Presence Of Histidine Research Articles

Antioxidant efficacy of amino acids on vitamin A palmitate encapsulated in OSA-starch electrosprayed core-shell microcapsules

The encapsulation and the oxidative stability of vitamin retinyl palmitate (AP), a vitamin A derivative, within coaxial electrosprayed (AP) core – octenyl succinic anhydride (OSA-modified starch) shell microcapsules were investigated. The antioxidant efficiency of amino acids (AAs) (namely histidine, leucine, valine, tryptophan, tyrosine, cysteine and lysine) added to the core, on the oxidative stability of AP was evaluated using differential scanning calorimetry at the isothermal temperature of 140 °C. Confocal microscopy confirmed the location of the AP within the core with AAs microcapsules, surrounded by the shell layer of OSA starch. Scanning electron microscopy revealed that the microcapsules are uniform in size with an average diameter ranging from 2.06 ± 1.05 to 2.41 ± 1.42 μm. The AAs contributed substantially to enhance the oxidative stability of AP, with histidine being the most efficient with an improvement in oxidative stability of about 214 times, while lysine showed the lowest protection (about 3.9 times), compared to non-encapsulated AP. For the encapsulated AP, the presence of histidine or lysine enhanced the oxidative stability of the vitamin by about 70.6 or 1.3 times, respectively. The enhancement of the oxidative stability was mainly due to both the hydrophobic interactions formed between AP and AAs, and the adsorption of AP on the surface of AAs crystals (except lysine), assisted by the suspension of the AAs in ethanol antisolvent, as confirmed with attenuated total reflection–Fourier transform infrared (ATR–FTIR) and X-ray diffraction (XRD) analyses.

Trivalent Copper Ion-Mediated Dual Oxidation in the Copper-Catalyzed Fenton-Like System in the Presence of Histidine.

The Cu(II)/H2O2 system is recognized for its potential to degrade recalcitrant organic contaminants and inactivate microorganisms in wastewater. We investigated its unique dual oxidation strategy involving the selective oxidation of copper-complexing ligands and enhanced oxidation of nonchelated organic compounds. L-Histidine (His) and benzoic acid (BA) served as model compounds for basic biomolecular ligands and recalcitrant organic contaminants, respectively. In the presence of both His and BA, the Cu(II)/H2O2 system rapidly degraded His complexed with copper ions within 30 s; however, BA degraded gradually with a 2.3-fold efficiency compared with that in the absence of His. The primary oxidant responsible was the trivalent copper ion [Cu(III)], not hydroxyl radical (•OH), as evidenced by •OH scavenging, hydroxylated BA isomer comparison with UV/H2O2 (a •OH generating system), electron paramagnetic resonance, and colorimetric Cu(III) detection via periodate complexation. Cu(III) selectively oxidized His owing to its strong chelation with copper ions, even in the presence of excess tert-butyl alcohol. This selectivity extended to other copper-complexing ligands, including L-asparagine and L-aspartic acid. The presence of His facilitated H2O2-mediated Cu(II) reduction and increased Cu(III) production, thereby enhancing the degradation of BA and pharmaceuticals. Thus, the Cu(II)/H2O2 system is a promising option for dual-target oxidation in diverse applications.

A Water-Soluble Wavy Coordination Polymer of Cu(II) as a Turn-On Luminescent Probe for Histidine and Histidine-Rich Proteins/Peptides.

Histidine plays an essential role in most biological systems. Changes in the homeostasis of histidine and histidine-rich proteins are connected to several diseases. Herein, we report a water-soluble Cu(II) coordination polymer, labeled CuCP, for the fluorimetric detection of histidine and histidine-rich proteins and peptides. Single-crystal structure determination of CuCP revealed a two-dimensional wavy network structure in which a carboxylate group connects the individual Cu(II) dimer unit in a syn-anti conformation. The weakly luminescent and water-soluble CuCP shows turn-on blue emission in the presence of histidine and histidine-rich peptides and proteins. The polymer can also stain histidine-rich proteins via gel electrophoresis. The limits of quantifications for histidine, glycine-histidine, serine-histidine, human serum albumin (HSA), bovine serum albumin, pepsin, trypsin, and lysozyme were found to be 300, 160, 600, 300, 600, 800, 120, and 290 nM, respectively. Utilizing the fluorescence turn-on property of CuCP, we measured HSA quantitatively in the urine samples. We also validated the present urinary HSA measurement assay with existing analytical techniques. Job's plot, 1H NMR, high-resolution mass spectrometry (HRMS), electron paramagnetic resonance (EPR), fluorescence, and UV-vis studies confirmed the ligand displacement from CuCP in the presence of histidine.

