Structural characterization and chemical response of a Ag-coordinated supramolecular gel

Supramolecular gels exhibit potential applications in the areas of sensors, nanodevices, drug and catalyst carriers, and so on. To develop a novel organogel with a multiresponse, we designed a component molecule bearing a pyridyl group for metal coordination and an amide group for the formation of intermolecular hydrogen bonding. A complex building block with a symmetrical structure was selectively constructed by the coordination of a silver cation to the organic component. The coordination existing in the complex and the hydrogen bonding existing between complexes were examined by IR, Raman, and 1H NMR spectroscopy. The gel formation and phase transition were examined by viscosity and differential scanning calorimetry measurements. The selection of metal ions for the formation of a gel has proved to be crucial as only the complex of a binary coordinated metal ion, Ag+, was found to form a gel structure. From the band shift of the L1 solution with different amounts of silver ion, the binding ratio of silver ion to L1 was estimated to be 1:2 and the calculated stability constant was 3.6 x 10(8) M(-2). On the basis of the analysis of X-ray diffraction and transmission electron microscopy results, we proposed a possible stacking structure of the complex in the fibrous aggregates. Of interest is that the organogel exhibits a 3-D network structure of a beltlike fiber composed of ordered lamellar arrangements of the coordinated complex and shows a rapid response to wide chemical stimulations such as anions I-, Br-, and Cl-, gases such as H(2)S and NH(3), and a change of pH.     

pH-dependent modulation of relaxivity and luminescence in macrocyclic gadolinium and europium complexes based on reversible intramolecular sulfonamide ligation

A series of macrocyclic Eu, Gd, and Tb complexes has been prepared in which the intramolecular ligation of a beta-arylsulfonamide nitrogen is rendered pH-dependent, giving rise to changes in the hydration state, q, at the lanthanide center. In complexes based on DO3A, variation of the p-substituent in the arylsulfonamide moiety determines the apparent protonation constant log K(MLH) with values of 5.7, 6.4, and 6.7 for the -CF(3), -Me, and -OMe substituents, respectively. Introduction of three beta-carboxyalkyl substituents, alpha to three ring nitrogens, inhibits displacement of the bound water by added protein and also suppresses intermolecular binding by endogenous anions (lactate, HCO(3)(-)). Measurements of the pH dependence of the form and intensity of the Eu complexes revealed that intramolecular carboxylate coordination occurred competitively. This was reduced either by enhancing the electron density at the sulfonamide nitrogen or by enlarging the chelate ring from 7--8. Amplification of the relaxivity changes in the pH range 8--5 occurred on protein binding, and over the pH range 7.4--6.8 a 48% change in relaxivity was defined for [Gd.3a] (298 K, 65.6 MHz) in 50% human serum solution.     

Design, synthesis and evaluation of ratiometric probes for hydrogencarbonate based on europium emission

A series of cationic, zwitterionic and anionic macrocyclic europium complexes has been prepared incorporating a N or C- linked acridone chromophore that allows sensitisation of Eu emission following excitation at 390-410 nm. Each of these complexes selectively binds bicarbonate at physiological pH and reversible binding is signalled by a change in the form and relative intensity of the Eu emission spectrum. Affinity for bicarbonate is regulated by overall complex charge and falls within the range required for intracellular or extracellular analyses. Monitoring the ratio of the intensity of Eu emission at up to three wavelengths, e.g. 618/588 or 618/702 nm allows the solution concentration of bicarbonate to be deduced in a background of competing anions such as lactate, citrate and phosphate. Preliminary screens reveal the complexes to be non-toxic to NIH-3T3 cells and to be taken inside the cell, encouraging further study.     

Synthesis, characterization, and DNA binding properties of ruthenium(II) complexes containing the redox active ligand benzo[i]dipyrido[3,2-a:2',3'-c]phenazine-11,16-quinone

