The Structure-Antiproliferative Activity Relationship of Pyridine Derivatives.

Pyridine, a compound with a heterocyclic structure, is a key player in medicinal chemistry and drug design. It is widely used as a framework for the design of biologically active molecules and is the second most common heterocycle in FDA-approved drugs. Pyridine is known for its diverse biological activity, including antituberculosis, antitumor, anticoagulant, antiviral, antimalarial, antileishmania, anti-inflammatory, anti-Alzheimer's, antitrypanosomal, antimalarial, vasodilatory, antioxidant, antimicrobial, and antiproliferative effects. This review, spanning from 2022 to 2012, involved the meticulous identification of pyridine derivatives with antiproliferative activity, as indicated by their minimum inhibitory concentration values (IC50) against various cancerous cell lines. The aim was to determine the most favorable structural characteristics for their antiproliferative activity. Using computer programs, we constructed and calculated the molecular descriptors and analyzed the electrostatic potential maps of the selected pyridine derivatives. The study found that the presence and positions of the -OMe, -OH, -C=O, and NH2 groups in the pyridine derivatives enhanced their antiproliferative activity over the cancerous cellular lines studied. Conversely, pyridine derivatives with halogen atoms or bulky groups in their structures exhibited lower antiproliferative activity.

Synthesis and Cytotoxicity Studies of Br-Substituted Salphen Organic Compounds.

We present the synthesis and characterization of organic Salphen compounds containing bromine substituents at the para/ortho-para positions, in their symmetric and non-symmetric versions, and describe the X-ray structure and full characterization for the new unsymmetrical varieties. We report for the first time antiproliferative activity in metal-free brominated Salphen compounds, by evaluations in four human cancer cell lines, cervix (HeLa), prostate (PC-3), lung (A549) and colon (LS 180) and one non-cancerous counterpart (ARPE-19). We assessed in vitro cell viability against controls using the MTT assay ((3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide)) and determined the concentration required for 50 % growth inhibition (IC50 ), together with their selectivity vs. non-cancerous cells. We found promising results against prostate (9.6 µM) and colon (13.5 µM) adenocarcinoma cells. We also found a tradeoff between selectivity (up to 3-fold vs. ARPE-19) and inhibition, depending upon the symmetry and bromine-substitution of the molecules, showing up to 20-fold higher selectivity vs. doxorubicin controls.

In vitro antiviral effect of Mexican and Brazilian propolis and phenolic compounds against human coronavirus 229E.

Propolis is a resinous substance collected by bees (Apis mellifera). It is used for its biological properties. This natural product is available as a safe therapeutic option. Herein, we report the antiviral effects of brown propolis extract from Mexico and green and red propolis extracts from Brazil, as well as their phenolic compounds (quercetin, caffeic acid, and rutin) in preventing infection of MRC-5 cells by HCoV-229E. Normal human fibroblast lung cells (MRC-5) were used to determine the cytotoxicity of the compounds. All samples studied showed antiviral activity. Green and brown propolis extracts, and quercetin exhibited the best EC50 values with values of 19.080, 11.240, and 77.208 µg/mL against HCoV-229E, respectively, and with TC50 of 62.19, 29.192, and 298 µg/mL on MRC-5 cells, respectively. These results are the first in vitro study of the effects of propolis on HCoV-229E and provide the basis for the development of natural formulations against other coronavirus strains.

Reynosin and santamarine: two sesquiterpene lactones from Ambrosia confertiflora with bactericidal activity against clinical strains of Mycobacterium tuberculosis.

