PGSE NMR Studies Research Articles

PGSE-NMR Study of a Series of New Silver–Carbosilane Dendrimers Displaying Different Coordination Modes

The first series of peripherally silver–phosphorus functionalized dendrimers have been obtained selectively using mono- or diphosphine-terminated carbosilane dendrimers and silver triflate. With the first kind of functionalized dendrimers, simple phosphine–Ag(OTf) terminal groups are formed, whereas in the second case, only one silver ion appears bonded to each diphosphine moiety (chelate form).

Size and shape assessment of organometallic gold(I) metallodendrimers through PGSE-NMR and molecular dynamics simulations

The reactions of the amino-terminated PAMAM-dendrimers (generations 0–2) with Ph2PCH2OH in the appropriate molar ratios give rise to the dendritic phosphines PAMAM-GZ-(N(CH2PPh2)2)n (Z=0, n=4 (1), Z=1, n=8 (2) and Z=2, n=16 (3)). Further reaction of phosphines 1–3 with one equivalent of [Au(C6F5)(tht)] (tht=tetrahydrothiophene) per P-donor site leads to metallodendrimers [{Au(C6F5)}2n{PAMAM-GZ-(N-(CH2PPh2)2)n}] (Z=0, n=4 (4), Z=1, n=8 (5) and Z=2, n=16 (6)). Phosphines 1–3 and metallodendrimers 4–6 have been characterized by 1H, 19F and 31P{1H} NMR spectroscopy and through IR spectroscopy. 1H PGSE NMR studies of the dendritic phosphines and the metallodendrimers permit the evaluation and comparison of the different molecular sizes through their corresponding hydrodynamic radius, depending on the dendrimer generation and on the coordination of the organometallic fragments [Au(C6F5)]. Molecular dynamics simulations allow the theoretical estimation of the macromolecular size through the calculation of the radius of gyration for each species and the calculation of the dendrimer flexibility.

Dendritic (phosphine)gold(i) thiolate complexes: assessment of the molecular size through PGSENMR studies

The reactions of the tetraphosphine ligand DAB-G0-(PPh2)4 (DAB = 1,4-diaminobutane; G0 = Generation 0) or the octaphosphine ligand DAB-G1-(PPh2)8 (G1 = Generation 1) with the gold precursor [AuCl(tht)] (tht =tetrahydrothiophene) and the corresponding 4-substituted benzenethiolate lead to the (phosphine)gold(I) thiolate complexes [Au4(S-C6H4-X)4[(DAB-G0-(PPh2)4]] (X = F (11), MeO (12), Me (13) and NO2 (14)) and [Au8(S-C6H4-X)8[(DAB-G1-(PPh2)4]] (X = F (15), MeO (16), Me (17) and NO2 (18)). Complexes [Au4Cl4[(DAB-G0-(PPh2)4]] and [Au4(S-C6H4-OMe)4[(DAB-G0-(PPh2)4]] have been characterized by X-ray diffraction studies showing tetranuclear gold complexes in which the P-Au-X (X = Cl or S) structural units do not display aurophilic interactions. PGSE NMR studies of free ligands EN-G0-(PPh2)(4) (EN = 1,2-ethylenediamine), DAB-G0-(PPh2)(4), DAB-G1-(PPh2)8 and the (phosphine)gold(I) thiolate complexes permit the evaluation and comparison of the different molecular sizes depending on the ligand and the dendrimer generation.

Synthesis, molecular structures and solution NMR studies of N-heterocyclic carbene–amine silver complexes

The synthesis of the Boc-protected 1-(2-aminoethyl)-3-methylimidazolium salts [BocNHCH 2CH 2ImMe]X [2]X (X = I, PF 6) and their straightforward transformation into [NH 2CH 2CH 2ImMe]X [3]X is reported. The reaction between [2]X and Ag 2O leads to the formation in the solid state of three different bonding motifs: a biscarbene salt [(NHC–NHBoc) 2Ag]PF 6 ( [4]PF 6, NHC–NHBoc = 1-(2-BocNH-ethyl)-3-methyl-imidazolin-2-ylidene), a tetranuclear complex [Ag(NHC–NHBoc) 2] 2[Ag 2I 4], ( 5), and a polymeric silver “staircase” [(NHC–NHBoc) 2–Ag 4–I 4] n , ( 6) composed of Ag 4I 4 clusters. The same reaction carried out with [3]I showed that a primary silver mono-NHC–NH 2 carbene complex of the type [(NHC–NH 2)AgI] ( 7) is likely to form but it is unstable in solution. The solid state molecular structures of [4]PF 6, 5 and 6 were determined by X-ray diffraction analysis, whereas PGSE NMR experiments were employed to investigate the hydrodynamic dimension of the imidazolium salts and silver complexes and, consequently, to gain information on the level of aggregation in solution. PGSE NMR studies were complemented by NOE NMR investigations in order to obtain information on anion–cation relative orientation within aggregates.

