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Alginates are fairly abundant in nature and possess many interesting properties, including their biocompatibility and ability to absorb large amounts of water. Hence, increasing interest in their derivatization has been observed and the determination of the number of newly introduced functionalities has become a key issue. For this purpose, literature generally reports on conventional H-1-NMR spectra, typically recorded at elevated temperatures and/or after hydrolysis of the alginate to circumvent line broadening effects resulting from the high viscosity. The present work reports on the modification of alginate with methacrylate functionalities and determination of the resulting degree of substitution (DS), i.e. the number of introduced methacrylate moieties relative to the initial amount of hydroxyl groups along the alginate backbone, via NMR spectroscopy. Freeze-drying and low power water presaturation were applied to improve the quality of the H-1 NMR spectra. Nevertheless, it remains a qualitative method, to be used only for mutual comparisons of samples. A new and accurate method for DS determination of methacrylated alginates, based on C-13-NMR spectroscopy, is proposed. Quantitative C-13-NMR spectra were recorded with reduced measuring times by addition of a paramagnetic relaxation agent. The proposed method will also be applicable for other water-soluble functionalized alginates and polysaccharides in general. (C) 2019 Elsevier B.V. All rights reserved.

Cyclic lipopeptides (CLiPs) are secondary metabolites produced by a variety of bacteria. These compounds show a broad range of antimicrobial activities; therefore, they are studied for their potential applications in agriculture and medicine. It is generally assumed that the primary target of the CLiPs is the cellular membrane, where they can permeabilize the lipid bilayer. Model membrane systems are commonly used to investigate the effect of lipid composition on the permeabilizing activity of CLiPs, but these systems do not represent the full complexity of true biological membranes. Here, we introduce a novel method that uses sterol-auxotrophic oomycetes to investigate how the activity of membrane-active compounds is influenced by alterations in membrane sterol composition. More specifically, we investigated how ergosterol, cholesterol, beta-sitosterol and stigmasterol affect the activity of the structurally related Pseudomonas-derived CLiPs tolaasin and sessilin against the oomycete Pythium myriotylum. Both compounds were effective against oomycetes, although tolaasin was considerably more active. Interestingly, tolaasin and sessilin effects were similarly reduced by the presence of sterols, with cholesterol showing the highest reduction of activity.

The current paper focuses on the functionalization of κ-carrageenan and gelatin as extracellular matrix polysaccharide and protein mimic respectively to produce hydrogel films for adipose tissue engineering. More specifically, κ-carrageenan as well as gelatin have been functionalized with methacrylate and methacrylamide moieties respectively to enable subsequent UV-induced crosslinking in the presence of a photo-initiator. The gel fraction, the mass swelling ratio and the mechanical properties of both the one-component hydrogels and the protein/polysaccharide blends have been evaluated. The mechanical and swelling properties of the blends could be tuned by varying the hydrogel composition as well as the crosslinking method applied. The in vitro biocompatibility assays indicated a significantly higher cell viability of adipose tissue-derived mesenchymal stem cells seeded onto the blends as compared to the one-component hydrogels. The results show that the blends of gelatin and κ-carrageenan clearly outperform the one-component hydrogels in terms of adipose tissue engineering potential.

Model experiments under laboratory conditions were carried out to assess the accumulation tendency of Zr from a silica-zirconia core–shell nanoparticles, synthesised for the assay. Acute exposition tests were conducted with Daphnia magna and Danio rerio and the accumulation tendency of the nano and the molecular form was compared. Significant elevation of Zr was found in the tissue of the test organisms treated by the NP compared to the control, however, the retention of zebrafish was lower than that of the daphnids. Increased level of bioconcentration factor and the strong correlation of the redundancy analysis data suggest accumulation tendency in D. magna, yet long-term experiments are required to prove and further assess the environmental risk of food-chain bioconcentration. The BCF results were under the REACH limit for the D. rerio groups indicating the low short-term accumulation tendency of Zr from the NP. However, Zr level was significantly higher in zebrafish individuals originating from the SiO2@ZrO2 NP exposed treatments compared to the groups supplemented by the same concentration of ZrOCl2, which did not result in the elevation of Zr in fish tissue. The trace element homeostasis of D. rerio was not affected by the acute SiO2@ZrO2 NP exposition and no lethality occurred.

