DETECTION OF POLYCYCLIC AROMATIC COMPOUNDS IN SINGLE LIVING CELLS USING OPTICAL NANOPROBES

Exposure of mammalian cells to polycyclic aromatic compounds (PACs) such as the carcinogen benzo[a]pyrene (BaP) leads to the formation of DNA adducts N²-deoxyguanosine (dG) and N⁶-deoxyadenosine (dA) with adenine and guanine nucleotides, which are integral parts of DNA, RNA, and ATP. DNA adduct formation causes alteration of the DNA (RNA) sequence since neither adenine nor guanine can normally bind to its complementary nucleotide base, thymine (uracil) and cytosine respectively. The inability to form these bonds leads to mutations in the DNA double-helix structure during DNA replication, and eventually carcinogenesis. Therefore, the capability to detect and measure PAC species such as BaP in single living cells is important for studies required to establish the limits of BaP exposure necessary for carcinogenesis. Along these lines, we have developed antibody-based optical nanoprobes capable of detecting and measuring BaP in single living cells. The results obtained in this work demonstrate the practical application of antibody-based nanoprobes for performing measurements inside single living cells with their elements and their relationships intact.     

Chemosensors for pyrophosphate

The selective detection of the anion pyrophosphate (PPi) is a major research focus. PPi is a biologically important target because it is the product of ATP hydrolysis under cellular conditions, and because it is involved in DNA replication catalyzed by DNA polymerase, its detection is being investigated as a real-time DNA sequencing method. In addition, within the past decade, the ability to detect PPi has become important in cancer research. In general, the sensing of anions in aqueous solution requires a strong affinity for anions in water as well as the ability to convert anion recognition into a fluorescent or colorimetric signal. Among the variety of methods for detecting PPi, fluorescent chemosensors and colorimetric sensors for PPi have attracted considerable attention during the past 10 years. Compared with the recognition of metal ions, it is much more challenging to selectively recognize anions in an aqueous system due to the strong hydration effects of anions. Consequently, the design of PPi sensors requires the following: an understanding of the molecular recognition between PPi and the binding sites, the desired solubility in aqueous solutions, the communicating and signaling mechanism, and most importantly, selectivity for PPi over other anions such as AMP and ADP, and particularly phosphate and ATP. This Account classifies chemosensors for PPi according to topological and structural characteristics. Types of chemosensors investigated and reported in this study include those that contain metal ion complexes, metal complexes combined with excimers, those that function with a displacement approach, and those based on hydrogen-bonding interaction. Thus far, the utilization of a metal ion complex as a binding site for PPi has been the most successful strategy. The strong binding affinity between metal ions and PPi allows the detection of PPi in a 100% aqueous solution. We have demonstrated that carefully designed receptors can distinguish between PPi and ATP based on their different total anionic charge densities. We have also demonstrated that a PPi metal ion complex sensor has a bioanalytical application. This sensor can be used in a simple and quick, one-step, homogeneous phase detection method in order to confirm DNA amplification after polymerase chain reaction (PCR).     

Conformations in partly ionized poly(methacrylic acid): 1. Ionic hydrogen bonds in syndiotactic chains

Comparisons of u.v. spectrophotometric titrations of some dicarboxylic acids, ‘conventional’ poly(methacrylic acid) and poly(acrylic acid) suggest that ionic or acid-salt hydrogen bonds form between adjacent carboxyl groups in racemic dyads in partly ionized forms of poly(methacrylic acid). The ionic hydrogen bonds form in tt conformations of the dyads. The maximum concentration of ionic hydrogen bonds occurs at 50% ionization in pure syndiotactic chains in the presence of electrolyte to give a chain having four-bond repeating units. Bonds 1 and 2 are presumed to be fixed in trans-trans conformations while bonds 3 and 4 retain some conformational freedom although this is somewhat reduced as a consequence of side group rotations necessary for hydrogen bonding. While ionic hydrogen bonds may form across meso dyads in t? conformations, isotactic chains incorporating ionic hydrogen bonds are predicted to be less stable than the corresponding syndiotactic chains.     

