Navigated bedside implantation of external ventricular drains with mobile health guidance: technical note and case series.

PURPOSE: External ventricular drain (EVD) implantation is one of the fundamental procedures of emergency neurosurgery usually performed freehand at bedside or in the operating room using anatomical landmarks. However, this technique is frequently associated with malpositioning leading to complications or dysfunction. Here, we describe a novel navigated bedside EVD insertion technique, which is evaluated in a clinical case series with the aim of safety, accuracy, and efficiency in neurosurgical emergency settings. METHODS: From 2021 to 2022, a mobile health-assisted navigation instrument (Thomale Guide, Christoph Miethke, Potsdam, Germany) was used alongside a battery-powered single-use drill (Phasor Health, Houston, USA) for bedside EVD placement in representative neurosurgical pathologies in emergency situations requiring ventricular cerebrospinal fluid (CSF) relief and intracranial pressure (ICP) monitoring. RESULTS: In all 12 patients (8 female and 4 male), navigated bedside EVDs were placed around the foramen of Monro at the first ventriculostomy attempt. The most frequent indication was aneurysmal subarachnoid hemorrhage. Mean operating time was 25.8 ± 15.0 min. None of the EVDs had to be revised due to malpositioning or dysfunction. Two EVDs were converted into a ventriculoperitoneal shunt. Drainage volume was 41.3 ± 37.1 ml per day in mean. Mean length of stay of an EVD was 6.25 ± 2.8 days. Complications included one postoperative subdural hematoma and cerebrospinal fluid infection, respectively. CONCLUSION: Combining a mobile health-assisted navigation instrument with a battery-powered drill and an appropriate ventricular catheter may enable and enhance safety, accuracy, and efficiency in bedside EVD implantation in various pathologies of emergency neurosurgery without adding relevant efforts.

Surgical Site Infections Associated With Implanted Pulse Generators for Deep Brain Stimulation: Meta-Analysis and Systematic Review.

OBJECTIVES: The aim of this study was to identify and systematically analyze relevant literature on surgical site infections (SSIs) associated with implantable pulse generator (IPG) procedures for deep brain stimulation (DBS). MATERIALS AND METHODS: In compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we conducted a systematic review and meta-analyses of 58 studies that reported SSI rates of 11,289 patients and 15,956 IPG procedures. A meta-analysis of proportions was performed to estimate the pooled proportion of SSIs across DBS procedures in general and to estimate the proportion of SSIs that occur at the IPG pocket. Moreover, a meta-analysis of odds ratio (OR) was conducted on those studies that reported their results of applying topical vancomycin powder during closure of the IPG wound. Results are presented as rates and OR with 95% CIs. RESULTS: The pooled proportion of SSIs was 4.9% (95% CI, 4.1%-6.1%) among all DBS procedures. The dominant SSI localization was the IPG pocket in 61.2% (95% CI, 53.4%-68.5%). A trend toward a beneficial effect of vancomycin powder over standard wound closure was found with an OR of 0.46 (95% CI, 0.21-1.02). Most studies (79.1%) that reported their treatment strategy in case of SSI had a strict protocol of removal of the IPG, followed by antimicrobial treatment and reimplantation of the IPG once the SSI had been eradicated. CONCLUSIONS: The IPG pocket was identified as the main site of SSI after DBS procedures. Most studies recommend complete IPG removal, antimicrobial treatment, and reimplantation of an IPG once the SSI has been eradicated. Future studies are needed to clarify the role of alternative approaches (eg, topical vancomycin powder) in the prevention of SSI associated with IPG.

High Frequency of Low-Virulent Microorganisms Detected by Sonication of Implanted Pulse Generators: So What?

INTRODUCTION: Deep brain stimulation (DBS) has become a well-established treatment modality for a variety of conditions over the last decades. Multiple surgeries are an essential part in the postoperative course of DBS patients if nonrechargeable implanted pulse generators (IPGs) are applied. So far, the rate of subclinical infections in this field is unknown. In this prospective cohort study, we used sonication to evaluate possible microbial colonization of IPGs from replacement surgery. METHODS: All consecutive patients undergoing IPG replacement between May 1, 2019 and November 15, 2020 were evaluated. The removed hardware was investigated using sonication to detect biofilm-associated bacteria. Demographic and clinical data were analyzed. RESULTS: A total of 71 patients with a mean (±SD) of 64.5 ± 15.3 years were evaluated. In 23 of these (i.e., 32.4%) patients, a positive sonication culture was found. In total, 25 microorganisms were detected. The most common isolated microorganisms were Cutibacterium acnes (formerly known as Propionibacterium acnes) (68%) and coagulase-negative Staphylococci (28%). Within the follow-up period (5.2 ± 4.3 months), none of the patients developed a clinical manifest infection. DISCUSSIONS/CONCLUSIONS: Bacterial colonization of IPGs without clinical signs of infection is common but does not lead to manifest infection. Further larger studies are warranted to clarify the impact of low-virulent pathogens in clinically asymptomatic patients.