Multifunctional carbon nanotube hydrogels with on-demand removability for wearable electronics

Wearable electronics that can convert various external stimuli into electrical signals hold great potential for diverse applications. Efforts in this area are focused on developing functional hydrogels to improve the values of these flexible electronics. Herein, we present a novel carbon nanotube (CNT)-based hydrogel with the synergistic features of good mechanical strength, high sensitivity, self-healing capability, and on-demand removability for wearable electronics. The hydrogel was fabricated by mixing dopamine-modified oxidized hyaluronic acid (OHA-DA), cyanoacetate group-functionalized dextran (DEX-CA), and carbon nanotubes (CNTs) in the presence of histidine. The catechol and aldehyde groups on OHA-DA impart the hydrogel with high tissue adhesiveness. Owing to the existence of CNTs, the hydrogel exhibited outstanding conductivity and could respond to different human motions and convert these stimuli as resistance signals. Notably, because of the photothermal conversion property of CNTs and thermally reversible performance of the generated C=C double bonds between aldehyde groups and cyanoacetate groups, the hydrogel was imparted with intriguing on-demand dissolution ability under near-infrared (NIR) irradiation and could be facilely removed from tissues whenever necessary. We believe that such hydrogel will open up new opportunities for the design and construction of next-generation wearable electronics.

Ionothermal synthesis of magnetic N-doped porous carbon to immobilize Pd nanoparticles as an efficient nanocatalyst for the reduction of nitroaromatic compounds

Carbon materials play important roles as catalysts or catalyst supports for reduction reactions owing to their high porosity, large specific surface area, great electron conductivity, and excellent chemical stability. In this paper, a mesoporous N-doped carbon substrate (exhibited as N–C) has been synthesized by ionothermal carbonization of glucose in the presence of histidine. The N–C substrate was modified by Fe3O4 nanoparticles (N–C/Fe3O4), and then Pd nanoparticles were stabilized on the magnetic substrate to synthesize an eco-friendly Pd catalyst with high efficiency, magnetic, reusability, recoverability, and great stability. To characterize the Pd/Fe3O4–N–C nanocatalyst, different microscopic and spectroscopic methods such as FT-IR, XRD, SEM/EDX, and TEM were applied. Moreover, Pd/Fe3O4–N–C showed high catalytic activity in reducing nitroaromatic compounds in water at ambient temperatures when NaBH4 was used as a reducing agent. The provided nanocatalyst's great catalytic durability and power can be attributed to the synergetic interaction among well-dispersed Pd nanoparticles and N-doped carbonaceous support.

Colorimetric Sensor Based on the Oxidase-Mimic Supramolecular Catalyst for Selective and Sensitive Biomolecular Detection.

We have engineered a colorimetric sensor capable of selective and sensitive detection of amino acids. This sensor employs a supramolecular copper-dependent oxidase mimic as the probe, stemming from our prior research. The oxidase mimic is constructed through the self-assembly of commercially available guanosine monophosphate (GMP), Fmoc-lysine, and Cu2+. It catalyzes the formation of a red product with a maximum absorbance at 510 nm. The changes in color and absorbance are responsive to both the concentrations and types of amino acids present. This effect is most pronounced in the presence of histidine, with a detection limit (LOD) of 6.4 nM. Furthermore, the catalytic probe can distinguish histidine from histamine and imidazole propionate, as well as 1-methyl-histidine from 3-methyl-histidine, based on their distinct coordination capacities with copper. This underscores the high selectivity of the sensing platform. Both theoretical simulations and experimental results (including UV-vis spectra, fluorescence, and EPR) indicate that the amino acids may engage in copper center coordination, thereby impeding O2 access to copper─a pivotal aspect of the oxidase catalysis. This sensing platform, characteristic of its swift response, simple fabrication, and exceptional sensitivity and selectivity, can also be applied to detect other biological analytes such as nucleotides. It holds potential for use in environmental and biochemical analyses.

