2D Nuclear Overhauser Enhancement Spectroscopy Research Articles

Comparing PVP and Polymeric Micellar Formulations of a PEGylated Photosensitizing Phthalocyanine by NMR and Optical Techniques.

Phthalocyanines are ideal candidates as photosensitizers for photodynamic therapy (PDT) of cancer due to their favorable chemical and photophysical properties. However, their tendency to form aggregates in water reduces PDT efficacy and poses challenges in obtaining efficient forms of phthalocyanines for therapeutic applications. In the current work, polyvinylpyrrolidone (PVP) and micellar formulations were compared for encapsulating and monomerizing a water-soluble zinc phthalocyanine bearing four non-peripheral triethylene glycol chains (Pc1). 1H NMR spectroscopy combined with UV-vis absorption and fluorescence spectroscopy revealed that Pc1 exists as a mixture of regioisomers in monomeric form in dimethyl sulfoxide but forms dimers in an aqueous buffer. PVP, polyethylene glycol castor oil (Kolliphor RH40), and three different triblock copolymers with varying proportions of polyethylene and polypropylene glycol units (termed P188, P84, and F127) were tested as micellar carriers for Pc1. 1H NMR chemical shift analysis, diffusion-ordered spectroscopy, and 2D nuclear Overhauser enhancement spectroscopy was applied to monitor the encapsulation and localization of Pc1 at the polymer interface. Kolliphor RH40 and F127 micelles exhibited the highest affinity for encapsulating Pc1 in the micellar core and resulted in intense Pc1 fluorescence emission as well as efficient singlet oxygen formation along with PVP. Among the triblock copolymers, efficiency in binding and dimer dissolution decreased in the order F127 > P84 > P188. PVP was a strong binder for Pc1. However, Pc1 molecules are rather surface-attached and exist as monomer and dimer mixtures. The results demonstrate that NMR combined with optical spectroscopy offer powerful tools to assess parameters like drug binding, localization sites, and dynamic properties that play key roles in achieving high host-guest compatibility. With the corresponding adjustments, polymeric micelles can offer simple and easily accessible drug delivery systems optimizing phthalocyanines' properties as efficient photosensitizers.

Synergism between betaine surfactants under high-salt conditions

Foam properties and surface dilational rheology of single and mixed LHSB (lauramidopropyl hydroxyl sulfobetaine)-OAB (oleic amide propyl betaine) surfactants were measured to investigate the synergism between the two components. Experimental results showed obvious synergistic effects in foam stability, dilational modulus, and phase angle between LHSB and OAB. Moreover, interaction parameters were calculated to quantitatively characterize the synergism. The negative interaction parameters between LHSB and OAB demonstrated that there was an attractive interaction between LHSB and OAB, and the attractive interaction contributed to forming the dense surfactant layer at the liquid/air layer, which in turn improved foam stability. The negative values of parameters reached their maximum when the LHSB: OAB molar ratio ranged from 1:1 to 1:2, the same time the foam stability reached its maximum. The interaction between LHSB and OAB was confirmed by 2D NOSEY (two-dimensional nuclear overhauser enhancement spectroscopy) experiments, the interaction between LHSB and OAB could be attributed to the hydrogen bonding or the electrostatic interaction between the hydrophilic groups of the two surfactants.

Biphenyl-Induced Superhelix in l -Phenylalanine-Based Supramolecular Self-Assembly with Dynamic Morphology Transitions

Biphenyl-Induced Superhelix in <scp>l</scp> -Phenylalanine-Based Supramolecular Self-Assembly with Dynamic Morphology Transitions

Contrasting effect of 1-butanol and 1,4-butanediol on the triggered micellar self-assemblies of C16-type cationic surfactants.

The self-assembly in aqueous solutions of three quaternary salt-based C16-type cationic surfactants with different polar head groups and identical carbon alkyl chain viz., cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number (Nagg) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the three cationic surfactants, the molecular dynamics (MD) simulation was performed for CPB micelles in an aqueous solution of alcohols that highlighted the micelle solvation and structural transition, which is further complemented in terms of critical packing parameter (PP) for the examined systems.

Interaction of Phenyl-Substituted Diazaperylenium with Cucurbit[n]uril: Complex versus Supramolecular Polymer.

A phenyl-substituted diazaperylenediium dication (DAP) was synthesized that shows concentration-dependent aggregation in water. The host–guest complexation of DAP was studied with the macrocyclic host cucurbit[n]uril (n = 7, 8) in water. With CB[7], it forms a 1:2 complex by placing two aryl substituents inside the CB[7]; whereas, with CB[8], a supramolecular polymer is formed. The resulting complex and supramolecular polymer have been characterized by ITC (isothermal titration calorimetry), ESI-MS (electrospray ionization mass spectrometry), 1H NMR (proton nuclear magnetic resonance), 2D NOESY (two-dimensional nuclear Overhauser enhancement spectroscopy), and DOSY (diffusion-ordered spectroscopy) spectra.