PGSE NMR Studies on RAPTA Derivatives: Evidence for the Formation of H-Bonded Dicationic Species

The self-aggregation tendency of RAPTA complexes {[Ru(η6-p-cymene){PTA(-R)}Cl2]X, R = H (1BPh4 and 1PF6) and Me (2BPh4 and 2OTf), and [Ru(η6-p-cymene)(PTA)2Cl]X (3BPh4 and 3BF4)} in acetone-d6 was ...

PGSE NMR Studies on DAB-Organo-Rhodium Dendrimers: Evaluation of the Molecular Size, Self-Aggregation Tendency, and Surface Metal Density

PGSE NMR measurements have been carried out for DAB-dendr-(NH2)n [n = 4 (Dab4), 8 (Dab8), 16 (Dab16), 32 (Dab32), and 64 (Dab64)] and DAB-dendr-[NH(O)COCH2CH2OC(O)C5H4Rh(NBD)]n [n = 4 (Rh-Dab4), 8 (Rh-Dab8), 16 (Rh-Dab16), 32 (Rh-Dab32), and 64 (Rh-Dab64)] in CD2Cl2 and CD3OD as a function of the concentration. The hydrodynamic radius (rH) and, consequently, the hydrodynamic volume (VH) of all the species are determined from the measured translational self-diffusion coefficients (Dt). In CD2Cl2, both Dab and Rh-Dab dendrimers show a tendency toward self-aggregation that increases with the generations. In addition, while the radii rH for Dab dendrimers is ca. 20−30% higher in CD3OD than in CD2Cl2, the rH values for Rh-Dab dendrimers are only slightly influenced by solvent variation. To estimate the Rh−Rh spatial proximity (dRh/Rh) on the surface, the internal radius (rint) of the Dab skeleton in Rh-Dab dendrimers was (i) considered equal to that of the Dab dendrimers (model A) or (ii) evaluated assuming that the additional solvent molecules derived from the attachment of Rh to Dab dendrimers were incorporated into the elongated dendritic skeleton (model B). It was found that dRh/Rh decreases from 17.2−19.8 Å (Rh-Dab4) to about 14.0 Å (Rh-Dab64) with the increase in dendrimer generation.

H 2O self-diffusion restricted by clay platelets with immobilized bound H 2O layers: PGSE NMR study of water-rich saponite gels

The role of bound or less-mobile H 2O layers near negatively charged clay platelets in water-rich saponite gels as obstacles to the diffusion of unbound H 2O molecules in the pore-space was examined. Self-diffusion coefficients of H 2O molecules, D, in gels of synthetic Na-rich saponite were measured by pulsed-gradient spin-echo proton nuclear magnetic resonance (PGSE proton NMR) to evaluate these obstruction effects. The clay weight fraction, w, of the gel samples ranged from 0.0 to 27.9 wt.% and the sample temperature was 20.0 to 60.6 °C. The NMR results showed that D normalized by D 0 was independent of sample temperature and decreased with increasing w: ln( D/ D 0)=1.33[exp(−0.0290 w)−1] where D 0 was D in bulk water. This diffusion behavior was interpreted through random-walk computer simulations of a gel-structure model originally developed for montmorillonite, hectorite and stevensite. In the model, unbound H 2O diffuses in the porous gel structure by avoiding randomly distributed obstacles representing clay platelets sandwiched between completely immobilized bound H 2O layers. A quantitative dependence of the platelet volume fraction and the bound H 2O layers thickness on D/ D 0 was obtained by the simulations. The ratio, χ=(volume of clay platelets and immobilized H 2O layers)/(volume of clay platelets), was introduced as a measure of the thickness of the immobilized H 2O layers. χ was estimated to be 5.7 for water-rich saponite gels ( w≤7.99 wt.%) by fitting the results of the random-walk simulation to the PGSE NMR diffusion data. This value corresponds to an immobilized bound H 2O layer thickness of 2.4 nm assuming that each clay particle in the gels consists of a single 1-nm-thick platelet. The thickness of immobilized H 2O layers in water-rich gels of six smectite species was identified on this basis to decrease in the following order: montmorillonite ( χ=18, 13)>saponite ( χ=5.7)>hectorite ( χ=4.2, 4.0)>stevensite ( χ=3.6). This order correlates well with the order of the cation exchange capacity (CEC), suggesting that the thickness of the bound H 2O layers increases with increasing layer charge. The present study confirmed that the gel-structure model developed previously for montmorillonite, hectorite and stevensite was also applicable to saponite.

