Syntheses of 5a'-homo-vinblastine and congeners designed to establish structural determinants for isolation of atropisomers

The syntheses of 5a'-homo-vinblastine (3a) and its C-20' methyl congener 62a were achieved. In contrast to vinblastine, these compounds did not allow isolation of atropisomers because of their lower conformational inversion barrier. However, annelation of a six-membered ring to the conformationally mobile D'-piperidine ring provided an isolated atropisomer 81a, which could be converted to its lower energy conformation 65a on heating. The 5a'-homo-vinblastine congeners 3a, 62a, and 65a showed vinblastine-like inhibition of tubulin polymerization and cytotoxicity to L1210 leukemia cells, albeit at lower potency for the latter activity, than that found with the corresponding compounds in the vinblastine series.     

The hydrogen salicylate ion as ligand. Complex formation equilibria with dioxouranium (VI), neodymium (III) and lead (II)

The complexation equilibria of the hydrogen salicylate ion, HL(-), have been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in 1 M NaClO4 for uranyl and Nd(III) ions and in 3 M NaClO4 for Pb(II) ion. The ligand concentration (CL) was varied between 10(-3) and 0.05 M. In the system with U(VI) the concentrations ranged between: 10(-3) < or = [U(VI)] < or = 0.01 M, 0.5 < or = CL /[U(VI)] < or = 10 and 10(-2) < or = [H+] < or = 10(-5) M; for neodymium system: 2 x 10(-3) < or = [Nd(III)] < or = 0.01, 1 < or = CL /[Nd(III)] < or = 10 and 10(-2) < or = [H+] < or = 10(-7) M; for lead system: 10(-3) < or = [Pb(II) < or = 3 x 10(-3), 1 < or = CL /Pb(II)] < or = 2 and 10(-5) < or = [H+] < or = 10(-7.3) M. The experimental data have been explained with the formation of UO2HL+, UO2L, UO2(OH)L(-), (UO2)2(OH)L2(-) UO2(HL)L(-), NdHL(2+), NdL(+), Nd(OH)L, PbHL(+), PbL and PbL2(2-). Equilibrium constants are given for the investigated ionic media and at infinite dilution.     

Suppression of stimulating cell activity by microtubule-disrupting alkaloids.

Microtubule-disrupting alkaloids and protein fixatives were used to investigate the nature of an active process that must occur within stimulator cells in order for them to initiate a unidirectional mixed lymphocyte response (MLR). Brief treatment of the stimulator cells (SC) with glutaraldehyde (0.15%), formalin (0.6%), or lanthanum chloride (10-3 M) abolished their capacity to activate responder cells (RC). Pretreatment of SC with microtubule-disrupting alkaloids, colchicine (c) (10-4 to 10-6 M) or colchicine + vincristine (c+v) (10-4 to 10-6 M) also abrogated their stimulating capacity. This capacity was not restored by the addition of supernates from untreated cultures, thereby excluding the possibility that the alkaloids acted by decreasing the release of soluble stimulatory factors from SC. The introduction of alkaloid-inactivated, mitomycin-treated RC as drug carriers did not affect the mitogenic response of untreated RC to concanavalin A. This excluded a significant leakage of alkaloids from the treated SC and uptake by RC during culture. Lumicolchicine produced no decrease in the stimulating capacity of SC. This suggested that the suppression induced by low concentrations of colchicine resulted from its specific disruption of microtubules. None of the above treatments quantitatively reduced the antigenicity of SC, as evaluated by humoral and cell-mediated lysis of the treated cells. Also, these treatments produced no significant changes in the specific binding of concanavalin A by SC. These results indicate there is a functional interaction of microtubular structures with cell surface antigens that appears to regulate either the capacity of SC to associate with RC, or the ability of SC to form and stabilize stimulatory antigenic configurations on the cell surface.     

