Biomedical Spectroscopy and Imaging - Volume 4, issue 3
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Biomedical Spectroscopy and Imaging (BSI) is a multidisciplinary journal devoted to the timely publication of basic and applied research that uses spectroscopic and imaging techniques in different areas of life science including biology, biochemistry, biotechnology, bionanotechnology, environmental science, food science, pharmaceutical science, physiology and medicine. Scientists are encouraged to submit their work for publication in the form of original articles, brief communications, rapid communications, reviews and mini-reviews.
The journal is dedicated to providing a single forum for experts in spectroscopy and imaging as applied to biomedical problems, and also for life scientists who use these powerful methods for advancing their research work. BSI aims to promote communication, understanding and synergy across the diverse disciplines that rely on spectroscopy and imaging. It also encourages the submission of articles describing development of new devices and technologies, based on spectroscopy and imaging methods, for application in diverse areas including medicine, biomedical science, biomaterials science, environmental science, pharmaceutical science, proteomics, genomics, metabolomics, microbiology, biotechnology, genetic engineering, nanotechnology, etc.
Abstract: Following its first observation over 40 years ago, Raman optical activity (ROA), which may be measured as a small difference in the intensity of vibrational Raman scattering from chiral molecules in right- and left-circularly polarized incident light or, equivalently, the intensity of a small circularly polarized component in the scattered light using incident light of fixed polarization, has evolved into a powerful chiroptical spectroscopy for studying a large range of biomolecules in aqueous solution. The long and tortuous path leading to the first observations of ROA in biomolecules in 1989, in which the author was closely involved from the very…beginning, is documented, followed by a survey of subsequent developments and applications up to the present day. Among other things, ROA provides information about motif and fold, as well as secondary structure, of proteins; solution structure of carbohydrates; polypeptide and carbohydrate structure of intact glycoproteins; new insight into structural elements present in unfolded protein sequences; and protein and nucleic acid structure of intact viruses. Quantum chemical simulations of observed Raman optical activity spectra provide the complete three-dimensional structure, together with information about conformational dynamics, of smaller biomolecules. Biomolecular ROA measurements are now routine thanks to a commercial instrument based on a novel design becoming available in 2004.
Keywords: Raman optical activity, vibrational optical activity, molecular chirality, ab initio computations, peptides, folded and unfolded proteins, carbohydrates, glycoproteins, nucleic acids, viruses
Abstract: We briefly review the field of Raman optical activity (ROA) for transition-metal containing systems with a focus on coordination compounds and solids. In contrast to ROA measurements for optically active solids, ROA for chiral metal complexes is a relatively novel field with only a few measurements and calculations published yet. Their results indicate a great sensitivity of ROA for the elucidation of such compounds, even in case of structurally very similar geometrical isomers, and the differentiation of several types of chirality. Resonance with one or more electronic transitions can lead to intensity enhancement in the ROA spectrum, which provides additional…advantages such as shorter measurement times, lower sample amounts and valuable information about involved excited electronic states. A widely unknown variant is magnetic ROA where an external magnetic field is applied. This form is applicable to both chiral and achiral systems and has, among others, been employed to probe Zeeman splittings and sign of g factors. This review shows that ROA is a very promising field for in-depth study and design of transition-metal containing compounds and materials. It is still in its infancy and possible next steps for future research, with an emphasis on computational developments, are outlined.