Deep brain stimulation for Parkinson's disease-related postural abnormalities: a systematic review and meta-analysis.

Deep brain stimulation (DBS) has become a well-established treatment modality for Parkinson's disease (PD), especially regarding motor fluctuations, dyskinesias, and tremor. Although postural abnormalities (i.e., Camptocormia [CC] and Pisa syndrome [Pisa]) are known to be a major symptom of PD as well, the influence of DBS on postural abnormalities is unclear. The objective of this study is to analyze the existing literature regarding DBS for PD-associated postural abnormalities in a systematic review and meta-analysis. In compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we conducted a systematic review and meta-analysis of 18 studies that reported the effect of DBS regarding postural abnormalities. After screening of 53 studies, a total of 98 patients (44 female, 53 males, 1 not reported; mean age: 62.3, range 30-83 years) with postural abnormalities (CC n = 98; Pisa n = 11) were analyzed from 18 included studies. Of those patients, 94.9% underwent STN-DBS and 5.1% had GPi as DBS target area. A positive outcome was reported for 67.8% with CC and 72.2% with Pisa. In the meta-analysis, younger age and lower pre-operative UPDRS-III (ON/OFF) were found as positive predictive factors for a positive effect of DBS. DBS might be a potentially effective treatment option for PD-associated postural abnormalities. However, the level of evidence is rather low, and definition of postoperative outcome is heterogenous between studies. Therefore larger, prospective trials are necessary to give a clear recommendation.

A noninvasive method to quantify the impairment of spinal motion ability in Parkinson's disease.

PURPOSE: There is a high demand on spinal surgery in patients with Parkinson's disease (PD) but the results are sobering. Although detailed clinical and radiological diagnostics were carried out with great effort and expense, the biodynamic properties of the spine of PD patients have never been considered. We propose a noninvasive method to quantify the impairment of motion abilities in patients with PD. METHODS: We present an analytical cross-sectional study of 21 patients with severe PD. All patients underwent a biodynamic assessment during a standardized movement-choreography. Thus, individual spinal motion profiles of each patient were objectively assessed and compared with a large comparative cohort of individuals without PD. Moreover, clinical scores to quantify motor function and lumbar back pain were collected and X-ray scans of the spine in standing position were taken and analysed. RESULTS: Biodynamic measurement showed that 36.9% of the assessed motions of all PD patients were severely impaired. Men were generally more functionally impaired than women, in 52% of all motion parameters. The neurological and radiological diagnostics recorded pathological values, of which UPDRS-III ON correlated with findings of the biodynamics assessment (R = 0.52, p = 0.02). CONCLUSIONS: The decision to operate on a PD patient's spine is far-reaching and requires careful consideration. Neurological and radiological scores did not correlate with the biodynamics of the spine. The resulting motion profile could be used as individual predictive factor to estimate whether patients are eligible for spinal surgery or alternative therapies.

Conformational Coupling and trans-Inhibition in the Human Antigen Transporter Ortholog TmrAB Resolved with Dipolar EPR Spectroscopy.

ATP-binding cassette (ABC) exporters actively move chemically diverse substrates across biological membranes. Their malfunction leads to human diseases. Many ABC exporters encompass asymmetric nucleotide-binding sites (NBSs), and some of them are inhibited by the transported substrate. The functional relevance of the catalytic asymmetry or the mechanism for trans-inhibition remains elusive. Here, we investigated TmrAB, a functional homologue of the human antigen translocation complex TAP using advanced electron-electron double resonance spectroscopy. In the presence of ATP, the heterodimeric ABC exporter exists in a tunable equilibrium between inward- and outward-facing conformations. The two NBSs exhibit pronounced asymmetry in the open-to-close equilibrium. The closed conformation is more favored at the degenerate NBS, and closure of either of the NBS is sufficient to open the extracellular gate. We define the mechanistic basis for trans-inhibition, which operates by a reverse transition from the outward-facing state through an occluded conformation. These novel findings uncover the central role of reversible conformational equilibrium in the function and regulation of an ABC exporter and establish a mechanistic framework for future investigations on other medically important transporters with imprinted asymmetry. Also, this study demonstrates for the first-time the feasibility to resolve equilibrium populations at multiple domains and their interdependence for global conformational changes in a large membrane protein complex.

