Synthesis and Biological Properties of Polyphenol-Containing Linear and Dendrimeric Cationic Peptides.

Natural polyphenols are promising compounds for the pharmacological control of oxidative stress in various diseases. However, low bioavailability and rapid metabolism of polyphenols in a form of glycosides or aglycones have stimulated the search for the vehicles that would provide their efficient delivery to the systemic circulation. Conjugation of polyphenols with cationic amphiphilic peptides yields compounds with a strong antioxidant activity and ability to pass through biological barriers. Due to a broad range of biological activities characteristic of polyphenols and peptides, their conjugates can be used in the antioxidant therapy, including the treatment of viral, oncological, and neurodegenerative diseases. In this work, we synthesized linear and dendrimeric cationic amphiphilic peptides that were then conjugated with gallic acid (GA). GA is a non-toxic natural phenolic acid and an important functional element of many flavonoids with a high antioxidant activity. The obtained GA-peptide conjugates showed the antioxidant (antiradical) activity that exceeded 2-3 times the antioxidant activity of ascorbic acid. GA attachment had no effect on the toxicity and hemolytic activity of the peptides. GA-modified peptides stimulated the transmembrane transfer of the pGL3 plasmid encoding luciferase reporter gene, although GA attachment at the N-terminus of peptides reduced their transfection activity. Several synthesized conjugates demonstrated the antibacterial activity in the model of Escherichia coli Dh5α growth inhibition.

Linear and dendrimeric antiviral peptides: design, chemical synthesis and activity against human respiratory syncytial virus.

Respiratory syncytial virus (RSV) is one of the most common viral pathogens. It is especially dangerous for newborns and young children. In some cases it could lead to severe bronchiolitis, pneumonia with hospitalization or even a lethal outcome. Despite decades of investigation of RSV biology, effective and safe therapeutics are still under development. Certain natural peptides have been found to exhibit antiviral activity against respiratory viruses, but their implementation is limited by low stability in biological media. One of the current approaches to enhance the peptide therapeutic opportunities is chemical synthesis of peptide dendrimers with hyperbranched structures. Taking into account the recent data of bioactive cationic and helical regions of natural peptides and the structure features of nucleolin identified as an RSV cellular receptor, the main goal of this study was to design relatively short linear and dendrimeric cationic peptides and to test their antiviral activity against RSV. As a result 3 linear cationic peptides and 4 peptide dendrimers were synthesized and compared with known LL-37 (cathelicidin family) and anti-F0 monoclonal antibodies in terms of cytotoxicity and antiviral activity. Their affinity to the supposed molecular target - nucleolin (C23) - was estimated in silico by molecular docking analysis. Four synthesized peptides demonstrated a cytotoxic effect, two of them were even more cytotoxic than LL-37, which could be explained by a combination of a high amount of positive charge and amphipathicity. Contrariwise, non-hydrophobic dendrimer peptides did not exhibit cytotoxicity in mammalian cells in the studied concentration range. Two of the seven synthesized peptides, LTP (dendrimer) and SA-35 (linear), used in this study had a stronger antiviral effect than natural peptide LL-37, and three others showed slightly lower activity than anti-F0 monoclonal antibodies. The data obtained in this study suggest that evenly distributed positive charge, and low or medium amphipathicity play a key role in the antiviral activity of the studied peptides. Moreover, the calculated free energy values of the peptide/nucleolin complex for the most active peptides supported the idea that the peptide ability of nucleolin interaction promotes the anti-RSV properties of the molecules.

Antihypertensive Effect Of Amlodipine In Co-Administration With Omeprazole In Patients With Hypertension And Acid-Related Disorders: Cytochrome P450-Associated Aspects.

