High Molecular Weight Precursor Research Articles

Solution ALD: A Versatility Process for the Growth of Sulfides and Selenides

We have proposed and demonstrated a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid. The technique can also be considered as a generalization of already established methods such as the ‘layer by layer’ growth or the ‘successive ion layer adsorption and reaction’ (SILAR). 'Solution ALD' (sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), specially the self-limiting growth and the ability to coat conformally deep pores. It has been already shown that it is possible to transfer standard reactions from gALD to sALD such as TiO2 deposition . However, sALD also offers novel opportunities such as overcoming the need for volatile and thermally robust precursors.To illustrate this, we establish sALD procedures for depositing films of non oxides layers such as Pb-compound deposition, MOF, selenides and sulfides. Those examples highlight how ionic, polar, or high-molecular weight precursors that only exist in the condensed phase are now rendered amenable to being utilized in surface-controlled thin film formation by sALD for depositing materials that would otherwise be more difficult or more expensive to achieve by gALD or hazardous. The deposition was achieved on small (2 cm*1 cm) and large samples (up to 10 cm*10 cm). The ALD behavior has been shown. The influence of the deposition parameters on the morphology, the crystalline structure and the chemical composition has been investigated by scanning electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. Additionally, the nucleation is studied in function of chemical pretreatment to control the growth and allow selective deposition of SnS, SnSe and Sb2Se3.This particular ALD process offer the growth of high quality and crystalline layers in middle conditions with the use of low cost and environmental friendly precursors. Y. Wu, D. Döhler, M. Barr, E Oks,M. Wolf, L. Santinacci and J. Bachmann, Nano Lett. 2015, 15, 6379 J. Fichtner, Y. Wu, J. Hitzenberger, T. Drewello and J. Bachmann, ECS J. Solid State Sci. Technol. 2017, 6, N171

Solution ALD: A Versatility Process for Various Material Growth

We have proposed and demonstrated a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid. The technique can also be considered as a generalization of already established methods such as the ‘layer by layer’ growth or the ‘successive ion layer adsorption and reaction’ (SILAR). 'Solution ALD' (sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), specially the self-limiting growth and the ability to coat conformally deep pores. It has been already shown that it is possible to transfer standard reactions from gALD to sALD such as TiO2 deposition . However, sALD also offers novel opportunities such as overcoming the need for volatile and thermally robust precursors.To illustrate this, we establish sALD procedures for depositing films of non oxides layers such as Pb-compound deposition, MOF, selenides and sulfides. Those examples highlight how ionic, polar, or high-molecular weight precursors that only exist in the condensed phase are now rendered amenable to being utilized in surface-controlled thin film formation by sALD for depositing materials that would otherwise be more difficult or more expensive to achieve by gALD or hazardous. The deposition was achieved on small (2 cm*1 cm) and large samples (up to 10 cm*10 cm). The ALD behavior has been shown. The influence of the deposition parameters on the morphology, the crystalline structure and the chemical composition has been investigated by scanning electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. Additionally, the nucleation is studied in function of chemical pretreatment to control the gowth and allow selective deposition of CuS, ZnS and SnS.This particular ALD process offer the growth of high quality and crystalline layers in middle conditions with the use of low cost and environmental friendly precursors. Y. Wu, D. Döhler, M. Barr, E Oks,M. Wolf, L. Santinacci and J. Bachmann, Nano Lett. 2015, 15, 6379 J. Fichtner, Y. Wu, J. Hitzenberger, T. Drewello and J. Bachmann, ECS J. Solid State Sci. Technol. 2017, 6, N171 Figure 1

Copolymers of sodium 4-styrene sulphonate and vinyl derivatives of nitrogen-containing heterocycles

