We used Fourier transform infrared (FTIR) microspectroscopy to investigate pressure-induced conformational changes in secondary structure of fibrinogen (FBG). Solid state FBG was compressed on a KBr pellet (1KBr method) or between two KBr pellets (2KBr method). The peak positions of the original and second-derivative ir spectra of compressed FBG samples prepared by the 1KBr method were similar to FBG sample without pressure. When FBG was prepared by the 2KBr method and pressure was increased up to 400 kg/cm(2), peaks at 1625 (intermolecular beta-sheet) and 1611 (beta-sheet aggregates structure and/or the side-chain absorption of the tyrosine residues) cm(-1) were enhanced. The peaks near 1661 (beta-sheet) and 1652 (alpha-helix) cm(-1) also exhibited a marked change with pressure. A linear correlation was found between the peak intensity ratio of 1611/1652 cm(-1) (r = 0.9879) or 1625/1652 cm(-1) (r = 0.9752) and applied pressure. The curve-fitted compositional changes in secondary structure of FBG also indicate that the composition of the alpha-helix structure (1657-1659 cm(-1)) was gradually reduced with the increase in compression pressure, but the composition of the beta-sheet structure (1681, 1629, and 1609 cm(-1)) gradually increased. This indicates that pressure-induced conformational changes in FBG include not only transformations from alpha-helix to beta-sheet structure, but also unfolding and denaturation of FBG and the formation of aggregates.

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There is lack of a worldwide standard technique for clinical diagnosis of interstitial cystitis (IC). Raman spectroscopy with higher specificity and sensitivity has been extensively used to act as a non-destructive analytical technique without special sample preparation. In this preliminary study, possible use of Raman microspectroscopy as an IC diagnostic tool was attempted. Twenty-two participants were screened by clinical features, history, urodynamic evaluations and potassium sensitivity test (PST). The freeze-dried water samples voided from all the participants after PST were directly determined by using a confocal Raman microspectroscopy to search the biomarker. Participants with or without IC symptom were separated into control and clinical groups, according to the above screening. The participants in the clinical group were further divided into mild and severe subgroups by PST. The symptom of urinary pain and urgency was significant difference between the mild and severe subgroups (p < 0.05). A significant increase in urinary frequency but a marked reduction in bladder capacity, maximum cystometric capacity and maximum voiding flow rate were obtained for clinical group of IC participants, as compared with the result of control group (p < 0.05). By using Raman microspectroscopic determination, the band near 1003 or 1005 cm−1 assigned to phenylalanine was respectively detected from the freeze-dried water sample of control group or mild subgroup, but the band at 1010 cm−1 due to tryptophan was found in the freeze-dried water sample of severe subgroup. The result of this preliminary study first suggests a possible application of Raman microspectroscopy to strongly certify the results of PST for IC diagnosis. Phenylalanine or tryptophan might be acted as a biomarker to assist the diagnosis of IC after PST. Particularly, the appearance of tryptophan might be used to discriminate the severity of IC symptom.

The stepwise reaction pathway of the solid-state Maillard reaction between glucose (Glc) and asparagine (Asn) was investigated using simultaneous differential scanning calorimetry (DSC)-FTIR microspectroscopy. The color change and FTIR spectra of Glc-Asn physical mixtures (molar ratio = 1:1) preheated to different temperatures followed by cooling were also examined. The successive reaction products such as Schiff base intermediate, Amadori product, and decarboxylated Amadori product in the solid-state Glc-Asn Maillard reaction were first simultaneously evidenced by this unique DSC-FTIR microspectroscopy. The color changed from white to yellow-brown to dark brown, and appearance of new IR peaks confirmed the formation of Maillard reaction products. The present study clearly indicates that this unique DSC-FTIR technique not only accelerates but also detects precursors and products of the Maillard reaction in real time.