CONTEXT: Tuberculosis is primarily caused by Mycobacterium tuberculosis (Mtb). Previous studies have shown that the dichloromethanic extract of Ambrosia confertiflora DC (Asteraceae) inhibited Mtb. OBJECTIVE: To isolate the compounds responsible for the mycobactericidal activity against clinical Mtb strains. MATERIALS AND METHODS: The dichloromethanic extract of aerial parts of A. confertiflora was separated using chromatography columns. Mycobactericidal activity of the isolated compounds was evaluated using the Alamar Blue bioassay (128-16 µg/mL, 7 days). Cytotoxicity was tested against normal cell line L929 using the MTT ([3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium]) assay (100-3.125 µg/mL, 48 h). Compound structures were elucidated by 1H and 13C uni- and bidimensional NMR. RESULTS: Two sesquiterpene lactones (SQLs) with mycobactericidal activity were identified: santamarine and reynosin. Reynosin was the most active compound, with a minimal bactericidal concentration (MBC) of 128 µg/mL against the H37Rv, 366-2009 and 104-2010 Mtb strains and a minimal inhibitory concentration (MIC) of 64, 64, 128, 128 and 128 µg/mL against the H37Rv, 104-2010, 63-2009, 366-2009 and 430-2010 Mtb strains, respectively. Santamarine had MBCs of 128 µg/mL against the H3Rv and 104-2010 Mtb strains and MICs of 128 µg/mL against the H37Rv, 366-2009 and 104-2010 Mtb strains. We also isolated 1,10-epoxyparthenolide but only showed mycobacteriostatic activity (MIC 128 µg/mL) against the Mtb strain. Compounds were tested against the L929 cell line and the calculated selectivity index was <1. DISCUSSION AND CONCLUSIONS: This is the first report of the mycobactericidal activity of these compounds against clinical Mtb strains. It is also the first report of the isolation of 1,10-epoxyparthenolide from A. confertiflora. The anti-mycobacterial activity of A. confertiflora was attributed to the SQLs identified.

In vitro anti-proliferative activity of Argemone gracilenta and identification of some active components.

BACKGROUND: Cancer is one of the leading causes of death worldwide. Natural products have been regarded as important sources of potential chemotherapeutic agents. In this study, we evaluated the anti-proliferative activity of Argemone gracilenta's methanol extract and its fractions. We identified those compounds of the most active fractions that displayed anti-proliferative activity. METHODS: The anti-proliferative activity on different cancerous cell lines (M12.C3F6, RAW 264.7, HeLa) was evaluated in vitro using the MTT colorimetric method. Identification of the active compounds present in the fractions with the highest activity was achieved by nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS) analyses. RESULTS: Both argemonine and berberine alkaloids, isolated from the ethyl acetate fraction, displayed high anti-proliferative activity with IC50 values of 2.8, 2.5, 12.1, and 2.7, 2.4, 79.5 µg/mL on M12.C3F6, RAW 264.7, and HeLa cancerous cell lines, respectively. No activity was shown on the normal L-929 cell line. From the hexane fraction, a mixture of fatty acids and fatty acid esters of 16 or more carbon atoms with anti-proliferative activity was identified, showing a range of IC50 values of 16.8-24.9, 34.1-35.4, and 67.6-91.8 µg/mL on M12.C3F6, RAW 264.7, and HeLa cancerous cell lines, respectively. On the normal L-929 cell line, this mixture showed a range of IC50 values of 85.1 to 100 µg/mL. CONCLUSION: This is the first study that relates argemonine, berberine, and a mixture of fatty acids and fatty acid esters with the anti-proliferative activity displayed by Argemone gracilenta.

Thiourea-Based Receptors for Anion Recognition and Signaling.

This work reports on two thiourea-based receptors with pyridine and amine units including 1-naphthyl (MT1N) and 4-nytrophenyl (MT4N) as signaling units. For both compounds, their affinity and signaling ability toward various anions of different geometry and basicity in DMSO were studied using UV-vis, fluorescence, and 1H NMR techniques. Anion recognition studies revealed that both MT1N and MT4N have, in general, high affinities toward basic anions. In this regard, a higher acidity of the MT4N receptor was demonstrated. Furthermore, MT4N has a higher affinity for fluoride (log K1 = 5.98) than for the other anions and can effectively detect it through colorimetric changes that can be monitored by the UV-vis technique. The interaction between receptors and anions mainly involves the hydrogens of the amino and thiourea groups of the former. Complementary single-crystal X-ray diffraction studies and molecular modeling at the DFT level were also performed.

Efficient and Sustainable Bidentate Amines-Functionalized Resins for Removing Ag+, Cu2+, Pb2+, and Fe3+ from Water.

