(S)-Mandelic acid enolate as a chiral benzoyl anion equivalent for the enantioselective synthesis of non-symmetrically substituted benzoins

A strategy for the enantioselective synthesis of non-symmetrically substituted benzoins from (S)-mandelic acid and aromatic aldehydes has been developed. This strategy is based on a diastereoselective aldol reaction of the lithium enolate of the 1,3-dioxolan-4-one derived from (S)-mandelic acid and pivalaldehyde with aromatic aldehydes, which gives the corresponding aldols in good yields. Subsequent hydroxyl group protection as MEM ethers, basic hydrolysis of the dioxolanone ring, oxidative decarboxylation of the α-hydroxy acid moiety, and hydroxyl group deprotection provides chiral non-symmetrically substituted benzoins with high enantiomeric excesses.     

Relationship of the Acid-Induced 13C Chemical-Shift Change in the α-Carbon Atom to the Stretching Frequency of the Hydroxy Group in Saturated Alcohols

A good linear relationship was found between the acid-induced ¹³C chemical shift change of the α-carbon atom and the OH stretching frequency of the hydroxy group in some saturated alcohols. The relationship is discussed with model calculations using the CNDO/2 method.

The trifluoroacetic acid-induced ¹³C chemical shift change in the α-carbon atom to the hydroxy group, Δδ¹³c, has been measured for a number, of saturated alcohols in carbon tetrachloride solution and provides information on the relative basicity and its dependence on the structural factor.¹ The free OH stretching frequency, v_OHis known to depend on the structural factor of the substituent._2–5 We reported that a linear relationship exists between the ¹⁷ O chemical shift, δ¹⁷ O, and the OH stretching frequency of the hydroxy group in saturated alchohols, R-OH.⁵ In this case, the ¹⁷O chemical shift change was reported to be governed by the ionization potential.⁶ The ionization potential of R-OH is expected to be correlated with its basicity. Regression analysis for Δδ¹³C was thus carried out for Δδ¹⁷OH reported for 14 and 19 typical alcohols, respectively. In order to explain the experimental results the oretically, we carried out CNDO/2 calculations for a series of methyl-substituted methanols.     

Identification of two aromatic isomers between 3- and 4-hydroxy benzoic acid by their perturbation on the potential oscillations of a Belousov-Zhabotinsky system

A novel method for identification of two aromatic isomers of mono hydroxy benzoic acid (HBA) was reported by using their different perturbation effects on the potential oscillations of a Belousov-Zhabotinsky (BZ) system. In such a system, a macrocyclic complex of Cu [CuL](ClO₄)₂ was used as catalyst in which ligand L is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. To the BZ system, 3-hydroxy benzoic acid (3-HBA) could temporarily quench and regenerate potential oscillations with damping characters after inhibition time (t_in) while 4-hydroxy benzoic acid (4-HBA) could only change the oscillation amplitude (ΔA) to give damping oscillations with no inhibition time. Thus, these two isomers of HBA were identified. Reaction mechanisms of BZ have been proposed by FKN model. An explanation of perturbation mechanism is that, although 3-HBA reacted with BrO₂ while 4-HBA reacted with BrO₃⁻, they all produced 1,4-quinone.     

Chiral N,N′-dioxide-Yb(III) complexes catalyzed enantioselective hydrophosphonylation of aldehydes

Chiral N,N′-dioxide-Ytterbium(III) complexes promoted the asymmetric addition of diethyl phosphate to aldehydes, giving the corresponding products with good yields and enantioselectivities. The addition of pyridine favored both reactivity and enantioselectivity. A possible catalytic cycle was proposed to explain the mechanism of the asymmetric hydrophosphonylation of aldehydes.     

三［（S）-α，α-二（4-甲基苯基）-2-吡咯烷甲醇］膦酰胺催化链状酮酯化合物的不对称还原反应

报道了三［（S）-α,α-二（4-甲基苯基）-2-吡咯烷甲醇］膦酰胺催化剂催化链状酮酯化合物的不对称还原反应。 研究发现,该方法对碳链长为5~11的链状酮酯具有较好的催化效果,在物质的量分数为5%手性膦酰胺催化作用下,产物手性羟基酯化合物的收率最高可达89%,对映体过量（ee）值最高可达95%。 此方法为手性链状羟基酯衍生物的合成提供了新选择。     

Specific Intermolecular Interactions in the Supramolecular Structure of 5‐Hydroxy‐6‐Methyluracil: A DFT Study of the Hydrogen‐bonded Dimers

Studying the self‐assembly of uracil derivatives has great importance for biochemistry and nanotechnology. For example, modification of the sorbent surfaces by 5‐hydroxy‐6‐methyluracil (HMU ) enhances their adsorption activity. It is assumed that these changes are caused by the self‐assembly of the network‐like supramolecular associates of the uracil derivative on the sorbent surface. In the present work, the relative stabilities of 15 hydrogen‐bonded dimers HMU have been studied by the TPSSh /TZVP density functional theory method and the strengths of the noncovalent interactions analyzed in terms of the reduced density gradient and natural bond orbital approaches. It was found that the symmetric dimer stabilized by two intermolecular hydrogen bonds N1 –H∙∙∙O–C2 (dimer 1‐1) is the most stable. This suggests that the self‐assembly of HMU should occur through the intermediate formation of the dimer 1‐1. The results may be useful for understanding the processes of self‐assembly of the uracil derivatives and the rationalized design of the uracil‐based supramolecular structures with specific properties.     

