Membrane Structure of Substance P. I. Prediction of Preferred Conformation,Orientation, and Accumulation of Substance P on Lipid Membranes

Preferred conformation, orientation, and accumulation of substance P on a neutral hydrophilic-hydrophobic interface was estimated and extrapolated to interactions with neutral and anionic lipid bilayer membranes according to our general procedure. Nine residues at the C-terminus were predicted to be transferred to the hydrophobic phase as an α-helical domain, oriented quite perpendicularly on the membrane surface. The N-terminal residues remained in the aqueous phase with their charges exposed to H₂O. The molecular amphiphilic moment vector was strong (338 arbitrary units) and pointed its hydrophilic end towards the N-terminus, only 15° away from the helix axis. The molecular electric dipole moment vector was also strong (124 debye) and pointed its positive end towards the N-terminus, only 9° away from the helix axis. Thus, it reinforced the effect of the amphiphilic moment of a peptide intruding into the membrane dipole layer. The estimated dissociation constant for the equilibrium between membrane-bound and free substance P was K_d ≈? 46 mM for neutral membranes, and K_d ≈?0.43 mM for anionic membranes with a Gouy-Chapman surface potential of ?40 mV. Thus, substance P behaved similarly to dynorphin A and adrenocorticotropin peptides which insert their N-terminal message segments as perpendicularly oriented helical domains into membranes, whereas their C-terminal address segments remain in the aqueous phase as random coils. Substance P is the first instance of a neuropeptide which is expected to insert a C-terminal message into lipid membranes.     

Membrane Structure of Substance P. III. Secondary Structure of Substance P in 2,2,2-Trifluoroethanol,Methanol, and on Flat Lipid Membranes Studied by Infrared Spectroscopy

IR data of the neuropeptide substance P ( 1 ) and its synthetic segments des-(Arg¹-Gln⁶)-substance P ( 6 ), des-(Arg¹-Pro⁴)-substance P ( 4 ), des-(Arg¹-Lys³)-substance P ( 3 ), and des-Arg¹-substance P ( 2 ) indicate predominant β-structures in the solid state and α-helical structures in CF₃CH₂OH (amide I band shape analysis). In MeOH, the spectra of 1 suggest a partly helical structure. On membranes prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, a C-terminal α-helix consisting of 8 or 9 peptide bonds appears to be induced (IR attenuated total reflection studies). Its perpendicular orientation on the membrane is suggested by the dichroic ratios of the amide-I and -II bands. This study is consistent with our CD experiments and lends support to the membrane structure of 1 predicted from the estimated amphiphilic moment, hydrophobic-association constant, and helix length.     

The Synthesis of [4-Carboranylalanine, 5-Leucine]-Enkephalin (Including an Improved Preparation of t-Butoxycarbonyl-L-o-carboranylalnine,New Derivatives of L-Propargylglycine,and a Note on Melanotropic and Opiate Receptor Binding Characteristics)

The title compound, an analogue of [Leu⁵]-enkephalin with L -o-carboranylalanine replacing L -phenylalanine in position 4, was prepared by fragment condensation. The analogue has a 3-fold higher affinity for rat brain opiate receptors in the [³H]naloxone competition assay than natural [Leu⁵]-enkephalin. Like [Leu⁵]-enkephalin and N^a-acetyl-[Leu⁵]-enkephalin, the N-terminal tripeptide fragment, H · Tyr-Gly-Gly · OH, had no melanotropic activity in the Rana pipiens frog skin assay. A convenient, direct synthesis of methyl t-butoxycarbonyl-L -propargylglycinate is described, and the ¹³C-NMR. spectra of L -o-carboranylalanine recorded. The procedure was extended to the preparation of BOC · Car-Leu · OMe from BOC · Pra-Leu · OMe. A number of new propargylglycine derivatives are reported.     

