Conventional Fluorescence Spectroscopy Research Articles

Unveiling large charge transfer character of PSII in an iron-deficient cyanobacterial membrane: A Stark fluorescence spectroscopy study.

In this work, we applied Stark fluorescence spectroscopy to an iron-stressed cyanobacterial membrane to reveal key insights about the electronic structures and excited state dynamics of the two important pigment-protein complexes, IsiA and PSII, both of which prevail simultaneously within the membrane during iron deficiency and whose fluorescence spectra are highly overlapped and hence often hardly resolved by conventional fluorescence spectroscopy. Thanks to the ability of Stark fluorescence spectroscopy, the fluorescence signatures of the two complexes could be plausibly recognized and disentangled. The systematic analysis of the SF spectra, carried out by employing standard Liptay formalism with a realistic spectral deconvolution protocol, revealed that the IsiA in an intact membrane retains almost identical excited state electronic structures and dynamics as compared to the isolated IsiA we reported in our earlier study. Moreover, the analysis uncovered that the excited state of the PSII subunit of the intact membrane possesses a significantly large CT character. The observed notably large magnitude of the excited state CT character may signify the supplementary role of PSII in regulative energy dissipation during iron deficiency.

Partial inhibition of complex I restores mitochondrial morphology and mitochondria‐ER communication in hippocampus of APP/PS1 mice

AbstractBackgroundAlzheimer’s Disease (AD) has no cure. We showed that partial inhibition of mitochondrial complex I (MCI) with small molecule CP2 induced adaptive stress response activating multiple neuroprotective mechanisms. Chronic treatment reduced inflammation, improved synaptic and mitochondrial functions, and blocked neurodegeneration in symptomatic APP/PS1 mice, a translational model of AD.MethodsAnalysis of mitochondrial morphology and mitochondria‐endoplasmic reticulum (ER) contacts (MERCS) was done in the hippocampal CA1 tissue from APP/PS1 mice treated with CP2 and compared to APP/PS1 and non‐transgenic mice treated with vehicle using serial block‐face scanning electron microscopy (SBFSEM) and three‐dimensional (3D) EM reconstructions combined with western blot analysis and next generation RNA sequencing.ResultsWe demonstrate that CP2 treatment restores mitochondrial morphology and mitochondria‐ ER communication, reducing ER stress in the APP/PS1 mouse brain. Using 3D EM reconstructions, we found that mitochondria in AD dendrites existed primarily as mitochondria‐on‐a‐string (MOAS), a morphological phenotype that is difficult to detect using conventional 2D EM or fluorescence spectroscopy. Compared to other morphological phenotypes, MOAS are extensively enveloped in the ER membranes forming multiple MERCS known to contribute to abnormal lipid and calcium homeostasis, and ER stress in AD. CP2 treatment specifically reduced MOAS formation, consistent with improved energy homeostasis in the brain, with concomitant reduction in MERCS, ER stress, and improved lipid homeostasis.ConclusionsThese data provide novel information on the role MOAS play in AD. Our data demonstrate that in response to energetic stress, mitochondria in dendrites acquire MOAS phenotype with increased interaction with the ER, which may synergistically contribute to the AD development. Since CP2 treatment alleviated the ER stress and improved mitochondrial dynamics and function, these data further support the development of partial MCI inhibitors as disease modifying strategy for AD.

A self-organizing map approach to the analysis of lake DOM fluorescence for differentiation of organic matter sources.

The sources and properties of dissolved organic matter (DOM) in two lakes with different non-point source inputs were investigated by combining conventional three-dimensional fluorescence spectroscopy methods with a self-organizing map (SOM). To assess the DOM humification level, the representative neurons 1, 11, 25, and 36 were assessed. The SOM model showed that the DOM humification level of the Gaotang Lake (GT) which has a mainly agricultural non-point source input was significantly higher than that of the Yaogao Reservoir (YG) which has a mainly terrestrial source input (P < 0.01). The GT DOM mainly came from factors such as agricultural-related farm compost and decaying plants, while the YG DOM originated from human activities around the lake. The source characteristics of the YG DOM are obvious, with a high level of biological activity. Five representative areas in the fluorescence regional integral (FRI) were compared. The comparison showed that during the flat water period, the GT water column showed more terrestrial characteristics, even though the humus-like fractions in the DOM of both lakes were derived from microbial decomposition. Principal component analysis (PCA) showed that the agricultural lake water DOM (GT) was dominated by humus components, while the urban lake water DOM (YG) was dominated by authigenic sources.

