Actomyosin interaction at low ATP concentrations.

In vitro motility assay (IVMA) experiments were performed to analyze the movement of actin filaments sliding on a pavement of myosin molecules at different [ATP] and [ADP]. In standard experimental conditions at [ATP] = 2 mM, about 80% of the actin filaments move in unloaded conditions with a constant velocity. However, a fraction of at least 20% static actin filaments is always present.

BC(50): a generalized, unifying affinity descriptor.

Assessing binding affinities is an unavoidable step that we come across any time interactions between binding species are investigated. A quantitative evaluation of binding affinities relies on the determination of binding constants but, whilst the binding constant fully defines the affinity of a reagent for a ligand when only one complex species is formed, the same is not true when the interacting partners form more than one complex of different stoichiometry, because all complexes contribute to the overall binding affinity. Unfortunately, this situation is the rule rather than the exception in chemical systems, but a generally accepted solution for this issue has not yet been settled.

Balanced biochemical reactions: a new approach to unify chemical and biochemical thermodynamics.

A novel procedure is presented which, by balancing elements and electric charge of biochemical reactions which occur at constant pH and pMg, allows assessing the thermodynamics properties of reaction Δ(r)G'⁰, Δ(r)H'⁰, Δ(r)S'⁰ and the change in binding of hydrogen and magnesium ions of these reactions. This procedure of general applicability avoids the complex calculations required by the use of the Legendre transformed thermodynamic properties of formation Δ(f)G'⁰, Δ(f)H'⁰ and Δ(f)S'⁰ hitherto considered an obligatory prerequisite to deal with the thermodynamics of biochemical reactions. As a consequence, the term "conditional" is proposed in substitution of "Legendre transformed" to indicate these thermodynamics properties.

Chiral diaminopyrrolic receptors for selective recognition of mannosides, part 1: design, synthesis, and affinities of second-generation tripodal receptors.

A new generation of chiral tripodal receptors for recognition of carbohydrates, featuring trans-1,2-diaminocyclohexane as a key structural element, and their recognition properties toward a set of glycosides of biologically relevant monosaccharides is described. The introduction of a chelating diamino unit into the pyrrolic tripodal architecture markedly enhanced their binding abilities compared with the parent aminopyrrolic receptors previously reported by our group. In addition, the chirality of the structure had a clear impact on affinities, as well as on selectivities, displaying high enantiodiscrimination levels.

Chemical and biochemical thermodynamics: from ATP hydrolysis to a general reassessment.

The Legendre-transformed Gibbs energy change for a biochemical reaction, Delta(r)G', is shown to be equal to the nontransformed Gibbs energy change, Delta(r)G, of any single reaction involving selected chemical species of the biochemical system. These two Gibbs energies of reaction have hitherto been thought to have different values. The equality of the quantities means that a substantial part of biochemical and chemical thermodynamics, previously treated separately, can be treated within a unified thermodynamic framework.

Ion-pair binding: is binding both binding better?

It is often tempting to explain chemical phenomena on the basis of intuitive principles, but this practice can frequently lead to biased analysis of data and incorrect conclusions. One such intuitive principle is brought into play in the binding of salts by synthetic receptors. Following the heuristic concept that "binding both is binding better", it is widely believed that ditopic receptors capable of binding both ionic partners of a salt are more effective than monotopic receptors because of a cooperative effect.

Binding of ionic species: a general approach to measuring binding constants and assessing affinities.

Bound together: The association of receptors with ionic species cannot be assimilated to the binding of neutral guests. When dealing with salts, both ion pairing and binding to the free and the ion-paired ionic guest determine the actual association pattern (see figure). The general issue of measuring association constants and assessing affinities for ions is addressed and validated in two cases of anion binding.

Pyrrolic tripodal receptors effectively recognizing monosaccharides. Affinity assessment through a generalized binding descriptor.

Pyrrolic and imino (3) or amino (4) H-bonding ligands were incorporated into a benzene-based tripodal scaffold to develop a new generation of receptors for molecular recognition of carbohydrates. Receptors 3 and 4 effectively bound a set of octylglycosides of biologically relevant monosaccharides, including glucose (Glc), galactose (Gal), mannose (Man), and N-acetyl-glucosamine (GlcNAc), showing micromolar affinities in CDCl3 and millimolar affinities in CD3CN by NMR titrations. Both receptors selectively recognized Glc among the investigated monosaccharides, with 3 generally less effective than 4 but showing selectivities for the all-equatorial beta-glycosides of Glc and GlcNAc among the largest reported for H-bonding synthetic receptors.

Quantitative mathematical expressions for accurate in vivo assessment of cytosolic [ADP] and DeltaG of ATP hydrolysis in the human brain and skeletal muscle.

Magnetic Resonance Spectroscopy affords the possibility of assessing in vivo the thermodynamic status of living tissues. The main thermodynamic variables relevant for the knowledge of the health of living tissues are: DeltaG of ATP hydrolysis and cytosolic [ADP], the latter as calculated from the apparent equilibrium constant of the creatine kinase reaction. In this study we assessed the stoichiometric equilibrium constant of the creatine kinase reaction by in vitro (31)P NMR measurements and computer calculations resulting to be: logK(CK)=8.

