Crea Francesco, De Stefano Concetta, Porcino Nunziatina, Sammartano Silvio
Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Salita Sperone, 31, I-98166 Messina, Vill. S. Agata, Italy.
Biophys Chem. 2008 Aug;136(2-3):108-14. doi: 10.1016/j.bpc.2008.05.001. Epub 2008 May 17.
The interaction between protonated branched poly(ethylenimine) [BPEI] and phytate (1,2,3,4,5,6 hexakis (di-hydrogen phosphate) myo-inositol) [Phy] was studied potentiometrically. The measurements were carried out at t=25 degrees C and at low ionic strength values, without addition of supporting electrolyte, to avoid interferences with other anions and cations. In order to simplify the data treatment, BPEI was considered as a simple tetramine. Different species Phy(BPEI)H(j), with j=6,7,8, and Phy(BPEI)(2)H(7) were found, having quite high stability. The ability of phytate to sequester BPEI was quantified by considering the parameter pL(50), namely the concentration (-log Phy) necessary to bind 50% of polyammonium cation (as trace). In our experimental conditions, for the system phytate-BPEI-proton we have pL(50)=7.01, at pH=7.4 and I=0.04 mol L(-1). As for other phytate-polyammonium cation systems, the stability of the phytate-BPEI species is strictly proportional to the charges involved in the formation reactions. Therefore, it was possible to calculate the free energy contribution per bond, DeltaG(b)(U)=4.4+/-0.4 kJ mol(-1). The dependence on temperature and ionic strength of the stability of phytate-low/high molecular weight polyammonium cations species, was studied using some semiempirical equations and enthalpy data for the protonation of both components. The dependence on temperature of the stability is quite low and the variation of pL(50) in the range 15< or =t/ degrees C< or =37 is less than 0.5 log units. On the contrary, the effect of ionic strength is highly significant, with a lowering of pL(50) of approximately 2 log units (I=0 to 0.15 mol L(-1)).
采用电位滴定法研究了质子化支链聚乙烯亚胺[BPEI]与肌醇六磷酸（1,2,3,4,5,6 - 六磷酸肌醇）[Phy]之间的相互作用。测量在t = 25℃且离子强度较低的条件下进行，不添加支持电解质，以避免其他阴离子和阳离子的干扰。为了简化数据处理，将BPEI视为简单的四胺。发现了不同的物种Phy(BPEI)H(j)（j = 6,7,8）和Phy(BPEI)₂H₇，它们具有相当高的稳定性。通过考虑参数pL(50)来量化肌醇六磷酸螯合BPEI的能力，pL(50)即结合50%多铵阳离子（作为痕量）所需的浓度（-log[Phy]ₜₒₜ）。在我们的实验条件下，对于肌醇六磷酸 - BPEI - 质子体系，在pH = 7.4和I = 0.04 mol L⁻¹时，pL(50)=7.01。对于其他肌醇六磷酸 - 多铵阳离子体系，肌醇六磷酸 - BPEI物种的稳定性与形成反应中涉及的电荷严格成比例。因此，可以计算每个键的自由能贡献，ΔG(b)(U)=4.4±0.4 kJ mol⁻¹。利用一些半经验方程和两种组分质子化的焓数据，研究了肌醇六磷酸 - 低/高分子量多铵阳离子物种稳定性对温度和离子强度的依赖性。稳定性对温度的依赖性相当低，在15≤t/℃≤37范围内pL(50)的变化小于0.5个对数单位。相反，离子强度的影响非常显著，pL(50)降低约2个对数单位（I = 0至0.15 mol L⁻¹）。
