Chemical selectivity of self-assembled monolayers of calix[4]resorcinarene

Selective molecular interactions at an interface formed by self-assembly of a macrocyclic synthetic host, calix[4]resorcinarene with four thiol groups (R4SH), are investigated. The recognition of guest adsorbates from aqueous solutions is monitored using surface plasmon resonance (SPR) and the orientation of the guest-molecule is probed using polarization modulation infrared absorption spectroscopy (PM-IRRAS). The experiments reported here demonstrate that the chemical selectivity of self-assembled monolayers (SAMs) of host molecules such as calix[4]resorcinarenes extends to isomers of several different guest molecules. By using structural isomers of guest molecules such as bipyridine and nitrophenol that are multidentate hydrogen bond acceptors, it is shown that geometric match between guest and host molecules is an integral aspect of the recognition phenomena. Results from SPR and PM-IRRAS experiments reported here highlight the interplay between steric size and forces such as hydrogen bonding and hydrophobic interactions. Competitive and sequential adsorption of guest molecules such as -hydroxy-γ-butyrolactone and 4,4′-bipyridine shows that these guests compete for the same binding sites on the surface and that the interplay between steric size and molecular forces underlies the preferential selectivity of one guest molecule over another.     

Potentiometric evaluation of solvent polymeric carbonate-selective membranes based on molecular tweezer-type neutral carriers

Potentiometric properties of the ion-selective electrodes) based on highly plasticized PVC membranes doped with the carbonate-selective cholic acid (CA) derivatives have been measured. The carbonate-selective neutral carriers have been prepared by coupling one to three trifluoroacetobenzoyl (TFAB) groups to a cholic acid derivative which has three hydroxyl linkers lining on the C3, C7, and C12 positions of its rigid steroidal ring structure. The membranes based on cholic acid derivatives with two TFABs [3,7-bis(TFAB)CA, 3,12-bis(TFAB)CA, and 7,12-bis(T-FAB)CA] exhibited remarkably improved carbonate selectivity, indicating that the bis(FAB)CAs behave like molecular tweezers for the carbonate ion. For example, 3,12-bis(TFAB)CA resulted in 10-300-fold-enhanced carbonate selectivity over other anions (e.g., salicylate, ClO4-, SCN-, (HPO4)2-, NO3-, NO2-, Br-, and Cl-) compared to that of the neutral carriers with a single TFAB group. The distances between the carbonate binding centers of bis(TFAB)CAs, i.e., the carbonyl carbons of the two TFAB groups, are in the 7.3-7.9-A range at the AM1 level semiempirical calculation, which is too far for the carbonate ion to form direct covalent bonding. The fast atom bombardment mass spectra of bis(TFAB)CAs show that significant fractions of the compounds are either mono- or dihydrated before complexing the carbonate ion. These findings seem to suggest that bis(TFAB)CAs recognize the incoming carbonate ion by forming both covalent and hydrogen bonding between the hydrated and unhydrated TFAB groups. The analytical utility of the carbonate-selective electrode based on 3,12-bis(TFAB)-CA has been demonstrated by measuring the total carbon dioxide in human serum in the presence of lipophilic anion interferents, e.g., salicylate.     

Interaction of bisphenol A with bovine hemoglobin using spectroscopic and molecular modeling methods

The interaction of bisphenol A with bovine hemoglobin (BHb) under physiological conditions was investigated by using fluorescence, ultraviolet-visible (UV-Vis) absorption, circular dichroism (CD), and molecular modeling. The experimental results showed that BPA can bind with BHb to form a complex. The binding constant Ka and the number of binding sites n were calculated to be 1.49 × 10(5) L mol(-1) and 1, respectively. Molecular modeling study revealed that BPA bound into BHb central cavity, and the binding mode of BPA-BHb complex could be hydrogen bonding. The UV-Vis absorption and CD spectra indicated that the secondary structure of BHb was altered, which may affect physiological functions of hemoglobin. This work is helpful for clarifying the molecular toxic mechanism of BPA in vivo.     