贮氢合金催化共轭二烯烃类聚合物双键加氢的研究

研究了共轭二烯烃类聚合物在贮氢合金氢化物存在下双键加氢的情况。结果表明AB；型贮氢合金[包括LaNi5和MINi5-x(CoMnAl)8]可催化NBR、NR、BR、SBS等共轭二烯烃聚合物双键加氢，其氢化度分别可达33．5％、31．1％、45．8％、32．3％。采用IR、^1H NMR、碘量分析法等手段对加氢产物进行了分析，表明聚合物中双键加氢的同时，NBR中的-C≡N和SBS中的苯环不受影响。此外。研究结果还表明合金组成、表面处理方式等对贮氢合金催化共轭二烯烃类聚合物双键加氢活性有影响。合金氢化物在共轭二烯烃类聚合物双键加氢过程中具有提供氢源与催化双重功能。     

Selective catalysis of μ-oxo-bismetalloporphyrins for 2-methylbutane oxidation with PhIO under mild conditions

Fourteen μ-oxo-bisironporphyrins and nine μ-oxo-bismanganeseporphyrins were synthesized, and their selective catalysis for the oxidation of the secondary and tertiary carbon–hydrogen bonds of 2-methylbutane with PhIO were also studied. The ratio of the relative reaction selectivity of tertiary carbon–hydrogen bonds to secondary carbon–hydrogen bonds was 3:1 when ironporphyrins were used as catalysts, and 4:1 when manganeseporphyrins were used as catalysts. The research showed that the substituents on the porphyrin rings influenced the catalytic selectivity of metalloporphyrins for the oxidation of the secondary and tertiary carbon–hydrogen bonds as well as the reaction rate. Whether ironporphyrins or manganeseporphyrins, the electron-attracting groups on porphyrin rings increased the catalytic selectivity of metalloporphyrins for the tertiary carbon–hydrogen bonds and the reaction rates, however, the electron-releasing groups increased the catalytic selectivity of metalloporphyrins for secondary carbon–hydrogen bonds, but reduced the reaction rates.     

PEEKWC microcapsules for selective oxidation of benzyl alcohols to aldehydes

In this study, we report on the preparation, characterization and use of new catalytic polymeric microcapsules for the selective oxidation of benzyl alcohols to benzaldehydes. The catalyst, ammonium molybdate tetrahydrate, was entrapped inside modified polyetheretherketone (PEEKWC) polymeric microcapsules during their preparation. Catalytic activity of the new PEEKWC microcapsules has been evaluated in the oxidation of substituted benzyl alcohols to benzaldehydes using hydrogen peroxide as oxidant.EDX analysis of the catalytic microcapsules showed a satisfactorily catalyst distribution on the shell and on the inner core. Proof of successful entrapment of catalyst inside polymeric matrix during the preparation was given by the different colorimetric reactions between the catalytic PEEKWC microcapsules and the oxidant (hydrogen peroxide).An interesting structure-reactivity behaviour, that may indeed be induced by the interaction between the polymeric membrane and the substrate, has been observed.PEEKWC catalytic microcapsules were stable under oxidation conditions and can be recycled without a loss of activity.     

α,β-不饱和羰基化合物中共轭碳碳双键的有机小分子选择性催化还原

α,β-不饱和羰基化合物的选择性还原具有很重要的应用意义,同时具有很大挑战性,利用有机小分子催化剂、以二氢吡啶酯为氢源可以高化学选择性、高对映选择性地催化还原α,β-不饱和羰基化合物的共轭双键。综述了有机小分子催化剂在α,β-不饱和醛、酮、酯以及串联反应中共轭碳碳双键选择性催化还原的研究进展,总结了每一催化体系的优缺点。     

Local spin density investigation of the chromium / polyimide interface

Bonding of chromium to the polyimide, PMDA-ODA, surface is still the subject of debate. In an attempt to clarify this problem, we have performed density functional theory calculations on different model molecules, phthalimide, PMDA, and PAP (p-amino phenol), which represent the most functionalities of the polyimide (PMDA-ODA). If we consider only the low spin case, we find that chromium bonds preferentially to the phenyl ring. However, when we release the spin constraint and optimize the structure, we find that the absolute stable configuration is that of chromium in a quintet state, at a carbonyl group. The energy difference is 0.30 eV. The complete infrared spectrum has been calculated for phthalimide and compared with experimental spectra. The agreement is excellent. A vibrational analysis for the Cr/phthalimide system, in both configurations (Cr on C=O and Cr on phenyl), in their stable spin states, is presented. We find that the former yields better agreement with experiment than the latter.     

