Dithiophene-Fused Oxadiborepins and Azadiborepins: A New Class of Highly Fluorescent Heteroaromatics

Access to dithiophene-fused oxadiborepins and the first azadiborepins attained via a modular synthesis route are presented. The new compounds emit intense blue light, some of which demonstrate fluorescence quantum yields close to unity. Cyclic voltammetry (CV) revealed electrochemically reversible one-electron reduction processes. The weak aromatic character of the novel 1,2,7-azadiborepin ring is demonstrated with in-depth theoretical investigations using nucleus-independent chemical shift (NICS) scans and anisotropy of the induced current density (ACID) calculations.

BNB-doped phenalenyls - aromaticity switch upon one-electron reduction

Fully aromatic, luminescent, and highly robust BNB-doped phenalenyls have been prepared, which are isoelectronic to the phenalenyl cation. B-Fluoromesityl-substitution leads to fluorescence in an extremely narrow range and significant increase in the reduction potential. Detailed theoretical investigations revealed an intramolecular aromaticity switch upon one-electron reduction.

Bifuran-bridged bisboranes: highly luminescent B-doped oligohetarenes

Boron-doping of oligohetarenes – via classical metathesis or silicon/boron exchange routes – led to strongly luminescent and twofold reversibly reducible oligomers.

Catalytic Si/B Exchange Condensation: A Green B–C Coupling Method That Provides Access to Monodisperse (Het)arylborane ‘Trimers’

The potential of our metal-free B–C coupling method using catalytic Si/B exchange condensation is demonstrated by the synthesis of a series of monodisperse (het)arylborane oligomers with four (het)arene moieties and three boron centers (i.e., ‘trimers’). Photophysical and electrochemical investigations evidenced effective π-conjugation over the (het)arene rings and the boron centers.

From Monodisperse Thienyl- and Furylborane Oligomers to Polymers: Modulating the Optical Properties through the Hetarene Ratio

The application of our newly developed B-C coupling method by catalytic Si/B exchange is demonstrated for the synthesis of a series of triarylboranes (1), monodisperse thienyl- and furylborane dimers (2) and trimers (9), extended oligomers (3) and polymers (3'), as well as mixed (oligo)thienyl-/furylboranes. The structures of 1 aa^Tip , 1 bb^Tip , and 2 bbb^Mes* , determined by X-ray crystallography, reveal largely coplanar hetarene rings and BR₃ environments, which are most pronounced in the furylborane species. Photophysical investigations, supported by TD-DFT calculations, revealed pronounced π-electron delocalization over the hetarene backbones including the boron centers. With an extended series of derivatives of varying chain lengths available, we were able to determine the effective conjugation lengths (ECL) of poly(thienylborane)s and poly(furylborane)s, which have been reached with the highest-molecular-weight derivatives of our study. Through variation of the furan-to-thiophene ratio, the photophysical properties of these materials are effectively modulated. Significantly, higher furan contents lead to considerably increased fluorescence intensities. Compounds 1 aa^Tip , 1 bb^Tip , and 3 a^Tip showed the ability to bind fluoride anions. The binding process is signaled by a distinct change in their optical absorption characteristics, thus rendering these materials attractive targets for sensory applications.

Difuryl(supermesityl)borane: a versatile building block for extended π-conjugated materials

B-Doping of oligo(hetarene)s led to very robust, air-stable π-conjugated materials that are strong electron-acceptors and blue light emitters.

Catalytic B-C Coupling by Si/B Exchange: A Versatile Route to π-Conjugated Organoborane Molecules, Oligomers, and Polymers

Conjugated organoboranes have emerged as attractive hybrid materials for optoelectronic applications. Herein, a highly efficient, environmentally benign catalytic B-C bond formation method is presented that uses organosilicon compounds, dibromoboranes, and the metal-free organocatalyst Me₃SiNTf₂. This Si/B exchange approach has been successfully applied to the synthesis of arylborane molecules 4a-c, oligomers 8a,b, and polymers 8a',b'. Photophysical investigations, supported by TD-DFT calculations, reveal highly effective π-conjugation in thienyl- and furylborane species; the latter are also highly emissive.

Access to N-cyanosulfoximines by transition metal-free iminations of sulfoxides

Sulfoxides are stereospecifically converted to N-cyanosulfoximines using N-chlorosuccinimide (NCS) as oxidising agent and cyanamide as nucleophilic amine source.

An Asymmetric Organocatalytic Quadruple Domino Reaction Employing a Vinylogous Friedel-Crafts/Michael/Michael/Aldol Condensation Sequence

An organocatalytic quadruple cascade initiated by a Friedel-Crafts-type reaction is described. The (S)-diphenylprolinol trimethylsilyl ether catalyzed reaction yields highly functionalized cyclohexenecarbaldehydes bearing a 1,1-bis[4-(dialkylamino)phenyl]ethene moiety and three contiguous stereogenic centers. The reaction tolerates various functional groups and all products are obtained with very good diastereoselectivity and with virtually complete enantiomeric excess.

[Practice-relevant, functional analysis for the maxillary-orthopedic consultation]

The author presents a mirror of maxillary-orthopedic, functional analyses for assessment of motions and positions of the lower jaw bone, for examinations of the jaw joint and for registration of the so-called attendant function. The pertinent paper of documentation enables an ergonomically favourable utilization for basic, progress and final examinations, also in an extensive number of patients.

