The phosphate clamp: sequence selective nucleic acid binding profiles and conformational induction of endonuclease inhibition by cationic Triplatin complexes

The substitution-inert polynuclear platinum(II) complex (PPC) series, [{trans-Pt(NH₃)₂(NH₂(CH₂)_nNH₃)}₂-μ-(trans-Pt(NH₃)₂(NH₂(CH₂)_nNH₂)₂}](NO₃)₈, where n = 5 (AH78P), 6 (AH78 TriplatinNC) and 7 (AH78H), are potent non-covalent DNA binding agents where nucleic acid recognition is achieved through use of the ‘phosphate clamp'' where the square-planar tetra-am(m)ine Pt(II) coordination units all form bidentate N–O–N complexes through hydrogen bonding with phosphate oxygens. The modular nature of PPC–DNA interactions results in high affinity for calf thymus DNA (K_app ∼5 × 10⁷ M⁻¹). The phosphate clamp–DNA interactions result in condensation of superhelical and B-DNA, displacement of intercalated ethidium bromide and facilitate cooperative binding of Hoechst 33258 at the minor groove. The effect of linker chain length on DNA conformational changes was examined and the pentane-bridged complex, AH78P, was optimal for condensing DNA with results in the nanomolar region. Analysis of binding affinity and conformational changes for sequence-specific oligonucleotides by ITC, dialysis, ICP-MS, CD and 2D-¹H NMR experiments indicate that two limiting modes of phosphate clamp binding can be distinguished through their conformational changes and strongly suggest that DNA condensation is driven by minor-groove spanning. Triplatin-DNA binding prevents endonuclease activity by type II restriction enzymes BamHI, EcoRI and SalI, and inhibition was confirmed through the development of an on-chip microfluidic protocol.     

Conformational Polymorphism and Extensibility of DNA Quadruplexes Formed by d(GT)nRepeats

We showed earlier that oligonucleotides 3"-d(GT)₅-pO(CH₂CH₂O)₃p-d(GT)₅-3" form bimolecular quadruplexes with parallel orientation of their strands, which are held by guanine quartets alternating with unpaired thymines (GT quadruplex). This work deals with the conformational polymorphism and extensibility of G quadruplexes in complex with molecules of an intercalating agent ethidium bromide (EtBr). A cooperative mechanism of EtBr binding to the GT quadruplex was revealed. The binding constant K= (3.3 ± 0.1)·10⁴M^–1, cooperativity coefficient = 2.5 ± 0.2, and maximal amount of EtBr molecules intercalated in GT quadruplex (N= 8) were determined. It was proved experimentally by analysis of adsorption isotherms and theoretically by mathematical modeling that the GT quadruplex is capable of double extension, which is indicative of the high elasticity of this four-stranded helix. Two most stable conformations of GT quadruplexes with thymine residues intercalated and/or turned outside were found by mechanico-mathematical modeling. The equilibrium is shifted toward the conformation with the looped out thymine residues upon intercalation of EtBr molecules into the GT quadruplex.     

Additivity and non-additivity effects in the conformational changes of 1,2-ethanediol diformatein vacuo and in solution.Ab-initio and molecular mechanics descriptions

The performances of MM2 andab-initio SCF STO-3G calculations to describe conformational changes in (CH₂OCHO)₂ in vacuo and in solution are examined. We present and justify a simple procedure to add solvent effects to the MM2 conformational energies. The analysis is focused on the detection of non-additive effects in simultaneous conformational changes. We have found that the -CH₂-CH₂-group is generally effective in decoupling simultaneous conformational changes. The non-additive effects, actually present in specific classes of conformational changes, are reduced by a solvent contribution when full SCF calculations are employed, and emphasized when MM2 + solvent calculations are employed. A rationale of this finding is presented, and some suggestions are made for the correction of this artifact, due to the use of rigid charges.     