Synthetic methods toward ruthenium(II) complexes incorporating the benzo[i]dipyrido[3,2-a:2',3'-c]phenazine-11,16-quinone ligand, qdppn, are reported. In several cases, it was found that complexes containing coordinated benzo[i]dipyrido[3,2-a:2',3'-c]phenazine, dppn, could be chemically or photochemically oxidized to their qdppn analogues. Since this method was not possible in all the cases, a new, higher yielding, convenient synthesis of qdppn was developed. The crystal structure of the complex [Ru(phen)(2)(qppn)](PF(6))(2) (phen = 1,10-phenanthroline) which was synthesized from free qdppn reveals that a combination of π-π stacking between coordinated phen and qdppn units, as well as anion-ligand hydrogen bonding, define large hexagonal channels which are occupied by anions and solvent molecules. Electrochemical and photophysical studies reveal that the new qdppn-based complexes are not luminescent and, in contrast to their dppn analogues, they are also poor singlet oxygen sensitizers. Time-resolved studies and density functional theory (DFT) calculations indicate that optical properties of the new complexes are due to a short-lived charge separated state involving the quinone moiety of qdppn. The DNA binding properties of the new complexes have also been investigated. It was found that they are intercalators, displaying binding affinities which are comparable to their dppn analogues.     

Substituent effects on Gd(III)-based MRI contrast agents: optimizing the stability and selectivity of the complex and the number of coordinated water molecules

Hydroxypyridinone (HOPO)-based Gd(III) complexes have previously been shown to exhibit high relaxivity, especially at the high magnetic fields that are clinically relevant for present and future clinical use. This is due to more than one coordinated water molecule exchanging rapidly with bulk solvent. These complexes, however, present poor water solubility. Heteropodal complexes which include a terephthalamide (TAM) moiety maintain the high relaxivity characteristics of the HOPO family and have been functionalized with solubilizing substituents of various charges. The charge of the substituent significantly affects the stability of the Gd(III) complex, with the most stable complex presenting a neutral charge. The solubilizing substituent also moderately affects the affinity of the complex for physiological anions, with the highest affinity observed for the positively charged complex. In any case, only two anions, phosphate and oxalate, measureably bind the Gd(III) complex with weak affinities that are comparable to other q = 1 complexes and much weaker than DO3A, q = 2 based complexes. Furthermore, unlike poly(amino-carboxylate)-based complexes, HOPO-based Gd(III) complexes do not show any noticeable interaction with carbonates. The nature of the substituent can also favorably stabilize the coordination of a third water molecule on the Gd(III) center and lead to a nine-coordinate ground state. Such complexes that attain q = 3 incorporate a substituent beta to the terminal amide of the TAM podand that is a hydrogen-bond acceptor, suggesting that the third water molecule is coordinated to the metal center through a hydrogen-bond network. These substituents include alcohols, primary amines, and acids. Moreover, the coordination of a third water molecule has been achieved without destabilizing the complex.     

para‐Sulfonated Calixarenes Used as Synthetic Receptors for Complexing Photolabile Cholinergic Ligand

The water‐soluble tetra‐, hexa‐ and octasulfonated calix[4]arenes, calix[6]arenes, and calix[8]arenes 1 – 3 , respectively, were investigated as potential synthetic receptors for photolabile cholinergic ligand A , a photolytic precursor of choline. Ligand A is a bifunctional molecule carrying a photolabile 2‐nitrobenzyl group at one end and a choline moiety at the other end. Results from NMR studies have shown that calixarenes 1 – 3 form stable 1 : 1 complexes with A , having similar binding potential to that observed with the cholinergic enzymes acetylcholinesterase and butyrylcholinesterase. Further studies have suggested that calix[8]arene forms a ditopic complex by binding concomitantly to both the cationic choline moiety and the aromatic photolabile group of A , whereas calix[4]arene and calix[6]arene form monotopic complexes with A . The ditopic complex between calix[8]arene and A results from mutually induced fitting process, while the monotopic complexes between calix[4]arene and A can be regulated by pH: at neutral pH, calix[4]arene specifically binds the cationic choline moiety, while, at acidic pH, it complexes unselectively both the cationic choline moiety and the aromatic group of A . Our results show that para‐sulfonated calixarenes are versatile artificial receptors which bind in various ways to the bifunctional photolabile cholinergic ligand A , depending on their size, geometry, and state of protonation.     