We evaluate the effectiveness of chelating resins (CR) derived from Merrifield resin (MR) and 1,2-phenylenediamine (PDA), 2,2'-dipyridylamine (DPA), and 2-(aminomethyl)pyridine (AMP) as adsorbent dosimeters for Ag+, Cu2+, Fe3+, and Pb2+ cations from water under competitive and noncompetitive conditions. MR-PDA, MR-DPA, and MR-AMP were obtained in a 95-97% yield and characterized by IR, fluorescence, and SEM. The ability of CRs as adsorbents was determined by batch and flow procedures. MR-PDA showed a batch adsorption capacity order of Fe3+ (29.8 mg/g) > Ag+ (2.7 mg/g) > Pb2+ (2.6 mg/g) at pH 3.4. The flow adsorption showed affinity towards the Ag+ cation at pH 7 (18.4 mg/g) and a reusability of 10 cycles. In MR-DPA, the batch adsorption capacity order was Ag+ (9.1 mg/g) > Pb2+ (8.2 mg/g) > Cu2+ (3.5 mg/g) at pH 5. The flow adsorption showed affinity to the Cu2+ cation at pH 5 (2.2 mg/g) and a reuse of five cycles. In MR-AMP, the batch adsorption capacity was Ag+ (17.1 mg/g) at pH 3.4. The flow adsorption showed affinity to the Fe3+ cation at pH 2 (4.3 mg/g) and a reuse of three cycles. The three synthesized and reusable CRs have potential as adsorbents for Ag+, Cu2+, Fe3+, and Pb2+ cations and showed versatility in metal removal for water treatment.

Tritopic Bis-Urea Receptors for Anion and Ion-Pair Recognition.

This work reports on the synthesis and characterization of three tritopic receptors and their binding properties toward various anions, as their tetrabutylammonium salts, and three alkali metal-acetate salts by UV-vis, fluorescence, 1H, 7Li, 23Na, and 39K NMR in MeCN/dimethyl sulfoxide (DMSO) 9:1 (v/v). Molecular recognition studies showed that the receptors have good affinity for oxyanions. Furthermore, these compounds are capable of ion-pair recognition of the alkali metal-acetate salts studied through a cooperative mechanism. Additionally, molecular modeling at the density functional theory (DFT) level of some lithium and sodium acetate complexes illustrates the ion-pair binding capacity of receptors. The anion is recognized through strong hydrogen bonds of the NH- groups from the two urea sites, while the cation interacts with the oxygen atoms of the polyether spacer. This work demonstrates that these compounds are good receptors for anions and ion pairs.

DNA-Binding Properties of Bis-N-substituted Tetrandrine Derivatives.

A series of bis-N-substituted tetrandrine derivatives carrying different aromatic substituents attached to both nitrogen atoms of the natural alkaloid were studied with double-stranded model DNAs (dsDNAs) to examine the binding properties and mechanism. Variable-temperature molecular recognition studies using UV-vis and fluorescence techniques revealed the thermodynamic parameters, ΔH, ΔS, and ΔG, showing that the tetrandrine derivatives exhibit high affinity toward dsDNA (K ≈ 105-107 M-1), particularly the bis(methyl)anthraquinone (BAqT) and bis(ethyl)indole compounds (BInT). Viscometry experiments, ethidium displacement assays, and molecular modeling studies enabled elucidation of the possible binding mode, indicating that the compounds exhibit a synergic interaction mode involving intercalation of one of the N-aryl substituents and interaction of the molecular skeleton in the major groove of the dsDNA. Cytotoxicity tests of the derivatives with tumor and nontumor cell lines demonstrated low cytotoxicity of these compounds, with the exception of the bis(methyl)pyrene (BPyrT) derivative, which is significantly more cytotoxic than the remaining derivatives, with IC50 values against the LS-180, A-549, and ARPE-19 cell lines that are similar to natural tetrandrine. Finally, complementary electrochemical characterization studies unveiled good electrochemical stability of the compounds.

Nutraceuticals/Drugs Promoting Mitophagy and Mitochondrial Biogenesis May Combat the Mitochondrial Dysfunction Driving Progression of Dry Age-Related Macular Degeneration.

