1H-13C Heteronuclear Correlation Research Articles

New Insights into the Hydrogen Bond Network in Al-MIL-53 and Ga-MIL-53

Metal−organic framework-type Al-, Ga-, and Ga(OH,F)-MIL-53 have been characterized by solid-state NMR and powder X-ray diffraction (PXRD). 1H 2D double-quantum–single-quantum (DQ–SQ) magic angle spinning (MAS) NMR experiments unambiguously evidence two inequivalent water molecules in Al-MIL-53_np_H2O. A careful reinvestigation of the XRD structure of hydrated Al-MIL-53 proves, for the first time, the doubling of the unit cell supporting the presence of two inequivalent water molecules. One type of water molecule is located in the type A channel, interacting with the aromatic protons of framework organic moieties, whereas the other type of water molecule is in the type B channel far away from aromatic protons. Assignment of the corresponding 1H resonances to each water molecule was possible. 1H 1D MAS NMR leads to the same conclusion (i.e., two inequivalent water molecules) for the isostructural gallium-based material thanks to the positioning of the hydrogen atoms by Rietveld refinement. Moreover, when Ga-MIL-53 is prepared with fluorine in the synthesis medium (giving Ga(OH,F)-MIL-53_np_H2O), the situation is different. 2D 1H–13C heteronuclear correlation MAS NMR, high-field 1H DQ–SQ, and radio-frequency-driven recoupling MAS NMR indicate that only one type of water molecule is found in this material, in agreement with the structure.

Understanding API-polymer proximities in amorphous stabilized composite drug products using fluorine-carbon 2D HETCOR solid-state NMR.

A simple and robust method for obtaining fluorine-carbon proximities was established using a (19)F-(13)C heteronuclear correlation (HETCOR) two-dimensional (2D) solid-state nuclear magnetic resonance (ssNMR) experiment under magic-angle spinning (MAS). The method was applied to study a crystalline active pharmaceutical ingredient (API), avagacestat, containing two types of fluorine atoms and its API-polymer composite drug product. These results provide insight into the molecular structure, aid with assigning the carbon resonances, and probe API-polymer proximities in amorphous spray dried dispersions (SDD). This method has an advantage over the commonly used (1)H-(13)C HETCOR because of the large chemical shift dispersion in the fluorine dimension. In the present study, fluorine-carbon distances up to 8 Å were probed, giving insight into the API structure, crystal packing, and assignments. Most importantly, the study demonstrates a method for probing an intimate molecular level contact between an amorphous API and a polymer in an SDD, giving insights into molecular association and understanding of the role of the polymer in API stability (such as recrystallization, degradation, etc.) in such novel composite drug products.

Structural Determination of a Novel Polymorph of Sulfathiazole–Oxalic Acid Complex in Powder Form by Solid-State NMR Spectroscopy on the Basis of Crystallographic Structure of Another Polymorph

Two polymorphic forms of a sulfathiazole (STZ):oxalic acid (OXA) 1:1 complex were successfully prepared by different cogrinding methods and characterized by multiple analytical techniques. Rod-milled and ball-milled ground mixtures had different powder X-ray diffraction patterns, showing polymorph formation of the STZ-OXA complex (complex A and complex B). The heat of fusion from differential scanning calorimetry curves and terahertz time-domain spectra helped differentiating the polymorphs. According to infrared spectra, 13C NMR chemical shifts, and the relative intensities of 15N NMR peaks, both polymorphs were salts where the proton of a −COOH group in OXA was transferred to a −NH2 group in STZ. High-resolution 1H NMR and 1H–13C heteronuclear correlation NMR spectra indicated that complex B in powder form had a cocrystal type structure compared to complex A having a clathrate-type structure. Complex B structure suggested by solid-state NMR coincided well with the experimentally determined one, which wa...

Cardo-Polyetherketone Anion Exchange Membranes with Suitable Chemical/Mechanical Stability and Performance for All-Vanadium Redox Flow Battery

Cardo-polyethereketone (PEK-C) based anion exchange membrane (AEM) was prepared by quaternization using trimethylammonium. The structures of intermediates and AEMs were confirmed by NMR spectroscopy. The ion exchange capacity of the PEK-C AEMs was 1.4±0.1 mmol g-1, which resulted in membranes with an ionic conductivity (sulfate form, 30 oC) of 5.6 ± 0.5 mS cm-1 and a vanadium (IV) permeability (at room temperature) of 8.2±0.2 ×10-9 cm2 s-1. Stability tests performed by immersion of PEK-C based AEMs in 1.5M VO2 + oxidizing solution during two months resulted in no change in the chemical structure of the polymer as demonstrated by 1H NMR, 13C NMR and 1H-13C heteronuclear multiple quantum correlation (HMQC). PEK-C based AEMs were also stable during vanadium redox flow battery operation (30 mAcm-2) for 50 charge/discharge cycles and showed coulombic and energy efficiency of 98% and 80%, respectively.

