An Exploration of the Hydrogen Bond Donor Ability of Ammonia.

Ammonia is an important molecule due to its wide use in the fertiliser industry. It is also used in aminolysis reactions. Theoretical studies of the reaction mechanism predict that in reactive complexes and transition states, ammonia acts as a hydrogen bond donor forming N-H⋅⋅⋅O hydrogen bond. Experimental reports of N-H⋅⋅⋅O hydrogen bond, where ammonia acts as a hydrogen bond donor are scarce. Herein, the hydrogen bond donor ability of ammonia is investigated with three chalcogen atoms i. e. O, S, and Se using matrix isolation infrared spectroscopy and electronic structure calculations. In addition, the chalcogen bond acceptor ability of ammonia has also been investigated. The hydrogen bond acceptor molecules used here are O(CH3 )2 , S(CH3 )2 , and Se(CH3 )2 . The formation of the 1 : 1 complex has been monitored in the N-H symmetric and anti-symmetric stretching modes of ammonia. The nature of the complex has been delineated using Atoms in Molecules analysis, Natural Bond Orbital analysis, and Energy Decomposition Analysis. This work presents the first comparison of the hydrogen bond donor ability of ammonia with O, S, and Se.

An Experimental Exploration of C-H⋠⋠⋠X Hydrogen Bond in [CHCl3 -X(CH3 )2 ] Complexes (X=O, S, and Se).

Among the conglomeration of hydrogen bond donors, the C-H group is prevalent in chemistry and biology. In the present work, CHCl3 has been selected as the hydrogen bond donor and are X(CH3 )2 are the hydrogen bond acceptors. Formation of C-H⋅⋅⋅X hydrogen bond under the matrix isolation condition is confirmed by the observation of red-shift in the C-H stretching frequency of CHCl3 and comparison with the simulated spectra. Stabilisation energy of all the three complexes is almost equal although the observed red-shift for the C-H⋅⋅⋅O complex is less compared to the C-H⋅⋅⋅S/Se complexes. The nature and origin of the hydrogen bond have been delineated using Natural Bond Orbital, Atoms in Molecules, Non-Covalent Interaction analyses, and Energy Decomposition Analysis. Charge transfer is found to be proportional to the observed red-shift. This work provides the first impression of C-H⋅⋅⋅Se hydrogen bond and its comparison with C-H⋅⋅⋅O/S hydrogen bond interaction under experimental condition.

Hydrogen bond properties of Se in [ROH-Se(CH3)2] complexes (R = H, CH3, C2H5): matrix-isolation infrared spectroscopy and theoretical calculations.

Se is now considered as a potential centre for hydrogen bond interactions. The hydrogen bond acceptor ability of Se has been investigated in [ROH-Se(CH3)2] complexes (R = H, CH3, and C2H5) using matrix-isolation infrared spectroscopy and electronic structure calculations. The first impression of the IR spectra of the hydrogen bond complexes of [ROH-Se(CH3)2] in N2 and Ar matrices is presented here. Moreover, no spectroscopic data are available for the [HOH-Se(CH3)2] complex. Vibrational spectra in the OH stretching region indicate the formation of the [ROH-Se(CH3)2] complex under the matrix-isolation conditions. Comparison of the experimental spectra with the simulated vibrational frequencies at different levels of theory confirms the formation of the 1 : 1 cluster of [ROH-Se(CH3)2] stabilised by O-H⋯Se hydrogen bond interactions. Multiple conformers of the [CH3OH-Se(CH3)2] complex having marginally different stabilisation energies have been predicted from electronic structure calculations and signatures of the same have been observed under the cold conditions of matrix isolation. Conformer specific assignment of the 1 : 1 cluster of [C2H5OH-Se(CH3)2] (anti and gauche forms) has been carried out in both the matrices. Concentration dependent experiments indicate the formation of higher order clusters and/or mixed clusters along with the formation of a 1 : 1 cluster for CH3OH and C2H5OH. The nature of the selenium centred hydrogen bond has been delineated using AIM, NBO and energy decomposition analysis. A comparison of similar complexes of H2O, CH3OH, and C2H5OH with O, S and Se indicates that Se is not far away in hydrogen bond acceptor ability compared to O and S.