Dynamics of Nucleic Acids at Room Temperature Revealed by Pulsed EPR Spectroscopy.

The investigation of the structure and conformational dynamics of biomolecules under physiological conditions is challenging for structural biology. Although pulsed electron paramagnetic resonance (like PELDOR) techniques provide long-range distance and orientation information with high accuracy, such studies are usually performed at cryogenic temperatures. At room temperature (RT) PELDOR studies are seemingly impossible due to short electronic relaxation times and loss of dipolar interactions through rotational averaging. We incorporated the rigid nitroxide spin label Ç into a DNA duplex and immobilized the sample on a solid support to overcome this limitation. This enabled orientation-selective PELDOR measurements at RT. A comparison with data recorded at 50 K revealed averaging of internal dynamics, which occur on the ns time range at RT. Thus, our approach adds a new method to study structural and dynamical processes at physiological temperature in the <10 µs time range with atomistic resolution.

Double quantum coherence ESR spectroscopy and quantum chemical calculations on a BDPA biradical.

Carbon-centered radicals are interesting alternatives to otherwise commonly used nitroxide spin labels for dipolar spectroscopy techniques because of their narrow ESR linewidth. Herein, we present a novel BDPA biradical, where two BDPA (α,α,γ,γ-bisdiphenylene-ß-phenylallyl) radicals are covalently tethered by a saturated biphenyl acetylene linker. The inter-spin distance between the two spin carrier fragments was measured using double quantum coherence (DQC) ESR methodology. The DQC experiment revealed a mean distance of only 1.8 nm between the two unpaired electron spins. This distance is shorter than the predictions based on a simple modelling of the biradical geometry with the electron spins located at the central carbon atoms. Therefore, DFT (density functional theory) calculations were performed to obtain a picture of the spin delocalization, which may give rise to a modified dipolar interaction tensor, and to find those conformations that correspond best to the experimentally observed inter-spin distance. Quantum chemical calculations showed that the attachment of the biphenyl acetylene linker at the second position of the fluorenyl ring of BDPA did not affect the spin population or geometry of the BDPA radical. Therefore, spin delocalization and geometry optimization of each BDPA moiety could be performed on the monomeric unit alone. The allylic dihedral angle θ1 between the fluorenyl rings in the monomer subunit was determined to be 30° or 150° using quantum chemical calculations. The proton hyperfine coupling constant calculated from both energy minima was in very good agreement with literature values. Based on the optimal monomer geometries and spin density distributions, the dipolar coupling interaction between both BDPA units could be calculated for several dimer geometries. It was shown that the rotation of the BDPA units around the linker axis (θ2) does not significantly influence the dipolar coupling strength when compared to the allylic dihedral angle θ1. A good agreement between the experimental and calculated dipolar coupling was found for θ1 = 30°.

Thoracolumbar Instrumentation Surgery in Patients with Parkinson's Disease: A Case-Control Study.

BACKGROUND: With increasing prevalence of Parkinson's disease (PD), instrumentation surgery of the thoracolumbar spine of PD patients grows in importance. Poor operative results with high rates of revision surgery have been reported. The goal of this study was to compare the biomechanical complications of thoracolumbar instrumentation surgery of patients with and without PD. METHODS: In a retrospective case-control study, we compared 16 PD patients with a matched cohort of 104 control patients regarding the following postinstrumentation complications: (1) adjacent joint disease, (2) material failure, and (3) material loosening. Also, we compared the spinal bone density, which is the main prognostic criteria for failed instrumentation surgery, between the groups. RESULTS: We found the rate of material revision to be significantly higher in PD patients (43.8 vs. 13.5%, p = 0.008, odds ratio (OR) = 5.0). Furthermore, the indications for revision surgery differed between the groups, with more hardware failures in the PD group and more adjacent segment degeneration in the control group. PD patients profited from modern operation techniques (percutaneous instrumentation and CT-navigated screw implantation). Hospitalization was significantly longer for PD patients (20.2 ± 15.1 vs. 14.1 ± 8.9 days, p = 0.03). CONCLUSION: PD patients exhibit challenging biomechanical demands on instrumenting the spine. Besides osteoporosis, especially sagittal imbalance, gait disturbance, and altered muscle tone may be contributive. PD patients may particularly profit from navigated and less invasive surgical techniques.

