Mapping of the cationic starch adsorbed on pulp fibers by ToF-SIMS

Cationic starch (CS) is routinely used in the papermaking process to improve the dry strength or printability of paper. The effectiveness depends on the distribution of the starch on the pulp fiber, and in this study, time-of-flight secondary ion mass spectrometry was used to investigate this distribution. The characteristic peak at 58m/z was applied to map the CS. Based on the imaging analysis of the handsheets with the CS as an internal additive, the distribution of CS became more uniform with decreasing freeness. The amount of adsorbed CS increased with increasing fiber length and was lower on vessels than on other fibers. These results were related to fibrillation. From the analysis of handsheets with CS as an external additive, the penetration depth of the starch into base paper increased with decreases in the sizing degree of the base paper.     

Utilization of Sodium Nitroprusside as an Intestinal Permeation Enhancer for Lipophilic Drug Absorption Improvement in the Rat Proximal Intestine

As advanced synthetic technology has enabled drug candidate development with complex structure, resulting in low solubility and membrane permeability, the strategies to improve poorly absorbed drug bioavailability have attracted the attention of pharmaceutical companies. It has been demonstrated that nitric oxide (NO), a vital signaling molecule that plays an important role in various physiological systems, affects intestinal drug absorption. However, NO and its oxidants are directly toxic to the gastrointestinal tract, thereby limiting their potential clinical application as absorption enhancers. In this study, we show that sodium nitroprusside (SNP), an FDA-approved vasodilator, enhances the intestinal absorption of lipophilic drugs in the proximal parts of the small intestine in rats. The SNP pretreatment of the rat gastrointestinal sacs significantly increased griseofulvin and flurbiprofen permeation in the duodenum and jejunum but not in the ileum and colon. These SNP-related enhancement effects were attenuated by the co-pretreatment with dithiothreitol or c-PTIO, an NO scavenger. The permeation-enhancing effects were not observed in the case of antipyrine, theophylline, and propranolol in the duodenum and jejunum. Furthermore, the SNP treatment significantly increased acidic glycoprotein release from the mucosal layers specifically in the duodenum and jejunum but not in the ileum and colon. These results suggest that SNP increases lipophilic drug membrane permeability specifically in the proximal region of the small intestine through disruption of the mucosal layer.     

Cyclotrisilenylium ion: the persilaaromatic compound

The highly crowded 3,3-bis(di-tert-butylmethylsilyl)-1,2-bis(tri-tert-butylsilyl)cyclotrisilene (3) was newly designed as a precursor of the cyclotrisilenylium ion and prepared by the reaction of 2 equiv of dilithiosilane (tBu2MeSi)2SiLi2 (1) with 2,2,3,3-tetrabromo-1,1,1,4,4,4-hexa-tert-butyltetrasilane. The reaction of 3 with triphenylmethylium tetraarylborate in toluene produced (di-tert-butylmethylsilyl)bis(tri-tert-butylsilyl)cyclotrisilenylium ion (4+), which was isolated in the form of the tetraarylborate salt as extremely air- and moisture-sensitive yellow crystals, representing the first isolable silicon congener of the cyclopropenylium ion. The molecular structure of 4+.TSFPB- (TSFPB- = tetrakis[4-(tert-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]borate) was established by X-ray crystallographic analysis, showing that the three-membered ring constitutes an almost equilateral triangle with average Si-Si bond lengths of 2.216(3) A. The X-ray crystal structure and spectral data show that 4+ is not only a free silyl cation but also a 2pi electron aromatic species with delocalization of the positive charge over the three-membered skeleton.     

Highly chemo- and regioselective intermolecular cyclotrimerization of alkynes catalyzed by cationic rhodium(I)/modified BINAP complexes

[reaction: see text] Cationic rhodium(I)/modified BINAP complexes are effective catalysts for highly regioselective intermolecular cyclotrimerization of terminal alkynes and highly chemo- and regioselective intermolecular cocyclotrimerization of diethyl acetylenedicarboxylate (DEAD) and terminal alkynes. It is a noteworthy example of intermolecular cocyclotrimerization of two different alkynes in terms of catalytic activity, chemo- and regioselectivity, scope of substrates, and ease of operation. The wide applicability of this new cocyclotrimerization procedure is demonstrated in the one-step synthesis of [6]metacyclophane.     

Chiral separation of enantiomeric 1,2-diamines using molecular imprinting method and selectivity enhancement by addition of achiral primary amines into eluents.

