The 1B1, 1B2, 1A1, 1A2, 3A′(2B2), and 2A1 states of the 1,1-difluoromethane ion studied using multiconfiguration second-order perturbation theory

The 1²B₁(X²B₁), 1²B₂, 1²A₁, 1²A₂, 2²B₂, and 2²A₁ states of the ion were studied using CASPT2 and CASSCF methods. Calculations suggest that one should consider the 3²A′ state instead of 2²B₂. The CASPT2 T₀ calculations predict the energy ordering of 1²B₁(X²B₁), 1²B₂, 1²A₁, 1²A₂, 3²A′, and 2²A₁, which is in line with the experimental results by Pradeep and Shirley. The CASPT2 T₀ values for the 1²B₂, 1²A₂, 3²A′, and 2²A₁ states are close to the experimental values. The F-loss and H-loss dissociation processes were studied at the CASPT2//CASSCF level. The energy levels of low-lying states of are compared.     

A new sample preparation and separation combination for precise,accurate, rapid,and simultaneous determination of vitamins B1, B2, B3, B5, B6, B7, and B9 in infant formula and related nutritionals by LC-MS/MS

An improved method was developed for simultaneous determination of the fortified forms of thiamine (B₁), riboflavin (B₂), nicotinamide and nicotinic acid (B₃), pantothenic acid (B₅), pyridoxine (B₆), biotin (B₇), and folic acid (B₉) in infant formulas and related nutritionals. The method employed a simple, effective, and rapid sample preparation followed by liquid chromatography tandem mass spectrometry (LC-MS/MS). It improved upon previous methodologies by offering facile and rugged sample preparation with improved chromatographic conditions, which culminated in a highly accurate and precise method for water-soluble vitamin determination in a wide range of formulas. The method was validated over six days in ten unique matrices with two analysts and on instruments in two different labs. Intermediate precision averaged 3.4 ± 2.6% relative standard deviation and over-spike recovery averaged 100.2 ± 2.4% (n = 160). Due to refinements in sample preparation, the method had high sample throughput capacity.     

Uroleuconaphins A2a, A2b, B2a, and B2b: four yellowish pigments from the aphid Uroleucon nigrotuberculatum (Olive)

Four novel yellowish pigments, uroleuconaphins A_2a, A_2b (3a, 3b), and B_2a, B_2b (4a, 4b), were isolated from the aphid Uroleucon nigrotuberculatum (Olive). Their structures were established by detailed analyses of 1D and 2D NMR spectra and mechanistic consideration of the interconversion between 3 (or 4) and uroleuconaphin A₁ (1) (or B₁ (2)).     

A multicommuted fluorescence-based sensing system for simultaneous determination of Vitamins B2 and B6

A multicommuted flow-through optosensor based on the direct fluorescence measurements of Vitamins B₂ and B₆ using a non-polar sorbent (C₁₈ silica gel) as solid sensing zone (to accomplish the separation and subsequent preconcentration/detection of the target analytes) have been developed. The proposed flow system was controlled by Java-written home-made software and designed using three-way solenoid valves for independent automated manipulation of sample and carrier solutions. The native fluorescence signal was simultaneously monitored at two pairs of excitation/emission wavelengths (450/519 and 294/395 for B₂ and B₆, respectively). The separation of the analytes was performed in the detection flow cell, using the differences in the sorption/elution process on the solid support between the two vitamins, due to their different polarity. Using an optimised sampling time, the analytical signal showed linearity in the range 0.01-0.4 and 0.15-3 μg ml⁻¹ with detection limits of 0.003 and 0.045 μg ml⁻¹ for B₂ and B₆, respectively, obtaining R.S.D. (%) values better than 2% for both analytes. The proposed methodology was applied to different pharmaceutical preparations, obtaining remarkably good results with recoveries ranging from 96 to 107.5%.     

Stereoselective syntheses of the glycosidase inhibitors hyacinthacine A2, hyacinthacine A3 and 5-epi-hyacinthacine A3

Stereoselective syntheses of the naturally occurring glycosidase inhibitors hyacinthacines A₂ and A₃ are reported. In the case of hyacinthacine A₂, the pyrrolizidine system was created from an acyclic precursor via a double cyclization procedure with a one-pot formation of two C-N bonds. In the case of hyacinthacine A₃, the two C-N bonds were created in separate steps. In addition, the non-natural epimer at C-5 of hyacinthacine A₃ was obtained.     

Toward carboxylate group functionalized A4, A2B2, A3B oxaporphyrins and zinc complex of oxaporphyrins

Series of new oxaporphyrins were isolated from the reaction of furan-1,4-diol, pyrrole, and an aldehyde under Lindsey’s conditions, which gives easy access to ester group functionalized oxaporphyrins. The ester substituents can be readily hydrolyzed to terminal carboxylic acid in the presence of KOH. The Zn(II) oxaporphyrins have been synthesized from the reaction of free base with ZnCl₂ and fully characterized by variable temperature NMR, 2D NMR, and single crystal X-ray diffraction studies.     

