Effect of the sugar moiety on complex formation of cycloamyloses with p-nitrophenyl glycosides

Circular diochroism (CD) spectra of four p-nitrophenyl glycosides and their cycloamylose complexes were investigated at various concentrations of cycloamylose and at temperatures ranging from 20 to 60°C. The CD spectra of p-nitrophenyl glycosides changed remarkably in the presence of cycloamyloses, and significant differences in spectral shape and intensity were observed between the cyclohexaamylose complex and the cycloheptaamylose complex. The difference CD spectra between the free guest and its complex indicates that the nitrophenyl group is included in the cycloamylose cavity but its disposition is different between the complexes with cyclohexaamylose and cycloheptaamylose. Values of enthalpy and entropy of the cyclohexaamylose complex are considerably larger than those of the corresponding cycloheptaamylose complex, although the free energy differs only slightly. It is suggested that the nitrophenyl group is more loosely bound to the cycloheptaamylose cavity than to the cyclohexaamylose cavity, and has much more flexibility in its disposition.     

Interaction of soybean beta-amylase with glucose

The interaction of soybean beta-amylase with glucose was investigated by inhibition kinetics studies and spectroscopic measurements. The inhibition type, inhibitor constant (Ki) and dissociation constant (Kd) of beta-amylase-glucose complex were dependent on pH. At pH 8.0, glucose behaved as a competitive inhibitor (Ki = 34 mM). Binding of glucose produced a characteristic difference spectrum and a change of circular dichroism (CD) at pH 8.1. By using difference absorbance at 292 nm and difference ellipticity at 290 nm, Kd values for beta-amylase-glucose complex were determined to be 45 and 46 mM, respectively. In contrast to pH 8.0, glucose behaved as a mixed-type inhibitor (Ki = 320 mM) at pH 5.4. The Kd values obtained from the difference spectrum were increased by lowering the pH from 8. The pH dependence of the Ki and Kd values suggested that one ionizable group of pK = 8.0, which is shifted to 6.9 by the binding of glucose, controls the binding affinity of glucose. The binding of glucose competed with the binding of cyclohexaamylose and maltose at pH 8.0. The modification of SH groups of the enzyme affected the binding of glucose but did not affect the binding of maltose or cyclohexaamylose at pH 8.0. It was concluded from these results that the binding site of glucose is different from that of maltose and cyclohexaamylose. Presumably, glucose may bind to the subsite 1 of soybean beta-amylase.     

Induced circular dichroism of cycloamylose complexes with meta- and para-disubstituted benzenes

Cycloamylose complexes with substituted benzenes in aqueous solutions were investigated by circular dichroism (CD) spectroscopy. The differences in CD spectra between cyclohexaamylose complexes and cycloheptaamylose complexes suggests that the orientation and disposition of the guest molecule differ in these two cycloamylose complexes. It was shown theoretically that the sign and intensity of CD are quite sensitive to the orientation of the guest chromophor in the cycloamylose cavity, but that the difference between the cyclohexaamylose complex and the cycloheptaamylose complex is only 13% if the guest molecule is included in the same geometry. Molecular ellipticity and thermodynamic parameters, which were determined by the least-squares curve-fitting procedure, indicate that the guest molecule is more closely packed in the cyclohexaamylose cavity, and that there is no stereospecificity in the complex formation between the meta-disubstituted benzenes and the para-disubstituted benzenes.     

The molecular disposition of sodium p-nitrophenolate in the cavities of cycloheptaamylose and cyclohexaamylose in solution

The extent to which sodium p-nitrophenolate penetrates the cycloheptaamylose and cyclohexaamylose cavities has been defined by nmr studies of the complexes in aqueous solution. Measurements of changes in the ¹H nmr spectra of both the sodium p-nitrophenolate guest and the cyclohexaamylose host, along with an intermolecular nuclear Overhauser effect, reveal that this guest only partially penetrates the cyclohexaamylose cavity and does so nitro end first. With cyclohepaamylose, sodium p-nitrophenolate penetrates more deeply, but the orientation may be less specific. These findings are in accord with the notion that both London dispersion forces and removal of high energy cavity water contribute to substrate binding.     

