Field Gradient Spin-echo NMR Research Articles

Shear Orientation in Nematic Carbon Nanotube Dispersions: A Combined NMR Investigation

Carbon nanotubes were dispersed in a sodium dodecylsulfate/decanol/water nematic fluid. The long-term stability of the dispersions is ensured by the small density gradients existing between nanotubes and the nematic fluid, and by its viscosity, as well. Presumably, surfactant or nematic micelles adsorb onto nanotubes and concur to stabilize them. A Rheo 2H NMR characterization was performed. It was supported by classical 2H quadrupole splitting and pulsed field gradient spin–echo NMR, allowing to ascertain the diffusive trends therein. The nematic fluid shows uniaxial spectral profiles and marked diffusion anisotropy. No such effects were observed in nanotube-containing nematic dispersions. In addition, the measured water self-diffusion values are substantially lower than the pure nematic fluid. In the absence of shear, dispersed nanotubes do not modify the quadrupole splitting amplitude, but affect the spectral profiles. The reasons for the observed behavior are briefly outlined. In the presence of shear...

Quantitative analysis of polymer mixtures in solution by pulsed field-gradient spin echo NMR spectroscopy

Pulsed Field-Gradient Spin Echo (PGSE) NMR, which associates to a spectral dimension the measure of diffusion coefficients, is a convenient technique for mixture analysis. Unfortunately, because of relaxation, the quantification of mixtures by PGSE NMR is far from straightforward for mixtures with strong spectral overlap. Antalek (J. Am. Chem. Soc. 128 (2006) 8402–8403) proposed a quantification strategy based on DECRA analysis and extrapolation to zero of the diffusion delay. More recently, Barrère et al. (J. Magn. Reson. 216 (2012) 201–208) presented a new strategy based also on DECRA and on the renormalization of the intensities using estimates of the T1 and T2 relaxation times. Here we report an alternative quantification approach in which the fractions are obtained by analyzing the PGSE attenuation profile with a general Stejskal–Tanner equation that explicitly includes the relaxation effects. The required values of T1 and T2 relaxation times are either independently measured with conventional sequences or determined, along with the fractions and the diffusion coefficients, from the simultaneous analysis of up to 6 PGSE data sets recorded with different diffusion delays. This method yields errors lower than 3% for the fractions, even for complete spectral overlap, as demonstrated on model binary and ternary mixtures of polystyrene in the case of a convection compensating double stimulated echo (DSTE) sequence.

Pyrazolium- versus Imidazolium-Based Ionic Liquids: Structure, Dynamics and Physicochemical Properties

Ionic liquids (ILs) composed of two different pyrazolium cations with dicyanamide and bis(trifluoromethanesulfonyl)imide anions have been synthesized and characterized by NMR, Kamlet-Taft solvatochromic parameters, conductivity and rheological measurements, as well as ab initio calculations. Density functional calculations for the two pyrazolium cations, 1-butyl-2-methylpyrazolium [bmpz] and 1-butyl-2,3,5-trimethylpyrazolium [bm(3)pz], provide a full picture of their conformational states. Homo- and heteronuclear NOE show aggregation motives sensitive to steric hindrance and the anions' nature. Self-diffusion coefficients D for the anion and the cation have been measured by pulsed field gradient spin-echo NMR (PGSE-NMR). The ionic diffusivity is influenced by their chemical structure and steric hindrance, giving the order D(cation) > D(anion) for all of the examined compounds. The measured ion diffusion coefficients, viscosities, and ionic conductivity follow the Vogel-Fulcher-Tammann (VFT) equation for the temperature dependencies, and the best-fit parameters have been determined. Solvatochromic parameters indicate an increased ion association upon going from bis(trifluoromethanesulfonyl)imide to dicyanamide-based pyrazolium salts, as well as specific hydrogen bond donor capability of H atoms on the pyrazolium ring. All of these physical properties are compared to those of an analogous series of imidazolium-based ILs.