An investigation into the hydrogen bond of poly (p‐phenylene benzobisoxazole)/carboxylic carbon nanotube composites,insight from quantum mechanics/molecular mechanics simulation

Poly (p‐phenylene benzobisoxazole)/carbon nanotube (PBO/CNTs) composites have already been experimentally synthesized with the outstanding mechanical and electrical properties. Carboxylic carbon nanotubes (CNT‐COOH), obtained by acid treatment, can better disperse than pristine nanotubes in PBO matrix, which is estimated due to hydrogen bonds between them and investigated by Quantum Mechanics/Molecular mechanics (QM/MM) calculation. In the dynamic simulation, the N atoms in PBO and H atoms in carboxyl can be close enough to form hydrogen bond and the angle of oxygen–hydrogen–nitrogen (OHN) is obtuse, suitable for hydrogen bond. Further more, the electrostatic potential (ESP) and ESP fit charge of N and O atoms in PBO has been measured by Density Functional Theory (DFT) calculation to prove that hydrogen bonds can be formed only by N atoms in the heterocycle of PBO and H atoms in carboxyl of the CNT‐COOH. POLYM. COMPOS., 36:1454–1461, 2015. © 2014 Society of Plastics Engineers     

A Facile Strategy for Synergistic Integration of Dynamic Covalent Bonds and Hydrogen Bonds to Surmount the Tradeoff between Mechanical Property and Self-Healing Capacity of Hydrogels

The self-healable hydrogels have attracted increasing attention due to their promising potential for ensuring the durability and reliability of hydrogels. However, they still face a serious challenge to achieve a positive balance between mechanical and healing performance, especially for the room-temperature autonomous self-healable hydrogels. Herein, a simple but efficient strategy to fabricate a kind of dynamic boronate and hydrogen bonds dual-crosslinked double network (DN) hydrogel based on a UV-initiated one-pot in situ polymerization of N-acryloyl glycinamide (NAGA) in polyvinyl alcohol-borax slime is reported. The obtained PN-x/PB hydrogels, especially with high content of PNAGA, are shown to possess high mechanical strength, high toughness, and fatigue-resistance properties as well as excellent self-healability at room temperature (nearly 88% self-healing efficiency based on the strain compression test), due to the dynamic DN structure, and the combination of the adaptable and reconfigurable dynamic boronate bonds and hydrogen bonds. Considering the easily available materials and simple preparation process, this novel strategy should offer not only a kind of dynamic DN hydrogel with robust mechanical performance and high self-healing capability, but also enrich the methodological toolbox for synergistic integration of dynamic covalent bonds and hydrogen bonds to surmount the tradeoff between mechanical properties and self-healing capacity of hydrogels.     

Dyeing and fastness properties of phthalimide‐based alkali‐clearable azo disperse dyes on poly(ethylene terephthalate)

The properties of a series of phthalimide‐containing azo disperse dyes and azo dyes with N‐methyl phthalimide moieties in their diazo component were investigated and compared when used to colour polyethylene terephthalate. The N‐substitution of the phthalimide gave a hypsochromic effect on the colour change and better colour yields on poly(ethylene terephthalate) fabrics, probably because of the electron‐donating property of the methyl group and the higher hydrophobicity of phthalimide‐containing azo dyes compared with those containing phthalimide moieties. The results show that phthalimide‐based azo disperse dyes have excellent dyeing fastness properties and that high wash fastness can be achieved using alkali clearance. This alternative clearance method is important for reducing the environmental impact of the dyeing process by replacing reductive clearing and, in particular, by removing the need for sodium hydrosulphite, which creates a high biological oxygen demand when released in conventional disperse dyeing effluent and which generates aromatic amines.     

