Intramolecular Hydrogen-bonding Interactions Research Articles

Crystal Structure of 3-(4-Methoxy-benzylidene)-isothiochroman-4-one

Abstract The title compound, 3-(4-methoxy-benzyli-dene)-isothiochroman-4-one (C 17 H 14 O 2 S) was preparedfrom the reaction of isothiochroman-4-one with benzalde-hyde in the presence of small amount of HCl. The structureof the synthesised compound was determined by IR, 1 HNMR and X-ray crystallography. The structure was solvedin monoclinic, space group P2 1 /n with a = 3.9773 (7) A˚ ,b = 10.918 (2) A˚ , c = 30.609 (6) A˚ , b = 90.615 (3) ,V = 1329.1 (4) A˚ 3 ,Z= 4 and with R int = 0.047. Thebicyclic ring of isothiochroman-4-one moiety does notadopt a planar geometry. The molecular conformation isstable via C10–H O1 and C16–H S1 intramolecularhydrogen-bonding interactions. These contacts involvemolecules in an extended two-dimensional sheet to the bcplane.Keywords Crystal structure 3-(4-Methoxy-benzylidene)-isothiochroman-4-one Benzaldehyde Isothiochroman-4-oneIntroductionSpiro-heterocyclic compounds containing one or two func-tionalised arms at various positions have emerged aspotentially interesting drugs owing to their patented selec-tive antitumoral behaviour against breast-cancer (MCF7-strains) [1], antitubercular agents [2] or anti-HIV agents [3].These studies showed that spiro-heterocyclic compoundsbearing an oxygen or sulfur heteroatom in the 3-position/C=O are highly active not only as anti-tubercular oranti-HIV agents but as potential combined antitubercular/anti-HIV agents [4]. From the general structure–activityrelationship, it appears that functionalized side chain(s)characterised by pendant sites such as (O=C–Y–Z), whereY–Z is N=N or O–N, are crucial for bioactivity. Theincorporated heteroatom centres S or O on 3-position seemto have critical interactions with the bacterial cell receptorsor may be as centre donors in metal complexation. Theisothiochroman-4-one, was prepared since a long time [5]by cyclising the chloride 4-phenyl-3-thiabutanoi¨c acid innitrobenzene in presence of tri-chloride aluminium. Thechloride 4-phenyl-3-thiabutanoi¨c acid has been cyclisedby addition of trichloride aluminium in a mixture of(chloroforme/disulfure-carbone). A group of researcher [6]has improved its yield by cyclising the 4-phenyl-3-thiabut-anoi¨cacid(3)byadditionofphosphoricanhydride[P

Conserved Polar Residues Stabilize Transmembrane Domains and Promote Oligomerization in Human Nucleoside Triphosphate Diphosphohydrolase 3

Polar residues play essential roles in the functions of transmembrane helices by mediating and stabilizing their helical interactions. To investigate the structural and functional roles of the conserved polar residues in the N- and C-terminal transmembrane helices of human nucleoside triphosphate diphosphohydrolase 3 (NTPDase3) (N-terminus, S33, S39, T41, and Q44; C-terminus, T490, T495, and C501), each was singly mutated to alanine. The mutant proteins were analyzed for enzymatic activities, glycosylation status, expression level, and Triton X-100 detergent sensitivity. The Q44A mutation decreased Mg-ATPase activity by approximately 70% and abolished Triton X-100 detergent inhibition of Ca-dependent nucleotidase activities while greatly attenuating Triton X-100 inhibition of Mg-dependent nucleotidase activities. The polar residues were also mutated to cysteine, singly and in pairs, to allow a disulfide cross-linking strategy to map potential inter- and intramolecular hydrogen bond interactions. The results support the centrality of Q44 for the strong intermolecular interactions driving the association of the N-terminal helices of two NTPDase3 monomers in a dimer, and the possibility that T41 may play a role in the specificity of this interaction. In addition, S33 and C501 form an intramolecular association, while S39 and T495 may contribute to helical interactions involved in forming higher-order oligomers. Lastly, Tween 20 substantially and selectively increases NTPDase3 activity, mediated by the transmembrane helices containing the conserved polar residues. Taken together, the data suggest a model for putative hydrogen bond interactions of the conserved polar residues in the transmembrane domain of native, oligomeric NTPDase3. These interactions are important for proper protein expression, full enzymatic activity, and susceptibility to membrane perturbations.

