A series of trimetallic Zn-Dy-Zn complexes of the general formula ZnX(μ-L)Dy(μ-L)XZnY·nS, where H2L is the compartmental ligand ...N,N'-dimethyl-N,N'-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylenediamine, X is the coligand (X = Cl, Br, I and N3), Y is the counteranion and S are the crystallization solvent molecules have been synthesized and magnetically characterized. In all these complexes, the Dy(iii) ions exhibit DyO8 coordination environments with a slightly distorted square-antiprism D4d symmetry. Due to the disposition of the oxygen atoms around the Dy(iii) ions, large easy-axis anisotropy is expected, which is responsible for the high thermal energy barriers for the reversal of the magnetization observed at zero field (in the 144-170 K range for all complexes). A preliminary correlation between the disposition of the oxygen atoms of the ligand (phenoxo and aldehyde) in the DyO8 coordination sphere and the value of Ueff has been established.
The elasticity (stretched/compressed) and helical sense (clockwise/anticlockwise) of a dynamic helical poly(phenylacetylene) (PPA), bearing (R)- alpha -methoxytrifluorophenyl acetic acid (MTPA) ...pendants poly-(R)-1, can be selectively controlled by the donor and the polar character of the solvent. The basis for this effect lies on the presence in the pendants of two independently tuneable bonds: (O&z.dbd; )C-C(-O) and (H-)N-C(&z.dbd; O). An increase in polarity shifts the conformational equilibrium of the (O&z.dbd; )C-C(-O) bond in favour of the most polar synperiplanar(sp) conformer, that is more sterically demanding, thus forcing the polymer to invert its helix. A donor solvent associates with the (H-)N-C(&z.dbd; O) bond favouring the shift to the cisform of the amide and inducing both the elongation of the polymer chain and the inversion of the helical sense (visualized as UV-Vis bathochromic shift and CD inversion respectively). This ability of poly-(R)-1 to respond to donor/polar properties occurs in solution as well as in film state. Poly-(R)-1 presents in CHCl sub(3) identical helical sense for both the internal (polyene backbone) and for the external (described by the pendants) helices (3/1 clockwise), while in THF their senses are opposite (internal anticlockwise; external 2/1 clockwise), as proven by DSC.
In this work a family of multidimensional (2‐(1H‐tetrazol‐5‐yl)ethyl) amino acid coordination compounds have been synthesized and thoroughly characterized. For this purpose, glycine, valine, ...phenylalanine and tyrosine have been selected as starting amino acids and Mn2+, Zn2+ and Cd2+ as metallic nodes. From one side, for Mn2+ based dimer magnetic resonance imaging studies have been conducted, prompted by the number and disposition of the coordinated water molecules and taking into consideration the promising future of manganese‐based coordination compounds as bio‐compatible substitutes to conventional Gd based contrast agents. From another side, d10 block metal‐based complexes allowed exploring photoluminescence properties derived by in situ synthesized ligands. Finally, amino acid preserved structural chirality allowed us to examine chiroptical properties, particularly focusing on circularly polarized luminescence.
A family of multidimensional coordination compounds have been synthesized based on glycine, valine, phenylalanine and tyrosine. Magnetic resonance imaging studies and chiroptical properties have been explored.
Vaccines based on isolated polysaccharides successfully protect humans from bacterial pathogens such as Streptococcus pneumoniae. Because polysaccharide production and isolation can be technically ...challenging, glycoconjugates containing synthetic antigens are an attractive alternative. Typically, the shortest possible oligosaccharide antigen is preferable as syntheses of longer structures are more difficult and time-consuming. Combining several protective epitopes or polysaccharide repeating units as blocks by bonds other than glycosidic linkages would greatly reduce the synthetic effort if the immunological response to the polysaccharide could be retained. To explore this concept, we bridged the well-understood and immunologically potent RU of S. pneumoniae serotype 14 (ST14) with an aliphatic spacer and conjugated it to the carrier protein CRM197. Mice immunized with the spacer-bridged glycan conjugates produced high levels of specific antibodies after just one or two vaccine doses, while the tetrasaccharide repeating unit alone required three doses. The antibodies recognized specifically ST14 CPS, while no significant antibody levels were raised against the spacer or unrelated CPS. Synthetic vaccines generated antibodies with opsonic activity. Mimicking polysaccharides by coupling repeating unit antigens via an aliphatic spacer may prove useful also for the development of other glycoconjugate vaccine candidates, thereby reducing the synthetic complexity while enhancing a faster immune response.
