条件下, 经过改性后MSU-X类介孔材料孔壁上接枝的烷基数目要远超过SBA-15 类介孔材料.     

Synthesis of allylic and homoallylic alcohols from unsaturated cyclic ethers using a mild and selective C-O reduction approach

Unsaturated cyclic ethers can be mildly and selectively reduced with catalytic amounts of B(C(6)F(5))(3) in the presence of an alkylsilane. The allylic position is preferentially reduced with minimal or no scrambling of olefin geometry. For electronically equivalent substrates, steric factors guide the reducing agent to the least substituted site.     

Electrochemical and spectroscopic study of the self-assembling mechanism of normal and chelating alkanethiols on copper

The self-assembly of aliphatic thiol (RSH), dithiol (R(SH)(2)), and dithiocarboxylic acid (RS(2)H) onto mildly oxidized and highly oxidized copper was studied in real time by in situ electrochemical impedance spectroscopy (EIS). Ex situ characterization of the films was carried out using linear sweep voltammetry (LSV), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). In situ EIS studies found a very fast adsorption of RSH, R(SH)(2), and RS(2)H (within 10-15 s). This fast adsorption step is followed by the long-term additional adsorption and consolidation of SAM. However, the self-assembly of RS(2)H passes through an intermediate step of molecule rearrangement for around 10 to 30 min after around 2 to 7 min of self-assembly. The binding of both sulfur moieties of R(SH)(2) with Cu happens simultaneous. The oxide reduction capacity of RSH, R(SH)(2), and RS(2)H was good. However, the XPS studies showed the decomposition of RS(2)H-based SAMs to Cu(2)S. Monolayers prepared on both mildly oxidized and heavily oxidized Cu with R(SH)(2) had the highest stability. Monolayers of RS(2)H showed the least stability on both mildly oxidized and heavily oxidized Cu. Although RSH-based SAMs had good organization on both mildly oxidized and highly oxidized Cu, R(SH)(2)-based SAMs did not show good organization in either case. The RS(2)H monolayer had good organization only on mildly oxidized Cu.     

Exploring a reaction mechanism for acetato ligand replacement in paddlewheel tetrakisacetatodirhodium (II,II) complex by ammonia: computational density functional theory study

This study focuses on the first step of interaction between DNA and the paddle-wheel dirhodium complex. The ammonia molecule was used to model the oligonucleotide sequence. The reaction was considered in neutral and acidic conditions, in gas phase, and in solvent, using the COSMO model. Molecular structures of the complexes were optimized in both models at the B3PW91/6-31G(d) level. The B3LYP functional and aug-cc-pvdz basis set were employed for single-point energy determination and electron distribution analyses. It was shown that in neutral solution the replacement of axial aqua ligand is mildly exoergic. The reaction is characterized by a relatively low activation barrier (10-12 kcal/mol), and, according to Eyring transition state theory, it proceeds very quickly. The breaking of the Rh-O(ac) bond in neutral solution is mildly endoergic (less than 1 kcal/mol) with an activation barrier of about 21 kcal/mol. However, this process can occur much more spontaneously (ΔG of -14 kcal/mol) when the dirhodium complex is protonated at the acetyl oxygen in remote position.     

A convenient,one-step,high-yield replacement of an anomeric hydroxyl group by a fluorine atom using dast. Preparation of glycosyl fluorides.

The anomeric hydroxyl group of various furanose and pyranose hemiacetals can be replaced by a fluorine atom stereoselectively, conveniently, mildly, and on gram-scale using DAST in THF at room temperature.     

7-Bromocavernicolenone,a New α-Bromoenone from the Mediterranean Sponge Aplysina (= Verongia) cavernicola. Implied,Unprecedented Involvement of a Halogenated Dopa in the Biogenesis of a Natural Product

A novel, mildly antibacterial, α-bromoenone (7-bromocavernicolenone) has been isolated from the Mediterranean sponge Aplysina (= Verongia) cavernicola. Its structure, 7-bromo-1,5-dihydroxy-2-azabicyclo[3.3.1]non-6-en-3,8-dione ( 3 ), is based on X-ray and NMR analysis and on the observation that acetylation of 3 affords two monoacetates. An unprecedented phenol oxidative biogenetic pathway is suggested leading to 7-bromocavernicolenone via 3-bromotyrosine and 5-bromodopa.     

Numerical study of a fragile three-dimensional kinetically constrained model

We numerically study the three-dimensional generalization of the kinetically constrained east model, the north-or-east-or-front (NEF) model. We characterize the equilibrium behavior of the NEF model in detail, measuring the temperature dependence of several quantities: alpha-relaxation time, distributions of relaxation times, dynamic susceptibility, dynamic correlation length, and four-point susceptibility. We show that the NEF model describes quantitatively experimental observations over an exceptionally wide range of time scales. We illustrate this by fitting experimental data obtained both in the mildly supercooled regime by optical Kerr effect and close to the glass transition by dielectric spectroscopy.     

