Probing the influence of substrate binding on photocatalytic dehalogenation with a heteroleptic supramolecular [M4La2Lb2] square containing PDI photosensitizers as ligands

Photoredox catalysis is a valuable tool in a large variety of chemical reactions. Main challenges still to be overcome are photodegradation of photocatalysts and substrates, short lifetimes of reactive intermediates, and selectivity issues due to unwanted side reactions. A potential solution to these challenges is the pre-organization of the photosensitizer, substrate and (co)-catalyst in supramolecular self-assembled structures. In such architectures, (organic) dyes can be stabilized, and higher selectivity could potentially be achieved through pre-organizing desired reaction partners via non-covalent interactions. Perylene diimide (PDI) is an organic dye, which can be readily reduced to its mono- and dianion. Excitation of both anions leads to highly reducing excited states, which are able to reduce a variety of substrates via single electron transfer. The incorporation of PDI into a heteroleptic [M4La2Lb2] supramolecular square has been recently demonstrated. Herein we investigate its photophysical properties and demonstrate that incorporated PDI indeed features photocatalytic activity. Initial results suggest that the pre-organisation by binding positively affects the outcome.

Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis

Because sunlight is the most abundant energy source on earth, it has huge potential for practical applications ranging from sustainable energy supply to light driven chemistry. From a chemical perspective, excited states generated by light make thermodynamically uphill reactions possible, which forms the basis for energy storage into fuels. In addition, with light, open-shell species can be generated which open up new reaction pathways in organic synthesis. Crucial are photosensitizers, which absorb light and transfer energy to substrates by various mechanisms, processes that highly depend on the distance between the molecules involved. Supramolecular coordination cages are well studied and synthetically accessible reaction vessels with single cavities for guest binding, ensuring close proximity of different components. Due to high modularity of their size, shape, and the nature of metal centers and ligands, cages are ideal platforms to exploit preorganization in photocatalysis. Herein we focus on the application of supramolecular cages for photocatalysis in artificial photosynthesis and in organic photo(redox) catalysis. Finally, a brief overview of immobilization strategies for supramolecular cages provides tools for implementing cages into devices. This review provides inspiration for future design of photocatalytic supramolecular host-guest systems and their application in producing solar fuels and complex organic molecules.

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

Transition metal catalysis is of utmost importance for the development of sustainable processes in academia and industry. The activity and selectivity of metal complexes are typically the result of the interplay between ligand and metal properties. As the ligand can be chemically altered, a large research focus has been on ligand development. More recently, it has been recognized that further control over activity and selectivity can be achieved by using the "second coordination sphere", which can be seen as the region beyond the direct coordination sphere of the metal center. Hydrogen bonds appear to be very useful interactions in this context as they typically have sufficient strength and directionality to exert control of the second coordination sphere, yet hydrogen bonds are typically very dynamic, allowing fast turnover. In this review we have highlighted several key features of hydrogen bonding interactions and have summarized the use of hydrogen bonding to program the second coordination sphere. Such control can be achieved by bridging two ligands that are coordinated to a metal center to effectively lead to supramolecular bidentate ligands. In addition, hydrogen bonding can be used to preorganize a substrate that is coordinated to the metal center. Both strategies lead to catalysts with superior properties in a variety of metal catalyzed transformations, including (asymmetric) hydrogenation, hydroformylation, C-H activation, oxidation, radical-type transformations, and photochemical reactions.

Increasing structural and functional complexity in self-assembled coordination cages

Progress in metallo-supramolecular chemistry creates potential to synthesize functional nano systems and intelligent materials of increasing complexity. In the past four decades, metal-mediated self-assembly has produced a wide range of structural motifs such as helicates, grids, links, knots, spheres and cages, with particularly the latter ones catching growing attention, owing to their nano-scale cavities. Assemblies serving as hosts allow application as selective receptors, confined reaction environments and more. Recently, the field has made big steps forward by implementing dedicated functionality, e.g. catalytic centres or photoswitches to allow stimuli control. Besides incorporation in homoleptic systems, composed of one type of ligand, desire arose to include more than one function within the same assembly. Inspiration comes from natural enzymes that congregate, for example, a substrate recognition site, an allosteric regulator element and a reaction centre. Combining several functionalities without creating statistical mixtures, however, requires a toolbox of sophisticated assembly strategies. This review showcases the implementation of function into self-assembled cages and devises strategies to selectively form heteroleptic structures. We discuss first examples resulting from a combination of both principles, namely multicomponent multifunctional host-guest complexes, and their potential in application in areas such as sensing, catalysis, and photo-redox systems.