Cationic Bismuth Amides: Accessibility,Structure, and Reactivity

The synthetic access to cationic bismuth compounds based on simple, monodentate, synthetically useful amido ligands, [Bi(NR₂)₂(L)_n]⁺, has been investigated (R=Me, iPr, Ph; L=neutral ligand). With [BPh₄]^? as a counteranion, the formation of contact ion pairs and subsequent phenyl transfer from B to Bi is observed. An intermediate of this reaction, [Bi(NMe₂)₂(HNMe₂)(BPh₄)] ( 1 ), could be isolated and fully characterized. The use of a fluorinated tetraarylborate as a counteranion leads to more stable cationic bismuth amides. The solvent‐separated ion pairs [Bi₂(μ₂‐NMe₂)₂(NMe₂)₂(thf)₆]²⁺ ( 4 ) and [Bi(NiPr₂)₂(thf)₃]⁺ ( 5 ) were fully characterized, with [B(3,5‐C₆H₃(CF₃)₂)₄]^? anions balancing the positive charge. The coordination chemistry, aggregation in solution, and spectroscopic features of these compounds were investigated. Compounds 4 and 5 show an increased reactivity towards diisopropylcarbodiimide compared to their neutral parent compounds. These reactions result in formation of the first cationic bismuth guanidinates. Characterization techniques include ¹H, ¹¹B, ¹³C, ¹⁵N, ¹⁹F, and ³¹P (VT)NMR and IR spectroscopy, single crystal X‐ray diffraction analysis, and DFT calculations.     

Conformational Studies of (±)‐11,12‐Didehydro‐11‐deoxycorynoline and (+)‐11,13‐Didehydro‐11‐deoxychelidonine,Hexahydrobenzo[c]phenanthridine‐Type Alkaloid Derivatives,by X‐Ray Crystal Structure and NMR Analyses

The X‐ray crystal analyses of the two 11‐deoxy‐didehydrohexahydrobenzo[c]phenanthridine‐type alkaloid derivatives 3 and 4 , derived from (±)‐corynoline ( 1 ) and (+)‐chelidonine ( 2 ), established their structures as (±)‐(5bRS,12bRS)‐5b,12b,13,14‐tetrahydro‐5b,13‐dimethyl[1,3]benzodioxolo[5,6‐c]‐1,3‐dioxolo[4,5‐i]phenanthridine ( 3 ) and (+)‐rel‐(12bR)‐7,12b,13,14‐tetrahydro‐13‐methyl[1,3]benzodioxolo[5,6‐c]‐1,3‐dioxolo[4,5‐i]phenanthridine ( 4 ). The conformations of 3 and 4 in CDCl₃ were determined on the basis of ¹H‐ and ¹³C‐NMR spectroscopy.     

Sequencing of cyclosporins by fast atom bombardment and linked-scan mass spectrometry

The mass spectrometric sequence determination of amino acid residues in cyclosporins using fast atom bombardment, collisionally activated dissociations in the first field-free region and linked B/E scan is described. The general fragmentation scheme was derived from the spectra of cyclosporins A, B, C, D, F, G, L and [DH-MeBmt¹]CS. The main fragmentation pathways start by primary splitting between amino acids 2–3, 1–11 and 5–6. The corresponding N-terminal b-type ions are common fragment types in the mass spectra. The 1–11 splitting can be enhanced by the introduction of a lactone group into the peptide ring by conversion of cyclosporins into isocyclosporins. The fragmentation scheme was used for amino acid sequence determination in four new natural cyclosporins, [MeLeu¹]CS, [Leu⁴]CS, [Ile⁴]CS and [Leu⁵]CS.     

Homologous Silver Bismuth Chalcogenide Halides (N,x)P. III. The (4, x)P, (5, x)P,and (7, x)P Structure Families of Modular Compounds with Tunable Composition and Structure

