Helicene‐Grafted Silica Nanoparticles Capture Hetero‐Double‐Helix Intermediates during Self‐Assembly Gelation

A mixture of a pseudoenantiomeric ethynylhelicene (M)‐tetramer and a (P)‐pentamer forms a hetero‐double‐helix in a solution, which self‐assembles and gelates solvents. When gelation was conducted in the presence of chiral silica (P)‐nanoparticles grafted with (P)‐helicene, the resulting hetero‐double‐helix intermediate was adsorbed on the (P)‐nanoparticles, and was removed from the solution by aggregation and precipitation. The resulting precipitates contained only the hetero‐double‐helix, not random coil or clusters of the hetero‐double‐helix. (P)‐Nanoparticles did not extract the hetero‐double‐helix from the self‐assembly gels. The hetero‐double‐helix was then isolated by liberating it from the precipitates in 2‐bromopropionic acid, and was crystallized from the solution. The crystalline hetero‐double‐helices were isolated for several other combinations of pseudoenantiomeric ethynylhelicene oligomers.     

Equilibrium Shift in Solution: Molecular Shape Recognition and Precipitation of a Synthetic Double Helix Using Helicene‐Grafted Silica Nanoparticles

Chiral silica nanoparticles (70 nm) grafted with (P)‐helicene recognized the molecular shape of double helix and random coil (P)‐ethynylhelicene oligomers in solution. A mixture of the (P)‐nanoparticles and double helix precipitated much faster than a mixture of the (P)‐nanoparticles and random coil, and the precipitate contained only the double helix. The mixture of the (P)‐nanoparticles and (P)‐ethynylhelicene pentamer reversibly dispersed in trifluoromethylbenzene upon heating at 70 °C and precipitated upon cooling at 25 °C. When a 10:90 equilibrium mixture of the double helix and random coil in solution was treated with the (P)‐nanoparticles, the double helix was precipitated in 53 % yield and was accompanied by equilibrium shift.     

Alkaline Earth Metal Ion Induced Coil–Helix–Coil Transition of Lysine–Coumarin–Azacrown Hybrid Foldamers with OFF–OFF–ON Fluorescence Switching

A new metal‐ion‐responsive and fluorescent foldamer, OPLM₈ , composed of eight lysine–coumarin–azacrown units, has been designed and synthesized. The flexible OPLM₈ can be forced into a well‐defined helix structure only upon the addition of alkaline earth metal ions. The structural change is based on the crown ether moieties being positioned in the requisite arrangement along the peptide chain, that is, at i, i+4 spacing, such that the alkaline earth metal ions can mediate the formation of four sandwich complexes between them. Moreover, varying the chelator‐to‐metal‐ion ratio from 2:1 to 1:1 resulted in disassembly of the sandwich complexes leading to collapse of the helical structure to a random coil. These metal‐ion‐induced structural transitions could not only be monitored by the CD amplitude change but also easily probed by unique “OFF–OFF–ON” fluorescence intensity changes from 0.7‐fold to 14‐fold as the structure changed from the folded helix to a random coil. To further verify that the helix formation was indeed induced by metal‐ion complexation, two kinds of control octamers with only four metal‐ion chelators on the side chains were studied. One, which was capable of forming two sandwich complexes between the i and i+4 residues, displayed a negative Cotton couplet with the magnitude of its A value close to half that of OPLM₈ , and the second had four metal‐ion chelators positioned in the same turn, and hence was incapable of forming intramolecular metal complexes and showed different induced CD signals. Collectively, the photospectroscopic data and the results of the control studies suggest that alkaline earth metal ions can efficiently promote the flexible octamer OPLM₈ into a well‐organized helix by the formation of sandwich complexes between substituents at an i, i+4 spacing.     

Molecular Function of Counting the Numbers 1 and 2 Exhibited by a Sulfoneamidohelicene Tetramer

The sulfoneamidohelicene tetramer in solution exhibits different molecular responses to the same cooling stimulus delivered once and twice under thermal hysteresis conditions. Its random‐coil state at a high temperature was cooled and maintained at a given temperature for which its molecules remained in a random coil (first cooling); the resulting solution was heated and cooled, after which a helix dimer formed (second cooling). Such a property can be regarded as a molecular function of counting the numbers 1 and 2.     