Paper‐based solid‐phase microextraction for analysis of 8‐hydroxy‐2’‐deoxyguanosine in urine sample by CE‐LIF

An easy‐to‐do paper‐based solid‐phase microextraction (p‐SPME) was developed for determination of 8‐hydroxy‐2’‐deoxyguanosine (8‐OHdG) in urine sample by CE‐LIF. Small piece of filter paper was used as a solid phase to extract 8‐OHdG from urine sample. Its primary mechanism is based on the hydrogen‐bonding interaction between 8‐OHdG and cellulose molecules. The effects of the pH of the sample solution, extraction time, and temperature on the peak area of the analyte were investigated in order to obtain the optimal p‐SPME conditions. Comparing with the untreated sample, the p‐SPME can significantly reduce the interference to the separation of 8‐OHdG by CE‐LIF. Meanwhile, the p‐SPEM can provide more than three times concentrated effect. The developed method was evaluated according to an FDA guideline for biological analysis. The precisions (RSD%, n = 5) of the peak area and migration time of the analyte at three different concentrations were within 3.02–5.82% and 0.92–1.58%, respectively. The limit of identification of the method is about 5 nM according to the significant difference between two sets of the samples with and without spiking the standard (Student's t ‐test, p < 0.05). Good linearity was obtained in the range of 10–1000 nM (R ²>0.99) based on the standard addition. The recoveries at three different concentrations were within 99.8–103.5%. The results of the real sample analysis are consistent with those reported in our previous paper (Electrophoresis 2014, 35, 1873–1879).     

Selective separation of hydroxy polychlorinated biphenyls (HO-PCBs) by the structural recognition on the molecularly imprinted polymers: direct separation of the thyroid hormone active analogues from mixtures

We developed novel separation media for hydroxy polychlorinated biphenyls (HO-PCBs) using the molecular imprinting techniques. The results of evaluation for the molecularly imprinted polymers (MIPs) by the liquid chromatography (LC) suggested that MIPs had selective separation ability for certain HO-PCB analogues. The results of the LC evaluations and molecular modeling indicated that the molecular volumes and pK_a values of template molecules were related with the retention factor of HO-PCBs. Additionally, according to the detail evaluation toward the selective separation behaviors of MIPs, these HO-PCB analogues have low pK_a values dependent on their chemical structures. In other words, the prepared MIPs had selective recognition ability against the analogues, which have an OH group on a phenyl carbon and two chlorine atoms on the both neighboring carbons of the carbon attached with the OH group. Moreover, these analogues may have a potential for thyroid hormone activities so that we attempted to separate these analogues directly from mixtures of HO-PCBs using a prepared MIP.     

Vibrational spectroscopy of selected minerals of the rosasite group

Minerals in the rosasite group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by a combination of infrared and Raman spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at approximately 3401 and 3311 cm-1. Two intense bands observed at approximately 1096 and 1046 cm-1 are assigned to nu1(CO3)2- symmetric stretching vibration and the delta OH deformation mode. Multiple bands are found in the 800-900 and 650-750 cm-1 regions attributed to the nu2 and nu4 bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C2v or Cs. A band at approximately 560 cm-1 is assigned to a CuO stretching mode.     

Determination of (E)-10-hydroxy-2-decenoic acid content in pure royal jelly: a comparison between a new CZE method and HPLC

A new CZE method was developed and compared with HPLC for the determination of (E)-10-hydroxy-2-decenoic acid (10-HDA) in royal jelly (RJ) samples of different geographical origin. The results obtained with the CZE method were highly correlated with those of HPLC (p < 0.01). Under optimized conditions, CZE employed minimal amounts of 50 mM tetraborate buffer as BGE, without the addition of organic solvents, EOF or pH modifiers. The CZE method showed a wide linear response range (0.006-0.808 mg 10-HDA/mL), a good sensitivity (LOD and LOQ were 0.002 and 0.004 mg/mL, respectively) and a satisfactory instrumental repeatability with respect to migration time and peak area (RSD% less than 1.0 and 2.0% on migration time for intra- and interday assay, respectively and less than 2.0 and for 4.0% on peak area for intra- and interday assay, respectively). The 10-HDA content in RJ ranged from 0.8 to 3.2 g/100 g of RJ and a significant difference (p < 0.05) was found between the Italian and extra-European average values: 2.5 and 1.6 g/100 g of RJ, respectively, according to the CZE data. The possibility of application of CZE for routine analyses on RJ and RJ based products to verify their authenticity is highlighted here.