Co-reporter:Ryo Nishihara, Hideyuki Suzuki, Emi Hoshino, Sakura Suganuma, Moritoshi Sato, Tsuyoshi Saitoh, Shigeru Nishiyama, Naoko Iwasawa, Daniel Citterio and Koji Suzuki
Chemical Communications 2015 vol. 51(Issue 2) pp:391-394
Publication Date(Web):11 Nov 2014
DOI:10.1039/C4CC06886F
Three novel coelenterazine (CTZ) derivatives with extension at the C-6 position of the imidazopyrazinone structure show significant bioluminescence emission with known renilla luciferase variants, indicating a promising method to develop CTZ derivatives with superior optical properties compared to hitherto reported compounds.
Co-reporter:Yuki Hiruta, Hikaru Koiso, Hitoshi Ozawa, Hiroyasu Sato, Kensaku Hamada, Satoshi Yabushita, Daniel Citterio, and Koji Suzuki
Organic Letters 2015 Volume 17(Issue 12) pp:3022-3025
Publication Date(Web):June 11, 2015
DOI:10.1021/acs.orglett.5b01299
Two distyryl-BODIPY-based NIR red-shifting ratiometric fluorescent probes are reported: KBHR-1 for pH and KBAHgR-1 for Ag+ and Hg2+. KBHR-1 showed a red-shifting ratiometric response to pH in the NIR region. The identical fluorophore core structure applied to KBAHgR-1 with a different recognition moiety resulted in a ratiometric response to Ag+ and Hg2+ in the NIR region.
Co-reporter:Yuki Hiruta, Takafumi Watanabe, Etsuko Nakamura, Naoko Iwasawa, Hiroyasu Sato, Kensaku Hamada, Daniel Citterio and Koji Suzuki
RSC Advances 2014 vol. 4(Issue 19) pp:9791-9798
Publication Date(Web):28 Jan 2014
DOI:10.1039/C3RA45700A
A novel series of tripodal ligands with thiophenylether arms connected to an anchoring nitrogen has been investigated. Seven tripodal ligands were synthesized by combining methyl, isopropyl, and tert-butyl residue bearing thiophenylether sites as groups with different steric hindrance effects. The tripodal ligands allowed for the extraction of Ag+ ions from the aqueous phase into a chloroform phase by forming 1:1 complexes with Ag+. Back-extraction was performed with 1 M HNO3 aqueous solution. Each ligand showed different extraction and back-extraction efficiency for Ag+, affected by changes in steric hindrance caused by the various combinations of sidearms. These results are further supported by X-ray single crystal structural analysis.
Co-reporter:Yuki Hiruta, Chikai Sato, Youhei Takahashi, Kei Kubobuchi, Yushi Shichi, Daniel Citterio and Koji Suzuki
RSC Advances 2013 vol. 3(Issue 18) pp:6499-6506
Publication Date(Web):20 Feb 2013
DOI:10.1039/C3RA22904A
This paper describes the development and the characterization of a Li+ optical sensor (optode) based on a Li+ selective fluoroionophore (KBL-01-Si), immobilized to a mesoporous silica thin film. KBL-01-Si was synthesized by the formation of a urethane bond between the hydroxyl terminated alkoxy chain of KBL-01 and 3-isocyanatopropyl-triethoxysilane. Li+ optodes with different amounts of KBL-01-Si fluoroionophore were fabricated by changing the grafting time of KBL-01-Si to mesoporous silica thin films with two different pore sizes. When the concentration of KBL-01-Si immobilized to the pore surface of the mesoporous silica thin films was low, response curves following a theoretical 1:1 complex formation equilibrium with binding constants for Li+ (log K) between 4.38 and 5.04 were observed. At higher concentrations of immobilized fluoroionophore, the response curves deviated from the fitting curve based on a theoretical chemical equilibrium, and the dynamic response was extended over a broad range from 10−6 to 1 M. In addition, it was observed by XPS depth profiling that KBL-01-Si was mainly localized on pore surface areas close to the channel entrances. These results indicate that not only the design of the fluoroionophore, but also the matrix for immobilization, and the microscale distribution of the fluoroionophore affect the characteristics of an ion sensor.
Co-reporter:Tetsuya Mizuno;Keitaro Umezawa;Yutaka Shindo;Daniel Citterio
Journal of Fluorescence 2013 Volume 23( Issue 5) pp:1007-1018
Publication Date(Web):2013 September
DOI:10.1007/s10895-013-1227-5
We report a new type of UV-excitable red/NIR-emissive fluorescent dyads (PKF series). Conjugation of a pyrene and a novel bright red/near-infrared (NIR) fluorophore resulted in large quasi-Stokes shift while retaining intense fluorescence emission and sharp spectral bands. Labeling of PKF dyads to biomolecules was performed by means of introduction of a succinimidyl ester. Simultaneous Ca2+/albumin dual-color intracellular imaging by PKF in combination with fura-2 (UV-excitable/VIS-emissive Ca2+ indicator) reveals its usefulness as a new bioimaging tool.
