Guanidinium Group Research Articles

C-Diazeniumdiolate Graminine in the Siderophore Gramibactin Is Photoreactive and Originates from Arginine.

Siderophores are synthesized by microbes to facilitate iron acquisition required for growth. Catecholate, hydroxamate, and α-hydroxycarboxylate groups comprise well-established ligands coordinating Fe(III) in siderophores. Recently, a C-type diazeniumdiolate ligand in the newly identified amino acid graminine (Gra) was found in the siderophore gramibactin (Gbt) produced by Paraburkholderia graminis DSM 17151. The N-N bond in the diazeniumdiolate is a distinguishing feature of Gra, yet the origin and reactivity of this C-type diazeniumdiolate group has remained elusive until now. Here, we identify l-arginine as the direct precursor to l-Gra through the isotopic labeling of l-Arg, l-ornithine, and l-citrulline. Furthermore, these isotopic labeling studies establish that the N-N bond in Gra must be formed between the Nδ and Nω of the guanidinium group in l-Arg. We also show the diazeniumdiolate groups in apo-Gbt are photoreactive, with loss of nitric oxide (NO) and H+ from each d-Gra yielding E/Z oxime isomers in the photoproduct. With the loss of Gbt's ability to chelate Fe(III) upon exposure to UV light, our results hint at this siderophore playing a larger ecological role. Not only are NO and oximes important in plant biology for communication and defense, but so too are NO-releasing compounds and oximes attractive in medicinal applications.

How to Stabilize Carbenes in Enzyme Active Sites without Metal Ions.

Carbenes are highly reactive compounds with unique value to synthetic chemistry. However, a small number of natural enzymes have been shown to utilize carbene chemistry, and artificial enzymes engineered with directed evolution required transition metal ions to stabilize the carbene intermediates. To facilitate the design of broader classes of enzymes that can take advantage of the rich carbene chemistry, it is thus important to better understand how to stabilize carbene species in enzyme active sites without metal ions. Motivated by our recent studies of the anaerobic ergothioneine biosynthesis enzyme EanB, we examine carbene-protein interaction with both cluster models and QM/MM simulations. The cluster calculations find that an N-heterocyclic carbene interacts strongly with polar and positively charged protein motifs. In particular, the interaction between a guanidinium group and carbene is as strong as ∼30 kcal/mol, making arginine a great choice for the preferential stabilization of carbenes. We also compare the WT EanB and its mutant in which the key tyrosine was replaced by a non-natural analogue (F2Tyr) using DFTB3/MM simulations. The calculations suggest that the carbene intermediate in the F2Tyr mutant is more stable than that in the WT enzyme by ∼3.5 kcal/mol, due to active site rearrangements that enable a nearby arginine to better stabilize the carbene in the mutant. Overall, the current work lays the foundation for the pursuit of enzyme designs that can take advantage of the unique chemistry offered by carbenes without the requirement of metal ions.

Effect of Cationic Groups on the Selectivity of Ternary Antimicrobial Polymers

Back Cover: In article 2200377, Cyrille Boyer and co-workers show the antimicrobial polymers as a promising approach to combat multidrugresistant pathogens. A library of 31 amphiphilic ternary polymers containing different cationic groups, including primary amine, guanidine, and sulfonium groups, is prepared to investigate the impact of cationic groups on antimicrobial activity and cytotoxicity against mammalian cells.

Guanidine-Containing Antifungal Agents against Human-Relevant Fungal Pathogens (2004-2022)-A Review.

The guanidine moiety is typically a highly basic group, and can be found in a wide variety of drugs, such as zanamivir (Relenza) and metformin (Fortamet), as well as in biologically active compounds for numerous disease areas, including central nervous system (CNS) diseases and chemotherapeutics. This review will focus on antifungal agents which contain at least one guanidine group, for the treatment of human-related fungal pathogens, described in the literature between 2004 and 2022. These compounds include small molecules, steroids, polymers, metal complexes, sesquiterpenes, natural products, and polypeptides. It shall be made clear that a diverse range of guanidine-containing derivatives have been published in the literature and have antifungal activity, including efficacy in in vivo experiments.

