CoII Complexes as Liposomal CEST Agents.

Three paramagnetic CoII macrocyclic complexes containing 2-hydroxypropyl pendant groups, 1,1',1'',1'''-(1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrayl)tetrakis- (propan-2-ol) ([Co(L1)]2+ , 1,1'-(4,11-dibenzyl-1,4,8,11-tetraazacyclotetradecane-1,8-diyl)bis(propan-2-ol) ([Co(L2)]2+ ), and 1,1'-(4,11-dibenzyl-1,4,8,11-tetraazacyclotetradecane-1,8-diyl)bis(octadecan-2-ol) ([Co(L3)]2+ ) were synthesized to prepare transition metal liposomal chemical exchange saturation transfer (lipoCEST) agents. In solution, ([Co(L1)]2+ ) forms two isomers as shown by 1 H NMR spectroscopy. X-ray crystallographic studies show one isomer with 1,8-pendants in cis-configuration and a second isomer with 1,4-pendants in trans-configuration. The [Co(L2)]2+ complex has 1,8-pendants in a cis-configuration. Remarkably, the paramagnetic-induced shift of water 1 H NMR resonances in the presence of the [Co(L1)]2+ complex is as large as that observed for one of the most effective LnIII water proton shift agents. Incorporation of [Co(L1)]2+ into the liposome aqueous core, followed by dialysis against a solution of 300 mOsm L-1 produces a CEST peak at 3.5 ppm. Incorporation of the amphiphilic [Co(L3)]2+ complex into the liposome bilayer produces a more highly shifted CEST peak at -13 ppm. Taken together, these data demonstrate the feasibility of preparing CoII lipoCEST agents.

Characterizing the Image Forming Particles of Modern Ungilded Daguerreotypes Using XRD and SEM.

X-ray diffraction (XRD) and high-resolution scanning electron microscopy (SEM) have been used to characterize the silver mercury amalgam particles resting on the surface that comprise the image of five daguerreotype plates that were not gilded and that were prepared by three different contemporary daguerreotype makers. The regions of interest of the surface that were examined were overexposed, solarized, and highlight (white) areas. The XRD portion of the study shows that the two main silver mercury amalgam particles identified using the International Center for Diffraction Data PF4 + database were the Schachnerite/ζ (zeta) phase amalgam, Ag1.1Hg0.9, and the mercury silver amalgam, Ag0.65Hg0.35. On one of the daguerreotypes a third silver mercury amalgam, Moschellandsbergite, Ag2Hg3, was also identified in small concentrations. High-resolution SEM images corroborate the diffraction data and show that the crystalline nature of the silver mercury amalgam particles on all five plates to be mostly hexagonal, which would correspond to the Schachnerite/ζ (zeta) phase amalgam, and fewer rectangular solid and cubic crystals corresponding to the mercury silver amalgam.

Inner-Sphere and Outer-Sphere Water Interactions in Co(II) paraCEST Agents.

High-spin Co(II) complexes are promising for development as paraCEST agents (paraCEST = paramagnetic chemical exchange saturation transfer) for magnetic resonance imaging applications. The first examples of Co(II) paraCEST agents with bound water ligands are presented here. Four Co(II) macrocyclic complexes based on 1,4,7-triazacyclononane and containing either pendent alcohol or pendent amide groups were prepared. Two of the macrocycles encapsulate the Co(II) and contain no water ligands as shown by X-ray crystallographic studies, and two complexes have macrocycles with only five ligand donor groups to leave an open coordination site for bound water. The ionization of alcohol, water, or amide groups in the complexes was characterized by using pH potentiometry. These data show that one of the complexes has a readily deprotonated group with a pKa close to 6, which is assigned as an alcohol pendent. Amide pendents deprotonate at high pH (>8), and the water ligands of the Co(II) complexes are not deprotonated at neutral pH. All complexes produce CEST peaks through either alcohol OH or amide NH proton exchange. The water ligands exchange too rapidly to produce a CEST effect as shown by variable-temperature 17O NMR spectroscopy studies. The complexes with available coordination sites for inner-sphere water ligands produce large paramagnetic shifts and broadening of the 17O resonances of bulk water, whereas the encapsulated complexes show much less shifting and broadening of 17O resonances. All complexes produce substantial paramagnetic shifts of the 1H resonances of bulk water, which is promising for the development of supramolecular CEST agents.