BACKGROUND: CYP2C19 and CYP3A are the main enzymes involved in omeprazole metabolism, while CYP3A is the principal enzyme family for amlodipine biotransformation. Concomitant use of these drugs in patients with hypertension and acid-related disorders (ARD) might lead to drug-drug interaction. PURPOSE: The aim of the study was to find if adding omeprazole for treating ARD to amlodipine long-term therapy of hypertension influenced blood pressure of CYP2C19 polymorphism carriers. PATIENTS AND METHODS: Fifty-one patients diagnosed with hypertension and ARD were enrolled in the study. Evaluation of antihypertensive therapy was performed by office (OBPM) and ambulatory (ABPM) blood pressure monitoring. Peripheral venous blood was collected for DNA extraction and real-time polymerase chain reaction was performed for CYP2C19*2G681A (rs4244285), CYP2C19*3G636A (rs4986893) and CYP2C19*17C-806T (rs12248560) polymorphisms analysis. RESULTS: Of 51 patients there were 21 extensive metabolizers (EMs), 18 ultrarapid metabolizers (UMs) and 12 intermediate metabolizers (IMs). The results of OBPM showed that antihypertensive effect was significantly more pronounced in IMs compared to EMs or UMs and the average group value in the following parameters: average office systolic blood pressure (BP), dynamics of the average office systolic BP. According to dynamics of diastolic BP, the antihypertensive effect was also significantly higher in IMs than in UMs and the average group value. The results of ABPM revealed that there was a significantly more pronounced antihypertensive effect in IMs compared to all other analyzed groups according to the dynamics of both daytime systolic and 24 hr diastolic BP. The average daytime diastolic BP and its dynamics, the average 24 hr systolic BP and its dynamics were higher in IMs compared to EMs and UMs. CONCLUSION: Adding omeprazole to long-term amlodipine therapy in patients with hypertension and ARD may lead to a significantly more pronounced antihypertensive effect in patients genotyped CYP2C19 IMs.

Lipidomic analysis as a tool for identifying susceptibility to various skin diseases.

This review is about the significance of the use of lipidomic analysis for identifying susceptibility to skin diseases. Exactly this article describes the use of lipidomic analysis in different studies to detect abnormalities in the lipid composition of the skin to diagnose and prevent various dermatological diseases.

A novel peptide dendrimer LTP efficiently facilitates transfection of mammalian cells.

One of the urgent problems of gene therapy is the search for effective transfection methods. Synthetic cationic peptides (CPs) are considered to be one of the most promising approaches for intracellular transport of oligonucleotides. Almost unlimited possibilities of the architectural design of CPs (linear and cyclic structures with a variation of chirality as well as dendrimers) make CPs an effective tunable carrier in this field. Cationic peptide dendrimers (PDs), as a relatively new direction, have significant advantages as gene delivery vehicles by virtue of non-natural ε-amide bonds that significantly increase their resistance to proteolysis. Moreover they also possess much lower cytotoxicity than linear peptides, which is crucial for the potential clinical application of CPs. In a further development of oligonucleotide delivery systems, we have synthesized a collection of 14 CPs, including linear peptides, lipopeptides and PDs. Their activity was evaluated by transfection of 293T cells with plasmids containing reporter genes encoding luciferase or a green fluorescent protein. The obtained results demonstrated that the greatest activity was exhibited by PDs, particularly LTP, an arginine-rich peptide dendrimer, which possesses low cytotoxic and hemolytic activity. The peptide exhibited high cell-penetrating activity, confirmed by fast dissipation of the membrane potential of cells probed by dis-C3-(5). The quantitative analysis of labelled LTP in tissue samples of mice revealed that the Cy5-LTP/siRNA complexes have a reasonable tropism to lung tissues.

CYP3A and CYP2C19 activity in urine in relation to CYP3A4, CYP3A5, and CYP2C19 polymorphisms in Russian peptic ulcer patients taking omeprazole.