Genistein Binding Mode to Doubly Nicked Dumbbell DNA. Dynamic and Diffusion Ordered NMR Study

New genistein derivatives were synthesized, which are fairly well soluble in water, with respect to parent genistein, and thus facilitate study of the interaction with dumbbell DNA dodecamer, mimicking the biological target for topoisomerase II inhibitors. A pulsed field gradient spin echo NMR experiment was used to check the binding and to estimate the association constants and its pH dependence of genistein with dumbbell DNA. Experimental restraints based on nuclear Overhauser spectroscopy spectra were used to calculate the NMR structure in solution in case of 6,8-disubstituted genistein with dimethylaminomethyl groups and were used in molecular modeling calculations. The structure is dynamic, and 10 molecular dynamics runs yield a family of conformations that essentially differ in a depth of inclusion of genistein into a nick. The paper experimentally shows evidence for binding, intercalation in the nick is proposed as a mode of genistein binding, and a model of the event is provided.

Designed post-self-assembly structural and functional modifications of a truncated tetrahedron.

Post-self-assembly modifications of a discrete metal-organic supramolecular structure have been developed. Such modifications allow the properties of the self-assembled supramolecular species to be changed in a simple and efficient manner (>90% yield). Initiated by the application of chemical stimuli, the post-self-assembly modifications described herein result in three distinct changes to the supramolecular system: an individual building-block component change, an overall structural modification, and a functional evolution of a [6+4] metal-organic supramolecular structure. The three modifications have been carefully examined by a range of characterization methods, including NMR and UV-vis spectroscopy, electrospray ionization mass spectrometry, pulsed field gradient spin echo NMR measurements, electrochemical analysis, and computational simulations.

Microemulsion Microstructure Influences the Skin Delivery of an Hydrophilic Drug

We aimed to investigate the influence of microemulsion nanoscale organization as either oil-in-water droplets, water-in-oil droplets, or bicontinuous structures on skin delivery of drugs assisted by microemulsions. Three microemulsions of different microstructure, o/w, w/o, and bicontinuous at the skin temperature (32°C), having the same oil and water contents and containing the same ingredients were selected using the Kahlweit fish phase diagrams method. The microemulsions are quaternary mixtures of the Polysorbate 21 (Tween®21) and Sorbitan monolaurate (Span®20) surfactants, isononyl isononanoate oil and water. The microemulsion nanostructure was characterized by electrical conductivity, Pulsed Field Gradient Spin-Echo NMR and Small-Angle Neutron Scattering measurements. The Franz cell method was used to monitor skin absorption of caffeine loaded in microemulsions over 24 h exposure to excised pig skin. Three microemulsions with the three structures were selected, keeping the same composition but the Tween®21/Span®20 ratio. The transdermal flux of caffeine was in the order aqueous solution ≈ w/o < bicontinuous < o/w microemulsion. The o/w microemulsion allows the permeation of 50% of the applied dose within 24 h. The structure of microemulsions is of relevance for skin absorption. The water-continuous structures allow faster transport of hydrophilic drugs.

Binding of small molecules to cavity forming mutants of a de novo designed protein

A central goal of protein design is to devise novel proteins for applications in biotechnology and medicine. Many applications, including those focused on sensing and catalysis will require proteins that recognize and bind to small molecules. Here, we show that stably folded α-helical proteins isolated from a binary patterned library of designed sequences can be mutated to produce binding sites capable of binding a range of small aromatic compounds. Specifically, we mutated two phenylalanine side chains to alanine in the known structure of de novo protein S-824 to create buried cavities in the core of this four-helix bundle. The parental protein and the Phe→Ala variants were exposed to mixtures of compounds, and selective binding was assessed by saturation transfer difference NMR. The affinities of benzene and a number of its derivatives were determined by pulse field gradient spin echo NMR, and several of the compounds were shown to bind the mutated protein with micromolar dissociation constants. These studies suggest that stably folded de novo proteins from binary patterned libraries are well-suited as scaffolds for the design of binding sites.