Dialkyl cationic surfactants, such as dioctadecyl dimethyl ammonium bromide (DODAB) form vesicles upon dispersion in water. In order to study the influence of the surfactant's counterion, the same dialkyl surfactant was prepared with a fluoride counterion (DODAF). Visually, quite transparent dispersions were prepared when fluoride was selected as counterion, whereas more turbid dispersions were obtained using the bromide surfactant. LR-NMR revealed that the permeability of the DODAF dispersions for water was much larger, which indicated that these rather contained uni- or oligolamellar vesicles, whereas the DODAB dispersions were multilamellar. These observations seemed to indicate an increasing degree of surface charge neutralization by the heavier anions, in line with the Hofmeister series, which was indeed confirmed by electrophoretic light scattering measurements. In order to further quantify the surfactant-counterion interaction, HR-NMR diffusometry measurements were performed on dispersions of a dialkyl cationic surfactant with methyl sulphate counterion in deuterated water. The diffusion data showed that the mobility of this organic anion increased when adding different sodium halides, with a stronger effect from fluoride over chloride and bromide to iodide, which clearly indicated the gradual displacement of the methyl sulphate counterion from the vesicular surface by the stronger binding anions.

Superabsorbent polymers (SAPs) based on polysaccharides, especially alginate, could offer a valuable solution in a plethora of applications going from drug delivery to self-healing concrete. This has already been proven with both calcium alginate and methacrylated alginate combined with acrylic acid. In this manuscript, the effect of varying the degree of methacrylation and use of a combination of acrylic acid and acrylamide is investigated to explore the effects on the relevant SAP characteristics. The materials showed high gel fractions and a strong swelling capacity up to 630gwater/gSAP, especially for superabsorbent polymers with a low degree of substitution. The SAPs also showed only a limited hydrolysis in aqueous and cement filtrate solutions. ispartof: CARBOHYDRATE POLYMERS vol:168 pages:44-51 ispartof: location:England status: published

Superabsorbent polymers (SAPs) have already found their way in many applications. Some of these polymers undergo major characteristic changes by small environmental variations which makes them interesting for self-healing of cracks in concrete. In the present work, polymer networks composed of dimethylaminoethyl methacrylate and N,N′-methylenebisacrylamide have been synthesized. Moisture uptake capacities up to 45% were measured at a relative humidity of 95%. They showed a desired pH-responsive swelling behavior with no degree of degradation. A small significant mortar strength reduction is found with addition up to 1 m% compared to the cement mass. All results were compared to commercially available SAPs.

Whereas Whey Protein Isolate may be used as an effective emulsifier, it suffers from limited stability upon heating. In this research, the effect of combining Whey Protein Isolate (WPI) with Low Methoxyl Pectin (LMP) on the heat stability of WPI was investigated. This was accomplished either by simple mixing or by conjugate formation by dry heat treatment. WPI-LMP mixtures and conjugates were prepared at a WPI to LMP ratio of 1:0, 4:1, 2:1, and 1:1. Conjugates were prepared by means of dry heat treatment at a temperature of 60 °C and 74% relative humidity by incubation for up to 16 days. The pH effect and brown color development of the WPI-LMP conjugates upon incubation was monitored. SDS-Page, free amino group determination, as well as diffusion coefficient analysis, all confirmed the formation of new compounds with high molecular weight. The heat stability of the conjugates was then tested and compared to the native WPI. Upon 2 min of heating at 80 °C and pH 6.5, the solubility of WPI was reduced by approximately 50% due to thermal denaturation and subsequent aggregation. However, dry heat treatment of the WPI-LMP mixtures highly improved the heat stability of WPI: as the incubation time was increased, the residual protein solubility upon heating of the WPI became higher. Upon 16 days of incubation, the protein solubility of the heated WPI-LMP conjugates was comparable to that of the conjugates before heating. Considering the emulsifying properties, it was found that WPI-LMP conjugates produced smaller oil droplet compared to either native WPI, dry heated WPI, or mixtures of WPI-LMP which were not subjected to conjugation by dry heat treatment. Heating the emulsions at 80 °C for 10 and 20 min revealed that WPI-LMP conjugates stabilized emulsions exhibited excellent stability towards heat: whereas pronounced aggregation and gelation occurred in emulsions stabilized by WPI or mixtures with LMP, the conjugate stabilized emulsions retained their original viscosity and particle size.