Human thrombomodulin gene is intron depleted: nucleic acid sequences of the cDNA and gene predict protein structure and suggest sites of regulatory control

We have isolated a human thrombomodulin cDNA, and a human genomic clone containing the putative promoter domain, as well as the translated and untranslated regions of the endothelial cell receptor. The nucleotide sequence of the thrombomodulin cDNA allows us to provide a complete picture of the structure of this endothelial cell receptor, and to confirm its homology to the human low density lipoprotein receptor. The nucleotide sequence of the thrombomodulin gene suggests areas within the putative promoter domain that may be critical for regulating expression of the human endothelial cell receptor, indicates a potential signal peptide, and shows that no introns are present within the coding region. The overall organization of the human thrombomodulin gene is surprising because it represents an example of a gene that contains epidermal growth factor type B repeats and a membrane spanning region, which are not isolated within discrete exons.

Microvascular heparin-like species with anticoagulant activity

Calf microvasculature was isolated from retina and cerebral gray matter. These preparations contained 0.048-0.060 U of heparin-like anticoagulant activity per gram of wet tissue. The retinal microvascular material contained no detectable mast cells. The anticoagulant potency of this product was associated solely with endothelial cells. This property appears to be due to a heparinlike proteoglycan since molecular species with biologic activity are precipitated with 10% (wt/vol) trichloroacetic acid and are destroyed by incubation with Flavobacterium heparinase. Furthermore, the above component functions in a manner virtually identical to heparin since approximately 60% of these species with anticoagulant activity bind to antithrombin-concanavalin A-Sepharose 4B, and only 15% of their biologic potency is expressed in the presence of antithrombin modified near the mucopolysaccharide binding domain. The cerebral microvascular tissue contained a trace subpopulation of mast cells (approximately 0.3%). The anticoagulant activity of this preparation is most probably associated with both endothelial cells and mast cells. However, complete separation of these two cellular elements has proven difficult with current methodology.

Development of gastrointestinal mucosal barrier. I. The effect of age on intestinal permeability to macromolecules

Indirect evidence has suggested that increased quantities of antigen may penetrate the intestinal mucosa and enter the systemic circulation during the newborn period compared to adult life. However, no direct measurement of macromolecular transport has been reported as a function of perinatal age. To study this process, we administered 100 mg of tritiated bovine serum albumin ([3H]BSA) by gavage to rabbits at birth, one wk, 2 wk, 6 wk, and one year of age and measured plasma radioactivity 4 hr after gavage. Plasma concentration of trichloroacetic acid insoluble radioactivity and immunoreactive bovine serum albumin radioactivity decreased significantly after one wk of age. When adult animals were gavaged with the same amount of [3H]BSA per body weight as the one-wk-old animals, they failed to transport as much of the antigen as the younger animals. This study, therefore, provides objective evidence that the intestinal mucosal barrier of newborns may be incompletely developed at birth and allow increased intestinal transport of antigens into the circulation.

Development of gastrointestinal mucosal barrier. II. The effect of natural versus artificial feeding on intestinal permeability to macromolecules

We have recently reported that the intestinal transport of intact macromolecules into the circulation decreases with age presumably due to maturation of mucosal barrier factors. To extend this observation and determine the effect of natural versus artificial feeding on maturation of intestinal mucosal "barrier function" we conducted experiments which assessed both macromolecular transport and epithelial cell morphology. To study barrier function, we gavage fed a physiologic quantity (100 mg) of bovine serum albumin (BSA) to weight-matched breast- and bottle-fed infant rabbits at 1 and 2 wk of age and quantitated intestinal macromolecular transport by measuring circulating plasma concentrations of the intact antigen 4 hr later. a significant decrease (P less than 0.02) in immunoreactive bovine serum albumin (I-BSA) concentration was noted in breast-fed (6.12 +/- 0.77 micrograms I-BSA per ml plasma) compared with bottle-fed (9.19 +/- 0.93 micrograms I-BSA per ml plasma) animals at one wk. However, at 2 wk, no difference could be demonstrated between the two groups. Furthermore, small intestinal morphology evaluated by light and electron microscopy was similar in both groups each age. To determine if the lower plasma I-BSA noted at one wk in naturally fed animals was related to the presence of anti-BSA antibodies in breast milk and/or in plasma of the pups, breast milk and plasma from the breast-fed animals was evaluated by counterimmunoelectrophoresis and hemagglutination. No anti-BSA antibodies were detected. Moreover, plasma from breast- and artificially fed rabbits not gavage fed BSA contained no I-BSA. These data suggest that intestinal transport of antigens in the immediate neonatal period is decreased earlier in breast- as compared to bottle-fed animals. Therefore, we suggest that breast milk may exert a protective function to control the transport of potentially antigenic molecules into the systemic circulation of newborn animals by either facilitating the early maturation of intestinal barrier function or by providing passive barrier factors until the newborn's natural barrier can develop.

Binding of exogenous protein fragments to native proteins: possible explanation for the overestimation of uptake of extrinsically labelled macromolecules from the gut

Investigators studying the transport of macromolecules across mucosal surfaces have noted that techniques involving exogenously labelled macromolecules result in estimation of transport which exceed estimates based on immunochemical methods. The present study tested the possibility that radio-labelled fragments of macromolecules might bind to host proteins resulting in an apparent increase in 'size' of the fragments. Fragments obtained by dialysis of bovine serum albumin (BSA) labelled with tritium gas by Wilzbach method, bound to normal rabbit serum in vitro and in vivo. Binding to BSA exceeded binding to bovine gamma globulin (BGG). Dinitrophenylated BGG was administered by gavage to adult rats; DNP-bearing fragments were identified in their serum and recovered by gel filtration. After radio-labelling, these serum fractions also bound to macromolecular constituents of normal rat serum. These findings suggest that several different fragments of proteins may bind to native serum components. These results may bear upon in vivo observations since it is likely that following intestinal instillation of extrinsically labelled protein, labelled amino acids or small peptides are generated by the digestive process, become absorbed, bind to serum macromolecules and thereby mimic the uptake of macromolecules.