Spatially Heterogeneous Nature of Self‐Catalytic Reaction in Hetero‐Double Helix Formation of Helicene Oligomers

A 1:1 mixture of pseudoenantiomeric aminomethylenehelicene oligomers, (P)‐tetramer and (M)‐pentamer, in fluorobenzene show a self‐catalytic phenomenon in the formation of hetero‐double helices from random coils. This study visualizes the spatially heterogeneous nature of the self‐catalytic reaction in dilute solution. UV/Vis imaging analysis of the mixture at 70 °C, containing random coils, exhibits a homogeneous bright area. When the solution is cooled from 70 to 30 °C and held at that temperature, dark domains of approximately 1 mm in size appear, which move approximately at a rate of 1 mm min^?1. The dark domains indicate that weaker UV/Vis absorption results from the formation of hetero‐double helices, which is supported by circular dichroism (CD) imaging experiments. Then a homogeneous mixture is regenerated upon heating to 55 °C, as shown by CD imaging. Under self‐catalytic conditions, a homogeneous solution spontaneously changed to a heterogeneous solution in the process of hetero‐double‐helix formation.     

Preferred 3D‐Structure of Peptides Rich in a Severely Conformationally Restricted Cyclopropane Analogue of Phenylalanine

Terminally blocked, homo‐peptide amides of (R,R)‐1‐amino‐2,3‐diphenylcyclopropane‐1‐carboxylic acid (c₃diPhe), a chiral member of the family of C^α‐tetrasubstituted α‐amino acids, from the dimer to the tetramer, and diastereomeric co‐oligopeptides of (R,R)‐ or (S,S)‐c₃diPhe with (S)‐alanine residues to the trimer level were prepared in solution and fully characterized. The synthetic effort was extended to terminally protected co‐oligopeptide esters to the hexamer, where c₃diPhe residues are combined with achiral α‐aminoisobutyric acid residues. The preferred conformations of the peptides were assessed in solution by FT‐IR absorption, NMR, and CD techniques, and for seven oligomers in the crystal state (by X‐ray diffraction) as well. This study clearly indicates that c₃diPhe, a sterically demanding cyclopropane analogue of phenylalanine, tends to fold peptides into β‐turn and 3₁₀‐helix conformations. However, when c₃diPhe is in combination with other chiral residues, the conformation preferred by the resulting peptides is also dictated by the chiral sequence of the amino acid building blocks. The (S,S)‐enantiomer of this α‐amino acid, unusually lacking asymmetry in the main chain, strongly favors the left‐handedness of the turn/helical peptides formed.     

NMR‐Structural Investigations of a β3‐Dodecapeptide with Proteinogenic Side Chains in Methanol and in Aqueous Solutions

The structural properties of an all‐β³‐dodecapeptide with the sequence H‐β‐HLys(N^ε‐CO(CH₂)₃‐S Acm)‐β‐HPhe‐β‐HTyr‐β‐HLeu‐β‐HLys‐β‐HSer‐β‐HLys‐β‐HPhe‐β‐HSer‐β‐HVal‐β‐HLys‐β‐HAla‐OH ( 1 ) have been studied by two‐dimensional homonuclear ¹H‐NMR and by CD spectroscopy. In MeOH solution, high‐resolution NMR spectroscopy showed that the β‐dodecapeptide forms an (M)‐3₁₄‐helix, and the CD spectrum corresponds to the pattern expected for an (M)‐3₁₄‐helical secondary structure. In aqueous solution, however, the peptide adopts a predominantly extended conformation without regular secondary‐structure elements, which is in agreement with the absence of the characteristic trough near 215 nm in the CD spectrum. The NMR and CD measurements with solutions of 1 in MeOH containing 3M urea further indicated that the peptide retains the regular secondary structural elements under these conditions, whereas, after addition of 40% (v/v) H₂O to the MeOH solution, the large ¹H‐chemical‐shift dispersion indicative of a defined spatial peptide fold was lost. The β³‐dodecapeptide is – so far – the longest β‐peptide shown to adopt a regular (M)‐3₁₄‐helix conformation in an organic solvent. The observation that the structure of this long β³‐peptide is not maintained in aqueous solution indicates that the (M)‐3₁₄‐fold is primarily stabilized by short‐range interactions.     