Single-Chain Glycopolymer Folding via Host-Guest Interactions and Its Unprecedented Effect on DC-SIGN Binding.

Reversible self-folding actions of natural biomacromolecules play crucial roles for specific and unique biological functions in Nature. Hence, controlled folding of single polymer chains has attracted significant attention in recent years. Herein, reversible single-chain folded glycopolymer structures in α-shape with different density of sugar moieties in the knot were created. The influence of folding as well as the sugar density in the knot was investigated on the binding capability with lectins, such as ConA, DC-SIGN, and DC-SIGNR. The synthesis of triblock glycocopolymers bearing β-CD and adamantane for the host-guest interaction and also mannose residues for the lectin interaction was achieved using the reversible addition-fragmentation chain transfer (RAFT) polymerization technique. The reversible single-chain folding of glycopolymers was achieved under a high dilution of an aqueous solution and the self-assembled folding was monitored by 2D nuclear overhauser enhancement spectroscopy (NOESY) NMR and dynamic light scattering. The lectin binding profiles consistently provided an unprecedented effect of single chain folding as the single-chain folded structures enhanced greatly the binding ability in comparison to the unfolded linear structures.

A study of the interaction between polyvinylpyrrolidone and gemini surfactant G12-3-12 by NMR

The interaction between a water-soluble polymer polyvinylpyrrolidone (PVP) and a gemini surfactant N,N'-didodecyl-N,N,N',N'-tetramethyl-N,N'-propanediyl-diammonium dibromide (G12-3-12) was investigated by means of NMR in a D2O solution at 298 K. The critical micelle concentration (СMC), critical aggregation concentration (СAC) and adsorption reached the saturated concentration (C2) were confirmed by chemical shift and self-diffusion coefficients, respectively. The results of the relaxation time ratio (T R = T 2/T 1) of G12-3-12 show that the motion of the ionic head N+–CH 3 * proton (G6) is seriously restricted, and thus, it can be proved that the cationic head groups are situated in the hydrophilic layer of the micelle. The size of the mixed-aggregates in the G12-3-12/PVP solution is larger than pure G12-3-12 micelles according to self-diffusion coefficients, indicating that the G12-3-12 and PVP has formed mixed micelles, and ionic heads N+–CH 3 * become more tightly packed in the hydrophilic layer of the micelle shell. On the other hand, strong cross peaks, such as G1-P2, G1-P3, and G2-P3, appear in the 2D nuclear Overhauser enhancement spectroscopy (2D NOESY) spectra of the G12-3-12/PVP system, further indicating that the interaction sites are located between the hydrophobic tail of G12-3-12 and PVP ring.

Stereochemical Investigations of DiastereomericN-[2-(Aryl)-5-methyl-4-oxo-1,3-thiazolidine-3-yl]-pyridine-3-carboxamides by Nuclear Magnetic Resonance Spectroscopy (1D and 2D)

Some newN-[2-(aryl)-5-methyl-4-oxo-1,3-thiazolidine-3-yl]-pyridine-3-carboxamides were synthesized and their structures were investigated by IR, NMR (1H,13C, and 2D), and mass spectra. The presence of C-2 and C-5 stereogenic centers on the thiazolidinone ring resulted in diastereoisomeric pairs. The configurations of two stereogenic centers were assigned based upon1H NMR analysis of coupling constants and 2D nuclear overhauser enhancement spectroscopy (NOESY) experiment. Resolution of the diastereoisomers was performed by high performance liquid chromatography (HPLC) using a chiral stationary phase.

Dynamic NMR study of cyclic derivatives of pyridoxine.

A series of pyridoxine derivatives was investigated by (1) H and 2D nuclear overhauser enhancement spectroscopy (NOESY) NMR. The free energies of activation for the pyridyl-oxygen rotation of the 2,4-dinitrophenyl ether of the seven-membered acetals of pyridoxine were measured by dynamic NMR. A conformational exchange between the chair and twist forms of the seven-membered acetal ring was confirmed by dynamic NMR and STO3G computations.