Validation of conventional and synchronous fluorescence emission of potable water

Water from filter plants and bottled water is generally safe to drink but regular quality monitoring of these facilities requires development of quick analytical technique to ensure public safety and health. This study presented the variation of two components in spectra of conventional fluorescence spectroscopy (CFS) and four components in synchronous fluorescence spectroscopy (SFS) to assess the quality of 25 water samples from different sources. Poor quality water either due to organic or inorganic contaminants presented high intensity fluorescence emission in the blue green region and low intensity water Raman peak unlike an intense water Raman peak originated from pure water when excited at 365 nm. Emission intensity in the blue green region and water Raman peak can be used as a marker for quick screening of water quality. Although few discrepancies were observed in CF spectra of samples with intense Raman peak but were found to be positive for bacterial contamination, thus questioning the sensitivity of CFS that needs to be addressed. Whereas, SFS presented highly selective and detailed picture of water contaminants emitting aromatic amino acid, fulvic and humic like fluorescence. It is suggested that the specificity of CFS can be enhanced by coupling it with SFS or use of multiple excitation wavelengths to target different fluorophores for water quality analysis.

Role of Polyanions and Surfactant Head Group in the Formation of Polymer-Colloid Nanocontainers.

This study was aimed at the investigation of the supramolecular systems based on cationic surfactants bearing cyclic head groups (imidazolium and pyrrolidinium) and polyanions (polyacrylic acid (PAA) and human serum albumin (HSA)), and factors governing their structural behavior to create functional nanosystems with controlled properties. Research hypothesis. Mixed PE-surfactant complexes based on oppositely charged species are characterized by multifactor behavior strongly affected by the nature of both components. It was expected that the transition from a single surfactant solution to an admixture with PE might provide synergetic effects on structural characteristics and functional activity. To test this assumption, the concentration thresholds of aggregation, dimensional and charge characteristics, and solubilization capacity of amphiphiles in the presence of PEs have been determined by tensiometry, fluorescence and UV-visible spectroscopy, and dynamic and electrophoretic light scattering. The formation of mixed surfactant-PAA aggregates with a hydrodynamic diameter of 100-180 nm has been shown. Polyanion additives led to a decrease in the critical micelle concentration of surfactants by two orders of magnitude (from 1 mM to 0.01 mM). A gradual increase in the zeta potential of HAS-surfactant systems from negative to positive value indicates that the electrostatic mechanism contributes to the binding of components. Additionally, 3D and conventional fluorescence spectroscopy showed that imidazolium surfactant had little effect on HSA conformation, and component binding occurs due to hydrogen bonding and Van der Waals interactions through the tryptophan amino acid residue of the protein. Surfactant-polyanion nanostructures improve the solubility of lipophilic medicines such as Warfarin, Amphotericin B, and Meloxicam. Surfactant-PE composition demonstrated beneficial solubilization activity and can be recommended for the construction of nanocontainers for hydrophobic drugs, with their efficacy tuned by the variation in surfactant head group and the nature of polyanions.

A Critical Study on the Potential of Solid-Phase Fluorescence Spectroscopy (SPFS) in Quantitative Analysis: Effect of Solid Diluent and Sampling Method on Signal Quality.

Solid-phase fluorescence spectroscopy (SPFS) is a very useful non-destructive technique for directly analyzing samples in solid form without the use of solvents. However, due to the so-called inner-filter effect, it is sometimes necessary to dilute solid samples using non-fluorescent solids as diluents. This study aimed to explore the potential of SPFS in the quantitative analysis of fluorescent species based on: (1) the type of solid diluent; and (2) the sampling method used in the SPFS analysis. Four different solids were used as solid diluents in the preparation of standard mixtures having different concentrations of rhodamine b and fluorescein as model compounds. Standard mixtures of model compounds were sampled by two different methods called: (1) the powder-cell method; and (2) the adhesive tape method. LOQ and calibration sensitivity calculated from the calibration graphs were used to assess the measurement performance. The usability of SPFS in real-sample analyses was also evaluated in detail. Among the solid diluents studied, the best results were obtained with sodium carbonate. The powder-cell method yielded a significant advantage over the adhesive tape method. The lowest LOQs for rhodamine b and fluorescein were obtained by sodium carbonate and the powder-cell method as 0.06 and 0.11 mg/kg, respectively. The results of real-sample analyses were verified using conventional liquid-phase fluorescence spectroscopy (LPFS). Solid-diluent type and sampling method were found to affect the performance of the SPFS technique. A combination of sodium carbonate and the powder-cell method gave the best results. According to the t-test, no difference was observed between the means obtained by SPFS and LPFS techniques in real-sample analyses. In SPFS, toxic organic solvents and difficult sample preparation steps are not required. This makes the method advantageous over conventional fluorescence analyses performed in the liquid phase.