Apoptosis and autophagy after mitochondrial or endoplasmic reticulum photodamage

Photodynamic therapy (PDT) can cause lethal photodamage by both direct and indirect mechanisms. Direct modes of cell death relate to nonspecific necrosis and the initiation of signaling pathways that elicit apoptosis, autophagy or both. In this report, effects of low-dose and high-dose PDT are explored, comparing sensitizers that localize in the endoplasmic reticulum (the porphycene termed CPO) or mitochondria (mesochlorin). To explore the role of autophagy, two cell lines were examined--the murine L1210 leukemia and an Atg7 knockdown derivative of L1210. The Atg7 gene is central to the process of autophagy. High-dose PDT with either sensitizer resulted in a substantial loss of the Bcl-2 protein. As Bcl-2 regulates both apoptosis and autophagy, loss of this protein can lead to initiation of either or both processes. Low-dose PDT with either sensitizer resulted in the initiation of apoptosis in the L1210/Atg7- cell line and a 20% loss of viability. In contrast, the same PDT dose led to the rapid appearance of autophagic cells in the L1210 line, less apoptosis and only a 5% loss of viability. These results are consistent with autophagy serving as a pro-survival response via the recycling of damaged organelles. At a higher PDT dose more apoptosis was again seen in the L1210/Atg7- line, but both cell lines exhibited comparable cytotoxicity in colony formation assays. We conclude that autophagy offers protection from the phototoxic effects of low-dose PDT, but can serve as an alternate death mode when the PDT dose is increased.     

Photochemical and phototoxic properties of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate, a new quinoline derivative

The present study demonstrates photoinduced generation of superoxide radical anion and singlet oxygen upon UVA irradiation of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate (DNQC), and its cytotoxic/phototoxic effects on murine leukemia L1210 cells. The formation of reactive oxygen species (ROS) was investigated by EPR spectroscopy using in situ spin trapping technique and 4-hydroxy-2,2,6,6-piperidine (TMP) for singlet oxygen ((1)O(2)) detection. The EPR spectra monitored upon photoexcitation of aerated solutions of DNQC in dimethylsulfoxide evidenced the efficient activation of molecular oxygen via Types I and II mechanisms. The cytotoxic/phototoxic effects of DNQC, analysis of cell cycle, induction of apoptosis/necrosis, DNA damage and molecular mechanism of apoptotic death of L1210 cells in dark and in the presence of UVA irradiation were compared. DNQC induced a different cytotoxic/phototoxic effect, which was concentration- and time-dependent. The four highest tested concentrations of non-photoactivated and photoactivated DNQC induced immediate cytotoxic/phototoxic effect after 24h cultivation of L1210 cells. This effect decreased with the time of treatment. The irradiation increased the sensitivity of leukemia cell line on DNQC, but the cell sensitivity decreased with time of processing. Quinolone derivative DNQC significantly induced direct DNA strand breaks in L1210 cells, which were increased with the irradiation of cells. The DNA damage generated by DNQC alone/with combination of UVA irradiation induced cell arrest in G(0)/G(1) and G(2)/M phases, decrease in the number of L1210 cells in Sphase and apoptotic cell death of certain part of cell population after 24 h of influence. DNQC alone/with combination of UVA irradiation induced apoptosis in L1210 cells through ROS-dependent mitochondrial pathway.     

Synthesis and cytotoxic activity of dimeric analogs of acronycine in the benzo[b]pyrano[3,2-h]acridin-7-one series

Coupling of 6-hydroxy-3,3-14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one (6) with alpha,omega-diiodoalkanes of varying length under alkaline conditions gave dimers 7-10. Halogenated ethers 11-14, cyclization products 15-17, and compounds 18-22 were also isolated in small yield from the reaction mixtures. Compounds 7-10 were more potent than acronycine and benzo[b]acronycine in inhibiting L1210 cell proliferation. The length of the alkyl ether linkage between the two benzopyranoacridone units had a dramatic influence on the cytotoxic activity. Compound 9 (n=5) was the most active, with an IC(50) value against L1210 cells within the same range of magnitude as diacetate 5, currently under clinical development.     