Structural Characterization of Amadori Rearrangement Product of Glucosylated Nα-Acetyl-Lysine by Nuclear Magnetic Resonance Spectroscopy

Maillard reaction is a nonenzymatic reaction between reducing sugars and free amino acid moieties, which is known as one of the most important modifications in food science. It is essential to characterize the structure of Amadori rearrangement products (ARPs) formed in the early stage of Maillard reaction. In the present study, the Nα-acetyl-lysine-glucose model had been successfully set up to produce ARP, Nα-acetyl-lysine-glucose. After HPLC purification, ARP had been identified by ESI-MS with intense [M+H]+ion at 351 m/zand the purity of ARP was confirmed to be over 90% by the relative intensity of [M+H]+ion. Further structural characterization of the ARP was accomplished by using nuclear magnetic resonance (NMR) spectroscopy, including 1D1H NMR and13C NMR, the distortionless enhancement by polarization transfer (DEPT-135) and 2D1H-1H and13C-1H correlation spectroscopy (COSY) and 2D nuclear overhauser enhancement spectroscopy (NOESY). The complexity of 1D1H NMR and13C NMR was observed due to the presence of isomers in glucose moiety of ARP. However, DEPT-135 and 2D NMR techniques provided more structural information to assign the1H and13C resonances of ARP. 2D NOESY had successfully confirmed the glycosylated site between 10-N in Nα-acetyl-lysine and 7′-C in glucose.

Combined application of 2D correlated spectroscopy and 2D nuclear Overhauser enhancement spectroscopy to the brain metabolites

The 2D NMR has great potential for routine use in organic chemistry, biochemistry and structural biology. The 2D correlated spectroscopy (COSY) and 2D nuclear Overhauser enhancement (NOE) spectroscopy are particularly powerful techniques for studies of scalar coupling connectivity and spatial connectivity. Here we present the 3-bond spatial connectivity of brain metabolites using in vitro 2D COSY and 2D NOE spectroscopy. The 2D spectra were obtained using 500 MHz NMR from solution of brain metabolites. In this study, we showed the 3-bond and spatial connectivity of brain metabolites detected by scalar coupling and dipolar NOE interaction. Our results may be helpful in promoting better understanding of the interactions in corresponding protons in each of metabolite and provide basic information for structure determination of neurochemicals.

Combined Application of 2D Correlated Spectroscopy and 2D Nuclear Overhauser Enhancement Spectroscopy to the Brain Metabolites

Combined Application of 2D Correlated Spectroscopy and 2D Nuclear Overhauser Enhancement Spectroscopy to the Brain Metabolites

Interactions between Dendrimers and Ionic Liquids Revealed by Pulsed Field Gradient and Nuclear Overhauser Effect NMR Studies

The host-guest interactions of cationic and anionic poly(amidoamine) (PAMAM) dendrimers with three ionic liquids including 1-butyl-3-methylimidazolium 2-(2-methoxyethoxy)ethyl sulfate ([BMIM][MDEGSO(4)]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]), and trihexyltetradecylphosphonium bis((trifluoromethyl)sulfonyl)imide ([THTDP][TFSI]) were investigated by several NMR techniques such as (1)H and (19)F NMR, pulsed field gradient (PFG) NMR, and 2D nuclear Overhauser enhancement spectroscopy (NOESY). Anionic PAMAM dendrimer interacts with the ionic liquids via ionic interactions. However, almost no interaction is observed between cationic PAMAM dendrimer and the ionic liquids without pH adjustment. Besides, no inclusion formation between the PAMAM dendrimers and the ionic liquids is observed on the basis of NOE NMR studies. The interactions between dendrimers and ionic liquids are very different from those between dendrimers and surfactants or amphiphilic drugs. The results obtained from PFG and NOE studies provide new insights into dendrimer-based host-guest systems.

Construction of Polypseudorotaxane from Low-Molecular Weight Monomers via Dual Noncovalent Interactions

The design and construction of polypseudorotaxanes via noncovalent interactions from low-molecular weight monomers (LMWMs) is playing an important role in the field of supramolecular polymers. In this work, we synthesized three low-molecular weight compounds for supramolecular polymerizations and attempted to employ the metal–ligand interaction between the pyridine nitrogen and Pd (II), for cooperating with the host–guest binding between azobenzene and β-cyclodextrin (β-CD), to complete the end-to-end connection of the polymer chains. Routes for stepwise introduction of two of the self-assembly behaviors as well as a one-pot preparation were investigated by 1H NMR and 2D nuclear Overhauser enhancement spectroscopy (NOESY) 1H NMR spectroscopy. The self-assembly strategies based on the full orthogonality of both noncovalent interactions will allow for a smart and rapid synthesis of precise structural controlled supramolecular polymeric assemblies.