Co-reporter:Yuki Hiruta, Naoto Yoshizawa, Daniel Citterio, and Koji Suzuki
Analytical Chemistry 2012 Volume 84(Issue 24) pp:10650
Publication Date(Web):November 19, 2012
DOI:10.1021/ac302178z
Long-term stable ratiometric fluorescent optical pH sensors (optodes) based on double sol–gel silica layers are prepared with the first layer embedding two types of quantum dots (QDs) and the second layer embedding light-absorbing pH indicators. The sensors are fabricated by a simple general sol–gel spin-coating method. The resulting double-layer pH optodes are designed as having long Stokes shift as well as ratiometric fluorescence emission response to pH in aqueous solutions of varying pH values. This optode has high durability against continuous light exposure, even under severe acidic condition (1 M HCl), and the storage stability is over a period of more than 6 months. These results indicate that the double-layer ratiometric fluorescence-based pH optode allows for long-term pH sensing. When two pH indicators of different pKa values with an optimized mixing ratio are embedded into the second layer, a double-layer pH optode with reproducible linear response in a wide pH range of over 6 pH units (from pH 4 to 10) can be designed and fabricated.
Co-reporter:Yushi Heta;Kentaro Kumaki;Hiroki Hifumi;Daniel Citterio;Akihiro Tanimoto
Photochemistry and Photobiology 2012 Volume 88( Issue 4) pp:876-883
Publication Date(Web):
DOI:10.1111/j.1751-1097.2012.01124.x
Abstract
Novel photochromic amphipathic molecules, KMR-AZn (Gd-DTPA-AZCn), composed of hydrophilic Gd-DTPA and hydrophobic alkylated azobenzene were prepared. In aqueous environment, KMR-AZn indicated self-assembly. The resulting aggregates were demonstrated to be able to include a hydrophobic drug substitute (hydrophobic fluorescent dye) into the internal core, and to release the included compound upon photoirradiation within 10 min through the influence of azobenzene photoisomerization. This micellar MRI contrast agent exhibited three- to four-fold higher r1 relaxivity (r1 = 14.5–16.5 mm−1 s−1, 0.47 T at 40°C) than the widely applied small molecule contrast agent Gd-DTPA (Magnevist®r1 = 4.1 mm−1 s−1, 0.47 T at 40°C). This dual functionality of encapsulated compound release and increased MR imaging contrast indicates that KMR-AZn is a potential candidate for application as a lipid-based MRI-traceable drug carrier.
Co-reporter:Akihiro Matsui, Keitaro Umezawa, Yutaka Shindo, Tomohiko Fujii, Daniel Citterio, Kotaro Oka and Koji Suzuki
Chemical Communications 2011 vol. 47(Issue 37) pp:10407-10409
Publication Date(Web):12 Aug 2011
DOI:10.1039/C1CC14045K
We report a novel near-infrared fluorescent calcium probe (KFCA), which has good optical properties such as intense NIR fluorescence emission (670 nm, QY: 0.24), excellent ON/OFF ratio (120-fold), and good wavelength-compatibility with visible-light-emissive fluorophores (Fluo-4, DsRed2), and which is applicable for real-time dual-colour intracellular Ca2+ imaging.
Co-reporter:Kosuke Takano, Shin-ichi Sasaki, Daniel Citterio, Hitoshi Tamiaki and Koji Suzuki
Analyst 2010 vol. 135(Issue 9) pp:2334-2339
Publication Date(Web):08 Jul 2010
DOI:10.1039/C0AN00173B
A fluorescent ratiometric optical chemical sensor (optode) for alcohol detection is presented. A lipophilized bacteriochlorin derivative possessing a trifluoroacetyl group at the 3-position was synthesized for alcohol detection. When embedded in a plasticized poly(vinyl chloride) (PVC) membrane, the fluororeceptor shows a significant signal change on exposure to aqueous ethanol solutions both in the absorbance and the fluorescence emission. This optode allows the determination of ethanol concentrations in aqueous sample solutions by ratiometric fluorometry. The fluorescent indicator responds with increasing fluorescence around 701 nm and decreasing fluorescence around 751 nm towards the presence of ethanol. The optode response was found to be fully reversible in a dynamic measurement range from 0.3% to at least 25% (v/v) ethanol. The limit of detection (LOD) and the limit of quantification (LOQ) of the sensor for ethanol were estimated to be 0.1% and 0.4% (v/v), respectively. These results indicate that the new optode can be employed as an ethanol-sensing device with high sensitivity for beverage and industrial analyses.