Evaluation of phenolic compounds in Brazilian propolis from different geographic regions

Chemometrics has been shown quite efficient to uncover relationships between chemical composition of a sample and its geographical origin. Forty propolis samples originated from the the South and South East of Brazil were analyzed by HPLC and 18 compounds of interest were studied which included: caffeic, p-coumaric and ferulic acids, and some of their derivatives, pinobanksin, a derivative of kaempferol and five phenolic compounds (assigned as 3-prenyl4-hydroxycinnamic acid (PHCA); 2,2-dimethyl-6-carboxyethnyl-2H-1-benzopyran (DCBE); 3,5-diprenyl-4-hydroxycinnamic acid (DHCA); compound E (still unknown) and 6-propenoic-2,2-dimethyl-8-prenyl-2H-1-benzopyran acid (DPB). Principal Component Analysis (PCA) indicated three different groups of propolis samples, having the same typical chromatogram, evaluated by HPLC. Samples from the South East group were rich in derivatives of kaempferol. Samples from the South group I had a high content of DPB compound, but a low concentration of kaempferol derivatives and of DCBEN compound. Samples from the South group II were characterized by a high concentration of DCBEN, DHCA, p-coumaric and DPB compounds. Therefore, the identification of new compounds in Brazilian propolis can give, useful information about the plant sources of a given geographic region.     

Decomposition of reactive oxygen species by copper(II) bis(1-pyrazolyl)methane complexes

Two bis(1-pyrazolyl)alkane ligands, bis(3,5-dimethyl-1-pyrazolyl)methane and bis(4-iodo-3,5-dimethyl-1-pyrazolyl)methane, and their copper(II) complexes, bis(3,5-dimethyl-1-pyrazolyl)methanedinitratocopper(II) [CuL₁(NO₃)₂] and bis(4-iodo-3,5-dimethyl-1-pyrazolyl)methanedinitratocopper(II) [CuL₂(NO₃)₂]·2H₂O, were prepared. Physiochemical properties of the copper(II) complexes were studied by spectroscopic (UV–vis, IR, EPR) techniques and cyclic voltammetry. Spectroscopic analysis revealed a 1:1 stoichiometry of ligand:copper(II) ion and a bindentate coordination mode for the nitrate ions in both of the complexes. According to experimental and theoretical ab initio data, the copper(II) ion is located in an octahedral hexacoordinated environment. Both complexes were able to catalyze the dismutation of superoxide anion () (pH 7.5) and decomposition of H₂O₂ (pH 7.5) and peroxynitrite (pH 10.9). In addition, both complexes exhibited superoxide dismutase (SOD) like activity toward extracellular and intracellular reactive oxygen species produced by activated human neutrophils in whole blood. Thus, these complexes represent useful SOD mimetics with a broad range of antioxidant activity toward a variety of reactive oxidants.     

The deacylation of acyl-cycloamyloses : The catalytic effects of benzimidazole derivatives on the rate

Cycloheptaamylose cinnamate, an intermediate in the hydrolysis of m-nitrophenyl cinnamate by cycloheptaamylose, was isolated in pure form. The deacylation of acyl-cycloamyloses (cinnamate and acetate) catalyzed by noncovalently complexed 6-nitrobenzimidazole (1) was studied. The reaction was enzyme-like. Saturation of acyl-cycloamylose by 1 was observed; the rate and dissociation constants were determined from Lineweaver-Burk plots. The catalyzed reaction rates at neutral pH were two to three times larger than those of the spontaneous reactions for cycloheptaamylose or cyclohexaamylose cinnamate, respectively. The catalytic effect of 1 on the deacylation rate of cyclohexaamylose cinnamate became smaller as the pH of the solution was raised. The deacylation of cyclohexaamylose acetate was followed by nmr spectroscopy, whereas the deacylation of cycloamylose cinnamates was followed by uv spectroscopy and extraction of trans-cinnamic acid with ether. Thermodynamic parameters for the rates of deacylation of cycloamylose cinnamates and dissociation constants of cycloamylose cinnamate-1 complexes were obtained and discussed.     

The effect of greening of sorghum leaves on the molecular weight of a complex containing 4-hydroxycinnamic Acid hydroxylase activity

During the greening of leaves of Sorghum bicolor var. Wheatland milo, the activity of 4-hydroxycinnamic (p-coumaric) acid hydroxylase in pH 6 buffered extracts was shifted from a relatively low to a high molecular weight fraction. Differences between these forms found in etiolated and green leaves were based on differential centrifugation, ammonium sulfate precipitation, and on elution patterns from Agarose A-15m. Both molecular weight forms were precipitated by protamine sulfate at pH 6, and approximately 40 to 80% of the activity of each form was associated with a 500 to 37,000g pellet when tissues were ground at pH 8 in media of either high or low osmotic concentration. Although no fraction with hydroxylase activity was ever found without any chlorogenic acid oxidase activity, the two activities frequently varied independently, and could be partially separated from each other, using the above techniques. Comparisons were made with the very small molecular weight form of 4-hydroxycinnamic acid hydroxylase characteristic of tissues of first internodes. The significance of these results in terms of possible multienzyme complexes capable of converting phenylalanine and tyrosine to cinnamic acid derivatives is discussed.     