PROTON, Mg2+ AND PROTEIN AS COMPETING LIGANDS FOR THE FLUORESCENT PROBE, MAG-INDO-1: A FIRST STEP TO THE QUANTIFICATION OF INTRACELLULAR Mg2+ CONCENTRATION

Abstract Increasing evidence of the role of magnesium in various cellular mechanisms has led to the need to develop an accurate method for the evaluation of magnesium concentration in cells. 1H-indole-6-carboxylic acid, 2–(4- bis- [carboxymethyl]amino-3–[carboxy]ethoxy) (mag-indo-1) is used as a fluorescent indicator for ionized magnesium concentration. A physicochemical study of this probe has pointed out (1) that at concentrations higher than 10 μ M , the presence of dimers can alter the different equilibria and (2) at concentrations, avoiding the dimer (≤ 10 μ M ), three fluorescent forms are in equilibrium with the deprotonated form of mag-indo-1 (L), which are the protonated form LH, the magnesium-bound form LM and the protein-bound form LP. A model is proposed that takes into account the equilibria between the four species. In a solution containing magnesium and protein, a complex fluorescence spectrum can be resolved by a combination of the three fluorescence spectra (L, LM, LP). However, under these conditions, the LH fluorescence spectrum is not taken into account for the spectral resolution. Finally, from the contribution of characteristic fluorescence spectra in the experimental fluorescence spectrum, the magnesium concentration can be estimated with accuracy. Such a method should be further applied to magnesium determination in different cell lines.     

Quinazoline Antifolate Thymidylate Synthase Inhibitors: Replacement of Glutamic Acid by Aminophosphonic Acids

The synthesis of six analogues of the potent thymidylate synthase (TS) inhibitor N -[4-[ N -[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinoyl)-methyl]- N -prop-2-ynylamino]benzoyl]- L -glutamic acid 2 is described in which the glutamic acid residue has been replaced by DL -aminophosphonic acids. New antifolates were tested as inhibitors of TS isolated from mouse L1210 leukemic cells as well as inhibitors of growth mouse leukemic L5178Y cells. In general these modifications result in compounds that are considerably less potent than 2 as TS inhibitors with K i 's 0.17-1.10 w M. Very poor solubility in water limited their proper assay of growth cells inhibition.     

Influence of Cu(II) on the interaction between sulfite and horseradish peroxidase in vitro

This paper discussed the quantitative influence of Cu(II) on the interaction between horseradish peroxidase (HRP) and sulfite (SO3(2-)), which is a derivate of sulfite dioxide in human bodies, by using fluorescence spectrum and ultraviolet (UV) absorption spectrometry in vitro. The results show that under the conditions of physiological pH and room-temperature, Cu(II) can bind strongly with both the protein part and the ferroporphyrin part in HRP at a low concentration (10(-4) mol L(-1)), and the combination constants are 2.047 x 10(3) and 7.66 x 10(2) L mol(-1), respectively. Under the same conditions, SO3(2-) at low concentrations (<0.15 mol L(-1)) has little quenching for the fluorescence of HRP at 330 nm, and the combination constant is 0.108 L mol(-1). While the fluorescence intensity at 440 nm enhance gradually with the increased concentration of SO3(2-) (<0.1 mol L(-1)), and the combination constant is 8.219 L mol(-1). These indicate that SO3(2-) at low concentration has little reaction with the enzyme protein part in HRP but obvious reaction with the ferroporphyrin part in HRP. After SO3(2-) at low concentrations is added into the HRP-Cu(II) binary system, the reaction constants between SO3(2-) and the enzyme protein part in HRP increase rapidly. Compared with the absence of Cu(II), the combination constant of SO3(2-) with the enzyme protein part in HRP increases nearly 70 times with a certain Cu(II) concentration (5.0 x 10(-4) mol L(-1)) in the system. However, the presence of Cu(II) in the system has little effect on the reaction constants between SO3(2-) and the ferroporphyrin part in HRP.     

Reduction and oxidation of hydroperoxo rhodium(III) complexes by halides and hypobromous acid

