Mapping ACE2 and TMPRSS2 co-expression in human brain tissue: implications for SARS-CoV-2 neurological manifestations.

The Coronavirus Disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily targets respiratory cells, but emerging evidence shows neurological involvement, with the virus directly affecting neurons and glia. SARS-CoV-2 entry into a target cell requires co-expression of ACE2 (Angiotensin-converting enzyme-2) and TMPRSS2 (Trans membrane serine protease-2). Relevant literature on human neurological tissue is sparse and mostly focused on the olfactory areas. This prompted our study to map brain-wide expression of these entry proteins and assess age-related changes. The normal brain tissue samples were collected from cerebral cortex, hippocampus, basal ganglia, thalamus, hypothalamus, brain stem and cerebellum; and were divided into two groups - up to 40 years (n = 10) and above 40 years (n = 10). ACE2 and TMPRSS2 gene expression analysis was done using qRT-PCR and protein co-expression was seen by immunofluorescence. The ACE2 and TMPRSS2 gene expression was observed to be highest in hypothalamus and thalamus regions, respectively. Immunoreactivity for both ACE-2 and TMPRSS2 was observed in all examined brain regions, confirming the presence of these viral entry receptors. Co-localisation was maximum in hypothalamus. Our study did not find any trend related to different age groups. The expression of both these viral entry receptors suggests that normal human brain is susceptibility to SARS-CoV-2, perhaps which could be related to the cognitive and neurological impairment that occur in patients.

Number of serotonergic neurons in the subthalamic nucleus and globus pallidus internus could influence the effects of deep brain stimulation in Parkinson's disease.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or globus pallidus internus (GPi) is a standard treatment for Parkinson's disease (PD), with both regions exhibiting similar treatment effectiveness. However, posttreatment neuropsychiatric side effects, such as severe depression, are common, primarily due to the loss of serotonergic cells. Identifying a region with fewer serotonergic neurons could potentially reduce these side effects. This study aimed to quantify the number of serotonergic neurons in the STN and GPi. Both regions were analyzed using hematoxylin and eosin staining and immunohistochemistry. The GPi exhibited a significantly lower number and H-score of serotonergic neurons than the STN. Within the STN, the number and H-score of serotonergic neurons were higher in the medial aspect than in the lateral aspect. Three different types of neurons, large and small, were observed. In STN, large neurons were concentrated in the center and small neurons in the periphery. This distribution was not observed in GPi. In addition, the concentration of the serotonergic neurons is less in GPi. These findings suggest that the GPi may be a safer target region, potentially reducing the incidence of post-DBS depression.

Surgical anatomy of the cerebellar tonsils: A cadaveric study.

BACKGROUND: Knowledge of the normal anatomy of the cerebellar tonsils is a prerequisite in various surgeries of the posterior cranial fossa Clinical conditions, as the Chiari I malformations (CIM) alter the normal position of the cerebellar tonsils. OBJECTIVE: Therefore, we aim to better elucidate the surgical anatomy of and around the cerebellar tonsils in regard to the CIM. METHODS: Fifty formalin-fixed adult cadavers injected with colored latex through vertebral arteries underwent craniotomy and durotomy to expose the cerebellar tonsils and related structures. The tonsils and their surrounding anatomy were then studied. RESULTS: Forty cerebellar tonsils were at or above the foramen magnum. Five specimens presented with CIM with the tonsils below (3-5 mm) the FM with a mean tonsillar decent of 7.9 ± 2.3 mm. Of the cadavers without CIM, in forty-two cases, the thickness of the dura mater was within ±3SD ranges. In three cases, the dura mater was thinner at the CVJ and one case; the dura adhered tightly to the inner aspect of the occipital squama. In five CIM cadavers, the dura mater was markedly thicker at the CVJ. The PICA caudal loop was 5.9 ± 1.6 mm long. In CIM cases, the PICA loop was longer, nearer the dura, 1 mm below the superior border of the C1 posterior arch. The distances from the PICA loop were markedly reduced by 3 mm from the spinal accessory nerve and 2 mm from the first spinal nerve. The DN was significantly closer to the tonsillar peduncle in CIM cases. CONCLUSION: These data are important for better understanding the intrinsic and extrinsic anatomy of the cerebellar tonsils in patients with and without CIM. Importantly, tonsillectomy/tonsillar coagulation must consider the close relationship of the dentate nucleus to the base of the cerebellar tonsil to avoid iatrogenic injury.