Self-Assembly of Artificial Nucleobase 1H-Benzimidazole-4,7-dione at the Liquid/Solid Interface

Self-assembly at the liquid/solid interface of an electrochemically active DNA nucleobase analogue, 1H-benzoimidazole-4,7-dione (Q), has been studied by means of scanning tunneling microscopy (STM). High-resolution STM images revealed the formation of well-ordered two-dimensional (2D) supramolecular nanostructures when the Q molecules are adsorbed onto the graphite surface from a 1-octanol solution. Detailed analysis shows that the observed 2D nanostructures are mainly dominated by hydrogen-bonded Q molecules. Since Q can be considered as a molecule mimicking the nucleobase guanine (G), which is known to form Watson-Crick base pairs with its complementary nucleobase cytosine (C), we have examined the binding ability of Q with C realized by available hydrogen-bonding sites on both Q and C molecules. Upon deposition of a mixture of Q and C molecules onto a graphite surface, one might expect that hydrogen-bonded QC dimers were observed in a new 2D self-assembled structure governed by inter- and intramolecular hydrogen-bonding interactions between Q and C molecules. However, our STM experiments showed that no well-ordered structures are formed and instead phase separation occurs where large-scale homodomains are formed consisting of the individual QQ and CC dimers. To gain further insight into the possible molecular arrangements of the Q and C nucleobases in the mixture phase, the high-resolution STM images are compared with the results from ab initio density functional theory (DFT) calculations.

Site-selective Intramolecular Hydrogen-Bonding Interactions in Phosphorylated Serine and Threonine Dipeptides

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionSite-selective Intramolecular Hydrogen-Bonding Interactions in Phosphorylated Serine and Threonine DipeptidesKyung-Koo Lee, Eunmyung Kim, Cheonik Joo, Jaewook Song, Hogyu Han, and Minhaeng Cho*Cite this: J. Phys. Chem. B 2009, 113, 11, 3590Publication Date (Web):February 25, 2009Publication History Published online25 February 2009Published inissue 19 March 2009https://doi.org/10.1021/jp811090cCopyright © 2009 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views345Altmetric-Citations-LEARN 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 (18 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Peptides and proteins,Monomers Get e-Alerts

Copper(II) and lanthanoid(III) complexes of a new β-diketonate ligand with an appended non-coordinating phenol group

New mononuclear compounds of the ligand 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-dione (H 2L) with Cu(II) and several lanthanoid(III) ions, where Ln(III) = Pr, Nd, Eu, Gd, have been synthesized and characterized by spectroscopic methods and X-ray crystal structure determinations. In all compounds, the ligand coordinates in a bidentate chelating manner, using the diketone function. In the [Cu(HL) 2], the coordination geometry of Cu(II) ion is slightly distorted square-planar; two strong intramolecular (OH⋯O) hydrogen-bonding interactions are established between the phenolate group and the neighboring ketone function. The lanthanoid(III) compounds have the general formula [Ln(HL) 3(CH 3OH) 2] · CH 3OH · 2H 2O; the lanthanoid(III) ion (Ln) is eight-coordinated and the coordination geometry is based on a distorted square-antiprism. In addition to the intramolecular hydrogen bonding (OH⋯O), intermolecular hydrogen-bonding interactions are also present between the coordinated methanol molecule and the non-coordinated methanol molecule giving rise to a three-dimensional network.

