2D HETCOR Research Articles

Secondary Structures in a Freeze-Dried Lignite Humic Acid Fraction Caused by Hydrogen-Bonding of Acidic Protons with Aromatic Rings.

A lignite humic acid (HA) was separated from inorganic and non-HA impurities (i.e., aluminosilicates, metals) and fractionated by a combination of dialysis and XAD-8 resin. Fractionation revealed a more homogeneous structure of lignite HA. New and more specific structural information on the main lignite HA fraction is obtained by solid-state nuclear magnetic resonance (NMR) spectroscopy. Quantitative (13)C multiple cross-polarization (multiCP) NMR indicated oxidized phenyl propane structures derived from lignin. MultiCP experiments, conducted on potassium HA salts titrated to pH 10 and pH 12, revealed shifts consistent with carboxylate and phenolate formation, but structural changes associated with enolate formation from aromatic beta keto acids were not detected. Two-dimensional (1)H-(13)C heteronuclear correlation (2D HETCOR) NMR indicated aryl-aliphatic ketones, aliphatic and aromatic carboxyl groups, phenol, and methoxy phenyl ethers. Acidic protons from carboxyl groups in both the lignite HA fraction and a synthetic HA-like polycondensate were found to be hydrogen-bonded with electron-rich aromatic rings. Our results coupled with published infrared spectra provide evidence for the preferential hydrogen bonding of acidic hydrogens with electron-rich aromatic rings rather than adjacent carbonyl groups. These hydrogen-bonding interactions likely result from stereochemical arrangements in primary structures and folding.

Fast experiments for structure elucidation of small molecules: Hadamard NMR with multiple receivers.

We propose several significant improvements to the PANSY (Parallel NMR SpectroscopY) experiments-PANSY COSY and PANSY-TOCSY. The improved versions of these experiments provide sufficient spectral information for structure elucidation of small organic molecules from just two 2D experiments. The PANSY-TOCSY-Q experiment has been modified to allow for simultaneous acquisition of three different types of NMR spectra-1D C-13 of non-protonated carbon sites, 2D TOCSY and multiplicity edited 2D HETCOR. In addition the J-filtered 2D PANSY-gCOSY experiment records a 2D HH gCOSY spectrum in parallel with a (1) J-filtered HC long-range HETCOR spectrum as well as offers a simplified data processing. In addition to parallel acquisition, further time savings are feasible because of significantly smaller F1 spectral windows as compared to the indirect detection experiments. Use of cryoprobes and multiple receivers can significantly alleviate the sensitivity issues that are usually associated with the so called direct detection experiments. In cases where experiments are sampling limited rather than sensitivity limited further reduction of experiment time is achieved by using Hadamard encoding. In favorable cases the total recording time for the two PANSY experiments can be reduced to just 40 s. The proposed PANSY experiments provide sufficient information to allow the CMCse software package (Bruker) to solve structures of small organic molecules.

Crystal structures of [η5-C5H4CR(SCH2)2]Cr(NO)2X (R = H, X = Cl or I; R = CH3, X = Cl) and unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of dicarbonyl(η5-cyclopentadienyl)nitrosylchromium, chloro(η5-cyclopentadienyl)dinitrosylchromium, (η5-cyclopentadienyl)iododinitrosylchromium, and (η5-cyclopentadienyl)methyldinitrosylchromium, bearing an electron-donating substituent via induction in 13C NMR spectra

After thioacetalization with 1,2-ethanedithiol complexes (η5-C5H4COR)Cr(CO)2(NO) (R=H, CH3) were converted to [η5-C5H4CR(SCH2)2]Cr(CO)2(NO). Chlorination/nitrosylation of the latter with hydrogen chloride/isoamyl nitrite gave [η5-C5H4CR(SCH2)2]Cr(NO)2Cl (R=H 2f, CH32g). Those complexes were converted to iodide analog, [η5-C5H4CR(SCH2)2]Cr(NO)2I (R=H 3f, CH33g) with potassium iodide. The diastereotopism of the two sets of methylene hydrogens on the dithiolanyl substituent was observed in 1H NMR spectra of 2f and 3f, but not in those of 2g and 3g. The environmental disparity revealed by X-ray structures may account for it. Based on the 2D HETCOR, the H(2,5) resonates at a lower field than H(3,4) on the Cp(Cr) ring in 3g, as ferrocene analog (η5-C5H4CH2CH3)FeCp, opposite to CpCr(CO)2(NO) analog (η5-C5H4CH2CH3)Cr(CO)2(NO). The electron density distribution in the cyclopentadienyl ring was discussed on the basis of 13C NMR data and was compared with calculations using the density functional B3LYP exchange–correlation method for those with X-ray diffraction studies.

