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PubMed2001

Sydnone derivatives. Part VII: Synthesis of some novel thiazoles and their pharmacological properties.

The synthesis of some 4-(arylsydnonyl)-2-(4-arylhydrazono-3-methyl-5-oxo-2-pyrazolin-1-yl)- thiazoles by reacting 1-thiocarboxamido-3-methyl-4-(aryihydrazono)-2-pyrazolin-5-ones with different 4-bromoacetyl-3-arylsydnones is described. A few compounds from this series were screened for their anti-inflammatory, analgesic, and CNS depressant activities. Among the tested compounds 6s, 6d, 6n, and 6u showed significant anti-inflammatory activity comparable with that of standard drug Ibuprofen. Compounds containing chlorine and carboxylic substituents are more active. 6f, 6r, and 6u showed marked analgesic activity and most of the compounds tested showed promising CNS depressant activity comparable with that of standard drug pentobarbitone.

Analgesia↗
PubMedDate not supplied

Antioxidant, pro-oxidant effect of the thiosemicarbazone derivative Schiff base (4-(1-phenylmethylcyclobutane-3-yl)-2-(2-hydroxybenzylidenehydrazino) thiazole) and its metal complexes on rats.

Adverse biological activities of thiosemicarbazone (TSC) and Schiff base (SB) derivatives have been widely studied in rats and in other animal species using different doses, times and routes of administration. However, there are few studies describing changes in some biochemical parameters in vivo which are indicative of oxidative stress in biological systems and of morphological changes of tissues. In this study, the rats were injected subcutaneously with a new thiosemicarbazone thiazole ring containing a Schiff base (LH) and its Cu(L)2 and Zn(L)2 complexes (25 mg kg(-1) body weight) and then sacrificed after 1, 2, 4, 8, 16, 32 and 64 days. The aim of this study was to determine the effect of the new compounds on the serum antioxidant vitamins (A, E, C), selenium (Se), malondialdehyde (MDA) levels, erythrocyte GSH-Px enzyme activity and morphological changes in the liver, kidney and adrenal gland tissues. It was observed that erythrocyte GSH-Px activity, serum MDA and vitamins A, E concentrations were statistically changed (p < 0.02), but serum levels of selenium, and vitamin C were not changed. In conclusion, the parameters measured show that Cu(L)2 caused considerable oxidative stress and Zn(L)2 behaved as an antioxidant. No oxidative stress in LH was observed compared to the control group.

Animals↗
PubMed1992

Determination of the partition of the tetramisole derivative (+-)-5,6-dihydro-6-phenyl-2-n-propyl-imidazo[2,1-b]thiazole into liposomal membranes by fluorescence quenching of the membrane probe 8-(2-anthryl)-octanoic acid.

Fluorescence quenching has been used to study the partition of the tetramisole derivative (+-)-5,6-dihydro-6-phenyl-2-n-propyl-imidazo[2,1-b]thiazole into liposomes, consisting of a mixture of egg L-alpha-phosphatidylcholine, egg phosphatidylethanolamine and dipalmitoylphosphatidic acid (2:1:0.06 w/w/w). The tetramisole derivative quenched the fluorescence of the intramembrane probe 8-(2-anthryl)-octanoic acid. The quenching process could be rationalized by a model for dynamic quenching in which an intermediate excited-state non-emitting complex (PQ)* between neutral quencher (Q) and excited probe (P*) is involved: [sequence: see text] where kd, k-d and ki represent the rate constants of complex formation, dissociation and deactivation, respectively. The subscripts A and L denote the aqueous and lipid phases, and the asterisk indicates the excited state. Linear Stern-Volmer plots were obtained from quenching experiments of fluorescence intensities and fluorescence life-times. The slopes of the plots were dependent on the lipid volume fraction of the liposomes. Measurement of the reciprocal of the apparent bimolecular quenching rate constant at various lipid volume fractions yielded the partition coefficient Kp and the overall quenching rate constant kq[kq = kdki/(ki+k-d)] of the tetramisole derivative. The steady-state measurements were performed at three different pH-values. Time-correlated single photon counting measurements revealed a single-exponential fluorescence decay for 8-(2-anthryl)-octanoic acid in the presence and absence of quencher. The quenching results were in accordance with the model that only the neutral form is capable of partitioning into the lipid phase. Combined average values of 318 and 6.59 x 10(8) M-1s-1 were calculated for the partition coefficient and the bimolecular quenching rate constant, respectively, from the steady-state and time-resolved quenching experiments.