The formation of ion-exchange composite materials based on high molecular weight precursors appears to be an intensively developing area in the synthesis of proton-conducting membranes for fuel cells. In such membranes, proton transfer is often provided by functional polymers simultaneously containing sulphonic acid groups in their composition units along with fragments of vinyl derivatives of nitrogen-containing heterocyclic bases. Proton exchange activity in the latter is determined by the possibility of doping with inorganic acids. In the framework of this study, for the further formation of hybrid composite membranes under conditions of radical initiation, copolymers of sodium 4-styrene sulphonate (SSt) with 4-vinylpyridine (VP) and 1-vinylimidazole (VIM) were obtained. The monomodal nature of the turbidimetric titration curves for solutions of copolymerisation reaction products indicates the presence of true copolymers during the process of formation. The composition and structure of the copolymers were characterised using data from elemental analysis, as well as from IR and 13 C NMR spectroscopy. Constants of the relative activity for the monomers and the microstructure parameters of the polymer chains are calculated according to the non-linear leastsquares method using the MathCAD package. The calculated copolymerisation constant values indicate a greater reactivity of SSt in comparison with nitrogen-containing monomers. The lengths of the monomer unit blocks depend on the composition of the initial mixture and vary over a wide range from 1 to 18. The possibility of varying the length of the unit blocks in the composition of the copolymers will affect the ion-conducting properties of hybrid composites formed on their basis. The stability of the copolymers to thermal oxidative degradation by heating in air was studied using the differential scanning calorimetry (DSC) method. The copolymers demonstrated significant thermo-oxidative stability. Decomposition temperatures were 350 °С and 400 °С for SSt-VIM and SSt-VP copolymers, respectively.

Engineering biologically extensible hydrogels using photolithographic printing

Biomaterials for tissue engineering that recapitulate the mechanical response and biological function of native tissue are highly sought after to lessen the burden of damaged or diseased tissue. Poly(ethylene glycol) diacrylate (PEGDA) hydrogels are a popular candidate because of their favorable bioactive properties. However, their mechanical behavior is very dissimilar to that of biological tissue, which behaves in a mechanically anisotropic, nonlinear, and viscoelastic fashion. It has been previously shown that PEGDA hydrogels can be patterned in alternating linear strips of different stiffnesses to generate anisotropic behavior, but these constructs still have a linear stress-strain response. In this study, we imparted nonlinear mechanical properties to PEGDA hydrogels by fabricating composite hydrogel constructs consisting of a stiff sinusoidal reinforcement embedded into a softer base matrix. This was achieved by polymerizing low molecular weight (MW) PEGDA hydrogel precursor into a stiff sinusoidal shape and then polymerizing this construct into a high MW precursor. Samples were generated with different relative stiffness between the two components and a range of sinusoid periodicities to assess the tunability of the resulting stress-strain curve. Tensile testing indicates that the sinusoidal patterning gives rise to nonlinear stress-strain behavior. Varying the relative stiffness was shown to tune the slope of the linear region of the stress-strain curve, and varying periodicity was shown to affect the length of the toe region of this curve. We conclude that composite hydrogels with stiff sinusoidally-patterned reinforcements display mechanical properties more similar to those of biological tissue than uniform or linearly-patterned hydrogels. Statement of SignificanceHydrogel biomaterials are a popular candidate for engineering constructs that can mimic the properties of native tissue for disease modeling and tissue-engineering applications. Studies have shown that poly(ethylene) glycol diacrylate (PEGDA) hydrogels can be fabricated to display many biological aspects of native tissue. However, they are unable to recapitulate fundamental mechanical properties of such tissue, such as anisotropy and nonlinearity. Photolithographic techniques have been employed to generate anisotropic linear PEGDA hydrogels via patterned reinforcement. The present study indicates that such techniques can be modified to generate PEGDA constructs with a sinusoidal reinforcement that display a strongly nonlinear response to tensile loading. This work sets the stage for more intricate patterning for providing increased control over hydrogel mechanical response.

Functional siloxanes with photo-activated, simultaneous chain extension and crosslinking for lithography-based 3D printing

A novel, poly(dimethyl siloxane)-based photopolymer that exhibits simultaneous linear chain extension and crosslinking was suitable for vat photopolymerization additive manufacturing. Photopolymer compositions consisted of dithiol and diacrylate functional poly(dimethyl siloxane) oligomers, where simultaneous thiol-ene coupling and free radical polymerization provided for linear chain extension and crosslinking, respectively. Compositions possessed low viscosity before printing and the modulus and tensile strain at break of a photocured, higher molecular weight precursor after printing. Photorheology and soxhlet extraction demonstrated highly efficient photocuring, revealing a calculated molecular weight between crosslinks of 12,600 g/mol and gel fractions in excess of 90% while employing significantly lower molecular weight precursors (i.e. < 5300 g/mol). These photocured objects demonstrated a 2× increase in tensile strain at break as compared to a photocured 5300 g/mol PDMS diacrylamide alone. These results are broadly applicable to the advanced manufacturing of objects requiring high elongation at break.