To date, the potential of several types of polymeric materials as healing agents for self-healing of concrete has already been investigated. Generally, for self-healing concrete with encapsulated polymeric healing agents, the curing mechanism is triggered upon contact with moisture/air or upon reaction with a second component provided by additional capsules. The present work explores the use of in-situ curable hydrogels formed as a result of the elevated pH of the cementitious matrix, via a Michael-type addition reaction, as potential healing/sealing materials for concrete applications. For this purpose, a variety of acrylate-endcapped urethane-based precursors were synthesized and combined with a thiol-based cross-linker. Various properties including the viscosity, the curing time, the swelling capacity and the cross-linking efficiency have been evaluated. The potential of the developed materials to seal concrete cracks was assessed through manual injection. The results indicate that the cross-linking reaction can readily occur in-situ due to the alkaline environment of the cementitious matrix and that the hydrogels exhibit favorable sealing properties. Keywords: Self-healing, Concrete, Hydrogel precursor, Michael-type addition reaction, In-situ curable hydrogels

The industrial application of whey proteins as a food emulsifier is still limited due to its susceptibility towards heating. In this study, dry heat conjugation of whey protein and lactose was investigated to improve the heat stability of WPC-stabilised oil in water (O/W) emulsions. A commercially available whey protein concentrate (WPC), containing 80 % protein and 12 % lactose, was dry heat incubated. Hereby, the effect of incubation temperature (60, 70, and 80 °C), relative humidity (64, 74, and 79 %), and preconditioning pH (4, 6, 8, 10) were determined. Temperature variation showed a pronounced effect on the required duration to obtain conjugates with excellent emulsion heat stabilising capacity. Four hours of incubation at 80 °C was sufficient to retain the original particle size and consistency after heating the emulsions at 80 °C for 20 min. Whereas circular dichroism spectroscopy revealed that this dry heat incubation condition (80 °C, 4 h) maintained the secondary structure of WPC, pulsed-field gradient NMR revealed that about 40 % of the lactose present should become protein-bound to generate conjugates with the desired functionality. The results indicated that a heat stable WPC with about 40 % of bound lactose could be obtained by some hours of dry heat treatment at 80 °C.

Whey protein–lactose conjugates were prepared by dry heat incubation (60 °C, 74% relative humidity) at 1:1 M ratio of protein amino groups to reducing sugar. Pulsed-field gradient-nuclear magnetic resonance (PFG-NMR) was introduced as a new and absolute method to determine the degree of conjugation without any sample pretreatment, based on the different diffusion behaviour of free and protein-bound lactose. Whereas the TNBS method revealed 73% conjugation, PFG-NMR results indicated that only 37% of lactose was bound to the protein after 8 h incubation. Circular dichroism spectra showed no change of WPI secondary structure upon dry heat incubation, whereas the electrophoretic mobility shifted towards more negative values. The emulsifying and, more importantly, heat stabilising properties of the conjugates were subsequently evaluated in oil/water emulsions. Eight hours of incubation was sufficient to produce conjugates that successfully stabilised the emulsion against heating (80 °C, 20 min), regarding the particle size and viscosity.

Silica@zirconia core@shell oxide nanoparticles of approx. 50 nm diameter were developed in view of an application as a novel carrier with adjuvant activities for cancer vaccines. To this end, the aim was to cover the surface of the nanocarrier by potent single stranded DNA (ssDNA) type immune stimulators used in cancer vaccination. Prior to characterizing the binding of ssDNA to the nanocarrier surface, the adsorption of deoxynucleoside monophosphate building blocks (dNMPs) was studied. After optimization of conditions for synthesis, solvent exchange and surface modification, the effects and possible interference of several buffers, such as HEPES, PIPES, MOPS and MOPSO, were also investigated. Formation of a new compound was revealed by UV–VIS spectroscopy during the recording of zeta potential vs. pH titration curves in the presence of HEPES and PIPES buffer in the neutral-acidic pH region. We identified this new species as gold ions etched from the electrode of the zeta cuvette, stabilized by the buffers via chelation, which is then followed by their conversion into gold nanoparticles.

In an attempt to decrease the degree of heat-induced intermolecular protein interactions in recombined concentrated milk, the effect of sunflower lecithin, a natural source of phospholipids, was examined. The obtained results proved that lecithin supplemented milk emulsions demonstrated a less pronounced increase in viscosity as well as particle size, upon severe heating. Additionally, enzymatic hydrolysis was performed using a phospholipase A1. Phosphorus nuclear magnetic resonance and high performance liquid chromatography revealed that the lysophospholipid content reached a maximum after 20 min of hydrolysis and gradually declined as the hydrolysis reaction duration was extended. This work showed that sunflower lecithin largely improves the heat stability of whey protein containing solutions and emulsions due to its high phospholipid content. As the phospholipid molecular structure is important, it follows that the heat stability of whey protein containing products may be optimised by appropriate processing, such as enzymatic hydrolysis of intact lecithins.