Selective excitation enables assignment of proton resonances and (1)H-(1)H distance measurement in ultrafast magic angle spinning solid state NMR spectroscopy.

Remarkable developments in ultrafast magic angle spinning (MAS) solid-state NMR spectroscopy enabled proton-based high-resolution multidimensional experiments on solids. To fully utilize the benefits rendered by proton-based ultrafast MAS experiments, assignment of (1)H resonances becomes absolutely necessary. Herein, we propose an approach to identify different proton peaks by using dipolar-coupled heteronuclei such as (13)C or (15)N. In this method, after the initial preparation of proton magnetization and cross-polarization to (13)C nuclei, transverse magnetization of desired (13)C nuclei is selectively prepared by using DANTE (Delays Alternating with Nutations for Tailored Excitation) sequence and then, it is transferred to bonded protons with a short-contact-time cross polarization. Our experimental results demonstrate that protons bonded to specific (13)C atoms can be identified and overlapping proton peaks can also be assigned. In contrast to the regular 2D HETCOR experiment, only a few 1D experiments are required for the complete assignment of peaks in the proton spectrum. Furthermore, the finite-pulse radio frequency driven recoupling sequence could be incorporated right after the selection of specific proton signals to monitor the intensity buildup for other proton signals. This enables the extraction of (1)H-(1)H distances between different pairs of protons. Therefore, we believe that the proposed method will greatly aid in fast assignment of peaks in proton spectra and will be useful in the development of proton-based multi-dimensional solid-state NMR experiments to study atomic-level resolution structure and dynamics of solids.

Co(II), Ni(II), Cu(II) and Zn(II) complexes of isatinyl‐2‐aminobenzoylhydrazone: synthesis, characterization and anticancer activity

This article describes the synthesis, structural aspects and biological studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes of a new hydrazone derived from the condensation of isatin and 2‐aminobenzoylhydrazide. The ligand is well characterized using 1H NMR, 13C NMR, 2D HETCOR, mass and IR spectral studies. The chelating tendency of the ligand towards transition metal ions is established using analytical and spectral studies, which reveal the monobasic tridentate nature of the ligand. Octahedral geometry for Co(II), Cu(II) and Zn(II) and tetrahedral geometry for Ni(II) are tentatively proposed. All the synthesized compounds were screened for in vitro anticancer activity against Ehrlich ascites carcinoma and human cancer cell lines (adenocarcinoma HT29, kidney cancer cell line K293 and breast cancer cell line MDA231) using tryphan blue exclusion method and MTT assay. Copyright © 2014 John Wiley & Sons, Ltd.

Mannich Reaction as a New Route for the Synthesis of Tetrahydro Pyrimido Benzimidazolyl Coumarins

Condensation of coumarin‐4‐acetic acids (1) with ortho‐phenylenediamine (2) in anhydrous phosphoric acid afforded 4‐((1H‐benzo[d]imidazol‐2‐yl)methyl)‐2H‐chromen‐2‐ones (3). Attempted Mannich reaction of 3 with formalin and primary amines resulted in 4‐(2‐phenyl‐1,2,3,4‐tetrahydrobenzo[4,5]imidazo[1,2‐c]pyrimidin‐4‐yl)‐2H‐chromen‐2‐ones (6). The structures of synthesized compounds were elucidated by analyses including 2D HETCOR and DEPT experiments. Synthesized compounds have been subjected for anti‐inflammatory activity. Compound 6j exhibited promising anti‐inflammatory activity.

Identifying Selective Host–Guest Interactions Based on Hydrogen Bond Donor–Acceptor Pattern in Functionalized Al-MIL-53 Metal–Organic Frameworks

We present a study analyzing the selectivity of host–guest interactions in a series of functionalized Al-MIL-53-X metal–organic frameworks with X = H, NH2, and NHCHO using acetone, ethanol, and water as probe molecules. While the amino group introduces additional hydrogen bond donor centers the NHCHO anchors function as donor and acceptor. The guests were chosen due to their ability to act solely as an acceptor in the case of acetone, whereas ethanol and water provide acceptor and donor qualities with a gradual decrease of the acceptor strength toward ethanol. The characterization of the host–guest interactions includes a comprehensive solid-state NMR spectroscopic study based on a full assignment of 1H and 13C high-resolution spectra using CRAMPS decoupling schemes to enhance 1H resolution combined with advanced 2D HETCOR (1H–13C, 1H–27Al, and 1H–14N) spectra at high magnetic fields. In spite of a pronounced dynamical disorder of the guests, we could identify a preferred binding of the acetone via a NH··...