From Silos to Solidarity: Case Study of a Patient-Centered, Integrative Approach to Opioid Tapering and Chronic Pain Mitigation in a Multidisciplinary AIDS Clinic

Background:

People with HIV (PWH) are at a disproportionate risk for experiencing both chronic pain and opioid use disorder (OUD). Prescription opioid tapering is typically addressed within the “silo model” of medical care, whereby attention is focused solely on opioid addiction rather than also addressing chronic pain management, and limited communication occurs between patient and providers.

Objective:

This descriptive case study examined an integrative, collaborative care model consisting of Provider, Physical Therapist (PT), and Patient aimed at decreasing chronic pain and opioid use within a multidisciplinary HIV/AIDS clinic.

Method:

A physical-therapy based model of chronic pain mitigation and physician-driven opioid tapering was implemented. The Provider, PT, and Patient worked collaboratively to address physiological pain, pain coping skills and opioid tapering. A patient case example was used to illustrate the implementation of the model for a future, larger study in the same patient population.

Results:

This model was feasible in this case example in terms of clinic workflow and acceptability to both the Patient and Providers in this clinic. After the intervention, the Patient’s pain was fully eliminated, and he had ceased all opioid use.

Conclusion:

Results of this case study suggest that utilizing an integrative, patient-centered approach to both chronic pain management and opioid tapering may be feasible within the context of a multidisciplinary HIV/AIDS clinic. Generalizability is limited by case study model; however, this gives insight into the value of a collaborative alternative compared to a “silo” model of opioid tapering and chronic pain management in preparation for a larger study.

On the Heterogeneous Nature of Cisplatin-1-Methyluracil Complexes: Coexistence of Different Aggregation Modes and Partial Loss of NH3 Ligands as Likely Explanation

The conversion of the 1 : 1-complex of Cisplatin with 1-methyluracil (1MeUH), cis-[Pt(NH3 )2 (1MeU-N3)Cl] (1 a) to the aqua species cis-[Pt(NH3 )2 (1MeU-N3)(OH2 )]+ (1 b), achieved by reaction of 1 a with AgNO3 in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH3 ligands. In dilute aqueous solution, 1 a, and dinuclear compounds cis-[(NH3 )2 (1MeU-N3)Pt(μ-OH)Pt(1MeU-N3)(NH3 )2 ]+ (3) as well as head-tail cis-[Pt2 (NH3 )4 (μ-1MeU-N3,O4)2 ]2+ (4) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of 1 H NMR and ESI-MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ-OH, μ-1MeU, and μ-NH2 bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N2 complex, [Pt(NH3 )(1MeU)(N2 )]+ appears to be formed in gas phase during the ESI-MS experiment. In the presence of Na+ ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non-metalated uracil quartets found in tetrastranded RNA.

Substrate and product binding inside a stimuli-responsive coordination cage acting as a singlet oxygen photosensitizer

An acridone-based, interpenetrated double cage [3BF₄Pd₄L₈] acts as a photosensitizer for generating singlet oxygen which adds to 1,3-cyclohexadiene in a [2+4] hetero-Diels-Alder reaction to form 2,3-dioxabicyclo[2.2.2]oct-5-ene. Photocatalytic activity was exclusively observed for the assembled cage, whereas the free organic ligand L decomposes upon irradiation. While cage [3BF₄Pd₄L₈] does not accept any organic guests, NMR, MS and single crystal X-ray results reveal that both substrate and product are readily encapsulated in the central pocket of its chloride-activated form [2Cl@Pd₄L₈]. The system combines multiple functions (photosensitization, allosteric activation and guest uptake) within a structurally complex, mechanically-bound self-assembly built up from a simple and readily accessible ligand.

Correction: Substrate and product binding inside a stimuli-responsive coordination cage acting as a singlet oxygen photosensitizer

Correction for ‘Substrate and product binding inside a stimuli-responsive coordination cage acting as a singlet oxygen photosensitizer’ by Sonja Pullen et al., Dalton Trans., 2020, 49, 9404–9410, DOI: 10.1039/D0DT01674H.