Selective alkylation of acidic hydroxyl groups in coal

The organic molecules which make up coal are held together not only by covalent bonds, but also by a substantial network of hydrogen bonds as well as certain other weak intermolecular associations, which together are called the secondary structure. It is believed that acidic hydroxyl groups are responsible for most of the secondary structure. These attractive forces have been diminished traditionally by solvent swelling the coal, then permanently removed by selective silylation or acetylation of the polar functionalities. A new selective alkylation procedure has been developed which converts polar hydroxyls into relatively non-polar ethers and esters, and has been successfully tested on a bituminous and sub-bituminous coal. This selective O-alkylation proceeds rapidly under very mild conditions and renders the coal essentially free from its secondary structure.     

Proton magnetic resonance investigation of the orientation of hydrogen bonds in nylon 66, poly(vinyl alcohol), and cotton yarn

Directional dependence of the PMR-narrow-band in oriented fibers of nylon 66, poly(vinyl alcohol), and cotton has been investigated to study the orientation of hydrogen bonds in the unit cell. Filaments of oriented fibers were conditioned to 75% relative humidity, then aligned together axially and packed in a teflon tube. The teflon tube was suspended in the NMR probe in such a manner that the fiber axis was horizontal and could be rotated to a desired angle with respect to the magnetic field. Variation of the narrow-band line width as a function of the angle between the fiber axis and the magnetic field-direction shows a minimum at 0° orientation for nylon 66 and PVA, but in the case of cotton it shows a minimum at about 80° orientation. This indicates that in the case of nylon 66 and PVA, hydrogen bonds are oriented nearly prependicular to the chain axis. This would suggest that nylon 66 and PVA have interchain hydrogen bonding, but the hydrogen bonds contributing to directional dependence, in the case of cotton fiber, are intrachain. The interchain hydrogen bonds between the lateral chains, if they exist, must be random and, therefore, do not contribute to directional dependence. The interchain H bonds between central and corner chains are probably oriented in such a way that the horizontal component of p–p vectors have nearly the same orientation in the unit cell as the p–p vectors of the intrachain hydrogen bonds.     

DNA stability in ionic liquids and deep eutectic solvents

DNA molecules are known as the genetic information carriers. Recently, they have been explored as a new generation of biocatalysts or chiral scaffolds for metal catalysts. There is also growing interest in finding alternative solvents for DNA preservation and stabilization, including two unique types of solvents: ionic liquids (ILs) and deep eutectic solvents (DES). Therefore, it is important to understand how DNA molecules interact with these novel ionic solvent systems (i.e. ILs and DES). It is well known that inorganic divalent and monovalent ions preferentially bind with major and minor grooves of DNA structures. However, in the case of ILs and DES, organic cations may intrude into the DNA minor grooves; more importantly, electrostatic attraction between organic cations and the DNA phosphate backbone becomes a predominant interaction, accompanied by hydrophobic and polar interactions between ILs and DNA major and minor grooves. In addition, anions may form hydrogen bonds with cytosine, adenine and guanine bases. Despite these strong interactions, DNA molecules maintain a double helical structure in most ionic solvent systems, especially in aqueous IL solutions. The exciting advances of G‐quadruplex DNA structures in ILs and DES are also discussed. © 2014 Society of Chemical Industry     

On the Case of the Misplaced Hydrogens

Few other elements play a more central role in biology than hydrogen. The interactions, bonding and movement of hydrogen atoms are central to biological catalysis, structure and function. Yet owing to the elusive nature of a single hydrogen atom few experimental and computational techniques can precisely determine its location. This is exemplified in short hydrogen bonds (SHBs) where the location of the hydrogen atom is indicative of the underlying strength of the bonds, which can vary from 1–5 kcal/mol in canonical hydrogen bonds, to an almost covalent nature in single-well hydrogen bonds. Owing to the often-times inferred position of hydrogen, the role of SHBs in biology has remained highly contested and debated. This has also led to discrepancies in computational, biochemical and structural studies of proteins thought to use SHBs in performing chemistry and stabilizing interactions. Herein, we discuss in detail two distinct examples, namely the conserved catalytic triad and the photoreceptor, photoactive yellow protein, where studies of these SHB-containing systems have permitted contextualization of the role these unique hydrogen bonds play in biology.     