Structural basis of polyamine-DNA recognition: spermidine and spermine interactions with genomic B-DNAs of different GC content probed by Raman spectroscopy

Four genomic DNAs of differing GC content (Micrococcus luteus, 72% GC; Escherichia coli, 50% GC; calf thymus, 42% GC; Clostridium perfringens, 27% GC) have been employed as targets of interaction by the cationic polyamines spermidine {[H₃N(CH₂)₃NH₂(CH₂)₄NH₃]³⁺} and spermine {[(CH₂)₄(NH₂(CH₂)₃NH₃)₂]⁴⁺}. In solutions containing 60 mM DNA phosphate (~20 mg DNA/ml) and either 1, 5 or 60 mM polyamine, only Raman bands associated with the phosphates exhibit large spectral changes, demonstrating that B-DNA phosphates are the primary targets of interaction. Phosphate perturbations, which are independent of base composition, are consistent with a model of non-specific cation binding in which delocalized polyamines diffuse along DNA while confined by the strong electrostatic potential gradient perpendicular to the helix axis. This finding provides experimental support for models in which polyamine-induced DNA condensation is driven by non-specific electrostatic binding. The Raman spectra also demonstrate that major groove sites (guanine N7 and thymine C5H₃) are less affected than phosphates by polyamine–DNA interactions. Modest dependence of polyamine binding on genome base composition suggests that sequence context plays only a secondary role in recognition. Importantly, the results demonstrate that polyamine binding has a negligible effect on the native B-form secondary structure. The capability of spermidine or spermine to bind and condense genomic B-DNA without disrupting the native structure must be taken into account when considering DNA organization within bacterial nucleoids or cell nuclei.     

Influence of glucose-templated proline mimetics on the β-turn conformation of the peptide fragment Ac-Leu-d-Phe-Pro-Val-NMe2 found in Gramicidin S

The synthesis of tetrapeptide-based β-turn mimetics containing spirocyclic glucose-templated 3-hydroxyproline hybrids Glc3′(S)-5′(R)(CH₂OH)HypH and Glc3′(S)-5′(S)(CH₂OH)HypH as proline mimetics is presented. NMR-based conformational analysis of Ac-Leu-d-Phe-[Glc3′(S)-5′(R)(CH₂OH)HypH]-Val-NMe₂ and Ac-Leu-d-Phe-[Glc3′(S)-5′(S)(CH₂OH)HypH]-Val-NMe₂ demonstrates the presence of β-turn conformations. Different turn structures were observed by changing the stereochemistry at 5′-position of Glc3′(S)-5′(R)(CH₂OH)HypH. The major prolyl amide cis isomer of glucose-protected tetrapeptide Ac-Leu-d-Phe-[Glc(MOM)₄3′(S)-5′(R)(CH₂OMOM)HypH]-Val-NMe₂11 and glucose unprotected Ac-Leu-d-Phe-[Glc3′(S)-5′(R)(CH₂OH)HypH]-Val-NMe₂13 forms a type VI β-turn conformation. In contrast, the major prolyl amide trans rotamer of tetrapeptide Ac-Leu-d-Phe-[Glc(MOM)₄3′(S)-5′(S)(CH₂OMOM)HypH]-Val-NMe₂12 conserves a similar β-turn conformation as the Gramicidin S-based peptide fragment Ac-Leu-d-Phe-Pro-Val-NMe₂16.     

Structural dynamics of proximal heme pocket in HemAT-Bs associated with oxygen dissociation

HemAT from Bacillus subtilis (HemAT-Bs) is a heme-containing O₂ sensor protein that acts as a chemotactic signal transducer. Binding of O₂ to the heme in the sensor domain of HemAT-Bs induces a conformational change in the protein matrix, and this is transmitted to a signaling domain. To characterize the specific mechanism of O₂-dependent conformational changes in HemAT-Bs, we investigated time-resolved resonance Raman spectra of the truncated sensor domain and the full-length HemAT-Bs upon O₂ and CO dissociation. A comparison between the O₂ and CO complexes provides insights on O₂/CO discrimination in HemAT-Bs. While no spectral changes upon CO dissociation were observed in our experimental time window between 10 ns and 100 μs, the band position of the stretching mode between the heme iron and the proximal histidine, ν(Fe–His), for the O₂-dissociated HemAT-Bs was lower than that for the deoxy form on time-resolved resonance Raman spectra. This spectral change specific to O₂ dissociation would be associated with the O₂/CO discrimination in HemAT-Bs. We also compared the results obtained for the truncated sensor domain and the full-length HemAT-Bs, which showed that the structural dynamics related to O₂ dissociation for the full-length HemAT-Bs are faster than those for the sensor domain HemAT-Bs. This indicates that the heme proximal structural dynamics upon O₂ dissociation are coupled with signal transduction in HemAT-Bs.     

