On form ideals and Artin-Rees condition

We look for conditions which make two ideals and in a noetherian ring A have the same form ideal in an associated graded ring G_A(α). More precisely, when and and f_i?f'_iεα ^m m?0, ? i , we give a necessary and sufficient condition to have , involving the first syzygies modules both of (f₁,...,f_n) and (f'₁,...,f'_n); our proof is based on the Artin-Rees lemma. Finally we show that, when the sequence f₁,...,f_n is regular and for an integer q, then f₁?f'_i ? α^q+1 ? i implies .     

Luminescent lanthanide complexes of a bis-bipyridine-phosphine-oxide ligand as tools for anion detection

The Gd(3+), Tb(3+), and Eu(3+) complexes of a bis-bipyridine-phenylphosphine oxide ligand PhP(O)(bipy)(2) 1 (bipy for 6-methylene-6'-methyl-2,2'-bipyridine) have been synthesized. In acetonitrile solutions at room temperature, the Tb(3+) and Eu(3+) complexes show a metal-centered luminescence, indicative of an efficient energy transfer from the two bipy subunits to the Ln center. The photophysical properties drastically depend on the nature of the anions present in solution. In particular, addition of 2 equiv of nitrate anions to a solution containing the [Ln.1](OTf-)(3) leads to an 11-fold increase of the luminescence intensity for the Eu(3+) and a 7-fold increase for the Tb(3+) complexes. Similar effects are provided with Cl-, F-, and CH(3)COO- anions. UV-vis titration experiments were used to determine association constants for binding of, respectively, one, two, and three anions. Stepwise anion addition has also been investigated on the molecular level using quantum mechanical (QM) calculations for the Eu complexes. These calculations reproduce the experimental findings, especially if solvent molecule addition is taken into account. The X-ray crystal structure of the nitrate salt of the Tb complex, as well as QM calculation of a similar Eu complex, demonstrates the coordination of three nitrate anions in a bidentate mode and the step-by-step relegation of the bipy subunits in the second coordination sphere. These features give valuable insights into the mechanism of the overall light amplification process.     

Polymers containing quaternary ammonium groups based on poly(N-vinylimidazole)

A poly(N-vinylimidazole) (PNVI)—based poly(carboxybetaine) with two methylene groups between the opposite charges was achieved by the nucleophilic addition reaction of the mentioned aminic polymer to the carbon-carbon double bond of acrylic acid (AA). Treatment of poly(carboxybetaine) with concentrated HCl (2 N) for long time leads to the corresponding cationic polyelectrolyte. The poly(carboxybetaine) is soluble in both water and aqueous solutions of salts such as: LiCl, NaCl, NaHCO₃, CaCl₂, Na₂SO₄. In water and in the first three salts, poly(carboxybetaine) exhibits a non-polyelectrolyte behaviour (a linear dependence of reduced viscosities on polymer or salt concentration), while in the remaining two salts, a slight polyelectrolyte behaviour is observed. The cationic polyelectrolyte is soluble in water and aqueous solutions of LiCl, NaCl, CaCl₂ and NaHCO₃, except Na₂SO₄. It has a polyelectrolyte behaviour in all solutions. Also, the binding trends of the added salts by polymers are discussed.     

Theoretical and Experimental Study of Medium Effects on the Structure and Spectroscopy of the [Fe(CN)(5)NO](2)(-) Ion