The 'Asx-Pro turn' as a local structural motif stabilized by alternative patterns of hydrogen bonds and a consensus-derived model of the sequence Asn-Pro-Asn

Analyses of databases derived from the Brookhaven Protein Data Bank have identified a set of related turn structures formed by the sequence Asx-Pro-Xxx(n). In a variety of flanking structural contexts, more than 60% of Asx-Pro sequences adopt a turn conformation stabilized by a set of alternative hydrogen bonds among the side chain O delta and backbone C = O carbonyl oxygens of Asx (residue i) and the backbone NH of residues i + 2, i + 3 and in some cases i + 4. In contrast, the structures adopted by Ser-Pro, His-Pro and other Xxx-Pro sequences reflect more heterogeneous hydrogen-bonding patterns. As expected, structures formed by Asx-Pro-Asx are similar to those formed by Asx-Pro- Xxx(n), but in some cases additional hydrogen bonds are formed between the Asx side chains. Hydrogen bond patterns within Asx-Pro and Asn-Pro- Asn turns are consistent with published NMR studies of helical (Asn-Pro- Asn-Ala)n peptides, indicating that a consensus structure reflecting these hydrogen bonds can serve as a partial model of the Asn-Pro-Asn- Ala tetrapeptide repeats of Plasmodium falciparum circumsporozoite protein.      

The investigation on states of water in different hydrophilic polymers by DSC and FTIR

The interaction between polymers and water in four hydrophilic polymer aqueous solutions were investigated by DSC and FTIR. DSC result shows that the different hydrophilic polymer/water mixtures have various water calorimetric behaviors in the melting temperature range of freezable bound water as well as free water. The melting temperature of freezable water and the amount of non-freezable water in the mixtures vary with the change of chemical structure of polymers. The melting point of the freezable bound water doesn’t change with the water content, revealing that water bound weakly to polymer chains can form a stable crystalline structure at high water content. For the three hydrophilic polymer/water mixtures with C=O group, the weight ratio of non-freezable water to polymers is constant, but varies with polymer chemical structures. The FTIR spectra confirmed the formation of the hydrogen bonds and it was found that there exist different states of water based on various strengths of hydrogen bonds. The OH stretching bands indicated the fraction of strongly bound water decreases with increasing water content. It was concluded that at least in hydrophilic polymer aqueous solutions with polar sites in polymer chains, the formation of non-freezable water is ascribed to the hydrogen bonds between hydrophilic polymers and water molecules. Different strengths of hydrogen bonds can affect the thermal behaviors of water in the hydrophilic polymer/water mixtures.     

Synthesis of a novel amphiphilic polymer containing nucleobases in the self-organized nanospheres

A simple strategy to achieve molecular recognition in water is to make the polymers self-organized into nanospheres which could incorporate the functional groups containing hydrogen bonding sites into hydrophobic-lipophilic regions. A novel amphiphilic polymer, Poly(polyoxyethylene-600)-oxy-5-(6-(1-thymine)hexyl)) isophthaloyl (PPETHI), has been synthesized. The PPETHI polymer could self-organize into nanospheres in dilute aqueous solution, which were 150–300 nm in diameter as estimated by SEM. The isophthaloyl with side hexyl thymine of the polymer self-organized into hydrophobic regions and the PEG surrounded it. Molecular recognition between thymine in PPETHI polymer and adenine substrate has been studied by FT-IR. The FT-IR studies demonstrate that C₄=O of thymine has recognized with N-H of adenine through complementary nucleobases. It shows that the typical characteristic band at 3,352 cm⁻¹ of N-H stretching vibration of adenine shifted to 3,373 cm⁻¹ and the band at 1,685 cm⁻¹ of C₄=O of thymine shifted to 1,680 cm⁻¹. To confirm the formation of hydrogen bonds, the N-H band at 3,373 cm⁻¹ and C₄=O band at 1,680 cm⁻¹ have retrieved to 3,312 cm⁻¹ and 1,685 cm⁻¹ respectively upon heating to 115 °C or higher by means of variable temperature FT-IR. The formations of hydrogen-bonds between thymine in the polymer and adenine substrate in nanospheres were confirmed. It could enhance their interaction and loading capacity.     