(Invited) Molecular Layer Deposition from Dissolved Precursors

We propose and demonstrate a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid. The technique can also be considered as a generalization of already established methods such as the ‘layer by layer’ growth of polyelectrolytes, the ‘successive ion layer adsorption and reaction’ (SILAR), and even the solid-phase peptide synthesis. 'Solution ALD' (sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), in particular the self-limiting surface chemistry and the ability to coat deep pores in a conformal manner. Furthermore, standard gALD reactions behave similarly when transferred into sALD mode. However, sALD also offers novel opportunities by overcoming the need for volatile and thermally robust precursors. To illustrate this, we establish sALD procedures for depositing films of MgO based on the hydrolysis of a Grignard reagent, and of a polyamine exploiting a strategy of protection, deprotection and activation that is standard in organic synthesis. Those two examples highlight how ionic, polar, or high-molecular weight precursors that only exist in the condensed phase are now rendered amenable to being utilized in surface-controlled thin film formation by sALD for depositing materials that would otherwise be more difficult or more expensive to achieve by gALD. Figure 1

Epoxy hybrid networks with high mass fraction molecular-level dispersion of pendant polyhedral oligomeric silsesquioxane (POSS)

A novel high shear continuous reactor method was developed to obtain molecular level incorporation of polyhedral oligomeric silsesquioxane (POSS) containing one amine group and seven isobutyl groups into epoxy network as pendant cage. The method consisted of optimizing reaction time and temperature for the synthesis of POSS-epoxy precursor in a high shear continuous reactor. A full conversion of POSS into POSS-epoxy precursor was achieved within 30–40 s of reaction time in a continuous reactor for all molar compositions from 1:140 to 1:1.05 in comparison to a batch process with the reaction time of 18 h. The structure of this precursor at the end of the reaction, determined by silicon Nuclear Magnetic Resonance spectroscopy (29Si NMR), was close to the ideal one. The distribution of reaction product was determined by size exclusion chromatography (SEC). The reaction product containing up to 1:3-mol ratio of POSS: epoxy molecules showed ‘epoxy-POSS-epoxy’ precursor as a primary product in comparison to 1:2 and 1:1.05-mol ratios with higher molecular weight precursor as the primary product. Hybrid networks containing up to 50 wt % POSS were prepared by curing these precursors with an aromatic amine curative 4, 4'diamino diphenyl methane (DDM). The resulting networks are completely transparent and no phase separation was observed by SEM and TEM in the course of polymerization despite the incompatibility of the isobutyl groups attached to the POSS with the aromatic epoxy-amine networks. In addition to that, DMA and TGA results prove that the introduction of high shear continuous reactor promotes the dispersion of pendant POSS to a molecular level into epoxy networks.

Adhesion ability of angiotensin II with model membranes

The octa-peptide angiotensin II (Ang II, (H2NAspArgValTyrIleHisProPheCOOH)) is one of the key player on blood pressure regulation in mammals. Predominantly binding to the Angiotensin type 1 and 2 receptors, the hormone is one of several peptide ligands binding to G protein coupled receptors (GPCR). The active hormone derives from a high molecular weight precursor sequentially cleaved by the proteases renin and the angiotensin converting enzyme (ACE). The chemical nature of the amino acid sequence has an impact on the behavior in the proximity of membranes, demonstrated using different membrane model systems and biophysical methods.Applying electrochemical impedance spectroscopy and small angle X-ray scattering a detailed view on the adhesion of the peptide with model membrane surfaces was performed. The role of specific amino acids involved in the interaction with the phospholipid head group were investigated and, studying a truncated version of Ang II, Ang (1-7), the key role of the C-terminal phenylalanine was proven. Truncation of the C-terminal amino acid abolishes the binding of the peptide to the membrane surface. A shift in pH, altering the protonation state of the central histidine residue impairs the adhesion of Ang II.