Temperature and Hydration-Dependent Rotational and Translational Dynamics of a Polyether Oligomer

Temperature-dependent rotational diffusion of tetraethylene glycol dimethyl ether (TEGDE) is measured by optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy and compared to previous measurements of rotational diffusion as a function of water content. Both types of data, temperature-dependent and hydration-dependent, follow the Debye-Stokes-Einstein (DSE) equation and agree quantitatively with hydrodynamic calculations. Of particular importance is the result that both types of data show nearly identical dependence on the viscosity divided by the temperature (η/T). We also compare the translational diffusion constants as previously measured by pulsed field gradient spin-echo (PFG-SE) NMR as a function of both temperature and water content. The temperature-dependent data follow the Stokes-Einstein (SE) equation. Similar to the rotation, the low water content mixtures obey the SE equation and show the same proportionality to η/T as the temperature-dependent data. At higher water fractions, the data do not obey the SE equation. The principal results are that the influence of temperature on dry TEGDE orientational relaxation is the same as the influence of water content at fixed temperature, and that the influence of temperature on translational diffusion of dry TEGDE is the same as the influence of water content over a range of relatively low water concentrations. The results demonstrate that there are no large TEGDE structural changes or specific, long-lived water-polyether interactions in the solutions over the entire concentration range.

Proton Transport Properties in Zwitterion Blends with Brønsted Acids

We describe zwitterion, 3-(1-butyl-1H-imidazol-3-ium-3-yl)propane-1-sulfonate (Bimps), mixtures with 1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methanesulfoneamide (HN(Tf)(2)) as new proton transport electrolytes. We report proton transport mechanisms in the mixtures based on results from several methods including thermal analyses, the complex-impedance method, and the pulsed field gradient spin echo NMR (pfg-NMR) method. The glass transition temperature (Tg) of the mixtures decreased with increasing HN(Tf)(2) concentration up to 50 mol %. The Tg remained constant at -55 °C with further acid doping. The ionic conductivity of HN(Tf)(2) mixtures increased with the HN(Tf)(2) content up to 50 mol %. Beyond that ratio, the mixtures showed no increase in ionic conductivity (10(-4) S cm(-1) at room temperature). This tendency agrees well with that of Tg. However, the self-diffusion coefficients obtained from the pfg-NMR method increased with HN(Tf)(2) content even above 50 mol % for all component ions. At HN(Tf)(2) 50 mol %, the proton diffusion of HN(Tf)(2) was the fastest in the mixture. These results suggest that Bimps cannot dissociate excess HN(Tf)(2), that is, the excess HN(Tf)(2) exists as molecular HN(Tf)(2) in the mixtures. The zwitterion, Bimps, forms a 1:1 complex with HN(Tf)(2) and the proton transport property in this mixture is superior to those of other mixing ratios. Furthermore, CH(3)SO(3)H and CF(3)SO(3)H were mixed with Bimps for comparison. Both systems showed a similar tendency, which differed from that of the HN(Tf)(2) system. The Tg decreased linearly with increasing acid content for every mixing ratio, while the ionic conductivity increased linearly. Proton transport properties in zwitterion/acid mixtures were strongly affected by the acid species added.

The Role of Ion Pairs in the Second‐Order NLO Response of 4‐X‐1‐Methylpiridinium Salts

A series of 4-X-1-methylpyridinium cationic nonlinear optical (NLO) chromophores (X = (E)-CH=CHC(6)H(5); (E)-CH=CHC(6)H(4)-4'-C(CH(3))(3); (E)-CH=CHC(6)H(4)-4'-N(CH(3))(2); (E)-CH=CHC(6)H(4)-4'-N(C(4)H(9))(2); (E,E)-(CH=CH)(2)C(6)H(4)-4'-N(CH(3))(2)) with various organic (CF(3)SO(3)(-), p-CH(3)C(6)H(4)SO(3)(-)), inorganic (I(-), ClO(4)(-), SCN(-), [Hg(2)I(6)](2-)) and organometallic (cis-[Ir(CO)(2)I(2)](-)) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second-order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second-order NLO response, investigated by the electric-field-induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10(-3) M, and their dipole moments were determined. Generally, below 5x10(-4) M, ion pairs start to dissociate into ions with parallel increase of the second-order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10(-3) M, some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second-order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self-aggregate.