Prediction on Critical Micelle Concentration of Nonionic Surfactants in Aqueous Solution： Quantitative Structure-Property Relationship Approach

IntroductionCriticalmicelleconcentration (cmc)ofsurfactantsinaqueoussolutionisoneofthemostusefulparametersforcharacterizingthepropertiesofsurfactants.Overaverynarrowconcentrationrangearoundthecmctransitionsoftheexistenceofsurfactantsoccurfrommonomer ,premicel lartomicellar .Andcompanyingthesetransitions ,manyotherimportantpropertiesofsurfactantsolution ,suchassurfacetension ,interfacialtension ,conductivity ,osmoticpressure ,detergency ,emulsification ,foamingandsoon ,alsochangesharplyatthepoi…     

Characterization of Silicate Complexes in Aqueous Sodium Sulfate Solutions by FAB-MS

When the sodium ion (Na⁺) concentration is increased above 0.5 mol-dm⁻³ (M), the concentrations of dissolved silica in aqueous sodium chloride (NaCl) and sodium nitrate (NaNO₃) solutions decrease because of the salting out effect. On the other hand, the concentration of the dissolved silica in aqueous sodium sulfate (Na₂SO₄) solutions increases monotonously as the concentration of Na⁺ is increased above 0.5 M. The purpose of this study is to determine the reasons why the salting-out effect is not observed in Na₂SO₄ solutions. FAB-MS (Fast Atom Bombardment Mass Spectrometry) was used to sample directly the silica species dissolved in aqueous Na₂SO₄, NaCl, and NaNO₃ solutions. In the FAB-MS spectra of these solutions, the peak intensity ratios of the linear tetramer to the cyclic tetramer largely increased for Na⁺ concentrations between (0.1 and 1) M. This shows that some characteristics of the Na₂SO₄ solutions are similar to those of the NaCl and NaNO₃ solutions. In Na₂SO₄ solutions, however, when the concentration of Na⁺ is higher than 1 M, the peak intensity of the dimer is much higher than those of the other silicate complexes. In Na₂SO₄ solutions, the SO₄²⁻ ion undergoes partial hydrolysis to form HSO⁻₄ and OH⁻ is produced. In particular, in the range where the concentration of SO₄²⁻ is high, the pH of the solution increases slightly. This higher pH yields more dimers from the hydrolysis of silicate complexes. This increase in dimer production agrees with the observation that silica dissolves in sodium hydroxide (NaOH) solutions mainly as a dimer when the concentration of NaOH is less than 0.1 M. In Na₂SO₄ solutions at high concentrations, a salting-out effect is not observed for silica. This is due to the increase in the concentration of OH⁻, which accelerates the hydrolysis of silica and results in dimer formation.     

Molecular Thermal Hysteresis in Helix‐Dimer Formation of Sulfonamidohelicene Oligomers in Solution

Sulfonamidohelicene oligomers up to the nonamer level were synthesized by the repeated coupling reactions of a building block. A tetramer formed a helix dimer in 1,3‐difluorobenzene, which unfolded to a random coil with heating. This structural change exhibited thermal hysteresis in which different thermal responses were observed in the course of temperature increase and decrease. The feature of the hysteresis was examined under different heating/cooling modes, and the mechanisms are discussed on the basis of the population change and the presence of an induction period. A proposal regarding the use of thermal hysteresis for sensing a temperature increase/decrease is also given.     

Two‐Component Fibers/Gels and Vesicles Formed from Hetero‐Double‐Helices of Pseudoenantiomeric Ethynylhelicene Oligomers with Branched Side Chains