Detailed structural characterization and photoluminescence properties of four new metal–organic frameworks (MOFs) based on zinc(II) or cadmium(II) metal ions, di- or tricarboxylic aromatic ligands, ...and bipyridyl-like elongated ancillary linkers, namely, {Zn2(μ4-bdc)2(μ-pbptz)·2DMF·3H2O} n (1), {Cd(μ3-bdc)(μ-pbptz)·3DMF} n (2), {Cd3(μ5-btc)2(μ-pbptz)·2DMF} n (3), and {Zn2(μ-dhbdc)2(μ-pbptz)(DMF)4·2DMF·H2O} n (4) (where bdc = benzene-1,4-dicarboxylato, btc = benzene-1,3,5-tricarboxylato, dhbdc = 2,5-dihydroxobenzene-1,4-dicarboxylato, pbptz = 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine, DMF = N,N-dimethylformamide) are reported. The occurrence of large accessible volumes and structural and topological diversity are a constant for crystal structures of these compounds, which is a result of the connectivity established among the metal-carboxylato building units formed in each case. Three-dimensional (3D) pcu frameworks of compounds 1 and 2 are built from the linkage of dimeric cores (established by the coordination of dicarboxylato bdc ligands) into two-dimensional networks that are further joined together by ancillary ligands, whereas the novel jcr7 topological 3D framework is achieved in 3 owing to the presence of the tricarboxylic btc ligand. Two-dimensional layers are generated in 4 given the bidentate coordination of both dhbdc and pbptz ligands. Interestingly, most crystal structures (3D frameworks of 1, 2, and 3) exhibit open architectures containing large solvent-occupied void systems that account for high relative void volumes. A deep analysis of the photophysical properties has been also accomplished for all compounds, confirming an overall blue emission under UV excitation in the steady state. Compound 3 is characterized with a strong phosphorescent emission that lasts a few seconds and is observed by the naked eye, which constitutes an infrequent photoluminescent behavior for metal–organic materials.
We have prepared a bis(compartmental) Mannich base ligand H
4
L (1,4,8,11-tetraaza-1,4,8,11-tetrakis(2-hydroxy-3-methoxy-5-methylbenzyl)cyclotetradecane) specifically designed to obtain bis(TM
II
Ln
...III
) tetranuclear complexes (TM = transition metal). In this regard, we have succeeded in obtaining three new complexes of the formula Zn
2
(μ-L)(μ-OAc)Dy
2
(NO
3
)
2
·Zn
2
(μ-L)(μ-OAc)Dy
2
(NO
3
)(OAc)·4CHCl
3
·2MeOH (
1
) and TM
2
(μ-H
2
L)
2
(μ-succinate)Ln
2
(NO
3
)
2
(NO
3
)
2
·2H
2
O·6MeOH (TM
II
= Zn, Ln
III
= Dy (
2
); TM
II
= Co, Ln
III
= Dy (
3
)). Compound
1
contains two different bis(ZnDy) tetranuclear molecules that cocrystallize in the structure, in which acetato bridging ligands connect the Zn
II
and Dy
III
ions within each ZnDy subunit. This compound does not exhibit slow magnetic relaxation at zero field, but it is activated in the presence of an applied dc magnetic field and/or by Dy/Y magnetic dilution, showing two relaxation processes corresponding to each of the two different bis(ZnDy) units found in the structure. As revealed by the theoretical calculations, magnetic relaxation in
1
is single-ion in origin and takes place through the first excited state of each Dy
III
ion. When using the succinato dicarboxylate bridging ligand instead of acetate, compounds
2
and
3
were serendipitously formed, which have a closed structure with the succinate anion bridging two ZnDy subunits belonging to two different ligands. It should be noted that only compound
2
exhibits slow relaxation of magnetization in the absence of an external magnetic field. According to experimental and theoretical data,
2
relaxes through the second excited Kramers doublet (
U
eff
= 342 K). In contrast,
3
displays field-induced SMM behaviour (
U
eff
= 203 K). However, the Co/Zn diluted version of this compound
3
Zn
shows slow relaxation at zero field (
U
eff
= 347 K).
