Carboxylic Function Research Articles

Enantioselective complexation of protonated tyrosine by a chiral crown-ether: the nature of the Hydrogen bonds makes the difference.

The complexes formed between (18-crown-6)-tetracarboxylic acid, denoted as 18C6TA, and the two enantiomers of protonated tyrosine, L- and D-Tyr, are studied in a cryogenic ion trap by combining mass spectrometry, laser spectroscopy, and DFT calculations. Both UV and IR photodissociation spectra indicate the formation of multiple isomers for each complex, some of them interconverting upon IR irradiation. Conformer-selective vibrational spectroscopy reveals that all structures involve an internally hydrogen-bonded folded structure of the crown ether. The complexes formed with L-Tyr involve two NH…O interactions with the ether oxygen atoms,and two hydrogen bonds to the crown ether carboxylic function, one from the NH group and the other from the COOH group of tyrosine. TheD-Tyr complexesshow more conformational mobility: two out of the three lowest energy conformers observed are tripodal, with three NH…O interactions between the amino acid ammonium and the crown ether oxygens. An additional conformer shows only one NH…O interaction, but has two interactions involving one of the cavity COOH moieties, one with the NH and one with the phenol OH. The increased calculated stability of the complex made from (-) 18C6TA and L-Tyr parallels its higher abundance in the mass spectrum of an isotopically labelled racemic mixture.

Cobalt(II) and Manganese(II) Complexes of Sodium Monensinate a Bearing Nitrate Co-Ligands

Monensic acid is a natural polyether ionophore and is a therapeutic of first choice in veterinary medicine for the control of coccidiosis. Although known as a sodium-binding ligand, it can also form a variety of coordination species depending on experimental conditions applied. In this study, we present the crystal structures and properties of Co(II) and Mn(II) complexes of sodium monensinate (MonNa) derived from the reaction of MonNa with cobalt or manganese dinitrates. The newly obtained coordination compounds have the same composition [M(MonNa)2(NO3)2] but the transition metal ions are placed in a different environment. The two nitrate ligands behave mono- or bidentately bound in the Co(II)- and Mn(II)-containing species, respectively, while the monensinate ligands act in a similar manner through their monodentate carboxylate functions. The formed CoO4 and MnO6 units determine the geometry of the corresponding inner coordination cores of the complexes as a tetrahedron in the case of Co(II), and as a strongly distorted octahedral structure in Mn(II) species. The effect of inorganic anions on the antibacterial performance of sodium monensinate appears to be negligible, while the presence of Co(II) or Mn(II) cations preserves or enhances the activity of unmodified MonNa, which differentially affects the growth of Bacillus subtilis, Bacillus cereus, Kocuria rhizophila, Staphilococcus aureus, and Staphilococcus saprophyticus strains.

Mechanism-based inactivators of sirtuin 5: A focused structure–activity relationship study

Sirtuin 5 (SIRT5) is a lysine deacylase enzyme that cleaves negatively charged ε-N-acyllysine posttranslational modifications, arising from short dicarboxylic acids. Inhibition of SIRT5 has been as a target for treatment of leukemia and breast cancer. In this work, we performed a focused structure–activity relationship study that identified highly potent inhibitors of SIRT5. Examples of these inhibitors were shown by kinetic evaluation to function as mechanism-based inactivators. Masking of a crucial carboxylate functionality in the inhibitors provided prodrugs, which were demonstrated to bind SIRT5 in cells. This work underscores the importance of kinetic characterization of enzyme inhibitors and provides insights for the further optimization of inhibitors of SIRT5 with potential for in vivo applications

Iron as a precursor of aggregation and vector of organic carbon to sediments in a boreal lake