Co-reporter:Hiroki Hifumi, Seiichi Yamaoka, Akihiro Tanimoto, Tomotaka Akatsu, Yutaka Shindo, Aki Honda, Daniel Citterio, Kotaro Oka, Sachio Kuribayashi and Koji Suzuki
Journal of Materials Chemistry A 2009 vol. 19(Issue 35) pp:6393-6399
Publication Date(Web):04 Jun 2009
DOI:10.1039/B902134E
Tumor detection is of great clinical interest. It is known that solid tumors have unique vascular pathophysiological features summarized under the term “enhanced permeability and retention (EPR) effect”, which induces the accumulation and prolonged retention of macromolecules from the blood into the tumor. We therefore have designed and synthesized dextran coated paramagnetic gadolinium phosphate nanoparticles (PGP/dextran) as a new magnetic resonance imaging (MRI) contrast agent. The main features of this new material are: (i) characteristics of a positive contrast agent providing higher imaging resolution, (ii) size of several tens of nanometres to accumulate and to be retained into tumors, and (iii) highly biocompatible dextran coating to prevent the rapid elimination from the blood stream. In this article, we describe the results of pharmacokinetic studies, toxicity tests, and MR imaging experiments to visualize tumors using PGP/dextran, and compare them to the clinically used contrast agent Magnevist®. Relying on the EPR effect, tumors in a rabbit were successfully visualized on conventional T1-weighted MR images using the particulate and positive PGP/dextran with only 1/10 of the applied dose compared to Magnevist®. This efficient visualization of a tumor is the result of the comprehensive features of PGP/dextran, having adequate characteristics of a positive contrast agent for MRI, a significantly long plasma half-life and a high biocompatibility. PGP/dextran could be used as a tumor specific contrast agent and as a vehicle to deliver drugs to a tumor.
Co-reporter:Yuki Hasegawa, Aki Honda, Keitaro Umezawa, Yusuke Niino, Kotaro Oka, Tomohiro Chiba, Sadakazu Aiso, Akihiro Tanimoto, Daniel Citterio and Koji Suzuki
Chemical Communications 2009 (Issue 27) pp:4040-4042
Publication Date(Web):10 Jun 2009
DOI:10.1039/B904055B
We report a method for specifically labelling the surface of cells with two kinds of chemical probes (near-infrared (NIR) fluorescent probes and magnetic resonance (MR) imaging probes) via two genetically expressed tags, and demonstrate the application for in vitro and in vivo dual imaging.
Co-reporter:Maki Sekiya, Keitaro Umezawa, Akemi Sato, Daniel Citterio and Koji Suzuki
Chemical Communications 2009 (Issue 21) pp:3047-3049
Publication Date(Web):09 Apr 2009
DOI:10.1039/B903751A
This communication reports the synthesis, chemiluminescence properties, and biological application of KEIO-BODIPY–imidazopyrazine (KBI), a yellow-green chemiluminescent probe for the detection of reactive oxygen species (ROS) generated from living cells.
Co-reporter:Yosuke Ando, Yuki Hiruta, Daniel Citterio and Koji Suzuki
Analyst 2009 vol. 134(Issue 11) pp:2314-2319
Publication Date(Web):15 Sep 2009
DOI:10.1039/B912756A
This paper presents the preparation and characterization of a single-excitation, dual-emission ratiometric optical Li+-sensing device using a newly designed and synthesized highly Li+-selective fluoroionophore (KBL-01) carrying 14-crown-4 ether with tetramethyl and benzene blocking subunits as Li+-binding site and boron-dipyrromethene as fluorophore. The indicator dye was covalently immobilized on the surface of a porous glass support having a large internal surface area using a silane-coupling agent. The resulting Li+-selective glass optode shows dual fluorescence emission response in pseudo-serum at varying Li+ concentrations, allowing ratiometric signal processing. The obtained signal is independent of the presence of possibly interfering cations (Na+, K+, Mg2+ and Ca2+) and pH. The sensor response was found to be reversible within the Li+ concentration range from 10−4 to 10−1 M, and showed good repeatability and light stability. The plots of the ratiometric signal versus the Li+ concentrations in spiked real human serum go along with the response curve in pseudo-serum. These results indicate that the novel Li+-selective glass optode can be employed as a Li+-sensing device with high durability, sensitivity and accuracy for medical analyses.