Platinum(IV) complexes with N-alkylphenothiazines: synthesis, characterization, and antibacterial activity

Two new platinum(IV) complexes (1, trifluoperazinehydrochloride-aquapentachloridoplatinate(IV) and 2, chlorpromazine-chlorpromazinehydrochloridepentachloridoplatinate(IV)) were synthesized in the reaction of K2[PtCl6] with trifluoperazine dihydrochloride (TF·2HCl) or chlorpromazine hydrochloride (CP·HCl). The complexes were characterized by elemental analysis, molar conductivity measurement, and spectral (IR, 1H, 13C, 2D 1H–13C heteronuclear correlation spectra, 195Pt NMR, and MS) methods. Outer-coordination sphere was proposed for 1; while in 2, the ligand was coordinated to the metal. The complexes exhibit antibacterial effect on strains of Bacillus subtilis, Bacillus cereus, Bacillus pumilus, and methicillin-resistant Staphylococci as Gram-positive bacteria and an Escherichia coli as Gram-negative bacteria, as well as the reference strains.

Investigation of Cation Degradation in Anion Exchange Membranes Using Multi-Dimensional NMR Spectroscopy

Low temperature anion exchange polymer electrolyte membrane (AEM) based fuel cells and electrolyzers have been successfully shown to convert hydrogen and oxygen to electricity (and vice-versa) with high efficiencies and energy densities with non-precious group metals. However, a significant challenge to realizing these technologies is the poor alkaline stability of the AEMs. In this work, we present the results of our multi-faceted approach to better understand AEM degradation in alkaline media. Several two-dimensional (2D) NMR techniques were applied to comprehensively elucidate cation degradation in polysulfone-based AEMs exposed to alkaline solutions. The 2D NMR tools utilized were: a) homonuclear correlation spectroscopy (COSY), b) 1H-X (X = 13C or 31P) heteronuclear multiple quantum correlation spectroscopy (HMQC), and c) 1H-13C heteronuclear multiple bond correlation spectroscopy (HMBC). Analysis of the 2D NMR spectra enabled precise identification of the degradation products for several different cation chemistries (quaternary ammonium, imidazolium, and phosphonium types). The observation of multiple degradation products highlighted the fact that the cation groups degraded through fundamentally different mechanisms. A clear understanding of the degradation mechanism is a critical requirement in the process of selecting or designing alternate cation chemistries for alkaline resilient AEMs.

Determining hydrogen-bond interactions in spider silk with 1H–13C HETCOR fast MAS solid-state NMR and DFT proton chemical shift calculations

Two-dimensional (2D) (1)H-(13)C heteronuclear correlation (HETCOR) solid-state NMR spectra collected with fast magic angle spinning (MAS) are used in conjunction with density functional theory (DFT) proton chemical shift calculations to determine the hydrogen-bonding strength for ordered β-sheet and disordered 310-helical structures in spider dragline silk. The hydrogen-bond strength is determined to be identical for both structures in spider silk with a 1.83-1.84 Å NH···OC hydrogen-bond distance.

Quantitation of components in complex mixtures utilizing two dimensional NMR spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy is well documented to provide qualitative data for structural determination of chemical compounds. More recently, numerous applications of NMR for quantitative analyses of chemical mixtures have been utilized. The majority of these applications use integration of discrete 1D NMR spectral resonances to quantitate individual components of the mixtures. 1D 1H NMR typically provides the highest sensitivity analyses with excellent linear response to component concentrations. Quantitative analyses of complex mixtures via 1D NMR however are often hindered by resonance overlap. Utilization of 1H-13C heteronuclear correlation (HSQC) and 2D J-resolved experiments provides dispersion in a second dimension, 13C chemical shift and 1H coupling constant respectively, for better identification and quantification of signals. The HSQC cross-peak volumes are influenced by uneven excitation, etc. and therefore the volumes for different resonances from the same molecule can vary based on these factors. Nevertheless, utilizing the same experimental parameters for any given cross-peak, the areas for the same peak should scale linearly with molar concentration. In this study, we have investigated the quantitative accuracy of these 2D spectra on a complex model system containing phenolics, alkaloids, sugars, terpenes, and polyketides and made comparisons to quantification using chemometric approaches. Applications to natural product extracts and formulations and ability to implement this into automated analysis methods will be presented.