Lead-OR: A multimodal platform for deep brain stimulation surgery.

Background: Deep brain stimulation (DBS) electrode implant trajectories are stereotactically defined using preoperative neuroimaging. To validate the correct trajectory, microelectrode recordings (MERs) or local field potential recordings can be used to extend neuroanatomical information (defined by MRI) with neurophysiological activity patterns recorded from micro- and macroelectrodes probing the surgical target site. Currently, these two sources of information (imaging vs. electrophysiology) are analyzed separately, while means to fuse both data streams have not been introduced. Methods: Here, we present a tool that integrates resources from stereotactic planning, neuroimaging, MER, and high-resolution atlas data to create a real-time visualization of the implant trajectory. We validate the tool based on a retrospective cohort of DBS patients (N = 52) offline and present single-use cases of the real-time platform. Results: We establish an open-source software tool for multimodal data visualization and analysis during DBS surgery. We show a general correspondence between features derived from neuroimaging and electrophysiological recordings and present examples that demonstrate the functionality of the tool. Conclusions: This novel software platform for multimodal data visualization and analysis bears translational potential to improve accuracy of DBS surgery. The toolbox is made openly available and is extendable to integrate with additional software packages. Funding: Deutsche Forschungsgesellschaft (410169619, 424778381), Deutsches Zentrum für Luft- und Raumfahrt (DynaSti), National Institutes of Health (2R01 MH113929), and Foundation for OCD Research (FFOR).

Deep brain stimulation is an established therapy for patients with Parkinson's disease and an emerging option for other neurological conditions. Electrodes are implanted deep in the brain to stimulate precise brain regions and control abnormal brain activity in those areas. The most common target for Parkinson's disease, for instance, is a structure called the subthalamic nucleus, which sits at the base of the brain, just above the brain stem. To ensure electrodes are placed correctly, surgeons use various sources of information to characterize the patient's brain anatomy and decide on an implant site. These data include brain scans taken before surgery and recordings of brain activity taken during surgery to confirm the intended implant site. Sometimes, the brain activity signals from this last confirmation step may slightly alter surgical plans. It represents one of many challenges for clinical teams: to analyse, assimilate, and communicate data as it is collected during the procedure. Oxenford et al. developed a software pipeline to aggregate the data surgeons use to implant electrodes. The open-source platform, dubbed Lead-OR, visualises imaging data and brain activity recordings (termed electrophysiology data) in real time. The current set-up integrates with commercial tools and existing software for surgical planning. Oxenford et al. tested Lead-OR on data gathered retrospectively from 32 patients with Parkinson's who had electrodes implanted in their subthalamic nucleus. The platform showed good agreement between imaging and electrophysiology data, although there were some unavoidable discrepancies, arising from limitations in the imaging pipeline and from the surgical procedure. Lead-OR was also able to correct for brain shift, which is where the brain moves ever so slightly in the skull. With further validation, this proof-of-concept software could serve as a useful decision-making tool for surgical teams implanting electrodes for deep brain stimulation. In time, if implemented, its use could improve the accuracy of electrode placement, translating into better surgical outcomes for patients. It also has the potential to integrate forthcoming ultra-high-resolution data from current brain mapping projects, and other commercial surgical planning tools.

Angulation Toward Coronal Convexity Measure and Catheter Length Indication Improves the Quality of Ventricular Catheter Placement-A Smartphone-Assisted Guidance Technique.

BACKGROUND: Accurate placement of a ventricular catheter (VC) is crucial to reduce the risk of shunt failure. In the randomized, prospective, multicenter GAVCA (guided application of ventricular catheters) trial, which evaluated the quality of VC placement, the subgroup of patients with detailed length-marked VCs (dVCs) reflected a difference in the primary endpoint of optimal VC placement compared with the subgroup of patients with simplified length-marked VCs (sVCs). The objective of the present analysis was to compare the dVC and sVC groups and the smartphone-assisted guidance technique (GA) with the standard freehand technique (FH) for VC placement. METHODS: We performed a further analysis of the GAVCA trial in 2 steps. First, we compared the dVCs, which provided a detailed distance from the tip to the base (3-13 cm) in 0.5-cm intervals, with the sVCs with a length indication at 5 and 10 cm from the tip to base. Second, we compared the GA technique with the FH in the dVC group. RESULTS: The data from 137 patients (104 dVC patients vs. 33 sVC patients) were eligible for the present analysis. Optimal VC placement was achieved in 72.1% of the dVC group and 39.4% of the sVC group (odds ratio, 3.9; 95% confidence interval, 1.7-9.3; P ≤ 0.001). In addition, we performed a subgroup analysis of the 104 dVC patients concerning the accuracy of catheter placement using 2 different techniques (GA, n = 54; and FH, n = 50). Optimal catheter placement was achieved in 81.5% of the GA group and 62.0% of the FH group (odds ratio, 2.7; 95% confidence interval, 1.1-6.8; P = 0.03). VC placement using the GA technique was successful in all patients at the primary puncture. In contrast, for 8.7% of the patients in the FH group, multiple attempts were necessary (P = 0.03). CONCLUSIONS: The results from the present analysis suggest that the combination of a GA technique and the use of a dVC will improve the rate of accurate VC placement. Compared with the FH technique, patient safety was increased by the reduction of unsuccessful VC placement attempts using the GA technique and dVCs.