The crystal structures of six members of the homologous series with general formula [BiQX]₂[Ag_xBi_1?xQ_2?2xX_2x?1]_N+1 (Q = S, Se; X = Cl, Br; 1/2 ≤ x ≤ 1) and N = 4, 5, or 7 were determined by single‐crystal X‐ray diffraction. The series are characterized by the parameters N and x and are denoted ^{(N, x)}P. Ag₃Bi₄S₆Cl₃ (x = 0.60) (I) , Ag_3.5Bi_3.5S₅Br₄ (x = 0.70) (II) and Ag_3.65Bi_3.35Se_4.70Br_4.30 (x = 0.73) (III) belong to ^{(4, x})P series Ag_5xBi_7?5xQ_12?10xX_10x?3 and adopt the AgBi₆S₉ structure type. The ^{(5, x)}P compound Ag_3.66Bi_4.34S_6.68Br_3.32 (IV) , which corresponds to x = 0.61 in Ag_6xBi_8?6xS_14?12xBr_12x?4, crystallizes isostructurally to AgBi₃S₅. The compounds Ag_4.56Bi_5.44Se_8.88Br_3.12 (x = 0.57) (V) and Ag_5.14Bi_4.86S_7.76Br_4.24 (x = 0.64) (VI) , which are members of ^{(7, x)}P series Ag_8xBi_10?8xQ_18?16xBr_16x?6, adopt the Ag₃Bi₇S₁₂ structure type. In the monoclinic crystal structures (space group C2/m) two kinds of layered modules alternate along [001]. Modules of type A uniformly consist of paired rods of face‐sharing monocapped trigonal prisms around Bi atoms with octahedra around mixed occupied metal positions (M = Ag/Bi) between them. Modules of type B are composed of [MZ₆] octahedra, which are arranged in NaCl‐type fragments of thickness N. All structures exhibit Ag/Bi disorder in octahedrally coordinated metal positions as well as Q/X mixed occupation of some anion positions. Corresponding to their black color, all compounds are narrow‐gap semiconductors (E_g = 0.35 eV for (II) ). General characteristics of the entire class of ^{(N, x)}P compounds are gathered in a catalogue.     

Structural Diversity in Thallium Chemistry. Part V

From thallium(III) bromide solution, the unsubstituted pyridinium cation yields a complex ( 1 ) with the [Tl₂Br₉]^3? anionic stoichiometry. The Raman spectrum and single‐crystal X‐ray crystallographic analysis showed that the salt contains independent [TlBr₄]^? and bromide anions. A variety of mono‐ and disubstituted pyridinium cations were also employed in similar syntheses. The 2‐bromopyridinium cation gave a salt 2 with [TlBr₅]^2? stoichiometry, but the crystal structure revealed very weakly interacting [TlBr₄]^? and bromide anions with a Tl ???Br^? distance of 4.1545(6) Å. The 2‐(ammoniomethyl)pyridinium and 2‐amino‐4‐methylpyridinium cations yielded complexes containing [TlBr₅]^2? ( 3 ) and [TlBr₄]^? ( 4 ) species, respectively, which were confirmed by Raman spectroscopy and X‐ray crystallographic analyses. For 3 , the [TlBr₅]^2? anion has a highly distorted trigonal bipyramidal conformation with one long axial Tl ???Br bond of 3.400(2) Å. Microanalytical results in conjunction with Raman spectra from a further five salts confirmed that they all contain the simple [TlBr₄]^? anion. N? H ???Br Hydrogen bonds clearly influence the nature of the anionic species obtained in these systems.     

Cobalt Carbonyls Stabilized by N,P-Ligands: Synthesis,Structure, and Catalytic Property for Ethylene Oxide Hydroalkoxycarbonylation

Reactions of N,P-Ligands as Ph₂P(o-NMe₂C₆H₄) (¹L), 2,6-iPr₂C₆H₃NHC(Ph)=NC₆H₄(o-PPh₂) (²L), and Ph₂PN(R)PPh₂ (R=iPr (³L), cyclo-C₆H₁₁ (⁴L), tBu (⁵L), CH₂C₄H₇O (⁶L)) each with dicobalt octacarbonyl produced complexes [¹LCo(CO)₃]₂ ( 1 ), [²LCo(CO)(μ-CO)₂Co(CO)₃] ( 2 ), [³LCo(CO)₃]⁺[Co(CO)₄]⁻ ( 3 ), [³LCo(CO)₂]₂ ( 4 ), [⁴LCo(CO)₂]₂ ( 5 ), [⁵LCo(CO)₂]⁺[Co(CO)₄]⁻ ( 6 ), and [⁶LCo(CO)₂]⁺[Co(CO)₄]⁻ ( 7 ). Complexes 1–7 have all been structurally characterized by X-ray crystallography, IR and NMR spectroscopies, and elemental analysis. Catalytic tests on transformation of ethylene oxide (EO), CO and MeOH into methyl 3-hydroxypropionate (3-HMP) indicate that complexes 1 – 7 are active, where ion-pair complexes 3 and 6 – 7 behave more excellently (by achieving 88.4–93.6% 3-HMP yields) than the neutral species 1 – 2 and 4 – 5 (35.0–46.5% 3-HMP yields) when the reactions are all operated at 2 MPa CO pressure and 50 °C in MeOH solvent. Density functional theory (DFT) study by selecting 3 as a model suggests a cooperative catalytic reaction mechanism by [Co(CO)₄]⁻ and its counter cation [³LCo(CO)₃]⁺. The cobalt-homonuclear ion-pair catalyzed hydroalkoxycarbonylation of EO is present herein.     