The influence of inorganic anions on the formation and stability of Fe3+-transferrin-anion complexes

Harris (Biochemistry 24 (1985) 7412) reports that inorganic anions bind to human apotransferrin in such a way as to perturb the ultraviolet spectrum. The locus of binding is thought to involve the specific metal/anion-binding sites since no perturbation is observed with Fe3+-transferrin-CO3(2-). Paradoxically, we were unable to demonstrate the formation of Fe3+-transferrin-inorganic anion complexes despite the presence of high concentrations of SO4(2-), H2PO4-, Cl-, ClO4- or NO3-. Similar results were found for human lactoferrin. Electron paramagnetic resonance spectroscopy and visible spectrophotometry were used to monitor the results. An attempt to form the H2PO4- complex by displacement of glycine from Fe3+-transferrin-glycine resulted only in the disruption of the ternary complex. A series of inorganic anions varied in their ability to release iron from Fe3+-transferrin-CO3(2-) at pH 5.5, the approximate pH of endosomes where iron release takes place within cells. The order of effectiveness was H2P2O7(2-) much greater than H2PO4- greater than SO4(2-) greater than NO3- greater than Cl- greater than ClO4-. The rate of iron removal from Fe3+-transferrin-CO3(2-) at pH 5.5 by a 4-fold excess of pyrophosphate was greatly enhanced by physiological NaCl concentration. Iron removal was complete within 10 min, the approximate time for iron release from Fe3+-transferrin-CO3(2-) in developing erythroid cells. Thus, inorganic anions may have a significant effect on the release of iron under physiological conditions despite the fact that such inorganic anions cannot act as synergistic anions. The results are discussed in relation to a special role for the carboxylate group in allowing ternary complex formation.     

Evaluation of antioxidant and antimicrobial activities and characterization of bioactive components of two Brazilian propolis samples using a pKa-guided fractionation

The ethanolic extracts of two Brazilian propolis samples were submitted to a fractionation procedure based on the pKa values of their components. The fractions obtained were evaluated for their antimicrobial activity against Staphylococcus aureus as well as for their antioxidant properties (reduction of DPPH radical). Their phenolic and flavonoid contents were measured spectrophotometrically, in order to establish the correlations between these contents and the measured activities. Further, the most active fractions of both extracts were analyzed by HRGC-MS and about twenty compounds could be characterized. Among them were 3-prenyl-4-hydroxycinnamic acid (drupanin) and 3,5-diprenyl-4-hydroxycinnamic acid (artepillin C), which seem to be the major antioxidant components of the bioactive fractions.     

Cycloamylose complexation of adamantane derivatives

Spectrophotometric and pH potentiometric studies indicate that cyclohexaamylose (alpha-cyclodextrin) and cycloheptaamylose (beta-cyclodextrin) form aqueous complexes with all adamantane derivatives examined to date. Thermodynamic complex formation constants are reported for the substrates 1-adamantaneamine (amantadine), 1-adamantaneammonium ion, 1-adamantanemethylamine, 1-adamantane-methylammonium ion, 1-adamantanecarboxylic acid, 1-adamantane-carboxylate ion, 1-adamantaneacetic acid and 1-adamantaneacetate ion. The existence of these complexes implies that cycloamylose might serve as a therapeutic sequestering agent for adamantane derivatives.     

pH stability of HLA-DR4 complexes with antigenic peptides

Complexes between antigenic peptides and class II proteins of the major histocompatibility complex (MHC) trigger cellular immune responses. These complexes usually dissociate more rapidly at mildly acidic pH, where they are formed intracellularly, as compared to neutral pH, where they function at the cell surface. This paper describes the pH dependence of the dissociation kinetics of complexes between MHC proteins and antigenic peptides containing aspartic and glutamic acid residues. Some of these complexes show an unusual pH dependence, dissociating much more rapidly at pH 7 than at pH 5.3. This occurs when the carboxylate group of the aspartic or glutamic acid residue is located in a neutral pocket of the protein. In contrast, solvent-exposed carboxylate groups or carboxylate groups buried in pockets where they form salt bridges with the protein do not show this unusual pH dependence. The kinetic data having the unusual pH dependence conform closely to a model in which there is a rapid reversible equilibration between a less stable deprotonated complex and a more stable protonated complex. In this model, the pK(a) of the protonation reaction for the partially buried peptide carboxylate group ranges from 7.7 to 8.3, reflecting the strongly basic conditions required for deprotonation. One of the few peptide/MHC complexes demonstrated to play a role in autoimmunity in humans contains a buried peptide carboxylate and shows this unusual pH dependence. The relevance of this finding to understanding the chemical basis of autoimmunity is briefly discussed.     