The non-polar extract of the tubers of Lepidium meyenii Walpers yielded two benzylated alkamides (macamides), N-(3,4-dimethoxybenzyl)-hexadecanamide (1) and N-benzyltetracosanamide (2). The structure elucidation of the compounds was based on 1D and 2D NMR spectroscopic analyses, including 1H–1H COSY, 1H–13C HSQC, 1H–13C HMBC, 1H–15N HSQC and HMBC experiments. Fil: Chain, Fernando Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina Fil: Grau, Alfredo. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional.; Argentina Fil: Martins, José C.. University of Ghent; Bélgica Fil: Catalan, Cesar Atilio Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina

This study aimed at the interception of flavour deviations of salt-reduced Gouda-type cheeses, salted in sodium-reduced brines (NaCl + KCl brine) compared with a reference brine (NaCl brine), by the addition of adjunct strains of Lactobacillus helveticus and Lactobacillus paracasei , next to the common mixed-strain starter culture for Gouda. A multiphasic analysis of carbohydrates, organic acids, amino acids, and volatile flavour compounds was performed. After 56 days of ripening, the sensory characteristics of the cheeses were evaluated. Trained taste panel analysis determined some significant differences ( P

Because most dairy processes require heat treatment to ensure microbiological safety during storage, dairy industry has invested a lot of effort to acquire knowledge related to all the changes that may take place during heating. More precisely, measures have to be taken to avoid undesired changes that can badly affect the quality of the final product. Whey protein denaturation is one of the major changes that take place upon sterilization. The purpose of the present study was to investigate and compare the degree and type of interaction that occurs between whey protein isolate and different kinds of dialkyl phospholipids, as a function of their molecular structure, upon heating at different temperatures. Circular Dichroism (CD) experiments were performed to assess the extent of secondary structural changes of β-lactoglobulin upon incubation in the presence of both anionic and zwitterionic phospholipids. The far-UV spectra of the former revealed a significant change in ellipticities in the region between 208 and 222 nm, which represents the α-helical content of peptides and proteins upon incubation in the presence of anionic phospholipids at temperatures above their phase transition temperature. On the other hand, these changes were not evident upon incubation with phospholipids in the gel state or when applying zwitterionic phospholipids. Nuclear Magnetic Resonance (NMR) has been used to investigate the whey protein–surfactant interaction into more detail. The chemical shift of the surfactant methyl groups toward a more hydrophobic region in the NMR spectra revealed a hydrophobic whey protein–phospholipid interaction. This finding was further supported by Saturation Transfer Difference-NMR (STD-NMR) measurements. The NMR experiments also revealed that the lack of protein structural reorganization upon incubation in the presence of zwitterionic (lyso)-phospholipids could not be ascribed to a lack of interaction, but was caused by the fact that the interaction did not affect the protein's structure. Overall, this work indicated that phospholipids can modify the secondary structure of whey proteins (i.e. when using anionic phospholipids in the liquid crystalline state) due to hydrophobic interactions. In addition, the results prove that the heat stability of whey protein containing products may be optimized by appropriate selection of the phospholipid composition.

Poly(styrene-maleic anhydride) or SMA are versatile copolymers available in different grades of molecular weight (Mw = 5500–170,000 g/mol) and molar percentage of maleic anhydride (22–50 mol-%). As specific grades can be used for the synthesis of nanoscale structures in paper industry, a better understanding of the molecular structure was needed. Therefore, a broad range of SMA grades was analyzed by means of size exclusion chromatography, infrared spectroscopy, Raman spectroscopy and nuclear magnetic resonance spectroscopy. While the nominal composition could be determined by 1H NMR and Raman spectroscopy, the combination with 13C NMR and FTIR allowed a more detailed characterization of the molecular structure. The high-molecular weight SMA grades show a heterogeneous molecular structure with segments including high styrene and maleic anhydride moieties, respectively. The formation of film patterns was evaluated by deposition from an acetone solution, resulting in homogeneous films, fibrous structures, or spherical shapes with decreasing diameter as a function of maleic anhydride content including primary particle sizes of 100 nm. This study illustrates intrinsic molecular features of SMA grades that are capable for self-assembly, and can provide a selection tool for future nanoparticle formulation.