Oxygen atom transfer from trans-L(H(2)O)RhOOH(2+) [L = [14]aneN(4) (L(1)), meso-Me(6)[14]aneN(4) (L(2)), and (NH(3))(4)] to iodide takes place according to the rate law -d[L(H(2)O)RhOOH(2+)]/dt = k(I)[L(H(2)O)RhOOH(2+)][I(-)][H(+)]. At 0.10 M ionic strength and 25 degrees C, the rate constant k(I)/M(-)(2) s(-)(1) has values of 8.8 x 10(3) [L = (NH(3))(4)], 536 (L(1)), and 530 (L(2)). The final products are LRh(H(2)O)(2)(3+) and I(2)/I(3)(-). The (NH(3))(4)(H(2)O)RhOOH(2+)/Br(-) reaction also exhibits mixed third-order kinetics with k(Br) approximately 1.8 M(-)(2) s(-)(1) at high concentrations of acid (close to 1 M) and bromide (close to 0.1 M) and an ionic strength of 1.0 M. Under these conditions, Br(2)/Br(3)(-) is produced in stoichiometric amounts. As the concentrations of acid and bromide decrease, the reaction begins to generate O(2) at the expense of Br(2), until the limit at which [H(+)] 2(NH(3))(4)(H(2)O)RhOH(2+) + O(2); i.e., the reaction has turned into the bromide-catalyzed disproportionation of coordinated hydroperoxide. In the proposed mechanism, the hydrolysis of the initially formed Br(2) produces HOBr, the active oxidant for the second equivalent of (NH(3))(4)(H(2)O)RhOOH(2+). The rate constant k(HOBr) for the HOBr/(NH(3))(4)(H(2)O)RhOOH(2+) reaction is 2.9 x 10(8) M(-)(1) s(-)(1).     

Equilibria occurring between beryllium (II) and salicylate ions

The complexation equilibria between Be2+ and the hydrogen salicylate (HL-) ions have been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in 3 M NaClO4. The concentrations of metal (CM) and ligand (CL) were varied between 10(-3) and 0.03 M and 2 x 10(-3) and 0.03 M, respectively, while 1 < or = CL/CM < or = 3. The hydrogen ion concentration ranged from 10(-3) to 10(-5.3) M when basic salts start to precipitate. The equilibria can be written in the general form as: pBe2+ + rHL- <==> Be(p)H(-q) (HL)r(2p-r-q) + qH+, log beta(pqr). The experimental data have been explained with the formation of BeHL+ (log beta101 = 1.46 +/- 0.05), BeL (log beta111 = -0.897 +/- 0.018), BeL2(2-) (log beta122 = -3.746 +/- 0.021), Be2(OH)L2- (log beta232 = -5.23 +/- 0.09), Be3(OH)3L3(3-) (log beta363 = -14.39 +/- 0.12). The uncertainties represent 3sigma. The predominant complex in the whole concentration range studied is the uncharged mononuclear species BeL.     

Environmental Effects on Cellular Photosensitization: Correlation of Phototoxicity Mechanism with Transient Absorption Spectroscopy Measurements

Abstract— Little is directly known about the influence of the local environment experienced by a photosensitizer in a biological system on its photophysics and photochemistry. In this paper, we have addressed this issue by correlating mechanistic studies using laser flash photolysis with cellular phototoxicity data, obtained under the same experimental conditions. In particular, we have focused on the interaction between local concentrations of photosensitizer (deuteroporphyrin) and oxygen in determining the mechanism of phototoxicity in L1210 cells. In cells, as well as in models such as liposomes and red blood cell ghosts, hypochromicity and a reduction in fluorescence and intersystem crossing yields are observed on increasing the photosensitizer concentration between 0.5 and 20 μM, which illustrates the onset of a self-association. In aerated cellular preparations, the phototoxicity is predominantly type II (singlet oxygen) for all concentrations studied but an oxygen-independent mechanism occurs at the higher concentrations in deaerated samples. These observations are readily explained by consideration of triplet state kinetics as a function of oxygen and photosensitizer concentrations in cells. The rate constant for quenching of the photosensitizer triplet state by oxygen in cells was measured as 6.6 × 10⁸ M^?1 s^?1 and by photosensitizer ground state as -10⁶M^?1s^?1 (in terms of local concentration). The latter reaction gave rise to a long-lived species that is presumably responsible for the oxygen-independent phototoxicity observed at the higher photosensitizer concentrations used. This self-quenching of the triplet state is postulated to arise from electron transfer resulting in radical ion formation. Under conditions where no self-quenching contributes, the phototoxicity measured as a function of oxygen concentration correlates well with a model based on the determined kinetic parameters, thus, unambiguously proving the intermediacy of singlet oxygen. These effects should be borne in mind when interpreting phototoxicity mechanisms from in vitro cell studies. The excellent correlation achieved between laser flash photolysis data and measured phototoxicity gives credence to the direct use of photophysical techniques to elucidate photochemical mechanisms in biological media.     