Substrate induced electronic phase transitions of CrI[Formula: see text] based van der Waals heterostructures.

We perform first principle density functional theory calculations to predict the substrate induced electronic phase transitions of CrI[Formula: see text] based 2-D heterostructures. We adsorb graphene and MoS[Formula: see text] on novel 2-D ferromagnetic semiconductor-CrI[Formula: see text] and investigate the electronic and magnetic properties of these heterostructures with and without spin orbit coupling (SOC). We find that when strained MoS[Formula: see text] is adsorbed on CrI[Formula: see text], the spin dependent band gap which is a characteristic of CrI[Formula: see text], ceases to remain. The bandgap of the heterostructure reduces drastically ([Formula: see text] 70%) and the heterostructure shows an indirect, spin-independent bandgap of [Formula: see text] 0.5 eV. The heterostructure remains magnetic (with and without SOC) with the magnetic moment localized primarily on CrI[Formula: see text]. Adsorption of graphene on CrI[Formula: see text] induces an electronic phase transition of the subsequent heterostructure to a ferromagnetic metal in both the spin configurations with magnetic moment localized on CrI[Formula: see text]. The SOC induced interaction opens a bandgap of [Formula: see text] 30 meV in the Dirac cone of graphene, which allows us to visualize Chern insulating states without reducing van der Waals gap.

Competition between the hydrogen bond and the halogen bond in a [CH3OH-CCl4] complex: a matrix isolation IR spectroscopy and computational study.

Methanol (CH3OH) is the simplest alcohol and carbon tetrachloride (CCl4) is widely used as a solvent in the chemical industry. CH3OH and CCl4 are both important volatile substances in the atmosphere and CCl4 is an important precursor for atmospheric ozone depletion. Moreover, mixtures of CH3OH and CCl4 are an important class of non-aqueous mixtures as they exhibit a large deviation from Raoult's law. The specific interaction between CH3OH and CCl4 is not yet investigated experimentally. The interaction between CH3OH and CCl4 at the molecular level can be twofold: hydrogen bond (O-HCl) and halogen bond (C-ClO) interaction. One halogen bonded minimum and two hydrogen bonded minima are identified in the dimer potential energy surface. Herein, the 1 : 1 complex of [CH3OH-CCl4] has been characterised using matrix-isolation infrared spectroscopy and electronic structure calculations to investigate the competition between hydrogen bonded and halogen bonded complexes. Vibrational spectra have been monitored in the C-Cl, C-O, and O-H stretching regions. The exclusive formation of halogen bonded 1 : 1 complexes in argon and nitrogen matrices is confirmed by a combination of experimental and simulated vibrational frequency, stabilisation energy, energy decomposition analysis, and natural bond orbital and atoms-in-molecules analyses. This investigation helps to understand the specific interactions in the [CH3OH-CCl4] mixture and also the possibilities of formation of halogen bonded atmospheric complexes that may influence the atmospheric chemical activities, and enhance aerosol formation and deposition of CCl4.

Experimental and theoretical investigation of ground state intramolecular proton transfer (GSIPT) in salicylideneaniline Schiff base derivatives in polar protic medium.

Ground state intramolecular proton transfer process has been comprehensively investigated in three salicylideneaniline Schiff base derivatives (SB1, SB2, and SB3) using experimental and theoretical methods. It has been confirmed that all the three Schiff base molecules in the ground electronic state exist in the enol form in non-polar and polar aprotic solvents. Keto form is being populated by the polar protic solvent through ground state intramolecular proton transfer (GSIPT) process. Ground state equilibrium between the enol and keto tautomers for SB1 and SB3 is mainly governed by the proton donating ability of the solvent. Ground state equilibria between the enol and keto tautomers of SB2 which is a positional isomer of SB3 is governed by the polarity and proton donating ability of the solvents. Excited state intramolecular proton transfer (ESIPT) process is also evidenced in all the three Schiff base molecules. Theoretical calculations at the B3LYP/cc-pVDZ level in the gas phase and in different solvents using polarisable continuum model (PCM) have failed to establish the GSIPT process. Microsolvation of individual enol and keto conformers has been investigated considering upto three solvent molecules. The energetics of the individual conformers together with the corresponding transition state have been calculated. It has been confirmed that the keto conformer is more stable compared to the enol conformer in microsolvated cluster of three methanol molecules. Lowering of activation energy for the enol to keto tautomerisation in the presence of methanol also supports the experimental observation for GSIPT process. TDDFT/B3LYP/cc-pVDZ single point calculations for microsolvated clusters of enol and keto form of the Schiff base molecules exhibit an excellent agreement with the experimentally obtained absorption spectra. Difference in spectral nature of the Schiff base molecules has been explained using natural bond orbital (NBO) analysis. Quantum theory of atoms in molecules (QTAIM) has also been utilised to understand the GSIPT process in detail.