NMR-crystallographic study of two-dimensionally self-assembled cyclohexane-based low-molecular-mass organic compounds

Using a combined approach based on scanning electron microscopy, powder X-ray diffraction as well as 1D and 2D multinuclear solid-state NMR spectroscopy, we were able to determine the morphology and the crystal structures for a set of three supramolecular compounds with different hydrogen bonding motifs, namely N,N′-(cyclohexane-trans-1,4-diyl)bis(2,2-dimethylpropanamide) 1, 1,1′-(cyclohexane-trans-1,4-diyl)bis(3-tert-butylurea) 2 and N1,N4-bis(tert-butylcarbamoyl)cyclohexane-trans-1,4-dicarboxamide 3. Based on a complete signal assignment of the 1D solid-state MAS NMR spectra (1H, 13C, 15N) employing 2D HETCOR experiments and a quantitative evaluation of the corresponding resonances, the content of the asymmetric unit was determined to one half of a molecule. Probing the molecular configuration with 1H–1H double-quantum experiments revealed an intramolecular hydrogen bond for compound 3 while 1 and 2 form exclusively intermolecular H-bonds. Ab initio structure solutions applying real space methods with an included close-contact penalty were carried out for all compounds. The following Rietveld refinements led to excellent wRp-values between 2.5% and 4.1%. Compounds 1 and 2 crystallise isostructurally in the monoclinic space group P21/c exhibiting a pseudo-biaxial hydrogen bond motif. 3 crystallises in the triclinic space group P with intermolecular head-to-tail hydrogen bonds connecting the molecules to one-dimensional ribbons. Nevertheless, all compounds grow in a sheet-like morphology with lateral dimensions of several hundred micrometres indicating a fast growth in two dimensions along two of the crystal axes. Since all three molecules possess inversion symmetry cancelling the molecular dipole moment the growth mechanism itself has to be dominantly driven by the formation of hydrogen bond networks.

Synthesis of 15‐, 16‐, and 17‐Membered Bis‐C‐Pivot Macrocycles Consisting of N2O2 Donor‐Type Crown Ethers and Dialkyl Phosphonates

ABSTRACTBis‐C‐pivot macrocycles containing aminophosphonate functions (5–10) have been synthesized and characterized by elemental analysis, FTIR, MS, 1D 1H, 13C and 31P NMR, and 2D HETCOR techniques. The phosphorylation reaction of dibenzo‐bis‐imino crown ethers (1–4) with dimethyl and diethyl phosphite used here has the potential to provide bis‐C‐pivot macrocycles (5–10), which possess two stereogenic C‐centers giving rise to diastereoisomers (meso and racemic). Detailed spectral assignments for the meso and racemic forms of the compounds are reported on the basis of chemical shifts, signal intensities, spin–spin coupling constants, and splitting patterns. The bis‐C‐pivot macrocycles (5–10) may serve as a potential new class of supramolecular host molecules.

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

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

Characterization of heterogeneities and domains in aquatic and sedimentary organic matter by 1H spin diffusion: Potential for elucidating the formation mechanisms

Although the information on domains and heterogeneities of natural organic matter (NOM) can provide insights into its formation mechanisms, the appropriate solid‐state NMR technique for measuring them is still lacking. The traditional technique requires mobility differences in NOM whereas NOM components are primarily rigid. We introduced a new 1H spin diffusion technique, 1H‐13C two‐dimensional heteronuclear correlation (2D HETCOR) NMR with 1H spin diffusion, for characterization of domains and heterogeneities in aquatic and sedimentary organic matter. It was achieved by collecting a series of 2D HETCOR spectra with a variable mixing time, tm, and monitoring the transfer of magnetization from one component to another. The rate of magnetization transfer provided the information on domains and heterogeneities because the magnetization of small domains or heterogeneities equilibrated faster than that of larger ones. Three samples, International Humic Substances Society (IHSS) Suwannee River NOM, IHSS Suwannee River humic acid (HA), and a sedimentary HA, were used. Two model polymers, a random copolymer poly(styrene‐n‐butyl methacrylate) with 0.6‐nm heterogeneity and a block copolymer polystyrene‐b‐poly(methyl methacrylate) with a domain size of 5 nm, were included for calibration. Within tm < 100 µs, half equilibration was reached for all three NOM samples and poly(styrene‐n‐butyl methacrylate), indicating that they were heterogeneous. In contrast, the spin diffusion of polystyrene‐b‐poly(methyl methacrylate) with 5‐nm domain was much slower. Unlike the traditional spin diffusion technique, this technique did not require the differential mobility in NOM and was suitable for investigating the domains and heterogeneities of NOM, which are mostly rigid.