Direct Spectroscopic Detection of Key Intermediates and the Turnover Process in Catalytic H2 Formation by a Biomimetic Diiron Catalyst

[FeFe(Cl₂ -bdt)(CO)₆ ] (1; Cl₂ -bdt=3,6-dichlorobenzene-1,2-dithiolate), inspired by the active site of FeFe-hydrogenase, shows a chemically reversible 2 e^- reduction at -1.20 V versus the ferrocene/ferrocenium couple. The rigid and aromatic bdt bridging ligand lowers the reduction potential and stabilizes the reduced forms, compared with analogous complexes with aliphatic dithiolates; thus allowing details of the catalytic process to be characterized. Herein, time-resolved IR spectroscopy is used to provide kinetic and structural information on key catalytic intermediates. This includes the doubly reduced, protonated complex 1H^- , which has not been previously identified experimentally. In addition, the first direct spectroscopic observation of the turnover process for a molecular H₂ evolving catalyst is reported, allowing for straightforward determination of the turnover frequency.

Restricted rotation of an Fe(CO)2(PL3)-subunit in [FeFe]-hydrogenase active site mimics by intramolecular ligation

Terminal ligand fixation by covalent linkage to the bridging bdt ligand hinders ligand rotations.

Mixed-Ligand Metal-Organic Frameworks and Heteroleptic Coordination Cages as Multifunctional Scaffolds-A Comparison

Porous nanostructures and materials based on metal-mediated self-assembly have developed into a vibrantly studied subdiscipline of supramolecular chemistry during the past decades. In principle, two branches of such coordination compounds can be distinguished: Metal-organic frameworks (MOFs) on the one side represent infinite porous networks of metals or metal clusters that are connected via organic ligands to give solid-state materials. On the other hand, metal-organic cages (MOCs) are discrete and soluble systems with only a limited number of pores. Formation of a particular structure type is achieved by carefully balancing the donor site angles within the ligands as well as the nature and coordination geometry of the metal component. Years of research on MOFs and MOCs has yielded numerous types of well-defined porous crystals and complex supramolecular architectures. Since various synthetic routes and postsynthetic modification methods have been established, the focus of recent developments has moved toward the preparation of multifunctional systems that are able to mimic the structural and functional complexity of natural enzymes. This Account compares different strategies to prepare multifunctional MOFs and heteroleptic MOCs and gives a perspective on where to move forward. While the preparative toolbox for multifunctional MOFs is already quite mature, pore accessibility and substrate diffusion within the crystal have been identified as major challenges yet to be overcome. Only recently have a set of different strategies for the assembly of heteroleptic MOCs been developed. Such multifunctional cages can be formed from either partially protected or "naked" metal cations. Controlled assembly, producing single products rather than statistical mixtures, leans on assembly-dependent approaches making use of either steric effects or shape complementarity between the ligands. Further strategies include coordination-site engineering and hierarchical assembly of preformed components. The main challenge with heteroleptic, functional MOCs is to find a balance between the required dynamic assembly fidelity and the stability of the resulting system under operating conditions. If these limitations can be overcome in the future, chemists will be able to design multifunctional systems of similar activity and complexity as nature's enzymes from simple and easily accessible synthetic building blocks. Major impacts on chemical sensing, small-molecule recognition and sequestration, drug delivery, and catalysis will be achieved by these materials.

Direct evidence of catalyst reduction on dye and catalyst co-sensitized NiO photocathodes by mid-infrared transient absorption spectroscopy

Co-sensitization of molecular dyes and catalysts on semiconductor surfaces is a promising strategy to build photoelectrodes for solar fuel production.

Co-sensitization of molecular dyes and catalysts on semiconductor surfaces is a promising strategy to build photoelectrodes for solar fuel production. In such a photoelectrode, understanding the charge transfer reactions between the molecular dye, catalyst and semiconductor material is key to guide further improvement of their photocatalytic performance. Herein, femtosecond mid-infrared transient absorption spectroscopy is used, for the first time, to probe charge transfer reactions leading to catalyst reduction on co-sensitized nickel oxide (NiO) photocathodes. The NiO films were co-sensitized with a molecular dye and a proton reducing catalyst from the family of [FeFe](bdt)(CO)₆ (bdt = benzene-1,2-dithiolate) complexes. Two dyes were used: an organic push–pull dye denoted E2 with a triarylamine–oligothiophene–dicyanovinyl structure and a coumarin 343 dye. Upon photo-excitation of the dye, a clear spectroscopic signature of the reduced catalyst is observed a few picoseconds after excitation in all co-sensitized NiO films. However, kinetic analysis of the transient absorption signals of the dye and reduced catalyst reveal important mechanistic differences in the first reduction of the catalyst depending on the co-sensitized molecular dye (E2 or C343). While catalyst reduction is preceded by hole injection in NiO in C343-sensitized NiO films, the singly reduced catalyst is formed by direct electron transfer from the excited dye E2* to the catalyst in E2-sensitized NiO films. This change in mechanism also impacts the lifetime of the reduced catalyst, which is only ca. 50 ps in E2-sensitized NiO films but is >5 ns in C343-sensitized NiO films. Finally, the implication of this mechanistic study for the development of better co-sensitized photocathodes is discussed.

