Origin and quantification of differences between normal and tumor tissues observed by terahertz spectroscopy.

The origin of the differences in the refractive index observed between normal and tumor tissues using terahertz spectroscopy has been described quantitatively. To estimate water content differences in tissues, we prepared fresh and paraffin-embedded samples from rats. An approximately 5% increase of water content in tumor tissues was calculated from terahertz time domain spectroscopy measurements compared to normal tissues. A greater than 15% increase in percentage of cell nuclei per unit area in tumor tissues was observed by hematoxylin and eosin stained samples, which generates a higher refractive index of biological components other than water. Both high water content and high cell density resulted in higher refractive index by approximately 0.05 in tumor tissues. It is predicted that terahertz spectroscopy can also be used to detect brain tumors in human tissue due to the same underlying mechanism as in rats.

Brain tumor imaging of rat fresh tissue using terahertz spectroscopy.

Tumor imaging by terahertz spectroscopy of fresh tissue without dye is demonstrated using samples from a rat glioma model. The complex refractive index spectrum obtained by a reflection terahertz time-domain spectroscopy system can discriminate between normal and tumor tissues. Both the refractive index and absorption coefficient of tumor tissues are higher than those of normal tissues and can be attributed to the higher cell density and water content of the tumor region. The results of this study indicate that terahertz technology is useful for detecting brain tumor tissue.

Glutathione maintenance is crucial for survival of melanocytes after exposure to rhododendrol.

Rhododendrol is a phenolic compound that shows a tyrosinase-dependent toxicity for melanocytes and occasionally induces a vitiligo-like skin depigmentation. The post-tyrosinase mechanisms determining melanocyte death or survival, however, are far from clear. Here, we find that rhododendrol treatment leads to a reduction in the levels of cellular glutathione but also induces a cellular antioxidant response that eventually increases glutathione levels. We further find that rhododendrol toxicity is enhanced when glutathione levels are experimentally reduced and alleviated when glutathione levels are increased. Hence, it appears that the size of the preexisting glutathione pool along with the capacity to supply glutathione via the antioxidant response determines whether melanocytes survive or die after rhododendrol exposure. It is conceivable, therefore, that rhododendrol-induced leukoderma depends on the capacity to maintain appropriate glutathione levels and that enhancement of glutathione levels may preserve a patient's melanocytes and potentially help in repigmentation.

Frequency dependence of vibrational energy relaxation and spectral diffusion of the N-H stretching band of pyrrole-base complexes in solution.

A study on the vibrational dynamics of the NH stretching mode of pyrrole-base complexes in carbon tetrachloride, using subpicosecond infrared pump-probe (PP) spectroscopy, is reported. The time evolution of the PP signal of the NH stretching mode for all the complexes was frequency-dependent; the signal decay time increased with the frequency. This frequency dependence was thought to originate from the relationship between vibrational energy relaxation (VER) and spectral diffusion. For hydrogen-bonded systems, spectral diffusion corresponds to the reorganization of the solvent environment. Qualitative analysis of the frequency dependence of the PP signal decay time indicated that a simple energy gap law could not be applied to all the pyrrole-base complexes. This conclusion was supported by spectral simulation of the PP signal using the modified Smoluchowski equation to clarify the frequency dependence of the VER and the spectral diffusion.

Roxbin B is cuspinin: structural revision and total synthesis.

Prompted by the outcome that the synthesized roxbin B was not identical to the natural roxbin B, the structural determination process and spectral data were re-examined, with the finding that roxbin B was very likely to be 1-O-galloyl-2,3-(R);4,6-(S)-bis-O-hexahydroxydiphenoyl-ß-d-glucose (cuspinin). Because the (R)-axial chirality is rare in natural products when the hexahydroxydiphenoyl group bridges the 2- and 3-oxygens, the proposed structure of cuspinin was confirmed by the total synthesis, leading to the conclusion that roxbin B is the same as cuspinin.

Total synthesis of the proposed structure of roxbin B; the nonidentical outcome.

A proposed structure of roxbin B was synthesized. For the synthesis, a new synthetic method for the preparation of the hexahydroxydiphenoyl (HHDP) bridge was developed that involved the stepwise esterification of axially chiral HHDP acid anhydride. The synthesized compound was not identical to the natural roxbin B.

Low-frequency modes of the benzoic acid dimer in chloroform observed by the optical Kerr effect.

The low frequency Raman spectral density associated with the intermolecular hydrogen-bonding interaction of benzoic acid in chloroform was investigated through the ultrafast optically-heterodyne-detected optical Kerr effect. The low-frequency solute Raman spectrum was obtained by Fourier transform analysis and subtraction of the solvent spectrum from the solution spectrum. The resulting difference spectrum has a broad band below 150 cm(-1) with a peak at around 80 cm(-1). Previous studies of aromatic liquids suggest that the origin of such a low-frequency band is librational motion, although intermolecular hydrogen-bonding modes in benzoic acid may also contribute. To clarify these contributions to the low-frequency band, methyl benzoate was used to estimate the librational component; its structure is similar to benzoic acid, but it forms no intermolecular hydrogen bonds. Both librational and intermolecular modes were found to contribute to the low-frequency Raman spectrum of the dimer and thus can be separated. These experimental results were compared with the results of density functional theory calculations. In addition, the effect of deuteration on the Raman spectrum was also investigated.

Intermolecular vibrational mode of the benzoic acid dimer in solution observed by terahertz time-domain spectroscopy.