Advanced Solid-State NMR Characterization of Marine Dissolved Organic Matter Isolated Using the Coupled Reverse Osmosis/Electrodialysis Method

Advanced (13)C solid-state techniques were employed to investigate the major structural characteristics of two surface-seawater dissolved organic matter (DOM) samples isolated using the novel coupled reverse osmosis/electrodialysis method. The NMR techniques included quantitative (13)C direct polarization/magic angle spinning (DP/MAS) and DP/MAS with recoupled dipolar dephasing, (13)C cross-polarization/total sideband suppression (CP/TOSS), (13)C chemical shift anisotropy filter, CH, CH(2), and CH(n) selection, two-dimensional (1)H-(13)C heteronuclear correlation NMR (2D HETCOR), 2D HETCOR combined with dipolar dephasing, and (15)N cross-polarization/magic angle spinning (CP/MAS). The two samples (Coastal and Marine DOM) were collected at the mouth of the Ogeechee River and in the Gulf Stream, respectively. The NMR results indicated that they were structurally distinct. Coastal DOM contained significantly more aromatic and carbonyl carbons whereas Marine DOM was markedly enriched in alkoxy carbon (e.g., carbohydrate-like moieties). Both samples contained significant amide N, but Coastal DOM had nitrogen bonded to aromatic carbons. Our dipolar-dephased spectra indicated that a large fraction of alkoxy carbons were not protonated. For Coastal DOM, our NMR results were consistent with the presence of the major structural units of (1) carbohydrate-like moieties, (2) lignin residues, (3) peptides or amino sugars, and (4) COO-bonded alkyls. For Marine DOM, they were (1) carbohydrate-like moieties, (2) peptides or amino sugars, and (3) COO-bonded alkyls. In addition, both samples contained significant amounts of nonpolar alkyl groups. The potential sources of the major structural units of DOM were discussed in detail. Nonprotonated O-alkyl carbon content was proposed as a possible index of humification.

NMR and MS study of the formation of β-d-glucopyranosylamine uronic acid in aqueous solution

The products of the reaction of d-glucuronic acid with various combinations of ammonia and volatile ammonium salts in water were studied by NMR and MS spectroscopy. For long reaction times (~24 h), the expected products β-d-glucopyranosylamine uronic acid and ammonium N-(β-d-glucopyranosyluronic acid)carbamate were obtained in good-to-high yield, whereas seven intermediate species were identified in samples taken at earlier reaction times. 1H–1H homonuclear and 1H–13C heteronuclear correlation experiments enabled a complete assignment of the 1H and 13C NMR spectra of the starting and final compounds, and a partial assignment of the peaks of intermediate species. Based on these results, a 1H NMR protocol for the quantification of the different compounds taking part in the reaction was developed, which was used to monitor the evolution of the composition of an early reaction sample redissolved in D2O. It was thus established that two of the observed intermediate species are actually the α anomer of the main products, whereas the others are precursors to the formation of α/β-d-glucopyranosylamine uronic acid and ammonium N-(α/β-d-glucopyranosyluronic acid)carbamate. The correct assignments for the 1H and 13C spectra of d-glucuronic acid in D2O are also reported.

Solid‐State NMR Analysis of Soil Organic Matter Fractions from Integrated Physical–Chemical Extraction