Huntington disease (HD) is a hereditary brain disease. Although the causative gene has been found, the exact mechanisms of the pathogenesis are still unknown. Recent investigations point to metabolic and energetic dysfunctions in HD neurons. Both univariate and multivariate analyses were used to compare proton nuclear magnetic resonance spectra of serum and cerebrospinal fluid (CSF) taken from presymptomatic HD transgenic rats and their wild-type littermates. N-acetylaspartate (NAA), was found to be significantly decreased in the serum of HD rats compared to wild-type littermates. Moreover, in the serum their levels of glutamine, succinic acid, glucose and lactate are significantly increased as well. An increased concentration of lactate and glucose is also found in CSF. There is a 1:1 stoichiometry coupling glucose utilization and glutamate cycling. The observed increase in the glutamine concentration, which indicates a shutdown in the neuronal-glial glutamate-glutamine cycling, results therefore in an increased glucose concentration. The elevated succinic acid concentration might be due to an inhibition of succinate dehydrogenase, an enzyme linked to the mitochondrial respiratory chain and TCA cycle. Moreover, reduced levels of NAA may reflect an impairment of mitochondrial energy production. In addition, the observed difference in lactate supports a deficiency of oxidative energy metabolism in rats transgenic for HD as well. The observed metabolic alterations seem to be more profound in serum than in CSF in presymptomatic rats. All findings suggest that even in presymptomatic rats, a defect in energy metabolism is already apparent. These results support the hypothesis of mitochondrial energy dysfunction in HD.

This work investigates the adsorption of polysorbate (Tween) 20 to paliperidone palmitate using the depletion technique, which analyzes the residual surfactant concentration in the aqueous continuous phase of the solid/liquid suspension. Total organic carbon determination was used to study the overall Tween concentration, whereas 1 H NMR was applied to differentiate between hydrophilic and amphiphilic ethoxylated sorbitan species. The investigation revealed that Tween 20 adsorption was proportional to the specific surface area of paliperidone palmitate particles, and can be approximated by the Langmuir model. The alkyl-chain-bound (amphiphilic) sorbitans were found to be more effectively adsorbed than the alkyl-chain-free (hydrophilic) sorbitan species, which indicates that the adsorption was driven by hydrophobic interactions. Temperature (room temperature versus 40 °C) was found to have an increasing effect on adsorption.

One of the main changes that occur during heat treatment of milk is whey protein denaturation, which in its turn may lead to protein aggregation and gelation. In this contribution, the effect of lysophospholipids, the main components of lysolecithins, as well as alternative surfactants, on heat-induced whey protein aggregation has been studied. Hereby, attention was paid to the relation between polar lipid molecular structure (e.g. effect of alkyl chain length, effect of polar head group) and heat-stabilising properties. Residual protein determination in the supernatant obtained after centrifugation of heated whey protein solutions learned that whey protein aggregation was at least partly prevented in the presence of surfactants. As the short alkyl chain lysophospholipids were particularly effective heat stabilisers, hydrophilic surfactants seemed to be most effective, which may be ascribed to their higher critical aggregation concentration. Upon more severe heat treatment, protein aggregation was probed either in-situ by oscillatory rheology, or ex-situ by yield rheometry. As some surfactants significantly reduced the gel strength, or even prevented heat-induced gel formation, these experiments corroborated the heat-stabilising effect of hydrophilic surfactants. Nuclear Magnetic Resonance (NMR) enabled a more direct evaluation of the protein–surfactant interaction. A strong hydrophobic interaction between small molecular weight surfactants and whey proteins became obvious from the chemical shift of the surfactant hydrophobic groups in the NMR spectrum and could be quantified by pulsed field gradient NMR (pfg-NMR) diffusiometry. The results indicated that protein–surfactant interaction did not occur upon thermal denaturation, but already took place at room temperature. However, the effect of this interaction became mainly obvious during thermal treatment. Overall, this work indicated that bound surfactants largely minimise heat-induced protein intermolecular interactions and hence prevent heat-induced protein aggregation. As the surfactant molecular structure plays a decisive role, it follows that the heat stability of whey protein containing products may be optimised by appropriate selection of ingredients such as (lyso)phospholipids.

