Effect of Sulfation Route and Subsequent Oxidation on Derivatization Degree and Biocompatibility of Cellulose Sulfates

Sulfated cellulose (CS) represents an interesting biopolymer due to bioactivity comparable to heparin. However, use of CS for making surface coatings or hydrogels requires the presence of reactive groups for covalent reactions. Here, an approach is presented to oxidize cellulose sulfates for subsequent cross‐linking reactions with amino groups to form imine bonds. Cellulose is sulfated by direct sulfation or acetosulfation, followed by a M alaprade oxidation. The CS obtained is characterized by elemental analysis and ¹³C‐NMR spectroscopy. The resulting oxidized cellulose sulfates (oxCS) have different degrees of sulfation ranging from 0.79 to 1.13 and oxidation degrees from 0.18 to 0.34, but also different mass average molecular mass (M_W). Toxicity studies are carried out with mouse 3T3 fibroblasts exposed to aqueous solutions of oxCS. The results show that all oxCS are non‐toxic at lower concentrations (0.5 mg mL^?1), but with both increasing degree of oxidation and concentrations, toxic effects are observed particularly for acetosulfated and lesser for direct sulfated oxCS, which is related to a decrease in the M_W of the products. It is concluded that oxCS obtained by direct sulfation with M_W above 70 kDa may represent a biocompatible material for the applications suggested above.     

Surfactant dependent morphology of polymeric capsules of perfluorooctyl bromide: influence of polymer adsorption at the dichloromethane-water interface

In a strategy to develop more stable ultrasound contrast agents (UCAs), we have designed a process to obtain nano/microcapsules with a single core of liquid perfluorocarbon within a biodegradable polymeric shell of homogeneous thickness. During the optimization of perfluorooctyl bromide (PFOB) encapsulation by solvent emulsion-evaporation, a marked influence of surfactants has been observed. While sodium cholate leads to spherical capsules of homogeneous thickness, sodium taurocholate induces to the formation of “acorn”-particles with one hemisphere of PFOB and another one of PLGA, and polyvinyl alcohol is responsible for the coexistence of both morphologies. Whereas the theoretical model proposed by Torza and Mason [J. Colloid Interface Sci. 33 (1970) 67] fails to predict the observed morphologies, microscopic observations of the evaporation and interfacial tension measurements provide an insight into the mechanism of formation of these structures. Most probably, there is a competition between PLGA and the surfactant stabilizing the emulsion at the dichloromethane–water interface. If PLGA is able to adsorb at the interface, the core–shell morphology is obtained, otherwise the acorn morphology is preferentially formed. When the surfactant rearrangement at the interface is long (>30 min), a coexistence of morphologies can be obtained.     

Molecular analysis of the kirromycin biosynthetic gene cluster revealed beta-alanine as precursor of the pyridone moiety

Kirromycin is a complex linear polyketide that acts as a protein biosynthesis inhibitor by binding to the bacterial elongation factor Tu. The kirromycin biosynthetic gene cluster was isolated from the producer, Streptomyces collinus Tü 365, and confirmed by targeted disruption of essential biosynthesis genes. Kirromycin is synthesized by a large hybrid polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) encoded by the genes kirAI-kirAVI. This complex involves some very unusual features, including the absence of internal acyltransferase (AT) domains in KirAI-KirAV, multiple split-ups of PKS modules on separate genes, and swapping in the domain organization. Interestingly, one PKS enzyme, KirAVI, contains internal AT domains. Based on in silico analysis, a route to pyridone formation involving PKS and NRPS steps was postulated. This hypothesis was experimentally proven by feeding studies with [U-13C3(15)N]beta-alanine and NMR and MS analyses of the isolated pure kirromycin.     

Femtosecond dynamics of electron transfer in a neutral organic mixed-valence compound

In this article we report a femtosecond time-resolved transient absorption study of a neutral organic mixed-valence (MV) compound with the aim to gain insight into its charge-transfer dynamics upon optical excitation. The back-electron transfer was investigated in five different solvents, toluene, dibutyl ether, methyl-tert-butyl ether (MTBE), benzonitrile and n-hexane. In the pump step, the molecule was excited at 760 nm and 850 nm into the intervalence charge-transfer band. The resulting transients can be described by two time constant. We assign one time constant to the rearrangement of solvent molecules in the charge-transfer state and the second time constant to back-electron transfer to the electronic ground state. Back-electron transfer rates range from 1.5 × 10¹² s⁻¹ in benzonitrile through 8.3 × 10¹¹ s⁻¹ in MTBE, around 1.6 × 10¹¹ s⁻¹ in dibutylether and toluene and to 3.8 × 10⁹ s⁻¹ in n-hexane.     

