Biomedical Spectroscopy and Imaging

Several illustrative examples are presented in this tutorial review to demonstrate the utility of 2D correlation spectroscopy, especially in life science applications. A set of IR spectra for a model protein system, which is undergoing complex thermally induced changes in the secondary structures, is analyzed by 2D correlation spectroscopy. The method of constructing 2D correlation maps from temperature-dependent IR spectra and their interpretation procedure are described. The resolution of overlapped protein IR bands by 2D correlation is demonstrated, and sequential order of spectral intensity changes is determined. Newly emerging techniques in the field, such as Pareto scaling, positive null-space projection, and 2D codistribution analysis, are discussed in some detail, in addition to the traditional application of 2D correlation spectroscopy.

Two-dimensional (2D) correlation spectroscopy provides an important approach to the study of subtle spectral variations caused by intermolecular interactions. In our previous work, DAOSD (Double Asynchronous Orthogonal Sample Design) scheme was introduced to analyze subtle spectral variations of characteristic peaks of substance under intermolecular interactions. In this paper, we apply DAOSD scheme to probe weak coordination between lanthanide (III) ions and lactone group of organic ligands from natural pharmaceutical. Weak coordinative interaction between Nd³⁺ and carbonyl group in Nd(ClO₄)₃/artemisinin in acetonitrile solutions is characterized by using 2D UV/IR hetero-correlation spectroscopy. Experimental results demonstrate that subtle band-shift and variation on the absorptivity can be observed on both carbonyl band of artemisinin and f–f transition band of Nd³⁺ ions upon coordination.

An approach, macro-interpretation based on FT-IR and 2DCOS-IR, has been developed for TCM classification and identification. It has been noted that every TCM has respective unique IR and 2DCOS-IR macro-fingerprints, every category (protein-rich, oil-rich, tannin-rich, inulin-rich, starch-rich, sucrose-rich and stachyose-rich) of TCMs, however, has common macro-fingerprints in specific wavenumber regions. Particularly, protein-rich TCMs have two strong absorption bands of amide I (∼1630 cm⁻¹) and amide II (∼1560 cm⁻¹) in the range of 1680–1500 cm⁻¹; oil-rich TCMs generally have characteristic regions with strong autopeaks around 2920 cm⁻¹, 2852 cm⁻¹ and 1740 cm⁻¹; starch-rich TCMs have a common pattern of positively correlated strong autopeak cluster (1139 cm⁻¹, 1120 cm⁻¹, 1102 cm⁻¹, 1070 cm⁻¹, 955 cm⁻¹, 907 cm⁻¹, 887 cm⁻¹) in the saccharide vibration regions; inulin-rich TCMs have a tower-like fingerprint with the strongest peak around 1033 cm⁻¹ in the region of 1200–800 cm⁻¹ in IR spectra and a 3*3 positively correlated strong autopeak cluster (1006 cm⁻¹, 954 cm⁻¹, 893 cm⁻¹) in 2DCOS-IR spectra. 2DCOS can enhance the spectral resolution in discriminating TCMs with high similarity in IR spectra. Based on the results of IR and 2DCOS-IR spectral macro-interpretation, TCM classification and identification can be achieved as general character for classification, specific character for identification.

One of the most powerful techniques used to gain structural information of membrane proteins is the Attenuated Total Reflectance Fourier Transformed Infrared spectroscopy (ATR-FTIR). Secondary structure, conformational changes, interactions with lipids and spatial positioning of membranes, proteins and peptides are commonly analyzed by this method that allows having a simultaneous vision of the membrane and the protein that is bound. In particular, ATR-FTIR is especially advantageous to evaluate the membrane lipids order and the effective position of a protein relative to the membrane. This technique has been successfully applied to study α-helical peptides and proteins, and also β-sheet, β-barrel and β-sandwich proteins, but potentially it could be applicable for any protein structure suitable for a geometric approximation. The present review wants to examine and summarize the different models developed to calculate the orientation of these proteins giving some practical examples, analyzing lipid alignment, protein secondary structure and orientation.