Nickel-assisted selective detection of histidine and histidine-rich proteins via an ON-OFF-ON fluorescent probe and its imaging in live cells

Amino acids and proteins are ubiquitous in all biological processes. Therefore, fluctuations in their levels profoundly impact the general well-being of any human being. Structural similarities between amino acids hamper their direct detection by fluorophores. Thus, it becomes crucial to employ an ancillary approach to accomplish this goal. In this work, the selective fluorescence response of Ni2+ towards a probe PyPP was used as a precursor for selective histidine sensing. The probe showed selectivity towards Ni2+ by fluorescence quenching, and it could be revived only in the presence of histidine. The limit of detection (LOD) for Ni2+ was 4 x10-6 M, whereas LOD for histidine was 1.08 × 10−6 M. The Ni2+ mediated selectivity could also be extended to histidine-rich proteins bovine serum albumin (BSA) and human serum albumin (HSA). The devised system was also applied to a macrophage cell line (RAW 264.7) to indicate the presence of Ni2+/histidine/HSA-BSA via confocal fluorescence microscopy, and quantitative response could be studied with flow cytometry.

Role of Alginate Composition on Copper Ion Uptake in the Presence of Histidine or Beta-Amyloid

The anomalous interaction between metal ions and the peptide beta-amyloid is one of the hallmarks of Alzheimer's disease. Metal-binding biopolymers, including polysaccharides, can elucidate the fundamental aspects of metal ions' interactions with biological tissue and their interplay in Alzheimer's disease. This work focuses on the role of the alginate composition on Cu(II) adsorption in the presence of histidine or β-amyloid, the peptide associated with the progression of Alzheimer's disease. Alginate samples with different mannuronic/guluronic (M/G) ratios led to similar Cu(II) adsorption capacities, following the Langmuir isotherm and the pseudo-second-order adsorption kinetic models. Although the presence of histidine produced up to a 20% reduction in the copper adsorption capacity in guluronic-rich alginate samples (M/G~0.61), they presented stable bidentate chelation of the metallic ion. Chemical analyses (FTIR and XPS) demonstrated the role of hydroxyl and carboxyl groups in copper ion chelation, whereas both crystallinity and morphology analyses indicated the prevalence of histidine interaction with guluronic-rich alginate. Similar results were observed for Cu(II) adsorption in alginate beads in the presence of beta-amyloid and histidine, suggesting that the alginate/histidine system is a simple yet representative model to probe the application of biopolymers to metal ion uptake in the presence of biological competitors.

Synthesis of amino acids by electrocatalytic reduction of CO2 on chiral Cu surfaces

<h2>Summary</h2> CO₂ reduction and fixation products, ranging from small molecules to biomolecules, are highly diverse in natural systems. Although various multicarbon products of CO₂ reduction were artificially obtained, the C₃₊ products with various functional groups (e.g., C–N and C–O bonds), especially biomolecules, have never been reported. Herein, we synthesized C₃₊ amino acids via electrocatalytic synthesis from CO₂ and NH₃, using chiral Cu films (CCFs) as electrodes. Electron microscopy and theoretical calculations suggested that chiral kink sites can possibly be formed on the surface of CCFs fabricated through electrodeposition in the presence of histidine (His). Serine (Ser), with an enantiomeric excess (ee) greater than 90%, is the main component of various amino acids. Experimental and computational data showed that the 3-hydropyruvic acid formation from H₂CO–CO∗ is the stereo-determining step in the Ser formation pathway. The chiral kink sites were speculated to be restricting the configuration changes of C₃₊ intermediates to involve a thermodynamically and kinetically favorable formation of enantiomeric Ser.

Extensive Characterization of Polysorbate 80 Oxidative Degradation Under Stainless Steel Conditions

