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Microbial polysaccharide characterization requires purification that often involves detergent precipitation and lyophilization. Here we examined physicochemical changes following lyophilization of Cryptococcus neoformans exopolysaccharide (EPS). Solution

The need for safe, effective preservatives is a prominent issue in the food and drug industries, reflecting demand for natural alternatives to synthetic chemicals viewed as harmful to consumers and the environment. Thus, this study determined the identities and scavenging capacities of antioxidant metabolites produced as a response to potato tuber wounding, using activity-guided fractionation of polar extracts from a Yukon Gold cultivar that had previously exhibited exceptionally high radical-scavenging activity. Activity-guided fractionation using the ABTS(+) radical scavenging assay and LC-MS with TOF-MS for compositional analysis of the most potent antioxidant fractions yielded identification of nine constituents: coumaroylputrescine; feruloylquinic acid; isoferuloylputrescine; ferulic acid; 22,25-dimethoxy-3-[[2,3,4-tri-O-methyl-6-O-(2,3,4,6-tetra-O-methyl-β-d-glucopyranosyl)-β-d-glucopyranosyl]oxy]-(3β)-lanost-9(11)-en-24-one; 4-(2Z)-2-decen-1-yl-5-[1-(4-hydroxyphenyl)decyl]-1,2-benzenediol; 8-[(2E)-3,7-dimethyl-2,6-octadien-1-yl]-5-hydroxy-2,8-dimethyl-6-(3-methyl-2-buten-1-yl)-2H-1-benzopyran-4,7(3H,8H)-dione; 3-[(2-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy]-20-[(6-O-β-d-xylopyranosyl-β-d-glucopyranosyl)oxy]-dammar-24-en-19-al; (3β)-28-oxo-28-(phenylmethoxy)oleanan-3-yl 2-O-β-d-galactopyranosyl-3-O-(phenylmethyl)-, butyl ester β-d-glucopyranosiduronic acid. A positive correlation was observed between the scavenging activities and the polarities of the active fractions. The antioxidant capacities of the fractions were also characterised by monitoring the activity throughout a 45-minute assay period.

Erwinia carotovora is a major cause of potato tuber infection, which results in disastrous failures of this important food crop. There is currently no effective antibiotic treatment against E. carotovora. Recently we reported antibacterial assays of wound tissue extracts from four potato cultivars that exhibit a gradient of russeting character, finding the highest potency against this pathogen for a polar extract from the tissue formed immediately after wounding by an Atlantic cultivar. In the current investigation, antibacterial activity-guided fractions of this extract were analyzed by liquid chromatography-mass spectrometry (LC-MS) utilizing a quadrupole-time-of-flight (QTOF) mass spectrometer. The most active chemical compounds identified against E. carotovora were: 6-O-nonyl glucitol, Lyratol C, n-[2-(4-Hydroxyphenyl)] ethyldecanamide, α-chaconine and α-solanine. Interactions among the three compounds, ferulic acid, feruloyl putrescine, and α-chaconine, representing metabolite classes upregulated during initial stages of wound healing, were also evaluated, offering possible explanations for the burst in antibacterial activity after tuber wounding and a chemical rationale for the temporal resistance phenomenon.

Periderms present in plant barks are essential protective barriers to water diffusion, mechanical breakdown, and pathogenic invasion. They consist of densely packed layers of dead cells with cell walls that are embedded with suberin. Understanding the interplay of molecular structure, dynamics, and biomechanics in these cell wall-associated insoluble amorphous polymeric assemblies presents substantial investigative challenges. We report solid-state NMR coordinated with FT-IR and tensile strength measurements for periderms from native and wound-healing potatoes and from potatoes with genetically modified suberins. The analyses include the intact suberin aromatic–aliphatic polymer and cell-wall polysaccharides, previously reported soluble depolymerized transmethylation products, and undegraded residues including suberan. Wound-healing suberized potato cell walls, which are 2 orders of magnitude more permeable to water than native periderms, display a strikingly enhanced hydrophilic–hydrophobic balance, a degradation-resistant aromatic domain, and flexibility suggestive of an altered supramolecular organization in the periderm. Suppression of ferulate ester formation in suberin and associated wax remodels the periderm with more flexible aliphatic chains and abundant aromatic constituents that can resist transesterification, attenuates cooperative hydroxyfatty acid motions, and produces a mechanically compromised and highly water-permeable periderm.