Co-reporter:Yosuke Ando, Yuya Homma, Yuki Hiruta, Daniel Citterio, Koji Suzuki
Dyes and Pigments 2009 Volume 83(Issue 2) pp:198-206
Publication Date(Web):November 2009
DOI:10.1016/j.dyepig.2009.04.008
A series of novel, fluorescent, solvatochromic dyes (KSD-series) carrying a 4-dimethylaminophenyl moiety as π-electron donor and an acetyl moiety as π-electron acceptor, conjugated with a five-membered aromatic monoheterocyclic π-linker, were synthesized. In the cases of dyes having a pyrrole, (KSD-1) furan (KSD-2) and thiophene (KSD-3) heterocycle as π-linker, respectively, the plot of Stokes shifts in different solvents as a function of ET(30) solvent polarity value showed good linear correlation. The fluorescence of KSD-4, a π-conjugation extended derivative of KSD-3, varied from blue (491 nm) in toluene to orange (616 nm) in DMSO; KSD-4C, a carboxyl group modified derivative, displayed longer wavelength emission (619 nm) and larger Stokes shift (229 nm, 9486 cm−1) than conventional dyes in methanol solution.
Co-reporter:Keitaro Umezawa Dr.;Akihiro Matsui;Yuki Nakamura;Daniel Citterio Dr. Dr.
Chemistry - A European Journal 2009 Volume 15( Issue 5) pp:1096-1106
Publication Date(Web):
DOI:10.1002/chem.200801906
Abstract
A new series of high-performance fluorophores named Keio Fluors (KFL), which are based on borondipyrromethene (BODIPY), are reported. The KFL dyes cover a wide spectral range from the yellow (547 nm) to the near-infrared (NIR, 738 nm) region, and their emission wavelength could be easily and subtly controlled based on simple molecular modifications only, without losing their optical properties. This “tailor-made” synthetic strategy for tuning the emission wavelength enabled the creation of fourteen KFL dyes with well-controlled emission colors (yellow, orange, red, far-red, and NIR). Moreover, these KFL dyes also retain their excellent optical properties, such as spectral bands sharper than quantum dots, high extinction coefficients (140 000–316 000 M−1 cm−1), and high quantum yields (0.56–0.98), without any critical solvent polarity dependent decrease of their brightness. These advantageous characteristics make the KFL dyes potentially useful as new candidates of fluorescent standard dyes to substitute or to complement existing long-wavelength fluorescent dyes, such as cyanines, oxazines, rhodamines, or other BODIPY dyes.
Co-reporter:Aki Honda, Yoshio Suzuki, Koji Suzuki
Analytica Chimica Acta 2008 Volume 623(Issue 1) pp:1-10
Publication Date(Web):8 August 2008
DOI:10.1016/j.aca.2008.05.064
After a soft ionizing method was established, MS (mass spectrometry) has become a more common tool in biochemistry because soft ionization made it possible to detect large molecules such as proteins. Many kinds of applications were established to further utilize MS for the identification or quantitation of biomolecules. In this review, we introduce recent applications with special focus on chemical modification techniques and chemical probes developed for the MS determination of biomolecules.
Co-reporter:Hiroki Hifumi, Akihiro Tanimoto, Daniel Citterio, Hirokazu Komatsu and Koji Suzuki
Analyst 2007 vol. 132(Issue 11) pp:1153-1160
Publication Date(Web):17 Aug 2007
DOI:10.1039/B707225B
Novel gadolinium complexes (KMR-series: KMR-K and KMR-Mg), which have a bis-15-crown-5 ether or a charged β-diketone structure as a recognition site, have been designed, synthesized and applied for the detection of K+ or of Mg2+ and Ca2+ using MRI or NMR techniques. The measurements are based on the modulation of the longitudinal relaxation time (T1) of water protons in proximity of the gadolinium complexes. Relaxivity measurements of KMR-K1 in aqueous solution showed that the initial longitudinal relaxivity value (r1) of 5.05 mM−1 s−1 is monotonously decreasing with increasing K+ concentrations, reaching a final value of 4.78 mM−1 s−1. This decrease is attributed to a change in the second sphere of hydration of the gadolinium (Gd3+) complex (KMR-K), resulting in a K+ concentration-dependent contrast in MR images. From stoichiometric analysis using mass spectrometry and UV/VIS spectrometry, a 1 : 1 complex formation between KMR-K1 and K+ in a sandwich-type manner with a logK of 3.20 was confirmed. In the case of KMR-Mg, the initial r1 value of 4.98 mM−1 s−1 is monotonously decreasing with increasing Mg2+ or Ca2+ concentrations, reaching a final value of 3.95 or 4.16 mM−1 s−1, respectively, resulting in Mg2+ and Ca2+ concentration-dependent contrast in MR images. The formation of a 1 : 1 complex with a logK of 2.33 for Mg2+ and 1.91 for Ca2+ was confirmed. KMR-K1 and KMR-Mg are the first ion-selective or ion-sensitive gadolinium complexes for K+ or Mg2+ and Ca2+, respectively.