NMR relaxometric study of new Gd(III) macrocyclic complexes and their interaction with human serum albumin

Five novel Gd(iii) complexes based on the structure of the heptadentate macrocyclic 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) ligand have been synthesized and their (1)H and (17)O NMR relaxometric properties investigated in detail. The complexes have been functionalised on the secondary nitrogen atom of the macrocyclic ring with different pendant groups for promoting their ability to interact non-covalently with human serum albumin (HSA). The analysis of the proton relaxivity, measured as a function of pH and magnetic field strength, have revealed that the three complexes bearing a poly(ethylene glycol)(PEG) chain possess a single coordinated water molecule, whereas the complexes functionalised with 1-[3-(2-hydroxyphenyl)]-propyl and 1-[3-(2-carboxyphenyloxy)]-propyl pendant groups have two inner sphere water molecules. The water exchange rates, measured by variable temperature (17)O NMR, cover a broad range of values (from 18 to 770 ns) as a function of their charge, the chemical nature of the substituent and its ability to organize a second sphere of hydration near the water(s) binding site. All the complexes have shown some degree of interaction with HSA, with a stronger binding affinity measured for those bearing an aromatic moiety on the pendant group. However, upon binding the expected relaxation enhancement has not been observed and this has been explained with the displacement of the coordinated water molecules by the protein and formation of ternary adducts.     

An electrospray ionization mass spectrometry investigation of 1-anilino-8-naphthalene-sulfonate (ANS) binding to proteins

The binding of 1-anilino-8-naphthalene-sulfonic acid (ANS) to various globular proteins at acidic pH has been investigated by electrospray ionization mass spectrometry (ESI-MS). Maximal ANS binding is observed in the pH range 3-5. As many as seven species of dye-bound complexes are detected for myoglobin. Similar studies were carried out with cytochrome c, carbonic anhydrase, triosephosphate isomerase, lysozyme, alpha-lactalbumin, and bovine pancreatic trypsin inhibitor (BPTI). Strong ANS binding was observed wherever molten globule states were postulated in solution. ANS binding is not observed for lysozyme and BPTI, which have tightly folded structures in the native form. Alpha-lactalbumin, which is structurally related to lysozyme but forms a molten globule at acidic pH, exhibited ANS binding. Reduction of disulfide bonds in these proteins leads to the detection of ANS binding even at neutral pH. Binding was suppressed at very low pH (<2.5), presumably due to neutralization of the charge on the sulfonate moiety. The distribution of the relative intensities of the protein bound ANS species varies with the charge state, suggesting heterogeneity of gas phase conformations. The binding strength of these complexes was qualitatively estimated by dissociating them using enhanced nozzle skimmer potentials. The skimmer voltages also affected the lower and higher charge states of these complexes in a different manner.     

Synthesis and characterization of lanthanide complexes of DO3A-alkylphosphonates

Eight DO3A-based lanthanide(III) complexes bearing ester protected and unprotected phosphonate groups at variable distances from the macrocyclic moiety have been synthesized and analyzed. The ligands were made by straightforward four-step synthetic procedures and purified with preparative RP-HPLC, after which they were used to prepare gadolinium(III) and europium(III) complexes. Relaxometric experiments were performed on the Gd(III) complexes at 300 MHz, varying the pH of the solutions or the concentration of human serum albumin (HSA). It was found that when the pH of the medium was changed from neutral to pH 4 the longitudinal relaxivity of GdDO3A-ethylphosphonate and GdDO3A-propylphosphonate complexes increased by 50% and 60%, respectively. Diethyl esters of these complexes did not change longitudinal relaxivity in the same pH range but their transverse relaxivity increased upon binding to HSA. 31P NMR experiments on Eu(III) complexes showed a change in the chemical shift of both acid complexes in the same region where the highest relaxivity changes were observed and proved the stability of the complexes in the investigated pH range, while no shift was observed for the diester complexes. Luminescence studies on europium(III) complexes additionally supported observations obtained by NMR methods. The change in the form of the luminescence emission spectra, and the reduction in the q value upon addition of HSA proved the ternary adduct formation between the charge neutral diester complexes and HSA. Similarly, the change in the emission spectra showing a phosphonate bound structure at pH 7 to a species where the phosphonate oxygen is not coordinated at pH 4 in parallel with the increase of q value is supporting the hypothesis that the deprotonation of phosphonates is the main reason for the distinct relaxivity change from slightly acidic to the neutral solution media.     