Social Self-Sorting: Alternating Supramolecular Oligomer Consisting of Isomers

The isomers of cinnamoyl alpha-CDs (2-CiO-alpha-CD and 3-CiO-alpha-CD) organize by themselves to give different types of supramolecular complexes in aqueous solutions. 2-CiO-alpha-CD was found to form a double-threaded dimer, which was characterized by single crystal X-ray analysis. The molecular sizes of supramolecular complexes consisting of CiO-alpha-CDs were estimated by pulsed field gradient spin-echo NMR, which gives the diffusion coefficient (D). D of 2-CiO-alpha-CD was found to be 2.3 x 10(-10) m(2)/s at concentrations over 10 mM and D was saturated. It should be noted that the hydrodynamic radius derived from D of 2-CiO-alpha-CD was found to be 9.6 A, which closely matched the result from the single crystal X-ray analysis. D of 3-CiO-alpha-CD, however, was smaller than that of 2-CiO-alpha-CD at concentrations over 32 mM, indicating that 3-CiO-alpha-CD formed a supramolecular oligomer. Two-dimensional (2D)-ROESY spectra of the mixture of 2-CiO-alpha-CD and 3-CiO-alpha-CD did not show a correlation between the same species; rather, correlation peaks between 2-CiO-alpha-CD and 3-CiO-alpha-CD were observed. D's of a mixture of 2-CiO-alpha-CD and 3-CiO-alpha-CD were found to be larger than those of 2-CiO-alpha-CD and 3-CiO-alpha-CD, respectively, indicating that the mixture of 2-CiO-alpha-CD and 3-CiO-alpha-CD formed an alternative supramolecular oligomer and not a self- or random- supramolecular complex. CDs recognize a guest molecule and the substitutional position of a guest molecule on CD, suggesting that CDs have social self-sorting capability.

Ionic Liquid/Oil Microemulsions as Chemical Nanoreactors

The phase diagram and microstructure of the ternary system ionic, liquid benzylpyridinium bis(trifluoromethanesulfonyl)imide)/nonionic surfactant (octylphenol ethoxylate)/toluene, were studied by using conductivity measurements, dynamic light scattering, pulse field gradient spin-echo NMR, and small-angle neutron scattering. Three microregions were identified by conductivity measurements according to the percolation theory. The sizes of IL-in-oil microemulsions with various IL fractions were then determined by NMR and DLS and were found to be in accordance with the radii of gyration (approximately 2 or 3 nm) determined by SANS. The reverse IL-in-oil microemulsions were used as nanoreactors to perform a Matsuda-Heck reaction between p-methoxyphenyl diazonium salt and 2,3-dihydrofurane in the presence of a palladium catalyst. The reaction yields obtained were greater in microemulsions (67%) than in bulk IL (33%), highlighting a strong effect of confinement. Moreover, a direct correlation between the quantity of IL and the reaction yield was observed.

Neutral and cationic main group element cages of germanium(ii) with pyrazolyl ligands: solid state structures, DFT calculations and advanced solution NMR investigations

Two equivalents of 3,5-bis(trifluoromethyl)pyrazole or 5-methyl-3-(trifluoromethyl)pyrazole react with [Ge{N(SiMe(3))(2)}(2)] to give dimeric homoleptic germanium(ii) compounds [{Ge(3,5-RR'pz)(2)}(2)] (R = R' = CF(3) (1); R = Me, R' = CF(3) (2)), which provide cationic triply pz-bridged cages of the general formula [Ge(mu(2)-3,5-RR'pz)(3)Ge](+)[OTf](-) (R = R' = CF(3) (3); R = Me, R' = CF(3) (4)) upon treatment with one equivalent of triflic acid (HOTf, HSO(3)CF(3)). The compounds were studied using the pulsed field gradient spin-echo (PGSE) NMR technique and (19)F,(1)H-HOESY NMR methods. Single crystal X-ray structure determinations of all compounds are reported. The results obtained are verified by density functional theory calculations.

Molecular Motions and Ion Diffusions of the Room-Temperature Ionic Liquid 1,2-Dimethyl-3-propylimidazolium Bis(trifluoromethylsulfonyl)amide (DMPImTFSA) Studied by 1H, 13C, and 19F NMR

