Studies of reaction heats and structure of complexes formed between strong N-bases and phenols

The heats of reactions between various phenols and two strong N-bases of guanidine-like character in acetonitrile, are determined. The values can be used as a measure of self-assembly abilities of the phenol molecules in the interactions with strong N-bases, playing a very important role in biological systems. In the case of TBD complexes with corresponding nitrophenols, the protonated N-base is hydrogen-bonded to the nitro group excluding the self-assembly process of the phenols. In the case of other phenols, the self-assembly abilities are dependent on pK_a values of phenols. With increasing acidity of phenols their ability to form the hydrogen-bonded chains decreases. The maximum of length of the chains is observed for 4-methylphenol, which has a similar pK_a value to that in the tyrosine residue in biological systems.     

Solubilization of organic compounds by arginine-derived polymers

Poor aqueous solubility of drugs is one of the major challenges in the pharmaceutical science. In this study, a guanidinium-containing polymer based on arginine was designed and synthesized, and was evaluated as a solubility enhancing additive for three model organic compounds (coumarin, pyrene and doxorubicin). At a guanidinium group concentration of 100 mmol/L, the polymer could significantly increase the solubility of pyrene and doxorubicin by 6-and 11-fold respectively, much more effective than arginine (2-and 3-fold, respectively). In contrast, its effect on the solubility of coumarin was less effective than arginine. The solubilizing effect may be explained by the enhanced interaction between the guanidinium group in the polymer and the aromatic compounds.     

Determination of asymmetric and symmetric dimethylarginines in human plasma by HPLC with electrochemical detection

A new HPLC method was developed and validated for the determination of asymmetric and symmetric dimethylarginines and l ‐arginine in human plasma. After SPE and evaporation of the eluate, the samples were derivatised with an o‐phthaldialdehyde reagent containing 3‐mercaptopropionic acid. The derivatives formed were analysed by isocratic RP‐HPLC with electrochemical detection at +320 mV. The mobile phase consisted of 50 mM phosphate buffer (pH 6.1) containing 10% v/v acetonitrile, the flow rate was 1 mL/min. The retention times of all compounds including monomethylarginine (internal standard) were <24 min. The LODs (S/N 3:1) were 0.012 μM for both dimethylarginines and 0.013 μM for l ‐arginine; the linearity of the method was from 0.1 to 20 μM for both dimethylarginines and from 1 to 200 μM for l ‐arginine. Absolute extraction recoveries measured for all analytes ranged from 85 to 88%.     

Ketopiperazines: Conformationally Constrained Peptidomimetic of Arginine Amides

We have synthesized guanidine‐containing ketopiperazines designed to be conformational mimics of peptidomimetic arginine amides. D‐Allylglycine was converted by an efficient approach to give enantiopure ketopiperazines in which the trans stereochemistry of the C‐substituents resulted from stereospecific enolate alkylation.     

Investigation of chemical activity,SCHIFF base reactions and staining effects of some amino acids by spectrophotometric and theorical methods

In this study, the staining properties of selected amino acids with Brassica oleraceae extract in alum and alum-free media were investigated. Basic, acidic and neutral amino acids (arginine, glutamic acid and glycine) were used to investigate the effect of staining. It was determined that all amino acids were stained in alum media. In the second step, the R group of amino acids found in the proteins of the cell nucleus was reacted with salicyl aldehyde. This reaction was successful only with Arginine. The staining properties of the newly formed compound were also investigated in alum and alum-free environments. Evaluation of the results was done using FT-IR and ¹H NMR methods. All compounds were optimized with the Gaussian G09 program (DFT/B3LYP/6.311 ?G(d.p) basic set. HOMO, LUMO and HOMO-LUMO gap values were determined. Chemical reaction capabilities of amino acids were discussed with the help of HOMO-LUMO gap values.     

Arginine-hydrolyzing enzymes for electrochemical biosensors

Since l-Arginine (Arg) is a semi-essential amino acid for humans, its adequate amount must be consumed in the diet to prevent certain negative consequences related to insufficient synthesis of this amino acid under specific physiological conditions. Arg metabolism results in the production of a biochemically diverse range of such products as urea, some amino acids, creatine, polyamines, nitric oxide, etc. Arg, an important biomarker in clinical diagnostics, is also used for prevention/treatment of different diseases, including cancer and COVID-19. Furthermore, it serves as an indicator of food and beverages quality.A variety of optic and electrochemical methods for Arg determination have already been suggested. The biosensor systems based on the enzymes of Arg metabolism were shown to be the most promising tools for Arg assay. This review focuses on the peculiarities of electrochemical biosensors for Arg assay based on the use of Arg-degrading enzymes and on the analysis of their advantages as compared to other approaches.     