Light-induced copper(II) coordination by a bicyclic tetraaza chelator through a ligand-to-metal charge-transfer reaction

To enable utilization of the broad potential of copper isotopes in nuclear medicine, rapid and robust chelation of the copper is required. Bowl adamanzanes (bicyclic tetraaza ligands) can form kinetically stable copper complexes, but they are usually formed at low rates unless high pH values and high temperatures are applied. We have investigated the effects of the variation in the pH, different anions, and UV irradiation on the chelation rate. UV spectra of mixtures of Cu(2+) and [2(4).3(1)]adz in water show the existence of a long-lived two-coordinated copper(II) intermediate (only counting coordinated amine groups) at pH above 6. These findings are supported by pH titrations of mixtures of Cu(2+) and [2(4).3(1)]adz in water. Irradiation of this complex in the ligand-to-metal charge-transfer (LMCT) band by a diode-array spectrophotometer leads to photodeprotonation and subsequently to formation of the four-coordinated copper(II) complex at a rate up to 7800-fold higher at 25 °C than in the dark. Anions in the solution were found to have three major effects: competitive inhibition due to Cu(II) binding anions, inhibition of the photoinduced transchelation from UV-absorbing anions, and photoredox inhibition from acido ligands capable of acting as electron donors in LMCT reactions. Dissolved O(2) was also found to result in photoredox inhibition.     

Vapochromic and mechanochromic tetrahedral gold(I) complexes based on the 1,2-bis(diphenylphosphino)benzene ligand

Tetrahedral gold(I) complexes containing the diphosphane ligand (dppb=1,2-bis(diphenylphosphino)benzene), [Au(dppb)(2)]X [X=Cl (1), Br (2), I (3), NO(3) (4), BF(4) (5), PF(6) (6), B(C(6)H(4)F-4)(4) (7)], and the ethanol and methanol adducts of complex 4, 8, and 9, were prepared to analyze their unique photophysical properties. These complexes are classified into two categories on the basis of their crystal structures. In Category I, the complexes (1-5) have relatively-small counter anions and two dppb ligands are symmetrically coordinated to the central Au(I) atom, and display an intense blue phosphorescence. Alternatively, the complexes (6-9) in Category II have large counter anions and two dppb ligands asymmetrically coordinated to Au(I) atom, and display a yellow or yellow orange phosphorescence. The difference in the phosphorescence color of the complexes between the Category I and II is ascribed to the change in the structure of the cationic moiety in the complex. According to DFT calculations, the symmetry reduction caused by the large counter anion of the complex in Category II gives the destabilization of HOMO (σ*) levels, leading to the red-shift of the emission peak. We have demonstrated that the symmetry reductions are responsible for the phosphorescence color alteration caused by external stimuli (volatile organic compounds and mechanical grinding).     

Bright Mono‐aqua Europium Complexes Based on Triazacyclononane That Bind Anions Reversibly and Permeate Cells Efficiently

A series of five europium(III) complexes has been prepared from heptadentate N₅O₂ ligands that possess a brightness of more than 10 mM ^?1 cm^?1 in water, following excitation over the range λ=330–355 nm. Binding of several oxy anions has been assessed by emission spectral titrimetric analysis, with the binding of simple carboxylates, lactate and citrate involving a common ligation mode following displacement of the coordinated water. Selectivity for bicarbonate allows the rapid determination of this anion in human serum, with K_d=37 mM (295 K). The complexes are internalised quickly into mammalian cells and exhibit a mitochondrial localisation at early time points, migrating after a few hours to reveal a predominant lysosomal distribution. Herein, we report the synthesis and complexation behaviour of strongly emissive europium (III) complexes that bind oxy‐anions in aqueous media with an affinity and selectivity profile that is distinctively different from previously studied systems.     

Ion-pair recognition based on halogen bonding: a case of the crown-ether receptor with iodo-trizole moiety

The development of halogen-bond-based ditopic receptors capable of binding simultaneously both a cation and an anion has attracted recent research interest. In this work, the crown-ether receptor 1, which consists of an iodo-trizole moiety for anion recognition through halogen bonding and a Lewis-basic center for cation binding, was investigated using density functional theory calculations. The structural and energetic features for the complexes of 1 with single cations, single halide anions, and ion pairs were explored. Intermolecular interactions in these complexes were systematically analyzed by the atoms in molecules and noncovalent interaction index methods. The presence of the coordinated cation significantly increases the anion-binding affinity, while the binding of halide anions has a slight influence on the cation-binding affinity. Anti-cooperative effects were found in the ion-pair recognition of 1, due to the strong attraction between the two counterions in the complexes. The solvent weakens the interaction strength considerably, and anti-cooperativity becomes very small in solvent. The results reported in this work are of fundamental importance in the design of ion-pair receptors based on halogen bonding.     

Expanded fullerides and electron localisation -- lithium-rich ammoniated C(60) phases

The synthesis and characterisation of alkali metal fullerides with complex counterions consisting of ammonia ligands coordinated to lithium cations is discussed. The body-centred cubic packing and accompanying low density of fulleride anions produces localisation of the t(1u) outer electrons of the fulleride anions. This is demonstrated by the electronic behaviour of the x = 3 and 5 members of the series, the latter representing the first detailed study of the electronic behaviour of a localised electron fulleride with five electrons per anion.     

