Synthesis, structure, and magnetic properties of tetranuclear cubane-like and chain-like iron(II) complexes based on the N(4)O pentadentate dinucleating ligand 1,5-bis[(2-pyridylmethyl)amino]pentan-3-ol

The tetranuclear complexes [Fe(4)(pypentO)(pym)(3)(Oac)(NCS)(3)] x 1.5EtOH (1), [Fe(4)(pypentO)(pym)(Oac)(2)(NCS)(2)(MeO)(2)(H(2)O)] x H(2)O (2), [Fe(2)(pypentO)(NCO)(3)](2) (3), and [Fe(2)(pypentO)(N(3))(3)](2) (4) have been prepared, and their structure and magnetic properties have been studied (pypentOH = 1,5-bis[(2-pyridylmethyl)amino]pentan-3-ol, pymH = 2-pyridylmethanol). The X-ray diffraction analysis of 1 (C(43)H(53)N(10)O(7.5)S(3)Fe(4), monoclinic, P2(1)/n, a = 11.6153(17) A, b = 34.391(17) A, c = 14.2150(18) A, beta = 110.88(5) degrees, V = 5305(3) A(3), Z = 4) and 2 (C(31)H(45)N(7)O(10)S(2)Fe(4), monoclinic, C2/c, a = 19.9165(17) A, b = 21.1001(12) A, c = 21.2617(19) A, beta = 104.441(10) degrees, V = 8652.7(12) A(3), Z = 8) showed a Fe(4)O(4) cubane-like arrangement of four iron(II) atoms, four mu(3)-O bridging ligands, one (1) or two (2) syn-syn bridging acetates. The X-ray diffraction analysis of 3 (C(40)H(46)N(14)O(8)Fe(4), monoclinic, P2(1)/c, a = 11.7633(18) A, b = 18.234(3) A, c = 10.4792(16) A, beta = 99.359(18) degrees, V = 2217.7(6) A(3), Z = 2) and 4 (C(34)H(46)N(26)O(2)Fe(4), monoclinic, P2(1)/c, V = 4412.4(10) A(3), a = 23.534(3) A, b = 18.046(2) A, c = 10.4865(16) A, beta = 97.80(2) degrees, Z = 4) showed a zigzag bis-dinuclear arrangement of four iron(II) cations, two mu(2)-O bridging pypentO ligands, four mu(2)-N-cyanato bridging ligands (3) or four end-on azido bridging ligands (4): they are the first examples of cyanato and azido bridged discrete polynuclear ferrous compounds, respectively. The M?ssbauer spectra of 1 are consistent with four different high-spin iron(II) sites in the Fe(4)O(4) cubane-type structure. The M?ssbauer spectra of 3 are consistent with two high-spin iron(II) sites (N(5)O and N(4)O). Below 190 K, the M?ssbauer spectra of 4 are consistent with one N(5)O and two N(4)O high-spin iron(II) sites. The temperature dependence of the magnetic susceptibility was fitted with J(1) approximately 0 cm(-1), J(2) = -1.3 cm(-1), J(3) = 4.6 cm(-1), D = 6.4 cm(-1), and g = 2.21 for 1; J(1) = 2.6 cm(-1), J(2) = 2.5 cm(-1), J(3) = - 5.6 cm(-1), D = 4.5 cm(-1), and g = 2.09 for 2; J(1) = 1.5 cm(-1), J(2) = 0.2 cm(-1), D = - 5.6 cm(-1), D' = 4.5 cm(-1), and g = 2.14 for 3; and J(1) = - 2.6 cm(-1), J(2) = 0.8 cm(-1), D= 6.3 cm(-1), D' = 1.6 cm(-1), and g = 2.18 for 4. The differences in sign among the J(1), J(2), and J(3) super-exchange interactions indicate that the faces including only mu(3)-OR bridges exhibit ferromagnetic interactions. The nature of the ground state in 1-3 is confirmed by simulation of the magnetization curves at 2 and 5 K. In the bis-dinuclear iron(II) compounds 3 and 4, the J(2) interaction resulting from the bridging of two Fe(2)(pypentO)X(3) units through two pseudo-halide anions is ferromagnetic in 3 (X = mu(2)-N-cyanato) and may be either ferro- or antiferromagnetic in 4 (X = end-on azido). The J(1) interaction through the central O(alkoxo) and pseudo-halide bridges inside the dinuclear units is ferromagnetic in 3 (X = mu(2)-N-cyanato) and antiferromagnetic in 4 (X = end-on azido). In agreement with the symmetry of the two Fe(II) sites in complexes 3 and 4, D (pentacoordinated sites) is larger than D' (octahedral sites).     