Chiral Transport in Nanochannel Based Artificial Drug Transporters.

The precise regulation of chiral drug transmembrane transport can be achieved through drug transporters in living organisms. However, implementing this process in vitro is still a formidable challenge due to the complexity of the biological systems that control drug enantiomeric transport. Herein, a facile and feasible strategy is employed to construct chiral L-tyrosine-modified nanochannels (L-Tyr nanochannels) based on polyethylene terephthalate film, which could enhance the chiral recognition of propranolol isomers (R-/S-PPL) for transmembrane transport. Moreover, conventional fluorescence spectroscopy, patch-clamp technology, laser scanning confocal microscopy, and picoammeter technology are employed to evaluate the performance of nanochannels. The results show that the L-Tyr nanochannel have better chiral selectivity for R-/S-PPL compared with the L-tryptophan (L-Trp) channel, and the chiral selectivity coefficient is improved by about 4.21-fold. Finally, a detailed theoretical analysis of the chirality selectivity mechanism is carried out. The findings would not only enrich the basic theory research related to chiral drug transmembrane transport, but also provide a new idea for constructing artificial channels to separate chiral drugs.

Ultrabright Föster Resonance Energy Transfer Nanovesicles: The Role of Dye Diffusion.

The development of contrast agents based on fluorescent nanoparticles with high brightness and stability is a key factor to improve the resolution and signal-to-noise ratio of current fluorescence imaging techniques. However, the design of bright fluorescent nanoparticles remains challenging due to fluorescence self-quenching at high concentrations. Developing bright nanoparticles showing FRET emission adds several advantages to the system, including an amplified Stokes shift, the possibility of ratiometric measurements, and of verifying the nanoparticle stability. Herein, we have developed Förster resonance energy transfer (FRET)-based nanovesicles at different dye loadings and investigated them through complementary experimental techniques, including conventional fluorescence spectroscopy and super-resolution microscopy supported by molecular dynamics calculations. We show that the optical properties can be modulated by dye loading at the nanoscopic level due to the dye’s molecular diffusion in fluid-like membranes. This work shows the first proof of a FRET pair dye’s dynamism in liquid-like membranes, resulting in optimized nanoprobes that are 120-fold brighter than QDot 605 and exhibit >80% FRET efficiency with vesicle-to-vesicle variations that are mostly below 10%.

Mass Spectrometric Analysis of the Photobleaching of Protoporphyrin IX Used in Photodynamic Diagnosis and Therapy of Cancer.

Photobleaching and photoproduct formations are considered essential phenomena in improving the efficacy of photodynamic diagnosis and therapy (PDD and PDT). We investigated the photobleaching of protoporphyrin IX (PpIX) by measuring its concentration with mass spectrometry (MS). The reduction in the concentration of PpIX dissolved in dimethyl sulfoxide was measured during PDD and PDT conditions using lasers with wavelengths of 405 and 635 nm, respectively, at a power density of 10, 50 or 100 mW/cm2 . The obtained results were compared with the results of conventional fluorescence spectroscopy and previously reported results. Our results demonstrate the variation in the MS-based photobleaching coefficient of PpIX with the power density, while the fluorescence-based photobleaching coefficient was independent of the power density. The results of MS also show faster photobleaching of PpIX in comparison with that obtained from fluorescence. The difference may be attributed to the change in the fluorescence quantum yield of PpIX with its concentration and the effect of fluorescence emission from the PpIX photoproducts. Thus, an MS-based investigation of the photobleaching poses to be a more stable investigation form. Our finding highlights the importance of recognizing the potential significance of these discoveries in the PDD and PDT dosimetry and efficacy.