Low-Spin Fe(III) Macrocyclic Complexes of Imidazole-Appended 1,4,7-Triazacyclononane as Paramagnetic Probes.

Two macrocyclic complexes of 1,4,7-triazacyclononane (TACN), one with N-methyl imidazole pendants, [Fe(Mim)]3+, and one with unsubstituted NH imidazole pendants, [Fe(Tim)]3+, were prepared with a view toward biomedical imaging applications. These low-spin Fe3+ complexes produce moderately paramagnetically shifted and relatively sharp 1H NMR resonances for paraSHIFT and paraCEST applications. The [Fe(Tim)]3+ complex undergoes pH-dependent changes in NMR spectra in solution that are consistent with the consecutive deprotonation of all three imidazole pendant groups at high pH values. N-Methylation of the imidazole pendants in [Fe(Mim)]3+ produces a complex that dissociates more readily at high pH in comparison to [Fe(Tim)]3+, which contains ionizable donor groups. Cyclic voltammetry studies show that the redox potential of [Fe(Mim)]3+ is invariant with pH ( E1/2 = 328 ± 3 mV vs NHE) between pH 3.2 and 8.4, unlike the Fe(III) complex of Tim which shows a 590 mV change in redox potential over the pH range of 3.3-12.8. Magnetic susceptibility studies in solution give magnetic moments of 0.91-1.3 cm3 K mol-1 (µeff value = 2.7-3.2) for both complexes. Solid-state measurements show that the susceptibility is consistent with a S = 1/2 state over the temperature range of 0 to 300 K, with no crossover to a high-spin state under these conditions. The crystal structure of [Fe(Mim)](OTf)3 shows a six-coordinate all-nitrogen bound Fe(III) in a distorted octahedral environment. Relativistic ab initio wave function and density functional theory (DFT) calculations on [Fe(Mim)]3+, some with spin orbit coupling, were used to predict the ground spin state. Relative energies of the doublet, quartet, and sextet spin states were consistent with the doublet S = 1/2 state being the lowest in energy and suggested that excited states with higher spin multiplicities are not thermally accessible. Calculations were consistent with the magnetic susceptibility determined in the solid state.

Tuning Up an Electronic Structure of the Subphthalocyanine Derivatives toward Electron-Transfer Process in Noncovalent Complexes with C60 and C70 Fullerenes: Experimental and Theoretical Studies.

Noncovalent π-π interactions between chloroboron subphthalocyanine (1), 2,3-subnaphthalocyanine (3), 1,4,8,11,15,18-(hexathiophenyl)subphthalocyanine (4), or 4-tert-butylphenoxyboron subphthalocyanine (2) with C60 and C70 fullerenes were studied by UV-vis and steady-state fluorescence spectroscopy, as well as mass (APCI, ESI, and CSI) spectrometry. Mass spectrometry experiments were suggestive of relatively weak interaction energies between compounds 1-4 and fullerenes. The formation of a new weak charge-transfer band in the NIR region was observed in solution only for subphthalocyanine 4 when titrated with C60 and C70 fullerenes. Molecular structures of the subphthalocyanines 2 and 4 as well as cocrystallite of 4 with C60 fullerene (4···C60) were studied using X-ray crystallography. One of the C60 fullerenes in the crystal structure of 4···C60 was found in the concave region between two subphthalocyanine cores, while the other three fullerenes are aligned above individual isoindole fragments of the aromatic subphthalocyanine. The excited-state dynamics in noncovalent assemblies were studied by transient absorption spectroscopy. The time-resolved photophysics data suggest that only electron-rich subphthalocyanine 4 can facilitate an electron-transfer to C60 or C70 fullerenes, while no electron-transfer from the photoexcited receptors 1-3 to fullerenes was observed in UV-vis and transient spectroscopy experiments. DFT calculations using the CAM-B3LYP exchange-correlation functional and the 6-31+G(d) basis set allowed an estimation of interaction energies for the noncovalent 1:1 and 1:2 (fullerene:subphthalocyanine) complexes. Theoretical data suggest that the weak (∼3.5-10.5 kcal/mol) van der Waals-type interaction energies tend to increase with an increase of the electron density at the subphthalocyanine core with compound 4 being the best platform for noncovalent interactions with fullerenes. DFT calculations also indicate that 1:2 (fullerene:subphthalocyanine) noncovalent complexes are more stable than the corresponding 1:1 assemblies.