Anthracenes↗
PubMed1993

Bisubstrates: substances that interact with renal contraluminal organic anion and organic cation transport systems. I. Amines, piperidines, piperazines, azepines, pyridines, quinolines, imidazoles, thiazoles, guanidines and hydrazines.

In order to evaluate whether N-containing substrates interact with the organic "anion" (p-aminohippurate, PAH) or only with the organic "cation" (N1-methylnicotinamide, NMeN) transport system or with both, the stop-flow peritubular capillary microperfusion method was applied in the rat kidney in situ and the apparent Ki values of several classes or organic substrate against contraluminal NMeN and PAH transport were determined. Organic "anion" and organic "cation" transport are in inverted commas because neither transporter sees the degree of ionization in bulk solution, and they also accept nonionizable substrates [Ullrich KJ, Rumrich G (1992) Pflügers Arch 421:286-288]. Amines must be sufficiently hydrophobic (phenylethylamine, piperidine, piperazine) in order to interact with NMeN transport. Additional Cl, Br, NO2 or other electronegative groups render them inhibitory towards PAH transport also. Such bisubstrate amines were identified as follows: metoclopramide, bromopride, diphenhydramine, bromodiphenhydramine, verapamil, citalopram, ketamine, mefloquine, ipsapirone, buspirone, trazodone, H7 and trifluoperazine. Imidazole analogues interact with both transporters if they bear sufficiently hydrophobic alkyl or aryl groups or electronegative sidegroups. Bisubstrate imidazole analogues are tinidazole, pilocarpine, clonidine, azidoclonidine and cimetidine. Pyridines and thiazoles interact with the NMeN transporter if they have an additional ring-attached NH2 group. Again with an additional Cl, Br, or NO2 group the aminopyridines and aminothiazoles also become inhibitors for the PAH transporter. Amongst the guanidines only substances with several electronegative side-groups such as guanfacine, amiloride, benzylamiloride and ranitidine, interact with both transporters. Amongst the phenylhydrazines only 4-bromophenylhydrazine interacts with the NMeN transporter and 4-nitrophenylhydrazine with both transporters. Quinoline (isoquinoline) and its amino and hydroxy analogues interact with both transporters, their pKa values correlate directly with the affinity to the NMeN transporter and reciprocally with their affinity to the PAH transporter. In experiments with labelled substrates only the sufficiently hydrophilic cimetidine, amiloride and ranitidine show a saturable transport, which can be inhibited by probenecid (apalcillin) and tetraethylammonium in an additive manner. The highly hydrophobic substrates verapamil, citalopram, imipramine, diltiazem and clonidine enter the cell very fast in an unsaturable and uninhibitable manner, apparently in the undissociated form, since N-methyl-4-phenylpyridinium, which--disregarding its ionization--is similarly hydrophobic, shows a transport behaviour similar to that of tetraethylammonium [Ullrich et al. (1991) Pflügers Arch 419:84-92]. Ethidium bromide and dimidium bromide, which have a permanent cationic quaternary nitrogen and two sufficiently electronegative NH2 groups, also interact with both transporters.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Partitioning of (+-)-5,6-dihydro-6-phenyl-2-n-alkyl-imidazo- [2,1-b]thiazoles into large unilamellar liposomes: a steady-state fluorescence quenching study.

The interaction of the tetramisole derivative (+-)-5,6-dihydro-6-phenyl-imidazo[2,1-b]thiazole and a number of its 2-n-alkyl homologues (-ethyl through -n-pentyl and -n-heptyl) with large unilamellar phosphatidylcholine/phosphatidylethanolamine/dipalmitoylphosphatidic acid (2:1:0.06, w/w) vesicles was studied by means of steady-state fluorescence quenching using 8-(2-anthryl)octanoic acid as membrane probe. Linear Stern-Volmer plots were obtained for each derivative, indicating dynamic quenching. The slopes of the plots decreased with increasing liposomal concentration. For four short-chain homologues (-H, -ethyl, -n-propyl and -n-butyl), the respective membrane partition coefficients Kp and bimolecular quenching rate constants kq were determined from the plots of the reciprocal of the apparent quenching rate constant (kappq)-1 against the lipid volume fraction alpha L of the liposomes. The partition coefficients increased with increasing chain-length of the tetramisoles. A linear relationship was found between the free energy of partitioning and the number of methylene units of the homologues (-delta G degrees per methylene group = 1.6 +/- 0.1 kJ mol-1). For the n-pentyl and n-heptyl derivatives, the fluorescence quenching technique did not allow one to determine their membrane partition coefficients. Analysis of the fluorescence intensity measurements with Scatchard plots gave further evidence for the partitioning nature of the tetramisole derivatives' association with the liposomal membranes.