Interaction of amide inhibitors with the active site of carbonic anhydrase: metal-induced deprotonation of the bound amide group is indicated by slow binding kinetics, by visible spectra of complexes with cobalt enzyme, and by pH effects on binding affinity

Most carbonic anhydrase (CA) inhibitors bind at the active site metal and either are anions or are capable of deprotonation to yield anions. Much less is known about the interaction of CA with inhibitors that have hitherto been considered to bind as neutral species. We report a study of the reversible amide inhibition of Co(II)-substituted CA by iodoacetamide and ethyl carbamate (urethane), as well as the ambivalent oxamate, the monoamide of oxalate. Visible cobalt spectral changes indicate coordination of all these inhibitors to the metal. The pH dependence of the affinity of carbonic anhydrase isozyme I (CA I) for ethyl carbamate and iodoacetamide is formally consistent with their binding either as anionic species to the acid form of the enzyme or as neutral species to the basic form of the enzyme. The former view is in better accord with the spectral data. Most strikingly, reversible binding of iodoacetamide and ethyl carbamate leads to uniquely slow kinetics of ligand association and dissociation that could be followed by simple mixing. The slow association kinetics suggest the involvement of energetically unfavorable deprotonation of the amide group preceding final coordination. The complex pH profile for inhibition of CA I by the ambivalent oxamate is consistent with coordination through the carboxylate group at low pH and through the deprotonated amide group at high pH. The visible spectrum of the complex of Co(II)CA I with oxamate shows a parallel dependence on pH, reflecting this dual coordination mode. Similarly, oxamate dissociation kinetics were biphasic and could be correlated with the pH-dependent spectral changes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peroxynitrite and NO donors form colored nitrite adducts with sinapinic acid: potential applications

Sinapinic acid (3,5-dimethoxy-4-hydroxycinnamic acid, SA) reacted with peroxynitrous acid at neutral pH with a second-order rate constant of 812 M(-1)s(-1), to yield a red product (lambda(max), 532 nm). The identical colored product could be formed with acidified decomposed peroxynitrous acid solutions or nitrite at slower rates (0.1M HCl, 8.32 M(-1)s(-1); 10% acetic acid, 0.0004 M(-1)s(-1)). The red compound is thought to be O-nitrososinapinic acid (3,5-dimethoxy-4-nitrosooxycinnamic acid) which can be formed by reaction with either peroxynitrous acid or nitrous acid. The extinction coefficient of O-nitrososinapinic acid (ONSA) was estimated to be 8419 M(-1)cm(-1) at 510 nm in 10% acetic acid and 90% acetonitrile. ONSA was also formed via NO(+) transfer from S-nitrosoglutathione (GSNO). ONSA in turn can S-nitrosate low molecular weight thiols and protein thiols. SA was also shown to act as a peroxynitrite sink as it effectively prevented the oxidation of dihydrorhodamine under physiological conditions. The fact that O-nitrososinapinic acid is stable and can be used to S-nitrosate thiol containing amino acids, peptides, and proteins makes it a potentially useful reagent in the study of S-nitrosothiol biochemistry and physiology. In addition, the relatively high extinction coefficient of O-nitrososinapinic acid means that it could be utilized as an analyte for the spectroscopic detection of peroxynitrite or NO(+)-donors in the submicromolar range.     

Ferric iron complexes of dopamine and 5,6-dihydroxyindole with nta, edda, and edta as ancillary ligands

Coordination of the neurotransmitter dopamine (DA) and the metal-binding component of neuromelanin 5,6-dihydroxyindole (DHI) with ferric iron has been studied in aqueous solution in the presence of ancillary ligands containing amine nitrogen and carboxylate oxygen donor sites. With nitrilotriacetic acid (nta) and ethylenediamine diacetic acid (edda) coligands, coordination of the catecholate ligands DA and DHI is observed to be complete at physiological pH. The resulting complexes of DA have the characteristic two-component electronic spectrum observed characteristically for L₄Fe(Cat) complexes. The spectrum obtained with DHI consists of a single broad absorption in the visible region. Both DA and DHI are able to coordinate with Fe³⁺ in the presence of edta, displacing carboxylate oxygen donors at pH values just above physiological pH. These results demonstrate the strong affinity of DA and DHI for Fe³⁺, pointing to in vivo complex formation in neuronal mixtures at physiological pH.     