AbstractWhile organic matter (OM) interactions in the water column prevent iron (Fe) precipitation and sedimentation, Fe also acts as a precursor of aggregation and a vector of OM to sediments. This study aims to characterize Fe–OM interactions to understand the role of Fe in promoting aggregation and transport of OM. Samples of Fe and OM were collected from water, settling material, and sediment along a gradient starting from the inlet and continuing offshore within a boreal lake. Fe speciation was determined using X-ray absorption spectroscopy (XAS), and the chemical composition of OM was assessed using Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT IR) and Nuclear magnetic resonance spectroscopy (NMR). The results show a decrease in Fe and OM concentrations in the water column with increasing distance from the inlet. Winter sampling revealed a shift in Fe speciation from dominance of organically complexed Fe to an increase in Fe(oxy)hydroxide, accompanied by a loss of aromatic and carboxylate function of OM. Summer sampling revealed no significant changes along the gradient, with Fe(oxy)hydroxide and carbohydrates dominating the water phase. Interestingly, settling particles and surface sediments were dominated by Fe(oxy)hydroxides and aliphatic OM. We propose that phototransformation may be an important process that influences the interaction between Fe and OM and, as a consequence, their fate along the spatial gradient. Our study suggests a photochemically induced loss of carboxylate groups, reflected by an increased carbohydrate-to-carboxylate ratio along the gradient, particularly in winter, and generally lower levels during summer. Loss of carboxylate function promotes the formation of Fe(oxy)hydroxides, which in turn, facilitates the aggregation and sinking of OM, particularly aliphatic components. These insights contribute to a broader understanding of carbon cycling and storage in lakes. Future studies should assess the significance of photochemical processes to OM burial and it how may change given trends in Fe and OM in northern regions.

Manganese nanoparticles catalyzed the formation of mesoporous helical nitrogen-doped carbon nanotubes enabled aldosterone biosensing

Primary aldosteronism (PA) is the foremost form of secondary hypertension that affects 5–20 % of healthy humans via the excessive secretion of aldosterone (ALD), which increases the level of potassium excretion and thus produces various critical combined diseases. Thus, determining trace-level ALD content in human blood or urine samples is a crucial factor in diagnosing a life-threatening disease called PA. Herein, nanosized manganese particles encapsulated within the tunable helical-shaped N-doped mesoporous carbon nanotubes (Mnx@H-NCNTs) are synthesized by a simple and facile ball-milling method at different reaction times (1, 6, 12, and 18 h). The influence of ball-milling process time on the final morphology of the as-synthesized Mnx@H-NCNTs nanostructures is systematically investigated. In order to fabricate an ALD biosensor electrode, the immobilization of Anti-ALD antibodies (Anti-ALD) on the surface of the Mn@H-NCNTs-12H electrode (Anti-ALD/Mn@H-NCNTs-12H) is achieved via the interactions of combined interactions of hydrogen bonds, Van der Waals’ force, negatively charged carboxylic acid functionalities of antibodies and positively charged metal centers, and π-π stacking interaction between nucleosides of Anti-ALD and mesoporous H-NCNTs. In addition, BSA was used as a blocking additive for covering non-specific adsorption sites of Anti-ALD/Mnx@H-NCNTs (BSA/Anti-ALD/Mn@H-NCNTs-12H) nanostructured electrodes. The BSA/Anti-ALD/Mn@H-NCNTs-12H can be used as an effective signal amplifying probe for ALD detection through a noticeable reduction in the amperometric i-t current response over a linear range from 1 to 2500 pM, with a LOD of 0.72 pM (S/N = 3). The practical applicability of BSA/Anti-ALD/Mn@H-NCNTs-12H is further demonstrated by the detection of ALD from 1 to 20 nM in human blood or urine samples with a recovery ranging from 90.5 to 97.0 %, indicating its potential use in clinical analysis.

Synthesis of (-)-Monanchoradin A and (-)-Crambescin A2 392 Based on a Cyclization-Carbonylation-Cyclization Cascade.

Syntheses of guanidino alkaloids (-)-monanchoradin A and (-)-crambescin A2 392 are described. The key feature of the syntheses is the cyclization-carbonylation-cyclization cascade of the optically active propargyl guanidine. The bicyclic guanidino cores bearing an asymmetric center and ester or carboxylic acid functionality were constructed in a single step. The carboxylic acid was then converted to (-)-monanchoradin A and (-)-crambescin A2 392.