BACKGROUND: Proton pump inhibitors (PPIs) are metabolized by cytochrome P450. CYP2C19 is the main isoenzyme for the majority of PPI, whereas CYP3A family is a secondary enzyme for PPI biotransformation. PURPOSE: The aim of the study was to find if CYP3A4*22, CYP3A5*3, CYP2C19*2, CYP2C19*3, and CYP2C19*17 genotypes are connected with CYP3A and CYP2C19 activities in Russian peptic ulcer patients taking omeprazole. PATIENTS AND METHODS: Forty-eight gastric or duodenal ulcer patients (15 men, 33 women; mean age 55.0±15.3 years, age range 18-91 years) from Moscow region of Russia were enrolled. Peripheral venous blood was collected for DNA extraction, and real-time polymerase chain reaction was performed for CYP3A5*3 A6986G (rs776746), CYP3A4*22 C>T in intron 6 (rs35599367), CYP2C19*2G681A (rs4244285), CYP2C19*3G636A (rs4986893), and CYP2C19*17C-806T (rs12248560) polymorphism analyses. Urine samples of patients were collected in the morning between 6 and 9 am before food or drug intake. Urine cortisol and 6ß-hydroxycortisol concentrations (for CYP3A activity) and omeprazole and 5-hydroxyomeprazole concentrations (for CYP2C19 activity) were measured using high-performance liquid chromatography/mass spectroscopy. RESULTS: We found a connection between CYP2C19 genotypes and CYP3A activity. Median metabolic ratios 6ß-hydroxycortisol/cortisol (25%-75% percentiles) were 2.84 (1.99-4.39) for CYP2C19 extensive metabolizers (EMs), 2.51 (1.86-4.73) for CYP2C19 ultra-rapid metabolizers (UMs), and 1.45 (1.12-2.16) for CYP2C19 intermediate metabolizers (IMs) + poor metabolizers (PMs). A statistically significant difference in CYP3A activity (Mann-Whitney test) was found between CYP2C19 EMs vs CYP2C19 IMs+PMs (p=0.006), between CYP2C19 UMs vs CYP2C19 IMs+PMs (p=0.018), and in multiple comparison Kruskal-Wallis test (p=0.014). CONCLUSION: In CYP2C19 IMs+PMs, CYP3A activity was significantly lower than in CYP2C19 EMs and UMs.

Which cytochrome P450 metabolizes phenazepam? Step by step in silico, in vitro, and in vivo studies.

BACKGROUND: Phenazepam (bromdihydrochlorphenylbenzodiazepine) is the original Russian benzodiazepine tranquilizer belonging to 1,4-benzodiazepines. There is still limited knowledge about phenazepam's metabolic liver pathways and other pharmacokinetic features. METHODS: To determine phenazepam's metabolic pathways, the study was divided into three stages: in silico modeling, in vitro experiment (cell culture study), and in vivo confirmation. In silico modeling was performed on the specialized software PASS and GUSAR to evaluate phenazepam molecule affinity to different cytochromes. The in vitro study was performed using a hepatocytes' cell culture, cultivated in a microbioreactor to produce cytochrome P450 isoenzymes. The culture medium contained specific cytochrome P450 isoforms inhibitors and substrates (for CYP2C9, CYP3A4, CYP2C19, and CYP2B6) to determine the cytochrome that was responsible for phenazepam's metabolism. We also measured CYP3A activity using the 6-betahydroxycortisol/cortisol ratio in patients. RESULTS: According to in silico and in vitro analysis results, the most probable metabolizer of phenazepam is CYP3A4. By the in vivo study results, CYP3A activity decreased sufficiently (from 3.8 [95% CI: 2.94-4.65] to 2.79 [95% CI: 2.02-3.55], p=0.017) between the start and finish of treatment in patients who were prescribed just phenazepam. CONCLUSIONS: Experimental in silico and in vivo studies confirmed that the original Russian benzodiazepine phenazepam was the substrate of CYP3A4 isoenzyme.

Urine metabolic ratio of omeprazole in relation to CYP2C19 polymorphisms in Russian peptic ulcer patients.