Final Results of the Prospective Multicenter Excimer Laser-Assisted High-Flow Bypass Study on the Treatment of Giant Anterior Circulation Aneurysms.

BACKGROUND: Both conventional bypass utilizing temporary recipient vessel occlusion and the excimer laser-assisted nonocclusive anastomosis (ELANA) bypass technique are possible strategies in the treatment of giant aneurysms. These treatments have only been studied in single institutional retrospective studies. The potential advantage of the ELANA technique is the absence of temporary occlusion of major arteries, decreasing the risk of intraoperative ischemia. OBJECTIVE: To investigate the risks and potential benefits of high-flow bypass surgery for giant and complex aneurysms of the anterior cerebral circulation. In addition, the effectiveness of the ELANA bypass procedure in the treatment of these aneurysms is determined. METHODS: A total of 37 patients were included in 8 vascular neurosurgical centers in the United States, Canada, and Europe. A 30-d postoperative bypass follow-up was studied by using digital subtraction angiography and/or magnetic resonance angiography and computed tomography angiography to assess patency as well as by clinical monitoring in all patients. RESULTS: In 35 patients, an ELANA high-flow bypass was performed and the aneurysm treated. Four patients had remaining neurological deficits after 30 d caused by stroke (11.4%). These strokes were not related to the ELANA anastomosis device. CONCLUSION: This study does not prove that the ELANA technique has an advantage over conventional bypass techniques, but it appears to be an acceptable alternative to conventional transplanted high-flow bypass in this very-difficult-to-treat patient group, especially in select patients whom cannot be bypassed using conventional means in which temporary occlusion is considered to be not recommended.

Technical Aspects and Operative Nuances Using a High-Definition 3-Dimensional Exoscope for Cerebral Bypass Surgery.

BACKGROUND: Cerebral bypass operation is a technically challenging operation that requires excellent surgical visibility and efficient ergonomics to minimize complications and maximize successful revascularization. Despite the operative microscope's utilization for the past two generations, there remains a need for continued improvement in operative visualization and surgical ergonomics. OBJECTIVE: To report the positives and negatives of our initial experience using a novel 4 K high-definition (4K-HD) 3-dimensional (3D) exoscope (EX) for cranial bypass surgery. METHODS: A retrospective review over 6 mo was performed of all patients who have undergone cerebral bypass surgery at a single institution using the 4K-HD 3D EX. Advantages and disadvantages of the EX and clinical outcome of the patients were assessed. RESULTS: A total of 5 patients underwent cerebral EC-IC bypass surgery with no EX-related complications and successful revascularization. The lightweight design of the EX allowed for easy instrument maneuverability as well as uncomplicated surgical set up in the operating room. The assistance of the cosurgeon was significantly more efficient compared to that of the operating microscope. The large monitor allowed for an immersive, collaborative, and valuable educational surgical experience. CONCLUSION: Using the EX for cerebral bypass surgery, with 3D ultra-high-definition optics, enhancements of ergonomics, and improved training, we believe that the 3D 4K-HD EX may represent the next generation of operative scopes in microneurosurgery.

Superselective intraarterial cerebral infusion of cetuximab with blood brain barrier disruption combined with Stupp Protocol for newly diagnosed glioblastoma.