Ab initio
theoretical calculations clearly show that the weak ferromagnetic coupling between Co
II
and Dy
III
ions is at the origin of the lack of slow relaxation of this compound at zero field. Compound
2
and its diluted analogues
2
Y
and
3
Zn
show hysteresis loops at very low temperature, thus confirming their SMM behaviour. Finally, compounds
1
and
2
show Dy
III
based emission even at room temperature that, in the case of
2
, allows us to extract the splitting of the ground
6
H
15/2
term, which matches reasonably well with theoretical calculations.
Introducing a dicarboxylate linker in a linear tetranuclear bis(ZnDy) complex enables the serendipitous formation of a cyclic version of the system with a
U
eff
= 342 K.
Two novel Ce(
iii
) metal organic frameworks (MOFs) with formulas Ce(5Meip)(H-5Meip)
n
GR-MOF-17
and CeCl(5Meip)(DMF)
n
GR-MOF-18
(5Meip = 5-methylisophthalate, DMF =
N
,
N
-dimethylformamide) have ...been synthesized, forming 3-dimensional frameworks. Magnetic measurements show that both compounds present field-induced slow magnetic relaxation under a small applied dc field. For
GR-MOF-17
, the temperature dependence of relaxation times is best described by a Raman mechanism, whereas for
GR-MOF-18
, relaxation occurs through a combination of Raman and local-mode pathways. Moreover, when avoiding short Ce Ce interactions by magnetic dilution in
GR-MOF-17@La
and
GR-MOF-18@La
, only the local-mode mechanism is responsible for magnetic relaxation. Photophysical studies show the occurrence of ligand-centred luminescence in both compounds and phosphorescence emission at low temperature for
GR-MOF-17
.
Two novel Ce(
iii
) metal organic frameworks (MOFs) with formulas Ce(5Meip)(H-5Meip)
n
GR-MOF-17
and CeCl(5Meip)(DMF)
n
GR-MOF-18
(5Meip = 5-methylisophthalate, DMF =
N
,
N
-dimethylformamide) have been synthesized, forming 3-dimensional frameworks.
The performance of the traffic system can drastically drop when nonrecurrent congestion caused by incidents occurs. Early detection and clearing of traffic incidents will enable the mitigation of the ...congestion and early restoration of normal traffic conditions. The research in this paper utilized the vehicle information from the recent technological advancement in transportation systems, connected vehicles (CV), and loop-detector information for nonconnected vehicles (NCVs) and developed a novel algorithm to (1) control traffic signals for normal traffic conditions in the absence of incidents, (2) detect traffic incidents using CV/NCV information, and (3) control traffic signals during the occurrence and dissipation of incidents. All the 3 strategies were integrated into one algorithm, which runs as per the real-time traffic conditions, in the presence or absence of incidents. Space-mean speeds of the vehicles on nonincident lanes and throughput maximization criteria were taken as the indicators for the activation of specific signal timings directed at the incident-affected approach. Diverse incident scenarios were tested on a four-legged isolated intersection using the VISSIM simulation tool. Incident detection results showed a higher detection rate and lower mean detection time at higher CV penetration and higher traffic volumes, and at the incident locations nearer to the stop-line. The proposed incident-responsive signal control strategy at 40% and higher CV penetration showed better performance over EPICS adaptive signal control solution, in reducing average travel time delay and the average number of stops per vehicle.
