Complementary Hydrogen-bonding Interactions Research Articles

Fluorinated Bisphenol Sorbent Materials for Spectroscopic Chemical Threat Sensing and Photonics Applications

Alcoholic and phenolic hydrogen-bond (HB) acidic absorbents activated by fluorine chemistries have been previously developed at the U.S. Naval Research Laboratory and elsewhere to augment sorbent HB acidity, reduce sorbent HB basicity and target complementary HB basicity of a wide range of hazardous target chemicals. A significant limitation of HB sorbents developed to date has been the propensity for sorbent self-association. This intermolecular bonding between sorbent molecules hinders sorbate access to active HB acid sites in the sorbent, limiting its overall efficacy. Sorbent self-association is evidenced by broadened hydroxyl peaks in the mid-infrared (MIR) region, which can obscure important absorption frequencies that appear upon absorption of an analyte into the sorbent. In this current work our aim is to develop improved HB acidic sorbent compounds which minimize undesired sorbent self-association in order to apply these sorbents to infrared- and Raman-based sensing devices for chemical threat detection.A series of new HB acidic sorbents have been synthesized and the subsequent sorbent-sorbate interactions have been characterized by a number of methods. MIR spectroscopy has been used to help elucidate sorbent-analyte vapor interactions. The newly synthesized sorbents have been challenged with various analyte vapors, including toxic industrial chemicals, chemical warfare agent simulants, and background interferents. A particular focus of these characterization efforts has been to observe the spectral changes that occur in the hydroxyl region of the MIR upon exposure of a sorbent material to an analyte vapor. Analyte binding of an HB base occurs principally at the sorbent hydroxyl site. The resulting redshift of the hydroxyl stretching frequency is characteristic of the basicity of the analyte.These sorbent materials are specifically designed to be selective toward hazardous chemicals through complementary hydrogen-bonding interactions between sorbent and analyte molecules. Generally, common interferents, such as hydrocarbons, have little or no hydrogen-bond basicity, while hazardous chemicals of interest have moderate to high basicity. More strongly HB basic analytes trigger larger redshifts of the hydroxyl absorption frequency. Benchtop FTIR characterization has confirmed that these newly designed sorbent materials are responsive to threat chemicals of interest at low concentrations and largely unresponsive to interferent chemicals, even at relatively high concentrations.Based on the strong affinity of these sorbents to threat chemicals of interest and the significant spectral changes that occur in the MIR upon formation of the hydrogen-bonded complex, these sorbent materials make useful candidates for MIR sensing applications. A frequency shift of the hydroxyl stretch indicates a sorbate has formed a HB with the sorbent. The magnitude of the frequency shift correlates with the basicity of the analyte, which is indicative of the class of compound to which the newly bound chemical belongs. In a sensing application, this feature can provide an alert that a hazardous chemical is present, even if it is an unknown threat. While the hydroxyl region allows for class specificity of unknown compounds, the fingerprint region complexity may facilitate specific analyte recognition. At present, this work has been focused on analysis of the hydroxyl region and distinction of different classes of compounds, but future efforts will turn to the fingerprint region to provide an avenue for specific chemical identification.Raman spectroscopy has also been used to characterize these sorbent materials. Specifically, a technique known as waveguide-enhanced Raman spectroscopy (WERS) has been used, which features the use of highly evanescent, low-loss waveguides with the sorbent material as a top cladding.2 WERS can be achieved using an incredibly small footprint with a sorbent-functionalized nanophotonic waveguide that is approximately a few centimeters long. Using WERS, the differential Raman spectra of the sorbent material interacting with different chemical warfare agent simulants has been measured at parts-per-billion detection levels. The spectra exhibit extrapolated three-sigma detection limits as low as 3 ppb. Continuing efforts are focused on adapting this technique to photonic integrated circuit-based fabrication and chip-scale Raman spectroscopy for trace chemical vapor detection.This presentation will highlight the design of these next-generation sorbents as a tool to facilitate MIR- and Raman-based sensing of threat chemicals. It will focus on analyzing sorbent-analyte spectral interactions and discuss how to exploit these features to develop MIR- and Raman-based sensors.