Enhanced Understanding of Facial Nerve Anatomy and Arborization in the Indian Population: Implications for Surgical Procedures.

The anatomy and arborization patterns of the extraparotid facial nerve show considerable variation among different populations, impacting surgical approaches in plastic, head and neck, and ENT surgeries. This study focuses on the Indian population to provide a detailed understanding of these variations, specifically highlighting the Davis type IV arborization pattern's prevalence and its clinical relevance. We conducted a comprehensive dissection of 16 formalin-preserved Indian cadaveric hemifaces. The study meticulously mapped the facial nerve trunk (FNT), its furcation points, and branches. Key anatomical landmarks for locating these nerve structures were identified, including the tip of the mastoid process, the angle of the mandible, and a novel line between the lateral palpebral fissure and otobasion superioris. The most common arborization pattern observed was Davis type IV (31.3%). The study provided precise measurements for locating the FNT and its branches, using identifiable landmarks. These findings facilitate more accurate surgical planning, crucial for procedures involving nerve repair or grafting. This research offers vital insights into the facial nerve anatomy specific to the Indian population, with significant implications for surgical precision and patient outcomes. By establishing reliable anatomical landmarks and elucidating the predominant arborization pattern, the study enhances the understanding of facial nerve behavior during surgical interventions, particularly in the context of facial paralysis treatment and reconstructive surgeries. Due to the small sample size, however, this study only acts as a pilot for further research.

Analysis of distribution and localization of proteins of the reelin signalling pathway in mesial temporal lobe epilepsy.

INTRODUCTION: Granule cell dispersion (GCD) is pathognomonic of hippocampal sclerosis seen in the mesial temporal lobe epilepsy (MTLE). Current animal studies indicate deficiency of Reelin is associated with abnormal granule cell migration leading to GCD. The present study aimed to evaluate complete Reelin signalling pathway to assess whether Reelin deficiency is related to MTLE. MATERIALS AND METHODS: Hippocampal sclerosis was confirmed by H and E stain. To explore the amount and cellular location of the Reelin cascade molecules, the hippocampal tissues from MTLE surgery and controls (n = 15 each) were studied using Immuno-histochemistry (IHC). Additionally, confocal imaging was used to validate the IHC findings by co-localization of different proteins. Quantification of IHC images was performed using histo-score and confocal images by Image J software. RESULTS: Immune expression of active Reelin was significantly reduced in patients. Reelin receptors were deranged, apolipoprotein E receptor 2 was increased while very low-density lipoprotein receptor was reduced. Disabled-1, a downstream molecule was significantly reduced in MTLE. Its ultimate target, cofilin was thus disinhibited and expressed more in MTLE. Reelin cleaving protease, matrix metalloprotease-9 (MMP-9) and MMP-9 inhibitor, tissue inhibitor of matrix protease-1, showed reduced expression in extracellular matrix. Semi-quantification of immunohistochemistry was done using Histo (H) score. H score of Reelin in diseased patients was 15 against 125 for control patients. These results were validated by confocal fluorescence microscopy. CONCLUSIONS: Reelin signalling cascade was deranged in chronic MTLE. Pharmacological manipulation of Reelin cascade can be done at various levels and it may provide novel treatment options for MTLE.

Revisiting the surgical anatomy of the triangle of doom and the triangle of pain.