To efficiently recycle CO(2) to economically viable products such as liquid fuels and carbon nanomaterials, the reactivity of CO(2) is required to be fully understood. We have investigated the reaction of CO(2) with ammonia borane (AB), both molecules being able to function as either an acid or a base, to obtain more insights into the amphoteric activity of CO(2). In the present work, we demonstrate that CO(2) can be converted to graphene oxide (GO) using AB at moderate conditions. The conversion consists of two consecutive steps: CO(2) fixation (CO(2) pressure < 3 MPa and temperature < 100 °C) and graphenization (600-750 °C under 0.1 MPa of N(2)). The first step generates a solid compound that contains methoxy (OCH(3)), formate (HCOO) and aliphatic groups while the second graphenization is the pyrolysis of the solid compound to produce graphene oxide-boron oxide nanocomposites, which have been confirmed by micro-Raman spectroscopy, solid state (13)C and (11)B magic angle spinning-nuclear magnetic resonance (MAS-NMR), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Our observations also show that the mass of solid product in CO(2) fixation process and raw graphene oxide nanocomposites is twice and 1.2 times that of AB initially charged, respectively. The formation of aliphatic groups without using metal-containing compounds at mild conditions is of great interest to the synthesis of various organic products starting from CO(2.).

Complementary degradative treatments with low-temperature hydrofluoric acid and methanolic potassium hydroxide have been used to investigate the protective biopolymer cutin from Citrus aurantifolia (lime) fruits, augmenting prior enzymatic and chemical strategies to yield a more comprehensive view of its molecular architecture. Analysis of the resulting soluble oligomeric fragments with one- and two-dimensional NMR and MS methods identified a new dimer and three trimeric esters of primary alcohols based on 10,16-dihydroxyhexadecanoic acid and 10-oxo-16-hydroxyhexadecanoic acid units. Whereas only 10-oxo-16-hydroxyhexadecanoic acid units were found in the oligomers from hydrofluoric acid treatments, the dimer and trimer products isolated to date using diverse degradative methods included six of the seven possible stoichiometric ratios of monomer units. A novel glucoside-linked hydroxyfatty acid tetramer was also identified provisionally, suggesting that the cutin biopolymer can be bound covalently to the plant cell wall. Although the current findings suggest that the predominant molecular architecture of this protective polymer in lime fruits involves esters of primary and secondary alcohols based on long-chain hydroxyfatty acids, the possibility of additional cross-linking to enhance structural integrity is underscored by these and related findings of nonstandard cutin molecular architectures.

Theaflavins and thearubigins are major pigments in black tea, and it is generally accepted that they are produced by oxidation of flavan-3-ols (catechins) during tea fermentation. In the course of studies on the oxidation mechanism of tea polyphenols, especially the formation of thearubigins, a method combining the enzymatic synthesis and LC/ESI-MS/MS analysis was developed to search for new higher molecular weight polymers from black tea. Three new dibenzotropolones, theadibenzotropolone A, B, and C, together with one new tribenzotropolone, theatribenzotropolone A, were formed by the reaction of theaflavins and tea catechins with horseradish peroxidase in the presence of H(2)O(2). The structures of these new benzotropolone derivatives were elucidated on the basis of MS and 2D NMR spectroscopic analyses. The existence of these compounds in black tea was characterized by LC/ESI-MS/MS. Theadibenzotropolone A and B were the first benzotropolone-type trimers of catechins found in the black tea extract. The observation that galloyl ester groups of theaflavins can be oxidized to form di- or tri-benzotropolone skeletons strongly implied that this type of oxidation is an important pathway to extend the molecular size of thearubigins.