基于凝胶过滤色谱的β2微球蛋白标准品单体定量检测方法

β2微球蛋白（B2M）标准品是研究透析相关淀粉样变和评估血液透析器透过效率的重要试剂。B2M易于聚集的特性导致其作为标准品的单体浓度降低,使得检测结果准确性下降。为了准确评价B2M标准品的质量,该研究建立了基于凝胶过滤色谱的B2M样品中非聚集单体的定量检测方法。使用TSKgel SuperSW2000（30 cm×4.6 mm,4 μm）凝胶筛分色谱柱,流动相为0.01 mol/L磷酸盐缓冲液（PBS,pH 7.2~7.4）,流速为0.5 mL/min,柱温为25℃。使用紫外检测器,检测波长为280 nm,外标法定量。在0.05~0.50 g/L的B2M单体质量浓度范围内线性良好,相关系数为0.9948。定量限（信噪比为10）为0.08 g/L,添加水平为0.10~0.30 g/L时,回收率为85.0%~96.7%,相对标准偏差为1.7%~3.3%。使用该方法对实验室自制重组人B2M标准品进行了质量检测,结果显示,该方法处理简单,准确度高,稳定性好,且不受溶液中B2M二聚体的干扰,适用于B2M标准品的质量分析。     

Further evaluation of 5-alkyl-5-deaza antifolates. 5-propyl- and 5-butyl-5-deaza analogues of aminopterin and methotrexate

5-Propyl-5-deaza and 5-butyl-5-deaza analogues of classical antifolates were synthesized by extensions of a previously reported general route which proceeds through 2,4-diamino-5-alkylpyrido[2,3-d]pyrimidine-6-carbonitrile intermediates followed by reductive condensation with diethyl N-4-(aminobenzoyl)-L-glutarnate to give diethyl esters of 5-alkyl-5-deazaaminopterin types. N¹⁰-Methyl derivatives, i.e., derivatives of 5-alkyl-5-deazamethotrexate, were also prepared by reductive methylation of the N¹⁰-H compounds. 5-Ethyl-5-deazamethotrexate was prepared using an alternative route through 6-(bromomethyl)-2,4-diamino-5-ethylpyrido[2,3-d]pyrimidine. These antifolates were evaluated for inhibition of dihydrofolate reductase (DHFR) from L1210 cells, their effect on L1210 and S180 tumor cell growth in culture, and carrier-mediated transport through L1210 cell membranes. Inhibitory effect on DHFR was lowered relative to methotrexate in 5-propyl-5-deazaaminopterin and 5-propyl-5-deazamethotrexate by 2- to 3-fold (K_i = 9.3 and 11.7 pM, respectively, vs. 4.3 pM for methotrexate) and by 17- to 18-fold in 5-butyl-5-deaza-aminopterin and 5-butyl-5-deazamethotrexate (K_i = 74 and 78 pM, respectively). Molecular modeling using graphics derived from human DHFR show the propyl and butyl compounds interacting with the enzyme in conformations that account for these slight decreases in binding.     

Altered flavin patterns in photobehavioral mutants of Phycomyces blakesleeanus.

Flavins were extracted from sporangiophores of the lower fungus Phycomyces blakesleeanus and identified by HPLC with fluorescence detection. In the wild-type strain NRRL1555 they were found to be present at the following concentrations: riboflavin (5.5 x 10(-6) M), flavin mononucleotide (FMN) (4.0 x 10(-6) M) and flavin adenine dinucleotide (1.4 x 10(-6) M). The HPLC elution profiles of the wild type were compared to a set of behavioral mutants (genotype mad) with specific defects in their light-transduction pathway. The photoreceptor mutants C109 (madB), C111 (madB) and L1 (madC) had normal amounts of flavins. The most prominent changes were found in single mutants with a defective madA gene which contained about 25% of riboflavin and about 10% of FMN and FAD normally found in the wild type. A hypertropic mutant with a defective madH gene contained instead 80% of riboflavin and 120% of FMN and FAD. The double mutant L52 (madA madC) and the triple mutant L72 (madA madB madC) had normal amounts of FAD and FMN. This indicates that the madC mutation, which itself causes loss of light sensitivity and which affects the near-UV/blue-light receptor (Galland and Lipson, 1985, Photochem. Photobiol. 41, 331-335) functions as a restorer of the flavin content in a genetic madA background. The double mutant L51 (madA madB) had about 40% of FMN and FAD, suggesting that the madB mutation functions as a partial restorer of flavin content. The photogravitropic thresholds (450 nm) reported for the wild type and the madA and madH mutants were positively correlated to the endogeneous concentrations of FMN and FAD.(ABSTRACT TRUNCATED AT 250 WORDS)     

