ABSTRACT
Early-time dynamics of nitroaromatics and its coressponding bases can give valuable insights into photo-induced reactions relevant to atmospheric and environmental processes. In this work, femtosecond broadband absorption spectroscopy between 350 and 700 nm has been applied to explore the ultrafast dynamics of o-, p- and m-nitrophenol anions (NP-) in basic organic and aqueous solution. Excitation at 400 nm promotes these compounds into the first bright electronic singlet state, which is a charge-transfer state. A surprising finding for all nitrophenolates was a characteristic, spectrally broad stimulated emission (SE) from the electronically excited state into the ground state. The corresponding lifetime was on the order of a few hundred femtoseconds for o- and p-NP- while it was roughly ten times larger for m-NP-. In line with earlier observations, the SE is governed by an out-of-plane torsional motion of the nitro group, leading to a close energetic approach of the relevant electronically excited singlet and ground states. Subsequent dynamics can be assigned to excited state absorption and ground state relaxation due to energy dissipation of the vibrational modes to the solvent that occur for up to several tens of picoseconds. No longer-lasting transient absorption (TA) was found; instead, a complete recovery of the ground state bleaching was observed indicating that triplet state relaxation is either not significantly involved in this spectral part or shifted to other regions. In the aqueous system, time constants for all processes are much smaller than in organic solution, a fact that can be explained by the larger dipole moment of the solvent and the correspondingly stronger intermolecular coupling between NP- and the aqueous solvent.
ABSTRACT
We present a general construction of all correlation functions of a two-dimensional rational conformal field theory, for an arbitrary number of bulk and boundary fields and arbitrary topologies. The correlators are expressed in terms of Wilson graphs in a certain three-manifold, the connecting manifold. The amplitudes constructed this way can be shown to be modular invariant and to obey the correct factorization rules.
ABSTRACT
In rats, the incorporation of L-[U-14C]leucine into proteins of cytosolic (soluble proteins) and of the 100,000 x g pellet fraction from ipsilateral hippocampus subregions (CA1, CA3 and CA4/area dentata) and visual cortex was studied from 5 min to 65 min after electrical tetanization of the right perforant path. The rates of protein synthesis were estimated calculating the relative specific radioactivity of proteins (RSA). The stimulation parameters used were identical to those of previous experiments inducing post-tetanic long-term potentiation (LTP) of both the amplitude of population spike and the slope function of the excitatory post-synaptic potential (EPSP) in the area dentata. Under these conditions, RSA-values of both fractions evaluated in the CA4/area dentata were found to be about two times higher in tetanized rats compared to either stimulated or passive controls (p less than 0.05). In all the other brain regions studied, no differences between tetanized and control animals were observed. These results provided evidence for an LTP-induced augmentation of protein synthesis in the ipsilateral dentate area which might be an essential prerequisite for those structural changes realizing the long-lasting enhanced efficacy of synaptic transmission at the perforant path-granular cell connections within this hippocampus subfield.
