Diffuse-reflectance Fourier transform-infrared spectroscopic microanalysis of the flavonolignans

Diffuse-reflectance Fourier transform-infrared spectroscopic (DRIFT) microanalysis (10 g samples) of a selected series of flavonoids was studied, comparing to transmission FT-IR spectroscopic analysis of the same samples at the mg level. DRIFT was shown to be a useful, sample-saving and reliable IR technique for the structural analysis and compound identification of the mainSilybum genus 3-OH-flavonolignans (silybin, isosilybin, silydianin, silychristin and isosilychristin) and the dihydroflavonol taxifolin.     

A multineuron interaction model for neural networks

A multineuron interaction model (RS model) with an energy function given by the product of the squared distances in phase space between the state of the net and the stored patterns is studied in detail within a mean-field approach. Two limits are considered: when the patterns and antipatterns are stored (as in the Hopfield model), PAS case, and when only the patterns are taken into account, OPS case. TheT=0 solutions for the proper memories are exactly obtained for all finite values of, as a consequence of the energy function: whenever one of the overlaps is exactly one the corresponding equations decouple and no configuration average is required. Special interest is focused on the OPS situation, which presents a peculiar phase space topology. On the other hand, the PAS configuration recovers the Hopfield model in the appropriate limit, while keeping associative memory abilities far beyond the critical values of other models when the full Hamiltonian is considered.     

Further studies on the rotational barriers of Carbamates. An NMR and DFT analysis of the solvent effect for Cyclohexyl N,N-dimethylcarbamate

The solvent effect on the Gibbs energy of activation for rotation around the (C=O)–N bond in cyclohexyl N,N-dimethylcarbamate was investigated by dynamic NMR spectroscopy and density-functional theory at the B3LYP/6-311+G^** level. The experimental barriers were about 15 kcal mol⁻¹ with no appreciable variation when the solvent polarity was changed. A reaction field model was applied to theoretically mediate the solvent effect and the results were comparable to the experimental data. An analysis, based on the Onsager solvation theory, showed that the solvent effect on rotational barriers can be understood employing the total molecular dipole moment, the difference between the dipole moments of the ground and the transition state structures, or both, as appropriate.     

Impact of solar ultraviolet radiation on marine phytoplankton of Patagonia, Argentina

Patagonia area is located in close proximity to the Antarctic ozone "hole" and thus receives enhanced ultraviolet B (UV-B) radiation (280-315 nm) in addition to the normal levels of ultraviolet A (UV-A; 315-400 nm) and photosynthetically available radiation (PAR; 400-700 nm). In marine ecosystems of Patagonia, normal ultraviolet radiation (UVR) levels affect phytoplankton assemblages during the three phases of the annual succession: (1) prebloom season (late summer-fall), (2) bloom season (winter-early spring) and (3) postbloom season (late spring-summer). Small-size cells characterize the pre- and postbloom communities, which have a relatively high photosynthetic inhibition because of high UVR levels during those seasons. During the bloom, characterized by microplankton diatoms, photosynthetic inhibition is low because of the low UVR levels reaching the earth's surface during winter; this community, however, is more sensitive to UV-B when inhibition is normalized by irradiance (i.e. biological weighting functions). In situ studies have shown that UVR significantly affects not only photosynthesis but also the DNA molecule, but these negative effects are rapidly reduced in the water column because of the differential attenuation of solar radiation. UVR also affects photosynthesis versus irradiance (P vs E) parameters of some natural phytoplankton assemblages (i.e. during the pre- but not during the postbloom season). However, there is a significant temporal variability of P vs E parameters, which are influenced by the nutrient status of cells and taxonomic composition; taxonomic composition is in turn associated with the stratification conditions (e.g. wind speed and duration). In Patagonia, wind speed is one of the most important variables that conditions the development of the winter bloom by regulating the depth of the upper mixed layer (UML) and hence the mean irradiance received by cells. Studies on the interactive effects of UVR and mixing show that responses of phytoplankton vary according to the taxonomic composition and cell structure of assemblages; therefore cells use UVR if >90% of the euphotic zone is being mixed. In fact, cell size plays a very important role when estimating the impact of UVR on phytoplankton, with large cells being more sensitive when determining photosynthesis inhibition, whereas small cells are more sensitive to DNA damage. Finally, in long-term experiments, it was determined that UVR can shape the diatom community structure in some assemblages of coastal waters, but it is virtually unknown how these changes affect the trophodynamics of marine systems. Future studies should consider the combined effects of UVR on both phytoplankton and grazers to establish potential changes in biodiversity of the area.     

Synthese und Charakterisierung neuer intramolekular stickstoffstabilisierter Organoaluminium‐ und Organogalliumalkoxide