Co-reporter:Akio Ueda;Osamu Niwa ;Kenichi Maruyama Dr.;Yutaka Shindo;Kotaro Oka
Angewandte Chemie 2007 Volume 119(Issue 43) pp:
Publication Date(Web):26 SEP 2007
DOI:10.1002/ange.200702617
Nur gucken, nicht anfassen: Um den direkten Kontakt zwischen Elektrode und Probe zu vermeiden, nutzt die im Titel genannte Technik eine gebogene Sonde, die von einer 100 nm dicken Schutzschicht umgeben ist. Als Ergebnis erhält man Bilder mit verbesserter Auflösung. Unter 1 μm große Strukturen und charakteristische chemische Zentren können auf dreierlei Weise abgebildet werden (siehe Beispiel: Neuriten von PC12-Zellen).
Co-reporter:Akio Ueda;Osamu Niwa ;Kenichi Maruyama Dr.;Yutaka Shindo;Kotaro Oka
Angewandte Chemie International Edition 2007 Volume 46(Issue 43) pp:
Publication Date(Web):26 SEP 2007
DOI:10.1002/anie.200702617
Protection is the key: Improved resolution imaging is demonstrated with the title technique, in which a bent probe is surrounded by a 100-nm protective layer to prevent direct contact between the electrode and the sample. Submicrometer structures and characteristic chemical sites can be imaged in three different modes, as demonstrated for neurites of PC12 cells (see picture).
Co-reporter:Aki Honda;Yoshio Suzuki
The Chemical Record 2006 Volume 6(Issue 2) pp:
Publication Date(Web):10 APR 2006
DOI:10.1002/tcr.20075
In this paper, we review the mass probes used for the derivation of a variety of biomolecules efficiently detected by the electrospray ionization–mass spectrometry and mass probe-assisted ionization method for total analysis and determination by consecutive detection with a single instrument. We describe mass probes for a variety of molecules including proteins, nucleobases, metallic cations, and other small molecules. © 2006 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 6: 100–106; 2006: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20075
Co-reporter:Daniel Citterio, Mio Omagari, Takashi Kawada, Shin-ichi Sasaki, Yoshio Suzuki, Koji Suzuki
Analytica Chimica Acta 2004 Volume 504(Issue 2) pp:227-234
Publication Date(Web):23 February 2004
DOI:10.1016/j.aca.2003.10.050
This paper describes the design, synthesis, and the characterization of the two new chromogenic crown ethers 2,2′-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diylbis(methylene)]bis[4-[(1-methyl-4-(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (KBC-001) and the lipophilic derivative 2,2′-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diylbis(methylene)]bis[4-[(1-dodecyl-4-(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (KBC-002). A merocyanine dye that forms a betainic structure upon intramolecular charge transfer and shows solvent polarity dependent spectral sensitivity was selected as the chromophore system to develop the new chromoionophores. This approach allows the design of overall electrically neutral ligands bearing charged groups without the need of external counter ions. A proton ionizable group in the dye moiety acts as a charged ion-binding site and is an integral part of a lariat crown ether ionophore. A chromoionophore for calcium ion sensing has been developed, which combines the size-selective binding character of a crown ether with strong electrostatic attraction between the positively charged calcium ion and two negatively charged lariat side arms in the overall neutral compound. This water-soluble dye selectively responds to the presence of calcium ions in water at pH 8.5 with a dynamic response range between 10 μM and 10 mM. The binding event can be monitored both by absorption spectrometry and by fluorescence spectrometry. No cross-sensitivity was found for the physiologically important cations Mg2+, Li+, Na+, and K+ up to concentrations of 0.1 M under the same experimental conditions. In contrast to the water-soluble reagent KBC-001, the lipophilized derivative KBC-002 having two long alkyl chains was successfully applied to ion-exchange type optode membranes made from plasticized poly(vinyl chloride) (PVC). The dynamic response range of the optode at pH 9.0 was between 10 μM and 10 mM while retaining the high calcium selectivity.