Site-selective Intramolecular Hydrogen-Bonding Interactions in Phosphorylated Serine and Threonine Dipeptides

To study the phosphorylation effect on the peptide conformation, we carried out nuclear magnetic resonance (NMR), circular dichroism (CD), Fourier transform (FT)-IR, and vibrational circular dichroism (VCD) experiments with serine and threonine dipeptides (SD and TD) and their phosphorylated ones (pSD and pTD). It is found that both unphosphorylated and phosphorylated serine and threonine dipeptides adopt two conformations, polyproline II (P(II)) and beta-strand. The pH-dependent NMR study shows that the side-chain dianionic phosphoryl group can form direct intramolecular hydrogen bonds with the backbone amide protons at both the acetyl and amide ends of pTD, but only at the acetyl end of pSD. Temperature- and pH-dependent CD studies reveal that, unlike pSD, pTD undergoes conformational transition from P(II) to beta-strand upon double ionization of the phosphoryl group. The subtle but distinct differences between pTD and pSD in site-selective intramolecular hydrogen-bonding interaction and charge-dependent conformational transition may sometimes become significant when choosing between serine and threonine for the conformational control of peptides and proteins by phosphorylation.

Tetrakis(3,5-dimethyl-1H-pyrazole-κN2)(nitrato-κ2O,O′)cadmium(II) nitrate

The title compound, [Cd(NO3)(C5H8N2)4]NO3, was prepared by reaction of cadmium nitrate and 3,5-dimethyl­pyrazole in ethanol solution. The Cd atom adopts a distorted cis-CdO2N4 octa­hedral geometry involving four dimethylpyrazole molecules and one bidentate nitrate anion. The mol­ecular structure and packing are stabilized by N—H⋯O and C—H⋯O inter- and intra­molecular hydrogen-bonding inter­actions.

Comparative study of patulin, ascladiol, and neopatulin by density functional theory

Patulin, a secondary metabolite produced by several fungal species, is a potential contaminant of fruit and vegetable products. To better understand the structure and electronic properties of this mycotoxin and its biosynthetic precursors, a density functional theory (DFT) study was performed on conformations of patulin, ascladiol, and neopatulin. Geometry optimization and transition state calculations were carried out using the three parameter B3LYP functional at the 6-311++G ∗∗ level of theory. Both aqueous solvation studies using a continuum solvation model and in vacuo calculations resulted in several geometry optimized conformations of patulin within a range 2 kcal/mol. One conformation for each enantiomer was preferred by ∼1 kcal/mol over the other geometry optimized conformations considered. Similar results were found for neopatulin. Multiple conformations of ascladiol possessed favorable intramolecular hydrogen bond interactions. The B3LYP/6-311++G ∗∗ results are in agreement with experimentally observed crystallographic data for patulin, and suggest several conformations may be important for structure–activity studies of this mycotoxin and its precursors.

Kinetic Resolution of Racemic Carboxylic Acids by anl-Histidine-Derived Sulfonamide-Induced Enantioselective Esterification Reaction

The direct and catalytic kinetic resolution of racemic carboxylic acids bearing a Brønsted base such as O-protected alpha-hydroxy carboxylic acids and N-protected alpha-amino acids has been accomplished through an L-histidine-derived sulfonamide-induced enantioselective esterification reaction with tert-butyl alcohol for the first time. Highly asymmetric induction [S( k fast/ k slow) = up to 56] has been achieved under the equilibrium between a chiral catalyst and two diastereomeric acylammonium salts through an intramolecular hydrogen-bonding interaction.

Use of molecular electrostatic potential for quantitative assessment of inductive effect