BACKGROUND: CYP2C19 is known to be the main enzyme of biotransformation of proton pump inhibitors (PPIs), whereas the CYP2C19 gene is highly polymorphic. Genotyping and phenotyping together represent more reliable data about patient's CYP2C19 activity. PURPOSE: The aim of the study was to investigate the applicability of urine metabolic ratio of omeprazole for CYP2C19 phenotyping in Russian peptic ulcer patients with different CYP2C19 genotypes. PATIENTS AND METHODS: A total of 59 patients (19 men and 40 women) aged 18-91 years (mean age 53.5±15.1 years) from four Moscow clinics who were diagnosed with an endoscopically and histologically proven peptic ulcer or had a history of endoscopically and histologically proven ulcers in the past were recruited. Peripheral venous blood (6 mL) was collected for DNA extraction, and real-time polymerase chain reaction was performed for the analysis of CYP2C19*2G681A (rs4244285), CYP2C19*3G636A (rs4986893) and CYP2C19*17C-806T (rs12248560) polymorphisms. Urine samples of patients were collected in the morning between 6 am and 9 am, before food or drug intake, after at least 3 days of twice daily (b.i.d.) omeprazole intake. Omeprazole and 5-hydroxyomeprazole concentrations in the urine were measured using high-performance liquid chromatography with mass spectrometry. RESULTS: Of the 59 patients, there were 27 (45.8%) extensive metabolizers (EMs; CYP2C19*1/*1), 16 (27.1%) ultrarapid metabolizers (UMs; CYP2C19*1/*17, CYP2C19*17/*17), 14 (23.7%) intermediate metabolizers (IMs; CYP2C19*1/*2, CYP2C19*2/*17, CYP2C19*3/*17) and two (3.4%) poor metabolizers (PMs; CYP2C19*2/*2). Median metabolic ratio (25%-75% percentiles) were 1.03 (0.69-1.36) for EMs, 1.95 (1.33-2.68) for UMs, 1.40 (0.78-2.13) for IMs+PMs and 1.26 (0.82-1.99) for the whole sample. A statistically significant difference in metabolic ratio (Mann-Whitney U test) was found between UMs and EMs (p=0.001) and in the multiple comparison Kruskal-Wallis test (p=0.005). CONCLUSION: We found a connection between particular CYP2C19 genotypes and urine metabolic ratio of omeprazole in Russian peptic ulcer patients. This method needs to be improved as in our modification it worked mainly for UMs and did not differentiate all patients according to omeprazole biotransformation activity.

Do CYP2C19 and ABCB1 gene polymorphisms and low CYP3A4 isoenzyme activity have an impact on stent implantation complications in acute coronary syndrome patients?

AIM: The aim of this study was to determine the impact of CYP2C19 and ABCB1 gene polymorphisms and CYP3A4 isoenzyme activity on stent implantation complications among patients with an acute coronary syndrome (ACS) who underwent percutaneous coronary intervention (PCI). PATIENTS AND METHODS: Seventy-six patients (median age 63, range 37-91 years) with an ACS who underwent PCI were screened for CYP2C19 and ABCB1 gene polymorphisms with real-time polymerase chain reaction: CYP2C19*2, CYP2C19*17, and ABCB1 3435. CYP3A4 isoenzyme activity was determined by urine cortisol and 6-beta-hydroxycortisol levels. Stent implantation complications such as stent thrombosis (n=2) and restenosis (n=1) were observed among drug-eluting stent recipients. RESULTS: Low mean 6-beta-hydroxycortisol/cortisol ratio is indicative of impaired CYP3A4 activity and was associated with higher risk of thrombosis (b coefficient=0.022, SE 0.009, p=0.021 in the linear regression model). The increase in the length of the implanted stent was associated with higher risk of restenosis (b coefficient=0.006, SE=0.002, p=0.001 in the linear regression model). The presence of the CYP2C19*2 polymorphism did not affect the incidence of stent thrombosis (b coefficient=-1.626, SE=1.449, p=0.262 in the logistic regression model), nor did the CYP2C19*17 (b coefficient=-0.907, SE=1.438, p=0.528 in the logistic regression model) and ABCB1 3435 polymorphisms (b coefficient=1.270, SE=1.442, p=0.378 in the logistic regression model). CONCLUSION: We did not find evidence that the presence of CYP2C19*2, CYP2C19*17, and ABCB1 3435 polymorphisms may jeopardize the safety of stent implantation in patients with an ACS. Patients with low CYP3A4 isoenzyme activity may have increased risk of stent thrombosis.

Catalytic activity of human indoleamine 2,3-dioxygenase (hIDO1) at low oxygen.