Surgical revision after Vagus Nerve Stimulation. A case series.

With increasing use of vagus nerve stimulation (VNS) as an adjunct treatment for drug-resistant epilepsy, revision surgery of VNS grows in importance. Indications for revision surgery are diverse and extend of surgery varies. We report a retrospective review on indications and complications of VNS revision surgery at our center. Of 90 VNS procedures 54.4% were revision surgeries. Among those the vast majority was due to depletion of the battery. The entire system was explanted in 15 patients, due to no beneficial effect detected (n = 4), due to irritating side effects (n = 4), and so further diagnostics could cbe carried out (n = 7). Interestingly in three of the patients who underwent further diagnostics, resective epilepsy surgery was performed. Surgical complications occurred in 8.2%. In our experience, revision surgery of VNS was a frequent and safe procedure. There is a need to carefully reviewthe initial indication for VNS implantation prior to revision surgery.

Preparation of Acute Human Hippocampal Slices for Electrophysiological Recordings.

Epilepsy affects about 1% of the world population and leads to a severe decrease in quality of life due to ongoing seizures as well as high risk for sudden death. Despite an abundance of available treatment options, about 30% of patients are drug-resistant. Several novel therapeutics have been developed using animal models, though the rate of drug-resistant patients remains unaltered. One of probable reasons is the lack of translation between rodent models and humans, such as a weak representation of human pharmacoresistance in animal models. Resected human brain tissue as a preclinical evaluation tool has the advantage to bridge this translational gap. Described here is a method for high quality preparation of human hippocampal brain slices and subsequent stable induction of epileptiform activity. The protocol describes the induction of burst activity during application of 8 mM KCl and 4-aminopyridin. This activity is sensitive to established AED lacosamide or novel antiepileptic candidates, such as dimethylethanolamine (DMEA). In addition, the method describes induction of seizure-like events in CA1 of human hippocampal brain slices by reduction of extracellular Mg2+ and application of bicuculline, a GABAA receptor blocker. The experimental set-up can be used to screen potential antiepileptic substances for their effects on epileptiform activity. Furthermore, mechanisms of action postulated for specific compounds can be validated using this approach in human tissue (e.g., using patch-clamp recordings). To conclude, investigation of vital human brain tissue ex vivo (here, resected hippocampus from patients suffering from temporal lobe epilepsy) will improve the current knowledge of physiological and pathological mechanisms in the human brain.

Effects of vagus nerve stimulation on symptoms of depression in patients with difficult-to-treat epilepsy.

PURPOSE: Vagus nerve stimulation (VNS) is well established in the treatment of epilepsy and disorders of depression. The prevalence of depression is high in patients with epilepsy, but still it remains unclear how patients with a comorbidity of epilepsy and symptoms of depression respond to VNS. METHODS: We investigated 59 patients with different subtypes of disorders of depression as a comorbidity of epilepsy, who underwent VNS-surgery. Before and one year after VNS surgery, the severity of symptoms of depression was evaluated by a psychiatrist using Montgomery-Åsberg Depression Rating Scale (MADRS) and Beck-Depressions-Inventory (BDI). Response towards epilepsy was measured by a seizure reduction of at least 50%. RESULTS: Symptoms of depression ameliorated in response to VNS in the overall of all patients MADRS 29 to 18 (p < 0,001) and BDI 24 to 14 (p < 0,001) and all subtypes of disorders of depression. Seizure reduction of at least 50% was achieved in two out of three of all patients two years after VNS. CONCLUSION: We were able to show the beneficial effect of VNS in the treatment of patients with pharmacoresistant epilepsy and a comorbidity of symptoms of depression.