Co(II) complexes of tetraazamacrocycles appended with amide or hydroxypropyl groups as paraCEST agents.

Co(II) complexes of 1,4,7,10-tetraazacyclododecane (CYCLEN) or 1,4,8,11-tetraazacyclotetradecane (CYCLAM) with 2-hydroxypropyl or carbamoylmethyl (amide) pendants are studied with the goal of developing paramagnetic chemical exchange saturation transfer (paraCEST) agents. Single-crystal X-ray diffraction studies show that two of the coordination cations with hexadentate ligands, [Co(DHP)]2+ and [Co(BABC)]2+, form six-coordinate complexes; whereas two CYCLEN-based complexes with potentially octadentate ligands, [Co(THP)]2+ and [Co(HPAC)]2+, are seven-coordinate with only three of the four pendant groups bound to the metal center. 1H NMR spectra of these complexes suggest that the six-coordinate complexes are present as a single isomer in aqueous solution. For the complexes which are seven-coordinate in the solid state, one is highly fluxional in aqueous solution on the NMR time scale ([Co(HPAC)]2+), whereas the NMR spectrum of [Co(THP)]2+ is consistent with an eight-coordinate complex with all pendants bound. Co(II) complexes of CYCLEN derivatives show CEST effects of low intensity that are assigned to NH or OH groups of the pendants. One complex, [Co(DHP)]2+, shows a highly-shifted CEST peak at 113 ppm versus bulk water, attributed to OH protons. However, the CEST effect is largest for two Co(II) CYCLAM-based complexes with coordinated amide groups that undergo NH proton exchange. All five complexes are inert towards dissociation in buffered solutions containing carbonate and phosphate and towards trans-metalation by excess Zn(II). These data give insight into the production of an intense CEST effect for tetraazamacrocyclic complexes with pendant groups containing NH or OH exchangeable protons. The intense and highly shifted CEST peak(s) of the CYCLAM-based complexes suggest that they are promising for further development as paraCEST agents.

Tris(5-methylpyrazolyl)methane: synthesis and properties of its iron(II) complex.

The new ligand, tris(5-methylpyrazolyl)methane (1), has been prepared by the reaction of n-butyl lithium with tris(pyrazolyl)methane followed by trimethylation of the tetralithiated species with methyl iodide. The BF(4)(-), ClO(4)(-), and BPh(3)CN(-) salts of the Fe(II) complex of this ligand were also synthesized. The X-ray crystal structure of the BF(4)(-) complex (2) at 100 K had Fe-N bond lengths of 1.976 Å, indicative of a low spin Fe(II) complex, while at room temperature, the structure of this complex had a Fe-N bond distance close to 2.07 Å, indicative of an admixture of approximately 50% low-spin and 50% high-spin. The solid-state structure of the complex with a ClO(4)(-) counterion was determined at 5 different temperatures between 173 and 293 K, which allowed the thermodynamic parameters for the spin-crossover to be estimated. Mössbauer spectra of the BF(4)(-) complex further support spin-state crossover in the solid state with a transition temperature near 300 K. UV-visible spectroscopy and (1)H NMR studies of 2 show that the transition temperature in solution is closer to 400 K. No spin-crossover was observed for [Fe(1)(2)](2+)·2BPh(3)CN(-). The results allow the separation of effects of groups in the 3-position from those in the 5-position on tpm ligands, and also point toward a small cooperative effect in the spin-crossover for the Fe(II) complex.

3-De-oxy-1,2-di-O-isopropyl-idene-5-O-tosyl-d-threo-pentofuran-ose.

In the crystal structure of the title compound, C(15)H(20)O(6)S, the two independent mol-ecules crystalllize in a chiral setting with two different conformations, twisted (4)T(3) and envelope (4)E, for the furan-ose rings. Weak C-H⋯O contacts strengthen the crystal structure.

Dimethyl hydrazine-1,2-dicarboxyl-ate-triphenyl-phosphine oxide (1/1).