Guanidyl-incorporated nanofiltration membranes toward superior Li+/Mg2+ selectivity under weakly alkaline environment

Positively charged nanofiltration membranes hold great potential in Li+/Mg2+ separation, but their application in alkaline solutions, such as alkaline salt-lake brines has not been reported. Herein, inspired by the arginine's unique structure and biological function, we explore superstrong basic triaminoguanidine (TG) molecule as aqueous monomer to fabricate positively charged polyamide nanofiltration membranes for Li+/Mg2+ separation. With the Li+/Mg2+ mass ratios of 1:50 and 1:120, at pH 9.6, the separation factors (SLi,Mg) of membranes reach 31.8 and 20.9. Meanwhile, at pH 5.6, the SLi,Mg are 46.4 and 36.4, which are the ever-reported highest value and such high SLi,Mg can be well retained in the pH range of 5.6–8.6. The superior Li+/Mg2+ selectivity stems from the superhigh protonation capacity of guanidine groups in a broad pH range.

COMPARATIVE STUDIES OF THE CHEMICAL INTERACTION OF GUANIDINE WITH DIALDEHYDE CELLU-LOSE AND PECTIN

The presence of reactive aldehyde groups in the elementary units of dialdehyde polysaccharides enables to enter easily into a condensation reaction with reagents containing primary amino groups in the structure. This naturally expands the possibilities of obtaining new derivatives of polysaccharides with physiologically active properties. In this study, we synthesized azomethine derivatives of cellulose and pectin differing in the degree of substitution and the content of the nucleophilic reagent in the composition of the reaction products through chemical interaction of guanidine with macromolecules of dialdehyde polysaccharides. Therefore, regularities of the reaction of nucleophilic substitution of aldehyde groups of oxidized polysaccharides with guanidine were revealed. It was found that the interaction of guanidine amino groups with oxidized pectin in contrast to dialdehyde cellulose occurs through the formation of azomethine and ionic bonds. Moreover, the possibility of obtaining guanidine-containing derivatives of cellulose and pectin with different structural characteristics by varying the molar ratio of the nucleophile and the oxidation state of the starting polysaccharides was proved. The composition and structure of the reaction products were studied by physicochemical methods of analysis. The stability and rate of cleavage of guanidine groups from the macromolecules of dialdehyde cellulose and dialdehyde pectin were studied by hydrolysis of the synthesized samples in acidic and alkaline media.

Role of the Guanidinium Groups in Ligand-Receptor Binding of Arginine-Containing Short Peptides to the Slow Sodium Channel: Quantitative Approach to Drug Design of Peptide Analgesics.

Several arginine-containing short peptides have been shown by the patch-clamp method to effectively modulate the NaV1.8 channel activation gating system, which makes them promising candidates for the role of a novel analgesic medicinal substance. As demonstrated by the organotypic tissue culture method, all active and inactive peptides studied do not trigger the downstream signaling cascades controlling neurite outgrowth and should not be expected to evoke adverse side effects on the tissue level upon their medicinal administration. The conformational analysis of Ac-RAR-NH2, Ac-RER-NH2, Ac-RAAR-NH2, Ac-REAR-NH2, Ac-RERR-NH2, Ac-REAAR-NH2, Ac-PRERRA-NH2, and Ac-PRARRA-NH2 has made it possible to find the structural parameter, the value of which is correlated with the target physiological effect of arginine-containing short peptides. The distances between the positively charged guanidinium groups of the arginine side chains involved in intermolecular ligand–receptor ion–ion bonds between the attacking peptide molecules and the NaV1.8 channel molecule should fall within a certain range, the lower threshold of which is estimated to be around 9 Å. The distance values have been calculated to be below 9 Å in the inactive peptide molecules, except for Ac-RER-NH2, and in the range of 9–12 Å in the active peptide molecules.

A Fukui Analysis of an Arginine-Modified Carbon Surface for the Electrochemical Sensing of Dopamine.

Amino acid-modified carbon interfaces have huge applications in developing electrochemical sensing applications. Earlier reports suggested that the amine group of amino acids acted as an oxidation center at the amino acid-modified electrode interface. It was interesting to locate the oxidation centers of amino acids in the presence of guanidine. In the present work, we modeled the arginine-modified carbon interface and utilized frontier molecular orbitals and analytical Fukui functions based on the first principle study computations to analyze arginine-modified CPE (AMCPE) at a molecular level. The frontier molecular orbital and analytical Fukui results suggest that the guanidine (oxidation) and carboxylic acid (reduction) groups of arginine act as additional electron transfer sites on the AMCPE surface. To support the theoretical observations, we prepared the arginine-modified CPE (AMCPE) for the cyclic voltammetric sensing of dopamine (DA). The AMCPE showed excellent performance in detecting DA in blood serum samples.