Density functional theory computations at the B3LYP/6-31G(d,p) level have been carried out for three types of model compounds, viz. (i) 4-substituted bicyclo[2.2.2]octane carboxylic acids, (ii) anions of 4-substituted bicyclo[2.2.2]octane carboxylic acids and (iii) 4-substituted quinuclidines where the substituents are NO(2), CN, Cl, Br, CF(3), F, CHO, CH(2)Cl, COOH, COCH(3), CONH(2), OH, OCH(3), C(6)H(5), NH(2), H, CH(3), CH(2)CH(3), CH(CH(3))(2), and C(CH(3))(3) to study the dependencies between molecular electrostatic potential minimum (V(min)) and the inductive substituent constant sigma(I). All the three model systems show excellent linear correlation between V(min) and sigma(I) suggesting that the calculation of V(min) parameter in these systems offers a simple and efficient computational approach for the evaluation of inductive substituent constants. The calculated linear equation for the models (i), (ii), and (iii) are V(min) = 12.982 sigma(I)- 48.867, V(min) = 13.444 sigma(I)- 182.760, and V(min) = 18.100 sigma(I)- 65.785, respectively. Considering the simplicity of the quinuclidine model, V(min) value at the nitrogen lone pair region of a 4-substituted quinuclidine system is recommended for the evaluation of sigma(I). Further, the additivity effect of sigma(I) is tested on multiply substituted quinuclidine and bicyclo[2.2.2]octane carboxylic acid derivatives using the V(min) approach and the results firmly supported the additivity rule of inductive effect. The systems showing considerable deviations from the additivity rule are easily recognized as those showing either steric effect or intramolecular hydrogen bond interactions at the V(min) response site. However, the distance relation of sigma(I) is not well represented in the caged molecular systems.

Intramolecular Hydrogen Bonding and Cooperative Interactions in Carbohydrates via the Molecular Tailoring Approach

In spite of many theoretical and experimental attempts for understanding intramolecular hydrogen bonding (H-bonding) in carbohydrates, a direct quantification of individual intramolecular H-bond energies and the cooperativity among the H-bonded networks has not been reported in the literature. The present work attempts, for the first time, a direct estimation of individual intramolecular O-H...O interaction energies in sugar molecules using the recently developed molecular tailoring approach (MTA). The estimated H-bond energies are in the range of 1.2-4.1 kcal mol(-1). It is seen that the OH...O equatorial-equatorial interaction energies lie between 1.8 and 2.5 kcal mol(-1), with axial-equatorial ones being stronger (2.0-3.5 kcal mol(-1)). The strongest bonds are nonvicinal axial-axial H-bonds (3.0-4.1 kcal mol(-1)). This trend in H-bond energies is in agreement with the earlier reports based on the water-water H-bond angle, solvent-accessible surface area (SASA), and (1)H NMR analysis. The contribution to the H-bond energy from the cooperativity is also estimated using MTA. This contribution is seen to be typically between 0.1 and 0.6 kcal mol(-1) when H-bonds are a part of a relatively weak equatorial-equatorial H-bond network and is much higher (0.5-1.1 kcal mol(-1)) when H-bonds participate in an axial-axial H-bond network.

N2,N2′-Bis[2-(ethoxycarbonylmethoxy)benzylidene]pyridine-2,6-dicarbohydrazide

In the title compound, C29H29N5O8, the ester group is disordered over two sites with site-occupancy factors of 0.91/0.09. The crystal structure is stabilized by inter- and intra­molecular hydrogen-bond inter­actions.

A Comparative Study of Amphiphilic PAMAM Dendrimers at the Air−Water Interface with Different Hydrophobe Attachment Groups

Generation 0 through 5 polyamidoamine (PAMAM) dendrimers with three different types of groups connecting to hydrophobic C12 tails and one type of group connecting to C18 tails were synthesized and studied as monolayers at the air-water interface with a Langmuir trough. The molecular areas were significantly influenced by the size and the type of connecting group. Higher-generation (e.g., G4 and G5) amphiphilic PAMAMs with amide connecting groups were more responsive to changes in compression rate and subphase temperature and less stable than the corresponding opened epoxide- or ester-connected counterparts. Intramolecular (and possibly also intermolecular) attractive hydrogen-bond interactions between the amide connectors are proposed as the reason for this behavior.