The Phase Diagram of the System [Ph4P]Br/BiBr3. Synthesis,Crystal Structure,Thermal Behaviour,and Vibrational Spectra of [Ph4P]3[Bi2Br9] · CH3COCH3 and two Modifications of [Ph4P]4[Bi6Br22]

The phase diagram of the system [Ph₄P]Br/BiBr₃ was investigated with the aid of DSC, TG and temperature dependent X‐ray powder diffraction measurements. By varying the reaction conditions, stoichiometry and crystallisation conditions of the reaction between BiBr₃ and [Ph₄P]Br four polynuclear bromobismuthates are formed. We report here the crystal structure of the solvation product [Ph₄P]₃[Bi₂Br₉] · CH₃COCH₃, which crystallises with monoclinic symmetry in the S. G. P2₁/n No. 14, a = 12.341(1), b = 32.005(3), c = 19.929(3) Å, β = 99.75(2)°, V = 7758(7) ų, Z = 4 and the crystal structures of two modifications of the compound [Ph₄P]₄[Bi₆Br₂₂]. The α‐form, crystallises with triclinic symmetry in the S. G. P1 No. 2, a = 13.507(4) Å, b = 14.434(4) Å, c = 17.709(5) Å, α = 81.34(2)°, β = 72.42(2)°, γ = 72.53(2)°, V = 3132.7(1) ų, Z = 2. The high‐temperature β‐form, crystallises with triclinic symmetry in the S. G. P1 No. 2, a = 13.893(4) Å, b = 14.267(3) Å, c = 16.580(3), α = 100.13(2)°, β = 96.56(2)°, γ = 110.01(2)°, V = 2985.5(1) ų, Z = 2. Lattice parameters of [Ph₄P]₄[Bi₈Br₂₈] are also given. The thermal behaviour of the compounds and in addition the vibrational spectra of [Ph₄P]₃[Bi₂Br₉] · CH₃COCH₃ are presented and discussed.     

Reactions of RSe− (R = Me,Ph) Groups in [RSeFe(CO)4I and [RSeCr(CO)5−]

The anionic [MeSeFe(CO)₄] and [MeSeCr(CO)₅] complexes were synthesized by reaction of [PPN][HFe(CO)₄] and [PPN][HCr(CO)₅] with MeSeSeMe respectively via nucleophilic cleavage of the Se-Se bond. The ease of cleavage of the Se-Se bond follows the nucleophilic strength of metal-hydride complexes. Methylation of [RSeCr(CO)₅^?] by the soft alkylating agent MeI resulted in the formation of neutral (MeSeMe)Cr(CO)₅ in THF at 0°C. In contrast, the [ICr(CO)₅^?] was isolated at ambient temperature. Reaction of [MeSeFe(CO)₄^?] or [MeSeCr(CO)₅^?] with HBF₄ yielded (CO)₃Fc(μ-SeMe)₂Fe(CO)₃ dimer and anionic [(CO )₅Cr (μ-SeMe)Cr(CO)₅^?] respectively, and no neutral (HSeMe)Fe(CO)₄ and (HSeMe)Cr(CO)₅ were detected spectrally (IR) even at low temperature. Reaction of NOBF₄ or [Ph₃C][BF₄] and [MeSeCr(CO)₅^?] resulted in the neutral monodentate (MeSeSeMe)Cr(CO)₅ complex. Addition of 1 equiv CpFe(CO)₂I to 2 equiv [MeSeCr(CO)₅^?] gave CpFe(CO)₂(SeMe) and the anionic [(CO)₅Cr(μ-SeMe)Cr(CO)₅^?] in THF at ambient temperature.     

Synthesis,characterization and monitoring of trans-[Ru{P(OMe)3}4Cl2] by reversed-phase high-performance liquid chromatography and 31P-n.m.r.