A methodology for the formation of fibers/gels and vesicles by molecular assembly and for controlling their properties is presented. Two‐component systems of pentamer (P)‐ 5 and tetramer (M)‐ 4 pseudoenantiomeric ethynylhelicenes with decyloxycarbonyl (D) and 4‐methyl‐2‐(2‐methylpropyl)‐1‐pentyloxycarbonyl (bD) side‐chains have been examined. Distinct aggregates were formed by changing the solvent for the three combinations of (P)‐bD‐ 5 /(M)‐bD‐ 4 , (P)‐D‐ 5 /(M)‐bD‐ 4 , and (P)‐D‐ 5 /(M)‐D‐ 4 . In toluene, (P)‐bD‐ 5 /(M)‐bD‐ 4 , (P)‐D‐ 5 /(M)‐bD‐ 4 , and (P)‐D‐ 5 /(M)‐D‐ 4 all formed gels and fibrous assemblies were observed by AFM. The minimum gel‐forming concentration (MGC) decreased in the order (P)‐bD‐ 5 /(M)‐bD‐ 4 >(P)‐D‐ 5 /(M)‐bD‐ 4 >(P)‐D‐ 5 /(M)‐D‐ 4 . In diethyl ether, vesicular formation was observed by dynamic light scattering (DLS), AFM, and TEM, and the size of the vesicles decreased in the order (P)‐bD‐ 5 /(M)‐bD‐ 4 >(P)‐D ‐ 5 /(M)‐bD‐ 4 >(P)‐D ‐ 5 /(M)‐D ‐ 4 . Both fiber/gel and vesicle formation were accompanied by enhanced CDs and redshifted UV/Vis absorption bands with a change in color to deep yellow. These are novel two‐component oligomeric systems that form assemblies of fibers/gels or vesicles depending on the solvent, and the structures and properties of the assemblies can be fine‐tuned by changing the combination of oligomers. In m‐difluorobenzene, a homogeneous solution was obtained with (P)‐D‐ 5 /(M)‐bD‐ 4 , which again exhibits enhanced CDs and redshifted UV/Vis absorptions. Vapor pressure osmometry analysis showed the formation of a bimolecular heteroaggregate. The study has indicated that pseudoenantiomeric oligomers form hetero‐double‐helices that hierarchically assemble to form fibers/gels and vesicles.     

Homo‐double helix formation of an optically active conjugated polymer bearing carboxy groups and amplification of the helicity upon complexation with achiral and chiral amines

An optically active, m‐terphenyl‐based π‐conjugated polymer bearing carboxy groups was synthesized by the copolymerization of the diethynyl monomer bearing a carboxy group with (S,S)‐2,5‐bis(2‐methylbutoxy)‐1,4‐dibromobenzene using Sonogashira reaction. The copolymer showed a weak circular dichroism (CD) in the main‐chain chromophore region due to a homo‐double helix formation with an excess helical handedness biased by the chiral alkoxy substituents through self‐association. However, upon complexation with achiral amines, such as piperidine, the CD intensity of the polymer significantly increased resulting in the formation of a greater excess one‐handed homo‐double helix via hydrogen‐bonded inclusion complexation with the achiral amines between each strand, leading to the amplification of the helicity. A preferred‐handed homo‐double helix was also induced in the polymer in the presence of nonracemic amines. The effect of the achiral and chiral amines on the homo‐double helix formation was investigated by comparing the CD spectra of the polymer to those of its model dimer. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 990–999     

Oligonucleosides with a Nucleobase‐Including Backbone. Part 11

A linear and a convergent synthesis of uridine‐derived backbone‐base‐dedifferentiated (backbone including) oligonucleotide analogues were compared. The Sonogashira cross‐coupling of the alkyne 1 and the iodide 2 gave the dimer 4 that was C‐desilylated and again coupled with 2 to give the trimer 6 (Scheme 1). Repeating this linear sequence led to the pentamer 10 . Coupling yields were satisfactory up to formation of the trimer 6 , but decreased for the coupling to higher oligomers. Similarly, coupling of the alkynes 5, 7 , and 9 with the iodouridine 3 gave, in decreasing yields, the trimer 12 , tetramer 13 , and pentamer 14 , respectively. The dimeric iodouracil 20 was synthesized by coupling the alkyne 17 with the iodide 16 to the dimer 18 , followed by iodination at C(6/I) to 19 and O‐silylation (Scheme 2). The iodinated dimer 23 was prepared by iodinating and O‐silylating the known dimer 21 . Coupling of 20 and 23 with the dimer 5 , trimer 7 , and tetramer 9 gave the tetramers 8 and 13 , the pentamers 10 and 14 , and the hexamer 15 , respectively (Scheme 3). The oligomers up to the pentamer 14 were deprotected to provide the trimer 24 , tetramer 25 , and pentamer 26 (Scheme 4). There was no evidence for the heteropairing of the pentamer 26 and rA₇ , nor for the pairing of rU₅ and rA₇, while a UV melting experiment showed the beginning of a sigmoid curve for the interaction of rU₇ with rA₇. Therefore, the pentamer 26 does not pair more strongly with rA₇ than rU₅.     