The lysis of isolated fish (Oncorhynchus mykiss) gill epithelial cells by surfactants

1. The interaction of a wide range of surfactants with isolated gill epithelial cells of rainbow trout (Oncorhynchus mykiss) was investigated as a function of the surfactant concentration up to and above the critical micelle concentration (cmc). The surfactants included a homologous series of n-alkyl sulphates, single and double chain tri and dimethylammonium bromides (TABs and DABs), cholates and the nonionics n-octylglucoside and Triton X-100.2. With the exception of the C₂₂ alkyl chain TAB and the double chain [(C₁₂)₂] DAB, the surfactants solubilized between 84 and 100% of the cell protein at high concentrations (>cmc).3. At low concentrations n-dodecyltrimethylammonium bromide and, to a lesser extent, Triton X-100 and sodium n-dodecylsulphate release a larger proportion of cell protein than they solubilize lipid in contrast to sodium cholate which initially preferentially solubilizes cell lipid. This differential pattern of solubilization is similar to that observed for other plasma membranes such as those of human erythrocytes and platelets.4. The surfactant concentration required to solubilize 50% (S_50%) of cell protein increases with the cmc. There is an approximately linear relationship between log(S_50%) and log cmc.5. Light microscopy shows that the surfactants at high concentrations (>cmc) fragment the secondary lamellae of the gill filaments.     

α-Chymotrypsin superactivity in aqueous solutions of cationic surfactants

α-Chymotrypsin (α-CT) activity was tested in aqueous media with the following cetyltrialkylammonium bromide surfactants in the series methyl, ethyl, propyl and butyl, different in the head group size, and for the sake of comparison also with the anionic sodium n-dodecyl sulfate and the zwitterionic myristyldimethylammonium propanesulfonate. N-glutaryl-l-phenylalanine p-nitroanilide hydrolysis rate was monitored at surfactant concentration above the critical micellar one. Only some cationic surfactants gave superactivity and the head group size had a major weight. The highest superactivity was measured in the presence of cetyltributylammonium bromide. The effect of both nature and concentration of three different buffers was also investigated. There is a dependence of enzyme superactivity on buffer type. Michaelis–Menten kinetics were found. The binding constants of substrate with micellar aggregates were determined in the used buffers and the effective improvement of reaction rate (at the same free substrate concentration in the medium) was calculated. k_cat significantly increased while K_m was little changed after correction to free substrate concentration. The ratio of k_cat to K_m was between 12 and 35 times higher than in pure buffer, depending on buffer and surfactant concentrations. The increase of α-CT activity (30%) was less important in the presence of 1×10⁻² M tetrabutylammonium bromide, a very hydrophobic salt, unable to micellise. Fluorescence spectra showed differences of enzyme conformation in the presence of various surfactants.     

Conformational changes induced by detergents during the refolding of chemically denatured cysteine protease ppEhCP-B9 from Entamoeba histolytica