Stereoselective Synthesis of ortho-Carbaborane-Containing P-Chiral Phosphanylferrocenes

Diastereomerically pure 1-[1-(1,2-dicarba-closo-dodecaboran(12)yl)chlorophosphanyl]-2-N,N-dimethylaminomethylferrocene ((RP,SFc/SP,RFc)-3) and enantiomerically pure (S)-N,N-dimethyl-1-{(R)-2-[(S)-{1-(1,2-dicarba-closo-dodecaboran(12)yl)}chlorophosphanyl]ferrocenyl}ethylamine ((SC,SP,RFc)-4) were prepared by reaction of monolithiated 1,2-dicarba-closo-dodecaborane(12) and the corresponding racemic or enantiomerically pure aminoalkylferrocenyldichlorophosphanes (1 or (S,R)-2). Two equivalents of 1 also reacted with dilithiated 1,2-dicarba-closo-dodecaborane(12) to yield stereoselectively the RP,RP‘,SFc,SFc‘/SP,SP‘,RFc,RFc‘ diastereomer of 1,2-bis[chloro(2-N,N-dimethylaminomethylferrocenyl)phosphanyl]-1,2-dicarba-closo-dodecaborane(12) ((RP,RP‘,SFc,SFc‘/SP,SP‘,RFc,RFc‘)-5). Chlorophosphane (RP,SFc/SP,RFc)-3 was treated with LiAlH4 to afford diastereoselectively the secondary phosphane 1-[1-(1,2-dicarba-closo-dodecaboran(12)yl)phosphanyl]-2-N,N-dimethylaminomethylferrocene ((RP,RFc/SP,SFc)-6) with inverted stereochemistry at the phosphorus center, which in this case was found to slowly undergo epimerization in solution. The chloro groups of (RP,SFc/SP,RFc)-3 and (SC,SP,RFc)-4 were also substituted by various alkoxides to give a series of diastereomerically and enantiomerically pure carbaboranylferrocenyl phosphinites ((RP,RFc/SP,SFc)-7, (RP,RFc/SP,SFc)-8, (RP,RFc/SP,SFc)-9, (SC,RP,RFc)-10, and (SC,RP,RFc)-11). The substitutions occurred with 100% stereoselective inversion of the configurations of the phosphorus centers. The phosphinites display high stability toward oxidation and epimerization. All new compounds were structurally characterized to verify the configurations of the stereogenic centers. The monophosphanyl-substituted carbaboranes exhibit intramolecular hydrogen-bonding interactions between the dimethylamino group and the proton of the second cluster carbon atom.

Phosphorylation effect on the GSSS peptide conformation in water: Infrared, vibrational circular dichroism, and circular dichroism experiments and comparisons with molecular dynamics simulations

The phosphorylation effect on the small peptide conformation in water has not been clearly understood yet, despite the widely acknowledged notion that control of protein activity by phosphorylation works mainly by inducing conformational change. To elucidate the detailed mechanism, we performed infrared (IR) absorption and vibrational and electronic circular dichroism studies of both unphosphorylated and phosphorylated tetrapeptides, GSSS 1 and GSSpS 2. The solution structure of the tetrapeptide is found to be little dependent on the presence of the neutral or negatively charged phosphoryl group, and to be a mixture of extended structures including polyproline II (PII) and beta-sheet conformations. The additional band at 1598 cm(-1) in the amide I IR spectrum of the phosphorylated peptide GSSpS at neutral pD appears to be clear spectroscopic evidence for direct intramolecular hydrogen-bonding interaction between the side chain dianionic phosphoryl group and the backbone amide proton. On the basis of amide I IR band analyses, the authors found that the probability of finding the phosphoryl group strongly H bonded to the backbone proton in GSSpS is about 43% at pD 7.0 and 37 degrees C. Such a H-bonding interaction in GSSpS has the biological standard enthalpy and entropy of -15.1 kJ/mol and -51.2 J/K mol, respectively. Comparisons between the experimentally measured IR and VCD spectra and the numerically simulated ones suggested that the currently available force field parameters need to be properly modified. The results in this paper may shed light on an unknown mechanism of controlling the peptide conformation by phosphorylation.

