Interpolyelectrolyte complexes as a new family of enzyme carriers

The ability of nonstoichiometric interpolyelectrolyte complexes of dissolving in water and reversible precipitation, induced by the changes of conditions (pH, ionic strength of the solution) was used to create the reversibly soluble immobilized enzymes. The techniques of the enzyme inclusion (penicillin amidase, α-chymotrypsin, urease etc.) in the interpolyelectrolyte complexes were worked out. It was shown that the application of the reversibly soluble immobilized enzymes allows: (1) to combine all advantages of the homogeneous catalysis with easy separation of enzyme molecules from the reaction mixture in the end of the process; (2) to increase significantly the thermostability of immobilized enzyme via its precipitation by pH decrease; (3) to protect the enzyme from high-molecular-weight inhibitors either in the precipitate or in a homogeneous solution; (4) to create self-regulating enzyme systems in which an attainment of the certain conversion degree results in process termination; (5) to design reversibly soluble polyenzymatic systems.     

Interpolyelectrolyte complexes of soybean peroxidase with thermoresponsive copolymers

Interpolyelectrolyte complexes of soybean peroxidase with thermoresponsive N-isopropylacrylamide-sodium styrenesulfonate copolymers of various compositions are studied by the methods of high-sensitivity differential scanning calorimetry, velocity sedimentation, and nephelometry. It is shown that the enzyme preserves its tertiary structure in complexes, although the conformational stability of bound protein is lower than that of free protein. Complexes of any compositions, including stoichiometric complexes, are soluble at room temperature but precipitate during heating in the region of the conformational transition of the copolymer accompanied by formation of the complex gel. Isotherms of enzyme binding by complex gels are constructed, and their analysis makes it possible to reveal two types of binding in the system: a relatively strong stoichiometric binding of the enzyme with the copolymers and a weaker binding of the protein in the coacervate phase of the complex gel. A high yield of the protein in the complex gel, reversibility of binding, and preservation of the tertiary structure of the enzyme in complexes with the copolymers make protein-thermoresponsive polyelectrolyte systems promising for bioseparation.     

Interpolyelectrolyte complexes of conjugated copolymers and DNA: platforms for multicolor biosensors

Interchain interactions modulate the frequency of emission from a cationic water-soluble conjugated polymer. The polymer, PFPB, is obtained by a Suzuki copolymerization of p-phenylenebisboronic acid with a 95:5 mixture of 2,7-dibromo-9,9-bis(6'-bromohexyl)fluorene and 4,7-dibromo-2,1,3-benzothiadiazole, followed by quarternization of the pendant groups by addition of NMe3. The structure of PFPB contains 5% of the 2,1,3-benzothiadiazole (BT) chromophore within a cationic poly(fluorene-co-phenylene) polymer chain. The emission of PFPB is blue under dilute conditions (<1 x 10-6 M in repeat units) and green at higher concentrations. Energy transfer to dye-labeled ss-DNA is more efficient, relative to the parent polymer poly(9,9-bis(6'-N,N,N,-trimethylammonium)hexyl)fluorene-co-alt-1,4-phenylene) dibromide (PFP), as a result of improved spectral overlap. By using a peptide nucleic acid (PNA-C*) labeled with a red-emitting chromophore one can obtain three different emission colors, depending on the nature of the substrate under interrogation. If no ss-DNA is present, the solution emits blue. With a ss-DNA that is noncomplementary to PNA-C*, green emission is observed. Red emission occurs upon addition of ss-DNA complementary to the PNA sequence.     

Interpolyelectrolyte complexes formation in dependence on the nature of polyelectrolytes

Interpolyelectrolyte complexes (PECs) were obtained starting from polycations with (N,N-dimethyl-2-hydroxypropylenammonium chloride) units in the main chain and sodium salts of the poly(acrylic acid), on one hand, and poly (2-acrylamido-2-methylpropane sulfonic acid), on the other hand, as polyanions. The polycations were different as concerns both the content of the quaternary ammonium salt groups and the degree of branching. The polyanions were different both by their structure and molecular weight. The complex formation was followed through the variation of the reduced viscosity and of the conductivity of the reaction medium vs. the unit molar ratio polyanion/polycation in two ranges of concentration.     