Better understanding of the surgical anatomy of the triangle of doom and the triangle of pain with fixed bony landmarks like the anterior superior iliac spine (ASIS) and the pubic symphysis (PS) can help in defining a safe location for trocar placement during laparoscopic surgeries and minimize neurovascular complications. Ten cadavers were dissected bilaterally to explore the surgical anatomy of both the triangles. ASIS and PS were evaluated in relation to the deep inguinal ring, external iliac artery, femoral nerve, and inferior epigastric artery. The deep inguinal ring was located at a depth of ~3 cm, about 4.9 ± 0.56 cm along the y-axis and 6.2 ± 0.94 cm along the x-axis, from the ASIS. The external iliac artery was located ~4.33 ± 0.6 cm along the y-axis and 7.29 ± 0.76 along the x-axis from the ASIS. The inferior epigastric artery was at ~4.31 ± 0.38 cm from the midline at the level of ASIS. This knowledge can help in the surface localization of both the triangles and prevent injury to the various neurovascular structures in relation to these triangles. In the current study, cranial to the ASIS lying at a distance of >5 cm from the midline was observed to be a safe zone for accessory trocar placement. The umbilical port has been observed to be safe for trocar placement. The mean angle between ductus deferens and testicular vessels was observed to be 43.5° ± 4.79°, which could help in determining their relative locations during various surgical procedures.

Digastric musculus sternalis.

PURPOSE: To report a rare variant muscle. METHODS: Aberrant muscle was observed in the anterior chest wall musculature during routine cadaver prosection. RESULTS: Musculus sternalis consisting of two muscular bellies united at an angle by an intermediate tendon was observed anterior to the pectoral major of the left side. The muscle did not have any bony attachment. CONCLUSIONS: The present case represents a hybrid muscle with superior belly derived from the prepectoral mass and inferior belly from ventral longitudinal muscle column. Clinically, the musculus sternalis may be misinterpreted as a pathological mass or lesion thus its accurate knowledge is significant to radiologists, angiologists and surgeons for better interpretation of mammographic images, safer interventions and for reconstructive surgeries.

Osseous deficiencies, pockets, superfluous lateral border thickening in scapula: a rare occurrence.

BACKGROUND: Beyond the nutrient and suprascapular foramen, the other foramina, holes or osseous deficiencies, pockets has rarely been reported in scapula. If present, the bony holes or deficiencies may lead to radiolucent areas and may be mistaken for sites of osteolytic destruction related to skeletal metastases, multiple myeloma or others. CASE REPORT: In the present case of left scapula, unusual osseous deficiencies of different size and shape along with pockets were observed in the body of scapula. The maximum height and width of largest bony deficiency was 35.8 mm and 12.6 mm. There was abnormal osseous thickening beside the lateral border of scapula along with the presence of some spines. Five nutrient foramina, three on the costal and two on the dorsal surface were noticed. CONCLUSIONS: The present case reports the osseous deficiencies, pockets and extra osseous growth along the lateral border, multiple nutrient foramina altogether in one specimen. Thorough anatomical knowledge of these unusual osseous variations can provide the clinicians, radiologists and forensic experts with better clinical judgement and may add insight to the surgical planning by orthopaedic surgeons.

Identification of novel pulmonary vein nodes as generators of ectopic arrhythmic foci for atrial fibrillation: an immunohistochemical proof.

PURPOSE: The atrial muscle sleeve (AMS) of the pulmonary vein is the most common source of the arrhythmogenic triggers in atrial fibrillation (AF). Anatomical substrate generating these ectopic currents is still elusive. The present study was designed to study the AMS of pulmonary veins with an emphasis on the structural basis which might govern AF initiation and perpetuation. METHODS: The study was conducted on a longitudinal tissue section of pulmonary vein, taken from 15 human cadaveric nondiseased hearts. Tissue was studied histologically using H&E and Gömöri trichrome stain. The pacemaker channels were identified by immunohistochemistry using monoclonal HCN4 and HCN1 antibodies. RESULTS: The AMS was identified in each pulmonary vein, located between the tunica adventitia and tunica media. A node-like arrangement of myocytes was seen within the AMS in 30% of veins. It had a compact zone limited by a fibrous capsule and contained much smaller, paler and interconnected myocytes. Outside the capsule, there was a zone of dispersed, singly placed myocytes separating the compact zone from the working myocytes of the AMS. HCN4 and HCN1 antibodies were expressed on the cell membrane of nodal myocytes, while the working myocytes demonstrated none to minimal staining. CONCLUSION: Pulmonary veins nodes are similar to the specialized cardiac conductive tissue in the histological arrangement of compact and transitional zones, cellular characteristics and the presence of pacemaker channels. They might be the anatomical basis of ectopic arrhythmogenic foci. To our knowledge, these nodes are being described for the first time in human.