手性聚苯胺的制备及其电磁学性能研究

采用二次掺杂法制备了具有手征特性的聚苯胺,利用傅立叶红外光谱(FT-IR)、X射线衍射仪(XRD)、圆二色谱仪(CD)和紫外一可见光分光光度计(UV-vis)等分析手段对聚苯胺的结构、性能和手征特性进行了表征.结果表明,通过过硫酸铵作引发剂、盐酸掺杂获得了导电的盐酸掺杂态聚苯胺(PANI-HCI);通过氨水脱掺杂后得到本征态聚苯胺(EB),EB通过手性樟脑磺酸(CSA)诱导,形成了手征性螺旋构型聚苯胺.电磁性能测试表明,与非手性聚苯胺相比,手性聚苯胺具有较优越的吸波性能.     

On the balance of interaction modes in supramolecular complexes of a carboxylic acid host and alcohol guests. X-ray crystal structures of inclusion compounds with MeOH and EtOH

Remarkable differences have been observed between the host–guest interaction modes in two closely related crystalline inclusion compounds [1·MeOH (1:1) and 1·EtOH(1:1)] of the same carboxylic host (1). The minor modification of the guest structure crucially affected the hydrogen bonding recognition pattern between given complementary groups, which demonstrates the sensitive balance of intermolecular interaction modes that must be controlled for successful crystal engineering and design of supramolecular compounds.     

Probing the in vitro binding mechanism between human serum albumin and La2 O2 CO3 nanoparticles

The interaction of La₂ O₂ CO₃ nanoparticles (La NPs) with human serum albumin (HSA) has been studied. Analysis of the fluorescence quenching data of HSA using Stern–Volmer method showed that La NPs quenched HSA fluorescence in static quenching mode. Thermodynamic analysis indicated that hydrogen bonds and Van der Waals interactions play a major role for HSA–La NPs associations. Fluorescent displacement measurements confirmed that the primary binding site of La NPs was mainly located within site I (subdomain IIA) of HSA. The binding distance was calculated by using Forster resonance energy transfer theory. Also, the results of Fourier‐transform infrared spectroscopy, circular dichroism, three‐dimensional fluorescence and UV–visible measurements indicated that the binding of above La NPs to HSA may induce conformational and micro‐environmental changes of protein. This study suggested that the conformational change of HSA was at secondary structure of it and the biological activity of this protein was changed in the present of La NPs.Inspec keywords: proteins, molecular biophysics, molecular configurations, nanoparticles, lanthanum compounds, fluorescence, radiation quenching, thermal analysis, biothermics, biochemistry, hydrogen bonds, van der Waals forces, Fourier transform infrared spectra, circular dichroism, visible spectra, ultraviolet spectra, nanobiotechnologyOther keywords: in vitro binding mechanism, human serum albumin, La₂ O₂ CO₃ nanoparticles, Stern‐Volmer method, La NPs quenched HSA fluorescence, static quenching mode, thermodynamic analysis, hydrogen bonds, Van der Waals interactions, HSA‐La NPs associations, fluorescent displacement measurements, primary binding site, subdomain IIA, binding distance, Forster resonance energy transfer theory, Fourier‐transform infrared spectroscopy, circular dichroism, three‐dimensional fluorescence, UV‐visible measurements, conformational changes, microenvironmental changes, protein, secondary structure, La₂ O₂ CO₃      

An energy conservation approach to adsorbate-induced surface stress and the extraction of binding energy using nanomechanics

Surface stress induced by molecular adsorption in three different binding processes has been studied experimentally using a microcantilever sensor. A comprehensive free-energy analysis based on an energy conservation approach is proposed to explain the experimental observations. We show that when guest molecules bind to atoms/molecules on a microcantilever surface, the released binding energy is retained in the host surface, leading to a metastable state where the excess energy on the surface is manifested as an increase in surface stress leading to the bending of the microcantilever. The released binding energy appears to be almost exclusively channeled to the surface energy, and energy distribution to other channels, including heat, appears to be inactive for this micromechanical system. When this excess surface energy is released, the microcantilever relaxes back to the original state, and the relaxation time depends on the particular binding process involved. Such vapor phase experiments were conducted for three binding processes: physisorption, hydrogen bonding, and chemisorption. Binding energies for these three processes were also estimated.     