Anthracenes↗
PubMed1986

Studies on the mechanism of action of tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide). VI. Biochemical and pharmacological studies on the degradation of thiazole-4-carboxamide adenine dinucleotide (TAD).

In order to exert its antitumor effects, the C-nucleoside tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) is converted to the dinucleotide TAD (thiazole-4-carboxamide adenine dinucleotide), an inhibitor of IMP dehydrogenase (IMPD). With few exceptions, sensitive tumors (such as the P388 leukemia) have been found to accumulate substantially more of this inhibitory dinucleotide than resistant strains (exemplified by the colon 38 carcinoma). Previous studies have attributed this difference to a depressed capacity to synthesize TAD on the part of tumors refractory to tiazofurin. In the present study, a second contributory factor has been identified, viz. an enhanced ability to degrade preformed TAD. This degradation has been traced to a soluble phosphodiesterase present at high levels in tumors naturally resistant to tiazofurin. Using standard techniques, this TAD-phosphodiesterase has been purified 200-fold from the colon 38 carcinoma. The activity so purified readily hydrolyzed TAD and ADP-ribose, but exhibited a comparatively weak activity toward NAD and thymidine-5'-monophosphate-nitrophenyl ester. ADP-Ribose was also an excellent inhibitor of the hydrolysis of TAD. It is concluded, on the basis of these results, that TAD-phosphodiesterase plays an important role in the expression of the oncolytic activity of tiazofurin. The suggestion is also made that ADP-ribose may be the natural substrate for this enzyme.

Adenine Nucleotides↗
PubMed1991

Determination of thiazole-4-carboxamide adenine dinucleotide (TAD) levels in mononuclear cells of leukemic patients treated with tiazofurin.

Tiazofurin is an oncolytic agent which has shown therapeutic activity in end-stage acute nonlymphocytic leukemia (ANLL) and blast crisis of chronic granulocytic leukemia (CGL-BC). Tiazofurin is anabolized to the active metabolite, thiazole-4-carboxamide adenine dinucleotide (TAD), which inhibits IMP dehydrogenase activity, leading to reduction of guanylate pools and cessation of cancer cell proliferation. The concentration of TAD in neoplastic cells of patients treated with tiazofurin should be a good indicator of sensitivity to the drug and also might herald the emergence of drug-resistant cells. Therefore, the precise quantitation of TAD in cancer cells during tiazofurin treatment is essential. In this paper we report a highly sensitive method for the determination of TAD in biological samples. With this technique, in addition to TAD, thirteen other biologically relevant adenine, guanine, cytosine and uridine nucleotides can be separated and quantitated accurately. TAD standard was separated on a Waters Partisil 10-SAX column in a RCM-10 module using an ammonium phosphate buffer system. TAD eluted at 21 min with a limit of detection of 15 pmol and linearity up to 3 nmol. The coefficient of variation was 0.6 +/- 0.1% for retention time and 2 +/- 0.3% for TAD concentration. Recovery of TAD was 96% with reproducibility of 98%. To examine the applicability of this method to a clinical setting, blood samples were obtained from a patient with CGL-BC and leukocytes were separated on a Ficoll-Hypaq gradient, extracted with trichloroacetic acid, and an aliquot was analyzed on HPLC. The TAD peak was identified by comparing the retention time and spectral analysis of the standard. After the patient was treated with a 2200 mg/m2 (12.7 mM) dose of tiazofurin, the TAD concentrations in the mononuclear cells at 2, 6, and 24 hr were 23.1, 13.6, and 0.8 microM. TAD levels at 2, 6, and 24 hr after a tiazofurin dose of 3300 mg/m2 (21.1 mM) were 42.8, 26.1, and 1.4 microM respectively.