Facile photometric quantification of aldehyde content in oxidized starches using 2-aminobenzamide oxime as an aldehyde selective reagent

AbstractThe oxidation of starch to aldehyde starch or dialdehyde starch introduces aldehyde groups to the starch core structure. This functionalization enables a wide range of further derivatization, e.g., oxidation to the corresponding carboxylic acid or functionalization to the corresponding amine via imine formation and reduction, which can be used for cross-linking. Herein, we report a novel method for efficiently quantifying these aldehyde groups based on the selective adduct formation of 2-aminobenzamide oxime (ABAO) and aldehydes. We initially implemented this photometric assay for C6-oxidized aldehyde starch using a plate reader, enabling parallel analysis of multiple samples in a fraction of the time and consistent with the conventional titration methods. Complementing this stream-lined analytical approach, we present an abbreviated workflow for faster downstream processing of reaction samples toward analysis. All of this was performed at a very small scale, cutting costs for (expensive) reagents and solvents, as well as drastically reducing working time. Finally, we also demonstrate our assay's applicability for quantifying the two aldehyde groups formed in dialdehyde starch derived from NaIO4 oxidation. Graphical abstract

Leveraging the Potential of Iqbal MCR: An Efficient Synthetic Route to Structurally Complex Tripeptidyl Ketones via Sequential Iqbal‐3CR/Ugi‐4CR

AbstractHighlighting the potential of Iqbal multicomponent reaction (MCR), a streamlined two‐step MCR synthetic strategy is proposed for the rapid assembly of structurally complex tripeptidyl ketones, which are valuable building blocks for developing novel peptidomimetics. The approach utilizes consecutive Iqbal MCR and Ugi MCR under mild room temperature conditions, eliminating the need for laborious column chromatography purification. This work demonstrates Iqbal MCR's propensity to generate a diverse library of N‐(3‐oxopropyl) carboxamides containing carboxyl functionality, which can be readily elaborated further to tripeptidyl ketones through subsequent Ugi MCR.

Biological characteristics of marine Streptomyces SK3 and optimization of cultivation conditions for production of compounds against Vibiriosis pathogen isolated from cultured white shrimp (Litopenaeus vannamei).

Antibiotic resistance in shrimp farms has emerged as an extremely serious situation worldwide. The main aim of this study was to optimize the cultural conditions for producing new antibiotic agents from marine Streptomyces species. Streptomyces SK3 was isolated from marine sediment and was identified by its 16S rDNA as well as biochemical characteristics. This microbe produced the highest concentration of bioactive secondary metabolites (BSMs) when cultured in YM medium (YM/2). It produced the maximum total protein (41.8 ± 6.36 mg/ml) during the late lag phase period. The optimum incubation temperature was recorded at 30 °C; BSMs were not produced at ≤10 °C within an incubation period of 3-4 days. The suitable agitation speed was found to be 200 rpm with pH 7.00. The proper carbon, nitrogen, and trace elements supplementation consisted of starch, malt extract, calcium carbonate (CaCO3), and magnesium sulfate (MgSO4). The ethyl acetate extract was found to act strongly against three vibriosis pathogens, Vibrio harveyi, Vibrio parahaemolyticus, and Vibrio vunificus, as indicated by the inhibition zones at 34.5, 35.4, and 34.3 mm, respectively. The extract showed the strongest anti-V. harveyi activity, as indicated by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 0.101 ± 0.02 and 0.610 ± 0.04 mg/ml, respectively. Basic chemical investigation of the crude extract using thin layer chromatography (TLC), bioautography, liquid chromatography tandem mass spectrometry (LC‒MS/MS), Fourier transform infrared spectroscopy (FTIR), and proton nuclear magnetic resonance (1H-NMR) revealed that the active components were the terpenoid and steroid groups of compounds. They showed carboxylic acid and ester functions in their molecules.