Characterization of Alizarin Red S binding sites and structural changes on human serum albumin: a biophysical study

Alizarin Red S (ARS), is a water-soluble, widely used anthraquinone dye synthesized by sulfonation of alizarin. In this report, the binding of ARS to human serum albumin (HSA) was characterized by employing fluorescence, UV/vis absorption, circular dichroism (CD), and molecular modeling methods. The data of fluorescence spectra displayed that the binding of ARS to HSA is the formation of HSA-ARS complex at 1:1 stoichiometric proportion. Hydrophobic probe 8-anilino-1-naphthalenesulfonic acid (ANS) was employed and elucidated that the dye was located in subdomain IIIA. This phenomenon corroborates the result of site-specific probe displacement experiments, which demonstrate the dye is at indole-benzodiazepine site (Sudlow's site II); and it is also consistent with guanidine hydrochloride (GuHCl) induced HSA unfolding studies and molecular modeling simulations. The features of the dye, which led to structural perturbations of HSA, have also been studied in detail by methods of UV/vis, CD and three-dimensional fluorescence spectroscopy.     

Studies on binding of single‐stranded DNA with reduced graphene oxide–silver nanocomposites

The binding reaction of reduced graphene oxide–silver nanocomposites (rGO–AgNCs) with calf thymus single‐stranded DNA (ssDNA) was studied by ultraviolet–visible absorption, fluorescence spectroscopy and circular dichroism (CD), using berberine hemisulphate (BR) dye as a fluorescence probe. The absorbance of ssDNA increases, but the fluorescence intensity is quenched with the addition of rGO–AgNCs. The binding of rGO–AgNCs with ssDNA was able to increase the quenching effects of BR and ssDNA, and induce the changes in CD spectra. All of the evidence indicated that there was a relatively strong interaction between ssDNA and rGO–AgNCs. The data obtained from fluorescence experiments revealed that the quenching process of ssDNA caused by rGO–AgNCs is primarily due to complex formation, i.e. static quenching. The increasing trend of the binding equilibrium constant (K a) with rising temperature indicated that the binding process was an endothermic reaction. The calculated thermodynamic parameters showed that the binding process was thermodynamically spontaneous, and hydrophobic association played predominant roles in the binding of ssDNA to the surface of rGO–AgNCs.Inspec keywords: DNA, fluorescence spectroscopy, circular dichroism, nanofabrication, nanobiotechnology, silver, hydrophobicity, molecular biophysics, radiation quenching, biochemistry, nanocomposites, visible spectra, ultraviolet spectra, dyes, fluorescence, association, graphene compoundsOther keywords: ssDNA increases, fluorescence intensity, fluorescence experiments, binding equilibrium constant, binding process, reduced graphene oxide‐silver nanocomposites, binding reaction, calf thymus single‐stranded DNA, fluorescence spectroscopy, fluorescence probe, complex formation, static quenching, calculated thermodynamic parameters, rGO‐AgNCs binding, ultraviolet‐visible absorption, berberine hemisulphate dye, circular dichroism, CO‐Ag     

Vibrational circular dichroism spectroscopy of solid polymer films: effects of sample orientation

Vibrational circular dichroism (VCD) spectra of anisotropic thin solid samples are often superimposed with large contributions of linear birefringence and linear dichroism. In this study a theoretical approach is given on how to extract the true VCD spectrum out of such superimposed spectra. To verify this approach, the VCD spectra of achiral polymer films were examined. The polymers are supposed to give a zero line as VCD spectrum after eliminating the linear contributions. Applying our approach, in which four VCD spectra in different but selected sample orientations are recorded, and calculating their average, leads to the expected result, i.e., a zero line for achiral polymers. The advantage of this method for the elimination of artifacts from solid-state VCD spectra is that no further measurements are required (e.g., linear dichroism measurements or the determination of the orientation with the maximum anisotropy).     

The combined effect of intercalated oxidant and thermal annealing on surface morphology and photo-physical properties of poly(3-octylthiophene) films

As intercalated oxidant (guest) is chemically de-intercalated stepwise from poly(3-octylthiophene) (P3OT) (host), a gradual evolution of a mat-type crystalline structure is observed. Moreover, the intercalated oxidant has marked effect on the arrangement of polymeric chains. Complete thermal de-intercalation of oxidant leads to interwoven cylindrical bundles of polymeric chains similar to corrugated-rod-type (CRT) morphology seen for thermally annealed pristine P3OT. The red shift along with increase in intensity and sharpness in UV–vis spectra and photoluminescence quenching indicate that the ripening of the self-assembling nature of pristine P3OT polymer leads to the formation of polymeric quasi-crystals when it is freed from oxidant impurity chemically or by prolonged soft-thermal annealing of oxidant intercalated polymer matrix. The present results enable the analysis of the effects of geometrical parameters characterizing the mutual host–guest complementarity as well as host–guest and guest–guest interactions on the crystal packing of intercalate.     