In the crystal structure of the title compound, C(4)H(8)N(2)O(4)·C(18)H(15)OP, two triphenyl-phosphine oxide mol-ecules and two dimethyl hydrazine-1,2-dicarboxyl-ate mol-ecules are connected via N-H⋯O hydrogen bonds of moderate strength and are related via a twofold rotational axis. Weak C(ar)-H⋯ O contacts strengthen the crystal structure.

2,6-Anhydro-1,3-di-O-benzyl-d-mannitol.

In the title compound, C(20)H(24)O(5), the six-membered pyran-ose ring adopts a chair conformation. The dihedral angle between the planes of the phenyl groups of the benzyl substituents is 63.1°. Two types of inter-molecular O-H⋯O hydrogen bonds lead to the formation of infinite chains along the b axis. Only weak C-H⋯O contacts exist between neighboring chains.

3'-O-Acetyl-2'-de-oxy-uridine.

In the two independent but very similar mol-ecules of the title compound, C(11)H(14)N(2)O(6), both nucleobase fragments are nearly planar (both within 0.01 Å) while the furan-ose rings exhibit (2)E-endo envelope conformations. In the crystal, the two 3'-O-acetyl-2'-de-oxy-uridine mol-ecules form a pseudosymmetric dimer of two bases connected via two nearly identical resonance-assisted N-H⋯O hydrogen bonds. The resulting pair is further connected with neighboring pairs via two similar O-H⋯O bonds involving the only hydroxyl group of the 2'-de-oxy-furan-ose fragment and the remaining carbonyl oxygen of the nucleobase. These inter-actions result in the formation of an infinite 'double band' along the b axis that can be considered as a self-assembled analogue of a polynucleotide mol-ecule with non-canonical Watson-Crick base pairs. The infinite chains of 3'-O-acetyl-2'-de-oxy-uridine pairs are additionally held together by C-H⋯O inter-actions involving C atoms of the uracyl base and O atoms of carbonyl groups. Only weak C-H⋯O contacts exist between neighboring chains.

6-[Bis(ethoxycarbonyl)methyl]-6-deoxy-1,2;3,4-di-O-isopropyl-idene-d-galacto-pyran-ose.

The title compound, C(19)H(30)O(9), was prepared by substitution at the C6 position in 1,2;3,4-di-O-isopropyl-idene-6-O-trifluoro-methane-sulfonyl-d-galactose using sodium eth-oxy-malonate in dimethyl-formamide. The conformation is skew-boat (0)S(2), slightly distorted towards boat B(2,5). The inflexible pyran-ose structure makes the title compound a suitable inter-mediate for further synthetic work by keeping stereogenic carbon atoms safe from inversion. Several short intra-molecular C-H⋯ O contacts may stabilize the conformation of the mol-ecule. Inter-molecular C-H⋯O inter-actions also occur.

Naphthalen-1-yl-methanol.

Apart from the OH group, the mol-ecule of the title compound, C11H10O, is almost planar with all carbon atoms located within 0.03 Šof their mean plane. In the crystal, the mol-ecules are linked by O-H⋯O hydrogen bonds, generating infinite chains running parallel to the [100] direction.

1,2-O-Iso-propyl-idene-ß-d-lyxo-furan-ose.

In the title compound C8H14O5, the pento-furan-ose five-membered ring has a twisted conformation on two carbon atoms while the five-membered ring of the iso-propyl-idene group has an envelope conformation on an oxygen atom. Hy-droxy groups are involved an infinite network of O-H⋯O hydrogen bonds that leads to the formation of a layer parallel to the (001) plane. Only weak C-H⋯O contacts exist between neighboring layers.

1,3-Bis(2-oxoprop-yl)thymine.

In the title compound [systematic name: 5-methyl-1,3-bis-(2-oxoprop-yl)pyrimidine-2,4(1H,3H)-dione], C11H14N2O4, the two 2-oxopropyl groups are nearly perpendicular to the planar thymine unit. One methyl group of oxopropyl substituent is disordered. In the crystal, C-H⋯O inter-actions help to connect the mol-ecules into (001) layers.

1,7,7-Trimethyl-3-(naphthalen-2-ylcarbon-yl)bi-cyclo-[2.2.1]heptan-2-one.