Adenine Nucleotides↗
PubMed1992

Effect of bromolevamisole and other imidazo [2,1-b] thiazole derivatives on adenylate cyclase activity.

We studied the effect of bromolevamisole (BL) and other imidazo [2,1-b] thiazole derivatives--bromodexamisole (BD) and levamisole (LV)--on adenylate cyclase (AC) activity. BL and BD both inhibited forskolin-activated human thyroid AC, while LV had no effect. This inhibition was non-stereospecific and the IC50 values, as measured with 1 mM ATP and 40 microM forskolin, were 0.95 and 0.80 mM for BL and BD, respectively. In contrast, human thyroid alkaline phosphatase (ALP) inhibition was stereospecific, with IC50 values of 0.0012 mM for BL and 0.9 mM for BD. LV was a 10-fold weaker inhibitor of ALP than BL. These results show that ALP inhibition is not correlated with forskolin-activated AC inhibition. Furthermore, in the presence of a competitive inhibitor of GTP (0.1 mM guanosine 5'-O-(2-thiodiphosphate), BL retained its antagonizing effect on forskolin-activated AC which suggests a direct action on the catalytic subunit. The inhibition was of the mixed type, indicating a complex interaction between BL and AC. Glucagon-activated AC activity in rat liver membranes was also inhibited by BL, although to a slightly lesser degree than thyroid stimulating hormone (TSH)-activated AC from human thyroid for a given BL concentration. In cultured human thyroid cells, BL (0.25 mM) induced a potent decrease in cAMP accumulation after 2 hr of stimulation by TSH. Taken together, these results show that BL inhibits AC and that this inhibition is not organ-specific.

Adenylyl Cyclase Inhibitors↗
PubMed1994

Neu is not involved in N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide- induced bladder carcinoma or 2-amino-4-(5-nitro-2-furyl)thiazole transformation of rat bladder epithelial cells.

Enhanced c-erbB-2/neu expression has been linked with a poor prognosis in human bladder cancer. Previous reports have shown that a point mutation at nucleotide T2012 in the coding region of the transmembrane domain of the rat gene is sufficient to confer transformation potential on this gene. We examined the comparative levels of p185neu as well as the sequence around the hotspot (T2012) of the neu gene of rat bladder cells transformed by 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT) or established in culture from N-[-4-(-5-nitro-2-furyl)-2- thiazolyl]formamide (FANFT)-induced rat bladder tumors. We concluded that increased p185neu expression did not correlate significantly with tumorigenicity. No alterations in nucleotide sequences of the neu gene were observed in either in vitro model.

3T3 Cells↗
PubMed1994

neu is not involved in N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide-induced bladder carcinoma or 2-amino-4-(5-nitro-2-furyl)thiazole transformation of rat bladder epithelial cells.

Enhanced c-erbB-2/neu expression has been linked with a poor prognosis in human bladder cancer. Previous reports have shown that a point mutation at nucleotide T2012 in the coding region of the transmembrane domain of the rat gene is sufficient to confer transformation potential on this gene. We examined the comparative levels of p185neu as well as the sequence around the hotspot (T2012) of the neu gene of rat bladder cells transformed by 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT) or established in culture from N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT)-induced rat bladder tumors. We concluded that increased p185neu expression did not correlate significantly with tumorigenicity. No alterations in nucleotide sequences of the neu gene were observed in either in vitro model.

Animals↗
PubMed1992

Determination of nicotinamide-adenine dinucleotide and thiazole-4-carboxamide-adenine dinucleotide in human leukocytes by reversed-phase high-performance liquid chromatography.

A high-performance liquid chromatographic assay for cellular nicotinamide-adenine dinucleotide and thiazole-4-carboxamide-adenine dinucleotide is presented that is appropriate for analysis of these dinucleotides in extracts of Ficoll-purified human leukemic cells. The separation, which is effected by reversed-phase chromatography, is highly reproducible and the limit of quantitation is as low as 10-15 pmol. The stability of these compounds in neutralized perchloric acid extracts is addressed and the applicability of the procedure to clinical specimens is demonstrated.