The imprinted polymers based on a transient complex formation between methacrylic acid and template molecules were prepared by using methacrylic acid and ethylene dimethacrylate as a cross-linking agent. The template molecules used were (R,R)-cyclohexanediamine (1), (S,S)-1,2-diphenylethylenediamine (2) and (S)-1,1'-binaphthyl-2,2'-diamine (3). Another group of templates were those in which the amino group of these templates had been substituted by the hydroxy group: (R,R)-1,2-cyclohexanediol (4) and (S,S)-hydrobenzoin (5). Racemic 2 was separated by the polymer prepared with template 2 (P2) and that with template 1 (P1). Template 2 is larger than template 1 in steric bulkiness, but P1 was effective for the enantiomer separation of racemic 2. P1 was not effective for the separation of racemic 4. Enantioselectivity observed in racemic 2 in P2 was higher than that in racemic 1 in P1. P2 has no definite predetermined shape for solute 1, but it was capable of separating racemic 1. This separation should be thus ascribed to the orientation of at least two carbonyl groups reflecting the conformation of template 2 in P2 cavity. Racemic 5, having the same configuration of the two bulky phenyl groups as that of solute 2, was separated in P2. When the primary amines such as propylamine, cyclohexylamine and 1-adamantanamine were added into the acetic acid-methanol mixtures as eluents, both enantioselectivity and retentivity for racemic 2 were enhanced along with the remarkable peak tailing.     

Stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes by using trifluoromethanesulfonic acid

Novel stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes in the presence of trifluoromethanesulfonic acid has been carried out to give the corresponding products, which are not obtained by general Lewis acid-promoted methods, with 70-92% de in 62-74% yield. No cycloadducts were detected in the crude product by ¹H NMR.     

Enhanced mass resolution tandem mass spectrometry method for 2,3,7,8-tetrachlorodibenzo-p-dioxin detection with ion trap mass spectrometry using high damping gas pressure

Damping gas flow was optimized for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) determination using ion trap mass spectrometer. A tandem mass spectrometry (MS-MS) method with better than unit-mass resolution (mass width, 0.3 u) was developed at a damping gas flow of 1.5 ml/min and a collision-induced dissociation (CID) voltage of 3.30 V. The relative standard deviation (R.S.D.) at the enhanced resolution was 2.9% in 24 h of consecutive injections. The detection limit was significantly improved because the efficiency of both precursor ion trapping and fragmentation increased with the damping gas flow. Product ion yield was 4.5 times higher and limit of detection was 3.2 times lower than at the default flow (0.3 ml/min and 1.65 V).     

Rhodium-catalyzed reductive coupling of disulfides and diselenides with alkyl halides, using hydrogen as a reducing agent

[reaction: see text] We have established that RhCl(PPh3)3 catalyzes a reductive coupling of disulfides and diselenides with alkyl halides in the presence of triethylamine using hydrogen as a reducing agent. This reaction serves as a convenient new method to produce unsymmetrical sulfides and selenides from disulfides and diselenides instead of unstable and odoriferous thiols and selenols.     

Mn2(saltmen)2Ni(pao)2(L)2](A)2 with L=pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole and A=ClO4-, BF4-, PF6-, ReO4-: a family of single-chain magnets

A series of single-chain magnets, [Mn2(saltmen)2Ni(pao)2(L)2](A)2 (saltmen(2-)=N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate), pao-=pyridine-2-aldoximate; A-=ClO4- with L=4-picoline; 2, 4-tert-butylpyridine; 3, N-methylimidazole; 4, and L=pyridine with A-=BF4-; 5, PF6-; 6, ReO4-; 7), was prepared by reactions between MnIII dimer units, i.e., [Mn2(saltmen)2(H2O)2](A)2 (A-=ClO4-, BF4-, PF6-) or Mn2(saltmen)2(ReO4)2, and NiII monomeric units, i.e., Ni(pao)2(L)2, in methanol/water media. The crystal structures of 4, 6, and 7 were established by single-crystal X-ray crystallography. These three compounds are isostructural with [Mn2(saltmen)2Ni(pao)2(py)2](ClO4)2 (1) (Clérac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837) and crystallize in monoclinic space group C2/c. The linear arrangement of MnIII dimer units and NiII building blocks leads to an alternating chain having a repeating unit, [-(O)2-Mn-ON-Ni-NO-Mn-]. The chains are well separated with the nearest interchain intermetallic distance of 10.36 A for 4, 10.51 A for 6, and 10.30 A for 7, and there is no significant pi-pi interchain interaction between ligands. The void space between the chains is occupied by counteranions, which control the three-dimensional organization of the chains. The X-ray diffraction analysis (XRD) on a powder sample was also performed for all compounds. The XRD patterns for 1, 2, and 4-7 are very similar, emphasizing the isostructural nature of these materials although they have individually slight different interchain distances. Inversely, the XRD pattern for 3 reveals a completely different shape being indicative of the peculiar crystal packing compared to the others. Nevertheless, the one-dimensional nature of the structure is also kept in 3 as indicated by magnetic measurements. The whole family of compounds exhibits quasi-identical magnetic behavior compared to that described for 1. Above 30 K, the heterometallic chain can be described as an assembly of antiferromagnetically coupled Mn...Ni....Mn trimers (via oximate bridge, -24.2 K相似文献