Effect of pH on heat-induced interactions in high-protein milk dispersions and application of fluorescence spectroscopy in characterizing these changes

This study investigated casein-whey protein interactions in high-protein milk dispersions (5% protein wt/wt) during heating at 90°C for 1.5 to 7.5 min at 3 different pH of 6.5, 6.8, and 7.0, using both conventional methods (gel electrophoresis, physicochemical properties) and fluorescence spectroscopy. Conventional methods confirmed the presence of milk protein aggregates during heating, similar to skim milk. These methods were able to help in understanding the denaturation and aggregation of milk proteins as a function of heat treatment. However, the results from the conventional methods were greatly affected by batch-to-batch variations and, therefore, differentiation could be drawn only in nonheated samples and samples heated for a longer duration. The front-face fluorescence spectroscopy was found to be a useful tool that provided additional information to conventional methods and helped in understanding differences between nonheated, low-, and high-heated samples, along with the type of sample used (derived from liquid or powder milk protein concentrates). At all pH values, tryptophan maxima in nonheated samples derived from powdered milk protein concentrates presented a blue shift in comparison to samples derived from liquid milk protein concentrates, and tryptophan maxima in heated samples presented a red shift. With the heating of the sample, Maillard emission and excitation spectra also showed increases in the peak intensities from 408 to 432 and 260 to 290 nm, respectively. As the level of denaturation increased with heating, a marked differentiation can be seen in the principal component analysis plots of tryptophan, Maillard emission, and excitation spectra, indicating that the front-face fluorescence technique has a potential to monitor and classify samples according to milk protein interactions as a function of pH and heat exposure. Overall, it can be said that the pattern of protein-protein interactions in high-protein dispersions was similar to the observation reported in skim milk systems, and fluorescence spectroscopy with chemometrics can be used as a rapid, nondestructive, and complementary method to conventional methods for following heat-induced changes.

Polarization gating technique extracts depth resolved fluorescence redox ratio in oral cancer diagnostics.

Mortality of oral cancer is often due to late diagnosis. Effective non-invasive diagnostic techniques may increase the survival rate based on an earlier diagnosis.. We report on the application of the polarization gating technique for isolating weakly scattered and highly scattered components of fluorescence emission from the superficial and deeper layers of tissue due to intrinsic fluorophores NADH and FAD. The fluorescence polarization spectra were collected from 21 normal and 67 oral squamous cell carcinoma biopsy tissues. The tissues were excited at 350 nm and the fluorescence emission had two peaks corresponding to NADH, and FAD respectively. The spectra were analyzed using the polarization gating technique along with the spectral deconvolution method to derive the optical redox ratio from different layers of tissue. The fractional change in redox ratio between superficial and deeper layers of tissue exhibits excellent statistical significance (p<10-3) which may be due to a shift in the metabolic pathway from oxidative phosphorylation to glycolysis in the cancer cell. Further, variation in collagen intensity in deeper layers of tissue is observed which may be attributed to the breakdown of collagen fibers in the stroma. Linear discriminant analysis showed that oral cancer tissue is discriminated with a better accuracy using polarization gating technique than that of conventional fluorescence spectroscopy.

Back Cover: Hydrogen‐Bond Free Energy of Local Biological Water (Angew. Chem. Int. Ed. 18/2020)

Biological water regulates the structure, dynamics, and function of the building blocks of life, which evolved in a hydrated environment. In their Research Article on page 7089, S. K. Kwak, T. H. Yoo, O.-H. Kwon, and co-workers present the development of an experimental method for measuring the hydrogen-bond free energy of biological water, which is the foundation of hydration, based on conventional time-resolved fluorescence spectroscopy and protein engineering.

Human cystic fibrosis monocyte derived macrophages display no defect in acidification of phagolysosomes when measured by optical nanosensors