P(OMe₃)₃ reacts with RuCl₃ · 3H₂O to produce the complex trans-[Ru{P(OMe)₃}₄Cl₂] from which the complexes trans-[Ru{P(OMe)₃}₄S₂]²⁺ and cis-[Ru{P(OMe)₃}₂S₄]²⁺ (S = Solvent) can be prepared by solvation in neutral and acidic solution, respectively. The aquation takes place with a specific rate of 1.0 × 10^–2 min^–1 (pH = 3.0) and 5.4 × 10^–3 min^–1 (pH 7.0) The trans-[Ru{P(OMe)₃}₄Cl₂] complex has been characterized by elemental analysis; electronic spectra [_max = 408 nm] ( = 1.7 × 10² M^–1 cm^–1), _max = 250 nm ( = 3.5 × 10³ M^–1 cm^–1) and a shoulder at = 280 nm ( 8.3 × 10² M^–1 cm^–1)]; cyclic voltametry ( = 0.75 V versus s.c.e.); HPLC (t _R = 5.7 min); and ³¹P-n.m.r. ( = 131 p.p.m.). In acidic solutions the ³¹P-n.m.r. variations point to a reaction intermediate, characterized as the complex ion trans-[Ru{P(OMe)₃}₄S₂]²⁺ ( = 136 p.p.m.) followed by the formation of the proposed product, cis-[Ru{P(OMe)₃}₂S₄]²⁺ ( = 145 p.p.m.). For this same complex, at pH = 7.0, the results show the formation of the trans-[Ru{P(OMe)₃}₄S₂]²⁺ ( = 136 p.p.m.). The HPLC results for the trans-[Ru{P(OMe)₃}₄Cl₂] complex show that the different species are present at different pH values. In acidic media a less polar species (t _R = 4.3 min) compared with the starting material (t _R = 5.7 min) was formed. At neutral pH (t _R = 4.6 min) the species generated were not modified, however they exhibited different properties from the species obtained at a lower pH.     

Molten Salt Synthesis, Crystal Structure and Optical Properties of a Novel Quaternary Metal Selenide, K2AgIn3Se6

K2AgIn3Se6 was synthesized by a molten-salt (alkali-metal polyselenide flux) reaction at 500 ℃. The orange red granular crystal crystallizes in monoclinic space group C2/c with cell parameters, a=1.16411(7) nm, b=1.16348(8) nm, c=2.14179(12) nm, V=2.8740(9) nm^3, and Z=8. The crystal has a new two-dimensional structure containing ^2∞[AgIn3Se6]^2- anionic layers separated by K^- cations and the ^2∞[AgIn3Se6]^2- layer is constructed with corner-shared [AgSe4] and [InSe4] tetrahedra. The optical band gap of K2AgIn3Se6 was determined to be ca. 2.9 eV by UV/vis/NIR diffuse reflectance spectra.     

The Preparation and X-Ray Structure of [AsPh4][Ph2P(S)NSiMe3] · 0.5 THF

The reaction of Ph₂P(S)N(SiMe₃)₂ with potassium tert-butoxide in a 1:1 molar ratio produces K[Ph₂P(S)NSiMe₃], which was converted to the AsPh₄⁺ salt by metathesis with [AsPh₄]Cl. The X-ray crystal structure of [AsPh₄][Ph₂P(S)NSiMe₃] · 0.5 THF consists of noninteracting AsPh₄⁺ and Ph₂P(S)NSiMe₃^? ions with d(P? S) = 1.980(4) Å and d(P? N) = 1.555(8) Å. The PNSi bite angle in the anion is 136.3(5)°. Electrophilic attack by Ph₂P(S)Cl occurs at the sulfur atom of Ph₂P(S)NSiMe₃^?. The oxidation of the anion with iodine produces a disulfide which regenerates K[Ph₂P(S)NSiMe₂] upon treatment with potassium tert-butoxide.     