Evaluation of two- and three-dimensional electrode platforms for the electrochemical characterization of organometallic catalysts incorporated in non-conducting metal-organic frameworks

The development of a reliable platform for the electrochemical characterization of a redox-active molecular diiron complex, [FeFe], immobilized in a non-conducting metal organic framework (MOF), UiO-66, based on glassy-carbon electrodes is reported. Voltammetric data with appreciable current responses can be obtained by the use of multiwalled carbon nanotubes (MWCNT) or mesoporous carbon (CB) additives that function as conductive scaffolds to interface the MOF crystals in "three-dimensional" electrodes. In the investigated UiO-66-[FeFe] sample, the low abundance of [FeFe] in the MOF and the intrinsic insulating properties of UiO-66 prevent charge transport through the framework, and consequently, only [FeFe] units that are in direct physical contact with the electrode material are electrochemically addressable.

[FeFe] Hydrogenase active site model chemistry in a UiO-66 metal-organic framework

The reactivity of [Fe2(dcbdt)(CO)6] (1) confined in a UiO-66(Zr) metal-organic framework towards CO ligand substitutions with phosphines of different sizes was investigated. The reaction with smaller phosphines (PX3, X = Me, Et) is more selective compared to analogous reactions in homogenous solution phase, and two CO ligands at up to 80% of all [FeFe] sites in UiO-66-1 are replaced. The produced [Fe2(dcbdt)(CO)4(PX3)2] complexes in the UiO-66 matrix behave like typical [FeFe] hydrogenase active site model complexes, are reduced at more cathodic potentials than their hexacarbonyl analogues, and form bridging hydrides under acidic conditions.

Catalyst accessibility to chemical reductants in metal-organic frameworks

This study of catalyst accessibility inside metal–organic frameworks demonstrates that pore dimensions, catalyst loadings, concentration of reductant, and reaction times all influence the proportion of catalysts within MOFs that engage in redox chemistry.

A molecular H₂-evolving catalyst, [Fe₂(cbdt)(CO)₆] ([FeFe], cbdt = 3-carboxybenzene-1,2-dithiolate), has been attached covalently to an amino-functionalized MIL-101(Cr) through an amide bond. Chemical reduction experiments reveal that the MOF channels can be clogged by ion pairs that are formed between the oxidized reductant and the reduced catalyst. This effect is lessened in MIL-101-NH-[FeFe] with lower [FeFe] loadings. On longer timescales, it is shown that large proportions of the [FeFe] catalysts within the MOF engage in photochemical hydrogen production and the amount of produced hydrogen is proportional to the catalyst loading.

Functional small-molecules & polymers containing PC and AsC bonds as hybrid π-conjugated materials

Switch the pnictogen: functional materials containing PC and AsC fragments for optoelectronic applications. An example of a polymer containing arsaalkenes is presented.

Homogeneous Cobalt/Vanadium Complexes as Precursors for Functionalized Mixed Oxides in Visible-Light-Driven Water Oxidation

The heterometallic complexes (NH₄ )₂ [Co(H₂ O)₆ ]₂ [V₁₀ O₂₈ ]⋅4 H₂ O (1) and (NH₄ )₂ [Co(H₂ O)₅ (β-HAla)]₂ [V₁₀ O₂₈ ]⋅4 H₂ O (2) have been synthesized and used for the preparation of mixed oxides as catalysts for water oxidation. Thermal decomposition of 1 and 2 at relatively low temperatures (<500 °C) leads to the formation of the solid mixed oxides CoV₂ O₆ /V₂ O₅ (3) and Co₂ V₂ O₇ /V₂ O₅ (4). The complexes (1, 2) and heterogeneous materials (3, 4) act as catalysts for photoinduced water oxidation. A modification of the thermal decomposition procedure allowed the deposition of mixed metal oxides (MMO) on a mesoporous TiO₂ film. The electrodes containing Co/V MMOs in TiO₂ films were used for electrocatalytic water oxidation and showed good stability and sustained anodic currents of about 5 mA cm^-2 at 1.72 V versus relative hydrogen electrode (RHE). This method of functionalizing TiO₂ films with MMOs at relatively low temperatures (<500 °C) can be used to produce other oxides with different functionality for applications in, for example, artificial photosynthesis.