L-Arginine/nanofish bone nanocomplex enhances bone regeneration via antioxidant activities and osteoimmunomodulatory properties

In this study,a promising strategy has been developed to promote bone regeneration by combining antioxidant activities and osteoimmunomodulatory properties.Herein,an L-arginine/nanofish bone(Arg/NFB) nanocomplex has been prepared and evaluated in vitro and in vivo.The Arg/NFB nanocomplex possesses good antioxidant activities and could modulate the polarization of non-activated macrophage into different types and induce the secretion of pre-inflammato ry,anti-inflammatory,osteogenic as well as angiogenic cytokines.Additionally,the regulated immune microenvironment can enhance the osteogenic differentiation of mouse embryo osteoblast precursor cells(MC3 T3-E1) and angiogenic capacity of human umbilical vein endothelial cells(HUVECs),leading to the improved formation of mineralized nodules,alkaline phosphatase activity and angiogenic effects.In vivo results with cranial defect models reveal that the treatment of Arg/NFB nanocomplex exhibited significant improvement of new bone formation and angiogenesis.All the results demonstrate Arg/NFB nanocomplex with antioxidant activities and osteoimmunomodulatory properties could be a new idea for developing the next generation of bone regeneration biomaterials.     

Simultaneous determination of <Emphasis Type="SmallCaps">L</Emphasis>-arginine and its mono- and dimethylated metabolites in human plasma by high-performance liquid chromatography–mass spectrometry

A simple, fast, sensitive, and reproducible isocratic liquid chromatography–mass spectrometry (LC-MS) method coupled with an atmospheric pressure chemical ionization (APCI) interface for simultaneous separation and determination of L-arginine (ARG) and its methylated metabolites, N-monomethyl-L-arginine (MMA), N^G,N^G-dimethylarginine (asymmetric dimethyl arginine, ADMA), and N^G,N^G-dimethylarginine (symmetric dimethyl arginine, SDMA), in human plasma is presented. Sample pretreatment is not required other than deproteinization with 5-sulfosalicylic acid (5-SSA). Satisfactory chromatographic separation was achieved on a 2.0×150-mm Shimadzu VP-ODS column by using a mobile phase consisting of water/acetonitrile (90/10, v/v) containing 0.5% trifluoroacetic acid (TFA). Positive selective ion monitoring (SIM) mode was chosen for quantification of each analyte. The positively protonated molecular ions [M+H]⁺ of ARG, MMA, ADMA, and SDMA were monitored at m/z 175, 189, 203, and 203, respectively. L-Homoarginine was used as the internal standard (IS) for the assay. The limits of quantification (LOQs) were found to be 1.0 mol L^–1 for ARG, and 0.2 mol L^–1 for MMA, ADMA, and SDMA. The inter-assay precision and accuracy were in the range of 1.8–4.9% and –3.0–5.0%, respectively. The intra-assay precision and accuracy were in the order of 1.7–4.6 and –2.6–4.0%, respectively. The recoveries were between 90.0 and 106.6%. The levels of ARG, MMA, ADMA, and SDMA in human plasma were also determined using the developed method.     

Evanescent wave infrared chemical sensor possessing a sulfonated sensing phase for the selective detection of arginine in biological fluids

This paper describes a new infrared (IR) sensing scheme for the determination of arginine (Arg). In this method, the surface of an IR evanescent wave sensing element was modified with sulfonic acid groups to selectively interact with Arg through specific interactions with its guanidine moiety. The sulfonated sensing phase was prepared using a two-layer modification approach. To demonstrate that this assembly could be used for selective infrared sensing, a large number of amino acids were subjected to analysis. Although the sulfonate groups on the surface of the sensing element did interact selectively with the guanidine groups of Arg species, lysine and histidine units caused some interference; this problem could be minimized because of the unique IR absorption bands of the guanidine moiety of Arg. To optimize the detection conditions, we studied the effects of both the pH and the composition of the polymer. The most intense signal was obtained at pH 9. We observed different adsorption rates for the detection of Arg at different values of pH, which we attribute to changes in the accessibility of the analytes to the pore structures of the sensing phase. The composition of the base polymer was also optimized; 60% PVBC (w/w) provided a water-stable, sensitive phase for the detection of Arg in aqueous solution. Under the optimized conditions, we obtained a linear range of detection up to 0.1 mM with a detection limit of ca. 5 μM.     

原子吸收硫化锌法间接测定精氨酸络合反应的机理研究

通过编程计算精氨酸和锌离子在不同pH条件下的各种存在形式,通过分析拟合分布图,研究了在硫化锌法原子吸收间接测定精氨酸时的pH对原子吸收响应的影响及络合反应的机理.经对不同形态的精氨酸与金属锌离子的共存区域的各种组合探讨,指出在pH 9.0左右最佳测定条件下的pH响应峰是由于精氨酸和锌离子的两种不同存在形式的变化所引起的左右峰边缘,精氨酸是以正一价荷电形态的精氨酸基Arg -与Zn(OH)2形成了可溶性络合离子[HN=CH(NH 3)-NH-(CH2)3-CH(NH 3)-COO]2Zn(OH)2.结果表明,理论分析计算的结果与实验数据得到了基本吻合,确定了硫化锌法原子吸收间接测定精氨酸时的络合物反应机理及络合物的组成结构.