Crystal structures and spectroscopic behavior of monomeric, dimeric and polymeric copper(II) chloroacetate adducts with isonicotinamide, N-methylnicotinamide and N, N-diethylnicotinamide

Substituted pyridines provide structural rigidity and thus permit the metal coordination geometry to guide the direction of propagation of the hydrogen-bonded links between building blocks. In this paper we present the crystal structures and spectroscopic properties of monomeric, dimeric and polymeric copper(II) chloroacetates with isonicotinamide (INA), N-methylnicotinamide (MNA) and N, N-diethylnicotinamide (DENA). The molecular structure of [Cu(ClCH 2CO 2) 2(INA) 2] 2 ( 1) consists of a rather interesting dinuclear molecule with copper atoms bridged by anti, anti- O, O′ bridging oxygens of two chloroacetate anions. Each copper atom is octahedrally coordinated thus forming a CuN 2O 4 core with two nitrogens, originating from two different isonicotinamide molecules, in trans positions. This complex is one of a very few examples of this rare type of structure in which both carboxylate oxygen anions are coordinated to two copper metal ions. The crystal structure of 1 revealed an infinite 1-D linear hydrogen-bonded chain formed by discrete molecules [Cu(ClCH 2CO 2) 2(INA) 2] 2 connected by strong hydrogen bonds between two amide groups. This structure is the first example, where two pairs of amide groups are involved in hydrogen bonding connecting two molecules. The X-ray structure of the complex [Cu(CCl 3CO 2) 2(INA) 2] n ( 3) revealed a tetragonal bipyramidal environment about the copper(II) atom. This structure represents the first example of copper(II) complex, where isonicotinamide acts as a bridging ligand. Strong intramolecular hydrogen bonds, N–H⋯O, create two eight-membered metallocycle rings which stabilizes the molecular structure. The crystal structure of 3 consists of 2-D sheets of a metal–organic framework. The coordination environment of the copper(II) atom in [Cu(CCl 3CO 2) 2(MNA) 2(H 2O) 2] · 2H 2O ( 6 · 2H 2O) is an elongated tetragonal bipyramid. Strong intramolecular hydrogen bond interactions involving an axial coordinated water molecule and a carboxylic oxygen atom stabilize the molecular structure. The crystal structure of [Cu 2(ClCH 2CO 2) 4(DENA)] n ( 7) shows that the complex is an extended zigzag coordination chain of alternating binuclear paddle-wheel units of the bridging tetracarboxylate type Cu 2(ClCH 2CO 2) 4 and N, N-diethylnicotinamide molecules. This complex represents the first example of copper(II) carboxylates where N, N-diethylnicotinamide molecule acts as a bidentate bridging ligand connecting binuclear paddle-wheel units. The variation in DENA coordination in the polymeric chain can be described by the following formula: –[Cu 2(ClCH 2CO 2) 4]–(DENA- N, O)– [Cu 2(ClCH 2CO 2) 4]–(DENA- O, N)–. All complexes were characterized by electron paramagnetic resonance (EPR) spectroscopy and IR spectroscopy. The present study shows that the pyridine-carboxyamides are very suitable molecules that can be employed as ligands in the construction of extended arrays of transition metal-containing molecules linked via hydrogen bonds.

Hydrogen Bonding and Cation Coordination Effects in Primary and Secondary Amines Dissolved in Carbon Tetrachloride

Raman and infrared spectroscopy were used to investigate hydrogen-bonding interactions and cation coordination effects in solutions of lithium triflate (LiCF3SO3) dissolved in two primary amines, hexylamine (HEXA) and N,N-dimethylethylenediamine (DMEDA), and in a secondary amine, dipropylamine (DPA). Strong intermolecular hydrogen-bonding interactions and weaker intramolecular hydrogen-bonding interactions that occur only in DMEDA were spectroscopically distinguished in a comparison of pure HEXA, pure DMEDA, and the dilute solutions of these amines in CCl4. The spectroscopic shifts in intensity and frequency in the NH stretching region of DPA and DPA diluted in CCl4 were similar to those of HEXA. Dilute electrolyte solutions in carbon tetrachloride were prepared to analyze specifically the cation coordination effect. In these solutions, limited intermolecular hydrogen-bonding interactions are present, and the observed spectral shifts correspond primarily to the cation-induced shifts. The symmetric SO3 stretching region of the triflate anion was investigated to probe further the coordination of the cation. The local structures of the triflate ions and the amine groups in the electrolyte solutions dissolved in CCl4 are similar to the local structures in the corresponding amine-salt crystals previously reported by us.