Chain Assembly and Disassembly Processes Differently Affect the Conformational Space of Ubiquitin Chains.

Ubiquitination is the most versatile posttranslational modification. The information is encoded by linkage type as well as chain length, which are translated by ubiquitin binding domains into specific signaling events. Chain topology determines the conformational space of a ubiquitin chain and adds an additional regulatory layer to this ubiquitin code. In particular, processes that modify chain length will be affected by chain conformations as they require access to the elongation or cleavage sites. We investigated conformational distributions in the context of chain elongation and disassembly using pulsed electron-electron double resonance spectroscopy in combination with molecular modeling. Analysis of the conformational space of diubiquitin revealed conformational selection or remodeling as mechanisms for chain recognition during elongation or hydrolysis, respectively. Chain elongation to tetraubiquitin increases the sampled conformational space, suggesting that a high intrinsic flexibility of K48-linked chains may contribute to efficient proteasomal degradation.

Perspectives of shaped pulses for EPR spectroscopy.

This article describes current uses of shaped pulses, generated by an arbitrary waveform generator, in the field of EPR spectroscopy. We show applications of sech/tanh and WURST pulses to dipolar spectroscopy, including new pulse schemes and procedures, and discuss the more general concept of optimum-control-based pulses for applications in EPR spectroscopy. The article also describes a procedure to correct for experimental imperfections, mostly introduced by the microwave resonator, and discusses further potential applications and limitations of such pulses.

Broadband spin echoes and broadband SIFTER in EPR.

Applications of broadband pulses for EPR have been reported for FID, echo detection and inversion pulses recently. Here we present a broadband Hahn, stimulated and refocused echo sequence derived from adiabatic pulses. The formation of echoes is accomplished by using variable chirp rates and pulse lengths. In all three broadband echo experiments the complete spectral shape of a nitroxide (about 70 Gauss at X-band frequency) could be recovered by Fourier transformation of the quadrature detected echo signals. Such broadband echoes provide an exciting opportunity to optimize pulse sequences where a full excitation of the spectrum is mandatory for an optimum performance. We applied our pulses to the SIFTER (single frequency technique for refocusing dipolar couplings) experiment, a solid echo based pulse sequence to measure the dipolar coupling between two unpaired electron spins. By employing our broadband Hahn echo sequence on a nitroxide biradical we could achieve an artifact free dipolar evolution time trace in the SIFTER experiment with 95% modulation depth at X-band frequency and of 10% modulation depth at Q-band frequency.

Carr-Purcell Pulsed Electron Double Resonance with Shaped Inversion Pulses.

Pulsed electron paramagnetic resonance (EPR) spectroscopy allows the determination of distances, in the range of 1.5-8 nm, between two spin-labels attached to macromolecules containing protons. Unfortunately, for hydrophobic lipid-bound or detergent-solubilized membrane proteins, the maximum distance accessible is much lower, because of a strongly reduced coherence time of the electron spins. Here we introduce a pulse sequence, based on a Carr-Purcell decoupling scheme on the observer spin, where each π-pulse is accompanied by a shaped sech/tanh inversion pulse applied to the second spin, to overcome this limitation. This pump/probe excitation scheme efficiently recouples the dipolar interaction, allowing a substantially longer observation time window to be achieved. This increases the upper limit and accuracy of distances that can be determined in membrane protein complexes. We validated the method on a bis-nitroxide model compound and applied this technique to the trimeric betaine transporter BetP. Interprotomer distances as long as 6 nm could be reliably determined, which is impossible with the existing methods.

Shaped optimal control pulses for increased excitation bandwidth in EPR.

A 1 ns resolution pulse shaping unit has been developed for pulsed EPR spectroscopy to enable 14-bit amplitude and phase modulation. Shaped broadband excitation pulses designed using optimal control theory (OCT) have been tested with this device at X-band frequency (9 GHz). FT-EPR experiments on organic radicals in solution have been performed with the new pulses, designed for uniform excitation over a significantly increased bandwidth compared to a classical rectangular π/2 pulse of the same B(1) amplitude. The concept of a dead-time compensated prefocused pulse has been introduced to EPR with a self-refocusing of 200 ns after the end of the pulse. Echo-like refocused signals have been recorded and compared to the performance of a classical Hahn-echo sequence. The impulse response function of the microwave setup has been measured and incorporated into the algorithm for designing OCT pulses, resulting in further significant improvements in performance. Experimental limitations and potential new applications of OCT pulses in EPR spectroscopy will be discussed.