EhCP-B9, a cysteine protease (CP) involved in Entamoeba histolytica virulence, is a potential target for disease diagnosis and drug design. After purification from inclusion bodies produced in Escherichia coli, the recombinant EhCP-B9 precursor (ppEhCP-B9) can be refolded using detergents as artificial chaperones. However, the conformational changes that occur during ppEhCP-B9 refolding remain unknown. Here, we comprehensively describe conformational changes of ppEhCP-B9 that are induced by various chemical detergents acting as chaperones, including non-ionic, zwitterionic, cationic and anionic surfactants. We monitored the effect of detergent concentration and incubation time on the secondary and tertiary structures of ppEhCP-B9 using fluorescence and circular dichroism (CD) spectroscopy. In the presence of non-ionic and zwitterionic detergents, ppEhCP-B9 adopted a β-enriched structure (ppEhCP-B9_β1) without proteolytic activity at all detergent concentrations and incubation times evaluated. ppEhCP-B9 also exhibits a β-rich structure in low concentrations of ionic detergents, but at concentrations above the critical micelle concentration (CMC), the protein acquires an α + β structure, similar to that of papain but without proteolytic activity (ppEhCP-B9_α + β1). Interestingly, only within a narrow range of experimental conditions in which SDS concentrations were below the CMC, ppEhCP-B9 refolded into a β-sheet rich structure (ppEhCP-B9_β2) that slowly transforms into a different type of α + β conformation that exhibited proteolytic activity (ppEhCP-B9_α + β2) suggesting that enzymatic activity is gained as slow transformation occurs.     

Complexes of the fac-{Re(CO)3} core with tridentate ligands derived from arylpiperazines

Arylpiperazines, XC₆H₄N(CH₂CH₂)₂NH, are readily alkylated to give the N-alkylpiperazines of the type XC₆H₄N(CH₂CH₂)₂N(CH₂)_nNH₂. The amine functions of these derivatives are in turn easily subjected to mono- or dialkylation to provide potentially tridentate ligands of the types XC₆H₄N(CH₂CH₂)₂N(CH₂)_nN(H)(CH₂Y) and XC₆H₄N(CH₂CH₂)₂N(CH₂)_nN(CH₂Y)(CH₂Z), respectively. The latter class of dialkylated derivatives may be symmetrically (Y=Z) or unsymmetrically (Y ≠ Z) substituted. The donor groups Y and Z of this study include pyridine, imidazole, methyl-imidazole, thiazole, carboxylate and thiolate.The reactions of these ligands with [NEt₄]₂[Re(CO)₃Br₃] yield complexes of the type [Re(CO)₃{(YCH₂)N(H)(CH₂)_n(H)_xN(CH₂CH₂)₂N(H)_yC₆H₄X}]ⁿ and [Re(CO)₃{(ZCH₂)(YCH₂)N(CH₂)_n(H)_xN(CH₂CH₂)₂N(H)_yC₆H₄X}]ⁿ where the molecular charge n (0, +1, or +2) depends on the nature of the donor groups Y and Z (whether neutral or anionic or a combination of neutral and anionic) and on the degree of protonation of the piperazine unit (x=0 or 1; y=0 or 1). This variety of tridentate chelators provides complexes with fac-{Re(CO)₃N₃}, {Re(CO)₃N₂O}, {Re(CO)₃NO₂}, {Re(CO)₃N₂S} and {Re(CO)₃NS₂} coordination geometries. The structures of the model compound [Re(CO)₃{(CH₃N₂C₃H₂CH₂)N(H)CH₂CH₂-piperidine}]Br · H₂O, [Re(CO)₃{(CH₃N₂C₃H₂CH₂)N(H)CH₂CH₂-Fphenpip}]Br, [Re(CO)₃{(NC₅H₄CH₂)N(H)CH₂CH₂-Fphenpip}]Br, [Re(CO)₃{(O₂CCH₂)₂NCH₂CH₂CH₂-CH₃OphenpipH}] · xCH₃OH (x≈0.875), [Re(CO)₃{(NC₅H₄CH₂)₂NCH₂CH₂CH₂-CH₃OphenpipH}]Br₂ · 2CH₂Cl₂ · H₂O and [Re(CO)₃{(CH₃N₂C₃H₂CH₂)(O₂CCH₂)NCH₂CH₂CH₂-CH₃OphenpipH₂}]BrCl · 1.5CH₃OH · H₂O are discussed (phenpip: phenylpiperazine, -C₆H₄N(CH₂CH₂)₂N-).     

