Improved detection of magnetic interactions in proteins based on long-lived coherences.

Living systems rely on molecular building blocks with low structural symmetry. Therefore, constituent amino acids and nucleotides yield short-lived nuclear magnetic responses to electromagnetic radiation. Magnetic signals are at the basis of molecular imaging, structure determination and interaction studies.

Cross polarization from dipolar-order under magic angle spinning: The ADRF-CPMAS NMR experiment.

Techniques for enhancing the signals arising from low-γ, insensitive (I) nuclei are central to solid-state nuclear magnetic resonance. One of the leading and best-established methods to sensitize these unreceptive species is Hartmann-Hahn cross polarization (HH-CP), a polarization transfer mechanism often executed under MAS. Herein, we explore the possibility of utilizing the 1H dipolar order created via adiabatic demagnetization in the rotating frame (ADRF), to enhance the unreceptive spins under MAS.

Identifying and Overcoming Artifacts in H-Based Saturation Transfer NOE NMR Experiments.

Magnetization transfer experiments are versatile nuclear magnetic resonance (NMR) tools providing site-specific information. We have recently discussed how saturation magnetization transfer (SMT) experiments could leverage repeated repolarizations arising from exchanges between labile and water protons to enhance connectivities revealed via the nuclear Overhauser effect (NOE). Repeated experience with SMT has shown that a number of artifacts may arise in these experiments, which may confound the information being sought - particularly when seeking small NOEs among closely spaced resonances.

Effective Hamiltonian and spin dynamics in fast MAS TRAPDOR-HMQC experiments involving spin-3/2 quadrupolar nuclei.

We present a theoretical and numerical description of the spin dynamics associated with TRAPDOR-HMQC (T-HMQC) experiment for a H (I) - Cl (S) spin system under fast magic angle spinning (MAS). Towards this an exact effective Hamiltonian describing the system is numerically evaluated with matrix logarithm approach. The different magnitudes of the heteronuclear and pure S terms in the effective Hamiltonian allow us to suggest a truncation approximation, which is shown to be in excellent agreement with the exact time evolution.

Selective Excitation of Long-Lived Nuclear Spin States.

Nuclear magnetization storage, once limited by longitudinal and transverse relaxation lifetimes, and , can be prolonged by symmetry-adapted nuclear spin order, i.e. long-lived states (LLS) and long-lived coherences (LLC), which have significantly extended relaxation time constants compared to and , respectively.

The Extended Hadamard Transform: Sensitivity-Enhanced NMR Experiments Among Labile and Non-Labile Hs of SARS-CoV-2-derived RNAs.

Hadamard encoded saturation transfer can significantly improve the efficiency of NOE-based NMR correlations from labile protons in proteins, glycans and RNAs, increasing the sensitivity of cross-peaks by an order of magnitude and shortening experimental times by ≥100-fold. These schemes, however, fail when tackling correlations within a pool of labile protons - for instance imino-imino correlations in RNAs or amide-amide correlations in proteins. Here we analyze the origin of the artifacts appearing in these experiments and propose a way to obtain artifact-free correlations both within the labile pool as well as between labile and non-labile Hs, while still enjoying the gains arising from Hadamard encoding and solvent repolarizations.

Heteronuclear transfers from labile protons in biomolecular NMR: Cross polarization, revisited.

INEPT- and HMQC-based pulse sequences are widely used to transfer polarization between heteronuclei, particularly in biomolecular spectroscopy: they are easy to setup and involve low power deposition. Still, these short-pulse polarization transfers schemes are challenged by fast solvent chemical exchange. An alternative to improve these heteronuclear transfers is J-driven cross polarization (J-CP), which transfers polarization by spin-locking the coupled spins under Hartmann-Hahn conditions.

A new approach to radon temporal correction factor based on active environmental monitoring devices.

The present study aims to identify novel means of increasing the accuracy of the estimated annual indoor radon concentration based on the application of temporal correction factors to short-term radon measurements. The necessity of accurate and more reliable temporal correction factors is in high demand, in the present age of speed. In this sense, radon measurements were continuously carried out, using a newly developed smart device accompanied by CR-39 detectors, for one full year, in 71 residential buildings located in 5 Romanian cities.

3D Heteronuclear Magnetization Transfers for the Establishment of Secondary Structures in SARS-CoV-2-Derived RNAs.