The title compound, C21H22O2, crystallizes in its keto form. The mol-ecules are connected via weak C-H⋯O inter-actions, forming infinite chains perpendic-ular to the [001] axis.

Isomeric Co(ii) paraCEST agents as pH responsive MRI probes.

A newly discovered isomer of Co(ii) (1,4,8,11-tetrakis(carbamoylmethyl)-1,4,8,11-tetraazacyclotetradecane = CCRM) produces four highly paramagnetically shifted chemical exchange saturation transfer (CEST) peaks. The 1,8-pendants of the complex are bound in a trans-arrangement to produce a Co(ii) complex of increased kinetic inertness. The isomers have a stabilized Co(ii) center (E1/2 of 540 to 550 mV versus SHE). Both the 1,8 and the 1,4-isomer are excellent pH probes in solution and in tissue homogenate by virtue of their highly paramagnetically shifted amide protons. These isomers produce both a ratiometric pH readout as well as amide proton exchange rate constants that correlate to pH.

Crystal structure of strontium and barium acesulafame (6-methyl-4-oxo-4H-1,2,3-oxa-thia-zin-3-ide 2,2-dioxide).

Both strontium and barium acesulfames, namely poly[aqua-bis-(µ3-6-methyl-2,2-dioxo-1,2λ6,3-oxa-thia-zin-4-olato)strontium(II)], [Sr(C4H4NO4S)2(H2O)] n , and the barium(II) analogue, [Ba(C4H4NO4S)2(H2O)] n , crystallize in nearly identical isotypic forms, with barium-oxygen inter-atomic distances being longer due to the larger ionic radius of the barium(II) ion. The coordination number of the metal ion is 9; the coordination polyhedra can be described as distorted capped square anti-prisms [Johnson solid J10; Johnson (1966). Can. J. Math.18, 169-200]. The conformation of the acesulafame ions is a distorted envelope with an out-of-plane S atom. Metal and acesulfame ions are assembled into infinitive chains along the [100] axis. These chains are connected via hydrogen bonds into a three-dimensional network.

Crystal structures of binary compounds of meldonium 3-(1,1,1-tri-methyl-hydrazin-1-ium-2-yl)prop-ano-ate with sodium bromide and sodium iodide.

3-(1,1,1-Tri-methyl-hydrazin-1-ium-2-yl)propano-ate (C6H14N2O2, M, more commonly known under its commercial names Meldonium or Mildronate) co-crystalizes with sodium bromide and sodium iodide forming polymeric hydrates poly[[tetra-µ-aqua-di-aqua-bis-[3-(1,1,1-tri-methyl-hydrazin-1-ium-2-yl)propano-ate]disodium] dibromide tetra-hydrate], [Na2(C6H14N2O2)2(H2O)6]Br2·4H2O, and poly[[di-µ-aqua-di-aqua-[µ-3-(1,1,1-tri-methyl-hydrazin-1-ium-2-yl)propano-ate]disodium] diiodide], [Na2(C6H14N2O2)2(H2O)4]I2. The coordination numbers of the sodium ions are 6; the coordination polyhedra can be described as distorted octa-hedra. Metal ions and M zwitterions are assembled into infinite layers via electrostatic inter-actions and hydrogen-bonded networks. These layers are connected via electrostatic attraction between halogenide ions and positive tri-methyl-hydrazinium groups into a three-dimensional structure.

Crystal structure of (S)-1-O-tert-butyl-diphenyl-silylglycerol: eight chiral mol-ecules in a triclinic cell.

The asymmetric unit of the title compound {systematic name: 3-[(tert-butyl-diphenyl-sil-yl)-oxy]propane-1,2-diol, C19H26O3Si}, contains eight chiral mol-ecules (Z' = 8). These mol-ecules are connected via a complex system of hydrogen bonds into an infinite assembly along the [100] axis; hydro-phobic tert-butyl and phenyl groups form an external coating of the assembly. These assemblies are packed by weak inter-molecular inter-actions in a peculiar formation resembling a 'header bond' masonry brick wall. Disorder of flexible fragments increases with temperature but the same crystal structure exists from 120 to 220 K (and most probably to the melting point at 334 K).