Syntheses, spectroscopic properties and stereochemistry of bis-C-pivot macrocycles with two dialkyl phosphonate groups

Bis-C-pivot macrocycles containing dimethyl ( 1a, 2a) or diethyl phosphonate ( 1b, 2b) groups have been prepared by adding dimethyl or diethyl phosphite to two –CH N bonds in corresponding dibenzo-bis-imino crown ethers ( 1 and 2). Bis-C-pivot macrocycles possess two equivalent stereogenic centres giving rise to diastereoisomers ( meso and racemate). The structures were characterized by elemental analysis, FTIR, MS, TGA, DSC and NMR measurements. 1H, 13C and 31P NMR assignments were made for the isolated meso form of compounds 2a and 2b and for the meso and racemic forms of compounds 1a and 1b by analysis of chemical shifts, signal intensities and splitting patterns and the DEPT and 2D HETCOR NMR techniques. Thermal analysis and 1H NMR showed that the crystallised form of compound 1a contained an equimolar amount of water of crystallisation.

Synthesis, characterization, anti‐inflammatory and analgesic activity of transition metal complexes of 3‐[1‐(2‐hydroxyphenyl) ethylideamino]‐2‐phenyl‐3,4‐dihydroquinazolin‐4(3H)‐one

AbstractA new quinazolinone derivative, 3‐[1‐(2‐hydroxyphenyl)ethylideamino]‐2‐phenyl‐3,4‐dihydroquinazolin‐4(3H)‐one (LH) was synthesized by the condensation of 2‐hydroxyacetophenone‐2‐aminobenzoylhydrazone and benzaldehyde. The cyclization to form 1,2‐dihydroquinazolinone was confirmed by IR, 1D and 2D HETCOR studies. Coordination compounds of Co(II), Ni(II), Cu(II) and Zn(II) of LH were synthesized and characterized using various physico‐chemical studies like stoichiometric, conductivity, magnetic moment measurements and spectral techniques such as IR, NMR, UV‐vis and EPR spectroscopy. The elemental analysis and thermal studies suggested a general stoichiometry [M(HEPDQ)Cl] for all the complexes. A four‐coordinate geometry was assigned to all the complexes. The complexes along with the parent ligand were screened for their anti‐inflammatory activity, using carrageenan‐induced rat paw edema, and for their analgesic activity by Eddy's hot plate method. The activity of the ligand was enhanced on complexation with metal ions. This enhanced activity was attributed to the increased lipophilic nature of the complexes. Notable anti‐inflammatory activity was observed for Ni(II), Cu(II) and Zn(II) complexes. The analgesic activity of the ligand was greater than the standard at 60 min. and at a 10 mg kg−1 dose, whereas the activity of Ni(II) and Cu(II) complexes at 10 mg kg−1 dose was comparable with the standard used. Copyright © 2011 John Wiley & Sons, Ltd.

Characterization of humic substances by advanced solid state NMR spectroscopy: Demonstration of a systematic approach