Multidimensional NOESY experiments targeting correlations between exchangeable imino and amino protons provide valuable information about base pairing in nucleic acids. It has been recently shown that the sensitivity of homonuclear correlations involving RNA's labile imino protons can be significantly enhanced, by exploiting the repolarization brought about by solvent exchanges. Homonuclear correlations, however, are of limited spectral resolution, and usually incapable of tackling relatively large homopolymers with repeating structures like RNAs.

Effective Hamiltonian and H-N cross polarization/double cross polarization at fast MAS.

In this work we investigate in detail the underlying spin-dynamics associated with H-N double CP experiments under fast MAS, recently demonstrated by Carnevale et al. We employ matrix logarithm and Floquet theory to compute numerically the effective Hamiltonian associated to the time-dependent problem. Certain common features related to construction of effective Hamiltonians by both approaches are discussed.

Comprehensive survey on radon mitigation and indoor air quality in energy efficient buildings from Romania.

Over the last 10 years applied scientific research has been carried out in Romania to tacked the residential radon issues. The increased interest to reduce the carbon footprint of buildings has lead to the implementation and use of new architectural solutions aimed to save energy in houses and other buildings. As a consequence, the degree of retrofit in existing buildings and energy efficiency of new buildings promoted the need to not only mitigate indoor radon, but improve indoor air quality overall.

VARIATION OF INDOOR RADON CONCENTRATION WITHIN A RESIDENTIAL COMPLEX.

A recent challenge in research dedicated to residential exposure to radon comes from the growing number of houses retrofitted to reduce energy consumption. Efficiently insulated buildings and modern architectural solutions can lead to the accumulation of high levels of indoor pollutants. A systematic analysis was conducted in a residential complex (consisting of six houses) in order to assess the annual radon concentration and to evaluate the intensity of the relationships with various factors, such as the indoor-outdoor temperature differences, wind speed and wind direction.

Sensitivity enhancement in 2D Double Cross Polarization experiments under fast MAS by recycling unused protons.

We demonstrate sensitivity enhancement via recycling of proton magnetization in 2D Double Cross Polarization (Double CP) experiments performed on fully protonated and uniformly labeled (C, N) samples at a magic angle spinning rate of 60 kHz. Unused proton magnetization is preserved during t evolution either by locking it with CW irradiation or by employing rotor-synchronized pi pulses. A flip-back pulse together with a modified second CP block preserves unused proton magnetization resulting in enhanced sensitivity.

The path from geology to indoor radon.

It is generally accepted that radon emission is strongly influenced by the geological characteristics of the bedrock. However, transport in-soil and entry paths indoors are defined by other factors such as permeability, building and architectural features, ventilation, occupation patterns, etc. The purpose of this paper is to analyze the contribution of each parameter, from natural to man-made, on the radon accumulation indoors and to assess potential patterns, based on 100 case studies in Romania.

The FIRST large-scale mapping of radon concentration in soil gas and water in Romania.

In the framework of the last Council Directive 2013/59 (Euratom, 2014) laying down basic safety standards for protection against the dangers arising from exposure to ionizing radiation, the problem of radon was assumed in Romania at national level by responsible authorities through the design and development of a National Radon Action Plan and an adequate legislation (HG nr. 526/2018). In order to identify radon risk areas, however, it is necessary to perform systematic radon measurements in different environmental media (soil gas, water, indoor air) and to map the results.

Tuning Zeolite Precursor Interactions by Switching the Valence of Polyamine Modifiers.

Nonclassical mechanisms of crystal growth often involve the formation of amorphous precursors that play a direct role in what is generally referred to as crystallization by particle attachment (or CPA). One of the most studied CPA systems in the literature is zeolite MFI, which is a microporous crystal with siliceous (silicalite-1) and aluminosilicate (ZSM-5) isostructures. The self-assembly, microstructural evolution, and mechanistic role of nanoparticle precursors (1-6 nm) during silicalite-1 crystallization have been the subjects of prior investigation by combined experimental and modeling techniques.

Multidimensional J-driven NMR correlations by single-scan offset-encoded recoupling.

Two-dimensional (2D) correlations between bonded heteroatoms, lie at the cornerstone of many uses given to contemporary nuclear magnetic resonance (NMR). Improving the efficiency with which these correlations are established is an important topic in modern NMR, with potential applications in rapid chemical analysis and dynamic biophysical studies. Alternatives have been developed over the last decade to speed up these experiments, based among others on reducing the number of data points that need to be sampled, and/or shortening the inter-scan delays.

