Low volatile monofunctional reactive diluents for radiation curable formulations

In the last decades the importance of UV curable formulations has increased continuously. Their fast curing speed, solvent-free polymerization conditions, and the formation of hard and highly crosslinked photopolymer networks represent major benefits. Commercial UV resins generally consist of multi-functional vinyl oligomers, photoinitiators, additives, and reactive diluents. Mono- and multi-functional reactive diluents serve as thinners to lower the overall resin viscosity and to improve processability. However, many monofunctional reactive diluents like isobornyl (meth)acrylate or benzyl (meth)acrylate exhibit high volatility, often already at room temperature. This causes adverse effects such as unpleasant odor, potential health risks, and changing resin composition during processing. A new group of monomers that show high potential for replacing traditional highly volatile reactive diluents are salicylate (meth)acrylates. In this work, salicylate-based thinners are synthesized, polymerized, and characterized with respect to their viscosity, volatility, thermal stability, photoreactivity, and thermomechanical properties of their homopolymers. Additionally, a first example of their diluting effect in a highly viscous difunctional polyester urethane methacrylate is demonstrated with 30 wt% of a cycloaliphatically and an aromatically substituted salicylate methacrylate. The polymers of the diluted resin exhibit similarly high glass transition temperatures of 110 and 126 °C, which are in the range of the polymers of the undiluted resin.     

Total Synthesis of a Partial Structure from Arabinogalactan and Its Application for Allergy Prevention

Arabinogalactan, a microheterogeneous polysaccharide occurring in plants, is known for its allergy-protective activity, which could potentially be used for preventive allergy treatment. New treatment options are highly desirable, especially in a preventive manner, due to the constant rise of atopic diseases worldwide. The structural origin of the allergy-protective activity of arabinogalactan is, however, still unclear and isolation of the polysaccharide is not feasible for pharmaceutical applications due to a variation of the activity of the natural product and contaminations with endotoxins. Therefore, a pentasaccharide partial structure was selected for total synthesis and subsequently coupled to a carrier protein to form a neoglycoconjugate. The allergy-protective activity of arabinogalactan could be reproduced with the partial structure in subsequent in vivo experiments. This is the first example of a successful simplification of arabinogalactan with a single partial structure while retaining its allergy-preventive potential.     

Rational Development of Guanidinate and Amidinate Based Cerium and Ytterbium Complexes as Atomic Layer Deposition Precursors: Synthesis,Modeling, and Application

Owing to the limited availability of suitable precursors for vapor phase deposition of rare-earth containing thin-film materials, new or improved precursors are sought after. In this study, we explored new precursors for atomic layer deposition (ALD) of cerium (Ce) and ytterbium (Yb) containing thin films. A series of homoleptic tris-guanidinate and tris-amidinate complexes of cerium (Ce) and ytterbium (Yb) were synthesized and thoroughly characterized. The C-substituents on the N-C-N backbone (Me, NMe₂, NEt₂, where Me=methyl, Et=ethyl) and the N-substituents from symmetrical iso-propyl (iPr) to asymmetrical tertiary-butyl (tBu) and Et were systematically varied to study the influence of the substituents on the physicochemical properties of the resulting compounds. Single crystal structures of [Ce(dpdmg)₃] 1 and [Yb(dpdmg)₃] 6 (dpdmg=N,N'-diisopropyl-2-dimethylamido-guanidinate) highlight a monomeric nature in the solid-state with a distorted trigonal prismatic geometry. The thermogravimetric analysis shows that the complexes are volatile and emphasize that increasing asymmetry in the complexes lowers their melting points while reducing their thermal stability. Density functional theory (DFT) was used to study the reactivity of amidinates and guanidinates of Ce and Yb complexes towards oxygen (O₂) and water (H₂O). Signified by the DFT calculations, the guanidinates show an increased reactivity toward water compared to the amidinate complexes. Furthermore, the Ce complexes are more reactive compared to the Yb complexes, indicating even a reactivity towards oxygen potentially exploitable for ALD purposes. As a representative precursor, the highly reactive [Ce(dpdmg)₃] 1 was used for proof-of-principle ALD depositions of CeO₂ thin films using water as co-reactant. The self-limited ALD growth process could be confirmed at 160 °C with polycrystalline cubic CeO₂ films formed on Si(100) substrates. This study confirms that moving towards nitrogen-coordinated rare-earth complexes bearing the guanidinate and amidinate ligands can indeed be very appealing in terms of new precursors for ALD of rare earth based materials.     

Click Chemistry in Ultra-high Vacuum – Tetrazine Coupling with Methyl Enol Ether Covalently Linked to Si(001)

The additive-free tetrazine/enol ether click reaction was performed in ultra-high vacuum (UHV) with an enol ether group covalently linked to a silicon surface: Dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate molecules were coupled to the enol ether group of a functionalized cyclooctyne which was adsorbed on the silicon (001) surface via the strained triple bond of cyclooctyne. The reaction was observed at a substrate temperature of 380 K by means of X-ray photoelectron spectroscopy (XPS). A moderate energy barrier was deduced for this click reaction in vacuum by means of density functional theory based calculations, in good agreement with the experimental results. This UHV-compatible click reaction thus opens a new, flexible route for synthesizing covalently bound organic architectures.     