Small Angle Neutron Scattering Studies on Miscible Blends of Poly(styrene-ran-vinyl phenol) with Liquid Crystalline Polyurethane

The production of uniformly dispersed rigid-rod liquid crystalline polymer (LCP) molecules in a flexible amorphous polymer, with an experimentally accessible miscibility window, has become possible by modifying the architecture of the flexible polymer, so as to induce favorable inter-species hydrogen bonding. The conformation of LCP chains that are uniformly dispersed in a flexible coil matrix are examined by studying a system consisting of a liquid crystalline polyurethane (LCPU) and a copolymer containing 12% vinylphenol and deuterated styrene, utilizing small-angle neutron scattering. Intramolecular hydrogen bond interaction within the vinylphenol segments of the copolymer leads to the formation of a dynamically cross-linked structure, characterized by the large amount of scattering seen at low angle. Addition of the LCPU in the blend results in formation of hydrogen bonding interactions between the LCP and the copolymer; demonstrated by an initial reduction in the correlated size of the dynamic networ...

A New Class of Intramolecularly Hydrogen-Bonded Dendrons Based on a 2-Methoxyisophthalamide Repeat Unit

The synthesis and conformational properties of folded dendrons based on a 2-methoxyisophthalamide (2-OMe-IPA) repeat unit are described. The hydrodynamic properties of dendrons preorganized via the syn-syn conformational preference of 2-methoxyisophthalamide are compared with 2,6-pyridinedicarboxamide (2,6-pydic) analogues. The effect of subtle differences in the nature of the conformational equilibria that exist within the 2-OMe-IPA and 2,6-pydic repeat units on the global structural properties of the corresponding dendrons was explored computationally, by (1)H-DOSY NMR spectroscopy and time-resolved fluorescence anisotropy (TRFA) measurements. Whereas the syn-syn preference of the 2-OMe-IPA branched repeat unit is stabilized entirely by intramolecular hydrogen-bonding interactions, this preference in the 2,6-pydic system is a consequence of both intramolecular hydrogen-bonding and dipole minimization effects. However, nonspecific solvophobic compression is more important in determining hydrodynamic properties than solvent-dependent shifts in the conformational equilibria of the repeat unit for both dendron series.

Copper(I) Coordination Chemistry of (Pyridylmethyl)amide Ligands

Copper(I) chloro complexes were synthesized with a family of ligands, HL(R) [HL(R) = N-(2-pyridylmethyl)acetamide, R = null; 2-phenyl-N-(2-pyridylmethyl)acetamide, R = Ph; 2,2-dimethyl-N-(2-pyridylmethyl)propionamide, R = Me3; 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide, R = Ph3)]. Five complexes were synthesized from the respective ligand and cuprous chloride: [Cu(HL)Cl]n (1), [Cu2(HL)4Cl2] (2), [Cu2(HL(Ph))2(CH3CN)2Cl2] (3), [Cu2(HL(Ph)3)2Cl2] (4), and [Cu(HL(Me)3)2Cl] (5). X-ray crystal structures reveal that for all complexes the ligands coordinate to the Cu in a monodentate fashion, and inter- or intramolecular hydrogen-bonding interactions formed between the amide NH group and either amide C=O or chloro groups stabilize these complexes in the solid state and strongly influence the structures formed. Complexes 1-5 display a range of structural motifs, depending on the size of the ligand substituent groups, hydrogen bonding, and the stoichiometry of the starting materials, including a one-dimensional coordination polymer chain (1) and binuclear (2-4) or mononuclear (5) structures.