Functionalization of robust Zr(iv)-based metal–organic framework films via a postsynthetic ligand exchange

A facile and efficient fabrication approach for homogeneous, crack-free UiO-66 films with exceptionally high crystallinity and tunable thickness on a transparent and conductive glass substrate is reported.

Direct observation of key catalytic intermediates in a photoinduced proton reduction cycle with a diiron carbonyl complex

The structure and reactivity of intermediates in the photocatalytic cycle of a proton reduction catalyst, [Fe2(bdt)(CO)6] (bdt = benzenedithiolate), were investigated by time-resolved spectroscopy. The singly reduced catalyst [Fe2(bdt)(CO)6](-), a key intermediate in photocatalytic H2 formation, was generated by reaction with one-electron reductants in laser flash-quench experiments and could be observed spectroscopically on the nanoseconds to microseconds time scale. From UV/vis and IR spectroscopy, [Fe2(bdt)(CO)6](-) is readily distinguished from the two-electron reduced catalyst [Fe2(bdt)(CO)6](2-) that is obtained inevitably in the electrochemical reduction of [Fe2(bdt)(CO)6]. For the disproportionation rate constant of [Fe2(bdt)(CO)6](-), an upper limit on the order of 10(7) M(-1) s(-1) was estimated, which precludes a major role of [Fe2(bdt)(CO)6](2-) in photoinduced proton reduction cycles. Structurally [Fe2(bdt)(CO)6](-) is characterized by a rather asymmetrically distorted geometry with one broken Fe-S bond and six terminal CO ligands. Acids with pK(a) ≤ 12.7 protonate [Fe2(bdt)(CO)6](-) with bimolecular rate constants of 4 × 10(6), 7 × 10(6), and 2 × 10(8) M(-1) s(-1) (trichloroacetic, trifluoroacetic, and toluenesulfonic acids, respectively). The resulting hydride complex [Fe2(bdt)(CO)6H] is therefore likely to be an intermediate in photocatalytic cycles. This intermediate resembles structurally and electronically the parent complex [Fe2(bdt)(CO)6], with very similar carbonyl stretching frequencies.

Enhanced photochemical hydrogen production by a molecular diiron catalyst incorporated into a metal-organic framework

A molecular proton reduction catalyst [FeFe](dcbdt)(CO)6 (1, dcbdt = 1,4-dicarboxylbenzene-2,3-dithiolate) with structural similarities to [FeFe]-hydrogenase active sites has been incorporated into a highly robust Zr(IV)-based metal-organic framework (MOF) by postsynthetic exchange (PSE). The PSE protocol is crucial as direct solvothermal synthesis fails to produce the functionalized MOF. The molecular integrity of the organometallic site within the MOF is demonstrated by a variety of techniques, including X-ray absorption spectroscopy. In conjunction with [Ru(bpy)3](2+) as a photosensitizer and ascorbate as an electron donor, MOF-[FeFe](dcbdt)(CO)6 catalyzes photochemical hydrogen evolution in water at pH 5. The immobilized catalyst shows substantially improved initial rates and overall hydrogen production when compared to a reference system of complex 1 in solution. Improved catalytic performance is ascribed to structural stabilization of the complex when incorporated in the MOF as well as the protection of reduced catalysts 1(-) and 1(2-) from undesirable charge recombination with oxidized ascorbate.

Mixed-valence [Fe(I)Fe(II)] hydrogenase active site model complexes stabilized by a bidentate carborane bis-phosphine ligand

A series of [FeFe]-hydrogenase active site analogues, with the general formula [Fe(2)(dt)(CO)(4)(BC)] 1-3 (dt = dithiolate, pdt = propyl-1,3-dt (1), bdt = benzene-1,2-dt (2), edt = ethyl-1,2-dt (3); BC = 1,2-bisdiphenylphosphine-1,2-o-carborane), has been prepared and structurally characterized. While the electrochemical reductions of 1-3 are largely invariant to the different nature of their dt bridges, the oxidations differ by more than 120 mV in between the series. Remarkably, all three compounds are reversibly oxidized, with complex 1 that contains the most electron-donating pdt ligand at the mildest potential of -0.09 V vs. Fc/Fc(+). The one-electron oxidized state 1(ox) is stable for several minutes and was spectroscopically characterized by FTIR and EPR. EPR spectroscopy provided evidence that in the mixed-valence [Fe(I)Fe(II)] state most of the spin density is located on the iron with the BC-ligand. This is monitored through the strong (31)P hyperfine coupling of the phenyl groups of the BC ligand, while further delocalization into the o-carborane unit is negligible.