Tea catechins, an important class of polyphenols, have been shown to have antioxidant activity and are thought to act as antioxidants in biological systems. However, the mechanisms of their antioxidant reactions remain unclear. The objective of this study was to characterize the reaction products of epicatechin with peroxyl radicals generated by thermolysis of the azo initiator azo-bisisobutyrylnitrile (AIBN). Structural elucidation of these products can provide insights into specific mechanisms of antioxidant reactions. Eight reaction products were isolated and identified using high-field 1D and 2D NMR spectral analysis. The observation of these compounds confirmed that the B-ring is the initial site for formation of reaction products in the peroxyl radical oxidant system.

The objective of the current study is to characterize the reaction products of theaflavin 3,3′-digallate, one of the major characteristic polyphenols of black tea, with hydroxyl radicals generated by hydrogen peroxide, with the aim of gaining insights into specific mechanisms of antioxidant reactions in physiological systems. Two major reaction products were isolated and identified using high-field 1D and 2D NMR spectral analysis. Both of them are A-ring fission products. The observation of these compounds indicates that the A ring rather than the benzotropolone moiety is the initial site for formation of reaction products in the hydrogen peroxide oxidant system.

A new unusual kauranoid diterpene glycoside, named amygdaloside, was isolated from the nuts of almond (Prunus amygdalus). It's structure was established as 17-O-β-D-glucopyranoside ent-6,7-epoxy-6-hydroxyl-6,7-secokaur-19-oic acid, 6,19-lactone 16β17-diol on the basis of high-resolution 1D and 2D NMR spectral studies.

Theaflavins and thearubigins are major pigments of black tea. In the course of studies on the oxidation mechanism of tea polyphenols, a new type of tea pigment, theadibenzotropolone A, together with theaflavin 3-gallate were formed by the reaction of (−)-epicatechin (EC) and (−)-epigallocatechin gallate (EGCG) with horseradish peroxidase in the presence of H 2 O 2 . The structure of theadibenzotropolone A was elucidated on the basis of MS and 2D NMR spectroscopic analyses. The observation that galloyl ester groups of theaflavins can be oxidized to form dibenzotropolone skeletons strongly implied that this type of oxidation as an important pathway to extend the molecular size of thearubigins. The existence of this compound in black tea was characterized by LC/ESI-MS/MS. Theadibenzotropolone A is the first theaflavin type trimer of catechins in black tea.

Tea catechins, an important class of polyphenols, have been shown to have wide spectrum of antitumor activity believed to be due mainly to their antioxidative effect. In this study, the radical scavenging behavior of catechins on 2,2-diphenyl-1-picrylhydrazyl (DPPH) was studied. Two reaction products of (+)-catechin, and two reaction products of (-)-epicatechin were purified and identified. Their structures were determined on the basis of detailed high-field 1-D and 2-D NMR spectral analysis. Structure elucidation of these products can provide insights into specific mechanisms of antioxidant reactions. A possible mechanism of the formation of reaction products is suggested.

Despite the essential functions of melanin pigments in diverse organisms and their roles in inspiring designed nanomaterials for electron transport and drug delivery, the structural frameworks of the natural materials and their biomimetic analogs remain poorly understood. To overcome the investigative challenges posed by these insoluble heterogeneous pigments, we have used l-tyrosine or dopamine enriched with stable (13)C and (15)N isotopes to label eumelanins metabolically in cell-free and Cryptococcus neoformans cell systems and to define their molecular structures and supramolecular architectures. Using high-field two-dimensional solid-state nuclear magnetic resonance (NMR), our study directly evaluates the assumption of structural commonality between synthetic melanin models and the corresponding natural pigments, demonstrating a common indole-based aromatic core in the products from contrasting synthetic protocols for the first time.