Polysorbate-80 (PS-80) is a common surfactant used in biologics formulations. However, the tendency of oxidation to PS-80 when exposed to stainless steel surfaces brings various challenges during manufacturing processes, such as inconsistent shelf-life of PS-80 solutions, which can further impact the biologics and vaccines production. In this work, the root causes of PS-80 oxidation when in contact with stainless steel conditions were thoroughly investigated through the use of various complementary analytical techniques including U/HPLC-CAD, LC-MS, ICP-MS, peroxide assay, and EPR spectroscopy. The analytical tool kit used in this work successfully revealed a PS-80 degradation mechanism from the perspective of PS-80 content, PS-80 profile, iron content, peroxide production, and radical species. The combined datasets reveal that PS-80 oxidative degradation occurs in the presence of histidine and iron in addition to being combined with the hydroperoxides in PS-80 material. The oxidative pathway and potential degradants were identified by LC-MS. The PS-80 profile based on the U/HPLC-CAD assay provided an effective way to identify early-signs of PS-80 degradation. The results from a peroxide assay observed increased hydroperoxide along with PS-80 degradation. EPR spectra confirmed the presence of histidine-related radicals during PS-80 oxidation identifying how histidine is involved in the oxidation. All assays and findings introduced in this work will provide insight into how PS-80 oxidative degradation can be avoided, controlled, or detected. It will also provide valuable evaluations on techniques that can be used to identify PS-80 degradation related events that occur during the manufacturing process.

Understanding the Stabilizing Effect of Histidine on mAb Aggregation: A Molecular Dynamics Study.

Histidine, a widely used buffer in monoclonal antibody (mAb) formulations, is known to reduce antibody aggregation. While experimental studies suggest a nonelectrostatic, nonstructural (relating to secondary structure preservation) origin of the phenomenon, the underlying microscopic mechanism behind the histidine action is still unknown. Understanding this mechanism will help evaluate and predict the stabilizing effect of this buffer under different experimental conditions and for different mAbs. We have used all-atom molecular dynamics simulations and contact-based free energy calculations to investigate molecular-level interactions between the histidine buffer and mAbs, which lead to the observed stability of therapeutic formulations in the presence of histidine. We reformulate the Spatial Aggregation Propensity index by including the buffer–protein interactions. The buffer adsorption on the protein surface leads to lower exposure of the hydrophobic regions to water. Our analysis indicates that the mechanism behind the stabilizing action of histidine is connected to the shielding of the solvent-exposed hydrophobic regions on the protein surface by the buffer molecules.

Viability of Glioblastoma Cells and Fibroblasts in the Presence of Imidazole-Containing Compounds.

The naturally occurring dipeptide carnosine (β-alanyl-L-histidine) specifically attenuates tumor growth. Here, we ask whether other small imidazole-containing compounds also affect the viability of tumor cells without affecting non-malignant cells and whether the formation of histamine is involved. Patient-derived fibroblasts and glioblastoma cells were treated with carnosine, L-alanyl-L-histidine (LA-LH), β-alanyl-L-alanine, L-histidine, histamine, imidazole, β-alanine, and L-alanine. Cell viability was assessed by cell-based assays and microscopy. The intracellular release of L-histidine and formation of histamine was investigated by high-performance liquid chromatography coupled to mass spectrometry. Carnosine and LA-LH inhibited tumor cell growth with minor effects on fibroblasts, and L-histidine, histamine, and imidazole affected viability in both cell types. Compounds without the imidazole moiety did not diminish viability. In the presence of LA-LH but not in the presence of carnosine, a significant rise in intracellular amounts of histidine was detected in all cells. The formation of histamine was not detectable in the presence of carnosine, LA-LH, or histidine. In conclusion, the imidazole moiety of carnosine contributes to its anti-neoplastic effect, which is also seen in the presence of histidine and LA-LH. Despite the fact that histamine has a strong effect on cell viability, the formation of histamine is not responsible for the effects on the cell viability of carnosine, LA-LH, and histidine.

Selective detection of manganese(II) ions based on the fluorescence turn-on response via histidine functionalized carbon quantum dots

Herein, water-soluble emissive carbon quantum dots (His-CQDs) were synthesized from pyrolysis of sodium citrate in the presence of histidine under hydrothermal conditions. The as-synthesized His-CQDs were characterized using Fourier transform infrared (FT–IR), fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques. The obtained His-CQDs display a strong emission peak at 534 nm when excited at 476 nm with a high quantum yield (61.8 %). The as-synthesized His-CQDs were applied as a new platform for highly selective determination of Mn(II) based on the fluorescence “turn-on” response with a limit of detection of 1.85 µg L−1 (at 3σ) and a linear range of 3.50–35.5 µg L−1 in aqueous solution. The sensing mechanism of the His-CQDs probe for the detection of Mn(II) was studied via density functional theory (DFT), FT-IR, and EDTA complexation methodology. In addition, His-CQDs were successfully applied to determine the accurate amounts of Mn(II) in whole blood control material. More importantly, the integrating such an efficient sensor with point-of-care technology can enable portable, easy-to-use, and rapid sensing systems for better biological and clinical applications.

