Structure and dynamics of urea/water mixtures investigated by vibrational spectroscopy and molecular dynamics simulation.

Urea/water is an archetypical "biological" mixture and is especially well-known for its relevance to protein thermodynamics as urea acts as a protein denaturant at high concentration. This behavior has given rise to an extended debate concerning urea's influence on water structure. On the basis of a variety of methods and of definitions of the water structure, urea has been variously described as a structure-breaker, a structure-maker, or as remarkably neutral toward water. Because of its sensitivity to microscopic structure and dynamics, vibrational spectroscopy can help resolve these debates. We report experimental and theoretical spectroscopic results for the OD stretch of HOD/H2O/urea mixtures (linear IR, 2DIR, and pump-probe anisotropy decay) and for the CO stretch of urea-D4/D2O mixtures (linear IR only). Theoretical results are obtained using existing approaches for water and a modification of a frequency map developed for acetamide. All absorption spectra are remarkably insensitive to urea concentration, consistent with the idea that urea only very weakly perturbs the water structure. Both this work and experiments by Rezus and Bakker, however, show that water's rotational dynamics are slowed down by urea. Analysis of the simulations casts doubt on the suggestion that urea immobilizes particular doubly hydrogen bonded water molecules.

Spinal cord injury: a ten-year report.

In the past 10 years, the RSCICDV has had a unique opportunity to serve and expand the bounds of knowledge regarding this most devastating injury. The RSCICDV has collaborated with other model SCI systems in research regarding the incidence of respiratory complications, the value of removing bullet fragments lodged within the spinal canal, the survival/cause of death following spinal cord injury, the cost of spinal cord injury care, and the recovery of motor strength after quadriplegia. Key on-site research efforts have focused on preventing deep vein thrombosis and in documenting the course of motor recovery after spinal cord injury. The identification of electrical stimulation plus low dose heparin as a prophylaxis has been a major breakthrough in the prevention of deep vein thrombosis. The documentation of motor recovery after injury has led to the designation of Thomas Jefferson University as a federally-funded National Rehabilitation Research and Training Center in Neural Recovery and Functional Enhancement (1988-1993). It cannot be stressed enough, however, that the accomplishments of the Regional Spinal Cord Injury Center of Delaware Valley would have been quite impossible without the cooperation and support of the many physicians who have referred their patients to this regional center program. Continuing and expanding this cooperative effort should result in even greater achievements for persons with spinal cord injury in the years to come.