The reaction of {RhCl(COD)}2 (COD = 1,5-cyclooctadiene) with L = pyrazole (Hpz), 3(5)-methylpyrazole (Hmpz) or 3,5-dimethylpyrazole (Hdmpz) and PPh2(o-C6H4CHO) (Rh : L : P = 1 : 2 : 1) gives ...hydridoacyl complexes RhHCl{PPh2(o-C6H4CO)}(L)2 (). Stereoselective formation of and with pyrazoles trans to hydrido and phosphorus and hydrogen bond formation with O-acyl and chlorido occur. is a mixture of two linkage isomers in a 9 : 1 ratio, with two 5-methylpyrazole ligands or with one 3- and one 5-methylpyrazole ligand, respectively. Fluxional undergoes metallotropic tautomerization and is a mixture of equal amounts of and , with hydrido trans to pyrazole or chlorido, respectively. Complexes readily exchange hydrido by chlorido to afford RhCl2{PPh2(o-C6H4CO)}(L)2 (, and ) as single isomers with cis chloridos and two N-HCl hydrogen bonds. The reaction of with PPh3 or PPh2OH affords static RhHCl{PPh2(o-C6H4CO)}(PPh3)L () or RhHCl{PPh2(o-C6H4CO)}(PPh2OH)L () respectively with trans P-atoms and pyrazoles forming N-HCl hydrogen bonds. and contain single species with hydrido cis to chlorido, while is a mixture of equal amounts of and . Complexes , with an additional O-HO hydrogen bond, selectively contain only the cis-H,Cl species with all the three ligands. The reaction of {RhCl(COD)}2 with L and PPh2(o-C6H4CHO) (Rh : L : P = 1 : 1 : 2) led to complexes with trans P-atoms, RhHCl{PPh2(o-C6H4CO)}{PPh2(o-C6H4CHO)-κP}L (, and ), at room temperature, and to RhCl{PPh2(o-C6H4CO)}{PPh2(o-C6H4CHOH)}(Hmpz) () or RhCl{PPh2(o-C6H4CO)}2L () with hydrogen evolution in refluxing benzene. DFT calculations were used to predict the correct isomers, their ratios and the particular intramolecular hydrogen bonds in these complexes. Single crystal X-ray diffraction analysis was performed on , and . Complexes are efficient homogeneous catalysts (0.5 mol% loading) in the hydrolysis of amine- or ammonia-borane (AB) to generate up to 3 equivalents of hydrogen in the presence of air.
A three-dimensional heterobimetallic porous structure with the formula {Y3.5Tb1.5L6(OH)3(H2O)1.5 (DMF)1.5 n ·1.5H2O·DMF} n (L = 3-amino-4-hydroxybenzoate) (Y/Tb-MOF) has been synthesized and ...characterized by single crystal and powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), inductively coupled plasma mass spectrometry (ICP-MS), electrophoretic mobility, and Fourier transform infrared (FTIR) spectroscopy. The structure presents two metal environments: a bioaugmented isosceles wedge (mm2) MO8 and a tricapped trigonal prism (−6m2) MN3O6. These configurations facilitate the creation of channels with a diameter of 10.7 Å, enabling its utilization as an active catalyst where the heterobimetallic nature of the assembly will be explored. This mixed-metal metal–organic framework has been tested in the cycloaddition of epoxides with carbon dioxide as well as in the cyanosilylation and hydroboration reactions of carbonylic substrates. Additionally, a monometallic Tb-MOF analogue has been synthesized for comparative evaluation of their catalytic performances. Both the mixed metal and monometallic variants exhibit outstanding activity in the cyanosilylation and hydroboration of carbonyls and in the synthesis of carbonates under CO2 pressure. However, only the latter exhibits high recyclability.
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