Interactions between phenol and cationic cetyltrimethylammonium bromide (CTAB) micelles have been investigated by means of nuclear magnetic resonance spectroscopy. The combined use of 1H and NOESY techniques revealed that phenol has different preferred locations of interaction depending on the pH. At neutral pH (6.70) conditions, phenol molecules are preferentially located in the outer micelle region, at the micelle–water interface, while at more basic pH (9.94), the deprotonated phenol molecules (C6H5O−) are immersed into the palisade layer of the micelle. In addition, quantitative estimates of the solubilized fraction of phenol were obtained by using PFG-NMR. The results indicate that the phenol–CTAB interactions, although already present in neutral pH conditions, are largely favored in basic conditions as a consequence of the strong electrostatic interaction between the negatively charged phenolate ions and the positive charge of the cationic surfactant head group.

Polysorbate surfactants (commercially available as Tween) are widely used in pharmaceutical, cosmetic and food products. They are generally considered as esters of ethoxylated sorbitan with fatty acids. Diffusion H1 NMR spectroscopy on a solution of polysorbate 20 in D2O revealed that only one diffusion coefficient was found for the fatty acyl part. Using the Stokes-Einstein equation, it became obvious that this diffusion behavior was caused by micelles. On the other hand, two significantly different diffusion coefficients were found for the methylene groups of ethylene oxide (EO). This indicates the presence of two distinct EO containing species in solution. Since the slowest diffusing EO species has the same diffusion coefficient as the fatty acyl part, it corresponds to the micellar (i.e. fatty acyl bound) ethoxylates. The diffusion coefficient of the fastest diffusing EO species was a factor of four larger than that of the slowly diffusing species and was attributed to water-soluble non-esterified ethoxylates. A solution of polysorbate 20 in the presence of NaOD was prepared to investigate if hydrolysis of the sorbitan ester could be the reason for the occurence of these hydrophilic ethoxylates. It was found that alkaline hydrolysis does lead to an increasing fraction of non-esterified ethoxylates, but is not the cause of its presence in untreated polysorbate samples since these species were also found in solutions of polyethylene glycol oleyl ether (commercially available as Brij), which are not susceptible to hydrolysis. Fractionation of the EO species present in polysorbate 20 into an amphiphilic and a hydrophilic fraction was only partly obtained by activated carbon adsorption. On the other hand, sequential extraction of aqueous polysorbate solutions by ethyl acetate and chloroform enabled a nearly complete fractionation. H1 NMR spectroscopy proved to be very useful since it allows in situ determination of the global composition of a surfactant sample, as well as quantification of both the amphiphilic and hydrophilic ethoxylate fractions via diffusion measurements.

Two new cyclic lipodepsipeptides named pseudodesmins A and B have been isolated from Pseudomonas bacteria collected from the mucus layer in the skin of the black belly salamander. Both compounds show moderate antibacterial activity against Gram positive bacteria, including MRSA. Complete 1H, 13C and 15N NMR assignment of both compounds afforded their covalent structure and served to guide the analysis of LC-MS and X-ray diffraction data from which the final stereochemistry could be established. Both molecules can be categorized as new members of the viscosin group of cyclic lipodepsipeptides.

Colloidal semiconductor nanocrystals or quantum dots are an important building block in bottom-up nanotechnology. They consist of an inorganic, crystalline core surrounded by a monolayer of organic ligands. As these ligands can be modified or exchanged for others, they provide a convenient way to give the quantum dots functionality. Here, we show that solution NMR is a useful tool to investigate the ligands of colloidal nanocrystals using InP quantum dots with trioctylphospine oxide ligands. Combining H 1 – C 13 HSQC spectroscopy with pulsed field gradient diffusion NMR, an unequivocal identification of the resonances of the bound ligands is possible. This leads to the determination of the diffusion coefficient of the nanocrystals in solutions and allows to verify capping exchange procedures. By calibrating the surface area of the NMR resonances using a solute of known concentration, the density of ligands at the nanocrystal surface can be quantified. This demonstrates that a dynamic equilibrium exists between bound and free ligands. Analysis of the corresponding adsorption isotherm – determined using H 1 NMR – leads to an estimation of the free energy of adsorption and the free energy of ligand–ligand interaction at the nanocrystals surface.