The low-frequency modes of the benzoic acid (BA) dimer and its analogues in carbon tetrachloride (CCl(4)) have been investigated by terahertz time-domain spectroscopy. The solute spectrum is obtained by subtracting the solvent contribution from that of the solution. The difference spectrum of BA in CCl(4) has a broad band with a peak at 68 cm(-1). To assign the observed band, the spectrum is compared with spectra of other aromatic molecules, such as benzene and phenol in addition to p-methyl BA and deuterated BA species (BA-d(OH) and BA-d(5)) in CCl(4). The band at 68 cm(-1) is assigned to the cogwheel mode of the BA dimer. Density functional theory calculations also support this assignment. Finally, spectral lineshape analysis based on the multimode Brownian oscillator model is applied to the THz spectra for all the samples.

Measuring acetic acid dimer modes by ultrafast time-domain Raman spectroscopy.

Acetic acid is capable of forming strong multiple hydrogen bonds and therefore different dimeric H-bonded structures in neat liquid phase and in solutions. The low frequency Raman spectra of acetic acid (neat, in aqueous solution and as a function of temperature) were obtained by ultrafast time and polarization resolved optical Kerr effect (OKE) measurements. Isotropic OKE measurements clearly reveal a specific totally symmetric mode related to the dimeric structure H-bond stretching mode. The effects of isotope substitution, water dilution and temperature on this mode were investigated. These results together with anisotropic OKE measurements and density functional theory calculations for a number of possible dimers provide strong evidence for the cyclic dimer structure being the main structure in liquid phase persisting down to acetic acid concentrations of 10 M. Some information about the dimer structure and concentration dependence was inferred.

Vibrational dynamics of hydrogen-bonded complexes in solutions studied with ultrafast infrared pump-probe spectroscopy.

In aqueous solution, the basis of all living processes, hydrogen bonding exerts a powerful effect on chemical reactivity. The vibrational energy relaxation (VER) process in hydrogen-bonded complexes in solution is sensitive to the microscopic environment around the oscillator and to the geometrical configuration of the hydrogen-bonded complexes. In this Account, we describe the use of time-resolved infrared (IR) pump-probe spectroscopy to study the vibrational dynamics of (i) the carbonyl CO stretching modes in protic solvents and (ii) the OH stretching modes of phenol and carboxylic acid. In these cases, the carbonyl group acts as a hydrogen-bond acceptor, whereas the hydroxyl group acts as a hydrogen-bond donor. These vibrational modes have different properties depending on their respective chemical bonds, suggesting that hydrogen bonding may have different mechanisms and effects on the VER of the CO and OH modes than previously understood. The IR pump-probe signals of the CO stretching mode of 9-fluorenone and methyl acetate in alcohol, as well as that of acetic acid in water, include several components with different time constants. Quantum chemical calculations indicate that the dynamical components are the result of various hydrogen-bonded complexes that form between solute and solvent molecules. The acceleration of the VER is due to the increasing vibrational density of states caused by the formation of hydrogen bonds. The vibrational dynamics of the OH stretching mode in hydrogen-bonded complexes were studied in several systems. For phenol-base complexes, the decay time constant of the pump-probe signal decreases as the band peak of the IR absorption spectrum shifts to lower wavenumbers (the result of changing the proton acceptor). For phenol oligomers, the decay time constant of the pump-probe signal decreases as the probe wavenumber decreases. These observations show that the VER time strongly correlates with the strength of hydrogen bonding. This acceleration may be due to increased coupling between the OH stretching mode and the accepting mode of the VER, because the low-frequency shift caused by hydrogen bond formation is very large. Unlike phenol oligomers, however, the pump-probe signals of phenol-base complexes did not exhibit probe frequency dependence. For these complexes, rapid interconversion between different conformations causes rapid fluctuations in the vibrational frequency of the OH stretching modes, and these fluctuations level the VER times of different conformations. For the benzoic acid dimer, a quantum beat at a frequency of around 100 cm(-1) is superimposed on the pump-probe signal. This result indicates the presence of strong anharmonic coupling between the intramolecular OH stretching and the intermolecular stretching modes. From a two-dimensional plot of the OH stretching wavenumber and the low-frequency wavenumber, the wavenumber of the low-frequency mode is found to increase monotonically as the probe wavenumber is shifted toward lower wavenumbers. Our results represent a quantitative determination of the acceleration of VER by the formation of hydrogen bonds. Our studies merit further evaluation and raise fundamental questions about the current theory of vibrational dynamics in the condensed phase.

Local and systemic expression of inducible nitric oxide synthase in comparison with that of cyclooxygenase-2 in rat carrageenin-induced pleurisy.

Expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) is up-regulated in response to inflammatory stimuli. To evaluate the extent to which local pleural inflammation involves additional site in the pleural cavity and elsewhere, we investigated the time course of the levels of iNOS and its product in the inflammatory and other sites, and compared those with a level of COX-2 in rat carrageenin-induced pleurisy. The exudate and plasma NOx levels rose, reaching peaks at 9 and 14 h, respectively. Both COX-2 and iNOS became detectable in exudate leukocytes, their levels reaching peaks at 3 and 9 h after irritation, respectively. COX-2 was detectable mainly in neutrophils, but iNOS was detectable in both neutrophils and mononuclear leukocytes. Furthermore, iNOS became detectable in neutrophils and mononuclear leukocytes in enlarged parathymic lymph nodes from 3h in addition to those in peripheral blood and Kupffer cells from 3 to 14 h, respectively. The gene product is also detectable in thymic large dendritic cells of pleurisy-induced rats as well as normal control rats. COX-2 became detectable in stellar dendritic cells of the enlarged draining lymph nodes from 14 h. Thus, these gene products were induced in the immediate proximity of regional lymph nodes, and even at a considerable distance of liver by the local inflammatory stimulus. Although their expression pattern was quite different from each other, these gene products were detectable in phagocytic cells.