Binding of Cu+ and Cu2+ with peptides: Peptides = oxytocin,Arg8‐vasopressin,bradykinin, angiotensin‐I,substance‐P,somatostatin, and neurotensin

The intrinsic binding ability of 7 natural peptides (oxytocin, arg⁸‐vasopressin, bradykinin, angiotensin‐I, substance‐P, somatostatin, and neurotensin) with copper in 2 different oxidation states (Cu^I/II) derived from different Cu^+/2+ precursor sources have been investigated for their charge‐dependent binding characteristics. The peptide‐Cu^I/II complexes, [M − (n‐1)H + nCu^I] and [M − (2n‐1)H + nCu^II], are prepared/generated by the reaction of peptides with CuI solution/Cu‐target and CuSO₄ solution and are analyzed by using matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight mass spectrometry. The MALDI mass spectra of both [M − (n‐1)H + nCu^I] and [M − (2n‐1)H + nCu^II] complexes show no mass shift due to the loss of ─H atoms in the main chain ─NH of these peptides by Cu⁺ and Cu²⁺ deprotonation. The measured m/z value indicates the reduction of Cu^I/II oxidation state into Cu⁰ during MALDI processes. The number and relative abundance of Cu⁺ bound to the peptides are greater compared with the Cu²⁺ bound peptides. Oxytocin, arg⁸‐vasopressin, bradykinin, substance‐P, and somatostatin show the binding of 5Cu⁺, and angiotensin‐I and neurotensin show the binding of 7Cu⁺ from both CuI and Cu targets, while bradykinin shows the binding of 2Cu²⁺, oxytocin, arg⁸‐vasopressin, angiotensin‐I, and substance‐P; somatostatin shows the binding of 3Cu²⁺; and neurotensin shows 4Cu²⁺ binding. The binding of more Cu⁺ with these small peptides signifies that the bonding characteristics of both Cu⁺ and Cu²⁺ are different. The amino acid residues responsible for the binding of both Cu⁺ and Cu²⁺ in these peptides have been identified based on the density functional theory computed binding energy values of Cu⁺ and the fragment transformation method predicted binding preference of Cu²⁺ for individual amino acids.     

Nuclear magnetic resonance data of pyrido[2,3-B] pyrazines and their σ-adducts with amide ion and water

¹³C nmr spectral data of the parent substance pyrido[2,3-b]pyrazine and several of its derivatives (containing one or more chloro, amino, oxo, bromo, fluoro, phenyl, methyl, hydrazino or t-butyl substituents) are reported. The ¹³C nmr spectrum of the parent substance has been assigned conclusively by ¹³C-labelling. Additionally we proved, the existence of anionic 1:1 σ-adducls i.e., 3-amino-3,4-dihydropyrido[2,3-b]pyrazine, the formation of 3-amino-2-t-butyl-6-chloro-3,4-dihydropyrido[2,3-b]pyrazinide ion and by ¹H nmr spectroscopy 2-amino-1,2-dihydro-3-phenylpyrido[2,3-b]pyrazinide ion. The ¹³C nmr data of the cation of the dihydrale 2,3-dihydroxy-1,2,3,4-tetrahydropyrido[2,3-b]pyrazine, present in a solution of the parent compound in N hydrochloric acid, are given.     

Structure of the neutral metal complex Pt(dddt)2

A neutral metal complex, [Pt(dddt)₂]° (1), has been obtained by oxidation of the [Pt(dddt)₂]^– anion with excess (Bu₄N)AuBr₄ in nitrobenzene. Crystallographic data for 1a=17.854(9) Å,b=18.409(9) Å,c=4.717(5) Å, =68.83(2)°, space group P2₁/n,Z=4,d _calc=2.55 g/cm³. In1 two independent centrosymmetric [Pt(dddt)₂]° molecules are packed in stacks that form layers parallel to the (110) plane. The molecules of1 in the layers have shortened S...S contacts 3.491(9) Å, and 3.594(10) Å. The average bond lengths Pt-S 2.242(7) Å, S-C 1.71(2) Å and C=C 1.40(3) Å, together with the square-planar coordination of Pt in PtS₄, suggest considerable conjugation in the metal cycles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1207–1209, July, 1993.     

Tetracyanoquinodimethane complexes of nickel(II) with an N,O-donor macrocycle

A nickel(II) chelate, NiL¹Cl₂, has been obtained by reaction of nickel(II) chloride with a 15-membered N,O-donor macrocyclic ligand. Single-crystal X-ray studies reveal an octahedral environment around nickel(II). 7,7′,8,8′-Tetracyanoquinodimethane (tcnq) derivatives of the nickel(II) chelate were prepared by reaction with Litcnq and Et₃N(tcnq)₂. Spectroscopic measurements show the presence of only anionic tcnq in [NiL₁(tcnq)₂]·4H₂O and a mixture of non-coordinating anionic and neutral tcnq species in [NiL₁](tcnq)₄·H₂O.     