Inorganic-organic hybrids formed by P,P'-diphenylmethylenediphosphinate, pcp2-, with the Cu2+ ion. X-ray crystal structures of [Cu(pcp)(H2O)2] x H2O and [Cu(pcp)(bipy)(H2O)].

Weakly coordinated [Cu(pcp)(H2O)n] complexes are formed in aqueous solution, at room temperature, by interaction of P,P'-diphenylmethylene diphosphinic acid (H2pcp) with copper(II) ions. However, heating of the solutions gives rise to the formation of two extended metal-oxygen networks of formulas [Cu(pcp)(H2O)2] x H2O, 1, and [Cu(pcp)(H2O)2], 2. In the presence of 2,2'-bipyridyl (bipy) the diamine derivative [Cu(pcp)(bipy)(H2O)], 4, has been isolated.

A new tripodal receptor for molecular recognition of monosaccharides. A paradigm for assessing glycoside binding affinities and selectivities by 1H NMR spectroscopy.

A new tripodal receptor for the recognition of monosaccharides is described. The prototypical host 1 features a 1,3,5-substituted 2,4,6-triethylbenzene scaffold bearing three convergent H-bonding units. The binding ability of the t-octyl derivative 1a toward a set of octylglycosides of biologically relevant monosaccharides, including Glc, Gal, Man, and GlcNAc, was investigated by 1H NMR in CDCl3.

Novel coordinating motifs for lanthanide(III) ions based on 5-(2-pyridyl)tetrazole and 5-(2-pyridyl-1-oxide)tetrazole. Potential new contrast agents.

Water-soluble and neutral Ln(III) and Zn (II) complexes of pyridine- and (pyridine-1-oxide)tetrazole have been synthesized and the Gd derivatives have great potential as high-relaxivity low-osmolarity MRI contrast agents.

Synthesis, characterization and coordination chemistry of the new tetraazamacrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt.

A new potentially hexadentate tetraazamacrocycle based on the cyclen skeleton has been synthesized and fully characterized. The macrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt (Me2DO2PME) contains mutually trans monoethyl ester phosphonate acid substituents on two nitrogen atoms, and trans methyl substituents on the other two nitrogen atoms. The protonation constants of this macrocycle and the stability constants of its complexes with Cu2+, Zn2+, Gd3+ and Ca2+ ions have been determined by pH potentiometric titrations.

Determination of protonation constants of some fluorinated polyamines by means of 13C NMR data processed by the new computer program HypNMR2000. Protonation sequence in polyamines.

The p K(a) values of 6-fluoro-4,8-diazadodecane-1,12-diamine (6-fluorospermine) (1), 6,6-difluoro-4,8-diazadodecane-1,12-diamine (6,6-difluorospermine) (2), 6-fluoro-4-azaoctane-1,8-diamine (6-fluorospermidine) (3) and 6,6-difluoro-4-azaoctane-1,8-diamine (6,6-difluorospermidine) (4) in D(2)O solution have been determined at 40 degrees C from (13)C NMR chemical shifts data using the new computer program HypNMR2000. The enthalpies of protonation of compounds 1-4 and the parent amines spermine (5) and spermidine (6) have been determined from microcalorimetric titration data. The values of Delta H degrees were used to derive basicity constants relative to 25 degrees C.

Complexation of beryllium(II) ion by phosphinate ligands in aqueous solution. Synthesis and XRPD structure determination of Be[(PhPO2)2CH2](H2O)2.

Two bifunctional ligands, phenyl(carboxymethyl)phosphinate (ccp(2-) and P,P'-diphenylmethylenediphosphinate (pcp(2-)), have been tested as chelating agents of beryllium(II). Both ligands have the same charge and a similar chelating structure, but whereas the 1:1 adduct of pcp(2-), Be(pcp)(H(2)O)(2), could be isolated as a white powder, no pure compound could be isolated from solutions containing beryllium(II) and ccp(2-). Instead, the solutions were examined by means of potentiometry and (9)Be NMR spectroscopy.

Different complexation properties of some hydroxy keto heterocycles toward beryllium(II) in aqueous solutions: experimental and theoretical studies.

Four heterocycles containing hydroxy and keto functionalities have been tested as chelating agents of beryllium(II). These are in the order (i) 3-hydroxy-2-methyl-4H-pyran-4-one (maltol, Hma), (ii) 5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one (kojic acid, Hka), (iii) 3-hydroxy-1,2-dimethyl-4-pyridinone (Hdpp), (iv) 1-(3-hydroxy-2-furanyl)ethanone (isomaltol, Hima). Although the skeletons of the first three species, with one nitrogen or oxygen heteroatom at the six-membered ring, are almost superimposable, straightforward synthesis and crystallization is achieved only for the 1:2 adduct Be(dpp)(2), 1.