1D and 2D NMR investigations of the micelle-formation process in 8-phenyloctanoate micelles

The micellization process of sodium 8-phenyloctanoate in a deuterated aqueous solution was studied, using 1H NMR spectroscopy and two-dimensional (2D) nuclear Overhauser enhancement spectroscopy (NOESY). 1H NMR spectra, acquired for the sodium 8-phenyloctanoate before and after the critical micelle concentration (CMC) value, showed that large chemical-shift changes were observed for both the aromatic proton peaks and the peaks for the methylene protons near the terminal phenyl group. The plots for the methylene protons near the headgroup do not show these large chemical-shift changes. These observations support the view that the terminal phenyl ring of the surfactant is primarily located in the micellar interior. The 2D NOESY experiments show significant cross-peaks, between the phenyl protons and the methylene protons of the surfactant, that substantiate the conclusions on those drawn from NMR aromatic solute induced shift (ASIS) experiments on the same and similar systems. All these observations are consistent with the Gruen model of the micelle and previous NMR NOESY experiments for other surfactant systems.Key words: surfactants, micelles, NMR, NOESY.

NMR analysis of duplex d(CGCGATCGCG)2 modified by Λ- and Δ-[Ru(bpy)2(m-GHK)]Cl2 and DNA photocleavage study

The interaction of the diastereomeric complexes Lambda-[Ru(bpy)2(m-GHK)]Cl2 and Delta-[Ru(bpy)2(m-GHK)]Cl2 (bpy is 2,2'-bipyridine, GHK is glycine-L-histidine-L-lysine) with the deoxynucleotide duplex d(5'-CGCGATCGCG)2 was studied by means of 1H NMR spectroscopy. At a Delta-isomer to DNA ratio of 1:1, significant shifts for the metal complex are observed, whereas there is negligible effect on the oligonucleotide protons and only one intermolecular nuclear Overhauser effect (NOE) is present at the 2D nuclear Overhauser enhancement spectroscopy spectrum. The 1Eta NMR spectrum at ratio 2:1 is characterized by a slight shift for the Delta-isomer's bpy aromatic protons as well as significant shifts for the decanucleotide G4 H1' and Eta2'', A5 H2, G10 H1', T6 NH and G2 NH protons. Furthermore, at ratio 2:1, 11 intermolecular NOEs are observed. The majority of the NOEs involve the sugar Eta2' and Eta2'' protons sited in the major groove of the decanucleotide. Increasing the Delta-isomer to d(CGCGATCGCG)2 ratio to 5:1 results in noteworthy spectral changes. The Delta-isomer's proton shifts are reduced, whereas significant shifts are observed for the decanucleotide protons, especially the sugar protons, as well as for the exchangeable protons. Interaction is characterized by the presence of only one intermolecular NOE. Furthermore, there is significant broadening of the imino proton signals as the ratio of the Delta-isomer to DNuAlpha increases, which is attributed to the opening of the two strands of the duplex. The Lambda-isomer, on the other hand, approaches the minor groove of the oligonucleotide and interacts only weakly, possibly by electrostatic interactions. Photocleavage studies were also conducted with the plasmid pUC19 and a 158-bp restriction fragment, showing that both diastereomers cleave DNA with similar efficiency, attacking mainly the guanines of the sequence probably by generating active oxygen species.

Solution 1H NMR study of the accommodation of the side chain of n-butyl-etiohemin-I incorporated into the active site of cyano-metmyoglobin

In order to identify the most readily deformable portion of the heme pocket in myoglobin, equine myoglobin was reconstituted with a meso-n-butyl substituent on centrosymmetric etiohemin-I. Solution 1H NMR data for the low-spin iron(III) cyanide complex of oxidized myoglobin that include 2D nuclear Overhauser enhancement spectroscopy contacts, paramagnetic relaxation, and dipolar shifts resulting from magnetic anisotropy show that the heme binds uniquely to the iron in a manner that arranges the methyl and ethyl substituents on a given pyrrole in a clockwise manner when viewed from the proximal side, and with the n-butyl group seated at the canonical alpha-meso position of native protohemin-IX. The butyl group is oriented sharply toward the proximal side and its protein contacts demonstrate that it is oriented largely into the "xenon hole" in myoglobin. The location of the n-butyl group on the proximal side near the vacancies places it within the region found to be most flexible in molecular dynamics simulation. A small, counterclockwise rotation of the pyrrole N-Fe-N vector of n-butyl-etiohemin-I relative to that for native protohemin, indicated by both the prosthetic group methyl contact shift pattern and the prosthetic group contacts to heme pocket residues, is proposed to allow the xenon hole to accommodate better the n-butyl group. In contrast to previous work, which showed that a bulky polar substituent on etiohemin-I preferentially seats at the canonical gamma-meso position, the nonpolar n-butyl group selects the alpha-meso position.