A guanidinium group is an effective mimic of the tertiary carbocation formed by isopentenyl diphosphate isomerase

Type I isopentenyl diphosphate isomerase is a metal-dependent enzyme that generates a tertiary carbocation intermediate during catalysis. This study describes an inhibitor (2-guanidinoethyl(dihydroxyphosphorylmethyl)phosphinate) of the isomerase that bears a guanidinium as a carbocation mimic and a phosphinylphosphonate as a non-hydrolyzable metal binding functionality. Inhibition kinetics show that the compound acts in a competitive manner with a Ki value of 129 nM (KM,IPP/Ki = 27). An analogous inhibitor bearing a tertiary ammonium as the carbocation mimic was 50-fold less potent, suggesting that the planar guanidinium is a more effective carbocation mimic. Inhibitors bearing an acylated methanesulfonamide or a hydroxamate group in place of the pyrophosphate inhibited the enzyme at millimolar concentrations indicating that the isomerase is highly specific for binding to the diphosphate portion of the intermediate.

Dielectric properties of chitosan and two ionic derivatives: Effect of counter anions

We report herein the dielectric properties response of two ionic chitosan derivatives. More specifically, we report here chitosan derivatives bearing guanidinium groups, prepared through the reaction between chitosan and cyanamide when scandium (III) triflate is present. The anionic counter ions of the guanidinium groups could be changed by working either in acetic acid or hydrochloric acid. In this way, two chitosan derivatives, namely N-guanidinium chitosan acetate (GChAc) and N-guanidinium chitosan chloride (GChCl), were produced. The materials were investigated by 13C solid state NMR, FT-IR spectroscopy, SEM and TEM analysis and compared with the parent chitosan. Dielectric spectroscopy has been used to study the relaxation behavior of the parent chitosan and the new chitosan derivatives over wide ranges of temperature and frequency, indicating that local motion is affected by counter ions. Due to these features, these materials are interesting candidates as high-power electrical materials for green technological applications.

Migration mechanism of microcystin-LR synergism with Cu2+ from algal cell to water environment using modified nano system

Effects on various macromolecules in algal cells occurred when heavy metals migrated to algal cells from the water environment. An innovative nanosystem was introduced to explore the synergistic process of MC-LR and Cu2+ in algal cells.In this method, the complex groups of Cu2+ and MC-LR were deeply analyzed by infrared spectroscopy, and the migration process and mechanism of MC-LR in cells were explored. The complexation of MC-LR with Cu2+ changed the exposure of hydrophobic and hydrophilic residues and affected their migration from intracellular to aqueous environment. Cu2+ mainly bound to =N-H in guanidine group of MC-LR, which changed the exposure of hydrophobic and hydrophilic residues of MC-LR and affected its migration from intracellular to water environment. In this paper, the effects of Cu2+ concentration and pH on the optimal coordination of MC-LR were studied. When the concentration of Cu2+ was 0.05 mm-2 mm, the complex of Cu2+ and MC-LR had synergistic amplification effect on the detection signal of the nanosystem, and the relative signal value reached the maximum when the pH value was 7. Part of the free copper ions complexed with MC-LR with changing conformation before migrating to the water environment.

Effect of Cationic Groups on the Selectivity of Ternary Antimicrobial Polymers.

Antimicrobial polymers (AMPs) have emerged as a promising approach to combat multidrug-resistant pathogens. Developed from binary polymers, which contain cationic and hydrophobic groups, ternary polymers are enhanced by adding neutral hydrophilic monomers to improve their biocompatibility. Cationic groups have attracted significant attention owing to their pivotal role in AMPs. Although many studies have investigated the effect of cationic groups on antimicrobial activity of binary AMPs, there is a lack of comprehensive and systematic evaluation for ternary AMPs. Therefore, a library of 31 statistical amphiphilic ternary polymers containing different cationic groups, including primary amine, guanidine, and sulfonium groups is prepared to investigate the impact of cationic groups on antimicrobial activity and biocompatibility. It is shown that the cationic balance appears to be a critical factor influencing polymers' antibacterial activity and selectivity. The results reveal that the polymers that have the ratio of the cationic groups ranging between 50% and 60%, coupled with a cationic/hydrophobic ratio in the range of [1.4-2] and an appropriate neutral hydrophilic/hydrophobic balance, exhibited the highest selectivity toward mammalian cells. This study elucidates a structure-property-performance relationship for ternary AMPs, which contributes to the development of AMPs capable of selectively targeting gram-negative pathogens.

A Series of New Pyrrole Alkaloids with ALR2 Inhibitory Activities from the Sponge Stylissa massa.