In patients with age-related macular degeneration (AMD), the crucial retinal pigment epithelial (RPE) cells are characterized by mitochondria that are structurally and functionally defective. Moreover, deficient expression of the mRNA-editing enzyme Dicer is noted specifically in these cells. This Dicer deficit up-regulates expression of Alu RNA, which in turn damages mitochondria-inducing the loss of membrane potential, boosting oxidant generation, and causing mitochondrial DNA to translocate to the cytoplasmic region. The cytoplasmic mtDNA, in conjunction with induced oxidative stress, triggers a non-canonical pathway of NLRP3 inflammasome activation, leading to the production of interleukin-18 that acts in an autocrine manner to induce apoptotic death of RPE cells, thereby driving progression of dry AMD. It is proposed that measures which jointly up-regulate mitophagy and mitochondrial biogenesis (MB), by replacing damaged mitochondria with "healthy" new ones, may lessen the adverse impact of Alu RNA on RPE cells, enabling the prevention or control of dry AMD. An analysis of the molecular biology underlying mitophagy/MB and inflammasome activation suggests that nutraceuticals or drugs that can activate Sirt1, AMPK, Nrf2, and PPARα may be useful in this regard. These include ferulic acid, melatonin urolithin A and glucosamine (Sirt1), metformin and berberine (AMPK), lipoic acid and broccoli sprout extract (Nrf2), and fibrate drugs and astaxanthin (PPARα). Hence, nutraceutical regimens providing physiologically meaningful doses of several or all of the: ferulic acid, melatonin, glucosamine, berberine, lipoic acid, and astaxanthin, may have potential for control of dry AMD.

Recent biotechnological advances as potential intervention strategies against COVID-19.

The emerging SARS-CoV-2 viral disease (COVID-19) has caused a global health alert due to its high rate of infection and mortality in individuals with chronic cardiovascular comorbidities, in addition to generating complex clinical conditions. This has forced the scientific community to explore different strategies that allow combating this viral infection as well as treating life-threatening systemic effect of the infection on the individual. In this work, we have reviewed the most recent scientific evidence to provide a comprehensive panorama regarding the biotechnological strategies that have been proposed to combat this new viral infection. We have focused our analysis on vaccine production, nanotechnology applications, repurposing of know drugs for unrelated pathologies, and the search for bioactive molecules obtained from natural products. The goals include safely use as potential prophylactic or therapeutic treatments, based on in silico and in vivo studies, including clinical trials around the world for the correct and timely diagnosis of the infection. This review aims to highlight the development of new ideas that can decrease the time lines for research output and improve research quality while at the same time, keeping in mind the efficacy and safety aspects of these potential biotechnological strategies.

The Dichloromethane Fraction of Croton sonorae, A Plant Used in Sonoran Traditional Medicine, Affect Entamoeba histolytica Erythrophagocytosis and Gene Expression.

Intestinal parasites are a global problem, mainly in developing countries. Obtaining information about plants and compounds that can combat gastrointestinal disorders and gastrointestinal symptoms is a fundamental first step in designing new treatment strategies. In this study, we analyzed the antiamoebic activity of the aerial part of Croton sonorae. The dichloromethane fraction of C. sonorae (CsDCMfx) contained flavonoids, terpenes, alkaloids, and glycosides. The ultrastructural morphology of the amoebae treated for 72 h with CsDCMfx was completely abnormal. CsDCMfx reduced erythrophagocytosis of trophozoites and the expression of genes involved in erythrocyte adhesion (gal/galnac lectin) and actin cytoskeleton rearrangement in the phagocytosis pathway (rho1 gtpase and formin1). Interestingly, CsDCMfx decreased the expression of genes involved in Entamoeba histolytica trophozoite pathogenesis, such as cysteine proteases (cp1, cp4, and cp5), sod, pfor, and enolase. These results showed that C. sonorae is a potential source of antiamoebic compounds.

Antiviral, Antioxidant, and Antihemolytic Effect of Annona muricata L. Leaves Extracts.