Adenine Nucleotides↗
PubMed2005

Synthesis, conformational analysis, and biological activity of new analogues of thiazole-4-carboxamide adenine dinucleotide (TAD) as IMP dehydrogenase inhibitors.

Thiazole-4-carboxamide adenine dinucleotide (TAD) analogues T-2'-MeAD (1) and T-3'-MeAD (2) containing, respectively, a methyl group at the ribose 2'-C-, and 3'-C-position of the adenosine moiety, were prepared as potential selective human inosine monophosphate dehydrogenase (IMPDH) type II inhibitors. The synthesis of heterodinucleotides was carried out by CDI-catalyzed coupling reaction of unprotected 2'-C-methyl- or 3'-C-methyl-adenosine 5'-monophosphate with 2',3'-O-isopropylidene-tiazofurin 5'-monophosphate, and then deisopropylidenation. Biological evaluation of dinucleotides 1 and 2 as inhibitors of recombinant human IMPDH type I and type II resulted in a good activity. Inhibition of both isoenzymes by T-2'-MeAD and T-3'-MeAD was noncompetitive with respect to NAD substrate. Binding of T-3'-MeAD was comparable to that of parent compound TAD, while T-2'-MeAD proved to be a weaker inhibitor. However, no significant difference was found in inhibition of the IMPDH isoenzymes. T-2'-MeAD and T-3'-MeAD were found to inhibit the growth of K562 cells (IC(50) 30.7 and 65.0muM, respectively).

Adenine Nucleotides↗
PubMed2006

Synthesis and SAR study of novel 7-(pyridinium-3-yl)-carbonyl imidazo[5,1-b]thiazol-2-yl carbapenems.

A new series of 1beta-methyl carbapenems, possessing a 7-substituted imidazo[5,1-b]thiazol-2-yl group directly attached to the C-2 position of the carbapenem nucleus, was synthesized and evaluated for antibacterial activity. These compounds showed potent activities against Gram-positive bacteria, in particular methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae (PRSP). They also exhibited potent activity against beta-lactamase-negative ampicillin-resistant Haemophilus influenzae (BLNAR).

Anti-Bacterial Agents↗
PubMed2004

The discovery of N-(1,3-thiazol-2-yl)pyridin-2-amines as potent inhibitors of KDR kinase.

An azo-dye lead was modified to a novel N-(1,3-thiazol-2-yl)pyridin-2-amine series of KDR kinase inhibitors through the use of rapid analog libraries. This new class has been found to be potent, selective, and of low molecular weight. Molecular modeling has postulated an interesting conformational preference and binding mode for these compounds in the active site of the enzyme.

Amines↗
PubMed2005

In vivo neuroprotective effects of the novel imidazolyl nitrone free-radical scavenger (Z)-alpha-[2-thiazol-2-yl)imidazol-4-yl]-N-tert-butylnitrone (S34176).

Herein, we report an extensive investigation of the neuroprotective effects of the compound (Z)-alpha-[2-thiazol-2-yl)imidazol-4-yl]-N-tert-butylnitrone (S34176) and the prototypic nitrone alpha-phenyl-N-tert-butylnitrone (PBN), in different in vivo paradigms of neuronal degeneration. Administration of S34176 (75 mg/kg i.p.) 30 min before transient (10 min) global ischaemia in Wistar rats significantly prevented delayed neuronal cell death in the hippocampal CA1 area 7 days post-ischaemia (24% vs. 73% in ischaemia control; P<0.05) whereas PBN was inactive under similar conditions. Furthermore, oral administration of S34176 (30 mg/kg) 60 min before and during (1 x 30 mg/kg p.o.) 6 days post-ischaemia, in combination with an acute post-ischaemia sub-protective dose (3 x 10 mg/kg i.p.) of the glutamate receptor antagonist, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), resulted in an increased neuroprotective action (29% cell loss in drug-treated vs. 84% in ischaemia control P<0.001) compared to either compound alone. S34176 (20 mg/kg i.p.) also partially prevented kainic acid-induced neuronal cell death at 7 days post-exposure in the CA1 (41% in drug-treated vs. 74% for kainate-treated controls; P<0.01) and CA3 hippocampal region (22% vs. 53%; P<0.01). Under similar conditions, S34176 administered orally (40 mg/kg) produced a more marked protection against kainate-induced neuronal cell loss in the CA1 (13% in drug-treated vs. 82%; P<0.001) and CA3 areas (10% vs. 52%; P<0.001). Sub-chronic oral administration of S34176 (10 mg/kg) also partially reduced kainate-induced hippocampal cell death in the CA1 (53% vs. 77%; P<0.01) and CA3 (23% vs. 53%; P<0.01) areas. Dopamine depletion in the striatum of C57BL/6 mice induced by systemic D-methamphetamine injection was significantly reduced by S34176 (40+/-5% vs. 11.5+/-8%; P<0.001) (150 mg/kg i.p.) whereas PBN was inactive under similar conditions. S34176 represents a new centrally acting nitrone-based radical scavenger with neuroprotective properties in in vivo models of delayed neuronal cell death, and supports the therapeutic potential of this class of compound for the treatment of cerebral pathologies implicating chronic neurodegeneration.