Pulsed laser polymerization study of the propagation kinetics of acrylamide in water

Pulsed laser polymerization was used in conjunction with aqueous‐phase size exclusion chromatography with multi‐angle laser light scattering detection to determine the propagation rate coefficient (k_p) for the water‐soluble monomer acrylamide. The influence of the monomer concentration was investigated from 0.3 to 2.8 M, and k_p decreased with increasing monomer concentration. These data and data for acrylic acid in water were consistent with this decrease being caused by the depletion of the monomer concentration by dimer formation in water. Two photoinitiators, uranyl nitrate and 2,2′‐azobis(2‐amidinopropane) (V‐50), were used; k_p was dependent on their concentrations. The concentration dependence of k_p was ascribed to a combination of solvent effects arising from association (thermodynamic effects) and changes in the free energy of activation (effects of the solvent on the structure of the reactant and transition state). Arrhenius parameters for k_p (M^?1 s^?1) = 10^7.2 exp(?13.4 kJ mol^?1/RT) and k_p (M^?1 s^?1) = 10^7.1 exp(?12.9 kJ mol^?1/RT) were obtained for 0.002 M uranyl nitrate and V‐50, respectively, with a monomer concentration of 0.32 M. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1357–1368, 2005     

Probing the Subunit-Subunit Interaction of the Tetramer of E. coli KDO8P Synthase by Electrospray Ionization Mass Spectrometry

Escherichia coli 3-Deoxy-D-manno-octulosonate 8-phosphate (KDO8P) synthase catalyzes the condensation reaction between D-arabinose 5-phosphate (A5P) and phosphoenolpyruvate (PEP) to form KDO8P and inorganic phosphate (Pi). This enzyme exists as a tetramer in solution, which is important for catalysis. Two different states of the enzyme were obtained: i) PEP-bound and ii) PEP-unbound. The effect of the substrates and products on the overall structure of KDO8P synthase in both PEP-bound and unbound states was examined using electrospray ionization mass spectrometry. The analysis of our data showed that the complexes of the PEP-unbound enzyme with PEP (or Pi) favored the formation of monomers, while the complexes with A5P (or KDO8P) mainly favored dimers. The PEP-bound enzyme was found to exist in the monomer and dimer with a small amount of the tetramer, whereas the PEP-unbound form primarily exists in the monomer and dimer, and no tetramer was observed, suggesting that the bound PEP have a role in stabilization of the tetrameric structure. Taken together, the results imply that the addition of the substrates or products to the unbound enzyme may alter the subunit-subunit interactions and/or conformational change of the protein at the active site, and this study also demonstrates that the electrospray ionization mass spectrometric method may be a powerful tool in probing the subunit-subunit interactions and/or conformational change of multi-subunit protein upon binding to ligand.     

Synthesis and Self‐assembly of a Helical Polymer Grafted from a Foldable Polyurethane Scaffold

Herein a polyurethane graft poly‐l ‐glutamate amphiphilic copolymer was synthesized from a polyurethane (PU)‐based macro‐initiator (containing pendant primary amine groups) through the ring opening polymerization of N‐carboxy anhydride of γ‐benzyl‐l ‐glutamate ( BLG‐NCA ). On average, twenty two l ‐glutamic acids were grafted from each amino group which was pendant on the polyurethane chain with 10 repeating units. The grafted polymer ( PU‐PP‐1 ) exhibits self‐assembly to produce a hydrogel in a wide pH window ranging from pH 5.0 to 8.0 with a critical gelation concentration (CGC) of 5.0 wt % (w/v) at pH 7.4. Furthermore, circular dichroism study revealed the transition of the α‐helix to a random coil upon increasing the pH. Due to the protonation of side chains at pH 4.0, PU‐PP‐1 adopted an α‐helical conformation whereas at pH >8.0 the side‐chain carboxylic acid groups of the PLGAs were ionized, leading to the formation of an extended random coil conformation as a result of charge repulsion. Conformational switching was also supported by FTIR spectroscopy.     