The potent anti-HIV protein cyanovirin-N contains two novel carbohydrate binding sites that selectively bind to Man(8) D1D3 and Man(9) with nanomolar affinity: implications for binding to the HIV envelope protein gp120.

Cyanovirin-N (CVN) is a monomeric 11 kDa cyanobacterial protein that potently inactivates diverse strains of human immunodeficiency virus (HIV) at the level of cell fusion by virtue of high affinity interactions with the surface envelope glycoprotein gp120. Several lines of evidence have suggested that CVN-gp120 interactions are in part mediated by N-linked complex carbohydrates present on gp120, but experimental evidence has been lacking. To this end we screened a comprehensive panel of carbohydrates which represent structurally the N-linked carbohydrates found on gp120 for their ability to inhibit the fusion-blocking activity of CVN in a quantitative HIV-1 envelope-mediated cell fusion assay. Our results show that CVN specifically recognizes with nanomolar affinity Man(9)GlcNAc(2) and the D1D3 isomer of Man(8)GlcNAc(2). Nonlinear least squares best fitting of titration data generated using the cell fusion assay show that CVN binds to gp120 with an equilibrium association constant (K(a)) of 2.4 (+/- 0.1) x 10(7) M(-1) and an apparent stoichiometry of 2 equiv of CVN per gp120, Man(8)GlcNAc(2) D1D3 acts as a divalent ligand (2 CVN:1 Man(8)) with a K(a) of 5.4 (+/- 0.5) x 10(7) M(-1), and Man(9)GlcNAc(2) functions as a trivalent ligand (3 CVN:1 Man(9)) with a K(a) of 1.3 (+/- 0.3) x 10(8) M(-1). Isothermal titration calorimetry experiments of CVN binding to Man(9)GlcNAc(2) at micromolar concentrations confirmed the nanomolar affinity (K(a) = 1.5 (+/- 0.9) x 10(8) M(-1)), and the fitted data indicated a stoichiometry equal to approximately one (1 Man(9):1 CVN). The 1:1 stoichiometry at micromolar concentrations suggested that CVN has not only a high affinity binding site-relevant to the studies at nM concentrations-but a lower affinity site as well that facilitates cross-linking of CVN-oligomannose at micromolar concentrations or higher. The specificity of CVN for Man(8) D1D3 and Man(9) over the D1D2 isomer of Man(8) indicated that the minimum structure required for high affinity binding comprises Manalpha1 --> 2Manalpha. By following the (1)H-(15)N correlation spectrum of (15)N-labeled CVN upon titration with this disaccharide, we unambiguously demonstrate that CVN recognizes and binds to the disaccharide Manalpha1 --> 2Manalpha via two distinct binding sites of differing affinities located on opposite ends of the protein. The high affinity site has a K(a) of 7.2 (+/- 4) x 10(6) M(-1) and the low affinity site a K(a) of 6.8 (+/- 4) x 10(5) M(-1) as determined by isothermal titration calorimetry. Mapped surfaces of the carbohydrate binding sites are presented, and implications for binding to gp120 are discussed.     

Spectrofluorimetric determination of thiols by use of N[P-(2-benzoxazolyl)phenyl]maleimide

The weak fluorescence of N-[P-(2-benzoxazolyl)phenyl]maleimide (BOPM) can be greatly enhanced by thiol-containing compounds. A sensitive and simple spectrofluorimetric method based on the use of BOPM has been developed for the determination of thiols such as cysteine (Cys) and reduced glutathione (GSH). Calibration plots were linear in the concentration range from 0 to 1.6 x 10(-7) mol L(-1) for Cys and 0 to 1.7 x 10(-7) mol L(-1) for GSH. The detection limits (3a) were 2.36 x 10(-10) mol L(-1) for Cys and 1.49 x 10(-10) mol L(-1) for GSH. Many other amino acids (present at 100-fold greater concentrations) did not interfere with the determination. The proposed method has been used for the determination of Cys in protein hydrolysate and cystine electrolyte or GSH in serum, with recoveries of 95.4-103.7%.     