Intrinsic Regulation of Thyroid Function by Thyroglobulin

The established paradigm for thyroglobulin (Tg) function is that of a high molecular weight precursor of the much smaller thyroid hormones, triiodothyronine (T3) and thyroxine (T4). However, speculation regarding the cause of the functional and morphologic heterogeneity of the follicles that make up the thyroid gland has given rise to the proposition that Tg is not only a precursor of thyroid hormones, but that it also functions as an important signal molecule in regulating thyroid hormone biosynthesis. Evidence supporting this alternative paradigm of Tg function, including the up- or downregulation by colloidal Tg of the transcription of Tg, iodide transporters, and enzymes employed in Tg iodination, and also the effects of Tg on the proliferation of thyroid and nonthyroid cells, is examined in the present review. Also discussed in detail are potential mechanisms of Tg signaling in follicular cells. Finally, we propose a mechanism, based on experimental observations of Tg effects on thyroid cell behavior, that could account for the phenomenon of follicular heterogeneity as a highly regulated cycle of increasing and decreasing colloidal Tg concentration that functions to optimize thyroid hormone production through the transcriptional activation or suppression of specific genes.

Investigating the Interaction Between Hcf106 Peptides and the Phospholipid Bilayer by Solid-State NMR Spectroscopy

In plant cells most thylakoid lumen proteins are synthesized in the cytosol as higher molecular weight precursors containing targeting sequences, which are imported into chloroplasts and localized to thylakoid lumen for function. Two thylakoid transport systems direct precursors to the thylakoid lumen. Our lab focuses on one of those transport systems: cpTat (chloroplast Twin arginine translocation) system, which transports fully folded proteins utilizing the trans-thylakoidal proton motive force as its only energy source. The cpTat pathway consists of three membrane-bound subunits, Tha4, Hcf106, and cpTatC. cpTatC and Hcf106 form a receptor complex where the precursor binds to initiate the translocation events, whereas Tha4 is initially found as a separate complex that joins the receptor once the precursor has bound. Hcf106 is predicted to contain a N-terminal transmembrane domain (TMD), followed by an amphipathic helix (APH) and an unstructured C-terminus. However, detailed structural information of Hcf106 remains unknown. In this study, peptides encompassing the Hcf106 TMD or APH domain were incorporated into POPC and POPC/MGDG vesicles and analyzed by solid-state NMR spectroscopy. Using 31P NMR we show that Hcf106 TMD/APH interact with the phospholipid headgroups. 2H-NMR revealed the perturbation of the deuterated acyl chain by the peptides. Lastly we used CD spectroscopy to analyze the secondary structure of Hcf106 TMD and APH peptides. The experimental results suggest: (1) Hcf106 TMD and APH peptides interact with both POPC and POPC/MGDG lipids with the lipid composition influencing the peptide-lipid interaction. (2) Hcf106 TMD and APH form alpha helical structures to varying degrees under the same conditions. (3) Hcf106 APH appears to be parallel to the membrane surface with a slight tilt into the hydrophobic region of phospholipids, whereas the TMD peptide appears to be perpendicular to the membrane surface.

Hydrolysis behaviour of crosslinked poly(ester anhydride) networks prepared from functionalised poly(ε-caprolactone) precursors

Biodegradable poly(ester anhydride) networks based on functionalised poly(ε-caprolactone) precursors with different hydrophobicities, molecular weights and architectures were synthesised. Networks that were prepared from the star-shaped precursors clearly showed higher gel contents and crosslinking densities than the networks that were prepared from the linear precursors. Functionalising with different alkenylsuccinic anhydrides and/or varying the molecular weight of the precursor, the thermal properties, surface hydrophobicity and erosion of the crosslinked networks were widely tailored. The dissolution behaviour of the networks changed dramatically as the molecular weight of the precursor increased from 2000 to 4000g/mol or the alkenyl chain of the alkenylsuccinic anhydride increased from 8 to 18 carbons. The networks that were prepared from the lower molecular weight precursors, without an alkenyl chain or with an 8 carbon alkenyl chain, lost their mass in a few days, whereas the networks that were prepared from higher molecular weight precursors or contained a hydrophobic 18 carbon alkenyl chain did not show any mass loss over a period of 8weeks.

Advanced Functional Polymers for Medicine

Advanced Functional Polymers for Medicine

Functional Microgels Tailored by Droplet‐Based Microfluidics

Monodisperse polymer gel particles with micrometer-scale dimensions serve for a variety of applications, including those as microcapsules for actives or as micrometer-sized matrixes for mesoscopic additives. These particles can be produced with exquisite control through the use of droplet-based microfluidic templating followed by subsequent droplet solidification. This can be achieved by two ways: One way is to use pre-microgel solutions of low molecular weight monomers and to form microgels by polymerizing these monomers. Another way is to use pre-polymerized, high molecular weight precursors and to gel them by polymer-analogous crosslinking. Both approaches have their specific advantages, allowing microgels to be tailored and optimized for specific needs such as those as delivery systems or scaffolds for living cells. This article highlights some recent achievements in the development and use of these microfluidic techniques to fabricate functional microgel particles.