The diffusive properties of an imidazolium room-temperature ionic liquid (RTIL), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide (DMPImTFSA), are studied from the ionic conductivity and the ion diffusion coefficients measured by pulsed field gradient spin echo NMR. The temperature-dependent (1)H, (19)F, and (13)C NMR spin-lattice relaxation time T(1) values were observed, and the (1)H T(1) for DMPIm showed T(1) minima for various protons. According to the Bloemberger-Purcell-Pound (BPP) equation, the correlation time tau(c) values were directly calculated from (1)H NMR. By using the (1)H tau(c) values, an evaluation of the (13)C T(1) was attempted for the carbons having protons. The tau(c) estimated for molecular motions of DMPIm changes from 1.3 ns at 253 K to 72 ps at 353 K. The Stokes-Einstein-Debye (SED) model suggests that the tau(c) is too short for the overall molecular reorientation near room temperature. Consequently, the possibility of small-angle molecular rotation is proposed and tentative flip angles are calculated by using the translational diffusion coefficient, the bulk viscosity measured in this study, and the tau(c) obtained from (1)H T(1) data in the temperature range between 283 and 353 K. The flip amplitude increases with the temperature. DMPIm has isotropic reorientational motions with temperature-dependent amplitude, in addition to fast intramolecular motions such as methylene segmental motions, methyl rotational motion, and conformational exchange of the imidazolium ring. The existence of fast motions of TFSA is also shown. The translational diffusion of the ions is the slowest dynamic process in the present RTIL. Ab initio molecular orbital calculations are performed to understand the geometries of stable complexes of DMPIm(+) and TFSA(-), and the formation energies from the isolated ions are evaluated. The computed results are important for interpreting the (1)H T(1) behaviors observed for the imidazolium ring protons.

NMR structure of biosynthetic engineered human insulin monomer B31Lys-B32Argin water/acetonitrile solution. Comparison with the solution structure of native human insulin monomer

A solution NMR-derived structure of a new long -acting, B31(Lys)-B32(Arg) (LysArg), engineered human insulin monomer, in H(2)O/CD(3)CN, 65/35 vol %, pH 3.6, is presented and compared with the available X-ray structure of a monomer that forms part of a hexamer (Smith, et al., Acta Crystallogr D 2003, 59, 474) and with NMR structure of human insulin in the same solvent (Bocian, et al., J Biomol NMR 2008, 40, 55-64). Detailed analysis using PFGSE NMR (Pulsed Field Gradient Spin Echo NMR) in dilution experiments and CSI analysis prove that the structure is monomeric in the concentration range 0.1-3 mM. The presence of long-range interstrand NOEs in a studied structure, relevant to the distances found in the crystal structure of the monomer, provides the evidence for conservation of the tertiary structure. Therefore the results suggest that this solvent system is a suitable medium for studying the native conformation of the protein, especially in situations (as found for insulins) in which extensive aggregation renders structure elucidations in water difficult or impossible. Starting from the structures calculated by the program CYANA, two different molecular dynamics (MD) simulated annealing refinement protocols were applied, either using the program AMBER in vacuum (AMBER_VC), or including a generalized Born solvent model (AMBER_GB). Here we present another independent evidence to the one presented recently by us (Bocian et al., J Biomol NMR 2008, 40, 55-64), that in water/acetonitrile solvent detailed structural and dynamic information can be obtained for important proteins that are naturally present as oligomers under native conditions.

Advances in Hybrid Organic-Inorganic Proton Exchange Polymer Membranes Incorporating Heteropoly Acids

We describe a new class of materials for proton conduction for proton exchange membrane (PEM) fuel cell applications based on the heteropoly acids (HPAs). HPAs are readily functionalized by a variety of moieties including polymerizable organic groups. These hybrid monomers are polymerized into polypolyoxometallates (polyPOMs). The materials are characterized by IR, NMR, and SAXS. Proton diffusion coefficients are measured by Pulse Field Gradient Spin Echo NMR and are observed to increase with temperature. In-plane proton conductivity measurements show that performance similar to a state-of-the-art PFSA ionomer is obtained at 80 {degree sign}C and 100% RH. Conductivities at lower RH or higher temperature are not yet sufficiently high. For these first generation materials many problems still need to be addressed in order to fabricate materials with all the required properties for a next generation PEM.

A theoretical study of the biselective double pulsed field gradient spin-echo NMR experiment

The application of a biselective radiofrequency pulse to a coupled homonuclear spin system produces effects that are exploited in liquid-state NMR experiments. The insertion of such an RF pulse in a double pulsed field gradient spin echo sequence results in a module for the biselective production of antiphase magnetization states. Biselectivity is obtained through cosine modulation of a singly selective pulse profile. A full description of the module behaviour is possible by means of four parameters, of which two are related to a property called ‘pulse ellipticity’. The theory is in good agreement with the experimental results and numerical simulations. It is thus possible to predict how a maximum of antiphase magnetization can be produced.