BackgroundDefective macrophage phagolysosomal acidification is implicated in numerous lung diseases including Cystic Fibrosis (CF) and may contribute to defective pathogen killing. Conflicting reports relating to phagolysosomal pH in CF macrophages have been published, in part related to the use of pH-sensitive fluorescent probes where potential inadequacies in experimental design can be a contributing factor (e.g. employing probes with incorrect pKa for the cellular compartment of interest). We developed a reliable method to quantify macrophage phagolysosomal pH using surface-enhanced Raman spectroscopy-based nanosensors. MethodsMonocyte-derived macrophages from CF and healthy control participants were incubated with nanosensors. Live cell imaging identified phagocytosed nanosensors, and surface-enhanced Raman spectroscopy was performed using para-mercaptobenzoic acid functionalised gold nanoparticles which produce Raman spectra that change predictably with their environmental pH. Conventional fluorescence spectroscopy was carried out in comparison. Nanosensor localisation to phagolysosomes was confirmed by transmission electron microscopy. ResultsNanosensors were actively phagocytosed by macrophages into phagolysosomes and acidification occurred rapidly and remained stable for at least 60 min. There was no difference in phagolysosomal pH between healthy control and CF macrophages (5.41 ± 0.11 vs. 5.41 ± 0.20, p > .9999), further confirmed by inhibiting Cystic Fibrosis Transmembrane Conductance Regulator in healthy control monocyte-derived macrophages. ConclusionsOptical nanosensors accurately measure macrophage phagolysosomal pH and demonstrate no phagolysosomal acidification defect in human CF monocyte-derived macrophages. Further studies using alveolar macrophages could extend the impact of our findings. Nanosensors represent a novel and precise means to measure organelle functions with widespread potential for the study and monitoring of several lung diseases.

The solid-state synchronous vs. conventional fluorescence spectroscopy and complementary methods to study the interactions of aluminum metal-organic framework Basolite A100 with dimethyl sulfoxide

Abstract We report, for the first time, an experimental study of interaction of metal-organic framework (MOF) with dimethyl sulfoxide (DMSO). Adsorption of DMSO on aluminum MOF Basolite A100 results in formation of the stoichiometric complex [A100]2[DMSO]3. The solid-state synchronous fluorescence spectroscopy allows observation of the following major excitation/emission transitions in Basolite A100 and its adsorption complex [A100]2[DMSO]3 which are not well-resolved in “conventional” fluorescence spectra: 1) narrow resonance of the isolated BDC linker, 2) excitation across optical bandgap, and 3) excimers. In the adsorption complex [A100]2[DMSO]3, the DMSO molecules interact with the μ2-OH group of Basolite A100 and with its BDC linker through the π-π system. We present, for the first time, the new variety of the solid-state synchronous fluorescence spectroscopy, which we denote as the solid-state enhanced-resolution synchronous fluorescence (excitation) spectroscopy. The accurate measurements of small changes in the optical bandgap of the adsorption complex [A100]2[DMSO]3 and Basolite A100 are described by the solid-state enhanced-resolution synchronous fluorescence (excitation) spectroscopy.

Determination of trace fluoroquinolones in water solutions and in medicinal preparations by conventional and synchronous fluorescence spectrometry

Abstract Simple, rapid and sensitive and synchronous fluorescence spectrometry (SFS) were developed for determination the fluoroquinolones of ciprofloxacin (CIP), norfloxacin (NOR) and enrofloxacin (ENR) separately in water solutions and in medicinal preparations. The optimized wavelength intervals between the emission and excitation wavelengths were 170 nm, 160 nm and 170 nm for CIP, NOR and ENR, respectively. The different experimental parameters affecting the synchronous fluorescence intensities of the three fluoroquinolones were carefully studied. Under the optimal conditions, good linearity was obtained over the range of 0.01 to 1.20 mg/L, 0.005 to 0.45 mg/L and 0.005 to 0.60 mg/L for the CIP, NOR and ENR, and with good relative standard deviations below 1.9% (n=9). In addition, the detection limits for CIP, NOR and ENR were 0.17 μg/L, 0.013 μg/L and 0.055 μg/L, respectively. What is more, compared with the conventional fluorescence spectrometry, the SFS could detect lower concentrations of each fluoroquinolone. Moreover, the proposed SFS were validated and successfully applied for the quantitative assay of each fluoroquinolone in medicinal preparations.

Pump-orientation-probe technique and its applications

The pump-orientation-probe technique is a recently-developed novel transient measurement technique, which has unique advantages in probing the ultrafast dynamics of charge separation in colloidal nanostructures. In this technique, the linearly-polarized pump pulse is applied to generating electron-hole pairs, and the circularly-polarized spin-orientation pulse is used to establish the electron spin polarization, whose dynamics is detected by monitoring the polarization change of the linearly-polarized probe pulse. Initially, the wavefunctions of the electron-hole pairs are spatially overlapped, and the lifetime of the electron spin is short because of the strong electron-hole exchange interaction. If the electrons or the holes are trapped by the surfaces of the colloidal nanostructures, the spatial separations between the electrons and the holes weaken the exchange effect, and thus the lifetime of the electron spin is largely lengthened. The evolutions of electrons and holes from their spatial overlap to separation can be revealed by monitoring the change of the electron spin dynamics. Based on the introduction of the conventional two-beam carrier pump-probe and spin pump-probe techniques, the features and optical layout of three-beam pump-orientation-probe technique are described in depth. The application to probing negative or positive photocharging in CdS colloidal quantum dots is taken for example and discussed in depth. Compared with the conventional time-resolved absorption or time-resolved fluorescence spectroscopy, the pump-orientation-probe technique can detect the dynamics of trapping electrons or holes and distinguish the type of charging state easily and directly, which has particular advantages under the high-power excitation condition. Further outlook of the three-beam pump-orientation-probe technique is also presented finally.