Animals↗
PubMed2002

Simultaneous LC determination of tiazofurin, its acetyl and benzoyl esters and their active metabolite thiazole-4-carboxamide adenine dinucleotide in biological samples.

A rapid and sensitive HPLC-RP method for simultaneous determination of tiazofurin, its 5'-O acetyl and benzoyl esters and their active metabolite thiazole-4-carboxamide adenine dinucleotide was developed and validated. The method allowed determination and quantification of nanomolar quantities of these substances in cell extracts of treated cells, and was also used in kinetic studies of cellular uptake of tiazofurin and its esters from the cultivation medium. Separation of the analyzed substances from unidentified peaks from both biological materials was achieved by gradient elution, thus reducing the possibility of interference. The mobile phase consisted of a 0.1 M sodium-hydrogen phosphate, pH 5.1 and methanol. Run time was 22 min, with 5 min equilibration time.

Adenine Nucleotides↗
PubMed1997

Synthesis and biological properties of a new series of anti-MRSA beta-lactams; 2-(thiazol-2-ylthio)carbapenems.

A series of 1 beta-methylcarbapenems containing variously C-2 substituted thiazol-2-ylthio groups were synthesized, and their in vitro anti-MRSA activity was examined. Among them, 1 beta-methyl-2-(4-arylthiazol-2-ylthio)carbapenems exhibited superior anti-MRSA activity. Introduction of a cationic moiety in the C-2 side chain not only reduced the binding to HSA but also increased the stability against DHP-I, without affecting the anti-MRSA activity. It was also found that the distance between the cationic moiety and the carbapenem skeleton was related to the strength of HSA binding and the stability against DHP-I.

Anti-Bacterial Agents↗
PubMed2000

Thiazole-containing benzo-crown ethers: a new class of ammonium-selective ionophores

A new class of crown ethers containing heterocyclic units has been designed to develop synthetic NH4+-selective ionophores whose resulting potentiometric properties in solvent polymeric membranes are superior or at least comparable to those of nonactin. It was found that the derivatives of thiazole containing dibenzo-18-crown-6 (1; TDB18C6) incorporated in PVC-based membranes provide enhanced NH4+ selectivities over alkali metal cations, especially over Na+, compared to those of the nonactin-doped membranes: for example, the selectivity coefficients, log K(POT)NH4+J (J = Li+, Na+, K+), for the 2-nitrophenyloctyl ether (NPOE) plasticized PVC membranes doped with the hexyl chain-substituted TDB18C6 (2) were -4.9, -3.9, and -1.3, while those for the same type of membranes with nonactin -4.4, -3.0, and -1.0, respectively. Unlike other synthetic NH4+-selective neutral carriers reported to date, TDB18C6-type compounds result in potentiometric performance highly comparable to that of the nonactin-based ones except their slightly higher detection limits (approximately 3 x 10(-6) vs 7 x 10(-7)). The complex formation between TDB18C6 and NH4+ was identified from 1H NMR spectra. The 1:1 complex formation constant of TDB18C6 with NH4+ in solvent polymeric membranes estimated using the method suggested by Bakker et al. and the NH4+ selectivity coefficient over K+ (K(POT)NH4+,K+) are approximately 200 times smaller than that of nonactin (1.8 x 10(7) vs 3.6 x 10(9)).

Journal Article↗