1,117 research outputs found
Automated assembly of oligosaccharides containing multiple cis-glycosidic linkages
Automated glycan assembly (AGA) has advanced from a concept to a commercial
technology that rapidly provides access to diverse oligosaccharide chains as
long as 30-mers. To date, AGA was mainly employed to incorporate trans-
glycosidic linkages, where C2 participating protecting groups ensure
stereoselective couplings. Stereocontrol during the installation of cis-
glycosidic linkages cannot rely on C2-participation and anomeric mixtures are
typically formed. Here, we demonstrate that oligosaccharides containing
multiple cis-glycosidic linkages can be prepared efficiently by AGA using
monosaccharide building blocks equipped with remote participating protecting
groups. The concept is illustrated by the automated syntheses of biologically
relevant oligosaccharides bearing various cis-galactosidic and cis-glucosidic
linkages. This work provides further proof that AGA facilitates the synthesis
of complex oligosaccharides with multiple cis-linkages and other biologically
important oligosaccharides
Pushing the Limits of Automated Glycan Assembly: Synthesis of a 50mer Polymannoside
Automated glycan assembly (AGA) enables rapid access to oligosaccharides. The overall length of polymers created via automated solid phase synthesis depends on very high yields at every step to obtain full length product. The synthesis of long polymers serves as the ultimate test of the efficiency and reliability of synthetic processes. A series of Man-(1[rightward arrow]6)-[small alpha]-Man linked oligosaccharides up to a 50mer, the longest synthetic sequence yet assembled from monosaccharides, has been realized via a 102 step synthesis. We identified a suitable mannose building block and applied a capping step in the final five AGA cycles to minimize (n-1) deletion sequences that are otherwise difficult to remove by HPLC
Transport control by coherent zonal flows in the core/edge transitional regime
3D Braginskii turbulence simulations show that the energy flux in the
core/edge transition region of a tokamak is strongly modulated - locally and on
average - by radially propagating, nearly coherent sinusoidal or solitary zonal
flows. The flows are geodesic acoustic modes (GAM), which are primarily driven
by the Stringer-Winsor term. The flow amplitude together with the average
anomalous transport sensitively depend on the GAM frequency and on the magnetic
curvature acting on the flows, which could be influenced in a real tokamak,
e.g., by shaping the plasma cross section. The local modulation of the
turbulence by the flows and the excitation of the flows are due to wave-kinetic
effects, which have been studied for the first time in a turbulence simulation.Comment: 5 pages, 5 figures, submitted to PR
Combination of automated solid-phase and enzymatic oligosaccharide synthesis provides access to α(2,3)-sialylated glycans
A synthetic strategy combining automated solid-phase chemical synthesis and enzymatic sialylation was developed to access α(2,3)-sialylated glycans.</p
Constraints of FL Motif on the Targeting and Function of Sodium-Bicarbonate Cotransporter 1
A C-terminal dihydrophobic FL motif plays a vital role in the basolateral targeting of sodium bicarbonate cotransporter 1. To further characterize the role of dihydrophobic FL motif, 1). the FL motif in wild type (PFLS) was reversed to LF (PLFS), 2). the FL motif (PFLS) was shifted upstream (FLPS), and 3). the FL motif (PFLS) was shifted downstream (PSFL). The wild type (PFLS) and its mutant (PLFS) were exclusively expressed on the basolateral membrane by con-focal microscopy, however, the mutant (FLPS) and (PSFL) were predominantly mistargeted to the apical membrane and the cytoplasm, respectively. Functional studies showed that the mutant (PSFL) displayed a remarkably reduced current (p value<0.05 vs wild type). The mutant (PSFL) displayed a more reduced membrane surface expression than the wild type and was co-localized with ER marker. The protein sequence spanning FL motif in kNBC1 C-terminal cytoplasmic tail shows a helical structure, mutants (PLFS) and (PSFL) reduce a-helical contents by circular dichroism study. Reversed FL isn't a constraint for basolateral targeting, but shifting it upstream and downstream are ones
Automated glycan assembly of oligosaccharides related to arabinogalactan proteins
Arabinogalactan proteins are heavily glycosylated proteoglycans in plants. Their glycan portion consists of type-II arabinogalactan polysaccharides whose heterogeneity hampers the assignment of the arabinogalactan protein function. Synthetic chemistry is key to the procurement of molecular probes for plant biologists. Described is the automated glycan assembly of 14 oligosaccharides from four monosaccharide building blocks. These linear and branched glycans represent key structural features of natural type-II arabinogalactans and will serve as tools for arabinogalactan biology
Shear-Flow Driven Current Filamentation: Two-Dimensional Magnetohydrodynamic Simulations
The process of current filamentation in permanently externally driven,
initially globally ideal plasmas is investigated by means of two-dimensional
Magnetohydrodynamic (MHD)-simulations. This situation is typical for
astrophysical systems like jets, the interstellar and intergalactic medium
where the dynamics is dominated by external forces. Two different cases are
studied. In one case, the system is ideal permanently and dissipative processes
are excluded. In the second case, a system with a current density dependent
resistivity is considered. This resistivity is switched on self-consistently in
current filaments and allows for local dissipation due to magnetic
reconnection. Thus one finds tearing of current filaments and, besides, merging
of filaments due to coalescence instabilities. Energy input and dissipation
finally balance each other and the system reaches a state of constant magnetic
energy in time.Comment: 32 Pages, 13 Figures. accepted, to appear in Physics of Plasmas
(049012
Modular automated solid phase synthesis of dermatan sulfate oligosaccharides
Dermatan sulfates are glycosaminoglycan polysaccharides that serve a multitude
of biological roles as part of the extracellular matrix. Orthogonally
protected D-galactosamine and L-iduronic acid building blocks and a photo-
cleavable linker are instrumental for the automated synthesis of dermatan
sulfate oligosaccharides. Conjugation-ready oligosaccharides were obtained in
good yield
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On the dynamics of turbulent transport near marginal stability
A general methodology for describing the dynamics of transport near marginal stability is formulated. Marginal stability is a special case of the more general phenomenon of self-organized criticality. Simple, one field models of the dynamics of tokamak plasma self-organized criticality have been constructed, and include relevant features such as sheared mean flow and transport bifurcations. In such models, slow mode (i.e. large scale, low frequency transport events) correlation times determine the behavior of transport dynamics near marginal stability. To illustrate this, impulse response scaling exponents (z) and turbulent diffusivities (D) have been calculated for the minimal (Burgers) and sheared flow models. For the minimal model, z = 1 (indicating ballastic propagation) and D {approximately}(S{sub 0}{sup 2}){sup 1/3}, where S{sub 0}{sup 2} is the noise strength. With an identically structured noise spectrum and flow with shearing rate exceeding the ambient decorrelation rate for the largest scale transport events, diffusion is recovered with z = 2 and D {approximately} (S{sub 0}{sup 2}){sup 3/5}. This indicates a qualitative change in the dynamics, as well as a reduction in losses. These results are consistent with recent findings from {rho} scaling scans. Several tokamak transport experiments are suggested
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