A Covalent Organic Helical Cage with Remarkable Chiroptical Amplification

Purely organic shape‐persistent chiral cages are designed through the use of rigid chiral axes. Covalent dimerization of a tripodal fragment bearing chiral allenes forms a molecular twisted prism with loop‐like lateral edges presenting 10‐fold chiroptical amplification compared to its isolated building blocks. The expected geometry of covalent organic helical cage (M,M)₃‐ 1 was confirmed by X‐ray crystal structure analysis. Comparison of the chiroptical responses of this shape‐persistent molecular container with more flexible analogues highlights how the control of the conformational freedom of the molecule can be used to obtain molecular cages with strong chiroptical responses. Selective inclusion‐complex formation with ferrocenium ions [(P,P)₃‐ 1 @Fc⁺] was confirmed and quantified with HR‐ESI‐MS and NMR spectroscopy.     

Helical Structures of Bicyclic α‐Amino Acid Homochiral Oligomers with the Stereogenic Centers at the Side‐Chain Fused‐Ring Junctions

Chiral bicyclic α‐amino acid (R,R)‐Ab_5,6=c with stereogenic centers at the γ‐position of fused‐ring junctions, and its enantiomer (S,S)‐Ab_5,6=c, were synthesized. The CD spectra of (R,R)‐Ab_5,6=c oligomers indicated that the (R,R)‐Ab_5,6=c hexapeptide formed a mixture of right‐handed (P)‐ and left‐handed (M)‐3₁₀‐helices, while, in the (R,R)‐Ab_5,6=c nonapeptide, a right‐handed (P)‐3₁₀‐helix slightly dominated over the (M)‐helix. X‐Ray crystallographic analyses of (S,S)‐tripeptide and (R,R)‐hexapeptide revealed that both the tripeptide and hexapeptide formed a mixture of (P)‐ and (M)‐3₁₀‐helices, respectively. These results indicated that the side‐chain environments around the stereogenic centers are particularly important to control the helical‐screw handedness of foldamers.     

Magnetic Control of Macromolecular Conformations in Supramolecular Anionic Polysaccharide–Iron Complexes

The anionic iota carrageenan polysaccharide is enriched with Fe^II and Fe^III by ion exchange against FeSO₄ and FeCl₃. With divalent iron, portions of polymer chains undergo a secondary structure transition from random coils to single helices. The single‐chain macromolecular conformations can be manipulated by an external magnetic field: upon exposure to 1.1 T, the helical portions exhibit 1.5‐fold stiffening and 1.1‐fold stretching, whereas the coil conformations respond much less as a result of lower contents of condensed iron ions. Along with the coil–helix transition, the trivalent iron triggers the formation of superstructures. The applicability of iron‐enriched iota carrageenan as functional ingredient for food fortification is tested by free Fe²⁺ and Fe³⁺ contents, respectively, with the most promising iota‐Fe^III yielding 53 % of bound iron, which is due to the superstructures, where the ferric ions are chelated by the supramolecularly self‐assembled polymer host.     

Rationalization of the behavior of M2(CH3CS2)4I (M = Ni,Pt) chains at room temperature from periodic density functional theory and ab initio cluster calculations

The electrical conductivities and plausible charge‐ordering states in the room temperature (r.t.) phase for MMX chains [Ni₂(dta)₄I]_∞ and [Pt₂(dta)₄I]_∞ (dta = CH₃CS) have been analyzed with periodic density functional theory (DFT) and correlated ab initio calculations combined with the effective Hamiltonian theory. Periodic DFT calculations show a more delocalized nature of the ground state in [Pt₂(dta)₄I]_∞ compared to [Ni₂(dta)₄I]_∞, which features a rather large energy gap between the occupied and empty bands, and charge polarized dimer units. A larger electrical conductivity for the Pt chain can be expected, especially because the Fermi level lies within a band with contributions from Pt and I orbitals. Electronic structure parameters extracted from ab initio cluster calculations show that the large difference between the observed conductivities at 300 K for Ni and Pt compounds, of 3 orders of magnitude, cannot be explained from the parameters extracted from an embedded M₂(dta)₄I₂ dimer fragment alone. When tetramer fragments are considered, we observe that the interdimer transfer integral (t) between neighboring M₂ units connected by an iodine atom at correlated level is comparable in both chains. On the other hand, the energy to transfer an electron from a dimer to the neighboring one (Coulomb repulsion U) is three times larger in the Ni compound with respect to the Pt chain, in line with the poor conductivity of the former. The electronic structure of the M₄(dta)₈I₃ fragment points to an alternate charge‐polarization state for Ni and an average valence state for Pt when the r.t. X‐ray structure is considered. © 2012 Wiley Periodicals, Inc.