The HeadPiece (HP) domain, present in several F-actin-binding multi-domain proteins, features a well-conserved, solvent-exposed PXWK motif in its C-terminal subdomain. The latter is an autonomously folding subunit comprised of three alpha-helices organised around a hydrophobic core, with the sequence motif preceding the last helix. We report the contributions of each conserved residue in the PXWK motif to human villin HP function and structure, as well as the structural implications of the naturally occurring Pro to Ala mutation in dematin HP. NMR shift perturbation mapping reveals that substitution of each residue by Ala induces only minor, local perturbations in the full villin HP structure. CD spectroscopic thermal analysis, however, shows that the Pro and Trp residues in the PXWK motif afford stabilising interactions. This indicates that, in addition to the residues in the hydrophobic core, the Trp-Pro stacking within the motif contributes to HP stability. This is reinforced by our data on isolated C-terminal HP subdomains where the Pro is also essential for structure formation, since the villin, but not the dematin, C-terminal subdomain is structured. Proper folding can be induced in the dematin C-terminal subdomain by exchanging the Ala for Pro. Conversely, the reverse substitution in the villin C-terminal subdomain leads to loss of structure. Thus, we demonstrate a crucial role for this proline residue in structural stability and folding potential of HP (sub)domains consistent with Pro-Trp stacking as a more general determinant of protein stability.

We present a study of the interaction between thioredoxin and the model enzyme pI258 arsenate reductase (ArsC) from Staphylococcus aureus. ArsC catalyses the reduction of arsenate to arsenite. Three redox active cysteine residues (Cys10, Cys82 and Cys89) are involved. After a single catalytic arsenate reduction event, oxidized ArsC exposes a disulphide bridge between Cys82 and Cys89 on a looped-out redox helix. Thioredoxin converts oxidized ArsC back towards its initial reduced state. In the absence of a reducing environment, the active-site P-loop of ArsC is blocked by the formation of a second disulphide bridge (Cys10-Cys15). While fully reduced ArsC can be recovered by exposing this double oxidized ArsC to thioredoxin, the P-loop disulphide bridge is itself inaccessible to thioredoxin. To reduce this buried Cys10-Cys15 disulphide-bridge in double oxidized ArsC, an intra-molecular Cys10-Cys82 disulphide switch connects the thioredoxin mediated inter-protein thiol-disulphide transfer to the buried disulphide. In the initial step of the reduction mechanism, thioredoxin appears to be selective for oxidized ArsC that requires the redox helix to be looped out for its interaction. The formation of a buried disulphide bridge in the active-site might function as protection against irreversible oxidation of the nucleophilic cysteine, a characteristic that has also been observed in the structurally similar low molecular weight tyrosine phosphatase. (C) 2004 Elsevier Ltd. All rights reserved.

Three dibutyltin perfluoroalkanecarboxylates have been synthesized, characterized by H-1-, C-13-, F-19- and Sn-117-NMR, Mossbauer, IR and mass spectroscopy. The structure of tetra-n-butylbis(trifluoroacetato)distannoxane has been elucidated by X-ray crystallography. The in vitro antitumour activity of the three compounds against seven human tumour cell lines was found to be as high as or even higher than that for reference compounds used clinically. (C) 2000 Published by Elsevier Science S.A.

The conformation in water of antimicrobial protein 2 from Amaranthus caudatus (Ac-AMP2) was determined using 1 H NMR, DIANA and restrained molecular modeling. Ac-AMP2 is a 30 amino acid residue, lectin-like protein that specifically binds to chitin, a polymer of β-1,4- N -acetyl- D -glucosamine. After sequence specific resonance assignments, a total of 198 distance restraints were collected from 2D NOESY buildup spectra at 500 MHz at pH 2, supplemented by a 2D NOESY spectrum at 600 MHz. The location of the three previously unassigned disulfide bridges was determined from preliminary DIANA structures, using a statistical analysis of intercystinyl distances. The solution structure of Ac-AMP2 is presented as a set of 26 DIANA structures, further refined by restrained molecular dynamics using a simulated annealing protocol in the AMBER force field, with a backbone r.m.s.d. for the well defined Glu3-Cys28 segment of 0.69(±0.12) A. The main structural element is an antiparallel β-sheet from Met13 to Lys23 including a β I -turn over Gln17-Phe18 with a β bulge at Gly19. In addition, a β′ I turn over Arg6-Gly7, a β′ III turn over Ser11-Gly12 and a helical turn from Gly24 to Cys28 are identified. This structure is very similar to the equivalent regions of the X-ray structure of wheat germ agglutinin and the NMR structure of hevein.