Annona muricata L. is a tropical tree that is used in traditional medicine around the world. The high content of flavonoid, alkaloid, acetogenin, phenolic and lipophilic compounds of this tropical tree forms the basis of its traditional medical uses. Our objective was to study soursop leaf extracts to support their use as antiviral therapies and investigate their protective effects against oxidative damage. The aqueous extract (AE) and acidified ethanolic extract (AEE) of soursop leaves were characterized by ultra performance liquid chromatography (UPLC), and their effects on human erythrocytes and in vitro antioxidant capacity, as evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays, were investigated. The antiviral effects were evaluated using a bacteriophage surrogate. AEE showed the highest phenolic content, with rutin as the predominant compound. This extract showed higher values in the DPPH and ABTS assays, with 23.61 ± 0.42 and 24.91 ± 0.16 mmol of Trolox equivalent per gram, respectively. Inhibition of hemolysis was 34% and 51% for AE and AEE, respectively. AEE was selected for the antiviral study because of its higher antioxidant activity. The viral reduction ranged from 5-6 log10 plaque-forming units/volume (PFU) at contact times of 15-360 min. Soursop leaves have a positive effect on reducing oxidative stress in human erythrocytes and viral infections.

Synthesis, spectroscopic, physicochemical and structural characterization of tetrandrine-based macrocycles functionalized with acridine and anthracene groups: DNA binding and anti-proliferative activity.

In this work, we report on the synthesis of two new mono-alkylated tetrandrine derivatives with acridine and anthracene units, MAcT and MAnT. The compounds were fully characterized by physicochemical techniques and single-crystal X-ray diffraction analysis. In addition, both derivatives were studied as nucleotide receptors and double-stranded DNA binders in aqueous phosphate buffer at pH = 7.2 using UV-vis and fluorescence spectroscopy. According to the molecular recognition studies, MAcT and MAnT exhibit high affinity (K ∼ 105 M-1) and selectivity for ds-DNA, presumably in an intercalation mode. Finally, the anti-proliferative effects of the tetrandrine derivatives on different cancer cell lines were explored, revealing promising activities. Particularly, the mono-anthracene tetrandrine derivative MAnT showed an IC50 of 2.74 µg/mL on the HeLa cervical cancer cell line, representing a value 3.3 times smaller than that obtained for unsubstituted tetrandrine. Examination of the cytotoxic effects on the HeLa cell line by inverted microscopy suggests that the cell death mechanism consists basically in apoptosis. The molecular modelling of three ds-DNA-MAcT complexes, suggested that the macrocycles may use an intercalation binding mode towards DNA. MAcT is predicted to bind into the major groove of the ds-DNA providing non-covalent interactions such as electrostatic, van der Waals and hydrophobic interactions that lead to selectivity. Overall experimental data supports the mode of action of MAnT and MAcT as cytotoxic compounds against cancer cell lines via a DNA interaction mechanism.

Highly sensitive ammonium tetraazidoaurates(III).

The preparation and characterization of selected ammonium and methylammonium tetraazidoaurates(III) are reported. All ammonium salts were shown to be highly explosive materials. The first crystal structure of such an ammonium salt, that of [Me(4)N][Au(N(3))(4)], features polymeric units of the anion, which are linked by weak Au...Au interactions.

BTA copper complexes.

Cupric oxide is one of the most important additives used (a) to catalyze decomposition reactions in gas generators to obtain cooler reaction gases, (b) as burning enhancer for ammonium perchlorate-based composite propellants, and (c) as coloring agent in pyrotechnics. In this context, the reaction of Cu(2+) ions in aqueous ammonia solution with bis(tetrazolyl)amine (H(2)bta) was investigated. Depending on the reaction conditions three complexes were obtained: Cu(bta)(NH(3))(2) (1), Cu(bta)(NH(3))(2).H(2)O (2), and (NH(4))(2)Cu(bta)(2).2.5H(2)O (3). The crystal structures of 1 and 2 are discussed with respect to the coordination mode of the dianion of N,N-bis(1(2)H-tetrazol-5-yl)-amine (bta), which mediates in the case of 1 and 2 weak superexchange interactions between the adjacent magnetic transition-metal Cu(II) cations. These antiferromagnetic interactions result from 1D copper chains over an hidden azide end-to-end bridge. Interestingly, the structural arrangement of 1 completely changes in the presence of crystal-bound water. Moreover, some physicochemical properties (e.g., heat of formation, friction, and impact sensitivity, DSC) of these complexes with respect to high-energetic materials are discussed.