Metallic Nanoparticle-Enabled Sensing of a Drug-of-Abuse: An Attempt at Forensic Application

γ-Hydroxybutyric acid (GHB) functions as a depressant on the central nerve system and serves as a pharmaceutical agent in the treatment of narcolepsy and alcohol withdraw. In recent years, GHB has been misused as a recreational drug due to its ability to induce euphoric feelings. Moreover, it has gained increasing attention as a popular drug of abuse that is frequently related to drug-facilitated sexual assaults. At the moment, detection methods based on chromatography exhibit extraordinary sensitivity for GHB sensing. However, such techniques require complicated sample treatment prior to analysis. Optical sensors provide an alternative approach for rapid and simple analysis of GHB samples. Unfortunately, currently reported probes are mostly based on hydrogen bonding to recognize GHB, and this raises concerns about, for example, the lack of specificity. In this work, we report a bioinspired strategy for selective sensing of GHB. The method is based on specific enzyme recognition to allow highly selective detection of GHB with minimum interference, even in a complex sample matrix (e. g., simulated urine). In addition, the result can be obtained by either quantitative spectroscopy analysis or colorimetric change observed by the naked-eye, thus demonstrating its potential application in drug screening and forensic analysis.     

Hydrogen bonding in the electronic excited state

Because of its fundamental importance in many branches of science, hydrogen bonding is a subject of intense contemporary research interest. The physical and chemical properties of hydrogen bonds in the ground state have been widely studied both experimentally and theoretically by chemists, physicists, and biologists. However, hydrogen bonding in the electronic excited state, which plays an important role in many photophysical processes and photochemical reactions, has scarcely been investigated. Upon electronic excitation of hydrogen-bonded systems by light, the hydrogen donor and acceptor molecules must reorganize in the electronic excited state because of the significant charge distribution difference between the different electronic states. The electronic excited-state hydrogen-bonding dynamics, which are predominantly determined by the vibrational motions of the hydrogen donor and acceptor groups, generally occur on ultrafast time scales of hundreds of femtoseconds. As a result, state-of-the-art femtosecond time-resolved vibrational spectroscopy is used to directly monitor the ultrafast dynamical behavior of hydrogen bonds in the electronic excited state. It is important to note that the excited-state hydrogen-bonding dynamics are coupled to the electronic excitation. Fortunately, the combination of femtosecond time-resolved spectroscopy and accurate quantum chemistry calculations of excited states resolves this issue in laser experiments. Through a comparison of the hydrogen-bonded complex to the separated hydrogen donor or acceptor in ground and electronic excited states, the excited-state hydrogen-bonding structure and dynamics have been obtained. Moreover, we have also demonstrated the importance of hydrogen bonding in many photophysical processes and photochemical reactions. In this Account, we review our recent advances in electronic excited-state hydrogen-bonding dynamics and the significant role of electronic excited-state hydrogen bonding on internal conversion (IC), electronic spectral shifts (ESS), photoinduced electron transfer (PET), fluorescence quenching (FQ), intramolecular charge transfer (ICT), and metal-to-ligand charge transfer (MLCT). The combination of various spectroscopic experiments with theoretical calculations has led to tremendous progress in excited-state hydrogen-bonding research. We first demonstrated that the intermolecular hydrogen bond in the electronic excited state is greatly strengthened for coumarin chromophores and weakened for thiocarbonyl chromophores. We have also clarified that the intermolecular hydrogen-bond strengthening and weakening correspond to red-shifts and blue-shifts, respectively, in the electronic spectra. Moreover, radiationless deactivations (via IC, PET, ICT, MLCT, and so on) can be dramatically influenced through the regulation of electronic states by hydrogen-bonding interactions. Consequently, the fluorescence of chromophores in hydrogen-bonded surroundings is quenched or enhanced by hydrogen bonds. Our research expands our understanding of the nature of hydrogen bonding by delineating the interaction between hydrogen bonds and photons, thereby providing a basis for excited-state hydrogen bonding studies in photophysics, photochemistry, and photobiology.