A Comprehensive Review of Xanthan Gum-Based Oral Drug Delivery Systems.

Xanthan gum (XG) is an exopolysaccharide synthesized by the aerobic fermentation of simple sugars using Xanthomonas bacteria. It comprises a cellulosic backbone with a trisaccharide side chain connected to alternative glucose residues in the main backbone through α (1→3) linkage. XG dissolves readily in cold and hot water to produce a viscous solution that behaves like a pseudoplastic fluid. It shows excellent resistance to enzymatic degradation and great stability throughout a broad temperature, pH, or salt concentration range. Additionally, XG is nontoxic, biocompatible, and biodegradable, making it a suitable carrier for drug delivery. Furthermore, the carboxylic functions of pyruvate and glucuronic acid offer a considerable opportunity for chemical modification to meet the desired criteria for a specific application. Therefore, XG or its derivatives in conjunction with other polymers have frequently been studied as matrices for tablets, nanoparticles, microparticles, and hydrogels. This review primarily focuses on the applications of XG in various oral delivery systems over the past decade, including sustained-release formulations, gastroretentive dosage forms, and colon-targeted drug delivery. Source, production methods, and physicochemical properties relevant to drug delivery applications of XG have also been discussed.

Intramolecular C-H Oxidation in Iron(V)-oxo-carboxylato Species Relevant in the γ-Lactonization of Alkyl Carboxylic Acids.

High-valent oxoiron species have been invoked as oxidizing agents in a variety of iron-dependent oxygenases. Taking inspiration from nature, selected nonheme iron complexes have been developed as catalysts to elicit C-H oxidation through the mediation of putative oxoiron(V) species, akin to those proposed for Rieske oxygenases. The addition of carboxylic acids in these iron-catalyzed C-H oxidations has proved highly beneficial in terms of product yields and selectivities, suggesting the direct involvement of iron(V)-oxo-carboxylato species. When the carboxylic acid functionality is present in the alkane substrate, it acts as a directing group, enabling the selective intramolecular γ-C-H hydroxylation that eventually affords γ-lactones. While this mechanistic frame is solidly supported by previous mechanistic studies, direct spectroscopic detection of the key iron(V)-oxo-carboxylato intermediate and its competence for engaging in the selective γ-C-H oxidation leading to lactonization have not been accomplished. In this work, we generate a series of well-defined iron(V)-oxo-carboxylato species (2c-2f) differing in the nature of the bound carboxylate ligand. Species 2c-2f are characterized by a set of spectroscopic techniques, including UV-vis spectroscopy, cold-spray ionization mass spectrometry (CSI-MS), and, in selected cases, EPR and Mössbauer spectroscopies. We demonstrate that 2c-2f undergo site-selective γ-lactonization of the carboxylate ligand in a stereoretentive manner, thus unequivocally identifying metal-oxo-carboxylato species as the powerful yet selective C-H cleaving species in catalytic γ-lactonization reactions of carboxylic acids. Reactivity experiments confirm that the intramolecular formation of γ-lactones is in competition with the intermolecular oxidation of external alkanes and olefins. Finally, mechanistic studies, together with DFT calculations, support a mechanism involving a site-selective C-H cleavage in the γ-position of the carboxylate ligand by the oxo moiety, followed by a fast carboxylate rebound, eventually leading to the selective formation of γ-lactones.

A Novel Approach for the Synthesis of Responsive Core-Shell Nanogels with a Poly(N-Isopropylacrylamide) Core and a Controlled Polyamine Shell.

