Kim Young-Teck, Hong Young-Shick, Kimmel Robert M, Rho Jeong-Hae, Lee Cherl-Ho
Department of Packaging Science, Clemson University, Clemson, South Carolina 29634, USA.
J Agric Food Chem. 2007 Dec 26;55(26):10678-84. doi: 10.1021/jf071092f. Epub 2007 Dec 4.
The behavior of protons in biopolymer films (BFs) formed with gelatin, water, and glycerol was investigated at various relative humidities (RHs) and concentrations of glycerol using a low field 1H NMR spectrometer. At a RH of approximately 0%, the distributed spin-spin relaxation times (T2) of protons in BFs showed two components: a rapidly relaxing proton with the shortest T2 derived from protons in the rigid backbone of the gelatin polymer such as CH1-, CH2-, and CH3-, and a slowly relaxing component with longer T2 from protons of the functional groups in amino acid residues in gelatin such as -OH, -COOH, and -NH3. These two components are referred to as nonexchangeable (T2N) and exchangeable protons (T2E), respectively, indicating the different mobility of the protons. The T2E increased as RH increased indicating the increase in relative mobility of protons due to the larger free volume in the BF matrix. Above a RH of 33%, the slowest relaxing component was found in all BFs and referred to as hydration-water protons (T2W) with the highest relative mobility of all protons in the films. It suggests that the free volume in BFs can be formed above a RH of 33% in the absence of glycerol. The behaviors of T2N, T2E, and T2W reveal the formation of free volume in the BF matrix associated with the presence of plasticizers (water and glycerol). The T2 behavior in BFs is consistent with the behavior of spin-lattice relaxation (T1). Our result is the first attempt to characterize using low field 1H NMR technology how all protons in a film matrix behave and to develop correlations between proton mobility and free volume in protein-based BFs plasticized with water and glycerol.
使用低场1H NMR光谱仪，研究了在不同相对湿度（RH）和甘油浓度下，由明胶、水和甘油形成的生物聚合物薄膜（BFs）中质子的行为。在相对湿度约为0%时，BFs中质子的分布自旋-自旋弛豫时间（T2）显示出两个成分：一个快速弛豫的质子，其T2最短，源自明胶聚合物刚性主链中的质子，如CH1-、CH2-和CH3-；另一个缓慢弛豫的成分，其T2较长，来自明胶中氨基酸残基官能团的质子，如-OH、-COOH和-NH3。这两个成分分别称为不可交换质子（T2N）和可交换质子（T2E），表明质子的迁移率不同。随着RH的增加，T2E增加，这表明由于BF基质中较大的自由体积，质子的相对迁移率增加。在RH高于33%时，在所有BFs中都发现了最慢弛豫的成分，称为水合水质子（T2W），其在薄膜中所有质子中具有最高的相对迁移率。这表明在没有甘油的情况下，BFs中的自由体积可以在RH高于33%时形成。T2N、T2E和T2W的行为揭示了BF基质中与增塑剂（水和甘油）的存在相关的自由体积的形成。BFs中的T2行为与自旋-晶格弛豫（T1）的行为一致。我们的结果是首次尝试使用低场1H NMR技术表征薄膜基质中所有质子的行为，并建立质子迁移率与用水和甘油增塑的基于蛋白质的BFs中自由体积之间的相关性。