Toxicity and histopathology of the growth regulator pyriproxyfen to adults and eggs of the cat flea (Siphonaptera:Pulicidae)

Adult cat fleas, Ctenocephalides felis (Bouché), exposed continuously to pyriproxyfen died within 8-10 d. Microscopic examination of 7-d-old adults indicated death was caused by histopathological damage to fat body, Malpighian tubules, midgut epithelia, salivary gland cells, and other internal tissues. Fleas were killed by pyriproxyfen regardless of whether they were held as unfed adults on treated filter paper or as feeding adults on treated dog hair. In addition to these toxic effects on adults, pyriproxyfen also induced formation of large autophagic vacuoles in maturing oocytes leading to partial reabsorption of yolk, degeneration of the nucleus, and lysis of the follicular epithelium. Consequently, most of the eggs laid by treated fleas lacked a nucleus, had a poorly formed chorion, and were ruptured during ovulation. These laboratory results suggest that continuous exposure of fleas to pyriproxyfen on a host animal could prevent deposition of viable eggs and eventually kill adults, thereby controlling all stages of flea development.

Tissue viability. Pressure relief in the community

The prevention of pressure sore development can make a major contribution to allowing at risk patients to remain in their own homes. This article describes a cooperative initiative between district nurses and medical engineers to provide appropriate pressure relieving devices quickly to patients in the community.

Report on International Medical Society of Paraplegia 31st Annual Scientific Meeting 8 to 10 September 1992

No abstract available

Reactivity of antisera to antigens of C-type viruses with leucocytes from patients with acute leukaemia

A number of previous studies have suggested that certain C-type viruses from non-human primates are associated with acute leukaemia in humans. The present study sought to examine this association further by detection of antigens related to these viruses on the surface of acute leukaemia cells. Antisera against the whole viruses or the major internal protein of simian sarcoma, endogenous baboon and Rauscher viruses were tested against mononuclear cells from patients with acute leukaemia at various stages of their disease in 51Cr release leucocyte dependent cytotoxic assays. A high proportion of the patients had antigens related to these viruses detectable on their blood leucocytes at some stage in their disease whereas with one exception blood leucocytes from non-leukaemic subjects did not. The expression of these antigens did not show a close relation to the number of blast cells in blood detected on morphological grounds. Antigens related to the non-human primate viruses were detected on mononuclear cells from bone marrow samples of several non-leukaemic patients which indicated they were not specifically associated with leukaemia. Antigens related to the Rauscher virus were detected on cells of practically all bone marrow samples tested. These results suggest that assays to detect these antigens would be of limited usefulness to monitor disease activity in patients with acute leukaemia. Their expression on blood leucocytes however appeared strongly associated with acute leukaemia and further studies to assess the prognostic and epidemiological significance of detection of these antigens appears warranted.

Expression of blood group-like antigens on the T lymphocytes of acute leukaemia patients in remission

A number of previous studies have described antibodies in normal sera reactive to human leukaemia cells. In the course of studies on humoral immunity to acute myeloid leukaemia (AML) cells it was noticed that sera from normal subjects were cytotoxic in complement lysis and leucocyte dependent antibody (LDA) assays to blood leucocytes from patients with AML in remission. Investigation of these reactions in eleven patients with acute leukaemia in complete or partial remission revealed that reactivity occurred most frequently between sera from normal blood group O or B subjects and leucocytes from patients of blood group A (five patients). Leucocytes from blood group O patients were largely unreactive. Blood leucocytes from five of six patients in relapse did not react with normal sera. Subsequent studies revealed that the antigens were detected only on T lymphocytes. Reactivity could be removed by absorption on red cells of blood group A but not sheep or Ox red blood cells suggesting the antigens concerned were closely related to blood group A antigens. Some reactivity with antisera to the blood group H antigens was also evident in these studies. Gel filtration studies indicated that lymphocyte dependent antibody mediated cytotoxicity was mediated by IgG antibodies while complement dependent lysis was mainly mediated by IgM antibodies. The biological significance of these findings has yet to be determined but these results suggest that reactivity with blood group antigens needs to be considered in in vitro cytotoxicity studies involving leucocytes from leukaemia patients.