ON THE FORMATION OF PHOTOSYNTHETIC MEMBRANES IN BEAN PLANTS*

Abstract— The formation of lamellar chlorophyll-protein complexes I and II, solubilized by sodium dodecyl sulfate, was studied by hydroxylapatite column chromatography during greening of etiolated Phaseohis vulgaris leaves.
The protein moiety of both complexes preexists in the prolamellar body of etiolated tissue. The complex II to complex I protein ratio is of the order of 0.5. During greening in intermittent illumination the 'proto'-chloroplast is agranal, and contains 'primary' thylakoids and chlorophyll a (Chl a ). At this stage the complex II to complex I protein ratio increases only slightly. Further greening of the plant tissue in continuous illumination results in grana, Chi b (chlorophyll b ) and more Chl a formation. The complex II to complex I protein ratio in unfractionated thylakoids is now of the order of 2.5, while in grana it is of the order of 4.0.
The binding of chlorophyll formed during greening to the protein moiety of the two complexes is found to be selective. The Chi a selectively formed under intermittent illumination is more strongly bound to the complex I protein. The Chi b and Chl a formed in continuous illunination are found bound to both complex I and complex II proteins.
Analysis by hydroxylapatite column chromatography of subchloroplast fractions obtained by different fractionation procedures have shown that these two chlorophyll-protein complexes are most probably derived from the PSI (photosystem I) and PSII (photosystem II) particles of the photosynthetic membrane. These findings suggest that PSI units are assembled ahead of PSII units. Moreover, they indicate that the complex I protein is the main protein component in the prolamellar body membranes, the 'primary' thylakoids. and the stroma lamellae, while in the grana membranes the major protein is the complex II protein. Finally our results show that formation of the photosynthetic membranes is a multi-step process.     

可生物降解肝素钠/两性壳聚糖复合物用于蛋白药物pH响应释放研究

制备了一类可生物降解肝素钠两性壳聚糖复合物(HPACS),并探索将其用于蛋白药物pH响应释放.两性壳聚糖由壳聚糖与丙烯酸加成反应得到,丙烯酸取代度可通过丙烯酸壳聚糖投料比调控;用胶体与pH浊度滴定研究了肝素钠与两性壳聚糖的复合作用,发现两组分在一定pH范围内能通过静电相互作用形成复合物,复合转变临界pH(pHΦ)与两性壳聚糖中丙烯酸取代度有关,取代度越低,pHΦ值越高.以牛血清白蛋白(BSA)为模型,测定了其在复合物中包埋及不同pH介质中的释药行为.结果表明,BSA可以在非常温和条件下有效包埋于复合物中,包埋率接近100%;BSA从复合物中释放具有很高的pH响应性,释放转变在很窄的pH范围内(<0.4pH单位)完成,释放转变临界pH(pH′Φ)可由两性壳聚糖中丙烯酸取代度调控.复合物形成和蛋白质释放在对pH依赖性上存在很好的相关性.同时还发现,在中性介质中(pH7.4),复合物对BSA具有很好的缓释作用,BSA持续释放时间可达15天左右.     

Synthesis,Spectroscopy, Semi‐empirical and Biological Activities of Organotin(IV) Complexes with o‐Isopropyl Carbonodithioic Acid

New organotin(IV) complexes have been synthesized by treating potassium o‐isopropyl carbonodithioate with R₂SnCl₂/R₃SnCl in 1 : 2/1 : 1 M/L ratio. All complexes have been characterized by IR and NMR (¹H, ¹³C) spectroscopy. IR results shows that ligand acts as bidentate which is also confirmed by semi‐empirical study. NMR data reveals four coordinated geometry in solution. Computed positive heat of formation shows that complex 5 is thermodynamically unstable. UV/visible spectroscopy was used to assess the mode of interaction and binding of the complexes with DNA which shows that complex 5 exhibits higher binding constant as compared to complex 3 . In protein kinase inhibition assay, compound 3 was found most active, while other biological activities shows that triorganotin(IV) complexes are biologically more active as compared to diorganotin(IV) complexes.     