Twelve new and four known alkaloids including five different structural scaffolds were isolated from the sponge Stylissa massa collected in the South China Sea. Compound 1 is the first identified precursor metabolite of the classic 5/7/5 tricyclic skeleton with unesterified guanidine and carboxyl groups, compounds 2–5 and 13–15 belong to the spongiacidin-type pyrrole imidazole alkaloids (PIAs). Z- and E-configurations of the spongiacidin-type PIAs often appeared concomitantly and were distinguished by the chemical shift analysis of 13C NMR spectra. The structures of all twelve new compounds were determined by NMR, MS, and ECD analysis combined with single-crystal data of compounds 1, 5, and 10. In the aldose reductase (ALR2) inhibitory assay, six 5/7/5 tricyclic compounds (2–5, 13–15) displayed significant activities. Compounds 13 and 14, as the representative members of spongiacidin-PIAs, demonstrated their ALR2-targeted activities in SPR experiments with KD values of 12.5 and 6.9 µM, respectively.

Catechol-Based Polymers with High Efficacy in Cytosolic Protein Delivery

Catechol-Based Polymers with High Efficacy in Cytosolic Protein Delivery

Dibenzocyclooctendiones (DBCDOs): Arginine-Selective Chemical Labeling Reagents Obtained through Benzilic Acid Rearrangement.

We demonstrate that dibenzocyclooctendiones (DBCDOs) are efficient chemical reagents for the site-specific labeling of arginine-containing biomolecules. Unlike the commonly used probes, DBCDOs undergo an irreversible ring-contracted rearrangement with the guanidinium group on arginine residues under mild reaction conditions. The regioselective dual-labeled arginine residues were obtained in a one-pot reaction with our tested substrates. The efficiency of DBCDOs reactions and their ease of synthesis make DBCDOs an attractive choice for the site-selective bioconjugation of arginine.

CASTING: A Potent Supramolecular Strategy to Cytosolically Deliver STING Agonist for Cancer Immunotherapy and SARS-CoV-2 Vaccination

CASTING: A Potent Supramolecular Strategy to Cytosolically Deliver STING Agonist for Cancer Immunotherapy and SARS-CoV-2 Vaccination

Nafamostat is a Potent Human Diamine Oxidase Inhibitor Possibly Augmenting Hypersensitivity Reactions during Nafamostat Administration.

Nafamostat is an approved short-acting serine protease inhibitor. However, its administration is also associated with anaphylactic reactions. One mechanism to augment hypersensitivity reactions could be inhibition of diamine oxidase (DAO). The chemical structure of nafamostat is related to the potent DAO inhibitors pentamidine and diminazene. Therefore, we tested whether nafamostat is a human DAO inhibitor. Using different activity assays, nafamostat reversibly inhibited recombinant human DAO with an IC50 of 300-400 nM using 200 µM substrate concentrations. The Ki of nafamostat for the inhibition of putrescine and histamine deamination is 27 nM and 138 nM, respectively For both substrates, nafamostat is a mixed mode inhibitor with P values of <0.01 compared with other inhibition types. Using 80-90% EDTA plasma, the IC50 of nafamostat inhibition was approximately 360 nM using 20 µM cadaverine. In 90% EDTA plasma, the IC50 concentrations were 2-3 µM using 0.9 µM and 0.18 µM histamine as substrate. In silico modeling showed a high overlap compared with published diminazene crystallography data, with a preferred orientation of the guanidine group toward topaquinone. In conclusion, nafamostat is a potent human DAO inhibitor and might increase severity of anaphylactic reaction by interfering with DAO-mediated extracellular histamine degradation. SIGNIFICANCE STATEMENT: Treatment with the short-acting anticoagulant nafamostat during hemodialysis, leukocytapheresis, extracorporeal membrane oxygenator procedures, and disseminated intravascular coagulation is associated with severe anaphylaxis in humans. Histamine is a central mediator in anaphylaxis. Potent inhibition of the only extracellularly histamine-degrading enzyme diamine oxidase could augment anaphylaxis reactions during nafamostat treatment.

