Mechanical Reversibility of Strain‐Promoted Azide–Alkyne Cycloaddition Reactions

Mechanophores, that is, molecules that show a defined response to force, are crucial building blocks of mechanoresponsive materials. The possibility of mechanically induced cycloreversion for a series of triazoles formed via strain‐promoted azide–alkyne cycloaddition reactions was investigated by density functional theory calculations, and these triazoles were compared to the 1,4‐ and 1,5‐regioisomers formed in the reaction of an azide with a terminal alkyne. We show that cycloreversion is in principal possible and that the pulling geometry is the most important parameter that determines the probability of cycloreversion. We further compared triazole stability to the mechanical stability of polymers that are frequently used as force transducers in mechanochemical experiments and identified DIBAC (azadibenzylcyclooctyne) as a promising mechanophore for future applications.     

Vinyl esters: Low cytotoxicity monomers for the fabrication of biocompatible 3D scaffolds by lithography based additive manufacturing

Lithography based additive manufacturing technologies (AMT) like stereolithography or digital light processing have become appealing methods for the fabrication of 3D cellular scaffolds for tissue engineering and regenerative medicine. To circumvent the use of (meth)acrylate‐based photopolymers, that suffer from skin irritation and sometimes cytotoxicity, new monomers based on vinyl esters were prepared. In vitro cytotoxicity studies with osteoblast‐like cells proofed that monomers based on vinyl esters are significantly less cytotoxic than (meth)acrylates. Photoreactivity was followed by photo‐differential scanning calorimetry and the mechanical properties of the photocured materials were screened by nanoindentation. Conversion rates and indentation moduli between those of acrylate and methacrylate references could be observed. Furthermore, osteoblast‐like cells were successfully seeded onto polymer specimens. Finally, we were able to print a 3D test structure out of a vinyl ester‐based formulation by μ‐SLA with a layer thickness of 50 μm. For in vivo testing of vinyl esters these 3D scaffolds were implanted into surgical defects of the distal femoral bone of adult New Zealand white rabbits. The obtained histological results approved the excellent biocompatibility of vinyl esters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Terpene bioconversion--how does its future look?

The usage of essential oils as such or of volatile fractions thereof is widespread in the flavor and fragrance industry to aromatize perfumery and cosmetic products, foodstuffs, and many household and pharmaceutical products. The increased market share of convenience food together with consumers' request for constant high quality and natural products have established a lasting increase in the demand for natural flavorings that cannot be satisfied by the traditional plant materials. This review summarizes selected work on terpene bioconversion/transformation and focuses on recently published papers dealing with novel strains and products, high product yields, intriguing genetic engineering approaches, and integrated bioprocesses. The future perspectives of an industrial realization of a biotechnological production of terpene-derived natural flavors are critically evaluated.     

Reduction of primary freeze-drying time by electric field induced ice nucleus formation

The potential of a high electric field was utilized to induce ice nucleus formation in aqueous solutions. Using this technique it was possible to reduce the primary drying time during lyophilization. Samples of 10% (w/v) hydroxyethylstarch (HES) solution were frozen at a constant rate of −1 K/min, while nucleation was initiated at temperatures of −1.5, −4.5 and −8.5°C. In contrast, spontaneous nucleation was observed in a range between −11.5 and −17.1°C. Electrically induced nucleus formation has proved to be a reliable method to start crystallization at a desired temperature. Continuous measurement of the weight allowed to determine the drying rate and to detect at which time primary drying was completed. The drying time and the drying rate were found to be strongly dependent on the nucleation temperature during freezing. A relation between the nucleation temperature, the structure of the frozen samples and the drying times could be established.