Fractions of soil organic matter (SOM) were extracted by an integrated physical–chemical procedure and their chemical natures were characterized through 13C nuclear magnetic resonance (NMR) spectroscopy. For the 0‐ to 5‐cm depth of a corn (Zea mays L.)–soybean [Glycine max. (L.) Merr.] soil in Iowa, we extracted in sequence the light fraction, two size fractions of particulate organic matter (POM), and two NaOH‐extractable humic acid fractions based on their binding to soil Ca2+: the unbound mobile humic acid fraction and the calcium humate fraction. Whole SOM was obtained by dissolving the soil mineral component through HF washes. All samples were analyzed by advanced 13C NMR techniques, including quantitative direct polarization/magic angle spinning, spectral‐editing techniques, and two‐dimensional 1H–13C heteronuclear correlation NMR. The NMR spectra were comparable for the light fraction and two POM fractions and were dominated by carbohydrates and to a lesser extent lignins or their residues, with appreciable proteins or peptides. By contrast, spectra of the two humic fractions were dominated by aromatic C and COO/N–C=O groups, with smaller proportions of carbohydrates and NCH/OCH3 groups, indicative of more humified material. This trend was yet more pronounced in the calcium humate fraction. The spectrum for whole SOM had signals intermediate between these two groups of SOM fractions, suggesting contributions from both groups. Our results for this soil suggest that either chemical or physical fractions alone will partially represent whole SOM, and their integrated use is likely to provide greater insight into SOM structure and possibly function, depending on the research issue.

Zinc chlorins for artificial light-harvesting self-assemble into antiparallel stacks forming a microcrystalline solid-state material

We introduce a concept to solve the structure of a microcrystalline material in the solid-state at natural abundance without access to distance constraints, using magic angle spinning (MAS) NMR spectroscopy in conjunction with X-ray powder diffraction and DFT calculations. The method is applied to a novel class of materials that form (semi)conductive 1D wires for supramolecular electronics and artificial light-harvesting. The zinc chlorins 3-devinyl-3(1)-hydroxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 1 and 3-devinyl-3(1)-methoxymethyl-13(2)-demethoxycarbonylpheophorbide a (3',5'-bis-dodecyloxy)benzyl ester zinc complex 2, self-assemble into extended excitonically coupled chromophore stacks. (1)H-(13)C heteronuclear dipolar correlation MAS NMR experiments provided the (1)H resonance assignment of the chlorin rings that allowed accurate probing of ring currents related to the stacking of macrocycles. DFT ring-current shift calculations revealed that both chlorins self-assemble in antiparallel pi-stacks in planar layers in the solid-state. Concomitantly, X-ray powder diffraction measurements for chlorin 2 at 80 degrees C revealed a 3D lattice for the mesoscale packing that matches molecular mechanics optimized aggregate models. For chlorin 2 the stacks alternate with a periodicity of 0.68 nm and a 3D unit cell with an approximate volume of 6.28 nm(3) containing 4 molecules, which is consistent with space group P2(1)22(1).

MetaboMiner – semi-automated identification of metabolites from 2D NMR spectra of complex biofluids

BackgroundOne-dimensional (1D) 1H nuclear magnetic resonance (NMR) spectroscopy is widely used in metabolomic studies involving biofluids and tissue extracts. There are several software packages that support compound identification and quantification via 1D 1H NMR by spectral fitting techniques. Because 1D 1H NMR spectra are characterized by extensive peak overlap or spectral congestion, two-dimensional (2D) NMR, with its increased spectral resolution, could potentially improve and even automate compound identification or quantification. However, the lack of dedicated software for this purpose significantly restricts the application of 2D NMR methods to most metabolomic studies.ResultsWe describe a standalone graphics software tool, called MetaboMiner, which can be used to automatically or semi-automatically identify metabolites in complex biofluids from 2D NMR spectra. MetaboMiner is able to handle both 1H-1H total correlation spectroscopy (TOCSY) and 1H-13C heteronuclear single quantum correlation (HSQC) data. It identifies compounds by comparing 2D spectral patterns in the NMR spectrum of the biofluid mixture with specially constructed libraries containing reference spectra of ~500 pure compounds. Tests using a variety of synthetic and real spectra of compound mixtures showed that MetaboMiner is able to identify >80% of detectable metabolites from good quality NMR spectra.ConclusionMetaboMiner is a freely available, easy-to-use, NMR-based metabolomics tool that facilitates automatic peak processing, rapid compound identification, and facile spectrum annotation from either 2D TOCSY or HSQC spectra. Using comprehensive reference libraries coupled with robust algorithms for peak matching and compound identification, the program greatly simplifies the process of metabolite identification in complex 2D NMR spectra.