Characterization of humic substances is challenging due to their structural complexity and heterogeneity. Solid state nuclear magnetic resonance (NMR) is regarded as one of the best tools for elucidating structures of humic substances. The primary solid state NMR technique that has been used so far is the routine 13C cross polarization-magic angle spinning (CP-MAS) technique. Although this technique has markedly advanced our understanding of humic substances, the full potential of NMR for characterizing humic substances has yet to be realized. Recent technical developments and applications of advanced solid state NMR have revealed the promise to provide deeper insights into structures of humic substances. In this paper, we summarized and demonstrated the systematic solid state NMR protocol for characterization of humic substances using a humic acid as an example. This protocol included (1) identification of specific functional groups using spectral editing techniques, occasionally assisted by 1H 13C two-dimensional heteronuclear correlation (2D HETCOR) NMR, (2) quantification of specific functional groups based on direct polarization-magic angle spinning (DP-MAS) and DP-MAS with recoupled dipolar dephasing, combined with spectral editing techniques, (3) determination of connectivities and proximities of specific functional groups by 1H 13C 2D HETCOR or 2D HETCOR combined with spectral editing techniques, and (4) examination of domains and heterogeneities by 1H 13C 2D HETCOR with 1H spin diffusion. We used a soil humic acid as an example to demonstrate how this protocol was applied to the characterization of humic substances step by step. Afterwards, based on typical 13C NMR spectra of humic substances we described how we could combine different NMR techniques to identify specific functional groups band by band from downfield to upfield. Finally, we briefly mentioned the potential new NMR techniques that could be developed to enrich the current systematic protocol. This systematic protocol is not only applicable to humic substances but also to other natural organic matter samples.

A solid-state NMR study of structure and segmental dynamics of poly(propylmethacryl-heptaisobutyl-pss)-co-styrene nanocomposites

The domain structure and mobility of poly(propylmethacryl-heptaisobutyl-pss)-co-styrene nanocomposites with different polyhedral oligomeric silsesquioxane (POSS) contents were investigated by various solid-state NMR techniques in combination with XRD. The NMR relaxation time measurements suggested that increasing POSS content trended to mobilize the chains in PS unit. Although XRD results showed that POSS was well dispersed into the polymer matrix, 2D WISE NMR indicated that the dispersion of POSS into the polymer matrix led to a composite structure composed of rigid and densely packed PS domain and mobile and amorphous POSS domain. This implied that the size of the two domains was very small. 2D HETCOR NMR implied that the distance between PS network and POSS unit gradually decreased when the POSS content successively increased. The dispersed POSS domain size determined by 2D spin-diffusion NMR experiments was increased with the POSS loading, being about 3.0, 3.9, 6.0 nm for the POSS15, POSS25 and POSS45 nanocomposites, respectively.

Chemical Structures of Corn Stover and Its Residue after Dilute Acid Prehydrolysis and Enzymatic Hydrolysis: Insight into Factors Limiting Enzymatic Hydrolysis

Advanced solid-state NMR techniques and wet chemical analyses were applied to investigate untreated corn stover (UCS) and its residues after dilute acid prehydrolysis (DAP) and enzymatic hydrolysis (RES) to provide evidence for the limitations to the effectiveness of enzyme hydrolysis. Advanced solid-state NMR spectral-editing techniques as well as 1H-13C two-dimensional heteronuclear correlation NMR (2D HETCOR) were employed. Our results indicated that dilute acid prehydrolysis selectively removed amorphous carbohydrates, increased aromatic CH/other protonated -C═C- and enriched alkyl CH and CH2 components. Cinnamic acids were increased, and proteinaceous materials and N-containing degradation or condensation compounds were absorbed or coprecipitated in RES. 2D HETCOR experiments indicated a close association between lignin and the residual carbohydrates. Ketones/aldehydes were not detected in the DAP, in contrast to a report in which an appreciable amount of ketones/aldehydes was generated from the acid pretreatment of a purified cellulose in the literature. This suggested that acid pretreatment may modify the structure of purified cellulose more than biomass and that biomass may be a better substrate than model biopolymers and compounds for assessing structural changes that occur with industrial processing. On the basis of NMR and wet chemical analyses, we found the following factors could cause the limitations to the effectiveness of enzymatic hydrolysis: (1) chemical modification of carbohydrates limited the biologically degradable carbohydrates available; (2) cinnamic acids in the residue accumulated; (3) accessibility was potentially limited due to the close association of carbohydrates with lignin; and (4) proteinaceous materials and N-containing degradation or condensation compounds were absorbed or coprecipitated.

Spectroscopic, magnetic and thermal studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes of 3-acetylcoumarin–isonicotinoylhydrazone and their antimicrobial and anti-tubercular activity evaluation