Synthesis and Characterization of New Intramolecularly Nitrogen‐stabilized Organoaluminium‐ and Organogallium Alkoxides The intramolecularly nitrogen stabilized organoaluminium alkoxides [Me₂Al{μ‐O(CH₂)₃NMe₂}]₂ ( 1a ), Me₂AlOC₆H₂(CH₂NMe₂)₃‐2,4,6 ( 2a ), [(S)‐Me₂Al{μ‐OCH₂CH(i‐Pr)NH‐i‐Pr}]₂ ( 3a ) and [(S)‐Me₂Al{μ‐OCH₂CH(i‐Pr)NHCH₂Ph}]₂ ( 4 ) are formed by reacting equimolar amounts of AlMe₃ and Me₂N(CH₂)₃OH, C₆H₂[(CH₂NMe₂)₃‐2,4,6]OH, (S)‐i‐PrNHCH(i‐Pr)CH₂OH, or (S)‐PhCH₂NHCH(i‐Pr)CH₂OH, respectively. An excess of AlMe₃ reacts with Me₂N(CH₂)₂OH, Me₂N(CH₂)₃OH, C₆H₂[(CH₂NMe₂)₃‐2,4,6]OH, and (S)‐i‐PrNHCH(i‐Pr)CH₂OH producing the “pick‐a‐back” complexes [Me₂AlO(CH₂)₂NMe₂](AlMe₃) ( 5 ), [Me₂AlO(CH₂)₃NMe₂](AlMe₃) ( 1b ), [Me₂AlOC₆H₂(CH₂NMe₂)₃‐2,4,6](AlMe₃)₂ ( 2b ), and [(S)‐Me₂AlOCH₂CH(i‐Pr)NH‐i‐Pr](AlMe₃) ( 3b ), respectively. The mixed alkyl‐ or alkenylchloroaluminium alkoxides [Me(Cl)Al{μ‐O(CH₂)₂NMe₂}]₂ ( 6 ) and [{CH₂=C(CH₃)}(Cl)Al{μ‐O(CH₂)₂NMe₂}]₂ ( 8 ) are to obtain from Me₂AlCl and Me₂N(CH₂)₂OH and from [Cl₂Al{μ‐O(CH₂)₂NMe₂}]₂ ( 7 ) and CH₂=C(CH₃)MgBr, respectively. The analogous dimethylgallium alkoxides [Me₂Ga{μ‐O(CH₂)₃NMe₂}]₂ ( 9 ), [(S)‐Me₂Ga{μ‐OCH₂CH(i‐Pr)NH‐i‐Pr}]_n ( 10 ), [(S)‐Me₂Ga{μ‐OCH₂CH(i‐Pr)NHCH₂Ph}]_n ( 11 ), [(S)‐Me₂Ga{μ‐OCH₂CH(i‐Pr)N(Me)CH₂Ph}]_n ( 12 ) and [(S)‐Me₂Ga{μ‐OCH₂(C₄H₇NHCH₂Ph)}]_n ( 13 ) result from the equimolar reactions of GaMe₃ with the corresponding alcohols. The new compounds were characterized by elemental analyses, ¹H‐, ¹³C‐ and ²⁷Al‐NMR spectroscopy, and mass spectrometry. Additionally, the structures of 1a , 1b , 2a , 2b , 3a , 5 , 6 and 8 were determined by single crystal X‐ray diffraction.     

Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin‐ Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π‐conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero‐field feature and local hyperfine fields. The zero‐field peak results from a quasistatic magnetic‐field effect of the RF radiation for periods comparable to the carrier‐pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero‐field peak, we suggest that this result may constitute a fundamental low‐field limit of magnetic resonance in carrier‐pair‐based systems. OLEDs offer an alternative solid‐state platform to investigate the radical‐pair mechanism of magnetic‐field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.     

Synthesis and characterization of the open-framework barium bisphosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O

Following the strategy of using polyfunctional phosphonic acids for the synthesis of open-framework metal phosphonates, the phosphonocarboxylic acid (H2O3PCH2)2NCH2C6H4COOH was used in the hydrothermal synthesis of new Ba phosphonates. Its decomposition led to the first open-framework barium phosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O. The synthesis was also successfully performed using iminobis(methylphosphonic acid), (H2O3PCH2)2NH, as a starting material, and the synthesis was optimized to obtain as a pure material. The reaction setup as well as the pH are the dominant parameters, and only a diffusion-controlled reaction led to the desired compound. The crystal structure was solved from single-crystal data: monoclinic; C2/c; a=2328.7(2), b=1359.95(7), and c=718.62(6) pm; beta=98.732(10) degrees ; V=2249.5(3)x10(6) pm3; Z=4; R1=0.036; and wR2=0.072 (all data). The structure of [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O is built up from BaO8 and BaO10 polyhedra forming BaO chains and layers, respectively. These are connected to a three-dimensional metal-oxygen-metal framework with the iminobis(methylphosphonic acid) formally coating the inner walls of the pores. The one-dimensional pores (3.6x4 A) are filled with H2O molecules that can be thermally removed. Thermogravimetric investigations and temperature-dependent X-ray powder diffraction demonstrate the stability of the crystal structure up to 240 degrees C. The uptake of N,N-dimethylformamide and H2O by dehydrated samples is demonstrated. Furthermore, IR, Raman, and 31P magic-angle-spinning NMR data are also presented.     

The influence of preparation method of OC1OC6-PPV films on the photo-oxidation process

Poly(p-phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). PPV derivatives are highly susceptible to photo-oxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that Langmuir-Blodgett (LB) films are less degraded than cast films of a PPV derivative (OC₁OC₆-PPV). Both films had similar thickness (∼50 nm) to allow for a more realistic comparison. Degradation was monitored with UV-vis and FTIR spectroscopies. The results indicated that cast films were completely degraded in ca. 400 min, while LB took longer time, i.e. about four times the values for the cast films. The differences can be attributed to the more compact morphology in the LB than in the cast films. With a compact morphology the diffusion of oxygen in the LB film is hampered and this causes a delay in the degradation process.