Kinetic and donor stabilization of organotellurenyl iodides and azides.

The first tellurium compounds containing the extremely bulky tris(phenyldimethylsilyl)methyl (Tpsi) and 2,6-bis(2,4,6-triisopropylphenyl)phenyl (2,6-Trip(2)C(6)H(3)) moieties have been synthesized and isolated. Careful oxidation of the tellurolate TpsiTeLi (1) resulted in the formation of the crowded ditellane (TpsiTe)(2) (2), and iodination of 2 gave the alkanetellurenyl iodide TpsiTeI (3). In a similar fashion, the terphenyl-substituted ditellane (2,6-Trip(2)C(6)H(3)Te)(2) (9) and the arenetellurenyl iodide 2,6-Trip(2)C(6)H(3)TeI (10) were prepared. Reaction of the iodides TpsiTeI (3) and 2,6-Trip(2)C(6)H(3)TeI (10), as well as TripTeI, MesTeI (Trip = 2,4,6-triisopropylphenyl, Mes = 2,4,6-tri-tert-butylphenyl), and the donor-stabilized 2-Me(2)NCH(2)C(6)H(4)TeI, with AgN(3) resulted in the formation and isolation of the corresponding tellurenyl azides TpsiTeN(3) (4), TripTeN(3) (7), MesTeN(3) (8), 2,6-Trip(2)C(6)H(3)TeN(3) (11), and 2-Me(2)NCH(2)C(6)H(4)TeN(3) (12). Furthermore, the corresponding tris(ethyldimethylsilyl)methyl-containing (Tesi) tellurium compounds (TesiTe)(2), TesiTeI (5), and TesiTeN(3) (6) have been prepared but could not be isolated in pure form. The crystal structures of TpsiTeLi (1), (TpsiTe)(2) (2), TpsiTeN(3) (4), 2,6-Trip(2)C(6)H(3)TeI (10), 2,6-Trip(2)C(6)H(3)TeN(3) (11), and 2-Me(2)NCH(2)C(6)H(4)TeN(3) (12) have been determined by X-ray diffraction. Additionally, computational studies of the molecules for which experimental structural data were available were performed.

Derivatives of 1,5-diamino-1H-tetrazole: a new family of energetic heterocyclic-based salts.

1,5-Diamino-1H-tetrazole (2, DAT) can easily be protonated by reaction with strong mineral acids, yielding the poorly investigated 1,5-diaminotetrazolium nitrate (2a) and perchlorate (2b). A new synthesis for 2 is introduced that avoids lead azide as a hazardous byproduct. The reaction of 1,5-diamino-1H-tetrazole with iodomethane (7a) followed by the metathesis of the iodide (7a) with silver nitrate (7b), silver dinitramide (7c), or silver azide (7d) leads to a new family of heterocyclic-based salts. In all cases, stable salts were obtained and fully characterized by vibrational (IR, Raman) spectroscopy, multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, X-ray structure determination, and initial safety testing (impact and friction sensitivity). Most of the salts exhibit good thermal stabilities, and both the perchlorate (2b) and the dinitramide (7c) have melting points well below 100 degrees C, yet high decomposition onsets, defining them as new (7c), highly energetic ionic liquids. Preliminary sensitivity testing of the crystalline compounds indicates rather low impact sensitivities for all compounds, the highest being that of the perchlorate (2b) and the dinitramide (7c) with a value of 7 J. In contrast, the friction sensitivities of the perchlorate (2b, 60 N) and the dinitramide (7c, 24 N) are relatively high. The enthalpies of combustion (Delta(c)H degrees ) of 7b-d were determined experimentally using oxygen bomb calorimetry: Delta(c)H degrees (7b) = -2456 cal g(-)(1), Delta(c)H degrees (7c) = -2135 cal g(-)(1), and Delta(c)H degrees (7d) = -3594 cal g(-)(1). The standard enthalpies of formation (Delta(f)H degrees ) of 7b-d were obtained on the basis of quantum chemical computations using the G2 (G3) method: Delta(f)H degrees (7b) = 41.7 (41.2) kcal mol(-)(1), Delta(f)H degrees (7c) = 92.1 (91.1) kcal mol(-)(1), and Delta(f)H degrees (7d) = 161.6 (161.5) kcal mol(-)(1). The detonation velocities (D) and detonation pressures (P) of 2b and 7b-d were calculated using the empirical equations of Kamlet and Jacobs: D(2b) = 8383 m s(-)(1), P(2b) = 32.2 GPa; D(7b) = 7682 m s(-)(1), P(7b) = 23.4 GPa; D(7c) = 8827 m s(-)(1), P(7c) = 33.6 GPa; and D(7d) = 7405 m s(-)(1), P(7d) = 20.8 GPa. For all compounds, a structure determination by single-crystal X-ray diffraction was performed. 2a and 2b crystallize in the monoclinic space groups C2/c and P2(1)/n, respectively. The salts of 7 crystallize in the orthorhombic space groups Pna2(1) (7a, 7d) and Fdd2 (7b). The hydrogen-bonded ring motifs are discussed in the formalism of graph-set analysis of hydrogen-bond patterns and compared in the case of 2a, 2b, and 7b.