Kinetics of Dissociation of Iron(III) Complexes of Tiron in Aqueous Acid

The kinetics of dissociation of the mono, bis, and tris complexes of Tiron (1,2-dihydroxy-3,5-benzenedisulfonate) have been studied in acidic aqueous solutions in 1.0 M HClO(4)/NaClO(4), as a function of [H(+)] and temperature. In general, the kinetics can be explained by two reactions, (H(2)O)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L(n)H) + H(+) (k(n), k(-n)) and (HO)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L(n)H) (k(n)', k(-n)'), a rapid equilibrium, (H(2)O)Fe(L(n)H) right arrow over left arrow (H(2)O)Fe(L)(n) + H(+) (K(cn)), and the formation constant (H(2)O)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L)(n) + 2H(+). For n = 1, the reaction was observed at 670 nm, and at [H(+)] of 0.05-0.5 M at temperatures of 2.0, 14.0, 25.0, and 36.7 degrees C. For n = 2, the analogous conditions are 562 nm, at [H(+)] of 1.5 x 10(-3) to 1.4 x 10(-2) M at temperatures of 2.0, 9.0, and 14.0 degrees C. For n = 3, the conditions are 482 nm, at pH 4.5-5.7 in 0.02 M acetate buffer at temperatures of 1.8, 8.0, and 14.5 degrees C. The rate or equilibrium constants (25 degrees C) with DeltaH or DeltaH degrees (kcal mol(-1)) and DeltaS or DeltaS degrees (cal mol(-1) K(-1)) in brackets are as follows: for n = 1, k(1) = 2.3 M(-1) s(-1) (8.9, -27.1), k(-1) = 1.18 M(-1) s(-1) (4.04, -44.8), K(c1) = 0.96 M (-9.99, -33.6), K(f1) = 2.01 M (-5.14, -15.85); for n = 2, k(-2)/K(c2) = 1.9 x 10(7) (19.9, 41.5) and k(-2)'/K(c2) = 1.85 x 10(3) (1.4, -38.8) and a lower limit of K(c2) > 0.015 M; for n = 3, k(3) = 7.7 x 10(3) (15.8, 12.3), k(-3) = 1.7 x 10(7) (16.2, 28.9), K(c3) = 7.4 x 10(-5) M (4.1, -5.1), and K(f3) = 3.35 x 10(-8) (3.7, -21.7). From the variations in rate constants and activation parameters, it is suggested that the Fe(L)(2) and Fe(L)(3) complexes undergo substitution by dissociative activation, promoted by the catecholate ligands.     

Potential DNA bis-intercalating agents: Synthesis and antitumor activity of novel,conformationally restricted bis(9-aminoacridines)

A series of bis(9-aminoacridines) bridged by conformationally restricted tethers was synthesized and evaluated against L1210 in vitro. Several of these compounds were found to be highly active in this test system, with ID₅₀ values below 10^?7 M. CPK molecular models suggest that this antitumor activity can be correlated to the ability of these bis(9-aminoacridines) to form bis-intercalative complexes with DNA.     

Circular Dichroism Measurements on C-Terminal Fragment of Heat Shock Protein from Rat

The secondary structure of the C-terminal fragment (10 kDa) of rat hsc70 (a. a. #546–646) was analyzed according to circular dichroism spectra. In the pH range 5–9 and at concentrations of Na+ up to 0.18 M, the protein is estimated to contain 32-34% a helix, 18–16% of β sheet, approximately 25% for both turns and disordered structures. This protein is most stable at pH between 6 and 7 in solution with 0.055 M Na⁺ concentration. However, all T_m are relatively large (57–73 °C) and alterations from one condition to another are small. Thus, the C-fragment (10 kDa) of hsc70 is a stably folded protein under physiological conditions.