Synthesis and crystal structures of novel glycoluril carboxylic acids conglomerates

The two novel conglomerates were obtained by crystallization of racemic (2'S,3aS,6aR)/(2'R,3aR,6aS) (glycoluril-1-yl)-3-methylbutanoic acid and (2'R,3aR,6aR)/(2'S,3aS,6aS) (4,6-dimethylglycoluril-1-yl)pentanoic acid synthesized by highly diastereoselective condensation of 4,5-dihydroxy- imidazolidin-2-ones with racemic ureido acids. The differences in the molecular geometry of synthesized racemates were studied by X-ray diffraction that showed them to crystallize as conglomerates in non-centrosymmetric space groups Pna2₁ and P2₁2₁2₁, respectively     

Highly diastereoselective multicomponent synthesis of polysubstituted 2-hydroxy-2-trifluoromethylpiperidineswith four and five stereogenic centers

The Michael–Mannich cascade cyclization of cyano olefins, ethyl 4,4,4-trifluoro-3-oxobutanoate, aromatic aldehydes and ammonium acetate provides convenient stereoselective formation of ethyl 5,5-dicyano-4,6-diaryl-2-hydroxy-2-(trifluoromethyl)piperidine-3-carboxylates with fourstereogenic centers and dialkyl 4,6-diaryl-5-cyano-2-hydroxy-2-(trifluoromethyl)piperidine-3,5-dicarboxylates with five stereogenic centers. Ammonium acetate plays dual role, acting as a base and as a nitrogen source.     

A convenient synthesis of 3-aryl-5-methylidene-2-thiohydantoins

3-Aryl-5-methylidene-2-thiohydantoins were constructed in one-pot reaction of aryl isothiocyanates and 3-morpholino- alanine in alkaline medium with the subsequent treatment with boiling hydrochloric acid.     

On the Brauer p-dimension of Henselian discrete valued fields of residual characteristic p > 0

Let $(K,v)$ be a Henselian discrete valued field with residue field $\stackrel{?}{K}$ of characteristic $p>0$, and ${\text{Brd}}_p(K)$ be the Brauer p-dimension of K. This paper shows that ${\text{Brd}}_p(K)\ge n$ if $[\stackrel{?}{K}:{\stackrel{?}{K}}^p]=p^n$, for some $n\in \mathbb{N}$. It proves that ${\text{Brd}}_p(K)=\infty$ if and only if $[\stackrel{?}{K}:{\stackrel{?}{K}}^p]=\infty$.     

低相对分子质量有机酸对α-FeO(OH)吸附As(Ⅲ)的影响

制备并表征了α-FeO(OH),探究了4种低相对分子质量有机酸(LMW)对α-FeO(OH)吸附As(Ⅲ)的影响,并阐明了机理。 单一和混合LMW对α-FeO(OH)吸附As(Ⅲ)均有抑制作用,4种LMW的影响大小顺序为:草酸(OA)>柠檬酸(CA)>乳酸(LA)、水杨酸(SA)。 混合LMW的影响为:OA会加剧CA对α-FeO(OH)吸附As(Ⅲ)的影响,而SA几乎不起作用。 当ρ(As(Ⅲ))较低,LMW通过与α-FeO(OH)的静电引力、与α-FeO(OH)表面的铁离子形成配合物、生成沉淀从而影响α-FeO(OH)对As(Ⅲ)的吸附;当ρ(As(Ⅲ))较高,LMW还通过阻碍As(Ⅲ)在α-FeO(OH)上的扩散和沉淀作用产生影响。 实验结果为土壤中As(Ⅲ)的迁移转化、污染治理提供技术支撑。     

A rapid,sensitive, and widely applicable method for quantitative analysis of underivatized amino acids in different biological matrices by UHPLC‐MS/MS

A rapid, sensitive, and widely applicable method for the simultaneous quantitative analysis of 20 underivatized amino acids in different biological matrices, including serum, plasma, and tissue homogenates, using ultra high performance liquid chromatography with tandem mass spectrometry was developed and validated. Only 4 µL of serum, plasma, or tissue homogenate was extracted with 996 µL of solution (1.7 mM ammonium formate in 85% acetonitrile containing 0.1% formic acid) containing 100 ng/mL phenylalanine‐d5 as an internal standard without any further derivatization step. In addition, the matrix effects were small because a large volume of extraction solution was used. The total run time including reequilibration was 13 min. The results of linearity, accuracy, repeatability, precision, limits of detection, limits of quantification, and sample stability were sufficient to allow the measurement of the amino acids in different biological matrices. We conclude that our method is rapid, sensitive, and widely applicable and represents an improvement over other currently available technologies.     

Bidentate Boron Lewis Acids: Selectivity in Host–Guest Complex Formation

Bidentate boron Lewis acids based on 1,8‐diethynylanthracene were synthesised in two steps by initial stannylation of the terminal alkynes and subsequent tin–boron exchange with different chloroboranes. The reactions were very selective, and the target compounds were obtained in high purity and good to excellent yields. Complexation experiments of 1,8‐bis[(diphenylboranyl)ethynyl]anthracene with nitrogen bases (pyridine, pyrimidine, TMEDA) afforded three stable adducts, which were structurally characterised by X‐ray diffraction. Competition experiments demonstrated the selective exchange of guests, and quantum‐chemical calculations provided information on their energetics. NMR experiments at low temperature gave insight into the dynamic behaviour of the TMEDA adduct.     

Mixed surfactant enabled EVA emulsion for PPD applications

PPD emulsion product is advantageous for use in sub-ambient temperature as it improve the physical handling characteristic compared to traditional product. However, existing PPD emulsion system is solely implementing a single anionic surfactant system which leads instability towards a series of temperature changes. Therefore, mixed surfactant (anionic and non-ionic) surfactant was introduced to overcome this problem. Through this research, sodium dodecyl sulfate (SDS) act as anionic surfactant and Tween 80 used as non-ionic surfactant in this study. The stability of an emulsion was identified through particle size and zeta potential. For the mixed surfactant composition, the result show the presence of SDS content contributes in reduction on particle size. Furthermore, the study on effectiveness of surfactant on EVA emulsion was evaluated. The result indicates with present of surfactant, interfacial surface tension was reduced. The freezing point and pour point depressant test of the EVA emulsion was evaluated. Present of non-ionic surfactant help in stability and flow-respond at low temperature. Mixed surfactant system provides sufficient protection from droplet size growth caused by the temperature changes which eventually leads to instability.     

IDPi Catalysis

High acidity and structural confinement are pivotal elements in asymmetric acid catalysis. The recently introduced imidodiphosphorimidate (IDPi) Brønsted acids have met with remarkable success in combining those features, acting as powerful Brønsted acid catalysts and “silylium” Lewis acid precatalysts in numerous thus far inaccessible transformations. Substrates as challenging to activate as simple olefins were readily transformed, ketones were employed as acceptors in aldolizations allowing sub‐ppm level catalysis, whereas enolates of the smallest donor aldehyde, acetaldehyde, did not polymerize but selectively added a single time to a variety of acceptor aldehydes.