Co(II), Ni(II), Cu(II) and Zn(II) complexes with a new heterocyclic Schiff base derived by the condensation of isonicotinoylhydrazide and 3-acetylcoumarin have been synthesized. 1H, 13C and 2D HETCOR NMR analyses confirm the formation of title compound and existence of the same in two isomeric forms. The metal complexes were characterized on the basis of various spectroscopic techniques like electronic, EPR, IR, 1H and 13C NMR studies, elemental analysis, magnetic properties and thermogravimetric analysis, and also by the aid of molar conductivity measurements. It is found that the Schiff base behaves as a monobasic tridentate ligand coordinating in the imidol form with 1:1 metal to ligand stoichiometry. Trigonal bipyramidal geometry has been assigned for Ni(II) and Cu(II) complexes, while tetrahedral for Co(II) and Zn(II) complexes. The compounds were subjected to antimicrobial and anti-tubercular activity screening using serial broth dilution method and Minimum Inhibitory Concentration (MIC) is determined. Zn(II) complex has shown significant antifungal activity with an MIC of 6.25 μg/mL while Cu(II) complex is noticeable for antibacterial activity at the same concentration. Anti-TB activity of the ligand has enhanced on complexation with Co(II) and Ni(II) ions.

ChemInform Abstract: Chromones and Flavanones from Artemisia campestris subsp. maritima.

Abstract From the acetone extract of Artemisia campestris subsp. maritima six flavanones, two chromones and the coumarin scopoletin were isolated. 5-Hydroxy-7-methoxychromone and 5,7-dimethoxychromone are new compounds, while the flavanone eriodictyol-7,3′-dimethyl ether is reported for the first time in this species. The structures were elucidated by 1D and 2D NMR techniques. The unequivocal assignments of carbon resonances, mainly made by using 1D selective INEPT and 2D HETCOR experiments, allowed us to correct some 1H and 13C resonances of the isolated flavanones and also to differentiate between the flavanone isomers sakuranetin⧹isosakuranetin and eriodictyol-7,3′-dimethyl ether⧹eriodictyol-7,4′-dimethyl ether.

Intramolecular hydrogen bonding and tautomerism in Schiff bases: Part VI. Syntheses and structural investigation of salicylaldimine and naphthaldimine derivatives

Salicyclaldimines (5–9) and naphthaldimines (10–13) derived from condensation reactions of N2O2 donor type bifunctional aminopodands (1–4), [(H2NPhO)2R, where R = CH2CH2, CH2CH2CH2 and CH2PhCH2], and hydrazine monohydrate with salicylaldehyde and 2-hydroxy-1-naphthaldehyde, respectively, have been prepared (scheme 1) and characterized by elemental analyses, UV-vis, FTIR, NMR and MS. NMR assignments were made using 1H, 13C NMR, DEPT and aided by 2D HETCOR and HMBC heteronuclear correlation techniques. The UV-vis spectra of the Schiff bases have been systematically studied in organic solvents of different polarity, acidic and basic media and found useful in understanding of tautomeric equilibria (phenol-imine, O-H…N and keto-amine, O…H-N forms) in this series. The molecular structure of 8 has been determined crystallographically, and observed that the compound is in the form of phenol-imine, defined by the strong intramolecular [O-H…N = 1·72(3), 1·81(2) Å] hydrogen bonds. Compound 8 crystallizes in the monoclinic space group P21/a with a = 8·4675(7), b = 38·448(3), c = 9·3875(7) Å, β = 103·0780(10)°, V = 2976·9(4) Å3, Z = 4 and D x = 1·271 Mg m−3, and contains acetonitrile molecule in the crystal lattice.

Molecular miscibility and chain dynamics in POSS/polystyrene blends: Control of POSS preferential dispersion states

Polyhedral oligomeric silsesquioxane (POSS)/polystyrene nanocomposites with two different POSS molecules, octaisobutyl POSS (Oib-POSS) and trisilanolphenyl POSS (Tsp-POSS), were prepared via solution blending in toluene. Solution dynamics analysis indicates random coil conformation of neat PS and POSS/PS blends. Morphology analysis (AFM/TEM) revealed differences in the preferential dispersion states of Tsp- and Oib-POSS molecules. Tsp-POSS, with its greater predicted solubility in PS, exhibited nanoscale dispersion throughout the bulk leading to transparent films. In contrast, Oib-POSS, with its reduced predicted solubility in PS, exhibited preferential surface segregation, aggregation of POSS particles and hazy films. Estimated fractional surface coverage for the materials, based on surface energy measurements, indicated 15% coverage by Tsp-POSS and 78% for Oib-POSS. Solid-state NMR relaxation studies suggest aggregation of Oib-POSS molecules. Additional NMR studies, including silicon CP/MAS, 2D HETCOR, and WISE, indicate close spatial proximity and interaction of Tsp-POSS molecules with PS chains, contrasting with poor interaction and immiscibility of Oib-POSS with PS.