Synthesis and thermo-optical stability of o-methyl red-intercalated Ni–Fe layered double hydroxide material

In the present letter, an anionic azo dye, o-methyl red (2-(4-(dimethyl-amino) phenylazo) benzoic acid, MR), was incorporated successfully into the interlayer domain of Ni–Fe layered double hydroxide (LDH) by coprecipitation route. X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR) and simultaneous thermogravimetric and differential thermal analysis (TG-DTA) revealed the presence of supramolecular host–guest interaction between the host matrix and interlayer anionic dye guest with an expanded interlayer distance. The UV–visible diffuse reflectance (UV–VIS/DR) spectra showed that the dye-intercalated LDH had higher photostability than the pristine dye. Moreover, there was no significant change for the interlayer MR anions in the UV–VIS/DR spectra of the dye-intercalated sample after heating up to 200 °C, indicating that the thermostability of dye is markedly enhanced by the intercalation into the gallery domain of NiFe-LDH.     

Dual source fourier transform polarization modulation spectroscopy: an improved method for the measurement of circular and linear dichroism

It is shown that the use of two sources in a four-port interferometer equipped with cube-corner mirrors leads to increased signal-to-noise ratios in Fourier transform (FT-IR) circular and linear dichroism spectra. The output beam to the sample is a superposition of two interferograms, one from each source, having opposite Fourier phases. These two interferograms cancel one another to the degree that the two sources are matched in intensity. If the radiation from each of the two sources is first polarized orthogonally with respect to the other and passed through a polarization modulator before reaching the sample, the resulting polarization-modulation interferograms are out of Fourier phase and out of polarization-modulation phase. As a result, the polarization-modulation interferograms, due to circular or linear dichroism in the sample, from the two sources combine positively rather than negatively. An improvement in signal-to-noise ratio of up to two (or a factor of four in scan-time reduction for the same signal-to-noise ratio) compared to single source operation can be realized, while at the same time, the potential for saturation of the detector signal is significantly reduced due to the reduction in magnitude of the combined ordinary infrared transmission interferogram. Absorption and circular dichroism spectra from a dual-source FT-IR spectrometer are presented and analyzed.     

Effects of molecular shape on the photoluminescence of dyes embedded in a chiral polymer with a photonic band gap

Circularly polarized photoluminescence has been generated by embedding fluorescent guest molecules in a helically aligned polymer host with a selective reflection band, which coincides with the emission wavelength of the embedded dyes. We have investigated the photoluminescence from a range of guest molecules of varying shapes and found that one circular polarization is suppressed within the reflection band of the host independently of the shape of the guest molecules. However, just outside the band edges, there is an enhancement of the same polarization and the relative magnitudes of the enhancement at the two band edges is strongly influenced by the shape of the guest molecules. This effect has been understood from the ordering of the guest molecules in the polymer host.     

Core–shell porphyrin·multi-walled carbon nanotube hybrids linked by multiple hydrogen bonds: nanostructure and electronic communication

In this paper, multiple hydrogen bonding interaction of ureidopyrimidinone (UPM) was employed as the linking bridge for the formation of a novel porphyrin·multi-walled carbon nanotube (MWNT) hybrid, which was then used to fabricate a layer-by-layer (LbL) film composed of porphyrin-UPM·MWNT-UPM. Both in the assembled hybrid and the LbL film, porphyrin was closely attached to the surface of the MWNT under the strong multiple hydrogen bonding interaction, forming the core–shell structure. In addition, strong electronic communication was observed between porphyrin and MWNT. The hydrogen bonding association behavior between porphyrin-UPM and MWNT-UPM was attentively analyzed by UV–Vis spectra, fluorescent spectra and transmission electron microscope experiments. It was found that the hydrogen bonding interactions were crucial for the formation of the supramolecular hybrid and the LbL film as well as the occurrence of interfacial electronic communication. This result indicated that the introduction of strong noncovalent bonding interaction between donor and acceptor is an appropriate way to control the material structure and facilitate the interfacial electronic communication in the hybrids which lay the groundwork for their application in electrochemical sensors or photovoltaic devices.     