Keywords: Optical activity, vibrational spectroscopy, density functional theory, chirality, transition metal
Abstract: Vacuum-ultraviolet (VUV) electronic circular-dichroism (ECD) spectra of methyl β -D-glucopyranoside (methyl β -D-Glc), methyl α - and β -D-galactopyranosides (methyl α - and β -D-Gal), and methyl α - and β -D-xylopyranosides (methyl α - and β -D-Xyl) were measured down to 163 nm in aqueous solution using a synchrotron-radiation VUV-ECD spectrophotometer. Five methyl aldopyranosides exhibited characteristic ECD spectra depending on the gauche (G) and trans (T) conformations of the hydroxymethyl group at C-5 and the α -/β -anomer configurations of the methoxy group at C-1. To elucidate the contributions of these structures to the spectrum, the ECD spectra of three…rotamers (GT, GG and TG) of methyl β -D-Glc, methyl α -D-Gal and methyl β -D-Gal were calculated using a time-dependent density functional theory and molecular dynamics simulations. These theoretical spectra were very similar to those observed experimentally, indicating that the GT and GG rotamers show negative and positive ECD around 170 nm, respectively, and that the α - and β -anomers exhibit negative and positive ECD around 160 nm, respectively. These spectral differences between the two rotamers and between the two anomers were attributable to changes in steric configurations, including the intramolecular hydrogen bond around the ring oxygen and the methoxy oxygen, respectively. These relationships were supported by the ECD spectra experimentally observed for methyl α -D-Xyl and methyl β -D-Xyl, demonstrating that the VUV-ECD spectroscopy is a powerful technique for characterizing the structures of saccharides in aqueous solution.
Keywords: Molecular dynamics simulations, saccharide, steric configuration, synchrotron radiation, time-dependent density functional theory
Abstract: While adequate photon migration through the tissue of interest is essential for near infrared spectroscopy (NIRS), the initial transmission of sufficient photons transcutaneously and ultimate capture of as many as possible returning from the interrogated tissue is also a requisite. Hence the relevance of both the interface between the emitter detector array of a NIRS instrument and the characteristics of the skin through which photons must migrate. We describe design components incorporated into a continuous wave NIRS instrument developed to monitor the bladder transcutaneously in subjects in rural African clinics; review the relevance and impact of melanin pigmentation, cutaneous hair…and skin composition on photon migration; and report the results of pilot testing. Sufficient photon transmission was achieved to transcutaneously monitor changes in chromophore concentration in the bladder effectively in darkly pigmented subjects during spontaneous voiding. We also confirmed the importance of a new protocol to optimize device positioning over the bladder and employing measures to avoid signal contamination caused by pubic hair; both enhance the quality of chromophore data.
Abstract: BACKGROUND: The use of T 2 relaxation contrast, as measured by MRI, is particularly commonplace in non-invasive assessment of the brain. However, the mechanisms and uses of T 2 relaxation in the brain are still not fully understood. The hypothesis that T 2 relaxation may show anisotropy in the human brain was studied at 3 T. T 2 anisotropy refers to the variation of T 2 in ordered structures…with respect to the direction of the applied magnetic field. METHODS: Using a 3 T clinical MRI scanner, we made quantitative multi-contrast spin-echo T 2 and diffusion tensor imaging (DTI) measurements in healthy volunteers, repeating the measurements with the subject’s head oriented differently relative to the applied field, for the measurement of possible spin-echo T 2 anisotropy. RESULTS: We report T 2 relaxation anisotropy measurements and present a means for visualising it according to the principal orientation of ordered structures in the brain parenchyma. We introduce a parameter for the model-free description of T 2 anisotropy, namely the T 2 “fractional anisotropy”, similar to that used to describe anisotropy of translational diffusion. This parameterisation enables the overall level of anisotropy in T 2 across a chosen region or tissue to be calculated. Anisotropic T 2 relaxation was observed in both gray and white matter, though to a greater extent in the latter, with a strong relationship with the anisotropy of translational diffusion. This is evidenced by making repeat measurements with the subject’s head tilted to different angles relative to the applied magnetic field, by which means we observed the T 2 at the same anatomical site to change. CONCLUSIONS: Relaxation anisotropy has a significant effect on T 2 in the brain parenchyma. It has the potential to offer non-invasive access to tissue microstructure not available by other imaging modalities, and may be sensitive to pathology or noxious factors not detected by other means.