Surgical anatomy of basal turn in relation to middle cranial fossa and round window as pertaining to middle fossa cochlear implant technique.

PURPOSE: The purpose of this investigation was to evaluate the relation of the basal turn of cochlea with middle cranial fossa and round window as pertaining to middle cranial fossa cochlear implant technique. METHODS: Fifty-four formalin preserved temporal bones were micro-dissected to expose the basal turn. The point (f) was marked on the basal turn of cochlea where there was minimum distance of basal turn of cochlea from the floor of middle cranial fossa (f1). The f-f1 distance, the angle (∠smf) and distance of point "f" from the round window (s-f) was measured. RESULTS: The mean minimum distance between basal turn of cochlea and floor of middle cranial fossa (f-f1) was 2.0 ± 0.7 mm.The point f was at mean distance (s-f) and angle (∠smf) of 14.7 ± 1.6 mm and 217° ± 13.7° from round window, respectively. CONCLUSIONS: The information may be helpful for designing appropriate electrode array for middle fossa technique especially for deciding the length of electrode array towards round window, as otherwise electrode may extend into vestibule of inner ear. In the cases where bone thickness between superior part of basal turn of cochlea and middle cranial fossa is < 1.5 mm, surgeon should be extra cautious.

Unusually Distorted Pseudo-Octahedral Coordination Environment Around CoII from Thioether Schiff Base Ligands in Dinuclear [CoLn] (Ln = La, Gd, Tb, Dy, Ho) Complexes: Synthesis, Structure, and Understanding of Magnetic Behavior.

The synthesis, structural characterization, and magnetic behavior of a new family of binuclear CoII-LnIII complexes of formula [LnIIICoIIL2(NO3)3]·H2O (Ln = La, 1; Gd, 2; Tb, 3; Dy, 4; Ho, 5; HL = 3-methoxy-N-(2-(methylsulfanyl)phenyl)salicylaldimine) have been reported. The chosen ligand system HL has adjacent soft ONS and hard OO binding pockets ideal for selective coordination of CoII and 4f metal ions. All the complexes 1-5 exhibit a CoII center in a highly distorted octahedral geometry with the LnIII centers in bicapped square-antiprism geometry. The unique distortion about the CoII center is introduced by the coordination of 4f metal ions in the hard OO coordination site. The distortion is further supported by the presence of -SMe groups giving an S donor atom which owing to its larger size can support large bond distances and angles. The geometry around the CoII centers is intermediate between meridional and facial geometric isomers. The magnetic properties of these complexes have been investigated by a "full model" approach using CONDON with the experimental magnetochemical analysis revealing ferromagnetic Co-Ln coupling in compounds 2-5. Ab initio calculations on the X-ray crystal structures of 1-5 paint a semiquatitative picture about the contribution of the individual anisotropic centers toward the overall magnetic properties of the compounds. Theoretical analysis predicts 1 and 2 as weak single-ion magnet (SIM) and single-molecule magnet (SMM) respectively with CoII being solely responsible for the complex anisotropy. In 2, JCoGd plays a crucial role in preserving the anisotropy contribution of Co by channelizing relaxation via a higher excited exchange doublet. Because of the inefficiency of JCoTb, JCoDy, and JCoHo in quenching single-ion Ln fragment transverse anisotropy and preserving CoII high axial anisotropy (favoring rhombicity), 3-5 lack SMM behavior.

Histological evaluation of atrial muscle sleeve of pulmonary veins as relevant to trigger mapping and ablation.