Synthesis, physico-chemical and DNA interaction studies of homo- and hetero-trinuclear complexes

Synthesis and characterization of three new trinuclear metal complexes of type Cu3, Cu2Zn and Cu2Ni have been achieved by assembling simple mononuclear complexes, namely 2,2'-bipyridyl 3,4-dihydroxo benzaldehyde copper(II) complex and diethylenetriamine complexes of copper(II), nickel(II) and zinc(II) ions, through the reaction of coordinated ligands. The FAB mass spectra for the complexes show fragmentation pattern in accordance with the molecular formula. The frozen electron paramagnetic resonance (EPR) spectrum of tricopper complex shows two sets of parallel lines with approximately 2:1 ratio. The simulation has been carried out by considering dipolar interaction between the two types of copper ions present in the complex. The trimetallic complexes, Cu3, Cu2Ni and Cu2Zn show strong intercalation type of interaction with Calf thymus DNA in 0.02 mol L(-1) of phosphate buffer containing 60 mmol sodium chloride at pH 7.0 at room temperature. The binding constant is found to be in the order Cu3相似文献   

The formation of non-soluble complexes between polyethyleneimine-anions and their potential use to isolate enzymes

The aqueous solution behavior of polyethyleneimine (a synthetic cationic polymer) in the presence of anions with two or more electrical charges (citrate, phosphate, sulphate, malate, malonate and succinate) was studied by means of turbidimetry and light scattering. Polyethyleneimine forms non-soluble complexes with these anions, which behave as a pseudo-polyampholyte with an isoelectrical pH value dependent on the type of anion. The effect of pH, polymer concentration and ionic strength on the non-soluble complexes formation was examined. The complex precipitation pH range was between 3.5 and 8.0 and also depended on the type of anion. The complex formation was inhibited by the ionic strength in agreement with the electrostatic mechanism of the non-soluble complex formation. Model proteins with isoelectric pH from 1 to 10 were assayed in orden to be precipitated by these complexes. It was found that the non-soluble polyethyleneimine-anion complexes have the property to precipitate macromolecules charged with an opposite electrical charge.     

Development of N-benzamidothioureas as a new generation of thiourea-based receptors for anion recognition and sensing

A series of neutral N-(substituted-benzamido)-N'-phenylthioureas (substituent = p-OC(2)H(5), p-CH(3), m-CH(3), H, p-Cl, p-Br, m-Cl, and p-NO(2)) were designed as anion receptors, in which the thiourea binding site was attached to the benzamido moiety via an N-N bond. The absorption spectra of these N-benzamidothioureas in acetonitrile peaked at ca. 270 nm were found to show unprecedented red shifts by 7 373 to 14 325 cm(-1) in the presence of anions such as AcO(-), F(-), and H(2)PO(4)(-). Under the same conditions, the classic neutral thiourea receptors, N-(substituted-phenyl)-N'-phenylthioureas, showed absorption spectral shifts in most cases of less than 800 cm(-1) with one exception of 6501 cm(-1). Control experiments, effects of protic solvent, and (1)H NMR titration confirmed the formation of hydrogen-bonding complexes between the new N-benzamidothiourea receptors and anions. The binding constants with AcO(-), for example, are at 10(5)-10(7) mol(-1) L order of magnitude, which are 13 to 590 times those of the corresponding classic N-phenylthioureas in the same solvent. It was found that, whereas the absorption of the N-benzamidothiourea receptors showed essentially no dependence on the substituent, the substantially red-shifted new absorption band of the N-benzamidothiourea-anion binding complex was sensitively subject to the substituent. A linear relationship was found between the absorption energies of the N-benzamidothiourea-acetate binding complexes and the Hammett constants of the substituents with a negative slope of -0.34 eV. This led to the assignment that the substantially red-shifted absorption band was the ground-state intramolecular charge-transfer absorption with the substituent locating in the electron acceptor moiety. It was concluded that anion binding to the thiourea moiety of the N-benzamidothiourea receptors switched on their ground-state charge transfer. An anion-binding induced structural change was suggested to occur around the N-N bond in N-benzamidothioureas, which resulted in a substantially increased electron donating ability of the electron donor in the receptor molecules. As a consequence, the ground-state charge transfer takes place in the N-benzamidothiourea-anion binding complexes, leading to unprecedented red shifts in the absorption spectra and substantially enhanced anion binding affinities than those of the corresponding N-phenylthiourea receptors. N-Benzamido-N'-phenylthioureas represent a new generation of neutral thiourea-based anion receptors that show substantially improved anion binding performance important for anion sensing and recognition.