Vibrational overtone initiated unimolecular dissociation of HOCH2OOH and HOCD2OOH: evidence for mode selective behavior

The vibrational overtone induced unimolecular dissociation of HMHP (HOCH(2)OOH) and HMHP-d(2) (HOCD(2)OOH) into OH and HOCH(2)O (HOCD(2)O) fragments is investigated in the region of the 4nu(OH) and 5nu(OH) bands. The unimolecular dissociation rates in the threshold region, corresponding to the 4nu(OH) band, exhibit measurable differences associated with excitation of the OH stretch of the alcohol versus the peroxide functional group, with the higher energy alcohol OH stretching state exhibiting a slower dissociation rate compared to the lower energy peroxide OH stretch in both HMHP and HMHP-d(2). Predictions using the Rice-Ramsperger-Kassel-Marcus theory give rates that are in reasonably good agreement with the measured dissociation rate for the alcohol OH stretch but considerably differ from the measured rates for the peroxide OH stretch in both isotopomers. The present results are interpreted as suggesting that the extent of intramolecular vibrational energy redistribution (IVR) is different for the two OH stretching states associated with the two functional groups in HMHP, with IVR being substantially less complete for the peroxide OH stretch. Analysis of the OH fragment product state distributions in conjunction with phase-space theory simulation gives a D(0) value of 38+/-0.7 kcal/mole for breaking the peroxide bond in HMHP.     

Estimating the spatial distribution of artificial groundwater recharge using multiple tracers

Stable isotopes of water, organic micropollutants and hydrochemistry data are powerful tools for identifying different water types in areas where knowledge of the spatial distribution of different groundwater is critical for water resource management. An important question is how the assessments change if only one or a subset of these tracers is used. In this study, we estimate spatial artificial infiltration along an infiltration system with stage–discharge relationships and classify different water types based on the mentioned hydrochemistry data for a drinking water production area in Switzerland. Managed aquifer recharge via surface water that feeds into the aquifer creates a hydraulic barrier between contaminated groundwater and drinking water wells. We systematically compare the information from the aforementioned tracers and illustrate differences in distribution and mixing ratios. Despite uncertainties in the mixing ratios, we found that the overall spatial distribution of artificial infiltration is very similar for all the tracers. The highest infiltration occurred in the eastern part of the infiltration system, whereas infiltration in the western part was the lowest. More balanced infiltration within the infiltration system could cause the elevated groundwater mound to be distributed more evenly, preventing the natural inflow of contaminated groundwater.

Dedicated to Professor Peter Fritz on the occasion of his 80th birthday     

Oxidative rearrangements of tricyclic vinylcyclobutane derivatives

Three tricyclic vinylcyclobutanes (3-methylenetricyclo[5.3.0.0(2,6)]decanes 1-3) have been subjected to ionization by photoinduced electron transfer in solution and by X-irradiation in Ar matrices. All three compounds undergo oxidative cycloreversion; the cleavage of the four-membered ring, however, occurs in a different direction depending on the presence of a methyl group in position 6 of the tricyclic framework. In those derivatives, cycloreversion is found to lead to 1-methyl-8-methylene-1,6-cyclodecadiene radical cations (5.+ from 1, 8.+) from 2) which upon back electron transfer yield two different hydrocarbons (6 from 5.+, 9 from 8.+), depending on the configuration around the endocyclic double bonds of the respective cyclodecadiene derivative. In the absence of a methyl group on C6, the cycloreversion leads to a radical cation complex between 1-methylenecyclopent-2-ene and cyclopentene (12.+) which appears to revert to 3 on back electron transfer. The intermediate radical cations 5.+, 8.+, and 12.+ have been identified and characterized by UV/Vis and IR spectra in Ar matrices. The mechanism of their formation is elucidated by quantum chemical calculations.     

Phosphatase-triggered fusogenic liposomes for cytoplasmic delivery of cell-impermeable compounds

License to fuse! A phosphorylated fusion peptide can mediate membrane fusion when the phosphates (green triangles, see scheme) are removed by phosphatases (blue spheres), delivering the contents of the liposome into the cytosol. This phosphatase-triggered approach may be useful to create target-specific lipid nanocarriers.     

Sensitive indoor air monitoring of monoterpenes using different adsorbents and thermal desorption gas chromatography with mass-selective detection

A simple method using active trapping on adsorbents and thermal desorption followed by GC-MS analysis was developed for the indoor air monitoring of monoterpenes. The study was carried out using a dynamically generated atmosphere consisting of 11 monoterpenes: camphene, camphor, delta 3-carene, 1,8-cineol, limonene, linalool, alpha-pinene, beta-pinene, alpha-terpinene, gamma-terpinene, fenchyl alcohol. The influence of the different adsorbents Tenax TA, Tenax GR, Carbosieve SIII, Chromosorb 106 on the yield of six selected monoterpenes at indoor air concentrations was studied. The adsorbent Tenax GR gave relatively the best yields followed by Tenax TA. Detection limits of approximately 1 microgram m3 were determined with Tenax GR for most of the monoterpenes.