The influence of the solvent on the structure and IR spectrum of the [Fe(CN)(5)NO](2)(-) ion is investigated by using gradient corrected density functional theory. IR spectra are also measured on different solvents and the results obtained are compared with the predicted ones. We have treated the solvent effects with a continuum model, based on the Onsager's reaction field approach; in order to mimic strong specific interactions, calculations were also performed on the complex protonated at the cyanide trans to the nitrosyl group. The reaction field calculations predict only qualitatively the most important observed trends, e.g., the shifts in the nitrosyl stretching wavenumber, but fail in accounting quantitatively for the differences between the spectra in water and acetonitrile. The possible role of specific interactions is consistently accounted for by interpreting the experimental shifts of the NO stretching wavenumber nu(NO), as well as the visible absorption energies, when changing the Lewis acidity of the solvent, as measured by the Gutmann's acceptor number. Ligand population analysis was performed to relate the solvent effects with the sigma donor and pi acceptor behavior of cyanide and nitrosyl ligands. The significance of nu(NO) shifts as a result of changes in the medium is discussed in view of the physiological relevance of transition-metal nitrosyl chemistry.     

Photoisomerization mechanism of 11-cis-locked artificial retinal chromophores: acceleration and primary photoproduct assignment

CASPT2//CASSCF/6-31G photochemical reaction path computations for two 4-cis-nona-2,4,6,8-tetraeniminium cation derivatives, with the 4-cis double bond embedded in a seven- and eight-member ring, are carried out to model the reactivity of the corresponding ring-locked retinal chromophores. The comparison of the excited state branches of the two reaction paths with that of the native chromophore, is used to unveil the factors responsible for the remarkably short (60 fs) excited state (S(1)) lifetime observed when an artificial rhodopsin containing an eight member ring-locked retinal is photoexcited. Indeed, it is shown that the strain imposed by the eight-member ring on the chromophore backbone leads to a dramatic change in the shape of the S(1) energy surface. Our models are also used to investigate the nature of the primary photoproducts observed in different artificial rhodopsins. It is seen that only the eight member ring-locked retinal model can access a shallow energy minimum on the ground state. This result implies that the primary, photorhodopsin-like, transient observed in artificial rhodopsins could correspond to a shallow excited state minimum. Similarly, the second, bathorhodopsin-like, transient species could be assigned to a ground state structure displaying a nearly all-trans conformation.     

Solvent-induced modulation of collective photophysical processes in fluorescent silica nanoparticles

In this paper we show how it is possible to control the nature and the efficiency of collective photophysical processes in a network composed of two different fluorescent units organized on the surface of silica nanoparticles. Such a structure is obtained by covering nanoparticles with a layer of dansyl moieties (Dns) and by partially protonating them in solution. The two fluorophores Dns and Dns.H(+) have very different photophysical properties and can be selectively excited and detected. The interaction between the two units Dns and Dns.H(+) has been first investigated in a reference compound obtained by derivatizing 1,6-hexanediamine with two dansyl units. The photophysical characterization of this compound (absorption spectra, fluorescence spectra, quantum yield, and lifetime) showed that the two moieties can be involved both in energy and electron-transfer processes. Dansylated nanoparticles were prepared by modifying preformed silica nanoparticles with dansylated (3-aminopropyl)trimethoxysilane. Photophysical studies indicated that protonation has a dramatic effect on the fluorescence of the nanoparticles, leading to the quenching of both the protonated units and the surrounding nonprotonated ones. This amplified response to protonation, due to charge-transfer interactions, is solvent-dependent and is less efficient in pure chloroform with respect to acetonitrile/chloroform (5/1 v/v) mixtures. The reduced efficiency of the electron-transfer processes responsible for the quenching makes energy transfer competitive to such an extent that in pure chloroform excitation energy migration takes place from Dns.H(+) to Dns with great efficiency.     

