Accurate estimation of essential enzyme kinetic parameters, such as Km and Vmax, is very important in modern biology. To this date, linearization of kinetic equations is still widely established practice for determining these parameters in chemical and enzyme catalysis. Although simplicity of linear optimization is alluring, these methods have certain pitfalls due to which they more often then not result in misleading estimation of enzyme parameters. In order to obtain more accurate predictions of parameter values, the use of nonlinear least-squares fitting techniques is recommended. However, when there are outliers present in the data, these techniques become unreliable. This paper proposes the use of a robust nonlinear regression estimator based on modified Tukey’s biweight function that can provide more resilient results in the presence of outliers and/or influential observations. Real and synthetic kinetic data have been used to test our approach. Monte Carlo simulations are performed to illustrate the efficacy and the robustness of the biweight estimator in comparison with the standard linearization methods and the ordinary least-squares nonlinear regression. We then apply this method to experimental data for the tyrosinase enzyme (EC 1.14.18.1) extracted from Solanum tuberosum, Agaricus bisporus, and Pleurotus ostreatus. The results on both artificial and experimental data clearly show that the proposed robust estimator can be successfully employed to determine accurate values of Km and Vmax.

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The cytotoxic activity of phenylboroxine acid was evaluated in vitro on mouse mammary adenocarcinoma 4T1, mouse squamous cell carcinoma SCCVII, hamster lung fibroblast V79 and mouse dermal fibroblasts L929 cell lines. The cytotoxic effects were dose dependent for all tested tumour and non-tumour cell lines. Under in vivo conditions, three application routes of phenylboronic acid were studied: intra-peritoneal (i.p.), intra-tumour (i.t.) and per-oral. After tumour transplantation in syngeneic mice, phenylboronic acid was shown to slow the growth of both tumour cell lines (4T1 and SCCVII) compared with the control. The inhibitory effects were pronounced during the application of phenylboronic acid. For both tested tumour cell lines, the most prominent antitumour effect was obtained by intraperitoneal administration, followed significantly by oral administration.

The boron heterocyclic compound dipottasium trioxohydroxytetraflourotriborate, K2[B3O3F4OH] has been listed as a promising new therapeutic for the epidermal changes treatment. In order to elucidate its free radical scavenging activity, several appropriate thermodynamic molecular descriptors were calculated with the help of quantum-chemistry methods and their values were compared with the data obtained for ascorbic acid, trimethlyboroxine and trimethoxyboroxine. Considering the results, it may be suggested that the single electron transfer followed by proton transfer (SET-PT) is more favourable reaction pathway than hydrogen atom transfer (HAT) for the halogenated boroxine K2[B3O3F4OH]. Experimental support is provided by evaluating the in-vitro antioxidant activity of the investigated compounds in terms of their ferric-reducing antioxidant power (FRAP). Our study reveals that all three examined boroxines are extremely weak antioxidants.

. In our research, we include two other simpler representatives of the boroxine family compounds: trimethoxyboroxine and trimethylboroxine, which are commercially available. The study objective is to explore the possibility of similar behavior within the same class of boron compounds, that is, to examine the activity of K2[B3O3F4OH] compared to simpler representatives of the same family of compounds. On the one hand, K2[B3O3F4OH], theoretically has the ability to exchange electrons in the extinction of reactive radicals, since two boron atoms are sp3-hybridized and use electrons from the inner shell. On the other hand, trimethoxyboroxine, and trimethylboroxine, in theory, should not exchange electrons. However, recent studies indicate the potential for the boron atom to act like carbon and participate in the exchange of protons. The study used the standard laboratory method of 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant assay. The selected boroxines were treated with a DPPH radical at a temperature of 35° C in various concentrations, and with a reaction time of one hour. Results of the DPPH test show an extremely weak antioxidant capacity exists for all investigated boroxines. When K2[B3O3F4OH] was tested at high concentrations, instead of decreased color in the DPPH radicals, there was an increase in absorbance readings, which could mean that this compound acts as a pro-oxidant at higher concentrations. Future research is recommended to examine the length of reaction times needed, and whether a change in the reaction conditions would boost the antioxidant capacity of K2 [B3O3F4OH]. Finally, future research could test the hypothesis that K2[B3O3F4OH], in the absence of the expected antioxidant activity, acts as a pro-oxidant.UDC Classification: 615.1; DOI: http://dx