BACKGROUND: Early detection of oral cancers can lead to improved survival rates. Due to limitations of existing methods, alternative approaches like Raman spectroscopy are therefore being explored. Ex vivo approaches are more suitable as they obviate need of on-site instrumentation and stringent experimental conditions. Serum Raman spectroscopy has shown potential in detecting cancers like cervical, breast, colorectal and head and neck cancers. Feasibility of classification of normal and oral cancer using serum Raman spectroscopy with 532 nm excitation has also been explored.

OBJECTIVE: In the present study, feasibility of differentiating normal and cancer serum samples using 785 nm excitation laser – the most widely used laser for biomedical applications was explored.

METHODS: 36 buccal mucosa, 33 tongue cancer patients and 17 healthy subjects were recruited and Raman spectra of sera were recorded using assembled Raman microprobe coupled with 40× objective. To eliminate heterogeneity, average of 3 spectra recorded from each sample was subjected to PCA and PC-LDA followed by leave-one-out cross-validation.

RESULTS: Findings indicate average classification efficiency of ∼78% for normal and cancer. Buccal mucosa and tongue cancer serum could also be classified with an efficiency of ∼68%.

CONCLUSIONS: Findings of the study corroborate with the previous study and indicate potential of this approach in management of oral cancer in future, after prospective validation.

The binding effects of Mn²⁺ and Ca²⁺ ions on the vibrational properties of adenine–thymine (AT) base pairs have been investigated using density functional theory. The metallic atoms were coordinated to N3 and N7 atoms of adenine, respectively. We analyze the geometric properties of different metal–AT base pairs structures, as well as the vibrational bands that can be used to detect the presence of metallic ions. In particular we have found that strong vibrational amplitudes of metallic atoms are expected for the vibrational bands in the range between 400–500 cm⁻¹. Also, we point out the effects of cations binding over a series of selected modes, corresponding to experimental data, providing values for the resulting shifts for each of these vibrational bands.

BACKGROUND: Recent evidence suggests that dementia affects hippocampal substructures differentially and thus identifying anatomical details of this structure is potentially clinically important. Visualising details of human hippocampal substructures in vivo is challenging by imaging due to the small size of the medial temporal lobe structure.

METHODS: MRI data were acquired with a 3 T MR scanner using a 2D multi-echo spin echo pulse sequence at such a spatial resolution to reveal hippocampal subfield boundaries. These images were used to develop a manual segmentation procedure for the hippocampal subfields based on image contrast within the structures and/or geometric constraints by anatomical landmarks.

RESULTS: The T2-images were used to devise a segmentation protocol for Cornu Ammonis (CA) CA1, CA2, CA3, dentate gyrus, subiculum and lumped Stratum Lacunosum + Stratum Moleculare + Stratum Radiatum. The segmentation protocol was applied to MRI data from healthy young and aged controls as well as a small cohort of mild cognitive impairment (MCI) subjects. The reported subfield volumes showed high levels of inter-rater reliability arguing for potential as a tool in documenting subfield volumetry in clinical research.

CONCLUSIONS: A comprehensive and robust MRI protocol which allows the labelling of six separate hippocampal subfields from images acquired with a 3 T clinical scanner is presented to promote hippocampal subfield volumetry of clinical cohorts.

Interactions between tetrakis(N, N′, N″, N‴-tetramethyl tetra-2,3-pridino)porphyrazine copper(II) (Cu(tmtppa)) with anionic surfactants: sodium dodecyl sulfate (SDS), sodium tetradecyl sulfonate (STS) and sodium hexadecyl sulfonate (SHS) were investigated in aqueous submicellar solutions using spectrophotometric method at 298.15, 303.15, 313.15, 318.15 and 323.15 K. Binding constants between the submicellar solutions of surfactants and Cu(tmtppa) system were calculated from the changes in absorbance values at different temperatures. The results showed that increasing alkyl chain length of surfactants caused a stronger interaction indicating the importance of hydrophobic forces. It was found that the values of binding constant increased with increasing temperature. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) were determined for the binding processes of porphyrazine–surfactant system. It was concluded from ΔG° and ΔH° values that the binding process occurred spontaneously and was endothermic in nature.