Conformational studies of a bombolitin III-derived peptide mimicking the four-helix bundle structural motif of proteins

Bombolitins are five structurally related heptadecapeptides originally isolated from the venom of a bumblebee. In aqueous solution, bombolitins at sufficiently high concentration form oligomeric aggregates with consequent conformational transition from a random coil to the alpha-helical structure. Previous studies suggested that oligomeric aggregates could mimic the four-helix bundle structural motif of proteins. In the present work, we synthesized the following peptide sequence formed by two bombolitin III sequences linked head-to-tail by the tetrapeptide bridge -Gly-Pro-Val-Asp-: I(1)-K(2)-I(3)-M(4)-D(5)-I(6)-L(7)-A(8)-K(9)-L(10)-G(11)-K(12)-V(13)-L(14)-A(15)-H(16)-V(17)-G(18)-P(19)-V(20)-D(21)-I(22)-K(23)-I(24)-M(25)-D(26)-I(27)-L(28)-A(29)-K(30)-L(31)-G(32)-K(33)-V(3)(4)-L(35)-A(36)-H(37)-V(38)-NH(2). The tetrapeptide GPVD connecting the two helical peptide sequences was chosen to facilitate the formation of the helix-loop-helix structural motif. The conformational properties of the peptide were studied by CD, NMR, and molecular dynamics calculations. The results indicate the presence of a helix-loop-helix conformation at 10(-)(5) M concentration. At higher concentrations, NOESY connectivities were detected which are compatible with the presence of dimers or higher aggregates of peptide molecules in the helix-loop-helix structure packed in an antiparallel fashion. Molecular dynamics simulation were run either with NOE distance restraints or without restraints in explicit solvent for extended time. The results of these simulations support the dimerization of the molecules in the helix-loop-helix structure with formation of the four-helix bundle motif.     

Determination of microscopic rate constants for CO binding and migration in myoglobin encapsulated in silica gels

CO rebinding kinetics after nanosecond photolysis of myoglobin encapsulated in wet silica gels exhibits an enhanced geminate phase that allows the determination of the microscopic rate constants and the activation barriers for distinct ligand docking sites inside the protein matrix. Using a maximum entropy method, we demonstrate that the geminate phase can be well-described by a biphasic lifetime distribution, reflecting rebinding from the distal and proximal sites. Microscopic rates and activation barriers were estimated using a four-state model.     

Study of some properties of poly(N-vinyl imidazole) partially quaternized with n-butyl bromide aqueous solutions

This paper presents a study of the properties of aqueous solutions of poly(N-vinyl imidazole) quaternized with n-butyl bromide (PVIQ3). The influence of the temperature and polymer concentration on refractive index, electrical conductivity and surface tension was studied. The critical micelar concentration of PVIQ3 in aqueous solution was determined and correlated with the polymer solubility in water.All the PVIQ3 aqueous solutions properties were compared with those of poly(N-vinyl imidazole) (PNVI) and the influence of the quaternization process on the polymer properties was evidenced.     

Hematological health-related intervals estimated using an indirect method in order to satisfy the accreditation standards

 The estimation of reference limits represents quite a taxing task for laboratories which frequently adopt the limits suggested by manufacturers or those reported in the literature. This practice does not meet the requirements of accreditation programs (i.e. Essential Criteria, Clinical Pathology Accreditation) that require laboratories to produce or check all their reference intervals. We collected 15 244 hematological results from females aged 0–99 years obtained by the Rovereto Hospital Laboratory and calculated the reference intervals, or to be more precise the health-related intervals, using an indirect method (based on all the inpatient and outpatient results). All the measurements were carried out using an automatic Coulter STK S analyzer, and the results were transferred to Verona by e-mail. The results for hemoglobin were: <1 year (n=154)=90–171 g/l; 2–8 years (n=619)=104–136 g/l; 9–14 years (n=322)=118–143 g/l; 15–44 years (n=6329)=106–144 g/l; 45–75 years (n=4893)=107–148 g/l; 75–99 years (n=2927)=90–153 g/l. The results appear different from the results currently used by Rovereto Hospital (120–160 g/l) but comparable to those reported in the literature with the exception of the subjects under 1 year and over 75 years, probably due to the excess of "diseased" subjects in these classes. The indirect method allows even small laboratories to produce or check their reference intervals for all age groups, increasing the clinical effectiveness of laboratory results and satisfying the accreditation standards. Received: 15 April 2000 · Accepted: 20 April 2000