(13)C nuclear magnetic resonance spectra of natural undiluted lipids: docosahexaenoic-rich phospholipid and triacylglycerol from fish.

In the (13)C NMR spectra of natural, unenriched docosahexaenoic acid-rich sardine oil and cod muscle glycerophosphocholine significant signal intensity differences across the 1D spectrum between undiluted and diluted samples were observed. In undiluted samples (13)C-(13)C 2D nuclear Overhauser enhancement spectroscopy (NOESY) interchain cross-peaks for CH, CH(2), CH(3), and C=C structures were observed. Results indicate that in undiluted natural lipids, NMR signal intensity is influenced by polarization transfer from the extended lipid structure. The NOE enhancement of specific molecular sites especially in unsaturated lipids is evidence that some natural lipids remain oriented relative to each other and in an orderly arrangement at the molecular level long enough for the effect to be detected by the NMR experiment. The presence of polyunsaturated fatty acids in mixtures of natural lipids could stabilize specific local molecular conformations within the remaining less saturated lipids.

Investigation of microstructure of the acrylonitrile‐styrene‐glycidyl methacrylate terpolymers by 1D and 2D NMR spectroscopy

AbstractAcrylonitrile‐styrene‐glycidyl methacrylate (N/S/G) terpolymers were prepared by bulk polymerization by using benzoyl peroxide as initiator and analyzed by NMR spectroscopy. The compositions of terpolymers were determined by quantitative 13C{1H}‐NMR spectra and compared with those calculated by Goldfinger's equation by using comonomer reactivity ratios: rNS = 0.04, rSN = 0.40; rNG = 0.22, rGN = 1.37; rSG = 0.44, rGS = 0.53. The 13C{1H}‐ and 1H‐NMR spectra were overlapping and complex. The spectral assignments were done with the help of distortionless enhancement by polarization transfer and two‐dimensional 13C‐1H heteronuclear single quantum correlation experiments. 2D total correlated spectroscopy was used to ascertain the various coupling between the protons. The methyl, methine, methylene, and oxymethylene carbon resonances showed compositional sensitivity. 2D nuclear Overhauser enhancement spectroscopy (NOESY) experiment was used to ascertain the spatial proton–proton couplings. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1779–1790, 2003

Characterization by NMR and molecular modeling of the binding of polyisoprenols and polyisoprenyl recognition sequence peptides: 3D structure of the complexes reveals sites of specific interactions.

The objective of these studies was to test the hypothesis that proteins that contain potential polyisoprenyl recognition sequences (PIRSs) in their transmembrane-spanning domain can bind to the polyisoprenyl (PI) glycosyl carrier lipids undecaprenyl phosphate (C55-P) and dolichyl phosphate (C95-P). A number of prokaryotic and eukaryotic glycosyltransferases that utilize PI coenzymes contain a conserved PIRS postulated to be the active PI binding domain. To study this problem, we first determined the 3D structure of a PIRS peptide, NeuE, by homonuclear 2D 1H-nuclear magnetic resonance (NMR) spectroscopy. Experimentally generated distance constraints derived from nuclear Overhauser enhancement and torsion angle constraints derived from coupling constants were used for restrained molecular dynamics and energy minimization calculations. Molecular models of the NeuE peptide were built based on calculations of energy minimization using the DGII program NMRchitect. 3D models of dolichol (C95) and C95-P were built based on our 2D 1H-NMR nuclear Overhauser enhancement spectroscopy (NOESY) results and refined by energy minimization with respect to all atoms using the AMBER (assisted modeling with energy refinements) force field. Our energy minimization studies were carried out on a conformational model of dolichol that was originally derived from small-angle X-ray scattering and molecular mechanics methods. These results revealed that the PIs are conformationally nearly identical tripartite molecules, with their three domains arranged in a coiled, helical structure. Analyses of the intermolecular cross-peaks in the 2D NOESY spectra of PIRS peptides in the presence of PIs confirmed a highly specific interaction and identified key contact amino acids in the NeuE peptide that constituted a binding motif for interacting with the PIs. These studies also showed that subtle conformational changes occurred within both the PIs and the NeuE peptide after binding. 3D structures of the resulting molecular complexes revealed that each PI could bind more than one PIRS peptide. These studies thus represent the first evidence for a direct physical interaction between specific contact amino acids in the PIRS peptides and the PIs and supports the hypothesis of a bifunctional role for the PIs. The central idea is that these superlipids may serve as a structural scaffold to organize and stabilize in functional domains PIRS-containing proteins within multiglycosyltransferase complexes that participate in biosynthetic and translocation processes.