BACKGROUND: The atrial myocardial sleeve of the pulmonary vein is the most common source of arrhythmogenic triggers in atrial fibrillation. The present study was designed to study the atrial muscle sleeve in detail, to help in planning and execution of "trigger mapping and ablation" procedure, used for treating resistant atrial fibrillation. METHODS: A longitudinal tissue section was taken along the length of each pulmonary vein including the posterior wall of the left atrium, from 15 normal human formalin fixed hearts. The histological and micro-morphometric details of the atrial muscle sleeve were studied. RESULTS: A muscle sleeve composed of cardiac muscle was found in each pulmonary vein, situated between adventitia and media, and separated from media by clearly defined connective tissue. The fiber arrangement was non uniform and angular changes in the fiber direction were frequent. Autonomic ganglia were found in the adventitia. The sleeve was tapering distally but reduction was not circumferentially uniform, minimum thickness was more for right (~ 0.2 mm) than for left veins (0.1 mm). The mean atrial sleeve length was 6.3 mm; the left veins had longer sleeve then right while left inferior veins had the maximum mean length. CONCLUSION: The trigger mapping should be done for 2 cm on pulmonary veins to fully cover the atrial muscle sleeve. The gradual tapering of the atrial sleeve indicates that the maximum intensity ablative lesions would be needed at the veno-atrial junction while the ablation power should be reduced distally. Distal triggers on right veins would need more ablation then on the left veins.

Translational anatomy of the left atrium and esophagus as relevant to the pulmonary vein antral isolation for atrial fibrillation.

PURPOSE: Pulmonary vein antrum isolation by radiofrequency ablation has become a preferred treatment for atrial fibrillation. The aim of our research is to study the anatomy of the PVantrum and its related structures with special emphasis on the esophageal relation to the various components of the antrum, as thermal injury is a common complication. METHODS: Mediastinal contents were extracted "en bloc" from 30 human formalin fixed adult cadavers to study the posterior wall of the left atrium along with the esophagus. RESULTS: The pulmonary antrum was measured. Each pulmonary ostium was assessed for circumference and muscle thickness. The esophagus was related to the left superior ostium in 90% of cases. The esophagus was traced on the atrial wall in each case; the distance from endocardium was measured at five equidistant lines. AV node distance from the right inferior pulmonary vein was 5 cm. The atrioventricular part of the membranous septum measured 4.2 mm. CONCLUSIONS: For antral isolation the ablation lines are about 3 cm superior, 3.5 cm inferior and about 1 cm apart. The esophagus is ~ 12 mm away at the superior and ~ 7 mm away at the inferior ablation line. On the left ablation line this distance would diminish from 15 to 7 mm. The pulmonary ostial circumference is ~ 5 cm with muscle thickness varying from 0.7 to 4 mm. The left ostia need more ablative power as they have a 60% (1 mm) thicker muscle coat. Care should be taken while ablating round the left superior ostium as the esophagus lies 1-3 cm behind it in 90% of the cases.

Anatomic variability of oval window as pertaining to stapes surgery.

PURPOSE: The purpose of the study is to study the details of dimensions and shape of oval window in different age groups, sides and genders and their clinical implications. The oval window is a key structure while performing surgeries in relation to stapes. An intricate knowledge of the shape and size of the oval window is important for the reconstruction and fitting of cartilage compatible with the native shape of the oval window. METHODS: Sixty normal wet cadaveric temporal bones of known age; gender and side were micro-dissected. The maximum height and width of the oval window was measured. The shape of the oval window was noticed. RESULTS: The mean value for maximum height and width of the oval window was 1.31 ± 0.28 mm and 2.67 ± 0.42 mm, respectively. The height and width of the oval window ranged between 1 mm and 1.5 mm and 2 mm and 3 mm in majority of the cases. he oval window was found to be oval shaped in 53.3% cases, other shapes such as kidney, D shape, rectangular or trapezoidal were also observed. CONCLUSIONS: The refined morphometric information of the oval window will help in preoperative assessment and surgical planning of various oval window-related surgical procedures. The knowledge may also help in designing and selecting proper cartilage shoe for the best outcome. Narrow oval window may cause procedural complications and surgeon discomfort in various stapes surgeries.

Reappraisal of the classical abdominal anatomical landmarks using in vivo computerized tomography imaging.