Histidine is essential for growth of Komagataella phaffii cultured in YPA medium.

Komagataella phaffii (a.k.a. Pichia pastoris) requires histidine for optimal growth when cultured in a medium containing yeast extract, peptone (YP), and acetate (YPA). We demonstrate that HIS4‐deficient, K. phaffii strain GS115 exhibits a growth defect on YP‐media containing acetate, but not on other carbon sources. K. phaffii X33, a prototroph, grows better than K. phaffii GS115 (his4), a histidine auxotroph in YPA. Normal growth of GS115 is restored either by the expression of HIS4 or by culturing in YPA containing ≥0.6 mM histidine. In the presence of histidine, expression of several genes is altered, including those encoding key subunits of mitochondrial ATP synthase, transporters of amino acids and nutrients, as well as biosynthetic enzymes. Thus, histidine should be included as an essential component for optimal growth of K. phaffii histidine auxotrophs cultured in YPA.

Chemically Influenced Self-Preservation Kinetics of CH4 Hydrates below the Sub-Zero Temperature

The self-preservation property of CH4 hydrates is beneficial for the transportation and storage of natural gas in the form of gas hydrates. Few studies have been conducted on the effects of chemicals (kinetic and thermodynamic promoters) on the self-preservation properties of CH4 hydrates, and most of the available literature is limited to pure water. The novelty of this work is that we have studied and compared the kinetics of CH4 hydrate formation in the presence of amino acids (hydrophobic and hydrophilic) when the temperature dropped below 0 °C. Furthermore, we also investigated the self-preservation of CH4 hydrate in the presence of amino acids. The main results are: (1) At T &lt; 0 ℃, the formation kinetics and the total gas uptake improved in the presence of histidine (hydrophilic) at concentrations greater than 3000 ppm, but no significant change was observed for methionine (hydrophobic), confirming the improvement in the formation kinetics (for hydrophilic amino acids) due to increased subcooling; (2) At T = −2 °C, the presence of amino acids improved the metastability of CH4 hydrate. Increasing the concentration from 3000 to 20,000 ppm enhanced the metastability of CH4 hydrate; (3) Metastability was stronger in the presence of methionine compared to histidine; (4) This study provides experimental evidence for the use of amino acids as CH4 hydrate stabilizers for the storage and transportation of natural gas due to faster formation kinetics, no foam during dissociation, and stronger self-preservation.

Amino acid-functionalized chitosan beads for in vitro copper ions uptake in the presence of histidine

One of the hallmarks of Alzheimer's Disease (AD) is the anomalous binding involving amyloid-β (Aβ) peptide and metal ions, such as copper, formed through histidine (His) residues. Herein, adsorption experiments were performed to test the in vitro ability of chitosan to uptake copper ions in the presence of histidine. The characterization of the beads was assessed before and after the adsorption process by scanning electron microscope, X-ray diffraction and Fourier-transform infrared spectroscopy. Amino acid functionalization of chitosan-based beads promoted an increase in the copper ions adsorption capacity (2.47 mmol of Cu(II)/gram of adsorbent). Nevertheless, depending on the order of addition of histidine to the system, different adsorption behaviors were observed. The kinetics showed that, once the Cu(II)-His bond was established, functionalized beads were less efficient to capture Cu(II), which promoted a decrease in the overall adsorption capacity. However, when chitosan and histidine were simultaneously added to the Cu(II) solution, there was no decrease in adsorption capacity. To sum up, chitosan-based materials are an interesting model to provide a better understanding on the biomolecules‑copper interactions that occur in AD, as well as a possible chelating agent that can interfere in the bonds between Aβ residues and copper ions.

A systematic study of halide-template effects in the assembly of lanthanide hydroxide cluster complexes with histidine

Controlled hydrolysis of lanthanide ions in the presence of histidine and halide templates of different sizes produced dodeca- and pentadecanuclear lanthanide hydroxide clusters.