Molecular wheels: new Mn12 complexes as single-molecule magnets

The preparation, structure and magnetic properties of three new wheel-shaped dodecanuclear manganese complexes, [Mn12(Adea)8(CH3COO)14] x 7 CH3CN (1 x 7CH3CN), [Mn12(Edea)8(CH3CH2COO)14] (2) and [Mn12(Edea)8(CH3COO)2(CH3CH2COO)12] (3), are reported, where Adea(2-) and Edea(2-) are dianions of the N-allyl diethanolamine and the N-ethyl diethanolamine ligands, respectively. Each complex has six Mn(II) and six Mn(III) ions alternating in a wheel-shaped topology, with eight n-substituted diethanolamine dianions. All variable-temperature direct current (DC) magnetic susceptibility data were collected in 1, 0.1, or 0.01 T fields and in the 1.8-300 K temperature range. Heat capacity data, collected in applied fields of 0-9 T and in the 1.8-100 K temperature range, indicate the absence of a phase-transition due to long-range magnetic ordering for 1 and 3. Variable-temperature, variable-field DC magnetic susceptibility data were obtained in the 1.8-10 K and 0.1-5 T ranges. All complexes show out-of-phase signals in the AC susceptibility measurements, collected in a 50-997 Hz frequency range and in a 1.8-4.6 K temperature range. Extrapolation to 0 K of the in-phase AC susceptibility data collected at 50 Hz indicates an S = 7 ground state for 1, 2, and 3. Magnetization hysteresis data were collected on a single crystal of 1 in the 0.27-0.9 K range and on single crystals of 2 and 3 in the 0.1-0.9 K temperature range. Discrete steps in the magnetization curves associated with resonant quantum tunneling of magnetization (QTM) confirm these complexes to be single-molecule magnets. The appearance of extra QTM resonances on the magnetic hysteresis of 1 is a result of a weak coupling between two Mn ions at opposite ends of the wheel, dividing the molecule into two ferromagnetic exchange-coupled S = 7/2 halves. The absence of these features on 2 and 3, which behave as rigid spin S = 7 units, is a consequence of different interatomic distances.     

Polynuclear mixed-ligand NiII complexes containing pivalate and hexafluoroacetylacetonate ligands: a new single-molecule magnet

The reaction of NiCl₂ with excess potassium pivalate (KPiv) in ethanol affords the chainpolymeric compound KNi₄(Piv)₇(OH)₂(EtOH)₆. In the solid compound, the tetranuclear nickel fragments alternate with potassium atoms. The use of KNi₄(Piv)₇(OH)₂(EtOH)₆ in the reaction with Ni(hfac)₂ (hfac is the hexafluoroacetylacetonate anion) gave the first polynuclear mixed-ligand complexes [K₂Ni₆(Piv)₇(hfac)₃(OH)₄(HPiv)₂(Me₂CO)₂]·1.5C₇H₁₆, [Ni₆(Piv)₄(hfac)₄(OH)₄(Me₂CO)₄], [K₂Ni₈(Piv)₈(hfac)₄(OH)₆(H₂O)₂(Me₂CO)₆], [Ni₈(Piv)₁₀(hfac)₂(OH)₂(MeO)₂(MeOH)₂(HPiv)₂]·C₆H₁₄, and [Ni₁₆(Piv)₁₀(hfac)₆(OH)₁₀(MeO)₆(MeOH)₈(H₂O)₆]·C₆H₁₄ containing both Piv and hfac as the anionic ligands. The molecular and crystal structures of all these compounds were established, and their magnetic properties were studied. All solids containing simultaneously Piv and hfac ligands tend to undergo ferromagnetic ordering with decreasing temperature. The solid [Ni₈(Piv)₁₀(hfac)₂(OH)₂(MeO)₂(MeOH)₂(HPiv)₂]·C₆H₁₄ undergoes cooperative magnetic ordering below T _c (2.5 K). Dedicated to the 90th anniversary of the L. Ya. Karpov Institute of Physical Chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1175–1182, June, 2008.     

Coordination-perturbed single-molecule magnet behaviour of mononuclear dysprosium complexes

By changing the ratio of reactants, two mononuclear Dy complexes, [Dy(phen)(acac)(3)] (1) and [Dy(phen)(2)(NO(3))(2)(acac)]·H(2)O (2) have been synthesized and structurally characterized. In 1, a Dy atom bearing square-antiprism coordination geometry exhibits SMM behaviour, while compound 2 with a bicapped-square-antiprism geometry does not show such SMM properties. The different magnetic behaviours seen in 1 and 2 are probably due to a different coordination environment and ligand field around the Dy(III) ions. The results proved the important influence of the structural environment of a SMM on its magnetic behaviour.     

