Synthesis of 5,6-carbonyldioxyindole,a melanogenic cyclic carbonate ester of 5,6-dihydroxyindole

5,6-Carbonyldioxyindole ( 4 ), a melanogenic derivative of 5,6-dihydroxyindole ( 1 ), was synthesized by a procedure starting with 3,4-methylenedioxycinnamic acid ( 5 ). Compound 4 is a stable crystalline solid which is readily hydrolyzed to 1 , a key intermediate on the biosynthetic pathway from tyrosine to melanin.     

Investigations of the Rheology and Reactivity of Extrudable Wood-Resin Compounds

The extrusion of wood composites based on thermosetting resins is a new application in the field of wood plastic composites. To enable the extrusion of wood thermosetting compounds, it is necessary to know their reactivity and rheology well beforehand, to prevent the system curing inside the extruder. This study shows the different techniques that were adapted to allow in combination an estimation of the processing behaviour of wood-resin compounds in extrusion.     

Cis-cis and trans-perp HOONO: action spectroscopy and isomerization kinetics

The weakly bound HOONO product of the OH+NO2+M reaction is studied using the vibrational predissociation that follows excitation of the first OH overtone (2nu1). We observe formation of both cis-cis and trans-perp conformers of HOONO. The trans-perp HOONO 2nu1 band is observed under thermal (223-238 K) conditions at 6971 cm(-1). We assign the previously published (warmer temperature) HOONO spectrum to the 2nu1 band at 6365 cm(-1) and 2nu1-containing combination bands of the cis-cis conformer of HOONO. The band shape of the trans-perp HOONO spectrum is in excellent agreement with the predicted rotational contour based on previous experimental and theoretical results, but the apparent origin of the cis-cis HOONO spectrum at 6365 cm(-1) is featureless and significantly broader, suggesting more rapid intramolecular vibrational redistribution or predissociation in the latter isomer. The thermally less stable trans-perp HOONO isomerizes rapidly to cis-cis HOONO with an experimentally determined lifetime of 39 ms at 233 K at 13 hPa (in a buffer gas of predominantly Ar). The temperature dependence of the trans-perp HOONO lifetime in the range 223-238 K yields an isomerization barrier of 33+/-12 kJ/mol. New ab initio calculations of the structure and vibrational mode frequencies of the transition state perp-perp HOONO are performed using the coupled cluster singles and doubles with perturbative triples [CCSD(T)] model, using a correlation consistent polarized triple zeta basis set (cc-pVTZ). The energetics of cis-cis, trans-perp, and perp-perp HOONO are also calculated at this level [CCSD(T)/cc-pVTZ] and with a quadruple zeta basis set using the structure determined at the triple zeta basis set [CCSD(T)/cc-pVQZ//CCSD(T)/cc-pVTZ]. These calculations predict that the anti form of perp-perp HOONO has an energy of DeltaE0=42.4 kJ/mol above trans-perp HOONO, corresponding to an activation enthalpy of DeltaH298 (double dagger 0)=41.1 kJ/mol. These results are in good agreement with statistical simulations based on a model developed by Golden, Barker, and Lohr. The simulated isomerization rates match the observed decay rates when modeled with a trans-perp to cis-cis HOONO isomerization barrier of 40.8 kJ/mol and a strong collision model. The quantum yield of cis-cis HOONO dissociation to OH and NO2 is also calculated as a function of photon excitation energy in the range 3500-7500 cm(-1), assuming D0=83 kJ/mol. The quantum yield is predicted to vary from 0.15 to 1 over the observed spectrum at 298 K, leading to band intensities in the action spectrum that are highly temperature dependent; however, the observed relative band strengths in the cis-cis HOONO spectrum do not change substantially with temperature over the range 193-273 K. Semiempirical calculations of the oscillator strengths for 2nu1(cis-cis HOONO) and 2nu1(trans-perp HOONO) are performed using (1) a one-dimensional anharmonic model and (2) a Morse oscillator model for the OH stretch, and ab initio dipole moment functions calculated using Becke, Lee, Yang, and Parr density functional theory (B3LYP), M?ller-Plesset pertubation theory truncated at the second and third order (MP2 and MP3), and quadratic configuration interaction theory using single and double excitations (QCISD). The QCISD level calculated ratio of 2nu1 oscillator strengths of trans-perp to cis-cis HOONO is 3.7:1. The observed intensities indicate that the concentration of trans-perp HOONO early in the OH+NO2 reaction is significantly greater than predicted by a Boltzmann distribution, consistent with statistical predictions of high initial yields of trans-perp HOONO from the OH+NO2+M reaction. In the atmosphere, trans-perp HOONO will isomerize nearly instantaneously to cis-cis HOONO. Loss of HOONO via photodissociation in the near-IR limits the lifetime of cis-cis HOONO during daylight to less than 45 h, other loss mechanisms will reduce the lifetime further.     