Growth of C12E8Micelles with Increasing Temperature. A Convection-Compensated PGSE NMR Study

ADVERTISEMENT RETURN TO ISSUEPREVNoteGrowth of C12E8 Micelles with Increasing Temperature. A Convection-Compensated PGSE NMR StudyN. Hedin, T. Y. Yu, and I. FuróView Author Information Division of Physical Chemistry, Department of Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden, and Department of Chemistry, National Taiwan University, TA-10764 Taipei, Taiwan Cite this: Langmuir 2000, 16, 19, 7548–7550Publication Date (Web):August 18, 2000Publication History Received20 April 2000Revised26 June 2000Published online18 August 2000Published inissue 1 September 2000https://doi.org/10.1021/la000595bCopyright © 2000 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views434Altmetric-Citations44LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (39 KB) Get e-AlertsSUBJECTS:Diffusion,Heat transfer,Micelles,Molecules,Surfactants Get e-Alerts

PGSE NMR studies of water states of hydrogel P(Am–NaA)

PGSE NMR studies of water states of hydrogel P(Am–NaA)

PGSE NMR studies of water states of hydrogel P(Am–NaA)

PGSE NMR studies of water states of hydrogel P(Am–NaA)

Mixed Micellar Aggregates of Anionic and Nonionic Surfactants with Short Hydrophobic Tails. A PGSE-NMR Study

Intradiffusion coefficients for the ternary system heavy water−sodium hexanesulfonate (C6SNa)−pentaethylene glycol monohexyl ether (C6E5), in both the premicellar and micellar composition ranges, were measured by the PGSE-NMR technique at 25 °C. Experimental data show the formation of mixed micelles and allow the determination of the cmc. In the premicellar composition range the monomer−monomer interactions are analyzed. The compositions of the aqueous and micellar pseudophase have been computed in the whole micellar composition range; they indicate that C6E5 has a larger tendency to form aggregates than C6SNa. The aggregation number and the free energy of micellization are calculated and interpreted in terms of interactions among the tensides in the micellar aggregates. The experimental results have been interpreted in terms of a regular solution model, and the interaction parameter β is computed. β increases by increasing the number of micellar aggregates in the system; this effect can be interpreted in terms of intermicellar interactions.

NMR and fractal modelling studies of transport in porous media

Magnetic Resonance Imaging (MRI) and PGSE NMR studies have shown that it is necessary to consider heterogeneities in the porous structure over different lengthscales in order to be able to understand the relationship between structure and transport in porous solids. Moreover, the spatial distribution in pore structure is seen to influence strongly mass transfer processes occurring within the porous medium. The MRI studies described here have suggested that a fractal representation might be appropriate in describing heterogeneous porous systems. Numerical simulations have been performed of transport within Cluster-Cluster Aggregate (CCA) structures. A comparison of methods of simulating the diffusion process is presented. The results of the simulations are compared with MRI and PGSE NMR measurements of the tortuosity of commercial catalyst pellets. In the light of complementary nitrogen desorption and mercury porosimetry data, a multifractal description of porous media is also proposed in the form of a Composite CCA structure in which both the macroscopic heterogeneity associated with the pore-size distribution and the fractal characteristics of the microscopic pore structure itself are represented.

Role of Molecular Architecture in Polymer Diffusion: A PGSE-NMR Study of Linear and Cyclic Poly(ethylene oxide)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRole of Molecular Architecture in Polymer Diffusion: A PGSE-NMR Study of Linear and Cyclic Poly(ethylene oxide)P. C. Griffiths, P. Stilbs, G. E. Yu, and C. BoothCite this: J. Phys. Chem. 1995, 99, 45, 16752–16756Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/j100045a041RIGHTS & PERMISSIONSArticle Views384Altmetric-Citations45LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (597 KB) Get e-Alerts

Self‐Diffusion of Charged Polycyclic Systems and Their Parent Compounds: A PGSE NMR Study

Self-diffusion coefficients of a series of polycyclic charged systems and their parent compounds were measured by using the PGSE NMR method. These data suggest that the dianions of naphthacene 2 and pyracylene 3 may exist as dimers with sandwich structure, just like the lithium salt of the tetraanion of corannulene 1.

Transport heterogeneity in porous pellets—II. NMR imaging studies under transient and steady-state conditions

In the first paper of this study, PGSE NMR was used to measure liquid diffusion in porous catalyst support pellets. The results were explained in terms of heterogeneity in the structure and transport properties of these materials. In this part of the study, NMR imaging is used to study diffusion within the same samples. By acquiring a series of images during the course of a transient diffusion process, it is possible to estimate the effective diffusivity of water confined within the pore space of the pellets. NMR imaging is also used to produce two-dimensional images which show clearly that porous catalyst support pellets contain significant heterogeneities, as suggested by the spatially non-resolved PGSE NMR experiments presented in Paper I (Hollewand and Gladden, Chem. Eng. Sci. 50, 309–326, 1995). Finally, the PGSE and imaging NMR experiments are combined to produce images of the local diffusivity of water contained within individual pellets. These images allow the degree of diffusional heterogeneity to be quantified and give results in agreement with the PGSE NMR study. The results demonstrate that it is necessary to consider heterogeneities in the porous structure over different lengthscales in order to be able to understand the relationship between structure and transport in porous solids.