Garcinol (1), a polyisoprenylated benzophenone, purified from Garcinia indica fruit rind, displays antioxidant properties and is thought to act as an antioxidant in biological systems. However, the mechanisms of its antioxidant reactions remain unknown. The objective of this study was to characterize the reaction products of garcinol with a stable radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH). Structural elucidation of these products can provide insights into specific mechanisms of antioxidant reactions. Two major reaction products, GDPPH-1 (2) and GDPPH-2 (3), were isolated and identified for the first time. Their structures were determined on the basis of detailed high field 1D and 2D spectral analysis. The identification of these products provides the first unambiguous proof that the principal sites of antioxidant reactions are on the 1,3-diketone and the phenolic ring part of 1. The induction of apoptosis in human leukemia HL-60 cells, the inhibition of NO generation, the effects on the activity of MMP, and the inhibitory effects on H2O2 production of TPA-stimulate HL-60 cells by 1 and its two oxidant products (2 and 3) were investigated and would also be discussed in this paper.

The cuticle of higher plants functions primarily as a protective barrier for the leaves and fruits, controlling microbial attack as well as the diffusion of water and chemicals from the outside environment. Its major chemical constituents are waxes (for waterproofing) and cutin (a structural support polymer). However, the insolubility of cutin has hampered investigations of its covalent structure and domain architecture, which are viewed as essential for the design of crop protection strategies and the development of improved synthetic waterproofing materials. Recently developed strategies designed to meet these investigative challenges include partial depolymerization using enzymatic or chemical reagents and spectroscopic examination of the intact polyesters in a solvent-swelled form. The soluble oligomers from degradative treatments of lime fruit cutin are composed primarily of the expected 10,16-dihydroxyhexadecanoic and 16-hydroxy-10-oxo-hexadecanoic acids; low-temperature HF treatments also reveal sugar units that are covalently attached to the hydroxyfatty acids. Parallel investigations of solvent-swollen cutin using 2D NMR spectroscopy assisted by magic-angle spinning yield well-resolved spectra that permit detailed comparisons to be made among chemical moieties present in the intact biopolymer, the soluble degradation products, and the unreacted solid residue.

Although suberin in potato wound periderm is known to be a polyester containing long-chain fatty acids and phenolics embedded within the cell wall, many aspects of its molecular structure and polymer-polymer connectivities remain elusive. The present work combines biosynthetic incorporation of site-specifically (13)C-enriched acetates and phenylalanines with one- and two-dimensional solid-state (13)C NMR spectroscopic methods to monitor the developing suberin polymer. Exogenous acetate is found to be incorporated preferentially at the carboxyl end of the aliphatic carbon chains, suggesting addition during the later elongation steps of fatty acid synthesis. Carboxyl-labeled phenylalanine precursors provide evidence for the concurrent development of phenolic esters and of monolignols typical of lignin. Experiments with ring-labeled phenylalanine precursors demonstrate a predominance of sinapyl and guaiacyl structures among suberin's phenolic moieties. Finally, the analysis of spin-exchange (solid-state NOESY) NMR experiments in ring-labeled suberin indicates distances of no more than 0.5 nm between pairs of phenolic and oxymethine carbons, which are attributed to the aromatic-aliphatic polyester and the cell wall polysaccharide matrix, respectively. These results offer direct and detailed molecular information regarding the insoluble intermediates of suberin biosynthesis, indicate probable covalent linkages between moieties of its polyester and polysaccharide domains, and yield a clearer overall picture of this agriculturally important protective material.

Cutin and suberin are support polymers involved in waterproofing the leaves and fruits of higher plants, regulating the flow of nutrients among various plant organs, and minimizing the deleterious impact of microbial pathogens. Despite the complexity and intractable nature of these plant biopolyesters, their molecular structure and development are amenable to study by suitable solid-state and solution-state NMR techniques. Interactions of tomato cutin with water were examined by solid-state 2H and 13C NMR, showing that water films enhance rapid segmental motions of the acyl chains and are associated with a fivefold increase in surface elasticity upon cutin hydration. The suberization of wounded potato tissues was studied by solid-state 13C NMR, revealing the likely phenylpropanoid structures that permit dense cross-linking of the suberin structure and their proximity to the cell-wall polysaccharides. Finally, two new approaches were developed to elucidate the molecular structures of these biopolymers: partial depolymerization followed by spectroscopic analysis of the soluble oligomers; and swelling of the intact materials followed by magic-angle spinning (MAS) NMR analysis.