Co-reporter:S. Sasaki, S. Ozawa, D. Citterio, K. Yamada, K. Suzuki
Talanta 2004 Volume 63(Issue 1) pp:131-134
Publication Date(Web):10 May 2004
DOI:10.1016/j.talanta.2003.12.034
The potentiometric response characteristics of electrodes based on organic trialkyl/aryl-tin compounds combined with various amounts of anionic additive (NaTFPB) were investigated in 0.1 M bis-Tris–H2SO4 buffer solution at pH 7.0. The best result for phosphate sensing was obtained for the electrode membrane containing tributyltin chloride and 25 mol% NaTFPB, where the electrode exhibits high selectivity towards phosphate anions with a slope of −60 mV per decade. It was demonstrated that the interference from more lipophilic anions is drastically suppressed (, i=H2PO4−: salicylate, 0.5; SCN−, −0.8; ClO4−, −2.3) under this optimized measurement conditions.
Co-reporter:Daniel Citterio, Takashi Kawada, Jun Yagi, Tomonori Ishigaki, Hideaki Hisamoto, Shin-ichi Sasaki, Koji Suzuki
Analytica Chimica Acta 2003 Volume 482(Issue 1) pp:19-28
Publication Date(Web):10 April 2003
DOI:10.1016/S0003-2670(03)00200-9
In this paper, new “multiinformation dyes” (MIDs) with extended spectral sensitivity reporting on both changes in solvent polarity (solvatochromism) and in pH (halochromism) by changes in their visible absorption spectra, are presented. The merocyanine dyes 2,6-dibromo-4-[4-(1-dodecyl-4(1H)-pyridinylidene)-2-butenylidene]-2,5-cyclohexadien-1-one (KD-M301) and 2,6-dibromo-4-[4-(1-dodecyl-4(1H)-quinolinylidene)-2-butenylidene]-2,5-cyclohexadien-1-one (KD-M402) were designed, synthesized, and characterized regarding analytical applications. The spectral sensitivity for the MIDs was extended into the near-infrared (NIR) wavelength range (λmax=800 nm in CHCl3 for KD-M402) and at the same time, the degree of solvent polarity-induced spectral shifts was strongly enhanced (Δλmax=202 nm for KD-M402 between tetrahydrofuran (THF) and methanol), reaching similar values to the standard solvatochromic dye Dimroth–Reichardt’s betaine on which the empirical ET(30) classification of solvent polarity is based. Compared to Dimroth–Reichardt’s betaine dye, the molar absorption coefficient ε, is increased more than 10-fold (ε of KD-M402 in THF: 7.7×104 M−1 cm−1), allowing sensitive measurements at low concentrations of the dye. The dodecyl-substituted KD-M402 is suitable as a lipophilic pH indicator in ion-exchange type optical sensors (optodes) with optical detection in the near-infrared wavelength range.
Co-reporter:Kazuyoshi Kurihara, Kaori Nakamura, Koji Suzuki
Sensors and Actuators B: Chemical 2002 Volume 86(Issue 1) pp:49-57
Publication Date(Web):30 August 2002
DOI:10.1016/S0925-4005(02)00146-6
An asymmetric surface plasmon resonance sensor response curve (SPR curve) equation derived from the three-layer Fresnel equation regarding p-polarization was proposed that can be used as a more general and appropriate SPR curve equation than Kretschmann’s equation given by R(X)=(1−α)/{(X−β)2+γ2}, where R is the reflectance of the incident light, α, β and γ are real parameters, and X the incident angle. The proposed equation is expressed as R(X)=A[1−{B+C(X−D)}/{(X−D)2+E2}] with a minimum reflectance at a conventional resonance angle of , where A, B, C, D and E are five real parameters that are very useful as fitting functions for a gold-based SPR curve in real-time measurement. In this equation, a modified resonance angle defined as parameter D is more appropriate than the conventional resonance angle as a variable that gives a linear response to changes in the refractive index of the sensing layer.
Co-reporter:Shin-ichi Sasaki Dr.;Akio Hashizume;Daniel Citterio Dr.;Eiji Fujii Dr.
Angewandte Chemie International Edition 2002 Volume 41(Issue 16) pp:
Publication Date(Web):21 AUG 2002
DOI:10.1002/1521-3773(20020816)41:16<3005::AID-ANIE3005>3.0.CO;2-F
Selective sensors: Trifluoroacetophenone derivatives were synthesized with a hexasubstituted benzene ring as a preorganized spacer (see scheme) and their characteristics as ionophores were examined for use in ion-selective electrodes. The electrode membranes based on these neutral carriers combined with a cationic additive showed a monoanionic Nernstian response to underivatized phenylalanine, with excellent selectivity towards other essential amino acids and inorganic anions.
Co-reporter:Shin-ichi Sasaki Dr.;Akio Hashizume;Daniel Citterio Dr.;Eiji Fujii Dr.