Identification of Mycobacterium tuberculosis Clinical Isolates with Altered Phagocytosis by Human Macrophages Due to a Truncated Lipoarabinomannan

Phenotypically distinct clinical isolates of Mycobacterium tuberculosis are capable of altering the balance that exists between the pathogen and human host and ultimately the outcome of infection. This study has identified two M. tuberculosis strains (i.e. HN885 and HN1554) among a bank of clinical isolates with a striking defect in phagocytosis by primary human macrophages when compared with strain Erdman, a commonly used laboratory strain for studies of pathogenesis. Mass spectrometry in conjunction with NMR studies unequivocally confirmed that both HN885 and HN1554 contain truncated and more branched forms of mannose-capped lipoarabinomannan (ManLAM) with a marked reduction of their linear arabinan (corresponding mainly to the inner Araf-alpha(1-->5)-Araf unit) and mannan (with fewer 6-Manp residues and more substitutions in the linear Manp-alpha(1-->6)-Manp unit) domains. The truncation in the ManLAM molecules produced by strains HN885 and HN1554 led to a significant reduction in their surface availability. In addition, there was a marked reduction of higher order phosphatidyl-myo-inositol mannosides and the presence of dimycocerosates, triglycerides, and phenolic glycolipid in their cell envelope. Less exposed ManLAM and reduced higher order phosphatidyl-myo-inositol mannosides in strains HN885 and HN1554 resulted in their low association with the macrophage mannose receptor. Despite reduced phagocytosis, ingested bacilli replicated at a fast rate following serum opsonization. Our results provide evidence that the clinical spectrum of tuberculosis may be dictated not only by the host but also by the amounts and ratios of surface exposed mycobacterial adherence factors defined by strain genotype.

Urinary Metabolite Quantification Employing 2D NMR Spectroscopy

Two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy is a fairly novel method for the quantification of metabolites in biological fluids and tissue extracts. We show in this contribution that, compared to 1D 1H spectra, superior quantification of human urinary metabolites is obtained from 2D 1H-13C heteronuclear single-quantum correlation (HSQC) spectra measured at natural abundance. This was accomplished by the generation of separate calibration curves for the different 2D HSQC signals of each metabolite. Lower limits of detection were in the low to mid micromolar range and were generally the lower the greater the number of methyl groups contained in an analyte. The quantitative 2D NMR data obtained for a selected set of 17 urinary metabolites were compared to those obtained independently by means of gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry of amino acids and hippurate as well as enzymatic and colorimetric measurements of creatinine. As a typical application, 2D-NMR was used for the investigation of urine from patients with inborn errors of metabolism.

Studying Organic Matter Molecular Assemblage within a Whole Organic Soil by Nuclear Magnetic Resonance

This work shows the applicability of two-dimensional (2D) (1)H-(13)C heteronuclear correlation (HETCOR) nuclear magnetic resonance (NMR) spectroscopy to the characterization of whole soils. A combination of different mixing times and cross polarization (CP) methods, namely Lee-Goldberg (LG)-CP and Ramp-CP are shown to afford, for the first time, intra- and inter- molecular connectivities, allowing for molecular assemblage information to be obtained on a whole soil. Our results show that, for the brackish marsh histosol under study, two isolated domains could be detected. The first domain consists of O-alkyl and aromatic moieties (lignocellulose material), while the second domain is comprised of alkyl type moieties (cuticular material). The role of these domains is discussed in terms of hydrophobic organic compound sorption within soil organic matter (SOM), including the possible effects of wetting and drying cycles.

Structural characterization of FCC feeds from Indian refineries by NMR spectroscopy

Fluid catalytic cracking (FCC) feeds from four Indian refineries are structurally characterized by 1H, gated-decoupled 13C, distortionless enhancement by polarization transfer (DEPT) and 2D 1H–13C HETeronuclear CORrelation (HETCOR) and other 2D nuclear magnetic resonance (NMR) methods. Detailed structural analyses are completely supported by a range of NMR information including chemical shifts of 1H and 13C, CHn type distributions and 1H –13C connectivities. The average structural parameters like branching sites, average number of branching per molecule, average length of side chains, percentage of saturates, aromatics and naphthenes are obtained from these NMR data. A novel approach based on “multipoint spline base line correction” is employed for estimation of naphthenes and n-paraffins that gives better quantitative estimation than the conventional methods. In this paper, importance is given to the study of those structural parameters that plays a key role in cracking chemistry as well as coke forming tendency of the feedstock. To the best of our knowledge, this is the first attempt to characterize and quantitatively estimate compositions of the high boiling fractions of petroleum feed by NMR methods and especially the complex structure of vacuum gas oil (VGO) fractions used in Indian refineries. The importance of this paper is to help in optimizing the product slate of Indian refineries through proper feedstock blending using few hundreds of million metric tons (MMT) of crude oil consisting of blends of light crudes with different heavy crudes and bottom of the barrel due to escalating cost of crudes.