Self-Assembly and Encoding of Polymer-Stabilized Gold Nanoparticles with Surface-Enhanced Raman Reporter Molecules

Polymer-stabilized gold nanoparticles (AuNPs) were prepared and encoded with a range of surface-enhanced Raman reporter molecules. A range of as-synthesized polymers produced by reversible addition fragmentation chain transfer (RAFT) polymerization were demonstrated to self-assemble at the surface of AuNPs dispersed in water. The method involved the coprecipitation of polymer-gold conjugates by the addition of polymer dissolved in a water-miscible solvent to gold AuNPs dispersed in water. This method represents a simplification of the preparation of polymer-stabilized AuNPs compared with other published methods, in that the AuNPs do not need to be first transferred to an organic solvent. The process enabled the polymer stabilized AuNPs to be easily recovered by filtration or by phase transfer of the AuNPs to an organic solvent in which the RAFT polymer was soluble. The polymer-stabilized AuNPs were characterized by a range of methods including UV-visible spectrophotometry, transmission electron microscopy, thermogravimetric analysis, dynamic light scattering, and attenuated total reflection Fourier transform infrared spectroscopy. Furthermore, 1H pulsed field gradient spin echo NMR was utilized to characterize the self-diffusion of the polymer-stabilized AuNPs. Finally, we then demonstrated that these polymer-stabilized AuNPs maintained their ability to be encoded with surface-enhanced Raman spectroscopy reporter molecules.

Method for modeling transport of particles in realistic porous networks: Application to the computation of NMR flow propagators

We model the transport of particles present in a fluid steadily flowing through a porous medium. The porous medium is described by a representative three-dimensional network. The particles are subjected to advection by the flow and to thermal diffusion. We propose to calculate their trajectories with the continuous time random walk framework. This enables us to efficiently sample disordered networks with realistic topology. The method proposed in this paper is general and can be adapted to model dispersion of tracers. It is applied here to simulate the measurement of the flow propagator [Formula: see text] which is defined as the ensemble density distribution of tracer displacements [Formula: see text], in a given time interval delta t. It can be extracted from pulsed magnetic field gradient spin echo NMR experiments carried out on porous media while fluid is flowing. Preliminary numerical results show good qualitative agreement with experiments.

Ultralarge Hyperpolarizability Twisted π-Electron System Electro-Optic Chromophores: Synthesis, Solid-State and Solution-Phase Structural Characteristics, Electronic Structures, Linear and Nonlinear Optical Properties, and Computational Studies

This contribution details the synthesis and chemical/physical characterization of a series of unconventional twisted pi-electron system electro-optic (EO) chromophores. Crystallographic analysis of these chromophores reveals large ring-ring dihedral twist angles (80-89 degrees) and a highly charge-separated zwitterionic structure dominating the ground state. NOE NMR measurements of the twist angle in solution confirm that the solid-state twisting persists essentially unchanged in solution. Optical, IR, and NMR spectroscopic studies in both the solution phase and solid state further substantiate that the solid-state structural characteristics persist in solution. The aggregation of these highly polar zwitterions is investigated using several experimental techniques, including concentration-dependent optical and fluorescence spectroscopy and pulsed field gradient spin-echo (PGSE) NMR spectroscopy in combination with solid-state data. These studies reveal clear evidence of the formation of centrosymmetric aggregates in concentrated solutions and in the solid state and provide quantitative information on the extent of aggregation. Solution-phase DC electric-field-induced second-harmonic generation (EFISH) measurements reveal unprecedented hyperpolarizabilities (nonresonant mubeta as high as -488,000 x 10(-48) esu at 1907 nm). Incorporation of these chromophores into guest-host poled polyvinylphenol films provides very large electro-optic coefficients (r(33)) of approximately 330 pm/V at 1310 nm. The aggregation and structure-property effects on the observed linear/nonlinear optical properties are discussed. High-level computations based on state-averaged complete active space self-consistent field (SA-CASSCF) methods provide a new rationale for these exceptional hyperpolarizabilities and demonstrate significant solvation effects on hyperpolarizabilities, in good agreement with experiment. As such, this work suggests new paradigms for molecular hyperpolarizabilities and electro-optics.