Synthesis and characterization of water-soluble poly( p-phenylene vinylene) derivatives via the dithiocarbamate precursor route

Two hydrophilic branched oligo(ethylene glycol)-substituted PPV derivatives, poly(2,5-bis(1,3-bis(triethoxymethoxy)propan-2-yloxy)-1,4-phenylene vinylene) (BTEMP-PPV) and poly(2-methoxy-5-(1,3-bis(triethoxymethoxy)propan-2-yloxy)-1,4-phenylene vinylene) (MTEMP-PPV), are presented. Polymerizations have been performed via the dithiocarbamate precursor route, using lithium hexamethyldisilazide (LHMDS) as a base, to obtain high molecular weight precursor polymers. After thermal conversion of the precursor polymers into the fully conjugated systems, the solubility of the polymers has been examined. The polar nonionic side chains of MTEMP-PPV and BTEMP-PPV render the PPV backbone soluble in a variety of solvents, including alcohols and even water, making these polymers suitable candidates to be used in optoelectronic devices that can be processed from environmentally friendly solvent systems.

Porous carbon nanofibers with narrow pore size distribution from electrospun phenolic resins

Phenolic resin-based porous carbon nanofibers (PCNFs) with large surface area and narrow pore size distribution have been successfully prepared using novolac-type phenolic resin as precursor. The high molecular weight precursor was first synthesized in this study, then was dissolved in methanol. The PCNFs were finally obtained through electrospinning the phenolic resin polymer solution followed by successive curing and carbonization without activation. The N2 adsorption/desorption isotherms reveal that the PCNFs have high specific surface area about 812m2/g, the pore size falls in the range of 0.4–0.7nm and the pore volume is 0.91cm3/g. The vapor adsorption testing demonstrated that PCNFs exhibited different adsorption performance for ethanol and water.

Telechelic siloxanes with hydrogen‐bonded polymerizable end groups. I. Liquid rubbers and elastomers

AbstractFunctional siloxanes are widely used in the synthesis of model networks used in rubber elasticity studies, and various functional siloxanes are also used in the synthesis of silicone rubbers. We present here the results of studies of two classes of telechelic, free‐radically polymerizable siloxanes carrying either amide or urea groups attached at both ends of siloxane chain. The presence of polar, hydrogen‐bonding end‐groups favors the formation of aggregates which is reflected in the drastically increased viscosity of the resulting “liquid rubbers.” In addition, such aggregation accounts for high local concentrations of reactive groups thus making it possible to have high molecular weight precursors undergo facile room temperature polymerization. In this article, we study the effect of the nature of these functional groups on the viscosity of polymerizable “liquid rubbers,” finding that the different endgroups lead to dramatically different viscosities. We also study the silicone rubber films obtained by a UV‐initiated free‐radical polymerization of the liquid rubbers, using dynamic mechanical analysis and large‐strain uniaxial deformation. We find here that important properties such as plateau modulus and Young's modulus are highly dependent on both endgroup type and precursor molecular weight. The crosslinking of telechelic siloxanes in dilution was also studied to further explore the effect of crosslink density of the mechanical properties of the model networks. Finally, we evaluated the role of dangling ends within the networks through the incorporation of monofunctional macromers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Evaluation on Pore Structures of Organosilicate Thin Films by Grazing Incidence Small-Angle X-ray Scattering

Nanoporous thin films fabricated by both a core-shell-shaped organic-inorganic hybrid sphere (octa(2,4-dinitrophenyl)silsesquioxane, ODNPSQ) and a four-leg-numbered surfactant (polyoxyethylene sorbitan monolaurate, Tween-20) for porogens in a higher molecular weight precursor (polyphenylsilsesquioxane, PPSQ) were characterized, respectively, by grazing incidence small-angle X-ray scattering (GISAXS), and the measured 2D GISAXS profiles were analyzed quantitatively by using a GISAXS formula based on the distorted wave Born approximation (DWBA). The fitted 2D GISAXS data show that the PPSQ porous thin films imprinted with ODNPSQ porogen exhibit sphere-shaped closed pores with the average pore size within a range of 1.18-3.12 nm and pore size distribution widths about 3.0 nm when the porogen loadings increase from 10 to 40 wt % and those imprinted with Tween-20 porogen give out an average pore size of 1.07-1.29 nm and pore size distribution widths about 2.0 nm with the porogen loading varying from 5 to 30 wt %. The nanoporous dielectric thin films imprinted with ODNPSQ porogen show a reducing to the molecular aggregation of porogens and significant antiphase separation behavior in the cross-linked matrix.