NMR Investigation of Enzymatic Coupling of Sulfonamide Antimicrobials with Humic Substances

Phenoloxidases mediate the oxidative transformation of soil phenolic constituents, contributing to the formation of humic substances and the chemical incorporation of some xenobiotic organic compounds into natural organic matter. We previously demonstrated phenoloxidase-mediated covalent coupling of sulfonamide antimicrobials with model humic constituents. Here, we investigate fungal peroxidase-mediated covalent coupling of 13C-sulfamethazine and 15N-sulfapyridine to humic substances. 1H-13C heteronuclear single quantum correlation (HSQC) nuclear magnetic resonance spectroscopy provided an initial indication of peroxidase-mediated covalent binding of 13C-sulfamethazine to humic acid. To confirm the role of the sulfonamide anilinic nitrogen in coupling to humic acid and to determine the nature of the covalent linkage, we incubated 15N-sulfapyridine with humic acid and peroxidase and examined reaction products in 1H-15N heteronuclear multiple bond (HMBC) experiments. The HMBC spectra revealed the presence of Michael adducts (i.e., anilinohydroquinones, anilinoquinones) and possibly other covalent linkages. No evidence for Schiff base formation was observed. Analogous experiments with the model humic constituent catechol provided corroborating evidence for these assignments. Michael adducts are expected to exhibit greater environmental stability than imine linkages that can form between sulfonamides and 2,6-dimethoxyphenols. Because the free anilinic nitrogen is required for the bioactivity of sulfonamide antimicrobials, nucleophilic addition occurring through this moiety could result in the biochemical inactivation of these compounds.

Structural Determinants That Target the Hepatitis C Virus Core Protein to Lipid Droplets

Hepatitis C virus core protein is targeted to lipid droplets, which serve as intracellular storage organelles, by its C-terminal domain, termed D2. From circular dichroism and nuclear magnetic resonance analyses, we demonstrate that the major structural elements within D2 consist of two amphipathic alpha-helices (Helix I and Helix II) separated by a hydrophobic loop. Both helices require a hydrophobic environment for folding, indicating that lipid interactions contribute to their structural integrity. Mutational studies revealed that a combination of Helix I, the hydrophobic loop, and Helix II is essential for efficient lipid droplet association and pointed to an in-plane membrane interaction of the two helices at the phospholipid layer interface. Aside from lipid droplet association, membrane interaction of D2 is necessary for folding and stability of core following maturation at the endoplasmic reticulum membrane by signal peptide peptidase. These studies identify critical determinants within a targeting domain that enable trafficking and attachment of a viral protein to lipid droplets. They also serve as a unique model for elucidating the specificity of protein-lipid interactions between two membrane-bound organelles.

Genetic Basis for the Synthesis of the Immunomodulatory Mannose Caps of Lipoarabinomannan in Mycobacterium tuberculosis

Lipoarabinomannan (LAM) is a high molecular weight, heterogenous lipoglycan present in abundant quantities in Mycobacterium tuberculosis and many other actinomycetes. In M. tuberculosis, the non-reducing arabinan termini of the LAM are capped with alpha1-->2 mannose residues; in some other species, the arabinan of LAM is not capped or is capped with inositol phosphate. The nature and extent of this capping plays an important role in disease pathogenesis. MT1671 in M. tuberculosis CDC1551 was identified as a glycosyltransferase that could be involved in LAM capping. To determine the function of this protein a mutant strain of M. tuberculosis CDC1551 was studied, in which MT1671 was disrupted by transposition. SDS-PAGE analysis showed that the LAM of the mutant strain migrated more rapidly than that of the wild type and did not react with concanavalin A as did wild-type LAM. Structural analysis using NMR, gas chromatography/mass spectrometry, endoarabinanase digestion, Dionex high pH anion exchange chromatography, and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry demonstrated that the LAM of the mutant strain was devoid of mannose capping. Since an ortholog of MT1671 is not present in Mycobacterium smegmatis mc(2)155, a recombinant strain was constructed that expressed this protein. Analysis revealed that the LAM of the recombinant strain was larger than that of the wild type, had gained concanavalin A reactivity, and that the arabinan termini were capped with a single mannose residue. Thus, MT1671 is the mannosyltransferase involved in deposition of the first of the mannose residues on the non-reducing arabinan termini and the basis of much of the interaction between the tubercle bacillus and the host cell.