M. Khalique Ahmed

Infrared spectroscopic investigation of in vivo and ex vivo human nails

Abstract Mid (700–4000 cm −1 ) and near (4000–10000 cm −1 ) infrared spectra of viable and clipped human finger nails are presented. Mid-infrared depth profiles acquired by physically etching the nail plate and those acquired nondestructively using photoacoustic spectroscopy (PAS) are compared. The dorsal, intermediate, and ventral layers of the nail plate could be discerned spectroscopically. Near infrared (NIR) attenuated total reflectance (ATR), NIR-PAS and NIR diffuse reflectance spectra of the nail plate are compared. At high energies (> 7000 cm −1 ), ATR lacks sensitivity while the diffuse reflectance spectra contain significant contributions from deep within the finger. At lower energies ( −1 ) ATR can be used to probe the near surface of the nail while diffuse reflectance and PA spectra contain only minor contributions from the nail bed and primarily represent the deeper portion of the nail. The low energy near infrared region appears to be the most valuable region for viable nail plate diagnostic spectroscopy. This region is discussed in considerable detail.

FT-IR spectroscopy of methylmercury-exposed mouse lung

Infrared spectrocopy which has traditionally been utilized by chemists and physicists for characterization and identification of the structural properties of chemical compounds is now becoming more relevant as a biodiagnostic tool. Recent reports suggest that arthritis and Alzheimers disease can be diagnosed by using this technique. Changes associated with these diseases diagnosable with this technique are generally overt. In this study we have used ‘Fourier transform infrared spectroscopy’ (FT-IR) to analyze subtle changes in composition and structure of lipids and proteins in lung tissue, bronchoal veolar lavage and purified lamellar body fraction of mice exposed to methylmercury. Infrared measurements were made in attenuated total reflection mode using the Split PeaTM (Harrick Scientific Corporation, USA). Mice were treated with 4 doses of methylmercuric chloride (15 mg/kg body weight/dose), and control animals received an equivalent volume of physiological saline. Comparison of the control and experimental spectra revaled alterations in the intensities and frequencies of vibrational modes of lipids following methylmercury exposure. Results indicate that FT-IR spectral analyses may be a valuable tool for detecting subtle variations in biological components associated with drug exposure to lungs and, in particular may be very useful for assessing changes in bronchoalveolar lavage.

Fourier-transform infrared spectroscopic analysis of rabbit lung surfactant: subfraction-associated phospholipid and protein profiles.

Surfactant obtained from bronchoalveolar lavage (BAL) can be separated into subfractions based on sedimentation characteristics. It has been suggested that the 10,000 x g, 60,000 x g and 100,000 x g subfractions isolated by this approach represent stages of surfactant extracellular processing. These three subfractions have been reported to differ in their morphology, composition and ability to lower surface tension. We wished to determine if infrared spectroscopy, which may be applied as a non-invasive technique could potentially prove useful for characterization and quantification of bronchoalveolar lavage (BAL) protein and phospholipid, and if this approach could detect differences in intermediate surfactant processing stages. Subfractions were collected from adult rabbit lungs by BAL and differential centrifugation and analyzed by Fourier transform infrared (FT-IR) spectroscopy. Biochemical assay of phospholipid and protein showed differences between subfractions that correlated well with the phospholipid/protein ratios obtained from FT-IR spectra (r = 0.939; r2 = 0.882). The subfraction sedimenting at 100,000 x g (P100) exhibited spectral shifts in the Amide I band, suggesting that the protein secondary structure was different compared to other fractions. Spectra obtained after separation of lipids and protein components showed an apparent disordering of protein secondary structure but little or no effect on the structure or mobility of phospholipids. These results support the idea that subfractions represent various processing stages of surfactant. In addition, they show that results from FT-IR analyses correlate significantly with traditional biochemical assay methods which may prove of clinical use.(ABSTRACT TRUNCATED AT 250 WORDS)

High pressure FTIR study of interaction of melittin with dimyristoylphosphatidyl glycerol bilayers

Infrared spectra of hydrated dimyristoylphosphatidyl glycerol (DMPG) and of aqueous dispersions of melittin and DMPG at peptide:lipid molar ratios of 1:10 and 1:4 were recorded as a function of pressure from atmospheric to 22 kbar. Spectral features corresponding to vibrations of the amide linkages in melittin and to various functional groups in DMPG (carbonyl, methlylene, phosphate) were monitored in order to investigate the structure and dynamics of melittin:DMPG dispersions. Melittin was found to cause conformational and orientational disordering of the acyl chains in DMPG bilayers. The magnitude of these disorders was higher for higher concentration of melittin in DMPG. The higher concentration of melittin was also found to disrupt the DMPG bilayers through interactions with the lipid head groups. Such disruption may be related to some of the biological properties of melittin.

Near-infrared photoacoustic spectra of model homo-polypeptides

The Fourier transform near infrared photoacoustic (FT-NIR-PA) spectra of a number of homo-polypeptides are measured. The observed NIR overtone and combination bands are assigned and the structural significance of the bands are discussed. The applicability of such spectra in the analysis of biological/biomedical samples is considered.

Fourier transform infrared spectroscopy of human saliva

FT-IR spectra of male and female dried human saliva were obtained. The assignments of the observed spectral peaks are presented. The possibility of the application of FT-IR spectroscopy of human saliva in monitoring the status of a wide variety of human diseases is discussed.

New Window Material for Near-Infrared Spectroscopy

Liquid-phase samples absorb very weakly in the near-infrared (NIR) region compared to the fundamental region. To detect weak vibrations in NIR region, one uses cells of relatively high pathlengths ranging from 0.1 cm to 5 cm. The selection of a particular pathlength depends upon the absorption strength of the vibration of interest.