Synthesis and characterization of a series of N3O-ligated mononuclear Mn(II) halide complexes

Treatment of a N₃O-donor chelate ligand (mpppa = N-methyl-N-((6-pivaloylamido-2-pyridyl)methyl)-N-(2-pyridylethyl)amine; bpppa = N-benzyl-N-((6-pivaloylamido-2-pyridyl)methyl)-N-(2-pyridylmethyl)amine) with equimolar amounts of Mn(ClO₄)₂ · 6H₂O and Me₄NX (X = Cl, Br, I) in methanol resulted in the production of a series of mononuclear Mn(II) halide complexes of the formula [(L)Mn-X(CH₃OH)]ClO₄ (L = mpppa or bpppa). X-ray crystallographic studies of [(mpppa)Mn-Cl(CH₃OH)]ClO₄ · CH₃OH (2 · CH₃OH), [(mpppa)Mn-Br(CH₃OH)]ClO₄ · CH₃OH (4 · CH₃OH), [(mpppa)Mn-I(CH₃OH)]ClO₄ · CH₃OH (6 · CH₃OH), and [(bpppa)Mn-I(CH₃OH)]ClO₄ · O₂(CH₂CH₃)₂ (7 · O(CH₂CH₃)₂) revealed for each a mononuclear Mn(II) center having tetradentate coordination of the chelate ligand, one coordinated halide anion, and one molecule of coordinated methanol. An increase in the Mn-X distance through the halide series (Cl, Br, I) correlates linearly with the increase in the radius of the anion. The magnetic moment of each halide complex, measured via Evans method in methanol, is consistent with the presence of a high-spin distorted octahedral Mn(II) center. The EPR features of the halide complexes in methanol do not change as a function of the nature of the halide coordinated to the Mn(II) center.     

Fatty acids,part X. Raman spectra of all dimethylene interrupted methyl cis,cis-octadecadienoates and octadecadiynoates

The Raman spectra of all the dimethylene interrupted methyl cis, cis-octadecadienoates and octadecadiynoates have been studied. The Raman band positions and their relative intensities for the ν(CC), ν(CC), ν(CO), ν(CH) and δ(CH₂) modes are recorded. The height intensity of the bands arising from ν(CC) relative to ν(CO) provides a means of determining the number of cis-ethylenic bonds in a mono-ester. In the acetylenic series, the intensity of the bands arising from ν(CC) relative to ν(CO) failed to indicate with certainty the number of acetylenic bonds in the mono-esters studied, due to the weak intensity of the band due to ν(CO). However a better correlation between the relative intensities of the ν(CC) and δ(CH₂) bands is established instead. An attempt to correlate the areas under the bands due to ν(CC), (CC), (CO) and δ(CH₂) failed to produce any significant results. The Raman spectra of the methyl octadec-cis-10-en-5-ynoate and methyl octadeca-5, 10-diynoate are also recorded.     

Temperature and pressure effects on structural and conformational properties of POPC/SM/cholesterol model raft mixtures—a FT-IR, SAXS, DSC, PPC and Laurdan fluorescence spectroscopy study

We report on the effects of temperature and pressure on the structure, conformation and phase behavior of aqueous dispersions of the model lipid “raft” mixture palmitoyloleoylphosphatidylcholine (POPC)/bovine brain sphingomyelin (SM)/cholesterol (Chol) (1:1:1). We investigated interchain interactions, hydrogen bonding, conformational and structural properties as well as phase transformations of this system using Fourier transform-infrared (FT-IR) spectroscopy, small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) coupled with pressure perturbation calorimetry (PPC), and Laurdan fluorescence spectroscopy. The IR spectral parameters in combination with the scattering patterns from the SAXS measurements were used to detect structural and conformational transformations upon changes of pressure up to 7-9 kbar and temperature in the range from 1 to about 80 °C. The generalized polarization function (GP) values, obtained from the Laurdan fluorescence spectroscopy studies also reveal temperature and pressure dependent phase changes. DSC and PPC were used to detect thermodynamic properties accompanying the temperature-dependent phase changes. In combination with literature fluorescence spectroscopy and microscopy data, a tentative p,T stability diagram of the mixture has been established. The data reveal a broad liquid-order/solid-ordered (l_o + s_o) two-phase coexistence region below 8 ± 2 °C at ambient pressure. With increasing temperature, a l_o + l_d + s_o three-phase region is formed, which extends up to ∼27 °C, where a liquid-ordered/liquid-disordered (l_o + l_d) immiscibility region is formed. Finally, above 48 ± 2 °C, the POPC/SM/Chol (1:1:1) mixture becomes completely fluid-like (liquid-disordered, l_d). With increasing pressure, all phase transition lines shift to higher temperatures. Notably, the l_o + l_d (+s_o) phase coexistence region, mimicking raft-like lateral phase separation in natural membranes, extends over a rather wide temperature range of about 40 °C, and a pressure range, which extends up to about 2 kbar for T = 37 °C. Interestingly, in this pressure range, ceasing of membrane protein function in natural membrane environments has been observed for a variety of systems.     