Exploring the Dithiocarbamate Precursor Route: Observation of a Base Induced Regioregularity Excess in Poly[(2-methoxy-5-(3′,7′-dimethyloctyloxy))-1,4-phenylenevinylene] (MDMO−PPV)

The dithiocarbamate precursor route is a suitable way to synthesize poly(p-phenylene vinylene) derivatives in an efficient manner. It is demonstrated that this precursor route combines the straightforward monomer synthesis of the Gilch route with the superior polymer quality of the more complex sulfinyl route. To obtain the polymers, the bisdithiocarbamate MDMO monomer has been polymerized using either lithium bis(trimethylsilyl)amide (LHMDS) or potassium tert-butoxide (KtBuO). The addition of either base results in the formation of high molecular weight precursor polymer. It is shown that the polymerization mechanism follows a radical pathway. Furthermore it is demonstrated that the molecular structure of the polymer shows a certain degree of regioregularity when LHMDS is used. The thermal conversion of the precursor polymer into the conjugated system is studied by in situ UV−vis and FT-IR spectroscopy. A NMR study on 13C-labeled MDMO−PPV reveals the presence of only a minimal amount of structural defect...

Nuclear cysteine‐protease involved in male chromatin remodeling after fertilization is ubiquitously distributed during sea urchin development

Previously we have identified a cysteine-protease involved in male chromatin remodeling which segregates into the nuclei of the two blastomeres at the first cleavage division. Here we have investigated the fate of this protease during early embryogenesis by immunodetecting this protein with antibodies elicited against its N-terminal sequence. As shown in this report, the major 60 kDa active form of this protease was found to be present in the extracts of chromosomal proteins obtained from all developmental stages analyzed. In morula and gastrula the 70 kDa inactive precursor, which corresponds to the major form of the zymogen found in unfertilized eggs, was detected. In plutei larvas, the major 60 kDa form of this enzyme was found together with a higher molecular weight precursor (90 kDa) which is consistent with the less abundant zymogen primarily detected in unfertilized eggs. As reported here, either the active protease or its zymogens were visualized in most of the embryonic territories indicating that this enzyme lacks a specific pattern of spatial-temporal developmental segregation. Taken together our results indicate that this protease persists in the embryo and is ubiquitously distributed up to larval stages of development, either as an active enzyme and/or as an inactive precursor. These results suggest that this enzyme may display yet unknown functions during embryonic development that complement its role in male chromatin remodeling after fertilization.

An Arabidopsis thaliana virescent mutant reveals a role for ClpR1 in plastid development

The ATP-dependent Clp protease has been well-characterized in Escherichia coli, but knowledge of its function in higher plants is limited. In bacteria, this two-component protease consists of a Ser-type endopeptidase ClpP, which relies on the ATP-dependent unfolding activity from an Hsp100 molecular chaperone to initiate protein degradation. In the chloroplasts of higher plants, multiple isoforms of the proteolytic subunit exist, with Arabidopsis having five ClpPs and four ClpP-like proteins termed ClpR predicted in its genome. In this work we characterized an Arabidopsis mutant impaired in one subunit of the chloroplast-localized Clp protease core, ClpR1. clpR1-1, a virescent mutant, carries a pre-mature stop codon in the clpR1 gene, resulting in no detectable ClpR1 protein. The accumulation of several chloroplast proteins, as well as most of the chloroplast-localized Clp protease subunits, is inhibited in clpR1-1. Unexpectedly, some plastid-encoded proteins do not accumulate, although their transcripts accumulate to wild-type levels. Maturation of 23S and 4.5S chloroplast ribosomal RNA (cp-rRNA) is delayed in clpR1-1, and both RNAs accumulate as higher molecular weight precursors. Also, chloroplasts in clpR1-1 are smaller than in wild type and have fewer thylakoid membranes with smaller grana stacks. We propose that a ClpR1-containing activity is required for chloroplast development and differentiation and in its absence both are delayed.