Multiple Reactive Groups Research Articles

Hemoglobins with multiple reactive sulphydryl groups: the reaction of dog hemoglobin with 5,5'-dithiobis (2-nitrobenzoate).

Dog hemoglobin has four sulphydryl groups per (tetramer) molecule located at the G18(111)alpha and F9(93)beta positions. The two sulphydryls at the G18(111)alpha positions are unreactive toward nonmercurial sulphydryl reagents, but those at the F9(93)beta positions are reactive toward these reagents. We have studied the kinetics of the reaction of dog hemoglobin with 5,5'-dithiobis (2-nitrobenzoic acid) as a function of pH. At all pH values studied, the reaction is kinetically monophasic. Quantitative analysis of the pH dependence of the apparent second-order rate constant shows that two ionizable groups are linked to the reaction of the sulphydryl group. Their pKa values are 5.57 and 9.0. These values are assigned to HisHC3(146)beta and to the CysF9(93)beta sulphydryl. We find that dog carbonmonoxyhemoglobin is significantly--almost an order of magnitude--less reactive than the aquomet, azidomet, and oxy derivatives. This result may be due to a greater tendency (at acid pH) for the salt bridge between HisHC3(146)beta and AspFG1(94)beta to form in the carbonmonoxy than in the other derivatives. Formation of this salt bridge is known to hinder access to the CysF9(93)beta sulphydryl [Perutz, M. F. (1970), Nature 228, 734-739].

STRUCTURE ACTIVITY HYPOTHESES IN OCCUPATIONAL ASTHMA CAUSED BY LOW MOLECULAR WEIGHT SUBSTANCES<xref ref-type="fn" rid="fn1"><sup>*</sup></xref>

Many substances with a low molecular weight (less than 1000 molecular weight) but of different chemical classes are recognized as causative agents of occupational asthma. Some of their major chemical properties are highlighted in relation to their putative interactions with human macromolecules. Thus, certain transition metals which form co-ordination complexes may chelate human proteins. Several organic substances have marked basic properties which are responsible for their chemical reactivity. Some of these, such as the bifunctional bases ethylene diamine, piperazine and para-phenylene diamine are known causative agents of asthma while their monofunctional counterparts, in spite of wide industrial application, are not similarly recognized causes. This suggests that the presence of multiple reactive groups is of importance in the molecular interactions with human macromolecules that eventually lead to occupational asthma. Reference is also made to other substances to exemplify hypothetical mechanisms of these interactions. Such generation of hypotheses is a prelude to quantitative studies of structure activity relationships (QSARs) where the hypotheses can be tested and revised. Structure activity hypotheses in isolation might not be adequate predictors of the risk of occupational asthma. However, if applied to novel chemical entities they might eventually prove useful in contributing to the development of policies for prospective health surveillance and in establishing priorities for epidemiological research.

Formaldehyde in certain marine products

A novel formaldehyde-free phosphorus–nitrogen flame retardant with multiple reactive groups, dioxo (3-triethylphosphite-5-chlorine−1−triazine) neopentyl glycol (DTCTNG), has been synthesized and was applied to cotton fabrics. The molecular structure of DTCTNG was characterized by FTIR, 1H NMR, and 31P NMR. The thermal degradation property of DTCTNG was assessed by thermogravimetric analysis (TGA), which revealed that it has good thermal stability on the high temperature condition. To achieve a covalent bond between DTCTNG and fiber matrix, the finishing conditions of cotton fabrics with different add-on's DTCTNG were investigated by using TGA, vertical flammability test, limiting oxygen index (LOI) and scanning electron microscope test (SEM). The water resistance of the treated cotton fabrics under optimal finishing condition was studied by LOI test. Furthermore, the mechanism of cross-linking reaction between DTCTNG and cotton fiber was discussed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). All the results showed that cotton fabrics treated with DTCTNG has good flame retardancy and steady water resistance.