Spectroscopic and kinetics studies of a high-salt-stabilized form of the purple acid phosphatase from bovine spleen.

Use of a revised purification procedure that maintains the enzyme in a high-salt environment has resulted in the isolation of a new form of the bovine spleen purple acid phosphatase. This enzyme cannot be distinguished from that previously described [Davis, J. C., Lin, S. S., & Averill, B. A. (1981) Biochemistry 20, 4062] by electrophoresis, isoelectric focusing, Western blot analysis, or N-terminal amino acid sequence and exhibits identical catalytic properties and EPR spectra in the reduced (pink) form. It does, however, possess a much more highly ordered structure as shown by CD spectra and exhibits markedly different reactivity upon oxidation and different visible spectra upon binding of inhibitory anions or changing pH. The properties of the new high-salt-stabilized form of the enzyme have permitted an extensive examination of the visible absorption spectra of complexes of the oxidized and reduced enzyme with inhibitory anions. It is found that these anions may be grouped into three classes on the basis of their effect on the visible absorption maximum and their sensitivity to pH: phosphate, arsenate, and AMP; tungstate and molybdate; and fluoride. This grouping is reinforced by a detailed examination of the steady-state kinetics of the enzyme in the presence of these inhibitors, which reveals that the first class exhibits mixed-type inhibition due to the presence of competitive and noncompetitive binding sites, while the second class exhibits simple non-competitive inhibition. Fluoride exhibits complex inhibition behavior characterized by curved Lineweaver-Burk plots; this behavior cannot be attributed to the presence of inhibitory aluminum fluoride complexes. Taken together, the spectral and kinetics data are consistent with a picture in which tetrahedral oxyanions bind in a noncompetitive fashion by bridging the two iron atoms in the dinuclear center, with the smaller anions also being able to bind in a competitive manner at a single iron atom.     

Synthesis, crystal structures, and anti-convulsant activities of ternary [Zn(II)(3,5-diisopropylsalicylate)(2)], [Zn(II)(salicylate)(2)] and [Zn(II)(aspirinate)(2)] complexes

Following observations that bis(3,5-diisopropylsalicylato)diaquazinc(II), [Zn(II)(3,5-DIPS)(2)(H(2)O)(2)], had anti-convulsant activity, bis(acetylsalicylate)diaquazinc(II), [Zn(II)(aspirinate)(2)(H(2)O)(2)], and the Zn(II) ternary 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neocuproine, NC) or dimethyl sulfoxide (DMSO) complexes of Zn(II)3,5-diisopropylsalicylate, salicylate, and acetylsalicylate were synthesized and spectroscopically characterized. Anti-convulsant and Rotorod toxicity activities of these complexes were determined to examine their anti-convulsant and undesirable central nervous stimulant or depressant activities of these Zn(II) non-steroidal anti-inflammatory agent complexes. Bis(3,5-diisopropylsalicylato)-1,10-phenanthorlinezinc(II), [Zn(II)(3,5-DIPS)(2)(phen)], (1) has one bidentate phen ligand and two mono-deprotonated 3,5-DIPS ligands. One of the carboxylates bonds in an asymmetric chelating mode. The Zn(II) atom exhibits a distorted bicapped rectangular pyramidal environment N(2)O(2)OO (4+1+1 *). In the neocuproine complex, bis(3,5-diisopropylsalicylato)-2,9-dimethyl-1,10-phenanthorlinezinc(II), [Zn(II)(3,5-DIPS)(2)(NC)] (2), the Zn(II) atom has a much more distorted bicapped rectangular pyramidal environment, N(2)O(2)O(2) (4+2 *), compared to 1. The two carboxylate ligands exhibit the same asymmetric coordinating mode with longer metalloelement-oxygen bond distances compared to 1. The space group of [Zn(II)(aspirinate)(2)(H(2)O)(2)] (3), which has been reported as Cc is corrected to C2/c. The zinc atom exhibits a (4+2 *) bicapped square pyramidal environment. While the two ternary phenanthroline-containing complexes, 1 and 2, evidenced weak protection against maximal electroshock (MES)- and subcutaneous Metrazol (scMET) induced seizures, [Zn(II)(3,5-DIPS)(2)(DMSO)(2)], [Zn(II)(aspirinate)(2)(H(2)O)(2)], and bis(salicylato)-1,10-phenanthorlinezinc(II), [Zn(II)(salicylate)(2)(phen)], were found to be particularly useful in protecting against MES and scMET seizures and [Zn(II)(aspirinate)(2)(H(2)O)(2)] and [Zn(II)(salicylate)(2)(phen)] were found to have activity in protecting against Psychomotor seizures, without causing Rotorod toxicity. Activities of these and other Zn(II) complexes of non-steroidal anti-inflammatory agents are consistent with the well-known anti-inflammatory responses of Zn(II)-dependent enzymes. There was also some evidence of Rotorod toxicity consistent with a mechanism of action involving sedative-hypnotic activity of recognized anti-epilepticdrugs.     