Cation-pi interactions stabilize the structure of the antimicrobial peptide indolicidin near membranes: molecular dynamics simulations

We implemented molecular dynamics simulations of the 13-residue antimicrobial peptide indolicidin (ILPWKWPWWPWRR-NH2) in dodecylphosphocholine (DPC) and sodium dodecyl sulfate (SDS) micelles. In DPC, a persistent cation-pi interaction between TRP11 and ARG13 defined the structure of the peptide near the interface. A transient cation-pi interaction was also observed between TRP4 and the choline group on DPC lipids. We also implemented simulation of a mutant of indolicidin in the DPC micelle where TRP11 was replaced by ALA11. As a result of the mutation, the boat-shaped conformation is lost and the structure becomes significantly less defined. On the basis of this evidence, we argue that cation-pi interactions determine the experimentally measured, well-defined boat-shaped structure of indolicidin. In SDS, the lack of such interactions and the electrostatic binding of the terminal arginine residues to the sulfate groups leads to an extended peptide structure. To the best of our knowledge, this is the first time that a cation-pi interaction between peptide side chains has been shown to stabilize the structure of a small antimicrobial peptide. The simulations are in excellent agreement with available experimental measurements: the backbone of the peptide is more ordered in DPC than in SDS; the tryptophan side chains pack against the backbone in DPC and point away from the backbone in SDS; the rms fluctuation of the peptide backbone and peptide side chains is greater in SDS than in DPC; and the peptide backbone order parameters are higher in DPC than in SDS.     

An "S"-shaped pentanuclear CuII cluster derived from the metal-assisted hydrolysis of pyCOpyCOpy: structural, magnetic and spectroscopic studies

Reaction of [Cu2(O2CMe)4(H2O)2] with 2,6-di-(2-pyridylcarbonyl)-pyridine (pyCOpyCOpy or dpcp) in MeCN-H2O 10:1, led to the pentanuclear copper(II) complex [Cu5(O2CMe)6{pyC(O)(OH)pyC(O)(OH)py}2] () which crystallizes in the triclinic P1 space group. The copper(II) atoms are arranged in an "S"-shaped configuration, and are bridged by the doubly deprotonated bis(gem-diol) form of the ligand, pyC(O)(OH)pyC(O)(OH)py2-. Magnetic susceptibility data indicate the interplay of both ferro- and antiferromagnetic intramolecular interactions stabilizing an S=3/2 ground state. Fitting of the data according to a next-nearest-neighbour model {H=-[J1(S1S2+S1'S2')+J2(S2S3+S3'S2')+J3(S1S3+S3'S1')+J4(S2S2')]} yields exchange coupling constants J1=+39.7 cm(-1), J2=-15.9 cm(-1), J3=-8.3 cm(-1) and J4=+4.3 cm(-1), leading to an S=3/2 ground state. X-Band EPR spectroscopy indicates a zero-field splitting of the ground state with |D3/2|=0.38 cm(-1).     

Microextraction combined with derivatization

Microextraction is still finding its niche in the world of analytical sample-preparation techniques and several alternatives have been explored for their ability to cover a wide range of analytes. Derivatization has been another important tool for analysis, especially using chromatography, and great strides have been made in developing key reactions for several classes of compounds. Combining microextraction with derivatization not only enhances analyte recovery, but also improves separation, detectability and compound identification. This article highlights operational principles, advances, directions and key strategies of microextraction combined with derivatization in analytical chemistry. The subjects covered also include design of microextraction–derivatization systems, integration of detection systems, operational requirements, derivatization reactions, typical applications and future prospects.     

Scale-up of Thermally Dried Kefir Production as Starter Culture for Hard-Type Cheese Making: An Economic Evaluation

This paper concerns the effect of thermal-drying methodology on the investment cost for dried kefir cells production in order to be used as starter culture in cheese manufacturing. Kefir cells were produced at pilot plant scale using a 250-L bioreactor and whey as the main substrate. Kefir cells were subsequently dried in a thermal dryer at 38?°C and used as a starter culture in industrial-scale production of hard-type cheeses. The use of thermally dried kefir as starter culture accelerated ripening of cheeses by increasing both lipolysis and fermentation rate as indicated by the ethanol, lactic acid, and glycerol formation. Additionally, it reduced coliforms and enterobacteria as ripening proceeded. This constituted the basis of developing an economic study in which industrial-scale production of thermally dried kefir starter culture is discussed. The industrial design involved a three-step process using three bioreactors of 100, 3,000, and 30,000 L for a plant capacity of 300 kg of thermally dried kefir culture per day. The cost of investment was estimated at 238,000 €, which is the 46% of the corresponding cost using freeze-drying methodology. Production cost was estimated at 4.9 €/kg of kefir biomass for a 300-kg/day plant capacity, which is the same as with the corresponding cost of freeze-dried cells. However, the estimated added value is up to 10.8?×?10⁹ € within the European Union.     

A New Process for Wine Production by Penetration of Yeast in Uncrushed Frozen Grapes

Different types of red and white wines were prepared by fermentation of the juice which was naturally separated from uncrushed frozen grapes during thawing (A) and from the residual juice by fermentation inside the berries (B). Yeast penetrated the skin of uncrushed grapes and fermented the content completely. The new types of wines were compared with wines prepared conventionally from the whole material of frozen grapes. Chemical and chromatographic analysis (gas chromatography (GC) and solid-phase microextraction–GC/mass spectrometry) showed similar profiles of the aroma volatiles but with significant quantitative differences among the new types of wines, which reflected to the differences observed during the sensory evaluations. The majority of identified compounds were esters, with higher amounts found in (A) wines due to the higher concentration of the must which was separated during thawing. The proposed process is new and of industrial interest for the production of different types of wines from the same raw material in one fermentation batch.