Rotational spectrum of cis-cis HOONO

The pure rotational spectrum of cis-cis peroxynitrous acid, HOONO, has been observed. Over 220 transitions, sampling states up to J'=67 and Ka'=31, have been fitted with an rms uncertainty of 48.4 kHz. The experimentally determined rotational constants agree well with ab initio values for the cis-cis conformer, a five-membered ring formed by intramolecular hydrogen bonding. The small, positive inertial defect Delta=0.075667(60) amu A2 and lack of any observable torsional splittings in the spectrum indicate that cis-cis HOONO exists in a well-defined planar structure at room temperature.     

Investigations of the Rheology and Reactivity of Extrudable Wood-Resin Compounds

Summary. The extrusion of wood composites based on thermosetting resins is a new application in the field of wood plastic composites. To enable the extrusion of wood thermosetting compounds, it is necessary to know their reactivity and rheology well beforehand, to prevent the system curing inside the extruder. This study shows the different techniques that were adapted to allow in combination an estimation of the processing behaviour of wood-resin compounds in extrusion.     

Simultaneous determination of NSO-heterocycles, homocycles and their metabolites in groundwater of tar oil contaminated sites using LC with diode array UV and fluorescence detection

For monitoring groundwater at tar oil contaminated sites a simple method of analysis was developed for the simultaneous detection of several NSO heterocyclic compounds, homocyclic compounds, mobile two- and three-cyclic PAHs and selected metabolites. The groundwater samples are enriched using SPE with polymer material at pH 4. Chromatographic separation and detection is performed by LC with diode array UV or fluorescence detection. The recoveries of 25 selected compounds were mostly between 80-110% and the detection limits were 0.4-2.4 microg/L for UV detection and for the fluorescence detectable compounds 0.4-140 ng/L. The method was successfully applied to groundwater samples from a wood preserving facility. Especially benzo(b)thiophene showed an increasing dominance downgradient of the source. Detection of metabolites, such as 1-hydroxyiso-, 2-hydroxyquinoline and 2-hydroxy-4-methylquinoline, 2-naphthoic acid, and 1-indanone, indicating in situ biodegradation, was confirmed by LC-ESI-MS analysis.     

A Detailed Analysis of the Morphology of Fibrils of Selectively Mutated Amyloid β (1–40)

A small library of rationally designed amyloid β [Aβ(1–40)] peptide variants is generated, and the morphology of their fibrils is studied. In these molecules, the structurally important hydrophobic contact between phenylalanine 19 (F19) and leucine 34 (L34) is systematically mutated to introduce defined physical forces to act as specific internal constraints on amyloid formation. This Aβ(1–40) peptide library is used to study the fibril morphology of these variants by employing a comprehensive set of biophysical techniques including solution and solid‐state NMR spectroscopy, AFM, fluorescence correlation spectroscopy, and XRD. Overall, the findings demonstrate that the introduction of significant local physical perturbations of a crucial early folding contact of Aβ(1–40) only results in minor alterations of the fibrillar morphology. The thermodynamically stable structure of mature Aβ fibrils proves to be relatively robust against the introduction of significantly altered molecular interaction patterns due to point mutations. This underlines that amyloid fibril formation is a highly generic process in protein misfolding that results in the formation of the thermodynamically most stable cross‐β structure.     

Front Cover: Small-Molecule Activation by Heteroleptic Metallasilylenes (Eur. J. Inorg. Chem. 2/2023)

We report on reactions of heteroleptic metallasilylenes L¹(Cl)MSiL² (M=Al 1 , Ga 2 , L¹=HC[C(Me)NDipp]₂, Dipp=2,6-ⁱPr₂C₆H₃; L²=PhC(N^tBu)₂) with CO₂, N₂O, and Me₃SiN₃, yielding the corresponding carbonate complexes L¹(Cl)MOSi(CO₃-κ²O,O−)L² (M=Al 3 , Ga 4 ), silanoic esters L¹(Cl)MOSi(O)L² (M=Al 5 , Ga 6 ), and silaimine L¹(Cl)GaSi(NSiMe₃)L² ( 8 ), whereas {L²Si[N(SiMe₃)Al(Cl)C(Me)NDipp][CHC(Me)N(Dipp)]} 7 was formed by C−C bond cleavage of the L¹ ligand. Compounds 3 – 8 were characterized by NMR (¹H, ¹³C) and IR spectroscopy, elemental analysis and single crystal X-ray diffraction.