咖啡酸苯乙酯衍生物抑制红细胞溶血和HL-60细胞增殖活性的构效关系研究

蜂胶中的主要成分咖啡酸苯乙酯作为重要的抗氧化剂和癌预防试剂分子,引起了人们相当的兴趣。为了研究其构效关系,作者通过酰基化反应合成了6个咖啡酸苯乙酯衍生物,即:咖啡酸苯乙酯(caffeic acid phenethyl ester,CAPE)、芥子酸苯乙酯(sinapic acid phenethyl ester,SAPE)、阿魏酸苯乙酯(ferulic acid phenethyl ester,FAPE)、4-羟基肉桂酸苯乙酯(4-hydroxycinnamicacid phenethyl ester,4-HCAPE)、3,5-二羟基肉桂酸苯乙酯(3,5-dihydroxycinnamic acidphenethyl ester,3,5-DHCAPE)和3-羟基肉桂酸苯乙酯(3-hydroxycinnamic acid phenethyl este,3-HCAPE)。以水溶性偶氮引发剂2,2'-偶氮二(2-脒基丙烷)二盐酸盐诱导的红细胞溶血为模型,研究了它们的抗氧化活性。根据实验测得的有效抑制溶血时间,其活性顺序为:CAPE≈4-HCAPE>SAPE>FAPE>3,5-DHCAPE>3-HCAPE。其活性显著...     

Pigment Production of Cryptococcus neoformans Grown with Extracts of Guizotia abyssinica

Brown pigment(s) formed in Cryptococcus neoformans when grown on media containing extracts of the seeds of Guizotia abyssinica cannot be extracted by common organic solvents or by 6 n HCl or 2 n NaOH. A similar pigmentation was observed in C. neoformans when grown on a medium containing caffeic acid isolated from the hydrolyzed methanol extract of G. abyssinica seeds. Its methyl ester and the diacetate thereof, as well as the following structurally related compounds, 3-hydroxytyramine, 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenylethanolamine, and 4-hydroxy-3,5-dimethoxycinnamic acid, brought about similar pigmentation. However, 2,4-, 2,5-, 2,6-, and 3,5-dihydroxybenzoic acids, tyrosine, phenylalanine, cinnamic acid, 4-hydroxycinnamic acid, and 4-hydroxy-3-methoxycinnamic acid did not cause coloration in C. neoformans.     

Study of copper(II) and nickel(II) ternary complexes involving tertiary amines and phenyl or hydroxylphenyl substituted amino acids

Formation constants of ternary complexes MAL, where M = Cu(II) or Ni(II). A = 2.2′bipyridyl. 1, 10-phenanthroline, and L = 3.4-dihydroxyphenylalanine (dopa), tyrosine, or phenylalanine have been determined by using the computer program SCOGS. It is observed that dopa coordinates with Cu(II)-A and Ni(II)-A through the aminocarboxylate and only over the pH range 3–8, though the ligand coordinates with free Cu(II) ion from the amino carboxylate end in the lower pH range (pH 2–4) and from the catechol end at the higher pH range (pH > 5). The visible spectrum of Cu-A-dopa is similar to that of Cu-A-phenylalanine or Cu-A-tyrosine over the entire pH range, confirming amino carboxylate coordination. Δ log K (K_MAL - log_KML) is found to be positive in all the six Cu(II) complexes. whereas it is negative in Ni(II) complexes. Release in the ternary complexes of the repulsion between the Cu(II) dπ electron and electrons delocalized over the phenyl ring has been proposed as a probable reason for the positive Δ log K.