Microgel particles can play a key role, e.g., in drug delivery systems, tissue engineering, advanced (bio)sensors or (bio)catalysis. Amine-functionalized microgels are particularly interesting in many applications since they can provide pH responsiveness, chemical functionalities for, e.g., bioconjugation, unique binding characteristics for pollutants and interactions with cell surfaces. Since the incorporation of amine functionalities in controlled amounts with predefined architectures is still a challenge, here, we present a novel method for the synthesis of responsive core-shell nanogels (dh < 100 nm) with a poly(N-isopropylacrylamide) (pNIPAm) core and a polyamine shell. To achieve this goal, a surface-functionalized pNIPAm nanogel was first prepared in a semi-batch precipitation polymerization reaction. Surface functionalization was achieved by adding acrylic acid to the reaction mixture in the final stage of the precipitation polymerization. Under these conditions, the carboxyl functionalities were confined to the outer shell of the nanogel particles, preserving the core's temperature-responsive behavior and providing reactive functionalities on the nanogel surface. The polyamine shell was prepared by the chemical coupling of polyethyleneimine to the nanogel's carboxyl functionalities using a water-soluble carbodiimide (EDC) to facilitate the coupling reaction. The efficiency of the coupling was assessed by varying the EDC concentration and reaction temperature. The molecular weight of PEI was also varied in a wide range (Mw = 0.6 to 750 kDa), and we found that it had a profound effect on how many polyamine repeat units could be immobilized in the nanogel shell. The swelling and the electrophoretic mobility of the prepared core-shell nanogels were also studied as a function of pH and temperature, demonstrating the successful formation of the polyamine shell on the nanogel core and its effect on the nanogel characteristics. This study provides a general framework for the controlled synthesis of core-shell nanogels with tunable surface properties, which can be applied in many potential applications.

Bioisosteric replacement of the carboxylic acid group in Hepatitis-C virus NS5B thumb site II inhibitors: phenylalanine derivatives

Hepatitis C virus (HCV) is a global health concern and the NS5B RNA-dependent RNA polymerase (RdRp) of HCV is an attractive target for drug discovery due to its role in viral replication. This study focuses on NS5B thumb site II inhibitors, specifically phenylalanine derivatives, and explores bioisosteric replacement and prodrug strategies to overcome limitations associated with carboxylic acid functionality. The synthesized compounds demonstrated antiviral activity, with compound 6d showing the most potent activity with an EC50 value of 3.717 μM. The hydroxamidine derivatives 7a-d showed EC50 values ranging from 3.9 μM to 11.3 μM. However, the acidic heterocyclic derivatives containing the oxadiazolone (8a-d) and oxadiazolethione (9a-d) rings did not exhibit measurable activity. A methylated heterocycle 10b showed a hint of activity at 8.09 μM. The pivaloyloxymethyl derivatives 11a and 11b did not show antiviral activity. Further studies are warranted to fully understand the effects of these modifications and to explore additional strategies for developing novel therapeutic options for HCV.

Redox Transformations of the OX063 Radical in Biological Media: Oxidative Decay of Initial Trityl with Further Formation of Structurally-Modified TAM.

Being a low-toxic and hydrophilic representative of TAM, OX063 has shown its suitability for in-vivo and in-cell EPR experiments and design of spin labels. Using 13C labeling, we investigated the course of oxidative degradation of OX063 into quinone-methide (QM) under the influence of superoxide as well as further thiol-promoted reduction of QM into TAM radical, which formally corresponds to substitution of a carboxyl function by a hydroxyl group. We found these transformations being quantitative in model reactions mimicking specific features of biological media and confirmed the presence of these reactions in the blood and liver homogenate of mice in vitro. The emergence of the trityl with the hydroxyl group can be masked by an initial TAM in EPR spectra and may introduce distortions into EPR-derived oximetry data if they have been obtained for objects under hypoxia. 13C labeling allows one to detect its presence, considering its different hyperfine splitting constant on 13C1 (2.04 mT) as compared to OX063 (2.30 mT). The potential involvement of these reactions should be considered when using TAM in spin-labeling of biopolymers intended for subsequent EPR experiments, as well as in the successful application of TAM in experiments in vivo and in cell.