Pressure-dependent <Superscript>13</Superscript>C chemical shifts in proteins: origins and applications

Pressure-dependent ¹³C chemical shifts have been measured for aliphatic carbons in barnase and Protein G. Up to 200 MPa (2 kbar), most shift changes are linear, demonstrating pressure-independent compressibilities. CH₃, CH₂ and CH carbon shifts change on average by +0.23, −0.09 and −0.18 ppm, respectively, due to a combination of bond shortening and changes in bond angles, the latter matching one explanation for the γ-gauche effect. In addition, there is a residue-specific component, arising from both local compression and conformational change. To assess the relative magnitudes of these effects, residue-specific shift changes for protein G were converted into structural restraints and used to calculate the change in structure with pressure, using a genetic algorithm to convert shift changes into dihedral angle restraints. The results demonstrate that residual ¹³Cα shifts are dominated by dihedral angle changes and can be used to calculate structural change, whereas ¹³Cβ shifts retain significant dependence on local compression, making them less useful as structural restraints.     

Laser-raman study of solute-solvent interactions in aqueous solutions of d-fructose, d-glucose,and sucrose

The solute-solvent interactions of d-fructose, d-glucose, and sucrose in aqueous solution were studied by comparison of characteristic, Raman of the water and the sugar components. Shifts in frequency and intensity were observed in both the bending and the stretching regions of CH₂ and H₂O. The ratios of integrated, Raman intensities I(CH₂)/I(H₂O) of the CH₂ peak and the H₂O bending band, and I(CH)/I(OH) of the C-H stretching line to O-H stretching band were determined. Their evolutions in terms of mass-concentration display discontinuities at specific concentrations for each of the three sugars. These breaks were interpreted as changes in the hydrogen bonding of the various species.     

Synthesis and characterization of metallatranes with phenyl substituents in atrane cage

A new series of mono- and diphenylsubstituted silatranes and boratranes N(CH₂CH₂O)₂(CHR³CR¹R²O)MZ (M = Si, Z = CH₂Cl, CCPh, H, OMenth, R¹, R², R³ = H, Ph; M = B, Z = nothing, R¹, R², R³ = H, Ph) have been synthesized. Both transalkoxylation and stepwise modification of a preformed metallatrane skeleton were used. The chloromethyl derivatives N(CH₂CH₂O)₂(CHRCHRO)SiCH₂Cl (R = H, Ph) react with tert-BuOK under intramolecular cycle expansion to give 1-tert-butoxy-2-carba-3-oxahomosilatranes N(CH₂CH₂O)(CH₂CH₂OCH₂)(CHRCHRO)SiO^tBu (R = H, Ph). The treatment of boratranes N(CH₂CH₂O)₂(CH₂CR¹R²O)B (R¹,R² = H, Ph) with triflic acid and trimethylsilyl triflate results in the products of electrophilic attack at the nitrogen atom. The molecular structures of four silatranes and one boratrane bearing phenyl groups in the atrane skeleton were determined by the X-ray structure analysis.     