INTRODUCTION: With expanding scope of interventions it becomes mandatory to have correct and evidence-based knowledge of surface anatomy of internal abdominal structures. Information available in text books is derived from work done on cadaveric studies. Current study was designed to provide data of key abdominal surface anatomical landmarks and their variations in living subjects using CT imaging of adult population. MATERIALS AND METHODS: Cross-sectional study was conducted using 100 abdominopelvic CT scans of patients of Indian origin. RESULTS: Vertebral levels of origin of celiac trunk varied from T11 to L1/2 intervertebral disc, superior mesenteric artery from T12 to L2, inferior mesenteric artery from L2 to L4 and aortic bifurcation from L3 to L5. Origin of both renal arteries varied between T12 and L2 and the formation of inferior vena cava varied from L3 to L5. Vertebral levels of upper pole of both kidneys ranged from T11 to upper L3. Spleen was related to 9th to 11th ribs in 36% and 10th to 12th ribs in 34% scans. Most common vertebral levels of subcostal plane, planum supracristale and planum intertuberculare noticed were lower L2, L4 and lower L5, respectively. CONCLUSIONS: Data derived from imaging investigations of living subjects and variations from the conventional descriptions observed in the current study might be helpful for clinicians.

Characterization and Reactivity of a Tetrahedral Copper(II) Alkylperoxido Complex.

A tetrahedral CuII alkylperoxido complex [CuII (TMG3 tach)(OOCm)]+ (1OOCm ) (TMG3 tach={2,2',2''-[(1s,3s,5s)-cyclohexane-1,3,5-triyl]tris-(1,1,3,3-tetramethyl guanidine)}, OOCm=cumyl peroxide) is prepared and characterized by UV/Vis, cold-spray ionization mass spectroscopy (CSI-MS), resonance Raman, and EPR spectroscopic methods. Product analysis of the self-decomposition reaction of 1OOCm in acetonitrile (MeCN) indicates that the reaction involves O-O bond homolytic cleavage of the peroxide moiety with concomitant C-H bond activation of the solvent molecule. When an external substrate such as 1,4-cyclohexadiene (CHD) is added, the O-O bond homolysis leads to C-H activation of the substrate. Furthermore, the reaction of 1OOCm with 2,6-di-tert-butylphenol derivatives produces the corresponding phenoxyl radical species (ArO. ) together with a CuI complex through a concerted proton-electron transfer (CPET) mechanism. Details of the reaction mechanisms are explored by DFT calculations.

Rare anatomic variations of the right hepatic biliary system.

PURPOSE: To report rare and clinically significant anatomic variations in the biliary drainage of right hepatic lobe. METHODS: Unique variations in the extra- and intrahepatic biliary drainage of right hepatic lobe were observed in 6 cadaveric livers during dissection on 100 formalin-fixed en bloc cadaveric livers. RESULTS: There was presence of aberrant drainage of right segmental and sectorial ducts in four cases and of accessory right posterior sectorial duct in two cases. CONCLUSIONS: We encountered some extensively complicated biliary drainage of right hepatic lobe, unsuccessful recognition of which can lead to serious biliary complications during hepatobiliary surgeries and biliary interventions.

Designing a Dy2 Single-Molecule Magnet with Two Well-Differentiated Relaxation Processes by Using a Nonsymmetric Bis-bidentate Bipyrimidine- N-Oxide Ligand: A Comparison with Mononuclear Counterparts.

Herein we report a dinuclear [(µ-mbpymNO){(tmh)3Dy}2] (1) single-molecule magnet (SMM) showing two nonequivalent DyIII centers, which was rationally prepared from the reaction of Dy(tmh)3 moieties (tmh = 2,2,6,6-tetramethyl-3,5-heptanedionate) and the asymmetric bis-bidentate bridging ligand 4-methylbipyrimidine (mbpymNO). Depending on whether the DyIII ions coordinate to the N^O or N^N bidentate donor sets, the DyIII sites present a NO7 ( D2 d geometry) or N2O6 ( D4 d) coordination sphere. As a consequence, two different thermally activated magnetic relaxation processes are observed with anisotropy barriers of 47.8 and 54.7 K. Ab initio calculations confirm the existence of two different relaxation phenomena and allow one to assign the 47.8 and 54.7 K energy barriers to the Dy(N2O6) and Dy(NO7) sites, respectively. Two mononuclear complexes, [Dy(tta)3(mbpymNO)] (2) and [Dy(tmh)3(phenNO)] (3), have also been prepared for comparative purposes. In both cases, the DyIII center shows a NO7 coordination sphere and SMM behavior is observed with Ueff values of 71.5 K (2) and 120.7 K (3). In all three cases, ab initio calculations indicate that relaxation of the magnetization takes place mainly via the first excited-state Kramers doublet through Orbach, Raman, and thermally assisted quantum-tunnelling mechanisms. Pulse magnetization measurements reveal that the dinuclear and mononuclear complexes exhibit hysteresis loops with double- and single-step structures, respectively, thus supporting their SMM behavior.