Phenoxido and alkoxido-bridged dinuclear dysprosium complexes showing single-molecule magnet behaviour

Two new dysprosium(iii) complexes, [Dy(2)(HL(1))(4)(CO(3))]·4H(2)O (1) and [Dy(2)(L(2))(2)(NO(3))(2)(CH(3)OH)(2)]·4CH(3)CN (2), have been synthesized from the Schiff-base ligands N'-((2-hydroxy-1-naphthyl)methylene)benzohydrazide (H(2)L(1)) and N'-((2-hydroxy-1-naphthyl)methylene) picolinohydrazide (H(2)L(2)). Single-crystal X-ray diffraction studies reveal that four mono-deprotonated H(2)L(1) ligands and two di-deprotonated H(2)L(2) ligands which have undergone keto-enol tautomerism coordinate to the two dysprosium centres of complexes 1 and 2, respectively. The dc magnetic properties of complexes 1 and 2 are different. The phenoxido bridges in complex 1 mediate antiferromagnetic interaction between Dy(III) ions, while ferromagnetic interaction was clearly observed in alkoxido-bridged dinuclear complex 2. Furthermore, both complexes show frequency-dependent ac magnetic susceptibilities, indicating a slow relaxation of the magnetization, typical of SMM behaviour.     

Gaining insight into the nanoscale properties of sol-gel-derived silicate thin films by single-molecule spectroscopy

The application of single-molecule spectroscopic methods in studies of individual nanoscale environments within sol-gel-derived silicate thin films is reviewed. Representative examples of the experiments performed and results obtained in several studies from the authors' laboratories are given. Included are investigations of the static and dynamic polarity properties of organically modified silicate (ORMOSIL) films. The results of these studies point to nonrandom variations in the film properties, providing strong evidence for the formation of phase-separated organic- and inorganic-rich domains. Studies of single-molecule diffusion through the same films yield important evidence for the formation of liquidlike silicate oligomers that facilitate probe molecule diffusion. Finally, single-molecule studies of the local pH within individual film environments are discussed. Valuable information on the contributions of local materials' acidity variations to overall sample heterogeneity is obtained. The results of immersion studies indicate that certain molecular environments are inaccessible to external solutions over periods as long as a few hours. The article concludes with a discussion of possible future challenges in this research that may be addressed by new and existing single-molecule methods.     

Mechanistic insight into fragmentation reactions of titanapinacolate complexes

Reactions between terminal alkynes or aromatic ketones and titanapinacolate complexes (DMSC)Ti(OCAr(2)CAr(2)O) (2, Ar = Ph, and 3, Ar = p-MeC(6)H(4); DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) occur via rupture of the C-C bond of the titanacycle. Thus, reactions of 2 and 3 with terminal alkynes produce 2-oxatitanacyclopent-4-ene or 2-oxatitanacycloheptadiene complexes along with free Ar(2)CO. These compounds have been characterized spectroscopically and by X-ray crystallography. Because metallapinacolate intermediates have been implicated in important C-C bond-forming reactions, such as pinacol coupling and McMurry chemistry, the mechanism of the fragmentation reactions was studied. Analysis of the kinetics of the reaction of (DMSC)Ti[OC(p-MeC(6)H(4))(2)C(p-MeC(6)H(4))(2)O] (3) with Bu(t)Ctbd1;CH revealed that the fragmentation reactions proceed via a preequilibrium mechanism, involving reversible dissociation of titanapinacolate complexes into (DMSC)Ti(eta(2)-OCAr(2)) species with release of a ketone molecule, followed by rate-limiting reaction of (DMSC)Ti(eta(2)-OCAr(2)) species with an alkyne or ketone molecule.     

Ligand field-tuned single-molecule magnet behaviour of 2p-4f complexes

Three new 2p-4f complexes of [Ln(acac)(3)(NIT-2Py)]·0.5NIT-2Py [Ln(III) = Gd(1), Dy(2)] and [Dy(tfa)(3)(NIT-2Py)]·0.5C(7)H(16) (3) (NIT-2Py = 2-(2'-pyridyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; acac = acetylacetonate and tfa = trifluoroacetylacetonate) have been synthesized, and structurally and magnetically characterized. The X-ray structural analysis exhibits that the three complexes show similar mononuclear structures, in which NIT-2Py radical chelates the Ln(III) ion through the oxygen atom of the NO group and the nitrogen atom from the pyridine ring. The static magnetic measurements on the three complexes exhibit ferromagnetic coupling between the lanthanide ion and the radical. Compared to the silence of the out-of-phase ac susceptibility of complex 3, the magnetic relaxation behavior of complex 2 is observed, suggesting single-molecule magnet behavior. The different magnetic relaxation behaviours of 2 and 3 are due to their slightly different crystal structure around the Dy(III) ions. It was demonstrated that the spin dynamic can be modified by the careful adjustment of the ligand field around the metal center.     