Analysis of the Characteristics of Groundwater Quality in a Typical Vegetable Field, Northern China

This study explores the impact of facility farming on the origin and composition of groundwater and on the distribution characteristics of inorganic salts, heavy metals, and dissolved organic matter in groundwater in a typical greenhouse vegetable planting area in North China plains. The methods used include conventional analysis, UV-Visible, and fluorescence spectroscopy combined with parallel factor analysis, principle components analysis, and two-dimensional (2D) hetero-spectral correlation spectra techniques. The results showed that the hydrochemistry type of groundwater in the facility vegetable field was Cl-SO4, the nitrogen content was higher than the National Groundwater V Class Quality Standard (GB/T14848-93), and the heavy metal content was lower than the National Drinking Water Standard (GB5749-2006). The nitrification process was blocked due to a strongly reducing atmosphere and shallow depth in groundwater, which caused high concentrations of NH4+-N. Part of the toxic sulfur-containing metal content increased after the application of inorganic fertilizers. The sources of dissolved organic matter in groundwater were similar; the organic manure components which leach into groundwater were recently produced by microbial metabolism. The main components of dissolved organic matter were small-molecule-biodegradable protein-like substances and the fulvic-like content binding to them. The fulvic-like content that bound to protein-like content in vegetable planting groundwater was stable, while the protein-like content was greatly influenced by the cultivation process of the organic manure application. In the process of vegetable planting, organic manure should be applied scientifically and the supervision of the planting area is crucial.

Strong Magneto-Optical Response of Nonmagnetic Organic Materials Coupled to Plasmonic Nanostructures.

Plasmonic nanoparticles (PNPs) can significantly modify the optical properties of nearby organic molecules and thus present an attractive opportunity for sensing applications. However, the utilization of PNPs in conventional absorption, fluorescence, or Raman spectroscopy techniques is often ineffective due to strong absorption background and light scattering, particularly in the case of turbid solutions, cell suspensions, and biological tissues. Here we show that nonmagnetic organic molecules may exhibit magneto-optical response due to binding to a PNP. Specifically, we detect strong magnetic circular dichroism signal from supramolecular J-aggregates, a representative organic dye, upon binding to silver-coated gold nanorods. We explain this effect by strong coupling between the J-aggregate exciton and the nanoparticle plasmon, leading to the formation of a hybrid state in which the exciton effectively acquires magnetic properties from the plasmon. Our findings are fully corroborated by theoretical modeling and constitute a novel magnetic method for chemo- and biosensing, which (upon adequate PNP functionalization) is intrinsically insensitive to the organic background and thus offers a significant advantage over conventional spectroscopy techniques.

Molecular Encapsulation and Association of Ionic Species with Dendrimers at Polarized Liquid|Liquid Interfaces