Removal of methyl orange and acid fuschin from aqueous solution by guanidinium functionalized cellulose prepared by radiation grafting

Dyeing wastewater released from dye-utilizing industries containing numerous hazardous dyes poses serious threat to environment and human beings, thus removal of dyes from wastewater is an important issue. In current work, guanidinium functionalized cellulose (GFC) was prepared by radiation emulsion grafting glycidyl methacrylate onto cellulose followed by further modification with guanidine hydrochloride. The radiation grafting and modification conditions were optimized. The GFC used for dyes removal was obtained with grafting yield of 238% at dose of 20 kGy and guanidinium group (%) of 16.49%. The adsorption behaviors towards methyl orange (MO) and acid fuschin (AF) were investigated. Adsorption kinetics was well described by pseudo-second-order kinetic mode. The adsorption isotherm was well fitted with Langmuir isotherm model. The adsorption capacity for MO and AF reached 63.25 mg/g and 120.4 mg/g, respectively. Therefore, the GFC exhibited excellent adsorption performance, which was applicable for MO and AF removal of water treatment.

Formation of versus Recruitment to RNA-Rich Condensates: Controlling Effects Exerted by Peptide Side Chain Identity.

Liquid-liquid phase separation (LLPS), the spontaneous formation of contiguous liquid phases with distinct compositions, has been long known in chemical systems and more recently recognized as a ubiquitous feature of cell biology. We describe a system involving biologically relevant components, synthetic peptides, and total yeast RNA, that has enabled us to explore factors that underlie phase separation. Coulombic complementarity between a cationic peptide and anionic RNA is necessary but not sufficient for formation of a condensed phase in our system. In addition to a net positive charge, the peptide must present the proper type of cationic moiety. Guanidinium groups, as found in the Arg side chain, support phase separation, but ammonium groups, as found in the Lys side chain, or dimethylguanidinium groups, as found in post-translationally modified Arg side chains, do not support phase separation in our system. However, the cationic groups that do not support phase separation via interaction with RNA can nevertheless enable recruitment to a condensed phase, which reveals that the network of forces governing condensed phase formation can differ from the network of forces governing recruitment to such a phase. We introduce a new method for measuring the concentrations of components in condensed phases based on fluorine-containing additives and 19F NMR.

Dependence of Antimicrobial Effects of Guanidine-containing Pectin Derivatives from Some Structural Characteristics

Introduction. Up to the present time, there are practically no studies on the relationship between the structural characteristics and biological activity of antimicrobial polymers synthesized by the chemical addition of guanidine groups to polysaccharide macromolecules. Therefore, there is a need to carry out the chemical modification of guanidine with natural polymers, in particular polyaldehyde pectin, and to conduct comparative studies of the antimicrobial activity of the obtained samples with different physicochemical characteristics. Aim. To conduct the synthesis of guanidine-containing pectin derivatives. In addition, to determine the influence of structural variations in the obtained samples on exhibiting antimicrobial properties. Materials and methods. The synthesis of guanidine-containing pectin derivatives consisted of the following stages: periodate oxidation of the polysaccharide, modification of guanidine using polyaldehyde pectin, and chemical reduction of azomethine bonds. The amount of guanidine in the obtained samples was calculated by acidimetric titration, the nitrogen content (N, %) was determined using a Eura EA (Italy) elemental analyzer. The рКα values of the synthesized compounds were found by the back titration method. Absorption spectra were analyzed on a "UV 1280" spectrophotometer (Shimadzu, Japan) in the range λ = 180–400 nm. IR spectra were recorded on a Vector-22 spectrometer in the wavelength range of 400–4000 cm -1 in KBr tablets (3 mg sample / 300 mg KBr). The molecular weight characteristics of the synthesized derivatives were determined by high-performance gel permeation chromatography on an Agilent 1260 Infiniti liquid chromatograph. The acute toxicity of guanidine-containing pectin derivatives was calculated by the Prozorovsky method. Comparative assessment of antimicrobial activity was conducted by agar diffusion method. Results and discussion. By varying the oxidation level of polyaldehyde pectin, synthesized compounds differ in the degree of substitution, guanidine content, molecular weight, and pKα value. It was found that the levels of the antibacterial and antifungal activity of the studied samples depend on the degree of substitution and the nature of the counterion. The antimicrobial effect increases with an increase in the quantitative content of guanidine groups in the macromolecular chain of pectin. Moreover, it was found that the change of low molecular weight Cl – , NO 3 – , F – , I – counterions by carboxylate anions leads to a sharp decrease in antimicrobial properties. Upon oral injection of the synthesized compounds to mice, it was found that all samples belong to the category of practically non-toxic substances (V-class). Conclusion. Comparative analysis of guanidine-containing pectin derivatives with different characteristics showed that the severity of the antimicrobial action of the synthesized compounds against bacteria and fungi of the genus Candida depends on the quantitative content of cationic groups and the nature of the counterion.