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61.
Thorsteinn Loftsson Ína B. Össurardóttir Thorsteinn Thorsteinsson Matt Duan Már Másson 《Journal of inclusion phenomena and macrocyclic chemistry》2005,52(1-2):109-117
The natural β-cyclodextrin (βCD) and its complexes have limited solubility in aqueous solutions. This low aqueous solubility, as well as low aqueous solubility of the guest molecule (i.e. triclosan or triclocarban (TCC)), can result in low complexation efficiency (CE). The purpose of this study was to enhance the apparent intrinsic solubility (S
0) of the guest molecule and its βCD complexes through ionization and addition of auxiliary compounds such as polymers, amino acids and metal ions. Both triclosan (pK
a
7.9) and TCC (pK
a
12.7) are weak acids. Addition of ethanol to the complexation medium enhanced S
0 of both triclosan and TCC but at the same time ethanol lowered the stability constant (K
c
) of their βCD complexes resulting in overall lowering of CE. Addition of small amount of water-soluble polymers enhanced the βCD solubilization of both guests, and addition lysine enhanced the solubilization of TCC. Ionization of triclosan resulted in significant enhancement of CE and enhanced triclosan release from tablets containing triclosan/βCD complex. The effect of ionization was not as pronounced in the case of TCC.This revised version was published online in July 2005 with a corrected issue number. 相似文献
62.
H. Pongratz K. K. Mayer W. Wiegrebe 《Monatshefte für Chemie / Chemical Monthly》1997,128(6-7):659-673
Summary N-Butoxy- and N-propoxy-imines derived fromo-,m-, andp-substituted benzaldehydes (X = F, Cl, Br, I) decompose upon electron impact to the respective aldoximes by loss of C
n
H2n
and competitivelyvia 1,5-distonic radical cations by loss of CH2O to 1,3-distonic ions which eliminate H and/or a halogen atom in the course of homolytic aromatic substitution, giving rise to cyclic (M-CH2O-H)+ or (M-CH2O-X
)+ ions.Dedicated with warm regards to Prof. Dr.D. Seebach, Zürich, on the occasion of his 60th birthday 相似文献
63.
A method to analyze human plasma proteins without fractionation, directly applying a plasma-matrix mixture on the target plate of a matrix-assisted laser desorption/ionization-time of flight-mass spectrometer (MALDI-TOF-MS), has been described. Peaks of ionized plasma proteins could not be detected applying a mixture of an undiluted plasma sample and a matrix solution, but they appeared when the plasma was diluted before mixing with the matrix. Tenfold diluted plasma provided well-resolved protein peaks in the m/z range from 4000 to 30,000. The addition of a simple post-crystallization washing procedure performed on the target plate further improved the quality of mass spectra. We numbered 58 peaks in the range of 4-160 kDa and 32 out of which were assigned to the plasma protein species which have been reported. Especially high sensitivity and resolution were obtained in the region < 30 kDa, where multiple isoforms of apolipoprotein A-I, apolipoprotein A-II, apolipoprotein C-I, apolipoprotein C-II, apolipoprotein C-III, and transthyretin could be assigned. Various post-translational modifications are involved in the isoforms, e.g., proteolytic cleavage, glycosylation and chemical modifications. This method will become complementary with the present electrophoretic techniques, especially for the analysis of low-molecular-mass proteins. 相似文献
64.
65.
66.
《Arabian Journal of Chemistry》2022,15(1):103472
As a representative of traditionally fermented Chinese medicine, Massa Medicata Fermentata (MMF) shows the functions of invigorating the spleen and stomach and promoting digestion, which plays an important role in the treatment of gastrointestinal diseases. The fermentation mechanism and the key factors that affect the quality of MMF have not been revealed yet, which has become an urgent issue that limits its clinical application. This article aims to systematically and comprehensively reveal the transformation of physical properties and the dynamic trend of chemical components including substrate components, volatile components, and lactic acid as anaerobic fermentation product during MMF fermentation. Along with obvious hyphae growth observed for MMF, the weight of MMF decreased, and the moisture and temperature increased. Through the quantified 14 components from substrate, ferulic acid increased from 45.53 ± 6.94 to 141.89 ± 78.40 μg/g, while glycosides and phenolic acids declined except caffeic acid. Also, within the 66 volatile components analyzed, alcohols and acids increased, while aldehydes and ketones decreased. Lactic acid was not detected in the fermentation substrate, but an apparent increase in lactic acid content was observed along with the increased fermentation days, resulting in 2.54 ± 0.15 mg/g on day 8. Based on the tested components, the fermentation process of MMF was discriminated into three distinct stages by principal component analysis, and an optimal fermentation time of four days was proposed. The results of this study will be of great significance to clarify the characteristics of fermentation and conduce to improving quality standards of MMF. 相似文献
67.