Drei Alkalimetall‐Erbium‐Thiophosphate: Von der Schichtstruktur bei KEr[P2S7] zur dreidimensionalen Vernetzung in NaEr[P2S6] und Cs3Er5[PS4]6

Three Alkali‐Metal Erbium Thiophosphates: From the Layered Structure of KEr[P₂S₇] to the Three‐Dimensional Cross‐Linkage in NaEr[P₂S₆] and Cs₃Er₅[PS₄]₆ The three alkali‐metal erbium thiophosphates NaEr[P₂S₆], KEr[P₂S₇], and Cs₃Er₅[PS₄] show a small selection of the broad variety of thiophosphate units: from ortho‐thiophosphate [PS₄]^3? and pyro‐thiophosphate [S₃P–S–PS₃]^4? with phosphorus in the oxidation state +V to the [S₃P–PS₃]^3? anion with a phosphorus‐phosphorus bond (d(P–P) = 221 pm) and tetravalent phosphorus. In spite of all differences, a whole string of structural communities can be shown, in particular for coordination and three‐dimensional linkage as well as for the phosphorus‐sulfur distances (d(P–S) = 200 – 213 pm). So all three compounds exhibit eightfold coordinated Er³⁺ cations and comparably high‐coordinated alkali‐metal cations (CN(Na⁺) = 8, CN(K⁺) = 9+1, and CN(Cs⁺) ≈ 10). NaEr[P₂S₆] crystallizes triclinically ( ; a = 685.72(5), b = 707.86(5), c = 910.98(7) pm, α = 87.423(4), β = 87.635(4), γ = 88.157(4)°; Z = 2) in the shape of rods, as well as monoclinic KEr[P₂S₇] (P2₁/c; a = 950.48(7), b = 1223.06(9), c = 894.21(6) pm, β = 90.132(4)°; Z = 4). The crystal structure of Cs₃Er₅[PS₄] can also be described monoclinically (C2/c; a = 1597.74(11), b = 1295.03(9), c = 2065.26(15) pm, β = 103.278(4)°; Z = 4), but it emerges as irregular bricks. All crystals show the common pale pink colour typical for transparent erbium(III) compounds.     

NMR Solution Structure of Phospholamban

Phospholamban (PLN), an amphipathic intrinsic membrane protein of 52 amino acids, is the modulator of the Ca²⁺ pump of cardiac, slow‐twitch, and smooth‐muscle sarcoplasmic reticulum. In response to β‐adrenergic stimulation, it becomes phosphorylated at Ser¹⁶ and/or Thr¹⁷, and dissociates from the pump, which, in turn, achieves its full activity. Here we present the three‐dimensional structure of chemically synthesized, monomeric PLN in an organic solvent. Monomerization (PLN normally forms homopentamers) was obtained by replacing Cys⁴¹ with phenylalanine (Phe=F), a modification that did not affect biological activity. The structure was determined by high‐resolution NMR in CHCl₃/MeOH of the unphosphorylated state of [F⁴¹]PLN (C41F). Of the hydrophilic cytoplasmic parts IA (Met¹ to Pro²¹) and IB (Gln²² to Asn³⁰) and the membrane‐spanning hydrophobic domain II (Leu³¹ to Leu⁵²) of PLN, domain IA, which contains the two phosphorylation sites Ser¹⁶ and Thr¹⁷, and domain II have been suggested to be helical and connected through the less‐structured hinge‐region IB. In the structural study presented here, [F⁴¹]PLN is composed of two α‐helical regions connected by a β‐turn (type III). The residues of the β‐turn (type III) are Thr¹⁷, Ile¹⁸, Glu¹⁹, and Met²⁰, the first being one of the two phosphorylation sites (Ser¹⁶ and Thr¹⁷). The hinge region is located at the C‐terminal end of domain IA, and domain IB is part of a second helix. The two α‐helices comprising amino acids 4 – 16 and 21 – 49 are well‐defined (the root‐mean‐square deviations for the backbone atoms, calculated for a family of the structures, are 0.58 and 0.92 Å, resp.). Pro²¹ is at the beginning of the C‐terminal helix and in the trans conformation.