The chemical deprotecting reagent iodotrimethylsilane has been used to achieve controlled breakdown of ester bonds in cutin, an insoluble protective biopolymer obtained from the fruit of Citrus aurantifolia (limes). Four soluble products that preserve essential features of the cuticular molecular architecture have been isolated chromatographically and identified by multidimensional NMR and liquid secondary-ion mass spectrometry, whereas the insoluble residue has been characterized by solid state 13 C NMR spectroscopy. The building blocks of the two dimers and one tetramer include the major Citrus cutin monomers 16-hydroxy-10-oxo-hexadecanoic acid and 10,16-dihydroxyhexadecanoic acid, which are joined by primary ester linkages. The CPMAS 13 C NMR spectra of the unreacted residue implicate a heterogeneous reaction in which esters of primary alcohols within the cross-linked cutin network are preferentially cleaved. These studies offer a direct and definitive description of molecular connectivities within the protective polyesters of fruit cuticles.

Two-dimensional 1H−13C wide-line separation (WISE) NMR, a technique developed for the characterization of synthetic copolymers and blends in the solid state, has been used to study the dynamic behavior and domain structure of the biopolymer suberin deposited within the wound periderm of potato tubers. This blend consists of cell-wall polysaccharides and cross-linked aromatic−aliphatic polyesters that regulate water transport and protect the plant tissue from pathogenic attack. Though most of the suberin chemical moieties are rigid, about 20% of its chain-methylene groups exhibit surprising flexibility on the 50-kHz frequency scale. The resulting motional narrowing is propagated rapidly by spin diffusion to other residues within the suberin domain, but much more slowly to the spatially separated cell-wall region. Using a selective spin-diffusion experiment with a dipolar filter, the suberin domain size has been estimated as 50 nm and compared with prior results from electron microscopy. Finally, the resist...

A very useful high-resolution magic-angle spinning (MAS) 1H NMR method for studying lipid dispersions is presented. The sample can be loaded into the spherical glass ampoule very easily, and a spinning speed of more than 10 kHz can be achieved without the problems of sample leakage or water loss. The line width at half height for the HDO peak is less than 1.5 Hz, and the method can be implemented by anyone who has access to a solid-state MAS NMR spectrometer. By using the spherical glass ampoule method we found two water peaks, which could be ascribed to bulk water outside of the multilamellar liposome (peak at high frequency) and interlamellar water (peak at low frequency), in both POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) liposomes. These are the first two examples of lipids without exchangeable protons that exhibit two distinct water resonances. The respective 1H spin-lattice relaxation times (T1) were measured, yielding values twice as long for bulk water as compared with interlamellar water. Both the chemical shift and spin relaxation results demonstrate the ability of MAS 1H NMR to rapidly monitor changes in physical properties that accompany water interactions with zwitterionic phosphatidylcholines.

A recently developed HPLC technique has been used to identify 10 major monomers from potassium hydroxide hydrolysis and transesterification of lime cutin, revealing 16-hydroxy-10-oxo-hexadecanoic and 10,16-dihydroxyhexadecanoic acids as the major constituents. Solid-state 13 CNMR spectroscopy has also been used to examine the unreacted residues following hydrolytic treatment. For transesterification with methanolic boron trifluoride, an alternative protocol using MS has been developed. Using HPTLC to separate epoxy and hydroxy fatty esters, and making a series of trimethylsilyl ether derivatives, the monomeric products have been subjected to analysis by GC-CI-mass spectrometry. Although GC cannot discriminate between positional isomers of oxo and dihydroxy fatty acids, the parent ions and fragmentation patterns obtained with CI-mass spectrometry allow definitive identification of each isomer and reveal five new constituents of the cutin biopolymer. Both the methodology and the monomeric structures are compared with prior reports for citrus fruit cuticle; implications for the molecular architecture and biosynthesis of the lime cutin polymer are also discussed.