Positron Emission Tomography‐Assisted Photothermal Therapy with Gold Nanorods

AbstractPhotothermal anticancer therapy based on plasmonic nanoparticles is proposed to enhance treatment efficacy while mitigating unintended side effects. However, most studies blindly rely on the accumulation of nanoparticles at the tumor site, which may result in inefficient treatment. In this study, the aim is to evaluate relevant parameters to improve plasmonic photothermal therapy. Gold nanorods (AuNRs) with an optimized aspect ratio and either amino or carboxylic acid surface functionalization are selected as photothermal agents. AuNR biocompatibility and photothermal activity in 2D and 3D human MDA‐MB‐231 triple‐negative breast cancer cell models, evaluating localized hyperthermal cell death upon irradiation with resonant near‐infrared (NIR) light, are analyzed first. To ensure reliable tracking of biodistribution in vivo, AuNRs are labeled with the positron emitter copper‐64 (64Cu), and their distribution in a murine MDA‐MB‐231 tumor model is studied via positron emission tomography (PET) imaging. PET images reveal enhanced tumor accumulation of carboxylic acid‐functionalized AuNRs compared to amino‐functionalized AuNRs post‐intravenous administration. Relatively low NIR laser power densities (0.5 W cm−2) are used for controlled heating – keeping local temperature below 50 °C – upon irradiation of intravenously and intratumorally administered AuNRs. As a result, tumor growth is significantly decelerated, even 9 days after application of photothermal therapy.

The Influence of Carbon Nanotube Functionalization on Water Contaminated by Diesel and Benzoic Acid: A Comparison of Two Case Studies

This article simply aims to compare two case studies concerning the purification, using carbon nanotubes, of water contaminated by the following two different common pollutants: benzoic acid and diesel. In particular, the aim is to highlight how the different natures of both of the polluting molecules and the carbon nanotubes play a fundamental role in water treatment. These two pollutants were taken into consideration because of their different chemical natures: benzoic acid is a polar pollutant, while the molecules present in diesel are substantially nonpolar. The carbon nanotubes used were both functionalized and nonfunctionalized. Functionalization is a process that allows for the introduction of functional groups onto the surface of carbon nanotubes. In this research, carboxylic functionalization was performed, which allowed for the insertion of carboxylic groups through attacks with sulfuric and nitric acids. Thanks to the results obtained, it was possible to quantify the optimization of the purification process depending on the types of carbon nanotubes and polluting molecules considered. The functionalized nanotubes exhibited greater performances in the treatment of water contaminated by benzoic acid compared to the nonfunctionalized ones. Instead, in the treatment of water contaminated by diesel, a greater purification capacity was shown by the nonfunctionalized carbon nanotubes compared to the functionalized ones.

Redox conditions influence the chemical composition of iron-associated organic carbon in boreal lake sediments: A synchrotron-based NEXAFS study

The global carbon and iron cycles are intimately linked as redox-sensitive iron oxides readily bind organic carbon in a variety of environmental settings, including marine and lacustrine sediments. While these iron-organic carbon complexes sequester vast quantities of organic carbon, the composition of the organic matter within them remains unknown for lacustrine environments. Here we present C K1s and Fe L3,2 edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of surface sediments and authigenic iron complexes from adjacent basins of a pristine boreal lake located in Québec, Canada, with contrasting oxygen exposure regimes. We demonstrate differences in organic carbon speciation in sediments from both basins, as well as co-localization of organic carbon and iron on a sub-micron scale in 100 nm thick samples. Differences in redox cycling across these two basins allow for a direct comparison of the effect of oscillating redox conditions on the composition of organic carbon sequestered by iron. Our results suggest that reactive organic molecules, which may be polysaccharides, were found preferentially associated with iron in the perennially oxic sediments compared to more phenol rich organics in the seasonally anoxic sediments, highlighting the importance of iron oxides in the protection and preservation of labile organic compounds. Traces of aliphatic carbon were observed in sediments from the anoxic basin, alongside carboxyl and aromatic functionalities. This carboxyl-rich aliphatic material could possibly interact with the sediment mineral matrix either through a ligand exchange mechanism between the mineral phases and the carboxyl functionalities, or via non-specific hydrophobic interactions involving the aliphatic moieties. Finally, our work also shows that OC:Fe ratios should be used with caution when inferring a binding mechanism between OC and iron oxides.