Fluorinated Azobenzenes Switchable with Red Light

Molecular photoswitches triggered with red or NIR light are optimal for photomodulation of complex biological systems, including efficient penetration of the human body for therapeutic purposes (“therapeutic window”). Yet, they are rarely reported, and even more rarely functional under aqueous conditions. In this work, fluorinated azobenzenes are shown to exhibit efficient E→Z photoisomerization with red light (PSS_660nm >75 % Z) upon conjugation with unsaturated substituents. Initially demonstrated for aldehyde groups, this effect was also observed in a more complex structure by incorporating the chromophore into a cyclic dipeptide with propensity for self-assembly. Under physiological conditions, the latter molecule formed a supramolecular material that reversibly changed its viscosity upon irradiation with red light. Our observation can lead to design of new photopharmacology agents or phototriggered materials for in vivo use.     

A Molecular Low-Coordinate [Fe-S-Fe] Unit in Three Oxidation States

A [Fe-S-Fe] subunit with a single sulfide bridging two low-coordinate iron ions is the supposed active site of the iron-molybdenum co-factor (FeMoco) of nitrogenase. Here we report a dinuclear monosulfido bridged diiron(II) complex with a similar complex geometry that can be oxidized stepwise to diiron(II/III) and diiron(III/III) complexes while retaining the [Fe-S-Fe] core. The series of complexes has been characterized crystallographically, and electronic structures have been studied using, inter alia, ⁵⁷Fe Mössbauer spectroscopy and SQUID magnetometry. Further, cleavage of the [Fe-S-Fe] unit by CS₂ is presented.     

Influence of the degree of ionization on the growth mechanism of poly(diallyldimethylammonium)/poly(acrylic acid) multilayers

pH‐dependent growth laws of the mass coverage Γ(n) of poly(diallyldimethylammonium) chloride and poly(acrylic acid) (PAA) layer‐by‐layer films are analyzed by Quartz Crystal Microbalance‐D. (Attenuated Total Reflection)‐FTIR spectroscopy shows a degree of dissociation of acrylic acid groups in the films identical to that in solution. Apart from pH‐regimes of differently pronounced exponential and linear growth, the corresponding kinetics indicate pH‐dependent adsorption, reorganization, and diffusion processes. As the thickest films form with almost uncharged PAA (low pH), the results can only partly be explained by the dissociation degree of PAA in the film. For intermediate and high pH values chain interdiffusion as a mechanism for nonlinear growth is strongly dependent on the charge density of the PAA chains. However, at low pH other types of interactions, most likely ion–dipole interactions, play a major role in the multilayer growth. Furthermore, a change in the symmetry of growth can be observed in the low to intermediate pH range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 425–434     

From Infinite Chains according to 1∞[Zr(S2O7)4/2] in Zr(S2O7)2 to the unprecedented [Zr(S2O7)4]4– Anion in Ag4[Zr(S2O7)4]

The reaction of ZrCl₄ with oleum (65 % SO₃) in the presence of Ag₂SO₄ at 250 °C yielded colorless single crystals of Zr(S₂O₇)₂ [orthorhombic, Pccn, Z = 4, a = 709.08(6) pm, b = 1442.2(2) pm, c = 942.23(9) pm, V = 963.5(2) × 10⁶ pm³]. Zr(S₂O₇)₂ shows Zr⁴⁺ ions in an eightfold distorted square antiprismatic coordination of oxygen atoms belonging to four chelating disulfate units. Each S₂O₇^2– ion is connected to a further Zr⁴⁺ ion leading to chains according to ¹_∞[Zr(S₂O₇)_4/2]. The same reaction at a temperature of 150 °C resulted in the formation of Ag₄[Zr(S₂O₇)₄] [monoclinic, C2/c, Z = 4, a = 1829.35(9) pm, b = 704.37(3) pm, c = 1999.1(1) pm, β = 117.844(2)°, V = 2277.6(2) × 10⁶ pm³]. Ag₄[Zr(S₂O₇)₄] exhibits the unprecedented [Zr(S₂O₇)₄]^4– anion, in which the central Zr⁴⁺ cation is coordinated by four chelating disulfate units. Thus, in Ag₄[Zr(S₂O₇)₄] the ¹_∞[[Zr(S₂O₇)_4/2] chains observed in Zr(S₂O₇)₂ are formally cut into pieces by the implementation of Ag⁺ ions.     

Use of ETAAS,FAAS and ICP-OES for production and post-certification monitoring of a multielemental certified reference material according to national regulation limits for elements in drinking water

Accreditation and Quality Assurance - This paper describes the development of a certified reference material (CRM), produced in the National Institute of Quality from Peru (INACAL) in order to...     

High asymmetric induction in diels-alder additions of cyclopentadiene to acrylates derived from isoborneol

Starting from (R)-(+)- and from (S)-(?)-camphor the chiral alcohols $\text{1}$, $\text{2}$ and $\text{3}$ have been prepared; their acrylates II underwent TiCl₂(OR)₂-promoted Diels-Alder additions to cyclopentadiene giving efficiently in a predictable manner either the (2R)- or the (2S)-adducts III with up to virtually quantitative asymmetric induction.