A cytokine-inducible extrahepatic human indoleamine 2,3-dioxygenase (hIDO1) catalyzes the first step of the kynurenine pathway. Immunosuppressive activity of hIDO1 in tumor cells weakens host T-cell immunity, contributing to the progression of cancer. Here we report on enzyme kinetics and catalytic mechanism of hIDO1, studied at varied levels of dioxygen (O2) and L-tryptophan (L-Trp). Using a cytochrome b5-based activating system, we measured the initial rates of O2 decay with a Clark-type oxygen electrode at physiologically-relevant levels of both substrates. Kinetics was also studied in the presence of two substrate analogs: 1-methyl-L-tryptophan and norharmane. Quantitative analysis supports a steady-state rather than a rapid equilibrium kinetic mechanism, where the rates of individual pathways, leading to a ternary complex, are significantly different, and the overall rate of catalysis depends on contributions of both routes. One path, where O2 binds to ferrous hIDO1 first, is faster than the second route, which starts with the binding of L-Trp. However, L-Trp complexation with free ferrous hIDO1 is more rapid than that of O2. As the level of L-Trp increases, the slower route becomes a significant contributor to the overall rate, resulting in observed substrate inhibition.

Tyrosine oxidation in heme oxygenase: examination of long-range proton-coupled electron transfer.

Heme oxygenase is responsible for the degradation of a histidine-ligated ferric protoporphyrin IX (Por) to biliverdin, CO, and the free ferrous ion. Described here are studies of tyrosyl radical formation reactions that occur after oxidizing Fe(III)(Por) to Fe(IV)=O(Por(·+)) in human heme oxygenase isoform-1 (hHO-1) and the structurally homologous protein from Corynebacterium diphtheriae (cdHO). Site-directed mutagenesis on hHO-1 probes the reduction of Fe(IV)=O(Por(·+)) by tyrosine residues within 11 Å of the prosthetic group. In hHO-1, Y58· is implicated as the most likely site of oxidation, based on the pH and pD dependent kinetics. The absence of solvent deuterium isotope effects in basic solutions of hHO-1 and cdHO contrasts with the behavior of these proteins in the acidic solution, suggesting that long-range proton-coupled electron transfer predominates over electron transfer.

Computational modeling of oxygen isotope effects on metal-mediated O2 activation at varying temperatures.

Oxygen equilibrium isotope effects ((18)O EIEs) upon the formation of metal superoxide and peroxide structures from natural abundance O(2) are reported. The (18)O EIEs determined over a range of temperatures are compared to those calculated on the basis of vibrational frequencies. Considering all vibrational modes in a "full frequency model" is found to reproduce the empirical results better than "cut-off" models which consider only the most isotopically sensitive modes. Theoretically, the full frequency model predicts that (18)O EIEs arise from competing enthalpic and entropic influences resulting in nonlinear variations with temperature. Experimental evidence is provided for an increase in the magnitude of the EIE, in some instances implicating a change from inverse to normal values, as the temperature is raised. This finding is not easily reconciled with the common intuition that (18)O EIEs arise from a reduction of the O-O force constant and attendant changes in zero point energy level splitting. Instead a dominant entropic effect, as described here, is expected to characterize isotope effects upon reversible binding of small molecules to metal centers in enzymes and inorganic compounds.

Inner-sphere mechanism for molecular oxygen reduction catalyzed by copper amine oxidases.

Copper and topaquinone (TPQ) containing amine oxidases utilize O2 for the metabolism of biogenic amines while concomitantly generating H2O2 for use by the cell. The mechanism of O2 reduction has been the subject of long-standing debate due to the obscuring influence of a proton-coupled electron transfer between the tyrosine-derived TPQ and copper, a rapidly established equilibrium precluding assignment of the enzyme in its reactive form. Here, we show that substrate-reduced pea seedling amine oxidase (PSAO) exists predominantly in the Cu(I), TPQ semiquinone state. A new mechanistic proposal for O2 reduction is advanced on the basis of thermodynamic considerations together with kinetic studies (at varying pH, temperature, and viscosity), the identification of steady-state intermediates, and the analysis of competitive oxygen kinetic isotope effects, (18)O KIEs, [kcat/KM((16,16)O2)]/[kcat/KM((16,18)O2)]. The (18)O KIE = 1.0136 +/- 0.0013 at pH 7.2 is independent of temperature from 5 degrees C to 47 degrees C and insignificantly changed to 1.0122 +/- 0.0020 upon raising the pH to 9, thus indicating the absence of kinetic complexity. Using density functional methods, the effect is found to be precisely in the range expected for reversible O2 binding to Cu(I) to afford a superoxide, [Cu(II)(eta(1)-O2)(-I)](+), intermediate. Electron transfer from the TPQ semiquinone follows in the first irreversible step to form a peroxide, Cu(II)(eta(1)-O2)(-II), intermediate driving the reduction of O2. The similar (18)O KIEs reported for copper amine oxidases from other sources raise the possibility that all enzymes react by related inner-sphere mechanisms although additional experiments are needed to test this proposal.