Angewandte Chemie 2002 Volume 114(Issue 16) pp:
Publication Date(Web):21 AUG 2002
DOI:10.1002/1521-3757(20020816)114:16<3131::AID-ANGE3131>3.0.CO;2-P
Selektive Sensoren: Trifluoracetophenon-Derivate wurden mit einem hexasubstituierten Benzolring als vororganisiertem Spacer synthetisiert (siehe Schema). Für einen möglichen Einsatz in ionenselektiven Elektroden wurden ihre Eigenschaften als Ionophore untersucht. Die auf diesen neutralen Carriermolekülen basierende Elektrodenmembran zeigt in Gegenwart eines kationischen Additivs eine monoanionische Nernst-Antwort auf underivatisiertes Phenylalanin und außerdem eine ausgezeichnete Selektivität bezüglich anderer essenzieller Aminosäuren sowie anorganischer Anionen.
Co-reporter:Kazuyoshi Kurihara, Motoichi Ohtsu, Takeo Yoshida, Toshihito Abe, Hideaki Hisamoto, Koji Suzuki
Analytica Chimica Acta 2001 Volume 426(Issue 1) pp:11-18
Publication Date(Web):1 January 2001
DOI:10.1016/S0003-2670(00)01148-X
The preparation and response features of a micrometer-sized lithium ion-selective optode based on a liquid membrane were examined. The optode membrane was a plasticized poly(vinyl chloride) (PVC)-based copolymer incorporating a lipophilic 14-crown-4 derivative as the neutral lithium ionophore and a dibromofluorescein derivative as the fluorescent anionic dye. The detection mode was a fluorescence change based on the ion-pair extraction/ion exchange principle caused by the fluorescent anionic dye and the lithium ionophore. The 5-μm-sized microoptode was prepared by the micropipette fabrication method and characterized by measuring the optical responses to Li+ concentrations with the time-resolved photon counting method. The microoptode responded to lithium ion concentrations of ∼0.5 to ∼500 mM. The micrometer-sized lithium ion-selective microoptode was successfully obtained when a tailed ionophore was used. The anchor effect of the tailed ionophore was useful for the lithium ion-selective microoptode to resolve leaching of the ionophore, which is a significant problem in a microoptode based on a liquid membrane. This demonstration indicates that other ion-selective microoptodes can be obtained simply by replacing the tailed ionophore.
Co-reporter:Shin-ichi Sasaki, Tsuyoshi Amano, Satoru Ozawa, Tomomi Masuyama, Daniel Citterio, Hideaki Hisamoto, Hisao Hori and Koji Suzuki
Organic & Biomolecular Chemistry 2001 (Issue 12) pp:1366-1371
Publication Date(Web):23 May 2001
DOI:10.1039/B008978H
Novel Hg2+ receptors having two N-benzyloxyamide groups are synthesized, and their complexation ability toward metal cations is examined. The structure of the formed complexes was elucidated by ESI-MS and 1H NMR spectroscopy. Deprotonation of the amide groups allows the receptors to form stable complexes with Hg2+. As an application of this neutral Hg2+ complex, an anion-selective electrode combined with a cationic additive is prepared, and exhibits an anti-Hofmeister selectivity pattern with enhanced selectivity for the iodide anion. The overall selectivity pattern of the electrode is I− > ClO4− > SCN−
≈ Br− > salicylate− > NO2− > Cl− > NO3−
≫ HCO3− > SO42− > F− > H2PO4−.
Co-reporter:Shin-ichi Sasaki, Daniel Citterio, Satoru Ozawa and Koji Suzuki
Organic & Biomolecular Chemistry 2001 (Issue 12) pp:2309-2313
Publication Date(Web):05 Nov 2001
DOI:10.1039/B105913K
Expecting a preorganization effect, tripodal anion host molecules were designed and synthesized. It was demonstrated that two kinds of new thiourea derivatives having a six-fold substituted benzene ring as a preorganized spacer were effective for recognition of the tetrahedral dihydrogen phosphate anion. A tripodal fluororeceptor 1 having a pyrene moiety adjacent to the thiourea binding site showed long-wavelength emission upon addition of guest anions in acetonitrile. On the other hand, a tripodal thiourea receptor 2 connected to anthracene groups via methylene units showed a decrease in fluorescence intensity upon addition of anions. In both cases, the degree of the change in emission intensity was in the order of H2PO4− > CH3COO− > Cl−
≫ ClO4−, which is clearly
different from that of reference compounds having only one binding site. Association constants (Ka) of these tripodal fluororeceptors also confirmed the dihydrogen phosphate selectivity over the more basic acetate anion in this homogeneous solution system. The characteristics of the fluororeceptors using the preorganization effect were shown to be promising for the development of chemical ion sensors with a specific anion selectivity.