OBJECTIVE: We describe the first case of a novel treatment for a newly diagnosed glioblastoma (GBM) using superselective intraarterial cerebral infusion (SIACI) of cetuximab after osmotic disruption of the blood-brain barrier (BBB) with mannitol. A 51year-old female underwent craniotomy for removal of a right frontal GBM. Pathology confirmed EGFR amplification, and she underwent three treatments of SIACI of cetuximab to the tumor site. The first treatment was given within a week of starting standard of care chemoradiation (Stupp protocol), which is a combination of radiation treatment (2 Gy per/ day x 30 days, total of 60 Gy) and oral temozolomide (75 mg/m2). The second and third SIACI of cetuximab were administered 3 and 6 months later, while the patient continued on maintenance temozolomide. Post-radiation changes on MRI were stable, and there were no signs of recurrence at 4 and 6 months post-resection. Herein, we detail the technical aspects of this novel treatment paradigm and suggest that SIACI of cetuximab after BBB disruption using mannitol, combined with the standard of care chemoradiation therapy, may be an effective treatment method for newly diagnosed EGFR amplified glioblastoma.

Neuroradiological and Neuropathological Changes After 177Lu-Octreotate Peptide Receptor Radionuclide Therapy of Refractory Esthesioneuroblastoma.

BACKGROUND AND IMPORTANCE: Olfactory neuroblastoma, also known as esthesioneuroblastoma (ENB), is a malignant neoplasm with an unpredictable behavior. Currently, the widely accepted treatment is inductive chemotherapy, with or without surgery, followed by radiotherapy. Since data on genetics and molecular alterations of ENB are lacking, there is no standard molecularly targeted therapy. However, ENB commonly expresses the somatostatin receptor (SSTR) that is also expressed by neuroendocrine tumors. Peptide receptor radionuclide therapy (PRRT) using radiolabeled somatostatin analogues, such as 177Lu-octreotate, is an effective treatment for the latter. We present the complex neuroradiological and neuropathological changes associated with 177Lu-octreotate treatment of a patient with a highly treatment-resistant ENB. CLINICAL PRESENTATION: A 60-yr-old male presented with an ENB that recurred after chemotherapy, surgery, stereotactic radiosurgery, and immunotherapy. Pathology revealed a Hyams grade 3 ENB and the tumor had metastasized to lymph nodes. Tumor SSTR expression was seen on 68Ga-octreotate positron emission tomography (PET)/computed tomography (CT), suggesting that PRRT may be an option. He received 4 cycles of 177Lu-octreotate over 6 mo, with a partial response of all lesions and symptomatic improvement. Four months after the last PRRT cycle, 2 of the lesions rapidly relapsed and were successfully resected. Three months later, 68Ga-octreotate PET/CT and magnetic resonance imaging indicate no progression of the disease. CONCLUSION: We describe imaging changes associated with 177Lu-octreotate PRRT of relapsing ENB. To our knowledge, this is the first report describing neuropathological changes associated with this treatment. PRRT is a promising therapeutic option to improve the disease control, and potentially, the survival of patients with refractory ENB.

Early Epidural Blood Patch to Treat Intracranial Hypotension after Iatrogenic Cerebrospinal Fluid Leakage from Lumbar Tubular Microdiscectomy.

Management of cerebrospinal fluid (CSF) leak during minimally invasive lumbar tubular microdiscectomy poses challenges unique to the surgical approach. Primary repair can be limited via tubular retractor systems, and onlay graft and dural sealant are often the treatment of choice intraoperatively. Postoperative persistent CSF leak may lead to intracranial hypotension (IH) and positional headaches. Early epidural blood patch (EBP) efficacy in the treatment of spinal CSF leaks of both spontaneous and iatrogenic origin is well-established in numerous studies. However, there is no consensus on treatment of persistent IH symptoms for patients undergoing lumbar tubular microdiscectomy. We describe the clinical courses of two patients who were treated with early EBP for IH symptoms following CSF leak during tubular microdiscectomy. Both patients underwent intraoperative repair with onlay autologous tissue graft followed by dural sealant after discectomy was completed without evidence of pseudomeningocele, but they developed postoperative positional headaches and presumed IH. Both patients received an early EBP with an immediate and complete resolution of positional headaches sparing them reoperation and/or lumbar drainage. EBP should be considered as a first-line treatment to treat postoperative IH symptoms without pseudomeningocele after iatrogenic CSF leak during tubular microdiscectomy.