Charge transfer and ion partitioning mechanisms at an interface between two immiscible electrolyte solutions (ITIES) have been extensively studied for separation sciences, pharmacokinetic analysis, and mass transport in vivo. Dendrimers are unique and nontraditional polymers with a well-defined macromolecular architecture consisting of a core, iterative branch units (interior), and terminal groups. Dendrimers have been demonstrated to be capable of encapsulating various molecules and examined as molecular capsule or container, in which a variety of organic molecules and metal ions can be accommodated in the internal cavity through electrostatic and hydrophobic interactions. The most widely studied poly(amidoamine) (PAMAM) dendrimer is constructed based on an ethylenediamine core and amidoamine branch units with various terminal groups. The net charge on the PAMAM dendrimer depends on the protonation equilibria of tertiary amines in the interior and terminal groups. The electrostatic interaction between the dendrimer and ionic species, thus, is considerably affected by the pH condition. This talk will present the characteristic interfacial behavior of amino- and carboxylate-terminated PAMAM dendrimers at the polarized water|1,2-dichloroethane (DCE) interface. The fundamental ion transfer reaction of the dendrimer was successfully analyzed by means of conventional voltammetric techniques and potential modulated fluorescence spectroscopy [1]. The spectroelectrochemical analysis clearly demonstrated that the interfacial mechanism of the dendrimer involves transfer and adsorption processes depending on the pH condition and the Galvani potential difference [2]. The molecular encapsulation and association of fluorescent species such as anilinonaphthalenesulfonates, porphyrin derivatives and ionizable drugs with the PAMAM dendrimer were investigated in detail at ITIES. The anionic dye species exhibited electrostatic association behavior with the positively charged dendrimer and the stability of the dendrimer-anionic dye associates was varied as a function of pH [3]. Although the dendrimers stably associated with anionic dye species under acidic conditions, the dye anions were released from the dendrimer at its transfer potential and then transferred across the interface. A negative shift of the transfer potential of dye anion compared to its intrinsic transfer potential was observed for each ion association system. The ion association stability between the dendrimer and dye species was quantitatively estimated from the shift of the transfer potential. The photoreactivity of the dendrimer−zinc(II) porphyrin associates was also studied at the polarized water|DCE interface [4]. The photocurrent generated through the heterogeneous photoreduction of the water-soluble zinc(II) porphyrin by a lipophilic ferrocene derivative in the organic phase was drastically enhanced by the formation of the dendrimer−zinc(II) porphyrin associates. Furthermore, the association property of several ionizable drug molecules with the dendrimer was examined at ITIES. While the spectroscopic data exhibited no specific association between ionizable drugs and the dendrimers in the bulk solution phase, the interfacial behavior of drug molecules was affected by the addition of the dendrimers, indicating that the dendrimers interact with the drug molecules only in the interfacial region [5]. These findings demonstrated that the ionic-partitioning and interfacial reactivity of ionic species can readily be modified through the ion association with the dendrimer. In particular, the membrane permeability and reactivity of ionizable drugs could be controlled by the dendrimer. References (a) H. Nagatani, “In Situ Spectroscopic Characterization of Porphyrins at Liquid Interfaces”, in Handbook of Porphyrin Science, Vol. 34, K. M. Kadish, K. M. Smith, R. Guilard, eds., World Scientific Publishing, Singapore, Chapter 176 (2014); (b) H. Nagatani, T. Sagara, Anal. Sci., 23, 1041 (2007). H. Nagatani, T. Ueno, T. Sagara, Electrochim. Acta, 53, 6428 (2008). (a) H. Nagatani, T. Sakamoto, T. Torikai, T. Sagara, Langmuir, 26, 17686 (2010); (b) H. Sakae, H. Nagatani, K. Morita, H. Imura, Langmuir, 30, 937 (2014). H. Nagatani, H. Sakae, T. Torikai, T. Sagara, H. Imura, Langmuir, 31, 6237 (2015). H. Sakae, H. Nagatani, H. Imura, Electrochim. Acta, 191, 631 (2016).

Silicon Nitride Bioceramics Induce Chemically Driven Lysis in Porphyromonas gingivalis.

Organisms of Gram-negative phylum bacteroidetes, Porphyromonas gingivalis, underwent lysis on polished surfaces of silicon nitride (Si3N4) bioceramics. The antibacterial activity of Si3N4 was mainly the result of chemically driven principles. The lytic activity, although not osmotic in nature, was related to the peculiar pH-dependent surface chemistry of Si3N4. A buffering effect via the formation of ammonium ions (NH4(+)) (and their modifications) was experimentally observed by pH microscopy. Lysis was confirmed by conventional fluorescence spectroscopy, and the bacteria's metabolism was traced with the aid of in situ Raman microprobe spectroscopy. This latter technique revealed the formation of peroxynitrite within the bacterium itself. Degradation of the bacteria's nucleic acid, drastic reduction in phenilalanine, and reduction of lipid concentration were observed due to short-term exposure (6 days) to Si3N4. Altering the surface chemistry of Si3N4 by either chemical etching or thermal oxidation influenced peroxynitrite formation and affected bacteria metabolism in different ways. Exploiting the peculiar surface chemistry of Si3N4 bioceramics could be helpful in counteracting Porphyromonas gingivalis in an alkaline pH environment.