Co-reporter:Hiroki Hifumi, Seiichi Yamaoka, Akihiro Tanimoto, Tomotaka Akatsu, Yutaka Shindo, Aki Honda, Daniel Citterio, Kotaro Oka, Sachio Kuribayashi and Koji Suzuki
Journal of Materials Chemistry A 2009 - vol. 19(Issue 35) pp:NaN6399-6399
Publication Date(Web):2009/06/04
DOI:10.1039/B902134E
Tumor detection is of great clinical interest. It is known that solid tumors have unique vascular pathophysiological features summarized under the term “enhanced permeability and retention (EPR) effect”, which induces the accumulation and prolonged retention of macromolecules from the blood into the tumor. We therefore have designed and synthesized dextran coated paramagnetic gadolinium phosphate nanoparticles (PGP/dextran) as a new magnetic resonance imaging (MRI) contrast agent. The main features of this new material are: (i) characteristics of a positive contrast agent providing higher imaging resolution, (ii) size of several tens of nanometres to accumulate and to be retained into tumors, and (iii) highly biocompatible dextran coating to prevent the rapid elimination from the blood stream. In this article, we describe the results of pharmacokinetic studies, toxicity tests, and MR imaging experiments to visualize tumors using PGP/dextran, and compare them to the clinically used contrast agent Magnevist®. Relying on the EPR effect, tumors in a rabbit were successfully visualized on conventional T1-weighted MR images using the particulate and positive PGP/dextran with only 1/10 of the applied dose compared to Magnevist®. This efficient visualization of a tumor is the result of the comprehensive features of PGP/dextran, having adequate characteristics of a positive contrast agent for MRI, a significantly long plasma half-life and a high biocompatibility. PGP/dextran could be used as a tumor specific contrast agent and as a vehicle to deliver drugs to a tumor.
Co-reporter:Maki Sekiya, Keitaro Umezawa, Akemi Sato, Daniel Citterio and Koji Suzuki
Chemical Communications 2009(Issue 21) pp:NaN3049-3049
Publication Date(Web):2009/04/09
DOI:10.1039/B903751A
This communication reports the synthesis, chemiluminescence properties, and biological application of KEIO-BODIPY–imidazopyrazine (KBI), a yellow-green chemiluminescent probe for the detection of reactive oxygen species (ROS) generated from living cells.
Co-reporter:Akihiro Matsui, Keitaro Umezawa, Yutaka Shindo, Tomohiko Fujii, Daniel Citterio, Kotaro Oka and Koji Suzuki
Chemical Communications 2011 - vol. 47(Issue 37) pp:NaN10409-10409
Publication Date(Web):2011/08/12
DOI:10.1039/C1CC14045K
We report a novel near-infrared fluorescent calcium probe (KFCA), which has good optical properties such as intense NIR fluorescence emission (670 nm, QY: 0.24), excellent ON/OFF ratio (120-fold), and good wavelength-compatibility with visible-light-emissive fluorophores (Fluo-4, DsRed2), and which is applicable for real-time dual-colour intracellular Ca2+ imaging.
Co-reporter:Yuki Hasegawa, Aki Honda, Keitaro Umezawa, Yusuke Niino, Kotaro Oka, Tomohiro Chiba, Sadakazu Aiso, Akihiro Tanimoto, Daniel Citterio and Koji Suzuki
Chemical Communications 2009(Issue 27) pp:NaN4042-4042
Publication Date(Web):2009/06/10
DOI:10.1039/B904055B
We report a method for specifically labelling the surface of cells with two kinds of chemical probes (near-infrared (NIR) fluorescent probes and magnetic resonance (MR) imaging probes) via two genetically expressed tags, and demonstrate the application for in vitro and in vivo dual imaging.
Co-reporter:Ryo Nishihara, Hideyuki Suzuki, Emi Hoshino, Sakura Suganuma, Moritoshi Sato, Tsuyoshi Saitoh, Shigeru Nishiyama, Naoko Iwasawa, Daniel Citterio and Koji Suzuki
Chemical Communications 2015 - vol. 51(Issue 2) pp:NaN394-394
Publication Date(Web):2014/11/11
DOI:10.1039/C4CC06886F
Three novel coelenterazine (CTZ) derivatives with extension at the C-6 position of the imidazopyrazinone structure show significant bioluminescence emission with known renilla luciferase variants, indicating a promising method to develop CTZ derivatives with superior optical properties compared to hitherto reported compounds.