Role of the Diamagnetic Zinc(II) Ion in Determining the Electronic Structure of Lanthanide Single-Ion Magnets.

Four complexes containing DyIII and PrIII ions and their LnIII -ZnII analogs have been synthesized in order to study the influence that a diamagnetic ZnII ion has on the electronic structure and hence, the magnetic properties of the DyIII and PrIII single ions. Single-crystal X-ray diffraction revealed the molecular structures as [DyIII (HL)2 (NO3 )3 ] (1), [PrIII (HL)2 (NO3 )3 ] (2), [ZnII DyIII (L)2 (CH3 CO2 )(NO3 )2 ] (3) and [ZnII2 PrIII (L)2 (CH3 CO2 )4 (NO3 )] (4) (where HL=2-methoxy-6-[(E)-phenyliminomethyl]phenol). The dc and ac magnetic data were collected for all four complexes. Compounds 1 and 3 display frequency dependent out-of-phase susceptibility signals (χM "), which is a characteristic signature for a single-molecule magnet (SMM). Although 1 and 3 are chemically similar, a fivefold increase in the anisotropic barrier (Ueff ) is observed experimentally for 3 (83 cm-1 ), compared to 1 (16 cm-1 ). To rationalize the larger anisotropic barrier (1 vs. 3), detailed ab initio calculations were performed. Although the ground state Kramer's doublet in both 1 and 3 are axial in nature (gzz =19.443 for 1 and 18.82 for 3), a significant difference in the energy gap (Ueff ) between the ground and first excited Kramer's doublet is calculated. This energy gap is governed by the electrostatic repulsion between the DyIII ion and the additional charge density found for the phenoxo bridging ligand in 3. This extra charge density was found to be a consequence of the presence of the diamagnetic ZnII ion present in the complex. To explore the influence of diamagnetic ions on the magnetic properties further, previously reported and structurally related Zn-DyIII complexes were analyzed. These structurally analogous complexes unambiguously suggest that the electrostatic repulsion is found to be maximal when the Zn-O-Dy-O dihedral angle is small, which is an ideal condition to maximize the anisotropic barrier in DyIII complexes.

Design of a Family of Ln3 Triangles with the HAT Ligand (1,4,5,8,9,12-Hexaazatriphenylene): Single-Molecule Magnetism.

A series of trinuclear Ln3 complexes (LnIII = Yb (1), Er (2), Dy (3) and Gd (4)) were prepared from the tris-chelate bidentate ligand 1,4,5,8,9,12-hexaazatriphenylene (HAT). 1 and 2 exhibited field-induced single-molecule-magnet (SMM) behavior with estimated Ueff values of 21.30 and 13.86 K, respectively. Complex 3 behaved as a SMM even at zero field, and two different thermally assisted relaxation processes were detected with Ueff values of 29.6 K (fast relaxation process, FR) and 69 K (slow relaxation process, SR) due to the existence of two magnetically different DyIII centers in the molecule. Ab initio studies reveal that all the Dy3+ centers have almost an Ising ground state. The local anisotropy axes are not coplanar but form angles with the Dy3 plane in the range 58-78°. The magnetic interaction between the anisotropic Dy3+ ions is antiferromagnetic in nature and very weak in magnitude. However, due to the extreme feebleness of the magnetic interaction with regard to the local excitation energies, the magnetization blockade is most probably of single-ion origin. Calculations support the existence of two relaxation processes, which take place through the first excited state following an Orbach/Raman mechanism. Finally, for complex 4, the magnetocaloric effect was simulated using the magnetic parameters extracted from the fit of the magnetization and susceptibility data and demonstrated that the simulated -ΔSm values were almost coincident with those extracted from the integration of the field dependence of the magnetization. The simulated MCE value at 2 K and 5 T (20.46 J kg-1 K-1) makes complex 4 an attractive candidate for cryogenic magnetization.