Fluorinated Bisphenol Sorbent Materials for Spectroscopic Chemical Threat Sensing and Photonics Applications

Alcoholic and phenolic hydrogen-bond (HB) acidic absorbents activated by fluorine chemistries have been previously developed at the U.S. Naval Research Laboratory and elsewhere to augment sorbent HB acidity, reduce sorbent HB basicity and target complementary HB basicity of a wide range of hazardous target chemicals. A significant limitation of HB sorbents developed to date has been the propensity for sorbent self-association. This intermolecular bonding between sorbent molecules hinders sorbate access to active HB acid sites in the sorbent, limiting its overall efficacy. Sorbent self-association is evidenced by broadened hydroxyl peaks in the mid-infrared (MIR) region, which can obscure important absorption frequencies that appear upon absorption of an analyte into the sorbent. In this current work our aim is to develop improved HB acidic sorbent compounds which minimize undesired sorbent self-association in order to apply these sorbents to infrared- and Raman-based sensing devices for chemical threat detection.A series of new HB acidic sorbents have been synthesized and the subsequent sorbent-sorbate interactions have been characterized by a number of methods. MIR spectroscopy has been used to help elucidate sorbent-analyte vapor interactions. The newly synthesized sorbents have been challenged with various analyte vapors, including toxic industrial chemicals, chemical warfare agent simulants, and background interferents. A particular focus of these characterization efforts has been to observe the spectral changes that occur in the hydroxyl region of the MIR upon exposure of a sorbent material to an analyte vapor. Analyte binding of an HB base occurs principally at the sorbent hydroxyl site. The resulting redshift of the hydroxyl stretching frequency is characteristic of the basicity of the analyte.These sorbent materials are specifically designed to be selective toward hazardous chemicals through complementary hydrogen-bonding interactions between sorbent and analyte molecules. Generally, common interferents, such as hydrocarbons, have little or no hydrogen-bond basicity, while hazardous chemicals of interest have moderate to high basicity. More strongly HB basic analytes trigger larger redshifts of the hydroxyl absorption frequency. Benchtop FTIR characterization has confirmed that these newly designed sorbent materials are responsive to threat chemicals of interest at low concentrations and largely unresponsive to interferent chemicals, even at relatively high concentrations.Based on the strong affinity of these sorbents to threat chemicals of interest and the significant spectral changes that occur in the MIR upon formation of the hydrogen-bonded complex, these sorbent materials make useful candidates for MIR sensing applications. A frequency shift of the hydroxyl stretch indicates a sorbate has formed a HB with the sorbent. The magnitude of the frequency shift correlates with the basicity of the analyte, which is indicative of the class of compound to which the newly bound chemical belongs. In a sensing application, this feature can provide an alert that a hazardous chemical is present, even if it is an unknown threat. While the hydroxyl region allows for class specificity of unknown compounds, the fingerprint region complexity may facilitate specific analyte recognition. At present, this work has been focused on analysis of the hydroxyl region and distinction of different classes of compounds, but future efforts will turn to the fingerprint region to provide an avenue for specific chemical identification.Raman spectroscopy has also been used to characterize these sorbent materials. Specifically, a technique known as waveguide-enhanced Raman spectroscopy (WERS) has been used, which features the use of highly evanescent, low-loss waveguides with the sorbent material as a top cladding.2 WERS can be achieved using an incredibly small footprint with a sorbent-functionalized nanophotonic waveguide that is approximately a few centimeters long. Using WERS, the differential Raman spectra of the sorbent material interacting with different chemical warfare agent simulants has been measured at parts-per-billion detection levels. The spectra exhibit extrapolated three-sigma detection limits as low as 3 ppb. Continuing efforts are focused on adapting this technique to photonic integrated circuit-based fabrication and chip-scale Raman spectroscopy for trace chemical vapor detection.This presentation will highlight the design of these next-generation sorbents as a tool to facilitate MIR- and Raman-based sensing of threat chemicals. It will focus on analyzing sorbent-analyte spectral interactions and discuss how to exploit these features to develop MIR- and Raman-based sensors.