Intact cells of Saccharomyces cerevisiae were examined as an aqueous paste by 13C-nmr spectroscopy with direct polarization and magic-angle spinning. The spectra obtained were highly resolved, showing numerous resonances in the 60-105 ppm range that were assigned to carbons of a liquid-like domain of the cell wall glucan. Assignments were confirmed by running the spectrum of S. cerevisiae in which the cell wall glucans were labeled with [13C] by feeding the cell [13C ] galactose. The spectra indicate that the glucan in the cell wall of intact S. cerevisiae assumes a helical conformation and suggest that strain 17A fed with galactose preferentially incorporates the resulting glucose into β(1 3)-linkages. © 1994 John Wiley & Sons, Inc.

A new unusual sesquiterpene lactone, named amygdalactone, was isolated from the hulls of almond ( Prunus amygdalus ). Complete assignment of the proton and carbon chemical shifts for the new lactone was accomplished on the basis of high-resolution 1D and 2D NMR data. Amygdalactone represents a new class of sesquiterpene with cyclohexa[7,12- g ]octalactone ring system. The cytotoxic activity of amygdalactone was determined.

An efficient protocol combining enzymatic and chemical methods has been developed for the isolation of lime fruit cutin and potato suberin in pure form and with excellent yields. Starting with the procedures specified by commercial assay kits for model substrates, the breakdown of cellulose, pectin, and hemicellulose cell-wall constituents was optimized with respect to enzyme concentration, substrate concentration, reaction time, and temperature. The optimized procedures were then applied to the plant polyesters cutin and suberin, with the isolation process monitored in parallel by gravimetric methods and with cross-polarization magic-angle spinning 13 C NMR

Suberized cell walls from wound-healing potato tubers ( Solanum tuberosum ) were depolymerized under mild conditions using methanolic potassium hydroxide in order to investigate the chemical linkages present in this protective plant biopolymer. Analysis of the resulting soluble oligomeric fragments with HPLC, 1D and 2D NMR, LC/MS, and MS(n) methods allowed identification of several novel compounds: a family of homologous triglycerides, a family of homologous aliphatic ester trimers, and an ether-linked phenylacetic acid dimer. These findings illustrate the diversity of rigid and flexible molecular linkages present in both poly(aliphatic) and poly(aromatic) domains of potato suberin, and they point toward architectures that may account for its function as a potent hydrophobic barrier to water, thermal equilibration, and microbial pathogens.

Measurements of the proton rotating-frame relaxation time T 1ρ (H) indicate that wound-healing involves the formation of spatially separated suberin and cell-wall domains. Suberin appears to be attached to the cell-wall domain at discrete sites, with both its methylene and phenylpropanoid groups divided into two populations having distinct chemical shifts and spin relaxation characteristics. Measurements of T 1ρ (C) and T 1 (C) in this biopolymer system sho significant site-specific and tissue-specific variations .

An anionic potato peroxidase (EC 1.11.1.7, APP) thought to be involved in suberization after wounding was isolated from slices of Solanum tuberosum in order to elucidate the first steps of dehydrogenative polymerization between pairs of different hydroxycinnamic acids (FA, CafA, CA and SA) present in wound-healing plant tissues. Use of a commercial horseradish peroxidase (HRP)-H2O2 catalytic system gave the identical major products in these coupling reactions, providing sufficient quantities for purification and structural elucidation. Using an equimolar mixture of pairs of hydroxycinnamic acid suberin precursors, only caffeic acid is coupled to ferulic acid and sinapic acid in separate cross-coupling reactions. For the other systems, HRP and APP reacted as follows: (1) preferentially with ferulic acid in a reaction mixture that contained p-coumaric and ferulic acids; (2) with sinapic acid in a mixture of p-coumaric and sinapic acids; (3) with sinapic acid in a mixture of ferulic and sinapic acids; (4) with caffeic acid in a reaction mixture of p-coumaric and caffeic acids. The resulting products, isolated and identified by NMR and MS analysis, had predominantly beta-beta-gamma-lactone and beta-5 benzofuran molecular frameworks. Five cross-coupling products are described for the first time, whereas the beta-O-4 dehydrodimers identified from the caffeic acid and sinapic acid cross-coupling reaction are known materials that are highly abundant in plants. These reactivity trends lead to testable hypotheses regarding the molecular architecture of intractable suberin protective plant materials, complementing prior analysis of monomeric constituents by GC-MS and polymer functional group identification from solid-state NMR, respectively.

