The dependence of the molecular first hyperpolarizabilities of merocyanines on ground-state polarization and length

We report here the dipole moment (µ) and first hyperpolarizability (β) determined by electric field-induced second harmonic generation, for several merocyanine dyes containing an 1,3,3-trimethylindoline heterocycle as a ‘donor’ in which the ‘acceptor’ end of the molecule and the polyene bridge length was systematically varied; dyes with hexamethine bridges gave positive β, while that with a dimethine bridge gave a negative β value

Response of Rubredoxin from Pyrococcus furiosus to Environmental Changes: Implications for the Origin of Hyperthermostability

The bases of the hyperthermostability of rubredoxin from Pyrococcus furiosus (RdPf) have been probed by structural perturbations induced by solution pH and ionic strength changes. Comparison of the solution behavior at pH 7 and pH 2, as probed by far- and near-UV circular dichroism, Trp fluorescence emission, l-anilinonaphthalene-8-sulfonate (ANS) binding, and NMR spectroscopy, reveals the presence of only minimal structural variations at room temperature. At pH 2, the protein displays a surprising nearly native-like behavior at high ionic strength while, at low ionic strength, it is capable of strongly binding the hydrophobic probe ANS. All the secondary and tertiary structural features, including the environment of the hydrophobic core, appear to be intact regardless of pH and ionic strength. The apparent "melting" or denaturation temperature at pH 2, however, is 42 °C lower than at pH 7. This is attributed to the perturbation of many electrostatic interactions, including the disruption of all the ion pairs, which is complete at pH 2, as indicated by electrometric pH titrations. The implications of these findings for the origins of the hyperthermostability of rubredoxin are discussed

Response of Rubredoxin from Pyrococcus furiosus to Environmental Changes: Implications for the Origin of Hyperthermostability

The bases of the hyperthermostability of rubredoxin from Pyrococcus furiosus (RdPf) have been probed by structural perturbations induced by solution pH and ionic strength changes. Comparison of the solution behavior at pH 7 and pH 2, as probed by far- and near-UV circular dichroism, Trp fluorescence emission, l-anilinonaphthalene-8-sulfonate (ANS) binding, and NMR spectroscopy, reveals the presence of only minimal structural variations at room temperature. At pH 2, the protein displays a surprising nearly native-like behavior at high ionic strength while, at low ionic strength, it is capable of strongly binding the hydrophobic probe ANS. All the secondary and tertiary structural features, including the environment of the hydrophobic core, appear to be intact regardless of pH and ionic strength. The apparent "melting" or denaturation temperature at pH 2, however, is 42 °C lower than at pH 7. This is attributed to the perturbation of many electrostatic interactions, including the disruption of all the ion pairs, which is complete at pH 2, as indicated by electrometric pH titrations. The implications of these findings for the origins of the hyperthermostability of rubredoxin are discussed

Structure-activity studies of delta-selective opioid analogues

The two structurally different peptides DPDPE and Dermenkephalin show a similar remarkably high affinity and selectivity for the delta opioid receptor subtype. An effort has been made to gain some insight into the factors responsible for the recognition ability of these two molecules by synthesizing some DPDPE-Dermenkephalin peptide hybrids and some conformationally restricted Dermenkephalin analogues. The results of the binding and the in-vitro bioassays have been compared with those of the parent peptides. A general decrease in receptor affinity has been observed in the peptide hybrids while the dermenkephalin analogues have shown a wider range of affinities and selectivities. The above findings contribute to the understanding of the structural requirements of the delta receptor, provide information about the sensitivity of Dermenkephalin to enzymatic degradation, and indicate directions for future research

Fluorescein: A Photo-CIDNP Sensitizer Enabling Hypersensitive NMR Data Collection in Liquids at Low Micromolar Concentration

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is a powerful approach for sensitivity enhancement in NMR spectroscopy. In liquids, intermolecular photo-CIDNP depends on the transient bimolecular reaction between photoexcited dye and sample of interest. Hence the extent of polarization is sample-concentration dependent. This study introduces fluorescein (FL) as a photo-CIDNP dye whose performance is exquisitely tailored to data collection at extremely low sample concentrations. The photo-CIDNP resonance intensities of tryptophan in the presence of either FL or FMN (i.e., the routinely employed flavin mononucleotide photosensitizer) in the liquid state show that FL yields superior sensitivity and enables rapid data collection down to an unprecedented 1 μM concentration. This result was achieved on a conventional spectrometer operating at 14.1 T and equipped with a room-temperature probe (i.e., noncryogenic). Kinetic simulations show that the excellent behavior of FL arises from its long excited-state triplet lifetime and superior photostability relative to conventional photo-CIDNP sensitizers