Room-temperature ferromagnetism in Cu doped GaN nanowires

We report magnetism in Cu doped single-crystalline GaN nanowires. The typical diameter and the length of the Ga1-xCuxN nanowires (x = 0.01, 0.024) are 10-100 nm and tens of micrometers, respectively. The saturation magnetic moments are measured to be higher than 0.86 microB/Cu at 300 K, and the Curie temperatures are far above room temperature. Anomalous X-ray scattering and X-ray diffraction measurement make it clear that Cu atoms substitute the Ga sites, and they largely take part in the wurtzite network of host GaN. X-ray absorption and X-ray magnetic circular dichroism spectra at Cu L(2,3) edges show that doped Cu has local magnetic moment and the electronic configuration of it is mainly 3d9 but mixed with a small portion of trivalent component. It seems that the ionocovalent bonding nature of Cu 3d orbital with surrounding semiconductor medium makes Cu atom a mixed electron configuration and local magnetic moments. These outcomes suggest that the Ga1-xCuxN system is a room-temperature ferromagnetic semiconductor.     

Circular Dichroic Study of the Interaction of Gelatin with Palladium(n)

The structure of the gelatin-palladium(u) complexes formed under a variety of conditions was studied by measuring CD and absorption spectra and comparing them with those of simple peptide complexes. The complex is considered to be tetragonal and tetracoordinate. In the acid pH region the formation of two types of complexes in which palladium(n) is bound by the carboxylate group is proposed, depending on the pH and gelatin concentration. The formation of complexes in which palladium(n) is bound by each of the imidazole and amino groups is shown above around pH 4.5. In the alkaline pH region all of the carboxyl, imidazole and amino groups are involved in complexing, and palladium(u) is presumably coordinated by three peptide nitrogen donor atoms in addition to the ionizable side-group. In both acid and alkaline pH regions an additional band is observed near 260 nm in the circular dichroism spectrum, which is ascribed to the complex with one imidazole nitrogen and three peptide nitrogen donor atoms.     

Imprinting Chirality onto the Electronic States of Colloidal Perovskite Nanoplatelets

The direct synthesis of chiroptical organic–inorganic methylammonium lead bromide perovskite nanoplatelets that are passivated by R‐ or S‐phenylethylammonium ligands is reported. The circular dichroism spectra can be divided into two components: (1) a region associated with a charge transfer transition between the ligand and the nanoplatelet, 300–350 nm, and (2) a region corresponding to the excitonic absorption maximum of the perovskite, 400–450 nm. The temperature‐ and concentration‐dependent circular dichroism spectra indicate that the chiro‐optical response arises from chiral imprinting by the ligand on the electronic states of the quantum‐confined perovskite rather than chiral ligand‐induced stereoselective aggregation.     

Chiral Plasmonic Hydrogen Sensors

In this article, a chiral plasmonic hydrogen‐sensing platform using palladium‐based nanohelices is demonstrated. Such 3D chiral nanostructures fabricated by nanoglancing angle deposition exhibit strong circular dichroism both experimentally and theoretically. The chiroptical properties of the palladium nanohelices are altered upon hydrogen uptake and sensitively depend on the hydrogen concentration. Such properties are well suited for remote and spark‐free hydrogen sensing in the flammable range. Hysteresis is reduced, when an increasing amount of gold is utilized in the palladium‐gold hybrid helices. As a result, the linearity of the circular dichroism in response to hydrogen is significantly improved. The chiral plasmonic sensor scheme is of potential interest for hydrogen‐sensing applications, where good linearity and high sensitivity are required.     

Polarimetric investigation of materials with both linear and circular anisotropy

Abstract

We investigate light propagation through materials with both linear and circular anisotropy and find the relation of the amplitude and polarization transfer functions to the four anisotropic characteristics: linear circular birefringence, and linear and circular dichroism. We determine these four characteristics of anisotropic samples by measuring the output intensity and polarization corresponding to different input polarization azimuths and fitting the theoretical and experimental results. In our experiments we have used films of side-chain azobenzene polyesters in which optical anisotropy had been previously induced on illumination with elliptically polarized light.