Entrapment of an adenine derivative by a photo-irradiated uracil-functionalized micelle confers controlled self-assembly behavior

HypothesisInvoking cooperative assembly of the uracil-functionalized supramolecular polymer BU-PPG [uracil end-capped poly(propylene glycol)] upon association with the nucleobase adenine derivative A-MA [methyl 3-(6-amino-9H-purin-9-yl)propanoate] as a model drug provides a new concept to control and tune the properties of supramolecular complexes and holds significant potential for the development of safer, more effective drug delivery systems. ExperimentsBU-PPG and A-MA were successfully developed and exhibited specific recognition and high affinity, which enabled reversible complementary adenine-uracil (A-U) hydrogen bonding-induced formation of spherical micelles in aqueous solution. The self-assembly and controllable A-MA release behavior of BU-PPG/A-MA micelles were studied using morphological analysis and optical and light scattering techniques to investigate the effect of photoirradiation and temperature on the complementary hydrogen bond interactions between BU-PPG and A-MA. FindingsThe resulting micelles possess unusual physical properties, including controlled photoreactivity kinetics, controllable self-assembled morphology and low cytotoxicity in vitro, as well as reversible temperature-responsive behavior. Importantly, irradiated micelles exhibited excellent long-term structural stability under normal physiological conditions and serum disturbance. Increasing the temperature triggered rapid release of A-MA by disrupting A-U complexes. These findings represent an entirely new, promising strategy for the development of multi-controlled release drug delivery nanocarriers based on complementary hydrogen bonding interactions.

Supramolecular assembly-induced enhanced emission of electrospun nanofibers.

A nucleobase-assembled supramolecular nanofiber is capable of forming network-like polymeric clusters through complementary hydrogen-bonding interactions. It behaves as an effective chromophore that greatly enhances the light emission efficiency of fluorescent fibers, reaching up to three times higher efficiency than the control samples.

Supramolecularly Engineered Functional π-Assemblies Based on Complementary Hydrogen-Bonding Interactions

Abstract As details of exciting photonic and electronic properties arising from self-assembled functional dyes and related π-conjugated molecules become clearer, strategies for control of short and long-range chromophore–chromophore orientations, regulation of π–π stacking arrangements, construction of self-organized nano-to-microscale architectures, diversification of materials properties, analysis of self-assembly pathways, and impartment of stimuli-responsive properties, are all becoming important issues in the research area of organic functional materials. This article focuses on the supramolecular assemblies of dyes and related π-conjugated systems whose organization processes are rationally controlled by complementary multiple hydrogen bonding (CMHB) interactions between melamine and barbituric acid/cyanurate functional units. The article includes an overview of the construction principle of such systems, but special attention is focused on the work carried out in the authors’s group (since 2002) using azobenzene, diarylethene, merocyanine, perylene bisimide dyes, and π-conjugated oligomers including oligo(p-phenylenevinylene), oligo(p-phenyleneethynylene), and oligothiophenes. The design principles discussed in this account could open up new avenues to novel functional aspect and application of functional dyes and small-molecular π-conjugated systems.

Synthesis of H-shaped carbon-dioxide-derived poly(propylene carbonate) for topology-based reduction of the glass transition temperature

H-shaped poly(propylene carbonate) (PPC) was synthesized from a tetrafunctional linear PPC. First, a linear α,ω-dihydroxy PPC (1) was synthesized via the alternating copolymerization of carbon dioxide (CO2) and propylene oxide (PO) catalysed by a cobalt porphyrin complex and DMAP system. A subsequent chain-end functionalization with 1,3,5-benzenetricarbonyl trichloride afforded a tetrafunctional linear PPC (2) with dicarboxylic acid groups at both chain ends. H-shaped PPC (3) was synthesized from 2, as the macromolecular chain-transfer agent, by further alternating copolymerization of CO2 and PO. Moreover, the thermal properties of 3, as determined by DSC, indicated that the glass transition temperature (Tg) of 3 (Tg = 21 °C) is significantly lower than that of linear PPC (Tg = 30 °C). This attribute of the H-shaped topology (lowering of Tg) was then applied to a new self-assembly system. Thus, a PPC with two thymine groups at both chain ends (4) and a PPC with a 2,6-diaminopyridine group at the centre of the main chain (5) were synthesized and self-assembled simply by mixing at a 1:2 ratio. Interestingly, the Tg of the self-assembled product (from 4 and 5) was comparable to that of 3, indicating the formation of an H-shaped topology through complementary hydrogen-bonding interactions.