Development of an LC-MS Method for the Identification of β-Casein Genetic Variants in Bovine Milk

Bovine β-casein is a highly polymorphic protein, with A1 and A2 representing the most frequent variants identified in Western cattle breeds. Depending on the presence of histidine or proline at position 67 of the sequence, β-casein variants can be grouped in two families: those within the A1 family (A1-like), possessing histidine, and those within the A2 family (A2-like), with proline. Upon gastrointestinal digestion, specific peptides endowed with opioid-like activity, called β-casomorphins, may be released from β-casein. Interestingly, the presence of histidine at position 67 seems to favor the release of a peptide called β–casomorphin-7, which has been proposed as a risk factor for the development of some non-communicable diseases. Based on these assumptions, the A2 milk market (i.e., a milk containing only A2 β-casein) is spreading worldwide. In the scientific community, however, the impact of A1 β-casein on human health remains a matter of debate. Aim of the present study was to develop an analytical method based on mass spectrometry to distinguish between bovine A2 milk and commercial milk, typically composed of a mixture of A1-like and A2-like β-casein. By enzymatically hydrolyzing β-casein, a specific peptide containing the critical mutation at position 67 has been identified. This peptide constituted a suitable marker to determine the presence of A1-like and/or A2-like β-casein in bovine milk. The developed method proved appropriate for the detection of β-casein in real milk samples; we estimated that contaminations of A2 milk with up to 1% commercial milk could be successfully detected.

The molecular mechanism of the photocatalytic oxidation reactions by horseradish peroxidase in the presence of histidine

Horseradish peroxidase initiates photocatalytic oxidation reactions in the presence of histidine without H2O2.

Ruthenium coordination preferences in imidazole-containing systems revealed by electrospray ionization mass spectrometry and molecular modeling: Possible cues for the surprising stability of the Ru (III)/tris (hydroxymethyl)-aminomethane/imidazole complexes.

Ruthenium is a platinoid that exhibits a range of unique chemical properties in solution, which are exploited in a variety of applications, including luminescent probes, anticancer therapies, and artificial photosynthesis. This paper focuses on a recently demonstrated ability of this metal in its +3 oxidation state to form highly stable complexes with tris (hydroxymethyl)aminomethane (H2 NC(CH2 OH)3 , Tris-base or T) and imidazole (Im) ligands, where a single RuIII cation is coordinated by two molecules of each T and Im. High-resolution electrospray ionization mass spectrometry (ESI MS) is used to characterize RuIII complexes formed by placing a RuII complex [(NH3 )5 RuII Cl]Cl in a Tris buffer under aerobic conditions. The most abundant ionic species in ESI MS represent mononuclear complexes containing an oxidized form of the metal, ie, [Xn RuIII T2 - 2H]+ , where X could be an additional T (n = 1) or NH3 (n = 0-2). Di- and tri-metal complexes also give rise to a series of abundant ions, with the highest mass ion representing a metal complex with an empirical formula Ru3 C24 O21 N6 H66 (interpreted as cyclo(T2 RuO)3 , a cyclic oxo-bridged structure, where the coordination sphere of each metal is completed by two T ligands). The empirical formulae of the binuclear species are consistent with the structures representing acyclic fragments of cyclo(T2 RuO)3 with addition of various combinations of ammonia and dioxygen as ligands. Addition of histidine in large molar excess to this solution results in complete disassembly of poly-nuclear complexes and gives rise to a variety of ionic species in the ESI mass spectrum with a general formula [RuIII Hisk Tm (NH3 )n - 2H]+ , where k = 0 to 2, m = 0 to 3, and n = 0 to 4. Ammonia adducts are present for all observed combinations of k and m, except k = m = 2, suggesting that [His2 RuIII T2 - 2H]+ represents a complex with a fully completed coordination sphere. The observed cornucopia of RuIII complexes formed in the presence of histidine is in stark contrast to the previously reported selective reactivity of imidazole, which interacts with the metal by preserving the RuT2 core and giving rise to a single abundant ruthenium complex (represented by [Im2 RuIII T2 - 2H]+ in ESI mass spectra). Surprisingly, the behavior of a hexa-histidine peptide (HHHHHH) is similar to that of a single imidazole, rather than a single histidine amino acid: The RuT2 core is preserved, with the following ionic species observed in ESI mass spectra: [HHHHHH·(RuIII T2 )m - (3m-1)H]+ (m = 1-3). The remarkable selectivity of the imidazole interaction with the RuIII T2 core is rationalized using energetic considerations at the quantum mechanical level of theory.