Tetracoordinate cobalt(II) complexes with neocuproine: single-molecule magnets with potential biological activity

Interaction of two mononuclear tetracoordinate complexes [Co(dmphen)Br₂] and [Co(dmphen)I₂] (dmphen = 2,9-dimethyl-1,10-phenanthroline), which have been recently reported to behave as single-molecule magnets (SMMs) in an applied external field, with calf thymus (CT) DNA in solution was studied by spectral methods (UV–Vis, fluorescence, and circular dichroism). Results indicate that both complexes along with their chlorido analogue [Co(dmphen)Cl₂] are able to bind with the CT DNA via intercalation, with the values of Stern–Volmer constants obtained from the linear quenching plot in range of 1.86 × 10⁴–2.11 × 10⁴ M^?1. Furthermore, Topoisomerase I inhibition studies suggest that all three complexes exhibit inhibition activity at concentrations of 45 μM.     

Synthesis of a single-molecule nanotruck

We report the synthesis of a new nanovehicle, a porphyrin-based nanotruck. The porphyrin inner core was designed for possible transportation of metals and small molecules across a surface.     

Thermodynamics, structure and properties of polynuclear lanthanide complexes with a tripodal ligand: insight into their self-assembly

Self-assembly processes between a tripodal ligand and Ln(III) cations have been investigated by means of supramolecular analytical methods. At an equimolar ratio of components, tetranuclear tetrahedral complexes are readily formed in acetonitrile. The structural analysis of the crystallographic data shows a helical wrapping of binding strands around metallic cations. The properties of this series of highly charged 3D compounds were examined by using NMR spectroscopy and optical methods in solution and in the solid state. In the presence of excess metal, a new trinuclear complex was identified. The X-ray crystal structure elucidated the coordination of metallic cations with two ligands of different conformations. By varying the metal/ligand ratio, a global speciation of this supramolecular system has been evidenced with different spectroscopic methods. In addition, these rather complicated equilibria were successfully characterised with the thermodynamic stability constants. A rational analysis of the self-assembly processes was attempted by using the thermodynamic free energy model and the impact of the ligand structure on the effective concentration is discussed.     

Interpolyelectrolyte reaction between the particles of oppositely charged microgels

Processes that take place in oppositely charged microgel particles were studied. It was shown that water-swollen microgel particles about 100 μm in size were capable of interacting in dilute and concentrated dispersions to produce continuous dispersed systems. This interaction is accompanied by the release of water and low-molecular-mass counterions of network polyelectrolytes. Their liberation is due to the interpolyelectrolyte reaction between peripheral regions of unlike charged microgel particles in the particle contact zone.     

Syntheses,structures and single-molecule magnetic behaviors of two dicubane Mn4 complexes

The reaction of MnX₂ · 4H₂O (X = Cl or Br) with 2,6-bis(hydroxymethyl)-4-methylphenol (H₃L) and NaOH in methanol solution yielded two tetranuclear manganese complexes, [Mn₄(HL)₄(MeOH)₄Cl₂] (1) and [Mn₄(HL)₄(MeOH)₄Br₂] (2). Both compounds crystallize in the monoclinic space group C₂/c with cell parameters: a = 26.0945(19) Å, b = 11.4999(8) Å, c = 21.2188(16) Å, β = 121.050(1)° and z = 4 for 1 · 2Et₂O; a = 25.8145(3) Å, b = 11.6734(2) Å, c = 21.3956(3) Å, β = 120.1277(6)° and z = 4 for 2 · 2Et₂O. Both complexes consist of a mixed-valence dicubane structure, which comprises two Mn^II and two Mn^III ions. Magnetic susceptibilities and magnetization of complexes 1 and 2 in the solid state indicate that two clusters have an S = 9 ground state. Frequency-dependent out-of-phase signals of alternating current magnetic susceptibilities were observed in the low temperature range (<3 K) for both complexes indicating a slow magnetic relaxation.     

基于席夫碱配体和两种苯甲酸盐构筑的两例Dy4配合物的合成、结构及单分子磁体性质

使用Dy (NO₃)₃·6H₂O与席夫碱配体2-(((2-羟基-3-甲氧基苄基)亚氨基)甲基)-4-甲氧基苯酚(H₂L)和2个辅助配体PhCO₂H和2-NO₂-PhCO₂H在乙醇中反应,得到2例Dy₄配合物[Dy₄(L)₄(PhCO₂)₂(NO₃)₂(EtOH)₂](1)和[Dy₄(L)₄(2-NO₂-PhCO₂)₂(NO₃)₂(EtOH)₂](2)。单晶X射线衍射解析表明配合物1和2均由Dy₂基本单元构建,形成中心对称的四核线性链状结构。配合物1和2中Dy₂单元中的一个Dy (Ⅲ)离子呈现七配位几何构型,另一个Dy (Ⅲ)离子呈现八配位几何构型。2例配合物均为单分子磁体,其能垒分别为110和108 K。通过理论计算对1和2的磁性能进行了分析。