Isotopic probing of molecular oxygen activation at copper(I) sites.

Copper-dioxygen (CuO2) adducts are frequently proposed as intermediates in enzymes, yet their electronic and vibrational structures have not always been understood. [Cu(eta1-O2)TMG3tren]+ (TMG3tren = 1,1,1-tris{2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl}amine) features end-on (eta1) O2 coordination in the solid state. Described here is an investigation of the compound's solution properties by nuclear magnetic resonance spectroscopy, density functional calculations, and oxygen isotope effects. The study yields two major findings. First, [Cu(eta1-O2)TMG3tren]+ is paramagnetic due to a triplet electronic structure; this is in contrast to other copper compounds where O2 is bound in a side-on manner. Second, the oxygen equilibrium isotope effect upon O2 binding to copper(I) (18O EIE [triple bond] K(16O16O)/K(16O18O) = 1.0148 +/- 0.0012) is significantly larger than those determined for iron and cobalt eta1-O2 adducts. This result is suggested to reflect greater ionic (CuII-O2-I) character within the valence bond description. A revised interpretation of the physical origins of the 18O EIEs upon O2 binding to redox metals is also advanced along with experimental data that should be used as benchmarks for interpreting 18O kinetic isotope effects upon enzyme reactions.

Mechanisms of electron transfer in catalysis by copper zinc superoxide dismutase.

Activated oxygen intermediates during copper zinc superoxide dismutase (SOD) catalysis were investigated using an isotope fractionation technique and natural abundance reagents. Competitive oxygen kinetic isotope effects (KIEs) are reported for the enzyme-catalyzed disproportionation of superoxide as well as the stoichiometric reaction of reduced SOD with molecular oxygen. Analysis within the context of quantum mechanical electron transfer theory provides evidence against an outer-sphere mechanism for O2*- oxidation. A CuII-O2-I intermediate is, therefore, proposed. The SOD-catalyzed oxidation of O2*- is characterized by an inverse (<1) KIE which is similar to those determined for the analogous reactions of synthetic copper compounds. An inverse kinetic isotope effect upon the enzymatic reduction of O2*- is also observed and proposed to arise from rate-determining proton transfer which leads to the formation of HO2* in the SOD active site.

Evidence for Cu-O2 intermediates in superoxide oxidations by biomimetic copper(II) complexes.

The mechanism by which [Cu(II)(L)](OTf)2 and [Cu(II)N3(L)](OTf) (L = TEPA: tris(2-pyridylethyl)amine or TMPA: tris(2-pyridylmethyl)amine; OTf = trifluoromethanesulfonate) react with superoxide (O2*-) to form [Cu(I)(L)](OTf) and O2 is described. Evidence for a CuO2 intermediate is presented based on stopped-flow experiments and competitive oxygen (18O) kinetic isotope effects on the bimolecular reactions of (16,16)O2*- and (18,16)O2*- ((16,16)k/(18,16)k). The (16,16)k/(18,16)k fall within a narrow range from 0.9836 +/- 0.0043 to 0.9886 +/- 0.0078 for reactions of copper(II) complexes with different coordination geometries and redox potentials that span a 0.67 V range. The results are inconsistent with a mechanism that involves either rate-determining O2*- binding or one-step electron transfer. Rather a mechanism involving formation of a CuO2 intermediate prior to the loss of O2 in the rate-determining step is proposed. Calculations of similar inverse isotope effects, using stretching frequencies of CuO2 adducts generated from copper(I) complexes and O2, suggest that the intermediate has a superoxo structure. The use of 18O isotope effects to relate activated oxygen intermediates in enzymes to those derived from inorganic compounds is discussed.