A structural and theoretical study of the intermolecular interactions in 8‐hydroxyquinolinium‐7‐carboxylate monohydrate

In the title compound, C₁₀H₇NO₃·H₂O, the zwitterionic organic molecules and the water molecules are connected by N—H...O and O—H...O hydrogen bonds to form ribbons, and π–π stacking interactions expand these ribbons into a three‐dimensional net. The energies of these hydrogen bonds adopt values typical for mildly weak interactions (3.33–7.75 kcal mol⁻¹; 1 kcal mol⁻¹ = 4.184 kJ mol⁻¹). The total π–π stacking interactions between aromatic molecules can be classified as mildly strong (energies of 15.3 and 33.9 kcal mol⁻¹), and they are made up of multiple constituent π–π interactions between six‐membered rings. The short intermolecular C—H...O contact between two zwitterionic molecules is nonbonding in character.     

Fe(III)-coordination properties of neuromelanin components: 5,6-dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid

The Fe(III)-coordination chemistry of neuromelanin building-block compounds, 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and 5,6-dihydroxy-N-methyl-indole (Me-DHI), and the neurotransmitter dopamine were explored in aqueous solution by anaerobic pH-dependent spectrophotometric titrations. The Fe(III)-binding constants and pH-dependent speciation parallel those of catechol in that mono, bis, and tris FeLx species are present at concentrations dependent on the pH. The bis FeL2 dihydroxyindole species are favorable for L = DHI and DHICA under neutral to mildly acidic conditions. DHI and DHICA are stronger Fe(III) chelates than catechol, dopamine, and Me-DHI at pH values from 3 to 10. Oxidation studies reveal that iron accelerates the air oxidation of DHI and DHICA.     

A systematic investigation of aluminium ion speciation at high temperature. Part 1. Solution studies

Speciation diagrams of aluminium ions in aqueous solution (0.2 M) at high temperature (90 degrees C) have been obtained from 48 h time-resolved multi-batch titration experiments monitored by 27Al NMR spectroscopy, potentiometry and dynamic light scattering. The quantitative speciation patterns and kinetic data obtained offer a dynamic picture of the distribution of soluble and insoluble Al species as a function of hydrolysis ratio h(h=[OH-]/[Al3+]) over a very broad range of conditions (-1.0 < or =h < or = 4.0). Monomeric, small oligomeric, tridecameric (the 'Al13-mer') and the recently characterised 30-meric aluminium species (the 'Al30-mer') as well as aluminium hydroxide have been identified and quantified. The Al13-mer species dominates over a relatively broad range of hydrolysis ratios (1.5 < or =h< or = 2.7) during the first 6 h of experiment, but are gradually replaced by Al30-mers at longer reaction times. Kinetic profiles indicate that the formation of the Al30-mer is limited by the disappearance of the Al13 species at mildly acidic conditions. The estimated rate constants of both hydrolytic processes show good internal correlation at h> or = 1.5. The effect of local perturbations leading to the formation of aluminium hydroxide below the electroneutrality point (h= 3.0) has been estimated quantitatively.     

A Semi-Analytical Semi-Experimental Solution for Flow Simulations in COSSERAT Continuum Mechanical Approach to Pulsatile Blood Flow in a Tapered Femoral Artery of a Dog

Flow simulations (investigation of velocity and microrotation fields) were carried out by solving the mass, linear momentum, and angular momentum equations in Cosserat continuum mechanics with a semi-analytical semi-experimental method; for unsteady, pulsatile, laminar, and locally fully developed blood flow and validation, using experimental pressure distribution in a mildly tapered femoral artery of a living dog. Finally, we present a time-dependent profile and an approximated Gaussian equation for k _v (a material quantity that shows influence of microrotation field on the stress tensor) in this article.     

A new oxidation of aldehydes to carboxylic acids

2-Hydroperoxyhexafluoro-2-propanol (HPHI) is a selective catalytic and stoichiometric reagent for the oxidation of aldehydes to acids under mildly basic conditions.     

碘作为Lewis酸催化剂在合成中的应用

碘催化的有机反应具有价廉易得、操作简单、温和、清洁、高效及高选择性等优点, 广泛应用于亲电反应、亲核反应、多组份反应以及其它涉及复杂官能团化合物的合成反应中, 在环境友好化学合成、复杂化合物合成及选择性合成领域具有应用价值.     

Synthesis of Complex Phenols Enabled by a Rationally Designed Hydroxide Surrogate

The conversion of aryl halides to phenols under mild reaction conditions is a longstanding and formidable challenge in organic chemistry. Herein, we report the rational design of a broadly applicable Pd‐catalyzed method to prepare phenols with benzaldehyde oxime as a hydroxide surrogate. These reactions occur under mildly basic conditions and enable the late‐stage hydroxylation of several functionally‐dense drug‐like aryl halides.