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- Biochemie und Chemie (1098) (remove)
The photoelectron (PE) spectra of dicyano methane and of its dimethyl derivative are tentatively assigned on the basis of a simple MO model. The interactions defined therein between the two cyano groups as well as with the R2C-framework can be parametrized using the PE data. Thus the hyperconjugation πCN/πCR₂ is estimated to amount to 1.7 eV in both compounds. Hyperconjugative effects in methane derivatives H3CX and H2CX2 with X = Br, Cl and CN are compared.
The cis-trans-isomerism of the WITTIG hydrocarbon was investigated in solid state and solution by means of fluorescence spectroscopy. The fluorescence behavior of both isomers in 2-methyltetrahydrofurane was determined as a function of concentration, temperature, and wavelength of exciting radiation. Furthermore, irradiation experiments were undertaken with light of various wavelengths.
The results obtained are in agreement with the assumption that the WITTIG hydrocarbon behaves with regard to the cis-trans-isomerism like a 1,3-butadien derivative, i.e. a thermal but no photochemical cis-trans-isomerisation can be detected. The enthalpy difference between the two isomers was estimated to ΔΗ = 250 ± 50 cal/mole. It could be shown that the fluorescence of the cis-isomer is quenched by the trans-isomer. This quenching occurs probably according to the resonance energy transfer mechanism.
1 reacts with SCl2 to yield 2. The methylsilane derivatives [OC–NCH3–CO–NCH3-SO2–N]nSi(CH3)4-n for n = 2, 3 and 4 are readily prepared from 1 and (CH3)2SiCl2, CH3SiCl3 and SiCl4. The IR and mass spectra are reported.
By substitution of a halogen atom in cyclic phosphazenes by isocyanate or isothiocyanate new members of this class of compounds are synthesized. These compounds are fairly stable against hydrolysis. Reaction of the new compounds with amines yields
P3N3F5NHC(O)N(CH3)2 and P3N3F5NHC(S)N(CH3)2. With elemental chlorine P3N3F5N = CCl2 is formed. Numerous IR, NMR and mass spectra data of the new compounds are reported.
P3N3F5NHNH2 reacts with P3N3F5Br to yield the symmetric hydrazide P3N3F5-NHNHP3N3F5. Compounds of the type P3N3F5NHNHC(O)CX3 and P3N3F5NHN = CX2 are readily prepared from P3N3F5NHNH2 and carbonic acid chlorides and respectively aldehydes and ketones.
The reaction product of P3N3F5NHNH2 and CH3CH2CHO gives a dimeric derivate. Its structure was proofed by molecular weight, IR- and mass spectra.
The transporter associated with antigen processing (TAP)-like (TAPL, ABCB9) belongs to the ATP-binding cassette transporter family, which translocates a vast variety of solutes across membranes. The function of this half-size transporter has not yet been determined. Here, we show that TAPL forms a homodimeric complex, which translocates peptides across the membrane. Peptide transport strictly requires ATP hydrolysis. The transport follows Michaelis-Menten kinetics with low affinity and high capacity. Different nucleotides bind and energize the transport with a slight predilection for purine bases. The peptide specificity is very broad, ranging from 6-mer up to at least 59-mer peptides with a preference for 23-mers. Peptides are recognized via their backbone, including the free N and C termini as well as side chain interactions. Although related to TAP, TAPL is unique as far as its interaction partners, transport properties, and substrate specificities are concerned, thus excluding that TAPL is part of the peptide-loading complex in the classic route of antigen processing via major histocompatibility complex class I molecules.
Synthesis and crystal structure of 2-(2-hydroxyphenyl)-1,3-bis(4-methoxybenzyl)-1,3-diazinan-5-ol
(2022)
The redetermined structure of 2-(2-hydroxyphenyl)-1,3-bis(4-methoxybenzyl)-1,3-diazinan-5-ol, C26H30N2O4, at 173 K has orthorhombic (Pbca) symmetry. It was previously described by Bolte et al. [ Private Communication (refcode EWICEV). CCDC, Cambridge, England]. The title compound resulted from the condensation reaction between 1,3-bis{[(4-methoxyphenyl)methyl]amino}propan-2-ol and 2-hydroxybenzaldehyde in CH3OH. The structure exhibits disorder. One of the 4-methoxybenzyl groups, the hydroxy group bonded to the 1,3-diazinan ring, and the methyl group of the methoxy residue are disordered over two orientations, with occupancies of 0.807 (3)/0.193 (3), 0.642 (5)/0.358 (5), and 0.82 (4)/0.18 (4), respectively. The dihedral angles between the mean planes of the central 1,3-diazinan-5-ol and the 4-methoxyphenyl rings (both occupancy components of the disordered ring) are 88.65 (13), 85.79 (14) and 83.4 (7)°. The crystal packing is sustained by C—H...O and O—H...π interactions, giving rise to infinite chains running along the b-axis direction.
The title compound, C8H16N4·2C11H16O, was synthesized from the corresponding sterically crowded phenol by treatment with the aminal cage polyamine. Single-crystal X-ray diffraction structural analysis revealed the three-molecule aggregate to crystallize in the monoclinic space group P2/c with one half of a 1,3,6,8-tetraaztricyclo[4.4.1.13,8]dodecane (TATD) molecule and one 2-tert-butyl-4-methylphenol molecule per asymmetric unit. The crystal structure features intermolecular O—H...N and C—H...O hydrogen bonds, as well as intermolecular C—H...π interactions.