Derivatives based on a benzotropolone skeleton (9-26) have been prepared by the enzymatic coupling (horseradish peroxidase/H2O2) of selected pairs of compounds (1-8), one with a vic-trihydroxyphenyl moiety, and the other with an ortho-dihydroxyphenyl structure. Some of these compounds have been found to inhibit TPA-induced mice ear edema, nitric oxide (NO) synthesis, and arachidonic acid release by LPS-stimulated RAW 264.7 cells. Their cytotoxic activities against KYSE 150 and 510 human esophageal squamous cell carcinoma and HT 29 human colon cancer cells were also evaluated.

A new iridoid glucoside (1), named citrifolinoside A, was isolated from the leaves of Morinda citrifolia along with the known iridoids asperuloside and asperulosidic acid. The structure of 1 was established by interpretation and full assignments of NMR spectroscopic data.

Singly and doubly labeled delta-aminolevulinic acid derivatives were used to prepare rat liver outer mitochondrial membrane (OM) cytochrome b5 containing a 13C-labeled heme active site. A variety of NMR experiments, including HMBC and INADEQUATE in conjunction with the more commonly used HMQC, NOESY, and COSY, were conducted to make unambiguous assignments of protonated carbons and the quaternary pyrrole-alpha and -beta carbons in both isomeric forms of the paramagnetic active center of OM cytochrome b5. Because the long interpulse delays in the HMBC experiment have a detrimental effect on the detectability of fast relaxing paramagnetically affected resonances. INADEQUATE is proposed as the experiment of choice for assigning quaternary carbons in paramagnetic hemes with carefully chosen macrocycle labeling patterns. Furthermore, the applicability of the INADEQUATE experiment to paramagnetic heme active sites should be facilitated greatly by the availability of biosynthetic methods for producing isotopically labeled b-hemes and, more recently, isotopically labeled c-hemes.

Environmentally significant materials including soils, plant tissues, melanin pigments, and urban surface films possess swollen or swellable constituents that are not studied ideally using either solution- or solid-state NMR. Beginning in the 1970s and accelerating during the past 15 years, high-resolution (HR)-MAS techniques have been developed to study these challenging materials, yielding unprecedented molecular detail and informing mechanistic hypotheses. This valuable information has been forthcoming without the need for soil or tissue extraction, and without subjecting the macromolecular entities of interest to chemical degradation. In this overview, we focus on practical HR-MAS NMR strategies, including both methodological fundamentals and illustrative architectural findings for soil organic matter, plant protective polymers and biomass, and ultraviolet-resistant melanin pigments. In addition to the acquisition of one-dimensional spectra tailored for mobile or immobilized constituents of whole soils, we illustrate the use of HR-MAS in conjunction with two-dimensional NMR experiments [COSY, TOCSY, heteronuclear multiple-quantum coherence (HMQC), and heteronuclear multiple-bond correlation (HMBC)] to elucidate the macromolecular chemistry of terrestrial plant litter decomposition and environmental stress resistance at plant surfaces.

High-resolution, solid-state 13C nuclear magnetic resonance (NMR) spectra are reported for suberized cell wall from potatoes (Solanum tuberosum L.). Through experiments combining the techniques of cross polarization and magic-angle spinning, we verified that suberin, like cutin, is a polyester and demonstrated that it also has phenylpropanoid groups characteristic of lignin. Roughly 50% of the suberized material consists of cell-wall polymers; aromatics and other unsaturated linkages outnumber methylene groups 2:1. In conjunction with traditional direct-polarization NMR results, these experiments provide support for prior suggestions that suberin and cell-wall components are chemically bonded via aromatic groups.