The widespread occurrence of the neutral loss of one to six amino acid residues as neutral fragments from doubly protonated tryptic peptides is documented for 23 peptides with individual sequences. Neutral loss of amino acids from the N-terminus of doubly charged tryptic peptides results in doubly charged y-ions, forming a ladder-like series with the ions [M + 2H](2+) = y(max) (2+), y(max - 1) (2+), y(max - 2) (2+), etc. An internal residue such as histidine, proline, lysine or arginine appears to favor this type of fragmentation, although it was sometimes also observed for peptides without this structure. For doubly protonated non-tryptic peptides with one of these residues at or near the N-terminus, we observed neutral loss from the C-terminus, resulting in a doubly charged b-type ion ladder. The analyses were performed by Q-TOF tandem mass spectrometry, facilitating the recognition of neutral loss ladders by their 2+ charge state and the conversion of the observed mass differences into reliable sequence information. It is shown that the neutral loss of amino acid residues requires low collision offset values, a simple mechanistic explanation based on established fragmentation rules is proposed and the utility of this neutral loss fragmentation pathway as an additional source for dependable peptide sequence information is documented. 相似文献
68.
在不确定性环境下,当决策单元(DMU)的投入产出数据为区间数形式时,为解决决策单元之间既不是合作也不是竞争关系时的交叉评价问题,本文提出一种中立型区间交叉效率模型。从所有被评价者的角度出发解决评价权重的选取问题,以决策单元投入得分的平均偏差与产出得分的平均偏差之和最小化为目标,建立决策单元在最佳和最差两种生产状态下的中立型区间交叉效率模型。在本文提出的中立型模型视角下,DMU的投入得分平均偏差和产出得分平均偏差之和达到最小。算例结果表明该中立型区间交叉效率模型的有效性,解决了不确定性环境下的交叉评价问题,保证评价的客观公正,更加符合现实。 相似文献
69.
Arturo ArduiniElisabetta Brindani Giovanna GiorgiAndrea Pochini Andrea Secchi 《Tetrahedron》2003,59(38):7587-7594
The synthesis of new hosts specifically designed for the recognition of neutral guests bearing donor-acceptor hydrogen bonding groups is described. These hosts are characterized by the presence of two distinct binding region in close proximity: the rigid π-donor cavity and the H-bond donor N-methylene-N′-phenylureido group inserted onto the upper rim of the calix[4]arene skeleton. The binding abilities of these receptors were investigated toward a series of neutral ditopic organic molecules in CDCl3 solution by 1H NMR spectroscopy. The results obtained show that rigidity of the calix[4]arene apolar cavity is the control element in determining efficiency. In fact, compared with the more rigid 2, host 10, where the rigidity of the cone structure is maintained by hydrogen bonding of the OH of the lower rim, a decrease of efficiency of almost one order of magnitude was observed. The cooperative effect of the two binding region of host 2 was verified with different classes of ditopic guests. Good efficiency in the recognition of urea derivatives and dimethylsulfoxide was achieved. 相似文献
70.
A small amount (≤ 10−6 mol fraction) of four alkaline earth metals, tin and yttrium were introduced into five, premixed, fuel-rich, H2–O2–N2 flames at atmospheric pressure in the temperature range 1820–2400 K. Aqueous salt solutions of the metals were sprayed into the premixed flame gas as an aerosol using an atomizer technique. Ions in a flame were observed by sampling flame gas through a nozzle into a mass spectrometer. The concentrations of the major neutral metallic species present in the flame were calculated from thermodynamic data currently available. The principal metallic ions observed were AOH+ (A = Mg, Ca, Sr, Ba, Sn) and A(OH)2+ (A = Y), formed initially by proton transfer to AO and OAOH from H3O+, a natural flame ion. Except for Mg, the ions were also produced by chemi-ionization processes. By adjusting the concentration(s) of the salt solution in the atomizer, it was found that a pair of ions could be brought into equilibrium within the time scale of the flame; the pairs included H3O+ with a metal ion or two metallic ions. Because water is a major product of combustion, a very large difference in proton affinity PA0(AO) − PA0(H2O) ≤ 490 kJ mol−1 (117 kcal mol−1) could be attempted for the proton transfer equilibrium. Using PA0(H2O) = 691.0 kJ mol−1 (165.2 kcal mol−1) as a reference base to anchor the proton affinity scale, ion ratio measurements led to proton affinity PA0 values of 766, 912, 1004, 1184, 1201, and 1222 kJ mol−1 (183, 218, 240, 283, 287, and 292 kcal mol−1) corrected to 298 K for OYOH, SnO, MgO, CaO, SrO, and BaO, respectively; of these, only the value for OYOH has not been reported previously. If it is assumed that the neutral thermodynamic data are correct (although some appear to be in error), the uncertainties in the PA results reported here are ± 21 kJ mol−1 (5 kcal mol−1). The realization that these equilibria can be achieved in flames provides a new approach to consolidate and build the high end of the proton affinity ladder, primarily of metallic species which are not accessible at lower temperatures. 相似文献