Block-copolymer-like supramolecules confined in nanolamellae

This paper describes the development of a new concept in supramolecular assembly of existing functional polypeptides to form diblock-like molecular clusters through complementary hydrogen-bonding interactions, providing a potential route toward design and fabrication of block copolymer-like supramolecular materials.

Rational Design of Nanofibers and Nanorings through Complementary Hydrogen‐Bonding Interactions of Functional π Systems

A simple protocol to create nanofibers and -rings through a rational self-assembly approach is described. Whereas the melamine-oligo(p-phenylenevinylene) conjugate 1a self-aggregates to form ill-defined nanostructures, conjugate 1b, which possesses an amide group as an additional interactive site, self-aggregates to form 1D nanofibers that induce gelation of the solvent. AFM and XRD studies have shown that dimerization through the melamine-melamine hydrogen-bonding interaction occurs only for 1b. Upon complexation with 1/3 equivalents of cyanuric acid (CA), conjugate 1a provides well-defined, ring-shaped nanostructures at micromolar concentrations, which open to form fibrous assemblies at submillimolar concentrations and organogels in the millimolar concentration range. Apparently, the enhanced aggregation ability of 1a by CA is a consequence of columnar organization of the resulting discotic complex 1a(3).CA. In contrast, coaggregation of 1b with CA does not provide well-defined nanostructures, probably due to the interference of complementary hydrogen-bonding interactions by the amide group.

Fabrication and Functionalization of Supramolecular Microgel Arrays Through Complementary Hydrogen‐Bonding Interactions

Polymer gels are selectively deposited on a pre-patterned substrate, making a microgel array. The microgel array (see image) can be crosslinked and selectively and reversibly functionalized by nanoparticles through complementary hydrogen-bonding interactions. A reusable polymer/nanoparticle composite microstructure pattern with fluorescent and magnetic properties is constructed through this method.

Self-assembly of a bis(adeninyl)–Cu(i) complex: a cationic nucleobase duplex mimic

The tetrahedral bis(adeninyl)-Cu(I) complex, , self-associates in polar solvent through complementary hydrogen-bonding interactions and appears to mimic the natural assembly of duplex DNA.

Nanophase-Separated Structures of AB Block Copolymer/C Homopolymer Blends with Complementary Hydrogen-Bonding Interactions

We report on the morphological variations of SP/H blends containing a poly(styrene-block−2-vinylpyridine) diblock copolymer (SP) (Mw = 130K) and poly(4-hydroxystyrene) (H) (Mw = 14K) with different blend compositions. The structures were observed by transmission electron microscopy (TEM) as well as by small-angle X-ray scattering (SAXS). The results were compared with those obtained from SP/P blends, where P denotes the poly(2-vinylpyridine) homopolymer. The neat SP diblock copolymer, with an S block volume fraction, ϕs, of 0.67, has a hexagonally packed cylindrical structure. As P (Mw of 6.6K) is added to the copolymer, morphology of the blend transits to a lamellar structure. Further addition of the homopolymer causes macrophase separation of P homopolymer chains. In contrast, macrophase separation of H homopolymer has never been observed in SP/H blends, even upon addition of large amounts of H. At first, it was noted that the unusual morphological transition from the cylindrical structure to the spherical structure occurs upon addition of H. Subsequently transitions to cylindrical, lamellar and, finally to inverse cylindrical structures occur with successive additions of H. This result is due to the miscibility of P and H via hydrogen-bonding interactions which appear to serve as the driving force for production of uniform nanophase-separated structures covering a wide composition range.