Improvement of methane biofiltration by the addition of non-ionic surfactants to biofilters packed with inert materials

The effect of non-ionic surfactants on the biofiltration of methane (CH₄) was analyzed. Two biofilters (BF) treating CH₄ were operated for one year at fixed CH₄ concentration of 4.8 g m⁻³ and air flow rate of 0.25 m⁻³ h⁻¹. Three polyoxyethylenes (Brijs), and 3 mono polyoxyethylenesorbitans (Tweens) were added to the nutrient solution at a concentration of 0.5% (w/w). Without surfactant, CH₄ conversion had an average level of 35%, with Brijs the CH₄ conversion varied between 38% and 46%, and with Tweens between 43% and 48%. The non-ionic surfactants decreased the biomass accumulation in the packed bed due to their detergent character. Biofilters were operated in a range of nitrogen concentration in the nutrient solution from 0.5 to 2 gN L⁻¹ using Tween 20 at a concentration of 0.5% (w/w). The EC_max observed in this study, 45 g m⁻³ h⁻¹, occurred when the nitrogen concentration was 1 gN L⁻¹.     

Raman spectra and conformations of the cis-unsaturated fatty-acid chains

Raman spectra of low (13°C) and high (16°C) m.p. crystals of oleic acid were recorded and the spectral differences were ascribed to different conformations around a pair of sp², CC axes, i.e. (skew, skew′) and (skew, skew). Crystalline modifications (m.p. 29°C and 29.5°C) of petroselinic acid were found for the first time; after spectral comparison with oleic acid conformations in those crystals were predicted to be (skew, skew′) and (skew, skew). Raman spectra of dioleoyl- and dipetroselinoyl-l-α-phosphatidylcholines were measured for different crystalline phases and the conformation was examined.The skeletal vibration bands of the polymethylene chains of cis- and trans-unsaturated fatty-acids were analysed by using the frequency-phase difference relationships of saturated fatty-acids. The ν₄ (stretching) vibrations were localised within each polymethylene chain and the bands of an acid CH₃(CH₂)_m?2CHCH(CH₂)_n?2COOH were explained in terms of the set of phase differences δ = kπ/m and kπ/n (k = 1, 2,..). A unique ν₄ vibration with δ = π/2m was also found. The ν₅ (bending) vibrations sometimes couple strongly with each other to form overall vibrations characterised by δ = kπ/(m + n).Implications of the cis-olefin group for the physical properties of phospholipid bilayers and the applicability of Raman spectroscopy in probing chain conformations were discussed.     

Synthesis and characterization of an N-coordinated amidate copper(II) complex of deprotonated N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide

The title ligand, N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide (DIPMAE-H), was prepared by a nucleophilic substitution reaction between N-(2,6-diisopropyl)phenyl-2-bromoethanamide and bis-(2-pyridylmethyl)amine. An analogous ligand (TBPMAE-H) in which the 2,6-diisopropylphenyl group was substituted for a tert-butyl group was also prepared in this manner. Then, [(DIPMAE-H)CuBr]⁺Br⁻ and [(TBPMAE-H)CuBr]⁺Br⁻ were prepared by heating one equivalent of ligand and CuBr₂ in CH₃CN. In both compounds the geometry about the copper center is square pyramidal with distortions due to the geometrical constraints of the ligand. The amide oxygen occupies the axial position, and the three amine nitrogens and the bromide ligand form the basal plane of the square pyramid. Pairs of complexes in the unit cell are associated via weak donation of a lone pair on the bromide ligand of one complex to the copper center of another (Cu?Br distances in the range of 3.3576-3.4022 Å).The title compound, (DIPMAE)CuBr, was prepared by deprotonation of [(DIPMAE-H)CuBr]⁺Br⁻ using NaH. The key feature of (DIPMAE)CuBr is the amidate group η¹- and N-coordinated to the copper center. The compound also exhibits distorted trigonal bipyramidal coordination geometry with the bromide and tertiary amine donors occupying the axial sites and the amidate and pyridyl donors occupying the equatorial positions. The copper atom is displaced from the trigonal plane towards the bromide donor apex due to the geometrical demands of the ligand.