Experimental investigations of ice recrystallization inhibition (IRI) efficacy have been performed for a large number of different substances, including natural antifreeze proteins (AFP) and antifreeze glycoproteins (AFGP), several synthetic AFGP analogues, as well as synthetic polymers. Here we define IRI efficacy as that concentration at which the ice recrystallization rate is dominated by the IRI compound. The investigated 39 compounds show IRI efficacies from about 2 mmol L −1 for the least effective compound still showing activity to about 1 nmol L −1 , which corresponds to the highest efficacy found for natural AFGP samples. Hence, the assay employed allows for a quantitative comparison of IRI efficacy over a range of at least 6 orders of magnitude, thereby enabling studies of distinguishing effects induced by even subtle structural variations in AFGP analogues that were synthesized. Our results show that AFGP are by far the most effective IRI agents in our assay, and we surmise that this particular efficacy may be due to their disaccharide moieties. This supposition is supported by the fact that IRI efficacy is strongly reduced for monosaccharide AFGP analogues, as well as for AFGP analogues with acetyl-protected monosaccharide moieties.

In Arctic and Antarctic marine regions, where the temperature declines below the colligative freezing point of physiological fluids, efficient biological antifreeze agents are crucial for the survival of polar fish. One group of such agents is classified as antifreeze glycoproteins (AFGP) that usually consist of a varying number (n = 4-55) of [AAT]( n )-repeating units. The threonine side chain of each unit is glycosidically linked to β-D: -galactosyl-(1 → 3)-α-N-acetyl-D: -galactosamine. These biopolymers can be considered as biological antifreeze foldamers. A preparative route for stepwise synthesis of AFGP allows for efficient synthesis. The diglycosylated threonine building block was introduced into the peptide using microwave-enhanced solid phase synthesis. By this versatile solid phase approach, glycosylated peptides of varying sequences and lengths could be obtained. Conformational studies of the synthetic AFGP analogs were performed by circular dichroism experiments (CD). Furthermore, the foldamers were analysed microphysically according to their inhibiting effect on ice recrystallization and influence on the crystal habit.

SummaryThis paper highlights recent advances in synthesis, self-assembly and sensing applications of monodisperse magnetic Co and Co-alloyed nanoparticles. A brief introduction to solution phase synthesis techniques as well as the magnetic properties and aspects of the self-assembly process of nanoparticles will be given with the emphasis placed on selected applications, before recent developments of particles in sensor devices are outlined. Here, the paper focuses on the fabrication of granular magnetoresistive sensors by the employment of particles themselves as sensing layers. The role of interparticle interactions is discussed.

A simple one-pot azidochlorination for the preparation of nitrogen-containing Koenigs-Knorr glycosyl donors proceeds upon reaction of protected glycals with sodium azide, ferric chloride, and hydrogen peroxide. Different mono- and disaccharide galactals and glucals are converted in a highly α-selective manner to the 2-azido glycosyl chlorides. Starting from disaccharide galactals, building blocks for the synthesis of the T-antigen are obtained in a straightforward manner. The simplicity of the reaction conditions allows for an efficient and scalable α-selective synthesis of 2-azido substituted glycosyl chlorides.

Glycosylation adds carbohydrate moieties to proteins and functional peptides. Glycans, highly branched carbohydrate heteropolymers that can be attached to amino acids either through N-or O-glycosylation, serve as coding entity, providing specificity for carbohydrate-protein interactions, or modifying dynamic and structural behaviour of proteins. Glycoconjugates present glycans of extraordinary large structural variety, enabling information coding by steering molecular recognition.[1] Glycosylated proteins and lipids usually present their glycan moieties solvent-exposed at the surface where they can serve as highly specific binding partners. Specific protein-glycan interactions generally are enthalpically driven through hydrogen bonding and van der Waals interactions. Strong interactions only come about through cooperative formation of many hydrogen bonds or hydrophobic interactions. Glycoproteins and -lipids contribute to a range of signaling interactions mostly in eukaryotic cells, help regulate cell-cell communication and immune response, [2] or control protein folding and turnover.[3]Often a protein's functional state or specific complex is stabilized by glycosylation analogous to the effects of molecular crowding. [3b,c] Glycoproteins also serve as antifreeze reagent when interacting with ice crystals. [4] Since glycoproteins often are partially or fully disordered and glycans themselves are highly flexible structures, [5] the question arises how conjugated glycans influence protein and peptide conformational dynamics. Extensive O-glycosylation of mucin-like glycopeptides seems to rigidify the peptide backbone and increase the overall radius of gyration.[6] The unfolded state in a dynamic folding/unfolding protein equilibrium is influenced by glycosylation, too.[3b] However, various and partly contradictory effects of N/O-glycosylation on peptide conformations were observed experimentally and in computer simulations. [5,7] Overall, there is no comprehensive understanding on the molecular scale how glycoconjugate conformational dynamics are shaped by glycans and we seek to address this issue by studying well-defined synthetic model peptides.Herein we give an account of the influence that b-galactose O-conjugated to serine residues impose on peptide conformational dynamics. We compare intramolecular dynamics of unstructured peptides made of either glycine-serine repeats [GlySer] or made of glycosylated serine-glycine repeats [Ser(b-Gal)-Gly)] and characterize influences from attached glycans on peptide dynamics. Conformational dynamics are monitored and analyzed by fluorescence correlation spectroscopy (FCS). [8] As reporter system for dynamic processes we introduce a fluorophore-quencher pair on opposite ends of the unstructured peptides that report on end-to-end contacts by on/off changes in the fluorescence emission. We use the oxazine fluorophore MR121 (Figure 1), attached via site-specific labeling chemistry to the N-terminus, and the fluorescence-quenching amino acid tryptophan (Trp), incorporated as...