Intraoperative MRI for resection of intracranial meningiomas.

OBJECTIVE: To examine whether intraoperative MRI can enhance safety and extent of resection of complex intracranial meningiomas, given its positive role in the resection of malignant brain tumors and pituitary tumors. METHODS: Over a ten-year period, 70 operations were performed on 66 patients with intracranial meningiomas using the compact, mobile PoleStar N20 iMRI navigation system. A retrospective review was conducted examining patient demographics, surgical characteristics, and outcomes. RESULTS: 36 meningiomas were above the skull base and 30 were of the skull base. Four (5.7%) operations were done for recurrent meningiomas. 63 patients (95.5%) had WHO grade I and 3 patients (4.5%) had WHO grade III meningiomas. 9 (12.8%) patients required additional tumor resection based on iMRI findings, and in 4 patients (6%) iMRI imaging allowed for avoidance of additional dissection near critical neurovascular structures. CONCLUSIONS: Up to 15.7% of patients had surgery positively affected by intraoperative imaging either improving the resection or avoiding unnecessary additional dissection which could potentially harm critical neurologic structures. As iMRI becomes more widely available it may be valuable to use in an appropriate subset of patients with intracranial meningiomas.

Management of Tiny Meningiomas: To Resect or Not Resect.

Meningiomas are most often benign primary intracranial tumors that are frequently found incidentally on imaging. Larger sized meningiomas may present with symptoms such as seizures and headaches. Smaller meningiomas are commonly asymptomatic and usually observed with serial imaging. We present two female patients, both of whom were found to have very small left frontal meningiomas that marginated Broca's area. The first patient in this case series experienced episodes resembling seizures which consisted of weakness, vision loss, and slurred speech, as well as subtle language dysfunction in her day-to-day conversations. The second patient presented with headaches and an enlarging meningioma. Both meningiomas were surgically resected and the patients' symptoms resolved. Small meningiomas should not be overlooked as they may very well be the source of neurologic symptoms.

Long-term benefit of intra-arterial bevacizumab for recurrent glioblastoma.

OBJECTIVE: Standard treatment for recurrent GBM is not yet established. We present a case demonstrating the benefit of intra-arterial (IA) bevacizumab with blood brain barrier disruption (BBBD) for the treatment of recurrent GBM. A 31 year-old man diagnosed with GBM, following primary resection, received temozolomide. After a second resection, he received one dose of IA bevacizumab with BBBD using mannitol, preventing regrowth for 2.5 years. Following tumor regrowth, the patient received another dose of IA bevacizumab with BBBD, which has prevented regrowth for another year.

Frameless and Maskless Stereotactic Navigation with a Skull-Mounted Tracker.

OBJECTIVE: In this series, we present 3 cases that show the use of a skull-mounted tracker for image-guided navigation for anterior skull base surgery and ventricular catheter placement procedures. This system obviates fiducials or face masks during the surgical procedure itself and allows for the performance of facial incisions using the Weber-Ferguson approach. METHODS: Our series presents the use of a novel intraoperative navigational system that uses a skull-mounted tracker to navigated anterior skull base surgery. RESULTS: We present 3 cases using this new system: 1 anterior skull base tumor removal that was operated on without a facemask for navigation and 2 ventricular catheter placement procedures. CONCLUSIONS: Intraoperative image-guided navigation has revolutionized neurosurgery. It undoubtedly increases the surgeon's confidence and the perception of safety. Although fiducials and facial masks are the most widely used tools for intraoperative navigation, their use is associated with certain complications. This technique permits free movement of the head during surgery, which in turn facilitates the exposure of head and neck lesions and expedites the approach to ventricular catheter placement. Our case series shows the precision and ease of our technique, which is less time consuming and less cumbersome than the traditional frame-based stereotaxy. In addition, the skull-mounted tracker system allows improved anatomic localization and shorter operating time and avoids the complications associated with the use of rigid fixating head frames.