Slow electron transfer rates for fluorinated cobalt porphyrins: electronic and conformational factors modulating metalloporphyrin ET.

The electron transfer (ET) properties of a series of closely related cobalt porphyrins, [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]cobalt, CoF(28)TPP, [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraphenyl)porphyrinato]cobalt, CoF(8)TPP, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]cobalt, CoF(20)TPP, and [5,10,15,20-tetraphenylporphyrinato]cobalt, CoTPP, were investigated by cyclic voltammetry, cyclic voltammetric digital simulation, in situ UV-vis and IR spectroelectrochemistry, kinetic ET studies, bulk electrolysis, (19)F NMR spectroscopy, X-ray crystallography, and molecular modeling. In benzonitrile containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF(6)) as supporting electrolyte, the ET rate constants for the Co(2+/3+) redox couples were found to be strongly substituent dependent; the heterogeneous ET rate constant (k(el)) varied by a factor of 10(4), and the ET self-exchange rate constants (k(ex)) varied over 7 orders of magnitude for the compounds studied. The remaining observed ring oxidation and metal and ring reduction events exhibited nearly identical k(el) values for all compounds. UV-vis and IR spectroelectrochemistry, bulk electrolysis, and (19)F NMR spectroscopic studies support attribution of different ET rates to widely varying inner sphere reorganization energies (lambda(i)) for these closely related compounds. Structural and semiempirical (PM3) studies indicate that the divergent kinetic behavior of CoTPP, CoF(8)TPP, CoF(20)TPP, and CoF(28)TPP first oxidations arises mainly from large nuclear reorganization energies primarily associated with core contraction and dilation. Taken together, these studies provide rational design principles for modulating ET rate constants in cobalt porphyrins over an even larger range and provide strategies for similar manipulation of ET rates in other porphyrin-based systems: substituents that lower C-C, C-N, and N-M vibrational frequencies or minimize porphyrin orbital overlap with the metal-centered orbital undergoing a change in electron population will increase k(ET). The heme ruffling apparent in electron transfer proteins such as cytochrome c is interpreted as nature's exploitation of this design strategy.

19F NMR and Structural Evidence for Spin-State Modulation of Six-Coordinate Cobalt(II) in a Weak Field Porphyrin Ligand(1).

The syntheses and characterization of [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraphenylporphinato]cobalt, Co(F(8)TPP), and [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphinato]cobalt, Co(F(28)TPP), are reported. Co(F(28)TPP).2tol (tol = toluene) crystallizes in the monoclinic space group C2/c-C(h)() (No. 15) with a = 22.1616(5) Å, b = 12.0274(3) Å, c = 19.9159(2) Å, beta = 110.645(1) degrees, V = 4967.6(2) Å(3), and Z = 4 {d(calcd) = 1.818 g/cm(3); &mgr;(a)(Mo Kalpha) = 0.50 mm(-)(1)}, and Co(F(28)TPP).2THF crystallizes in the triclinic space group P&onemacr; (No. 2) with a = 11.0691(1) Å, b = 12.0451(1) Å, c = 12.9558(2) Å, alpha = 62.531(1) degrees, beta = 69.544(1) degrees, gamma = 76.181(1) degrees, V = 1429.71(3) Å(3) and Z = 1 {d(calcd) = 1.700 g/cm(3); &mgr;(a)(Mo Kalpha) = 0.45 mm(-)(1)}. A comparison of the X-ray crystal structure data from Co(F(28)TPP).2tol and Co(F(28)TPP).2THF indicates that the porphyrin core expands dramatically (0.08 Å) in the six-coordinate complex. Optical and (19)F NMR spectroscopic studies of Co(F(28)TPP) in the presence of added ligand demonstrate that spin-state modulation of the six-coordinate Co(II) center is facile. Partial population of the (4)E(g) state is accessed upon coordination of the cobalt center with THF sigma-donor ligands, while six-coordinate complexes with 1-methylimidazole result in complete conversion to the high spin state, as evinced by 280 ppm downfield chemical shifts for the beta-fluorine resonances in the (19)F NMR spectrum. Co(F(28)TPP) is the first example of a porphyrin which supports a high-spin cobalt ion.