In situ imaging of silicalite-1 surface growth reveals the mechanism of crystallization.

The growth mechanism of silicalite-1 (MFI zeolite) is juxtaposed between classical models that postulate silica molecules as primary growth units and nonclassical pathways based on the aggregation of metastable silica nanoparticle precursors. Although experimental evidence gathered over the past two decades suggests that precursor attachment is the dominant pathway, direct validation of this hypothesis and the relative roles of molecular and precursor species has remained elusive. We present an in situ study of silicalite-1 crystallization at characteristic synthesis conditions.

Heteronuclear cross-relaxation effects in the NMR spectroscopy of hyperpolarized targets.

Dissolution dynamic nuclear polarization (DNP) enables high-sensitivity solution-phase NMR experiments on long-lived nuclear spin species such as (15)N and (13)C. This report explores certain features arising in solution-state (1)H NMR upon polarizing low-γ nuclear species. Following solid-state hyperpolarization of both (13)C and (1)H, solution-phase (1)H NMR experiments on dissolved samples revealed transient effects, whereby peaks arising from protons bonded to the naturally occurring (13)C nuclei appeared larger than the typically dominant (12)C-bonded (1)H resonances.

Rapid acquisition of 14N solid-state NMR spectra with broadband cross polarization.

Nitrogen is an element of utmost importance in chemistry, biology and materials science. Of its two NMR-active isotopes, (14)N and (15)N, solid-state NMR (SSNMR) experiments are rarely conducted upon the former, due to its low gyromagnetic ratio (γ) and broad powder patterns arising from first-order quadrupolar interactions. In this work, we propose a methodology for the rapid acquisition of high quality (14)N SSNMR spectra that is easy to implement, and can be used for a variety of nitrogen-containing systems.

Two-dimensional RF pulses: a new approach to selectively exciting J-coupled spins in nuclear magnetic resonance.

A new scheme for the excitation of spins according to the joint values of their heteronuclear or homonuclear J couplings and of their chemical shifts, is proposed and demonstrated. The principles of the new pulses involved derive from those employed in NMR imaging for exciting arbitrary 2D spatial shapes, using so-called "multidimensional" RF pulses. It is shown that if recast in a suitable spectroscopic framework, the distinction that π-pulses enable to establish between linear and bilinear interactions, support the selective excitation of coherences possessing arbitrary combinations of chemical shift and J-coupling values--a flexibility akin to that provided by a 2D J-resolved NMR spectrum.

A facile strategy to design zeolite L crystals with tunable morphology and surface architecture.

Tailoring the anisotropic growth rates of materials to achieve desired structural outcomes is a pervasive challenge in synthetic crystallization. Here we discuss a method to selectively control the growth of zeolite crystals, which are used extensively in a wide range of industrial applications. This facile method cooperatively tunes crystal properties, such as morphology and surface architecture, through the use of inexpensive, commercially available chemicals with specificity for binding to crystallographic surfaces and mediating anisotropic growth.

Broadband adiabatic inversion pulses for cross polarization in wideline solid-state NMR spectroscopy.

Efficient acquisition of ultra-wideline solid-state NMR powder patterns is a continuing challenge. In particular, when the breadth of the powder pattern is much larger than the cross-polarization (CP) excitation bandwidth, transfer efficiencies suffer and experimental times are greatly increased. Presented herein is a CP pulse sequence with an excitation bandwidth that is up to ten times greater than that available from a conventional spin-locked CP pulse sequence.

Toward single-shot pure-shift solution 1H NMR by trains of BIRD-based homonuclear decoupling.

Achieving homonuclear 1H decoupling remains one of the key challenges in liquid-state NMR. Such spectra would endow a variety of organic and analytical applications with an increased resolution, and would ideally do so even in a one-dimensional format. A number of parallel efforts aimed at achieving this goal using two-dimensional acquisitions have been proposed; approaches demonstrated over recent years include, among others, new modes for achieving purely-absorptive J spectroscopy, the use of spatially-selective manipulations, and exploiting the natural spin dilution afforded by heteronuclei.

Tailoring silicalite-1 crystal morphology with molecular modifiers.

Modified point of view: a bio-inspired approach was used to tailor silicalite-1 crystallization. Growth modifiers (ZGMs) with molecular recognition for binding to specific crystal faces produced drastic changes in zeolite crystal morphology. This facile approach offers an efficient method for tuning zeolite properties.