Richard Mendelsohn Professor Rutgers University Department of Chemistry 73 Warren Street Newark. NJ 07102 (201) 648-5613 FAX - 1264 mendelso@newark.rutgers.edu

Membrane biophysics. vibrational spectroscopy. phospholipid/protein interaction. lung surfactants

Our research. which has been supported for the past fifteen years by the National Institutes of Health. centers around applications of infrared spectroscopy to biophysical and biomedical problems. Three projects currently underway offer a good illustration of the nature of this work.

1. Structural studies of ultrathin films at the A/W Interface as models for pulmonary surfactant.

Monolayers at the A/W interface form an important experimental paradigm for many problems in membrane biophysics. To date. molecular structure information from molecular films at the A/W interface has been sparse. a consequence of the absence of physical techniques with sufficient sensitivity to acquire molecular structure information. To overcome this problem. we have designed and built an accessory to measure IR spectra of monolayer films in situ at the A/W interface. under conditions of controlled surface tension. We have acquired the first spectra of proteins in monolayers and so can acquire conformational information.
An important application of the above conformational analysis approach has been to the study of structure-function relationships in lung surfactant. This complex mixture of lipids and proteins functions by unknown physical methods in vivo to reduce surface tension at the alveolar/air interface to near zero. thereby reducing the work of breathing. Surfactant consists of three main proteins which act in concert with a fairly simple lipid mixture (50 % DPPC) to produce the required result. We and our collaborators have isolated and purified the three surfactant proteins and have undertaken a series of experiments geared to understanding how these proteins regulate pulmonary physiology
From the theoretical side. we have tested the three-layer Fresnel equations modified for anisotropic systems. in order to determine molecular orientations at the A/W interface. We have successfully monitored the effects of DPPC on the orientation of pulmonary surfactant proteins. and have synthesized peptides of particular conformational states to judge their interaction with phospholipid monolayers in situ at the air/water interface.
A recent encouraging development is the observation that the tilt angle of the helical portions of one of the surfactant proteins (SP-C)) changes markedly in going from bilayers in bulk phases to monolayers at the Air/Water interface. This observation has allowed us to define a model for the mechanism by which peptides aid the spreading of surfactant across the A/W interface.

2. FT-IR microscopy and microscopic imaging of biomineralizing tissue

The interfacing of an FT-IR spectrometer with an optical microscope offers unique possibilities for investigation of living cells. The combination of spatial resolution (to the diffraction limit of 10-20 microns) coupled with availability of molecular structure information is a seductive goal. Since the experimental problems in the sampling of heterogeneous. multicomponent systems are severe. we chose to begin the biomedical applications of FT-IR microscopy with a study of the biomineralization process. It was anticipated. and borne out in reality. that the developing hydroxyapatitic phase would yield intense and interpretable (in terms of molecular structure) FT-IR spectrum .
The spectra-structure correlations gained from model compound studies have been used in conjunction with IR microscopic techniques to map out carbonate substitution. mineral -to-matrix ratios. mineral size/perfection. and collagen cross-links in normal and pathological states of bone (osteoporosis. osteogenisis imperfecta. etc.) at a spatial resolution of 3-10 microns.
In a further application of these studies to biomedical problems. we have begun an experiment with the novel technology of IR microscopic imaging with array detectors to map out molecular markers for disease states in human and animal models as well to see the effect of pathological bone conditions on mineral and collagen structure. We interface daily with the medical community to develop a diagnostic protocol for the efficacy of therapeutic interventions for this disease states and for the molecular characterization of other pathological states of bone.

3. Molecular characterization of the permeability barrier in skin.

A recent interest in my lab has been the development of IR experiments to look at the molecular interactions between the main chemical components of the permeability barrier in the stratum corneum (the outermost layer of skin). We have discovered that the components are not organized in a uniform way. but that microdomains of particular constituents occur. We have found the there are two main determinants to barrier formation. namely hydrogen bonding of the polar regions of lipids and packing properties of the hydrophobic regions of these molecules. These two effects cannot always be optimized in the same structure.

View Dr. Mendelsohn's publications in Pub Med