On the Development of Polylactic Acid/Polycaprolactone Blended Films with High Retention Capacity.

The retention capacity of polymers is related to the development of systems that combine high surface-to-volume ratio with good handling and specific functionality. Biodegradability and biocompatibility are also key features for extending the field of applications to areas such as biomedicine. With this in mind, the aim of this work is to develop biodegradable, biocompatible, and highly functionalized porous films, that ensure suitable handling and a good surface-to-volume ratio. Polylactic acid (PLA) is applied as a polymer matrix to which a polycaprolactone with a star-shaped architecture (PCL-COOH) to ensure a high concentration of carboxylic end functionalities is added. The porous films are prepared using the phase inversion technique, which, as shown by Scanning Electron Microscopy (SEM) analysis, promotes good dispersion of the PCL-COOH domains. Absorption and release measurements performed with a positively charged model molecule show that the retention capacity and release rate can be tuned by changing the PCL-COOH concentration in the systems. Moreover, the adsorption properties for the formulation with the highest PCL-COOH content are also demonstrated with a real and widely used drug, namely doxorubicin. Finally, the bio- and hemocompatibility of the films, which are enzymatically degradable, are evaluated by using human keratinocytes and red blood cells, respectively.

Cryogenic Ion Vibrational Spectroscopy of Protonated Valine: Messenger Tag Effects.

We report the infrared photodissociation spectrum of tagged protonated valine in the range 1000-1900 cm-1, prepared in a cryogenic ion trap. Comparison of experimental results with calculated infrared spectra based on density functional theory shows that the hydroxyl group of the carboxylic acid functionality and the protonated amine group adopt a trans configuration. Nitrogen and methane molecules were used as messenger tags with optimal tagging temperatures of 30 K for N2 and 60 K for CH4. While the calculated infrared spectra of the tagged ion suggest only a weak influence of the messenger tag on the frequency positions of ValH+, the measured intensities for N2-tagged ValH+ appear strongly suppressed for all but the highest frequency feature at 1773 cm-1. We trace this behavior to the binding energy of the N2 tag, which is significantly higher than that of CH4, based on density functional and coupled cluster calculations and rate estimates for photoinduced unimolecular dissociation from statistical theory.

Ultrastable Carboxyl-Functionalized Pore-Space-Partitioned Metal-Organic Frameworks for Gas Separation.

Isoreticular chemistry, which enables property optimization by changing compositions without changing topology, is a powerful synthetic strategy. One of the biggest challenges facing isoreticular chemistry is to extend it to ligands with strongly coordinating substituent groups such as unbound -COOH, because competitive interactions between such groups and metal ions can derail isoreticular chemistry. It is even more challenging to have an isoreticular series of carboxyl-functionalized MOFs capable of encompassing chemically disparate metal ions. Here, with the simultaneous introduction of carboxyl functionalization and pore space partition, a family of carboxyl-functionalized materials is developed in diverse compositions from homometallic Cr3+ and Ni2+ to heterometallic Co2+/V3+, Ni2+/V3+, Co2+/In3+, Co2+/Ni2+. Cr-MOFs remain highly crystalline in boiling water. Unprecedentedly, one Cr-MOF can withstand the treatment cycle with 10m NaOH and 12m HCl, allowing reversible inter-conversion between unbound -COOH acid form and -COO- base form. These materials exhibit excellent sorption properties such as high uptake capacity for CO2 (100.2 cm3g-1) and hydrocarbon gases (e.g., 142.1 cm3g-1 for C2H2, 110.5 cm3g-1 for C2H4) at 1 bar and 298K, high benzene/cyclohexane selectivity (up to ≈40), and promising separation performance for gas mixtures such as C2H2/CO2 and C2H2/C2H4.