Dichroic, dinuclear mu2-(eta2-NO)-nitrosoaniline-bridged complexes of rhenium of the type [[(CO)3Re(mu-X)]2ONC6H4NR2] (X = Cl, Br, I; R = Me, Et).

A series of unusual dinuclear mu2-(eta2-NO)-nitrosoaniline-bridged complexes [[(CO)3Re(mu-X)]2ONC6H4NR2] (X = Cl, Br, I; R = Me, Et) with dichroic properties have been synthesised by reaction of pentacarbonylhalogenorhenium(I) [(CO)5ReX] (X = Cl, Br, I) with the corresponding nitrosoaniline derivatives R2NC6H4NO (R = Me, Et). The deeply coloured solutions in CH2Cl2 show broad UV/Vis absorptions from 595 to 620 nm depending on the halogen bridges and N substituents. Single crystals of all six compounds exhibit a pronounced linear dichroism. The molecular structures have been determined by single-crystal X-ray analyses. All the compounds contain two face-shared octahedra, with two halogens and one NO ligand as bridges. The NO ligand coordinates in a nonsymmetrical eta2-like fashion with N or O coordination to each Re centre. Therefore, the C-nitroso group and the planar NC2 moiety of NR2 both lie almost exactly within the symmetry plane of the dinuclear complexes. These complexes belong to the novel and simple class of neutral dinuclear C-nitroso complexes that include the rare, non-assisted mu2-(eta2-NO) ligand function and have only single halogen atoms in bridging positions.

Organometallic aluminum compounds derived from 2-(1,3,5-dithiazinan-5-yl)ethanol ligands.

The reactions of AlMe(2)Y (Y = Me or Cl) with new ligands 2-(1,3,5-dithiazinan-5-yl)ethanol (1), 2-(1,3,5-dithiazinan-5-yl)-1-methylethanol (2), and 2-(1,3,5-dithiazinan-5-yl)-1-phenylethanol (3) are described. The ligands are coordinated to aluminum atoms by nitrogen and oxygen atoms, with a nitrogen based spiranic structure. Equimolar reactions gave dimeric structures bearing pentacoordinated aluminum atoms O-(AlMeY)-2-(1,3,5-dithiazinan-5-yl)ethanolates (4-7) as well as monometallic compounds with tetracoordinated aluminum atoms O-(AlMeY)-2-(1,3,5-dithiazinan-5-yl)ethanolates (8-9). Reactions with 2 equiv of the aluminum reagents afforded tetracoordinated dialuminum complexes O-(AlMeY)-O-(AlMe(2)Y)-2-(1,3,5-dithiazinan-5-yl)ethanolate (10-18). The structures of the new compounds were determined by NMR ((1)H,(13)C, and (27)Al) and complemented by X-ray diffraction of compounds 4, 10, and 16-18. Relevant intermolecular interactions C-H...S, C-H...Cl, and C-H...pi found in the crystalline network are reported.