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Retention behavior of carboyxlic acids on highly cross-linked poly(styrene-divinylbenzene)-based and silica-based cation exchangers

A highly cross-linked porous poly(styrene-divinylbenzene) resin was reacted with sulfuric acid to give strong cation-exchange resins with capacities from 0.2 to 1.9 mequiv./g. The retention behavior of mono- and dicar☐ylic acids on these resins was compared with results obtained from silica-based cation exchangers functionalized with alkylsulfonic acid or phenylsulfonic acid groups. The contribution of different retention mechanisms like ion exclusion, hydrophobic interaction and adsorption to the separation of the analytes on these chromatographic supports was discussed. Additionally the applicability of silica-based cation exchangers was tested in the field of silage analysis.     

SU(3) flux tubes in a model of the stochastic vacuum

We calculate the squared gluon field strengths of a heavyq- $\bar q$ -pair in the model of the stochastic vacuum. We observe that with increasing separation a chromoelectric flux tube is built. The properties of the emerging flux tube are investigated.     

Rapid determination of urinary globotriaosylceramide isoform profiles by electrospray ionization mass spectrometry using stearoyl-d35-globotriaosylceramide as internal standard

Globotriaosylceramide is a neutral glycolipid containing the trihexoside Gal(alpha1-4)Gal(ss1-4)Glc(ss1-1') covalently bound to N-acylsphingosine. It was identified as the main storage substance in the kidney of patients with Fabry disease, an X-linked deficiency of lysosomal alpha-galactosidase A which can significantly be ameliorated by enzyme replacement therapy. Unlike hemizygote males, affected heterozygote females cannot be identified by enzyme assays and therefore may remain untreated. A quantitation of urinary globotriaosylceramides was proposed as an alternative method for their diagnosis. However, the required studies on physiological and pathological variations in the excretion of trihexosides so far have been prevented by a lack of suitable methods. A validated, robust and quick high-throughput method for the quantitative analysis of globotriaosylceramide isoforms using stable-isotope-dilution/internal standardization and electrospray ionization mass spectrometry (ESI-MS) was developed. An internal standard, stearoyl-d35-globotriaosylceramide, was synthesized by enzymatic coupling of d35-stearic acid to the corresponding lyso-ceramidetrihexoside. Glycolipid isoforms of high purity were obtained from a 5-mL urine portion by extraction on C18 solid-phase columns and a novel washing protocol. ESI-MS analysis was performed in full and neutral loss scan modes. Urinary trihexosyl- and some of the di- and monohexosylceramide isoforms can be quantified within a single experiment. All glycolipid isoforms were above detection limit in healthy male and female subjects (n = 63). Prominent elevations of tetracosanoyl-(C24:0 plus C24:1)-globotriaosylceramides were found in urines from female (>2.5-fold above normals) or male Fabry patients (>5.8-fold above normals), but not among controls. Globotriaosylceramide isoforms shall now be analyzed in Fabry patients, non-genetic kidney disease and healthy subjects to define the conditions for a safe diagnosis of heterozygotes.     

Expanding the frequency range of the solid-state T1rho experiment for heteronuclear dipolar relaxation

Solid-state spin–lattice relaxation in the rotating frame permits the investigation of dynamic processes with correlation times in the range of microseconds. The relaxation process in organic solids is driven by the fluctuation of the local magnetic field due to the dipole–dipole interaction of the probe nuclei (¹³C,¹⁵N) with ¹H in close proximity. However, its effect is often hidden by a competing relaxation process due to the contact between the rotating frame ¹³C/¹⁵N Zeeman and ¹H dipolar reservoirs. In most cases the latter process becomes superior for the commonly applied low and moderate spin-lock fields and practically does not provide information about the molecular dynamics. To suppress this undesired process and to expand the dynamic range of T_{1 ρ} experiments, we present two approaches. The first one uses a resonance offset of the frequency of the spin-lock irradiation, which leads to a significant enhancement of the effective spin-lock frequency without the application of destructive high transmitter powers. We derive the theory and demonstrate the applicability of the method on various model compounds. The second approach utilizes heteronuclear ¹H decoupling during the ¹³C/¹⁵N spin-lock irradiation which disrupts the contact between the ¹³C/¹⁵N Zeeman and ¹H dipolar reservoirs. We demonstrate the method and discuss the results qualitatively.