Halide Anion Mediated Dimerization of a meso‐Unsubstituted N‐Confused Porphyrin

The new N-confused porphyrin (NCP) derivatives, meso-unsubstituted beta-alkyl-3-oxo N-confused porphyrin (3-oxo-NCP) and related macrocycles, were synthesized from appropriate pyrrolic precursors by a [3+1]-type condensation reaction. 3-Oxo-NCP forms a self-assembled dimer in dichloromethane that is stabilized by complementary hydrogen-bonding interactions arising from the peripheral amide-like moieties. The protonated form of 3-oxo-NCP was observed to bind halide anions (F(-), Cl(-)) through the outer NH and the inner pyrrolic NH groups, thus affording a dimer in dichloromethane. The structure of the chloride-bridged dimer in the solid state was determined by X-ray diffraction analysis.

Supramolecular Control of Oligothienylenevinylene−Fullerene Interactions: Evidence for a Ground-State EDA Complex

Complementary hydrogen-bonding interactions between a barbituric acid-substituted fullerene derivative (1) and corresponding receptor (2) bearing thienylenevinylene units are used to assemble a 1:1 supramolecular complex (K = 5500 M(-1)). Due to the close proximity of the redox-active moieties within the assembly, strong ground-state electron-donor-acceptor interactions are observed. Photoinduced electron transfer from electron-rich thienylenevinylene subunits to the fullerene is very fast (k(et) = 5.5 x 10(12) s(-1)), as determined by fs-time-resolved transient absorption spectroscopy. [reaction: see text]

Binding and Electrochemical Recognition of Barbiturate and Urea Derivatives by a Regioisomeric Series of Hydrogen-Bonding Ferrocene Receptors

A series of ferrocene-containing amidopyridyl receptors, in two regioisomeric forms (1,1' and 1,3), have been shown to bind cyclic organic molecules in chloroform through complementary hydrogen-bonding interactions. Complexation was monitored by NMR spectroscopy and by cyclic voltammetry. The magnitude of the host-guest binding strength and the redox response to complexation depend on both the type and the relative position of the amidopyridyl groups on the cyclopentadienyl rings of the ferrocene.

A heterodifunctionalised ferrocene derivative that self-assembles in solution through complementary hydrogen-bonding interactions.

A heterodifunctionalised ferrocene, containing a carboxylic acid and an amidopyridine unit, self-assembles in organic solvents through complementary hydrogen bonds.

Hydrogen-bonded supramolecular arrays of the [Re6(μ3-Se)8]2+core-containing clusters

Site-differentiated clusters of the general formula [Re6(μ3-Se)8(PEt3)nL6−n](SbF6)2 [L = nicotinamide: 1 (n = 5), 2 (n = 4, trans-), and 3 (n = 4, cis-)] have been made by ligand substitution reactions of the corresponding acetonitrile solvates [Re6(μ3-Se)8(PEt3)n(MeCN)6−n](SbF6)2 (n = 5; n = 4, cis- and trans-) with nicotinamide. De-iodination of [Re6(μ3-Se)8(PEt3)nI6−n]In−4 [n = 4 (cis- and trans-), 5] with AgSbF6 in the presence of 3,5-pyridinedicarboxylic acid (PDCA) produced a related series of cluster complexes [Re6(μ3-Se)8(PEt3)nL6−n](SbF6)2 [L = PDCA: 4 (n = 5), 5 (n = 4, trans-), and 6 (n = 4, cis-)]. Retention of stereochemistry in each case was confirmed by 1H and 31P NMR and these new cluster derivatives were further characterized by satisfactory microanalyses (CHN). In addition, the solid-state structure of trans-[Re6(μ3-Se)8(PEt3)4(PDCA)2](SbF6)2 (5) was established crystallographically, which revealed zigzag arrays of clusters mediated by complementary hydrogen-bonding interactions involving only one of the acid groups per PDCA ligand; the second acid group extends into a small space between the chains and appears to be in close contact with a Se atom on a neighboring cluster, as well as a hydrogen atom of that cluster's triethylphosphine ligands. Each polymer chain is skewed with respect to its neighbors, forming a pronounced lamellar structure.

High-yield synthesis of a chiroporphyrin by hydrogen bond-directed cyclisation

A new chiroporphyrin is prepared in 60% yield using complementary intramolecular hydrogen-bonding interactions between N-acylurea substituents to direct the cyclisation of the tetrapyrrolic intermediate; similar hydrogen-bond assistance by carboxylic acid functions is suggested for cyclisation of hydroxymethylbilane to uroporphyrinogen I.