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Glycine Series as a Model to Study near Infrared Reflectance Spectra¹

Near infrared reflectance (NIR) spectra supply the basic information utilized to relate vibrational information of functional groups to the quality analysis of forages and feedstuffs. The spectra are used to quantify the mathematical relationship between functional group information and the chemical analyses currently in use. This paper was developed using the amino acid glycine and its di-, tri-, and tetrapeptide forms to demonstrate that the information due to various chemical functional groups appearing in the mid-infrared region could be located and identified in the NIR region. Spectra for the glycine series were obtained on a spectro-computer system. Absorption peak assignment was conducted using mathematical calculations and direct comparison with published spectra. The region from 1000 to 1900 nm was found to be an overtone region and 1900 to 2600 nm a combination region. Three regions of the spectra contained primarily carbon information. They were 1000 to 1460,1600 to 1900, and 2240 to 2600 nm. The N regions were 1460 to 1590 and 1900 to 2230 nm. These findings verify that the fundamental information originating in the mid-infrared (IR) region is contained in the NIR region in a complicated form as overtones and combinations of the primary IR absorption. A better understanding of these principals will be useful in future quantitative research with forage and feed.

Key Words: Overtones • Combination bands • Peptide • Zwitterion • Forage • Feed • Analysis

² Former graduate student, Pennsylvania State Univ., University Park, PA 16802. Present address: Route 2, Box 8, Middletown, MD 21769; professor of plant breeding, Dep. of Agronomy, Pennsylvania State Univ., University Park, PA 16802; and research biochemist, USDA-ARS, University Park, PA 16802.

Received for publication September 30, 1985.