Zur Bestimmung der Aflatoxine B1, B2, G1 und G2 in Baumwollsaat-Produkten

Ohne Zusammenfassung     

Flow injection renewable drops spectrofluorimetry for sequential determinations of Vitamins B1, B2 and B6

A novel optical chemical sensor based on the dynamic liquid drops combined with flow injection-solid phase has been developed for continuous and sequential determinations of the mixture of Vitamin B₁, Vitamin B₂ and Vitamin B₆. The design and characteristics of the sensor system are described. The dynamically growing and falling drops serve as windowless optical cells. The adsorption, desorption and quantitative determinations of VB₁, VB₂ and VB₆ were carried out based on selective adsorption of Sephadex CMC-25 and different fluorescence characteristics of VB₂, VB₆ in the basic solutions. The optimum analytical conditions for compound Vitamin B assay have been established. Under these conditions, linear calibration curves were obtained over the range of 0.01-8.00, 0.01-10.00 and 0.01-3.00 μg/ml for VB_1, VB₂ and VB₆ with the limits of determination of 0.008, 0.005 and 0.006 μg/ml, respectively. This method has been applied in the determination of synthetic mixture of VB_1, VB₂, VB₆ and Vitamin B compound tablets with satisfactory results. The technique, which has been described, provides a simple, effective and sensitive method to assay the biological samples.     

Vitamin B2

Ohne Zusammenfassung     

Synthesis of gibberellins A8 and A56 from gibberellin A3

A mixture of gibberellin A₃ derivatives with 1(10)-ene-2,3-diol and 1(10)-ene-2,3-diol (2:5) groups, readily obtained from gibberellin A₃, has been used for a new and simple synthesis of gibberellin A₈ and its esters. The hydrolysis of GA₃ and the iodolactonization of a mixture of the 2-epimers was carried out in aqueous solution in a single flask, as also was a synthesis of GA₅₆ from GA₃ by a method that we have modified. The mixture of 1-iodides of GA₈ and GA₅₆ was separated by chromatography on SiO₂ in the form of methyl or p-bromophenacyl esters which were then deiodinated and the methyl or p-bromphenacyl ester of GA₈ was isolated. Free GA₈ was obtained by the dephenylation of the latter ester. By two-dimensional NMR spectroscopy we succeeded in assigning all the signals in the¹³C and¹H NMR spectra of the methyl esters of GA₈ and GA₅₆. In an attempt to obtain GA₅ methyl ester by the action of trimethylchlorosilane/sodium iodide on the 2,3-diol system in GA₅₆ methyl ester, the 8,13-epimer of the latter was formed, the structure of its molecule being established from the results of X-ray structural analysis.Novosibirsk Institute of Organic Chemistry, Siberian Division of the Russian Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 663–669, September–October, 1994.     

Directional crystallization of B4C-NbB2 and B4C-MoB2 eutectic compositions

We studied the directional crystallization of different compositions in B₄C-NbB₂ and B₄C-MoB₂ systems. The eutectic compositions for both systems are evaluated. It is shown that in the first system the rod-like eutectic structure is formed, in second, the “Chinese hieroglyphics”. In both cases high hardness and high microplasticity are observed, which are much more than for individual component phases. These compositions may be considered as a new kind of self-strengthening composite materials.     

Structures of OA-6129A,B1, B2 and C,new carbapenem antibiotics

The structures of carbapenems OA-6129A, B₁, B₂ and C were determined by spectroscopy and chemical transformation.     

A convenient route to (+)-(9,11)-epithia-(11,12)-methano-thromboxane A2, from prostaglandin E2, methyl ester

(+)-(9,11)-Epithia-(11,12)-methano-thromboxane A₂ which is of great importance in thromboxane research, has been synthesized from prostaglandin E₂ methyl ester.     

Synthesis of thromboxane A2 analogs—3 : (+)-Thiathromboxane A2

(+)-11a-methano-9,11-thiathiromboxane A₂(1) was synthesized from prostaglandin A₂ and prostaglandin E₂.     

Uroleuconaphins A1 and B1, two red pigments from the aphid Uroleucon nigrotuberculatum (Olive)

Two novel red pigments, uroleuconaphins A₁ (1) and B₁ (2) were isolated from the aphid Uroleucon nigrotuberculatum (Olive). The structures and the absolute configurations of 1 and 2 were determined by single-crystal X-ray analysis of their derivatives. These structures were constituted as dimeric compounds of two molecules of quinone A (3), which were linked via a dihydrofuran ring system.